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Underground coal gasification (UCG) is an industrial gasification process, which is carried out in non-mined coal seams. It involves injection of a gaseous oxidizing agent , usually oxygen or air, and bringing the resulting product gas to the surface through production wells drilled from the surface.
Coal gasification is a process whereby a hydrocarbon feedstock (coal) is converted into gaseous components by applying heat under pressure in the presence of steam. Rather than burning, most of the carbon-containing feedstock is broken apart by chemical reactions that produce "syngas."
The underground coal gasification process. Underground coal gasification converts coal to gas while still in the coal seam (in-situ). Gas is produced and extracted through wells drilled into the unmined coal seam. Injection wells are used to supply the oxidants (air, oxygen) and steam to ignite and fuel the underground combustion process ...
Typically coal liquefaction processes are associated with significant CO 2 emissions from the gasification process or as well as from generation of necessary process heat and electricity inputs to the liquefaction reactors, [10] thus releasing greenhouse gases that can contribute to anthropogenic global warming.
The chemical composition of syngas varies based on the raw materials and the processes. Syngas produced by coal gasification generally is a mixture of 30 to 60% carbon monoxide, 25 to 30% hydrogen, 5 to 15% carbon dioxide, and 0 to 5% methane. It also contains lesser amount of other gases. [10]
In the gasification of fine, undensified biomass such as rice hulls, it is necessary to blow air into the reactor by means of a fan. This creates very high gasification temperature, as high as 1000 C. Above the gasification zone, a bed of fine and hot char is formed, and as the gas is blow forced through this bed, most complex hydrocarbons are ...
The Fischer–Tropsch process is an important reaction in both coal liquefaction and gas to liquids technology for producing liquid hydrocarbons. [ 1 ] In the usual implementation, carbon monoxide and hydrogen, the feedstocks for FT, are produced from coal , natural gas , or biomass in a process known as gasification .
It is the largest coal liquefaction plant and the largest single emitter of greenhouse gas in the world. Secunda CTL consists of two production units. The Sasol II unit was constructed in 1980 and the Sasol III unit in 1984. [1] It has total production capacity of 160,000 barrels per day (25,000 m 3 /d). [2]