Gasification is the conversion of biomass into combustible gas, volatiles and ash in an enclosed reactor or gasifier. The gas produced can be used either for heat generation or for power generation. A wide range of biomass materials (wood, charcoal, coconut shells, rice husk, bagasse, Pellets etc.) can be used to fuel gasifiers. In most of agro industries thermal processing is one of the step involved in the production chain. Many industry segments also use high cost fuels such as diesel, LPG or electricity to meet their thermal requirements such as drying, sterilization, direct and indirect heating, steam generation in boilers, melting and other applications. With increasing cost of imported oil and electricity, industry is increasingly loosing its competitive edge, both in the local and global markets.
Biomass gasification is a process of converting biomass to a combustible gas in a reactor vessel, known as gasifier under controlled conditions. The combustible gas, known as producer gas has a composition of approx. 19 % CO, 10 % CO2, 50% N2, 18% H2 and 3 % CH4. This gas has a calorific value of 4.5 - 5.0 MJ/cubic metre. It has to be cooled and cleaned before using in internal combustion engines for power generation purposes.
High Conversion efficiency from solid Biomass to gaseous fuel of upto 85% in hot gas mode, 75% in cold gas mode and 65% with rice husk is possible. Each Kg of biomass can producer 2.5 to 3.0 cubic meters of gas having a average calorific value of 4.5 - 5.0 MJ/cubic metre.
For thermal applications, gasifiers are a good option as a gasifier can be retrofitted with existing devices such as ovens, furnaces, boilers, etc. Thermal energy of the order of 4.5 to 5.0 MJ is released by burning one cu.m of producer gas in the burner. Flame temperatures as high as 1200° C can be obtained by optimal air preheating and pre-mixing of air with gas. Producer gas can thus replace fossil fuels in a wide range of devices. A few of the devices which could be retrofitted with gasifiers are furnaces for melting non-ferrous metals and for heat treatment, tea dryers, ceramic kilns, boilers for process steam and thermal fluid heaters.
A diesel engine can be operated on dual fuel mode using producer gas. Diesel substitution of over 80% at high loads and 70 - 80% under normal load variations can be achieved. The mechanical energy thus derived can be used either for driving water pumps for irrigation or for coupling with an alternator for electrical power generation. Alternatively, a gas engine can be operated with producer gas on 100% gas mode with suitably modified air / fuel mixing and control system.