基于孔隙结构的煤屑瓦斯放散动力学规律与模型

Most methane diffusion dynamic rules or models of coal cutting are based on homogenous coal cutting, which did not conside the difference between soft coal and hard coal on pore structure and molecule structure.Engineering practices show that calculation of gas leakage amounts and determining of gas desorption index by drill cuttings exit a little big deviation, especially to the soft coal sample. Through this project, the X-ray diffraction, the EPR, the NMR, the mercury,the low temperature liquid nitrogen adsorption isotherm will be used to study molecular structure and pore structure variation laws of the extent of damage to coal, to reveal metamorphic degree and extent of the damage to coal gas diffuse impact mechanism. A high-efficiency methane absorption-desorption experimental system on large mass coal sample with the function of controlling temperature will be established, which can be used to study the differences of soft and hard coal gas diffusion law. According to the gas diffusion theory in porous medium, combine with the containing methane cinder structural features, the study goes to estabish the physical and mathematical model of describing non-homogeneous clinder methane diffusion dynamic process, then to obtain the relationship between the amount of methane diffusion and the time of diffusion, finally combine with numerical computation and numerical simulation to carry on theoretical study and verification. The study lays the theoretical foundation for accurate determination of coal mine outburst prediction parameters and predicting and preventing methane accidents in underground coal mines.

煤屑瓦斯放散动力学规律和模型大多是基于均质煤屑建立，没有考虑软、硬煤在孔隙结构和分子结构方面的差异，及其对瓦斯放散规律的影响，工程实践表明，软煤瓦斯含量损失量推算、钻屑瓦斯解吸指标等参数测定偏差较大。项目拟采用X射线衍射、顺磁共振、核磁共振、压汞、低温液氮吸附法等手段，研究不同煤阶典型软硬煤分子结构和孔隙结构的差异特征；结合高压容量法，研究软硬煤初始瓦斯扩散浓度（吸附瓦斯能力和极限解吸率）的差异特征；采用瓦斯放散实验法，实验研究不同煤阶、典型软硬煤瓦斯放散动态过程的差异特征，探讨动力变质对瓦斯放散规律的影响。根据气体在多孔介质运移理论，揭示孔隙结构对软硬煤屑瓦斯放散的影响机理。引入孔隙结构参数，建立能统一描述软硬煤屑瓦斯放散动态过程的多重孔隙结构动力学物理数学模型，求解瓦斯放散量与时间关系式，采用数值模拟研究不同煤阶、破坏类型煤屑瓦斯放散规律。为瓦斯灾害预测与防治、煤层气开发奠定理论基础。

项目选取8组不同煤阶和变质变形环境的典型软硬煤样，改造了煤粒瓦斯吸附解吸实验系统，开展了软硬煤粒瓦斯扩散规律实验研究，分析了软硬煤瓦斯扩散动力学参数差异特征。采用x射线衍射、傅立叶红外光谱等手段研究了软、硬煤分子结构的差异，结合分子动力学模拟，分析了动力变质量化程度及其对瓦斯吸附解吸扩散行为的影响。采用压汞法、低温液氮、二氧化碳吸附法和小角x射线散射等方法，查明了典型软硬煤孔隙结构差异特征，提出了煤的全孔径孔隙结构测定方法，探讨了煤中封闭孔隙的测定方法，揭示了孔隙结构对软煤瓦斯扩散过程的影响机理。建立了基于孔隙结构参数的三层结构煤粒瓦斯扩散模型和煤粒瓦斯动态扩散模型，求出了解析解，进行了验证。建立了基于煤屑瓦斯动态扩散的损失量推算简化模型和煤层瓦斯含量快速测定技术，开展了现场应用。发表学术论文25篇，申请发明专利4项，目前授权2项，出版专著2部，完成了预期任务和目标。. 研究结果表明，软煤吸附能力和初始质量浓度、扩散速度显著大于硬煤且衰减更快，其差异随软硬煤粒的减小而减小；瓦斯扩散系数随时间呈指数衰减特征。软煤延展度与堆砌度的比值（La/Lc）均大于硬煤，可衡量化软煤动力变质程度及其对吸附能力影响程度；软煤的含氧官能团均小于硬煤，含氧官能团和表面缺陷的存在降低了吸附量与等量吸附热，1.5nm孔径狭缝孔对瓦斯吸附能力最强。这些因素通过影响解吸扩散初始质量浓度，影响煤粒瓦斯放散行为。软煤的比表面积、总孔容、各阶段孔容、孔隙连通度和孔容分形维数均大于硬煤，使软煤的解吸扩散初始质量浓度和扩散系数均增大。建立的三层结构煤粒瓦斯扩散模型反映了软硬煤孔隙结构差异对煤粒瓦斯扩散行为的影响，优于均质模型。煤粒瓦斯动态扩散模型验证结果表明，相关指数均在0.98以上，最大相对误差为4%，用来精确估算瓦斯损失量。煤层瓦斯含量快速测定技术现场应用结果表明，绝对误差为0.15m3/t~0.5m3/t，相对误差5%以内。