Biomass energy is a generic term applied to energy production achieved from organic material broken down into two broad categories:
■ Woody biomass. Forestry timber, residues and co-products, other woody material including thinning and cleaning from woodlands (known as forestry arisings), untreated wood products, energy crops such as willow, short rotation coppice (SRC), and miscanthus (elephant grass).
■ Non-woody biomass. Animal wastes, industrial and biodegradable municipal products from food processing and high-energy crops such as rape, sugarcane, and corn.
Biomass, mainly in the form of industrial and agricultural residues, provided electricity for many years with conventional steam turbine power generators. The United States currently has more than 8000 MWe of generating capacity fueled from biomass. Existing steam turbine conversion technologies are cost competitive in regions where low-cost biomass fuels are available, even though these technologies are comparatively inefficient at the small sizes required for biomass electricity production.
The performance of biomass electric systems can be improved dramatically by adapting to biomass advanced gasification technologies developed originally for coal. Biomass is a more attractive feedstock for gasification than coal because it is easier to gasify and has very low sulfur content, so expensive sulfur removal equipment is not required. Biomass integrated gasifier-gas turbine power systems with efficiencies of more than 40% have been commercially available since the early 1990s. These systems offer high efficiency and low unit capital costs for base load power generation at relatively modest scales of 100 MWe or less and can compete with coal-fired power plants, even when fueled with relatively costly biomass feedstocks.
Another form of energy related to agriculture is biogas. Animal waste is usually used for the generation of electricity from biogas. In these systems, the manure from animals is collected in special tanks, and by the addition of oxygen, methane is produced, which can be used directly in a diesel engine driving a generator to produce electricity. For these systems to be feasible, large farms or consortiums of farms are required. This method also solves the problem of disposing the manure, and as a by-product, we have the creation of a very good fertilizer. In the following subsections only biomass and biofuels are examined.
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