bahan kuliah biomass

Energy from Biomass

Lecture 2

Jeroen van Oijen

Energy from biomass

/ Mechanical Engineering PAGE 1 15-11-2012

Course outline

1. Introduction

• Global warming

• Resources and potential

2. Properties and characterization

3. Conversion processes

4. Modelling reacting flows

5. Conversion of spherical particles

6. Front propagation in a fixed bed

7. Emissions

8. Conversion systems

Course outline

1. Introduction

2. Properties and characterization

• Physical and chemical properties

• Composition of biomass

• Proximate and ultimate analyses

• Heating value

3. Conversion processes

4. Modelling reacting flows

5. Conversion of spherical particles

6. Front propagation in a fixed bed

7. Emissions

8. Conversion systems

Energy from biomass


Properties and characterization


Characteristics of biomass fuels

• Wide range of fuel types

• Important for

• Conversion technology

• Plant design

• Homogeneity

• Economy of scales

• Standardization

• CEN, ISO, DIN, ASTM


Biomass properties

• Internet databases

• ECN www.ecn.nl/phyllis

• DoE Biomass program


• Wood (untreated, treated)

• Grass

• Manure

• Waste

• Sludge

• Straw

• Husk/shell/pit

• Organic residue

• Algae

• Vegetable oil

http://www.ecn.nl/phyllis

http://www.ecn.nl/

Physical properties (1)


Moisture content Storage, dry-matter losses

Volatile content/

composition

Thermal decomposition,

combustion technology

Ash content Dust emission, ash manipulation

Fixed carbon Combustion technology

Calorific/Heating

Value

Fuel utilization, plant design

Physical properties (2)


Ash melting Safety, process control

Fungi

Health risks

Bulk density Logistics

Particle density, heat

capacity, conductivity

Thermal decomposition

Dimension, shape,

distribution

Conveying, drying, bridging,

combustion technology

Chemical properties / elements (1)


Carbon C Heating Value

Hydrogen H Heating Value

Oxygen O Heating Value

Nitrogen N NOx, N2O emissions

Chlorine Cl HCl, PCDD/F emissions, corrosion

Sulphur S SOx emissions, corrosion

Fluor F HF emissions, corrosion

Chemical properties / elements (2)


Potassium K Corrosion, ash melting

Sodium Na Corrosion, ash melting

Magnesium Mg Ash melting, utilization

Calcium Ca Ash melting, utilization

Phosphor P Ash utilisation

Heavy metals Emission, ash melting

Structure of wood


Softwood Hardwood

Composition of woody biomass


Tracheids

Middle

Lamella


Combination of three CHO components

1. Cellulose

2. Hemicellulose

3. Lignin



1. Cellulose (C6H10O5)n

• Structure, fibre walls

• Carbohydrate C6(H2O)5

• Polysaccharide

• Polymer of glucose C6H10O6

• n = ~104



2. Hemicellulose (C5H8O4)n

• Encasing of cellulose fibre, cross links

• Carbohydrate, polysaccharide

• Other than glucose: xylose,…

• Branched shorter chain (~103)



3. Lignin (C40H44O6)

• Fills the spaces

• Binding agent / strength

• Non-sugar polymer

• Aromatic structure


http://upload.wikimedia.org/wikipedia/commons/e/ee/Lignin_structure.svg



Cellulose Hemicellulose Lignin

Beech 45.2 32.7 22.1

Birch 44.5 36.6 18.9

Pine 45.0 26.4 28.6

Spruce 48.5 21.4 27.1

Characterization methods

• Proximate analysis

• Moisture content

• Volatile matter

• Fixed carbon

• Ash content

• Ultimate analysis

• C, H, O, N, S, …

• Bomb calorimeter

• Calorific/Heating value


Proximate analysis

• Place biomass sample on a scale in an oven filled with inert gas

• Heat up to 110˚C → moisture evaporates

• Measure weight loss → moisture content

• Wet basis:

• w = (wet weight-dry weight)/wet weight

• Dry basis:

• u = (wet weight-dry weight)/dry weight

• Conversion:

• w = u/(1+u) u = w/(1-w) u > w


Moisture content

Moisture content may vary a lot


Proximate analysis continued

• Sample is heated to 600˚C

• Devolatilization, pyrolysis

• Volatile matter (VM) is released from sample

• Tar: parts/monomers of (hemi)cellulose, lignin

• Gas: CO, H2, CH4, CO2, H2O…

• Weight loss gives VM content

YVM = weight loss / dry weight (wt % d.b.)


Proximate analysis continued

• Air is allowed to enter the system

• The sample burns and ash remains

• Ash content

YAsh = weight ash / dry weight (wt % d.b.)

• Fixed carbon content determined by difference

YFC = 1 - YVM - YAsh (wt % d.b.)


Proximate analyses


VM FC Ash VM FC Ash

Thermo-Gravimetric Analysis (TGA)

• Put sample in inert atmosphere

• Pure nitrogen N2

• Slowly heat up sample

• Heating rate ~20 °C/min

• Measure weight loss as function of time

• Typical result…


TGA of pine bark


10.47% moisture(0.5128mg)

49.41% Volatiles(2.419mg)

37.96% F.C.(1.858mg)

Residue:2.037% Ash(0.09972mg)

0

200

400

600

Te

mp

era

ture

(°C

)

0

20

40

60

80

100

120

We

igh

t (%

)

0 20 40 60 80 100 120

Time (min)

Sample: Bark 90 micronSize: 4.8961 mgMethod: BiomassComment: first test

DSC-TGAFile: C:\TA\Data\TGA\Bark90micron.002Operator: AdrianRun Date: 5-Nov-03 13:58

Universal V3.0G TA Instruments

Results of pine bark


% Wet % Dry % DAF

Moisture 10.5 - -

Ash 2.1 2.3 -

Volatile Matter 49.4 55.2 56.5

Fixed Carbon 38.0 42.4 43.4

Low

Derivative TGA curve


Cellulose

Hemicellulose

Lignin

TGA and DTG for softwood biomass


TGA and DTG for hardwood


A devolatilization model


Exam question


Sample is put in N2 filled

furnace. After 45 min. the

temperature is increased to

110 ℃. After 30 min. it is

slowly increased to 600 ℃.

Finally, air is supplied.

a) Explain the curve.

b) Determine composition

on wet basis, and dry-

and-ash-free basis.

Answer


Ultimate analysis

• Sample is burned in O2 atmosphere with He as carrier gas

• Combustion gases are CO2, H2O, NO, NO2, SO2, SO3 and N2

• SO3, NO and NO2 are reduced at copper contact to SO2 and N2

• H2O, SO2 and CO2 are captured in different adsorption columns


Ultimate analysis continued

• N2 is not captured and is detected by a thermal conductivity detector (TCD)

• N2 → N

• Consecutively, H2O, SO2 and CO2 will be sent to TCD

• H2O → H

• SO2 → S

• CO2 → C

• Mass percentage is determined integrally

• O is found by difference


Ultimate analyses


Coalification (Van Krevelen) diagram


Gross calorific / Higher heating value

• Empirical relation for biomass

GCV = 34.91 YC + 117.83 YH + 10.05 YS

– 1.51 YN – 10.34 YO – 2.11 Yash [MJ/kg d.b.]

Yi is content in wt% d.b.


Calculation exercise for CH1.0O0.4375

Bomb calorimeter

Device to measure

heating value


Effect of moisture on heating value

• Gross Calorific Value (GCV) Higher Heating Value (HHV)

• Heat released during combustion per mass unit fuel

• Final temperature same as initial temperature

• Water is formed in liquid phase

• Net Calorific Value (NCV) Lower Heating Value (LHV)

• Water is formed in gaseous phase

• Latent heat + sensible heat (100-25℃)


Lower heating value

Derived from HHV

Dry basis:

Wet basis:

YH = hydrogen wt% d.b. (~6%)

w = moisture content wt% w.b.


18

2.442

db

HLHV HHV Y

Calculation exercise for dry CH1.0O0.4375

(1 ) 2.44wb dbLHV LHV w w

Ash

• Inherent ash versus entrained ash

• Bottom ash versus fly ash

• Constituents

• Plant nutrients: CaO, MgO, K2O,

P2O5, Na2O

• Other oxides: SiO, Al2O3, Fe2O3

• Heavy metals: Cu, Zn, Cr

• Organic contaminants: PCDD/F

and PAH

• Ash utilization: manufacturing

cement and concrete, road

construction, soil improver,…


Ash melting behavior

• Sintering: agglutination of particles

• Softening temperature: change of surface, rounding,

shrinking.

• Hemisphere temperature: spherically shaped

• Melting temperature: size reduced to 1/3

• Ca and Mg increase

• K and Na decrease


Improving biomass quality

• Growing phase

• Harvesting date (moisture)

• Fertiliser (Cl in straw)

• Rainfall during storage on the field

• Supply phase: Upgrading

• Increase energy density

• More homogeneous

− Chunking, chipping, grinding

− Drying

− Compressing (pellets and briquettes)


Leaching of barley straw by rainfall


Conversion processes


Biomass conversion routes


Thermochemical conversion

• Advantage: High throughput, second generation

biomass

• Three main processes

• Pyrolysis Air ratio = 0

• Gasification Air ratio = 0.25 – 0.50

• Combustion Air ratio = 1 – inf.

• Difference: the amount of oxidizer (air) available


Air ratio = Actual air fuel ratio

Air fuel ratio for stoichiometric combustion

Questions


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