Study on the influence of external stress and temperature on CH4 adsorption and diffusion in coal by molecular dynamic simulation

Abstract

The molecular simulation was conducted to study CH₄ adsorption and diffusion in deformed coal under various stress and temperature in this paper. Five stresses (0, 0.5, 1, 1.5, and 2 GPa) were loaded to coal matrix under four temperatures (303, 313, 323, and 333 K) to explore the coal deformation. Subsequently, CH₄ of 5 MPa was injected into coal matrix, and the adsorption amount and self-diffusion coefficient of CH₄ in deformed coal were obtained. The results shown that the temperature had a significant effect on the coal strain subjected to external stress. At a higher temperature, coal was more prone to be compressed, and the pore structure of coal was weakened correspondingly, which also reduced the adsorption ability of CH₄ in coal. The self-diffusion coefficient of CH₄ in coal decreased with the increasing stress and decreasing temperature. Discovered by quantitative linear analysis, CH₄ adsorption were highly dependent on the surface area of the matrix, while CH₄ diffusion was mainly affected by free volume. The characteristics of CH₄ flow in mining coal can be clarified by conducting this research, so as to achieve efficient gas extraction and prevent it from being discharged into the atmosphere.