为探究粒径及气体压力对煤中CO2动态扩散规律的影响机制,利用自主研制的煤层高压吸附解吸实验系统,以容量法吸附实验为基础,结合经典单孔扩散模型对不同时间下的CO2扩散系数进行计算,分析煤中气体吸附平衡前的动态扩散特征。结果表明:吸附平衡时间与煤样粒径呈正相关,随吸附平衡压力增加呈减小趋势,且煤样粒径越大,吸附平衡时间减小趋势越明显;有效扩散系数比扩散系数能更好地解释粒径大小与平衡时间的关系,煤样粒径越小,有效扩散系数越大,达到吸附平衡的时间越短;有效扩散系数与时间成幂函数关系;初始有效扩散系数(De0)和有效扩散衰减系数(β)都随粒径增大而减小,De0随平衡压力增大先增大后减小,不同粒径煤样β随平衡压力增大呈现不同规律。粒径越小的煤孔隙间的连通性越好,气体分子扩散路径越短、扩散阻力越小,更容易进行吸附。气体压力对CO2吸附扩散有驱动作用,但随着煤样不断吸附,煤基质膨胀堵塞孔隙,扩散通道变窄,驱动作用减弱。

This study investigates the influence mechanism of particle size and gas pressure on the dy- namic diffusion law of CO in coal. We used a self-developed high pressure adsorption and desorption experimental system for coal seam to analyze the dynamic adsorption-diffusion characteristics before the adsorption equilibrium of gas in coal based on the volumetric adsorption experiment,which was com- bined with the classical single hole diffusion model to calculate the CO diffusion coefficient at different times. The results show that the adsorption equilibrium time is positively correlated with the coal particle size,and decreases with the increase of adsorption equilibrium pressure. Larger coal particle size would OF MINING SCIENCE AND TECHNOLOGY result in more obvious decreasing trend. The effective diffusion coefficient is found to be more effective than the diffusion coefficient in explaining the relationship between particle size and equilibrium time. Smaller particle size would result in higher effective diffusion coefficient and shorter adsorption e- quilibrium time. The effective diffusion coefficient shows a power function with time. The initial effective diffusion coefficient (D ) and effective diffusion attenuation coefficient (β) both decrease with the in- crease of particle size. D first increases and then decreases with the increase of equilibrium pressure, and the β exhibits varying relationships with the increase of equilibrium pressure depending on different particle sizes of the coal. Smaller particle size would result in better connectivity between the pores of coal,leading to shorter diffusion paths of gas molecules and lower diffusion resistance,thus more facili- tated to adsorption. Gas pressure poses a driving effect on CO adsorption and diffusion,but with the continuous adsorption of coal samples,the coal matrix expands and blocks the pores,leading to a narro- wing of the diffusion channel and diminished driving effects.