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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.
Pyrolysis is different from gasification. In the chemical process industry, pyrolysis refers to a partial thermal degradation of carbonaceous materials that takes place in an inert (oxygen free) atmosphere and produces both gases, liquids and solids.
The pyrolysis (or devolatilization) process occurs at around 200–300 °C. Volatiles are released and char is produced, resulting in up to 70% weight loss for coal. The process is dependent on the properties of the carbonaceous material and determines the structure and composition of the char, which will then undergo gasification reactions.
Gasification is the process of subjecting a feedstock to chemical reactions that produce gas. [10] [11] The first process used was the carbonization and partial pyrolysis of coal. The off gases liberated in the high-temperature carbonization of coal in coke ovens were collected, scrubbed and used as fuel.
Steam and carbon dioxide can also be used as the oxidants. As the metal oxide also serves as the heat transfer medium in the chemical looping process, the exergy efficiency of the reforming and gasification processes like that for the combustion process is also higher as compared to the conventional processes. [1] [2]
Underground coal gasification (UCG) is an industrial process which converts coal into product gas. UCG is an in-situ gasification process, carried out in non-mined coal seams using injection of oxidants and steam. The product gas is brought to the surface through production wells drilled from the surface. [1]
Initially biomass undergoes pyrolysis process to produce pyrolysis gases and biochar.The volatile organic compounds in pyrolysis gases further undergo gasification process to produce syngas rich in hydrogen and carbon monoxide gases which is further converted in to methanol (CH 3 OH). [3]
The process configuration at Eastman is fairly complex, as a consequence of the feedstock requirements associated with multiple chemical syntheses involved. Part of the syngas resulting from the gasification of feed coal is shifted, and a Rectisol process is utilized for sulfur removal and CO 2 removal.