Coal gas
Gasification of coal or lignite or pet coke or biomass produces synthetic natural gas or syngas (also known as coal gas or wood gas) which is a mixture of hydrogen, carbon monoxide and carbon dioxide gases. Coal gas can be converted into synthetic natural gas by using the Fischer–Tropsch process at low pressure and high temperature. Coal gas can also be produced by underground coal gasification if the coal deposits are located deep in the ground or it is uneconomical to mine the coal. Synthetic natural gas production technologies promise to dramatically improve India's supply of natural gas. The Dankuni coal complex produces syngas that is piped to industrial users in Calcutta. Many coal-based fertiliser plants can also be economically retrofitted to produce synthetic natural gas. It is estimated that the production cost for syngas could be below US.