Biomass has been one of the main energy sources for the mankind ever since the dawn of civilisation, although its importance dwindled after the expansion in use of oil and coal in the late 19^th century. There has been a resurgence of interest in the recent years in biomass energy in many countries considering the benefits it offers. It is renewable, widely available, and carbon-neutral and has the potential to provide significant productive employment in the rural areas. Biomass is also capable of providing firm energy. Estimates have indicated that 15% - 50% of the world?s primary energy use could come from biomass by the year 2050. Currently, about 11% of the world?s primary energy is estimated to be met with biomass.

For India, biomass has always been an important energy source. Although the energy scenario in India today indicates a growing dependence on the conventional forms of energy, about 32% of the total primary energy use in the country is still derived from biomass and more than 70% of the country?s population depends upon it for its energy needs.

India produces a huge quantity of biomass material in its agricultural, agro-industrial and forestry operations. According to some estimates, over 500 million tonnes of agricultural and agro-industrial residue alone is generated every year. This quantity, in terms of heat content, is equivalent to about 175 million tonnes of oil. A portion of these materials is used for fodder and fuel in the rural economy. However, studies have indicated that at least 150-200 million tonnes of this biomass material does not find much productive use, and can be made available for alternative uses at an economical cost. These materials include a variety of husks and straws. This quantity of biomass is sufficient to generate 15 000-25 000 MW of electrical power at typically prevalent plant

Biomass Gasification

Biomass gasification is the process through which solid biomass material is subjected to partial combustion in the presence of a limited supply of air. In what is known as a gasifier, solid fuel is convertedm by a series of thermo-chemical processes like drying, pyrolysis, oxidation, and reduction to a gaseous fuel called producer gas. The ultimate product is a combustible gas mixture known as ?producer gas?. If atmospheric air is used as the gasification agent, which is the normal practice, the producer gas consists mainly of carbon monoxide, hydrogen, and nitrogen. A typical composition of the gas obtained from wood gasification, on volumetric basis, is as follows:

Carbon monoxide 18 ? 22%

Hydrogen 13 ? 19%

Methane 1 ? 5%

Heavier hydrocarbons 0.2 ? 0.4%

Heavier hydrocarbons 9 ? 12%

Water vapour 4%

The calorific value of this gas is about 1000 ? 1200 kcal.Nm³.

Biomass gasifier based systems

The major applications of a producer gas produced from a biomass gasifier are as follows .

i) Mechanical shaft power applications, i.e., water pumping for irrigation/drinking and grinding, where the gas is used as fuel for internalcombustion engine running on dual fuel or 100% producer gas mode.

ii) Direct heat applications where it is burnt directly in a boiler, furnace or kiln, burner for institutional cooking, etc., to provide heat.

iii) Electricity generation through shaft power application viz., (engine coupled to an alternator/generator set).