粒度对软硬煤粒瓦斯解吸扩散差异性的影响

Effect of particle size on difference of gas desorption and diffusion between soft coal and hard coal

基于气体在多孔介质的运移理论,采用物理模拟实验的方法,研究了软、硬煤粒瓦斯扩散速度、扩散系数的差异特征随粒径的变化规律;采用压汞法考察了软、硬煤粒孔隙结构特征的差异,分析了粒径对软硬煤瓦斯扩散行为差异性的影响机理。研究结果表明,当粒度大于等于硬煤的极限粒度时,软、硬煤瓦斯扩散初速度差值和扩散系数比值达到最大值,且基本趋于稳定;当粒度小于硬煤的极限粒度时,软、硬煤瓦斯扩散初速度差值和扩散系数比值随粒度的减小而减小;当粒径减小到一定程度——称该粒度为原始粒度,软、硬煤的瓦斯扩散速度和扩散系数几乎没有差别。软煤相对于硬煤和粒度减小,均使大中孔的孔容显著增大,即粒度减小会缩小软硬煤之间瓦斯解吸扩散通道的差别。软硬煤孔隙结构差异是导致瓦斯扩散速度和瓦斯扩散系数随粒径变化规律产生差别的本质原因。以上研究成果为钻屑瓦斯解吸指标、瓦斯放散初速度和煤层瓦斯含量等测定过程中粒度选择与结果修正提供理论参考。

Engineering practice shows that the gas diffusion rules during desorption of hard and soft coal particles are significantly different.This is the key reason leading to the distinction of coal and gas outburst hazard between soft coal and hard coal.The difference of gas diffusion can be used to predict and prevent outburst disaster.Particle size is one of the key factors that cause the difference.Influence rules and mechanisms of particle size have not been found yet.Based on gas transport theory in multi-porous medium,D-values of gas diffusion velocity between soft coal and hard coal with different particle sizes were studied using physical simulation method.The study shows that the D-value declines with particle size decreases when the particle is between basic size and limited size.If particle size is less than the basic size,then the gas diffusion velocity and gas diffusion parameters are no difference between the different coals.If the particle size is equal to or more than the limited size,then the D-value will reach its maximum value,to which is almost stable.The ratios of soft coal to hard coal on gas diffusion kinetic parameters appear to have similarvariation rules.According to the Fick's second law,the variation rule of gas diffusion kinetic parameters is a direct reason that results in the change rules of gas diffusion velocity.Different characteristics of pore structure between soft coal and hard coal were investigated using the mercury injection.Also,the influence mechanism of particle size on the different gas diffusion between coals was analyzed.The research results show that the volumes of macropore and mesopore are larger in soft coal,therefore they increase with the particle size decrease.That is,particle size decrease reduces the gap of pore structure between soft coal and hard coal.It reduces the difference of gas diffusion path channels,which is a natural reason.The research results provide a theory base for choosing particle size during determination of gas initial diffusion velocity index(Δp),gas desorption index of drill cuttings(K1,Δh2),and coal seam gas content.