The law and mechanism of dynamic methane diffusion from coal particles under different moisture content.

As a theoretical basis, methane diffusion from coal particles can be used to determine the coalbed gas content, gas desorption index by drill cuttings of coal, evaluation parameters of coal gas mining, and the gas outburst prediction. Moisture content is one of the significant factors influencing the diffusion law of gas-bearing coal particles. In this paper, three deformed coal samples with diverse metamorphic degrees, taken from three different coal mines with coal and gas outburst hazard, were investigated through the self-made devices. The variation law of diffusion flux, diffusion coefficient, and diffusion speed with moisture content was experimentally studied. The results show that diffusion flux, diffusion speed, and diffusion coefficients of high-, medium-, and low-rank coal samples decrease significantly with the increasing moisture content until they reach equilibrium moisture content. The diffusion coefficient of dry coal particles is 3–5 times larger than that of coal particles with equilibrium moisture at the same metamorphic degree. The diffusion coefficient of coal samples at different ranks decreases with time and ranges from 1.58E-08 to 3.03E-07 cm²/s. Based on gas migration theory in porous media and experimental results, the influence mechanism of moisture on gas diffusion rules was discussed. [ABSTRACT FROM AUTHOR]