I. Introduction
In India, the concept of energy as " Shakti " has been at the focus of philosphic, scientific and metaphysical thought from time immemorial. The conventional energy sources like fossil fuels, crude oil, natural gas etc. are dwindling fast. The world stock of non-renewable natural sources indeed have decreased. There is every necessity of going for renewable alternative resources for energy. The energy crisis of 1973 left scientists to accelerate the renewable energy programmes.The important renewable energy sources are sun, wind, tides, waves, biomass, hydro-power (from water) charcoal, peat, fuelwood, geothermal energy etc. The pattern of energy consumption in India shows that 56.5 % of total energy is from the commercial sources like coal, oil " electricity and remaining 43.5% is non-commercial energy. Fire wood, charcoal, agricultural residues, vegetable wastes, cow dung, urban and industrial wastes, forest residues are the main sources of this non-commercial energy.
The most efficient utilization of these resources comes when they are converted to biomass by appropriate technologies. The non-commercial biomass fuels are the main sources of energy available in the rural areas. The 80% of our population resides in villages are dependent on this non-commercial biomass fuels.
II. Concept of Biomass
The term biomass refers to all organic matter generated through photosynthesis and other biological processes. The ultimate source of this renewable biomass is the inexhaustible solar energy which is captured by plants through photosynthesis. It includes both terrestrial as well as aquatic matter such as wood, herbaceous plants, algae, aquatic plants and residues, like straw, husks, corncobs, cow dung, saw-dust, wood shavings and other wastes like disposable garbage, night soil, sewage solids, industrial refuse etc. In spite of all these biomass resources available in India, they are not being properly utilized. In fact, a large amount of it is disposed off by burning in open fields causing serious air pollution.
In order to utilise these resources properly, biomass should be converted to energy which can meet a sizeable percentage of the country's demands for fuel as well as energy. Three main approaches can be adopted for generation and proper utilization.
1. Collection of agricultural and forest residues to produce fuels, organic manures and chemical feed stock.
2. Collection of urban and industrial wastes as fuel in boilers and as a feedstock for producing methane and some liquid fuels.
3. Growth of some specific energy plants for use as energy feed stock and cultivation of commercial forestry, aquatic and marine plants for different products.
By a number of processes, the collected wastes can be converted into solid, liquid and gaseous fuels. The technologies include thermal, thermo-chemical and bio-chemical conversions. The actual processes in these technologies are combustion, pyrolysis, gasification, alcoholic fermentation, liquefaction etc.
The main products of conversion technologies are energy (thermal, steam, electricity), solid fuels (charcoal, combustibles) and synthetic fuels (methanol, methane, hydrogen gas etc.). These can be used for different purposes like cooking, lighting, heating, water pumping, electricity generation and as industrial and transport fuels.
III. Types of Biomass
Depending on the nature and availability of these wastes and organic residues they can be utilized in different manners as described here.
1. Fuel biomass
By some processes and procedures, biomass products like fuel gas, liquid fuels, gaseous fuels etc. are obtained, which are given here
a. Biomass from plants or animal origin are directly burnt for cooking and other purposes. Municipal and sewage wastes, industrial wastes and agricultural wastes are converted to energy which can meet the demand for energy in rural sector.
b. Paddy straw and rice husk can be profitably converted to fuel gas by thermal decomposition (Combustion)
c. Ethanol, which is used as a liquid fuel can be produced from carbohydrates by alcoholic fermentation.
d. When wood and agricultural residues are heated in the absence of air (pyrolysis), charcoal is the resultant product which can be used as a fuel more advantageously than wood.
e. By the process of gasification, gas is evolved which can be used as a fuel for engines.
f. Biogas, which is popular in rural areas is produced by anaerobic fermentation from farm wastes.
2. Feed biomass
Conventionally, crop residues are used as cattle-feed. However, some of them with high percentage of lignin or non-digestible constituents need certain treatments such as soaking in water, alkali/alcohol to make their use as a fuel. The oil-cakes of various crop seed like cotton, rubber, tobacco etc. can also be used as a feed after extraction of toxic materials.
3. Organic fertilizer biomass
Dry fermented slurry can be used as a direct organic fertilizer for crop land.
4. Fibre biomass
The fibrous agricultural wastes and residues are being profitably utilised for making pulp for cheap grade paper.
5. Chemical biomass
Highly siliconous agricultural residues like rice husk and rice straw can be converted into useful chemicals like morphous silicon, silicate products and solar grade silicon. Furfural an another chemical can be produced from biogases, cotton seed hulls, corn-cobs, flax fibres, oat hulls etc., which is used as a solvent for some petroleum products.
