Effect of Freeze-Thaw Cycles on Coal Pore Structure and Gas Emission Characteristics.

Here, we aim to clarify the influence of freeze-thaw cycle on pore structure and gas emission characteristics of coal body and to improve the application level of antipermeability and pumping technology based on freezing-induced cracking in a low-permeability coal seam. Freeze-thaw cycles of anthracite and coking coal were carried out in a freezer (-20 °C). Nuclear magnetic resonance was used to test the transformation characteristics of the freeze-thaw cycles on the pore structure of coal samples. The effect of freeze-thaw cycles on the gas emission characteristics of coal particles (1-3 mm) was studied using a self-built gas emission experimental platform (adsorption equilibrium gas pressure was 1.5 MPa). The results show that the pore structure of coal samples changes after the freeze-thaw cycle and the number of large pores and medium pores increases. The amount of gas emission, emission velocity, and gas diffusion coefficient of anthracite and coking coal all increase to different degrees after freeze-thaw cycles. The freeze-thaw damage of coking coal is greater than that of anthracite. In the third freeze-thaw cycle, the increase of each parameter is the largest, and the third freeze-thaw cycle is considered the optimal number of freezing-thawing cycles. The research results provide a theoretical basis for the production of low-permeability coal seam.