New method for the production of a deposit of coal or lignite by underground gasification under high pressure

摘要

1501310 Underground gasification of coal INSTITUT NATIONAL DES INDUSTRIES EXTRACTIVES 21 July 1976 [31 July 1975] 30342/76 Heading C5E Coal or lignite in an underground deposit in the form of a plurality of layers situated at a depth of more than 500 metres is gasified by circulation of a gaseous current with filtration across the layers, obtained by injecting air or other gasifying agent through one or more boreholes drilled from the surface and by collecting in one or more other boreholes the gas produced in the deposit by the action of the gasifying agent, the gasification being carried out under pressure by alternating in a cyclic manner periods of increase in pressure up to a maximum value of 30 to 50 bars with periods of decompression down to a minimum value of 15 to to 25 bars, the seam being ignited by a source of heat introduced into one of the boreholes, characterized by the combination of a continuous production of gas and a cyclic fluctuation of pressure in the underground gas generator obtained by variation in the rate of flow and the pressure of the injected gasifying agent, the pressure of gas along the whole circuit remaining constantly below the hydrostatic pressure prevailing in the overlying terrain. Following a phase of gasification, air may be blown in to bring about combustion of fuel which has escaped gasification to convert this potential energy into sensible heat. The boreholes used for evacuating the gas may be equipped with cooling devices. The gasification process may be associated with the production of electricity in a power station.