Biomass fuel was the first energy source harnessed by man predominantly in the form of wood. Although wood and other biomass fuels account for only 11% of energy used worldwide, it remains the primary source of energy for more than half the world’s population. Biomass energy involves the conversion of organic feedstocks, such as wood or peat, into useful forms of energy such as heat, electricity or liquid fuels. Biomass energy provides an attractive alternative to fossil fuels, in developing countries, as it readily available and when properly managed the resource is renewable and has little adverse environmental impact. Although practical considerations place limitations on the amount of biomass that can be collected and used if all the energy stored in biomass were made available for human use it could provide about 10 times the total energy requirement world-wide. However, efficient management of biomass is of utmost importance as indiscriminate harnessing of sources without proper compensation can lead to large-scale deforestation and disturb the ecological balance with disastrous consequences.
Energy production from biomass through combustion is the most common technology, but is usually economical only when the raw material is available at little or no cost and is burnt near the source. Transportation costs for unprocessed biomass are far greater than for fossil fuels as they contain less energy per unit volume than fossil fuels. Therefore, before being transported, biomass must first be converted into a fuel with higher energy density. This is done by compressing the material. Wood and its residues, for example, can be converted into dense pellets, cubes or briquettes.
Simple biogas producing devices create anaerobic digestion by decomposing organic matter like crop residues or domestic wastes in an oxygen deprived environment. The resulting biogas-a mix of other gases-can be burnt to provide energy for cooking and space heating, or create electricity to power other equipment. Since many of the parasites and disease producing organisms in the waste are killed by the relatively high temperature in the digester tanks, the digested material can also be used as fertiliser or fish feed.
In waste-to-energy conversion, municipal solid waste (MSW), which is typically collected and disposed off in landfills at considerable cost, is converted to liquid or gaseous fuel. It has several distinct advantages. Unlike other biomass, MSW must be collected regardless of whether it is used for energy production or not. The extraction of biogas from landfills converts potentially explosive methane into energy, also reducing the risk that it will infiltrate surrounding air and buildings. The greatest disadvantage with the system is that a greater initiative is required from the Government for the setting up and functioning of such plants due to the high initial costs associated with the plants.
Gasification and pyrolysis
This involves the conversion of biomass to other fuels by using heat. In gasification, biomass is heated in the presence of oxygen to produce primarily gaseous fuels. Pyrolysis involves the heating of biomass in the absence of oxygen to produce a mixture if oils, gases and solid charcoal. The use of gases thus produced is not competitive, however, where natural gas prices are low.
Some conventional food crops that are high in starches and sugars, like sugarcane, corn, sorghum, etc. can be fermented to produce ethanol, a relatively clean burning, high-energy fuel. The commercial production of ethanol, however, requires a major surplus of crops or the production of crops specifically energy purposes. Other less expensive biomass feedstocks such as wood or plant wastes can also be used for ethanol production but present conversion techniques in this field are not very efficient, hence overall cost of ethanol produced from these sources is relatively greater.
The environmental repercussions of using biomass as a source of fuel vary according to the type of conversion technology. The combustion of biomass produces significantly fewer nitrogen oxides and sulphur dioxide than the burning of fossil fuels. Liquid biomass fuels like ethanol and methanol produce less carbon monoxide, hydrocarbons and potentially carcinogenic compounds than gasoline and diesel. Unlike fossil fuel combustion, the use of biomass fuels in a well managed, sustainable production programme will not contribute to carbon dioxide levels that cause global warming. If, however, a forest region is indiscriminately cleared for fuel, carbon dioxide levels will increase, because carbon dioxide released into the atmosphere is not recycled for new growth. Conversely, if large sparse areas are converted into biomass plantations, the overall increase in vegetation cover will reduce atmospheric carbon dioxide levels. In fact, massive reforestation can provide a partial answer to global warming. Yet improper management of energy farms could create serious environmental problems such as topsoil erosion, depletion of nutrients, soil salinization and water pollution due to fertiliser and pesticide runoff. With proper planning, energy farms will be able to provide sustained yields without depleting the land.
Waste-to-energy conversion has its own problems. Though the facilities produce substantial amount of energy and reduce the volume of landfill, waste incineration of recycled products may release toxic heavy metals like mercury and cadmium into the atmosphere. But, it should be noted that great progress has been made in incinerator technology. Some new incinerators burn waste at high temperature-2500 degrees F-which destroys most of the toxic chemicals, which along with scrubbing and filtering systems remove nearly all heavy metals and toxic chemicals.