Jia Tianrang, Liu Cao, Wei Guoying, Yan Jiangwei, Zhang Qinghao, Niu Lifei, Liu Xiaolei, Zhang Mingjie, Ju Yiwen, Zhang Yongjun
State Key Laboratory Cultivation Base for Gas Geology and Gas Control, Jiaozuo 454000, China.
Key Laboratory of Computational Geodynamics, College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China.
J Nanosci Nanotechnol. 2021 Jan 1;21(1):422-430. doi: 10.1166/jnn.2021.18733.
The adsorption and diffusion characteristics of coal are important parameters for coalbed methane (CBM) extraction and mine gas control. However, the adsorption test can only obtain the apparent adsorption amount, and it cannot obtain the actual adsorption amount, which leads to a large error during the calculation of the coal diffusion coefficient. Taking the anthracite coal in the Jiulishan Mine as the research object, the micro-nanostructure and instantaneous apparent methane adsorption isotherms of the primary structure coal and tectonic coal were determined by low-temperature CO₂ adsorption, mercury intrusion and methane diffusion kinetics tests, and the instantaneous apparent adsorption isotherms of methane were corrected to the instantaneous actual adsorption isotherm by the Langmuir model. The results demonstrate that the micro-nanopore, Density Function Theory (DFT) pore volume and specific surface area values below 1-2 nm in tectonic coal are larger than those in the primary structure coal, which is the fundamental reason why the ultimate adsorption capacity of tectonic coal is larger than that of the primary structure coal. The apparent adsorption amounts of the tectonic coal and the primary structure coal reach the maximum at 8 MPa and 10 MPa, respectively. Thereafter, the instantaneous isotherms of the apparent adsorption amount decrease with increasing of gas pressure. However, the instantaneous isotherms of the actual adsorption amount tend to be stable. The diffusion coefficient undergoes a rapid decay with time under low gas pressure, and undergoes a slow decay with under the high gas pressure.
煤的吸附与扩散特性是煤层气开采和矿井瓦斯治理的重要参数。然而，吸附试验只能获得表观吸附量，无法得到实际吸附量，导致在计算煤的扩散系数时误差较大。以九里山矿无烟煤为研究对象，通过低温CO₂吸附、压汞和甲烷扩散动力学试验，测定了原生结构煤和构造煤的微观纳米结构及瞬时表观甲烷吸附等温线，并采用朗缪尔模型将甲烷的瞬时表观吸附等温线校正为瞬时实际吸附等温线。结果表明，构造煤中1-2nm以下的微孔、密度泛函理论（DFT）孔容和比表面积值均大于原生结构煤，这是构造煤极限吸附能力大于原生结构煤的根本原因。构造煤和原生结构煤的表观吸附量分别在8MPa和10MPa时达到最大值。此后，表观吸附量的瞬时等温线随气体压力升高而降低。然而，实际吸附量的瞬时等温线趋于稳定。在低气压下，扩散系数随时间快速衰减，在高气压下随时间缓慢衰减。
