Adsorption simulation of methane on coals with different metamorphic grades

In order to study the adsorption capacity of methane on coals with different metamorphic grades and its influencing factors, the new macromolecular structure models of lignite, bituminous coal and anthracite were constructed, and the grand canonical Monte Carlo (GCMC) method was used to simulate the adsorption process of methane in coals. The results show that the adsorption amount of methane is related to the volume of pore formed by macromolecular accumulation. Gas adsorption is mainly caused by van der Waals force. The adsorption amount of methane decreases linearly with the increase of temperature. Water molecules in coal inhibit methane adsorption. The amount of methane adsorbed in coal decreases with moisture content increasing, especially for anthracite. When methane and water are simultaneously isostatically adsorbed, the amount of water is much larger than that of methane, and the amount of methane in micropores is nearly zero. In simulations, we find the construction of the unit cell of coal is critical to the accuracy of the amount of methane. The structure of the supercell represents the grades of metamorphism of coal, which has a great influence on the amount of methane adsorbed in coal. Compared with the metamorphic grade, the temperature has small effect on the amount of methane.