The processes vary in the gasification medium, mean pressure, gasification temp., direction of gas flow, etc. More rapid gasification can be used, and coal consumed which cannot be reached in a single process. In an example, a coal seam is fractured by hydrocracking and subjected to hydrogenating gasification using alternating pressure from a single borehole. After sufficient opening of the passages, this if followed by oxidising gasification between boreholes and then by hydrogenating gasification between boreholes.
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