The invention relates to a
microwave liquid nitrogen synergic
freeze thawing coal seam anti-reflection method. According to the method, a
freeze thawing drill hole is drilled in a
coal seam, and two gas extraction
drill holes are constructed at two sides of the
freeze thawing drill hole. A
microwave antenna, a coaxial
waveguide, a water injection tube and a
liquid nitrogen tube are sent into the freeze thawing
drill hole together; firstly, a water
injection pump is started, and water is injected into the freeze thawing
drill hole; then a
liquid nitrogen pump is started, and liquid
nitrogen is injected into the freeze thawing
drill hole to freeze water in the hole into ice so as to fracture the
coal seam; and finally, a
microwave generator is started, and produced microwave reaches the microwave antenna via a rectangular
waveguide, a
waveguide converter and the coaxial waveguide and is radiated to the freeze thawing drill hole by the microwave antenna, so that ice in the hole is quickly melted and gasified, high-temperature high-pressure water steam continues to fracture the coal seam, and gas is continuously desorbed at high temperature and rushes to the gas extraction drill holes along fractures in coal. According to the invention, microwave
radiation is combined with liquid
nitrogen freeze thawing, thus greatly improving the
porosity and the permeability of the coal seam, promoting gas
desorption, and further greatly improving the gas extraction efficiency and having wide practicability.