Abstract—This short paper communicates various methods for

recovering energy value from fine coal discards generated by the

South African coal mining industry. The cost of dewatering or drying

these fines <150µm exceeds the fuel value of the fines. However the

quality of these fines is equivalent to that of run- of –mine coal.

These fines are normally disposed into the slurry dams. They have

negative environmental impact such as acid mine drainage, dust

release and spontaneous combustion. Various technologies for

treating and recovering the value out of these fines are discussed.

This paper, thus presents energy and material recovery from coal fine

coal discards. It also highlights the waste minimization and

utilization options for this abundantly available waste and resource.

Keywords—Energy, Environment, Fuel, Mining, Waste.

I. INTRODUCTION

LOBAL economic crisis reduced electricity and steel

production in many developed and developing countries.

The global coal production was about 6 billion metric

tonnes in 2009 with China producing about half of that [1].

Known coal reserves are spread over 100 countries. At the

production levels of 1999, world reserves were expected to

last over 100 years compared to oil and gas reserves at 45 and

65 years respectively [2]. However, in South Africa about 200

years – worth of supply is still available. In 2009, the total

world primary energy consumption by fuel was coal (26%),

gas (24%), oil (40%), nuclear (7%) and renewables (3%) [2].

Coal provides around 30% of global primary energy needs,

generates 41% of the world's electricity and is used in the

production of 70% of the world's steel [3]. The coal mining

industry was the largest component of the South African

mining sector by sales volume (R65.3 billion) with a coal

production of about 250.5 million tonnes in 2009 [1]. The

South African coal mining industry is currently disposing over

10 million tons of ultra-fine coal (<150µm) per year which is

approximately 4% of the annual coal production [4]. Coal

fines are an unavoidable by-product of the production of coal.

These fines have an average calorific value of 22.83MJ/kg

with average size fraction of 150µm. Dewatering of the high

quality fines is advantageous for several reasons including

reducing transport cost. Flotation is the only effective method

Edison Muzenda is a full professor in the Department of Chemical

Engineering Technology at the University of Johannesburg, Doornfontein,

South Africa e-mail: emuzenda@uj.ac.za

of beneficiating ultra-coal fines, and many coal producers in

the world commonly use these flotation plants. In terms of

dewatering, there are several kinds of equipment suitable for

the purpose, including screen-bowl-centrifuge, horizontal

vacuum belt filters and thermal drying. A recent study

concluded that thermal drying to 1% of the surface moisture is

the most economical method of dewatering the ultra fines. The

beneficiated and dewatered ultra-fines can be blended with

coarser coal for export market.

Un-beneficiated fines are low quality ultra-fines and

generally sold to local power stations as a feed stock. The

ultra-fines have ash content of 45%, particle size of 150

microns with nett calorific values ranging between 2-14.6

MJ/kg [5]. Thermal drying of these fines is not economically

feasible owing to the low value of coal. Waste Energy

Recovery and Management (WERM), has patented a process

of drying and recovering ultra-fines from slimes dams using

solar energy. Every 2-3 days the top of 300mm layer of the

dam is ploughed and stockpiled. The ultra-fines are dried

between to 12-18% because they become difficult to handle

outside this range [4]. Once the coal is dried, its not easy to re-

wet if it is stockpiled. This enables drying to occur during the

rainy seasons, although 30-40% decrease in yield may be

experienced.

The dried ultra-fine material is blended with re-washed

coarse waste rock. The purpose of blending the fines with

waste rock is to lower the overall moisture content. This

process converts the ultra-fines to a valuable product because

WERM operates until the slimes dam is empty. The dried

material is transported to site as a feed stock to power station.

The material is further dried by waste heat energy in the form

of flue gases from the power stations.

The fine coal plant consists of drying plant, dust separation

plant and medium phase pneumatic conveying. Drying of coal

fines is done through fluidized bed dryers using hot flue gas.

As the flue gas is inert, the drying process is safe from coal-

dust explosion [6].

II. TECHNOLOGY DISCUSSIONS

A. Ultra-fines into a low smoke fuel

This method entails converting the ultra-fine coal to a low

smoke fuel (LSF).These fuels release low levels of smoke

when burnt. These fuels are ideal for domestic usage,

particularly in the townships. Thus, this helps to reduce the

energy poverty for these disadvantaged communities by

Potential uses of South African Coal Fines:

A Review

Edison Muzenda

G

3rd International Conference on Mechanical, Electronics and Mechatronics Engineering (ICMEME'2014) March 19-20, 2014 Abu Dhabi (UAE)

37

providing them with affordable green energy. In order to

convert the ultra-fine coal into Low smoke fuels, the coal

should be agglomerated to make it easier to handle. Various

methods of agglomeration are available, including palletizing,

extrusion, binder and binder- less briquetting. Coal briquetting

can be achieved by means of pressure and / or chemical

bonding. Coal briquetting has drawbacks which have to be

addressed for this resource to be economically exploited. The

application of untreated fines and super fines cause process

difficulties as these fines can agglomerate and clog up process

equipment initially designed to use large coal particles. The

transportation and storage of fine coal pose environmental and

logistical problems. For example these fines may collect water

during transportation and become unusable. South Africa

produces millions tonnes of coal annually, hence the

production and storage of these fines is an increasing

environmental disaster that needs to be eliminated. Briquetting

offers a potential solution to these challenges. However for

briquetting to be successful, the following conditions have to

be met (i) The particles must be in the same size range (ii)

Briquettes must be water resistant for possible outside storage

(iii) Briquettes must be strong enough not to disintegrate

during transportation and handling (iv) Briquettes should have

similar properties such as heat value, fixed carbon, sulphur

content and ash content to the original coal. Laboratory tests

have been conducted at Kleinkopje by Coaltech 2020 to

establish the technical feasibility of the production of LSF

from ultra-fines in South Africa. The tests confirmed that the

process is technically feasible in South Africa [5].

B. Methane and Polymers Production

Methane gas and polymers may be produced from coal fines

through a process of solubilisation. Coal solubilisation is the

process through which coal is converted by micro organisms

and enzymes into a solution of macromolecules. These in turn

can be converted into various products, such as methane or

polymers. Low rank coals such as lignite are more susceptible

to solubilization because of their higher moisture content,

softness and low abrasion index. However certain micro-

organisms can solubilize high rank coals as well. This

technology is not commercially available in South Africa,

however research is currently being undertaken at local

universities to optimize and commercialise this process [7].

The research is driven by Coal Tech 2020, a collaborative

research programme which was formed by major coal

companies, Universities, Council for Scientific and Industrial

Research (CSIR), National Union of Mine Workers (NUM)

and the State to address the specific needs of the coal mining

industry in South Africa using local and international

knowledge and skills. The vision of Coal Tech 2020 is “The

development of technology and the application of research

findings to enable the South Africa coal industry to remain

competitive, sustainable and safe well into the Twentyfirst

Century”

C. Ultra-fines to Coal Water Fuel

Coal water fuels (CWF) are concentrated suspensions of

highly beneficiated ultra fines in water. They contain 60-70%

solids with ash content of not more than 4%.The CWF can be

produced from ultra fine slurries by undergoing extensive

grinding and crushing to improve liberation of high grade coal

so that the low ash requirement can be met. This fuel is

normally piped directly to a power station where it is burnt as

heavy oil, rather than being added to the coarse coal [8]. CWF

have several advantages over traditional dry coal, the problems

of spontaneous combustion and dust generation during

transportation and storage are eliminated. The cost of drying

and dewatering are significantly reduced and CWF are more

easily handled because, being liquid, they do not require large

scale transportation of handling facilities. There is currently no

power station in South Africa that can utilize CWF.

D. Fluidized Bed Technology

A fluidized bed reactor is a combustor in which coal

particles are suspended in a bed by updraft of gas that keeps

the coal fines in turbulent state. Research conducted by the

Council for Scientific and Industrial Research (CSIR), South

Africa has established that it is technically feasible to combust

ultra fines of 63% moisture in a fluidized bed reactor[5].A

conventional pulverized fuel boiler requires that the feed coal

contains at most 10% moisture. Therefore the cost of drying or

dewatering is greatly reduced in a fluidized bed reactor.

Although thermal efficiency of 67 is achieved, the cost of

obtaining this coal is reasonably low. The fines are unstable,

thus transport other than pipeline is not feasible. There are no

commercial fluidized bed combustion power stations in South

Africa that run on coal, although Eskom plans to install them

in the unspecified future.

E. Production of Solid Fuel

The following three fuel formulations were developed using

combinations of commonly available biomass, waste materials,

and recovered beneficiated coal fines to produce economical,

new solid fuels that reduce emissions from coal-fired boilers

[9].

Premium Fuel: Anthracite Fines & Waste Plastic

This formulation was developed for a premium fuel market,

specifically the stoker and home-heating market which

requires a very high-quality solid fuel, beneficiated anthracite

(90% by weight) is pelletized using waste mixed plastics as a

binder (10% by weight). The final pelletized low-moisture;

high-energy product is projected to have the following

qualities: 1.5% moisture, 9.0% ash, 0.56% total sulphur, and

30.27MJ/kg. The use of waste plastic as a binder reduces fuel

production costs. Fuel pellets have a high volatile content

(>90%), which can be adjusted to meet customer needs by

varying the amount of plastics in the formulation. Plastic also

has essentially no ash or sulphur and is high in heating value.

Low ash reduces particulate emissions, and the combination of

high heat content and low sulphur reduces SO2 emissions.

3rd International Conference on Mechanical, Electronics and Mechatronics Engineering (ICMEME'2014) March 19-20, 2014 Abu Dhabi (UAE)

38

Medium Quality: Coal Fines & Sewage Sludge.

This formulation was developed for a medium grade fuel

market, specifically the electric utility steam coal market.

Beneficiated coal fines (80% by weight, dry basis), such as the

type recovered from waste coal slurry impoundments, and

treated sewage sludge (20% by weight, dry basis) are mixed

and pelletized. The sewage sludge is typically received with

very high moisture content (80-85 percent), and a combination

of thermal drying and the pelletizer-dewatering would be used

to reduce the moisture content of the final product to 15

percent. The final pelletized product is projected to have the

following quality: 15.0% moisture, 10.0% ash, 1.4% total

sulphur, and 25.2MJ/kg.

Low Quality: Coal Fines & Sawdust

This formulation was developed for a low-grade fuel

market, specifically the electric utility steam coal market.

Beneficiated coal fines (90% by weight), such as the type

recovered from waste coal slurry impoundments, and sawdust

(10% by weight) are slurried during the coal preparation

process. An asphalt emulsion (at 2% dosage) is added to the

slurry prior to the mechanical dewatering step. This results in

an agglomerated product with improved dewatering

characteristics and flow ability properties, and reduces dust

generation during handling; it also improves the recovery of

fine-sized coal during the beneficiation process. This produce

is only considered to be "low quality" because of its finer size

and high moisture content as compared to typical steam-grade

bituminous coals. This agglomerated product is projected to

have the following quality: 19.0% moisture, 5.2% ash, 1.2%

total sulphur, and 23.3 MJ/kg

III. CONCLUSIONS

The current production of coal discards and slurry ponds are

35.5 and 3.26 million tonnes per year respectively. The coal

discards are generally compacted with soil and vegetated to

prevent further oxidation. These dumps are reclaimable and

can be used as feed stock to power stations. There are 29

active discards dumps (310Mt) and 17 active slurry ponds

(51Mt) available in South African coal mines. The utilization

of coal fines should aim to optimize the sometimes competing

economic, social and environmental objectives.

ACKNOWLEDGMENT

The author acknowledges Jefrey T Pilusa his PhD student

for collecting and reviewing the information as well as

assisting with drafting the manuscript. He is also indebted to

South African National Energy Development Institute

(SANEDI) through its Waste to Energy project at the

University of Johannesburg for partly funding conference

attendance. The University of Johannesburg’s Faculty of

Engineering and the Built Environment’s Research Committee

is also acknowledged for financial and technical support.

REFERENCES

[1] www.bullion.org.za/Publications/Facts and Figures 2009/ Accessed 18

February 2014

[2] BP Amoco Statistical Review of World Energy 1999 (1998 data)

[3] World Coal Association, www.worldcoal.org/resources/coal-statistics/

[4] J.F. Reddick, H. von Blottnitz, and B. Kothuis (2007). “A cleaner

production assessment of the ultra-fine coal waste generated in South

Africa” The Journal of The Southern African Institute of Mining and Metallurgy.

Vol 107, pp 55-60

[5] S.J. Mangena and G.J. de Korte (2004). “Development of a Process for

Producing Low-Smoke Fuels from Coal Discards”

[6] Horsfall, D.W. (1994). Low-smoke fuel from discards. DME Report No.

ES9017, 48 p.

[7] L.Wibberley (2011). “Coal base-load power using Micronised Refined

Coal (MRC)”, Energy Generation.

[8] B. G., Miller, D. K. Johnson, M. LaBarbera, B. A. Maben, J. L.

Morrison, R. S. Wasco, R. T. Wincek (2008). “Formulation, Production,

and Combustion Testing of a Coal-Water Mixture Prepared from Fine

Coal – Final Report,” Teck Cominco Metals Ltd.

[9] A. G. Shirey, D. J. Akers (2005). Production of New Biomass/Waste-

Containing Solid Fuels

Biography: Edison Muzenda is a Full Professor of Chemical Engineering,

the Research and Postgraduate Coordinator as well as Head of the

Environmental and Process Systems Engineering Research Group in the

Department of Chemical Engineering at the

University of Johannesburg. Professor

Muzenda holds a BSc Hons (ZIM, 1994)

and a PhD in Chemical Engineering

(Birmingham, 2000). He has more than 15

years’ experience in academia which he

gained at different Institutions: National

University of Science and Technology,

University of Birmingham, Bulawayo

Polytechnic, University of Witwatersrand,

University of South Africa and the

University of Johannesburg. Through his academic preparation and career,

Edison has held several management and leadership positions such as

member of the student representative council, research group leader,

university committees’ member, staff qualification coordinator as well as

research and postgraduate coordinator. Edison’s teaching interests and

experience are in unit operations, multi-stage separation processes,

environmental engineering, chemical engineering thermodynamics,

entrepreneurship skills, professional engineering skills, research methodology

as well as process economics, management and optimization. He is a recipient

of several awards and scholarships for academic excellence. His research

interests are in waste water treatment, gas scrubbing, environment, waste

minimization and utilization, green energy engineering as well as phase

equilibrium measurement and computation. He has published more than 180

international peer reviewed and refereed scientific articles in journals,

conferences and books. Edison has supervised 28 postgraduate students, 4

postdoctoral fellows as well as more than 140 Honours and BTech research

students. He serves as reviewer for a number of reputable international

conferences and journals. Edison is a member of the Faculty of Engineering

and Built Environment Research and Process, Energy and Environmental

Technology Committees. He has also chaired several sessions at

International Conferences. Edison is an associate member of the Institution of

Chemical Engineers (AMIChemE), member of the International Association

of Engineers (IAENG); associate member of Water Institute of Southern

Africa (WISA), Associate Editor for the South African Journal of Chemical

Engineering as well as a member of the Scientific Technical Committees and

Editorial Boards of several scientific organizations.

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