Coal Gasification is the term used for process that use thermo-chemical means to break down coal, rather than burning the coal directly.
Coal or virtually any carbon material can be "gasified" into its basic chemical constituents. Coal Gasification facilities use high temperatures and pressure to break apart the carbon molecules in coal. This results in chemical reactions that typically produce a mixture of carbon monoxide, hydrogen and other gaseous compounds.
The next generation of Coal Gasification facilities, FutureGen, is being develop by USDOE. This technology will integrated CO2 sequestration and hydrogen production.
Underground Coal Gasification (UCG) is a gasification process applied to non-mined coal seams, using injection and production wells drilled from the surface, which enables the coal to be converted in situ into product gas. The process has produced commercial quantities of gas for both chemical processes and power generation.
The UCG process developed, refined and practiced by Ergo Exergy is called the Exergy UCG™ Technology or εUCG™ Technology. It differs from generic UCG in its higher exergy efficiency - hence lower exergy dissipation into the environment.
During the εUCG process, much as in conventional gasification methods, an oxidant reacts with coal of the underground coal seams, and part of released sensible heat is used in coal drying, pyrolysis and the endothermic reactions that reduce the combustion products. The resulting mixture is εUCG gas. The gas composition depends on the coal geology as well as the process parameters. It can be produced using a variety of oxidants, including air and oxygen-rich gaseous blends.
Or, if you are asking about the Integrated Gasification Combined Cycle plants to produce electricity from coal with lower emmissions, read here:
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