受载含瓦斯煤吸附/解吸特性及分子动力学机制研究

As mining activity rapidly develops to deeper and deeper ground, there has been an increasing number of coal and gas outbursts accidents occurring in China. The adsorption/desorption characteristics of gas-filled coal is one of the important factors relating to the gas drainage as well as coal and gas outburst prediction index. Most of the studies focus their research objects on coal particles, failing to consider the coupling effect of multiphysics such as ground stress, temperature and gas pressure. In addition, there has been a lot of study on the influential factors of gas-filled coal from the macroscopic perspective, while few of them revealed the essence of gas adsorption-desorption in loaded gas-filled coal from the microscopic point of view. Therefore, the project plans to establish the adsorption-desorption model of gas-filled coal under the multiphysics coupling effect and study the adsorption-desorption dynamics and migration law through independent research and development of coal containing gas load field coupling adsorption-desorption experiment system. By contrasting test analysis of coal particles and the gas adsorption and desorption characteristics of coal containing and using quantum chemistry "ab initio" method of molecular dynamics simulation parameters to confirm the microcosmic skeleton structure of loaded gas-filled coal. Thus the relationship of microscopic and macroscopic phenomena of adsorption/desorption dynamic process will be established to reveal molecular dynamics mechanism adsorption/desorption of loaded gas-filled coal. The project can provide guidance and theoretical support on the theory and methods for coal bed methane extraction, coal mine gas disaster prevention.

随着煤矿开采向深部延伸，煤与瓦斯突出灾害愈加严重。含瓦斯煤体吸附/解吸特性是煤层瓦斯抽采和突出预测指标的重要影响因素之一，而现有研究多是以颗粒煤为研究对象，且没有考虑地应力、瓦斯压力与温度等综合作用下的多场耦合效应；另一方面，国内外对煤吸附/解吸瓦斯影响因素的宏观研究成果较多，但尚未从微观上揭示受载煤体吸附/解吸瓦斯的本质。本项目拟通过自主研发的受载含瓦斯煤多场耦合吸附-解吸实验系统，对比测试分析颗粒煤与受载含瓦斯煤的瓦斯吸附、解吸特性，建立多场耦合作用下受载含瓦斯煤吸附/解吸数学模型，模拟分析吸附-解吸动态过程及运移规律；确立受载含瓦斯煤体的微观骨架结构，采用量子化学“从头计算”的方法模拟计算其吸附/解吸的分子动力学参数，建立吸附/解吸动态过程中微观指标与宏观现象的关系，揭示受载含瓦斯煤吸附/解吸的分子动力学机制，为煤层气抽采提供理论与方法上的指导，为煤矿瓦斯灾害防治提供理论支撑。

本课题对受载含瓦斯煤的孔隙演化特征、瓦斯吸附/解吸特性以及吸附/解吸动态过程中微观结构、能量演化与宏观现象的关系开展了深入的研究。主要研究内容包括搭建受载含瓦斯吸附/解吸实验系统，研究含瓦斯煤在不同受载阶段吸附/解吸的特性；同时综合考虑气固两相多场耦合下建立受载含瓦斯煤的吸附/解吸的模型，采用数值模拟的方法分析受载煤体瓦斯吸附/解吸的动态规律；依据受载煤体吸附/解吸瓦斯过程中的能量演化规律及其微观结构的变化，进行受载含瓦斯煤的分子动力学模拟，建立宏观现象与微观结构的关系，从煤体微观结构上揭示受载煤体吸附/解吸瓦斯的本质与机理。依据项目申请书内容，经过系统的研究，总体上达到了预期目标。研究取得了五个方面的代表性成果：(1)改造搭建了受载含瓦斯煤吸附/解吸实验系统，该实验系统功能完备，测量准确，获得授权国家发明专利；(2)系统分析了受载煤体孔隙特征的演化规律，建立了受载条件下煤体孔隙率动态演化模型，应力载荷的施加会使煤样在卸载前孔隙发生变形甚至孔隙损伤，但其作用不到纳米级微孔上，应力载荷能对煤样产生扩容作用，但对煤样的孔比表面积基本无影响；（3）通过受载含瓦斯煤的瓦斯吸附实验，发现随着应力载荷的增加煤样的吸附量减小，经理论分析认为受载煤吸附瓦斯的主要作用机制是煤的表面吸附域、单位表面的吸附位以及煤表面与瓦斯气体分子之间的吸附势能大小；（4）基于煤吸附瓦斯的Langmuir动力学方程，引入表面覆盖率的概念，通过受载煤样吸附瓦斯的能量演化规律，阐述其吸附瓦斯的作用机理，并利用蒙特卡洛分子模拟方法对受载煤样吸附瓦斯过程及相关参数进行模拟计算，利用微观结构的能量变化解释了宏观的吸附现象；（5）在综合考虑气固两相多场耦合下建立受载含瓦斯煤的吸附/解吸的模型，利用COMSOL模拟计算了煤体内气体浓度的分布规律，阐明了受载煤体瓦斯吸附/解吸的动态特性。项目研究成果为深部煤矿开采中的瓦斯灾害的防治和煤层中CO2-ECBM提供了理论指导。