Method and system for underground gasification of coal or browncoal

A method for the underground gasification of coal or browncoal in an inclined coal seam, comprising:

• drilling a first borehole in a substantially vertical direction from the ground surface into said seam towards a lower level thereof from which the gasification is to be started upslope, said first borehole being deviated from the vertical direction into a direction substantially parallel to the strike of said seam and having an ending and being used for igniting the coal and initiating the gasification process,
• supplying an oxygen containing gas through said first borehole and discharging the produced combustible gases through a second borehole ending in the vicinity of said first borehole, such that, a first chamber is formed in said seam by the combustion of coal,
• filling said chamber, after bleeding off the gas pressure, with a filler suspended in a carrier liquid, which is supplied through one of said boreholes, said suspension having such a concentration and flow rate that the filler, because of the speed reduction when entering the chamber, will precipitate, leading through this suspension being continued until the chamber is completely filled with the filler with the exception of a channel, that connects both boreholes and runs along a high coal face,
• removing the carrier liquid from the channel with a gas and restarting the gasification process to form a second chamber updip of the first chamber, and
• repeating the filling and gasification steps for driving the gasification front updip in the coal seam, such that the boreholes remain in communication with each other by the channel and the gasification chamber, wherein said first and second boreholes are the only two boreholes drilled, and the supply and discharge of gases and the supply of the filler suspension is performed through these two boreholes only.