Gasification, an exothermic reaction, yields mostly producer gas, a mixture of carbon monoxide, hydrogen, and methane at temperatures

above 1000oC, mostly in the absence of air. The starting materials may be any kind of organic matter, preferably waste materials like cotton and jute sticks, corn cobs, bagasse, and many other plant and vegetation products. In India, annually 16 million tons of rice husk, 160 million tons of paddy straw, 2 million tons of jute sticks, and 2.2 million tons of groundnut shells are available as agricultural by-products.

The gas can be directly used as fuel or used to drive irrigation pump sets. Several designs are available.

Pyrolysis, a thermochemical conversion, also performed in absence of air at a temperature of 500-6000C, yields gaseous components, hydro­carbons, carbon monoxide, hydrogen, methane, butane, some liquids, tars, and a little coke, all of which have very high energy content. Starting materials are similar to those mentioned under gasification. The vegetable matter in the municipal refuse (as much as 50%) is also good feed for pyrolysis. Very optimistic economic analysis for the pyrolytic process has been put forward by investigators, and a properly designed plant, say capable of handling 250 tons of organic refuse per day, will be fully paid off at the end of 5 years. There are 20 domestic or family-size models suggested by organizations. As per the available information, large-scale use of either gasifier or pyrolyser has not been noticed so far. But for the municipalities, the responsibility of quick dis­posal of the refuse and the environmental issues will prompt installa­tion of such plants in the near future. One such flowchart of a model plant is given in Fig. 1.12.