Thesis Abstract

<p> This work studied the effect of groundnut shell and maize cob on coal<br>briquette. The ratio of coal biomass prepared were 9010, 8515, 8020,<br>7525, 7030, 1000. The mixture was treated with Ca(OH) which serves<br>as a desulphurizing agent, before briquetting. The chemical analysis<br>carried out on the raw materials (i.e. groundnut shell, maize cob and<br>coal) indicated the presence of Ca, Mg, Al, Na, Fe, Cu, K, Zn, Mn, Pb,<br>Ni, Cr, As, S. The proximate analysis of the raw materials was also<br>carried out. Burning and viability tests carried out revealed that maize<br>cob-coal briquettes ignite and burn faster, smoke less, produce flame<br>and small quantity of ash after burning, than the other briquettes.<br>Hardness compressive strength and density test of the briquettes<br>produced showed that coal briquette has better hardness, compressive<br>strength, and density results than the other briquettes. Also, the bio-coal<br>briquette with the highest percentage of biomass (i.e. 30%) gave the<br>best viability, burning, porosity, porosity index, ash content, calorific<br>value results than the other briquettes. However, maize cob-coal<br>briquettes gave the best results compared to the groundnut shell-coal<br>briquettes and the coal briquette which was used as the standard. <br></p>

Thesis Overview

<p> </p><p>INTRODUCTION:<br>Energy is the ability to do work. Sources of energy include<br>electricity, petroleum, nuclear power, solar energy, tar sand, burning of<br>coal, wood and biomass, etc. Nigeria is blessed with abundant energy<br>resources: oil, gas, coal, wood, biomass, solar, wind, nuclear and<br>hydropower.<br>Energy availability in Nigeria and its supply has been a source of<br>constant friction between the people and the government. This however,<br>should not be so because, among the abundant energy resources<br>available in Nigeria, only oil and gas sector have so far been well<br>developed. The industrial and domestic sectors of the Nigerian economy<br>continue to suffer from perennial shortage of energy. This shortage has<br>led to accurate energy crisis at the household level. The bulk of the<br>energy used for cooking at the household level in Nigeria is mainly<br>derived from wood fuel and fossil fuel (kerosene).<br>The fossil fuels are produced and delivered at a cost most<br>Nigerians cannot afford. As a result, a greater percentage of the ever<br>growing population of the country have resorted to depend on the<br>country’s forest waste as a source of fuel for agricultural, domestic and<br>small-scale industrial activities in semi urban and rural areas. The use of<br>wood fuel encourages cutting down/felling of trees (deforestation). This<br>leads to desertification in the Northern part of Nigeria; and flooding, soil<br>erosion and loss of top soil fertility in the Southern part of Nigeria. In<br>some cases, it can lead to extinction of wild life.<br>Energy is the key factor in economic development in most<br>countries today. In Nigeria, there is overdependence on oil and gas for<br>energy for industrial and domestic purposes, since it is the only source of<br>2<br>energy that is well developed. Hence, there is need to develop the other<br>sources of energy so that energy supply will be enough and affordable<br>for industrial and domestic purposes, and our oil and gas be conserved<br>(and used for transportation). Most advanced countries today are<br>adapting the concept of preserving and also retaining their natural<br>resources. As the world adjusts itself to the new millennium and its<br>technology, the demand for fuel and energy increases, therefore, it<br>should be conserved.<br>Of all the available energy resources in Nigeria, coal and coal<br>derivatives such as smokeless coal briquettes, bio-coal briquettes, and<br>biomass briquettes have been shown to have the highest potential for<br>use as suitable alternative to coal/wood fuel in industrial boiler and brick<br>kiln for thermal application and domestic purposes, therefore, it will serve<br>as the most direct and effective method of combating deforestation in the<br>country. Coal and biomass are available, and cheap.<br>There is a worldwide acceptance of briquettes and growing<br>demand for the briquetting plants. In June 2009, a workshop on<br>“Investment Potentials of the Nigerian Coal Industry” was organized by<br>the Nigerian Coal Coporation. It was clear from the workshop that<br>substantial progress has been made in briquetting technology and<br>practice in recent years.<br>In countries like Japan, China and India, it was observed that<br>agricultural waste (agro residues) can also be briquetted and used as<br>substitute for wood fuel. Every year, millions of tons of agricultural waste<br>are generated. These are either not used or burnt inefficiently in their<br>loose form causing air pollution to the environment. The major residues<br>are rice husk, corn cob, coconut shell, jute stick, groundnut shell, cotton<br>stalk, etc. These wastes provide energy by converting into high-density<br>fuel briquettes. These briquettes are very cheap, even cheaper than coal<br>3<br>briquettes. Adoption of briquette technology will not only create a safe<br>and hygienic way of disposing the waste, but turn into a cash rich<br>venture by converting waste into energy and also contributing towards a<br>better environment.<br>Coal can be blended with a small quantity of these agricultural<br>waste (agro residues) to produce briquettes (bio-coal briquettes) which<br>ignites fast, burn efficiently, producing little or no smoke and are cheaper<br>than coal briquettes.<br>Briquetting technology is yet to get a strong foothold in developing<br>countries including Nigeria, because of the technical constrains involved<br>and lack of knowledge to adopt the technology to suit local conditions.<br>Overcoming the many operational problems associated with this<br>technology and ensuring the quantity of the raw material used are crucial<br>factors in determining its commercial success. In addition to this<br>commercial aspect, this technology encourages conservation of wood.<br>Hence, briquette production technology can prevent flooding and serve<br>as a global warming countermeasure through the conservation of forest<br>resources.<br>1.1 Coal:<br>1.1.1 Concept of coal:<br>Coal is a carbon containing, combustible solid, usually stratified which<br>is formed by debris from the decay of ferns, vines, trees and other plants<br>which flourished in swamps millions of years ago. Over time, the debris<br>became buried and the actions of bacteria, heat, and pressure<br>transformed the debris first into peat (a precursor of coal) and then into<br>the various types of coal .This process of transformation is referred to as<br>metamorphosis, coalition or lithification. Coal is composed chiefly of<br>carbon, hydrogen, oxygen, with a minor amount of nitrogen and sulphur,<br>and varying amounts of moisture and mineral impurities such as<br>4<br>phosphorus. Coal lumps are black or dark brown in colour, its colour,<br>luster, texture, etc vary with the type, rank and grade [1]<br>Classification of coal:<br>There are four main classifications of coal, arising from progressive<br>variation in their carbon content.<br>i. Peat: contains about 60% carbon.<br>ii. Lignite coal: contains about 65% carbon.<br>iii. Sub bituminous coal: contains about 70% carbon.<br>iv. Bituminous coal: contains about 85% carbon.<br>v. Anthracite coal: contains about 94% carbon [2].<br>Destructive distillation of coal: This involves heating coal to a very high temperature (600-12000C) in<br>the absence of air. During this process, the coal decomposes to give<br>coal gas, coal tar, coke and ammoniacal liquor.</p><p>Coal heat coke + coal tar + coal gas + ammoniacal liquor. i. Coal gas: This is a mixture of hydrogen, carbon(iv) oxide and small<br>amount of ethane, hydrogen sulphide, and sulphur (iv) oxide. The<br>main use of coal gas is as fuel.<br>ii. Coal tar: A thick brownish-black liquid is a mixture of many organic<br>chemicals including benzene, toluene, phenol, naphthalene and<br>anthracene. The component can be separated by fractional<br>distillation and are used for the manufacture of commercial products<br>including drugs, dyes, paints, insecticides , etc.<br>iii. Coke: This is non-volatile residue which contains about 90%<br>amorphous carbon and is chemically similar to hard coal. Coke is<br>used in the manufacture of carbide as fuel and as reducing agent in<br>the extraction of metals. Coke is used to make producer gas and<br>water gas.<br>5<br>iv. Ammoniacal liquor: This is an aqueous solution containing mainly<br>ammonia, and is used in the manufacture of ammonium<br>tetraoxosulphate (iv) [3].<br>Coal mining in Nigeria:<br>Coal was first discovered in Nigeria in 1909 near Udi by the mineral<br>survey of Southern Nigeria. Between 1909 and 1913, more coal<br>outcrops were located. Coal is found in the following Nigerian States:<br>Enugu, Imo, Kogi, Delta, Plateau, Abia , Benue ,Edo, Bauchi, Adamawa,<br>Gombe, Cross River States. In 1950, the Nigerian Coal Corporation<br>(NCC) was formed and given the responsibility for exploration,<br>development and mining of the coal resources [4].<br>Nigerian coal resources:<br>Nigerian coal resources has been found suitable for boiler fuel,<br>production of high calorific gas, domestic heating, briquettes, formed<br>coke, and the manufacture of a wide range of chemicals including<br>waxes, resins, adhesives and dyes. The characteristic properties of<br>Nigerian coal (low sulfur, and ash content and low thermoplastic<br>properties) make these sub-bituminous coals ideal for coal-fired electric<br>power plant [4].<br>Coal deposits of Nigeria:<br>Coal exploration in Nigeria started as far back as 1916. Available<br>data show that coal (mainly sub-bituminous steam coals except for the<br>Lafi-obi bituminous coking coal) occurrences in Nigeria have been<br>indicated in more than 22 coal field spread over 13 States of the<br>Federation. The proven coal reserves so far in Nigeria total about 639<br>million metric tones while the inferred reserves sum up to 2.75 billion<br>metric tones. In addition, an estimated 400 million tones of coal lie<br>untapped under the soil of Enugu. [5]<br>6<br>Presently, the Nigeria coal industry has four existing mines at Okpara<br>and Onyeama underground mines in Enugu State, Okaba surface mine<br>in Kogi State and Owukpa underground mine in Benue state. In addition,<br>there are more than 13 undeveloped coal fields. The undeveloped coal<br>fields in Nigeria are of two categories:<br>The virgin coal fields where further detailed exploration work and/or<br>access roadways are required and the developing coal fields where<br>reserved have been proven and mine access roadways developed. The<br>developed coal fields include Azagba Lignite field in Delta State,<br>Ogboyoga coal field in Kogi State, Ezimo coal field in Enugu State, Lafi<br>obi coal field in Nassarawa State and Inyi coal field in Enugu State while<br>others are located in Amansiodo in Enugu state, Ute in Ondo State,<br>Lamja area of Adamawa State, Gindi-Akunti in Plateau State, Afuze in<br>Edo State, Janata-Koji area of Kwara State and extension of Okpara<br>mine south in Enugu State [6].<br>Table1: EXISTING POTENTIAL COAL MINE SITES WITH RESERVES IN<br>NIGERIA [6]</p><p>S/N<br>Mine<br>location<br>State Type of<br>coal<br>Estimated<br>reserves<br>(million<br>tonnes)<br>Proven<br>reserves<br>(million<br>tonne)<br>Depth of<br>coal (m)<br>Mining<br>Method<br>1 Okpara mine<br>Enugu Sub<br>bituminous</p><p>100</p><p>24</p><p>180</p><p>Underground<br>2 Onyeama mine<br>Enugu Sub<br>bituminous</p><p>150</p><p>40</p><p>180</p><p>Underground<br>3 Ihioma Imo Lignite 40</p><p>NA</p><p>20-80</p><p>Open cast<br>4 Ogboyoga Kogi Sub bituminous</p><p>427</p><p>107</p><p>20-100<br>Open cast/<br>underground<br>5 Ogwashi Azagba<br>Delta Lignite<br>250</p><p>63</p><p>15-100<br>Open cast/<br>underground<br>7<br>6 Ezimo Enugu Sub bituminous</p><p>156</p><p>56</p><p>30-45<br>Open cast/<br>underground<br>7 Inyi Enugu Sub bituminous</p><p>50</p><p>20</p><p>25-78<br>Open cast/<br>underground<br>8 Lafia/obi Nassarawa Bituminous 156</p><p>21-42</p><p>80</p><p>Underground<br>9 Nnewi / Ota<br>Anambra Lignite 30<br>NA</p><p>18-38</p><p>Underground<br>10 Amasiodo Enugu Bituminous 1000 NA 563 Underground<br>11 Afikpo/ Okigwe<br>Ebonyi/ Imo Sub<br>bituminous</p><p>50</p><p>N.A</p><p>20-100</p><p>Underground<br>12 Okaba Kogi Sub bituminous</p><p>250</p><p>3</p><p>20-100</p><p>Underground<br>13 Owukpa Benue Sub bituminous</p><p>75</p><p>57</p><p>10-100<br>Opencast/<br>underground<br>14 Ogugu/ Agwu<br>Enugu Sub<br>bituminous</p><p>NA</p><p>NA</p><p>NA</p><p>Underground<br>15 Afuji Edo Sub bituminous</p><p>NA</p><p>NA</p><p>NA</p><p>Underground<br>16 Ute Ondo Sub bituminous</p><p>NA</p><p>NA</p><p>NA</p><p>Underground<br>17 Doho Bauchi Sub bituminous</p><p>NA</p><p>NA</p><p>NA</p><p>Underground<br>18 KurumuPindosa<br>Bauchi Sub<br>bituminous</p><p>NA</p><p>NA</p><p>NA</p><p>Underground<br>19 Garin Maigunga<br>Bauchi Sub<br>bituminous</p><p>NA</p><p>NA</p><p>NA</p><p>Underground<br>20 Lamja Adamawa Sub bituminous</p><p>NA</p><p>NA</p><p>NA</p><p>Underground<br>21 Janata koji Kwara Sub bituminous</p><p>NA</p><p>NA</p><p>NA</p><p>Underground<br>22 Gindi akwati<br>Plateau Sub<br>bituminous</p><p>NA</p><p>NA</p><p>NA</p><p>Underground<br>N/B: NA= Not available.<br>8<br>1.1.2 Uses of coal:<br>(a). Cement production: Coal is used for cement manufacture. In<br>Nigeria, Okaba, Ogboyoga and Owukpa coals are suitable for cement<br>manufacturing. Their physical properties qualify them for the purpose [6]<br>(b). Power generation: Coal is one of the two most principal sources of<br>fuel and energy, the other being petroleum [7]<br>Power plays a central and crucial role in national development.<br>Nigeria‘s power supply falls far short of demand. This inadequacy<br>represents a major constraint on industrial growth, and underscores the<br>need to make electricity more widely available, and more specifically in<br>the rural areas. This is in order to encourage the development of cottage<br>industries in the countryside, ameliorate the living conditions of the rural<br>dwellers and thus reduce the incidence of flight to the cities in search of<br>gainful employment, especially by the youth and trained man power. To<br>ensure a regular and dependable supply of the requisite amount of<br>power in the country, coal can be used for power generation [8]. In<br>Nigeria, Okaba, Ogboyoga, and Onyeama coals are suitable for power<br>generation. Their physical properties which include high calorific value,<br>low sulphur content (about 0.69%), low ash, low moisture, and high<br>volatility qualify them for this purpose [6].<br>(c). Metallurgical purposes: The most important non fuel use of coal is in<br>smelting of iron ores. The main process for iron production from its ore is<br>still the blast furnace. The blast furnace process of making iron and steel<br>employs coke (the solid product from coal carbonization) as a major raw<br>material [7]. Not all coal can yield the type of coke (metallurgical coke)<br>that can be utilized in a blast furnace. The Nigerian coals are generally<br>non–coking, and hence, the coals derived from there are not directly<br>utilizable in blast furnace [8]. Onyeama mine and Okpara West area<br>9<br>mine coals are suitable as the process require very high temperatures<br>[6].<br>(d). Coal for export: Onyeama mine and Okpara mine coals have been<br>mapped out mainly for export.<br>(e). Industrial fuel: Coke char will also find widespread use in a variety of<br>industrial enterprises such as cement factories, foundries, ceramics<br>plants, bakeries, laundries and brick manufacture. Because of the<br>unreliability of electric supply, coke char and solid briquettes could also<br>be effectively deployed as non-polluting prime energy resources by rural<br>cottage industries [8].<br>(f). Coal is also used in making chemicals: For instance, the solvent<br>extraction studies of Enugu coals using benzene /methanol<br>(C6H6/CH3OH) as the extracting solvent system, it was possible to<br>fractionate the extract into pre-asphaltenes (benzene insoluble, pyridine<br>soluble), asphaltene (n-hexane insoluble) and oils (n-hexane solubles)<br>and determine the n-paraffin content of the oils by urea adduction<br>technique. Also, montan wax has been obtained from brown coal by<br>solvent extraction. The waxes have immense industrial uses in candle<br>making, waxing paper, medicinal and cosmetics preparation among<br>others [9].<br>Coal Chemicals:-<br>For about 100 yrs, chemicals obtained as by-product in the primary<br>processing of coal to metallurgical coke have been the main source of<br>aromatic compounds used as intermediates in the synthesis of dyes,<br>drugs, antiseptics and solvent. Although some aromatic hydrocarbons<br>such as toluene and xylene are now obtained largely from petroleum<br>refineries, the main sources of others such as benzene, naphthalene,<br>anthracene, and phenanthrene is still the by-product of coke oven.<br>10<br>Heterocyclic nitrogen compounds such as pyridines and quinolines are<br>also obtained largely from coal tar.<br>Table 2: Coal tar chemicals:<br>Compound Use<br>Naphthalene Phthalic acid<br>Acenaphthenes Dye intermediates<br>Fluorene Organic synthesis<br>Phenanthrene Dyes, explosives<br>Anthracene Dye intermediates<br>Carbazole and other similar compounds Dye intermediates<br>Phenol Plastics<br>Cresols and xylenols Antiseptics<br>Pyridine, picolines, Intidines, quinolines, Drugs, dyes,antioxidants<br>acridine, and other tar bases.</p><p>Coal can also be converted to liquid fuels by:<br>a. Fischer Tropsch process:- Here, coal is heated in the presence of steam to a temperature of 12000C to give water gas.<br>C+ H2O 12000C CO + H2<br>b. Bergius process: Here, coal is heated in the presence of hydrogen to the temperature of 4500C and pressure of 200 atm to give<br>gasoline.<br>C + H2 4500C/ 200 atm gasoline<br>The use of a particular coal depends on its rank (i.e. peat, lignite,<br>bituminious, anthracite). The diagram below provides the estimated<br>percentage of the world’s coal reserves for each coal rank and also the<br>use of each coal rank.<br>11<br>% of world resources<br>Carbon and heating value high<br>High moisture content</p><p>Low rank coal (47%) Hard coal (53%)</p><p>Lignite (17%) sub bituminious (30%) anthracite (1%)<br>Bituminious (52%)<br>Largely power generation domestic industries<br>Power generation, cement manufacture, industrial uses .</p><p>thermal steam coal metallurgical coking coal<br>power generation, cement manufacture of iron steel manufacture, industrial uses.</p><p>Fig 1: Diagram of the typical uses and the estimated percentage of<br>the worlds’ coal reserves for each coal rank [10].</p><p>1.1.3 Coal as an alternative energy resource:<br>The great exploitation of fossil fuel began with the industrial<br>revolution, about two centuries ago. The newly built steam consumed<br>large quantity of fuel, but in England, where the revolution began, wood<br>was no longer readily available. Most of the forest has already been cut<br>down. Coal turned out to be an even better energy source than wood<br>because it yields more heat per gram. This difference in heat of<br>combustion is a consequence of differences in chemical composition.<br>When wood or coal burns, a major energy source is the conversion of<br>carbon to carbon (iv) oxide. Coal is a better fuel than wood because it<br>contains a high percentage of carbon and low percentage of oxygen and<br>water. Although coal is not a single compound, it can be approximated<br>by the chemical formula C135H96O19NS. This formula corresponds to a<br>carbon content of 85% by mass [11].<br>12<br>The exploitation of coal for energy (electricity) generation and the<br>production of bio-coal briquettes for domestic and industrial heating will<br>[12,13]:<br>i. Provide a more reliable energy (electricity supply),<br>ii. lower the cost of electrical supply,<br>iii. expand industrialization of the economy,<br>iv. increase employment and human recourses development,<br>v. increase capacity utilization of existing industry,<br>vi. increase national income through taxes,<br>vii. reduce deforestation and prevent desert encroachment in the<br>Northern part of the country.</p><p>1.1.4 Nigerians’ overdependence on oil and gas:<br>At the peak of its importance, coal was a major article of world trade<br>because it was the source of fuel for industrial and domestic purposes. It<br>was used in steam engine to generate power to drive ships, railway<br>locomotives and industrial machines.<br>Petroleum was discovered in commercial quantity at Oloibori in<br>Rivers state in the year 1956. Since the inception of petroleum in<br>Nigeria, the use of coal for electricity generation, cooking and for heating<br>up houses in the cold period to create warmth has long been neglected<br>inspite of its abundance in the country, because of the overdependence<br>on oil and gas. This results to constant failure in power supply, political<br>and economical instability due to insufficient and increase in price of<br>petroleum product [14].</p><p>1.1.5 A forecast of coal demand in Nigeria:<br>Presently in Nigeria, coal is not in demand. Infact, people depend<br>on oil and gas as source of fuel for domestic and commercial purposes.<br>13<br>With the introduction of briquette fuel for domestic and commercial<br>purposes, it is expected that the demand of coal in Nigeria will rise. In<br>countries like China, Nepal, Japan, India and United States where these<br>briquettes are already being used constantly and effectively [15], coal<br>demand has tremendously increased. For instance, in China, domestic<br>coal demand in 2002 reached 1370 metric tonne, accounting for 66% of<br>the total primary energy consumption [16], Japan total primary energy<br>supply, which was 459 million tonne oil equivalent (toe) in 1990 reached<br>466 million toe in 2001, indicating an increase of 1-6% for the period<br>[17]. In these countries, the demand for coal is expected to increase<br>from 1.051 billion tonnes in 2001 to 1.444 billion tonne in 2025 and coal<br>for electricity generation will constitute about 90% of total coal demand in<br>United States of America [18].<br>China and India together account for almost three quarters of the<br>increase in world coal demand. In all regions, the coal use becomes<br>increasingly concentrated in power generation which accounts for almost<br>90% of the increases in demand between 2000 and 2030 [19].<br>If Nigerian coal will be utilized in power generation and as domestic<br>fuel, its demand will increase, coal mining will be effective again, and our<br>oil and gas will be conserved for transportation purposes.</p><p>1.1.6 Environmental issues.<br>Coal contains carbon, hydrogen, sulphur, and other minerals. When<br>coal is burnt, carbon, hydrogen and sulphur react with oxygen in the<br>atmosphere to form carbon (iv) oxide, water and sulphur (iv) oxide. The<br>sulphurdioxide can react with more oxygen to form sulphur trioxide, SO3.<br>2S02(g) + O2(g) ————-&gt;2S03(g)<br>The SO3 dissolves readily in water droplets in the atmosphere to form<br>an aerosol of sulphuric acid which falls as rain.<br>14<br>H2O(l) + SO3(g)—————-&gt;H2SO4<br>When inhaled, the suphuric acid aerosol is small enough to be<br>trapped in the lung tissues, where they cause severe damage. Acid rain<br>destroys vegetation and forest as well as life in the sea, lake, ocean,<br>streams, etc. Also, CO2 is produced when coal is burnt. The total<br>quantity of CO2 released by the human activities of deforestation and<br>burning of fossil fuel is 6-7 billion metric tonnes per year. Carbon (iv)<br>oxide causes global warming and depletes the ozone layer.<br>Bio-coal briquette contains less percentage of coal than in coal<br>briquette (since there is partial substitution of coal with biomass). Hence,<br>there will be lesser emission of carbon, sulphur, dust, etc, into the<br>environment.<br>In order to reduce the emission of these gases into the environment,<br>lime based products such as Ca(OH)2 can be incorporated into the<br>mixture to fix the pollutants to the sandy ash, or the coal can be<br>carbonized.<br>Since the use of bio-coal briquettes will reduce cutting down of trees<br>for the purpose of using them as fire wood, briquette technology can<br>serve as global warming countermeasure by conserving forest resources<br>which absorbs CO2, through provision of bio-coal briquettes.</p><p>1.1.7 Coal analysis:<br>The composition of a coal is usually reported in terms of its proximate<br>analysis and its ultimate analysis: The proximate analysis consists of<br>four items: fixed carbon, volatile matter, moisture and ash, all on a<br>weight percent basis.<br>Volatile matter: The portion of a coal sample which, when heated in the<br>absence of air at prescribed conditions, is released as gases. It includes<br>15<br>carbon (iv) oxide, volatile organic and inorganic gases containing sulphur<br>and nitrogen.<br>Moisture: The water inherently contained within the coal and existing in<br>the coal in its natural state of deposition. It is measured as the amount of<br>water released when a coal sample is heated at prescribed conditions. It<br>does not include any free water on the surface of the coal. Such free<br>water is removed by air drying the coal sample being tested.<br>Ash: The inorganic residue remaining after the coal sample is<br>completely burned and is largely composed of compounds of silica,<br>aluminum, iron, calcium, magnesium and others. The ash may vary<br>considerably from the mineral matter present in the coal (such as clay,<br>quartz, pyrites, and gypsum) before being burned.<br>Fixed carbon: This is the remaining organic matter remaining after the<br>volatile matter and moisture have been released. It is typically calculated<br>by subtracting from 100 the percentages of volatile matter, moisture and<br>ash. It is composed primarily of carbon with lesser amounts of hydrogen,<br>nitrogen and sulphur. The ultimate analysis provides an element-by<br>element composition of the coal’s organic fraction, namely: carbon,<br>hydrogen, oxygen, and sulphur, all on a weight percent basis.<br>Coal can also be analysed in terms of mineral value and heating<br>value. Mineral matter consists of the various minerals contained in the<br>coal. Heating value is the energy released as heat when coal undergoes<br>complete combustion with oxygen [20].</p><p>1.2 Briquetting Technology:<br>Introduction:<br>Briquetting is the agglomeration of fine particles charred or<br>uncharred, by applying pressure to them and compacting them into<br>various shapes using binding agent. Pressure is applied to coal,<br>16<br>biomass, etc in a mould so that the particles can adhere to each other in<br>a stable manner for subsequent handling [21]. A briquette is a block of<br>compressed coal, biomass or charcoal dust that is used as fuel. It can<br>also be said to be a block of flammable matter which is used as fuel to<br>start and maintain fire [21].</p><p>1.2.1 Advantages of briquette production:<br>Briquette production will:<br>i. provide a cheap source of fuel for domestic purposes, which will be<br>affordable by all Nigerians.<br>ii. provide a good means of converting coal fines, low rank coal, waste<br>agro residue into a resourceful substance of economic value.<br>iii. Help to conserve some of our natural resources since it is a good<br>substitute for fire wood. Therefore, it will help to reduce the quantity of<br>firewood, oil and gas that is used in the production of energy for<br>domestic uses and generating plants.<br>iv. Help to develop the demand for coal. Coal is used in making bio-coal<br>and coal briquette. This will in turn promote coal mining which seems<br>dormant for sometime.<br>v. Create employment opportunities for people since people will be<br>needed to operate the briquette machine, get the raw materials (i.e. coal<br>and agro-residue, etc), sell the briquettes produced, etc [22].</p><p>1.2.2 Types of briquettes:-<br>i. Coal briquettes:- These are briquettes formed by agglomeration and<br>application of pressure to coal fines (i.e. coal particles) [16].<br>ii. Charcoal briquettes:- They are briquettes formed by agglomeration<br>of fine particles of charcoal and applying pressure to give shapes<br>17<br>[23]. Charcoal is a form of carbon consisting of black residue from<br>partially burnt wood.<br>iii. Biomass briquettes:- These are briquettes formed by agglomeration<br>of biomass (e.g. rice husk, corncob, cotton stalks, coconut shell,<br>groundnut shell, saw dust, etc) and applying pressure to them to<br>give them shapes. Biomass briquettes are a renewable source of<br>energy and it avoids adding fossil carbon to the atmosphere.<br>iv. Bio-coal briquettes: They are briquettes formed by blending coal<br>with vegetable matter (biomass), and then treating with<br>desulphurizing agent (Ca(OH2)), using an amount corresponding to<br>the sulphur content in the coal. When high pressure is applied in the<br>briquetting process, the coal particles and fibrous vegetable matter<br>in the bio-briquette strongly intertwined and adhere to each other,<br>and do not separate from each other during combustion [24].<br>v. Wood briquettes: are made of dry untreated wood chips (e.g. wood<br>shavings). They have lower ash and sulphur content compared to<br>the fossil fuels. The CO2 balance is even, because wood briquette<br>release just as much as CO2 to the atmosphere as the tree absorbs<br>through growth by photosynthesis [24, 25].</p><p>1.2.2.1 Coal briquetting:<br>This is the agglomeration of coal (fines) particles by applying<br>pressure to them and compacting them into various shapes with binding<br>agents.<br>History of coal briquetting:<br>The first patent for the briquetting of fines dates back to the mid<br>1800s. In 1848, a patent was granted to William Easby for a method of<br>converting fines into lumps. In his application, Easby made only one<br>claim “the formation of particles of any variety of coal into solid lumps by<br>18<br>pressure”. A list of work has been done on briquetting technology of<br>biomass, charcoal and coal briquetting as an alternative to fuel wood to<br>prevent deforestation that results in desertification in some countries like<br>Northern India, Kyrgyz Republic, Karaganda, Nepal, Kenya, Japan, etc.<br>A. Coal briquetting in the Kyrgyz Republic:<br>An assessment team, during its field work in October and<br>November 1994, identified and reported work done by researchers in<br>Kyrgyz Republic in recent years. Their findings were summarized as<br>follows: In November 1994, a briquetting laboratory existed in Osh, in<br>apparently new quarters for the institution of integrated use of natural<br>resources of the Academy of Science, Kyrgyz Republic. A brief visit to<br>this facility showed that it was operational with two piston and mould<br>heating capacity. In 1995, a modified brick press was used to produce<br>about 700 briquettes to test various binders and additives such as clay,<br>lime powders, and cotton processing residues, etc. Also, briquettes with<br>adequate thermal stability could be made using residues from cotton and<br>animal fat processing in the Fegana Valley [26].<br>B. Bentonite-clay binder coal briquetting technology in Kyrgyz<br>Republic.<br>The potential of absorbent clay, a binder for the manufacture of a<br>briquette from whole (uncarbonized) coal, which would be smokeless<br>during combustion appears to have been first recognized in researches<br>at Chulakongkorn University in Bangkok, Thailand during 1980’s. The<br>original clay used for the work was fuller’s earth, but latter work focused<br>on the use of bentonites because of superior result in suppressing the<br>emission of unburnt volatile materials from the combustion of the coal.<br>Hydrated lime was incorporated in the recipe for the purpose of<br>suppressing the emission of sulphur (iv) oxides. Kyrgyz coals do not<br>have as much sulphur as the coals used in the Pakistan briquetting<br>19<br>work, the amount of the lime that was incorporated in the recipe for a<br>Kyrgyz briquetting industry was significantly less. However, lime could<br>have a beneficial effect on the ultimate strength of the briquette to<br>withstand handling and shipping. Some potassium nitrate was also<br>incorporated in the recipe in order to promote ease of initial ignition.<br>When the briquettes produced were burnt, it was observed that they<br>were smokeless [24, 19, 20]<br>C. The beehive charcoal briquette and briquette stove in the Khubu<br>region, Nepal:<br>The Nepal biomass (such as firewood and agricultural by-products) is<br>used almost exclusively for cooking and space heating in the rural areas.<br>Indoor air pollution from open fire causes eye irritation and lung disease<br>dominantly for women and children [28]. This is especially so for high<br>altitude areas, where open fires are also used for space heating.<br>Processing forest waste and agro biomass (by product) first into<br>charcoal and then compacting the charcoal into briquettes allow this to<br>be used inside the house for cooking and heating purposes. To minimize<br>the smoke, the beehive stove was invented. The smoke emission from<br>the beehive briquettes is far less as compared to an open air.<br>The beehive charcoal briquettes are made from charcoal produced<br>from agricultural residue such as rice husk, wheat chaff and forest waste<br>vegetation (fallen pine needles, pinecones, grassy weeds, etc). This is<br>an efficient method of utilizing bio-waste. All woody biomass material<br>can form the raw material for charcoal briquettes. Emphasis was placed<br>on using agricultural residues and invasive biomass. The biomass<br>material is first sun dried until it has humidity below 15%. It is then<br>heated in a 220 litres metal charring drum. The resulting charcoal is<br>ground to dust and mixed with 30% dry clay-soil (in volume). Water is<br>added to make a paste. Using a 5kg hand weight, the paste is<br>20<br>compacted into a round mould which produces a charcoal briquette with<br>19 holes after moulding. These holes not only allow the briquette to dry<br>evenly but also enhance burning by allowing flames and gases to<br>escape evenly from the briquette [29,30].</p><p>It was also observed that in the North-Eastern region of India, there<br>were considerable reserves of oil and gas. With a view to conserve oil<br>and gas for more productive uses in industrial establishments and mass<br>transportation, the reserves of coal can be more usefully exploited for<br>domestic applications. The raw materials that are used are low grade<br>coal and coal particles, bentonite, molasses, plastic clay, lime and<br>sodium silicate as binders. The processes they used in manufacturing<br>the briquettes are as follows:<br>i. Crushing/ grinding of coal to below 2mm particle size.<br>ii. Preparation of binder in a semi-liquid form<br>iii. Mixing of coal with binders<br>iv. Briquette making using the briquetting machines<br>v. Drying<br>vi. Packaging [31]<br>Technology of coal briquetting:<br>Coal briquetting requires a binder to be mixed with coal fines, a press<br>to form the mixture into a cake or briquette, which is then passed<br>through a drying oven to cure or set it by drying out the water so that the<br>briquette will be strong enough to be used in a stove [32]. Coal<br>briquettes can be produced through the following technique:<br>Carbonization production process:<br>The coal briquette carbonization production process, consist of a<br>carbonization stage and a forming stage.</p><p>21<br>Carbonization stage:<br>The raw coal (5-50mm particle size) is preliminarily dried in a rotary<br>dryer. The dried raw coal is put in a furnace, and subjected to fluidization carbonization at temperature of about 450oC. The semi-coke is<br>discharged from the top of the furnace together with the carbonization<br>gas. The semi-coke is separated from the carbonization gas by the<br>cyclone, producing smokeless semi-coke containing approximately 20%<br>of volatile matter.<br>Forming stage:<br>The smokeless semi-coke and auxiliary raw materials, hydrated lime<br>(desulfurizer), clay (binder) and water (caking additive) are mixed by<br>kneading. The mixture is formed using a briquetting machine (i.e. a<br>moulding machine) at normal temperature and pressure of about 3-5<br>MPa. The briquettes formed are dried in the continuous drier, cooled and<br>packaged for sell, or it is ready for use [33].</p><p>Fig 2: Process flow of briquette production.</p><p>22</p><p>1.2.2.2 Biomass briquetting:-<br>This is the agglomeration of biomass (such as rice husk, groundnut<br>shell, coconut shell, corn cob, etc) by applying pressures to them to<br>compact them into various shapes with binding agents.<br>Technology of biomass briquetting:<br>Biomass, particularly agricultural residues seems to be one of the<br>most promising energy resources for developing countries. The idea of<br>utilizing the residues from agricultural sectors as primary or secondary<br>energy resources is considerably attractive. This kind of waste is<br>available as free, indigenous and environmentally friendly energy<br>sources. Moreover, decreasing availability of firewood has necessitated<br>that efforts be made towards efficient utilization of agricultural wastes.<br>They have acquired considerable importance as fuels for many purposes<br>viz: domestic cooking, industrial process heating, power generation etc.<br>Some of agricultural residues such as coconut shell, wood chip and<br>wood waste, are ready to be directly used as fuel. Nevertheless, the<br>majority of these bulky materials are not appropriate to be used directly<br>as fuel without a suitable process, because of the fact they have low<br>density, high moisture content, and low energy density. All of these<br>issues may cause problems in transportation, handling, storage,<br>entrained particulate emission control including direct combustion [34].<br>Biomass briquetting requires a binder to be mixed with pulverized<br>biomass, and a press to form the mixture into cake or briquette, which is<br>then passed through a drying oven so that any water contained in the<br>briquette will be driven off. The biomass to be used must be dried and<br>pulverized. It must also be combustible and should not constitute<br>environmental hazard [35].</p><p>23<br>1.2.2.3 Bio-coal briquetting:-<br>Bio-coal briquette or biomass-coal briquette may be defined as a type<br>of solid fuel prepared from coal and biomass. When pressure is applied<br>during the process, the coal particles and biomass material adhere and<br>interface to each other. Thus, these two materials do not separate from<br>each other during the storage, traveling and combustion. During<br>combustion, the biomass is simultaneously burnt with the coal at low<br>ignition temperature. Since the biomass part in the briquette has lower<br>ignition temperature as compared to the other part, it can assure that the<br>quality of combustion of the coal volatile matter at low temperature is<br>improved. Besides, it is widely accepted that biomass-coal briquette<br>technique is one of the most promising technologies for reducing SO2<br>emission. With regard to the sulphur content of the coal, a desulfurizing<br>agent can be added for sulphur capturing purpose. The agent effectively<br>reacts with suphur in the coal to fix the sulphur into the sandy ash. Thus,<br>several coal ranks, including low grade coal containing high sulphur and<br>ash contents can be used for producing biomass coal briquettes [34].<br>Many researches about biomass- coal briquettes have been carried out.<br>Olive stone [35-35], sawdust [37], rice straw [38] are examples of the<br>biomass material in the briquettes.</p><p>1.2.2.3.1 Characteristics of bio-coal briquettes:<br>Bio-coal briquettes has the following characteristics:<br>1. It is made from coal and biomass: Bio-coal briquettes can be<br>produced from either high quality coal or low quality coal.<br>2. Bio-coal briquette ash is also beneficial to improving soil in the desert<br>and semi-desert [39]. The table below shows the chemical components<br>of bio-coal briquettes ash. It contains higher silica and alumina, but lower<br>calcium compounds such as CaO, CaCO3, and CaSO4, in general<br>24<br>similar to gypsum. An experiment performed in Shenyang in 2001 using<br>gypsum, produced gypsum improved soil, and actually it helps corn<br>growth significantly [39,40]. The experiment also concludes that ash of<br>bio-coal briquettes have similar effect on soil improvement, although it is<br>not so successful as gypsum but effective, because it contains less<br>calcium compounds than gypsum.<br>Table 3: Chemical analysis on bio-coal briquette ash [40].</p><p>Gypsum from<br>desulphurization<br>Bio-coal briquette<br>ash<br>Ca(OH)2 2% 1%<br>CaO 31% 9%<br>CaSO3 2% 1%<br>CaCO3 29% 5%<br>CaSO4 .2H2O 32% 10%<br>SiO2 9% 27%<br>Al2O3 4% 19%</p><p>3. They can be in different shapes- rectangular, cylindrical, square<br>shapes, etc.<br>4. Since fibrous biomass is intertwined with the coal particles, there is no<br>fear of the fused ash in the coal adhering and forming clinker lumps<br>during combustion.<br>5. The bio-coal briquettes are formed under high compressive force.<br>Because of this, the desulphurizing agent and coal particles strongly<br>adhere to each other, and they effectively react during combustion. With<br>the addition of a desulphurizing agent at a ratio approximately 1.2:2 of<br>Ca/S, 60-80% of the sulphur in the coal is fixed in the ash [22].</p><p>25</p><p>1.2.2.3.2 Advantages of bio-coal briquettes:<br>1. Briquettes from biomass and coal are cheaper than briquette from<br>coal. This is so, since some of the biomass materials used are of less<br>economic importance and are always left to waste, except in cases<br>where they are to be used, which is rare. E.g. in Abakaliki rice mill, the<br>rice husk is left to waste.<br>2. High sulphur content of oil and coal when burnt pollutes the<br>environment. In bio-coal briquettes, part of the coal is substituted with<br>biomass, hence the sulphur content is reduced [22].<br>3. Bio-coal briquettes have a consistent quality high burning efficiency,<br>and are ideally sized for complete combustion.<br>4. Combustion of bio-coal briquettes produces ashes which can be<br>added to soil to improve soil fertility.<br>5. Bio–coal briquettes are usually produced near the consumption<br>centers and supplies do not depend on erratic transportation from long<br>distance.<br>Based on these facts, bio-coal can replace the following conventional<br>fuel that are used in mass quantities: diesel, kerosene furnace oil, fire<br>wood, coal, lignite, etc [41].<br>1.2.2.3.3 Bio-coal briquetting technology:-<br>Bio-coal briquettes are a very valuable source of energy. They are<br>made by thermal conversion of biomass and coal into bio-coal, which is<br>subsequently compacted. Practically, any type of solid residue or waste<br>from forestry, agriculture and the wood processing and agro-industries<br>can be used as raw materials, e.g. wood waste, corncob, rice husk,<br>bagasse, coffee husk, etc. The calorific value of bio-coal briquettes is<br>almost double that of biomass alone. They also have clean combustion<br>26<br>behaviour (little smoke, a low level of toxic emissions), and are easy to<br>store and transport [42]. Bio-coal briquettes can be produced using<br>i. manual briquetting machine e.g. briquetting press machine, and<br>ii. sophisticated briquetting machine such as briquetting plants.<br>The manual briquetting machine is cheaper than the briquetting plant,<br>which is more efficient.<br>The need for a smokeless bio-coal briquette:<br>Smoke is a collection of airborne solid and liquid particles and gases<br>emitted when a material undergoes combustion or pyrolysis, together<br>with the quantity of air that is entrained or mixed into the mass. It is<br>commonly an unwanted by product of fire [43]. All fires produce smoke,<br>the nature and density of which depend on the burning material. Smoke<br>contains particulate matter, liquids, as well as gases. The major<br>problems caused by smoke are eye irritation and reduced visibility,<br>coughing and sneezing (i.e. when the smoke is inhaled deep into the<br>lungs) [44]. Also, inhalation of smoke is the primary cause of death in<br>victims of indoor fires. Smoke kills by a combination of thermal damage,<br>poisoning, and pulmonary irritation caused by CO, HCN and other<br>combustion products [43]. Hence, it is very important that the briquettes<br>produced should be smokeless to avoid or prevent smoke when burning<br>the briquettes. This can be achieved by carbonizing the coal into coalite<br>(semi-coke), or by incorporating additives which can help to drive off the<br>volatile matters that cause smoke.<br>Production processes of bio-coal briquettes:<br>Method 1:<br>By this method, the coal is carbonized. This involves internal heating<br>at low temperature in a fluidized-bed carbonization furnace (approximately 4500C) to produce a smokeless semi-coke containing<br>approximately 20% volatile matter. The smokeless semi-coke, biomass<br>27<br>(pulverized) and auxiliary raw materials; hydrated lime and binder e.g.<br>starch, clay, etc, are thoroughly mixed at a predetermined mixing ratio.<br>After pulverizing, the mixture is blended with a caking additive while<br>water is added to adjust the water content of the mixture. The mixture is<br>kneaded to uniformly distribute the caking additive, and to increase the<br>viscosity in order to make the forming of the briquettes easy. The mixture<br>is then introduced into the molding machine to prepare the briquettes.<br>The briquettes are then dried [45]. A cross sectional view of<br>carbonization furnace and a basic process flow for bio-coal briquette<br>production are shown in Fig 3 and 4 [57].</p><p>Fig 3: Cross- sectional view of carbonization furnace.</p><p>Fig 4: Basic process flow for bio-coal briquette production [45].<br>28</p><p>Method 2:<br>The biomass is dried, pulverized and sieved with a sieve of known<br>mesh size. The biomass is pre-treated (if need be ) with 3% wt/wt sodium hydroxide solution at 900C for 1 hr. Coal fines is mixed with the<br>sodium hydroxide treated biomass at a predetermined ratio. The mixture<br>is then compacted at ambient temperature by using a hydraulic press,<br>producing bio-coal briquettes which is then dried [46].<br>The bio-coal briquettes can also be dried at high temperature (curing)<br>to remove volatile matters.<br>Method 3:-<br>This is the most widely used method. By this method, the coal and<br>biomass (dried) are pulverized, and mixed with sulphur and chlorine<br>fixation agents such as calcium carbonate, calcium hydroxide, etc (ie<br>lime based products). The fixing agent added is equal to the amount of<br>sulphur in the coal. These desulphurizng agents fix the sulphur into the<br>sandy ash during combustion, making the ash rich in nutrients (that can<br>be used by plants). Thus, several coal ranks, including low grade coal<br>containing high suphur and ash contents can be used for producing bio<br>coal briquettes [47].<br>An experiment performed on the desulphurizing efficiencies of<br>different coals using desulphurizing agents such as calcium carbonate,<br>calcium hydroxide, magnesium carbonate showed that calcium<br>hydroxide or calcium oxide is the best desulphurizing agent with<br>desulphurizing efficiency reaching over 80%. The desulphurization<br>efficiencies related calcium are above 80% MgCO3 was also used, but<br>do not show promising results with desulphurization efficiencies below<br>50% for most coals [47].<br>29<br>Calcium hydroxide is the best desulphurizing agent because of the following: Calcium hydroxide was decomposed at 3500C, and H2S is<br>released from volatile matter,<br>Ca(OH)2 ——-&gt;CaO + H2O<br>CaO + H2S ———&gt; CaS + H2O<br>Ca(OH)2+ SO2 ———&gt;CaSO3. ½ H2O + ½ H2O<br>The schematic manufacturing process of bio-coal briquette is shown in<br>Fig 5.</p><p>Coal Biomass</p><p>dried up sulphur and chlorine fixation agent dried up</p><p>pulverized pulverized</p><p>heating and mixing</p><p>briquetting ( using briquetting machine)</p><p>Biocoal briquettes.<br>Fig 5: Schematic manufacturing process of bio-coal briquette.<br>1.2.3. Biomass as a feedstock for the production of bio-coal<br>briquette.<br>Biomass is made through process of photosynthesis, which uses<br>carbon (iv) oxide from the atmosphere, while releasing oxygen. During<br>photosynthesis, the solar energy (light) is captured by pigments in plants<br>and is used to reduce atmospheric carbon dioxide gas into<br>30<br>carbohydrates through biological reaction with water. The solar energy is<br>stored in the form of carbohydrate chemicals such as cellulose,<br>hemicelluloses and lignin.<br>Cellulose and hemicelluloses are polysaccharides of glucose (i.e.,<br>they are polymers of glucose). Hemicelluloses have a less ordered<br>structure than cellulose, and can be more easily hydrolyzed to simple<br>sugars and other products. Lignin is an amorphous polymer, and plays<br>an important role in developing structure of the plants [48].<br>Biomass feedstock utilized in energy system.<br>Biomass feedstock used for energy purposes can be generally<br>divided into dedicated energy crops and residues (wastes or by-products<br>of various process and activities), and range from woody to grassy<br>materials, as shown in Table 4 below. Examples of common biomass<br>include crop residues (wheat straw, corn stalks, nut shells, orchard<br>pruning, vineyard stakes, sugar cane bagasse, etc), forest residence<br>(slash, forest thinning, urban wood waste (construction residues, grass<br>dipping and backyard pruning), and several energy crops [48]. Many<br>different types of biomass can be utilized for bio-briquette production and<br>also in co-firing systems. Co-firing experience includes wood, residues<br>from forestry and related industries, agricultural residues, as well as<br>various biomasses in refined form such as pellets, are popular in<br>Denmark and the Netherlands. Also, oil, sugar and starch energy crops<br>can be used for production of liquid fuels with high energy value (bio<br>diesel and bio-ethanol respectively) for use in the transport sector and<br>their utilization for power production is not economically justified at<br>current [49].</p><p>31<br>Table 4: Types of biomass feedstock used for energy purposes<br>[50,51]<br>SUPPLY SECTOR TYPE EXAMPLES<br>1 Agricultural residues Dry lignocellulosic<br>agricultural residues.<br>Straw (maize, cereal,<br>rice) sugar beet<br>leaves, residue flows<br>from bulb sector, etc.<br>Livestock waste Solid manure (chicken<br>manure) cattle, pig,<br>sheep dung, etc.<br>2 Dedicated energy<br>crops<br>Dry lignocellulosic<br>woody energy crops.<br>Willow,<br>Popular Eucalyptus,<br>etc.<br>Dry lignocellulosic<br>herbaceous energy<br>crops .<br>Miscanthus, switch<br>grass, common reed,<br>reed canary grass,<br>giant reed, cynara<br>cardunculus, Indian<br>shrub, etc.<br>Oil energy crops. Rapeseed, sunflower<br>seeds, soybean, olive-<br>kernel, calotropis<br>procera, groundnut<br>(nut, shell), etc<br>Sugar energy crops Sugar beet, cane beet,<br>sweet sorghum,<br>Jerusalem Artichole,<br>sugar millet, etc.<br>Starch energy crops Wheat, potatoes,<br>32<br>maize, barley, triticae,<br>amaranth ,corn cob.<br>Others Flax (linum), Hemp<br>(cannabis) Tobacco<br>stems, Aquatic plants,<br>(lipids from algae),<br>cotton stalks, kenaf,<br>etc.<br>3 Forestry Forestry by- products Bark, wood blocks,<br>wood chips from tops<br>and branches, wood<br>chips from thinning,<br>logs from thinnings.<br>4 Industry Wood industry<br>residues<br>Industrial waste wood<br>from sawmills and<br>industrial waste wood<br>from timber mills<br>(bark, sawdust, wood<br>chips, slabs, off- cuts)<br>Fibrous vegetable<br>waste from virgin pulp<br>production and from<br>production of paper<br>from pulp, including<br>black liquor.<br>Food industry<br>residues<br>Wet cellulosic<br>materials (beet root<br>tails) fat (used cooking<br>oils) tallow, yellow<br>33<br>grease, protein<br>(slaughter house<br>waste)<br>Industrial products Pellets from sawdust<br>and shavings.<br>Briquettes from saw<br>dust and shavings.<br>Bio-oil (pyrolysis oil)<br>Ethanol, Bio- diesel.<br>Parks and gardens Herbaceous Grass<br>Woody Pruning<br>Waste Contaminated waste Demolition wood<br>Biodegradable<br>municipal waste,<br>Sewage sludge, land<br>fill gas, sewage gas<br>Others Roadside hay Grass/hay<br>Husks/shells Almond, olive, walnut,<br>coconut, palm pit<br>(imported),cacao<br>(imported).</p><p>Note: Dry lignocellulosic feedstock is the category of feedstock, which<br>can be used for thermochemical conversion (gasification, combustion<br>and liquefaction). Wet lignocellulosic feedstock is a feed stock that can<br>be used for biological conversion (digestion).<br>Properties of biomass in relation to co-firing:<br>Generally, proximate analysis of biomass gives 80% volatile matter<br>and 20% fixed carbon (moisture free and ash free bases), whereas<br>34<br>bituminous coal (for instance), gives 70-80% fixed carbon and just 20<br>30% volatile matter [48, 52].<br>There are factors to consider before a biomass qualifies for use as<br>feed stock for briquetting. Apart from its availability in large quantities, it<br>should have the following properties:<br>i. Low moisture content: Biomass usually has high moisture content,<br>resulting in a relatively low calorific value of the fuel [52,53]. Fresh wood<br>typically contains 50% of water by weight, whereas the moisture content<br>for bituminous coal is approximately 5% [52]. Moisture content of<br>biomass affects its combustion properties. Higher moisture content will<br>reduce the maximum combustion temperature, and increase the<br>necessary residence time of feedstock in a combustion chamber, and<br>consequently could result in an incomplete combustion and increased<br>emissions related to it (volume of flue gas produced per energy unit)<br>[50]. Therefore moisture content should be as low as possible, generally<br>in the range of 10-15% or less. High moisture content will pose problems<br>in burning and excessive energy is required for drying [54].<br>ii. Ash content and composition: Typical biomass contains fewer<br>ashes than coal, and their composition is based on the chemical<br>components required for plant growth, whereas coal ashes reflect the<br>mineralogical composition [55]. In both coal and biomass, ash forming<br>matter can be present in four general forms: easily leachable salts,<br>inorganic elements associated with the organic matter of the biomass,<br>minerals included in the fuel structure, and inorganic materials, typically,<br>sand, salt or clay [52].<br>Alkaline metals that are usually responsible for fouling of heat transfer<br>surfaces are high in biomass ashes, and are released in the gas phase<br>during combustion. In biomass, these inorganic compounds are in the<br>form of salts or bound in the organic matter, but in peat, for example,<br>35<br>inorganic matter is bound mostly in silicates, which are more stable at<br>high temperature. The elemental composition of ash, (alkali metals (e.g<br>potash, phosphorus, chlorine, silicon and calcium), affects ash melting<br>behaviour. Even a small concentration of chlorine in the fuel can result in<br>deposition of harmful alkaline and chlorine compounds on boiler heat<br>transfer surfaces [52]. The ash content of some types of biomass are<br>given in the Table 5 below:<br>Table 5: Ash content of different biomass types [54].<br>Biomass Ash content (%) Biomass Ash content (%)<br>Corncob 1.2 Tannin waste 4.8<br>Jute stick 1.2 Almond shell 4.8<br>Sawdust (mixed 1.3 Areca nut shell 5.1<br>Pine needle 1.5 Castor stick 5.4<br>Soya bean stalk 1.5 Groundnut shell 6.0<br>Bagasse 1.8 Coir pith 6.0<br>Coffee spent 1.8 Bagasse pith 8.0<br>Coconut shell 1.9 Bean straw 10.2<br>Sunflower stalk 1.9 Barley straw 10.3<br>Jowar straw 3.1 Paddy straw 15.5<br>Olive pits 3.2 Tobacco dust 19.1<br>Arhar Stalk 3.4 Jute dust 19.1<br>Lantana<br>Camara<br>3.5 Rice husk 22.4<br>Subabul leaves 3.6 Tamarind husk 4.2<br>Teawaste 3.8 Deoiled Bran 28.2</p><p>iii Chemical properties: With regard to chemical properties of biomass,<br>it generally has less sulphur, fixed carbon, and fuel bond nitrogen, but<br>more oxygen than coal.<br>36<br>iv Also, biomass should have low bulk energy density, hydrophillic and<br>non- friable character.<br>Most of the challenges that co-firing poses to boiler operation<br>originate from fuel properties (the differences in characteristics of coal<br>and biomass) and can be summarized as follows [55]: ï‚· Pyrolysis starts earlier for biomass than for coal. ï‚· The volatile matter content of biomass is higher than in coal. ï‚· The fractional heat contribution by volatile substances in<br>biomass is approximately 70% compared with 30-40% in coal. ï‚· The specific heating value (kJ/kg) of volatiles is lower for<br>biomass compared with coal. ï‚· Biomass char has more oxygen compared with coal and it is<br>more porous and reactive. ï‚· Biomass ash is more alkaline in nature, which may aggravate<br>the fouling problems.<br>Characteristics of biomass feedstock and their effect on co-firing are<br>shown in Table 6.<br>Table 6: The physical and chemical characteristics of biomass<br>feedstock and their effects on co-firing [55].<br>Properties Effects<br>PHYSICAL Moisture content Storage durability,<br>dry- matter losses ,<br>self ignition.<br>Bulk density Fuel logistics (storage,<br>transport, handling) cost.<br>Ash content Dust, particle emissions,<br>ash utilization/disposal costs.<br>Particle dimension<br>and size distribution.<br>Determines fuel feeding system,<br>Determines combustion<br>37<br>technology ,<br>Drying properties,<br>Dust formation,<br>Operational safety during fuel<br>conveying.<br>CHEMICAL Carbon, C GCV (positive)<br>Chlorine, Cl Corrosion<br>Nitrogen, N NOx, N2o, HCN emissions.<br>Sulphur, S SOx emissions, corrosion<br>Fluorine, F Hf emissions, corrosion.<br>Potassium, K Corrosion (heat exchangers,)<br>Super heaters<br>Lowering of ash melting<br>temperatures.<br>Aerosol formation<br>Ash utilization (plant nutrient)<br>Sodium, Na Corrosion (heat exchangers,<br>super heaters)<br>Lowering of ash melting<br>temperatures,<br>Aerosol formation,<br>Ash utilization (plant nutrient).<br>Magnesium, Mg Increase of ash melting<br>temperature,<br>Ash utilization (Plant nutrient).<br>Calcium,