Abstract
In order to study differences in the methane adsorption characteristics of coal pores of different metamorphic degrees, 4 nm pore structure models based on three typical coal structure models with different metamorphic degrees were constructed. Based on the molecular mechanics and dynamics theory, the adsorption characteristics of methane in different coal rank pores were simulated by the grand canonical Monte Carlo (GCMC) and molecular dynamics methods. The isothermal adsorption curve, Van der Waals energy, concentration distribution, and diffusion coefficient of methane under different conditions were analyzed and calculated. The results showed that at the same pore size, the adsorption capacity of CH4 is positively correlated with pressure and metamorphic degree of coal, and the adsorption capacity of CH4 in high metamorphic coal is more affected by temperature. The relative concentration of CH4 in high-order coal pores is low, and the relative concentration at higher temperature and pressure conditions is high. The CH4 diffusion coefficient in high-rank coal is low, corresponding to the strong Van der Waals interaction between CH4 and coal. The research results are of great significance for further exploration of the interaction mechanism between CH4 and coal with different metamorphic degrees and can provide theoretical support for the selection of gas extraction parameters.
Highlights
China is rich in CBM resources, and many studies have shown that CBM reserves at a burial depth of less than 2000 m in China can reach 36.8 trillion m3 [1]
Because they are prominent sites of methane, it is of great significance to study the adsorption, desorption, seepage, and diffusion laws of pore structures in pore channels to improve gas extraction efficiency and prevent coal and gas outbursts
A 4nm pore structure was constructed as the methane migration channel, and the differences in the adsorption characteristics of pore methane in coal with different metamorphic degrees at different temperatures and pressures were analyzed to provide a theoretical basis for further exploration of the interaction mechanism between gas molecules and coal
Summary
China is rich in CBM resources, and many studies have shown that CBM reserves at a burial depth of less than 2000 m in China can reach 36.8 trillion m3 [1]. It is necessary to construct a pore structure model that can reflect the actual situation of coal Based on this conclusion, we selected three typical coal structural models with different metamorphic degrees at the present stage, including the Wender model, Wiser model, and Xiang model, which represented the structures of lignite, bituminous, and anthracite, respectively. A 4nm pore structure was constructed as the methane migration channel, and the differences in the adsorption characteristics of pore methane in coal with different metamorphic degrees at different temperatures and pressures were analyzed to provide a theoretical basis for further exploration of the interaction mechanism between gas molecules and coal. The three typical coal structure models used in this study were the Molecules 2021, 26, x FOR PEER REVIEW Molecules 2021, 26, x FOR PEER REVIEW
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