Biomass consists of all organic matter of vegetable and animal origin; it can be considered as solar energy stored in the chemical bonds of organic molecules through the process of photosynthesis.
The main sources of biomass include:
- Energy crops: e.g. sugar cane, rapeseed, corn, short-rotation plantations (as eucalyptus and willow), perennial annual crops (miscanthus)
- Agricultural residues; e.g. bagasse (sugar cane waste)
- Forestry residues; e.g. wood waste from forestry operations, residues from short rotation crops such as straw and husks
- Organic wastes from animal husbandry and sewage sludge
- Municipal solid waste (green waste and wood)
- Industrial wastes; e.g. whey from dairies, pulp waste from paper mills, other wastes from food processing industry
It is estimated that biomass contributes to around 15% of the world’s primary energy supply. In developing countries, about 35% of the energy used is generated by combustion of biomass, but most of this is used in non-commercial applications such as cooking. In industrialised countries, the total contribution of biomass to the primary energy supply is in the range of 2% to 4%. This mainly involves the combustion of commercial biomass fuels – e.g. woodchip-fired co-generation plants for heat and power. Other applications are domestic space heating and cooking, industrial heat supply, and large-scale power generation in coal-fired plants [Source: IEA Bioenergy].
Commercial biomass-to-energy (bioenergy) systems have been widely explored in the last 20 years. Mature technologies are available for converting biomass into thermal and electrical energy or into liquid and gaseous fuels. Definitions for types of biomass feedstock, conversion processes and end uses are presented below.
Solid biomass: covers solid non-fossil material of biological origin which may be used as fuel for bioenergy production. It comprises:
- purpose grown wood (from agriculture or forestry)
- conventional crops (e.g. oil and starch crops)
- wood wastes (e.g. from forestry or wood processing activities)
- other solid wastes (e.g. straw, rice husks, nut shells, poultry litter, biodegradable fraction of municipal solid waste).
Liquid biofuels : liquid fuels derived, comprising:
Biogas: a gas composed principally of methane and carbon dioxide produced by anaerobic digestion of biomass, comprising:
- landfill gas
- sewage sludge gas
- other biogas e.g. from anaerobic fermentation of animal slurries and of wastes in abattoirs, breweries and other agro-food industries.
Bio-hydrogen: hydrogen produced from biomass for use as an energy carrier by several routes:
- Gasification or pyrolysis of solid biomass
- Reforming of biogas
- Novel technologies based on use of photosynthetic algae or bacteria, or on fermentative bacteria
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