Study on the Mechanism of Gas Diffusion in Coal Particles under the Coupled Effects of Gas Pressure and Temperature

To investigate the gas diffusion mechanism in coal particles under the coupled effects of gas pressure and temperature, a low-temperature liquid nitrogen adsorption experiment was first conducted to obtain the pore structure characteristics and pore size distribution patterns of the coal samples. Subsequently, a methane diffusion experiment was performed on coal particles with simultaneous increases in gas pressure and temperature using a unipore model to solve the diffusion coefficient. Finally, models for the diffusion coefficient of free-state methane and adsorbed-state methane were established, with their applicability discussed. The results indicate that the pore structure of the coal samples exhibits an approximately unimodal distribution, predominantly consisting of mesopores. As the gas pressure and temperature increase, the tortuosity of the coal sample pores also increases. Both the desorption volume and desorption rate of gas rise with the simultaneous increase in gas pressure and temperature, and overall, the diffusion coefficient of coal particles tends to increase under these conditions. Methane diffusion in coal particles is primarily governed by the surface diffusion of adsorbed methane, with gas pressure exerting a greater influence on surface diffusion than temperature. The findings of this study contribute to the understanding of the gas diffusion mechanism in coal and are of significant importance for improving gas extraction rates and preventing gas-related disasters.