Biofuels are obtained by biomass like wood and straw, which are released by, direct combustion of dry matter and converts it into a gaseous and liquid fuel. Wet organic matters (like sewage, sludge and vegetable oils matter) may also be converted into biofuels by a wet process like digestion and fermentation. There are three solid biofuels: wood, straw and refuse, which are used to provide useful heat.
It is an ideal fuel. It is dried, sorted and then burnt to provide heat and power. However, even while doing this, advantages of recycling, refuse or composting of the wastes should be kept in view.
Liquid Biofuels are now used to replace petrol and diesel as transport fuels. Alcohol and vegetable oils are used as liquid Biofuels.
Methanol & Ethanol
They are now going to be used with unleaded petrol and burn in internal combustion engine. Alcohol has high octane number but lower calorific value than petrol. In some growing regions of developed countries such as US, alcohol is produced by fermentation! Grains, starches, sugar or similar food products Methanol have 25 per cent less energy per gall than ethanol and 50 per cent less than petrol.
Hence alcohol can be used as an efficient fuel petrol and diesel. They burn with higher efficiency.
Many parts of the world suffer from shortage of food for their rapidly growing population thereby leading to widespread malnutrition. Further, alcohol by itself is clean burning.
Methane: It is a clean gas with high calorific value. It can be used on site or convert! Into methanol by treatment with catalysts at high temperature and pressure
In raising energy from biomass, following steps have been taken in India:
1. A 10 MW rice straw-based thermal plant has been set up by BHEL at Jharkari in Punjab.
2. A pilot plant was established to generate electricity from municipal waste at Timorpur, Delhi.
3. The first large-scale plant to produce fuel pellets from municipal garbage began with trial runs at Mumbai.
The environmental impacts of biomass depend widely on the type of biomass (residua versus growing energy crops) as well as its use as a fuel or other energy source. Although the burning of biomass does release some air pollutants, since biomass is part of the carbon cycle carbon dioxide emissions are substantially reduced or nearly equal to what was captured during its growth phase.