Methane Adsorption Capacity of Deep-Buried Coals Based on Pore Structure in the Panji Deep Area of Huainan Coalfield, China
Qiang Wei, Kaige Zheng, Baolin Hu, Xianqing Li, Songbao Feng, Wei Jiang, Wenwei Zhu, Wenqing Feng
Abstract
Pore structure characterization of deep-buried coals and its implications on methane adsorption capacity are of great significance for further understanding the adsorption mechanism of methane molecules by pores in deep strata. In this study, a series of several experiments, including high-pressure mercury intrusion porosimetry, N2/CO2 adsorption, field emission scanning electron microscopy, and methane adsorption, were used to investigate the pore structure and methane adsorption capacity of deep-buried coals from the Panji Deep Area in Huainan Coalfield, China. The methane adsorption capacity of coal samples was obtained by experiment and correction based on the results by tests, and molecular simulation; the latter one adopted the pore filling and monolayer coverage theories. Results show that deep-buried coals developed with multiple types of pores and microfractures. Micropores provide the majority of the specific surface area, whereas the pore volume of deep-buried coals is dominated by macropores. On the basis of experiments, the measured methane adsorption capacity of deep coals shows a medium to high value compared with the adjacent coalmines, and the corrected methane adsorption capacity is in the range of 14.56–24.07 cm3/g with an average of 18.91 cm3/g. The number of methane molecules adsorbed as a state of micropore filling is (32.98–59.83) × 1019 pcs, whereas in a form of monolayer coverage it is (0.51–2.05) × 1019 pcs; the former is the primary contributor and accounts for 94.98–98.46% of the total. Notably, molecular simulated volume is close to that of measured methane adsorption volume, and both of them are significantly and positively correlated with volume and specific surface area of micropores. Methane adsorption capacity is dependent on the micropore volume and external surface area, and the adsorption process consists of a majority of micropore filling and a small amount of monolayer coverage.