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LIGNITE DRYING TECHNOLOGIES

FOR POWER GENERATION:

PHYSICOCHEMICAL PROPERTIES,

PYROLYSIS AND COMBUSTION

OF DRIED LIGNITE PRODUCTS

A thesis submitted in fulfilment of the

requirements for the degree of

Doctor of Philosophy

By

George Favas

Faculty of Engineering and Industrial Science

Swinburne University of Technology

2008

Abstract ii

ABSTRACT

Three technologies have been under serious consideration for reducing the moisture

content of Latrobe Valley lignites – namely, hydrothermal dewatering (HTD),

mechanical thermal expression (MTE) and steam drying (SD). This thesis compares

the relative effectiveness of these technologies in terms of water retention in the

product, solids recovery from the process and organic carbon in the by-product

water.

For the same Loy Yang lignite, containing 59% water (on a wet basis), it is shown

that the temperature at which 50% of this water is removed is, for MTE: 125°C, for

SD: 210°C and for HTD: 350°C.

With MTE, the processing temperature required to achieve high moisture reductions

was significantly reduced by simultaneous application of mechanical pressure. For

Loy Yang lignite the optimum applied pressure was identified as approximately

5.1MPa. Further increases had relatively little effect on the moisture content of the

product pellet.

The relatively high temperatures required to achieve 50% water removal by HTD

also leads to poor solids recovery (86%) due to decarboxylation and devolatilisation

processes that concomitantly occur under these conditions. Poor solids recovery is

also observed when SD is carried out at high temperatures (>250°C).

Abstract iii

Much of the sodium removed from drying was in the form of NaCl. In MTE,

processing temperature was more effective in removing sodium than applied pressure

(within the experimental parameters tested). In contrast, SD processing temperatures

above 280°C had no effect on the proportion of sodium leached out from the lignite.

The slurrying of the lignite with water in HTD facilitated removal of sodium,

magnesium, calcium and chlorine during the process compared to MTE and SD. This

considerably higher removal of inorganic material, particularly sodium, is an

advantage in that it will reduce fouling and slagging propensities during combustion

of the product.

Rapid pyrolysis of the HTD product gave significantly lower yields of methane,

ethene, carbon monoxide and carbon dioxide when compared to corresponding yields

of the raw lignite, MTE and SD products. The lower yields for the HTD product

were attributed to volatilisation during hydrothermal dewatering and also to the

reduction of catalytic reforming cations. The significant volatile yield loss during

hydrothermal dewatering could be disadvantageous in some industrial processes,

which convert the carbon matter to lower molecular weight fractions (eg gasification,

liquefaction).

The combustion reactivity of MTE, HTD and SD products did not demonstrate

significant differences from the raw lignite. The combustion reactivity of the

thermally dried products decreased with increasing severity of the conditions.

However these changes were quite minimal suggesting that the conventional boiler

Abstract iv

systems currently in operation in the Latrobe Valley would be more than adequate in

combusting thermally treated products from any of the three drying processes.

The effectiveness of catalytic inorganic species clearly outweighed pore volume

effects for affecting the combustion reactivity of the lignites. The chemical form and

concentration of the inorganic component in the hydrocarbon macromolecular matrix

can influence the rate of combustion at 400°C. The removal of inorganic components

from the coal by washing or by HTD or MTE has a much larger impact on reducing

the combustion reactivity and reducing the peak temperature of the sample when

compared to significant reductions in porosity resulting from thermal drying.

Additional combustion experiments on a diverse suite of well-characterised lignites

sourced from the Latrobe Valley confirmed that catalytic inorganic species clearly

outweighed other physico-chemical effects for affecting the combustion reactivity of

the lignites. The combined catalytic effects of iron, magnesium and calcium

accounted for more than 95% of the variation in the combustion reactivity of the raw

coals. In addition, the combustion reactivity of Latrobe Valley lignite samples was

strongly correlated to the sum of the univalent charges of the AAEM species plus the

univalent charge of the acid-extractable iron.

Finally, the surface area and pore volumes of carbons/chars have negligible effect on

the combustion reactivity and the inorganic components in the carbon

macromolecular structure are the major influences in the combustion rate of the

sample at 400°C.

Acknowledgements v

Acknowledgements

The first acknowledgement in every thesis should always be given to the supervisor.

In this case I would like to thank Dr Francois Malherbe and Professor Ian Harding

for the opportunity to undertake this degree.

I would also like to thank the CRC for Clean Power from Lignite, the executives Dr

David Brockway, Mr Malcolm MacIntosh and the late Dr Peter Jackson, for

supplying the raw lignite samples and permission to operate their MTE batch cell.

Also, I would like to thank the School of Chemistry at Monash University and Dr

Alan Chaffee for the use of their analytical equipment. Also, I would like to thank Dr

Chun-Zhu Li for his support at the commencement of this research project, and

Professor Roy Jackson and Dr Marc Marshall for their encouragement and guidance

throughout the years.

A very special acknowledgment goes out to my wife, Mrs Marija Favas. Her

persistence, inspiration and ability to whip up a meal during all hours of the day have

been the sole source of time management for this project. I would also like to thank

Marija for her persistence and understanding, in particular the late nights and early

mornings during the write up of this thesis.

Acknowledgements vi

Last but surely not least, to my twin boys, Ivan and Christian, who were born

December 2007 and have already provided much joy and happiness to my family.

Declaration vii

DECLARATION

To the best of my knowledge this thesis contains no material which has been

accepted for the award of any other degree or diploma in any university and

contains no material previously published or written by another person except

where due reference is made. Also, where the work is based on joint

research or publications, discloses the relative contributions of respective

workers or authors.

George Favas

Faculty of Engineering and Industrial Science

Swinburne University of Technology

2008

Table of Contents viii

Table of Contents

CHAPTER 1 ......................................................................................................................... 1

INTRODUCTION ................................................................................................................. 1

1.1 Project aims............................................................................................................ 1

1.2 Introduction............................................................................................................ 2

1.2.1 Mechanical thermal expression (MTE).......................................................... 4

1.2.2 Hydrothermal dewatering (HTD)................................................................... 7

1.2.3 Steam drying ................................................................................................ 11

1.3 Factors affecting the combustion reactivity of lignites ........................................ 15

1.3.1 Inorganic material in Latrobe Valley lignites .............................................. 15

1.3.2 Pore structure ............................................................................................... 17

1.4 Scope of the thesis................................................................................................ 18

CHAPTER 2 ....................................................................................................................... 20

EXPERIMENTAL ............................................................................................................... 20

2.1 Methodology ........................................................................................................ 20

2.2 The lignites........................................................................................................... 21

2.3 Preparation of lignite slurries (HTD only) ........................................................... 21

2.4 Discrete particle size lignite preparation.............................................................. 21

2.5 Water washing and acid washing of lignites........................................................ 22

2.6 Autoclaves............................................................................................................ 23

2.7 Hydrothermal dewatering .................................................................................... 24

2.8 HTD and SD work-up procedure ......................................................................... 25

2.9 Mechanical thermal expression............................................................................ 27

2.10 MTE workup procedure ....................................................................................... 28

Table of Contents ix

2.11 Steam drying experiments.................................................................................... 29

2.12 Pore size distribution analysis.............................................................................. 32

2.13 Determination of lignite moisture content ........................................................... 32

2.14 Wet and dry pellet density measurements............................................................ 33

2.15 Slow and rapid pyrolysis of raw and thermally treated products......................... 34

2.15.1 Pre-treatment of raw and thermally dried products...................................... 34

2.15.2 Particle feeder............................................................................................... 34

2.15.3 Quartz reactor design ................................................................................... 37

2.15.4 Slow pyrolysis experiments ......................................................................... 39

2.15.5 Fast pyrolysis experiments........................................................................... 41

2.15.6 Char collection ............................................................................................. 43

2.16 Volatile matter and fixed carbon determination................................................... 44

2.17 Combustion reactivities........................................................................................ 44

2.18 Ash determinations .............................................................................................. 45

2.19 Total inorganic contents....................................................................................... 45

2.20 Product water analysis ......................................................................................... 46

2.20.1 Cation and anion analysis ............................................................................ 46

2.19.1 Total organic carbon (TOC)......................................................................... 47

2.21 Surface area and micropore volume..................................................................... 47

2.22 Helium density ..................................................................................................... 49

2.23 Pyrolysis-gas chromatography............................................................................. 50

2.24 Pyrolysis–gas chromatography–mass spectrometry ............................................ 54

2.25 Scanning Electron Microscope (SEM) - Energy Dispersion X-rays (EDX)........ 55

2.26 X-ray diffraction .................................................................................................. 55

2.27 Errors.................................................................................................................... 56

CHAPTER 3 ....................................................................................................................... 57

Table of Contents x

LIGNITE DRYING TECHNOLOGIES.............................................................................. 57

3.1 Effect of HTD conditions on retained moisture................................................... 57

3.2 Mechanical Thermal Expression (MTE).............................................................. 60

3.2.1 Effect of processing temperature ................................................................. 60

3.2.2 Effect of mechanical pressure ...................................................................... 63

3.3 Steam drying (SD) - effect of SD conditions on retained moisture ..................... 65

3.4 Pore structure of HTD, MTE and SD products.................................................... 67

3.5 Inorganic analysis of dried products .................................................................... 75

3.5.1 Sodium in dried lignite products .................................................................. 77

3.5.2 Calcium and magnesium in dried lignite products....................................... 80

3.5.3 Inorganic reduction in dried products versus water removal ....................... 80

3.5.4 Chlorine in dried lignite products ................................................................ 84

3.6 Conclusions.......................................................................................................... 87

CHAPTER 4 ....................................................................................................................... 90

PYROLYSIS OF RAW LIGNITE AND DRIED PRODUCTS.......................................... 90

4.1 Introduction.......................................................................................................... 90

4.2 Proximate analysis ............................................................................................... 91

4.3 Differential Scanning Calorimetry....................................................................... 95

4.3.1 Pyrolysis DSC of SD products..................................................................... 95

4.3.2 Combustion DSC at 950°C of SD products ................................................. 99

4.4 Quartz reactor pyrolysis experiments................................................................... 99

4.4.1 Slow pyrolysis experiments ....................................................................... 100

4.4.2 Fast pyrolysis experiments......................................................................... 103

4.5 Tar yields............................................................................................................ 107

4.6 Inorganic contents .............................................................................................. 109

4.7 Pyrolysis-gas chromatography........................................................................... 114

Table of Contents xi

4.7.1 Py-gc-ms with a HP-5 chromatography column........................................ 124

4.7.2 Volatile yield balance................................................................................. 128

4.8 Pyrolysis-gas chromatography-mass spectrometry............................................ 130

4.9 Py-gc of thermally treated products ................................................................... 132

4.10 Conclusion ......................................................................................................... 135

CHAPTER 5 ..................................................................................................................... 138

COMBUSTION OF RAW LIGNITE AND DRIED PRODUCTS ................................... 138

5.1 Introduction........................................................................................................ 138

5.1.1 Effect of particle size ................................................................................. 141

5.1.2 Effect of sample mass loading on combustion rates .................................. 144

5.1.3 Combustion of 1mm raw Loy Yang particles ............................................ 147

5.1.4 Effect of combustion temperature.............................................................. 152

5.2 Effect of particle size (monolayer loading)........................................................ 157

5.3 Combustion reactivity of thermally dried lignites ............................................. 160

5.4 Combustion reactivity of thermally dried lignites at 450ºC............................... 162

5.5 Combustion reactivity of MTE Morwell and Yallourn lignites......................... 167

5.6 Conclusions........................................................................................................ 174

CHAPTER 6 ..................................................................................................................... 175

COMBUSTION OF RAW LIGNITES.............................................................................. 175

6.1 Introduction........................................................................................................ 175

6.2 Latrobe Valley lignites – background information ............................................ 176

6.3 Characterisation of Latrobe Valley lignites ....................................................... 177

6.4 X-ray Diffraction................................................................................................ 184

6.5 Combustion reactivity of Latrobe Valley lignites.............................................. 187

6.6 Multiple regression analysis............................................................................... 191

6.6.1 Multiple regression analysis of raw lignites............................................... 191

Table of Contents xii

6.6.2 Multiple regression of raw, water washed and acid washed samples. ....... 195

6.7 Catalytic effects of iron...................................................................................... 200

6.8 Catalytic effects of AAEM cations .................................................................... 203

6.8.1 Calcium ...................................................................................................... 204

6.8.2 Magnesium................................................................................................. 207

6.8.3 Sodium ....................................................................................................... 212

6.8.4 Aluminium ................................................................................................. 214

6.8.5 Chlorine...................................................................................................... 216

6.9 Effect of surface area on combustion reactivity................................................. 219

6.10 Conclusions........................................................................................................ 221

CHAPTER 7 ..................................................................................................................... 223

COMBUSTION OF CHARS............................................................................................. 223

7.1 Introduction........................................................................................................ 223

7.2 Char reactivity.................................................................................................... 224

7.3 Porosity of chars................................................................................................. 231

7.4 Conclusions........................................................................................................ 237

CHAPTER 8 ..................................................................................................................... 239

OVERALL CONCLUSIONS ............................................................................................ 239

APPENDIX A ................................................................................................................... 242

Chemical composition of high temperature grade stainless steel ...................................... 242

APPENDIX B ................................................................................................................... 243

Nitrogen BET on lignites ................................................................................................... 243

APPENDIX C ................................................................................................................... 245

Pore size distributions ........................................................................................................ 245

APPENDIX D ................................................................................................................... 247

Table of Contents xiii

Physical measurments of MTE density.............................................................................. 247

APPENDIX E ................................................................................................................... 257

Determination of soluble ionic salts and carboxylate ions................................................. 257

APPENDIX F.................................................................................................................... 258

Product water from MTE, HTD and SD ............................................................................ 258

Inorganic analysis of the product waters.................................................................... 258

pH of the product water ............................................................................................. 267

Total Organic Carbon................................................................................................. 269

APPENDIX G................................................................................................................... 273

Sample calculations............................................................................................................ 273

APPENDIX H................................................................................................................... 277

Actual mass (g) of ash, acid extractable inorganics, chlorine and total sulphur in raw and processed lignite. ......................................................................................................... 277

APPENDIX I .................................................................................................................... 278

Molar values of acid extractable inorganics, chlorine and total sulphur in raw and processed lignite................................................................................................................. 278

APPENDIX J .................................................................................................................... 279

APPENDIX K................................................................................................................... 280

Calculation of carbonate and bicarbonate ion concentration in product water. ................. 280

APPENDIX L ................................................................................................................... 281

Proximate analysis of HTD, MTE and SD products.......................................................... 281

APPENDIX M .................................................................................................................. 285

Combustion of MTE, HTD and SD products .................................................................... 285

APPENDIX N ................................................................................................................... 290

Multiple regression analysis............................................................................................... 290

Table of Contents xiv

APPENDIX O................................................................................................................... 292

APPENDIX P.................................................................................................................... 294

APPENDIX Q................................................................................................................... 304

Abbreviations and Glossary ............................................................................................... 304

REFERENCES................................................................................................................. 307

List of Figures xv

List of Figures

Figure 1.1 Latrobe Valley brown coal deposits and the location of the power plants........... 3

Figure 1.2 Schematic diagram of the MTE pilot press at the University of Dortmund. ........ 6

Figure 1.3 German 25t h-1 MTE demonstration unit ............................................................. 6

Figure 1.4 Schematic flow diagram of the 100 kgh-1 HTD process development unit

at EERC............................................................................................................... 9

Figure 1.5 Schematic diagram of the HRL's continuous HTD reactor ................................ 10

Figure 1.6 Schematic diagram of JGC's 8.4 tonne per day pilot plant................................. 11

Figure 1.7 Schematic of the pressurised fluidised bed drying system at BTU Cottbus,

Germany............................................................................................................ 14

Figure 1.8 Pressurised fluidised bed drying system at BTU Cottbus, Germany.................. 14

Figure 2.1 Schematic diagram of the 70mL autoclave ........................................................ 26

Figure 2.2 Schematic diagram of the MTE batch unit ......................................................... 27

Figure 2.3 Components of the MTE batch cell .................................................................... 27

Figure 2.4 Schematic of the 500mL batch autoclave used for steam drying lignite............ 30

Figure 2.5 Temperature heat up profile for the steam drying experiments.......................... 31

Figure 2.6 Schematic of a wet MTE pellet .......................................................................... 33

Figure 2.7 Schematic of the lignite particle feeder .............................................................. 36

Figure 2.8 Fluidized quartz reactor design........................................................................... 38

Figure 2.9 Schematic diagram of the pulley system used to lower and raise the quartz

reactor from the tubular furnace........................................................................ 40

Figure 2.10 Schematic of experimental rig .......................................................................... 42

List of Figures xvi

Figure 2.11 Schematic of the method for collecting the char particles from the quartz

reactor................................................................................................................ 43

Figure 3.1 Effect of temperature on the retained water in the HTD product; MTE

pellet with 5.1MPa of applied mechanical pressure; and in the SD

product............................................................................................................... 62

Figure 3.2 Effect of applied mechanical pressure on the retained water in the MTE

pellet at 150°C................................................................................................... 64

Figure 3.3 Effect of applied pressure on the surface area of MTE products ....................... 69

Figure 3.4 Relationship between surface area and processing temperature for

(1) MTE, (2) HTD, (3) SD and (4) all three drying processes.......................... 71

Figure 3.5 Changes in pore volume of LYLA lignite with MTE, HTD and SD

processing.......................................................................................................... 73

Figure 3.6 Relationship between pore volume and retained water (a) in HTD and

MTE products, (b) in SD products. ................................................................... 74

Figure 3.7 Relationship between drying process on product moisture and sodium

contents in the dried products. Note, the dotted line has been used in each

graph for illustrative purposes only (i.e. 1:1 ratio) and should not be taken

as the trendline for all the given values............................................................. 81

Figure 3.8 Relationship between the proportions of water and soluble sodium

removed by MTE, HTD and SD processing. .................................................... 82

Figure 3.9 Relationship between the proportions of water and soluble chlorine

removed by MTE, HTD and SD processing. .................................................... 85

Figure 3.10 Relationship between the proportion of sodium and chlorine present in

the dried solid products from the MTE, HTD and SD processes...................... 86

List of Figures xvii

Figure 4.1 TGA thermograms used in determining proximate analysis of a lignite

sample ............................................................................................................... 92

Figure 4.2 The effect of temperature on volatile yield from HTD, MTE and SD. .............. 95

Figure 4.3 Comparisons between the heat flow of 130°C and 350°C SD products,

30mLmin-1air flow, 30.0mg sample.................................................................. 97

Figure 4.4 Deconvoluted curve fit of the DSC from the 130°C SD product. ...................... 98

Figure 4.5 Comparisons of char yields from the pyrolysis of raw LYLA lignite with

(a) MTE (b) SD (c) HTD treated products as a function of temperature in

the fluidized-bed/fixed-bed reactor operated at the slow heating rate

mode. ............................................................................................................... 102

Figure 4.6 Comparisons of char yields from the pyrolysis of raw and water washed

LYLA lignite operated at the slow heating mode, as a function of

temperature in the fluidized-bed/fixed-bed reactor......................................... 103

Figure 4.7 Comparisons of char yields from the pyrolysis of raw LYLA lignite

operated at the slow and fast heating rate mode, as a function of


Figure 4.8 Comparisons of char yields from the pyrolysis of (a) MTE (b) SD

(c) HTD treated products as a function of temperature in the fluidized-

bed/fixed-bed reactor operated at the slow and fast heating rate mode .......... 106

Figure 4.9 Comparisons of tar yields from the pyrolysis of raw LYLA lignite

operated at the slow and fast heating rate mode, as a function of


Figure 4.10 Comparisons of volatilized (a) sodium, (b) chlorine, (c) magnesium

and (d) calcium, from the pyrolysis of raw LYLA lignite operated at

List of Figures xviii

the slow and fast heating rate mode, as a function of temperature in the

fluidized-bed/fixed-bed reactor ....................................................................... 113

Figure 4.11 Gc trace of pyrolysed Loy Yang raw lignite using a GS-GasPro column...... 115

Figure 4.12 Quantification of volatilised (a) methane, ethane, ethane, ethylene

(b) propane, propene (c) carbon monoxide, carbon dioxide and water,

from the py-gc of Loy Yang raw lignite as a function of temperature

using a GS-GasPro column. ............................................................................ 116

Figure 4.13 Illustration of the concurrent primary and secondary pyrolysis reactions

in the breakdown of tar ................................................................................... 118

Figure 4.14 Shin et al.’s [243] proposed catalytic cracking reaction pathway of

catechols and hydroquinones to produce carbon monoxide, carbon

dioxide and water. ........................................................................................... 120

Figure 4.15 Quantification of volatilised (a) benzene, toluene, xylenes and phenol

using a GS-GasPro column. ............................................................................ 123

Figure 4.16 Gc trace of pyrolysed Loy Yang raw lignite at 600°C using a

HP-5 column ................................................................................................... 124

Figure 4.17 Quantification of volatilised alkanes/alkenes (C4-C30) using a HP-5

column, from the py-gc of Loy Yang raw lignite as a function of

temperature...................................................................................................... 125

Figure 4.18 Gc trace of pyrolysed Loy Yang raw lignite using a HP-5 column................ 126

Figure 4.19 Pyrolysis-gas chromatography-mass spectrometry of the Loy Yang lignite

at 700°C........................................................................................................... 131

Figure 4.20 Quantification of volatilised (a) methane, (b) ethane, (c) ethene, (d)

ethylene (e) carbon monoxide, (f) carbon dioxide, from the py-gc of Loy

List of Figures xix

Yang raw lignite, MTE, SD and HTD treated products as a function of

temperature using a GS-GasPro column. ........................................................ 134

Figure 5.1 Combustion of raw, discrete particle sized lignite. 30mLmin-1 air flow,

30mg sample ................................................................................................... 143

Figure 5.2 Combustion of 1mm lignite particles, loaded into a large crucible.................. 146

Figure 5.3 Schematic of two 1mm lignite particles positioned inside the TGA

crucible. ........................................................................................................... 147

Figure 5.4 Combustion-oxidation of two particles (1mm diameter) at 450°C. ................. 149

Figure 5.5 Weight loss, heat flow and DTG curves of two 1mm particles (one particle

igniting and one particle undergoing combustion-oxidation) heated to

450°C in a TGA. ............................................................................................. 150

Figure 5.6 Weight loss, heat flow and DTG curves of two particles igniting during

heating to 450°C in a TGA.............................................................................. 151

Figure 5.7 Relationship between........................................................................................ 153

Figure 5.8 Schematic diagram of the TGA crucible containing 2 mg of 250-500mm

particles of raw lignite. (A) before combustion, (B) after combustion at

450°C............................................................................................................... 154

Figure 5.9 Effect of combustion temperature versus the weight loss and DTG

respectively. Dotted line gives the point where the desired temperature

has been reached. ............................................................................................ 156

Figure 5.10 Combustion of raw lignite of different discrete particle size in the TGA at

400°C. Conditions: 30mLmin-1 air flow, 2.0mg sample................................. 159

Figure 5.11 Combustion of MTE products (90-125μm particle size) in the TGA at

400°C. Conditions: 30mLmin-1 air flow, 2.0mg sample ................................. 163

List of Figures xx

Figure 5.12 Combustion of MTE products (90-125μm particle size) in the TGA at

400°C. Conditions: 30mLmin-1 air flow, 2.0mg sample ................................. 164

Figure 5.13 Combustion of raw and HTD products (90-125μm particle size) in the

TGA at 400°C. Conditions: 30mLmin-1 air flow, 2.0mg sample.................... 165

Figure 5.14 Combustion of raw and SD products (90-125μm particle size) in the TGA

at 400°C........................................................................................................... 166

Figure 5.15 Pore volumes of MTE processed Loy Yang, Morwell and Yallourn

lignites at 150°C/5.1MPa ................................................................................ 168

Figure 5.16 Combustion of Loy Yang, Morwell and Yallourn MTE products at

150ºC/ 5.1MPa ................................................................................................ 169

Figure 5.17 Combustion of Loy Yang, Morwell and Yallourn MTE products at

150ºC/ 5.1MPa ................................................................................................ 171

Figure 5.18 Combustion of Loy Yang, Morwell and Yallourn raw lignite, MTE

products (150ºC/ 5.1MPa) and water washed lignite ...................................... 173

Figure 6.1 XRD spectra of coal (a) Loy Yang coals: LYLA, LYMNa and LYHNa (b)

Morwell coals: MMTE and MMg................................................................... 185

Figure 6.2 XRD spectra of coal (c) Yallourn East Field coals: YMTE, YEFFe and

YEFD (d) Yallourn Township coals: YTP and YTD...................................... 186

Figure 6.3 Integration of the specific reactivity of raw Loy Yang lignite as a function

of conversion. .................................................................................................. 188

Figure 6.4 Combustion reactivity versus peak temperature of the raw, water washed

and acid washed Latrobe Valley lignites. ....................................................... 190

Figure 6.5 Normal P-P plot of regression standardized residual of the dependent

variable combustion reactivity of the raw lignites. ......................................... 194

List of Figures xxi

Figure 6.6 Scatterplot of regression standardized residual and predicted combustion

reactivity values .............................................................................................. 195

Figure 6.7 Normal P-P plot of regression standardized residual of the combustion

reactivity value from the raw, water washed and acid washed lignites. ......... 199


reactivity values from the raw, water washed and acid washed lignites......... 199

Figure 6.9 AAEM concentration versus combustion reactivity for the raw, water

washed and acid washed lignite samples. ....................................................... 210

Figure 6.10 AAEM and iron concentration (cation concentration) versus the

combustion reactivity value for the raw, water washed and acid washed

lignite samples................................................................................................. 211

Figure 6.11 Cation concentration (AAEM and iron concentration) minus anion

concentration (chloride and sulphide) versus the combustion reactivity

value for the raw, water washed and acid washed lignite samples. ................ 218

Figure 6.12 Surface area versus the combustion reactivity of the Latrobe Valley

lignite samples................................................................................................. 220

Figure 7.1 Comparisons of the combustion reactivity of chars from the pyrolysis of

MTE lignite operated at the slow and fast heating rate mode, as a function

of temperature in the fluidized-bed/fixed-bed reactor..................................... 225

Figure 7.2 Concentration on charge to char mass ratio versus combustion reactivity of

the char from the slow and fast pyrolysis experiments using the fluidized-

bed/fixed-bed reactor ...................................................................................... 230

List of Figures xxii

Figure 7.3 Comparisons of pore volume of Loy Yang MTE coal (150°C/5.1MPa) and

chars from the pyrolysis of MTE operated at the slow and fast heating rate

mode, as a function of temperature in the fluidized-bed/fixed-bed reactor. ... 232

Figure 7.4 Comparisons of the surface area of chars from the pyrolysis of MTE

lignite operated at the slow and fast heating rate mode, as a function of


Figure 7.5 Pore size distribution of a synthetic activated carbon from Helsa-werk .......... 235

Figure 7.6 Comparisons of pore volume of a synthetic activated carbon and the pore

volumes of chars from the pyrolysis of a MTE sample, operated at the

slow and fast heating rate mode, as a function of temperature in the

fluidized-bed/fixed-bed reactor. ...................................................................... 236

Figure B.1 Nitrogen adsorption isotherms at -196°C and corresponding BET surface

areas for the HTD products ............................................................................. 244

Figure C.1 Pore volume distribution of raw lignite attained from mercury

porosimetry, CO2 surface area and helium pycnometry (values are given

as the radius of the pores)................................................................................ 246

Figure D.1 Relationship between wet density of the MTE pellet versus (a) reaction

temperature (b) applied mechanical pressure.................................................. 248

Figure D.2 Relationship between wet porosity of the MTE pellet versus (a) reaction

temperature (b) applied mechanical pressure.................................................. 249

Figure D.3 Relationship between proportions of the original size of MTE pellet after

drying to zero moisture versus (a) reaction temperature (b) applied

mechanical pressure (c) wet density of the MTE pellet. ................................. 252

List of Figures xxiii

Figure D.4 Relationship between the dry and wet density of MTE pellets, processed

under different conditions ............................................................................... 253

Figure D.5 Relationship between retained water and pore volume determined from

mercury porosimetry and gas adsorption; wet and dry pore volumes

determined from the MTE pellet..................................................................... 256

Figure F.1 Molarity concentration of inorganics present for the product water from

MTE, HTD and SD processing (equivalent to 10g of dried raw lignite) ........ 263

Figure F.2 Relationship between chlorine and sodium ions present in the water

(mmol) collected from the MTE, HTD and SD processes.............................. 266

Figure F.3 Relationship between the concentration of weak acid anions and the pH of

the product waters from MTE, HTD and SD.................................................. 268

Figure F.4 Total Organic Carbon of the product water collected from the MTE, HTD

and SD processes at different temperatures. (Note: all TOC values have

been calculated on a 10g db). .......................................................................... 271

Figure F.5 The log of Total Organic Carbon of the product water collected from the

MTE, HTD and SD processes at different temperatures (Note: all TOC

values have been calculated on a 10g db). ...................................................... 271

Figure F.6 Relationship between total organic carbon leached out into the product

water versus the proportion of water removed from MTE, HTD and SD

(all TOC values have been calculated on a 10g db)........................................ 272

Figure L.1 Proximate analysis of HTD products processed at different temperatures.

30mLmin-1 air flow, 30.0mg sample............................................................... 281

Figure L.2 Heat Flow of HTD products processed at different temperatures.

30mLmin-1 air flow, 30.0mg sample (from proximate analysis). ................... 281

List of Figures xxiv

Figure L.3 Proximate analysis of MTE products processed at different temperatures,


Figure L.4 Heat flow of MTE products processed at different temperatures,


Figure L.5 Proximate analysis of MTE products processed at different mechanical

pressures, 30mLmin-1 air flow, 30.0mg sample .............................................. 283

Figure L.6 Heat Flow of MTE products processed at different mechanical pressures,


Figure L.7 Proximate analysis of SD products processed at different temperatures,


Figure L.8 Heat Flow of SD products processed at different temperatures, 30mLmin-1

air flow, 30.0mg sample.................................................................................. 284

Figure M.1 Combustion of MTE products produced at different processing

temperatures ranging from 125°C to 250°C.................................................... 286

Figure M.2 Combustion of MTE products produced at different applied pressures

ranging from 2.1MPa to 25.0MPa................................................................... 287

Figure M.3 Combustion of HTD products produced at different processing


Figure M.4 Combustion of SD products produced at different processing


List of Tables xxv

List of Tables

Table 1.1 Typical operating conditions of a SFBD .......................................................... 13

Table 2.1Discrete particle sized lignite fractions.............................................................. 22

Table 2.2 Set-up temperatures for 70mL autoclave HTD reactions ................................. 24

Table 2.3 Set-up temperatures for 500mL autoclave SD reactions .................................. 31

Table 2.4 Run conditions for pyrolysis-gas chromatography ........................................... 51

Table 2.5 Capillary Column properties............................................................................. 52

Table 2.6 Standard gas mixtures ....................................................................................... 52

Table 2.7 Liquid standards................................................................................................ 53

Table 2.8 Run conditions for gas chromatography-mass spectrometry............................ 54

Table 2.9 Run conditions for SEM-EDX.......................................................................... 55

Table 3.1 Effect of temperature on the filter cake moisture content from the HTD

process............................................................................................................ 58

Table 3.2 Mass recovery and moisture content of raw lignites and MTE products

treated at different temperatures and 5.1MPa mechanical pressure............... 61

Table 3.3 Mass recovery and moisture content of raw lignites and MTE products

treated at 150°C and at different mechanical pressures. ................................ 63

Table 3.4 Effect of temperature on the filter cake moisture content from the SD

process............................................................................................................ 66

Table 3.5 Effect of processing conditions on the large pore (mercury porosimetry),

micropore (CO2 surface area) and carbon density (helium pycnometry) of

MTE, HTD and SD products, respectively. ................................................... 70

List of Tables xxvi

Table 3.6 Acid extractable inorganics, chlorine and total sulphur in raw and solid

MTE products (100g of wet raw lignite, actual mass in g) ............................ 76

Table 3.7 Acid extractable inorganics, chlorine and total sulphur in raw and solid

HTD and SD products (10g of dried raw lignite, actual mass in g)............... 76

Table 3.8 Proportions of inorganics, and chlorine removed by drying............................. 79

Table 4.1 Proximate analysis of raw lignite, HTD, MTE and SD products ..................... 94

Table 4.2 Mass balance of volatile yield quartz reactor versus pyrolysate yield

measured in the programs ............................................................................ 130

Table 5.1 Effect of particle size on the surface area of raw lignite................................. 158

Table 5.2 Ash, acid extractable inorganics and chlorine in the raw lignites and MTE

products (wt% db). MTE conditions: 150°C/5.1MPa .................................. 170

Table 6.1 Moisture holding capacity, proximate analysis, ultimate analysis and

calorific value of the Latrobe Valley coals used in this study ..................... 180

Table 6.2 Inorganic analysis of the raw, water washed and acid washed Loy Yang

and Morwell coals used in this study ........................................................... 182

Table 6.3 Inorganic analysis of the raw, water washed and acid washed Yallourn

coals used in this study................................................................................. 183

Table 6.4 Combustion reactivity arbitrary values and peak temperatures for the raw,

water and acid washed Latrobe Valley coals. .............................................. 189

Table 6.5 Intercorrelations among the physicochemical variables for the ten raw

Latrobe Valley lignites ................................................................................. 192

Table 6.6 Linear multiple regression analysis model summary...................................... 193

Table 6.7 Intercorrelations among the physicochemical variables for the raw, water

washed and acid washed Latrobe Valley lignites ........................................ 196

List of Tables xxvii

Table 6.8 Linear multiple regression analysis model summary...................................... 197

Table 6.9 Multiple regression coefficients for the combustion reactivity value

determined from the raw, water washed and acid washed samples ............. 198

Table 6.10 AAEM species, iron, chloride and sulphide ions present in the raw lignite,

water washed and acid washed products (mmol of univalent charge;

equivalent to 1g of dry raw lignite).............................................................. 209

Table 6.11 Combustion reactivity arbitrary values and surface area for the raw, water

and acid washed Latrobe Valley coals. ........................................................ 219

Table 7.1 Intercorrelations among reactivity and inorganic ion species for MTE

charred samples ............................................................................................ 226

Table D.1 Pore volumes of wet and dry MTE pellets and the proportion of the

original pellet size upon drying to zero moisture......................................... 250

Table D.2 Comparison between large pore region (measured by mercury

porosimetry) and pore volume calculated by measuring the dimensions of

the dry MTE pellet ....................................................................................... 255

Table E.1 Acid extractable inorganics, chlorine and total sulphur in raw and water

washed lignite (100g of wet raw lignite, actual mass in g) ......................... 257

Table F.1 Amount of inorganics present and pH for the product water from MTE

processing 100g of wet raw lignite (i.e. 40g db raw lignite; all values are

in mg) ........................................................................................................... 260

Table F.2 Amount of inorganics present and pH for the product water from HTD and

SD processing 10g of dried raw lignite (All values are in mg).................... 260

List of Tables xxviii

Table F.3 Concentration of inorganics present for the product water from MTE

processing 100g of wet raw lignite (i.e. 40g db lignite; all values are in

mgmL-1)........................................................................................................ 262

Table F.4 Concentration of inorganics present for the product water from HTD and

SD processing 10g of dried raw lignite (All values are in mgmL-1) ............ 262

Table F.5 The ions present in the product water (mmol of univalent charge) from

MTE, HTD and SD processing (equivalent to 10g of dry raw lignite)........ 265

Table G.1 Acid extractable inorganics, chlorine and total sulphur in raw and solid

dried products (wt%db)................................................................................ 275

Table G.2 Proportion of inorganic material removed and associated errors for MTE,

HTD and SD................................................................................................. 276

Table J.1 Molarity concentration of inorganics present for the product water from

MTE processing 100g of wet raw lignite (i.e. 40g db lignite; all values

are in M)....................................................................................................... 279

Table J.2 Molarity concentration of inorganics present for the product water from

HTD and SD processing 10g of dried raw lignite (All values are in M) ..... 279

Chapter 1: Introduction 1

CHAPTER 1 INTRODUCTION

1.1 Project aims • Investigation of a typical Latrobe Valley, Loy Yang lignite for the effect of

process conditions on the extent of dewatering of the lignite using a batch

mechanical thermal expression (MTE), hydrothermal dewatering (HTD) and

steam drying (SD) systems, respectively.

• Investigation of the physicochemical properties of the MTE, HTD and SD

products and their respective product waters, as a function of the original

properties of the lignite.

• Investigation of the effects of the physicochemical structure of the raw

lignite, MTE, HTD and SD products on the combustion reactivity of the raw

lignite and thermally dried products

• Investigation of two additional Latrobe Valley lignites (Morwell and

Yallourn) and comparison of their physicochemical properties and

combustion reactivity with those of the Loy Yang lignite.


1.2 Introduction The lignite in the state of Victoria represents an important state and national

resource. In Victoria, more than 95% of the electrical energy generated is fuelled

with lignites having moisture contents typically in the range of 60-67% on a wet

basis [1, 2]. Three major open cut mines are in operation in the Latrobe Valley

(Figure 1.1). The lignite reserves are vast (many hundreds of years supply according

to most estimates) and very cheap to mine. Alternative primary energy resources are

more limited and more expensive than lignite.

Latrobe Valley lignites are one of the world’s cleanest coals. These lignites typically

have very low sulphur and nitrogen contents (much less than 1%daf) and ash yields

of less than 2wt%db but their high moisture content is a major drawback for power

generation. The power generation from lignite produces higher levels of greenhouse

gas (GHG) than a plant of similar capacity fuelled with gas or even black coal.

Although thermal efficiency is dependant on the design of the plant, efficiency is

also substantially influenced by fuel moisture content [3]. For high moisture lignites a

significant part of the fuel energy is used to evaporate the water in the lignite, which

represents a major disadvantage for power generation by comparison with higher

rank coals. One means of reducing greenhouse gas emissions and improving the

thermal efficiency of existing lignite power stations is via the implementation of

more efficient drying technologies.


Figure 1.1 Latrobe Valley brown coal deposits and the location of the power plants [4].

In recent years several drying technologies have been assessed with regard to their

applicability to lignite power plants. Three of the major technologies under

consideration are:

• Mechanical thermal expression (MTE)

• Hydrothermal dewatering (HTD)

• Steam drying (SD)

The present study was carried out to investigate the changes in chemical and physical

structure that occurs when a Latrobe Valley lignite is processed in MTE, HTD and

SD laboratory batch units. The main features of the drying technologies listed above

and the background of the various batch, pilot and demonstration drying units

worldwide are summarised in the following sections.


1.2.1 Mechanical thermal expression (MTE) The application of a mechanical press for removing water from peat [5-8] and lignites

with a high moisture content [9-11] has been widely investigated. Banks and

Burton [10, 11] reported significant reductions in water content, for a much smaller

energy expenditure than that required for evaporative drying. In mechanical

expression (i.e. no heat applied), the pressures required to achieve significant

dewatering are very high. Hall et al. [12] reported a 21% moisture reduction in Loy

Yang lignite with an applied mechanical pressure of 54MPa. Guo et al. [13, 14]

reported that mechanical pressing of HTD products (at room temperature)

significantly reduced its macroporosity, and that the application of heat to the

mechanical press (i.e. MTE) further reduced the moisture content and macroporosity

of the product.

In MTE the fluid pressure is maintained greater than saturation pressure to prevent

evaporation, thereby avoiding the need to supply the latent heat of vaporisation. The

water from the lignite is therefore removed as a liquid and the net wet specific energy

(NWSE) of the final product is significantly improved. An advantage of MTE over

normal mechanical expression is that significantly lower applied pressures are

required to dewater high moisture lignites. With the co-application of mild heat (i.e.

150°C) and mild mechanical pressure (6MPa), the moisture reduction in the final

product for a Latrobe Valley lignite has been reported to be almost 70% [15]. In

addition, the MTE process causes irreversible pore collapse which limits the capacity

for the product to reabsorb water [16] .


The MTE process is very similar to the 1960’s briquetting process which

incorporated a combination of the Fleissner process and hydraulic presses to produce

dense pellets [17, 18]. The major difference in the 1960’s briquetting process compared

to batch MTE units is the periodic pressure releases whilst the system was under

pressure.

Previous MTE processes have had the disadvantages of long residence times and

high pressing pressures (16MPa). A novel MTE approach that has sparked new

interest in the MTE technology was a Rheinbraun Co. funded project at the

University of Dortmund. The novelty of this process was the application of a

commercial press commonly used in the preparation of chipboard (Figure 1.2). This

approach was found to significantly reduce process times, energy requirements and

pressing pressures (i.e. only up to 6MPa) [19-21]. The major advantage of this process

over the hydrothermal dewatering (HTD) technology is that the processing

temperatures are much lower (180-200°C), therefore significantly reducing the

concentration of organic matter in the water removed. The semi-batch process was

found to significantly reduce the moisture content of German high moisture coals

(typically 50-60%wb) to 24%wb. Based on the success at the University of

Dortmund MTE unit, several patents have been awarded [22-25]. Furthermore, a

demonstration unit with the capacity of 25t h-1 has been constructed at the

Niederaussem power station of RWE in Germany, and has been in operation since

2001 [26]. A schematic of this unit is shown in Figure 1.3.


Figure 1.2 Schematic diagram of the MTE pilot press at the University of Dortmund [20].

Figure 1.3 German 25t h-1 MTE demonstration unit [21]


The MTE technology was also developed by the Cooperative Research Centre (CRC)

for Clean Power from Lignite to dewater lignites and improve the overall efficiency

of power generation. In continuation of the comprehensive MTE work of Guo, the

CRC had developed a laboratory scale continuous MTE process [27], a 1t h-1 pilot

plant [28] and a 15t h-1 demonstration unit [29, 30]. The CRC claimed that the MTE

process was less expensive and more efficient than HTD and steam fluidised bed

drying (SFBD) [31]. Similarly, in a separate study conducted on external dryers for

Greek lignite-fired power stations, the MTE process was also postulated to be

marginally more efficient than SFBD [32].

1.2.2 Hydrothermal dewatering (HTD) Hydrothermal dewatering (HTD) or hot water washing is a non-evaporative drying

process for upgrading lignites with high moisture contents. The major advantages of

this process are that water is removed as a liquid so that the latent heat of

vaporisation is saved and much of the water-soluble inorganic material is leached

out, decreasing the inorganic content of the lignite [33].

The concept of HTD was developed by Fleissner [34] in Austria during the late 1920’s

and patented in 1927 [35, 36]. The Fleissner process used steam to heat coarse lumps of

lignites from Austria and Eastern Europe in a batch autoclave system at temperatures

between 180°C to 240°C, to produce an upgraded hard lump fuel. When the pressure

was reduced from the autoclave, liquid water was drained off with some loss of

steam, and the sensible heat remaining in the lignite product facilitated more water

being removed via evaporation. Fleissner process plants have been built in Victoria


(pilot plant) [37] and in Europe [38-40], including a large commercial plant (capacity of

855,000t yr-1 db) in Kolubara in the former Yugoslavia [41].

Evans and Siemon [42] patented a process in 1970 [43] and 1971 [44] in which 75% of

the water was removed as a liquid from the raw lignite, at temperatures above 250°C

whilst under pressure. The Evans and Siemon’s concept could be applied to lump,

granular or lignite slurry mixtures.

Murray and Evans [45] found that in HTD, the removal of water is primarily initiated

by thermal decomposition of hydrophilic groups and that pressure may serve no

other purpose than to prevent evaporation and consequent energy loss. The process is

completed by expulsion of water caused by carbon dioxide evolution, resulting in

changes in surface wettability and a reduction of volume.

A range of HTD processes have been developed, with several continuous bench scale

and pilot scale reactors being commissioned. Potas and Anderson [46] found that HTD

products were more easily slurried than the original coal and hence could be

transferred more efficiently to the generators.

The Grand Forks Energy and Environmental Research Centre (EERC) at the

University of North Dakota initially developed a HTD pilot plant with a process

capacity of 100kg h-1 of coal slurry [47-49] and later upgraded the plant to a 312kg h-1

capacity [50] (Figure 1.4). Similar to the Evans-Siemon process, a coal-water slurry


instead of raw coal was used as a solid fuel, which eliminated problems associated

with spontaneous combustion of coal fines.

Figure 1.4 Schematic flow diagram of the 100 kgh-1 HTD process development unit

at EERC [50].

The SECV Research and Development Department [now known as the Herman

Research Laboratory (HRL)] had constructed and operated a 1t h-1 coal slurry pilot

plant (Figure 1.5), giving a product that was suitable for gas turbine combustion,

industrial boilers, pressurized fluidised bed combustion and liquefaction

applications [51-53]. HTD products from Victorian and International lignites gave a

product with a maximum solids concentration of around 45 to 50wt%db [54].


Figure 1.5 Schematic diagram of the HRL's continuous HTD reactor [55].

The Japan COM. and JGC Corporation, in their joint research and development

program for upgrading lignites, built a continuous hot water drying plant with the

capability of processing 8.4 tonne of slurry per day (Figure 1.6) [55-57]. This Japanese

HTD plant reported very high maximum solids concentrations (>60wt%db) in their

coal-water mixtures and credited this success on the addition of chemical additives to

the slurry mixture [56, 58]. However, subsequent investigations into the rheology of

HTD slurries have found that differences in the viscosity measurement techniques

may have contributed to these higher maximum solids concentrations [59].


Figure 1.6 Schematic diagram of JGC's 8.4 tonne per day pilot plant [60].

1.2.3 Steam drying Steam drying is a process that utilises superheated steam to remove water from high

moisture coals. Steam-heated plate driers were used in Germany as early as 1874 to

dry low-rank coals for briquetting [61]. Rozgonyi and Szigeti [62] reported that up to

80% of the water and 50% of the sulphur can be removed from North American

lignites using steam as a drying medium. Potter et al. [63-65] commissioned a small

scale steam fluidised bed drying process at Monash University and found improved

thermal efficiency. This concept was further developed as a single stage process with

the capacity of 8t h-1 (evaporation) at Borna in the former East Germany [66-68]. In this

single stage system, the lignite was dried in a superheated steam fluidised bed with

part of the vapour being compressed and utilised as the heating steam (commonly

known as vapour recompression). Subsequently, this process offered major energy

efficiency advantages over conventional evaporative drying systems. Two

atmospheric, commercial demonstration size, steam fluidised bed drying (SFBD)


plants based on the Potter et al.’s technology were designed and constructed by

Rheinbraun and Lurgi at Wachtberg, near Frechen [69, 70] (in the former East

Germany) and at Loy Yang in the Latrobe Valley. A feature of these plants was that

the steam generated from the lignite provided an inert environment [71] and itself

assisted in further drying of the lignite, so that much of the latent heat of vaporisation

was recovered. The operating conditions for the SFBD are given in Table 1.1. Both

of these SFBD plants had an output capacity of 20t h-1 of dried lignite. The SFBD

plant at Loy Yang (Figure 1.7) operated from 1992 [72] to 2003 in supplying part of

the feed to the Loy Yang B power station [73] and for auxiliary firing of the boiler

during start up. This 150,000t yr-1 (dry basis; db) SFBD plant had an operating

temperature of 107°C to produce a lignite product with only 12% moisture. In

contrast, the Wachtberg plant operated from 1993 to 1999 which mainly supplied

dried lignite into the briquette factory. Furthermore, the Rhenish lignite that was

dried at the Wachtberg plant had a lower initial moisture content and subsequently,

in order to achieve the same degree of dying as the Loy Yang lignite, a marginally

higher operating temperature at 112°C was required [74-76].


Table 1.1 Typical operating conditions of a SFBD [77-79]

Bed conditions 1-10kPa g, 106-120°C

Fluidising steam 15-25kPa g, slightly superheated

Heating steam 400-500kPa g, saturated

Coal feed size 0-6mm

Product size 0-4mm

Product moisture 10-20%

Heat transfer coefficient 50 Wm-2K

Coal residence time 60-90min

Based on the success of the Loy Yang and Wachtberg SFBD units, RWE Energie

built a significantly larger demonstration SFBD unit at the Niederaussem lignite

power station with a maximum capacity of 100t h-1 db [80]. This larger unit was

commissioned in 2000 but closed in 2002 [81]. Also in 2002, a pressure loaded steam

fluidised bed drying pilot plant with a maximum capacity of 500kg h-1 of raw fine

coal (<6mm) and a maximum fluidising steam pressure of 6.5bar (absolute) was

commissioned by the Brandenburg Technical University (BTU) in Cottbus, Germany

(Figure 1.7 and Figure 1.8). The pressurised SFBD has been postulated to give better

recovery of latent heat of evaporation than the atmospheric SFBD systems [82, 83].


Figure 1.7 Schematic of the pressurised fluidised bed drying system at BTU Cottbus,

Germany [83]

Figure 1.8 Pressurised fluidised bed drying system at BTU Cottbus, Germany [84]


1.3 Factors affecting the combustion reactivity of lignites The properties of the products relevant to their use in power generation (e.g. in

combustion or gasification-combustion) are also of interest. The presence of high

concentrations of alkali and alkaline earth metals (AAEM) in the dried products can

be disadvantageous to power generation as it can cause significant fouling and

slagging in the boilers. However AAEM species can also be advantageous in

improving the conversion of the solid products. Furthermore, changes in the

product’s physical properties during drying (e.g. pore reduction/product hardness)

may also play a significant role in the milling process prior to combustion. The

products of the different drying methods would be expected to vary with respect to

these properties. The fate of inorganic material and the changes in physical properties

from MTE, HTD and SD processes are summarised in the following sections.

1.3.1 Inorganic material in Latrobe Valley lignites The mineral and inorganic components in Latrobe Valley lignites can cause profound

operational problems during power generation [85-89]. Latrobe Valley lignites have a

very low mineral and inorganic composition compared to other coals around the

world, with typical ash yields between 1 to 2% of the weight (wt%) of the lignite [90]

(on a dry basis; db). However, Latrobe Valley lignites also contain relatively high

levels of AAEM species within the ash component, which can lead to significant

fouling and slagging during power generation and subsequently, reduce plant

performance and increase the cost of maintenance. Ash deposition on furnace walls,

superheaters and economiser tubes have been found to reduce the heat transfer and

restrict the gas flow [91-93]. Furthermore high levels of sodium have been reported [94,

95] to cause excessive erosion and corrosion of gas turbine blades in a coal-fired

turbine.


On the other hand, AAEM species are very good catalysts for pyrolysis [96-98],

combustion [99], gasification [100, 101] and liquefaction [102, 103] processes. The presence

of ion-exchangeable AAEM species in lignite can greatly affect the rate of

conversion of the solid products but also the quality of the volatiles being released

from each of these processes.

SD is an evaporative drying technology and the inorganics are often retained within

the coal product [104]. In contrast, in HTD, the coal is heated under pressure and the

water in the system is removed from the coal as a liquid. The removal of liquid water

also facilitates the leaching of water-soluble inorganic material which decreases the

inorganic content of the product coal. HTD experiments performed at SECV’s pilot

plant, using Loy Yang lignites (<1% db inorganics), showed a reduction in sodium

levels of about 30% and in sulphur levels of about 25%, with no effect on the levels

of calcium and magnesium [105].

Similar to HTD, in MTE, the water in the coal is maintained in the liquid state with

the application of heat and mechanical pressure, and subsequently soluble inorganic

species are also leached from the coal along with the expelled liquid water. MTE

experiments by Kealy et al. [106] found that the removal of sodium was related to the

volume of water pressed out from the lignite whereas the levels of calcium,

magnesium, iron and aluminium were unaffected with MTE processing.


1.3.2 Pore structure The porosity of Latrobe Valley lignites is a significant factor in influencing its

behaviour during drying and its reactivity [107]. For Latrobe Valley lignites, the

average bed-moist porosity is about 70%, however, due to shrinkage on drying, the

average dry porosity is around 40%. Furthermore, as coal rank increases, the porosity

of the coal generally decreases, with black coals generally having porosities of less

than 10% [108].

The internal pore volume measured by mercury porosimetry has been found to

correlate with the maximum solids concentration in a pumpable coal-water slurry and

the moisture-holding capacity for the HTD products [59]. These HTD products, were

found to retain their internal pore volume when completely dried, however, for raw

lignites, the internal pore structure collapsed during complete drying, and

subsequently, no correlation was found between mercury porosimetry results and

maximum slurry concentrations [109].

Currently, very little information is available on whether significant changes in the

product’s pore volume can affect its combustion reactivity. Low porosity products of

HTD compared with high porosity products have been reported to take longer to

combust completely than their parent coal [59]. This study will compare differences in

the internal pore structure of MTE, HTD and SD products and also evaluate the

effect of porosity on the combustion reactivity of the thermally treated products.


1.4 Scope of the thesis This study aims at investigating how variations in processing conditions affect the

physico-chemical properties of MTE, HTD and SD treated Loy Yang lignites. The

influence of the product’s pore structure and the effect of AAEM species on the

combustion reactivity are also investigated.

There are 8 chapters in the manuscript, including this chapter. For Chapters 3 to 7,

the main conclusions from each of these chapters are given at the end of the chapter.

Detail structures of each chapter are given below.

To investigate the effectiveness of MTE, HTD and SD, a Loy Yang lignite was

processed under various temperatures and for MTE, different applied mechanical

pressures, and the product moisture content and the coal mass recoveries from each

process is discussed in Chapter 3. Furthemore, the change in the physical pore

structure of the lignite resulting from MTE, HTD and SD processing, is also

discussed in Chapter 3. In addition, the behaviour of inorganic material during MTE,

HTD and SD processing is examined in Chapter 3. Quantification of the inorganic

material remaining in the solid products and the amount leached out into the product

waters are reviewed.

In Chapter 4, several pyrolysis techniques are utilised to investigate the pyrolysis

behaviour of the raw lignite and of the MTE, HTD and SD products. In addition, the

quantification and characterisation of the volatilised components from the pyrolysis


of the raw lignite and its thermally treated products, as a function of temperature are

also discussed.

In Chapter 5, the combustion reactivity of the raw lignite and MTE, HTD and SD

products are measured using a thermogravimetric analyser (TGA). The effect of pore

size distribution and the effect of catalytic inorganic species on the combustion

reactivity of the products are investigated.

The combustion reactivities of a number of well-characterised lignites sourced from

the Latrobe Valley open cut mines are examined in Chapter 6. The intercorrelations

between physicochemical properties and the combustion reactivities of the lignites

are performed using statistical analysis. In addition, the transformations of cationic

components during volatilisation and combustion, and the effectiveness of these

species in facilitating the breakdown of organic components are also discussed.

In Chapter 7, the combustion reactivity of the chars produced from the pyrolysis of

an MTE product is investigated. The influence of the catalytic components in the

char and their effect on the combustion-oxidation process are investigated. In

addition, the effect of the char surface area and the large pore volume on the

combustion reactivity of the char is also examined.

The overall conclusions from the work performed in this thesis is presented in

Chapter 8.

Chapter 2 Experimental 20

CHAPTER 2

EXPERIMENTAL

2.1 Methodology The methodology adopted for this study involved:

• Selection of three Latrobe Valley lignites varying in lithotype, atomic H/C,

inorganic constituents and as-mined moisture contents.

• Drying one of the selected lignites in a batch hydrothermal dewatering

(HTD), mechanical thermal expression (MTE) and steam drying (SD) reactor

system, respectively.

• Characterisation of raw lignites and thermally dried products using a wide

range of physical and chemical techniques, including elemental analysis

(organic and inorganic), mercury porosimetry, carbon dioxide adsorption (to

determine surface area), helium density and proximate analysis using a

thermogravimetric analyser (TGA).

• Analysis of the product water from the drying processes by atomic absorption

spectroscopy (AAS), pH measurement, and determination of its total organic

carbon (TOC) and sulphur content.

• Investigation of the pyrolysis behaviour of raw lignites and thermally dried

products using several slow and fast pyrolysis systems including TGA (slow

pyrolysis), quartz fluidized-bed/fixed-bed reactor system (slow and fast

pyrolysis) and pyrolysis-gas chromatography (fast pyrolysis).


• Measurement of the combustion reactivity and peak temperatures of the raw

lignites and thermally dried products using a TGA.

2.2 The lignites Ten lignites were chosen from the three Latrobe Valley open-cut mines namely; Loy

Yang, Yallourn and Morwell (see Figure 1.1). The majority of the work presented in

this study is on Loy Yang lignite. The lignite samples received had been preground

and sieved to particles sizes of <4mm. The lignites were coned and quartered to

provide representative samples. Excess lignite was stored in airtight containers to

minimise oxidation.

2.3 Preparation of lignite slurries (HTD only) The lignite moisture content of representative samples [3g wet basis (wb)] was

measured as described in Section 2.13 on the day of each HTD reaction. This value

was used to calculate the additional water necessary to make up lignite-water

mixtures with 1:3 dry lignite-water ratios, from 200g of raw lignite (<4mm particle

size).

2.4 Discrete particle size lignite preparation 10kg (wb) of raw Loy Yang lignite was dried under vacuum for 3 days to reduce the

moisture content to 15%wb. A Fisher-Wheeler sieve shaker was used to assist in

sieving the dried lignite into 19 sized fractions (Table 2.1) using British test sieves

ranging from 2000 to 45μm. All sieved fractions were then stored in airtight

containers and placed in a fridge to prevent oxidation.


Table 2.1Discrete particle sized lignite fractions

1400≤μm≤2000

180≤μm≤250

1180≤μm≤1400

150≤μm≤180

1000≤μm≤1180

125≤μm≤150

850≤μm≤1000

106≤μm≤125

710≤μm≤850

90≤μm≤106

600≤μm≤710

75≤μm≤90

500≤μm≤600

63≤μm≤75

425≤μm≤500

45≤μm≤63

355≤μm≤425

≤45μm

250≤μm≤355

For Yallourn and Morwell samples, the raw lignite was passed through 125μm and

90μm sieves (without milling) and the fraction 90<μm<125 was collected (mean

particle size ~100μm) for combustion reactivity tests.

2.5 Water washing and acid washing of lignites The proportion of water soluble salts (mainly free ionic metals) and water insoluble

ions (metals bound to the lignite as phenolates and carboxylates) were determined by

comparing analyses of the original lignite and the same lignite washed with distilled

water. For lignite water washing, lignite [100g (wb)] and distilled water (500mL)

were slurried and stirred in a conical flask for 24h and then filtered. The lignite was


again slurried with 500mL distilled water, stirred for 24h and filtered. Washing was

repeated 3 times and the lignite then stored in airtight containers prior to analysis.

For acid washing, the same procedure as above was performed however the washing

was carried out with 0.1M HCl solution. The lignite slurry was washed and filtered 3

times with HCl solution followed by an additional 3 washes with distilled water to

remove residual acid solution. The water washed and acid washed samples were then

sieved to 90<μm<125, stored in airtight containers prior to combustion reactivity

tests.

2.6 Autoclaves Three batch autoclave systems were used in this study:

1. For hydrothermal dewatering experiments, a 70mL 316 SS autoclave heated in a

stationary position in a fluidised sandbath.

2. For steam drying experiments, a 500mL 316 SS autoclave heated in a stationary

position.

3. For mechanical thermal expression, a batch 300mL 316 SS autoclave heated in a

stationary position using a heating jacket.


2.7 Hydrothermal dewatering A schematic diagram of a 70mL autoclave is shown in Figure 2.1. 40.00g (weighed

to an accuracy of 0.01g) of 1 part lignite : 3 parts water (1:3 lignite:water ratio) was

loaded into the autoclave. The autoclave was sealed and leak tested with hydrogen

(~8MPa) using a thermal conductivity leak detector “Leak Seeker 96” and the

autoclave was then evacuated and kept under vacuum for 5min so to remove any

trapped gases. The autoclave was mounted onto a stainless steel cradle and lowered

into the sandbath, the temperature of which had been preset to the values summarised

in Table 2.2, varying with the desired autoclave temperature. The autoclave

temperature was monitored by a thermocouple placed inside the thermocouple well

(thermowell) of the autoclave.

Table 2.2 Set-up temperatures for 70mL autoclave HTD reactions

Autoclave

temperature

(°C)

Sandbath preset

temperature

(°C)

Equilibration

Point *

(°C)

180 220 199

200 240 218

230 270 248

250 300 281

280 340 306

300 360 325

320 390 354

350 430 378

* Equilibration point is the temperature of the sandbath which gives the desired temperature inside the autoclave

Chapter 2 Experimental

25

The air pressure used to agitate the sandbath was set at 250kPa and after the

autoclave had been lowered, the sandbath temperature setting was then lowered to

the equilibration point given in Table 2.2.

The temperature of the autoclaves and the temperature of the sandbath were

monitored using a Shimaden SR41 and Eurotherm controller, respectively. The

desired autoclave temperature (Table 2.2) was reached within 10min with a

maximum overshoot of 1°C and then maintained for an additional 10min at the

processing temperature. After the 10min holding time, the reactor was quenched in

cold water and further cooled in a stream of compressed air until the autoclave

temperature fell to 10°C above the room temperature (see Section 2.8 for workup

procedure).

2.8 HTD and SD work-up procedure After cooling, a stream of compressed air was used to clear all sand from around the

sealing surfaces of the reactor. The gas in the reactor was then slowly vented and the

solid/liquid products were thoroughly scraped out and carefully collected by washing

with distilled water. For experiments involving Total Organic Carbon (TOC) analysis

of the product water, the water from the reaction was filtered with no further dilution

and immediately collected and sealed in an airtight container, before more water was

added to wash the entire solid product out of the autoclave. The solid products were

collected and dried in an oven at 105°C for 3h under a stream of nitrogen gas.

26

1.25”

4.50”

0.75”

1.00”

1.75”

0.625”

1.50”

1.437”

Angle 60O

0.060”

0.040”1.437”

1.850”

1.696”

0.375”

1.00”

0.125”

0.0625” Hole

0.406” 0.427”

1.00”

1.850”

1.00”0.1875”

Pressure Ring

Top View

Side ViewAutoclave Head

Autoclave Body 2.625”

0.50”

1.00”

2.125”

1.4375” 2.625”

Autoclave Head

Thermowell and ClosureSide View

Top View

Figure 2.1 Schematic diagram of the 70mL autoclave

Chapter 2 Experimental


2.9 Mechanical thermal expression MTE experiments were conducted using a batch MTE unit (Figure 2.2)

Figure 2.2 Schematic diagram of the MTE batch unit

Raw lignite (~600μm particle size, 100g wb) was placed inside a compression-

permeability cell consisting of a piston and die assembly with a 50mm internal bore

diameter (Figure 2.3).

Figure 2.3 Components of the MTE batch cell


A new flexible O-ring was used for each experiment so to ensure that no steam

escaped the cell during each test. The cell was filled with a known weight of distilled

water (~100g) to expel air from the lignite sample, sealed and heated up to the

desired temperature (125 to 250°C). Once the desired temperature was reached, a

computer controlled Instron Universal Testing Apparatus (Model 5569) was used to

automatically increase the force on the MTE cell at a compression rate of

50mm min-1 until the final pressing pressure was reached (typically 2.5MPa, 5.1MPa,

12.7MPa or 25.0MPa). The pressing pressure was maintained for 20min before

cooling down the sample and collecting the pressed product. Water expelled from the

sample during the experiment was allowed to pass through porous brass sintered

plates (Figure 2.2) to a lower collection chamber of the cell and also to the hollow

piston chamber.

2.10 MTE workup procedure On completion of the MTE run, the applied pressure on the MTE cell was released

and the cell dismantled. The MTE pellet was collected, weighed immediately and

stored inside two air tight bags.

The MTE product water was then collected and stored in a separate bottle. The entire

system was then thoroughly rinsed with distilled water and the rinsing water also

collected in a separate bottle. Both the product water and rinsing water were then

filtered through a glass fibre filter and stored below 5°C for subsequent use. Analysis

of the product water and rinse water were conducted separately and the resulting

values combined to give a total concentration.


2.11 Steam drying experiments A container with a 75μm mesh top and bottom was charged with 25.00g wb

(weighed to an accuracy of 0.01g) of raw lignite and then attached to the

thermocouple rod of a 500mL autoclave. Distilled water (50.00g, weighed to an

accuracy of 0.01g) was poured into the autoclave and the thermocouple with the

container was then lowered to a position above the water level (Figure 2.4). The

autoclave was sealed, leak tested and then heated up to the desired temperature (130

to 350°C) which was then held for 30min at the processing temperature (Figure 2.5).

After the 30min holding time had elapsed, the reactor was quenched in cold water

and further cooled in a stream of compressed air until the autoclave temperature fell

to 10°C above room temperature. The container inside the autoclave was removed,

weighed and the solid lignite products dried in an oven at 105°C for 3h under a

stream of nitrogen gas.


Figure 2.4 Schematic of the 500mL batch autoclave used for steam drying lignite


0

50

100

150

200

250

300

350

0 5 10 15 20 25 30 35 40 45 50

Reaction time (min)

Aut

ocla

ve te

mpe

ratu

re (°

C)

350°C

330°C

320°C

310°C

300°C

280°C

250°C

230°C

200°C

180°C

150°C

130°C

Figure 2.5 Temperature heat up profile for the steam drying experiments.

Table 2.3 Set-up temperatures for 500mL autoclave SD reactions Autoclave

temperature

(°C)

Sandbath preset

temperature

(°C)

Equilibration

point

(°C)

130 170 145

150 200 170

180 220 200

200 240 220

230 310 250

250 350 280

280 380 305

300 415 330

310 435 340

320 450 345

330 470 355

350 500 380

Note: Compressed air bubbling through the fluidized sandbath was often adjusted during the experiment in order to achieve a 15min heat up time and to prevent overshoot of the autoclave temperature.


2.12 Pore size distribution analysis Pore size distributions on the lignite samples were performed on a Micromeritics

AutoPore porosimeter. Approximately 0.2g of pre-dried raw or dried products

(~0.2g) was loaded into the penetrometer and the mass recorded on a balance (four

figure accuracy). Low pressure and high-pressure mercury intrusions were measured

in the range of 0.76 to 29.99psia (5kPa to 207kPa) and 29.99 to 60,000psia

(0.2 to 414MPa), respectively. Each pressure step was allowed to equilibrate for

15sec before the intrusion measurement was recorded. On completion of the high-

pressure analysis, the mercury was emptied into a plastic polyethylene bottle and the

penetrometer cleaned using a 50:50 mixture of methylethylketone and toluene.

2.13 Determination of lignite moisture content The moisture contents of the raw lignite and the thermally treated products were

performed in duplicate and were determined similarly to the Australian Standard

Method (AS2434.1) [110]. For HTD and SD products, a representative sample

weighing approximately 5g was weighed and dried under nitrogen at 105°C for 3h.

For MTE products, the solid pellet (approximately 40g db) was also dried at 105°C

under nitrogen but for 6h. The dried products were then placed inside of desiccator,

sealed, and the air evacuated to prevent moisture reabsorption from the air. The

samples were allowed to cool down inside the desiccator for 15min before being

weighed to determine their respective moisture contents.


2.14 Wet and dry pellet density measurements Wet and dry density measurements of the MTE pellet were conducted using a

calliper and calculated using the equations 2.1 to 2.4 given below:

31.0mm (b)

50.0mm (a)

42.0mm (c)

Y

Figure 2.6 Schematic of a wet MTE pellet

YY

XX

x 21 (%) shrinkage Vertical

wet

dry

wet

dry⎟⎟⎠

⎞⎜⎜⎝

⎛+= Equation 2.1

100 x aa

(%) shrinkage Horizontalwet

dry= Equation 2.2

drywet pellet of Mass -pellet of Mass pellet in water of mass Total = Equation 2.3

x100pellet wet of volumeTotal

pelletin water of volumeTotal(%)porosity Wet = Equation 2.4


2.15 Slow and rapid pyrolysis of raw and thermally treated products

Slow and fast pyrolysis experiments of the raw lignite and thermally treated products

were carried out using a quartz fluidised-bed/fixed-bed reactor (Figure 2.8) heated

with an external tubular furnace. The reaction system consisted of a particle feeder

and a quartz reactor system. Rapid heating of the raw lignite and the thermally

treated products was achieved by injecting a stream of particles directly into a

heated, fluidised bed of zircon sand. Details of the particle feeder, quartz reactor and

the experimental protocol are described below.

2.15.1 Pre-treatment of raw and thermally dried products Prior to a pyrolysis experiment, the raw lignite or thermally treated products were

vacuum dried overnight at room temperature. The moisture contents of the vacuum

dried lignite particles were determined in duplicate before being placed into the

particle feeder. Tests involving passing argon into the particle feeder for 20min gave

no additional loss in moisture from the vacuum dried particles.

2.15.2 Particle feeder A schematic diagram of the particle feeder system is shown in Figure 2.7. The design

of the particle feeder was based on similar systems published elsewhere [111, 112]. The

particle feeder consisted of three tubes; an outer 1/2” glass tube, a 3/8” stainless steel

tube (gas stream tube) which was positioned inside the 1/2”glass tube and a 1/4”

stainless steel tube (particle carrier tube) positioned inside the 3/8” tube (Figure 2.7).

The glass tube contained a rubber seal and a Viton-A® O-ring inside a male and

female nut which provided a gentle seal against any leakage of the argon gas stream

and also allowed the movement of the glass tube along the outer of the 3/8” stainless

steel tube. A stepper motor, controlled by a Thurlby Thandar Instruments TG215


2MHz function generator, moved the glass tube upwards which in turn, brought the

particle bed closer to the ends of the stainless steel tubes. The passing of argon

through the ends of the stainless steel tubes created a dilute particle dispersion above

the particle bed. Part of this particle dispersion was blown into the 1/4” tube and fed

into the quartz reactor. The rate of the particles being blown into the quartz reactor

was controlled by the speed of a stepper motor and the flow of argon passing through

the feeder. For all of the fast heating pyrolysis experiments, the output frequency of

the function generator was set at 4Hz and the flow rate of the argon carrier gas was

maintained at 1.0L min-1. Under these conditions, the stepper motor moved the glass

tube upwards at 3mm min-1 and the particle feed rate into the quartz reactor was

~100mg min-1. A vibrator attached to the bottom of the glass tube holder also

facilitated the agitation of the reservoir particle bed and enhanced the dispersion of

particles. In addition, the vibrator minimised channelling, prevented particle

deposition on the glass tube walls and prevented tube blockages on the inlet of the

1/4” carrier tube.


Lignite or thermally treated particles

” SS tubing1/4

” SS tubing1/4

3/8” Union Tee

Lignite particlesentrained in gas

(to quartz reactor)

” SS tubing3/8

O-ring

Rubber seal

Gas in

Female nut

Glass tube” 1/2

Male nut

VibratorScrew connectedto stepper motor

Gla

s s tu

be m

ove m

ent

(Gas stream tube; tube position fixed)

(Particle carrier tube; tube position fixed)

Figure 2.7 Schematic of the lignite particle feeder


2.15.3 Quartz reactor design Quartz fluidised bed reactors have been used by a number of groups in studying the

pyrolysis and gasification of lignites [113-116]. The design of the quartz reactor system

for this study was based on a similar system previously used in coal pyrolysis [100].

Quartz instead of high temperature grade stainless steel was selected as the reactor

material because the impurities in stainless steel (such as Cr, Mn, Ni and S) could

potentially catalyse [117, 118] and interfere with pyrolytic reactions as these metallic

species are also known to be very good petrochemical catalysts (see Appendix A for

the chemical analysis of high temperature grade stainless steel (SS253MA)). In

contrast, quartz is relatively inert [119, 120], it can withstand temperatures above

1000°C and is relatively inexpensive. Furthermore, similar quartz reactors [113, 121]

heated in an external furnace have reported rapid particle heating rates of the order

104°C s-1.

The quartz reactor for this study consisted of a 40mm diameter chamber with two

quartz frits (porosity 0) spaced 130mm from one another (Figure 2.8). The upper frit

prevented the elutriation of char particles and permitted the removal of evolved

volatile material out of the quartz reactor during pyrolysis whilst the bottom frit

reduced the incidence of gas channelling through the sand bed. Furthermore, a

second argon stream containing the coal particles facilitated in fluidising the sand

bed. This second stream was injected directly into the chamber via a ¼” tube located

approximately 20mm above the bottom glass frit. To achieve rapid particle heating

rates, this ¼” particle injection tube was surrounded by a water cooled 1/2”

condenser.


Fluidisinggas

Coolingwater

in

Sandbed

Quartzfritz

Lignite or thermally treated

particles entrainedin gas

Thermocouple

Volatiles

Water cooledprobe

Coolingwaterout

Collection tube(collection of

charred particles)

Volatiles andgas out

130m

m

40mm60mm

480m

m

20m

m

Figure 2.8 Fluidized quartz reactor design


2.15.4 Slow pyrolysis experiments For the slow heating experiments, 160g of acid washed dried zircon sand was loaded

into the quartz reactor and the reactor weighed. The raw lignite or thermally treated

products (3.00g db) were also fed into the reactor at room temperature. Ultra high

purity (>99.99%) argon (total flow rate of 3.0L min-1) was used to fluidised the sand

bed and to thoroughly mix the lignite material inside the reactor. The argon was fed

into the reactor at two separate points, from the bottom and from a tube inside the

condenser arm (Figure 2.8). The flow of argon into the reactor was controlled using

two Aalborg Mass Flow Controllers (MFCs). A flow of water (1L min-1) was also

used to cool the gas inlet inside the condenser arm and prevent subsequent blockages

during the experiment.

The quartz reactor was then lowered into a Ceramic Engineering tubular furnace

(Figure 2.9) and slowly heated (40-50°C min-1) from room temperature to the desired

pyrolysis temperature. The quartz reactor was maintained at temperature for 15min

before being lifted out from the furnace and cooled down. The pyrolysis temperature

was measured with a K-type thermocouple positioned on the upper frit of the quartz

reactor (Figure 2.8). The maximum temperature overshoot allowed was 0.5°C. The

tubular furnace contained three separate heating zones which provided uniform

heating along the quartz reactor chamber (Figure 2.9).


Fluidising gas

Coolingwater

Coal particlesfrom feeder

Thermocouple

Volatiles and gas out

Furnace walls

Quartz reactor

Pulley

Reel

Furnace Thermocouple 1



Figure 2.9 Schematic diagram of the pulley system used to lower and raise the quartz

reactor from the tubular furnace.


2.15.5 Fast pyrolysis experiments For fast heating experiments, a particle feeder was used to inject a stream of raw

lignite and thermally treated particles directly into the reactor at pyrolysis

temperature (Figure 2.7). The schematic of the experimental rig for the fast pyrolysis

tests is shown in Figure 2.10. Similar to the slow heating experiments, 160g of acid

washed dried zircon sand was loaded into the quartz reactor and the reactor weighed.

The flow of argon and cooling water were also kept the same as described above.

The quartz reactor was then heated to the desired temperature and allowed to

equilibrate for 15min before injecting the lignite material (~3.0g db) from the particle

feeder and into the hot reactor. The particles were fed from a particle feeder (see

Section 2.15.2) at a rate of ~100mg min-1.

On completion of the experiment, the quartz reactor was cooled down to room

temperature, the water within the condenser was evaporated using a Bunsen burner

and any residual tar material that was deposited within the thermocouple and exit

tubes was burnt off. The quartz reactor was then reconnected to the experimental rig

and heated to 150°C. A stream of argon passed through the sand/char bed to drive

off absorbed moisture for 60min and then cooled to room temperature. The weight

loss during pyrolysis (i.e. the total volatile yield) was determined by direct

measurement of the reactor weights before and after each experiment.


Arg

on

P

P P

Feeder

Reactor

Exhaust

P

MFC

T

Mass Flow Controller

Pressure gauge

Thermocouple

Valve

MFC

MFC

Figure 2.10 Schematic of experimental rig


2.15.6 Char collection A schematic of the method for collecting the char particles is shown in Figure 2.11.

The char particles were retrieved from the quartz reactor via the collection tube. To

collect the char particles, the particle injection and thermocouple tubes were plugged

and a stream of argon was passed through the fluidising gas tube and out of the

collection tube. The heavy zircon sand made it easy to separate the residual char

from the sand due to differences in density. The flow rate of the argon was increased

until the char was separated from the sand and collected in a cellulose thimble. The

char material was then placed in a plastic container and stored in a freezer for

subsequent analysis.

Tube plugged

Argon in

Argon out

Sand and charred particles

Charred particlesin collection tube

Figure 2.11 Schematic of the method for collecting the char particles from the quartz

reactor.


2.16 Volatile matter and fixed carbon determination Proximate analysis using a Setaram Labsys thermogravimetric analyser (TGA) was

conducted on raw and thermally treated products. Approximately 25 to 30mg of oven

dried lignite (105°C, Argon, see Section 2.13) of less than 250μm particle size was

weighed to ±0.00001g into the TGA’s ceramic crucible. The TGA was purged with

argon gas to provide an inert atmosphere. The sample was initially heated at 20°C for

30sec. The temperature was then increased at a rate of 30°C per min up to 110°C and

maintained at this value for 15min so as to remove any reabsorbed water. The sample

was then heated at a rate of 50°C per min to 950°C and held at 950°C for 15min. The

purging gas in the TGA was then switched over to air to allow combustion of the

lignite material. The analysis was completed after a flat baseline was obtained. The

ash yield of the sample was determined from the mass remaining in the crucible.

2.17 Combustion reactivities Combustion reactivities for the lignite samples (125 to 250μm particle size) were

measured using a TGA. The sample was initially heated at 20°C for 30sec in air. The

temperature was then increased at a rate of 30°C per min up to 400°C (non-

isothermal) and maintained until complete conversion was achieved (isothermal).

Combustion experiments were also conducted on Morwell and Yallourn MTE

products (150°C/5.1MPa) up to 400°C (90 to 125μm and 250-500μm particle size,

respectively) and also up to 450°C for the 250-500μm particle size only. The

combustion reactivity (Rx) was calculated from the DTG data (dW/dt) according to

the formula: dt

dWW

RX ⋅−=1

where W is the weight of the sample (dry ash free) at any given time (t).


2.18 Ash determinations Ash determinations on raw and thermally treated lignites were conducted using a

Carbolite (type ESF 12/2) furnace. Two representative samples of the lignite to be

ashed (~1g) were pre-dried at 105°C under a flow of nitrogen (see Section 2.13). The

dried samples were taken out of the oven, immediately placed in silica crucibles of

known mass and then weighed to ±0.0001g. A third empty crucible was weighed at

the same time. The three crucibles were heated without lids in a muffle furnace at

400°C for 3h. The temperature of the oven was then raised to 600°C (to avoid loss of

sodium), and was held for 6h. The crucibles plus ash were cooled for 30min in a

desiccator and weighed. The mass of the ash was calculated, correcting for the

change in mass of the crucibles during heating from the change in mass of the empty

crucible.

2.19 Total inorganic contents The total sodium (Na), calcium (Ca), magnesium (Mg), iron (Fe), aluminium (Al),

potassium (K), silicon (Si) and titanium (Ti) were determined according to the

Australian Standard method (AS 1038.14.1) [122]. The acid extractable metals Na, Ca,

Mg, Fe and Al were determined by a method based on the Australian Standard

method (AS 2434.9) [123]. An oven dried (see Section 2.13) lignite sample was wetted

with ethanol in a beaker, then 60mL of a solution of 0.003M H2SO4 was added and

the mixture brought to boil, allowed to simmer uncovered for 15min and covered

(with a watch glass) for a further 45min. The mixture was then filtered and the filter

cake was further washed with hot 0.003M H2SO4.


The Al, Fe, Mg, Ca and Na contents of the filtrate were determined by Atomic

Absorption Spectrophotometry (AAS). The instrument was calibrated against

solutions of known concentration. The sample absorption was then used to obtain the

sample concentration by reading off the calibration curve. Analyses were done in

triplicate with regular re-calibrations and blank solution checks.

2.20 Product water analysis

2.20.1 Cation and anion analysis Cation and anion analysis were performed at Monash University Water Studies

Centre (WSC) on the product water obtained from the drying processes. A Perkin

Elmer flow injection system (FIAS 200) coupled to a Perkin Elmer atomic

absorption spectrometer was used to analyse for potassium (WSC test method 11A),

sodium (WSC test method 12A), calcium (WSC test method 10A) and magnesium

(WSC test method 13A). Direct AAS was used for aluminium analysis using WSC

test method 14.

Chloride was determined colourimetrically by reacting mercury (II) thiocyanate

(Hg(SCN)2) and iron (III) to form the complex ion Fe(SCN)2+, which is red in

colour. The absorbance of the coloured complex, measured spectrophotometrically,

is proportional to the Cl– in the sample (WSC test method 7).

Sulphate was detected by mixing barium chloride and methyl thymol blue solution

with the wastewater sample. Sulphate present in the wastewater precipitated as

barium sulphate. Excess barium in the solution was detected by the formation of a


blue coloured chelate at high pH, the concentration of which depends on the

concentration of sulphate in the solution. As the sulphate concentration increased, the

amount of barium available to form the chelate was reduced and the absorbance

decreased (WSC test method 8).

2.19.1 Total organic carbon (TOC) The TOC present in the water produced from the drying processes was determined

according to WSC test method 57A, using a Shimadzu TOC-5000 analyser.

The product water sample was injected into the TOC analyser and heated to 700°C in

the presence of high purity oxygen. The oxidation of the organic carbon material to

carbon dioxide (CO2) was detected and recorded by the instrument. A calibration

curve was produced and the peak area was proportional to the concentration of the

carbon in the sample.

2.21 Surface area and micropore volume CO2 and N2 adsorption isotherms were conducted on the lignites and thermally

treated products to determine the surface areas and pore size distributions,

respectively. The adsorption isotherms were measured using a Micromeritics Tristar

surface area analyser. The glass sample tube, equipped with a Transeal™ valve, was

weighed on a five-figure balance. Samples were placed in the sample cell (0.15 to

0.25g) and the entire set-up reweighed on the same balance. The samples were then

heated at 105°C for 6 hours under vacuum. The individual glass tubes were cooled

down to room temperature and the entire set-up reweighed to determine the mass of

the dried sample.


The sample tubes were then connected to the Tristar analyser and the entire surface

area analyser system placed under vacuum for 4 hours.

Typical run conditions for CO2 adsorption were :

Bath temperature (°C) 0

Adsorption cut off pressure (P Po-1

) 0.040

Desorption cut off pressure (P Po-1

) 0.020

Adsorbate dose : (cm3g

-1 STP) 1.000

Desorbate dose : (cm3g

-1 STP) 1.000

Equilibration sampling time (s) 180

The surface area and micropore volume of the carbon samples were calculated via

the Dubinin-Radushkevich equation from the CO2 adsorption isotherm. The carbon

dioxide isotherms were completed within a 6h period in order to avoid swelling

effects of the lignite from long exposure to CO2 [124-126].

Typical run conditions for N2 adsorption were:

Bath temperature (°C) -196

Adsorption cut off pressure (P Po-1

) 0.995

Desorption cut off pressure (P Po-1

) 0.700

Adsorbate dose : (cm3g

-1 STP) 5.000

Desorbate dose : (cm3g

-1 STP) 5.000

Equilibration sampling time (s) 30

The BET method [127] was applied to calculate the surface area from the N2

adsorption isotherm.


2.22 Helium density Density determinations were made by helium displacement using a Micromeritics

Accupye 1330 pycnometer. In contrast to mercury, the helium penetrates the

micropore structure of the sample and the density determined is therefore the true

density of the sample. Regulated pressure from the helium cylinder was manually set

at 135kPa. Calibration of the pycnometer was conducted on each day of the analysis

using Micromeritics stainless steel ball standards. Conditions for calibrating the

instrument using the standard and performing an analysis of the sample was:

Cell volume 11.753 cm3

Number of runs / purges 10

Equilibration rate 35 Pa min-1

Maximum fill pressure 133kPa

The pycnometer automatically measured the room temperature and zeroed the

pressure transducers during the analysis. Reported results are the average and

standard deviation of ten sequential determinations for each sample.


2.23 Pyrolysis-gas chromatography Pyrolysis gas chromatography (py-gc) was carried out on the raw Loy Yang lignite

and on the thermally treated products. An Agilent 6890N series gas chromatograph

connected to a SGE Pyrojector II was used. The gas chromatograph was equipped

with a flame ionisation detector (FID) and a thermal conductivity detector (TCD).

Two columns, a 30m GS-GasPro and a 30m HP-5 obtained from Agilent

Technologies (see Table 2.5) were used.

For each experiment, a solid pelletizer was used for injecting the carbon products

into the projector. Each pelletizer was weighed to an accuracy of ±0.00001g using a

Sartorius ME balance. The raw lignite and thermally treated products (particle size

90-125μm) were pre-dried in a vacuum oven at 80°C for a minimum of 24h prior to

loading ~1.0mg of sample into the pelletizer. The pelletizer assembly was then

placed in a separate vacuum oven at 30°C for a minimum of 3h and then re-weighed.

The pelletizer assembly was then connected to the pyrojector and the air inside the

pelletizer removed by purging helium through the assembly for a minimum of

30min, prior to injection into the pyrojector furnace.

For Loy Yang lignite and the thermally dried products, pyrolysis was performed at

600°C, 700°C, 800°C and 900°C. Several raw lignites from the Latrobe Valley were

also pyrolysed at 900°C. The py-gc conditions are given in Table 2.4. After each

experiment, the pyrojector furnace was cooled down and the entire pyrojector

assembly dismantled. The charred carbon within the furnace liner was removed and


the quartz furnace liner and transfer tube cleaned by burning off residual organic

matter in an external ceramic furnace at 400°C.

Table 2.4 Run conditions for pyrolysis-gas chromatography

Column GS-GasPro HP-5

Pyrojector pressure (psi) 25.0 25.0

Initial oven temperature 30°C 30°C

Time at initial oven temperature 4.0min 4.0min

Temperature program Rate : 3°C/min to 260°C 3°C/min to 320°C

Final temperature 260°C 320°C

Time at final temperature 10min 30min

Injector temperature 250°C 250°C

Injector pressure (psi) 22.75 22.75

Injector split splitless splitless

FID detector temperature 320°C 450°C

FID Hydrogen flow (mL min-1) 40.0 40.0

FID Air flow (mL min-1) 450 450

FID Helium makeup flow (mL min-1) 10.0 10.0

TCD detector temperature 320°C 320°C

TCD reference flow (mL min-1) 20.0 20.0

TCD Helium makeup flow (mL min-1) 7.0 7.0

Carrier gas He He

Carrier gas flow 5.5mL/min 5.5mL/min


Table 2.5 Capillary Column properties

Column GS-GasPro HP-5

length 30m 30m

ID mm 0.32mm 0.53mm

Film layer 10μm 0.15μm

Standard gas mixtures from BOC gases (Table 2.6) were used to identify and

quantify the concentration of the chromatogram peaks. Also, the water peak in the

TCD gc-trace was identified and quantified by injecting water vapour in the gas

chromatograph containing the GS-GasPro column. The water vapour was generated

with a Setaram Wetsys humidifier system.

Calibration curves for each of the standard gas mixtures were performed by varying

the injection volume of the gas sampling valve. Three injection volumes were

performed for each calibration curve, 0.200mL, 0.500mL and 1.000mL, respectively.

Table 2.6 Standard gas mixtures

Standard gas mixture 1 (in helium)

Concentration (%)

Standard gas mixture 2 (in methane)

Concentration (%)

Methane 4.11 ± 0.08 Carbon monoxide 5.02 ± 0.5

Ethane 1.40 ± 0.03 Carbon dioxide 20.2 ± 0.2

Ethylene 1.60 ± 0.03 Hydrogen 29.0 ± 0.2

Propane 1.10 ± 0.02

Propylene 2.35 ± 0.05

iso-butane 0.889 ± 0.018 Standard gas mixture 3

Concentration (%)

n-butane 0.636 ± 0.013 Acetylene 100


Liquid standards obtained from Sigma-Aldrich (Table 2.7) were also used to identify

and quantify chromatogram peaks. Injection of liquid samples was performed using

an Agilent 7683B autoinjector on the gas chromatograph.

Table 2.7 Liquid standards

n-hexane methanol benzene

1-hexane ethanol toluene

n-heptane n-propanol o-xylene

n-octane n-butanol m-xylene

n-nonane n-pentanol p-xylene

n-decane n-hexanol phenol

C8-C20 alkane solution n-heptanol hydroquinone

C21-C40 alkane solution n-octanol acetone

formaldehyde n-nonanol methylacetate

acetaldehyde n-decanol ethylacetate


2.24 Pyrolysis–gas chromatography–mass spectrometry Pyrolysis – gas chromatography – mass spectrometry (py-gc-ms) analysis was

utilised to identify conclusively the chemical nature of the peaks observed in

chromatograms. Py-gc-ms was performed only for the raw Loy Yang lignite. An

Agilent 6890N series gas chromatograph connected to a SGE Pyrojector II and an

Agilent 5973N Mass Selective Detector (MSD) were used. The analysis conditions

are shown in Table 2.8. The column was a HP-5, (30 meter in length, 0.53mm

internal diameter (id)). All gc runs were conducted with a 10:1 split mode.

Table 2.8 Run conditions for gas chromatography-mass spectrometry

Column HP-5

Initial oven temperature 40°C

Time at initial oven temperature 2.0min

Temperature program Rate : 4°C/min to 320°C

Final temperature 320°C

Time at final temperature 15min

Injector temperature 250°C

Detector temperature 320°C

Carrier gas He

Carrier gas flow 1.0mL/min


2.25 Scanning Electron Microscope (SEM) - Energy Dispersion X-rays (EDX)

Qualitative and semi-quantitative elemental chemical analyse of the samples were

performed using a JEOL JSM-6490LA SEM connected to an Energy Dispersive X-

ray (EDX) probe. The analysis conditions for the SEM-EDX are shown in Table 2.9.

The SEM-EDX was used to scan the surface of raw lignites or the surface of ash, to

detect the presence of metallic species.

Table 2.9 Run conditions for SEM-EDX

SEM dwell time 0.1 msec

Sweep count 100

Working distance (WD) 11 mm

Voltage 20.0 kV

Probe Current 1.00 nA

PHA mode T3

Energy Range 0 - 20 keV

2.26 X-ray diffraction XRD analyses were conducted on raw Latrobe Valley lignites to detect the presence

of ionic salts. X-ray diffraction analysis was conducted using a Bruker AXS D8 X-

ray Diffractometer (XRD) at Swinburne University of Technology. The XRD

experiments were carried out using a Cu Kα radiation source in the 2θ scan mode.


2.27 Errors The errors for the measured quantities are given in the Tables. They are derived from

three sources.

• For those quantities measured in accordance with an Australian Standard, the

errors are based on the reproducibility quoted in the standard.

• For other quantities measured by outside laboratories, the errors are those

given by the analyst.

• For other quantities, the errors are based on variation found in multiple

determinations for the sample.

Chapter 3 Lignite drying technologies 57

CHAPTER 3 LIGNITE DRYING TECHNOLOGIES

The key to reducing greenhouse gas emissions and improving the efficiency of

existing lignite power stations is the implementation of more efficient drying

technologies. This chapter will investigate the HTD, MTE and SD technologies

under different processing conditions. Factors, which may affect the combustion

reactivity of the dried products such as pore structure and inorganic compositions,

will also be investigated in this chapter. Furthermore, the combustion reactivity of

the products is investigated in Chapter 5.

3.1 Effect of HTD conditions on retained moisture A major problem associated with moisture determinations of HTD products is the

difficulty in distinguishing between the surface water encapsulating the particles and

the residual moisture inside the particles. Equilibrium moisture holding capacities

(MHC) are commonly used to determine the moisture contents of products at

different humidities [128], but these would be misleading in a continuous

(commercial) process where a filtration step is likely to be incorporated prior to

combustion. The moisture content of the filter cake should provide a better indication

of the extent of dewatering from the HTD process than MHC.


The filter cake moisture contents from the HTD process at different temperatures are

shown in Table 3.1.

Table 3.1 Effect of temperature on the filter cake moisture content from the HTD process.

H2O

Water retained in the filter

cake

Proportion water removed

Solids recovery

% wb g/g db %db % db ±0.5* ±0.05+ ±0.55+ ±0.2 Loy Yang raw 59.7 1.48 - -

180°C 59.5 1.47 0.7 99.7

200°C 58.7 1.42 4.0 99.5

230°C 57.9 1.38 7.1 98.2

250°C 55.9 1.27 14.4 98.0

280°C 53.6 1.16 22.0 95.2

300°C 49.6 0.98 33.5 92.0

320°C 43.2 0.76 48.6 86.3

350°C ^ 34.7 0.53 64.1 74.5

All experiments repeated in triplicate (^duplicate experiments) * Error determined from reproducibility of results + Error determined from summation of errors in analytical results

It can be seen that increasing the treatment temperature reduced the moisture content

of the HTD product material; however, moisture reductions (outside the error limits)

were only observed for processing temperatures of 200°C and above (Figure 3.1). At

200°C, the moisture content of the HTD product was reduced by 4% db and, at

230°C, by 7% db. Such low moisture reductions are inadequate and unacceptable in a

commercial process. It was only when the HTD temperature was raised to 320°C that

the moisture in the product material was reduced to approximately half of that in the

parent lignite.


High HTD temperatures give drier products; however, such high temperatures also

lead to high levels of organic material in the product water (see APPENDIX F). At

320°C, the quantity of TOC removed to the product water was about 100 mg (see

APPENDIX F). This represents approximately 1.0% of the organic matter originally

charged to the HTD reactor and highlights the fact that substantial product water

remediation facilities would be required as part of any commercial development of

this process. Furthermore, high processing temperatures also lead to a significant

reduction in solids recovery in the final product. At 350°C, only 75%db of the

original mass could be recovered (Table 3.1).

The reduced moisture content for HTD products is thought to be largely due to

structural changes (both chemical and physical) that take place during processing and

that are enhanced at higher temperatures. Some of the structural changes that occur

include:

1. Decarboxylation: An increase in temperature will increase the extent of

decarboxylation [129-131]. Decarboxylation, reduces the concentration of polar sites

and, thus, reduces the capacity of the product to retain water [132, 133].

2. Migration of waxes: At higher processing temperatures the lignocellulosic

structure of the lignite becomes less rigid. This may facilitate the migration of

loosely bound lignite components, such as waxes [134] to the surface, thus increasing

the hydrophobicity of the product material [54, 59, 135].

3. Changes in spatial arrangement: The migration of water and waxes out of the

original structure may cause irreversible changes in the spatial arrangement of the

atoms leading to a reduction in porosity [136].


A HTD processing temperature of 320°C has been advocated by several previous

workers [105, 136]. Generally, the physico-chemical changes that occur for lignites at

this temperature also facilitates the formation of higher concentration lignite-water

slurries than can be achieved at lower processing temperatures [59]. So, in HTD

processing, temperature is a key factor. Other process variables, such as reaction

time, heatup time, agitation, autoclave size, slurry concentration and lignite mean

particle size (>50mm) have relatively little effect on the (large) pore volumes that

remain in the product material [136] and hence on the retained moisture in the product.

3.2 Mechanical Thermal Expression (MTE)

3.2.1 Effect of processing temperature The effect of temperature on the retained water in the MTE beneficiated product is

shown in Table 3.2 and in Figure 3.1. The relationship between processing

temperature and retained moisture is almost linear. It is also evident (Table 3.2) that

more than half of the water present in the raw lignite was removed under very mild

MTE conditions (125°C and 5.1MPa). Increasing the temperature to 150°C led to

64% of the water being removed (i.e. 0.5% water removed from the MTE pellet per

1°C increase from 125°C to 150°C). Further increases in processing temperature

from 150°C to 250°C resulted in additional water being removed from the MTE

pellet however at a much reduced rate (i.e. 0.12% water reduction per 1°C increase

from 150°C to 250°C; Figure 3.1).


Table 3.2 Mass recovery and moisture content of raw lignites and MTE products treated at different temperatures and 5.1MPa mechanical pressure

H2O

Water retained in product


Solids recovery


125°C 42.0 0.72 51.2 99.6

150°C 34.8 0.53 63.9 99.6

180°C 32.3 0.48 67.8 99.6

200°C 29.5 0.42 71.7 99.6

250°C 22.4 0.29 80.5# 99.0

All experiments repeated in triplicate * Error determined from reproducibility of results + Error determined from summation of errors in analytical results # Error is less than 1.5 (see APPENDIX A for all errors)

Several workers have also reported similar linear trends between processing

temperature and retained moisture in their batch MTE systems [15, 137]. Guo [15]

reported a rate of moisture reduction of about 0.12% per 1°C increase from 150°C to

300°C at 12MPa applied pressure. A similar moisture reduction rate was obtained in

this study from 150°C to 250°C (Table 3.2 and Figure 3.1).


0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0 100 200 300 400

Temperature (°C)

Ret

aine

d m

oist

ure

(g/g

db)

Raw lignite HTD MTE SD

50% moisture reduction line

raw lignite

Figure 3.1 Effect of temperature on the retained water in the HTD product; MTE

pellet with 5.1MPa of applied mechanical pressure; and in the SD product.

In contrast, Kealy et al. [106] reported that increasing the processing temperature

beyond 150°C gave only marginal improvements in reducing the moisture content of

the final MTE product. These apparent different conclusions can be rationalized by

realizing that Kealy et al. [106] had deduced this at lower applied pressures (i.e. at

2.5MPa and 5MPa) whereas other workers (except for this study) had based their

conclusions at 12MPa. On the contrary, Guo [15] did report that at low applied

mechanical pressures (eg 3MPa), an increase in processing temperature from 180°C

to 200°C gave products with similar moisture contents whereas, further increasing

the processing temperature to 230°C gave an adverse effect with a significant

increase in the product moisture content (more than 10%wb). Guo [15] explained this

phenomenon as a significant reduction in the effective compression pressure caused

by the sharp increase in the saturation vapour pressure of water. Based on the results


from this study there is no particular optimum temperature for the MTE process; but

it is clear that the proportion of water removed at any given temperature is far higher

by MTE than by HTD.

3.2.2 Effect of mechanical pressure The effect of applied mechanical pressure on the retained water in the MTE

beneficiated product is shown in Table 3.3 and in Figure 3.2. Almost half of the

moisture in the lignite was removed at relatively low mechanical pressures (2.5MPa)

at 150°C. An increase in mechanical pressure from 2.5MPa to 5.1MPa at 150°C

reduced the moisture content of the product significantly by an additional 15%db,

whereas a further increase in mechanical pressure had relatively little effect.

Table 3.3 Mass recovery and moisture content of raw lignites and MTE products treated at 150°C and at different mechanical pressures.

H2O



Solids recovery


2.5 MPa 43.0 0.76 48.9 99.6

5.1 MPa 34.8 0.53 63.9 99.6

12.7 MPa 32.0 0.47 68.2 99.6

25.0 MPa 29.5 0.43 71.0 99.5

All experiments repeated in triplicate (^duplicate experiments) * Error determined from reproducibility of results + Error determined from summation of errors in analytical results Over the range of the variables tested for MTE, there appears to be an optimum

pressure (approx 5.1MPa) beyond which further increases have relatively little effect

on the moisture content of the final pellet. In regards to processing temperature, an

optimum condition could not be deduced in this study.


0

5

10

15

20

25

30

0.0 0.2 0.4 0.6 0.8 1.0

Retained moisture (g/g)

App

lied

mec

hani

cal p

ress

ure

(MP

a)

Figure 3.2 Effect of applied mechanical pressure on the retained water in the MTE pellet at 150°C

(Data points are represented by symbols, lines are interpolated)

Preliminary MTE studies on some Indonesian [138] and German [139] lignites under

different MTE processing conditions suggest that there is no single set of optimum

MTE condition for all lignites. In general, these studies suggest that lignites with

high moisture contents require milder MTE processing (i.e. lower temperatures and

mechanical pressures); conversely lignites with lower inherent moisture contents,

require more severe MTE processing conditions.

The operating regime can be compared with the processing conditions employed in

the 25 tonne per hour demonstration plant at Niederaussem, which was (typically)

200°C and 12MPa mechanical pressure A processing temperature of 200°C is

relatively mild when compared to effective HTD temperatures (refer above).

Similarly, mechanical pressures of 12MPa are also mild when compared to simple

the 25 tonne per hour demonstration plant at Niederaussem, which was (typically)

200°C and 12MPa mechanical pressure A processing temperature of 200°C is

relatively mild when compared to effective HTD temperatures (refer above).

Similarly, mechanical pressures of 12MPa are also mild when compared to simple


mechanical expression, where mechanical pressures up to 50MPa have been

employed at ambient temperature [12].

Over the temperature range examined in this study (< 250°C), the changes in the

organic structure in the MTE products are minimal. Not surprisingly, the overall

mass recovery was also very high with more than 99% of the original mass being

recovered after the MTE process. It is only at temperature above 250°C that

substantial decarboxylation takes place [104] and migration of waxes may occur [136].

3.3 Steam drying (SD) - effect of SD conditions on retained moisture

Prior studies on steam drying [140, 141] have suggested that increasing the processing

temperature will lower the lignite’s moisture content, increase the rate of drying,

increase the degree of decarboxylation and devolatilisation, and increase the

concentration of organic material in the condensate. However, very little quantitative

information is available regarding changes to the lignite’s chemical and physical

properties. Similar to prior studies, the water content of the SD product decreased

with increasing temperature and the relationship was approximately linear over the

range of 130°C to 320°C (Table 3.4, Figure 3.1). Between 320°C and 350°C, the

further reduction in the water content was slight since, overall, the residual water

content was already very low.

The advantage that comes with increasing the temperature to reduce the moisture

content is counterbalanced by the increased loss of volatile material (see solids

recovery values in Table 3.4). Temperatures higher than 250°C were accompanied by


increasingly large losses of volatile matter and reduced solids recoveries.

It should be noted that in SD, unlike HTD and MTE, the residence time of particles

at processing temperature and pressure can have a significant effect on the proportion

of moisture removed. Also, in situations where steam removal has been continuous

(as distinct from the batch approach used here) the levels of retained moisture have

typically been much lower than the values reported here (see Bongers et al. [140]).

Table 3.4 Effect of temperature on the filter cake moisture content from the SD process.

H2O



Solids recovery


130°C 59.6 1.48 0.7 99.9

150°C 55.8 1.26 15.0 98.8

180°C 50.5 1.02 31.6 98.5

200°C 44.9 0.81 45.2 98.4

230°C 38.4 0.62 56.1 97.6

250°C 27.4 0.38 74.7 95.5

280°C 15.4 0.18 87.7 91.6

300°C 11.5 0.13 91.3 88.5

310°C 6.8 0.07 95.1 85.8

320°C 4.7 0.05 96.7 83.5

330°C 2.2 0.02 98.5 80.6

350°C 1.4 0.01 99.0 72.0

All experiments repeated in triplicate * Error determined from reproducibility of results + Error determined from summation of errors in analytical results


3.4 Pore structure of HTD, MTE and SD products Changes in the product’s physical properties during drying (e.g. pore

reduction/product hardness) may play a significant role in the milling process prior to

combustion. Measuring the internal pore volume of thermally treated products can

also provide useful information into the product’s maximum slurry concentration in a

coal water mixture [59, 105, 142], and into the product’s moisture holding capacity [59].

Low porosity products have been produced in both the MTE [142] and from the HTD

process [59]. Currently, very little information is available on whether significant

changes in the product’s pore volume can affect its combustion reactivity. Low

porosity HTD products from high porosity lignites have been reported to take

considerably longer to reach complete combustion [59].

The internal pore structure of the products as determined by mercury porosimetry,

surface area analysis and helium pycnometry are shown in Table 3.5. The surface

area of the lignite products was measured by carbon dioxide gas adsorption and

calculated using the Dubinin equation [107]. Differences between carbon dioxide gas

adsorption and nitrogen BET gas adosprtion on lignites are further discussed in

APPENDIX B. For MTE, increasing the processing temperature resulted in a gradual

increase in the product surface area (about 20m2g-1 from 125°C to 250°C) (Table 3.5

and Figure 3.4). Similarly, for SD, the surface area of the products marginally

increased from 130°C to 230°C but at higher temperatures, the surface area fell at an

average rate of ~0.6 m2g-1 per 1°C increase (i.e. from 231m2g-1 at 230°C to 164m2g-1

at 350°C). In contrast, the surface area of the HTD products also decreased

significantly with increasing processing temperatures above 250°C but at an average


rate of ~0.9 m2g-1 per 1°C increase (i.e. from 229m2g-1 at 250°C to 138m2g-1 at

350°C). The lower surface areas for the HTD products compared to SD products

could be the result of loosely bounded components within the lignite such as waxes

and tars [143] which become mobilized at the higher temperatures. These mobilized

components may in turn permeate into the micropore region of the particle and

subsequently occupy some of the volume within this pore region. As a consequence,

the product’s surface area is also reduced (see Section 3.1). For MTE, an increase in

applied mechanical pressure from 2.5MPa to 12.7MPa resulted in a gradual increase

in the product’s surface area from 205m2g-1 to 219m2g-1. However, further increases

in mechanical pressure beyond 12.7MPa resulted in a decline in the product’s surface

area (Figure 3.3). This inverted hyperbolic relationship between surface area and

applied mechanical pressure is likely to be the result of physical (rather than

chemical) changes that occur at the different mechanical pressures. The rise of the

product’s surface area with increasing mechanical pressure could be the result of the

larger pores (not measured by CO2 adsorption) being compressed into the micropore

region (Figure 3.3). Whereas, the fall in the product surface area with higher applied

mechanical pressures may be attributed to micropores collapsing by the additional

force of the mechanical press.

It should be pointed out that the micropore region measured by CO2 adsorption only

covers a very small portion of the overall pore size distribution (i.e. 1.0 to 0.25nm

pore radius) of the lignite products. Subsequently, the pore regions from mercury

porosimetry, surface area and helium pycnometry, respectively, (Table 3.5) were

combined to give a better representation on the overall pore size distribution of the


thermally treated products (see APPENDIX C). The volume occupied by ‘carbon’

(impermeable to He) marginally decreased with increasing processing temperature

(MTE, HTD and SD) and with increasing applied mechanical pressure (MTE only)

(Table 3.5). This decrease could be attributed to some organic carbon being leached

out from the lignite during the drying process.

200

205

210

215

220

225

0 5 10 15 20 25 30

Mechanical pressure (MPa)

Sur

face

are

a (m

2 g-1)

Figure 3.3 Effect of applied pressure on the surface area of MTE products

Increasing the MTE temperature from 125°C to 250°C (fixed pressure) did not

change either the micropore or large pore volume significantly. However, for HTD,

there was a marked reduction in the large pore (intra-particle) volume of the product

with increasing temperature. The micropore volume and carbon density were also

reduced (Table 3.5). Increasing the MTE pressure (fixed temperature) substantially

reduced the large pore volume but not the micropore volume or carbon density. Over

the range of conditions investigated, the effect of mechanical pressure was greater

than that of temperature.

Chapter 3 Lignite drying technologies

70

Table 3.5 Effect of processing conditions on the large pore (mercury porosimetry), micropore (CO2 surface area) and carbon density (helium pycnometry) of MTE, HTD and SD products, respectively.

Hg porosimetry

CO2 Adsorption at 273K

He pycnometry

Large pores (1000 to 1.5nm

pore radius) (cm3g-1) ±0.02

Dubinin surface area (m2g-1)

±2

Micropores (1.0 to 0.25nm pore

radius) (cm3g-1) ±0.001

Carbon density (>0.08nm pore

radius) (g cm-3) ±0.0005

MTE 125°C / 5.1MPa 0.28 212 0.057 1.4001

MTE 150°C / 5.1MPa 0.27 214 0.057 1.3995

MTE 180°C / 5.1MPa 0.27 219 0.059 1.3990

MTE 200°C / 5.1MPa 0.25 224 0.060 1.3984

MTE 250°C / 5.1MPa 0.24 233 0.062 1.3956

MTE 150°C / 2.5MPa 0.31 205 0.055 1.3987

MTE 150°C / 5.1MPa 0.27 214 0.057 1.3995

MTE 150°C / 12.7MPa 0.27 219 0.059 1.3947

MTE 150°C / 25.0MPa 0.23 210 0.056 1.3992

HTD 200°C 0.61 234 0.063 1.3974

HTD 250°C 0.62 229 0.061 1.3907

HTD 280°C 0.56 218 0.058 1.3861

HTD 300°C 0.52 182 0.049 1.3805

HTD 320°C 0.46 161 0.043 1.3774

HTD 350°C 0.39 138 0.037 1.3696

SD 130°C 0.55 223 0.060 1.3952

SD 150°C 0.55 226 0.061 1.3953

SD 180°C 0.56 226 0.061 1.3945

SD 200°C 0.65 232 0.062 1.3923

SD 230°C 0.67 231 0.062 1.3919

SD 250°C 0.62 214 0.057 1.3901

SD 280°C 0.52 200 0.054 1.3836

SD 300°C 0.51 199 0.053 1.3816

SD 310°C 0.50 194 0.052 1.3810

SD 320°C 0.48 188 0.050 1.3764

SD 330°C 0.48 176 0.047 1.3745

SD 350°C 0.46 164 0.044 1.3723

71


Figure 3.4 Relationship between surface area and processing temperature for (1) MTE, (2) HTD, (3) SD and (4) all three drying processes

120 140 160 180 200 220 240 260 280 300210

215

220

225

230

235

1 MTE

Surfa

ce A

rea

(m2 g-1

)

Processing Temperature (°C)150 200 250 300 350 400

140

160

180

200

220

2402 HTD

Surfa

ce A

rea

(m2 g-1

)

Processing Temperature (°C)

100 150 200 250 300 350 400

140

160

180

200

220

240

3 SD


Surfa

ce A

rea

(m2 g-1

)

100 150 200 250 300 350 400

140

160

180

200

220

240

4 MTE HTD SD

Surfa

ce A

rea

(m2 g-1

)



72

For SD, increasing the temperature from 130°C to 180°C had no apparent effect on

pore volume but an increase to 230°C gave a significant increase in porosity

(Figure 3.5). This increase is likely attributable to changes in the lignite’s rigidity at

these temperatures, resulting in less shrinkage when the material is dried to zero

moisture for pore volume determination. It is unlikely that the pore volume of the

initial steam dried product is actually higher at 230ºC than at 180ºC (see Bongers et

al. [140]). A further increase in processing temperature above 230°C gave a small but

gradual decrease in the intra-particle large pore and micropore volumes and the

carbon density (Table 3.5). The trends at processing temperatures above 230°C are

similar to those for products of HTD but above 280ºC, the rate of decrease of large

pore and micropore volumes with temperature was greater for the product of HTD

than for the products of SD.

The volume of the retained water exceeded the available internal pore volume of the

products of MTE and HTD (Figure 3.6a) possibly because for both types of products,

some water may be adsorbed on particle surfaces. For products of SD (Figure 3.6b),

the volume of water retained did not appear to be related to the product’s pore

volume. It is believed that this is an artefact of the experimental protocol. At high

temperatures surface water may evaporate during cooling of the autoclave. At lower

temperatures very little evaporation would be expected, but excess water may be

retained on the particle surfaces (as for products of HTD) and/or the measured

porosity may be lower than its true value as a result of shrinkage during the drying to

zero moisture which precedes porosity measurement. As noted above, the effect of

temperature on pore volume suggests that the product of SD at lower temperatures is

not rigid.

73


0.72 0.71 0.71 0.71 0.72 0.72 0.71 0.71 0.72 0.71 0.72 0.72 0.72 0.72 0.73 0.73 0.72 0.72 0.72 0.72 0.72 0.72 0.72 0.72 0.72 0.73 0.73 0.73

0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.05 0.04 0.04 0.06 0.06 0.06 0.06 0.06 0.06 0.05 0.05 0.05 0.05 0.05 0.04

0.54

0.28 0.27 0.27 0.25 0.240.31 0.27 0.27

0.23

0.61 0.620.56

0.520.46

0.39

0.55 0.55 0.560.65 0.67

0.62

0.52 0.51 0.50 0.48 0.48 0.46

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6R

aw c

oal

125°

C/5

.1M

Pa

150°

C/5

.1M

Pa

180°

C/5

.1M

Pa

200°

C/5

.1M

Pa

250°

C/5

.1M

Pa

150°

C/2

.5M

Pa

150°

C/5

.1M

Pa

150°

C/1

2.7M

Pa

150°

C/2

5MP

a

HTD

200

°C

HTD

250

°C

HTD

280

°C

HTD

300

°C

HTD

320

°C

HTD

350

°C

SD

130

°C

SD

150

°C

SD

180

°C

SD

200

°C

SD

230

°C

SD

250

°C

SD

280

°C

SD

300

°C

SD

310

°C

SD

320

°C

SD

330

°C

Tota

l vol

ume

(cm

3 g-1)

SD

350

°C

Vol. occupied by carbon Micropore volume Large pore volume

Effect of temperature

on MTE processing

Effect of mechanical pressure on MTE processing

Effect of temperature on HTD processing

Effect of temperature on SD processing

Figure 3.5 Changes in pore volume of LYLA lignite with MTE, HTD and SD processing.


The large pore volumes reported by Chaffee et al. [144] correlated well with the MTE

and HTD values measured given in Figure 3.5. However, the method for measuring

the micropore region in this study was different. Here the micropore volumes were

deduced directly from the CO2 adsorption, whereas those reported by

Chaffee et al. [144] were obtained by an indirect method. Pores of radii 1-1.5nm and

0.08-0.25nm will not be included in the current determination. However, since the

micropore volume (CO2 adsorption) and the pore volume measured by mercury

porosimetry for pores with radii just above 1.5nm are relatively small, the pores not

accounted for would not be expected to have much effect on the overall pore volume.

The lower values for micropore volume in this study explain why the volume of

moisture retained in the MTE products was lower than the internal pore volume,

whereas Chaffee et al. [144] found that the two volumes were nearly equal.

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

Retained water (g/g db)

Por

e vo

lum

e (c

m3 g-1

)

MTE pressure MTE temperature HTD SD

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6


Pore

vol

ume

(cm

3 g-1)

a b

Figure 3.6 Relationship between pore volume and retained water (a) in HTD and MTE products, (b) in SD products.


75

75

3.5 Inorganic analysis of dried products Latrobe Valley lignites have some of the lowest ash yields in the world [145]. The

inorganic content of the Loy Yang lignite had a very low ash yield of only 0.9%db

(see Table 4.1). Higher ash lignites in Loy Yang do exist however they often contain

relatively high sodium contents which are generally not used in combustion without

blending with lower ash lignites [146] and are generally located on the overburden and

interseam sediment layers [85]. Much of the work within the CRC for New

Technologies for Power Generation from Low-Rank Coal and the CRC Clean Power

from Lignite, used numerous batches of Loy Yang lignite, all of which with ash

yields ~1%db [147-150] . As a consequence, the low concentration of inorganic material

in the Loy Yang lignite has made it more difficult to elucidate the behaviour of

inorganics during drying. The inorganic components in Latrobe Valley lignites are

mainly in the form of soluble salts or carboxylate complexes [85]. Intuitively, one

would expect that as the liquid water is forced from the lignite matrix, it would carry

soluble inorganic species (salts) with it. Thus, it is expected that more of any soluble

species would be removed as more water is expelled from the lignite. Comparisons

between raw lignite and dried products on a wt%db must be treated with caution

because mass losses occurring during the drying process are not factored into the

results. Instead, a better method for quantitating changes in the inorganic and total

sulphur contents between raw lignite and dried products is to convert wt%db values

(Table G.1) into the actual mass values (Table 3.6). This conversion is illustrated in

the sample calculation given in APPENDIX G and the converted values are shown in

Table 3.6. (The converted values are also given in APPENDIX I, expressed on a

molar basis.)

0.005

0.005

0.005

0.005

0.006

0.007

0.006

0.007

0.006

76

Table 3.6 Acid extractable inorganics, chlorine and total sulphur in raw and solid MTE products (100g of wet raw lignite, actual mass in g)a, b

Table 3.7 Acid extractable inorganics, chlorine and total sulphur in raw and solid HTD and SD products (10g of dried raw lignite, actual mass in g)a

Process condition Na

Ca

Mg

Al

FeNPc

Stot

Cl

Process condition Na

Ca

Mg

Al

FeNPb

Stot

Cl

0.007

0.004

0.005

0.006

0.004

0.003

0.003

LY raw lignite 0.038 0.017 0.030 0.004 0.025 0.12 0.030 LY raw lignite 0.009 0.004 0.007 0.001 0.006 0.028

MTE 125°C / 5.1MPa 0.021 0.017 0.025 0.004 0.025 0.12 0.023 HTD 180°C 0.006 0.004 0.006 0.001 0.006 0.028

MTE 150°C / 5.1MPa 0.019 0.017 0.025 0.004 0.025 0.12 0.021 HTD 200°C 0005 0.004 0.005 0.001 0.006 0.027

MTE 180°C / 5.1MPa 0.018 0.017 0.025 0.004 0.021 0.12 0.021 HTD 230°C 0.004 0.004 0.005 0.001 0.006 0.027

MTE 200°C / 5.1MPa 0.017 0.017 0.025 0.004 0.025 0.12 0.021 HTD 250°C 0.003 0.004 0.005 0.001 0.006 0.026

MTE 250°C / 5.1MPa 0.015 0.015 0.019 0.004 0.023 0.11 0.020 HTD 280°C 0.002 0.004 0.004 <0.001 0.006 0.026

HTD 300°C 0.001 0.003 0.003 <0.001 0.006 0.025

MTE 150°C / 2.5MPa 0.021 0.016 0.025 0.004 0.025 0.12 0.023 HTD 320°C 0.001 0.002 0.002 <0.001 0.005 0.022

MTE 150°C / 5.1MPa 0.019 0.017 0.025 0.004 0.025 0.12 0.021 HTD 350°C <0.001 0.001 0.001 <0.001 0.004 0.019* 0.002

MTE 150°C / 12.7MPa 0.017 0.017 0.025 0.004 0.021 0.12 0.021

MTE 150°C / 25.0MPa 0.017 0.017 0.021 0.004 0.025 0.12 0.021 SD 130°C 0.009 0.004 0.007 0.001 0.005 0.028 a Note that 100g wb raw lignite is equivalent to 40g of dried lignite SD 150°C 0.008 0.004 0.007 0.001 0.005 0.028 b the error is ±0.004g for Na, Ca, Mg, Al, FeNP and Cl whereas error in S tot is ±0.01g. SD 180°C 0.007 0.004 0.007 0.001 0.006 0.028 c NP = non-pyritic SD 200°C 0.006 0.004 0.007 0.001 0.006 0.028

SD 230°C 0.005 0.004 0.007 0.001 0.005 0.026

SD 250°C 0.004 0.004 0.006 0.001 0.005 0.026

SD 280°C 0.004 0.004 0.005 0.001 0.005 0.025

SD 300°C 0.004 0.004 0.004 0.001 0.004 0.024

SD 310°C 0.003 0.003 0.004 0.001 0.004 0.023* 0.004

SD 320°C 0.004 0.003 0.004 0.001 0.005 0.023* 0.004

SD 330°C 0.004 0.003 0.004 0.001 0.006 0.021* 0.004

SD 350°C 0.004 0.002 0.003 0.001 0.005 0.019* 0.004

a For HTD and SD, the error is ±0.001g for Na, Ca, Mg, Al, FeNP and Cl whereas error in S tot is ±0.005g; * the error for S tot is ±0.004g, b NP = non-pyritic.



Within the limits of error, it cannot be concluded whether any aluminium, non-

pyritic iron or sulphur was removed from any of the three drying processes

(Table 3.6 and Table 3.7). A decrease of aluminium and iron during MTE and HTD

is not often encountered for Latrobe Valley lignites [139, 151, 152] and for higher ash

South Australian lignites [139, 153, 154], however, some Indonesian coals have reported

reductions in aluminium and iron contents from both HTD [155] and MTE [138].

3.5.1 Sodium in dried lignite products Sodium species present during high temperature lignite combustion play an

important part in boiler fouling and are often a major cause of corrosion in turbine

blades [156]. Subsequently, the removal of sodium during drying can also significantly

improve the quality of the final product.

Both MTE and HTD gave significant reductions in sodium under all of the

experimental conditions tested whereas for SD, significant sodium reductions were

only found at temperatures above 230°C. Even at the mildest MTE processing

temperature, the level of sodium was reduced by 45% and further increases in

temperature only resulted in marginal additional sodium being removed (compare

Table 3.6 and Table 3.8). An increase in applied mechanical pressure from 2.5MPa

to 25MPa had no significant effect in removing more sodium.

For HTD processing at 200°C, the proportion of sodium removed was significant at

45%, despite the negligible water removal. This sodium reduction is probably due to

sodium salts washed out of the lignite from the additional water added to make up

the lignite slurry for the HTD process. The level of sodium was reduced by an

additional 22% with an increase in processing temperature up to 250°C (the


maximum temperature used in the MTE process), and further increases in HTD

processing temperature resulted in more sodium being removed. At 350°C, the level

of sodium in the HTD product was negligible. Within the limits of error, the removal

of sodium in the MTE process was as efficient as for the HTD process at the same

temperature.

In most Latrobe Valley lignites the sodium is predominantly in the form of sodium

chloride [151] (also see APPENDIX E) but some of the cations present are bound to

carboxylate groups in the lignite [85]. Since the reduction in sodium levels in the HTD

process continued to increase with temperature till all the sodium had been removed,

sodium originally in carboxylate form was also leached out at sufficiently high

temperatures. It is likely that this sodium carboxylate had been converted to

carbonate/bicarbonate following degradation of the carboxylic groups and thus

became leachable.

The sodium level of the SD product also fell with increasing temperature, which is

not consistent with previous studies [90]. The major difference between the studies

described by Allardice [90] and this work is the method by which the steam is supplied

to the system. In most SD systems, a constant flow of steam is passed through the

lignite, so that all the removed water is converted to vapour. Hence it will not remove

any appreciable quantities of soluble inorganics. In the closed system used in this

study, liquid water will be present in equilibrium with the vapour phase, so that

soluble inorganics may be leached from the lignite into the liquid phase at the bottom

of the autoclave.


Table 3.8 Proportions of inorganics, and chlorine removed by drying

Process condition Na Ca Mg Cl

MTE 125°C / 5.1MPa 45 ± 13 NS NS NS

MTE 150°C / 5.1MPa 50 ± 12 NS NS NS

MTE 180°C / 5.1MPa 54 ± 12 NS NS NS

MTE 200°C / 5.1MPa 56 ± 12 NS NS NS

MTE 250°C / 5.1MPa 60 ± 11 NS 36 ± 16 33 ± 16

MTE 150°C / 2.5MPa 46 ± 13 NS NS NS MTE 150°C / 5.1MPa ± 12 NS NS 50 NS

MTE 150°C / 12.7MPa 56 ± 12 NS NS NS MTE 150°C / 25.0MPa 56 ± 12 NS NS NS

HTD 180°C 34 ± 13 NS NS NS

HTD 200°C ± 13 NS NS 45 NS

HTD 230°C 56 ± 12 NS NS NS

HTD 250°C 67 ± 12 NS NS 37 ± 17

HTD 280°C 79 ± 11 NS 46 ± 16 46 ± 16

HTD 300°C 90 ± 10 NS 61 ± 14 55 ± 15

HTD 320°C 90 ± 10 57 ± 24 75 ± 13 58 ± 14

HTD 350°C NA 81 ± 19 89 ± 11 68 ± 12

SD 130°C NS NS NS NS



SD 200°C 29 ± 14 NS NS NS

SD 230°C 41 ± 13 NS NS NS

SD 250°C 53 ± 12 NS NS NS

SD 280°C 59 ± 11 NS NS 33 ± 16

SD 300°C 61 ± 11 NS 37 ± 16 36 ± 16

SD 310°C 62 ± 11 NS 39 ± 15 37 ± 15

SD 320°C 58 ± 10 NS 40 ± 15 39 ± 15

SD 330°C 59 ± 10 NS 42 ± 14 41 ± 14

SD 350°C 58 ± 9 NS 59 ± 12 43 ± 13

Note: the proportions of aluminium, non-pyritic iron and total sulphur removed for all three drying processes are within the error limits of this analysis and therefore are not included in this table; NS = Not Significant; NA = Not Applicable (the concentration of the inorganic ion was too low to be detected, i.e. <0.01wt%db)


3.5.2 Calcium and magnesium in dried lignite products All of the calcium and magnesium in Latrobe Valley lignites occur as exchangeable

cations associated with carboxyl groups [85]. In the MTE process, a significant

reduction in magnesium was only found at the higher processing temperature (i.e.

250°C / 5.1MPa). Similarly, for HTD and SD, significant reductions in the level of

magnesium were found at 280°C and 300°C, respectively (Table 3.8).

The behaviour of calcium and magnesium are expected to be very similar during the

drying processes however because the level of calcium was half that of magnesium,

the error associated in the analysis was higher. Significant reductions in calcium

were only present in HTD at processing temperatures ≥320°C however within the

limits of error, no significant differences were evident between Ca and Mg under

these conditions.

Similar to sodium, the reduction in magnesium and calcium levels are likely due to

extensive degradation of carboxylate groups and an increase in water removal at

these higher temperatures.

3.5.3 Inorganic reduction in dried products versus water removal The relationship between sodium removal and the proportion of water removed in

the dried products is given in Figure 3.7. For MTE and SD, the fraction of sodium

removed from the raw lignite was less than the fraction of water removed. In

contrast, for HTD, a significantly higher proportion of sodium was removed than

water (Figure 3.7). The higher proportion of sodium removed can be attributed to


some washing of the lignite by the distilled water added to the HTD and MTE

systems (see Experimental). Direct comparisons between the proportion of water and

the proportion of total sodium removed from the lignite should be treated with

caution, as not all of the sodium in the lignite is soluble. Some of the sodium in Loy

Yang lignite is insoluble and is bound to the lignite as carboxylates and phenolates. It

is more meaningful to compare the proportion of water-extractable sodium removed

(calculated from distilled water washing of the lignite) with the proportion of water

removed.

0 10 20 30 40 50 60 70 80 90 100

-20

0

20

40

60

80

100 SD

% s

odiu

m re

mov

ed (d

b)

Proportion of water removed (%)

0

20

40

60

80

100 HTD

% s

odiu

m re

mov

ed (d

b)

0

20

40

60

80

100 MTE

% s

odiu

m re

mov

ed (d

b)

Figure 3.7 Relationship between drying process on product moisture and sodium

contents in the dried products. Note, the dotted line has been used in each graph for illustrative purposes only (i.e. 1:1 ratio) and should not be taken as the trendline for

all the given values.


Figure 3.8 gives the proportion of water-soluble sodium leached out from the lignite

during the MTE, HTD and SD processes. Comparison of the data from the raw and

water-washed lignite (see APPENDIX E) showed only minor differences suggesting

that much of the inorganic material in these samples was strongly bound (Table E.1).

The level of sodium in Loy Yang lignite was reduced by 68 ± 11%db and chlorine by

45 ± 16%db. No significant differences were found in the levels of Ca, Mg, Al, FeNP

and Stot with water washing.

0 20 40 60 80 100 120 1400

20

40

60

80

100

120

140

% w

ater

-ext

ract

able

sodi

um re

mov

ed (d

b)

Proportion of water removed (%) HTD MTE SD

Figure 3.8 Relationship between the proportions of water and soluble sodium removed by MTE, HTD and SD processing.

Much of the sodium removed from the three drying processes under mild processing

temperatures (i.e. <250°C) was in the form of NaCl. The extent of decarboxylation at

temperatures below 250°C was relatively low and therefore sodium carboxylate


degradation would also be marginal. For MTE, the proportion of water-soluble

sodium leached out was greater than the proportion of water removed which is also

likely attributable to some washing of the lignite by the distilled water added to the

MTE cell to displace the air in the system (see Section 2.9). In contrast, for SD, the

proportion of water-soluble sodium removed at temperatures <280°C was directly

proportional to the amount of water removed. However at processing temperatures

greater than 280°C, the proportion of sodium was less than the proportion of water.

As described in Section 3.5.1, the liquid water will be present in equilibrium with the

vapour phase and some soluble inorganic material may be leached out from the

lignite however it appears that with higher processing temperatures (above 280°C),

more water is being removed from the lignite as steam, thus reducing the ability for

sodium to be leached out from the lignite in liquid form. Furthermore, it is expected

that at temperatures above 250°C, significant decarboxylation occurs [130, 157] and that

additional sodium (previously in the form of a carboxylate) would be removed from

the lignite however as depicted in Figure 3.7, this is clearly not the case. This further

supports that at higher processing temperature, more water from the lignite is

removed as steam. In HTD, the proportion of sodium removed from the lignite was

significantly greater than the proportion of water removed (Figure 3.8). At 250°C,

99%db of the water-soluble sodium was removed. Increasing the HTD processing

beyond 250°C resulted in water-soluble sodium reductions of greater than 100% (up

to 140% for the 350°C sample). These very high sodium reductions can be attributed

to detachment of sodium – carboxylate bonds at the higher processing temperatures

and due to some washing of the lignite while in slurry form.


3.5.4 Chlorine in dried lignite products Chlorine salts are very soluble in water. From the water washing experiments, less

than half of the chlorine was leached out from the lignite after repeated distilled

water washings (Table E.1). This suggests that a significant proportion of the

chlorine in Loy Yang lignite is strongly bound within the coal matrix. Chlorine anion

interactions within coals have been reported elsewhere [158-164].

Vassilev et al. [164] postulated that water-insoluble chlorine can be ionically and

covalently bound to the organic portion of the coal. Huggins and Huffman [165]

reported that the interaction between the maceral surface and the chlorine anion was

relatively strong however no evidence was found for any organic chlorine in the Loy

Yang lignite.

For MTE, the error associated in calculating the proportion of water-soluble chlorine

was high therefore no solid conclusions can be reached from the data given in

Figure 3.9. The change in water-extractable chlorine with temperature for HTD and

SD broadly parallelled in the three drying processes to that of sodium, in agreement

with the proposal that the water-soluble chlorine was predominantly in the form of

NaCl. For SD, above 280ºC there was no significant increase in the proportion of

chlorine removed with increasing processing temperature. However for HTD, the

proportion of water-soluble chlorine leached out was significantly greater than the

proportion of water removed suggesting that as for sodium, chlorine was washed out

of the lignite in the water added to make up the slurry for HTD.


0 20 40 60 80 100 120 140 160 1800

20

40

60

80

100

120

140

160

180

% w

ater

ext

ract

able

ch

lorin

e re

mov

ed (d

b)

Proportion of water removed (%) HTD MTE SD

Figure 3.9 Relationship between the proportions of water and soluble chlorine

removed by MTE, HTD and SD processing.

The proportion of water-extractable chlorine versus the proportion of water-

extractable sodium is shown in Figure 3.9 for MTE, HTD and SD products. For

HTD, higher processing temperatures (eg >280°C) resulted in more than 100% of

the water-soluble chlorine being removed. This high proportion of water-soluble

chlorine was likely associated to some of the more strongly bounded chlorine anions,

which are not normally washed out with water, being removed from the lignite.

Similarly, SD at higher processing temperatures, chlorine anion dissociation could

account for the proportion of water-soluble chlorine removed also exceeding the

100% mark. It is expected that at these higher processing temperatures (eg 320°C),

some of the chlorine could be removed as a gas (HCl or Cl2) along with the steam. In

contrast, appreciable amounts of Na are not leached from the lignite when the water

is removed as steam instead of as a liquid [90].


0 20 40 60 80 100 120 140 160 1800

20406080

100120140160180

% w

ater

-ext

ract

able

ch

lorin

e re

mov

ed (d

b)

HTD

0 20 40 60 80 100 1200

20

40

60

80

100

120

% water-extractable sodium removed (db)

SD

% w

ater

-ext

ract

able

ch

lorin

e re

mov

ed (d

b)

0 20 40 60 80 1000

20

40

60

80

100MTE

% w

ater

-ext

ract

able

ch

lorin

e re

mov

ed (d

b)

Figure 3.10 Relationship between the proportion of sodium and chlorine present in the dried solid products from the MTE, HTD and SD processes.

Analysis of the product water support the findings deduced from the solid products

(APPENDIX F). In addition, traces of sulphate in the product water suggested that a

small portion of the total sulphur was water-soluble. The MTE process was most

favourable in regards to the amount of water removed from the lignite and the low

concentration of organic matter being leached out into the product water. The SD

process also gave high moisture reductions but at higher temperatures than MTE and


with significantly higher TOC in the product water. However for HTD, the fact that

significant moisture reductions can only be achieved at much higher processing

temperatures than MTE and SD and that its product water was highly concentrated

with organic matter is a major hindrance in its commercialisation as a drying process.

3.6 Conclusions The extent of water removal from MTE, HTD and SD processing of the same sample

of Loy Yang lignite was conducted. For comparative purposes, the effectiveness of

each drying process can be evaluated by examining the parameter at which 50%

water removal is achieved. For HTD, the processing temperature had to be increased

to 320°C to achieve a 50% moisture reduction. At this high temperature, the

proportion of mass recovered was only 86%db because of decarboxylation and

devolatilisation reactions. Under these conditions, the net wet specific energy

(NWSE) of the HTD product had increased by 57% when compared to the raw

lignite (i.e. 8.3 MJ kg-1 to 13.1 MJ kg-1). In contrast, for MTE, the processing

temperature required to achieve high moisture reductions was significantly reduced

by simultaneous application of mechanical pressure. For Loy Yang lignite the

optimum applied pressure was identified as approximately 5.1MPa, which is

relatively mild when compared to the Niederaussem MTE plant. Further increases

had relatively little effect on the moisture content of the product pellet. At 125°C and

5.1MPa of applied mechanical force, the moisture content was reduced by 50%

compared to the parent lignite (NWSE 13.4 MJ kg-1). Similarly, at 150°C and

2.5MPa applied mechanical force also resulted in a 50% moisture reduction (NWSE

15.5 MJ kg-1). Under both MTE processing conditions, lignite mass recoveries were

very high (>99%db).


In SD, the temperature necessary to remove half of the water from the parent lignite

was significantly lower than HTD but higher than MTE. A SD temperature of

approximately 215°C was necessary to achieve a 50% moisture reduction. The

lignite mass recovery in steam drying at 215°C was also high at 98%db. The NWSE

for the 230°C SD product was 14.4 MJ kg-1, an increase of 74% compared to the raw

lignite.

The internal pore structure of thermally dried products was characterised using

mercury porosimetry, surface area gas adsorption and helium pycnometry. The MTE

process was more effective in reducing the large pore volume of the products than

HTD and SD. An increase in mechanical pressure up to 12MPa increased the

micropore volume, which was likely attributed to the compression of larger pores

into the micropore region. Furthermore, additional increases in mechanical pressure

beyond 12MPa resulted in a decline in the micropore volume, which was probably

due to the micropores themselves being compressed under these high pressures. In

addition, the micropore volume and the carbon density of MTE, HTD and SD

decreased at higher processing temperatures. The micropore volume being small,

these changes did not greatly affect the overall internal pore volume.

The retained moisture in the MTE pellet correlated well with the dry density however

the relationship was not equally proportional on a gram per gram basis. Similarly to

MTE, the volume of retained water in the HTD products exceeded the available dry

pore volume. However for SD products, the pore volume and retained water did not


follow a linear relationship thus suggesting the water retained is not related to the

product’s pore volume.

Much of the sodium removed from drying was in the form of NaCl. In MTE,

processing temperature was more effective in removing sodium than applied pressure

(within the experimental parameters tested). In contrast, SD processing temperatures

above 280°C reduced the ability of sodium to be leached out from the lignite.

Furthermore, the lignite slurry used in HTD facilitated significantly higher levels of

sodium, magnesium, calcium and chlorine to be removed from the process compared

to MTE and SD. This considerably higher removal of inorganic material, in

particularly sodium, is an advantage to the process in regards to reducing fouling and

slagging propensities during combustion.

The detachment of carboxylate bonds from the lignite with increasing processing

temperature could explain the higher than expected inorganic matter being removed

from the lignite during drying. Furthermore, at higher processing temperatures, some

of the more strongly bounded chlorine anions (not associated with the sodium ion)

were removed.

Chapter 4 Pyrolysis of Raw Lignite and Dried Products 90

CHAPTER 4 PYROLYSIS OF RAW LIGNITE AND

DRIED PRODUCTS

4.1 Introduction Coal pyrolysis is a very complex process and plays a part in nearly all coal

conversion processes, such as combustion, gasification and liquefaction. The word

“pyrolysis” is of Greek origin and means “to decompose by heat”. In simple terms,

pyrolysis is the thermal fission of a sample in the absence of oxygen into molecules

of lower mass. Most coal structures consist of structural units joined together by

either weak or strong linkages to form a three-dimensional macromolecular network.

During pyrolysis, the weakest bridges break, producing molecular fragments that are

released as tar, light hydrocarbons and non-organic gases (carbon monoxide, carbon

dioxide, water etc).

In this chapter, several pyrolysis techniques are utilised to investigate the pyrolysis

behaviour of the Loy Yang lignite and its thermally treated products. The slow

pyrolysis of the lignite/lignite products was investigated in two systems; a

thermogravimetric analysis system and a quartz fluidized-bed/fixed-bed reactor

system. The flash pyrolysis of the lignite/lignite products was also investigated in

two systems; the quartz reactor system used for the slow pyrolysis experiments and a

pyrolysis-gas chromatography system. The quantification and characterisation of


volatised components from the pyrolysis of the lignite and its thermally treated

products as a function of temperature is also described.

4.2 Proximate analysis Thermogravimetric analysis (TGA) has been extensively used as a tool for

investigating the pyrolysis mechanisms of samples over a range of gases and

pressures. A number of groups have also used TGA for determining proximate

analysis in both bituminous and low-rank coals [166-173].

A typical TGA thermogram that was used to determine the proximate analysis of the

raw lignite and its dried products is shown in Figure 4.1. The procedure followed has

been detailed by Earnest [174] and is fully described in Section 2.15. Furthermore, the

TGA thermograms for the MTE, HTD and SD products are given in Appendix G.

The TGA thermograms show that some mass was lost when the lignite sample was

heated to 110°C in an inert atmosphere (Ar), predominantly due to the loss of

reabsorbed water from the oven dried lignite sample. A second, larger weight loss

(due to the loss of volatiles) was observed when the sample was heated at 50°Cmin-1

to 950°C and maintained at this temperature for 15min. After the 15min, the gas

atmosphere was changed from argon to air, allowing the sample to burn until a

constant weight was obtained. The remaining sample weight represented the ash

yield of the lignite. The ash, volatile and fixed carbon yields, determined from the

proximate analysis, for the raw lignite, HTD, MTE and SD products are given in

Table 4.1.


-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

Time (seconds)

Wei

ght L

oss

(%)

0

100

200

300

400

500

600

700

800

900

1000

0 600 1200 1800 2400 3000 3600 4200 4800 5400

Temperature (ºC

)

Weight Loss (%)Temperature

-50.11 % : Volatiles

-6.30 % : Water

-48.96 % (db)

Air

-50.14 % (db)

-48.92 % : Fixed Carbon

-0.89 % : Ash-0.90 % (db)

Figure 4.1 TGA thermograms used in determining proximate analysis of a lignite sample

Within the limits of error, processing temperatures beyond 250°C gave significant

reductions in volatile yield for the HTD and the MTE products when compared to the

raw lignite whereas, significant reductions in the SD products were noted at

temperatures beyond 230°C. For HTD and MTE, proximate analysis on a 230°C

treated product was not conducted but it is expected to be similar to the SD product

at 230°C. Furthermore, the effect of applied mechanical pressure at 150°C in MTE

had a negligible effect on the volatile yield of its products (Table 4.1).

The devolatilisation rate was significantly increased at temperatures beyond 250°C

(Figure 4.2). It is expected that an increase in processing temperature will lead to an

increase in C, accompanied by a reduction in O and volatile matter, an elimination of

CO2 via decarboxylation of the lignite structure [175] and the removal of some small


molecular weight hydrocarbons in the product water stream [144, 176]. Furthermore, the

higher volatile yield in the HTD products compared to the SD products at processing

temperatures beyond 250°C could be attributed to enhanced entrapment of mobile

waxes/tars etc, which are part of the volatile fraction in the HTD product. These

mobile volatile constituents are likely to re-solidify on the surface of the HTD

product during cooling however for the SD products, these fractions are likely to be

volatilised from the product and re-condensed into the product water. This is also

supported by the higher organic carbon concentrations measured for the SD product

waters compared to HTD product waters (see Table F.2).

In Chapter 3, it was concluded that for HTD, a temperature of 320°C was necessary

to achieve a 50% moisture reduction but at the expense of a significantly lower mass

recovery. For HTD at 320°C, this lower mass recovery corresponds to ~6wt%daf

volatile yield loss in the final product (Table 4.1). This significant volatile yield loss

could be disadvantageous in some industrial processes, which convert the carbon

matter to lower molecular weight fractions (eg gasification, liquefaction).

In contrast, for SD, an estimated temperature of 215°C would dedicate a 50%

moisture reduction however, advantageously, without the sacrifice in volatile yield

(Table 4.1). Similarly, the operating temperature in the MTE process was relatively

low and subsequently the volatile yield in the final products was not affected

(Table 4.1).


Table 4.1 Proximate analysis of raw lignite, HTD, MTE and SD products Ash

(db)

(±0.1)

Volatile Matter

(daf)

(±0.4)

Fixed Carbon

(daf)

(±0.4)

Raw 0.9 50.6 49.4

HTD 200°C 0.9 50.7 49.3

250°C 0.9 49.5 50.5

280°C 0.9 48.4 51.6

300°C 0.9 46.6 53.4

320°C 0.9 44.8 55.2

350°C 0.9 41.7 58.3 125°C / 5.1 MPa 0.9 50.6 49.4

MTE 150°C / 5.1 MPa 0.9 50.6 49.4

180°C / 5.1 MPa 0.9 50.6 49.4

200°C / 5.1 MPa 0.9 50.2 49.8

250°C / 5.1 MPa 0.9 49.4 50.6

2.1 MPa / 150°C 0.9 50.7 49.3

5.1 MPa / 150°C 0.9 50.6 49.4

12.7 MPa / 150°C 0.9 50.5 49.5

25.0 MPa / 150°C 0.9 50.5 49.5 SD 130°C 0.8 50.5 49.5

SD 150°C 0.8 50.5 49.5

SD 180°C 0.8 49.9 50.1

SD 200°C 0.8 50.0 50.0

SD 230°C 0.8 48.8 51.2

SD 250°C 0.6 48.5 51.5

SD 280°C 0.6 45.9 54.1

SD 300°C 0.5 45.3 54.7

SD 310°C 0.5 43.1 56.9

SD 320°C 0.5 42.9 57.1

SD 330°C 0.5 41.5 58.5

SD 350°C 0.5 38.9 61.1


100 150 200 250 300 35037.5

40.0

42.5

45.0

47.5

50.0

52.5

HTD MTE SD

Vol

atile

mat

eria

l (da

f)

Processing temperature (ºC)

Figure 4.2 The effect of temperature on volatile yield from HTD, MTE and SD.

4.3 Differential Scanning Calorimetry Differential Scanning Calorimetry (DSC) is a technique for measuring thermal

changes in a sample when a physical or chemical change takes place with the sample.

This detection is in the form of a temperature difference between a test sample and a

reference sample (a thermally inert material).

4.3.1 Pyrolysis DSC of SD products The DSC curves for the SD products are given in Appendix G, Figure L.8. To

simplify comparisons between DSC curves, a low temperature (130°C) and a high

temperature (350°C) SD product is discussed in this section. The heat flow data

given in conjunction with the proximate analysis shows the endothermic and

exothermic history during pyrolysis and during combustion of the lignite sample.


Heating the sample to 110°C exhibited an endothermic peak from the removal of

moisture from the lignite. These endothermic peaks are normally associated with the

dehydration of lignites [177-183]. A further increase in temperature from 110°C to

200°C also resulted in an endothermic effect. This second endothermic peak is likely

attributed to further release of the more strongly bound water to the lignite but also

can be attributed to the evolution of low molecular weight gases (eg. CO, CO2) [130]

and to the devolatilisation of low molecular weight hydrocarbons [184]. At this point,

the extent of pyrolysis of the lignite sample is still relatively low.

It is well known that increasing the temperature from 200°C to 950°C in an inert

atmosphere, will cause a number of physico-chemical reactions to occur e.g.

decarboxylation, devolatilisation, polymerization, condensation, cracking,

isomerisation, molecular rearrangement, hydrogen transfer etc. [184]. These reactions

are often concurrent and produce opposite thermal effects [184, 185].

Comparison between the two SD products reveal a significant decrease in the

amplitude of the first exothermic peak for the 350°C SD product when compared to

the 130°C SD product (see Figure 4.3 for numbering of the peaks). Elder and

Harris [186] reported that primary carbonisation commences at ~350°C with the initial

release of carbon dioxide and hydrogen. This suggests that for the 350°C SD product,

some carbonisation had occurred during the SD process which can account for the

lower amplitude in the first exothermic peak. All the other heat flow peaks within

this pyrolysis period (as numbered in Figure 4.3) are very similar between the two

SD products.


Note: Numbers on the convoluted peaks in

A deconvoluted plot of the heat flow curve (in the region 250°C to 950°C) for the

130°C SD product is shown in Figure 4.4. Much research has been conducted in

attempt to relate the pyrolysis behaviour of carbonaceous materials at different

temperatures. It is generally accepted that the weight loss of peat and lignite below

350°C is the result of decarboxylation of acid groups , the dehydration of

hydroxylated aliphatic structures and the generation of low molecular

weight alcohols . Francioso et al. [182] reported the first exothermal peak generated

below 350°C was due to these effects.

The second exothermic peak (Figure 4.4 and Figure 4.3) has been previously linked

with polymerisation and molecular rearrangement [184]. Similarly, Ding et al. [183]

convoluted peaks in

A deconvoluted plot of the heat flow curve (in the region 250°C to 950°C) for the

130°C SD product is shown in Figure 4.4. Much research has been conducted in

attempt to relate the pyrolysis behaviour of carbonaceous materials at different

temperatures. It is generally accepted that the weight loss of peat and lignite below

350°C is the result of decarboxylation of acid groups , the dehydration of

hydroxylated aliphatic structures and the generation of low molecular

weight alcohols . Francioso et al. [182] reported the first exothermal peak generated

below 350°C was due to these effects.

The second exothermic peak (Figure 4.4 and Figure 4.3) has been previously linked

with polymerisation and molecular rearrangement [184]. Similarly, Ding et al. [183]

-20

-10

0

10

20

30

40

50

60

70

80

90

100

Time (seconds)

Hea

t Flo

w (m

W)

0

100

200

300

400

500

600

700

800

900

1000

0 600 1200 1800 2400 3000 3600 4200 4800

Tem

pera

ture

(ºC

)

Steam dried 130°CSteam dried 350°CTemperature

2

3

4

1

Figure 4.3 Comparisons between the heat flow of 130°C and 350°C SD products, 30mLmin-1air flow, 30.0mg sample.

heat flow curves correspond to the de deFigure 4.4. Figure 4.4.

[182, 187, 188]

[182, 187, 188]

[187]

[182, 187, 188]

[182, 187, 188]

[187]


reported that exothermic peaks >450°C are due to condensation and carbonization

reactions during pyrolysis.

1200 1400 1600 1800 2000 2200 2400 2600 2800

-10

0

10

20

30

40

43

2

1

Time (seconds)

Hea

t flo

w (m

W)

200

300

400

500

600

700

800

900

1000

Tem

pera

ture

(ºC

)

Figure 4.4 Deconvoluted curve fit of the DSC from the 130°C SD product. Black line shows the raw DSC curve, green lines are the peaks identified from devolution and

the red line is the sum of the green peaks. The temperature profile is in blue.

Exothermic peaks 3 and 4 in Figure 4.4 are more likely the sum of concurrent

xothermic and endothermic reactions during pyrolysis. Martinez-Alonso et al. e

ported that devolatilisation and cracking reactions are endothermic and that

[184]

re

polymerization and condensation reactions are exothermic. The effects of rapid

decomposition of the organic mass (exothermic) overlaps the volatile evolution

effects (endothermic) [189]. These effects could not be distinguished from the heat

flow curves.


4.3.2 Combustion DSC at 950°C of SD products Switching the gas stream from argon to air in the TGA marked the commencement

of the combustion stage. Comparing the low temperature (130°C) and high

temperature (350°C) SD products in Figure 4.3, show similar exothermic behavioural

combustion phase. This spike is attributed to the residual carbon in the sample

igniting (see Appendix G). The variables that affect combustion and ignition are

further discussed in Chapter 5. Interestingly, a higher SD processing temperature

resulted in longer periods to complete the combustion of the sample (Figure 4.3).

This longer combustion period is likely attributed to the higher char to volatile ratio

for the 350°C SD product as a result of its treatment at the higher processing

temperature (see Table 4.1). That is, after devolatilisation, the SD products that had

subsequently, would require longer periods to completely combust.

4.4 Quartz reactor pyrolysis experiments

raw lignite and

e thermally treated products as a function of temperature and heating rates. Similar,

n applied to measure the

volatile yields of carbonaceous materials under different heating profiles and

pyrolysis temperatures [190]. The overall behaviour of the raw lignite and the

thermally treated products as a function of pyrolysis temperature and heat-up mode is

discussed in this section.

patterns. Both products were found to increase the rate of heat given off with

increasing time followed by a large exothermic spike, which marked the end of the

been treated at higher temperatures contain a higher proportion of fixed carbon and

Pyrolysis experiments were conducted in a fluidized-bed/fixed bed quartz reactor for

the purpose of identifying differences in volatile yield between the

th

fluidized-bed/fixed bed quartz reactor systems have also bee


4.4.1 Slow pyrolysis experiments The slow pyrolysis refers to the experiments where the lignite sample was loaded

into the fluidised-bed/fixed reactor and then heated at 40-50°C min to the indicated

temperature with a 15min

-1

holding time. Char yields produced from the slow heat-up

pyrolysis of the raw lignite and the thermally treated products as a function of

increasing pyrolysis temperature were discussed in the previous sections of this

chapter from the TGA-DSC curves (see Section 4.3). In this section, slow heat-up

pyrolysis of the raw lignite and thermally treated products is re-examined using a

quartz reactor system. A major difference between pyrolysis in the TGA and

pyrolysis in the quartz reactor system is the experimental sample size (i.e. in the

quartz reactor 100 times more sample was pyrolysed). Also, with the quartz reactor,

the char yield (and hence volatile yield) at each incremental temperature increase is

examined and compared to the thermally treated products.

The data in Figure 4.5 indicate that for the raw lignite, the majority of the sample

weight loss took place at temperatures lower than 400°C with a volatile yield of more

°C to 600°C resulted in

n additional volatile yield of 18wt%db. The primary pyrolysis products evolved

[188]

[191]

temperature is shown in Figure 4.5. The physicochemical changes to the lignite with

than 20wt%db. Increasing the pyrolysis temperature from 400

a

below 600°C for lignites are water and carbon dioxide . Murray reported that for

a Latrobe Valley lignite, 70% of the carboxyl groups were lost by 300°C and 92% by

600°C . Further increases in temperature to 900°C at the slow heating rate

resulted in less than 7wt%db additional weight loss for the raw lignite.

Chapter 4 Pyrolysis of Raw Lignite and Dried Products

101

the raw lignite (Figure 4.5b).

all difference is attributed to some volatiles having been lost (approximately

, gave the largest difference in volatile yield when compared to the raw

E and SD products (Figure 4.5c). This difference is primarily due to the

The char yield profile of the MTE 150°C / 5.1MPa treated product as a function of

temperature did not show any significant difference compared to the raw lignite

(Figure 4.5a). These similarities support the TGA proximate analysis results which

also showed no significant difference in char yield between the raw lignite and the

MTE 150°C / 5.1MPa treated product (Table 4.1).

For the SD 230°C product, the char yield profile from slow heat-up pyrolysis as a

function of temperature was marginally different to

This sm

2wt%db) during the SD treatment process (see Section 3.3; Table 3.4). The quartz

reactor slow pyrolysis char yield results also support the TGA proximate results in

Table 4.1.

The char yield profile for the HTD 320°C product as a function of slow pyrolysis

temperature

lignite, MT

significant amount of volatiles lost (Section 3.1) during the hydrothermal dewatering

process at 320°C.


45

50

55

60

65

70

75

80

85

350 450 550 650 750 850 950

Pyrolysis temperature (ºC)

Cha

r yie

ld (%

daf)

LYLA raw lignite; slow heat up

MTE 150ºC / 5.1MPa; slow heat up

45

50

55

60

65

70

75

80

85

350 450 550 650 750 850 950


Cha

r yie

ld (%

daf)


SD 230ºC; slow heat up

45

50

55

60

65

70

75

80

85

350 450 550 650 750 850 950


Cha

r yie

ld (%

daf)


HTD 320ºC; slow heat up

a b c

102

Figure 4.5 Comparisons of char yields from the pyrolysis of raw LYLA lignite with (a) MTE (b) SD (c) HTD treated products as a function of temperature in the fluidized-bed/fixed-bed reactor operated at the slow heating rate mode.


103

Furthermore, the char yield profile as a function of temperature of the raw lignite

versus the water-washed lignite did not show in any notable differences (Figure 4.6).

45

50

55

60

65

70

75

80

85

350 450 550 650 750 850 950


Cha

r yie

ld (%

daf)

LYLA raw lignite; slow heat up LYLA water washed; slow heat up

Figure 4.6 Comparisons of char yields from the pyrolysis of raw and water washed LYLA lignite operated at the slow heating mode, as a function of temperature in the

fluidized-bed/fixed-bed reactor.

4.4.2 Fast pyrolysis experiments In Section 4.2, proximate analysis determinations were performed using a TGA with

a slow heating rate of 50°C min-1. A limitation to the TGA is that very fast heat up

rates (eg. > 100°C s-1) cannot be achieved. Furthermore, in slow heating rate

experiments, most of the H2O and CO2 are released from the lignite by the time the

reactor has reached 500°C [130]. That is, the presence of H2O and CO2 at elevated

temperatures (>700°C) could facilitate in the gasification of the char [192]. Instead,

fast heat up rates (i.e. flash pyrolysis) of lignite particles, can be accomplished with a


104

fluidized-bed/fixed-bed quartz reactor system. Similar quartz reactors [113, 121] heated

in an external furnace have reported rapid particle heating rates in the order of

104°C s-1.

Pyrolysis at the fast heating rate and slow heating rate showed no significant

differences in the char yield profile as a function of temperature for the raw lignite

(Figure 4.7). In addition, no significant differences in the char yield profile were

found between the slow heating rate and fast heating rate for the MTE, SD and HTD

products (Figure 4.8).

45

50

55

60

65

70

75

80

85

350 450 550 650 750 850 950


Cha

r yie

ld (%

daf)

LYLA raw lignite slow heat up LYLA raw lignite fast heat up

Figure 4.7 Comparisons of char yields from the pyrolysis of raw LYLA lignite operated at the slow and fast heating rate mode, as a function of temperature in the

fluidized-bed/fixed-bed reactor.


105

Similarly, Zeng et al. [193] reported that varying the pyrolysis heating rate had a

marginal effect on the char yield of Loy Yang lignite when pyrolysed to 900°C in a

wire mesh reactor. Furthermore, Takarada et al. [194] reported that the coexistence of

steam at ~700°C, which is removed during the slow heat up experiments, did not

cause significant additional volatile yield during the pyrolysis/gasification of

Yallourn lignite. In contrast, pyrolysis of biomass conducted by Kweon et al. [190]

using a similar fluidized bed/fixed-bed reactor to this study, reported that

temperatures greater than 700°C, the fast heating rate gave noticeably lower char

yields than the corresponding slow heating rate experiments. The differences in

volatile/char yields with biomass were explained by the onset of in situ reforming of

the char from the inherent biomass AAEM species. The data in Figure 4.7 and Figure

4.8 suggest that in situ reforming of Loy Yang lignite and of the thermally dried

products is negligible as a function of pyrolysis temperature. Furthermore, the Loy

Yang lignites used in this study and by Zeng et al. [193] had low AAEM contents

which may account for the negligible in situ reforming of the char during flash

pyrolysis.


45

50

55

60

65

70

75

80

85

350 450 550 650 750 850 950


Cha

r yie

ld (%

daf)

MTE 150ºC / 5.1MPa; slow heat up

MTE 150ºC / 5.1MPa; fast heat up

45

50

55

60

65

70

75

80

85

350 450 550 650 750 850 950


Cha

r yie

ld (%

daf)

SD 230ºC; slow heat up

SD 230ºC; fast heat up

45

50

55

60

65

70

75

80

85

350 450 550 650 750 850 950


Cha

r yie

ld (%

daf)

HTD 320ºC; slow heat up

HTD 320ºC; fast heat up

a b c

106

Figure 4.8 Comparisons of char yields from the pyrolysis of (a) MTE (b) SD (c) HTD treated products as a function of temperature in the fluidized-bed/fixed-bed reactor operated at the slow and fast heating rate mode


4.5 Tar yields For many coals, tar represents the major initial volatile species released during

pyrolysis. Previous works have reported that the yields and nature of tars depend not

only on coal type but also on pyrolysis conditions, including particle heating rate,

reactor residence time, nature of gaseous atmosphere and pressure [85, 195-199] . Work

with Loy Yang lignite have also reported that high heating rate favours the release of

(larger) aromatic ring systems during pyrolysis [199-201].

The tar yield produced from the pyrolysis of raw LYLA lignite operated at the slow

and fast heating rate mode, as a function of temperature is shown (Figure 4.9). Tar

from coal pyrolysis is normally released at relatively low temperatures [121]. For the

LYLA lignite, pyrolysis at 500°C produced 5wt%db of tar in both the slow and fast

heating rate modes (Figure 4.9). Increasing the pyrolysis temperature to 600°C

resulted in an additional ~18wt%db tar yield. Significant differences in the heating

modes were only found at pyrolysis temperatures above 700°C. For the slow heating

mode, the tar yield marginally increased from 700°C and 900°C, whereas for the fast

heating mode, the tar yield decreased substantially from 18wt%db to 2wt%db,

respectively. These differences in tar yields between the slow and fast heating modes

for pyrolysis temperatures above 700°C is likely attributed to secondary vapour-

phase reactions resulting in the formation of hydrocarbon gases and modified tar [121].

Mochida et al. [202] suggested that the volatile fractions can modify the pyrolysis

process because of its ability to act as a solvent for the system and/or as a hydrogen

donor. Similarly, Bermejo et al. [203] also reported that low molecular weight

components can modify the rheological properties of the tar (pitch) during pyrolysis.


In relation to the fast heating experiments (Figure 4.9), the coexistence of

devolatilised low molecular weight components and tar in the same reactor system

could potentially facilitate in the breakdown of the tar at pyrolysis temperatures

above 700°C. In contrast, for the slow heating rate experiments, most of the low

molecular weight components devolatilised from the lignite, are carried out of the

reactor and subsequently cannot partake in any secondary vapour-phase reactions

with the tar at the higher pyrolysis temperatures. Furthermore, the volatilisation of

alkali and alkaline earth metal (AAEM) species at pyrolysis temperatures above

700°C could also facilitate in the catalytic breakdown of the tars. The behaviour of

AAEM species during pyrolysis for the slow and fast heating rate modes is discussed

in Section 4.6.

500 600 700 800 9000

5

10

15

20

25

30

Tar y

ield

wt%

of c

oal (

db)

Pyrolysis temperature (°C)

Slow heatup Fast heatup

Figure 4.9 Comparisons of tar yields from the pyrolysis of raw LYLA lignite

operated at the slow and fast heating rate mode, as a function of temperature in the fluidized-bed/fixed-bed reactor.


4.6 Inorganic contents Pyrolysis of coal is considered the initial steps of all thermochemical utilisation

processes such as combustion, gasification, carbonisation and liquefaction. The

release of volatile inorganic species in pyrolysis is of significant importance to these

power generation processes. In conventional coal combustion systems, the inorganic

components in the lignite are largely responsible for slagging and fouling [85] whereas

in advanced gasification/reforming based power generation systems, the volatilised

inorganic components are also one of the major causes the erosion and corrosion of

the gas turbine components [94, 95].

The behaviour of sodium, calcium, magnesium and chlorine from the pyrolysis of

raw LYLA lignite operated at the slow and fast heating rate mode, as a function of

temperature is shown in Figure 4.10. The behaviour of sodium, calcium, magnesium

and chlorine was also conducted on the pyrolysed thermally dried products (except

for HTD because of its low inherent inorganic content after the process) and the

overall trends between the samples were found to be relatively similar. Subsequently,

to simplify the discussion in the behaviour of these ionic species only the raw lignite

will be discussed in this thesis.

For sodium, pyrolysis at 500°C resulted in 5wt%db loss from the original lignite and

an increase in pyrolysis temperature to 600°C resulted in an additional ~12wt%db

volatilisation in both the slow and fast heating rate modes. The volatilisation of

sodium at temperatures up to 600°C from a Loy Yang lignite has been attributed to

the release of low molecular mass carboxylates during pyrolysis [96, 98, 100]. The


pyrolysis heating rate mode only showed significant differences in the volatilised

sodium at temperatures of 700°C and above. In the slow heating mode, the sodium

volatilisation marginally increased by 5wt%db from 700°C to 900°C, whereas, in the

fast heating more than half of the original sodium in the lignite was volatilized at

700°C and at 900°C, negligible sodium was detected in the remaining char.

The volatilisation of sodium at pyrolysis temperatures of 700°C and above, in the

fast heating rate mode (Figure 4.10), appears to be correlated to the catalytic

breakdown of the tars (Figure 4.9). The cations in Latrobe Valley lignites are known

to play an important role in the final tar yields during rapid pyrolysis [113, 201]. Tyler

and Schafer flash pyrolysed lignites in a fluidised bed reactor and reported that the

removal of cations present in lignites markedly increased the tar yield [114].

Furthermore, the volatilisation of sodium from Latrobe Valley lignites at

temperatures higher than 700°C have reported to be linked to volatile-char

interactions causing the reforming/cracking of volatiles on the char surface [97, 204]

and also causing the condensation of aromatic ring structures in the char [205, 206]. The

tar (precursors) produced from Loy Yang lignites are highly aliphatic which, if

retained in the solid phase, crack to form mainly gases during pyrolysis [207].

In contrast, in the slow heating mode, the small loss of sodium from 700°C to 900°C

did not result in proportional reductions in tar yield. A likely explanation is that most

of the volatilised sodium in the slow heating rate mode was carried out of the reactor

and subsequently could not partake in any secondary catalytic vapour-phase

reactions with the tar at the higher pyrolysis temperatures.


On the contrary to sodium, calcium and magnesium volatilisation was not affected by

differences in pyrolysis heating modes (Figure 4.10). The majority of volatised

calcium and magnesium had occurred at 500°C with losses of 7wt%db and

13wt%db, respectively, and further increases in pyrolysis temperatures only

marginally increased the volatilisation of these cations. A number of researchers

have attributed the reduction in the tar yield by divalent cations to the cross-linking

effects of the divalent ions, bringing the (carboxylic) groups closer in the coal

structure. These marginal increases in volatile calcium and magnesium at pyrolysis

temperatures greater than 600°C (Figure 4.10) cannot account for the significant

reductions in the tar yields, in particularly when the proportion of calcium and

magnesium retained in the char did not change between the different heating rate

modes. Wu et al. [97] also reported that volatilisation of calcium and magnesium had

little effect on radical-char interactions during the flash pyrolysis of a Latrobe Valley

lignite in a fluidised bed reactor.

The volatilisation behaviour of chlorine followed an entirely different trend to the

volatilisation of sodium in both heating rate modes and at the different pyrolysis

temperatures (Figure 4.10). At 500°C, more than half of the initial chlorine in the

lignite was volatilised whereas under the same corresponding conditions, the

volatilisation of sodium was minimal at 5wt%db. Prior work with Loy Yang lignite

has found that about 10% of the chlorine in a NaCl-loaded sample was volatilised at

temperatures as low as 200°C [100].


In the slow heating mode, the chlorine volatilisation remained relatively unchanged

from 500°C to 700°C whereas from 700°C to 900°C, an additional 25wt%db of the

chlorine was volatilised. At 900°C, about 80% of the initial chlorine in the lignite

was volatilised whereas under the same corresponding conditions, only 30wt%db of

sodium was removed from the char.

In contrast, the chlorine volatilisation trend in the fast heating mode was opposite to

chlorine behaviour in the slow heating mode and also contrastingly different to the

trend reported for sodium in the fast heating mode (Figure 4.10). An increase in

pyrolysis temperature above 500°C in the fast heating mode gave significantly less

volatilised chlorine. At 700°C, 30wt%db of the chlorine was volatilised which

corresponds to 25wt%db less volatilised chlorine than at 500°C. An increase in

pyrolysis temperature above 700°C in the fast heating mode did not result in any

further changes in the volatilised chlorine. The significantly different behaviours

between the volatilisation of chlorine and that of sodium clearly suggests that not all

of the sodium and chlorine, if any, were volatilised as NaCl molecules. In addition,

no significant increases in sodium or chlorine volatilisation were found around the

melting point of NaCl (800.7°C) which further supports the conclusion that sodium

and chlorine did not volatilise as NaCl. Similar conclusions have also been reported

elsewhere [100].

The decrease in the volatilisation of chlorine in the fast heating mode over the

temperature range from 500°C to 700°C is likely attributed to the recombination of

chlorine containing species such as HCl, with the nascent char. Quyn et al. [100]


postulated that the retention of chlorine coincided with the onset of massive bond

breakages in the pyrolysing coal/char matrix and that some forms of chlorine could

have recombined with some of the newly formed free radical sites inside the char at

high temperatures. Whereas, in the slow heating mode, the chlorine containing

species were swept out of the reactor and subsequently could not react with the char

in the reactor at high temperature.

500 600 700 800 900

0

20

40

60

80

100

500 600 700 800 900

0

20

40

60

80

100

500 600 700 800 900

0

20

40

60

80

100

dc

a b

Na

vola

tilis

atio

n, %

Na

in li

gnite

Temperature (°C)


Cl v

olat

ilisa

tion,

%C

l in

ligni

te

Temperature (°C)


Mg

vola

tilis

atio

n, %

Mg

in li

gnite

Temperature (°C)


500 600 700 800 900

0

20

40

60

80

100

Ca

vola

tilis

atio

n, %

Ca

in li

gnite

Temperature (°C)


Figure 4.10 Comparisons of volatilized (a) sodium, (b) chlorine, (c) magnesium and (d) calcium, from the pyrolysis of raw LYLA lignite operated at the slow and fast

heating rate mode, as a function of temperature in the fluidized-bed/fixed-bed reactor


4.7 Pyrolysis-gas chromatography Analytical pyrolysis methods including pyrolysis-mass spectrometry (py-ms),

pyrolysis-gas chromatography (py-gc) and pyrolysis-gas chromatography / mass

spectrometry (py-gc-ms) have been commonly used to characterize both low-rank

lignites [147, 208, 209] and high-rank coals [210, 211] and also in characterising the

pyrolysed products from coal derived fractions such as coal macerals [211, 212] and

humic acids [147, 213, 214]. The fragments volatilised from coal pyrolysis are separated

by gas chromatography. The obtained pyrogram constitutes a fingerprint of the

starting macromolecule and gives information on the relative amount of its

monomeric components [215]. The pyrolysis-gas chromatography of the raw Loy

Yang lignite at temperatures of 600°C, 700°C, 800°C and 900°C is shown in

Figure 4.11.

Curves for the individual hydrocarbon gas yields (methane (CH4), ethane (C2H6),

ethene (C2H4), ethylene (C2H2), propane (C3H8), propene (C3H6), water (H2O),

carbon monoxide (CO) and carbon dioxide (CO2) from the pyrolysis of Loy Yang

lignite are shown in Figure 4.12. The two major hydrocarbon components volatilised

during the pyrolysis the raw Loy Yang lignite were methane and ethene.

Furthermore, the yields of both methane and ethene increased as a function of

pyrolysis temperature from 600°C to 900°C. At 900°C, more than 6wt%db of

methane and about 4wt%db of ethene was volatilised from the raw lignite.


C H3 8

500000

0

xylenes

toluene

phenol

C5

C6

C H3 8

C H3 6

benzene

benzene

8000000

4000000

0

Abun

danc

e

600 C

10 20 30 40 50 60 70 80

500000

1000000

0

6000000

3000000

0

80000

0

C6

C7toluene

xylenes

phenol

C5 C7

C8

C4

C H3 8

C H3 6

benzene

300000

0

toluenexylenes

phenol

C5C7

C8

C6

C H3 6

C H3 8

5000000

2500000

0

0

toluene

phenolC5 xylenesC H2 2

C H3 6

benzene

600000

Abun

danc

eAb

unda

nce

Abun

danc

e

Time (min)

900 C

800 C

700 C

Figure 4.11 Gc trace of pyrolysed Loy Yang raw lignite using a GS-GasPro column


600 650 700 750 800 850 9000

2

4

6

8

10

12

14

600 650 700 750 800 850 9000.0

0.1

0.2

0.3

0.4

0.5

c

Prod

uct y

ield

wt%

of c

oal (

db)

Temperature (°C)

CO CO2 H2O

b

Prod

uct y

ield

wt%

of c

oal (

db)

C3H8 C3H6

600 650 700 750 800 850 9000

1

2

3

4

5

6

7a

Prod

uct y

ield

wt%

of c

oal (

db)

CH4 C2H6 C2H4 C2H2

Figure 4.12 Quantification of volatilised (a) methane, ethane, ethane, ethylene (b)

propane, propene (c) carbon monoxide, carbon dioxide and water, from the py-gc of Loy Yang raw lignite as a function of temperature using a GS-GasPro column.


The increase in yield of methane with increasing pyrolysis temperature is likely

attributed to the thermal cracking of the char [216], tar and volatilised hydrocarbon

gases. An example of the thermal cracking process can be illustrated with ethane

(Equation 4.1 to Equation 4.3).

C2H6 → CH3● + CH3

●Equation 4.1

C2H6 + CH3●→ C2H5

● + CH4 Equation 4.2

CH3● + H●→ CH4 Equation 4.3

Similarly, ethene, propene and propylene increased yields with increasing pyrolysis

temperature while their correspondent saturated hydrocarbons, ethane and propane,

reached maximum yields at 700°C and 800°C, respectively, before declining with

further increases in pyrolysis temperatures (Figure 4.12). The decline in yields of

ethane and propane and the subsequent increases in correspondent olefin yields are

likely attributed to concurrent chemical reforming processes at the higher pyrolysis

temperatures. The reforming of alkanes into olefins is well documented in the

literature and can occur via numerous different reaction pathways including steam

cracking [217, 218], catalytic dehydrogenation [219-223] or oxidative dehydrogenation [223-

231], oxidative coupling [232, 233] or conversion into aromatic hydrocarbons (that is, for

alkanes greater than ethane) [234-236]. The light hydrocarbons produced during rapid

pyrolysis of the lignite are aliphatic in nature [206, 207, 237, 238] and prone to thermal

cracking at elevated temperatures. At the higher pyrolysis temperatures, significant

amounts of free radicals (especially H radicals) would be generated from the mass

bond breaking of the pyrolysing char. The generation of these free radicals with the


char would facilitate numerous different parallel-consecutive reforming/cracking

reaction pathways with the volatile species (Figure 4.13).

Catalytic and thermal cracking

+ H O (Steam reforming)2

+ H (Hydroreforming, hydrocracking)2

+ CO (Dry reforming)2

TARCO

H2

CH4

CO2

Figure 4.13 Illustration of the concurrent primary and secondary pyrolysis reactions

in the breakdown of tar

The volatilisation of sodium during the rapid pyrolysis of the Loy Yang lignite at

temperatures above 700°C (Section 4.6) is also likely to play an important role in the

reforming/cracking of volatiles [113, 201]. Machocki and Denis reported that Na/CaO

catalysed the reforming of ethane [233]. Several authors have also postulated that the

sodium present in the lignite facilitated the catalytic reforming/cracking of volatiles

on the char surface [201, 239]. In addition to sodium, the presence of calcium,

magnesium, aluminium and iron on the surface of the char may also facilitate the

catalytic cracking of the tar and the reforming of saturated hydrocarbons at

temperatures above 700°C. Wornat and Nelson [240] pyrolysed raw and calcium

exchanged Yallourn lignite in a fluidised bed reactor and reported that the tar yields

were lower for the calcium form sample than the raw lignite, indicating that calcium

catalysed the conversion of tar. In addition, these authors reported that the catalytic

influences of calcium affected the yields of aromatic hydrogen and unsaturated

hydrocarbon substituents in the tar compared to the raw lignite. Vernaglia et al. [241]


also found that the aromatic/aliphatic composition of tar to change with the type of

cation (H, Na, and Ca).

The rapid pyrolysis of the Loy Yang lignite also produced significant yields of

carbon monoxide, carbon dioxide and water (Figure 4.12). For carbon dioxide, the

yield reached a maximum of more than 9wt%db at 700°C and further increases in the

pyrolysis temperature resulted in a marginal decline in yield. In contrast, the carbon

monoxide and water yields from the pyrolysis of the lignite increased with increasing

temperature. At 900°C, more than 11wt%db of carbon monoxide and more than

4wt%db of water was volatilised from the raw lignite.

Prior to pyrolysis, all of the water from the raw lignite was removed and therefore

the water measured (Figure 4.12) was generated from the pyrolysis of the lignite.

Doolan and Mackie [242] proposed that phenols decompose to produce carbon

monoxide, via a free radical route involving phenyl and hydroxyl radicals, with the

phenolic oxygen finishing up as a water molecule. Also, Shin et al. [243] pyrolysed

catechols and hydroquinones, which are abundant in lignites [244], and reported that

these model compounds eventually converted to carbon monoxide, carbon dioxide

and water and suggested the catalytic cracking reaction pathway shown in

Figure 4.14.


Figure 4.14 Shin et al.’s [243] proposed catalytic cracking reaction pathway of catechols and hydroquinones to produce carbon monoxide, carbon dioxide and water.

The considerable amount of water produced from the primary pyrolysis of the lignite

is likely to be consumed by secondary pyrolysis reactions [245-247]. Steam reforming

(also known as steam gasification and/or the water gas shift reaction) has been

extensively investigated for lignites [192] and is normally simplified by the chemical

reaction shown as Equation 4.4.

C + H2O → CO + H2 (ΔH° 298K = 205.9 kJ/mol) Equation 4.4

Many authors have reported that the water gas shift reaction is the major chemical

process responsible for the concurrent reduction in tar yield (see Section 4.5) and the

increase in carbon monoxide yield (Figure 4.12). Matsuo et al. [197] postulated that

pyrolytic water produced from the pyrolysis of an iron-impregnated lignite in a drop-

tube reactor, played a vital role in the catalytic steam reforming of the tar on the char

surface, which was accompanied by a significant reduction of the tar yield and

considerable increases in yields of hydrogen and carbon monoxide. Rapid pyrolysis


experiments with a Yallourn lignite using a drop tube furnace have also found that

the primary tar can undergo rapid steam reforming with the pyrolysis-derived water

at residence times as short as 2 sec [245] and that longer residence times of about 15

sec can almost fully convert the tar (i.e. 99%) to gaseous hydrocarbons, hydrogen

and carbon monoxide/dioxide [248].

The pyrolysis of the Loy Yang lignite at 900°C in the quartz reactor under the fast

heating mode (see Section 4.5) gave a tar yield of 2wt%db. The presence of tar at the

high pyrolysis temperature may be attributed to a short contact time between the

pyrolysis-derived water and the tar. In the quartz reactor, the pyrolysis-derived water

would be swept out of the reactor and subsequently unable to react with the tar in

secondary steam reforming reactions at high temperature. Furthermore, the

significant yield of water (more than 4wt%db) during the pyrolysis of the Loy Yang

lignite at 900°C, in the pyrojector, also suggests that the contact time between the tar

and volatilised hydrocarbons was short. That is, according to the water gas shift

reaction, the volatilised water would be consumed along with the organic carbon in

the tar or with volatilised hydrocarbons to form additional carbon monoxide and

hydrogen.

The increase in carbon monoxide yield with increasing pyrolysis temperature could

also be attributed to the carbon dioxide reforming of the tar and volatilised

hydrocarbons (Equation 4.5). The marginal decrease in carbon dioxide yield and the

corresponding increase in carbon monoxide yield at pyrolysis temperatures above

700°C (Figure 4.12) suggests that carbon dioxide reforming may have also played a


role in the production carbon monoxide. Carbon dioxide reforming of hydrocarbons

(also known as the Boudouard reaction) at high temperatures to produce carbon

monoxide and hydrogen (syngas) has been studied by several authors [249, 250] and the

chemical reaction is generally expressed as:

CH4 + CO2 → 2CO + 2H2 (ΔH°298K = 247.1 kJ/mol) [251, 252] Equation 4.5

Haghighi et al. [253] investigated the reaction mechanism of carbon dioxide reforming

of methane over a bed of coal char at temperatures between 800°C and 950°C and

reported the production of syngas with a maximum H2/CO ratio of one. In addition,

Mark et al. [254] modelled the reaction kinetics of carbon dioxide reforming methane

in the temperature range of 700°C to 850°C and concluded that the reaction was

approximately first order. The high yields of carbon dioxide and methane produced

during the pyrolysis of the raw Loy Yang lignite (Figure 4.12) would therefore

rapidly facilitate the conversion of these gases into carbon monoxide and hydrogen.

The yields of benzene, toluene, xylene (BTX) and phenol from the pyrolysis of the

raw Loy Yang lignite as a function of temperature are shown in Figure 4.15. At

700°C, the yields of the BTX and phenol were relatively similar at 0.01%wtdb. An

increase in pyrolysis temperature gave increases in yields for all the single ringed

aromatic hydrocarbons which is likely due from the thermal cracking / catalytic

reforming of the tar at the elevated pyrolysis temperatures [245]. The BTX yields

measured for the Loy Yang lignite are of approximately an order of magnitude lower

than the yields reported by Muira et al. [255] in the pyrolysis of Morwell lignite at

750°C. Similarly, Takarada et al. [256] investigated the pyrolysis of Yallourn lignite


over the temperature range 600°C to 1000°C using a fluidized bed reactor and also

reported at least an order of magnitude higher BTX yields compared to the Loy Yang

lignite used in this study. The higher BTX yields of the Morwell and Yallourn

lignites could be attributed to a number of factors including: differences in the extent

of secondary reactions of volatile matter in the pyrolyser reactor systems; differences

in the lignin-derived macromolecular structure; and differences in the typically

higher catalytic cation components in Morwell and Yallourn lignites (see Chapter 6).

The formation and volatilisation of aromatic compounds at different pyrolysis

temperatures is further discussed in the following Section.

600 650 700 750 800 850 900

0.00

0.02

0.04

0.06

0.08

0.10

0.12

Pro

duct

yie

ld w

t% o

f coa

l (db

)

Temperature (°C)

Benzene Toluene Xylenes Phenol

Figure 4.15 Quantification of volatilised (a) benzene, toluene, xylenes and phenol

using a GS-GasPro column.


4.7.1 Py-gc-ms with a HP-5 chromatography column The GS-GasPro chromatography column used in the gas chromatogram performed

well in separating low molecular weight hydrocarbons (Figure 4.11) and non-organic

gases however a limitation to this column was that long chain aliphatic and high

molecular weight triterpenoid materials which have been reported to be pyrolysis

components of Latrobe Valley lignites [208] were not eluted. Subsequently, pyrolysis

gas chromatography experiments were also conducted with the raw Loy Yang lignite

using a HP-5 chromatography column (Figure 4.16).

Figure 4.16 Gc trace of pyrolysed Loy Yang raw lignite at 600°C using a HP-5 column

The pyrogram of the raw Loy Yang lignite at 600°C, using a HP-5 chromatography

column (Figure 4.16), can be separated into four main regions:

• Light weight hydrocarbon gases

• Lignin derived phenolic region

• Lipid derived long chain aliphatics

• High molecular weight triterpenoid region.


The pyrograms from the pyrolysis of the raw Loy Yang lignite as a function of

temperature, using a HP-5 chromatography column is shown in (Figure 4.18). The

sum product yield of the phenolic region and the long chain aliphatic region (C4 to

C30 alkane / alkenes) from the pyrolysis of the raw lignite at 700°C using the HP-5

chromatography column was less than 1wt%db (Figure 4.17). Similarly,

Chaffee et al. [208] had estimated that less than 1wt%db of what is eluted is alkanes

and alkenes from pyrolysis-gc of lignite at 700°C. In contrast, the sum product yield

of the phenolic region and the long chain aliphatic (C4 to C30) region at 800°C

increased significantly to 3wt%db, and at 900°C, the sum product yield decreased to

about 1wt%db (Figure 4.17). The decrease in the sum product yield (long chain

aliphatic region plus phenolic region) is attributed to the thermal cracking/catalytic

reforming of the volatiles to form light hydrocarbon and inorganic gases (see

Section 4.7).

600 650 700 750 800 850 9000

1

2

3

4

5

6

7

Prod

uct y

ield

wt%

of c

oal (

db)

Temperature (°C)

Aliphatic and aromatic hydrocarbons (C4 - C30)

Figure 4.17 Quantification of volatilised alkanes/alkenes (C4-C30) using a HP-5 column, from the py-gc of Loy Yang raw lignite as a function of temperature.


Figure 4.18 Gc trace of pyrolysed Loy Yang raw lignite using a HP-5 column


The relative abundances and product distribution of the pyrolysis products changed

significantly with increasing pyrolysis temperature. Inspection of the relative

abundances from the 600°C pyrogram showed a low product distribution in the

phenolic region and a high product distribution of the long chain aliphatics. The sum

product yields of the phenolic region and the long chain aliphatic region (C4 to C30

alkane / alkenes) at 600°C and 700°C remained relatively unchanged (Figure 4.17)

however a comparison of the product distribution yields at 700°C showed an increase

in the phenolic region and a decrease of the long chain aliphatic region. Furthermore,

at 600°C and at 700°C, the peak for pristine (a vitamin E-derivative [257]) is easily

identified in the pyrograms between the peaks corresponding to C17 and C18 n-

alkanes/alkenes (Figure 4.17) whereas, the pyrogram at 800°C did not show the

presence of pristine nor many of the long chain aliphatic alkane/alkenes or the

characteristic triterpenoid peaks.

Christiansen et al. [258] flash pyrolysed a Columbian coal and reported that the

aliphatic hydrocarbons which were eluded at 750°C were not detected at 1025°C and

that the major components at 1025°C were single and multi-ringed aromatics.

Similarly, the pyrogram at 900°C in Figure 4.18 showed a significant increase in

single and multi-ringed aromatics (i.e. based on the retention times of selected

aromatic standards). Christiansen et al. [258] also pyrolysed a mixture of unbranched

alkanes at different temperatures and found the degradation of aliphatic material

under high pyrolysis temperatures, led to the formation of aromatic compounds and

that the degree of transformation increased with increasing temperature.

Furthermore, the formation of aromatic compounds from long chain polymers was


demonstrated by Purser and Wolley [259] who reported the presence of benzene,

toluene, xylene and styrene from the pyrolysis of polypropylene. The reductions of

the long chain aliphatic alkanes/alkenes region and the triterpenoid region and the

subsequent increase in aromatic/phenolic region with increasing pyrolysis

temperature (Figure 4.18) are likely attributed to the thermal cracking/catalytic

reforming of these hydrocarbons (see Section 4.7).

4.7.2 Volatile yield balance The mass balance of the different volatile fractions from the pyrolysis of the raw

lignite measured from the quartz reactor experiments and from the pyrograms, as a

function of temperature is shown in Table 4.2. In Section 4.4.2, the volatile yield

was found to be unaffected by the heating rate of the lignite and subsequently, it is

reasonable to assume that a similar volatile yield would result from the pyrolysis of

the raw lignite using the pyrojector. Also, the tar yield values from the quartz reactor,

fast heatup pyrolysis experiments have been included in Table 4.2 as guide for

estimating approximate non-tar volatiles.

The pyrolysis-gas chromatography setup used in this study shows that an estimated

70% of the non-tar volatiles were accountable (Table 4.2). This is a vast

improvement from earlier work by Chaffee et al. [208] which estimated that only 9-

15% of the pyrolysis material is eluted from the column from pyrolysis-gas

chromatography of lignite up to 700°C. Chaffee et al. [208] explained that most of the

volatiles from the pyrolysis of lignites could not be detected in their system because

of low-molecular weight compounds being eluded too rapidly from the

chromatographic system so their contribution to the pyrolysate could not be assessed


and that the presence of gases such as carbon monoxide, carbon dioxide, water and

hydrogen could not be detected with a flame ionisation detector (FID) [208].

Advantageously, the gas chromatogram used in this thesis was equipped with a FID

detector (for detection of hydrocarbons) and TCD detector (for detection of fixed

gases) and the application of GS-GasPro and HP-5 chromatography columns proved

effective in measuring a large proportion of the non-tar volatiles. The drawback

however was the inability to measure hydrogen gas which is a major non-tar volatile

gas from the pyrolysis of the lignite. Interestingly, the proportion of unaccounted

pyrolysates increased with increasing pyrolysis temperature which could be

attributed to the increase in hydrogen production from the catalytic reforming of

volatiles (see Section 4.7). Furthermore, inorganic nitrogen (eg NH3, NOx etc) and

sulphur (SOx) gas components were also eluded too rapidly from the

chromatographic system used in this study however the concentrations are expected

to be low because of the lignite’s low nitrogen (0.66wt%daf) and sulphur

(0.27wt%daf) contents. Alternative chromatography columns could overcome these

limitations thus increasing the overall mass balance accountability of the non-tar

volatiles.


Table 4.2 Mass balance of volatile yield quartz reactor versus pyrolysate yield measured in the programs

Product yield weight % of coal (daf)

Quartz reactor 600°C 700°C 800°C 900°C

Volatile yield * 44 48 50 51

Tar yield * 24 18 6 2

Non-tar volatiles (volatile yield – tar yield)

20 30 44 49

Pyrolysis-gas chromatography 600°C 700°C 800°C 900°C

Total eluted pyrolysates 14 22 32 36

Unaccounted pyrolysates (non tar volatiles – total pyrolysates)

6 8 12 13

* Measured from the fast heatup pyrolysis of the raw lignite using a quartz reactor

4.8 Pyrolysis-gas chromatography-mass spectrometry Pyrolysis-gas chromatography-mass spectrometry (py-gc-ms) of the Loy Yang

lignite is shown in Figure 4.19. The py-gc-ms trace (Figure 4.19) is similar to the py-

gc program (Figure 4.16) with the exception that the light hydrocarbon gases (which

are the major components during pyrolysis) are not detected. The absence of these

light hydrocarbon gases in py-gc-ms is likely attributed to the experimental setup of

the mass spectrometer system which was set to ignore light molecules because of

detector saturation from solvent peaks.

Similarly, many investigations using py-gc-ms have not detected light hydrocarbon

gases from the pyrolysis of biomass [260], or pyrolysis of coal / coal fractions, and as a

consequence, have reported that single ringed aromatic components as the smallest


and most abundant organic volatile product from pyrolysis [261-264]. In contrast,

quantification of hydrocarbon yields greater than C3 that were eluded from the py-gc

setup used in this study, revealed that only 0.5wt%db was eluded at 600°C and less

than 2wt%db at 900°C. In a nutshell, the pyrograms from py-gc-ms, despite being a

small proportion of the overall volatile yield, is a valuable tool in confirming the

identity of chemical components being eluded from the column.

Figure 4.19 Pyrolysis-gas chromatography-mass spectrometry of the Loy Yang lignite at 700°C.


4.9 Py-gc of thermally treated products Curves for the individual hydrocarbon gases yields (methane, ethane, ethene, and

ethylene) and the inorganic gases (carbon monoxide and carbon dioxide) from the

pyrolysis-gas chromatography of the Loy Yang raw lignite and from MTE, SD and

HTD treated products as a function of temperature are shown in Figure 4.20. Similar

to the raw lignite, the major hydrocarbon products from the pyrolysis of the

thermally treated products were methane and ethene.

For the HTD product, the methane yields as a function of pyrolysis temperature were

significantly lower when compared to the methane yields of the raw lignite and MTE

and SD products (Figure 4.20a). These differences in methane yield as a function of

temperature can be explained by two main contributing factors; firstly, the

demethylation resulting from hydrothermal dewatering (i.e. demethylation being part

of the 14wt%db mass loss; see Section 3.1) and secondly, the significantly lower

inherent cation content of the HTD product which would consequently reduce the

extent of catalytic reforming of volatiles on the char surface (see Section 4.6). The

HTD product with its low inherent cation content, gave a methane yield which

increased linearly as a function of pyrolysis temperature. In contrast, for the raw

lignite and for the MTE and SD products, the methane yields increased sharply at

800°C and at 900°C, relative to the HTD product methane yields. A similar trend for

ethene yields as a function of temperature was also visible between the HTD product

and the raw lignite and MTE and SD products (Figure 4.20c). The effectiveness of

catalytic reforming at the higher pyrolysis temperatures may explain the differences

in yields of methane and ethene between the HTD product and the raw lignite, MTE


and SD products. As for ethane and ethylene yields (Figure 4.20b and Figure 4.20b,

respectively), no significant differences were evident between the raw lignite and the

thermally treated products as a function of temperature.

The significantly lower yields of carbon monoxide (Figure 4.20e) and carbon dioxide

(Figure 4.20f) from the pyrolysis of the HTD product relative to the pyrolysis yields

of the raw lignite and MTE and SD products can be mainly attributed to the

decarboxylation from the hydrothermal dewatering process. However

decarboxylation alone cannot explain the divergence of the carbon monoxide and

carbon dioxide curves between the HTD product and the raw lignite and MTE and

SD products as a function of pyrolysis temperature. Over the pyrolysis temperature

range, the carbon monoxide yield from the HTD product, did not increase of equal

proportions which indicates a low degree of catalytic decomposition of oxygen

containing aromatic compounds and a lower degree of catalytic steam reforming of

hydrocarbons on the char surface (see Section 4.7). Furthermore, the carbon dioxide

yield from the pyrolysis of the HTD product increased with increasing temperature

which did not follow the trend of the raw lignite and the MTE and SD products. This

behaviour may be attributed by the lower cation content of the HTD product thus

resulting in a lower proportion of carbon dioxide reforming at pyrolysis temperatures

above 800°C.


600 650 700 750 800 850 9000

1

2

3

4

5

6

7

600 650 700 750 800 850 9000

1

2

600 650 700 750 800 850 9000

1

2

3

4

5

600 650 700 750 800 850 9000

1

a

Prod

uct y

ield

wt%

of c

oal (

db)

Temperature (°C)

Raw lignite (CH4)

MTE 150°C/5.1MPa (CH4)

SD 230°C (CH4)

HTD 320°C (CH4)

b

Prod

uct y

ield

wt%

of c

oal (

db)

Temperature (°C)

Raw lignite (C2H6) MTE 150°C/5.1MPa (C2H6) SD 230°C (C2H6) HTD 320°C (C2H6)

c

Prod

uct y

ield

wt%

of c

oal (

db)

Temperature (°C)

Raw lignite (C2H

4)

MTE 150°C/5.1MPa (C2H

4)

SD 230°C (C2H

4)

HTD 320°C (C2H

4)

d

Prod

uct y

ield

wt%

of c

oal (

db)

Temperature (°C)

Raw lignite (C2H2) MTE 150°C/5.1MPa (C2H2) SD 230°C (C2H2) HTD 320°C (C2H2)

600 650 700 750 800 850 9000

2

4

6

8

10

12 e

Prod

uct y

ield

wt%

of c

oal (

db)

Temperature (°C)

Raw lignite (CO) MTE 150°C/5.1MPa (CO) SD 230°C (CO) HTD 320°C (CO)

600 650 700 750 800 850 900

2

4

6

8

10

12 f

Prod

uct y

ield

wt%

of c

oal (

db)

Temperature (°C)

Raw lignite (CO2) MTE 150°C/5.1MPa (CO2) SD 230°C (CO2) HTD 320°C (CO2)

Figure 4.20 Quantification of volatilised (a) methane, (b) ethane, (c) ethene, (d) ethylene (e) carbon monoxide, (f) carbon dioxide, from the py-gc of Loy Yang raw

lignite, MTE, SD and HTD treated products as a function of temperature using a GS-GasPro column.


4.10 Conclusion For a drying process, a high level of water removal from the raw lignite is desirable

however significant losses in volatile material could be disadvantageous for some

industrial processes which convert the carbon matter to lower molecular weight

fractions (eg gasification, liquefaction etc). For MTE and SD, the operating

parameters for achieving a 50% moisture reduction from the raw lignite were

relatively mild (<250°C) and advantageously, the volatile fraction in the lignite was

not affected. In contrast, for HTD, the drying temperatures necessary for achieving a

similar moisture reduction were much higher (i.e. 320°C), and subsequently a

significant amount of volatile yield was lost from the raw lignite after processing.

Pyrolysis experiments with raw Loy Yang lignite using a quartz fluidized-bed/fixed

bed reactor system showed that the heating rate had no effect on the char yield of the

product as a function of temperature. Similarly, no significant differences in the char

yield profile were found between the slow heating rate and fast heating rate for the

MTE, SD and HTD products. In contrast, heating rate did affect the composition of

the volatile products in particular the tar yield and volatilisation of sodium and

chlorine. When the lignite particles were rapidly pyrolysed above 700°C, marked

increases in sodium volatilisation coincided with significant reductions in tar yield

whereas, for slow heating particles, sodium volatilisation and tar yield remained

relatively unchanged. The volatilisation of sodium in the fast heatup process at

temperatures above 700°C, is believed to be linked to volatile-char interactions

causing the reforming/cracking of the tar. In contrast to sodium, the volatilisation

chlorine during fast heatup pyrolysis was found to decrease at temperatures above


600°C which was postulated to be the result of recombination of chlorine with newly

formed radical sites inside the carbon macromolecular structure at high temperatures.

Furthermore, the concentrations of the alkaline metals calcium and magnesium were

not affected by differences in pyrolysis heating modes.

Rapid heat-up was also achieved with a pyrolysis-gas chromatography system. The

two major hydrocarbon components detected from the rapid pyrolysis of Loy Yang

lignite were methane and ethene which increased in yield as a function of

temperature from 600°C to 900°C. The yields of ethylene, propene and propylene

increased yields with increasing pyrolysis temperature while their correspondent

saturated hydrocarbons, ethane and propane, reached maximum yields at 700°C and

800°C, respectively, before declining with further increases in pyrolysis

temperatures. In addition, the increase in single aromatic hydrocarbon as a function

of increasing pyrolysis temperature also coincided with the breakdown of terpenoid

material and long-chain aliphatic compounds.

The pyrolysis-gas chromatography system which was equipped with a FID detector

(for detection of hydrocarbons) and TCD detector (for detection of inorganic gases)

and the application of GS-GasPro and HP-5 chromatography columns proved

effective in measuring a large proportion of the non-tar volatiles. An estimated 70%

of the non-tar volatiles were accountable which is a vast improvement over previous

studies. In contrast, quantification of non-tar volatiles using a py-gc-ms system,

which has been the instrument of choice in prior studies, could only account up to

15% of the non-tar volatiles.


Rapid pyrolysis of the thermally treated products in the py-gc system showed that the

methane, ethene, carbon monoxide and carbon dioxide yields for the HTD product

were significantly lower when compared to the methane yields of the raw lignite and

MTE and SD products. The lower yields for the HTD product is likely attributed to

volatilisation during hydrothermal dewatering and also from the reduction of

catalytic reforming cations. The significant volatile yield loss during hydrothermal

dewatering could be disadvantageous in some industrial processes, which convert the

carbon matter to lower molecular weight fractions (eg gasification, liquefaction).

Chapter 5 Combustion of Raw Lignite and Dried Products 138

CHAPTER 5 COMBUSTION OF RAW LIGNITE AND

DRIED PRODUCTS 5.1 Introduction Combustion is generally the process where fuel and oxygen burn together at

sufficiently high temperature to evolve heat and combustion products. The events

that lead to combustion when a coal particle is progressively heated in air can be

separated into three main stages [265]:

• Devolatilisation of the coal particles and the consequent charring of the

particles

• Combustion of the volatile matter in the gas phase

• Combustion (or burning) on the solid surface of the residual char particle

Thermogravimetric tests for measuring combustion reactivities for carbonaceous

materials are widely reported in the literature. Generally, the applied techniques fall

into two categories (i) isothermal, where the sample is maintained at constant

temperature and (ii) non-isothermal, where the sample is heated at a constant rate.

The choice of technique for evaluating the combustion reactivity of the sample is

important. Isothermal measurements are often conducted by heating the sample to

the desired temperature in an inert gas before switching the gas stream to an oxygen-

containing supply. This technique is similar to the proximate analysis tests described

in the Section 4.2 however the combustion temperatures used in isothermal

measurements are milder ranging from 350°C to 500°C [266]. Isothermal


measurements taken at different temperatures can also give additional kinetic

information (e.g. Arrhenius plots of log [reaction rate] against inverse absolute

temperature can be applied to calculate the activation energy of the samples [266-268]).

The isothermal technique has been found to be ideal in measuring the combustion

reactivity of high temperature treated char products from pyrolysis and/or

gasification (eg >500°C) however this technique cannot be applied to raw

lignites [269] or to the thermally dried products described in Chapter 3. That is, it is

difficult to use isothermal techniques to investigate oxidation-combustion kinetics of

raw lignite or thermally treated products (Chapter 3) because of the high reactivity

nature of the sample upon exposure to oxygen. Furthermore, heating the samples to

an isothermal temperature greater than the processing temperature used to generate

the thermally treated products (Chapter 3) will make the raw lignite and thermally

treated products more alike (eg similar volatile/char ratios, elemental composition,

oxygen group functionality, etc) and therefore, the information obtained would be

meaningless.

Alternatively, the non-isothermal approach is more applicable for investigating

differences between the raw lignite [270-273] and thermally treated products. Previous

workers who have used the non-isothermal approach have heated the sample at a

constant rate up to 900°C. Under such conditions, complete conversion normally

occurs before the sample has reached 900°C [266, 268]. Non-isothermal measurements

in the TGA are relatively fast (the sample can be heated to 900°C within 1h).

Furthermore, in a non-isothermal measurement, the peak temperature can be


determined (i.e. the temperature at which the rate of weight loss from the sample is at

a maximum; a high peak temperature is indicative of a less reactive fuel [268]). In

addition, the ignition temperature [274] and the burnout temperature (i.e. the rate of

weight loss is less than 1% per min) can also be deduced [275]. A disadvantage of the

non-isothermal approach is the inability to accurately assess the catalytic activity of

alkali and alkaline earth metal species (AAEM) at a given temperature [111].

In this study, a combination between isothermal and non-isothermal techniques was

used to evaluate the reactivity differences between the raw lignite and its thermally

dried products. That is, the samples were heated at a constant rate to the desired

combustion temperature (non-isothermal) and maintained until complete conversion

was achieved (isothermal). The experimental parameters, which may affect the

combustion reactivity of the dried products in the TGA, are investigated in following

sections.


5.1.1 Effect of particle size Thirteen discrete particle size intervals were investigated using the raw lignite. For

comparative purposes, 30.0mg of sample was used in each combustion test.

Figure 5.1 suggests that particle size of the sample had very little effect on the

combustion rate. This behaviour is in direct contradiction to what other workers have

reported in their combustion investigations (i.e. with increasing particle size, the

combustion reactivity is decreased). This contrasting difference can be rationalised

by understanding the experimental protocol that was applied for the combustion tests

in this study.

The combustion process in a TGA can be described by the following several

steps [276]:

• The diffusion of gaseous reactants and products (mass transfer) from the bulk

of the gas phase to the internal surface of the reacting solid particle

• Adsorption of gaseous reactants on and desorption of reaction products from

the solid surfaces

• Chemical reaction between the adsorbed gas and solid

It is expected that with an increase in particle size, the diffusion of gaseous products

through the pores of the particle will take longer and will therefore reduce the

combustion rate of the particle. Various combustion models have attempted to

include gaseous diffusion through pores and between particles [277-283].

Morgan et al. [284] reported that particle size and coal properties were responsible for

different coal-burning profiles obtained from TG/DTG analysis. Morgan et al. [284]

Chapter 5 Combustion of Raw Lignite and Dried Products

142

also mentioned that oxygen uptake and particle reactivity increased with decreasing

particle size. In addition, particle sizes greater than 125μm gave significantly

different curve profiles compared to smaller particle sized samples. Gold [285]

concluded that the temperature and the magnitude of the exothermic peak were

affected by the heating rate, sample mass and particle size.

Based on the results of previous workers mentioned above, a likely explanation for

the similarity between combustion curves given in Figure 5.1 is the result of gaseous

diffusion limitations of reactants and products through the internal and external

surface of the particles. This diffusion limitation is attributed to the large sample

mass used in each TGA experiment. The effect of sample mass on the combustion

rates is further elucidated in the following section.


143

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250

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350

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450

500

0 600 1200 1800 2400 3000 3600 4200 4800 5400 6000

Tem

pera

ture

(ºC

)

< 63 microns63 to 75 microns75 to 90 microns90 to 106 microns106 to 125 microns125 to 150 microns150 to 180 microns180 to 250 microns250 to 355 microns425 to 500 microns600 to 710 microns850 to 1000 microns 1180 to 1400 micronsTemperature

Figure 5.1 Combustion of raw, discrete particle sized lignite. 30mLmin-1 air flow, 30mg sample


5.1.2 Effect of sample mass loading on combustion rates The amount of sample placed inside the TGA crucible had a significant effect on the

combustion rate obtained (Figure 5.2). The rate of combustion increased with a

reduction of sample loading. The combustion reactivity of dried products will be

dependant on the transport of oxygen and heat to the surface of the particle where

oxidation-combustion takes place. In the TGA, the diffusion of oxygen to the surface

and the removal of product gases (eg CO2) from the surface can significantly affect

the observed combustion rate. That is, the carbon dioxide released during combustion

must diffuse through the pore structure of the particle, through the empty spaces

between the particles and then to the upper surface of the char bed where it is carried

away from the furnace. Internal diffusion limitations have been reported by Hemati

and Laguerie [286] in their investigation on steam gasification kinetics of charcoal in a

TGA. Ollero et al. [283] also reported that the internal diffusion resistance of a 3mm

deep char bed was quite significant thus affecting the measured gasification rates in

the TGA. In addition, Ollero et al. [283] suggested that if the removal of CO2 was not

fast enough, the temperature of the inside layers of the bed may be lower than that of

the surface of the bed. This endothermic effect (i.e. lower combustion temperature)

and the slow external diffusion of CO2 from the sample bed can explain the slow

combustion rates observed with an increase of sample loaded in the crucible.

In Figure 5.2 the combustion rate of the 5.8 and 6.7mg sample was similar therefore

suggesting that the internal diffusion limitations of air and product gases were

significantly reduced. In order to eliminate diffusion limitations of gases, a smaller

crucible and smaller sample masses were used in each of the combustion tests


145

described from here onwards. For comparative purposes, it was also decided to apply

a monolayer bed of particles and a constant sample mass of 2.0mg. These changes

would allow comparative differences in combustion reactivity of the dried products

to be more meaningful.


146

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oss

(%)

0

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250

300

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450

500

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000

Tem

pera

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(ºC

)

5.84mg sample loading6.69mg sample loading15.67mg sample loading20.51mg sample loading 30.25mg sample loading31.95mg sample loading34.82mg sample loading35.23mg sample loading41.26mg sample loadingTemperature

Figure 5.2 Combustion of 1mm lignite particles, loaded into a large crucible


5.1.3 Combustion of 1mm raw Loy Yang particles The gaseous diffusion limitations of reactants and products in the TGA system, as

discussed in Sections 5.1.1 and 5.1.2, have been reduced in this section with the use

of a smaller cup and a monolayer of particles (Figure 5.3). To further optimise the

parameters for investigating the combustion reactivity of thermally dried products, it

was decided to test the combustion behaviour of large particles in the TGA system. It

is accepted that particles of greater than 125μm can significantly reduce the rate of

combustion because of gas diffusion within the pore structure of the particle [284] (see

also Section 5.1.1) however, the advantages of using single large particles in the

TGA system are the elimination of inter-particle gas diffusion effects and the ease in

determining particle ignition (see Figure 5.6). Combustion tests in the TGA on

smaller particles sizes (90 to 125μm) are also discussed later in this chapter.

2 mm

Coal particles(1 mm diameter)

Figure 5.3 Schematic of two 1mm lignite particles positioned inside the TGA crucible.

The combustion-oxidation reaction requires the chemical action of the reactant gas

(i.e. oxygen) on the active site of the lignite particle. Figure 5.4 shows the gradual

weight loss of the two lignite particles attributed to the combustion-oxidation

reaction during heating to 450°C. The heat flow and DTG curves were relatively

steady over the combustion-oxidation history (Figure 5.4). This type of behaviour is


desirable for investigating differences in combustion reactivity between samples. In

contrast, in Figure 5.5 and Figure 5.6, very sharp weight losses, sharp exothermic

peaks and sharp DTG peaks were given during the combustion of the two particles.

This type of behaviour is attributed to the particles igniting.

The particle ignition mechanism of a coal particle in a hot oxidising environment has

been argued by many workers [277, 287-297]. The two generally accepted mechanisms

for particle ignition are homogeneous and heterogenous. In a homogeneous system,

the initial step is pyrolysis followed by ignition of the volatiles and then ignition of

the char. That is, homogeneous ignition occurs in the gas phase in a mixture of

released volatiles and oxygen. In contrast, the heterogeneous reaction involves the

direct attack of oxygen on the surface of the whole coal particle. The fact that weight

loss occurred before ignition, it could therefore be assumed that the ignition of the

particle was homogeneous.

The rapid weight losses and significant heat gains associated with particle ignition

are undesirable for investigating the combustion reactivity of samples. Figure 5.4 to

Figure 5.6 demonstrate the heterogeneous nature of the lignite and the difficulties

associated in repeating combustion experiments. For these reasons, it was decided to

investigate the combustion reactivity of the two particles under a range of

combustion temperatures, as an attempt to identify the best TGA parameters for

examining the differences between the thermally dried products.


0 2000 4000 6000 8000-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

No particle ignition

dW/dT

Time (sec)

d w

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t / d

tim

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Hea

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w (m

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Weight lossW

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t los

s (%

)

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300

400 Temperature

Tem

pera

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(°C

)

0

100

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300

400

500

Tem

pera

ture

(°C

)

0

100

200

300

400 Temperature

Temperature

Tem

pera

ture

(°C

)

Figure 5.4 Combustion-oxidation of two particles (1mm diameter) at 450°C.


0 2000 4000 6000 8000-0.4

-0.3

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-0.1

0.0

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2nd particle no ignition

1st particle - ignition

dW/dT

Time (sec)

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2nd particle - no ignition

1st particle - ignition Heat Flow

Hea

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w (m

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Weight loss

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(%)

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Tem

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(°C

)

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500

Tem

pera

ture

(°C

)

0

100

200

300

400 Temperature

Temperature

Tem

pera

ture

(°C

)

Figure 5.5 Weight loss, heat flow and DTG curves of two 1mm particles (one

particle igniting and one particle undergoing combustion-oxidation) heated to 450°C in a TGA.


0 2000 4000 6000 8000-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

2nd particle ignition1st particle - ignition

dW/dT

Time (sec)

d w

eigh

t / d

tim

e

0

50

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200

2nd particle - ignition


Heat Flow

Hea

t Flo

w (m

W)

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2nd particle - ignition


Weight lossW

eigh

t los

s (%

)

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400 Temperature

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(°C

)

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500

Tem

pera

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(°C

)

0

100

200

300

400 Temperature

Temperature

Tem

pera

ture

(°C

)

Figure 5.6 Weight loss, heat flow and DTG curves of two particles igniting during

heating to 450°C in a TGA.


5.1.4 Effect of combustion temperature Intrinsic char reactivity is normally measured at relatively low temperatures when the

reaction rates are relatively low [266]. Choosing the appropriate temperature for

measuring the combustion reactivity of the thermally dried products is important for

obtaining meaningful comparable results between samples. Too high of a combustion

temperature, the combustion rate would be too fast and differences between samples

may be difficult to distinguish. Furthermore, a high combustion temperature may

promote ignition of the sample [275]. In contrast, if the combustion temperature is too

low, then complete combustion may not be achieved within an acceptable time

frame. Russell et al. [266] investigated the intrinsic char combustion reactivity at

500°C on a TGA and reported that a typical unburnt char took 3h to reach 50%

conversion and more than 10h to reach >99% conversion. Tseng and Edgar [298]

reported that above 550°C, the measurement of the intrinsic reaction rate of lignite

char was limited by diffusion resistance.

A range of combustion temperatures were tested on raw Loy Yang lignite in order to

choose an appropriate set of conditions to carry out subsequent tests on the thermally

dried products. Figure 5.7 shows the weight loss of the Loy Yang raw lignite, heated

at 30°C per min to the desired temperature (non-isothermal) and maintained until

complete conversion was achieved (isothermal). Increasing the combustion

temperature beyond 450°C did not significantly give faster conversion rates.

Furthermore, the heat flow history from the 450°C sample suggests some particles

had ignited during the heating process (Figure 5.7). This is further illustrated in

Figure 5.8 which clearly shows the different appearances between charred and

ignited particles.


1000 2000 3000

0

40

80

120

160

200 C Ignition 350°C 400°C 450°C 500°C 550°C

Hea

t Flo

w (m

W)

Time (sec)

2000 3000 4000

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0 B 350°C 400°C 450°C 500°C 550°C

Wei

ght l

oss

(%)

0 2000 4000 6000 8000 10000 12000

-100

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-60

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-20

0 A

Wei

ght l

oss

(%)

350°C 400°C 450°C 500°C 550°C

Figure 5.7 Relationship between

(A) weight loss and combustion temperature (B) weight loss and combustion temperature (time scale 1500 to 4000 sec)

(C) combustion temperature and heat flow during combustion. Reaction conditions: 2.0mg Loy Yang raw lignite, 250-500μm particle size


Ignited particleNon-ignited particle

2 mm

Coal particles(250-500 m diameter)μ

BEFORE AFTER

A B

Figure 5.8 Schematic diagram of the TGA crucible containing 2 mg of 250-500mm

particles of raw lignite. (A) before combustion, (B) after combustion at 450°C.

The weight loss, heat flow and DTG histories for the 450°C, 500°C and 550°C

combustion tests are given in Figure 5.9. As mentioned in Section 5.1 the non-

isothermal technique is often used to determine the peak temperature (the point

where burning is at a maximum) of the sample. For the 450°C experiment, the peak

temperature was not reached during the non-isothermal heating stage (as indicated by

the DTG curve which reached its peak during the isothermal period; i.e. right side of

the vertical dotted line). Whereas, for the 500°C and 550°C experiments, the peak

temperature was achieved during the non-isothermal heating period and was found to

be at 465°C (Figure 5.9). This peak temperature is relatively high when compared to

the results by Cumming [268] who reported peak temperatures for lignites between

370°C to 430°C and for bituminous coals 475°C to 560°C. Similarly,

Ozbas et al. [299] reported peak temperatures for Turkish, Soma lignite (500μm


particle size) to be at 408°C. The major difference between this study and the work

by Cumming and Ozbas et al. is the amount of sample used in the crucible.

Cumming placed 20mg sample in a narrow crucible (~10mm wide) and Ozbas et al.

used ~10mg of sample (dimensions of the crucible not given). These higher mass

loadings suggest that a monolayer of particles was not used during the experiment

and that diffusion resistance limitations of the gases may have been present during

their experiment (see Section 5.1.2). In contrast, Benfell et al. [300] investigated the

combustion behaviour of New Zealand lignites using 5mg samples in their TGA

experiments and reported peak temperatures between 377°C to 416°C.

Benfell et al. [300] did report that both the organic and inorganic aspects of the lignite

were responsible for differences in the peak temperature for the New Zealand

samples.

Furthermore, in the 550°C experiment, the burnout temperature of the sample was

measured at 545°C (i.e. burnout had already occurred before the isothermal

temperature period was reached) (Figure 5.9). This burnout temperature is also

significantly higher relative to values reported by other workers. The very low

inorganic content of the Loy Yang lignite used in this study is likely responsible for

the higher peak and burnout temperatures measured. The effect of inorganic species

on the combustion reactivity is further discussed in Section 5.5.

On the basis of the results presented in this section, it was decided to carry out all

subsequent experiments at 400°C so as to reduce the burning rate of the sample and

allow comparative differences between samples to be more easily identified. Also,


reducing the experimental temperature to 400°C would reduce the likelihood of

particle ignition. Experiments conducted at 450°C have also been included for

comparative purposes only.

2000-100

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C 550°C

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Tem

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-0.4

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DTG

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0.0

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DTG

-0.4

-0.2

0.0

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0.4

DTG

DTG

Figure 5.9 Effect of combustion temperature versus the weight loss and DTG

respectively. Dotted line gives the point where the desired temperature has been reached.


5.2 Effect of particle size (monolayer loading) In Section 5.1.1, the effect of particle size on the combustion behaviour of raw lignite

was investigated at 450°C using a crucible packed with the lignite sample (30mg

sample mass). The results described in Section 5.1.1 were argued to be misleading

because of diffusion limitation of gases passing between particles. Furthermore, in

Section 5.1.4, it was reported that a combustion temperature of 450°C may be too

high for testing the reactive nature of the Loy Yang lignite because of its propensity

to ignite. Based on these findings, it was decided to re-investigate the effect of

particle size but using a monolayer of particles (2mg) and a lower maximum

combustion temperature (400°C).

In Figure 5.10, the combustion rate of particles ranging from 75μm to 850μm did not

give significant differences whereas for larger particles (1.00 to 1.18mm particles),

the combustion rate was considerably slower. The reduction in combustion activity

with increasing particle size was described in Sections 5.1.1 and 5.1.2 as the result of

longer gaseous diffusion times of reactants and products through the pores of the

solid product. For the very small particles (45 to 63μm region), the combustion rate

was marginally faster than the larger particles (75μm to 850μm). This faster

combustion rate could be attributed to the higher surface area of the smaller particles

(Table 5.1). Tseng and Edgar [301] postulated that the combustion rate of coal char

was proportional to the internal surface area of the sample. Furthermore, several

researchers have also reported that with decreasing particle size, the specific surface

area and pore volume of the particle were significantly increased [302, 303] and that the

time required to reach burnout decreased with decreasing particle size [303].


158

Several other workers have also described that the surface area was a contributing

factor in the combustion rate of coal or coal chars [274, 304].

Table 5.1 Effect of particle size on the surface area of raw lignite

Particle Size Region

(μm)

CO2 adsorption at 273K Dubinin Surface Area

(m2g-1) (±1)

1000 to 1180 181

710 to 850 182

500 to 600 180

355 to 425 184

150 to 180 189

106 to 125 208

75 to 90 213

45 to 63 227

To elucidate the differences between the combustion rates of the raw lignite and the

thermally treated products, two particle size regions (90-125μm and 250-500μm)

were chosen. The latter particle size corresponds to the region used for measuring the

pore structure of the thermally dried products (see APPENDIX C) whereas the

former region was chosen for the purpose of eliminating gaseous diffusion limitation

effects but also because of the larger sample mass obtained within this fraction.

w Lignite and Dried Products

159

0.0 0.2 0.4 0.60.00

0.02

0.04

0.06

0.08

0.10

0.12

0.8 1.0

45 - 63μm 75 - 90μm 106 - 125μm 150 - 180μm 355 - 425μm 500 - 600μm 710 - 850μm 1000 - 1180μm

Spec

ific

reac

tivity

(min

-1)

Conversion (daf)2000 3000 4000 5000

0

20

40

60

80

100

120

140 45 - 63μm 75 - 90μm 106 - 125μm 150 - 180μm 355 - 425μm 500 - 600μm 710 - 850μm 1000 - 1180μm

Hea

t Flo

w (m

W)

Time (sec)2000 3000 4000 5000

100

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0

-

Wei

ght l

oss

(%)

Time (sec)

45 - 63μm 75 - 90μm 106 - 125μm 150 - 180μm 355 - 425μm 500 - 600μm 710 - 850μm 1000 - 1180μm

Figure 5.10 Combustion of raw lignite of different discrete particle size in the TGA at 400°C. Conditions: 30mLmin-1 air flow, 2.0mg sample

Chapter 5 Combustion of Ra


5.3 Combustion reactivity of thermally dried lignites In summary of the earlier chapters, the MTE process removed the highest proportion

of water at the lowest processing temperature, the sodium in the products was

reduced by about half and the large pore volumes of the products were significantly

lower than HTD and SD. In spite of these physico-chemical changes, the effect of

increasing processing temperature and increasing applied mechanical pressure

resulted in only marginal decreases in the combustion reactivity compared to the raw

lignite (Figure 5.11 and Figure 5.12). A similar trend was also evident for the 250-

500μm particle sized samples combusted at 400ºC, respectively (see Appendix H,

Figure M.1 and Figure M.2, respectively).

In contrast to MTE and SD, the HTD process required significantly higher

processing temperatures to achieve acceptable moisture reductions and consequently

gave lower mass recoveries and high TOC in the product waters. Nevertheless, the

HTD process removed the highest levels of sodium, magnesium, calcium and

chlorine from the raw lignite. Furthermore, the dried large pore volume of HTD

products was significantly higher than MTE products. Regardless of these physico-

chemical transformations for the HTD products, only a small but significant

differences in the combustion reactivity and burnout times was found with increasing

HTD processing temperature (Figure 5.13, also see Appendix H, Figure M.3).

Similarly, the combustion reactivities of MTE and HTD products were not much

different to the raw lignite.


For SD, significantly lower processing temperatures than HTD but higher

temperatures than MTE were required to achieve significant dewatering. The SD

large pore volume was similar to HTD, but the proportion of ions removed were

similar to MTE under the same temperature regime. Furthermore, at higher

processing temperatures, SD products extracted more organic matter into the product

water. Similarly to the MTE and HTD processes, the combustion reactivity decreased

with increasing processing temperature however these changes were only marginal

(Figure 5.14). In addition, combustion of the SD, 250-500μm particle sized samples

(see Appendix H, Figure M.4) gave similar marginal reductions in combustion

reactivity with increasing processing temperature.

Interestingly, the combustion reactivity for the 350ºC SD product was less reactive at

the lower conversion levels (i.e. <40% conversion) but more reactive at the higher

conversion levels (i.e. >60% conversion) compared to the SD products that were

processed at lower temperatures (Figure 5.14). At the lower conversion levels, the

more reactive components (eg volatiles; Table 4.1) would preferentially be consumed

first. Consequently, with increasing conversion the concentration of cation to carbon

ratio would increase. In Chapter 3, it was discussed that at higher SD processing

temperatures, ions were trapped in the SD product because of more water being

removed from the lignite as steam and the cation to anion ratio in the products was

also increased. These remaining cations, in particular sodium, could enhance the

catalytic activity of the products at the higher conversion levels.


In contrast, the HTD product treated at 350ºC was less reactive throughout its

conversion history compared to lower temperature HTD products (Figure 5.13). In

HTD, the cation to anion ratio in the products also increased with increasing

processing temperature however the very low cation concentration remaining in the

HTD products had little effect on the product’s reactivity at the higher conversion

levels.

5.4 Combustion reactivity of thermally dried lignites at 450ºC

In Section 5.1.4, combustion tests at 450ºC resulted in some particles igniting during

the heating process and for this reason, it was concluded that all tests conducted at

this temperature should be treated with caution. Nevertheless, combustion tests at

400ºC and 450ºC did demonstrate differences in the dried product’s tendency to

ignite during heating (Appendix H).

Combustion tests at 400ºC gave a single exothermic peak and the differences in the

heat flow history were negligible between the raw and thermally dried products

whereas, combustion tests at 450ºC resulted in additional exothermic peaks likely

due to some particles igniting. Surprisingly, the combustion reactivity of the products

also declined with increasing processing temperature (and with increasing

mechanical pressure for MTE) (see Appendix H). More interestingly was the

difference in combustion reactivity between the HTD and SD products. The HTD

products had a marked reduction in combustion reactivity at 450ºC compared to the

raw lignite (Figure M.3) whereas for SD, these differences were only marginal

(Figure M.4). For the HTD products, the reduction in combustion reactivity and the


163

reduction in the likelihood for the product to ignite could also be attributed to the

significant decrease in catalytic ion species from the drying process (see Section 3.5).

-100

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Time (sec)

2

raw 150°C / 2.5MPa 150°C / 5.1MPa 150°C / 12.7MPa 150°C / 25.0MPa

Wei

ght l

oss

(%)

Figure 5.11 Combustion of MTE products (90-125μm particle size) in the TGA at 400°C.

Conditions: 30mLmin-1 air flow, 2.0mg sample

1 raw 125°C / 5.1MPa 150°C / 5.1MPa 180°C / 5.1MPa 200°C / 5.1MPa 250°C / 5.1MPa

Wei

ght l

oss

(%)

(1) Effect of processing temperature - weight loss versus time (2) Effect of applied mechanical pressure - weight loss versus time


164

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1a raw 125°C / 5.1MPa 150°C / 5.1MPa 180°C / 5.1MPa 200°C / 5.1MPa 250°C / 5.1MPa

Wei

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oss

(%)

Time (sec)2000 3000 4000 5000

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0 2a raw 150°C / 2.5MPa 150°C / 5.1MPa 150°C / 12.7MPa 150°C / 25.0MPa

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(%)

Time (sec)

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20

40

60

80

100

120 raw 125°C / 5.1MPa 150°C / 5.1MPa 180°C / 5.1MPa 200°C / 5.1MPa 250°C / 5.1MPa

1b

Time (sec)

Hea

t Flo

w (m

W)

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20

40

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100

120 raw 150°C / 2.5MPa 150°C / 5.1MPa 150°C / 12.7MPa 150°C / 25.0MPa

2b

Hea

t Flo

w (m

W)

Time (sec)

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0.02

0.04

0.06

0.08

raw 125°C / 5.1MPa 150°C / 5.1MPa 180°C / 5.1MPa 200°C / 5.1MPa 250°C / 5.1MPa

1c

Conversion (daf)

Spec

ific

reac

tivity

(min

-1)

0.0 0.2 0.4 0.6 0.80.00

0.02

0.04

0.06

0.08

raw 150°C / 2.5MPa 150°C / 5.1MPa 150°C / 12.7MPa 150°C / 25.0MPa

2c

Spec

ific

reac

tivity

(min

-1)

Conversion (daf)

Figure 5.12 Combustion of MTE products (90-125μm particle size) in the TGA at 400°C. Conditions: 30mLmin-1 air flow, 2.0mg sample

(1) Effect of processing temperature, (a) weight loss versus time (b) heat flow versus time (c) specific reactivity versus conversion (2) Effect of applied mechanical pressure, (a) weight loss versus time (b) heat flow versus time (c) specific reactivity versus conversion


2000 3000 4000 5000-100

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raw, 200°C, 250°C, 280°C, 300°C, 320°C, 350°C

1a

Wei

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oss

(%)

Time (sec)

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20

40

60

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100

120 1b

Time (sec)

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t Flo

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0.04

0.06

0.08

0.10

0.12 1c

Spe

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reac

tivity

(min

-1)

Conversion (daf)

Figure 5.13 Combustion of raw and HTD products (90-125μm particle size) in the

TGA at 400°C. Conditions: 30mLmin-1 air flow, 2.0mg sample


2000 3000 4000 5000-100

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Raw coal, SD 130°C, SD 250°C, SD 300°C, SD 350°C

1b

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w (m

W)

Time (sec)

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0.05

0.10

0.15

0.201c

Conversion (daf)

Spe

cific

reac

tivity

(min

-1)

Figure 5.14 Combustion of raw and SD products (90-125μm particle size) in the

TGA at 400°C


5.5 Combustion reactivity of MTE Morwell and Yallourn lignites

The combustion reactivity of Loy Yang lignite and of the dried products from HTD,

MTE and SD have been extensively discussed in previous sections of this chapter.

The physico-chemical changes arising from drying Loy Yang lignite with the MTE,

HTD or SD process, resulted in only small differences in the combustion reactivity

when compared to the parent lignite. To further examine the effects of thermal

drying and physico-chemical properties affecting the combustion reactivity of

lignites, it was decided to extend this study using two additional Latrobe Valley

lignites from the Morwell and Yallourn open cut mines, respectively. The MTE

process was decided to be the best process to further evaluate the combustion

reactivity of thermally dried coal. The MTE process was chosen because of the

process’s very high lignite mass recovery at relatively low processing temperatures,

the significant reductions in the large pore region and the considerable reductions in

the inherent inorganic species in the final product.

The pore volumes of MTE processed Loy Yang, Morwell and Yallourn lignites at

150°C/5.1MPa are shown in Figure 5.15. Comparing the MTE products from the

three lignites show that the MTE Morwell product gave the lowest large pore volume

(0.18cm3g-1) whereas identical pore volumes (0.27cm3g-1) were measured for MTE

Loy Yang and MTE Yallourn. Despite the three lignites having marginally different

large pore volumes, the combustion reactivity for the Loy Yang MTE product was

contrastingly different to the Morwell and Yallourn MTE products (Figure 5.16). The

Loy Yang MTE product clearly demonstrated a significantly longer duration for

complete combustion-oxidation to be achieved. This difference could not be


explained by the sodium contents in the MTE products because all three had similar

concentrations (Table 5.2).

0.71 0.70 0.70

0.06 0.06 0.06

0.27

0.180.27

0.00

0.20

0.40

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0.80

1.00

1.20

Loy

Yan

g

Mor

wel

l

Yal

lour

n

Por

e vo

lum

e (c

m3 g-1

)


Figure 5.15 Pore volumes of MTE processed Loy Yang, Morwell and Yallourn lignites at 150°C/5.1MPa


2000 3000 4000-100

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-60

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0

Loy Yang 150°C / 5.1MPa, Morwell 150°C / 5.1MPa, Yallourn 150°C / 5.1MPa

1a

Wei

ght l

oss

(%)

Time (sec)

2000 3000 40000

4080

120160200240280320

1b

Time (sec)

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t Flo

w (m

W)

0.0 0.2 0.4 0.6 0.8 1.00.0

0.1

0.2

0.3

0.4

0.5

0.6 1c

Spec

ific

reac

tivity

(min

-1)

Conversion (daf)

Figure 5.16 Combustion of Loy Yang, Morwell and Yallourn MTE products at 150ºC/ 5.1MPa

(1) 90-125μm, combustion 400°C (a) weight loss vs time (b) heat flow vs time (c) specific reactivity vs conversion


170

Despite the MTE Morwell product having a lowest large pore volume (Figure 5.15),

the MTE Yallourn product was found to be more reactive at 400ºC (Figure 5.16).

This contrasting difference was more evident in the 250-500μm MTE products

(Figure 5.17) whereas at 450ºC, the Yallourn MTE product was still marginally more

reactive than the Morwell MTE product. The order of reactivity of the three lignites

can be explained if iron catalysed the combustion reactions (Figure 5.17). Indeed,

multiple linear regression on the inter-relationships between inorganic components

and the combustion reactivity of the coals does confirm that iron is more effective

than the AAEM cations in catalysing the combustion-oxidation process (see Section

6.6.2. Furthermore, the effect of iron and AAEM cations on the combustion

reactivity of lignites is further discussed in Section 6.7 and Section 6.8, respectively.

Table 5.2 Ash, acid extractable inorganics and chlorine in the raw lignites and MTE products (wt% db)a, b. MTE conditions: 150°C/5.1MPac

Lignite Ash Na Ca Mg Al FeNPd Cl

Loy Yang raw lignite 0.9 0.09 0.04 0.07 0.01 0.06 0.07

Loy Yang MTE 0.9 0.05 0.04 0.06 0.01 0.06 0.05

Morwell raw lignite 2.2 0.08 0.32 0.21 0.02 0.36 0.06

Morwell MTE 2.2 0.05 0.31 0.19 0.02 0.35 0.05

Yallourn raw lignite 2.0 0.07 0.14 0.18 0.01 0.57 0.05

Yallourn MTE 2.0 0.04 0.15 0.17 0.01 0.58 0.05 a The error is ±0.01wt% for concentrations of 0.01 - 0.10wt% and ±0.02wt% for concentrations greater than 0.10wt% for all elements. b Actual mass values (g) for the raw and MTE products is given in Appendix C. c MTE products are shown in bold so to allow easier comparison between the inorganics of the different lignites and their specific reactivities shown in Figure 5.16 to Figure 5.18. d NP = non-pyritic.


171

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(%)

Time (sec)

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2a

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oss

(%)

Time (sec)

1500 2000 2500-100

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0

3a

Time (sec)

Wei

ght l

oss

(%)

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100120140160180200220240260280300320

1b

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t Flo

w (m

W)

Time (sec)

1000 2000 3000 40000

20406080

100120140160180200220240260280300320

2b

Time (sec)

Hea

t Flo

w (m

W)

1000 1500 2000 2500 30000

20406080

100120140160180200220240260280300320

3b

Hea

t Flo

w (m

W)

Time (sec)

0.0 0.2 0.4 0.6 0.8 1.00.0

0.1

0.2

0.3

0.4

0.5

0.6

1c

Spe

cific

reac

tivity

(min

-1)

Conversion (daf)

0.0 0.2 0.4 0.6 0.8 1.00.0

0.1

0.2

0.3

0.4

0.5

0.6

2c

Conversion (daf)

Spe

cific

reac

tivity

(min

-1)

0.0 0.2 0.4 0.6 0.8 1.00.0

0.2

0.4

0.6

Loy Yang 150°C / 5.1MPa, Morwell 150°C / 5.1MPa, Yallourn 150°C / 5.1MPa

3c

Conversion (daf)

Spe

cific

reac

tivity

(min

-1)

Figure 5.17 Combustion of Loy Yang, Morwell and Yallourn MTE products at 150ºC/ 5.1MPa

(1) 90-125μm particle size, combustion at 400°C (a) weight loss versus time (b) heat flow versus time (c) specific reactivity versus conversion (2) 250-500μm particle size, combustion at 400°C (a) weight loss versus time (b) heat flow versus time (c) specific reactivity versus conversion (3) 250-500μm particle size, combustion at 450°C (a) weight loss versus time (b) heat flow versus time (c) specific reactivity versus conversion


172

Despite the expected large differences in the large pore volumes between the MTE

products and the raw lignites (see Chapter 3), only marginal differences were evident

between the combustion reactivity of the raw lignite and its products (Figure 5.18).

MTE processing had a marginal impact on removing acid extractable inorganics and

chlorine ions from the Latrobe Valley lignites (Table 5.2). Subsequently, differences

in the combustion reactivity arising from the removal of catalytic inorganic

components from the coal were not evident when compared to the parent lignite.

Advantageously, these marginal differences suggests that the conventional boiler

systems currently in operation in the Latrobe Valley would be more than adequate in

combusting thermally treated products and water washed lignites from their

respective mines.

173

Chapter 5 Combustion of Ra

(1) Loy Yang 90-125μm particle size, combustion at 400°C (a) weight loss versus time (b) heat flow versus time (c) specific reactivity versus conversion (2) Morwell 90-125μm particle size, combustion at 400°C (a) weight loss versus time (b) heat flow versus time (c) specific reactivity versus conversion (3) Yallourn 90-125μm particle size, combustion at 400°C (a) weight loss versus time (b) heat flow versus time (c) specific reactivity versus conversion

w Lignite and Dried Products

Figure 5.18 Combustion of Loy Yang, Morwell and Yallourn raw lignite, MTE products (150ºC/ 5.1MPa) and water washed lignite

2000 3000 4000-100

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1a

Wei

ght l

oss

(%)

Time (sec)

2000 3000 4000-100

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2a

Wei

ght l

oss

(%)

Time (sec)

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0

3a

Time (sec)

Wei

ght l

oss

(%)

2000 3000 40000

20406080

100120140160180200220240260280300320

1b

Hea

t Flo

w (m

W)

Time (sec)

1000 2000 3000 40000

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100120140160180200220240260280300320

2b

Time (sec)

Hea

t Flo

w (m

W)

1000 2000 3000 40000

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100120140160180200220240260280300320

3b

Hea

t Flo

w (m

W)

Time (sec)

0.0 0.2 0.4 0.6 0.8 1.00.0

0.2

0.4

0.6

0.8

1c

Spe

cific

reac

tivity

(min

-1)

Conversion (daf)

0.0 0.2 0.4 0.6 0.8 1.00.0

0.2

0.4

0.6

0.8

2c

Conversion (daf)

Spe

cific

reac

tivity

(min

-1)

0.0 0.2 0.4 0.6 0.8 1.00.0

0.2

0.4

0.6

0.8

Raw lignite, MTE 150C/5.1MPa, Washed lignite

3c

Conversion (daf)

Spe

cific

reac

tivity

(min

-1)


5.6 Conclusions Differences in the combustion reactivity of MTE, HTD and SD products were

measured using a TGA. A monolayer of lignite particles inside the TGA crucible was

found to eliminate gaseous diffusion limitations of oxygen and product gases.

Furthermore, an isothermal combustion temperature of 400°C was found to be

adequate in achieving a steady combustion-oxidation state and subsequently also

reducing the likelihood of particle ignition.

The physico-chemical changes arising from drying Loy Yang lignite in MTE, HTD

or SD resulted in only marginal differences on the combustion reactivity between the

sample products. Differences in the large pore volume of the dried products only had

a minor affect on combustion reactivity. Furthermore, the effectiveness of catalytic

inorganic species clearly outweighed pore volume effects for increasing the

combustion reactivity of the products. The results suggest that non-pyritic iron and

AAEM cations are the major combustion promoters among the metal constituents of

Latrobe Valley lignites.

The minor differences in combustion reactivity between the parent lignite and the

thermally dried products suggests that conventional boiler systems currently in

operation in the Latrobe Valley would be more than adequate in combusting the

dried products from any of the three drying processes.

Chapter 6 Combustion of Raw Lignites

175

CHAPTER 6 COMBUSTION OF RAW LIGNITES

6.1 Introduction The previous two chapters have investigated in detail the pyrolysis and combustion

reactivity of a Loy Yang lignite and of the dried products from HTD, MTE and SD.

Furthermore, the combustion reactivity of a single Morwell and Yallourn lignite was

also investigated in Chapter 5. Restricting a study to a single lignite from each mine

can lead to misleading conclusions, particularly if one of the lignites has unusual

features. It was envisaged that relating the chemical and structural properties of a

series of lignites to reaction results could be used to investigate the parameters which

govern the combustion reactivity of lignites. Correlation of lignite properties with

reaction results also can suggest mechanistic explanations of any trends found.

In this chapter, combustion on a diverse suite of well-characterised lignites sourced

from the Latrobe Valley open cut mines is examined. In addition, the

intercorrelations between physicochemical properties and the combustion reactivity

of the lignites are investigated using multiple regression analysis. Furthermore, the

transformations cationic components during volatilisation and combustion, and the

effectiveness of these species in facilitating the breakdown/oxidation of the organic

components in the coal are discussed.


176

6.2 Latrobe Valley lignites – background information The major economic coal deposit of the Gippsland Basin occurs in the Latrobe

Valley, which is located in the southern-eastern part of Australia, approximately

150km east of Melbourne, Victoria. The Latrobe Valley coals are amongst the lowest

rank coals commercially utilized anywhere in the world. The lignite resources in this

area are vast by world standards and are concentrated in exceptionally thick seams

under a relatively thin cover of overburden. Latrobe Valley lignites are of Tertiary

age and are typically soft, high in moisture and low in ash.

Three major open cut mines are in operation in the Latrobe Valley (Figure 1.1). The

first of the major open cut mines which was first operated by the State Electricity

Commission of Victoria was Yallourn. The Yallourn open cut mine has been

providing fuel to the Yallourn power stations since 1924. The average thickness of

the Yallourn seam mined is 60m with a coal to overburden ratio of 3.5:1 [305]. To the

south of the Yallourn open cut mine is the Morwell open cut mine which provides

fuel for the Hazelwood power station and for the Morwell briquette factory. Two

major seams are present in this area, with the Morwell 1 seam reaching a maximum

thickness of 165m beneath the Morwell Township, and the Morwell 2 seam reaching

up to 55m in thickness [305]. The Yallourn and Morwell seams are also mined at the

Loy Yang open cut mine, with up to 230m thickness of continuous low ash coal [305].

The Loy Yang open cut mine is the major source of energy for the largest of the

power stations in the Latrobe Valley.


177

A total of ten Latrobe Valley coals from the three fields were selected for this study

to examine the effects of variation in lithotype, atomic H/C ratio, inorganics, porosity

combustion reactivity and pyrolysis. The coals were:

• Loy Yang Open Cut run-of-mine low ash – medium dark lithotype (LYLA)

• Loy Yang Open Cut medium sodium content – medium dark lithotype (LYMNa)

• Loy Yang Open Cut high sodium content – medium dark lithotype (LY Na)

• Morwell Open Cut medium magnesium content – medium dark lithotype (MMTE)

• Morwell Open Cut high magnesium content – medium dark lithotype (MMg)

• Yallourn Open Cut East Field run-of-mine – medium dark lithotype (YMTE)

• Yallourn Open Cut pale lithotype mined from under the former townsite (YT Pale)

• Yallourn Open Cut dark lithotype mined from under the former townsite (YT Dark)

• Yallourn Open Cut East Field high iron content – medium dark lithotype (YEF Fe)

• Yallourn Open Cut East Field dark lithotype (YEF Dark)

Analytical information for these coals is listed in Table 6.1, Table 6.2 and Table 6.3.

6.3 Characterisation of Latrobe Valley lignites The proximate analysis (moisture, ash, volatile matter and fixed carbon), the ultimate

analysis (carbon, hydrogen, nitrogen and sulphur), the moisture holding capacity and

the calorific value for the Latrobe Valley lignites are shown in Table 6.1. The coal

rank as measured by the calorific value of the coals on an ash-free, moist (a.f.m.)

basis (Table 6.1) and according to the Australian Standard [306], classifies the Latrobe

Valley lignites as lower-rank brown coals.


178

Brown coal lithotypes in the Latrobe Valley refers to coal-banding visible in air-

dried coal. George [307] characterised the lithotype of brown coals into 5 categories;

pale, light, medium-light, medium-dark and dark and reported that from dark to light,

the moisture content decreased up to 5%, volatile matter increased from 48% to 63%,

specific energy (gross dry basis) increased from 26 to 29 MJ kg-1 and the hardness

decreased in the air-dried state. Similarly, the lithotype of the Yallourn coals in Table

6.1 also demonstrated similar characteristics from dark to pale. The dark lithotypes

(YEFD and YTD) had the highest MHC and correspondingly lowest gross calorific

value (a.f.m.) whereas the MHC of the medium dark lithotypes (YMTE and YEFFe)

was significantly lower than the dark lithotypes. The pale lithotype YTP had the

lowest MHC within the Yallourn coal suite (Table 6.1).

The YTP lithotype was also contrastingly different from all the other Latrobe Valley

coals in the suite by its relatively low oxygen content, high volatile matter and high

atomic H/C ratio. Higgins et al. [308] also reported similar trends with lithotype and in

addition also found an increase in porosity, a decrease in surface area and a decrease

in apparent density from dark to pale lithotypes.

The only two Morwell coals in Table 6.1 were medium-dark lithotypes and in

comparison to the Yallourn medium-dark lithotype coals, the moisture content and

MHC were significantly lower. The Yallourn seam is the top most and hence

youngest of the seams in the Latrobe Valley and the Morwell seam underlies the

Yallourn seam [309]. As coalification proceeds the moisture content of the coal

decreases due to loss of oxygen containing functional groups (–OH, –COOH, –C=O).


179

The Morwell and Yallourn medium-dark lithotypes had similar oxygen contents

(25.1 to 26.7wt%d.a.f.) and similar atomic H/C ratio (0.83 to 0.85) thus coalification

differences between the samples were not evident. Alternatively, the burial depth of

the mined coals could be an underlying factor in the differences in the moisture

contents between the Yallourn and Morwell medium-dark lithotype coals.

Holdgate [310] reported that the average moisture content of the seams in the Latrobe

Valley decrease approximately 1% every 20m burial depth due to compression. The

Morwell and Yallourn medium-dark lithotypes did not show any other

distinguishable differences that could explain the variation in moisture contents,

MHC and corresponding calorific values.

The Yallourn and Morwell seams are mined in the Loy Yang open cut mine. The

three Loy Yang coals in the suite, of medium-dark lithotype, have similar physical

and organic characteristics with the only exception of lower ash yield and oxygen

content of the LYLA coal. In terms of proximate and ultimate analysis the Loy Yang

coals (except for LYLA) are not clearly distinguishable between the Yallourn and

Morwell coals of similar lithotype.

180

Table 6.1 Moisture holding capacity, proximate analysis, ultimate analysis and calorific value of the Latrobe Valley coals used in this study Elemental Analysis

(%d.a.f.)

Calorific Value

(MJ kg-1)

Moisture content

Moisture Holding Capacity

Ash Yield

(%d.b.)

Volatile Matter

(%d.a.f.)

Fixed Carbon

(%d.a.f.)

C

H N S Oa H/C (gr, d.b.)

(gr,v,afm)

Coal Type (±0.2) (±1.2) (±0.1) (±0.4) (±0.4) (±0.3) (±0.1) (±0.05) (±0.03) (±0.6) (±0.02) (±0.3) (±0.3) Loy Yang Low Ash (LYLA) 59.7 56.7 0.9 50.6 49.4 69.4 5.0 0.66 0.27 24.7 0.86 26.6 11.6 Loy Yang Medium Sodium (LY MNa) 62.1 57.3 3.7 50.9 49.1 66.3 4.7 0.56 0.39 28.1 0.84 24.9 11.1 Loy Yang High Sodium (LY HNa) 60.1 56.8 5.0 51.3 48.7 66.9 4.5 0.63 0.65 27.3 0.81 24.2 11.0 Morwell MTE (MMTE) 57.2 54.6 2.2 51.8 48.2 68.7 4.9 0.69 0.24 25.5 0.86 25.8 12.0 Morwell High Magnesium (MMg) 60.6 52.9 4.3 49.4 50.6 69.0 4.8 0.70 0.39 25.1 0.83 25.7 12.6 Yallourn MTE (YMTE) 64.4 55.2 2.0 51.9 48.1 67.7 4.8 0.63 0.16 26.7 0.85 25.3 11.6 Yallourn Township Pale (YT Pale) 58.2 46.2 1.8 66.9 33.1 71.2 6.8 0.50 0.30 21.2 1.15 29.1 16.0 Yallourn Township Dark (YT Dark) 64.1 59.3 2.1 53.1 46.9 66.6 4.9 0.66 0.35 27.5 0.88 25.0 10.4 Yallourn East Field High Iron (YEF Fe) 63.6 56.7 2.3 52.7 47.3 68.6 4.9 0.58 0.24 25.7 0.86 25.8 11.5

Yallourn East Field Dark (YEF Dark) 67.2 60.4 2.0 49.6 50.4 68.2 4.6 0.55 0.20 26.5 0.81 24.9 10.0



181

The inorganic content variation of the Latrobe Valley coals bears no relation to the

ultimate or proximate analysis. A general feature of the Latrobe Valley coals is that

much of the sodium is in the form of NaCl which can be easily be removed by water

washing the coal. Furthermore, most of the Mg, Ca, Al, Fe and remaining Na are also

extractable with weak acid (Table 6.2 and Table 6.3) thus suggesting ionic

associations in the form of carboxylate/phenolates or simple

carbonates/hydroxides/chlorides rather than being contained in clays or other

refractory silicates.

Most of the iron in the Latrobe Valley coals is almost entirely non-pyritic. The

Yallourn East Field coals have the highest Fe contents (0.57 to 0.70%db) with

LYHNa and MMTE also containing reasonable Fe contents of 0.43 and 0.36%db,

respectively. The Yallourn East Field coals also have comparable concentrations of

Na, Ca, Mg, Al, K, Si, Ti and Cl to those for the low-ash Loy Yang coals. The

Yallourn Township coals have appreciable quantities of acid soluble aluminium, with

lower Fe contents than the Yallourn East Field coals, but similar Na, Ca and Mg. The

higher ash yield of the LYMNa and MMg coal is due to its appreciable Si content

(perhaps as silica sand, SiO2). The Morwell coals also have substantial calcium and

the highest magnesium (except for LYMNa and YEFFe). For the other main

inorganic elements (Al, K, and Si), the Morwell concentrations are comparable to the

Loy Yang coals.

Table 6.2 Inorganic analysis of the raw, water washed and acid washed Loy Yang and Morwell coals used in this study

Elemental components (%d.b.)a Acid extractable (%d.b.)a

Coal Type Ash Yield(%d.b.)

Na

Ca

Mg

Fe

Al

K

Si

Ti

Cl

Al

FeNP

Ca

Mg

Na

Loy Yang Low Ash Raw 0.9 0.09 0.04 0.08 0.07 0.02 0.002 0.05 0.001 0.07 0.02 0.07 0.04 0.08 0.09 (LYLA) H2O 0.6 0.04 0.04 0.07 0.07 0.02 0.001 0.04 0.001 0.05 0.02 0.07 0.04 0.07 0.04 Acid 0.3 <0.01 <0.01 <0.01 0.05 <0.01 <0.001 0.04 0.001 0.01 <0.01 0.05 <0.01 <0.01 <0.01 Loy Yang Medium Sodium Raw 3.7 0.37 0.04 0.16 0.05 0.41 0.007 0.62 0.016 0.44 0.29 0.04 0.04 0.16 0.46 (LYMNa) H2O 2.3 0.11 0.04 0.12 0.04 0.35 0.005 0.36 0.013 0.05 0.24 0.03 0.04 0.12 0.10 Acid 1.5 <0.01 <0.01 0.01 0.03 0.17 0.005 0.45 0.023 0.01 0.07 0.02 <0.01 <0.01 <0.01 Loy Yang High Sodium Raw 5.0 0.67 0.19 0.54 0.49 0.02 0.009 0.08 0.005 0.33 0.02 0.43 0.19 0.54 0.67 (LYHNa) H2O 3.1 0.15 0.18 0.50 0.38 0.02 0.004 0.08 0.003 0.05 0.02 0.38 0.18 0.5 0.15 Acid 0.9 0.02 0.02 0.02 0.30 0.01 0.002 0.08 0.002 0.01 0.01 0.30 0.02 0.02 0.01 Morwell MTE Raw 2.2 0.08 0.32 0.21 0.37 0.02 0.002 0.06 0.002 0.06 0.02 0.36 0.32 0.21 0.08 MMTE H2O 1.6 0.05 0.31 0.19 0.35 0.02 0.002 0.06 0.002 0.04 0.02 0.35 0.31 0.19 0.05 Acid 0.7 <0.01 0.01 <0.01 0.30 0.02 0.002 0.07 0.002 0.01 0.01 0.25 0.01 <0.01 <0.01 Morwell High Magnesium Raw 4.3 0.21 0.49 0.39 0.06 0.04 0.007 0.39 0.018 0.10 0.04 0.04 0.49 0.39 0.21 (MMg) H2O 3.0 0.10 0.48 0.39 0.04 0.03 0.004 0.38 0.017 0.04 0.03 0.03 0.48 0.39 0.1 Acid 2.9 0.01 0.02 0.01 0.04 0.03 0.002 0.38 0.016 0.01 0.03 0.03 0.02 0.01 0.01


182

183

Table 6.3 Inorganic analysis of the raw, water washed and acid washed Yallourn coals used in this study

Elemental components (%d.b.)a Acid extractable (%d.b.)a

Coal Type Ash Yield(%d.b.)

Na

Ca

Mg

Fe

Al

K

Si

Ti

Cl

Al

FeNP

Ca

Mg

Na

Yallourn MTE Raw 2.0 0.07 0.14 0.18 0.61 0.01 0.003 0.03 0.001 0.05 0.01 0.57 0.14 0.18 0.07 (YMTE) H2O 1.7 0.05 0.15 0.17 0.59 0.01 0.002 0.03 0.001 0.04 0.01 0.58 0.15 0.17 0.05 Acid 0.7 <0.01 <0.01 <0.01 0.38 <0.01 0.002 0.03 0.001 0.01 <0.01 0.25 <0.01 <0.01 <0.01 Yallourn Township Pale Raw 1.8 0.04 0.12 0.13 0.23 0.31 0.003 0.02 0.030 0.07 0.24 0.22 0.12 0.13 0.04 (YT Pale) H2O 1.7 0.02 0.12 0.13 0.24 0.29 0.003 0.02 0.026 0.07 0.23 0.21 0.11 0.12 0.01 Acid 0.8 <0.01 0.01 0.01 0.26 0.14 0.002 0.03 0.039 0.01 0.06 0.14 <0.01 <0.01 <0.01 Yallourn Township Dark Raw 2.1 0.05 0.17 0.18 0.33 0.21 0.002 0.01 0.001 0.04 0.20 0.33 0.17 0.18 0.05 (YT Dark) H2O 2.1 0.01 0.16 0.17 0.31 0.20 0.001 0.01 0.001 0.04 0.20 0.31 0.16 0.17 0.01 Acid 0.7 0.01 0.01 0.01 0.24 0.07 <0.001 0.01 0.001 0.01 0.07 0.24 0.01 0.01 0.01 Yallourn East Field High Iron Raw 2.3 0.05 0.17 0.24 0.72 0.01 0.003 0.03 0.001 0.09 0.01 0.70 0.16 0.24 0.05 (YEF Fe) H2O 2.2 0.03 0.17 0.24 0.72 0.01 0.002 0.03 0.002 0.06 <0.01 0.67 0.16 0.24 0.03 Acid 1.0 <0.01 <0.01 <0.01 0.61 0.01 0.001 0.02 0.002 0.01 <0.01 0.47 <0.01 <0.01 <0.01 Yallourn East Field Dark Raw 2.0 0.07 0.17 0.16 0.57 0.02 0.011 0.01 0.001 0.05 0.02 0.57 0.17 0.16 0.07 (YEF Dark) H2O 1.8 0.03 0.16 0.15 0.53 0.02 0.003 0.01 0.001 0.04 0.02 0.53 0.16 0.15 0.03 Acid 0.7 0.01 0.01 0.01 0.36 <0.01 0.001 0.01 0.001 0.01 <0.01 0.36 0.01 0.01 0.01


Chapter 6 Combustion of Raw Lignites 184

6.4 X-ray Diffraction X-rays have been extensively used to study the structural regularities and

irregularities of solids. For coals, x-ray diffraction has been extensively used to

determine the ordering of the carbon macromolecular structure and for the

identification of the structure of crystalline salts present within the carbon

framework [311-315]. The XRD spectra of the Latrobe Valley coals are shown in Figure

6.1 and Figure 6.2.

In this study, XRD analysis was applied to identify the presence of inorganic

crystalline salt constituents in coal. The XRD spectra (Figure 6.1 and Figure 6.2) do

not show the presence of inorganic crystalline salts thus suggesting that the cations

present in Latrobe Valley coals are predominately associated with oxygen functional

groups and/or that the concentration of inorganic crystalline salts within the

macromolecular structure of the coal are finely dispersed and are of low

concentration which as a consequence, cannot be discretely identified from other x-

ray diffracting components within the coal. Indeed, scanning electron microscope

(SEM) - energy dispersion x-ray (EDX) analysis on the raw Loy Yang lignite with a

high sodium content (LYHNa) and on the raw Yallourn lignite with a high iron

content (YEFFe) show that the inorganic components present within the carbon

macromolecular framework are well dispersed and that no direct correlation can be

made between the distribution cationic and anionic components within the coal (see

Appendix J). Furthermore, the XRD spectra also supports that very little pyrite is

present in the coals [316, 317]. The nature of the inorganic ions present in the


macromolecular structure of the coal and their effect on the combustion reactivity of

the coal is further discussed in Section 6.7 and in Section 6.8.

0

50

100

150

200

250

300

350

0 10 20 30 40 50 60 70 80 9

2 θ

Diff

ract

ion

inte

nsity

(arb

itrar

y un

its)

0

LYLALYMNaLYHNa

a

0

50

100

150

200

250

300

0 10 20 30 40 50 60 70 80 9

2 θ

Diff

ract

ion

inte

nsity

(arb

itrar

y un

its)

0

MMTEMMg

b

Figure 6.1 XRD spectra of coal (a) Loy Yang coals: LYLA, LYMNa and LYHNa

(b) Morwell coals: MMTE and MMg


0

50

100

150

200

250

300

0 10 20 30 40 50 60 70 80 9

2 θ

Diff

ract

ion

inte

nsity

(arb

itrar

y un

its)

0

YMTEYEFFeYEFD

c

0

50

100

150

200

250

300

350

0 10 20 30 40 50 60 70 80 9

2 θ

Diff

ract

ion

inte

nsity

(arb

itrar

y un

its)

0

YTPYTD

d

Figure 6.2 XRD spectra of coal (c) Yallourn East Field coals: YMTE, YEFFe and

YEFD (d) Yallourn Township coals: YTP and YTD


6.5 Combustion reactivity of Latrobe Valley lignites In Section 5.5, the MTE process did not significantly affect the combustion reactivity

of the final product relative to the parent coal despite significant changes to the

internal pore structure and the leaching of inherent inorganic species from its

macromolecular structure. However, differences were found in the combustion

reactivates between the Loy Yang, Morwell and Yallourn coals and it was eluded

that inorganic ions present in the coals are the major contributing factor. This section

will widen the combustion reactivity investigation to include ten Latrobe Valley

lignites varying in physicochemical and inorganic properties. Also, the effect of

water washing and acid washing the raw Latrobe Valley lignites and the

consequential effect on the combustion reactivity will be discussed.

Figure 6.3 shows the specific reactivity of Loy Yang lignite as a function of

conversion. A combustion reactivity arbitrary value was assigned to each of the coals

and their water washed and acid washed products by calculating the area under the

graph from the specific reactivity versus conversion data (Figure 6.3). This

combustion reactivity arbitrary value provides the basis for comparing the factors

responsible for the burning rate of each coal. The combustion reactivity values for

the raw, water washed and acid washed coals are given in Table 6.4. Furthermore,

the peak temperatures (i.e. the point where the burning rate is at a maximum) were

determined by heating the samples at a constant rate up to 900°C (see Section 5.1.4).

The peak temperatures for the raw lignites and their washed products are also given

in Table 6.4.


Figure 6.3 Integration of the specific reactivity of raw Loy Yang lignite as a function of conversion.

Table 6.4 shows that the combustion reactivity of the parent lignite decreased after

water washing the lignite and the combustion reactivity further decreased for the

corresponding weak acid washed samples. Furthermore, as the combustion reactivity

values decreased, the corresponding peak temperatures for each sample significantly

increased (Table 6.4). The graph for the combustion reactivity arbitrary values versus

the peak temperatures of the raw coals, water washed and acid washed products

(Figure 6.4) shows a very strong linear relationship with a correlation coefficient

value of 0.87. The removal of inorganic species from the macromolecular coal

matrix clearly had a marked effect on the coal’s combustion reactivity and on the

peak temperature of the sample.


189

Table 6.4 Combustion reactivity arbitrary values and peak temperatures for the raw, water and acid washed Latrobe Valley coals.

Combustion reactivity

value ±0.01

Peak temperature

(°C) ±2


value ±0.01

Peak temperature

(°C) ±2

LYLA Raw 0.06 465 YMTE Raw 0.28 418 H2O 0.05 489 H2O 0.23 423 Acid 0.03 502 Acid 0.13 453 LYMNa Raw 0.09 471 YTP Raw 0.16 445 H2O 0.07 481 H2O 0.14 453 Acid 0.03 507 Acid 0.10 460 LYHNa Raw 0.33 408 YTD Raw 0.18 448 H2O 0.29 424 H2O 0.13 455 Acid 0.11 477 Acid 0.08 470 MMTE Raw 0.27 407 YEF Fe Raw 0.36 399 H2O 0.25 435 H2O 0.31 407 Acid 0.09 464 Acid 0.19 434 MMg Raw 0.24 451 YEFD Raw 0.27 415 H2O 0.23 453 H2O 0.20 429 Acid 0.04 511 Acid 0.14 445 Much work has been conducted on impregnating known concentrations of AAEM

species onto low rank coals and then pyrolysing and measuring the specific reactivity

of the char. Quyn et al. [318] and Wu et al. [319, 320] pyrolysed NaCl-loaded Loy Yang

brown coal samples and reported that the combustion reactivity of the char is highly

dependant on the structure of the char and on the remaining sodium in the char.

Similarly, Li et al. [204] found that the combustion reactivity of a pyrolysed char from

Loy Yang coal can be influenced by the concentration and chemical form of Ca in

the char. The inorganics present in the coal indicatively influence the combustion

reactivity and peak temperatures of the sample however the question still remains

whether all cations are equally effective in catalysing the combustion process.


190

190

Figure 6.4 Combustion reactivity versus peak temperature of the raw, water washed and acid washed Latrobe Valley lignites.

YEFFeLYHNaYEFFe

LYHNa

MMTEYEFDYMTE

MMTE

YMTE

MMgMMg

YEFDYEFFe

YTDYTPYEFDYTP

YTDYMTEYTP

MMTELYLA

LYHNaLYMNa

LYLA

LYLAMMgLYMNa

LYMNaYTD

R2 = 0.87

350

370

390

410

430

450

470

490

510

530

550

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40

Combustion reactivity value

Pea

k te

mpe

ratu

re (º

C)

Raw lignite Water washed lignite Acid washed lignite


191

6.6 Multiple regression analysis In this study, the objective of multiple regression analysis is to identify which of the

independent physicochemical variables have the largest impact on combustion

reactivity of the coals (i.e. the dependant variable). Multiple regression analysis can

establish the relative predictive importance of the independent variables (by

comparing beta weights) and the significance of each of the relationships (through a

significance test of R2). The definition of multiple regression analysis and the

statistical terminology is further described in Appendix I.

6.6.1 Multiple regression analysis of raw lignites To determine the variables that affect the combustion reactivity, multiple regression

analysis was performed on the ten Latrobe Valley raw lignites using the independent

physicochemical variables of shown in Table 6.1 (proximate, ultimate and calorific

value) and the inorganic contents of the raw coals shown in Table 6.2 and Table 6.3.

The intercorrelations between the physicochemical variables are shown in Table 6.5.

From the sample of ten raw lignites, there is a very strong positive linear relationship

between the combustion reactivity and the iron content of the coal (r = 0.804; Table

6.5). Furthermore, a moderate positive linear relationship is present between the

combustion reactivity and the magnesium and calcium contents with correlation

coefficient values of 0.592 and 0.445, respectively. In contrast, the aluminium

content gave a strong negative linear correlation (r = -0.608) thus suggesting that the

form of aluminium present in the raw lignites inhibits the combustion reactivity of

the coal. Also, the ultimate (C, H, N, S, O), proximate analysis (volatile and fixed

carbon), calorific value (g.r. d.b.) and the surface area of the raw coals gave very

weak linear relationships with the combustion reactivity of the coals.

192

Table 6.5 Intercorrelations among the physicochemical variables for the ten raw Latrobe Valley lignites Reactivity Al Fe Ca Mg Na Cl Surf

area C H N S O H/C Volatiles Fixed

Carbon Senergy (gr.d.b.)

Reactivity 1.000 Al -.608* 1.000 Fe .804** -.492 1.000 Ca .445 -.367 -.072 1.000 Mg .592* -.325 .100 .544*** 1.000 Na .057 .118 -.230 -.033 .698* 1.000 Cl -.163 .401 -.319 -.258 .385 .896*** 1.000

Surf area -.001 -.581* -.009 .357 -.263 -.419 -.461 1.000 C -.094 -.108 -.123 .149 -.280 -.530 -.541 .149 1.000 H -.271 .476 -.186 -.149 -.356 -.376 -.272 -.396 .756** 1.000 N .083 -.472 -.205 .575* .327 .026 -.199 .471 -.229 -.528 1.000 S .065 .136 -.306 .130 .792** .901*** .710* -.531 -.315 -.164 .103 1.000 O .157 -.065 .187 -.095 .261 .462 .460 .037 -.975*** -.871*** .291 .215 1.000

H/C -.287 .522 -.175 -.204 -.363 -.352 -.241 -.454 .698* .995*** -.539 -.142 -.828** 1.000 Volatiles -.170 .509 -.059 -.231 -.268 -.266 -.178 -.556* .627* .972*** -.594* -.067 -.769** .984*** 1.000

Fixed Carbon .170 -.509 .059 .231 .268 .266 .178 .556* -.627* -.972*** .594* .067 .769** -.984*** -1.000*** 1.000 Senergy -.282 .262 -.248 -.129 -.286 -.323 -.276 -.277 .875*** .939*** -.403 -.093 -.952*** .919*** .880*** -.880** 1.000


Note: * p < 0.05, ** p < 0.01, *** p < 0.001


An advantage of multiple regression analyses is the ability to explore how predictors

combine to explain the variation in the dependent variable. Table 6.6 shows the

relative effect of a combination of inorganic ions on the combustion reactivity of the

raw coals using the linear multiple regression analysis model. As previously

mentioned, the combustion reactivity was highly correlated to the iron content of the

raw lignite with a regression coefficient value of 0.804 (Table 6.5). Combining the

effects of iron and magnesium, the combustion reactivity coefficient is increased to

0.955 (Table 6.6), and when the effect of calcium is also included, the regression

coefficient is further increased to 0.990. That is, 98% of the variation in the

combustion reactivity of the raw coals can be explained by the inherent iron,

magnesium and calcium contents.

Table 6.6 Linear multiple regression analysis model summary Model R R Square Adjusted R

Square Std. Error of the Estimate

1 .804(a) .646 .602 .06246 2 .955(b) .911 .886 .03343 3 .990© .980 .971 .01695

a Predictors: (Constant), Fe b Predictors: (Constant), Fe, Mg c Predictors: (Constant), Fe, Mg, Ca d Dependent Variable: Reactivity

An additional statistical test to confirm whether the effects of iron, magnesium and

calcium are linearly correlated to the combustion reactivity of the coal, a probability

plot of the residuals (Figure 6.5), and a regression residual plot (Figure 6.6) can be

used. The residual value is the difference between the observed value and the

predicted value using the regression line. The normal probability plot of the residuals

(Figure 6.5) shows that the linearity and equal variance assumptions are met within

the population tested. Furthermore, the residuals are reasonably evenly spread around


the zero line, with no apparent pattern (Figure 6.6) thus suggesting that the samples

are random with a constant residual variance and that linear regression model has

captured most of the essential features of the relationship between combustion

reactivity and the synergistic cationic effects of iron, magnesium and calcium.

1.00.80.60.40.20.0

Observed Cum Prob

1.0

0.8

0.6

0.4

0.2

0.0

Expe

cted

Cum

Pro

b

LYLA

LYMNa

LYHNa

MMTE

MMgYMTE

YTP

YTD

YEFFe

YEFD

__

Figure 6.5 Normal P-P plot of regression standardized residual of the dependent variable combustion reactivity of the raw lignites.


210-1-2

Regression Standardised Predicted Value

2

1

0

-1

-2

Reg

ress

ion

Stan

dard

ised

Res

idua

l

__

Figure 6.6 Scatterplot of regression standardized residual and predicted combustion reactivity values

__

6.6.2 Multiple regression of raw, water washed and acid washed samples.

In Section 6.5, it was reported that the combustion reactivity of the parent lignite

decreased after water washing the lignite and the combustion reactivity further

decreased for the corresponding weak acid washed samples. Also, that the removal

of inorganic species from the macromolecular coal matrix had a marked effect on the

coal’s combustion reactivity. In addition, multiple linear regression on the

physicochemical properties of ten raw lignites statistically predicted that iron,

magnesium and calcium contents significantly affect the combustion reactivity of the

sample. In this Section, multiple linear regression was also performed to determine

individual and collaborative effects of the inorganic species on the combustion


reactivity of the lignite samples. The intercorrelations between the physicochemical

variables for the raw, water washed and acid washed lignite samples are shown in

Table 6.7.

Table 6.7 Intercorrelations among the physicochemical variables for the raw, water washed and acid washed Latrobe Valley lignites

Reactivity Al Fe Ca Mg Na Cl

Reactivity 1.000

Al -.289 1.000

Fe .760*** -.355* 1.000

Ca .642*** -.079 .115 1.000

Mg .742*** -.020 .241 .753*** 1.000

Na .313* .177 -.040 .255 .646*** 1.000

Cl .202 .384* -.050 .128 .460** .908*** 1.000 Note: * p < 0.05, ** p < 0.01, *** p < 0.001, N = 30

Relative to the combustion reactivity of the samples, the iron, magnesium and

calcium contents showed strong positive linear correlations with r2 values of 0.760,

0.742 and 0.642, respectively (Table 6.7). Furthermore, the sodium content of the

coal samples showed a weak positive linear correlation with the measured

combustion reactivity (Table 6.7). In contrast, aluminium which was postulated to

hinder the combustion reactivity of the raw coals (Table 6.5) also gave a weak

negative linear correlation when the water washed and acid washed samples are also

included into the sample size (Table 6.7). The acid extractable aluminium is likely to

be predominately in the form of simple carbonates/hydroxides/chlorides instead of

being linked to oxygen functional groups such as carboxylates and phenolates within

the coal macromolecular structure. The form of the inorganic species and their effect

on the combustion reactivity is discussed later in Section 6.7 and in Section 6.8.


Using the linear multiple regression analysis model to predict the synergistic

inorganic catalytic effects on the combustion reactivity values, the iron and

magnesium contents can account for 91% of the variation in the combustion

reactivity (Table 6.8). Furthermore, 95% of the variation in the combustion reactivity

of the coal samples can be explained by the inherent iron, magnesium and calcium

contents.

Table 6.8 Linear multiple regression analysis model summary Model R R Square Adjusted R

Square Std. Error of the Estimate

1 .760(a) .578 .563 .06425 2 .953(b) .909 .902 .03042 3 .972© .945 .939 .02404

a Predictors: (Constant), Fe b Predictors: (Constant), Fe, Mg c Predictors: (Constant), Fe, Mg, Ca d Dependent Variable: Reactivity

The multiple regression coefficients (Table 6.9) predict that the combustion

reactivity value can be estimated using the formula below:

Combustion Reactivity value = 0.023 + 0.295 Fe + 0.241 Mg + 0.212 Ca

where, Fe, Mg and Ca are the measured cation contents in the raw coal on a wt%d.b.

Furthermore, as the significance p < 0.05, it is reasonable to reject the null hypothesis

and conclude that there is a linear relationship between combustion reactivity and the

cooperative effects of iron, magnesium and calcium.


Table 6.9 Multiple regression coefficients for the combustion reactivity value determined from the raw, water washed and acid washed samples

Model Unstandardized Coefficients Standardized Coefficients

B Std. Error Beta 1 (Constant) .069 .020 Fe .351 .057 .760 2 (Constant) .030 .010 Fe .285 .028 .617 Mg .388 .039 .593 3 (Constant) .023 .008 Fe .295 .022 .638 Mg .241 .047 .368 Ca .212 .051 .291

a Dependent Variable: Reactivity

The linear relationship is also confirmed by the probability plot of the residuals

(Figure 6.7) and the regression residual plot (Figure 6.8) which illustrates that the

linearity and equal variance assumptions are met within the number of samples

tested. That is, the samples are random with a constant residual variance and that the

linear model has captured most of the essential features of the relationship between

combustion reactivity and the synergistic cationic effects of iron, magnesium and

calcium. The catalytic effects of the individual cations in the combustion of lignite

are further discussed in the following section.


1.00.80.60.40.20.0

Observed Cum Prob

1.0

0.8

0.6

0.4

0.2

0.0

Expe

cted

Cum

Pro

b

Figure 6.7 Normal P-P plot of regression standardized residual of the combustion reactivity value from the raw, water washed and acid washed lignites.

210-1-2

Regression Standardized Predicted Value

3

2

1

0

-1

-2

-3

Reg

ress

ion

Stan

dard

ized

Res

idua

l


reactivity values from the raw, water washed and acid washed lignites


6.7 Catalytic effects of iron Alkali and alkaline earth metals have been extensively investigated in recent years

for their catalytic effects in gasification and combustion however the effect of iron

has often been overlooked, in particular in low rank coals. Iron has been reported to

be an excellent catalyst in coal liquefaction and in coal gasification [321] for Latrobe

Valley lignites however the effect of iron on the combustion reactivity of lignites is

very limited. Furthermore, the chemical form of the acid extractable iron in Latrobe

Valley lignites is also not well understood. The XRD performed in this study (see

Section 6.4) did not reveal the presence of ionic salts in the raw Latrobe Valley

lignites thus suggesting the iron was either complexed within the organic

macromolecular structure of the coal or that the iron salt concentration was too low

to be clearly resolved by the XRD. Instead, the chemical form of iron in Latrobe

Valley lignites can be postulated by understanding the chemistry of iron. A

comprehensive review on the chemistry of iron has been conducted by Cornell and

Schwertmann [322] and by Hong-Xiao and Stumm [323]. According to these authors a

number of Fe3+ species are formed in the pH range of 2 to 4 which include:

Type A – Fe3+, Fe2(OH)24+, Fe3(OH)4

5+

Type B – Fe4(OH)66+

Type C – Fex(OH)y(3x-y)+

Type D – FexOz(OH)y(3x-2z-y)+

Subsequently, the oxidation state of iron in Latrobe Valley lignites would be

dependant on the acidity of the lignite in its bed moist form. Latrobe Valley lignites

contain a very high oxygen content and half of this oxygen can be accounted for by

carboxylic and phenolic acid groups and thus, as a consequence, bed moist coals are


acidic [107]. For Latrobe Valley lignites the pH of bed moist coals are in the range of 4

(for Loy Yang and Yallourn lignites) to 5 (for Morwell lignites) [107]. Mössbauer

spectroscopy of Fe2+ and Fe3+

iron complexes in Victorian lignites have shown that

the pH strongly influences the oxidation state and crystalline structure of the iron in

the coal [324] and that several different iron species are present in the lignites. Cook

and Cashion [324] also reported that the dominant iron phase was a poorly-ordered

ferric oxyhydroxide which, upon exposure to air, slowly crystallised to goethite (α-

FeO(OH)) and most of the remaining iron occurred as Fe(II) associated to the

organic structure of the coal. The proportion of iron bonded to the organic functional

groups is also dependent on the macromolecular structure of the coal.

Ozaki et al. [325] ion exchanged iron using Loy Yang lignite and reported that the

maximum trivalent iron exchanged onto carboxyl groups was approximately 6% with

the remaining carboxyl groups in the coal remaining isolated from the metal ion.

This was also supported by Domazetis et al. [321] who modelled multi-iron species in

lignite and postulated that monodentate carboxyl coordination to metals is sterically

favoured whereas mononuclear Fe(III) with bidentate carboxyl coordination formed

distorted charges on metal centres which are energetically unfavoured. Furthermore,

Bocquet et al. [326] suggested that octahedral iron complexes may be present with

some bonding between carboxylate and to other iron complexes via hydrogen-

bonded water molecules.

Upon heating in air, the inherent iron in the lignite would also undergo significant

transformations as a result of decarboxylation, dehydration and oxidation.

Bocquet et al. [326] found that the removal of water reduced the distance between the


iron complexes which in turn, caused supercharging between ferric ions [326] within

the coal. Hippo et al. [327] reported that aggregation of metallic iron can significantly

reduce its effectiveness as a catalyst in gasification and that the reduced form of iron

was more effective. Similarly, Ohtsuka et al. [328] reported that the catalytic activity

of iron in gasification was highly dependant on its ionic phase and that the size of

fine nano-sized iron particles could account for the higher catalytic performance

during reforming processes. Asami et al. [329] impregnated lignite with an aqueous

solution of FeCl3 and reported that precipitated iron existed as fine FeOOH particles

which are reduced to Fe3C on charring and then oxidised to FeO (which itself is very

reactive and can cause explosions as it readily ignites [322]) and Fe3O4 in the presence

of carbon dioxide. Furthermore, Domazetis et al. [321] found that preheating iron

impregnated Loy Yang lignite upto 200ºC caused some CO2 and CO volatilisation

and hypothesized that the inherent iron complexes in the raw coal are transformed to

oxide/carbonate complexes during pyrolysis and gasification at 250ºC - 450ºC.

The higher reactivity of iron during combustion compared to the AAEM ions found

in this study could be attributed to ion’s higher capacity to promote the cleavage of

oxygen bonds in the coal and its ability to readily transform and re-attach itself to the

organic component of the coal during devolatilisation and combustion. The repeated

bond-breaking and bond-forming process would result in an increased concentration

of free radical sites on the surface of the burning particle, thus increasing the

likelihood for cross-linking and the subsequent thermal cracking of the coal’s organic

component. Furthermore, iron influences the carbonization of the coal by liberating

hydrogen bonds from carboxyl groups to form carboxylates and isolated carboxyl


groups which decompose more easily [325]. The higher proportion of hydrogen

radicals generated by thermal cracking could further facilitate the breakdown of the

organic carbon structure.

6.8 Catalytic effects of AAEM cations In recent years, much work has been conducted on the effects of AAEM species on

the pyrolysis and gasification of Loy Yang lignite and the combustion of the resultant

char product. Figure 6.9 shows that the combustion reactivity value is moderately

correlated to the sum of AAEM (sodium, calcium and magnesium) univalent charge

(Table 6.10) with a correlation coefficient of 0.48. In contrast, when the univalent

charge of iron is also taken into account, the correlation coefficient is significantly

increased to 0.83 signifying a very strong positive linear relationship (Figure 6.10).

The complex transformations of iron and its interrelationship with the coal matrix

during different stages of combustion were discussed in Section 6.7. Similar to iron,

the ionic forms of the AAEM cations present in the raw coals also have a

contributing factor during different stages of the oxidation combustion process. The

AAEM cations in the Latrobe Valley lignites were extractable with weak acid thus

suggesting that these cations are in the form of carboxylate/phenolates or simple


refractory silicates. The form of the AAEM cations in the lignite can have a

significant effect of the reactivity of the coal. The behaviour of AAEM cations

associated with the organic carbon structure of the coal can be separated into two

main events during the oxidation-combustion process; the detachment of cations

from organic functional groups from subsequent

decarboxylation/devolatilisation/combustion and secondly, the gradual


transformation of AAEM cations into ionic salts and ash. The transformation of

AAEM salts can also affect the combustion reactivity of the coal/char. The ionic salt

forms of AAEM species and their effect on the combustion of lignite is discussed in

the following sub-sections.

6.8.1 Calcium Calcium has also been investigated in as a catalyst in pyrolysis [330], gasification [331]

and combustion [332]. In combustion, calcium (and magnesium) have been reported to

remain condensed within the coal/char matrix whereas in gasification systems, these

elements may vapourise into the gas phase [333]. The amount of calcium present in the

lignite can influence the catalytic activity during these processes.

Murakami et al. [334] ion exchanged Loy Yang lignite with a range of metal ions and

reported that an increase in calcium loading did increase the yields of methane,

carbon monoxide and carbon dioxide during pyrolysis. Similarly, Li et al. [335]

investigated the combustion of pyrolysed calcium-exchanged coals and reported that

the mass of calcium remaining in a coal/char sample influenced that sample’s

combustion reactivity.

Similar active forms of calcium catalyst have been reported for all three conversion

processes. The basic form of calcium (Ca(OH)2) has been reported as an excellent

catalyst in gasification and its activity is as effective as sodium in the conversion of

hydrocarbons into lightweight materials [336, 337]. Calcium hydroxide has also been

found as an effective catalyst in lowering the peak combustion temperature [332],

increasing combustion efficiency [338] and in reducing soot formation [339] during coal

combustion. During pyrolysis and combustion, calcium hydroxide is converted to the


active catalyst calcium oxide (CaO) [340]. Timpe and Sears [341] investigated the

catalytic effect of calcium on low-rank coals and reported that CaO and Ca(OAc)2

increased the reactivity whereas, limestone had no positive effect and CaSO4

inhibited the reactivity of the coals. Furthermore, a well dispersed CaO catalyst on

the surface of the coal has been shown to increase the reactivity of the coal whereas

crystalline crystal growth of CaO has been reported to deactivate the effectiveness of

the catalyst [342-344].

Calcium carbonate has also been reported to develop during low temperature

pyrolysis and combustion. Wornat [345] investigated the effects of calcium during

pyrolysis and proposed that the mechanism involves the decomposition of calcium-

carboxylate structure to eliminate CaCO3, which takes some of the organically bound

oxygen that would otherwise be able to form O-containing organic gases and hence

increased yields of CO. Furthermore, Elder and Reddy [346] investigated combustion

of kerogen in a TGA and reported the conversion of calcium oxide to calcium

carbonate from carbon dioxide released during the combustion process. The

formation of calcium carbonate may consequently not be as catalytically effective

during combustion when compared to other calcium-containing ionic salts [341, 347].

Similarly, the presence of calcium chloride has been reported to inhibit the catalytic

activity during low temperature combustion [348].

Furthermore, Vamvuka et al. [349] reported that the calcium and magnesium minerals

acted as inert materials, inhibiting the combustion rate in both biomass and a Greek

lignite however the presence of these metals in chars resulted in lowering the peak


temperature during combustion. The inhibition of catalytic activity of the calcium

and magnesium in the raw Greek lignite could be connected with the alkaline metal’s

anionic association [350] which may not play a significant role during combustion.

The transformation of organically bound calcium to its ionic salt form during the

isothermal combustion of the coal samples at 400ºC can be summarised by the

chemical reactions below:

Stage 1: Detachment of calcium from organic functional groups

(hydrocarbon-COO-Ca) (hydrocarbon –Ca) + CO⎯→⎯ 2

(hydrocarbon –Ca-Ca-hydrocarbon) + O2 (hydrocarbon –Ca-CaO) + CO⎯→⎯ 2

Stage 2: Formation of ionic salts and ash

(hydrocarbon –Ca-CaO) + O2 (CaO-CaO) + CO⎯→⎯ 2

CaO + CO2 CaCO⎯→⎯ 3 ΔHº923 = -177.5kJ mol-1 [340]

Alternatively, Kumar et al. [351] reported that CaO can also be transformed to CaCO3

via the hydration and carbonation pathway

CaO + H2O Ca(OH)⎯→⎯ 2

Ca(OH)2 + CO2 CaCO⎯→⎯ 3 + H2O

According to the reaction schemes above and according to previous investigators, the

form of calcium in the hydrocarbon matrix can influence the rate of the oxidation-

combustion process. The association of dispersed complexed calcium and active


catalytic ionic salts can facilitate excellent catalytic activity during combustion

whereas other forms such as calcium carbonate and calcium chloride may not be as

effective in improving the rate of combustion.

6.8.2 Magnesium Multiple linear regression analysis on the parameters which affect the combustion

reactivity of the Latrobe Valley samples, identified that the magnesium content had a

stronger influence on the rate of combustion than calcium, with correlation

coefficient constants of 0.74 and 0.64, respectively (see Section 6.6.2). Magnesium

and calcium are alkaline earth metal and therefore their chemistry is comparable.

Analogous to calcium, magnesium ions are also associated to organic oxygen in the

lignites and upon low temperature decarboxylation/devolatilisation/combustion, the

chemical transformations from carboxylate to ionic salt are also expected.

Comparative combustion tests in the catalytic effectiveness of magnesium versus

calcium are very limited, in particular for lignites. Badin [332] speculated that the

catalytic effectiveness of cations was related to the proton-transfer capacity of the

cations in water (pKa values). Badin claimed that cations with a high pKa value were

analogous to the strength of the cations to undergo base-forming reactions by

hydrolysis (or solvolysis) during early stages of coal combustion. Subsequently,

Badin hypothesized that calcium would be more effective than magnesium as a

combustion catalyst and that the order of effectiveness would follow in the order of

Na+ > Ca2+ > Mg2+ >Al3+. Similarly, Yan et al. [352] investigated the effect of mineral

species of the combustion oxidation of coke and reported the catalytic activity of

calcium was greater than magnesium with the order of Fe > Na ≈ K > Ca > Mg > Ti.


In addition, Sujanti and Zhang [353] investigated the role of inherent inorganic matter

in low temperature oxidation of a Victorian brown coal and reported that calcium

carbonate was more reactive and promoted spontaneous combustion whereas the

carbonated form of magnesium inhibited spontaneous combustion. In contrast,

catalytic activity in the combustion of graphite have found that magnesium had a

higher activity than calcium [354].

The combustion of coal is a complex, multiphase, multicomponent chemically

reacting system involving concurrent heterogenous chemical reactions with organic

and inorganic components in the coal. Unfortunately, research into comparing the

catalytic effectiveness of magnesium and calcium during combustion is very limited.

Some studies (mentioned above) claim calcium is more effective than magnesium

whereas others claim vise versa. In this study, magnesium was statistically calculated

to have more of an influence into promoting the combustion reactivity of the coal

when compared to calcium. These differences are likely stemmed down from the

chemical forms of magnesium and calcium, and their connection and involvement

within the hydrocarbon macromolecular framework of the sample under the different

stages of volatilisation and combustion. Furthermore, the transformation of these

cations during the volatilisation and combustion process, from cationic complexation

with organic oxygen function groups within the coal matrix, to an active catalytic

oxidising agent, would also determine its effectiveness in facilitating the

breakdown/oxidation of the organic components in the coal.


209

Table 6.10 AAEM species, iron, chloride and sulphide ions present in the raw lignite, water washed and acid washed products (mmol of univalent charge; equivalent to 1g

of dry raw lignite).

Na+ Fe2+/3+ Ca2+ Mg2+ Cl- S2- Total +ve ions

Total -ve ions

LYLA Raw 0.004 0.004 0.002 0.007 0.002 0.001 0.017 0.003 H2O 0.002 0.004 0.002 0.006 0.001 0.001 0.014 0.002 Acid <0.001 0.001 <0.001 0.001 <0.001 0.001 0.002 0.001 LYMNa Raw 0.020 0.002 0.002 0.013 0.012 0.001 0.037 0.013 H2O 0.004 0.002 0.002 0.010 0.001 0.001 0.018 0.002 Acid 0.001 0.001 <0.001 0.002 <0.001 0.001 0.004 0.001 LY HNa Raw 0.029 0.023 0.009 0.044 0.009 0.001 0.105 0.010 H2O 0.007 0.020 0.009 0.041 0.001 0.001 0.077 0.002 Acid <0.001 0.016 <0.001 <0.001 <0.001 0.001 0.016 0.001 MMTE Raw 0.003 0.019 0.016 0.017 0.002 0.001 0.055 0.003 H2O 0.002 0.019 0.015 0.016 0.001 0.001 0.052 0.002 Acid <0.001 0.013 <0.001 <0.001 <0.001 0.001 0.013 0.001 MMg Raw 0.009 0.002 0.024 0.032 0.003 0.001 0.067 0.004 H2O 0.004 0.002 0.024 0.032 0.001 0.001 0.062 0.002 Acid <0.001 0.002 0.001 0.001 <0.001 0.001 0.004 0.001 YMTE Raw 0.003 0.031 0.007 0.015 0.001 0.001 0.056 0.002 H2O 0.002 0.031 0.007 0.014 0.001 0.001 0.054 0.002 Acid <0.001 0.013 0.001 0.002 <0.001 0.001 0.016 0.001 YT Pale Raw 0.002 0.012 0.006 0.011 0.002 0.001 0.031 0.003 H2O <0.001 0.011 0.005 0.010 0.002 0.001 0.026 0.003 Acid <0.001 0.008 <0.001 <0.001 <0.001 0.001 0.008 0.001 YT Dark Raw 0.002 0.018 0.008 0.015 0.001 0.001 0.043 0.002 H2O <0.001 0.017 0.008 0.014 0.001 0.001 0.039 0.002 Acid <0.001 0.013 <0.001 0.001 <0.001 0.001 0.014 0.001 YEF Fe Raw 0.002 0.038 0.008 0.020 0.003 0.001 0.068 0.004 H2O 0.001 0.036 0.008 0.020 0.002 0.001 0.065 0.003 Acid <0.001 0.025 <0.001 <0.001 <0.001 0.001 0.025 0.001 YEF Dark Raw 0.003 0.031 0.008 0.013 0.001 <0.001 0.055 0.001 H2O 0.001 0.028 0.008 0.012 0.001 <0.001 0.049 0.001 Acid <0.001 0.019 <0.001 0.001 <0.001 <0.001 0.020 <0.001 Example: Charge balances for MMTE raw Total positive charge = Na + Fe + Ca + Mg = 0.003 + 0.019 + 0.016 + 0.017 = 0.055 mmol Total negative charge = Cl + S = 0.002 + 0.001 = 0.003 mmol Note: Alkali metals lithium and potassium univalent charges were <0.001. Also, qualitative analysis using a scanning electron microscope (SEM) – energy dispersion x-ray (EDX) system confirms that all the major inorganic components in the coal have been identified (see Appendix K).

LYHNa

LYHNa

YEFFeYEFFe

MMTE

MMg

MMg

MMTE

YEFDYMTEYMTE

YEFD

YTD

YTPYTP

YTD

LYMNa

LYMNa

LYLALYLA

LYMNaMMg

LYLAYTD YMTE

YEFDMMTE LYHNaYTP YEFFe

R2 = 0.48

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40


AA

EM

con

cent

ratio

n (m

mol

cha

rge)

Raw lignites Water washed lignites Acid washed lignites

Figure 6.9 AAEM concentration versus combustion reactivity for the raw, water washed and acid washed lignite samples.


210


Figure 6.10 AAEM and iron concentration (cation concentration) versus the combustion reactivity value for the raw, water washed and acid washed lignite samples.

211

YTDMMg

LYMNaLYLA

LYMNaMMg

LYLA

LYLA

YMTEMMTE

LYHNa

YEFFe

YEFD

YEFFeYTP

YTD

MMg

MMg

LYHNa

YEFFe

MMTEYEFDYMTE

YTDLYMNa

LYHNa

YEFFe

YTP

YMTEYEFD

R2 = 0.83

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40


Cat

ion

conc

entra

tion

(mm

ol c

harg

e)



6.8.3 Sodium Sodium was the only alkali metal detected in the raw Latrobe Valley lignites that was

in reasonable concentration that could affect the combustion reactivity. The levels

lithium and potassium were not included in the total cationic concentration because

their levels were low and therefore their influence on the combustion reactivity of the

coal samples would be negligible. Multiple regression analysis expressed that the

sodium content had a weak positive linear correlation with the measured combustion

reactivity with a correlation coefficient of 0.31. According to this statistical analysis,

sodium was not as effective as iron, magnesium and calcium, respectively in

promoting the oxidation-combustion process. In contrast, previous studies have

reported that sodium is more effective than alkaline metals in the combustion

reactivity of the coal [332, 352]. Furthermore, char derived samples from the pyrolysis

of Loy Yang lignite (from Section 4.4) gave a strong correlation between the

concentration of sodium remaining in the char and the combustion reactivity of the

sample, whereas the calcium and magnesium contents which remained relatively

unchanged as a function of pyrolysis temperature, did not influence the rate of

combustion to the same extent (see Chapter 7). The contrasting differences in the

catalytic activity of sodium for the raw coals compared to the charred pyrolysed

samples is likely attributed to the chemical forms of sodium in these samples during

the combustion-oxidation process.

The behaviour and chemical transformations of sodium during pyrolysis and

combustion are different. The pyrolysis of the Loy Yang lignite (see Section 4.6)

found that some of the sodium in the coal volatilised at temperatures as low as


500ºC. Furthermore, prior work has also reported sodium volatilisation during

pyrolysis can occur as low as 300ºC [355]. In contrast, in a slow heatup combustion

process at 400ºC, the sodium present in the coal sample is unlikely to be volatilised

but instead be bonded continuously within the carbon macromolecular network.

Similar to alkaline earth metals, the transformation of organically bound sodium to

its ionic salt form during the isothermal combustion of the coal samples at 400ºC can

be simplified and summarised by the chemical reactions below:

Stage 1: Detachment of calcium from organic functional groups

(hydrocarbon-COO-Na) (hydrocarbon –Na) + CO⎯→⎯ 2

Stage 2: Formation of ionic salts and ash

(hydrocarbon –Na) + O2 Na⎯→⎯ 2O

Na2O + CO2 ⎯→⎯ Na2CO3

According to the reaction schemes above, the form of the sodium in the raw coal and

its transformation during the oxidation combustion process would significantly

influence the reactivity of the sample. Studies on impregnating sodium containing

compounds into a coal/char have reported that sodium in the form of NaCl would not

be as catalytically effective as other forms of sodium such as Na2CO3 [356, 357]. Upon

combustion, finely dispersed catalytic material would agglomerate into fine particles

would could affect the combustion rate of the sample. In addition, the dispersion of

the sodium in the carbon macromolecular matrix would also govern the catalytic

effects of sodium during combustion [358].


6.8.4 Aluminium Aluminium salts such as alumina oxide (Al2O3), are excellent catalysts in

liquefaction and gasification of coal which is predominately attributed to its alkaline

properties. In contrast, aluminium cations during combustion have been found to

exhibit low catalytic effectiveness during combustion when compared to reforming

processes [359]. In this study, statistical multiple linear regression identified that the

presence of acid extractable aluminium had a negative, effect of the combustion

reactivity of the coal samples. This negative behaviour could be the consequence of

two separate inhibiting effects: (1) the production of water from the combustion

process; and (2) the obstruction of active catalysts (eg AAEM cations and iron)

resulting from the complexation with aluminium cations.

Several investigations have reported reduced catalytic performance in the

combustion of hydrocarbons due to aluminium cations. Burch et al. [360] and

Aquila et al. [361] investigated the activation of C-H bonds in different hydrocarbons

on the surfaces of metal oxides and metal catalysts and reported that alumina can

deactivate highly active catalysts under oxidizing conditions. This group proposed

that the deactivation by alumina was attributed to dehydroxylation (i.e. the

generation of water from the combustion process) on the surface of the alumina. The

production of water from the chemical breakdown of the coal structure is beneficial

in pyrolysis and gasification however in combustion, the presence of water has a

significant impediment effect. Burch et al. [360] proposed that the presence of water

on the active sites of catalysts could result in the active site being blocked for

catalytic oxidation of C-H bonds. Prior investigations have also proposed that some

form of hydroxyl radical blocks reaction sites on the surface of the catalyst [362].


Ciuparu et al. [363, 364] also proposed that water inhibited the oxygen exchange

between the catalyst surface and the gas phase, as well as reoxidation of a partially

reduced catalyst with oxygen.

The second inhibiting effect by aluminium cations could be the impediment of active

catalysts within the coal matrix during the combustion-oxidation process. Inhibition

of coal combustion by mineral matter occurs via possible restrictions for access of

oxygen to combustible surfaces. Experiments with aluminium treated Loy Yang

lignite have shown the formation of aluminium phases such as MgAlO4 and sodium

aluminosilicates [365]. Furthermore, aluminium in the coal can combine with calcium

and magnesium compounds during combustion to form Ca3Al2O6, CaAl2O4 and

MgAl2O4 [366]. As previously mentioned, the chemical forms AAEM species and iron

(including associations with aluminium ions), and their involvement within the

hydrocarbon macromolecular structure under the different stages of combustion,

could affect the catalytic performance in facilitating the breakdown/oxidation of the

organic components in the coal.

Of the two inhibiting courses of action for the aluminium cations, the obstruction of

active catalysts (eg AAEM cations and iron) is likely to be the more prominent

consequential effect during combustion. The first inhibiting effect of water

occupying active sites on the aluminium would still catalyse the breakdown of C-H

bonds in the coal but at a reduced rate, and the overall effect for combustion would

be a net positive. However, multiple linear regression exhibited a net negative effect


for aluminium signifying that the impediment of active catalysts in the coal is the

more significant inhibiting process during combustion-oxidation of the coal.

6.8.5 Chlorine Multiple linear regression analysis on the parameters which affect the combustion

reactivity of the Latrobe Valley samples, identified that the chlorine content gave a

weak linear and net positive effect on the rate of combustion with correlation

coefficient constant 0.20 (see Section 6.6.2). Furthermore, when the counter anion

charges of chloride and sulphide are subtracted from the sum of AAEM + iron

univalent charge, the correlation coefficient constant between univalent charge and

combustion reactivity is further improved to 0.87 (Figure 6.11). The sulphide

contents in the Latrobe Valley samples remained relatively unchanged and therefore

changes resulting from anionic influences on the surface of the catalyst was

predominantly chlorine (other than oxygen).

Chlorine in many ways can act as a catalyst poison and as a catalyst promoter. As a

catalyst poison, alkali and alkaline halides pronouncedly inhibit the combustion with

oxygen [367-369]. Minkoff and Tipper [370] reported that the presence of halide salts

such as NaCl significantly hampered hydrogen-oxygen combustion at 460ºC.

Quyn et al. [358] also reported that the retention of chlorine in char can greatly

decrease the reactivity of the char. The inhibiting effect of chlorine when associated

with a potentially active catalyst (eg NaCl, CaCl2, FeCl3 etc) would result in an

overall negative correlation effect in the combustion-oxidation process.


217

As a catalyst promoter, chlorine can facilitate the combustion process by freeing up

active sites within the coal matrix and allowing the transformation of cations into a

more active catalytic form. During combustion, the weakly bonded chlorine within

the coal would be dissociated and volatilised as HCl. In Section 4.6, more than half

of the chlorine in the lignite was volatilised during pyrolysis at 500ºC and prior work

has also reported that about 10% of the chlorine in a NaCl-loaded sample was

volatilised at temperatures as low as 200ºC [100, 355]. The departure of chlorine from

the coal/char matrix would constructively free-up corresponding AAEM cations and

iron to potentially become more active catalysts [371]. Furthermore, with the removal

of acidic vapours such as HCl would lead to the promotion and transformation of

metal species into their highly catalytic basic and oxide chemical forms. Finally,

multiple linear regression exhibited a net positive effect for chlorine signifying that

the volatilisation of chlorine out from the coal matrix and allowing inherent cationic

ions to transform into a more active catalytic form is the more dominant process for

chlorine during combustion-oxidation of Latrobe Valley lignites.


218

Figure 6.11 Cation concentration (AAEM and iron concentration) minus anion concentration (chloride and sulphide) versus the combustion reactivity value for the raw, water washed and acid washed lignite samples.

YTDMMgLYMNaLYLA

LYMNaMMg

LYLA

LYLA

YMTEMMTE

LYHNa

YEFFe

YEFD

YEFFeYEFFe

YTD

MMgMMg

LYHNa

YEFFe

MMTEYEFDYMTE

YTD

LYMNa

LYHNa

YEFFe

YTP

YMTEYEFD

R2 = 0.87

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40


Cat

ion

min

us a

nion

con

cent

ratio

n (m

mol

cha

rge)



6.9 Effect of surface area on combustion reactivity The effect of washing the raw lignites with water or with dilute acid on the surface

area of the product is shown in Table 6.11. Washing the lignites with water to

remove water-soluble salts from the coal matrix had no significant affect on the

surface area of the samples (except for YTP where the increase in surface area was

only marginal). In contrast, washing the raw lignites with dilute acid did result in

marginal increases in the surface area in the acid-washed product. This increase in

surface area is likely associated with the metallic cations present in the raw lignites

which are unlikely to contribute to the adsorption capacity of the coal but instead

contribute to the weight of the sample [372-375].

Table 6.11 Combustion reactivity arbitrary values and surface area for the raw, water and acid washed Latrobe Valley coals.


value

Surface area*

(m2 g-1)


value

Surface area*

(m2 g-1) LYLA Raw 0.06 223 YMTE Raw 0.28 213 H2O 0.05 225 H2O 0.23 214 Acid 0.03 227 Acid 0.13 215 LYMNa Raw 0.09 200 YTP Raw 0.16 190 H2O 0.07 210 H2O 0.14 192 Acid 0.03 233 Acid 0.10 206 LYHNa Raw 0.33 171 YTD Raw 0.18 199 H2O 0.29 171 H2O 0.13 207 Acid 0.11 185 Acid 0.08 206 MMTE Raw 0.27 229 YEF Fe Raw 0.36 203 H2O 0.25 232 H2O 0.31 204 Acid 0.09 240 Acid 0.19 205 MMg Raw 0.24 194 YEFD Raw 0.27 227 H2O 0.23 194 H2O 0.20 228 Acid 0.04 220 Acid 0.14 230 * The surface area error is ±2 m2 g-1


The surface area of the lignite samples was weakly correlated to the combustion

reactivity of the coal with a correlation coefficient of only 0.06 (Figure 6.12). Similar

results were found using multiple linear regression analysis to determine the physico-

chemical properties affecting the combustion reactivity of the lignite samples (see

Section 6.6.1, Table 6.5).

LYHNa

MMg

YEFD

YTPYTP

YTD

YEFD

YMTE YMTE YMTE

MMTEYEFD

YTDYEFFe YEFFE YEFFe

MMTE

MMgMMgLYMNa

YTPYTDLYMNa

LYLA

LYHNa

LYHNa

MMTE

LYLALYLALYMNa

R2 = 0.06

100

120

140

160

180

200

220

240

260

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40


Sur

face

are

a (m

2 g-1)

Raw lignite Water washed lignite Acid washed lignite Figure 6.12 Surface area versus the combustion reactivity of the Latrobe Valley

lignite samples

The effect of washing the raw coals with water and dilute acid also had no significant

differences in the large pore volumes or carbon densities (determined by helium

pycnometry) when compared with the parent coal. The results confirm that the

removal of inorganic components from the coal by washing has a much larger impact

on reducing the combustion reactivity of the sample when compared to significant

reductions in porosity resulting from thermal drying.


6.10 Conclusions Multiple linear regression was a valuable tool for investigating the parameters

affecting the combustion reactivity of coals. Combustion on a diverse suite of well-

characterised lignites sourced from the Latrobe Valley open cut mines showed that

catalytic inorganic species clearly outweighed other physico-chemical effects for

affecting the combustion reactivity of the lignites. The catalytic effects of iron in

combustion have often been overlooked. Multiple regression analysis clearly

identified a very strong positive linear relationship between the combustion reactivity

and the iron content of the coal and moderate relationships between the combustion

reactivity and the magnesium and calcium contents. The combined catalytic effects

of iron, magnesium and calcium accounted for more than 95% of the variation in the

combustion reactivity of the raw coals. In contrast, the aluminium present in the raw

lignites inhibited the combustion-oxidation process whereas chlorine was found to

marginally improve combustion.

The combustion reactivity of Latrobe Valley lignite samples was also found to be

strongly correlated to the sum of the univalent charges of the AAEM species plus the

univalent charge of the acid-extractable iron. In contrast, only a moderate correlation

with the combustion reactivity of the samples was found when the sum of AAEM

species were only considered as the major catalytic components in the coal.

The chemical form of the inorganic components in the hydrocarbon matrix can

influence the rate of the oxidation-combustion process. The SEM-EDX results

showed that the inorganic components in the raw coals were well dispersed and the


XRD spectra did not reveal the presence of inorganic crystalline salts on the surface

of the coal. Furthermore, a general feature of the Latrobe Valley coals was that much

of the sodium was easily be removed by water washing the coal and that most of the

Mg, Ca, Al, Fe and remaining Na was also extractable with weak acid thus

suggesting ionic associations in the form of carboxylate/phenolates or simple


refractory silicates. The removal of the inorganic species from the macromolecular

coal matrix by water washing or by acid washing the lignite, had a marked effect on

the combustion reactivity and on the peak temperature of the coal sample.

Furthermore, the effectiveness of catalytic inorganic species clearly outweighed pore

volume effects for affecting the combustion reactivity of the lignites. The removal of

inorganic components from the coal by washing or by HTD or MTE has a much

larger impact on reducing the combustion reactivity of the sample when compared to

significant reductions in porosity resulting from thermal drying.

Chapter 7 Combustion of Chars 223

CHAPTER 7 COMBUSTION OF CHARS

7.1 Introduction The combustion reactivity of char is of particular importance in several next

generation coal power plant systems such as advanced pressurised fluid bed

combustion (APFBC). In an APFBC system, the coal is firstly pyrolysed (or partially

gasified) to produce a fuel gas and a stream of char. The char is then burnt separately

in a pressurised fluid bed boiler to generate steam. The fuel gases from the carboniser

are mixed with the combustion products of the char and burnt with air in a separate

combustor system [376].

The physico-chemical properties of char are contrastingly different to that of the raw

coal. The combustion reactivity of char has been found to be affected with variations

in pyrolysis temperature due to alterations in the hydrocarbon macromolecular

network [377-380] and because of catalytic inorganic component transformations within

the char [381-384]. In addition, an increase in aromaticity and changes in porosity could

also have significant impacts on the combustion reactivity of the char [385-387].

In this chapter, the combustion reactivity of the chars produced from the pyrolysis of

an MTE product (see Chapter 4) is investigated. The influence of catalytic

components present in the char and their effect on the combustion-oxidation process

will be compared with the results reported for the raw lignites, thermally dried

products (see Chapter 5) and from the products of water and acid washing (see


Chapter 6). In addition, the effect of the char surface area and large pore volume on

the combustion reactivity of the char is also examined.

7.2 Char reactivity In the previous chapter, it was concluded that the inorganic components are the

backbone to the differences in the combustion reactivity for the raw, water washed

and acid washed lignite samples. This section continues on the combustion reactivity

theme by exploring the combustion behaviour of char samples generated from the

pyrolysis of the MTE product (150°C/5.1MPa) using the quartz fluidized-bed/fixed-

bed reactor (see Section 4.4). The combustion reactivity values of the pyrolysed

MTE samples as a function of temperature and as a function of heating mode are

shown in Figure 7.1.

The combustion reactivity of the char samples decreased as a function of temperature

with marked reductions at pyrolysis temperatures of 700°C and above. In addition,

the char samples that were produced from the fast pyrolysis of the MTE product gave

significantly lower combustion reactivity values when compared to the slowly heated

pyrolysed char samples. Correspondingly, differences in the remaining cationic

components in the macromolecular structure of the char after pyrolysis are likely to

account for the differences in the combustion reactivity as a function of temperature

and as a function of heating mode.


500 600 700 800 900

0.00

0.01

0.02

0.03

0.04

0.05

0.06

Com

bust

ion

reac

tivity

val

ue



Figure 7.1 Comparisons of the combustion reactivity of chars from the pyrolysis of

MTE lignite operated at the slow and fast heating rate mode, as a function of temperature in the fluidized-bed/fixed-bed reactor.

The major cationic ion volatilised from the char during pyrolysis of the MTE product

was sodium (see Section 4.6) which could account for the differences in the

combustion reactivity of the chars. The form of the sodium ions present in the char

would significantly affect the combustion reactivity of the char. Chen and Yang [388]

reported that the formation of alkali clusters on the surface of the char were

beneficial to the catalytic effectiveness of these species. Furthermore, alkali catalytic

clusters were more effective than alkali phenolated forms on the char surface [389]. At

500°C, the char would contain a high organic oxygen concentration and the sodium

present in the char would likely be bonded to this organic oxygen. The association of

sodium with organic oxygen function groups in the char would therefore, reduce its


effectiveness in catalysing the combustion-oxidation of the char when compared to

the existing alkali clusters. The similar combustion reactivities between the 500°C

slow and fast pyrolysed char samples suggest similar forms of sodium associations

within the char matrix. Increasing the pyrolysis temperature would result in further

loss of organic oxygen and the formation of sodium clusters on the surface of the

char. The pyrolysis heating rate mode showed significant volatilisation of sodium at

temperatures above 700°C whereas for the slowly heated chars only a small loss of

sodium was reported from 700°C to 900°C (see Section 4.6). As a consequence, the

higher proportion of sodium retained in the slow heated char sample would also

contain a higher proportion of sodium clusters which could account for the higher

combustion reactivities when compared to the fast pyrolysed chars. Indeed, multiple

linear regression confirm that the sodium content remaining in the char after

pyrolysis was the major contributing cation in influencing the combustion reactivity

of the char sample (Table 7.1).

Table 7.1 Intercorrelations among reactivity and inorganic ion species for MTE charred samples

Reactivity Na Cl Mg Ca

Reactivity 1.000

Na .918 1.000

Cl -.138 -.434 1.000

Mg .786 .774 -.067 1.000

Ca .630 .687 .018 .820 1.000

Note: * p < 0.05, ** p < 0.01, *** p < 0.001, N = 10


In comparison, the magnesium and calcium contents in the char were not

significantly affected by differences in heating modes and marginally increased as a

function of pyrolysis temperature from 500°C to 900°C (see Section 4.6). Multiple

linear regression analysis also found a strong linear correlation between the calcium

and magnesium contents versus the combustion reactivity of the char. However, the

magnesium and calcium contents in the chars were not as influential as the sodium

content in effecting the combustion behaviour of the char (Table 7.1). That is,

magnesium and calcium had been found to be more active than sodium during the

combustion of the raw lignite, the water washed and the acid washed samples (see

Section 6.6) but for the char samples, this behaviour was reversed.

In contrast to sodium, the formation of crystalline growth of alkaline metal oxides on

the surface of the char have been linked to the reduction in char reactivity as a

function of pyrolysis temperature [390]. Hence, these marked differences in the

performance of calcium and magnesium are likely associated with a number of

factors including: crystalline growth, catalytic dispersion, chemical transformations

and associations within the hydrocarbon matrix and also the chemical ionic forms

during the different stages of pyrolysis which may consequently reduce their

effectiveness in catalysing the oxidation-combustion of the char.


Furthermore, the chlorine content in the char after pyrolysis had a negative impact on

the combustion reactivity of the char thus instigating the inhibition of active catalysts

such as magnesium and calcium, within the char matrix. Similarly, prior work has

also reported that the retention of chlorine in the char can greatly decrease the

reactivity of the char [358, 391].

Also, acid extractable iron which had been found to be the most effective catalyst in

raw coals (see Section 6.6), could not account for the differences in combustion

reactivities between the slow and fast pyrolysed char samples. The iron contents

between a slow or a fast pyrolysed char sample as a function of pyrolysis

temperature showed no significant differences. For example, a slow and fast

pyrolysed char sample at 900°C had the same iron contents. Instead, the reduction in

the combustion reactivity between the slow and fast pyrolysed char samples as a

function of pyrolysis temperature could also be attributed to the chemical

transformation of the iron into a less effective catalytic form during the slow

pyrolysis of the MTE lignite.

As discussed above and in Section 6.8, the concentration of the inorganic

components within the char matrix would be the main factor influencing the

combustion reactivity of carbonaceous materials. Comparison of ionic charge to char

mass ratio versus the combustion reactivity of the chars from the two different

heating modes is shown in Figure 7.2. The combustion reactivity of the char samples

were found to decrease as the inorganic concentration charge balance (Na+ + Ca2+ +

Mg2+ + Fe2+/3+ - Cl-) to char mass ratio decreased, however the chars produced under

Chapter 7 Combustion of Chars

229

the different heating regimes behaved remarkably different (Figure 7.2). For the

chars collected from fast pyrolysis, the inorganic charge to char mass ratio decreased

considerably at pyrolysis temperatures above 600°C and as a consequence, the

combustion reactivity of these chars were significantly lower than the slowly

pyrolysed chars. Furthermore, the profile for the fast pyrolysed chars shown in

Figure 7.2 suggests that the inorganic components in the char are more effective in

catalysing the combustion-oxidation process than the inorganic forms present in the

slow pyrolysed chars. These differences in the combustion profiles (Figure 7.2)

imply that the pyrolysis heating modes affect the chemical transformations of

catalytic cationic components within the macromolecular structure of the char during

the different stages of pyrolysis.

230

0.00 0.01 0.02 0.03 0.04 0.05 0.060.008

0.010

0.012

0.014

600°C 500°C

700°C800°C

900°C

Con

cent

ratio

n io

n ch

arge

to c

har m

ass

ratio

(mol

uni

vale

nt io

n ch

arge

per

gra

m d

b)


500°C

600°C

700°C

800°C

900°C


Chapter 7 Combustion of chars

Figure 7.2 Concentration on charge to char mass ratio versus combustion reactivity of the char from the slow and fast pyrolysis experiments using the fluidized-bed/fixed-bed reactor

Chapter 7 Combustion of chars 231

7.3 Porosity of chars Recapping previous porosity results, the MTE process was found to be the most

effective drying process in reducing the large pore volume in the final product

however despite these large pore volume reductions, only marginal differences were

evident between the combustion reactivity of the raw lignite and its products. Also,

the effect of surface area (or micropore volume) on the combustion reactivity of raw,

water washed and acid washed Latrobe Valley lignites was found to be weakly

correlated to the combustion reactivity of the samples. Furthermore, the effectiveness

of catalytic inorganic species in the coal clearly outweighed pore volume effects in

the combustion reactivity of raw lignites.

In this section, the effect of porosity on the combustion reactivity is re-investigated

for char samples instead of raw lignites. Combustion tests were performed on the

char samples produced from a MTE sample during the slow and fast pyrolysis

experiments in the quartz fluidized-bed/fixed-bed reactor (see Section 4.4). The

purpose of this re-visit is to compare the physico-chemical properties of char

materials and their effects on the combustion reactivity; and also to compare these

correlations with those previously reported for the unpyrolysed samples. In addition,

the effect of the micropore volume (which is associated to the adsorptive capacity of

the sample) on the combustion reactivity of the sample has not clearly been resolved

because surface area differences between the raw lignites were relatively small (see

Table 6.11).


The pore volume of Loy Yang MTE coal (150°C/5.1MPa) and the pore volumes of

chars from the pyrolysis of MTE operated at the slow and fast heating rate mode, as a

function of temperature in the fluidized-bed/fixed-bed reactor are shown in Figure

7.3. Interestingly, the char particles showed larger pore volumes than the parent MTE

product despite loosing a significant amount of mass during the pyrolysis process.

For example for the 900°C char, 50% of its original weight (db) was volatilised

during pyrolysis however its large pore volume remained high at 0.42cm3g-1

(Figure 7.3). Similarly, Sainsbury and Hawksley [392] reported that Yallourn chars

prepared above 800°C with rapid heating rates, showed large pores and that the

overall shrinkage of the lignite particle was only small despite losing 25 per cent of

its weight during pyrolysis. Similar findings have also been made for chars from

other Latrobe Valley lignites [393].

0.71 0.70 0.69 0.670.60

0.52 0.48

0.70 0.68 0.660.59

0.52 0.47

0.06 0.05 0.14 0.170.20

0.220.23

0.05 0.14 0.180.21

0.230.24

0.27

0.540.51 0.47

0.460.45

0.42

0.550.51 0.46

0.440.43

0.39

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

LY MTE(parentsample)

400 500 600 700 800 900 400 500 600 700 800 900


Tota

l vol

ume

(cm

3 g-1)


Fast heat-up pyrolysisSlow heat-up pyrolysis

150°

C/5

.1M

Pa

Figure 7.3 Comparisons of pore volume of Loy Yang MTE coal (150°C/5.1MPa) and chars from the pyrolysis of MTE operated at the slow and fast heating rate mode, as a

function of temperature in the fluidized-bed/fixed-bed reactor.


It is yet unclear on whether the micropore volume which is associated with the

absorptive capacity of the material has any positive affect in facilitating the

combustion of the material. Kamishita et al. [394] had postulated that the reduction of

a lignite char reactivity in air was attributed to both a decrease in active surface area

and deactivation of catalytic inorganic components. One would expect that a material

with a high absorptive capacity would facilitate the rate of exchange between oxygen

and vapourous volatiles on the surface of the micropores whereas the presence of a

large pore volume would facilitate the pathway of these gases out of the

macromolecular structure. Furthermore, a high surface area should be beneficial in

the dispersion of active catalysts on the surface of the char and in the reduction of

alkaline metal clusters which have been reported to deactivate the effectiveness of

alkaline catalysts in the char [390]. Subsequently, it is speculated that a high absorptive

capacity and large pore volumes should be beneficial to the combustion process. The

surface area of the char samples from the pyrolysis of MTE lignite operated at the

slow and fast heating rate mode, as a function of temperature in the fluidized-

bed/fixed-bed reactor is shown in Figure 7.4.

The surface area of the char samples increased as a function of pyrolysis temperature

and only small differences were evident between the char samples produced from the

slow and fast heating rate regimes. At 900°C, the rapidly heated pyrolysed char

sample had an adsorptive capacity of almost 900m2g-1 which is comparative to some

activated carbon adsorbents [395-402]. In contrast, the surface areas of the char samples

do not show any positive evidence in enhancing the combustion process. That is, as a

function of pyrolysis temperature, the surface area of the char samples significantly


increased whereas the combustion reactivity substantially decreased. The reduction

in combustion reactivity in the char samples with increasing pyrolysis temperature is

clearly influenced by the extent of volatilisation of active catalytic species from the

coal macromolecular structure during pyrolysis whereas surface area and large pore

volumes had no noticeable affect.

400 500 600 700 800 900100

200

300

400

500

600

700

800

900

Sur

face

are

a (m

2 g-1)



Figure 7.4 Comparisons of the surface area of chars from the pyrolysis of MTE lignite operated at the slow and fast heating rate mode, as a function of temperature

in the fluidized-bed/fixed-bed reactor.


To further elucidate the influence of surface area and porosity on the combustion of

chars, combustion tests were also performed on a synthetic activated carbon

containing no inorganic components and with a high surface area (1068m2g-1) and a

significantly large pore volume (Figure 7.5). The total pore volume of the synthetic

activated carbon relative to the char samples from the pyrolysis of the MTE product

as a function of pyrolysis temperature is shown in Figure 7.6.

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.0010.010.11

Pore radius (μm)

Incr

emen

tal i

ntru

sion

(m

L g-1

)

Figure 7.5 Pore size distribution of a synthetic activated carbon from Helsa-werk


0.70 0.69 0.67 0.60 0.52 0.480.70 0.68 0.66 0.59 0.52 0.47

1.12

0.05 0.14 0.17 0.200.22 0.23

0.05 0.14 0.18 0.210.23 0.24

0.43

0.54 0.51 0.47 0.460.45 0.42

0.55 0.51 0.46 0.440.43

0.39

1.35

0.00

0.50

1.00

1.50

2.00

2.50

3.00

400 500 600 700 800 900 400 500 600 700 800 900 Activecarbon


Tota

l vol

ume

(cm

3 g-1)


Fast heat-up pyrolysisSlow heat-up pyrolysis

Figure 7.6 Comparisons of pore volume of a synthetic activated carbon and the pore volumes of chars from the pyrolysis of a MTE sample, operated at the slow and fast

heating rate mode, as a function of temperature in the fluidized-bed/fixed-bed reactor.

Combustion tests on the synthetic activated carbon at 400°C showed that despite its

high surface area and pore volume, the activated carbon burnt very slowly and gave a

combustion reactivity value of <0.001. That is, at 400°C, the synthetic activated

carbon took more than 24 hours to completely burn a 2mg sample which is

considerably longer when compared to the coal samples combusted in this study (eg

of the coal samples, the Loy Yang Low Ash (LYLA) acid washed sample had the

lowest combustion reactivity value and it took less than 90 minutes to completely

burn). The results definitively support that the surface area and pore volumes of

carbonaceous materials have negligible affect on the combustion reactivity and that

inorganic components in the carbon macromolecular structure are the major

promoters in enhancing the combustion reactivity of the sample.


7.4 Conclusions The individual inorganic components in coal/char are the major contributors in

dictating the rate of combustion-oxidation at 400°C. Pyrolysis temperature and

pyrolysis heating mode were found to significantly affect the combustion reactivity

of chars at temperatures above 600°C. The concentrations of individual cationic

components in the macromolecular structure of the char after pyrolysis account for

the differences in the combustion reactivity of the char samples.

The volatilisation of sodium during pyrolysis of the MTE product can explain the

differences in the combustion reactivity of the chars. Multiple linear regression also

confirmed that the sodium content remaining in the char after pyrolysis was the

major contributing cation in influencing the combustion reactivity of the char

samples.

Transformations of inorganic components during pyrolysis play important roles in

determining char reactivity. Magnesium and calcium were more active than sodium

during the combustion of the raw lignite but for the char samples, this behaviour was

reversed. The formation of crystalline growth of alkaline metal oxides on the surface

of the char during pyrolysis is likely responsible for the reduction in the effectiveness

of these cations in the combustion-oxidation of the char. The presence of chlorine in

the char also inhibited the catalytic activity of the inherent inorganic components.


The combustion reactivity of the char samples were found to decrease as the

inorganic concentration charge balance (Na+ + Ca2+ + Mg2+ + Fe2+/3+ - Cl-) to char

mass ratio decreased, however the chars produced under the different heating

regimes behaved remarkably different. The inorganic components in the char

produced from fast pyrolysis were more effective in catalysing the combustion-

oxidation process than the inorganic forms present in the slow pyrolysed chars.

These differences in the combustion profiles imply that the pyrolysis heating modes

affect the chemical transformations of catalytic cationic components within the

macromolecular structure of the char during the different stages of pyrolysis.

The surface area of the char samples increased as a function of pyrolysis

temperature. Also the char samples pyrolysed at 900°C were found to contain very

high surface areas of almost 900m2g-1 which was comparative to some activated

carbon adsorbents. In addition, it was definitively concluded that the surface area and

pore volumes of carbons have negligible affect on the combustion reactivity and that

inorganic components in the carbon macromolecular structure are the major

influences in the combustion rate of the sample.

Chapter 8 Overall conclusions 239

CHAPTER 8 OVERALL CONCLUSIONS

Three technologies for reducing the moisture content of Latrobe Valley lignites,

namely, hydrothermal dewatering (HTD), mechanical thermal expression (MTE) and

steam drying (SD) were investigated.

Of the three drying technologies, MTE was most effective in removing the water as a

function of processing temperature from a Loy Yang coal containing 59% water. A

water reduction of more than 50% from the original lignite was achieved with a

processing temperature of 125°C and 5.1MPa of applied mechanical pressure. Under

these conditions, the overall net wet specific energy of the fuel increased by 87%.

Subsequently, on a carbon dioxide per megawatt basis, significantly less MTE fuel is

required to produce the same energy output compared to the raw lignite. The MTE

process also achieved the lowest levels of organic carbon in the by-product water

stream and removed significant amounts of ash fouling constituents from its

macromolecular structure during dewatering. For SD, a processing temperature of

210°C was required to achieve similar moisture reductions and subsequent increases

in calorific value of the final fuel product.

In contrast, for HTD, the relatively higher processing temperatures required to

achieve similar moisture reductions also led to poor solids recovery and significantly

higher concentrations of organic carbon in the by-product water. These attributes

could hinder the development of a commercial scale HTD plant because of the higher


processing costs and the requirement to develop water treatment facilities for the

product water.

Rapid pyrolysis of the HTD product gave significantly lower yields of methane,

ethene, carbon monoxide and carbon dioxide when compared to corresponding yields

of the raw lignite, MTE and SD products. The lower yields for the HTD product

were attributed to volatilisation during hydrothermal dewatering and also to the

reduction of catalytic reforming cations. The significant volatile yield loss during

hydrothermal dewatering could be disadvantageous in some industrial processes,

which convert the carbon matter to lower molecular weight fractions (eg gasification,

liquefaction).

The combustion reactivity of MTE, HTD and SD products did not exhibit significant

differences from the raw lignite. Advantageously, conventional boiler systems

currently in operation in the Latrobe Valley would be more than adequate in

combusting the thermally treated products from any of the three drying processes.

The catalytic inorganic species inherently present in the raw lignites clearly

outweighed other physico-chemical effects for affecting the combustion reactivity.

Combustion experiments on a diverse suite of well-characterised lignites sourced

from the Latrobe Valley found that Yallourn lignites burnt more effectively

compared to Morwell and Loy Yang lignites because of the higher iron contents

found in the lignites from this region. The combined catalytic effects of iron,


magnesium and calcium accounted for more than 95% of the variation in the

combustion reactivity of the raw coals.

The inorganic components in the char produced from fast pyrolysis were more

effective in catalysing the combustion-oxidation process than the inorganic forms

present in the slow pyrolysed chars. These differences in the combustion profiles

imply that the pyrolysis heating modes affect the chemical association of catalytic

cationic components within the macromolecular structure of the char during the

different stages of pyrolysis.

Finally, the surface area and pore volumes of carbons/chars have negligible effect on

the combustion reactivity and the inorganic components in the carbon

macromolecular structure are the major influences in the combustion rate of the

sample at 400°C.

Appendix A: Chemical composition of high temperature grade stainless steel 242

APPENDIX A Chemical composition of high temperature

grade stainless steel

Appendix B: Nitrogen BET on lignites 243

APPENDIX B Nitrogen BET on lignites

Most studies have preferentially calculated the surface area of solid samples using

nitrogen (N2) adsorption and the Brunauer, Emmett, Teller (BET) equation [403].

Unfortunately, for carbon materials such as lignite, the surface area values obtained

with the BET, N2 adsorption method are significantly lower than the true value of the

sample [107, 404]. For example, the surface area calculated with the BET, N2 adsorption

method for the HTD products gave extremely small unrealistic values of <20m2g-1

(Figure B.1). It is generally believed that the micropore structure of carbons is so fine

that it is virtually inaccessible to nitrogen at the liquid nitrogen temperature (-196°C;

77K) because of activated diffusion effect and/or pore shrinkage [404-406].

Alternatively, carbon dioxide gas adsorption at 0°C (273K) is normally applied to

carbons in determining the micropore volumes and surface areas because carbon

dioxide is able to access the micropore structure within the carbon matrix at these

temperatures [265, 406]. Furthermore, the BET approach is only applicable for a

multilayer adsorption process and should not be used on isotherms which represent a

monolayer capacity [407]. Despite this fact, extensive work on the surface area of

carbons using the BET, N2 adsorption method is still widespread in the

literature [270, 408-416].

Appendix B: Nitrogen BET on lignites

244

0

10

20

30

40

50

60

70

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Relative pressure (p/p0)

Volu

me

adso

rbed

(cm

3 g-1 S

TP)

HTD 200°C HTD 250°C HTD 280°C HTD 300°C HTD 320°C HTD 350°C

BET region (0.01 to 0.35p/p0

)

BET surface areas

HTD 350°C : 1.7m2g-1

HTD 320°C : 3.1m2g-1

HTD 300°C : 4.5m2g-1

HTD 280°C : 8.7m2g-1

HTD 250°C : 12.9m2g-1

HTD 200°C : 18.5m2g-1

Figure B.1 Nitrogen adsorption isotherms at -196°C and corresponding BET surface areas for the HTD products

Previous works on determining the surface area of lignites have supported the use of

the Dubinin equation for low pressure carbon dioxide adsorptions (CO2) [404, 417-419].

Subsequently, in this thesis, the Dubinin equation [107] was applied to calculate

carbon dioxide adsorption at 0°C (273K) on the raw lignite and its thermally dried

products.

Appendix C: Pore size distributions 245

APPENDIX C Pore size distributions

In determining the pore volume of coal products, complete drying of the sample is

required, during which significant pore collapse can occur, particularly in raw

lignites, which have a less rigid structure than thermally treated products [59]. Pore

collapse is particularly serious for the larger pores [134]. Thus comparisons between

raw and processed lignites should be treated cautiously, but comparisons between

thermally treated products, which have a more rigid structure, are meaningful.

Helium density and mercury porosimetry data are best compared after conversion to

a volume basis (Figure C.1) as follows:

• Volume occupied by ‘carbon’ (pore radius (p.r.)> 0.08nm) = Heρ1

• Micropores (from CO2 adsorption, i.e. 0.25nm< p.r. <2nm [420])

• Large pores (intruded by mercury, i.e. 1.5nm< p.r. <1000nm)

Thus, the total internal pore volume (intra-particle volume) can be taken as the sum

of the micropore and large pore volumes. A representation of the overall pore

volume for raw lignite is given in Figure C.1. As noted above, the porosity of raw

lignites cannot be measured reliably by these methods. The true total internal pore

volume of raw Victorian lignite has been estimated as 1.5mLg-1 db [421] (cf 0.60mLg-1

db for the sum of the micropore and large pore volume of the raw lignite in

Figure 3.5).

Appendix C: Pore size distributions 246

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Raw coal

Tota

l vol

ume

(cm

3 g-1

)

Large pore volume

Micropore volume

Vol. occupied by carbon

Mercury porosimetry1000 to 1.5nm

CO2 surface area1.0 to 0.25nm

Helium pycnometry>0.08nm

Pore volume1000 to 0.08nm

Figure C.1 Pore volume distribution of raw lignite attained from mercury porosimetry, CO2 surface area and helium pycnometry (values are given as the radius

of the pores).

Appendix D: Physical measurements of MTE density

247

APPENDIX D Physical measurments of MTE density

In the MTE process, a pellet is obtained as the final product. The advantage of a

pellet is that accurate physical measurements such as wet and dry densities can be

measured using a calliper (see Experimental) before and after drying. These physical

measurements can provide useful information on the extent of shrinkage during

drying to zero moisture prior to analysis. Furthermore, these measurements can help

validate the total pore volume determinations described in Section 3.4. A schematic

of the MTE pellet is shown in Section 2.14.

The wet density of the MTE pellet is expected to increase with more water being

removed from the lignite because of the increase in the ratio of carbon density (i.e. ~

ρ 1.4gcm-3) to water (ρ 1.0gcm-3). Increasing the MTE temperature (fixed pressure)

resulted in a linear increase in the pellet wet density (Figure D.1a) whereas

increasing the MTE applied mechanical pressure resulted in an exponential increase

in the pellet wet density (Figure D.1b). These trends are also expected because the

wet density is dependant on the retained moisture in the MTE pellets (see

Section 3.2). Correspondingly, and not surprisingly, as the wet density of the MTE

product was increased, the wet porosity of the product also decreased (i.e. porosity

(cm3g-1) = 1/density (gcm-3); Figure D.2).

0

5

10

15

20

25

30

1.08 1.13 1.18 1.23 1.28

Wet density (gcm-3)

App

lied

mec

hani

cal p

ress

ure

(MP

a)

R2 = 0.96

100

150

200

250

300

1.08 1.13 1.18 1.23 1.28

Wet density (gcm-3)

Rea

ctio

n te

mpe

ratu

re (°

C)

a b

Figure D.1 Relationship between wet density of the MTE pellet versus (a) reaction temperature (b) applied mechanical pressure

Appendix D: Physical measurements of MTE density 248

249

Appendix D: Physical meas

0

5

10

15

20

25

30

0 5 10 15 20 25 30 35 40 45 50 55 60

Wet porosity (%)

App

lied

mec

hani

cal p

ress

ure

(MP

a)

R2 = 0.97

100

150

200

250

300

0 5 10 15 20 25 30 35 40 45 50 55 60

Wet porosity (%)

Rea

ctio

n te

mpe

ratu

re (°

C)

a b

urements of MTE density

Figure D.2 Relationship between wet porosity of the MTE pellet versus (a) reaction temperature (b) applied mechanical pressure


The pellet dimensions measured for the wet density results are of particular

importance for calculating the extent of pellet shrinkage upon drying (see Section

2.14 for Equations). Removing the retained water from the wet MTE pellets resulted

in the collapse of a significant amount of pores. Under the mildest processing

conditions, 125°C/5.1MPa and 150°C/2.5MPa, approximately 65% of the pore

volumes were retained after drying (Table D.1). A higher proportion of the original

pore volume was preserved with increasing processing temperature and applied

mechanical pressure, thus suggesting an increase in lignite structure rigidity. Within

the experimental parameters investigated, the effect of temperature was more

effective than applied pressure in conserving the internal pore structure during drying

to zero moisture. At 250°C/5.1MPa, approximately 87% of the original pore volume

in the wet pellet was maintained after drying. These results further emphasize the

caution in comparing the pore volumes between raw and mildly processed lignites

because of the significant pore collapse that occurs during complete drying.

Table D.1 Pore volumes of wet and dry MTE pellets and the proportion of the original pellet size upon drying to zero moisture.

Wet pore volume (cm3g-1)

Wet porosity

(%)

Dry pore volume (cm3g-1)

Dry porosity

(%)

Proportion of original porosity

(%) MTE 125°C / 5.1MPa 0.72 48.5 0.48 40.1 66 MTE 150°C / 5.1MPa 0.53 41.2 0.38 34.8 71 MTE 180°C / 5.1MPa 0.48 38.6 0.36 33.6 76

MTE 200°C / 5.1MPa 0.42 35.6 0.33 31.3 78 MTE 250°C / 5.1MPa 0.29 28.2 0.25 26.0 87 MTE 150°C / 2.5MPa 0.75 47.2 0.48 40.3 64

MTE 150°C / 5.1MPa 0.53 41.2 0.38 34.8 71 MTE 150°C / 12.7MPa 0.47 39.2 0.37 33.9 78 MTE 150°C / 25.0MPa 0.42 37.0 0.33 31.4 78


251

The proportion of the original pellet size that was maintained after drying to zero

moisture was highly correlated to the wet density of the final product (r2 value of

0.98; Figure D.3c). In general, with an increase in MTE processing temperature

and/or applied mechanical pressure, the product’s large pore volume decreased (see

section 3.4), its rigidity and hardness increased and as a consequence to these

changes, the extent of shrinkage upon drying decreased. These physical changes to

the pellet’s properties are further supported by the reasonable linear correlation

(r2 value of 0.8; Figure D.4a) of the wet versus dry MTE pellet density and the

excellent correlations between dry density versus retained moisture, and dry density

versus wet porosity of the pellets (Figure D.4b and c, respectively). Unfortunately,

due to time limitations of this study, this correlation has only been proven for the

MTE processed Loy Yang lignite and further work is required to establish whether

these relationships are also true for other coals. Nevertheless, the significance of

these correlations is that the pellet dry density (as measured by the calliper

procedure) can be used to extrapolate the moisture content and wet porosity of the

MTE pellet. Also the meaningfulness of the mercury porosimetry and the helium

pycnometry measurements which was questioned earlier because of the shrinkage

and the internal pore collapse of lignite products when completely dried, can be

elucidated by comparing the physical dry density measurements obtained from

measuring the MTE pellet and the dry density values given by the analytical

techniques.


0

5

10

15

20

25

30

90 92

94 96 98 100

Proportio of original size (%)

App

lied

mec

hani

cal p

ress

ure

(MP

a)

R2 = 0.98

100

150

200

250

300

90 92 94 96 98 100

Proportion of original size (%)

Rea

ctio

n te

mpe

ratu

re (°

C)

a b

R2 = 0.98

1.08

1.10

1.12

1.14

1.16

1.18

1.20

1.22

1.24

1.26

1.28

90 92 94 96 98 100

Proportion of original size (%)

Wet

den

sity

(gcm

-3)

c

n

Figure D.3 Relationship between proportions of the original size of MTE pellet after drying to zero moisture versus (a) reaction temperature (b) applied mechanical pressure (c) wet density of the MTE pellet.


R2 = 0.99

0

5

10

15

20

25

30

35

40

45

50

55

60

0.8 0.9 1.0 1.1

Dry density (gcm-3)

Ret

aine

d m

oist

ure

(% H

2 O

, wb)

R2 = 0.80

.9 1.0 1.1

Dry density (gcm-3)

b

0.8

0.9

1.0

1.1

1.2

1.3

1.4

0.8 0

Wet

den

sity

(gcm

-3)

a

R2 = 0.98

0

10

20

30

40

50

60

0.8 0.9 1.0 1

Dry density (gcm-3)

Wet

por

osity

(%)

c

.1

Figure D.4 Relationship between the dry and wet density of MTE pellets, processed under different conditions


254

The large pore volumes measured analytically with mercury porosimetry were

considerably lower than the physical pore volumes of the solid MTE pellet (Table

D.2), in particular for the milder processed MTE products (e.g. 125°C/5.1MPa and

150°C/2.5MPa). These lower values are likely due to the unaccounted micropore

volumes (measured by gas adsorption; ~0.06 cm3g-1; Table 3.5) and the pore regions

between 1 to 1.5nm and 0.08 to 0.25nm, respectively. Taking these unaccounted

regions into consideration, the results obtained by analytical methods (except for the

milder processed products) are very close to the dry pore volumes measured with the

solid MTE pellet (Figure D.5).

Based on the very good correlations between the physically measured dry density of

the pellet versus the pellet’s wet density, and against the pellet’s retained moisture

then it may also be possible to translate the total pore volumes measured by mercury

porosimetry and gas adsorption back to the retained moisture content and the wet

porosity of the thermally treated lignite products. However, caution should still be

taken when interpreting the total pore volumes of completely dried products because

unless the extent of shrinkage is known, then calculation of the wet porosity would

be difficult. For the purpose of this study, the total pore volumes of the completely

dried products will be used to compare the differences in the combustion reactivity of

each of the products (see Chapter 3).


255

Table D.2 Comparison between large pore region (measured by mercury porosimetry) and pore volume calculated by measuring the dimensions of the dry

MTE pellet

Large pores (1000 to 1.5nm

pore radius) (cm3g-1) ±0.02

Pore volume

dry (cm3g-1)

Difference

(cm3g-1)

MTE 125°C / 5.1MPa 0.28 0.48 0.20

MTE 150°C / 5.1MPa 0.27 0.38 0.11

MTE 180°C / 5.1MPa 0.27 0.36 0.09

MTE 200°C / 5.1MPa 0.25 0.33 0.07

MTE 250°C / 5.1MPa 0.24 0.25 0.01

MTE 150°C / 2.5MPa 0.31 0.48 0.18

MTE 150°C / 5.1MPa 0.27 0.38 0.11

MTE 150°C / 12.7MPa 0.27 0.37 0.10

MTE 150°C / 25.0MPa 0.23 0.33 0.10


256

256

Figure D.5 Relationship between retained water and pore volume determined from mercury porosimetry and gas adsorption; wet and dry pore volumes determined from the MTE pellet

0.0

0.2

0.4

0.6

0.8

1.0

0.0 0.2 0.4 0.6 0.8 1.0


Por

e vo

lum

e (c

m3 g-1

)

Determined from Hg and He pycnometry Wet pore volume (MTE pellet) Dry pore volume (MTE pellet)

milder MTE processed products

Appendix E: Determination of soluble ionic salts and carboxylate ions 257

APPENDIX E Determination of soluble ionic salts and

carboxylate ions

Results from washing the Loy Yang lignite with distilled water and the remaining

ash and inorganic concentrations in the washed product are given in Table E.1. In

addition, Figure 3.8 gives the proportion of water-soluble sodium leached out from

the lignite during the MTE, HTD and SD processes.

Table E.1 Acid extractable inorganics, chlorine and total sulphur in raw and water washed lignite (100g of wet raw lignite, actual mass in g) a.

Process condition Na Ca Mg Al FeNPb Stot Cl

Loy Yang raw 0.036 0.017 0.030 0.004 0.025 0.12 0.030

Loy Yang washed 0.010 0.020 0.028 0.004 0.028 0.11 0.018

Note, the error is ±0.004g for Na, Ca, Mg, Al, FeNP and Cl whereas error in S tot is ±0.02g b NP = non-pyritic

Comparison of the data from the raw and water-washed lignite showed only minor

differences suggesting that much of the inorganic material in these samples was

strongly bound (Table E.1). The level of sodium in Loy Yang lignite was reduced by

68 ± 11%db and chlorine by 45 ± 16%db. No significant differences were found in

the levels of Ca, Mg, Al, FeNP and Stot with water washing.

Appendix F: Product water from MTE, HTD and SD 258

APPENDIX F Product water from MTE, HTD and SD

Inorganic analysis of the product waters Analysis of the product water collected from each of the experiments helps to

validate the conclusions deduced from the solid products. Table F.1 and Table F.2

give the quantities of inorganic species leached from the lignite during the MTE,

HTD and SD processes. The major inorganic species leached out into the product

water were sodium and chlorine and to a lesser extent sulphate. This suggests that

most of the soluble sodium in Loy Yang lignite was likely ionically bound to the

chlorine ion and to a lesser extent to the sulphate ion. A significant reduction in total

sulphur was not measured in the solid dried product thus suggesting that only small

portion of the sulphur in the lignite was water-soluble. Furthermore, the negligible

changes in Ca and Mg contents of the solid lignite products during drying made it

unsurprising that the levels of these elements in the product water were also small.

Potassium salts, similar to sodium salts, are very soluble in water. The level of

potassium was not measured in the raw lignite or solid products however its

concentration in the product water was marginally higher than Ca. Furthermore,

similar to sodium, the level of potassium in the product water significantly increased

with increasing processing temperatures in HTD and SD thus suggesting that a

majority of the potassium was also in carboxylate form.

The total ionic mass in the product water for all three drying processes was very low.

Appendix F: Product water from MTE, HTD and SD

259

For MTE, approximately 60mg of inorganic material was leached out into the

product water from 100g of wet raw lignite (i.e. 40g db). Similarly, in SD at 250°C,

the total inorganic mass leached was in proportion to the amount leached out in the

MTE process (i.e. from 10g db of raw lignite, 15mg of inorganic matter was

measured). However, for HTD, considerably more inorganic matter was dissolved

into the water at the same processing temperature (i.e. 24mg from 10g db raw

lignite). The higher proportion of inorganic material leached out from the HTD

process was because of the addition of water to the raw lignite to make up the slurry

therefore some washing of the lignite had occurred prior to HTD treatment.

In the solid products, an increase in processing temperature beyond 250°C (for HTD

and SD) resulted in both additional water and additional inorganic matter being

removed from the lignite. Furthermore, it is postulated that at these higher

processing temperatures, carboxylate bonds in the lignite detach resulting in

additional inorganic material being removed. Analysis of the product water for HTD

and SD validate the results of the solid products. The levels of sodium and chlorine,

the two most abundant extractable ions in the lignite, were found to increase in

concentration in the product water with increasing temperature.

The lower analytical error in measuring the inorganic species in the product water

compared to the solid product allowed the behaviour of the inorganic matter in

lignite to be better elucidated. The levels of Ca, which did not exhibit significant

differences in the solid products, did however display a small and gradual increase in

concentration in the product water with increasing processing temperature.

E, HTD and SD 260

Table F.1 Amount of inorganics present and pH for the product water from MTE processing 100g of wet raw lignite (i.e. 40g db raw lignite; all values are in mg)

Table F.2 Amount of inorganics present and pH for the product water from HTD and SD processing 10g of dried raw lignite (All values are in mg)

Process condition pH Na Ca K Mg Cl SO42-

Total massa

TOCb Process condition pH Na Ca K Mg Cl SO42-

Total massa

TOCb

MTE 125°C / 5.1MPa 5.9 14.3 1.0 1.6 0.8 21.1 6.5 45.3 11 HTD 200°C 4.5 5.3 0.22 0.31 0.15 7.6 2.2 15.8 2.3

MTE 150°C / 5.1MPa 5.7 16.6 0.9 1.9 0.9 23.8 7.4 51.5 20 HTD 250°C 4.3 7.7 0.27 0.72 0.36 10.9 3.5 23.5 8.7

MTE 180°C / 5.1MPa 5.4 17.8 1.0 1.7 0.9 24.8 8.0 54.2 30 HTD 280°C 4.3 8.2 0.28 0.96 0.48 11.9 3.7 25.5 22

MTE 200°C / 5.1MPa 3.8 18.2 0.8 1.4 0.7 25.5 8.3 54.9 37 HTD 300°C 4.2 9.0 0.34 1.3 0.65 13.4 4.3 29.0 46

MTE 250°C / 5.1MPa 3.7 19.4 0.8 1.6 0.8 27.3 9.8 59.7 48 HTD 320°C 4 10.2 0.41 1.7 0.84 15.7 4.4 33.3 93

HTD 350°C 4 10.3 0.45 2.0 0.99 16.5 4.2 34.4 201

MTE 150°C / 2.5MPa 5.7 13.9 0.9 1.3 0.7 21.5 6.7 45.0 16

MTE 150°C / 5.1MPa 5.9 16.6 0.9 1.9 0.9 23.8 7.4 51.5 20 SD 130°C 6.3 0.05 0.03 0.08 0.01 0.04 0.05 0.26 0.20

MTE 150°C / 12.7MPa 5.4 17.3 1.0 1.4 0.7 24.2 8.0 52.6 19 SD 150°C 6.2 0.52 0.06 0.13 0.05 0.58 0.35 1.7 2.3

MTE 150°C / 25.0MPa 5.5 19.0 1.1 1.5 0.7 26.9 8.3 57.4 20 SD 180°C 5.2 1.8 0.07 0.14 0.21 2.6 1.1 5.9 8.8

a = Total mass only includes the inorganics and not the total organic carbon mass SD 200°C 4.7 3.1 0.10 0.22 0.38 4.2 1.8 9.8 11

b = TOC (Total Organic Carbon) SD 230°C 3.9 4.2 0.12 0.27 0.39 5.3 2.8 13.1 20

The presence of Fe and Al could not be detected in the product water SD 250°C 3.8 4.8 0.17 0.28 0.39 6.1 2.8 14.5 30

Error in the product water analysis in mg = 5% (mgL-1) x Volume of water SD 280°C 3.9 5.8 0.25 0.34 0.50 8.2 3.0 18.1 63

SD 300°C 3.8 6.2 0.25 0.38 0.51 9.6 2.6 19.5 109

Note: HTD 180°C and 230°C product water measurements on the pH and inorganic SD 310°C 3.8 6.3 0.26 0.39 0.41 10.2 2.2 19.8 122

analysis were not conducted however the total organic carbon of the product water was SD 320°C 3.8 6.4 0.28 0.40 0.41 10.5 2.7 20.7 142

calculated to 1.8mg and 3.8mg, respectively. SD 330°C 3.8 6.5 0.31 0.50 0.35 11.0 2.5 21.2 175

SD 350°C 3.7 6.6 0.33 0.55 0.36 11.7 2.6 22.1 286

a = Total mass only includes the inorganics and not the total organic carbon mass

b = TOC (Total Organic Carbon)

Appendix F: Product water from MT


261

In SD, the level of sulphate in the product water did not increase significantly with

increasing processing temperature beyond 250°C but a small increase was reported

in the HTD water. These differences are also likely attributed to sulphate ions being

trapped in the SD product because of more water being removed from the lignite as

steam, thus reducing its ability to be leached out from the lignite in liquid form.

In Table J.1 and Table J.2, these data are recalculated to determine the maximum

possible concentration of these species in a product water stream (where there is no

added water). Note that the data are tabulated in mgmL-1 (in other words, parts per

thousand). Furthermore, the molarity concentration (M) of the ionic species in the

product water is also given in Figure F.1 and in APPENDIX J.

In Chapter 3, a minimum HTD processing temperature of 320°C was proposed for

achieving approximately 50% moisture reduction. At this temperature, the total

inorganic mass leached into the product water was 4mgmL-1 (~60% more than MTE

and SD; Table F.4) which is still relatively low when compared to concentrations

from higher ash lignites [153]. A higher proportion of inorganic removal from the

lignite (in particular sodium) is advantageous because of fouling and slagging

problems associated during combustion [104]. However, product waters of very high

salt concentration may require some cleaning before being released back into the

environment.

Table F.3 Concentration of inorganics present for the product water from MTE processing 100g of wet raw lignite (i.e. 40g db lignite; all values are in mgmL-1)

Table F.4 Concentration of inorganics present for the product water from HTD and SD processing 10g of dried raw lignite (All values are in mgmL-1)

Process condition Amount of water removed

(mL)

Na Ca K Mg Cl SO42-

Total massa


(mL)

Na Ca K Mg Cl SO42-

Total massa

MTE 125°C / 5.1MPa 32.3 0.44 0.05 0.03 0.03 0.65 0.20 1.4 HTD 200°C 0.7 7.9 0.46 0.32 0.23 11.3 3.3 23.5

MTE 150°C / 5.1MPa 40.2 0.41 0.05 0.02 0.02 0.59 0.18 1.3 HTD 250°C 2.4 3.2 0.30 0.11 0.15 4.6 1.5 9.8

MTE 180°C / 5.1MPa 42.6 0.42 0.04 0.02 0.02 0.58 0.19 1.3 HTD 280°C 3.8 2.2 0.25 0.07 0.13 3.1 0.97 6.7

MTE 200°C / 5.1MPa 45.1 0.40 0.03 0.02 0.02 0.57 0.18 1.2 HTD 300°C 5.8 1.6 0.23 0.06 0.11 2.3 0.74 5.0

MTE 250°C / 5.1MPa 51.8 0.38 0.03 0.02 0.02 0.53 0.19 1.2 HTD 320°C 8.2 1.2 0.20 0.05 0.10 1.9 0.53 4.0

HTD 350°C 10.9 0.95 0.18 0.04 0.09 1.5 0.38 3.2

MTE 150°C / 2.5MPa 31.7 0.44 0.04 0.03 0.02 0.68 0.21 1.4

MTE 150°C / 5.1MPa 40.2 0.41 0.05 0.02 0.02 0.59 0.18 1.3 SD 150°C 2.3 0.23 0.06 0.03 0.02 0.25 0.15 0.74

MTE 150°C / 12.7MPa 42.9 0.40 0.03 0.02 0.02 0.56 0.19 1.2 SD 180°C 4.8 0.37 0.03 0.01 0.04 0.54 0.23 1.2

MTE 150°C / 25.0MPa 45.1 0.42 0.03 0.02 0.02 0.60 0.18 1.3 SD 200°C 6.8 0.45 0.03 0.02 0.06 0.62 0.26 1.4

a = Total mass only includes the inorganics and not the total organic carbon mass SD 230°C 8.7 0.48 0.03 0.01 0.05 0.61 0.32 1.5

SD 250°C 11.2 0.43 0.02 0.02 0.03 0.54 0.25 1.3

SD 280°C 13.2 0.44 0.03 0.02 0.04 0.62 0.23 1.4

SD 300°C 13.7 0.45 0.03 0.02 0.04 0.70 0.19 1.4

Note: SD 130°C has not been included in this table because it did not undergo any SD 310°C 14.2 0.44 0.03 0.02 003 0.71 0.15 1.4

moisture reduction relative to the raw lignite and hence the concentration of inorganics SD 320°C 14.5 0.44 0.03 0.02 0.03 0.72 0.19 1.4

could not be calculated SD 330°C 14.7 0.44 0.03 0.02 0.02 0.75 0.17 1.4

SD 350°C 14.8 0.44 0.04 0.02 0.02 0.79 0.18 1.5


Appendix F: Product water from MTE, HTD and SD 262

263

Appendix F: Product water from MT

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40 MTE Na HTD Na SD Na

Ion

conc

etra

tion

(M)

0.000

0.002

0.004

0.006

0.008

0.010 MTE K HTD K SD K

Ion

conc

etra

tion

(M)

0.000

0.002

0.004

0.006

0.008

0.010

0.012 MTE Ca HTD Ca SD Ca

Ion

conc

etra

tion

(M)

100 150 200 250 300 350

0.0010.0020.0030.0040.0050.0060.0070.0080.0090.010

MTE Mg HTD Mg SD Mg

Ion

conc

etra

tion

(M)

Processing temperature (°C)

100 150 200 250 300 3500.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35


MTE Cl HTD Cl SD Cl

Ion

conc

etra

tion

(M)

100 150 200 250 300 3500.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040 MTE SO

4 HTD SO

4 SD SO4

Ion

conc

etra

tion

(M)


Figure F.1 Molarity concentration of inorganics present for the product water from MTE, HTD and SD processing (equivalent to 10g of dried raw lignite)

E, HTD and SD


264

Calculating an overall ion charge balance in the product water can be used for

checking the values given in Table F.1 and Table F.2. In general, most of the cations

(Na+, K+, Ca2+ and Mg2+) were paired up with the anions Cl- and SO42- (Table F.5).

For MTE and HTD, the net positive ions were slightly higher to the net negative ions

however in SD at higher processing temperatures, the opposite trend was true

(Table F.5). The carbonate (CO32-) and bicarbonate (HCO3

-) concentrations in the

water at the measured pH and CO2 concentration will be too low to explain the

difference between positive and negative ions (APPENDIX K). Instead, the slight

acidity of the product water (pH ~4) and the difference between positive and

negative ions could be attributed to traces of soluble organic acids (eg. CH3COOH,

acetic acid) in the product water [155].

The dotted line in Figure F.2 indicates a 1:1 mole ratio between sodium and chlorine.

For SD, at processing temperatures above 200°C, the product waters gave an Na:Cl

molar ratio of greater than 1:1 suggesting possible carboxylate bond cleavage.

However at temperatures of above 300°C, Na:Cl fell below 1. Similarly, for HTD,

temperatures above 320°C resulted in more chlorine moles than sodium moles in the

product water. In addition, the same behaviour was also observed in the solid

products for the higher temperature SD and HTD products (Figure 3.9). This

increase in chlorine content could be due to loss of chlorine not bound to sodium

from the lignite.


265

Table F.5 The ions present in the product water (mmol of univalent charge) from MTE, HTD and SD processing (equivalent to 10g of dry raw lignite).

Na+ Cl- K+ Ca2+ Mg2+ SO42- Total

+ve ions

Total -ve ions

MTE 125°C / 5.1MPa 0.16 0.15 0.01 0.02 0.02 0.03 0.21 0.18

MTE 150°C / 5.1MPa 0.18 0.17 0.01 0.02 0.02 0.04 0.23 0.21

MTE 180°C / 5.1MPa 0.19 0.17 0.01 0.02 0.02 0.04 0.24 0.21

MTE 200°C / 5.1MPa 0.20 0.18 <0.01 0.02 0.01 0.04 0.23 0.22

MTE 250°C / 5.1MPa 0.21 0.19 0.01 0.02 0.02 0.05 0.26 0.24

MTE 150°C / 2.5MPa 0.15 0.15 0.01 0.02 0.01 0.03 0.19 0.18

MTE 150°C / 5.1MPa 0.18 0.17 0.01 0.02 0.02 0.04 0.23 0.21

MTE 150°C / 12.7MPa 0.19 0.17 0.01 0.02 0.01 0.04 0.23 0.21

MTE 150°C / 25.0MPa 0.21 0.19 0.01 0.02 0.02 0.04 0.26 0.23

HTD 200°C 0.23 0.21 0.01 0.02 0.01 0.05 0.27 0.26

HTD 250°C 0.33 0.31 0.01 0.04 0.03 0.07 0.41 0.38

HTD 280°C 0.36 0.33 0.01 0.05 0.04 0.08 0.46 0.41

HTD 300°C 0.39 0.38 0.01 0.06 0.05 0.09 0.51 0.47

HTD 320°C 0.44 0.44 0.01 0.08 0.07 0.09 0.60 0.53

HTD 350°C 0.45 0.47 0.01 0.10 0.08 0.09 0.64 0.56

SD 150°C 0.02 0.02 <0.01 0.01 <0.01 0.01 0.03 0.03

SD 180°C 0.08 0.07 <0.01 0.01 0.02 0.02 0.11 0.09

SD 200°C 0.13 0.12 <0.01 0.01 0.03 0.04 0.17 0.16

SD 230°C 0.18 0.15 <0.01 0.01 0.03 0.06 0.22 0.21

SD 250°C 0.21 0.17 <0.01 0.01 0.03 0.06 0.25 0.23

SD 280°C 0.25 0.23 0.01 0.02 0.04 0.06 0.32 0.29

SD 300°C 0.27 0.27 0.01 0.02 0.04 0.05 0.34 0.32

SD 310°C 0.27 0.29 0.01 0.02 0.03 0.05 0.33 0.34

SD 320°C 0.28 0.30 0.01 0.02 0.03 0.06 0.34 0.36

SD 330°C 0.28 0.31 0.01 0.02 0.03 0.05 0.34 0.36

SD 350°C 0.29 0.33 0.01 0.03 0.03 0.05 0.36 0.38

Example: Charge balances for HTD 350°C Total positive charge = Na + K+ Ca + Mg = 0.45 + 0.01 + 0.10 + 0.08 = 0.64mmol Total negative charge = Cl + SO4

2- = 0.47 + 0.09 = 0.56 mmol


266

0.0 0.1 0.2 0.3 0.4 0.50.0

0.1

0.2

0.3

0.4

Sodium (mmol charge)

SD

Chl

orin

e (m

mol

cha

rge)

0.0

0.1

0.2

0.3

0.4HTD

Chl

orin

e (m

mol

cha

rge)

0.0

0.1

0.2

0.3

0.4

0.5

Chl

orin

e (m

mol

cha

rge)

MTE

Figure F.2 Relationship between chlorine and sodium ions present in the water

(mmol) collected from the MTE, HTD and SD processes


267

pH of the product water The general rules of ionic equilibrium [422] would predict that the pH should increase

with the charge of the weak acid anions per unit volume (i.e. the charge per unit

volume on the weak acid anions which were not determined in the analysis). These

rules are only applicable in the absence of hydrolysable cations, such as Fe3+ or Al3+.

The level of iron and aluminium did not change in the solid products and were also

undetectable in the product water for all three drying processes. The pH of the

product waters should in theory be equal to the difference between the charge on the

cations and that on the strong acid anions (Cl-, SO42-).

These expectations were partly fulfilled for the lower temperature SD product waters

(Figure F.3), in that the pH tended to increase with the weak acid anion charge per

unit volume calculated from the product water analyses of Table F.5. However, for

MTE and HTD and for SD at higher processing temperatures, this theory could not

be sustained. The carbonate (CO32-) and bicarbonate (HCO3

-) concentrations in the

water at the measured pH and CO2 concentration will be too low to explain the

difference between positive and negative ions (APPENDIX K).

Alternatively, the amount and nature of the organic acid dissolved in the product

water is likely to play a contributing role in its pH. Previously, workers have reported

significant concentration of anions such as acetate in hydrothermal processing

wastewaters [423]. Furthermore, the greater acidic functional group content of the low-

rank lignites [424] would be consistent with a greater organic-acidic functional group

content of the corresponding waters.


268

0 1 2 3 4 5 6 7

-0.04

-0.02

0.00

0.02

0.04

0.06

0.08

Product water pH

SD

Con

cent

ratio

n of

wea

k ac

id a

nion

s (m

ol u

niva

lent

ions

/L)

0.00

0.02

0.04

0.06

0.08HTD

Con

cent

ratio

n of

wea

k ac

id a

nion

s (m

ol u

niva

lent

ions

/L)

0.00

0.02

0.04

0.06

0.08

0.10

Con

cent

ratio

n of

wea

k ac

id a

nion

s (m

ol u

niva

lent

ions

/L)

MTE

Figure F.3 Relationship between the concentration of weak acid anions and the pH of the product waters from MTE, HTD and SD


269

Thus the pH of product waters from the drying processes is probably usually

controlled by the concentration and nature of weak organic acid molecules leached

out during processing into the water and the concentration of alkali and alkaline earth

cations in the water. The pH will increase with the concentration of cations and,

other things being equal, with decreasing average strength of the weak acid.

Total Organic Carbon The major disadvantages of higher processing temperatures include (i) the higher

water vapour pressure in the system and (ii) an increase in the amount of loosely

bounded components (such as waxes and tars) from the lignite during processing.

Corresponding to (ii) there is an increase of total organic carbon (TOC) in the

product water. The latter is illustrated in Table F.1 and in Figure F.4 and

Figure F.5.

On a commercial scale, it is desirable that any dewatering process is able to achieve

a high degree of water removal from the raw lignite while minimising the costs

associated in handling by-products from the process. High TOC concentrations are

undesirable since they will increase the cost of the product water treatment. For

MTE, very high moisture reductions were achieved with only relatively small

amounts of organic material being leached into the product water (Figure F.4 and

Figure F.6). For MTE, the total organic carbon in the water increased linearly with

increasing proportion of water removed from the raw lignite (Figure F.4).

For HTD, an appreciable amount of water was only removed from the lignite at

much higher temperatures than for MTE (or SD) and, under such conditions, the


270

product water also contained very high concentrations of organic material

(Figure F.4 and Figure F.6). For HTD, the TOC in the product water increased

exponentially with increasing proportion of water removed from the lignite

(Figure F.5). Analysis of HTD product waters have shown the presence of phenols

and cresols as the major components [423, 425]. Nakajima et al. [426] have also reported

a similar exponential increase in the product water TOC with increasing HTD

processing temperature with Loy Yang lignite. This high concentration of organic

material in the product water is therefore a major disadvantage for the HTD process.

SD also achieved very high moisture reductions at relatively mild processing

temperatures (e.g. 56%db at 230°C) however the concentration of dissolved organic

material in its product water was an order of magnitude higher compared to an MTE

product of a similar moisture content (e.g. 125°C/5.1MPa; 51%db H2O reduction).

Furthermore, for SD, the TOC in the product was found to increase exponentially

above 180°C (Figure F.5) whereas for HTD, an exponential increase was found

above 230°C. This is consistent to previous HTD work [427].


271

0

50

100

150

200

250

300

0.1

1

10

100

Tota

l Org

anic

Car

bon

(mg)

MTE

0.1

1

10

100 MTE

Tota

l Org

anic

Car

bon

(mg)

0

50

100

150

200

250HTD

Tota

l Org

anic

Car

bon

(mg)

Tota

l Org

anic

Car

bon

(mg)

HTD

0 50 100 150 200 250 300 350 400

50

100

150

200

250


SD

Tota

l Org

anic

Car

bon

(mg)

0 50 100 150 200 250 300 350 4000.1

1

10

100SD


Tota

l Org

anic

Car

bon

(mg)

Figure F.4 Total Organic Carbon of the product water collected from the MTE, HTD and SD processes at different temperatures. (Note: all TOC values have been calculated on a 10g db).

Figure F.5 The log of Total Organic Carbon of the product water collected from the MTE, HTD and SD processes at different temperatures (Note: all TOC values have been calculated on a 10g db).


272

0 20 40 60 80 10

50

100

150

200

250

0

Tota

l Org

anic

Car

bon

(mg)

SD

50

100

150

200

250

Proportion of water removed (%)

HTD

Tota

l Org

anic

Car

bon

(mg)

50

100

150

200

250

300

MTE

Tota

l Org

anic

Car

bon

(mg)

Figure F.6 Relationship between total organic carbon leached out into the product water versus the proportion of water removed from MTE, HTD and SD (all TOC

values have been calculated on a 10g db).

Note: For MTE the curve fitting is linear, for HTD it is exponential growth and for SD, the curve fitting is Lorentzian.

Appendix G: Sample calculations

273

APPENDIX G Sample calculations

Mass recovery (sample calculation for 150°C / 5.1MPa) 105g (wb) of raw lignite was used in the experiment. This corresponds to 42.20g lignite db After MTE 64.49g of lignite (wb) was recovered Dry mass of recovered lignite was 65.2 % of 64.49g = 42.05g lignite (db)

Therefore, % recovery = 20.4205.42 x 100 = 99.6% db

Water removed (sample calculation for 150°C / 5.1MPa) To work out the proportion of water removed from the lignite during MTE processing from the results In 105g of MTE lignite there is 64.49g of lignite and 35.51g of H2O

This corresponds to 35.51 x49.6420.42 = 23.24g of H2O in the original lignite

Original water content in 105g of lignite = 62.80g

% of water removed = 10080.62

24.2380.62 xg

gg − = 63 % H2O


274

Sample calculation of the conversion of wt%db values to actual mass values

(example sodium conversion for 150°C / 5.1MPa)

Mass of species (g) = 100

valuewt%db x Mass of lignite sample (db)

Mass of sodium in raw Loy Yang lignite = 100090.0

x 42.20 = 0.038g

Mass of sodium in MTE product = 100045.0

x 42.05 = 0.019g

Sample calculation of % sodium removal for 150°C / 5.1MPa

% Na removal = 100- ⎟⎟⎠

⎞⎜⎜⎝

⎛100x

coal YangLoy rawin sodium ofWeight product MTEin sodium ofWeight

= 100 - (038.0019.0 x 100) = 50.0%

The error in the proportion of species Z is given by the equation below Error = Proportion of species Z x

⎥⎦

⎤⎢⎣

⎡⎟⎠⎞

⎜⎝⎛+⎟

⎠⎞

⎜⎝⎛+⎟

⎠⎞

⎜⎝⎛+⎟

⎠⎞

⎜⎝⎛ 2222

wt%dbraw Mass0.01

wt%dbrawin Z0.02or 0.01

wt%dbMTE Mass0.01

wt%dbMTEin Z0.02or 0.01

⎥⎦

⎤⎢⎣

⎡⎟⎠⎞

⎜⎝⎛+⎟

⎠⎞

⎜⎝⎛+⎟

⎠⎞

⎜⎝⎛+⎟

⎠⎞

⎜⎝⎛= 2222

42.200.01

0.0090.01

42.050.01

0.0450.01 x 0.50removal Na %in Error = 12%


275

Table G.1 Acid extractable inorganics, chlorine and total sulphur in raw and solid dried products (wt%db)a

Process condition Na Ca Mg Al FeNPb S tot Cl

LY raw 0.09 0.04 0.07 0.01 0.06 0.28 0.07

MTE 125°C / 5.1MPa 0.05 0.04 0.06 0.01 0.06 0.28 0.06

MTE 150°C / 5.1MPa 0.05 0.04 0.06 0.01 0.06 0.28 0.05

MTE 180°C / 5.1MPa 0.04 0.04 0.06 0.01 0.05 0.28 0.05

MTE 200°C / 5.1MPa 0.04 0.04 0.06 0.01 0.06 0.28 0.05

MTE 250°C / 5.1MPa 0.04 0.04 0.05 0.01 0.06 0.28 0.05

MTE 150°C / 2.5MPa 0.05 0.04 0.06 0.01 0.06 0.28 0.06

MTE 150°C / 5.1MPa 0.05 0.04 0.06 0.01 0.06 0.28 0.05

MTE 150°C / 12.7MPa 0.04 0.04 0.06 0.01 0.05 0.28 0.05

MTE 150°C / 25.0MPa 0.04 0.04 0.05 0.01 0.06 0.28 0.05

HTD 180°C 0.06 0.04 0.06 0.01 0.06 0.28 0.06

HTD 200°C 0.05 0.04 0.05 0.01 0.06 0.27 0.05

HTD 230°C 0.04 0.04 0.05 0.01 0.05 0.27 0.05

HTD 250°C 0.03 0.04 0.05 0.01 0.06 0.27 0.05

HTD 280°C 0.02 0.04 0.04 <0.01 0.06 0.27 0.04

HTD 300°C 0.01 0.03 0.03 <0.01 0.05 0.27 0.03

HTD 320°C 0.01 0.02 0.02 <0.01 0.06 0.26 0.03

HTD 350°C <0.01 0.01 0.01 <0.01 0.05 0.26 0.03

SD 130°C 0.09 0.04 0.07 0.01 0.05 0.28 0.07

SD 150°C 0.08 0.04 0.07 0.01 0.05 0.28 0.07

SD 180°C 0.07 0.04 0.07 0.01 0.06 0.28 0.06

SD 200°C 0.07 0.04 0.07 0.01 0.06 0.28 0.06

SD 230°C 0.05 0.04 0.07 0.01 0.05 0.27 0.06

SD 250°C 0.04 0.04 0.06 0.01 0.05 0.27 0.05

SD 280°C 0.04 0.04 0.06 0.01 0.05 0.27 0.05

SD 300°C 0.04 0.04 0.05 0.01 0.05 0.27 0.05

SD 310°C 0.04 0.04 0.05 0.01 0.05 0.27 0.05

SD 320°C 0.05 0.03 0.05 0.01 0.06 0.27 0.05

SD 330°C 0.05 0.04 0.05 0.01 0.07 0.26 0.05

SD 350°C 0.05 0.03 0.04 0.01 0.07 0.26 0.06

a The error is ±0.01wt% for concentrations of 0.01 - 0.10wt% and ±0.02wt% for concentrations greater than 0.10wt% for all elements except sulphur, for which it is ±0.05wt%. The error in the ash is ±0.1wt%. b NP = non-pyritic.


276

Table G.2 Proportion of inorganic material removed and associated errors for MTE, HTD and SD

Process condition Na Ca Mg Cl

MTE 125°C / 5.1MPa 45 ± 13 0 ± 35 15 ± 19 22 ± 18

MTE 150°C / 5.1MPa 50 ± 12 0 ± 35 15 ± 19 29 ± 18 MTE 180°C / 5.1MPa 54 ± 12 0 ± 35 15 ± 19 29 ± 18 MTE 200°C / 5.1MPa 56 ± 12 0 ± 35 15 ± 19 30 ± 18 MTE 250°C / 5.1MPa 60 ± 11 10 ± 32 36 ± 16 33 ± 16

MTE 150°C / 2.5MPa 46 ± 13 3 ± 35 17 ± 19 24 ± 18 MTE 150°C / 5.1MPa 50 ± 12 0 ± 35 15 ± 19 29 ± 18

MTE 150°C / 12.7MPa 56 ± 12 0 ± 35 15 ± 19 29 ± 18 MTE 150°C / 25.0MPa 56 ± 12 1 ± 35 29 ± 18 30 ± 18

HTD 180°C 34 ± 13 0 ± 35 15 ± 19 19 ± 19

HTD 200°C 45 ± 13 1 ± 35 29 ± 18 25 ± 18

HTD 230°C 56 ± 12 2 ± 35 30 ± 17 31 ± 17

HTD 250°C 67 ± 12 2 ± 35 30 ± 17 37 ± 17

HTD 280°C 79 ± 11 5 ± 34 46 ± 16 46 ± 16

HTD 300°C 90 ± 10 31 ± 29 61 ± 14 55 ± 15

HTD 320°C 90 ± 10 57 ± 24 75 ± 13 58 ± 14

HTD 350°C NA 81 ± 19 89 ± 11 68 ± 12

SD 130°C 0 ± 16 0 ± 35 0 ± 20 0 ± 20

SD 150°C 12 ± 15 1 ± 35 1 ± 20 5 ± 20

SD 180°C 23 ± 14 2 ± 35 2 ± 20 11 ± 19

SD 200°C 29 ± 14 2 ± 35 2 ± 20 16 ± 19

SD 230°C 41 ± 13 2 ± 35 2 ± 20 21 ± 18

SD 250°C 53 ± 12 5 ± 34 18 ± 18 28 ± 17

SD 280°C 59 ± 11 8 ± 33 21 ± 17 33 ± 16

SD 300°C 61 ± 11 12 ± 31 37 ± 16 36 ± 16

SD 310°C 62 ± 11 14 ± 30 39 ± 15 37 ± 15

SD 320°C 58 ± 10 37 ± 26 40 ± 15 39 ± 15

SD 330°C 59 ± 10 19 ± 29 42 ± 14 41 ± 14

SD 350°C 58 ± 9 46 ± 23 59 ± 12 43 ± 13

Appendix H: Actual mass of inorganic components in MTE products

277

APPENDIX H Actual mass (g) of ash, acid extractable inorganics, chlorine and total sulphur

in raw and processed lignite. MTE conditions: 150°C/6MPa except for LYLA where 5.1MPa was used.

ash

Al FeNP Ca Mg Na Cl S tot

Loy Yang LA raw 0.322 ± 0.040 0.004 ± 0.004 0.028 ± 0.004 0.016 ± 0.004 0.032 ± 0.004 0.036 ± 0.004 0.028 ± 0.004 0.113 ± 0.008Loy Yang LA MTE 0.320 ± 0.040 0.004 ± 0.004 0.028 ± 0.004 0.020 ± 0.004 0.032 ± 0.004 0.020 ± 0.004 0.020 ± 0.004 0.112 ± 0.008

Yallourn raw 0.712 ± 0.037 0.004 ± 0.004 0.203 ± 0.008 0.050 ± 0.007 0.064 ± 0.007 0.025 ± 0.004 0.018 ± 0.004 0.071 ± 0.007Yallourn MTE 0.680 ± 0.036 0.003 ± 0.003 0.210 ± 0.008 0.050 ± 0.007 0.066 ± 0.007 0.014 ± 0.003 0.021 ± 0.003 0.073 ± 0.007 Morwell raw 0.942 ± 0.044 0.009 ± 0.004 0.154 ± 0.009 0.137 ± 0.009 0.090 ± 0.009 0.034 ± 0.004 0.026 ± 0.004 0.107 ± 0.009Morwell MTE 0.941 ± 0.044 0.013 ± 0.004 0.156 ± 0.009 0.137 ± 0.009 0.084 ± 0.009 0.021 ± 0.004 0.017 ± 0.004 0.097 ± 0.009

Appendix I: Molar values of inorganic components in raw and processed lignite

278

APPENDIX I Molar values of acid extractable inorganics, chlorine

and total sulphur in raw and processed lignite. Al FeNP Ca Mg Na Cl S tot ±0.001 ±0.001 ±0.001 ±0.001 ±0.001 ±0.001 ±0.002

raw 0.0002 0.0005 0.0004 0.0012 0.0017 0.0008 0.0037

MTE 125°C / 5.1MPa 0.0002 0.0005 0.0004 0.0010 0.0009 0.0008 0.0037

MTE 150°C / 5.1MPa 0.0002 0.0005 0.0004 0.0010 0.0008 0.0006 0.0037

MTE 180°C / 5.1MPa 0.0002 0.0004 0.0004 0.0010 0.0008 0.0007 0.0037

MTE 200°C / 5.1MPa 0.0002 0.0005 0.0004 0.0010 0.0007 0.0007 0.0037

MTE 250°C / 5.1MPa 0.0001 0.0004 0.0004 0.0008 0.0007 0.0005 0.0033

MTE 150°C / 2.5MPa 0.0002 0.0004 0.0004 0.0010 0.0009 0.0007 0.0036

MTE 150°C / 5.1MPa 0.0002 0.0005 0.0004 0.0010 0.0008 0.0006 0.0037

MTE 150°C / 12.7MPa 0.0002 0.0004 0.0004 0.0010 0.0007 0.0006 0.0037

MTE 150°C / 25.0MPa 0.0002 0.0005 0.0004 0.0009 0.0007 0.0006 0.0037

raw 0.00004 0.00011 0.00010 0.00029 0.00039 0.00020 0.00087

HTD 180°C 0.00004 0.00011 0.00010 0.00025 0.00026 0.00017 0.00087

HTD 200°C 0.00004 0.00011 0.00010 0.00020 0.00022 0.00017 0.00084

HTD 230°C 0.00004 0.00011 0.00010 0.00020 0.00017 0.00014 0.00083

HTD 250°C 0.00004 0.00011 0.00010 0.00020 0.00013 0.00014 0.00083

HTD 280°C <0.00001 0.00010 0.00010 0.00016 0.00008 0.00013 0.00080

HTD 300°C <0.00001 0.00010 0.00007 0.00011 0.00004 0.00010 0.00077

HTD 320°C <0.00001 0.00009 0.00004 0.00007 0.00004 0.00010 0.00070

HTD 350°C <0.00001 0.00007 0.00002 0.00003 0.00002 0.00006 0.00060

SD 130°C 0.00004 0.00009 0.00010 0.00029 0.00039 0.00020 0.00087

SD 150°C 0.00004 0.00009 0.00010 0.00028 0.00034 0.00020 0.00086

SD 180°C 0.00004 0.00011 0.00010 0.00028 0.00030 0.00019 0.00086

SD 200°C 0.00004 0.00011 0.00010 0.00028 0.00030 0.00017 0.00086

SD 230°C 0.00004 0.00009 0.00010 0.00028 0.00021 0.00017 0.00082

SD 250°C 0.00004 0.00009 0.00010 0.00024 0.00017 0.00013 0.00080

SD 280°C 0.00003 0.00008 0.00009 0.00023 0.00016 0.00013 0.00077

SD 300°C 0.00003 0.00008 0.00009 0.00018 0.00015 0.00012 0.00075

SD 310°C 0.00003 0.00008 0.00009 0.00018 0.00015 0.00012 0.00072

SD 320°C 0.00003 0.00009 0.00006 0.00010 0.00018 0.00012 0.00070

SD 330°C 0.00003 0.00010 0.00008 0.00017 0.00018 0.00011 0.00065

SD 350°C 0.00003 0.00009 0.00005 0.00012 0.00016 0.00008 0.00058

ation of inorganics in product waters

279

APPENDIX J Table J.1 Molarity concentration of inorganics present for the product water from MTE processing 100g of wet raw lignite (i.e. 40g db lignite; all values are in M)

Table J.2 Molarity concentration of inorganics present for the product water from HTD and SD processing 10g of dried raw lignite (All values are in M)


(mL)

Na Ca K Mg Cl SO42-

Process

condition Amount of

water removed(mL)

Na Ca K Mg Cl SO42-

MTE 125°C / 5.1MPa 32.3 0.019 0.0008 0.001 0.001 0.018 0.002 HTD 200°C 0.7 0.041 0.001 0.005 0.004 0.043 0.004

MTE 150°C / 5.1MPa 40.2 0.018 0.0006 0.001 0.001 0.017 0.002 HTD 250°C 2.4 0.054 0.001 0.005 0.004 0.054 0.006

MTE 180°C / 5.1MPa 42.6 0.018 0.0006 0.001 0.001 0.016 0.002 HTD 280°C 3.8 0.068 0.002 0.006 0.005 0.066 0.008

MTE 200°C / 5.1MPa 45.1 0.018 0.0004 0.001 0.001 0.016 0.002 HTD 300°C 5.8 0.094 0.002 0.006 0.005 0.088 0.010

MTE 250°C / 5.1MPa 51.8 0.016 0.0004 0.001 0.001 0.015 0.002 HTD 320°C 8.2 0.14 0.003 0.008 0.006 0.13 0.015

HTD 35 °C 0 10.9 0.34 0.008 0.011 0.009 0.32 0.034

MTE 150°C / 2.5MPa 31.7 0.019 0.001 0.001 0.001 0.019 0.002

MTE 150°C / 5.1MPa 40.2 0.018 0.001 0.001 0.001 0.017 0.002 SD 150°C 2.3 0.010 0.001 0.001 0.001 0.007 0.002

MTE 150°C / 12.7MPa 42.9 0.017 0.001 0.001 0.001 0.016 0.002 SD 180°C 4.8 0.016 <0.001 0.001 0.002 0.015 0.002

MTE 150°C / 25.0MPa 45.1 0.018 0.001 0.001 0.001 0.017 0.002 SD 200°C 6.8 0.020 <0.001 0.001 0.002 0.017 0.003

SD 230°C 8.7 0.021 <0.001 0.001 0.002 0.017 0.003

a = Total mass only includes the inorganics and not the total organic carbon mass SD 250°C 11.2 0.019 <0.001 0.001 0.001 0.015 0.003

SD 280°C 13.2 0.019 0.001 0.001 0.002 0.018 0.002

SD 300°C 13.7 0.020 0.001 0.001 0.002 0.020 0.002

Note: SD 130°C has not been included in this table because it did not undergo any SD 310°C 14.2 0.019 0.001 0.001 0.001 0.020 0.002

moisture reduction relative to the raw lignite and hence the concentration of inorganics SD 320°C 14.5 0.019 0.001 0.001 0.001 0.020 0.002

could not be calculated SD 330°C 14.7 0.019 0.001 0.001 0.001 0.021 0.002

SD 350°C 14.8 0.019 0.001 0.001 0.001 0.022 0.002


Appendix J: Molarity concentr

Appendix K: Calculations of carbonate and bicarbonate ion concentration

280

APPENDIX K Calculation of carbonate and bicarbonate ion

concentration in product water. If water is in equilibrium with an atmosphere containing the usual amount of CO2

(~10-3.5 atm) then at ~25°C, [CO2]tot = ~10-5 M (with known Henry’s law

constraints) [422].

[CO2]tot = [CO2] + [H2CO3]

H2CO3 is a polyprotic acid, but at pH ~5.5, the concentration of CO32- is negligible

so that the equilibrium HCO3- = H+ + CO3

2- does not have to be taken into account.

Thus tot2

3

][CO]][H[HCO +−

= 4.2 x 10-7

[HCO3-] ~ 6

57

3x1010 x 10 x 4.2

−

−−

at pH 5.5, and the expected level of CO2 in the water.

[HCO3-] = 1.4 x 10-6 M = 1.4 x 10-3 mM

We have ~40mL of water removed from 100g of wet raw lignite.

This will contain 1.4 x 10-3 x 0.04 = 5.6 x 10-5 moles

Univalent ion as [HCO3-] = 0.056mmol

This is too small (by a factor of 10) to explain the difference between the positive

and negative ion concentration.

Appendix L: Proximate Analysis of HTD, MTE and SD products

281

APPENDIX L Proximate analysis of HTD, MTE and SD products

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

Time (seconds)

Wei

ght l

oss

(%)

0

100

200

300

400

500

600

700

800

900

1000

0 600 1200 1800 2400 3000 3600 4200 4800 5400 6000

Tem

pera

ture

(ºC

)

HTD 350ºCHTD 320ºCHTD 300ºCHTD 280ºCHTD 250ºCHTD 200ºCTemperature

AIRArgon

Figure L.1 Proximate analysis of HTD products processed at different temperatures. 30mLmin-1 air flow, 30.0mg sample

Figure L.2 Heat Flow of HTD products processed at different temperatures. 30mLmin-1 air flow, 30.0mg sample (from proximate analysis).

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IGNITION


282

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Argon AIR

Figure L.3 Proximate analysis of MTE products processed at different temperatures, 30mLmin-1 air flow, 30.0mg sample

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Argon AIR

Figure L.4 Heat flow of MTE products processed at different temperatures, 30mLmin-1 air flow, 30.0mg sample

Figure L.4 Heat flow of MTE products processed at different temperatures, 30mLmin-1 air flow, 30.0mg sample


283

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Tem

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(ºC

)MTE 150ºC/2.5MPaMTE 150ºC/5.1MPaMTE 150ºC/12.7MPaMTE 150ºC/25MPaTemperature

AIRArgon

Figure L.5 Proximate analysis of MTE products processed at different mechanical pressures, 30mLmin-1 air flow, 30.0mg sample

sed at different mechanical pressures,

sed at different mechanical pressures,

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MTE 150ºC/2.5MPaMTE 150ºC/5.1MPaMTE 150ºC/12.7MPaMTE 150ºC/25MPaTemperature

Argon AIR

Figure L.6 Heat Flow of MTE products procesFigure L.6 Heat Flow of MTE products proces30mLmin-1 air flow, 30.0mg sample 30mLmin-1 air flow, 30.0mg sample


284

igure L.8 Heat Flow of SD products processed

Figure L.7 Proximate analysis of SD products processed at different temperatures, 30mLmin-1 air flow, 30.0mg sample

F at different temperatures, 30mLmin-1 air flow, 30.0mg sample

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Tem

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(ºC

)

Weight loss 130°CWeight loss 150°CWeight loss 180°CWeight loss 200°CWeight loss 230°CWeight loss 250°CWeight loss 280°CWeight loss 300°CWeight loss 310°CWeight loss 320°CWeight loss 330°CWeight loss 350°CTemperature

TemperatureSteam dried 350°CSteam dried 330°CSteam dried 320°CSteam dried310°CSteam dried 300°CSteam dried 280°CSteam dried 250°CSteam dried 230°CSteam dried 200°CSteam dried 180°CSteam dried 150°CSteam dried 130°C

Argon AIR

Argon AIR

Appendix M: Combustion of MTE, HTD and SD products

285

APPENDIX M Combustion of MTE, HTD and SD products


2000 3000 4000 5000-100

-80

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1a

125°C / 5.1MPa, 150°C / 5.1MPa, 180°C / 5.1MPa, 200°C / 5.1MPa, 250°C / 5.1MPa

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(%)

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0.10

1c

Spe

cific

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(min

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Conversion (daf)

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0.08

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Conversion (daf)

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(min

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0.15

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0.30

3c

Conversion (daf)

Spe

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(min

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Figure M.1 Combustion of MTE products produced at different processing temperatures ranging from 125°C to 250°C.



286

2000 3000 4000 5000-100

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150°C / 2.5MPa, 150°C / 5.1MPa, 150°C / 12.7MPa, 150°C / 25.0MPa

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ght l

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(%)

Time (sec)

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(min

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(min

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0.15

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0.25

0.30 3c

Conversion (daf)

Spe

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tivity

(min

-1)

Figure M.2 Combustion of MTE products produced at different applied pressures ranging from 2.1MPa to 25.0MPa.



287

2000 3000 4000 5000-100

-80

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raw, 200°C, 250°C, 280°C, 300°C, 320°C, 350°C

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(%)

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Time (sec)

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w (m

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Time (sec)

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(min

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(min

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0.5

0.6

3c

Spe

cific

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tivity

(min

-1)

Conversion (daf)

Figure M.3 Combustion of HTD products produced at different processing temperatures ranging from 200°C to 350°C.



288

HTD and SD products

289

Appendix M: Combustion of MTE,

Figure M.4 Combustion of SD products produced at different processing temperatures ranging from 130°C to 350°C. (1) 90-125μm particle size, combustion at 400°C (a) weight loss versus time (b) heat flow versus time (c) specific reactivity versus conversion (2) 250-500μm particle size, combustion at 400°C (a) weight loss versus time (b) heat flow versus time (c) specific reactivity versus conversion (3) 250-500μm particle size, combustion at 450°C (a) weight loss versus time (b) heat flow versus time (c) specific reactivity versus conversion

1500 2000 2500 3000 3500 4000 4500 5000-100

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raw SD 130°C SD 250°C SD 300°C SD 350°C

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Conversion (daf)

Spec

ific

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(min

-1)

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Conversion (daf)

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(min

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0.6

0.8 raw SD 130°C SD 250°C SD 300°C SD 350°C

3c

Conversion (daf)

Spe

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(min

-1)

Appendix N: Multiple regression analysis

290

APPENDIX N

Multiple regression analysis Multiple regression analysis is a statistical tool for the investigation of relationships

between variables. The objective of multiple regression analysis is to establish which

of the set of independent variables (proximate, ultimate, inorganic elemental analysis

etc) has a proportional effect on a dependent variable (eg combustion reactivity area

values). Multiple regression analysis can establish the relative predictive importance

of the independent variables (by comparing beta weights) and the significance of

each of the relationships (through a significance test of R2). Furthermore, the level of

significance by adding more than one independent variable (eg Na + Fe) to the model

can be tested. Using hierarchical regression, the most variance in the dependent

variable (combustion reactivity) can be determined by one or a set of independent

variables. The estimates (b coefficients and constant) can be used to construct a

prediction equation and generate predicted scores on for the independent variable(s).

Multiple regression analysis provides a predictive equation:

Y= a+b1x1+ b2x2+……+bnxn

Where, a = constant

The constant is where the regression line intercepts the y axis, representing

the amount the dependent y will be when all the independent variables are 0.

Appendix N: Multiple regression analysis

291

b1, b2, ….. bn = beta coefficient or standardized partial regression coefficients.

The beta regression coefficients, represent the amount the dependent variable

y changes when the corresponding independent changes by 1 unit (i.e.

reflecting the relative impact on the dependant variable)

x1, x2, ….. xn = scores on different predictors.

The ratio of the beta coefficients is the ratio of the relative predictive power

of the independent variables.

The multiple correlation (R2) is the percent of variance in the dependent variable

explained collectively by all of the independent variables.

Appendix O: SEMs of Latrobe Valley raw lignites

292

APPENDIX O LYHNa raw lignite

0.00 3.00 6.00 9.00 12.00 15.00 18.00 21.00

keV

020

0

150

300

450

600

750

900

1050

1200

1350

1500

Cou

nts

C

N

O

NaMg

Al

SiP

S

ClCl

KKCa

Ca

TiTi

TiTi

Fe

Fe Fe

Appendix O: SEMs of Latrobe Valley raw lignites

293

YEFFe raw lignite

0.00 3.00 6.00 9.00 12.00 15.00 18.00 21.00

keV

023

0

800

1600

2400

3200

4000

4800

5600

6400

Cou

nts

C

N

O

NaMg

AlSi

PSClCl

KKCa

CaTiTi

TiTi

Fe

Fe Fe

Appendix P: SEMs of ash from Latrobe Valley raw lignites

294

APPENDIX P LYLA ashed at 500°C

Element (keV) mass% Error% At%

C K 0.277 26.37

0.15 37.86

O K 0.525 41.34 0.22 44.57

Na K 1.041 5.73 0.12 4.30

Mg K 1.253 4.25 0.10 3.02

Al K 1.486 2.31 0.09 1.48

Si K 1.739 1.60 0.09 0.98

P K 2.013 0.10 0.08 0.05

S K 2.307 7.53 0.07 4.05

Cl K 2.621 0.06 0.08 0.03

K K 3.312 0.23 0.10 0.10

Ca K 3.690 2.62 0.11 1.13

Ti K 4.508 0.15 0.14 0.05

Fe K 6.398 7.71 0.25 2.38

0.00 3.00 6.00 9.00 12.00 15.00 18.00 21.00

keV

002

0

300

600

900

1200

1500

1800

2100

2400

2700

3000

Cou

nts

C

N

O

NaMg

AlSi

P

S

ClCl

KKCa

Ca

Ti

Ti

TiTi

Fe Fe

Fe

Total 100.00 100.00


295

LYMNa ashed at 500°C


C K 0.277 21.17

0.19 30.73

O K 0.525 40.24 0.19 43.84

Na K 1.041 13.93 0.10 10.56

Mg K 1.253 5.68 0.10 4.07

Al K 1.486 5.99 0.09 3.87

Si K 1.739 1.71 0.09 1.06

P K 2.013 0.15 0.08 0.09

S K 2.307 9.02 0.07 4.90

Cl K 2.621 0.44 0.08 0.21

K K 3.312 0.09 0.10 0.04

Ca K 3.690 1.08 0.11 0.47

Ti K 4.508 0.02 0.14 0.01

Fe K 6.398 0.48 0.25 0.15 0.00 3.00 6.00 9.00 12.00 15.00 18.00 21.0

keV

009

0

150

300

450

600

750

900

1050

1200

Cou

nts

C

N

ONa

MgAl

Si

P

S

ClCl

KKCa

CaTi

Ti

TiTi

Fe

Fe Fe

Total 100.00

100.00


296

LYHNa ashed at 500°C

0.00 3.00 6.00 9.00 12.00 15.00 18.00 21.00

keV

001

0

300

600

900

1200

1500

1800

2100

2400

Cou

nts

C

N

O

Na

Mg

AlSi

P

S

ClCl

KKCa

Ca

Ti

Ti

TiTi

Fe

FeFe


C K 0.277 41.34 0.12 52.55

O K 0.525 37.13 0.30 35.43

Na K 1.041 8.18 0.13 5.43

Mg K 1.253 4.97 0.11 3.12

Al K 1.486 0.35 0.11 0.20

Si K 1.739 0.39 0.10 0.21

P K 2.013 0.02 0.09 0.01

S K 2.307 4.11 0.07 1.96

Cl K 2.621 0.19 0.09 0.08

K K 3.312 0.03 0.11 0.01

Ca K 3.690 0.88 0.13 0.33

Ti K 4.508 0.00 0.16 0.00

Fe K 6.398 2.38 0.30 0.65

Total 100.00 100.00


297

Morwell MTE ashed at 500°C


C K 0.277 15.61

0.17 25.44

O K 0.525 39.99 0.29 48.93

Na K 1.041 3.74 0.16 3.19

Mg K 1.253 9.63 0.13 7.75

Al K 1.486 1.38 0.12 1.00

Si K 1.739 0.27 0.11 0.19

P K 2.013 0.06 0.10 0.04

S K 2.307 5.25 0.08 3.20

Cl K 2.621 1.03 0.09 0.57

K K 3.312 0.29 0.12 0.15

Ca K 3.690 11.31 0.13 5.52

Ti K 4.508 0.15 0.17 0.06

Fe K 6.398 11.29 0.31 3.96 0.00 3.00 6.00 9.00 12.00 15.00 18.00 21.00

keV

016

0

150

300

450

600

750

900

1050

Cou

nts

C

N

O

Na

Mg

AlSi

P

S

Cl

ClK

K

Ca

Ca

Ti

Ti

TiTi

FeFe

Fe

Total 100.00 100.00


298

MMg ashed at 500°C


C K 0.277 23.58

0.13 34.25

O K 0.525 41.21 0.25 44.93

Na K 1.041 5.32 0.11 4.04

Mg K 1.253 11.15 0.09 8.00

Al K 1.486 0.85 0.10 0.55

Si K 1.739 0.66 0.09 0.41

S K 2.307 4.55 0.06 2.47

Cl K 2.621 1.24 0.07 0.61

K K 3.312 0.12 0.10 0.05

Ca K 3.690 9.32 0.11 4.06

Ti K 4.508 0.19 0.14 0.07

Fe K 6.398 1.81 0.26 0.57

Total 100.00 100.00 0.00 3.00 6.00 9.00 12.00 15.00 18.00 21.00

keV

011

0

150

300

450

600

750

900

1050

1200

1350

1500

Cou

nts

C

N

O

Na

Mg

AlSi

P

S

Cl

ClKK

Ca

CaTi

Ti

TiTi

Fe

FeFe


299

Yallourn MTE ashed at 500°C


C K 0.277 22.30

0.15 35.13

O K 0.525 37.55 0.25 44.41

Na K 1.041 2.49 0.17 2.05

Mg K 1.253 8.15 0.13 6.34

Al K 1.486 0.34 0.12 0.24

Si K 1.739 0.18 0.11 0.12

P K 2.013 0.02 0.10 0.01

S K 2.307 4.03 0.08 2.38

Cl K 2.621 0.65 0.09 0.35

K K 3.312 0.29 0.11 0.14

Ca K 3.690 5.18 0.13 2.45

Ti K 4.508 0.08 0.16 0.03

Fe K 6.398 0.30 6.36 0.00 3.00 6.00 9.00 12.00 15.00 18.00 21.0

keV

006

0

150

300

450

600

750

900

1050

1200

1350

Cou

nts

C

N

O

Na

Mg

AlSi

P

S

ClCl

KK

Ca

CaTi

Ti

TiTi

Fe Fe

Fe

Total 100.00 100.00


300

YTP ashed at 500°C


C K 0.277 33.57

0.11 45.82

O K 0.525 39.08 0.23 40.05

Na K 1.041 1.34 0.11 0.96

Mg K 1.253 4.14 0.08 2.79

Al K 1.486 8.61 0.08 5.23

Si K 1.739 0.06 0.08 0.04

P K 2.013 0.00 0.07 0.00

S K 2.307 3.70 0.06 1.89

Cl K 2.621 0.05 0.07 0.02

K K 3.312 0.07 0.09 0.03

Ca K 3.690 3.27 0.10 1.34

Ti K 4.508 0.71 0.13 0.24

Fe K 6.398 5.39 0.23 1.58 0.00 3.00 6.00 9.00 12.00 15.00 18.00 21.00

keV

003

0

150

300

450

600

750

900

1050

1200

Cou

nts

C

N

O

Na

Mg

Al

SiP

S

ClCl

KK

Ca

CaTi

Ti

TiTi

Fe

Fe

Fe

Total 100.00 100.00


301

YTD ashed at 500°C


C K 0.277 10.27

0.22 17.57

O K 0.525 42.03 0.24 54.00

Na K 1.041 3.10 0.19 2.77

Mg K 1.253 7.76 0.14 6.56

Al K 1.486 6.95 0.14 5.29

Si K 1.739 0.00 0.00 0.00

P K 2.013 0.13 0.12 0.09

S K 2.307 6.86 0.09 4.40

Cl K 2.621 0.16 0.11 0.09

K K 3.312 0.10 0.13 0.05

Ca K 3.690 5.78 0.15 2.96

Ti K 4.508 0.12 0.19 0.05

Fe K 6.398 16.74 0.34 6.16 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00

keV

005

0

100

200

300

400

500

600

700

800

900

1000

Cou

nts

CN

O

Na

MgAl

Si P

S

ClCl

K K

Ca

Ca

TiTi

Ti Ti

Fe

Fe

Fe

Total 100.00 100.00


302

YEFFe ashed at 500°C


C K 0.277 16.67 0.17 26.78

O K 0.525 41.95 0.22 50.60

Na K 1.041 4.45 0.18 3.74

Mg K 1.253 8.60 0.14 6.82

Al K 1.486 0.49 0.13 0.35

Si K 1.739 0.18 0.12 0.13

P K 2.013 0.05 0.10 0.03

S K 2.307 5.64 0.08 3.40

Cl K 2.621 0.16 0.09 0.08

K K 3.312 0.15 0.12 0.08

Ca K 3.690 3.71 0.14 1.79

Ti K 4.508 0.05 0.17 0.02

Fe K 6.398 17.90 0.31 6.18

0.00 3.00 6.00 9.00 12.00 15.00 18.00 21.00

keV

007

0

200

400

600

800

1000

1200

1400

1600

1800

Cou

nts

C

N

O

Na

Mg

AlSi

P

S

ClCl

KK

CaCa

Ti

Ti

TiTi

Fe Fe

Fe

Total 100.00 100.00


303

YEFDark ashed at 500°C


C K 0.277 26.85 0.12 40.74

O K 0.525 35.40 0.24 40.32

Na K 1.041 2.50 0.14 1.98

Mg K 1.253 7.15 0.11 5.36

Al K 1.486 0.95 0.10 0.64

Si K 1.739 0.49 0.09 0.32

P K 2.013 0.00 0.00 0.00

S K 2.307 4.37 0.07 2.48

Cl K 2.621 0.51 0.08 0.26

K K 3.312 0.20 0.10 0.09

Ca K 3.690 5.84 0.11 2.66

Ti K 4.508 0.03 0.14 0.01

Fe K 6.398 15.70 0.26 5.12

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00

keV

013

0

100

200

300

400

500

600

700

800

900

1000

Cou

nts

C

N

O

Na

Mg

AlSi

P

S

ClCl

KK

Ca

CaTi

Ti

Ti Ti

Fe

Fe

Fe

Total 100.00 100.00

Reference List

304

APPENDIX Q Abbreviations and Glossary

SECV

State Electricity Commission of Victoria

HRL Herman Research Laboratories

EERC Energy and Environmental Research Center

JGC

Japan Com.

Japan Gasoline Company Corporation

Japan Communication Company

HTD Hydrothermal dewatering

MTE

SFBD

Mechanical Thermal Expression

Steam Fluidised Bed Drying

PDU Process Development Unit

UBC Upgrading Brown Coal

LRC Low Rank Coal

Ash The inorganic material left behind after combustion of the

coal

Volatile matter Material given off when heated in an inert atmosphere

Fixed carbon The coal mass (char) remaining after devolatisation

Reference List

305

Lithotype A band of coal which has defined appearance and

properties e.g. colour, hardness, weathering pattern.

Differences in lithotype are believed to correspond to

differences in depositional environment.

Lignite Coal with a gross calorific value (a.f.m.) of less than

19.30MJ/kg (U.S. classification).

Intra-particle porosity

Pore radius of less than 1μm

(the porosity within a coal particle)

elutriation The process of separating the lighter particles of a powder

from the heavier ones by means of an upward directed

stream of fluid (gas or liquid).

CWM Coal-Water Mixture

CWR Coal-Water Ratio

wb wet basis

db dry basis

daf dry ash free basis

wt% Percentage weight

MHC Moisture Holding Capacity

TOC Total Organic Carbon

AAS Atomic Absorption Spectrophotometry

TGA Thermogravimetric Analysis

Reference List

306

DSC Differential Scanning Calorimetry

NWSE Net Wet Specific Energy

SS Stainless Steel

™ Trademark

Loy Yang Loy Yang lignite – Latrobe Valley

Morwell Morwell lignite – Latrobe Valley

Yallourn Yallourn lignite – Latrobe Valley

Reference List

307

REFERENCES 1. ACIL Tasman, Australia, (2003) 'SRMC and LRMC of Generators in the

NEM : A report to the IPC and NEMMCO.'

2. Electricity Supply Association of Australia Limited (ESAA), (2000) 'Electricity

Australia 2000.'

3. St Baker, T. C., and Juniper, L. A. (1982) 'Combustion utilization assessment

of brown coals and lignites.' Australian Coal Geology, 4, 187-201.

4. State Electricity Commission of Victoria, Office of Corporate Relations,

(1980) 'Victoria's thermal power.'

5. Aho, M. J., and Pirkonen, P. M. (1993) 'Efficiency and environmental effects

of peat dewatering by mechanical pressing.' Fuel, 72, 239-243.

6. Jonsson, B., Pattersson, E., and Lindman, B. (1987) 'Mechanical dewatering

of peat.' Fuel, 66, 785-793.

7. Luukkainen, V. M. (1993) 'Artificial dewatering of peat. Part 6. Peat

production methods for the mechanical dewatering process.' VTT Tied, 1526,

1-43.

8. Joensson, B., Petersson, E., and Lindman, B. (1987) 'Mechanical dewatering

of peat.' Fuel, 66 (6), 785-793.

9. Readett, D. J., Quast, K. B., Hall, S. F., and Ketteridge, I. B. (1987)

'Mechanical beneficiation of Bowmans brown coal', Chemeca '87,

Melbourne, Victoria, Australia, R5.1, 1-12.

10. Banks, P. J., and Burton, D. R. (1984) 'Behaviour of brown coal in press

dewatering', Proceedings of the Australian Coal Science Conference,

Churchill, Victoria, Australia, 199-206.

Reference List

308

11. Banks, P. J., and Burton, D. R. (1989) 'Press dewatering of brown coal : Part

1 - Exploratory studies.' Drying Technology, 7(3), 443-476.

12. Hall, S. F., Quast, K. B., and Readett, D. J. (1988) 'Sorption isotherms of

pretreated brown coal', Final Report submitted to the Coal Corporation of

Victoria.

13. Guo, J., Hodges, S., and Uhlherr, P. H. T. (1996) 'Increasing solids

concentration of brown coal by mechanical expression', Proceedings of the

7th Australian Coal Science Conference, Gippsland, Victoria, Australia, 583-

590.

14. Guo, J., Hodges, S., and Uhlherr, P. H. T. (1996) 'Pore destruction and

dewatering of HTD coal slurry', Proceedings of the 3rd Annual Conference :

Coorperative Research Centre for New Technologies for Power Generation

from Low Rank Coal, University of Adelaide, Waite Campus, Adelaide,

Australia, 123-128.

15. Guo, J. (2000) 'Hydrothermal-mechanical dewatering of brown coal', Monash

University, Melbourne, Victoria, Australia.

16. Favas, G., Kealy, T., Chaffee, A. L., and Tiu, C. (2001) 'Mechanical Thermal

Expression - Effect of kneading coal prior to MTE processing', 18th Annual

International Pittsburgh Coal Conference, Newcastle, New South Wales,

Australia.

17. Rammler, E., Kropfe, E., and Scholle, H. (1966) 'Briquetting of brown coal

from Kolubra (Yugoslavia) by the Fleissner process.' Freiberger

Forschungsh, 364, 31-65.

18. Lovrecek, I., and Beer, E. (1962) 'Drying of lignite under pressure.' Technicki

Pregled, 14, 17-27.

Reference List

309

19. Strauss, K., Berger, C. B., Bielfeldt, F. B., Erken, M., and Hoffman, M. (1996)

'Mechanical/thermal dewatering as a pre-drying stage for brown coal fired

power plants.' VDI Berichte, 1280, 165-173.

20. Bohlmann, M., Strauss, K., Bergins, C., and Berger, S. (1999)

'Mechanical/thermal dewatering and its beneficial effects on efficiency and

performance of lignite fired power stations', Flame Days '99; Combustion and

the Environment International Conference, Prague, Czech Republic, 135-

142.

21. Berger, S., Bergins, C., Strauss, K., Bielfeldt, F. B., Elsen, R. O., and Erken,

M. (1999) 'Mechanical/thermal dewatering of brown coal', VGB PowerTech

99, 2, 44-49.

22. Strauss, K. (1996) 'Method and device for reducing the water content of

water-containing brown coal', Patent No. WO 96/10064.


water-containing brown coal', Patent No. AU695187.

24. Strauss, K. (1997) 'Process for reducing the water content of lignite', Patent

No. WO9731082.


water-containing brown coal', Patent No. EP0784660B1.

26. Bergins, C. (2003) 'Kinetics and mechanism during mechanical/thermal

dewatering of lignite.' Fuel, 82 (4), 355-364.

27. Clayton, S., Hoadley, A., Tiu, C., Huynh, S., and McIntosh, M. (2003)

'Development of a laboratory scale continuous MTE process', Proceedings of

the 10th Annual Conference : Coorperative Research Centre for Clean

Power from Lignite, Swinburne University of Technology, Melbourne,

Victoria, Australia, 19-24.

Reference List

310

28. Huynh, D., Huynh, S., Ellis, H., Kazi, A., and McIntosch, M. (2003)

'Development program of MTE lignite dewatering process', Proceedings of

the 10th Annual Conference : Coorperative Research Centre for Clean

Power from Lignite, Swinburne University of Technology, Melbourne,

Victoria, Australia, 25-30.

29. Huynh, S., McIntosch, M., and Huynh, D. (2003) 'Process design

considerations for MTE plant', Proceedings of the 10th Annual Conference :

Coorperative Research Centre for Clean Power from Lignite, Swinburne

University of Technology, Melbourne, Victoria, Australia, 31-36.

30. Brockway, D. J., and Jackson, P. J. (2003) 'Improving the efficiency of lignite

based power generation', 12th International Conference on Coal Science,

Cairns, Australia.

31. McIntosch, M. (2001) 'Advanced power generation technologies for lignite

including repowering of boiler plant', Australia-China Workshop on Clean

Power from Coal with Maximised Efficiency, Taiyuan, China.

32. Kakaras, E., Ahladas, P., and Syrmopoulos, S. (2002) 'Computer simulation

studies for the integration of an external dryer into a Greek lignite-fired power

plant.' Fuel, 81, 583-593.

33. Okuma, O., Inoue, T., Yasumuro, M., Shindo, A., Hirano, T., and Matsumura,

T. (1993) 'Hydrothermal pretreatment of Victorian brown coal for liquefaction',

3rd Japan/Australian Joint Technical Meeting on Coal, Brisbane, Australia

34. Fleissner, H. (1927) 'The drying of fuels and the Austrian coal industry.'

Sonderduck Sparwirtschaft, 10 & 11.

35. Fleissner, H. (1927) 'Method of drying coal and the like', Patent No.

US1632829.

36. Fleissner, H. (1928) 'Method of drying coal and like fuels', Patent No.

US1679078.

Reference List

311

37. Bainbridge, J. R., and Satchwell, K. (1947) 'Experiments in Fleissner drying

Victorian brown coal.' Fuel, 26, 28-38.

38. Fohl, J., Lugscheider, W., and Wallner, F. (1987) 'Removal of moisture from

brown coal. 1. Basic principles and thermal drying process.' Braunkohle, 39,

46-47.

39. Fohl, J., Lugscheider, W., Tessmer, G., and Wallner, F. (1987) 'Removal of

moisture from brown coal. 2. Thermal dehydration.' Braunkohle, 39, 78-87.

40. Anderson, C. M., DeWall, R. A., Ljubicic, B. R., Musich, M. A., and Richter, J.

J. (1994) 'Preparation and combustion of Yugoslavian lignite-water fuel', DE-

FC21-86MC10637, Energy and Envirnomental Research Centre, University

of North Dakota, Grand Forks, North Dakota, USA.

41. Guzijan, D., Borojevic, S., and Ninkovic, R. (1989) 'The complex testings of

the coal drying system in the Fleissner type of drying plant.' Journal of

Aerosol Science, 20 (8), 1469-1472.

42. Evans, D. G., and Siemon, S. R. (1970) 'Dewatering of brown coal before

combustion.' Journal of the Institute of Fuel, 43, 413-419.

43. Evans, D. G., and Siemon, S. R. (1970) 'Separation of water from solid

organic materials', Patent No. AU 430626.

44. Evans, D. G., and Siemon, S. R. (1971) 'The separation of water from solid

organic materials', Patent No. US 3552031.

45. Murray, J. B., and Evans, D. G. (1972) 'The brown-coal/water system: Part 3.

Thermal dewatering of brown coal.' Fuel, 51, 290-296.

46. Potas, T. A., and Anderson, C. M. (1988) 'Rheology of low-ash, hot-water

dried coal/water fuels', 13th International conference on coal and slurry

technology, Denver, USA

47. Sears, R. E., Baker, G. G., Maas, D. J., Potas, T. A., and Patel, R. (1985)

'Production and combustion of hot-water dried low-rank coal slurries', 13th

Reference List

312

Biennial Lignite Symposium on Technology and Use of Low-Rank Coal,

Bismark, North Dakota, USA, DOE/FE/60181-60130.

48. Potas, T. A., Sears, R. E., Maas, D. J., Baker, G. G., and Willson, W. G.

(1984) 'Preparation of hydrothermally treated LRC-water fuel slurries',

DOE/FE/60181-95, United States Department of Energy Office of Fossil

Energy Morgantown Energy Technology Center, Grand Forks, North Dakota,

USA.

49. Olson, E. S., Maas, D. J., Potas, T., Malterer, T. J., and Smit, F. J. (1987)

'Low-ash, low-rank coal/water fuel', 4th Annual Pittsburgh Coal Conference,

Pittsburgh, Pennsylvania, USA.

50. Swanson, M. L., Musich, M. A., and Tibbetts, J. E. (2004) 'Coal-water fuels

from Chinese low-rank coals', 21st Annual International Pittsburgh Coal

Conference, Osaka, Japan Session 39-5, 1-9.

51. Anderson, B. (1991) 'Hydrothermal drying of brown coal', 1st

Japan/Australian Joint Technical Meeting on Coal, Melbourne, Australia, 1-7.

52. Anderson, B. (1993) 'Hydrothermal dewatering of brown coal: Pilot plant

results', 3rd Japan/Australia Joint Technical Meeting on Coal, Gazebo Hotel,

Brisbane, Australia.

53. Anderson, B., and Johnson, T. R. (1993) 'Hydro-thermal dewatering of low-

rank coal for use in a direct fired gas turbine', 3rd Japan/Australia Joint

Technical Meeting on Coal, Gazebo Hotel, Brisbane, Australia, 1-12.

54. Woskoboenko, F., and Allardice, D. J. (1996) 'Hydrothermal dewatering of

low rank coals and slurry rheology', Australian-Indonesian Low Rank Coal

Science and Technology Workshop, Jakarta, Indonesia, 1-19.

55. Shibata, K., Yui, M., Hashimoto, N., and Takinami, T. (1994) 'Project for

development of low-rank coals upgrading and their CWM producing

technology', Coal Slurry Technology Research Centre, Japan.

Reference List

313

56. Shibata, K., and Tsurui, M. (1996) 'Low rank coals upgrading and CWM

production technology', 6th Japan-Australia Joint Technical Meeting on Coal,

Sapporo, Japan, 45-56.

57. Yui, M., Shibata, K., Katagiri, T., and Hashimoto, N. (1995) 'Development for

production technology of CWM from low-rank coals', 20th International

technical conference on coal utilization and fuel systems, Clearwater, FL,

United States 125-137.

58. Hashimoto, N., Katagiri, T., Shibata, K., and Imai, T. (1994) 'CWM

production by low rank coals upgrading', IEA-CLM Workshop'94 on Coal

Water Mixture (CWM) for Advanced Coal Utilization toward the

Environmentally Friendly System, Tsukuba City, Ibaraki, Japan 283-291.

59. Favas, G., Jackson, W. R., and Marshall, M. (2003) 'Hydrothermal

dewatering of lower rank coals. 3. High-concentration slurries from

hydrothermally treated lower rank coals.' Fuel, 82, 71-79.

60. Shibata, K., Hashimoto, N., and Sugiyama, T. (1996) 'CWM production by

low rank coals upgrading', Florida, USA, 233-244.

61. Herman, H. 'Brown coal' (1952) ed. Publisher: State Electricity Commision

of Victoria

62. Rozgonyi, T. G., and Szigeti, L. (1985) 'Upgrading of high moisture content

lignite using saturated steam.' Fuel Processing Technology, 10, 1-18.

63. Potter, O. E., and Keogh, A. J. (1979) 'Cheaper power from high-moisture

brown coals Part I and II.' Journal Institute of Fuel, 143, 143-149.

64. Potter, O. E., and Keogh, A. J. (1981) 'Drying high-moisture coals before

liquefaction or gasification.' Fuel Processing Technology, 4, 217-227.

65. Xi-Guang, L., Beeby, C., and Potter, O. E. (1986) 'Pilot-plant steam-drying of

brown coal', Proceedings of the 2nd Australian Coal Science Conference,

Newcastle, New South Wales, Australia, 299-304.

Reference List

314

66. Wolf, B. (1998) 'Use and experiences with steam-based fluidised-bed coal

dryers.' Energietechnik, 38, 245-249.

67. Weiss, H. J., Klutz, H. J., and Hamilton, C. J. (1991) 'Drying of brown coal in

the steam fluidized bed.' VGB Kraftwerkstechnik, 71 (7), 664-668.

68. Hamilton, C. (1990) 'Steam fluidised drying of coal', Institute of Engineers

Australia, International Coal Engineering Conference, Sydney, New South

Wales, Australia.

69. Schmalfeld, J., and Twigger, C. (1998) 'Experience with the operation of the

steam-fluidised-bed-drying (SFBD) plant Loy Yang, Australia', The Science

and Technology of Low-Rank Coal. Structure, Properties and Consequences

for Utilisation in Power Generation, Monash University - Gippsland, Victoria,

Australia.

70. Bocker, D., Klocker, K. J., and Klutz, H.-J. (1989) 'Das WTA-Verfahren zur

braunkohletrocknung fur Kombi-Kraftwerke.' BWK Bd, 41 (5), 231-234.

71. Johnson, T. (1991) 'New technologies for generating electricity from brown

coal', 1st Japan/Australian Joint Technical Meeting on Coal, Melbourne,

Australia, 1-16.

72. Schmalfeld, J., and McKenzie, L. (1993) 'A commercially successful coal

drying plant for the power industry', Process Industries Power the Pacific

Rim: Official Proceedings of Combined Conference, 6th Conference of the

Asia Pacific Confederation of Chemical Engineering; 21st Australasian

Chemical Engineering Conference, Barton, Australia, Publisher: Institution of

Engineers, 2, 255-262.

73. Anderson, B., Huynh, D., and Johnson, T. (1992) 'New technologies for

environmentally friendly use of brown coal for power generation', Australian

Institute of Mining and Metallurgy Gippsland Basin Symposium, Melbourne

Hilton Hotel, Victoria, Australia.

Reference List

315

74. Schmalfeld, J., and Twigger, C. (1996) 'Experience with the operation of the

steam fluidised bed drying plant at Loy Yang, Australia', VGB Conference on

Energy and Power Technology, Siegen, Germany.

75. Klutz, H.-J., Klocker, K. J., and Lambertz, J. (1994) 'Die Rheinbraun-WTA-

Trocknungstechnik - Entwicklung und erste Betriebserge-bnisse der WTA-

demonstrationsanlage.' Braunkohle, 6, 4-11.

76. Klutz, H.-J., Klocker, K. J., and Lambertz, J. (1996) 'Das WTA-Verfahren als

Vortrocknungsstufe fur moderne Kraftwerkskonzepte auf basis braunkohle.'

VGB Kraftwerkstechnik, 76 (3), 224-229.

77. Weiss, H. J., Klutz, H.-J., and Hamilton, C. J. (1991) 'Progress in steam

fluidised bed drying.' VGB Kraftwerkstechnik, 71, 664-668.

78. Bocker, D., Klocker, K. J., and Klutz, H.-J. (1992) 'Verfahren zur Trocknung

und Mahlung von Braunkohle.' BWK Bd, 44 (7/8), 315-322.

79. Klutz, H.-J., and Holzenkamp, M. (1996) 'Verfahren und Anlagen zur

Braunkohle trocknung.' VDI Berichte, 1280, 91-105.

80. Gotte, C., Schreier, W., and Vonderbank, R. (2000) 'Concept of Co-

combustion of dry coal dust in power plant Niederaussem, Germany.' VGB

Kraftwerkstechnik, 80 (8), 49-55.

81. Ewers, J., Klutz, H.-J., Renzenbrink, W., and Scheffknecht, G. (2003)

'Development of predrying and BoA-Plus technology', VGB Conference -

Power Plants in Competition - Technology, Operation and Environment,

Cologne, Germany.

82. Martin, J. S., Loffler, S., and Krautz, H. J. (2003) 'Druckaufgeladene

Dampfwirbelschichttrocknung grubenfeuchter Braunkohle – Innovatives

Verfahren zur Erhöhung des Kraftwerkswirkungsgrades und Reduzierung

der Stromgestehungskosten.' 21. German flame day, VDI reports, VDI

publishing house, Duesseldorf 1750, 1-7.

Reference List

316

83. Martin, J. S., Hohne, O., Krautz, H. J., and Mandel, H. (2004)

'Dampfwirbelschichttrocknung von Braunkohlen - Inbetriebnahme und erste

Untersuchungsergebnisse am Versuchstrockner der BTU Cottbus.' XXXVI.

Kraftwerkstechnisches Kolloquium Entwicklungspotentiale für Kraftwerke mit

fossilen Brennstoffen, Dresden, Germany

84. Wagener-Lohse, G. (2003) 'Pressurized fluidized bed steam drying process',

Vattenfall Europe, Germany

85. Brockway, D. J., Ottrey, A., and Higgins, R. S. (1991) 'Inorganic

constituents', in Durie, R. A. (ed) The Science of Victorian Brown Coal -

Structure, Properties and Consequences for Utilisation, Oxford, Butterworth-

Heinemann, pp. 597-650.

86. Ottrey, A., and Johnson, T. R. (1982) 'Victorian brown coal ash. Past,

present and future problems', GO/82/54, SECV, Research and Development

Department Report.

87. Bonafede, G. (1968) 'Survey of some physico-chemical problems associated

with boiler fouling', LR-8, SECV, Research and Development Department

Report.

88. Brown, H. R., Durie, R. A., and Shires, G. L. (1961) 'Investigation into

problems associated with the combustion of Morwell brown coal', 31, CSIRO

Division of Coal Research, Investigation Report.

89. Brown, H. R., Durie, R. A., and Taylor, G. H. (1963) 'Factors influencing the

formation of fireside deposits during combustion of Morwell brown coal',

Proceedings of the International Conference on Mechanisms of Corrosion by

Fuel Impurities, Marchwood, United Kingdom, 469-482.

90. Allardice, D. J. (1998) 'The water in low rank coals', The Science and

Technology of Low-Rank Coal Workshop. Structure, Properties and

Reference List

317

Consequences for Utilisation in Power Generation, Monash University-

Gippsland, Victoria, Australia.

91. Clark, D. (1984) 'Combustion of brown coal for electricity generation.' Aus. I.

M. M. Monograph Series 11, Victoria's Brown Coal, 127-154.

92. Su, S., Pohl, J. H., and Holcombe, D. (2003) 'Fouling propensities of blended

coals in pilverized coal-fired power station boilers.' Fuel, 82, 1653-1667.

93. Kyi, S., and Chadwick, B. L. (1999) 'Screening of potential mineral additives

for use as fouling preventatives in Victorian brown coal combustion.' Fuel,

78, 845-855.

94. Anderson, B. (1989) 'Long term fouling tests on LaTrobe Valley brown coal

and the effects of soluble aluminium on deposits', Proceedings of the

Engineering Foundation Conference on Slagging and Fouling due to

Impurities in Combustion Gases, United Engineering Trustees

95. Anderson, B., Haque, H., Ottrey, A., and Sarapelli, R. (1992) 'The removal of

inorganics from brown coal by the hydro-thermal dewatering process and its

effect on fouling in a gas turbine', 5th Australian Coal Science Conference,

University of Melbourne, Australia.

96. Quyn, D. M., Wu, H., Bhattacharya, S. P., and Li, C.-Z. (2002) 'Volatilisation

and catalytic effects of alkali and alkaline earth metallic species during

pyrolysis and gasification of Victorian brown coal. Part II. Effects of chemical

form and valence.' Fuel, 81, 151-158.

97. Wu, H., Quyn, D. M., and Li, C.-Z. (2002) 'Volatilisation and catalytic effects

of alkali and alkaline earth metallic species during pyrolysis and gasification

of Victorian brown coal. Part III. The importance of the interactions between

volatiles and char at high temperature.' Fuel, 81, 1033-1039.

Reference List

318

98. Li, C.-Z., Sathe, C., Kershaw, J. R., and Pang, Y. (2000) 'Fates and roles of

alkali and alkaline earth metals during the pyrolysis fo a Victorian brown

coal.' Fuel, 79, 427-438.

99. Sentorun, C., and Kucukbayrak, S. (1996) 'The effect of mineral matter on

the combustion characteristics of some Turkish lignite samples.'

Thermochimica Acta, 287, 139-147.

100. Quyn, D. M., Wu, H., and Li, C.-Z. (2002) 'Volatilisation and catalytic effects

of alkali and alkaline earth metallic species during pyrolysis and gasification

of Victorian brown coal. Part I. Volatilisation of Na and Cl from a set of NaCl-

loaded samples.' Fuel, 81, 143-149.

101. Poeze, A., and Zhang, D. K. (1996) 'The effect of conversion level on the

gasification kinetics of a low-rank coal', Proceedings of the 3rd Annual

Conference : Coorperative Research Centre for New Technologies for Power

Generation from Low Rank Coal, University of Adelaide, Waite Campus,

Adelaide, Australia, 49-54.

102. Clemow, L. M., Favas, G., Jackson, W. R., Marshall, M., Patti, A. F., and

Redlich, P. J. (1999) 'Humic acids and methylated humic acids as models for

reactions of brown coal with CO/H2O and with H2.' Fuel, 78, 567-572.

103. Cassidy, P. J., Jackson, W. R., Larkins, F. P., Louey, M. B., and Sakurovs,

R. J. (1986) 'Promoters for the liquefaction of wet Victorian brown coal in

carbon monoxide.' Fuel Processing Technology, 14, 231-246.

104. Allardice, D. J., and Newell, B. S. (1991) 'Industrial implications of the

properties of brown coals', in Durie, R. A. (ed) The Science of Victorian

Brown Coal - Structure, Properties and Consequences for Utilisation, Oxford,

Butterworth-Heinemann, pp. 651-701.

Reference List

319

105. Hodges, S., and Woskoboenko, F. (1991) 'Hydrothermal dewatering brown

coal slurries; fundamental studies', 9th International Conference on Coal

Research, Washington, USA.

106. Kealy, T., Favas, G., Tiu, C., and Chaffee, A. L. (2001) 'Lignite upgrading by

mechanical-thermal expression (MTE)', 6th World Congress of Chemical

Engineering, Melbourne, Victoria, Australia.

107. Woskoboenko, F., Stacy, W. O., and Raisbeck, D. (1991) 'Physical structure

and properties of brown coal', in Durie, R. A. (ed) The Science of Victorian



108. Campisi, A., Hodges, S., and Woskoboenko, F. (1996) 'Chemical and

physical characterisitics of low rank coals', Australia-Indonesia Low Rank

Coal Science and Technology Workshop, 1-28.

109. Favas, G., Chaffee, A. L., and Jackson, W. R. (2002) 'Reducing greenhouse

emissions from lignite power generation by improving current drying

technologies', 221st American Chemical Society National Meeting-Division of

Fuel Chemistry, San Diego, California, USA, 13, 175-187.

110. Australian Standard, (1991) 'Methods for the analysis and testing of brown

coal and brown coal char. Part 1: Determination of the total moisture content

of lower rank coals.'

111. Quyn, D. M. (2002) 'Transformations of alkali and alkaline earth metallic

species during gasification of Victorian brown coal', Department of Chemical

Engineering, Monash University, Melbourne, Victoria, Australia.

112. Tang, L., and Chen, W. Y. (1999) 'Improvements on a particle feeder for

experiments requiring low feed rates.' Review of Scientific Instruments, 70

(7), 3143-3144.

Reference List

320

113. Tyler, R. J. (1979) 'Flash pyrolysis of coals. 1. Devolatilization of a Victorian

brown coal in a small fluidized-bed reactor.' Fuel, 58, 680-686.

114. Tyler, R. J., and Schafer, H. N. S. (1980) 'Flash pyrolysis of coals: influence

of cations on the devolatilization behaviour of brown coals.' Fuel, 59, 487-

494.

115. Feng, J., Li, W. Y., Xie, K. C., Liu, M. R., and Li, C. Z. (2003) 'Studies of the

release rule of NOx precursors during gasification of coal and its char.' Fuel

Processing Technology, 84, 243-254.

116. Tan, L. L., and Li, C.-Z. (2000) 'Formation of NOx and SOx precursors during

the pyrolysis of coal and biomass. Part I. Effects of reactor configuration on

the determined yields of HCN and NH3 during pyrolysis.' Fuel, 79 (15), 1883-

1889.

117. Milham, R. C. (1968) 'High temperature properties of activated carbon: Part

I: Desorption of iodine; Part II: Standard method for ignitiion temperature

measurement', IAEA Symposium on Treatment of Airborne Radioactive

Wastes, New York SM110/149, 417.

118. Hardman, J. S., Street, P. J., and Twamley, C. S. (1980) 'Studies on

spontaneous combustion in beds of activated carbon.' Fuel, 59, 151-156.

119. van Veen, A. C., Zanthoff, H. W., Hinrichsen, O., and Muhler, M. (2001)

'Fixed-bed microreactor for transient kinetic experiments with strongly

adsorbing gases under high vacuum conditions.' Journal of Vacuum Science

& Technology A: Vacuum, Surfaces, and Films, 19 (2), 651-655.

120. Franklin, H. D., Peters, W. A., and Howard, J. B. (1982) 'Mineral matter

effects on the rapid pyrolysis and hydropyrolysis of a bituminous coal. 1.

Effects on yield of char, tar and light gaseous volatiles.' Fuel, 61, 155-160.

Reference List

321

121. Doolan, K. R., Mackie, J. C., and Tyler, R. J. (1987) 'Coal flash pyrolysis:

secondary cracking of tar vapours in the range 870-2000K.' Fuel, 66, 572-

578.

122. Australian Standard, (1995) 'Coal and coke - analysis and testing Part 14.1:

Higher rank coal ash and coke ash - major and minor elements - borate

fusion/flame atomic absorption spectrometric method.'

123. Australian Standard, (1991) 'Methods for the analysis and testing of lower

rank coal and its chars. Part 9: Determination of four acid-extractable

inorganic ions in lower rank coal.'

124. Reucroft, P. J., and Patel, K. B. (1983) 'Surface area and swelling of coal.'

Fuel, 62, 279-284.

125. Reucroft, P. J., and Patel, K. B. (1986) 'Gas induced swelling in coal.' Fuel,

65, 816-820.

126. Rodrigues, C. F., and Lemos de Sousa, M. J. (2002) 'The measurement of

coal porosity with different gases.' International Journal of Coal Geology, 48,

245-251.

127. Barrett, E. P., Joyner, L. G., and Halenda, P. P. (1951) 'The determination of

pore volume and area distributions in porous substances. I. Computations

from nitrogen isotherms.' Journal of American Chemical Society, 73, 373-

380.

128. Allardice, D. J., Clemow, L. M., Favas, G., Jackson, W. R., Marshall, M., and

Sakurovs, R. J. (2003) 'The characterisation of different forms of water in low

rank coals and some hydrothermally dried products.' Fuel, 82, 661-667.

129. Ohki, A., Xie, X. F., Nakajima, T., and Maeda, S. (1998) 'Chemical structure

and properties of low-rank coals treated by hydrothermal process', 15th

Annual International Pittsburgh Coal Conference, Pittsburgh, Pennsylvania,

USA.

Reference List

322

130. Schafer, H. N. S. (1980) 'Pyrolysis of brown coals 3. Effect of cation content

on the gaseous products containing oxygen from Yallourn coal.' Fuel, 59,

295-301.

131. Eskay, T. P., Britt, P. F., and Buchanan, A. C. (1996) 'Does decarboxylation

lead to cross-linking in low -rank coals ?' Energy and Fuels, 10, 1257-1261.

132. Ohki, A., Xie, X. F., Umihira, Y., Nakajima, T., and Maeda, S. (1999)

'Properties of hydrothermally-treated coals and the coal water mixture

(CWM)', Taiyuan, China, 2,, 1103-1106.

133. Yokokawa, C., Eguchi, K., Fukuhara, Y., Oda, H., and Wasaka, S. (1990)

'Up-grading of low-rank coals by hydrothermal treatment', Tokyo, 169-174.

134. Evans, D. G. (1973) 'The brown-coal/water system: Part 4. Shrinkage on

drying.' Fuel, 52, 186-190.

135. Maas, D. J., Sears, R. E., and Potas, T. A. (1986) 'Dewatering dilute fine

coal/water slurries to produce coal/water fuel', DOS/FE/60181-179,

University of North Dakota, Grand Forks, North Dakota, USA.

136. Favas, G., and Jackson, W. R. (2003) 'Hydrothermal dewatering of lower

rank coals. 1. Effects of process conditions on the properties of dried

product.' Fuel, 82, 53-57.

137. Scholes, O., Tiu, C., and Kealy, T. (2002) 'Radial mechanical-thermal

expression dewatering of Australian lignite', Proceedings of the 9th Annual

Conference : Coorperative Research Centre for Clean Power from Lignite,

Monash University, Melbourne, Victoria, Australia, 143-148.

138. Priambodo, T. B., Favas, G., and Chaffee, A. L. (2002) 'BPPT- LSDE

(Indonesia) - CRC Clean Power (Australia) International collaboration on the

MTE process', 20019, CRC Clean Power from Lignite Report.

Reference List

323

139. Favas, G., Qi, Y., and Chaffee, A. L. (2002) 'Comparative MTE processing of

German, South Australian and Latrobe Valley lignites', 20023, CRC Clean

Power from Lignite Report.

140. Bongers, G. D., Jackson, W. R., and Woskoboenko, F. (1998) 'Pressurised

steam drying of Australian low-rank coals Part 1. Equilibrium moisture

contents.' Fuel Processing Technology, 57, 41-54.

141. Woskoboenko, F., and Black, C. (1994) 'Pressurised steam drying of

Victorian brown coal : steam equilibrium content', 6th Australian Coal

Science Conference, Newcastle, Australia, 473-480.

142. Guo, J., Hodges, S., Tiu, C., and Uhlherr, P. H. T. (1997) 'Hydrothermal-

mechanical dewatering of brown coal slurries', Proceedings of the 4th Annual

Conference : Coorperative Research Centre New Technologies for Power

Generation from Low Rank Coal, Swinburne University of Technology,

Melbourne, Victoria, Australia, 27-32.

143. Favas, G., and Jackson, W. R. (2001) 'High quality lignite derived fuels to

rival bituminous coals', 11th International Conference On Coal Science,

Exploring the Horizons of Coal, San Francisco, USA.

144. Chaffee, A. L., Favas, G., and Jackson, W. R. (2000) 'Drying technologies

for more efficient power generation from low rank coal: Comparison of

products from various processes', 17th Annual International Pittsburgh Coal

Conference, Pittsburgh, USA, Paper No. 7-6.

145. Allardice, D. J., and Young, B. C. (2001) 'Utilisation of low rank coals',

Proceedings of the 18th Annual International Pittsburgh Coal Conference,

Newcastle, New South Wales, Australia.

146. Laird, M. (2000) 'Mine operations', Industry Induction Course, CRC Clean

Power from Lignite Workshop, Gippsland, Victoria, Australia.

Reference List

324

147. Bongers, G. D. (1997) 'Brown coal drying processes and aspects of

fundamental coal structure', PhD thesis, Department of Chemistry, Monash

University, Melbourne, Australia.

148. Qi, Y., and Chaffee, A. L. (2001) 'Effects of processing conditions on the

nature of product water from a novel coal drying process', Proceedings of the

8th Annual Conference : Coorperative Research Centre for Clean Power

from Lignite, Monash University, Melbourne, Australia, 41-46.

149. Guo, J., Tiu, C., Hodges, S., and Uhlherr, P. H. T. (1998) 'How is

hydrothermal-mechanical dewatering efficient ?' Proceedings of the 5th

Annual Conference : Coorperative Research Centre New Technologies for

Power Generation from Low Rank Coal, Monash University, Melbourne,

Australia, 17-22.

150. Bongers, G. D., Jackson, W. R., and Woskoboenko, F. (1996) 'High pressure

steam drying of brown coal', Proceedings of the 3rd Annual Conference :

Coorperative Research Centre for New Technologies for Power Generation

from Low Rank Coal, University of Adelaide, Waite Campus, Adelaide,

Australia, 113-118.

151. Favas, G., and Chaffee, A. L. (2002) 'MTE processing of Latrobe Valley

lignites', 02005, CRC Clean Power from Lignite Report.

152. Favas, G., and Chaffee, A. L. (2002) 'Beneficiation of Latrobe Valley lignites

with MTE processing', Proceedings of the 9th Annual Conference :

Coorperative Research Centre Clean Power from Lignite, Monash University,

Melbourne, Australia, 153-158.

153. Favas, G., and Chaffee, A. L. (2001) 'MTE processing of South Australian

lignites', 01009, CRC Clean Power from Lignite Report.

Reference List

325

154. Favas, G., and Chaffee, A. L. (2001) 'Mechanical Thermal Expression:

Evaluation of the process on Leigh Creek coal', 01010, CRC Clean Power

from Lignite Report.

155. Favas, G., and Jackson, W. R. (2003) 'Hydrothermal dewatering of lower

rank coals. 2. Effects of coal characteristics for a range of Australian and

International coals.' Fuel, 82, 59-69.

156. Anderson, B., and Johnston, T. (1991) 'Alternative technologies for the

generation of electricity from Victorian brown coal', Sixteenth Biennial Low-

rank Fuels Symposium of the Energy and Environmental Research Centre,

University of North Dakota, Grand Forks, North Dakota, USA, 221-225.

157. Jones, J. C. (1991) 'Pyrolysis', in Durie, R. A. (ed) The Science of Victorian



158. Jimenez, A., Martinez-Tarazona, M. R., and Suarez-Ruiz, I. (1999) 'The

mode of occurrence and origin of chlorine in Puertollano coals (Spain).' Fuel,

78, 1559-1565.

159. Cox, J. A., Larson, A. E., and Carlson, R. H. (1984) 'Estimation of the

inorganic-to-organic chlorine ratio in coal.' Fuel, 63 (9), 1334-1335.

160. Martinez-Tarazona, M. R., and Cardin, J. M. (1990) 'Chlorine in Austurian

coals.' Journal of Coal Quality, 9 (2), 66-70.

161. Huggins, F. E., and Huffman, G. P. (1991) 'An XAFS investigation of the

form-of-occurrence of chlorine in U.S. coals.' Coal Science and Technology,

17, 43-61.

162. Fenghua, Z., Deyi, R., Shuangquan, Z., and Wang, Z. (1998) 'Distribution of

chlorine in coal', 15th Annual International Pittsburgh Coal Conference,

Pittsburgh, Pennsylvania, USA.

Reference List

326

163. Hodges, N. J., Ladner, W. R., and Martin, T. G. (1983) 'Chlorine in coal: A

review of its origin and mode of occurrence.' Journal of the Institute of

Energy, 56, 158-169.

164. Vassilev, S. V., Eskenazy, G. M., and Vassileva, C. G. (2000) 'Contents,

modes of occurrence and origin of chlorine and bromine in coal.' Fuel, 79,

903-921.

165. Huggins, F. E., and Huffman, G. P. (1995) 'Chlorine in coal: an XAFS

spectroscopic investigation.' Fuel, 74 (4), 556-559.

166. Ghetti, P. (1980) 'Analysis of coal by thermogravimetric methods.' Rivista dei

Combustibili, 34 (9-12), 403-409.

167. Cumming, J. W. (1981) 'The application of thermogravimetry to coal testing.'

Proceedings of the European Symposium on Thermal Analysis, 2, 512-516.

168. Ottaway, M. (1982) 'Use of thermogravimetry for proximate analysis of coals

and coke.' Fuel, 61 (8), 713-716.

169. Elder, J. P. (1983) 'Proximate analysis by automated thermogravimetry.'

Fuel, 62 (5), 580-584.

170. Sadek, F. S., and Herrell, A. Y. (1984) 'Methods of proximate analysis by

thermogravimetry.' Thermochimica Acta, 81, 297-303.

171. Hill, J. O., Charsley, E. L., and Ottaway, M. R. (1985) 'Thermal analysis of

Victorian brown coal.' Thermochimica Acta, 93, 741-744.

172. Ghetti, P. (1986) 'DTG combustion behavior of coal. Correlations with

proximate and ultimate analysis data.' Fuel, 65 (5), 636-639.

173. Mayoral, M. C., Izquierdo, M. T., Andres, J. M., and Rubio, B. (2001)

'Different approaches to proximate analysis by thermogravimetric analysis.'

Thermochimica Acta, 370 (1-2), 91-97.

Reference List

327

174. Earnest, C. M. (1988) 'Compositional analysis by thermogravimetry', ASTM

Special Technical Publications: 997, Philadelphia, Pennsylvania, USA, 1-

298.

175. Xie, X. F., Ohki, A., and Maeda, S. (1999) 'Improvement of thermal

properties of low-rank coals treated by hydrothermal process', 16th Annual

International Pittsburgh Coal Conference, Pittsburgh, Pennsylvania, USA.

176. Racovalis, L., Hobday, M. D., and Hodges, S. (2002) 'Effect of processing

conditions on organics in wastewater from hydrothermal dewatering of low-

rank coal.' Fuel, 81, 1369-1378.

177. Janikowski, S. K., and Stenberg, V. I. (1989) 'Thermal analysis of coals using

differential scanning calorimetry and thermogravimetry.' Fuel, 68, 95-99.

178. Kok, M. V., and Pamir, M. R. (1995) 'Pyrolysis and combustion studies of

fossil fuels by thermal analysis methods.' Journal of Analytical and Applied

Pyrolysis, 35, 145-156.

179. Cetinkaya, S., and Yurum, Y. (2000) 'Oxidative pyrolysis of Turkish lignites in

air up to 500°C.' Fuel Processing Technology, 67, 177-189.

180. Piskin, S., Unal, S., Kuyulu, A., and Dincer, S. (1992) 'Thermal reactivities of

some Turkish lignites.' Fuel Science and Technology International, 10 (2),

243-266.

181. Wagner-Beeger, S. (1961) 'Characterization of brown coal from Niederlausitz

by differential thermal analysis.' Freiberger Forschungsh, A194, 1-66.

182. Francioso, O., Ciavatta, C., Montecchio, D., Tugnoli, V., Sanchez-Cortes, S.,

and Gessa, C. (2003) 'Quantitative estimation of peat, brown coal and lignite

humic acids using chemical paramters, 1H-NMR and DTA analyses.'

Bioresource Technology, 88, 189-195.

183. Ding, F., Wang, J., and Qian, J. (1991) 'Study of the pressure pyrolysis of

coal by DTA method.' Ranliao Huaxue Xuebao, 19 (2), 189-192.

Reference List

328

184. Martinez-Alonso, A., Bermejo, J., Granda, M., and Tascon, J. M. D. (1992)

'Suitability of thermogravimetry and differential thermal analysis techniques

for characterization of pitches.' Fuel, 71, 611-617.

185. Lewis, I. C. (1987) 'Chemistry of pitch carbonization.' Fuel, 66 (11), 1527-

1531.

186. Elder, J. P., and Harris, M. B. (1984) 'Thermogravimetry and differential

scanning calorimetry of Kentucky bituminous coals.' Fuel, 63, 262-267.

187. Sheppard, J. D., and Forgeron, D. W. (1987) 'Differential thermogravimetry

of peat fractions.' Fuel, 66, 232-236.

188. Elliott, D. C. (1980) 'Decarboxylation as means of upgrading the heating

value of low rank coals.' Fuel, 59, 805-806.

189. Nikanorova, L. P., and Chibisova, K. I. (1968) 'Use of thermographic analysis

for studying lignites.' Trudy Instituta Goryuchikh Iskopaemykh, 24 (1), 17-25.

190. Keown, D. M., Favas, G., Hayashi, J., and Li, C.-Z. (2005) 'Volatilisation of

alkali and alkaline earth metallic species during the pyrolysis of biomass:

differences between sugar cane bagasse and cane trash.' Bioresource

Technology, 96, 1570-1577.

191. Murray, J. B. (1973) 'The yields and properties of chars and volatiles from

carbonised Morwell brown coals', Report 277, State Electricity Commission

of Victoria.

192. Mulcahy, M. F. R., Morley, W. J., and Smith, I. W. (1991) 'Combustion,

gasification and oxidation', in Durie, R. A. (ed) The Science of Victorian



193. Zeng, C., Wu, H., Hayashi, J., and Li, C.-Z. (2005) 'Effects of thermal

pretreatment in helium on the pyrolysis behaviour of Loy Yang brown coal.'

Fuel, 84, 1586-1592.

Reference List

329

194. Takarada, T., Ohtsuka, Y., and Tomita, A. (1988) 'Pressurized fluidized-bed

gasification of catalyst-loaded Yallourn brown coal.' Journal of the Fuel

Society Japan, 67, 683.

195. Doolan, K. R., and Mackie, J. C. (1984) 20th Symposium (International) on

Combustion, Pittsburgh, PA : The Combustion Institute 1463-1469.

196. Wornat, M. J., and Nelson, P. F. (1990) 23rd Symposium (International) on

Combustion, Pittsburgh, PA : The Combustion Institute 1239-1245.

197. Matsuo, Y., Hayashi, J., Kusakabe, K., and Morooka, S. (1995) Coal

Science: coal science and technology 24. In: Pajares, J. A.; Tascon, J. M. D.

editors. Proceedings of the Eighth International Conference on Coal Science,

Oviedo, Spain 929-932.

198. Morooka, S., Mori, T., Isoda, T., Kusakabe, K., Kumagai, H., Hayashi, J., and

Chiba, T. (1997) 'Effect of preheating of coal on product distributions in flash

pyrolysis', DGMK Tagungsbericht, Proceedings International Coal Science

Conference (ICCS), Germany 2, 577-580.

199. Sathe, C., Hayashi, J., and Li, C.-Z. (2002) 'Release of volatiles from the

pyrolysis of a Victorian lignite at elevated pressures.' Fuel, 81, 1171-1178.

200. Kershaw, J. R., Sathe, C., Hayashi, J., Li, C.-Z., and Chiba, T. (2000)

'Fluorescence spectroscopic analysis of tars from the pyrolysis of a Victorian

brown coal in a wire-mesh reactor.' Energy Fuels, 14, 476-482.

201. Sathe, C., Pang, Y., and Li, C.-Z. (1999) 'Effects of heating rate and ion-

exchangeable cations on the pyrolysis yields from a Victorian brown coal.'

Energy and Fuels, 13, 748-755.

202. Mochida, I., Amamoto, K., Maeda, K., and Takeshita, K. (1977)

'Carbonization of pitch: Compatibility of components in carbonization.' Fuel,

56 (1), 49-56.

Reference List

330

203. Bermejo, J., Menendez, R., Figueiras, A., and Granda, M. (1995) 'The role of

low-molecular-weight components in the pyrolysis of pitches.' Fuel, 74 (12),

1792-1799.

204. Li, X., Wu, H., Hayashi, J., and Li, C. Z. (2004) 'Volatilisation and catalytic

effects of alkali and alkaline earth metallic species during the pyrolysis and

gasification of Victorian brown coal. Part VI. Further investigation into the

effects of volatile-char interactions.' Fuel, 83, 1273-1279.

205. Wu, H., Li, X., Hayashi, J., Chiba, T., and Li, C. Z. (2005) 'Effects of volatile-

char interactions on the reactivity of chars from NaCl-loaded Loy Yang brown

coal.' Fuel, 84, 1221-1228.

206. Kashimura, N., Hayashi, J., Li, C. Z., Sathe, C., and Chiba, T. (2004)

'Evidence of poly-condensed aromatic rings in a Victorian brown coal.' Fuel,

83, 97-107.

207. Li, C. Z., and Nelson, P. F. (1996) 'Fate of aromatic ring systems during

thermal cracking of tars in a fluidized-bed reactor.' Energy and Fuels, 10,

1083-1090.

208. Chaffee, A. L., Perry, G. J., and Johns, R. B. (1983) 'Pyrolysis-gas

chromatography of Australian coals. I. Victorian brown coal lithotypes.' Fuel,

62, 303-310.

209. Zhiguang, S., Batts, B. D., and Smith, J. W. (1998) 'Hydrous pyrolysis

reactions of sulphur in three Australian brown coals.' Organic Geochemistry,

29, 1469-1485.

210. Tromp, P. J. J. (1987) 'Coal pyrolysis : Basic phenomena relevant to

conversion processes', PhD thesis, Institute of Chemical Technology,

University of Amsterdam, Netherlands.

211. Chaffee, A. L., Perry, G. J., and Johns, R. B. (1983) 'Pyrolysis-gas

chromatography of Australian coals. 2. Bituminous coals.' Fuel, 62, 311-316.

Reference List

331

212. Han, Z., and Kruge, M. A. (1999) 'Chemistry of maceral and groundmass

density fractions of torbanite and cannel coal.' Organic Geochemistry, 30,

1381-1401.

213. Finotello, F., and Johns, R. B. (1986) 'Some inter-relationships of kerogen

and humic acid fractions in the Victorian brown coal pale lithotype.' Organic

Geochemistry, 9 (5), 265-273.

214. Olivella, M. A., del Rio, J. C., Palacios, J., Vairavamurthy, M. A., and de las

Heras, F. X. S. (2002) 'Characterization of humic acid from leonardite coal:

an integrated study of PY-GC-MS, XPS and XANES techniques.' Journal of

Analytical and Applied Pyrolysis, 63, 59-68.

215. Irwin, W. J. 'Analytical pyrolysis: A comprehensive guide ' (1982) ed. Marcel

Dekker, New York

216. Gale, T. K., Bartholomew, C. H., and Fletcher, T. H. (1996) 'Effects of

pyrolysis heating rate on intrinsic reactivities of coal chars.' Energy and

Fuels, 10 (3), 766-775.

217. Dente, M., Bozzano, G., Faravelli, T., Marongiu, A., Pierucci, S., and Ranzi,

E. (2007) 'Kinetic modelling of pyrolysis processes in gas and condensed

phase ' Advances in Chemical Engineering, 32, 51-166.

218. Godínez, C., Cabanes, A. L., and Víllora, G. (1995) 'Experimental study of

the front-end selective hydrogenation of steam-cracking C2-C3 mixture '

Chemical Engineering and Processing, 34 (5), 459-468.

219. Bhasin, M. M., McCain, J. H., Vora, B. V., Imai, T., and Pujadó, P. R. (2001)

'Dehydrogenation and oxydehydrogenation of paraffins to olefins.' Applied

Catalysis A: General, 221, 397-419.

220. Benson, M. T., and Cundari, T. R. (1997) 'Transition metal-catalyzed alkane

dehydrogenation.' Inorganica Chimica Acta, 259, 91-100.

Reference List

332

221. Tsyganok, A., Harlick, P. J. E., and Sayari, A. (2007) 'Non-oxidative

conversion of ethane to ethylene over transition metals supported on Mg-Al

mixed oxide: Preliminary screening of catalytic activity and coking ability.'

Catalysis Communications, 8, 850-854.

222. Heracleous, E., and Lemonidou, A. A. (2006) 'Reaction pathways of ethane

oxidative and non-oxidative dehydrogenation on γ-Al2O3 studied by

temperature-programmed reaction (TP-reaction) ' Catalysis Today, 112, 23-

27.

223. Heracleous, E., and Lemonidou, A. A. (2004) 'Homogeneous and

hetrogeneous pathways of ethane oxidative and non-oxidative

dehydrogenation studied by temperature-programmed reaction.' Applied

Catalysis A: General, 269, 123-135.

224. Silberova, B., Fathi, M., and Holmen, A. (2004) 'Oxidative dehydrogenation

of ethane and propane at short contact time.' Applied Catalysis A: General,

276, 17-28.

225. Beretta, A., Ranzi, E., and Forzatti, P. (2001) 'Production of olefins via

oxidative dehydrogenation of light paraffins at short contact times.' Catalysis

Today, 64, 103-111.

226. Mamedov, E. A., and Corberán, V. C. (1995) 'Oxidative dehydrogenation of

ethane on supported vanadium-containing oxides.' Applied Catalysis A:

General, 127, 1-40.

227. Mulla, S. A. R., Buyevskaya, O. V., and Baerns, M. (2002) 'A comparative

study on non-catalytic and catalytic oxidative dehydrogenation of ethane to

ethylene.' Applied Catalysis A: General, 226, 73-78.

228. Henning, D. A., and Schmidt, L. D. (2002) 'Oxidative dehydrogenation of

ethane at short contact times: species and temperature profiles within and

after the catalyst.' Chemical Engineering Science, 57, 2615-2625.

Reference List

333

229. Cavani, F., Ballarini, N., and Cericola, A. (2007) 'Oxidative dehydrogenation

of ethane and propane: How far from commercial implementation?' Catalysis

Today, 127, 113-131.

230. Bodke, A. S., Henning, D., Schmidt, L. D., Bharadwaj, S. S., Maj, J. J., and

Siddall, J. (2000) 'Oxidative dehydrogenation of ethane at millisecond contact

times: effect of H2 addition.' Journal of Catalysis, 191, 62-74.

231. Beretta, A., Ranzi, E., and Forzatti, P. (2001) 'Oxidative dehydrogenation of

light paraffins in novel short contact time reactors. Experimental and

theoretical investigation.' Chemical Engineering Science, 56, 779-787.

232. Xu, L., Xie, S., Liu, S., Lin, L., Tian, Z., and Zhu, A. (2002) 'Combination of

CH4 oxidative coupling reaction with C2H6 oxidative dehydrogenation by

CO2 to C2H4.' Fuel, 81, 1593-1597.

233. Machocki, A., and Denis, A. (2002) 'Simulataneous oxidative coupling of

methane and oxidative dehydrogenation of ethane on the Na+/CaO catalyst.'

Chemical Engineering Journal, 90, 165-172.

234. Giannetto G., Montes A., Gnep N. S., Florentino A., P., C., and M., G. (1993)

'Conversion of Light Alkanes into Aromatic Hydrocarbons .VII. Aromatization

of Propane on Gallosilicates: Effect of Calcination in Dry Air ' Journal of

Catalysis, 145 (1), 86-95.

235. Xu, W. Q., and Suib, S. L. (1994) 'Coupling of oxidative dehydrogenation and

aromatization reactions of butane.' Journal of Catalysis, 145, 65-72.

236. Bhan, A., Hsu, S. H., Blau, G., Caruthers, J. M., Venkatasubramanian, V.,

and Delgass, W. N. (2005) 'Microkinetic modeling of propane aromatization

over HZSM-5.' Journal of Catalysis, 235, 35-51.

237. Collin, P. J., Tyler, R. J., and Wilson, M. A. (1980) '1H n.m.r. study of tars

from flash pyrolysis of three Australian coals.' Fuel, 59 (7), 479-486.

Reference List

334

238. Collin, P. J., Tyler, R. J., and Wilson, M. A. (1980) 'Influence of pyrolysis

temperature on the aromatic fraction of flash pyrolysis tars.' Fuel, 59, 819-

820.

239. Wu, H., Hayashi, J., Chiba, T., Takarada, T., and Li, C. Z. (2004)

'Volatilisation and catalytic effects of alkali and alkaline earth metallic species

during the pyrolysis and gasification of Victorian brown coal. Part V.

Combined effects of Na concentration and char structure on char reactivity.'

Fuel, 83, 23-30.

240. Wornat, M. J., and Nelson, P. F. (1992) 'Effects of ion-exchanged calcium on

brown coal tar composition as determined by fourier transform infrared

spectroscopy.' Energy and Fuels, 6, 136-142.

241. Vernaglia, B. A., Wornat, M. J., Li, C. Z., and Nelson, P. F. (1996) 'The

effects of pyrolysis temperature and ionexchanged metals on the

composition of brown coal tars produced in a fluidized bed reactor',

Proceedings of 26th Symposium (International) on Combustion The

Combustion Institute, Pittsburgh 3287-3294.

242. Doolan, K. R., and Mackie, J. C. (1985) 'Products from the rapid pyrolysis of

a brown coal in inert and reducing atmospheres ' Fuel, 64 (3), 400-405.

243. Shin, E. J., Miser, D. E., Chan, W. G., and Hajaligol, M. R. (2005) 'Catalytic

cracking of catechols and hydroquinones in the presence of nano-particle

iron oxide.' Applied Catalysis B: Environmental, 61 (1-2), 79-89.

244. Behar, F., and Hatcher, P. G. (1995) 'Artificial coalification of a fossil wood

from brown coal by confined system pyrolysis.' Energy and Fuels, 9, 984-

994.

245. Hayashi, J., Takahashi, H., Iwatsuki, M., Essaki, K., Tsutsumi, A., and Chiba,

T. (2000) 'Rapid conversion of tar and char from pyrolysis of a brown coal by

reactions with steam in a drop-tube reactor.' Fuel, 79 (3-4), 439-447.

Reference List

335

246. Hesp, W. R., and Waters, P. L. (1970) 'Thermal cracking of tars and volatile

matter from coal carbonization.' Ind. Eng. Chem. Prod. Res. Develop., 9 (2),

194-202.

247. Hayashi, J., Norinaga, K., Yamashita, T., and Chiba, T. (1999) 'Effect of

sorbed water on conversion of coal by rapid pyrolysis.' Energy and Fuels, 13,

611-616.

248. Hayashi, J., Iwatsuki, M., Morishita, K., Tsutsumi, A., Li, C. Z., and Chiba, T.

(2002) 'Roles of inherent metallic species in secondary reactions of tar and

char during rapid pyrolysis of brown coals in a drop-tube reactor.' Fuel, 81,

1977-1987.

249. Spiro, C. L., McKee, D. W., Kosky, P. G., Lamby, E. J., and Maylotte, D. H.

(1983) 'Significant parameters in the catalysed CO2 gasification of coal

chars.' Fuel, 62 (3), 323-330.

250. Rao, Y. K., Adjorlolo, A., and Haberman, J. H. (1982) 'On the mechanism of

catalysis of the Boudouard reaction by alkali-metal compounds.' Carbon, 20

(3), 207-212.

251. Wu, J., Fang, Y., and Wang, Y. (2005) 'Combined coal gasification and

methane reforming for production of syngas in a fluidized-bed reactor.'

Energy and Fuels, 19, 512-516.

252. Aznar, M. P., Corella, J., Delgado, J., and Lahoz, J. (1993) 'Improved steam

gasification of lignocellulosic residues in a fluidized bed with commercial

steam reforming catalysts.' Industrial and Engineering Chemistry Research,

32, 1-10.

253. Haghighi, M., Sun, Z., Wu, J., Bromly, J., Wee, H. L., Ng, E., Wang, Y., and

Zhang, D. (2007) 'On the reaction mechanism of CO2 reforming of methane

over a bed of coal char.' Proceedings of the Combustion Institute, 31, 1983-

1990.

Reference List

336

254. Mark, M. F., Maier, W. F., and Mark, F. (2004) 'Reaction kinetics of the CO2

reforming of methane.' Chemical Engineering and Technology, 20 (6), 361-

370.

255. Miura, K., Mae, K., Sakurada, K., and Hashimoto, K. (1992) 'Flash pyrolysis

of coal-following thermal pretreatment at low temperature.' Energy and Fuels,

6, 16-21.

256. Takarada, T., Tonishi, T., Takezawa, H., and Kato, K. (1992) 'Pyrolysis of

Yallourn coal in a powder-particle fluidized bed.' Fuel, 71, 1087-1092.

257. Goossens, H., DeLeeuw, J. W., Schenck, P. A., and Brassell, S. C. (1984)

'Tocopherols as likely precursors of pristane in ancient sediments and crude

oils.' Nature, 312, 440-442.

258. Christiansen, J. V., Feldthus, A., and Carlsen, L. (1995) 'Flash pyrolysis of

coals. Temperature-dependent product distribution.' Journal of Analytical and

Applied Pyrolysis, 32, 51-63.

259. Purser, D. A., and Woolley, W. D. (1983) 'Biological studies of combustion

atmospheres.' Journal of Fire Sciences, 1, 118-144.

260. Vila, F. J. G., Tinoco, P., Almendros, G., and Martin, F. (2001) 'Pyrolysis-gc-

ms analysis of the formation and degradation stages of charred residues

from lignocellulosic biomass.' Journal of Agric. Food Chem. , 49, 1128-1131.

261. Burgess, C. E., and Schobert, H. H. (1998) 'Relationship of coal

characteristics determined by pyrolysis/gas chromatography/mass

spectrometry and nuclear magnetic resonance to liquefaction reactivity and

product composition.' Energy and Fuels, 12, 1212-1222.

262. Bocchini, P., Galletti, G. C., Camarero, S., and Martinez, A. T. (1997)

'Absolute quantification of lignin pyrolysis products using an internal

standard.' Journal of Chromatography A, 773, 227-232.

Reference List

337

263. Hartgers, W. A., Damste, J. S. S., deLeeuw, J. W., Ling, Y., and Dyrkacz, G.

R. (1994) 'Molecular characterization of flash pyrolysates of two

carboniferous coals and their constituting maceral fractions.' Energy and

Fuels, 8, 1055-1067.

264. Islas, C. A., Suelves, I., Carter, J. F., Li, W., Morgan, T. J., Herod, A. A., and

Kandiyoti, R. (2002) 'Pyrolysis-gas chromatography/mass spectrometry of

fractions separated from a low-temperature coal tar: an attempt to develop a

general method for characterising structures and compositions of heavy

hydrocarbon liquids.' Rapid Communications in Mass Spectrometry, 16, 774-

784.

265. van Krevelen, D. W. 'Coal: typology - physics - chemistry- constitution'

(1993) ed. Elsevier Science Publishers

266. Russell, N. V., Beeley, T. J., Man, C. K., Gibbins, J. R., and Williamson, J.

(1998) 'Development of TG measurements of intrinsic char combustion

reactivity for industrial and research purposes.' Fuel Processing Technology,

57, 113-130.

267. Patel, M. M., Grow, D. T., and Young, B. C. (1988) 'Combustion rates of

lignite char by TGA.' Fuel, 67, 165-169.

268. Cumming, J. W. (1984) 'Reactivity assessment of coals via a weighted mean

activation energy.' Fuel, 63, 1436-1440.

269. Ma, S., Hill, J. O., and Heng, S. (1989) 'A thermal analysis study of the

oxidation of brown coal chars.' Journal of Thermal Analysis, 35, 1611-1619.

270. Kucukbayrak, S., Haykiri-Acma, H., Ersoy-Mericboyu, A., and Yaman, S.

(2001) 'Effect of lignite properties on reactivity of lignite.' Energy Conversion

and Management, 42, 613-626.

Reference List

338

271. Boiko, E. A. (2000) 'Research on kinetics of the thermal processing of brown

coals of various oxidative ageing degree using the non-isothermal methods.'


272. Rincon, M., Jose, M., Escallon, M. M., Baquero, M. C., Monero, G., and

Diaz, J. J. (1996) 'Reactivity of Colombian coals toward combustion', 212th

ACS National Meeting, Orlando, Florida, USA.

273. Li, W., Wanzi, W., Pilarczyk, E., and Leonhardt, P. (1997) 'Relationship

between combustion properties and formation of volatile matter of coal and

biomass', Proceedings ICCS ' 97, Essen, Germany, 2, 967-970.

274. Haykiri-Acma, H., Esroy-Mericboyu, A., and Kucukbayrak, S. (2002)

'Combustion reactivity of different rank coals.' Energy Conversion and

Management, 43, 459-465.

275. Pranda, P., Prandova, K., and Hlavacek, V. (1999) 'Combustion of fly-ash

carbon Part I. TG/DTA study of ignition temperature.' Fuel Processing

Technology, 61, 211-221.

276. Kok, M. V. (1999) 'Particle size effect on the oxidation mechanism of lignites.'


277. Hunag, G., Vastola, F. J., and Scaroni, A. W. (1998) 'Temperature gradients

in the gas phase surrounding pyrolyzing and burning coal particles.' Energy

and Fuels, 2, 385-390.

278. Morris, R. M. (1990) 'Effect of particle size and temperature on volatiles

produced from coal by slow pyrolysis.' Fuel, 69, 776-779.

279. Brunello, S., Flour, I., Maissa, P., and Bruyet, B. (1996) 'Kinetic study of char

combustion in a fluidized bed.' Fuel, 75 (5), 536-544.

280. Vamvuka, D., and Woodburn, E. T. (1998) 'A model of the combustion of a

single small coal particle using kinetic parameters based on

Reference List

339

thermogravimetric analysis.' International Journal of Energy Research, 22,

657-670.

281. He, R., Sato, J., Chen, Q., and Chen, C. (2002) 'Thermogravimetric analysis

of char combustion.' Combustion Science and Technology, 174 (4), 1-18.

282. Gilot, P., and Stanmore, B. R. (1995) 'A study of oxygen mass transfer

during the thermogravimetric analysis of porous solid reactivity', Proceedings

of the International Symposium on Transport Phenomena in Combustion,

San Francisco, USA, 1397-1408.

283. Ollero, P., Serrera, A., Arjona, R., and Alcantarilla, S. (2002) 'Diffusional

effects in TGA gasification experiments for kinetic determination.' Fuel, 81

1989-2000.

284. Morgan, P. A., Robertson, S. D., and Unsworth, J. F. (1986) 'Combustion

studies by thermogravimetric analysis. 1. Coal oxidation.' Fuel, 65, 1546-

1551.

285. Gold, P. I. (1980) 'Thermal analysis of exothermic processes in coal

pyrolysis.' Thermochimica Acta, 42, 135-152.

286. Hemati, M., and Laguerie, C. (1988) 'Determination of the kinetics of the

steam gasification of charcoal in a thermobalance.' Entropie, 24 (142), 29-40.

287. Sun, C. L., and Zhang, M. Y. (1998) 'Ignition of coal particles at high

pressure in a thermogravimetric analyzer.' Combustion and Flame, 115, 267-

274.

288. Annamalai, K., and Durbetaki, P. (1979) 'Combustion behavior of

char/carbon particles', Proceedings Symposium (International) on

Combustion, Providence, Rhode Island, USA, 17, 169-178.

289. Thomas, G. R., Stevenson, A. J., and Evans, D. G. (1973) 'Ignition of coal

particles without temperature jump.' Combustion and Flame, 21 (1), 133-136.

Reference List

340

290. Gomez, C. O., and Vastola, F. J. (1985) 'Ignition and combustion of single

coal and char particles. A quantitative differential approach.' Fuel, 64 (4),

558-563.

291. Annamalai, K., and Durbetaki, P. (1977) 'A theory on transition of ignition

phase of coal particles.' Combustion and Flame, 29 (2), 193-208.

292. Gomez, C. O., and Vastola, F. J. (1983) 'Ignition and combustion of coal

particles', American Chemical Society, Division of Petroleum Chemistry,

USA, 28, 1145-1152.

293. Wall, T. F., Gupta, R. P., Gururajan, V. S., and Zhang, D. K. (1991) 'The

ignition of coal particles.' Fuel, 70 (9), 1011-1016.

294. Essenhigh, R. H., Misra, M. K., and Shaw, D. W. (1989) 'Ignition of particles:

a review.' Combustion and Flame, 77 (1), 3-30.

295. Stevenson, A. J., Thomas, G. R., and Evans, D. G. (1973) 'Modeling the

ignition of brown-coal particles.' Fuel, 52 (4), 281-287.

296. Gururajan, V. S., Wall, T. F., Gupta, R. P., and Truelove, J. S. (1990)

'Mechanisms for the ignition of pulverized coal particles.' Combustion and

Flame, 81 (2), 119-132.

297. Du, X., Gopalakrishnan, C., and Annamalai, K. (1995) 'Ignition and

combustion of coal particle streams.' Fuel, 74 (4), 487-494.

298. Tseng, H. P., and Edgar, T. F. (1984) 'Identification of the combustion

behaviour of lignite char between 350 and 900°C.' Fuel, 63, 385-393.

299. Ozbas, K. E., Hicyilmaz, C., Kok, M. V., and Bilgen, S. (2000) 'Effect of

cleaning process on combustion characteristics of lignite.' Fuel Processing


300. Benfell, K. E., Beamish, B. B., and Rodgers, K. A. (1997) 'Aspects of

combustion behaviour of coals from some New Zealand lignite-coal regions

determined by thermogravimetry.' Thermochimica Acta, 297, 79-84.

Reference List

341

301. Tseng, H. P., and Edgar, T. F. (1987) 'On analysing the combustion

characteristics of coal char.' Fuel, 66, 723-724.

302. Androutsopoulos, G. P., and Linardos, T. J. (1986) 'Effects of drying upon

lignite macro-pore structure.' Powder Technology, 47 (1), 9-15.

303. Xiumin, J., Chuguang, Z., Che, Y., Dechang, L., Jianrong, Q., and Jubin, L.

(2002) 'Physical structure and combustion properties of super fine pulverized

coal particle.' Fuel, 81 793-797.

304. Ghetti, P., De Robertis, U., D'Antone, S., Villani, M., and Chiellini, E. (1985)

'Coal combustion. Correlation between surface area and thermogravimetric

analysis data.' Fuel, 64 (7), 950-955.

305. Gloe, C. S., and Holdgate, G. R. (1991) 'Geology and resources', in Durie, R.

A. (ed) The Science of Victorian Brown Coal - Structure, Properties and

Consequences for Utilisation, pp. 1-43.

306. Australian Standard, (1987) 'Classification and coding for Australian coals.'

307. George, A. M. (1975) 'Brown coal lithotypes in the Latrobe Valley deposits',

17, Victorian State Electricity Commission Planning and Investigation

Department Petrological Report, 17, pp44.

308. Higgins, R. S., Kiss, L. T., Allardice, D. J., George, A. M., and King, T. N. W.

(1980) 'Properties of brown coals from the Latrobe Valley - A basis for the

evaluation of quality', SECV Research and Development Department,

Victoria, Australia.

309. George, A. M., and Mackay, G. H. (1991) 'Petrology', in Durie, R. A. (ed) The

Science of Victorian Brown Coal - Structure, Properties and Consequences

for Utilisation, pp. 45-102.

310. Holdgate, G. R. (2005) 'Geological processes that control lateral and vertical

variability in coal seam moisture contents - Latrobe Valley (Gippsland Basin)

Australia.' International Journal of Coal Geology, 63, 130-155.

Reference List

342

311. Vuthaluru, H. B., Zhang, D., and Linjewile, T. M. (2000) 'Behaviour of

inorganic constituents and ash characteristics during fluidised-bed

combustion of several Australian low-rank coals.' Fuel Processing


312. Ward, C. R., Spears, D. A., Booth, C. A., Staton, I., and Gurba, L. W. (1999)

'Mineral matter and trace elements in coals of the Gunnedah Basin, New

South Wales, Australia.' International Journal of Coal Geology, 40, 281-308.

313. Ruan, C. D., and Ward, C. R. (2002) 'Quantitative X-ray powder diffraction

analysis of clay minerals in Australian coals using Rietveld methods.' Applied

Clay Science, 21, 227-240.

314. Tarazona, M. R. M., Spears, D. A., Palacios, J. M., Alonso, A. M., and

Tascon, J. M. D. (1992) 'Mineral matter in coals of different rank from the

Asturian Central basin.' Fuel, 71, 367-372.

315. Ward, C. R., and Taylor, J. C. (1996) 'Quantitative mineralogical analysis of

coals from the Callide Basin, Queensland, Australia using X-ray

diffractometry and normative interpretation.' International Journal of Coal

Geology, 30, 211-229.

316. Querol, X., Alastuey, A., Chinchon, J. S., Turiel, F. J. L., and Soler, A. L.

(1993) 'Determination of pyritic sulphur and organic matter contents in

Spanish subbituminous coals by X-ray powder diffraction.' International

Journal of Coal Geology, 22, 279-293.

317. Rubio, B., and Izquierdo, M. T. (1997) 'Influence of low-rank coal char

properties on their SO2 removal capacity from flue gases: I. Non-activated

chars.' Carbon, 35 (7), 1005-1011.

318. Quyn, D. M., Wu, H., Hayashi, J., and Li, C. Z. (2003) 'Volatilisation and

catalytic effects of alkali and alkaline earth metallic species during pyrolysis

Reference List

343

and gasification of Victorian brown coal. Part IV. Catalytic effects of NaCl and

ion-exchangeable Na in coal on char reactivity ' Fuel, 82, 587-593.

319. Wu, H., X., L., Hayashi, J., Chiba, T., and Li, C. Z. (2005) 'Effects of volatile-

char interactions on the reactivity of chars from NaCl-loaded Loy Yang brown

coal.' Fuel, 84, 1221-1228.

320. Wu, H., Hayashi, J., Chiba, T., Takarada, T., and Li, C. Z. (2004)

'Volatilisation and catalytic effects of alkali and alkaline earth metallic species

during the pyrolysis and gasification of Victorian brown coal. Part V.

Combined effects of Na concentration and char structure and char reactivity.'

Fuel, 83, 23-30.

321. Domazetis, G., Liesegang, J., and James, B. D. (2005) 'Studies of inorganics

added to low-rank coals for catalytic gasification.' Fuel Processing

Technology, 86 (5), 463-486.

322. Cornell, R. M., and Schwertmann, U. 'The iron oxides: Structure, Properties,

Reactions, Occurrences and Uses' (2003) Second edition ed. Cornell, R. M.,

and Schwertmann, U. Wiley-VCH Verlag GmbH and Co, KGaA, Weinheim

323. Hong-Xiao, T., and Stumm, W. (1987) 'The coagulating behaviors of Fe(III)

polymeric species - I. Preformed polymers by base addition.' Water

Research, 21 (1), 115-121.

324. Cook, P. S., and Cashion, J. D. (1987) 'Mössbauer spectroscopic study of

iron in Victorian brown coals.' Geochimica et Cosmochimica Acta, 51 (6),

1467-1475.

325. Ozaki, J., Nishiyama, Y., Cashion, J. D., and Brown, L. J. (1999)

'Carbonization of iron-treated Loy Yang coal.' Fuel, 78 (4), 489-499.

326. Bocquet, S., Cashion, J. D., and Cook, P. S. (1998) 'Paramagnetic relaxation

of ferric "oxyhydroxide" in Victorian brown coal and its structural implications.'

Physics and Chemistry of Minerals, 25 (5), 328-337.

Reference List

344

327. Hippo, E. J., Jenkins, R. G., and Walker, P. L. (1979) 'Enhancement of lignite

char reactivity to steam by cation addition.' Fuel, 58 (5), 338-344.

328. Ohtsuka, Y., Xu, C., Kong, D., and Tsubouchi, N. (2004) 'Decomposition of

ammonia with iron and calcium catalysts supported on coal chars.' Fuel, 83

(6), 685-692.

329. Asami, K., Sears, P., Furimsky, E., and Ohtsuka, Y. (1996) 'Gasification of

brown coal and char with carbon dioxide in the presence of finely dispersed

iron catalysts.' Fuel Processing Technology, 47 (2), 139-151.

330. Stojanowska, G., and Jones, J. M. (2005) 'Influence of minerals and added

calcium on the pyrolysis and co-pyrolysis of coal and biomass.' Journal of the

Energy Institute, 78 (3), 126-138.

331. Shibaoka, M., Ohtsuka, Y., Wornat, M. J., and Thomas, C. G. (1996)

'Investigation of brown coal gasification residues using light microscopy.'

Fuel, 75 (6), 775-779.

332. Badin, E. J. (1984) 'Coal combustion chemistry-correlation aspects', in

Anderson, L. L. (ed) Coal Science and Technology 6, Elsevier Science

Publishers, Amsterdam, pp. 259.

333. Benson, S. A., and Sondreal, E. A. (1998) 'Impact of low-rank coal properties

on advanced power systems.' Fuel Processing Technology, 56, 129-142.

334. Murakami, K., Shirato, H., Ozaki, J., and Nishiyama, Y. (1996) 'Effects of

metal ions on the thermal decomposition of brown coal.' Fuel Processing

Technology, 46 (3), 183-194.

335. Li, X., Wu, H., Hayashi, J., and Li, C. Z. (2004) 'Volatilisation and catalytic

effects of alkali and alkaline earth metallic species during pyrolysis and

gasification of Victorian brown coal. Part VI. Further investigation into the

effects of volatile-char interactions.' Fuel, 83 (10), 1273-1279.

Reference List

345

336. Ohtsuka, Y., and Asami, K. (1996) 'Steam gasification of coals with calcium

hydroxide.' Fuel and Energy Abstracts, 37 (3), 183.

337. Shibaoka, M., Ohtsuka, Y., Wornat, M. J., Thomas, C. G., and Bennett, J. R.

(1995) 'Application of microscopy to the investigation of brown coal pyrolysis.'

Fuel, 74 (11), 1648-1653.

338. Xu, W., and Du, H. (1996) 'Research on combustion catalysts for pulverized

coal injected into blast furnace.' Gangtie, 31 (1), 10-15.

339. Stanislaw, G., and Katarzyna, G. (1994) 'Catalyst for elimination of soot

formation during coal combustion', Patent No. PL 165406 B1.

340. Florin, N., and Harris, A. (2007) 'Hydrogen production from biomass.'

Environmentalist, 27, 207-215.

341. Timpe, R. C., and Sears, R. E. (1990) 'Anion effects on calcium catalysis of

low-rank coal char-steam gasification.' American Chemical Society, Division

of Fuel Chemistry, 35 (2), 530-534.

342. Radovic, L. R., Walker, P. L., and Jenkins, R. G. (1983) 'Importance of

catalyst dispersion in the gasification of lignite chars.' Journal of Catalysis, 82

(2), 382-394.

343. Radovic, L. R., Walker, P. L., and Jenkins, R. G. (1984) 'Catalytic coal

gasification: use of calcium versus potassium.' Fuel, 63 (7), 1028-1030.

344. Solano, A. L., Hippo, E. J., and Walker, P. L. (1986) 'Catalytic activity of

calcium for lignite char gasification in various atmospheres.' Fuel, 65 (6),

776-779.

345. Wornat, M. J., and Nelson, P. F. (1991) 'Oxygen-containing gases from the

rapid pyrolysis of a brown coal: the effects of ion-exchanged calcium', 23rd

Symposium (International) on Combustion, Pittsburgh, PA : The Combustion

Institute, 1239-1245.

Reference List

346

346. Elder, J. P., and Reddy, V. B. (1986) 'A thermogravimetric study of kerogen

combustion in the presence of calcium oxide.' Fuel Processing Technology,

13 (3), 233-241.

347. Smith, A. C., Miron, Y., and Lazzara, C. P. (1988) 'Inhibition of spontaneous

combustion of coal', RI 9196, Report of Investigation - USA Bureau of Mines.

348. Pan, W. P., and Serageldin, M. A. (1988) 'Effect of calcium chloride and

calcium acetate on the reactivity of a lignite coal at low heating rate.'


349. Vamvuka, D., Troulinos, S., and Kastanaki, E. (2006) 'The effect of mineral

matter on the physical and chemical activation of low rank coal and biomass

materials.' Fuel, 85, 1763-1771.

350. Lang, R. J. (1986) 'Anion effects in alkali-catalysed steam gasification.' Fuel,

65 (10), 1324-1329.

351. Kumar, G. S., Ramakrishnan, A., and Hung, Y. T. (2007) 'Lime calcination',

in Wang, L. K., Hung, Y. T., and Shammas, N. K. (ed) Advanced

Physicochemical Treatment Technologies, Handbook of Environmental

Engineering, 5, The Humana Press Inc, Totowa, NJ, pp. 611-633.

352. Yan, X., Che, D., and Xu, T. (2005) 'Effects of coal rank, dimineralization and

inherent mineral species on SO2 emission in coal combustion process.'

Ranliao Huaxue Xuebao, 33 (3), 273-277.

353. Sujanti, W., and Zhang, D. (2000) 'Investigation into the role of inherent

inorganic matter and additives in low-temperature oxidation of a Victorian

brown coal.' Combustion Science and Technology, 152, 99-114.

354. Amariglio, H., and Duval, X. (1966) 'Etude de la combustion catalytique du

graphite.' Carbon, 4 (3), 323-332.

355. Mody, D., and Li, C. Z. (1999) 'The loss of Na and Cl during the pyrolysis of

a NaCl-loaded brown coal sample in a fluidized-bed reactor', Proceedings of

Reference List

347

the 16th Annual International Pittsburgh Coal Conference, Pittsburgh, USA

202-208.

356. Li, C. Z. (2007) 'Some recent advances in the understanding of the pyrolysis

and gasification behaviour of Victorian brown coal.' Fuel, 86, 1664-1683.

357. Krishnan, G. N., Wood, B. J., Brittain, R. D., and Lau, K. H. (1996)

'Vaporization of alkali and trace metal impurities in coal gasification and

combustion systems.' International Symposium and Exhibition on Gas

Cleaning at High Temperatures, 651-663.

358. Quyn, D. M., Wu, H., Hayashi, J., and Li, C.-Z. (2003) 'Volatilisation and

catalytic effects of alkali and alkaline earth metallic species during pyrolysis

and gasification of Victorian brown coal. Part IV. Catalytic effects of NaCl and

ion-exchangeable Na in coal on char reactivity.' Fuel, 82, 587-593.

359. Li, B., Maruyama, K., Nurunnabi, M., Kunimori, K., and Tomishige, K. (2004)

'Thermographical studies on noble metal catalysts during reforming and

combustion of methane', 228th American Chemical Society National

Meeting, Philadelphia, PA, USA

360. Burch, R., Crittle, D. J., and Hayes, M. J. (1999) 'C-H bond activation in

hydrocarbon oxidation on heterogeneous catalysts.' Catalysis Today, 47 (1-

4), 229-234.

361. Aguila, G., Gracia, F., Cortes, J., and Araya, P. (2008) 'Effect of copper

oxide and the presence of reaction products on the activity of methane

oxidation on supported CuO catalysts.' Applied Catalysis B: Environmental,

77 (3-4), 325-338.

362. Ciuparu, D., Perkins, E., and Pfefferle, L. (2004) 'In situ DR-FTIR

investigation of surface hydroxyls on γ-Al2O3 supported PdO catalysts during

methane combustion.' Applied Catalysis A: General, 263 (2), 145-153.

Reference List

348

363. Ciuparu, D., and Pfefferle, L. (2002) 'Contributions of lattice oxygen to the

overall oxygen balance during methane combustion over PdO-based

catalysts.' Catalysis Today, 77 (3), 167-179.

364. Ciuparu, D., and Pfefferle, L. (2001) 'Support and water effects on palladium

based methane combustion catalysts.' Applied Catalysis A: General, 209 (1-

2), 209-215.

365. Vuthaluru, H. B., and Wall, T. F. (1998) 'Ash formation and deposition from a

Victorian brown coal - modeling and prevention.' Fuel Processing

Technology, 53 (3), 215-233.

366. Wei, X., Lopez, C., von Puttkamer, T., Schnell, U., Unterberger, S., and

Klaus, R. G. (2002) 'Assessment of chlorine-alkali-mineral interactions during

co-combustion of coal and straw.' Energy and Fuels, 16 (5), 1095-1108.

367. Badin, E. J. (1949) 'The atomic hydrogen-molecular oxygen reaction and

hydrocarbon oxidation inhibited by atomic hydrogen at low pressures', Third

Symposium on Combustion Flame and Explosion Phenomena, Baltimore,

Maryland, USA 382-385.

368. Badin, E. J. (1948) 'The reaction between atomic hydrogen and molecular

oxygen at low pressures.' Journal of the American Chemical Society, 70,

3651-3655.

369. Fujiwara, T. (1976) 'Slowdown of oxyhydrogen detonation by surface

catalysis', Sixteenth Symposium (International) on Combustion, Pittsburgh,

USA 1771-1780.

370. Minkoff, G. J., and Tipper, C. F. H. (1962) 'Chemistry and Combustion

Reactions', Butterworth and Company Ltd, London, England 46-53.

371. Roth, D., Gelin, P., Primet, M., and Tena, E. (2000) 'Catalytic behaviour of

Cl-free and Cl-containing Pd/Al2O3 catalysts in the total oxidation of methane

at low temperature.' Applied Catalysis A: General, 203 (1), 37-45.

Reference List

349

372. Wan, Y. Z., Wang, Y. L., and Wen, T. Y. (1999) 'Effect of specific surface

area and silver content on bacterial adsorption onto ACF(Ag).' Carbon, 37,

351-358.

373. Bradley, R. H. (1995) 'Surface studies of Cu/Cr/Ag impregnated microporous

carbons.' Applied Surface Science, 90, 271-276.

374. Park, S. J., and Jang, Y. S. (2003) 'Preparation and characterization of

activated carbon fibers supported with silver metal for antibacterial behavior.'

Journal of Colloid and Interface Science, 261, 238-243.

375. Li, C. Y., Wan, Y. Z., Wang, J., Wang, Y. L., Jiang, X. Q., and Han, L. M.

(1998) 'Antibacterial pitch-based activated carbon fiber supporting silver.'

Carbon, 36 (1-2), 61-65.

376. Li, C. Z., and Sathe, C. (2000) 'The pyrolysis behavior of Victorian lingite at

elevated pressures: contrast to bituminous coal.' Energeia, 11 (3), 1-4.

377. Khan, M. R. (1987) 'Significance of char active surface area for appraising

the reactivity of low- and high-temperature chars.' Fuel, 66 (12), 1626-1634.

378. Kyotani, T., Kubota, K., Cao, J., Yamashita, H., and Tomita, A. (1993)

'Combustion and CO2 gasification of coals in a wide temperature range.' Fuel

Processing Technology, 36 (1-3), 209-217.

379. Radovic, L. R., Walker, P. L., and Jenkins, R. G. (1983) 'Importance of

carbon active sites in the gasification of coal chars.' Fuel, 62 (7), 849-856.

380. Solomon, P. R., Serio, M. A., and Heninger, S. G. (1986) 'Variations in char

reactivity with coal type and pyrolysis conditions.' American Chemical

Society, Division of Fuel Chemistry, 31 (3), 200-209.

381. McKee, D. W., and Chatterji, D. (1975) 'The catalytic behavior of alkali metal

carbonates and oxides in graphite oxidation reactions.' Carbon, 13 (5), 381-

390.

Reference List

350

382. Lund, C. R. (1985) 'Nickel catalyst deactivation in the steam-carbon

reaction.' Journal of Catalysis, 95 (1), 71-83.

383. Wigmans, T., van Doorn, J., and Moulijn, J. (1983) 'Deactivation of nickel

during gasification of activated carbon, studied by X-ray photoelectron

spectroscopy.' Surface Science, 135 (1-3), 532-552.

384. Formella, K., Leonhardt, P., Sulimma, A., van Heek, K. H., and Juntgen, H.

(1986) 'Interaction of mineral matter in coal with potassium during

gasification.' Fuel, 65 (10), 1470-1472.

385. Charpenay, S., Serio, M. A., and Solomon, P. R. (1992) 'Prediction of coal

char reactivity under combustion conditions', Proceedings to the 24th

Symposium (International) on Combustion, Pittsburgh, P.A., USA 1189-1197.

386. Zimbardi, F. (2000) 'Evaluation of reaction order and activation energy of

char combustion by shift technique.' Combustion Science and Technology,

156 (1-6), 251-269.

387. Lu, Y. (1996) 'Laboratory studies on devolatilization and char oxidation under

pfbc conditions. 1. Volatile release and char reactivity.' Energy and Fuels, 10

(2), 348-356.

388. Chen, S. G., and Yang, R. T. (1997) 'Unified mechanism of alkali and

alkaline earth catalyzed gasification reactions of carbon by CO2 and H2O.'

Energy and Fuels, 11 (2), 421-427.

389. Chen, S. G., and Yang, R. T. (1993) 'The active surface species in alkali-

catalyzed carbon gasification: Phenolate (C-O-M) groups vs cluster

(particles).' Journal of Catalysis, 141 (1), 102-113.

390. Radovic, L. R., Walker, P. L., and Jenkins, R. G. (1983) 'Effect of lignite

pyrolysis conditions on calcium oxide dispersion and subsequent char

reactivity.' Fuel, 62 (2), 209-212.

Reference List

351

391. Hengel, T. D., and Walker, P. L. (1984) 'Catalysis of lignite char gasification

by exchangeable calcium and magnesium.' Fuel, 63 (9), 1214-1220.

392. Sainsbury, R. B., and Hawksley, P. G. W. (1968) 'Devolatilisation and

combustion rate measurements on pulverised fuel particles of Yallourn Open

Cut Coal', Combustion note 825, British Coal Utilisation Research

Association.

393. Roberts, R. A., and Loveridge, D. J. (1969) 'Devolatilisation and combustion

rate measurements on pulverised fuel particles of Morwell, Morwell woody

and Loy Yang coal', Document 4C/47, British Coal Utilisation Research

Association.

394. Kamishita, M., Mahajan, O. P., and Walker, P. L. (1977) 'Effect of carbon

deposition on porosity and reactivity of a lignite char.' Fuel, 56 (4), 444-450.

395. Liu, L., Liu, Z., Yang, J., Huang, Z., and Liu, Z. (2007) 'Effect of preparation

conditions on the properties of a coal-derived activated carbon honeycomb

monolith.' Carbon, 45 (14), 2836-2842.

396. Zondlo, J. W., and Velez, M. R. (2007) 'Development of surface area and

pore structure for activation of anthracite coal.' Fuel Processing Technology,

88 (4), 369-374.

397. Yu, J., Yang, M., Lin, T. F., Guo, Z., Zhang, Y., Gu, J., and Zhang, S. (2007)

'Effects of surface characteristics of activated carbon on the adsorption of 2-

methylisobornel (MIB) and geosmin from natural water.' Separation and

Purification Technology, 56 (3), 363-370.

398. Skodras, G., Diamantopoulou, I., and Sakellaropoulos, G. P. (2007) 'Role of

activated carbon structural properties and surface chemistry in mercury

adsorption.' Desalination, 210 (1-3), 281-286.

Reference List

352

399. Ganan, J., Garcia, C. M. G., Gonzalez, J. F., Sabio, E., Garcia, A. M., and

Diez, M. A. D. (2004) 'Preparation of activated carbons from bituminous coal

pitches.' Applied Surface Science, 238 (1-4), 347-354.

400. Gryglewicz, G., Grabas, K., and Grabowska, E. L. (2002) 'Preparation and

characterization of spherical activated carbons from oil agglomerated

bituminous coals for removing organic impurities from water.' Carbon, 40

(13), 2403-2411.

401. Pis, J. J., Mahamud, M., Pajares, J. A., Parra, J. B., and Bansal, R. C. (1998)

'Preparation of active carbons from coal Part III: Activation of char.' Fuel

Processing Technology, 57 (3), 149-161.

402. Julien, F., Baudu, M., and Mazet, M. (1998) 'Relationship between chemical

and physical surface properties of activated carbon.' Water Research, 32

(11), 3414-3424.

403. Brunauer, S., Emmett, P. H., and Teller, E. (1938) 'Adsorption of gases in

multimolecular layers.' Journal of the American Chemical Society, 60, 309-

319.

404. Allardice, D. J., George, A. M., Hausser, D., Neubert, K.-H., and Smith, G. C.

(1977) 'The variation of Latrobe Valley brown coal properties and utilisation

parameters with lithotype', 342, SECV Research and Development

Department Report.

405. Anderson, R. B., Bayer, J., and Hofer, L. J. E. (1965) 'Determining surface

area from CO2 isotherms.' Fuel, 44 (6), 443-452.

406. Clarkson, C. R., and Bustin, R. M. (1999) 'The effect of pore structure and

gas pressure upon the transport properties of coal: a laboratory and

modeling study. 1. Isotherms and pore volume distributions.' Fuel, 1333-

1344.

Reference List

353

407. Bansal, R. C., Donnet, J. B., and Stoeckli, F. 'Active carbon' (1988) ed.

Publisher: Marcel Dekker, Inc., New York and Basel

408. Nakajima, T., Kanda, T., Fukuda, T., Takanashi, H., and Ohki, A. (2005)

'Characterization of eluent by hot water extraction of coals in terms of total

organic carbon and environmental impacts.' Fuel, 84, 783-789.

409. Kini, K. A., Nandi, S. P., Sharma, J. N., Iyengar, M. S., and Lahiri, A. (1956)

'Surface area of coal.' Fuel, 35, 71-76.

410. Senel, G., Guruz, A. G., Yucel, H., Kandas, A. W., and Sarofim, A. F. (2001)

'Characterization of pore structure of Turkish coals.' Energy and Fuels, 15,

331-338.

411. Yoshino, Y., Matsumoto, A., Ohishi, K., and Yoshida, A. (1997) 'Manufacture

of activated carbon from coal having large BET specific surface', Patent No.

EP 765841 A2 19970402.

412. Larsen, J. W., Hall, P., and Wernett, P. C. (1995) 'Pore structure of the

Argonne premium coals.' Energy and Fuels, 9, 324-330.

413. Amarasekera, G., Scarlett, M. J., and Mainwaring, D. E. (1995) 'Micropore

size deteminations and specific interactions in coals.' Fuel, 74 (1), 115-118.

414. Wells, W. F., Kramer, S. K., Smoot, L. D., and Blackham, A. U. (1985)

'Reactivity and combustion of coal chars', Twentieth Symposium

(International) on Combustion, The Combustion Institute, Pittsburgh,

Pennsylvania, USA, 1539-1546.

415. Sun, Q., Li, W., Chen, H., and Li, B. (2004) 'The CO2-gasification and

kinetics of Shenmu maceral chars with and without catalyst.' Fuel, 83, 1787-

1793.

416. Kopac, T., and Toprak, A. (2007) 'Preparation of activated carbons from

Zonguldak region coals by physical and chemical activations for hydrogen

sorption.' International Journal of Hydrogen Energy, 32 (18), 5005-5014.

Reference List

354

417. Gutierrez, M. C., Cukierman, A. L., and Lemcoff, N. O. (1988) 'Study of

subbituminous coal chars: effect of heat treatment temperature on their

structural characteristics.' Journal of Chemical Technology and

Biotechnology, 41 (2), 85-93.

418. Clarkson, C. R., and Bustin, R. M. (1996) 'Variation in micropore capacity

and size distribution with composition in bituminous coal of the Western

Canadian sedimentary basin. Implications for coalbed methane potential.'

Fuel, 75 (13), 1483-1498.

419. Bongers, G. D., Jackson, W. R., and Woskoboenko, F. (2000) 'Pressurised

steam drying of Australian low-rank coals Part 2. Shrinkage and physical

measurements of steam dried coals, preparation of dried coals with very high

porosity.' Fuel Processing Technology, 64 (1-3), 13-23.

420. Marsh, H. (1987) 'Adsorption methods to study microporosity in coals and

carbons - a critique.' Carbon, 25 (1), 49-58.

421. Leong, Y. K., Boger, D. V., Christie, G. B., and Mainwaring, D. E. (1993)

'Rheology of low viscosity, high concentration brown coal suspensions.'

Rheol.Acta, 32, 277-285.

422. Stumm, W., and Morgan, J. J. 'Aquatic chemistry - Chemical equilibrium

rates in natural waters' (1996) 3rd Edition ed. New York, John Wiley and

Sons

423. Willson, W. G., Baker, G. G., Farnum, S. A., Maas, D. J., Potas, T. A., Sears,

R. E., and Tye, C. (1986) 'Low-rank coal-water slurries for gasification:

Phase 2 Analytic studies', EPRI Report AP-4905, Energy and Mineral

Research Center, North Dakota University, Grand Forks, USA.

424. Redlich, P. J. (1987) 'The chemical and structural characteristics of coals

and their relationship to liquefaction', Department of Chemistry, Monash

University, Melbourne, Victoria, Australia.

Reference List

355

425. Hodges, S., and Ottrey, A. (1993) 'GC-MS analysis of soluble organics in

HTD wastewater', SECV, Research and Development Dept.

426. Nakajima, T., Fukuda, T., Takanashi, H., and Ohki, A. (2004) 'Leaching or

organic matters from coal into aqueous media and their ecotoxicities', 21st

Annual International Pittsburgh Coal Conference, Pittsburgh, Pennsylvania,

USA.

427. Favas, G., Chaffee, A. L., and Jackson, W. R. (2000) 'The future of brown

coal drying technologies for power generation. Comparison of products from

various processes', Proceedings of the 9th Australian Coal Science

Conference, Brisbane, Queensland, Australia.

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