Design, construction and experimental evaluation of the products of a low cost briquette machine for rural communities in nigeria

Thesis Overview

<p> </p><p>INTRODUCTION<br>Approximately 2000 million people world wide; most rural people and many urban<br>as well, all depend on wood fuels as their main or sole source of energy to cook their food<br>and keep warm. Nine-tenths of all the wood harvested annually is used for energy; “it<br>accounts for over two-thirds of total energy consumption in 24 tropical countries of which<br>16 are least-developed countries” (Rodas, 1981).<br>The demand for fuel wood is expected to have risen to about 213.4×103 metric<br>tones, while the supply would have decreased to about 28.4×103 metric tones by the year<br>2030 (Adegbulugbe, 1994).<br>In Nigeria, the Energy Commission of Nigeria (ECN) recently (2005) reported that<br>Nigeria’s fossil led economy is under severe pressure and gave data of potential renewable<br>energy for utilization including crop residue as shown in table 1.1 below.<br>Table 1.1: Nigeria’s renewable energy resources<br>Energy Source Capacity<br>Hydropower, large scale 10,000MW<br>Hydropower, small scale 734MW<br>Fuel wood 13,071,464 hectares (forest land)<br>Animal waste 61 million tones/yr<br>Crop Residue 83 million tones/yr<br>Solar Radiation 3.5 – 7.0 kW/m2-day<br>Wind 2-4 m/s (annual average)<br>Source: ECN (2005)<br>2<br>1.1 Statement of Problem<br>As wood fuel supplies diminish, the people who depend on wood fuels are<br>suffering increase in physical or economic burdens in maintaining even a minimal daily<br>fuel supply. The use of firewood and misuse of the existing energy resources (agricultural<br>residues) is creating human and environmental crisis in developing countries which is<br>resulting in deforestation. Traditionally, wood in form of fuel wood, twigs and charcoal<br>has been the major source of renewable in Nigeria, accounting for about 51% of the total<br>annual energy consumption; the other sources of energy include natural gas (5.2%),<br>hydroelectricity (3.1%), and petroleum products (41.3%) (Akinbami, 2001).<br>In many developed and developing countries, the forest covers at least 25% of the<br>total land area, the minimum level required by international standard. The first indicative<br>forest inventory project completed in Nigeria in 1977 put reserved forest at approximately<br>10% of the total land area. Between 1976 and 1990, deforestation proceeded at an average<br>rate of 400,000 ha. per annum, in 1981-1985 at 3.48% while in 1986-1990 it was 3.57%<br>including some forest reserves. The FAO concluded that if this rate was maintained, the<br>remaining forest in Nigeria would disappear by the year 2020. The degradation and<br>depletion of the forest reserve base has major effects on other sectors of the economy. The<br>disappearance of forest cover leads to erosion, soil degradation and unfavorable<br>hydrological changes (Government of Nigeria, 1997).<br>The decreasing availability of fuel wood, coupled with the ever rising prices of<br>kerosene and cooking gas in Nigeria, draw attention to the need to consider alternative<br>sources of energy for domestic and cottage level industrial use in the country<br>(Olorunnisola, 2007). Such energy sources should be renewable and should be accessible<br>3<br>to the poor. As rightly noted by Stout and Best (2001), a transition to a sustainable energy<br>system is urgently needed in the developing countries such as Nigeria. This should, of<br>necessity, be characterized by a departure from the present subsistence energy level usage<br>which is based on decreasing firewood resources, to a situation where human and farming<br>activities would be based on sustainable and diversified energy forms.<br>The realization that deforestation and wood fuel shortages are likely to become<br>pressing problems in many countries has turned attention to other types of biomass fuel.<br>Agricultural residues are, in principle, one of the most important of these. They arise in<br>large volumes and in the rural areas which are often subject to some of the worst pressures<br>of wood shortage (Eriksson and Prior 1990). If one or more efficient method of using the<br>abundant agricultural and wood residues could be developed on a large scale the energy<br>situation could be sustainable and the deforestation problem could be controlled.<br>The lack of capital among most house holds in the rural communities makes it<br>difficult to move from either firewood or charcoal, to a more advanced energy sources<br>where small initial capital investment can be used. Hence, the substitute of these fuels<br>requires a minimal capital investment, be as cheap and accessible as charcoal and<br>firewood. At the same time be environmentally sustainable.<br>1.2 Agricultural and wood residues<br>Large quantities of agricultural and wood residues are generated yearly in<br>developing countries but they are neither managed nor utilized efficiently. Agricultural<br>residues which are freely available are often discarded or burned as wastes. They occur in<br>large amounts and have the potential to be an important industrial input for fuel production<br>in briquette forms, particle board and straw board for furniture making, biogas fuel,<br>4<br>gasification, biomass combustion, ruminant feeding, absorbent for industrial effluents<br>treatment, grain storage structure and regulation/reduction of geothermal temperature.<br>The procedures for manufacturing these products are described briefly below;<br>1.2.1 Particle board and straw board production.<br>Wood residues resulting from furniture making industries or stalks like cotton<br>stalks after harvesting cotton are either grounded into particles for particle board or steam<br>heated to breakdown the residues into fibers for medium density fiberboard, then dried to<br>lower moisture content. After the fiber is dried, it is blended with wax, a synthetic resin<br>such as urea formaldehyde, and other addictives, and formed into mats. The mats are<br>processed in large presses that use heat and pressure to cure the resin and form the products<br>into sheets or boards. Primary finishing steps of particle and medium density fiber board<br>include cooling or hot stacking, grinding, trimming/cutting and sanding. Secondary steps<br>include fooling, painting, laminating and edge finishing. Straw boards are made from straw<br>and bagasses, which undergo the same production procedure as particle board production.<br>They are used for making doors, furniture and cabinets (Gary and Rajiva, 2001).<br>1.2.2 Biogas production by anaerobic decay of organic materials.<br>Anaerobic reactors are generally used for the production of methane biogas, from<br>manure (human and animal waste) and agricultural residues. They utilize mixed<br>methanogenic bacterial cultures which are characterized by defined optimal temperature<br>ranges for growth. These mixed cultures allow digesters to be operated over a wide range<br>i.e. above 0oC up to 60oC. When functioning well, the bacteria convert about 90% of the<br>feedstock energy content into biogas containing about 55% methane, which is a readily<br>5<br>useable energy source for cooking and lighting. Fig.1 below shows the route path of biogas<br>energy production.<br>Figure 1: Biogas energy route Source: Elizabeth, et al, (1999)<br>1.2.3 Gasification.<br>Gasification is the process involving the burning of biomass fuels (human, animal<br>and agricultural wastes) at very high temperatures with a limited supply of oxygen so that<br>the burning process is only partially completed (Elizabeth et al, 1999). High temperatures<br>and a controlled environment lead to virtually all the raw materials being converted to gas.<br>This takes place in two stages. In the first stage, the biomass is partially combusted to form<br>producer gas and charcoal. In the second stage, the carbon dioxide (CO2) and water (H2O)<br>produced in the first stage is chemically reduced by the charcoal, forming carbon<br>monoxide (CO) and hydrogen (H2). The composition of the gas is 18% to 20% H2 gas<br>equal portion of CO, 2% to 3% methane (CH4), 8% to 10% CO2 and the rest nitrogen.<br>These stages are spatially in the gasifiers. Gasifiers require temperature of about 800oC and<br>is carried out in closed-top or open top gasifiers. These gasifiers can be operated at<br>Anaerobic<br>Digestion<br>Methane<br>Digester Sludge Heating and<br>lighting<br>Manure/Soil Mechanical power<br>Conditioner<br>Animal waste<br>Human/municipal<br>wastes<br>Agricultural or<br>crop wastes<br>Industrial<br>Carbonaceous<br>waste<br>Electrical power<br>6<br>atmospheric pressure or higher. The producer gas can be burned directly in processes<br>which normally use oil fired boilers. It can be burned in ovens, kilns and driers to replace<br>fuels otherwise, used in this equipment. The gas can also be cleaned and used to run an<br>engine for generating electricity.<br>Figure 2: Gasification process. Source: Vannbush, (2006)<br>1.2.4 Biomass Combustion.<br>Biomass fuel (agricultural residue) is burned in a furnace or boiler. The heat is used<br>to produce high pressure steam. This steam is introduced into a steam turbine where it<br>flows over a series of aerodynamic turbine blades, causing the turbine to rotate. The<br>turbine shares a common shaft with an electric generator so as the steam flows it causes the<br>turbine to rotate, the electric generator is turned and electricity is produced. Also it can be<br>used to produce hot water for goods processing.<br>7<br>1.2.5 Briquetting.<br>This involves the densification process of loose organic materials, such as rice<br>husk, sawdust and coffee husk aiming at improving handling and combustion<br>characteristics. There are two principal methods of briquetting, with or without a binder.<br>The binder technology is used where low pressure presses are employed to produce<br>briquette. Binders are added to this process to improve mechanical strength and also allow<br>dry materials to be briquetted using low pressure techniques as simple block presses or<br>extrusion presses. The binderless technology is a high pressure technique which produces<br>briquettes from fine dry particle size materials without a binder being added. Three types<br>of press are commonly used. Piston press, pelletizers and screw extrusion presses.<br>Briquettes are burned the same way as wood and can be used directly in open fires,<br>gasifiers, boilers, furnaces and kilns.<br>1.2.6 Ruminant Feeding.<br>Fibrous agricultural residues such as rice straw, sugarcane tops, cassava leaf,<br>soyabean-straw, peanut vines and sweet potato vines are important component of the feed<br>base for ruminant livestock particularly in areas where land grazing is limited and pasture<br>growth is seasonal (Dixon, 1985).<br>1.2.7 Construction of village level grain storage structure.<br>Agricultural residues could be used to construct village level grain storage<br>structure, called rhumbu which may be thatched, mud or underground pit. Thatched<br>rhumbus are commonly found in the north-Eastern parts of Nigeria. They are cylindrical in<br>shape with floors made of wooden grass stems or fibers and overhanging conical roof<br>made with straws or grass. The structure normally is supported on low wooden structure or<br>8<br>by stones. The wall is provided with tension rings in two or three positions using local rope<br>material. Mud rhumbus are found in Zaria and Sokoto towns in Nigeria. They are circular<br>in cross section and supported on stone pieces or pillars which are about 25-50cm above<br>the ground. The floor is made of wood and plastered with mud; the roof is conical and<br>made of thatch. Underground pits are found in the Sahel part of the Sudan savanna Zone<br>where water table is low. The pit is either round or square is 2-3m deep and 1.5-3m in<br>diameter or square. The pit is lined with straw mat (Zare) with corn husk padding or<br>insulation is provided at the bottom of the pit, it is covered with a polyethylene or metal<br>sheet, then a layer of husk and finally with layers of laterite (Olumeko and Igbeka, 1996).<br>1.2.8 Regulation and reduction of geothermal temperature.<br>In animal structures agricultural residues such as groundnut shells, maize husk or<br>sawdust of 6mm particles are spread on the floors of poultry houses, horse stables and<br>goat/sheep pens to serve as an absorbent material to keep the structure dry and the animals<br>away from cold floors.<br>1.3 Justification of Research<br>The abundantly available agricultural and wood residues can efficiently be used for<br>resolving energy problems to a significant extent by adopting proper measures.<br>Olorunnisola (2002) states that of the various types of biomass processing technologies<br>that are being considered, and for which there are currently potentially viable local markets<br>for in the country, which include biomass combustion, gasification and<br>briquetting/pelletizing it is evident that none of these alternatives can compete with the low<br>capital investment that is required; with the briquetting technology. Several kinds of<br>agricultural residues can be utilized properly by densifying loose residues to produce a<br>9<br>compact product of different sizes. Briquetting is essentially a mechanical process<br>requiring investment in equipment and training to ensure a product of reasonable quality<br>that will perform the task for which it is intended. Russell, (1997) considered that<br>briquetting is often seen as a relatively high-cost high-pressure technology, and that it is<br>possible to use a low-cost low-pressure technique to produce acceptable briquettes.<br>For rural communities the most suitable briquetting methods are those which are based<br>on available waste and building materials. The manufacturing should be done in locally<br>made hand operated presses and the briquettes held together mainly by a binder.<br>ï‚· Briquette making saves trees and prevents problems like soil erosion and<br>desertification by providing an alternative to burning wood for heating and<br>cooking.<br>ï‚· Briquetting substitutes agricultural waste like hulls, husk, corn stocks, grass, leaves<br>and other garbages for a valuable resource.<br>ï‚· Briquetting engenders many micro enterprise opportunities making the presses<br>from locally available materials, supplying materials, supplying materials and<br>making the briquettes, selling and delivering the briquettes.<br>ï‚· The availability of briquette as an alternative fuel to replace firewood can also<br>improve the living conditions of the rural women and children, who spend most of<br>their time collecting firewood instead of engaging in other income generating<br>activities or attending school.<br>10<br>1.4 Existing Briquetting Techniques<br>1.4.1 Wu-Presser<br>The Wu-presser was developed by the Washington University. It is constructed<br>from either metal or wooden parts as shown in figure 3 below.<br>Figure 3: The Wu-presser Source: Legacy Foundation (2003)<br>The Wu-presser presses briquettes in three steps shown in the illustration above. Each step<br>will press with increasing pressure. This takes advantage of the non-linear force to distance<br>property of briquetting pressing.<br>1.4.2 Earth Rams<br>Presses currently in use for making stabilized earth blocks might be modified to<br>make briquettes. The Combustaram, similar to the CINVA-Ram and Tersaram, is<br>commercially available or can be manufactured locally, see figure 4 below. The lever arm<br>is put in the open position, feed stock is poured into the molds and the lever is then quickly<br>pushed up, over the top of the press, and down. This movement positions the lever over the<br>top of the press and compresses the briquettes on the downward stroke.<br>11<br>Figure 4: Combustaram Source: Davies (1985)<br>The lever is then moved back to the original position and again pushed down, thus forcing<br>the briquettes out of the molds. Finished briquettes are set in the sun to dry. The process<br>requires at least two workers.<br>1.4.3 Tube-Presses<br>Metal or plastic pipe provides a good briquetting mould since it produces<br>cylindrical briquettes. The tube press, illustration shown in Figure 5 below,<br>Figure 5: Tube Press Source: Davies (1985)<br>Moulding Box<br>Roller Fulcrum<br>for Ejection<br>Adjustable piston<br>guide<br>Handle Latch<br>Toggle Linkage<br>Tube with<br>feed stock<br>Press<br>Removable Base<br>Plate<br>Hole to<br>push<br>finished<br>briquette<br>through<br>Close fitting ram<br>for hand<br>compression<br>Tube partially<br>filled with<br>briquetting<br>feedstock<br>Frame<br>Piston<br>12<br>consist of a tube mounted vertically on a platform and a close fitting ram used for<br>compaction. The basic design can be varied considerably, as the figure indicates. Feed<br>stock is poured into the tube and compressed with the ram. The tube is then positioned<br>over a hole (or a slide is removed) below the tube exposing a hole and the briquette is<br>pushed through. Briquettes are then dried in the sun before storage and use.<br>1.4.4 Screw Presser<br>The screw presser makes briquettes in upright cylinders. The raw material is<br>compressed by lowering a metal disc which is moved vertically by a screw that is turned<br>by hand. The screw press is most commonly made of metal as shown in figure 6 below.<br>Figure 6: Screw presser in use. Source: Olle and Olof (2006)<br>1.4.5 Hydraulic Press<br>These machines operate by hydraulic pressure acting upon a piston that extrudes<br>the material through a longitudinal die. The machine operates rather slowly which<br>minimizes the wave rates. However, they operate at much lower pressures and the<br>briquette quality is of lower density. They are typically used for low outputs of 40kg/hr but<br>can be made to achieve up to 80kg/hr.<br>13<br>1.4.6 Piston Press<br>These machine works best with dry (15% moisture content maximum) cellulose<br>material, which is fed into a compression chamber. A reciprocating piston then forces the<br>material through a tapered die to form a long briquette as shown in figure 7 below.<br>Typically flywheel drive machines produce between 300kg and 500kg of briquettes per<br>hour.<br>Figure 7: Piston Press Source: Bhattacharya et al, (1984)<br>The machine can achieve a service life of between 500 hours and 1000 hours using<br>relatively clean material such as sawdust. Use of agricultural wastes containing high levels<br>of silica (sand) will reduce the operating hours considerably. The initial cost of this type of<br>machine is high and the briquettes are prone to breaking.<br>1.4.7 Pelletizer<br>Pellet presses have dies with small diameter (usually about 30mm). The machine<br>has a number of dies arranged as holes bored in a thick steel disk or ring. The material is<br>forced into the dies by means of a ram, perpendicular to the centerline of the dies. The<br>14<br>main force applied results in shear stresses in the material which often is favorable to the<br>final quality of the material. The pellets are cut to lengths normally about one or two times<br>the diameter (Eriksson and Prior, 1990). Pelletizers can produce up to 1000kg of pellets<br>per hour but require high initial capital investment and high energy input.<br>1.4.8 Heat Die Extrusion Screw Press<br>The heat die extrusion screw press is an industrial machine for producing briquettes<br>(see figure 8 below). It consists basically of an electric motor, a hopper, a die heater and<br>muff, and the screw which densifies the raw material.<br>Figure 8: Heated die extrusion screw press Source: Bhattacharya et al, 1984<br>The electric motor drives the briquetting screw, which is housed inside the die,<br>through a V-belt and pulley arrangement. Biomass raw material is fed to the screw through<br>the hopper. The electric die-heater softens the lignin in the raw material as it passes<br>through the die which acts as a binding material. A smoke trapping system traps and<br>removes the smoke from the vicinity during the briquetting process. Besides the cost of the<br>Electric Motor<br>Die Heater<br>Hopper<br>Muff<br>15<br>investment, the machine has a cost for the electricity consumed. Another cost is the screw<br>that gets worn and has to be replaced frequently.<br>1.5 Objectives of study<br>The objective of this project is to:<br>ï‚· Design and construct a simple, low cost briquette machine which can be used in<br>rural communities.<br>ï‚· Test the design briquette machine using selected agricultural residues (sawdust, rice<br>husk, rice straw) with cassava starch as binder.<br>ï‚· Evaluate the calorific value of briquetted residues.<br>ï‚· Compare calorific value and performance with firewood.<br>16</p><p><b>GET TH</b></p> <br><p></p>