Experimental Study on Gas Desorption and Diffusion Behavior of Coal Samples with Different Moisture Contents

To investigate the influence of moisture content on gas desorption behavior in coal, this study designed and utilized a high-temperature steam adsorption system to prepare coal samples with varying moisture contents. Gas desorption experiments were conducted under an adsorption equilibrium pressure of 1.5 MPa to explore the effect of moisture on desorption performance. The results indicate that the coal samples from Liyuan Coal Mine exhibit strong desorption capability in the initial stage, with approximately 90% of the total desorption amount released within the first 100 min. As the moisture content increases, the desorption capacity significantly declines. At the desorption equilibrium state, the gas desorption amount of the coal sample with a moisture content of Mad = 0.37% was 19.11284 mL/g, which is approximately 2.5 times that of the coal sample with a moisture content of Mad = 3.97%, whose desorption amount was 8.3995 mL/g. A mathematical model was developed to calculate the gas diffusion coefficients under different moisture conditions, and the diffusion characteristics were systematically analyzed. The results show that, at the same moisture content, the diffusion coefficient reaches a peak during the initial characteristic time segment (t2), then gradually decreases over time. Across different moisture contents, the diffusion coefficient decreases linearly with increasing moisture. At high moisture levels, the suppression effect is more pronounced, with the diffusion coefficient reduced by up to an order of magnitude. At the characteristic time t2, the diffusion coefficient decreased from 44.03 × 10–4 to 25.12 × 10–4 m2/s; at t1, it decreased from 8.42 × 10–4 to 1.53 × 10–4 m2/s; and at t0, it decreased from 2.50 × 10–6 to 0.78 × 10–6 m2/s. This is primarily because water molecules occupy pore spaces and frequently collide with gas molecules, shortening diffusion paths and reducing effective diffusion areas, thereby inhibiting gas diffusion. In conclusion, appropriately reducing moisture content in coal can improve gas desorption efficiency and diffusion performance, providing theoretical and technical support for efficient gas extraction.