Gas Desorption Characteristics of Different Coal Ranks

It is crucial to understand the desorption and diffusion characteristics of coal seam gas to prevent gas disasters in coal mines. This study conducted constant-temperature gas dispersion tests on lignite, fiery coal, and anthracite to uncover the complexities of gas diffusion in coal samples under the influence of coal metamorphism. The main focus was on determining their gas desorption and diffusion characteristics and analyzing the mathematical models of gas dispersion for coal samples with varying degrees of metamorphism over different durations. The results indicated that highly metamorphosed coal samples reached the desorption limit quickly, while low-rank lignite required more time to reach the limit. The gas desorption diffusion rate was notably sensitive to the level of coal metamorphism. In the first 10 min, the gas desorption rate remained stable for lignite and fiery coal, whereas anthracite exhibited a rapid desorption rate in the initial 4 min followed by stability in the subsequent 6 min. Additionally, the effective gas diffusion coefficient showed a strong negative linear correlation with the degree of metamorphism, indicating reduced gas diffusion ability with increased metamorphism. The empirical formulas applied to anthracite showed stable correlation indices, with Formula 3 considered more suitable for describing the gas desorption processes of lignite and fiery coal.