Experimental study on the influence of liquid nitrogen cyclic freezing and thawing on the evolution characteristics of coal porosity and gas adsorption performance

Based on the high pressure capacity method, helium injection method was used to carry out corresponding experimental research on the influence of liquid nitrogen cycle freezing and thawing on the evolution characteristics of coal porosity and gas adsorption performance. The results show that with the increase of the times of liquid nitrogen cycle freezing and thawing, the parameters of coal porosity and gas adsorption performance show a very significant increase trend. The analysis shows that the mechanism of the effect of liquid nitrogen cyclic freezing and thawing on the evolution characteristics of coal porosity and gas adsorption performance is as follows: the damage effect of liquid nitrogen cycle freezing and thawing on the cracks of coal mass itself; the coupling effect of expansion force and temperature stress associated with the water phase change in the pores and fractures of coal mass damages the structure of coal mass; the deformation of mineral particles in coal mass under the action of severe temperature difference, which leads to the destruction of coal cementation structure.