低阶煤吸附孔结构特征及其对甲烷吸附性能影响

低阶煤甲烷吸附特性研究对瓦斯含量预测、瓦斯抽采及危害防治有着重要意义，为此，选取陕西6个典型矿井低阶煤样，进行低温氮吸附、低压二氧化碳吸附及甲烷等温吸附实验，获得低阶煤吸附孔结构特征。利用微孔填充及单分子层吸附理论定量表征甲烷吸附特征参数与吸附孔结构参数之间的关系，明确吸附孔中甲烷吸附机理。结果表明：吸附孔的比表面积主要由微孔提供，甲烷吸附能力主要受吸附孔孔容大小控制，微孔孔容对吸附孔总孔容的贡献率在74.71%～88.97%。甲烷极限吸附量与吸附孔平均孔径呈线性负相关，与吸附孔孔容、比表面积呈线性正相关，Langmuir压力常数随吸附孔平均孔径、孔容和比表面积的增加仅在小范围内波动，无明显线性相关。6个低阶煤样的分形特征明显，综合分形维数为2.573～2.720，平均值为2.647，说明低阶煤吸附孔非均质性强，甲烷极限吸附量随分形维数增加先增加后减小，整体呈上升趋势。基于微孔填充和单分子层吸附理论可以定量表征低阶煤吸附孔结构与甲烷吸附能力之间的关系，甲烷极限吸附量计算值与实验测试值相对误差较小，长焰煤相对误差为4.47%～6.65%，不黏煤为13.77%～16.02%。研究成果可为后...

Structural characteristics of adsorption pores in low-rank coals and their effects on methane adsorption performance

The study of the CH₄ adsorption characteristics of low-rank coals is of great significance for gas content prediction, gas drainage, and hazard prevention. Therefore, this study selected six typical low-rank coal samples from coal mines in Shaanxi Province, on which low-temperature N₂ adsorption experiments, low-pressure CO₂ adsorption experiments, and CH₄ isothermal adsorption experiments were carried out. As a result, the structural characteristics of adsorption pores in low-rank coals were obtained. Moreover, this study quantitatively characterized the relationships between the parameters of CH₄ adsorption characteristics and those of adsorption pore structure using the micropore filling and monolayer adsorption theories, determining the CH₄ adsorption mechanism of adsorption pores. The results are as follows: (1) The specific surface area of the adsorption pores was mainly contributed by micropores; the CH₄ adsorption capacity primarily depended on the pore volume of the adsorption pores; micropores contributed 74.71%?88.97% of the total pore volume of the adsorption pores; (2) The ultimate CH₄ adsorption capacity of the adsorption pores was negatively linearly correlated with their average pore size and was positively linearly correlated with their pore volume and specific surface area. The Langmuir pressure constant fluctuated only in a small range with an increase in the average pore size, pore volume, and specific surface area of the adsorption pores, with no strong linear correlation between the former and the latter three elements; (3) The six low-rank coal samples exhibited significant fractal characteristics, with comprehensive fractal dimensions of 2.573?2.720 (average: 2.647), indicating that the adsorption pores of low-rank coals had had strong heterogeneity. The ultimate CH4 adsorption capacity first increased and then decreased with an increase in the fractal dimension, exhibiting an overall upward trend; (4) The relationships between the structure and CH₄ adsorption capacity of adsorption pores can be quantitatively characterized using the micropore filling and monolayer adsorption theories. There were small relative errors between the calculated values and the experimental values of the ultimate CH₄ adsorption capacity, which were 4.47%?6.65% for long-flame coal and 13.77%?16.02% for non-caking coal. The results of this study can provide theoretical guidance for the subsequent quantification of the relationships between CH₄ adsorption characteristics and adsorption pore structure, as well as the accurate prediction of the gas content in coal seams.