Review of Related Literature Group Spectrum Title: Comparative Study on the Heating Value of the Charcoal Briquettes from Agricultural/Forest Waste Using Molasses, Cassava Starch and wood tar as Binders
Yearly, huge amounts of agricultural residues and forest waste are produced. But these are either wasted or burnt inefficiently in their loose form causing air pollution. Faulty use of these biodegradable wastes may cause certain pollutions in the atmosphere. Fortunately, these can be utilized for the production of fuel briquettes. Charcoal briquettes could be used as an alternative energy source for household use. These are made from a combination of organic materials such as grass, leaves, saw dust, rice husk or any type of paper. These materials are then compressed in a fuel briquette press. The fuel briquette produced is environment-friendly since it utilized waste materials. In comparison with fossil fuels, the briquettes are easier to produce because it is a renewable source of energy. (Shrestha n.d.) Charcoal briquettes are useful and can be used as an alternative substitute to expensive cost of kerosene, liquefied petroleum gas and electricity. The briquettes are mostly composed of organic waste and other materials that are biodegradable, and are commonly used as heat and cooking fuel. The composition of the briquettes may vary due to the availability of the raw materials in an area. These materials are compressed and made into briquettes. The briquettes are different from charcoal because they do not possess large concentrations of carbonaceous substances. In comparison to fossil fuels, the briquettes produce low net total greenhouse gas emissions because the materials used are already a part of the carbon cycle. Environmentally, the use of briquettes produces less greenhouse gases. (Wikipedia, 2011) Wood is has been an important source of fuel for mankind throughout the ages. From the earliest times, mankind has added coal to his fuel resources, and much later, gases manufactured from coal and mineral oils. The common fuels differ much in the heat which they give out when burned. While many factors are concerned in the value of a fuel, the chief one is its heat of
combustion, or calorific value. The calorific value of a solid or liquid fuel is the heat given off in the combustion of one gram of the fuel. (McPherson, 1942) The choice good fuel should not be expensive, and it should kindle readily and should have a respectable amount of heat content. There must be little or no ash, and no waste products that would become a nuisance. Few if any fuels meet all these conditions. Local conditions and personal taste influence the consumer in his choice of fuel. (Dull, 1958) Using wood and crop residues as an energy source will reduce consumption of fossil fuels, and in the process, reduces the emission of greenhouse gases to the environment. In other countries, the interest in pellet burners is starting to increase. Biomass may be utilized as energy carriers (charcoal, oil, or gas). Combustion is the most developed and most frequently applied process used for solid biomass fuels because of its low costs and high reliability (Gravalos, 2010). Briquettes have various uses from household to industrial. With the increasing prices of fuel, practical consumers are finding cheaper alternative sources of heat that may be usable for cooking, heating water and productive processes, firing ceramics, fuel for gasifiers to generated electricity and for powering boilers to generate steam. Briquettes are most commonly produced using briquette presses, but when it is not available, briquettes may also be mold by hand. However, using briquette presses add value to the product and can increase the amount of briquettes produced in a day. (Grover 1996) One of the most important characteristics of a fuel is its calorific value, that is the amount of energy per kg it gives off when burnt. The calorific value can thus be used to calculate the competitiveness of a processed fuel in a given market situation. There is a range of other factors, such as ease of handling, burning characteristics etc., which also influence the market value, but calorific value is probably the most important factor and should be recognized when selecting the raw material input. (Lehra Fuel Tech Pvt. Ltd., 2012) Charcoal is a material totally lacking plasticity and hence needs addition of a sticking or agglomerating material to enable a briquette to be formed. The binder should preferably be combustible, though a non-combustible binder effective at low concentrations can be suitable. These are the following binders used clay, starch, gum Arabic, molasses and wood tar. Clay has the advantage that in many areas it is widely available at practically no cost. (Chardust Ltd. 2004) (p 27) describes that 20 kg water, 7.5 kg clay and 42.5 kg carbonised
sawdust was used to produce 50 kg of charcoal briquettes, which means that the end product contains around 15% of clay. Main disadvantage is that clay does not add to the heating value of the briquette; if a large amount of clay is used for briquetting the briquette will ignite and burn poorly or not at all. Furthermore, all clay added to the briquette will turn into ash. On the other hand, briquettes with high ash content are reported to burn and glow long, which can be advantageous for specific applications like coffee making. The most common binder is starch. About 4-8% (usually 5%) of starch made into paste with hot water is adequate (FAO 1983). Starch sources are commercial starch, rice powder, boiled rice water (rice starch), cassava starch and other materials (Foley 1986) (Seboka 2009) (MCRC 2008). The binder is mixed with water and heated for some time after which it is ready for mixing with the charcoal powder. Starch is preferred as a binder though it is relatively expensive. Because starch is a main food product as well, it is widely available and often promoted as a binder in low-tech carbonization and briquetting projects (Doe 2009), (Sugumaran and Seshadri 2010). Gum arabic, also known as acacia gum, is a natural gum made of hardened sap taken from two species of the acacia tree; Acacia senegaland Acacia seyal. The gum is harvested commercially from wild trees throughout the Sahel. It is edible, used in syrup drinks like Coca Cola, and other traditional and modern industrial applications. Gum arabic is successfully being applied as binder for charcoal briquettes. Other gum types like gum obtained from Bauhinia retusahave been tested with good results as well (Foley 1986) (p 156). Arabic gum as binder does not emit heavy smoke, and no thermal treatment step is needed. Gum can be expensive, but lower grade qualities are expected to be affordable. Molasses is a by-product from the sugar cane industry. For each tonne of briquettes about 20-25% molasses is needed. Each unit of pure molasses is diluted with 2-3 units of water before entering the briquetting process. Briquettes made by molasses burn well, however the briquettes have an unpleasant smell during the initial phases of burning. To avoid this smell, the briquettes can be thermally treated before use, also called “curing”, which is in fact a light torrefaction step. Molasses can be used as fodder and for ethanol production as well and needs to be purchased.In some countries with low alcohol consumption, molasses was a waste product that was being dumped (van Essen 2012). At least it was possible to buy the molasses at a relatively low price (Visser, Vis, and Siemons 2002). Given the increased demand for molasses for fuel ethanol production, it is expected that the molasses prices will rise considerably. Wood tars that arise during the carbonisation process could be recovered and used
as a binder for briquetting. The recovery of tars helps to reduce the emissions to the air, but tar recovery technologies are only applied in stationary kilns and retorts. Briquettes made with wood tar require a full carbonisation step to avoid the emission of heavy smoke. (Mills, James E. Binders for Coal Briquettes. Washington. Government Printing Office, 1908) A study on the feasibility of biomass fuel briquettes from banana plant waste examined the issues with making fuel briquettes from banana plant waste. Several mixture/blend formulations were prepared which included materials such as sawdust, paper pulp, leaves, banana fronds and plant bark, peanut shells, composted hostas plants, peanut shells, wood chips. Briquettes were made using the micro compound lever press with mold diameter of three inches and a center hole of one inches. Alternative briquettes were made using a caulking gun press or hand-made ball briquettes. Some formulations were over dried at 300°F for two hours and some five hours. Tests performed were moisture test and burn test. Results showed that any formulation made from the trunk of a wood tree (paper pulp, wood chips or sawdust) can dry to about six percent moisture in 36 hours in Ohio sun. However adding leaves to the mixture doubles the drying time to 72 hours. Adding banana fibers to a formulation significantly lengthened the drying time. At the end of the first 24 hours, the briquettes rapidly absorbed moisture to above ten percent by weight. Most briquettes released some moisture when it stopped raining. Furthermore, the rate at which the water temperature increased was dependent on the available BTU from the briquettes, the mass of the three selected test briquettes, moisture content and air supply to briquette material. Conclusions and recommendations includes the following: that to prevent clogging the wet process with long fibers, both the green and dry material need to be cut into small lengths (under three inches). No natural biomass binding properties exist within the chopped green or dry material.
Self binding was possible after the green material had been softened via a
composting like process and then mashed into a sludge using a mortar and pestle. The natural antimicrobial and antibacterial properties of the banana plant worked against the composting process used to help expose the fibers. The chunks of banana waste turned brown and softened but never decayed after months in the composting process. The binding of dry fonds was only possible after cutting to lengths of less than three inches and grinding to expose the available fibers, then mixing with a large amount of mashed dead banana skins and mashed banana fruit. This process was difficult to press because of the sticky mixture. In addition, it required an
excessive amount of dead banana skins and fruit to bind a small amount of fronds. Air-drying a banana biomass briquette was nearly impossible. Unobstructed by other surrounding material the banana fiber normally releases its moisture quickly. When pressed into a briquette the release of the moisture was very slow, even when oven dried. When surrounded with other biomass to enhance binding or burning, release of the fiber moisture was difficult to achieve even in an oven at 300°F. Complete burn using an air-dried briquette containing banana fibers was not successful because of excessive smoke from the burn. Perhaps the briquette would burn better in a forced air stove like a gasifier. Packing the briquette mold with the fibrous material was difficult, tedious and time consuming. The fibers were interwoven with other fibers and did not pour well. Hand packing worked better. Softening by freezing was tested but not included in this report. A batch of fresh green chopped stalks was exposed to a single freeze/thaw cycle as a softening methodology. While that process did significantly hasten and enhance the softening process, it was not considered a practical solution for a tropical climate.
In the researchers’ opinion
producing a biomass fuel briquette from the waste of the banana plant is not worth the effort. It may be more practical to harvest and use the fibers from the stalk for commercial purposes. If one could find an adequate process to emulate the wet grinding accomplished by using a food blender, then a small amount of those fibers (around 10% to 15%) could be effective as a binder for sawdust. (Hite, Smith, 2011) Emerhi, E. A.(2011) has conducted a study on mixed sawdust of three tropical hardwood species (Afzelia africana, Terminalia superba, Melicia elcelsa) bonded with different binding agents (starch, cow dung and wood ash). Sawdust from each of the species was mixed with the binder in ratio of 70:30 for cow dung and wood ash and 70:15 of starch. The sawdust where mixed in a ratio 50:50 for each briquette combination produced. Combustion related properties namely percentage volatile matter, percentage ash content, percentage fixed carbon and calorific value of the briquettes where determined. All processing variables assessed in this study were not significantly different except for percentage fixed carbon at five percent level of probability. The result shows that briquette produced from sample of Afzelia africana and Terminalia superba combination bonded with starch had the highest calorific value of 33116kcal/kg while briquette produced from sample of Afzelia Africana and Terminalia superba bonded with ash had the least calorific value of 23991kcal/kg. Since the aim of briquetting is to produce briquette that will serve as good source of fuel and support combustion, the best briquette was produced when
sawdust was mixed with starch. Also the use of mixed wood residue from the selected species and other hardwood species for briquette production should be encouraged as this will provide an alternative to firewood for household cheap energy source. Ogwu, I.Y1, Tembe, E.T2 ., and Shomkegh, S.A.(2014) also conducted a study on the Comparative performance in calorific value from the binary and tertiary combination of briquettes produced from biomass materials (sawdust) of Afzelia africana, Daniella oliveri and Rice husk at 20% 30%, and 40% starch binder levels. From the proximate analysis of the samples, it was observed that there were significant differences (p<0.05) between the densities, Percentage Ash content, Percentage Volatile matter and Percentage Fixed carbon of the samples. A progressive increase in heating value was observed among briquettes produced as the starch level increased. Briquettes produced at the tertiary combination of Afzelia africana + Daniella oliveri + Rice husk biomass recorded the highest heating value of 4827.20kcal/kg at 40% starch level while Daniella oliveri + Rice husk briquettes at binary level recorded the least heating value of 4586.72kcal/kg at 20% starch level. Among the various starch levels the tertiary combination had the least Ash content of 4.30% at 40% starch level while Daniella oliveri + Rice husk briquettes at 20% starch level had the highest Ash content of 9.29%. It is therefore recommended that 40% starch level be used for briquettes production at binary and tertiary combinations using Afzelia africana, Daniella oliveri and Rice husk biomass.
