Method and device for improving permeability of low-permeability coal bed by utilizing freezing process

The invention discloses a method and a device for improving permeability of a low-permeability coal bed by utilizing a freezing process and belongs to the method and the device for improving the permeability of the coal bed. The device comprises a freezing circulating system, a refrigerating circulating system and a condensate water circulating system; the method comprises the following steps that freezing pipelines are arranged in a coal and rock mass by utilizing the principle of the freezing process after the layout of a roadway and a working face is finished; the refrigerating circulating system and the condensate water circulating system are installed in the roadway; deep holes are drilled for water injection in the coal and rock mass and the drilled holes are sealed; the refrigerating system runs for freezing; water injected into the drilled holes previously condenses after the freezing is finished, and the water has 9 percent of expansion rate after condensing, so that fractures in the coal and rock mass are increased; the refrigerating circulating system and the condensate water circulating system are shut off after the freezing is finished; the underground high-temperature environment coal and rock mass naturally unfreezes; the water is injected for hole sealing again after the water in the drilled holes in the coal and rock mass is unfrozen, and a freezing and thawing process is circulated; after several circulation, the fractures of the coal and rock mass are obviously increased; the permeability of the coal and rock mass is improved, and the extraction rate of occurrence gas in the coal and rock mass is improved.