Spatial–Temporal Evolution of Temperature and Gas Pressure in Soft and Hard Coal During Cryogenic Treatment: An Experimental and Theoretical Investigation

An experimental apparatus was custom-designed to scrutinize the evolution of temperature and methane pressure during the freezing process in both soft and hard coal samples. Additionally, a thermal–hydrological–mechanical coupling theoretical model was developed, and temperature and methane pressure evolutions were simulated using COMSOL software. It was observed that methane pressure and temperature within the coal samples underwent two distinct phases during the freezing process: an initial rapid decline followed by a more gradual reduction. An exponential function was found to describe aptly the correlation of methane pressure or temperature in the coal samples with both freezing time and radial direction. Moreover, it was discerned that the thermal conductivity of soft coal is inferior to that of hard coal, and the radial decay coefficient of methane pressure or temperature in both types of coal is inversely proportional to freezing time. Significantly, it was revealed that, in post-freezing treatment, ethane pressure in both soft and hard coal could be reduced to 0.74 MPa. This finding elucidates the potential applicability of cryogenic methods for the theoretical elimination of coal seam outbursts. The results furnish a vital understanding of the physical properties of coal under cryogenic conditions, and they can inform the optimization of cryogenic treatment procedures for industrial applications.