Project Abstract

<p> </p><p></p> The urgent need to protect our forest, to mitigate health hazards faced by<br>the people from the use of firewood for cooking and to find an effective<br>means of managing agro wastes has prompted a research on improving the<br>properties of coal briquette using spear grass (Imperata cylindrica) and<br>elephant grass (Pennisetum purpureum). In the research, proximate<br>analysis and the elemental composition of the plant materials were carried<br>out alongside with a coal sample. Briquettes of different composition were<br>produced by blending the plant materials with the coal at various<br>concentrations 0%, 10%, 20%, 30%, 40%, 50% and 100%. The physical,<br>mechanical and combustion properties of the briquettes were compared. It<br>was found that the ignition, burning rate and reduction in smoke emission<br>showed improvement with increase in biomass concentration. Compressive<br>strength and cooking efficiency – water boiling time and specific fuel<br>consumption showed initial improvement and rendered to break with<br>briquette containing biomass concentration of 50% for elephant grass<br>briquette. For spear grass, the compressive grass was at maximum at<br>biomass concentration of 30%. <br><p></p>

Project Overview

<p> </p><p>INTRODUCTION<br>1.1 Background of the Study<br>Nigeria, like other sub-Saharan countries, has faced forest degradation<br>problems due to combination of factors. Some of the factors are<br>clearing of land for agricultural and industrialization purposes, over<br>grazing, bush fires, drought, over exploitation, ever- increasing<br>deforestation along with the increased in the consumption of fuel wood<br>etc.<br>About 80% of Nigerians live in the rural or semi-urban areas and they<br>depend solely on fuel wood for their energy needs. Fuel wood accounts<br>for about 37% of the total energy demand of the country. Investigations<br>showed that out of the total wood demand from the forest, 90% goes to fuel wood. Presently, Nigeria reportedly consumes about 43 x 109 kg of<br>fuel wood annually [1] and it will be far more than this by the end of<br>2010 if the present trend continues [2]. However, it is very obvious that<br>reduction in the use of fuel wood will drastically reduce the pressure<br>mounted on the forest in search of wood.<br>Meanwhile, it was reported that the total forest cover of Nigeria is still<br>less than 10% of the land area, which is far below the 25%<br>recommended by the United Nation Development Programme (UNDP)<br>[2]. Therefore, it is imperative that concerted efforts are needed to<br>address this situation.</p><p>2</p><p>Furthermore, in the recent years, global warming has become an<br>international concern. Global warming is caused by green house gasses<br>which carbon dioxide is among the major contributors. It was shown<br>that increased emission of CO2 in the atmosphere in the recent time has<br>exacerbated the global warming [3]. Part of the reasons for this can be<br>explained from the fact that the forest resources which act as major<br>absorbers of CO2 have been drastically reduced owing to the fact that<br>the rate of deforestation is higher than the afforestation effort in the<br>country.<br>Apart from environmental effects, the use of fuel wood for cooking has<br>health implications especially on women and children who are<br>disproportionately exposed to the smoke. Women in rural areas<br>frequently with young children carried on their backs or staying around<br>them, spend one to six hours each day cooking with fuel wood. In<br>some areas, the exposure is even higher especially when the cooking is<br>done in an unventilated place or where fuel wood is used for heating of<br>rooms. Generally, biomass smoke contains a large number of<br>pollutants which at varying concentrations pose substantial risk to<br>human health. Among hundreds of the pollutants and irritants are<br>particulate matters, carbon monoxide, formaldehyde and carcinogens such as benzo[α]pyrene, 1,2–butadiene and benzene [4]. Studies<br>showed that indoor air pollution levels from combustion of bio fuels in<br>Africa are extremely high, and it is often many times above the</p><p>3</p><p>standard set by US Environmental Protection Agency (US-EPA) for ambient level of these pollutants [5].<br>Also, consistent evidence revealed that exposure to biomass smoke<br>increases the risk of a range of common diseases both in children and<br>in adults. The smoke causes acute lower respiratory infection (ALRI)<br>particularly pneumonia in children [6, 7]. Among the women, it causes<br>chronic bronchitis and chronic obstructive pulmonary diseases (COPD)<br>(Progressive and incompletely reversible air ways obstruction) [8,9].<br>Eyes irritation (sore, red eyes, tears) from the smoke is also a common<br>experience in the use of fuel wood. A hospital based case – control<br>studies proved that a person exposed to smoke of biomass has high risk<br>of cataracts disease [10]. This evidence was further substantiated by an<br>experiment carried out on animals which showed that biomass smoke<br>is capable of damaging eye lens [11].<br>In the whole, it was summed up that the total deaths attributed to the<br>use of fuel wood in Nigeria are about 79,000. Also nearly 45% of the<br>national burden diseases are related to solid fuel use, according to a WHO Survey [2]. Again, combustion of raw coal has equally been<br>reported to have detrimental effects on both environments and the<br>health of the people. Among other effects, inhalation of coal smoke<br>increases the risk of lung cancer [12].<br>Frankly speaking, transition to electricity or gas would have been the<br>healthiest solution to these problems but the likelihood of a complete</p><p>4</p><p>transition in the poorer urban and rural communities in the near future<br>is minimal. Therefore it is pertinent that other intervention measures<br>especially ones recommended by WHO [4] should be adopted to<br>mitigate these health risks to the lowest possible level and equally to<br>relieve the forest resources from pressure mounted on it.<br>Fortunately, researches have shown that a cleaner, affordable fuel<br>source which is a substitute to fuel wood can be produced by blending<br>biomass (agricultural residues and wastes) with coal. Nigeria has large<br>coal deposit which has remained untapped since 1950’s, following the<br>discovery of petroleum in the country. Also, millions of tonnes of<br>agricultural wastes are generated in Nigeria annually. But it is<br>unfortunate that farmers still practise “slash–and-burn” agriculture.<br>These agricultural wastes they encounter during clearing of land for<br>farming or during processing of agricultural produce are usually burnt<br>off. By this practice, not only that the useful raw materials are wasted,<br>it further pollutes the environment and reduces soil fertility.<br>Fire affects soil below ground biodiversity, geomorphic process, and<br>volatilizes large amount of nutrients and carbon accumulated in the soil<br>organic matter [13]. Furthermore, during process of burning of<br>agricultural wastes on the field, if it is not properly controlled, it can<br>inadvertently lead to bush fire, destroying further the forest which has<br>suffered much from the hand of wood seekers.</p><p>5</p><p>Forest fire is one of the severe environmental problems in Nigeria and<br>every year various forest types are burnt as a result of fire set up<br>deliberately or inadvertently through careless or uncared acts. Forest<br>fire destroys the fresh saplings, seedlings and arrest regeneration of<br>native species [13].<br>However, these health hazard faced by people from the use of fuel<br>wood, along with the agricultural wastes management and reduction of<br>pressure mounted on the forest can be mitigated if Nigeria will switch<br>over to production and utilization of bio-coal briquette; a cleaner and<br>environmental friendly fuel wood substitute made from agricultural<br>wastes and coal. Moreover, this will offer a good potential for<br>utilization of a large coal reserve in Nigeria for economic<br>diversification and employment generation through bio-coal briquette<br>related SMEs.<br>1.2 Literature Review<br>1.2.1 Briquetting Process<br>Briquetting is a mechanical compaction process for increasing the<br>density of bulky materials. This process is used for forming fine<br>particles into a designed shape. It can be regarded as a waste control<br>measure in the case of production of briquettes from agricultural<br>wastes. However, depending on the material of interest, briquetting can<br>be used to provide fuel source as a preventive measure to many<br>ecological problems. Briquetting is a high- pressure process which can</p><p>6</p><p>be done at elevated temperature [14] or at ambient temperature [15, 16]<br>depending on the technology one wants to employ.<br>During this process, fine material is compacted into regular shape and<br>size which does not separate during transportation, storage or<br>combustion. In some briquetting techniques, the materials are simply<br>compressed without addition of adhesive (binderless briquettes) [17,<br>18] while in some, adhesive material is added to assist in holding the particles of the material together [15, 16].<br>Generally, briquetting process has focused more on the production of<br>smokeless solid fuels from coal and agricultural wastes. There are<br>various techniques which have been used to produce smokeless solid<br>fuel from coal fine. The most common technique is the use of roller<br>press using only moderate pressure and binder. Note that the machines<br>employed for this process are also used to make other kind of non-fuel<br>briquettes from inorganic materials such as metal ores. However,<br>briquetting of organic materials (agricultural wastes) requires<br>significantly higher pressure as additional force is needed to overcome<br>the natural springness of these materials. Essentially, this involves the<br>destruction of the cell walls through some combination of pressure and<br>heat. High pressure involved in this process suggests that organic<br>briquetting is costlier than coal briquettes.<br>Various briquetting machines have been designed, ranging from very<br>simple types which are manually operated to more complex ones</p><p>7</p><p>mechanically or electrically powered. Generally, briquetting operations<br>have developed in two directions, mechanically compression<br>(hydraulic or pistons) and worm screw pressing types.<br>1.2.2 Historical Background of Briquetting Process [18- 21]<br>Although, compaction of loose combustible materials for fuel making<br>purposes is a technique which has been in existence thousands of years<br>ago but industrial method of briquetting seems to be dated back to<br>eighteenth century. In 1865, report was made on machines used for<br>making fuel briquettes from peats and are recognized as the<br>predecessors of the present briquetting machines. Since then, there has<br>been a wide spread use of briquettes made from brown coal and peat<br>etc.<br>The use of organic briquettes (biomass briquettes) started more<br>recently compared to coal briquette. It seams to have been common<br>during World War and during the 1930s depression. The modern<br>mechanical piston briquetting machine was developed in Switzerland<br>based upon German development in the 1930s. Briquetting of saw dust<br>are widespread in many countries in Europe and America during World<br>War II because of fuel shortages. However, after the World War,<br>briquettes were gradually phased out of the market because of<br>availability and cheapness of hydrocarbon fuels.<br>As time went on, the use of organic briquette was revitalized due to<br>high energy prices in the 1970s and early 1980s mainly for industrial</p><p>8</p><p>heating in USA, Canada and Scandinavia, etc. In Japan, the use of<br>briquette seems to be very common especially the use of “Ogalite” fuel<br>briquettes made from saw dust and rice husk. The Japan technology<br>has spread to Taiwan, and from there to other countries such as<br>Thailand, Asia, USA and some other European countries. This type of<br>briquette has been in use in Japan since 1950s as a substitute for<br>charcoal which was then a widespread fuel source.<br>Furthermore, in Great Britain, the first fuel briquette was manufactured<br>by the Powell Dul Fryn Company in 1938 by heating anthracite chips bound with pitch to a temperature of around 750oC to produce a<br>briquette known as phurnacite and this production was taken over by<br>the National Coal Board in 1942. They were able to produce half a<br>million tonne of coal annually. It was also reported that the same<br>technique was tried on production of smokeless coal briquette from<br>low-rank coal containing as much as 30-40% volatile materials. But the<br>problem was how to reduce the volatile component of the coal to<br>prevent smoke formation and at the same time, retaining sufficient<br>active constituents to give an easily lighted bright fire with a high<br>radiation. It was found that moderate heating (carbonization) of the low<br>rank coal not only drives off a portion of the volatile matter but appears<br>to change the remaining volatile portion in such a way that it does not smoke even with a volatile content as high as 23%. Phurnacite was<br>produced from low-rank coal by heating the coal bound with pitch to</p><p>9</p><p>200oC. Since then, other technologies for production of smokeless<br>briquettes were developed in Britain. These include the multi heat<br>briquette marketed by the National Coal Board. This brand of<br>smokeless briquette was made by curing pitch bound briquette in a bed of sand which is fluidized and kept at a temperature of about 380oC.<br>Other types of briquettes developed were home fire and room heat.<br>Today, many other developing countries have adopted and developed<br>briquetting technology, owing to high cost and scarcity of fuel.<br>Common types of briquettes so far in use are coal briquettes, peat<br>briquettes, charcoal briquettes and biomass briquettes, etc. Most<br>recently, researches showed that blending of coal and biomass will give<br>rise to a briquette with better combustion properties and pollutants<br>emission reduction. This type of briquette is known as bio-coal<br>briquette. Some authors simply called it biobriquette [16].<br>1.3 Bio-Coal Briquettes<br>Bio-coal briquette is a type of solid fuel prepared by blending coal,<br>biomass, binder and sulphur fixation agent [23,24]. Other additives<br>may also be added. A research showed that bio-coal briquettes may be<br>prepared by blending the following [15]: ï‚· Biomass (25% to 50%) ï‚· Coal (75% to 50%) ï‚· Sulphur fixation agent (up to 5%) ï‚· Binder (up to 5%)</p><p>10</p><p>Also, according to clean coal technologies Japan, bio-coal briquettes<br>are prepared by blending: ï‚· Biomass (10% to 25%) ï‚· Coal (75% to 90%) ï‚· Sulphur fixation agent (depending on the sulphur content of the<br>coal).<br>In this process, Ca(OH)2 acts as both sulphur fixation agent and the<br>binder [16]. Also, activators such as iron oxide, potassium manganate<br>and sodium chloride have been reported to have the ability of<br>improving the thermal efficiency of the briquette [26].<br>The high pressure involved in the process ensures that the coal particles<br>and the fibrous biomass material interlace and adhere to each other as a<br>result, do not separate from each other during combustion,<br>transportation and storage. During combustion, the low ignition<br>temperature of the biomass simultaneously combusts with the coal. The<br>combined combustion of both gives a favorable ignition and fire<br>properties; emits little dust and soot, generates sandy combustion ash,<br>leaving no clinkers [16, 24]. Also the desulfurizing agent such as<br>Ca(OH)2 in the briquette effectively reacts with the sulphur content of<br>the coal to fix about 60-80% of it into the ash [16]. It was showed that<br>lime (CaO) as a desulfurizing agent was able to capture up to 90-95%<br>of the total sulphur in the coal, leaving only 5-10% emitted as sulphur<br>oxides [25]. The equation of the reaction is as follows:</p><p>11</p><p>CaO(s) + SO2 (g) + ½ O2 (g) CaSO4(s).<br>Evidence also revealed that lime when used as desulfurizer also acts as<br>a binder. Also clay has been reported to be a good desulfurizing agent.<br>Clay contains CaO and MgO which acts as desulfurizing agents. Also<br>it contains Fe2O3 which has been shown to have a catalytic effect on<br>the sulfation reaction [25].<br>There are various biomass resources available for production of bio<br>coal briquettes. Some of them are straw, sugar bagasse (fibrous residue<br>of processed sugar cane), corn stalk, groundnut – shell, wheat straw,<br>palm husk, rice husks, corn cob, forest wastes, and other agricultural<br>wastes. Several researches on bio–coal briquette have been carried out<br>using some of these biomass resources. There are records of researches<br>carried out on production of bio-coal briquettes using sawdust [27],<br>rice straw [28], olive stone [29, 30] and maize cob [24], etc.<br>Furthermore, it has been shown that any grades of coal can be used for<br>bio-coal production, even low grade coal containing high sulphur<br>contents [24, 26]. This implies that, by this technology, extra cost of<br>carbonizing low grade coal before briquetting is saved.<br>Binder is an adhesive material which helps to hold the particles of the<br>material together in the briquette. Apart from its function to hold the<br>particle from separation, it also protects the briquette against moisture<br>in case of long storage [13]. There are several binders that can be used.<br>Some of them are starch (from various starchy root such as cassava,</p><p>12</p><p>and cereals), molasses, clay and even tree gum, etc. Some chemical<br>substances have also been used as binding agent for production of<br>briquettes. Some of them are asphalt [31], potassium [32], magnesia<br>[33], ammonium nitrohumate [34] and commercial pitch [35]. Though<br>the use of starch as binder is satisfactory in every respect, it<br>disintegrates under moist or tropical condition. However, the use of<br>small additional hydrocarbon binder such as pitch or bitumen has been<br>reported to improve the water resisting property [36]. Moreover, the<br>nature of the binder has influence in the combustibility of the briquette<br>produced. For instance, briquette produced using clay takes longer time<br>to ignite than the one produced using starch [13]. The reason for this is<br>because of non-combustibility of clay compared to starch.<br>1.3.1 Characteristics of Bio-Coal Briquettes<br>(1) Bio-coal briquette decreases the generation of dust and soot up to<br>one-tenth that of direct combustion of coal [16]. Combustion of<br>coal generates dust and soot because, during the combustion, the<br>volatile components of the coal are released at low temperature (200-4000C) as incomplete combusted volatile matter. For bio-coal<br>briquette, since the biomass component of the briquette ignites at<br>low temperature compare to the coal, this ensures that the volatile<br>matter in the coal which would have otherwise been liberated as<br>smoke at low combustion temperature combusts completely. By so<br>doing, there is a significant reduction in the amount of dust and</p><p>13</p><p>soot generated. Note that smoke is a complex mixture of air-borne<br>solid and liquid particulates as well as gases evolved on pyrolysis<br>or combustion of material [45].<br>(2) Bio-coal briquette has a significant shorter ignition time when<br>compared with coal or conventional coal briquette [15]. This is<br>because of the biomass component of the briquette. Biomass has<br>low ignition time.<br>(3) Bio-coal briquette has superior combustion-sustaining properties.<br>Because of low expansibility and caking properties of bio-coal<br>briquette, sufficient air flow is maintained between the briquettes<br>during combustion in a fire-place. Hence it has very good<br>combustion-sustaining properties and does not die out in a fireplace<br>or other heater even when the air supply is decreased [16]. This<br>property offers the opportunity of adjusting the combustion rate of<br>the bio-coal briquette easily.<br>(4) Bio-coal briquette emits less SO2. It contains desulfurizing agent<br>and the high pressure involved in the process enables the coal<br>particles to adhere strongly to the desulfurizing agent. During<br>combustion, the desulfurizing agent effectively reacts with the<br>sulphur content of the coal to form a solid compound instead of<br>being released as oxides of sulphur to the atmosphere. However, it<br>is widely accepted that bio-coal briquette technology is one of the</p><p>14</p><p>most promising technologies for the reduction of SO2 emission<br>associated with burning of coal [24,37].<br>(5) Bio-coal briquette has high breaking strength for easy<br>transportation. The high pressure involved in the process coupled<br>with the binder, compressed the raw materials into a rigid mass<br>which does not break easily, hence can be stored and transported<br>safely [16].<br>(6) Bio-coal briquette generates sandy ash which can be utilized in<br>agriculture for soil improvement [38]. In the briquette, since the<br>fibrous biomass intertwined with the coal particles, the resulted ash<br>after combustion does not adhere or form clinch-lump, therefore,<br>the ash is always sandy.</p><p>(7) Bio-coal briquette burns nearly perfect; therefore the flame has<br>significant higher temperature than simple biomass burning [39] or<br>coal [26].</p><p>15</p><p>1.3.2 Table 1: Comparative Tests of Bio-coal Briquettes [40]</p><p>Briquettes</p><p>Calorific value (kcal/kg)<br>Mass(in kg) of Evaporated water by 1kg of the briquette<br>Time(in minute) to cook a mixture of 1kg of mansuli rice, 0.25kg of rahar dal and 0.5kg of potatoes<br>Mass (in kg) of fuel consumed.<br>75% coal (Jumlepani ghorahi coal) and 25% biomass (Lumibini bagasse.</p><p>4222.5</p><p>1.5</p><p>64</p><p>1.535<br>80% coal (40% Jumlepani Ghorahi coal and 40% lignite) and 20% biomass (Lumbini bagasse)</p><p>____</p><p>____</p><p>104</p><p>1.650<br>20% coal (Abidara coal) and 80% biomass (Chitiwan rice husk)</p><p>3806</p><p>1.0</p><p>_____</p><p>_____</p><p>40% of coal<br>(Abidara coal) and<br>58% biomass<br>(Nawalparasi rice<br>husk) and 2%<br>Chovar lime.</p><p>____</p><p>_____</p><p>83</p><p>2.643<br>Coal (Indian coal) 5900 2.46 ____ ____<br>Cowdung 3710 1.2 144 4.00<br>Rice husk. 3688 0.86 112 3.035<br>Fuelwood. 3600 0.68 85 2.992</p><p>16</p><p>1.3.3 Comparison of Efficiency of Bio-Coal Briquette with Fuel<br>Wood.<br>Comparative tests of different bio-coal briquettes with fuel wood<br>showed that [40]: ● Bio-coal briquettes can boil more water than fuel wood using an<br>appropriate stove, under similar condition. ● Bio-coal briquette takes less time to cook the same amount of<br>foodstuffs than fuel wood. ● Only half the weight of bio-coal briquette (75% of coal and 25% of<br>biomass) is required to achieve the same results compared to fuel<br>wood. ● Bio-coal briquettes are easier to ignite and last for a longer period of<br>time than fuel wood. ● The combustion temperature of bio-coal briquette is higher than that<br>of fuel wood [29].<br>1.3.4 Production Process of Bio-Coal Briquette<br>The production process of bio-coal briquette is very simple and cost<br>effective. The raw materials; coal and biomass are pulverized to a size<br>of approximately 3mm and then dried. Research showed that 0-5mm is<br>the optimum particle size of the raw materials for a briquette [41]. The<br>dried pulverized materials, a desulfurizing agent and binder are mixed<br>together in appropriate proportions and are compressed with briquette<br>machine into a designed shape. The type of briquette machine</p><p>17</p><p>determines the shape and size of the briquette. Some briquette<br>machines have small mould while some have relatively larger mould.<br>For a large mould, there is always a facility which creates holes in the<br>briquettes when formed. These holes are necessary for efficient<br>combustion of the briquette. It allows for proper flowing of air needed<br>to maintain the combustion [42].<br>In this production process, high temperature is not required. The<br>process is simple, safe and does not require skilled operating technique.<br>Hence the process can easily be adopted and sustained in Nigeria. The<br>basic process flow for bio-coal production is shown in Fig.1.</p><p>18</p><p>Fig.1: Basic process flow for bio-coal production</p><p>Crushing<br>Drying<br>Briquetting<br>Mixing<br>Biomass<br>Pressure: 1-3t/cm2 Temperature: room temp.<br>Drying<br>Storage<br>Desulfurizer, binder, water<br>Raw coal<br>Drying<br>Crushing</p><p>19</p><p>Production of Bio-coal Briquette by Co–pyrolysis of Coal and<br>Biomass<br>In this method, the raw materials; coal and biomass are first co<br>carbonized. The coal and the biomass are dried up to 15% moisture of<br>the materials. And the material is ground and sieved to get fractions<br>between 0-5mm. After that, the fine coal and biomass are mixed together and co-carbonized to a temperature of 500-600oC for 20-30<br>minutes. Then, a binder and desulfurizing agent are added in the<br>appropriate amount. The mixture is blended very well and compressed<br>into briquettes and the mechanical strength and water resistance is improved by curing the briquette at a temperature between 120-180oC<br>for 2-4 hours. However, this method of production of bio-coal briquette<br>seems to be more expensive than the previous method due to extra<br>energy needed for carbonization of the raw materials.<br>1.3.5 Bio-coal Briquette Ash<br>The ash of bio-coal briquette has been shown to be effective for soil<br>improvement [43,37]. Table 2 shows the chemical composition of the<br>ash of a bio-coal briquette sample {coal (72.5%), biomass (13% saw<br>dust, and 1.5% straw), CaO (7%)} [26]. The ash contains calcium<br>compounds such as Ca(OH)2, CaO, CaSO4.2H2O, CaSO3, CaCO3, etc<br>which make it to have an acid neutralizing ability and as well,<br>functions as plant nutrient. Also, because sulphuric by-products in bio<br>coal ash is generated from sulphur in the coal, bio-coal briquette</p><p>20</p><p>produced with a coal having higher sulphur contents might produce<br>more effective soil improving ash [26].<br>Furthermore, there was a plan by China to employ the use of bio-coal<br>briquette and its ash as a CDM (Clean Development Mechanism) to<br>obtain carbon credit in order to implement the reduction of CO2. The<br>plan was to switch from the use of coal to bio-coal briquette and<br>utilization of the ash to improve the soil on desert and semi-desert<br>areas along with planting of trees in the improved soil of the areas [26].<br>This suggests that it is possible to reduce CO2 and at the same time<br>keep coal consumed.<br>Table 2: chemical analysis on bio-coal briquette ash<br>Compounds Percentage composition (%)<br>Ca(OH)2 1<br>CaO 9<br>CaSO3 1<br>CaSO4.2H2O 10<br>SiO2 27<br>CaCO3 5<br>Al2O3 19</p><p>21</p><p>1.4 Preparation of other types of Briquettes<br>As it has been mentioned earlier, briquette is a kind of solid smokeless<br>fuel produced by compressing pulverized raw material under high<br>pressure at ambient or elevated temperature. The raw materials are<br>generally coal and biomass of various forms. The name given to any<br>fuel briquette depends on the materials of which it was made. For<br>instance, common briquettes; peat briquettes, charcoal briquettes,<br>biomass briquettes and coal briquettes are prepared as follows:<br>Peat briquettes: Peat briquette consists of shredded peat, compressed<br>to form a solid fuel [44].<br>Charcoal briquettes: Charcoal briquette is a common type of briquette<br>made by compressing pulverized wood charcoal with a binder.<br>However, other activator such as sodium nitrate may be added as an<br>accelerant.<br>Biomass briquettes: Biomass briquette is made from agricultural<br>wastes. It is a renewable source of energy. Lignin and cellulose are the<br>two major compounds of biomass. The lignin distributed among<br>cellulose determines the structural strength of biomass [39]. Lignin is a<br>non-crystallized aromatic polymer with no fixed melting point. When heated to 200-300oC, lignin melts and liquefies. When pressure is<br>applied in this case, the melted lignin glues the cellulose together;<br>hence the biomass is briquetted when cooled. This method of<br>production of biomass briquette is based on lignin plasticization</p><p>22</p><p>mechanism [39]. However, biomass briquette can also be produced at<br>room temperature by the application of another briquetting technique;<br>in that case binder is used.</p><p>Fig.2: Basic process flow for production of biomass briquette by<br>plasticization mechanism</p><p>Coal briquette: Coal briquettes are made by compressing finely<br>divided coal particles. The coal is dried, crushed into appropriate<br>particle sizes. Binder and desulfurizing agents are added, then the<br>material is compressed into briquette [25]. Also, coal briquette can<br>Biomass<br>Crushing<br>Drying<br>Briquetting<br>Cooling<br>Storage<br>Diameter &lt; 10mm<br>Moisture 6-14%<br>Pressure: 4-60Mpa Temperature: 160-280oC</p><p>23</p><p>be produced by first carbonizing the coal before it is used [16].<br>During the carbonization, some of the volatile components of the<br>coal are driven off.</p><p>Fig.3: basic process flow for production of coal briquette</p><p>Crushing<br>Drying<br>Briquetting<br>Carbonization<br>Mixing<br>Diameter: 5-50mm<br>Moisture: 10% or lower<br>Pressure of 300-500kg/cm2 (roll-molding briquette machine) and room temperature.<br>Raw coal<br>Drying<br>Storage<br>450oC<br>Desulfurizer, binder, water</p><p>24</p><p>1.5 Combustion Process<br>Burning process is a self-sustaining exothermic chemical reaction.<br>Burning is first initiated by initial supply of external heat. When this<br>initial heat is being supplied to a material, the temperature of the<br>material is raised until at a certain temperature, the material begins to<br>degrade into various gases (combustible and non-combustible gases) as<br>well as carbonaceous char. This process is known as pyrolysis. Then;<br>ignition occurs between the combustible gases produced and oxygen at<br>ignition temperature to produce flame [45]. If there is insufficient<br>supply of oxygen, there will be incomplete combustion resulting into<br>formation of carbonaceous products (such as char), smoke, unburnt<br>flammable volatile and non-flammable gases.<br>Smouldering:<br>Smouldering simply means burning of substance without flame. It is a<br>heterogeneous oxidation of a solid surface by a gaseous oxidant<br>(oxygen) [45]. Charcoal is an example of substance that smoulders.</p><p>Factors which Control Burning of Material<br>Some factors which control the burning of substances are listed below; ● Chemical composition of the material ● Geometry of the material (bulk, packing, orientation and surface<br>contour, etc) ● Size of the material</p><p>25</p><p>● Condition of burning such as initial temperature, relative humidity<br>and draught.<br>However, the chemical composition and physical properties of a<br>briquette such as thermal conductivity, porosity, calorific value and the<br>moisture contents, etc, will have a great influence on the combustion<br>performance of the briquette. Again, the rate of adsorption of oxygen<br>and desorption of the combustible products also have rolls to play in<br>the general combustion rate. Therefore, the spatial configuration of the<br>briquettes on the combustion boat is important. Loosely packed<br>briquettes in the combustion boat will have tendency to promote rapid<br>diffusion of the oxidants for a better combustion.<br>1.5.1 Pyrolysis and Combustion of Cellulosic Materials (Grasses)<br>As it has been mentioned earlier, burning of substance proceeds in two<br>stages; first, pyrolysis of the material and then the combustion<br>(oxidation) of the combustible pyrolysis products with release of<br>energy. In practice, pyrolysis and combustion of the resulted volatiles<br>may occur at almost the same time. The gas or gases evolved from<br>pyrolysing substances depend upon the heating rate and largely on the<br>nature of the substance. Common gaseous pyrolysates (pyrolysis<br>products) arising from pyrolysis of cellulosic materials include: carbon<br>dioxide (CO2), carbon monoxide (CO), ammonia (NH3), methane<br>(CH4), hydrogen (H2), hydrogen cyanide (HCN) and water vapor<br>(H2O), etc [45].</p><p>26</p><p>The degradation of cellulose may arise from the cleavage of the<br>glucosidic bond or by dehydration or breakdown of the anhydroglucose units. Below 300oC, dehydration, elimination and breakdown occur.<br>The result of this process is gradual charring and depolymerization of<br>the macromolecules. At higher temperature, there is rapid cleavage of<br>the glucosidic bond accompanied by evaporation of the products.<br>Cellulosic pyrolysis takes either of these routes [45].</p><p>Laevoglucosan CO + other combustible<br>Volatiles eg. Alkanes,<br>1 alkenes, alkanols,<br>aldehydes and ketones.<br>(C6H10O5)n<br>2<br>H2O + C (Char).</p><p>The first route involves depolymerization of dehydrocellulose chain<br>forming laevoglucosan which further decomposes to form flammable<br>volatiles; carbon monoxide, alkanes, alkenes, alkanols, aldehydes etc.<br>The volatiles can subsequently form secondary pyrolysis products and<br>or combust in the presence of oxygen with release of heat.</p><p>27</p><p>The second route involves a complete dehydration of the material to<br>form water and char. The char is then oxidized by the oxygen to CO2<br>and CO with release of heat.<br>1.5.2 Pyrolysis and Combustion of Coal<br>Pyrolysis of coal (bituminous coal) converts about half of the coal<br>mass into gases including many fuel compounds. The subsequent<br>secondary pyrolysis and the combustion of these volatile compounds<br>accounts for large portions of the heat release, pollutant formation and<br>soot evolution during coal combustion. The pyrolysis of bituminous coal at temperature between 2670C to 3620C revealed the presence of<br>the following compounds, in the volatile as determined by gas<br>chromatography and non-dispersive infrared analysis [46]. The<br>compounds are H2, CO, CH4, C2H4, C2H6, C2H2, C3H6, CO2, H2O and<br>light oil. H2, CH4 and CO was found to be more abundant in the<br>volatile composition while the remaining hydrocarbons contribute<br>about the half of the heat released during the combustion of the<br>volatiles. In fact, the light oil alone contributes the quarter of the heat<br>released. This is because of their high molecular weights, very small<br>mole fractions of these higher hydrocarbons contribute significant<br>amount of energy released.<br>However, it is expected that lower rank coal, on pyrolysis will produce<br>more amount of these volatiles than the ones released by bituminous<br>coal.</p><p>28</p><p>It is worthy to note that in the study of the pyrolysis products of<br>material, the volatiles isolated may consist of the primary and<br>secondary pyrolysis products. The secondary pyrolysis products result<br>from either the thermolysis of the primaries or the interaction of these<br>in either the gas or the condensed phase. This poses a complication in<br>the identifications of the pyrolysis products of a material.<br>1.6.1 Coal<br>Coal was formed by the remains of vegetable that were buried under<br>ground million of years ago under great pressure and temperature in the<br>absence of air. Coal is a complex mixture of compounds composed<br>mainly of carbon, hydrogen and oxygen with small amounts of sulphur,<br>nitrogen, and phosphorus as impurities. Dry anthracite was found to<br>have the following compositions [47].<br>Carbon – 90%<br>Hydrogen – 3%<br>Oxygen – 2%<br>Nitrogen – 1%<br>Sulphur – 1%<br>Ash – 3%.<br>Lower rank coal is expected to have lower percentage of carbon with<br>increased percentages of other component elements. Examination of<br>coal revealed that its structure is composed of aromatic and cyclic<br>structures [49]. Fig.4 shows an example of chemical structure of coal.</p><p>29</p><p>1.6.2 Types of Coal<br>Coals are classified according to their fuel properties. The higher the<br>carbon contents of coal, the better the fuel properties. Therefore, coal<br>classification is based on the degree to which the original plant<br>materials have been transformed into carbon. The older the coal, the<br>higher the carbon content and the better the fuel properties. This also<br>implies that the rank of coal is an indication of how old the coal is.<br>Types of coal are as follows [47,48]:</p><p>CH<br>OH OH<br>OOCH3<br>OH<br>OH H<br>OH HO</p><p>HO H<br>OH<br>OH<br>OH<br>Fig.4: Chemical structure of coal</p><p>30</p><p>● Peat: Peat is considered to be precursor of coal. It is used as fuel in<br>some countries. In a dehydrated form, peat is an effective absorbent for<br>oil spill on land and water. ● Lignite: Lignite coal is also called brown coal. It is the lowest rank<br>of coal, brownish black and has high moisture content (up to 45%),<br>calorific value of less than 5kw/kg and high sulfur content. It is<br>generally used as fuel for generation of electricity. ● Sub-bituminous coal: The properties of sub-bituminous coal ranges<br>from those of lignite to those of bituminous coal. It is black in colour.<br>It contains 20-30% moisture, calorific value of between 5-6.8kw/kg.<br>Sub-bituminous coal is primarily used as fuel for steam-electric power<br>generation. ● Bituminous coal: It is black and sometimes dark brown in colour. It<br>is most common coal, has moisture content of less than 20% and<br>calorific value ranging from 6.8-9kw/kg. It is mainly used for<br>generation of electricity. ● Anthracite: Anthracite is the highest rank of coal and is referred to<br>as hard coal. It is hard and lustrous. Anthracite is high in carbon<br>content, low in sulphur content and moisture content. The calorific<br>value is about 9kw/kg or above. It is mainly used for residential and<br>space heating.</p><p>31</p><p>1.6.3 Gasification of Coal<br>Coal gasification can be used to produce syngas. Syngas is a mixture of<br>carbon monoxide and hydrogen. The syngas can then be converted into<br>transportation fuel like gasoline and diesel through the Fischer-Tropsch<br>process [49]. This process has recently been used by the Sasol<br>Chemical Company of South Africa to make gasoline from coal and<br>natural gas [49]. Furthermore, the hydrogen obtained from the<br>gasification of coal can be used for other purposes such as powering of<br>hydrogen economy, making ammonia or upgrading fossil fuels.<br>During the process of gasification of coal, the coal is mixed with<br>oxygen and steam, heated and pressurized. The oxygen and the water<br>molecule oxidize the coal into carbon monoxide (CO) and hydrogen<br>(H2) is equally formed.<br>(Coal) + O2+ H2O H2 + CO ………………… (1)<br>Syngas<br>1.6.4 Liquefaction of Coal<br>Coal can be converted into liquid fuel like gasoline or diesel. There are<br>many methods that can be used. One of them is liquefaction process.<br>During the process, the coal is either hydrogenated or carbonized.<br>Hydrogenation process is also known as Bergius Process [49]. In this process, the coal is carbonized at low temperature, between 360oC – 750oC to form coke and coal tar. This temperature optimizes the<br>production of coal tar richer in hydrocarbons than normal coal tar. The</p><p>32</p><p>coal tar is then processed into fuel. Alternatively, coal can be converted<br>to a gas first before it is liquefied by employing the Fischer-Topsch<br>process.<br>1.6.5 Coke<br>Coke is obtained by heating bituminous coal to very high temperature (about 1300oC) in the absence of air to drive away all the volatile<br>constituents of the coal. This process is generally referred to as<br>destructive distillation of coal. Coke is basically used as fuel because it<br>burns with no smoke and leaves very little residue. It also has many<br>important industrial applications. It is used as an industrial reducing<br>agent. It is equally used in the extraction of metals such as iron from its<br>ore. Coke is also used in the production of gaseous fuel such as water<br>gas and producer gas and in the manufacturing of graphite. Water gas<br>is a mixture containing equal volumes of hydrogen and carbon monoxide prepared by passing steam over white-hot coke at 1000oC.<br>C(s) + H2O(g) CO(g) + H2(g) ………………… (2)<br>Producer gas is a mixture of nitrogen and carbon monoxide. It is<br>prepared by passing a stream of air through red-hot coke. The oxygen<br>in the air oxidizes the coke to carbon monoxide while the nitrogen in<br>the mixture remains unchanged.<br>2C(s) + O2 (g) 2CO(g) ………………. (3)</p><p>33</p><p>1.6.6 Coal in Nigeria<br>In Nigeria, coal was discovered in the year 1909 in Enugu State. It was<br>estimated that the Nigeria coal reserve is about 2 billion metric tonnes<br>and it has low sulphur content. Among the coal types found in Nigeria<br>are sub-bituminous coal, bituminous coal and lignite coal. Nigeria has<br>the largest lignite deposit in Africa with a reserve of about 30 million<br>tonnes. Nigeria lignite extends from Oriu in the South-East, through<br>Urnuezealar, Umuahia, Nnewi, Oba, in a 2Km to 40km wide belt<br>across the Niger to Ogwashi, Asaba, Mgbiguba and Adiase-Uti in<br>Delta State [50]. After the discovery of coal, many mines were opened<br>in Nigeria and Nigeria had been mining coal until 1950’s when oil was<br>discovered. After then, the Coal Corporation began to suffer a set back.<br>Names and the locations of some of mines in Nigeria are listed below<br>[50]: ● Amansiodo coal mines in Enugu State. ● Ezinmo coal field in Enugu State. ● Onyeama mine in Enugu State. ● Ogboyoga I coal field in Kogi State. ● Ogboyoga II coal field in Kogi State. ● Okaba coal field in Kogi State. ● Ogwashi-Azagba lignite field in Delta State. ● Okpara mine in Anambra State. ● Owukpa mine in Benue State.</p><p>34</p><p>1.7 Biomass Resources of Nigeria [1]<br>Biomass is organic non-fossil material of biological origin. The<br>biomass resources of Nigeria can be identified as wood, forage,<br>grasses, shrubs, animal wastes and wastes arising from forest,<br>agricultural, municipal and industrial activities as well as aquatic<br>biomass. Generally, biomass can be converted into energy either by<br>thermal or biological process.<br>Biomass energy resources base in Nigeria is estimated to be about 144<br>million tonnes per year. Nigeria has about 71.9 million hectares of land<br>considered to be arable and grasses of different kinds are among the<br>major agricultural wastes farmers encounter during clearing of the land<br>for agricultural purposes. Spear grass and elephant grass are very<br>common and dominant grasses in many parts of the country.<br>The potential for the use of biomass as energy source in Nigeria is very<br>high. This can be explained from the fact that about 80% of Nigerians<br>are rural or semi-urban dwellers and they depend solely on biomass for<br>their energy source. Biomass may be used directly as energy source for<br>heating or are better converted to a cleaner fuel source. For instance,<br>conversion of wood into charcoal and biomass based briquettes is<br>always encouraged. Other energy sources that are got from biomass<br>include: biogas, biodiesel and bio-ethanol etc. All these energy sources<br>have been shown to have better combustion performance and are more<br>environmental friendly than direct combustion of biomass.</p><p>35</p><p>However, owing to the fact that firewood is the energy choice of the<br>rural dwellers and the urban poor, pressure is mounted on the forest in<br>search of fuel wood while on the other hand, vast majority of other<br>biomass resources in form of agricultural wastes are wasted either<br>deliberately or inadvertently. Meanwhile, researches have proved that<br>this category of biomass resources can be converted to better fuel<br>sources compared to fire wood and at the same time, it will act as a<br>pollution control measure.<br>Charcoal:<br>Types of charcoal are: wood charcoal, sugar charcoal and animal<br>charcoal. They are produced by burning wood, sugar and animal refuse<br>(blood, bones), respectively in a limited supply of oxygen. Wood<br>charcoal is a common fuel source used by some people. It is a cleaner<br>fuel source than fire wood. In fact, analysis shows that transition from<br>fuel wood to charcoal would have been a best option for reducing<br>exposure to indoor pollution but such transition could lead to even<br>more severe environmental degradation and fuel scarcity as more wood<br>is needed per meal using charcoal compared to fuel wood [4].<br>Apart from its use for cooking and heating, wood charcoal is used as<br>gas-masks for adsorbing poisonous gases. It is also used for<br>purification of the noble gases and recovery of industrial solvent.</p><p>36</p><p>Biogas:<br>Biogas is produced when biomass is subjected to biological<br>gasification. Biogas is a methane-rich gas produced from anaerobic<br>digestion of organic materials. The gas is typically composed of 55<br>70% methane, 25-45% carbon dioxide, 1-10% hydrogen, 1-3%<br>nitrogen 0.1% oxygen, carbon monoxide and traces of hydrogen<br>sulphide. It is mainly used for cooking and heating.<br>Biodiesel:<br>Biodiesel is produced when vegetable oil or animal fat is subjected to a<br>chemical reaction known as transesterification. During the reaction, the<br>vegetable oil or the animal fat is reacted with alkanol (usually<br>methanol) in the presence of catalyst (usually base) to give the<br>corresponding alkyl esters of the fatty acid mixture present in the lipid.<br>Biodiesel when blended with diesel can be used in an unmodified<br>diesel engine [1]<br>Bio-ethanol:<br>Bio-ethanol is simply ethanol (CH3CH2OH). Ethanol is a colorless<br>liquid derived from agricultural sources mainly by fermentation<br>process although it can be produced from ethane. Agricultural sources<br>usually used for production of bio-ethanol are those capable of yielding<br>sugar in a large amount. Such agricultural materials are grouped as<br>follows;</p><p>37</p><p>(i) Saccharine (sugar containing) materials e.g. Sugar cane, sugar<br>beat, sweet sorghum, fruits such as pears and orange etc.<br>(ii) Starchy materials e.g. Cassava, potatoes, cereals such as maize,<br>guinea corn, millet and rice, etc.<br>(iii) Cellulose materials e.g. agricultural plant wastes (such as corn<br>cob and stalk, sugar cane bagasse etc). Other cellulosic materials<br>include paper pulp, municipal solid wastes such as old newspapers.<br>Bio-ethanol, just like other renewable energy sources produces lower<br>emission on combustion and is carbon neutral. It is used as petrol<br>substitute or fuel additive for road transportation.<br>1.7.1 Spear Grass (Imperata cylindrica)<br>Spear grass (Imperata cylindrica (L) Raeuschel) is a rhizomatous,<br>perennial grass weed which is widely distributed throughout the humid<br>and sub-humid tropics and some parts of the warm temperate regions<br>of the world. It ranked as the world’s seventh worst weed [51] and in<br>the West Africa, it is one of the most dominant and noxious weeds in<br>agricultural and non-agricultural field. In the region, it is found in the<br>forest/savanna transition zone where recurrent fires and farming<br>activities prevent the natural vegetation from growing up to levels that<br>can shade out weeds. Spear grass is a serious weed, a potential fire<br>hazard in plantation crops and arable crops farmland because most of<br>the control methods employed by farmers are not effective [52]. In<br>Nigeria, reports showed that spear grass has potential to invade 260</p><p>38</p><p>million hectares of land and negatively affects nearly 80 million people<br>residing in intensively cultivated areas of the moist savanna and humid<br>forest zone [53].<br>Strategies for spear grass management include hoe-weeding, slashing,<br>deep tillage, chemical control, burning, abandoning the land for fallow<br>and the use of short-term planted fallow (e.g. cover crops and alley<br>cropping). Traditionally, small scale farmers abandoned severely<br>infested fields to fallow for 5 to 15 years. This allowed bush re-growth<br>to levels that shade and smother weeds. However, long fallow periods<br>are no longer possible as increasing human population puts pressure on<br>land. Therefore, the simple method of managing this grass from a piece<br>of land is to clear and gather them and possibly recycle them into a<br>useful product such as biomass briquettes and bio-coal briquettes, etc<br>as unlike leguminous plants, it does not decay easily when cleared.</p><p>Plate 1: Spear Grass (imperata cylindrica) Plate2: Elephant Grass (pennisetum purpureum)</p><p>39</p><p>1.7.2. Elephant Grass (Pennisetum purpureum)<br>Elephant grass is an indigenous grass found all over the tropic. In<br>Nigeria, it is one of the dominating grasses found in the farmlands and<br>non-agricultural fields. When fully grown, it is cane-like specie of<br>grass and can grow up to 3 meters especially in wet land. Because of its<br>high productivity (rapid growth), Brazil cultivates and utilizes it to<br>produce charcoal, cellulose, biofuels and also as direct fuel source for<br>thermoelectric power plants and furnaces [54].<br>Sykue Bio-energia has already commissioned a thermoelectric power<br>plant that will be fueled by elephant grass [54]. As a solid biofuel,<br>elephant grass can be burnt either in dedicated, highly efficient biomass<br>power plants, in blast furnaces as an alternative to coal, or co-fired with<br>coal in existing power plants. There has been research to mix cellulosic<br>feed stock with coal slurry as fuel in thermoelectric power plant.<br>Instead of biomass fueled thermoelectric power plant biomass is added<br>to coal and fed into an entrained flow gasifier. This is to increase<br>security and to reduce carbon emissions. This idea was presented by<br>Nobilis for NETL/USAF [54].<br>However, in Nigeria, although elephant grass is traditionally used as<br>animal feed (at younger stage) and for preparation of compost manure,<br>a greater amount of them are burnt every year either during land<br>clearing for agricultural or construction purposes or by bush fire.</p><p>40</p><p>1.8. Starch as a Binder<br>Starch is a white granule organic chemical compound that occurs<br>naturally in all green plants. The percentage of occurrence varies with<br>plant and in different parts of the same plant. The natural function of<br>the starch is to provide a reserve food supply for the plant. Though<br>starch can be extracted from many kinds of plants, only a few plants<br>can yield starch in commercial quantities. Such plants are maize,<br>potato, rice, sorghum and cassava, etc.<br>Cassava plants are the major source of starch. The plant thrives in the<br>equatorial region between the tropics of Capricom, and as well it<br>thrives very well in Nigeria. There are many varieties of cassava plants<br>of which two varieties-bitter and sweet varieties are widely grown for<br>the purpose of manufacturing of starch. They contain high content of<br>starch which ranges from 12-33%. A typical composition of the<br>cassava root is moisture (70%), starch (24%), fiber (2%), protein (1%) and other substance including minerals (3%). The general formula for<br>starch molecule is C6H10O5. Starch obtained from cassava tubers has<br>high polymeric structure the granule size in microns is between 5 to 36µm. The granule shape may be truncated, round or oval [55].<br>When starch is cooked, it gelatinizes to form viscous solution with<br>water. The starch granules begin to swell as they are heated in water<br>until they absorb most of the water and starch paste which differs in<br>clarity, texture and gelling strength is formed. Cassava starch has</p><p>41</p><p>numerous industrial uses. They are used as an additive in cement to<br>improve the setting time. It is used to improve the viscosity of drilling<br>moulds in oil wells. It is used to seal the walls of bore holes and<br>prevent fluid loss. It is also the main raw material in glue and adhesive<br>industries. In briquetting industries, it is widely used as a binder.<br>Briquette produced using starch as the binder is easily ignitable and<br>burns with less ash deposit.<br>1.9. Calcium Hydroxide<br>Calcium hydroxide is also known as slaked lime, hydrated lime, slake<br>lime or pickling lime. It is a chemical compound with the formula,<br>Ca(OH)2. It is a white powder or colorless crystal. Commercially, it is<br>produced when calcium oxide (CaO) (also known as quick lime or<br>lime) is mixed with water. This process is known as slaking of lime.<br>CaO(s) + H2O(l) Ca(OH)2(s) ………………(4)<br>Naturally, calcium hydroxide occurs in mineral form called portlandite<br>[56]. Portlandite is a relatively rare mineral known from some<br>volcanic, plutonic, and metamorphic rocks. It has also been known to<br>arise in burning of coal dumps.<br>Quicklime is a white solid obtained when limestone (calcium trioxocarbonate (iv)) is heated to a very high temperature, about 900oC. CaCO3(s) 900oC CaO(s) + CO2(g) ………………(5)<br>In Nigeria, calcium hydroxide is expected to be very cheap and<br>available in abundance because there is large deposit of limestone in</p><p>42</p><p>the country and besides, the production of calcium hydroxide is a<br>simple process. Many investigations have shown that calcium<br>hydroxide is an effective sulphur fixation agent (desulfurizing agent)<br>for production of briquettes.<br>Apart from the use of calcium hydroxide as a desulfurizing agent, it has<br>many other uses. It is commonly used for treatment of acidic soil. Also,<br>because of its anti-microbial actions, it is used in dentistry for dressing.<br>It has been proposed that when slake lime is added in sea water in great<br>quantities, it reduces atmospheric CO2 and fights the greenhouse effect<br>[56]. However, since calcium hydroxide is produced commercially by<br>calcinations of limestone (decomposition of limestone by heat), and<br>during this process, the limestone releases in the atmosphere the same<br>amount of carbon dioxide as calcium hydroxide can absorb, then it<br>implies that this method of using calcium hydroxide to fight<br>greenhouse effect is at best carbon neutral.<br>Properties of Calcium Hydroxide [56]<br>Molecular formula —– Ca(OH)2<br>Molar mass —– 74.093g/mol.<br>Appearance —– soft white powder/colorless<br>liquid<br>Odour —– odourless Density —– 2.211g/cm3, solid Melting point —– 512oC (decomp.)</p><p>43</p><p>Solubility in water —– 0.189g/100ml (0oC)<br>Basicity (pkb) —– 2.37.</p><p>Objectives of the Study<br>The main objectives of this study are as follows: ï‚· To determine the optimum biomass composition for production<br>of bio-coal briquettes from sub-bituminous coal and the<br>individual grass samples. ï‚· To investigate the variation in the properties of bio-coal<br>briquettes as the proportion of the biomass components changes. ï‚· To compare the fuel properties of the bio-coal briquette with<br>ordinary coal briquette.</p> <br><p></p>