Molecular simulation of flue gas and CH4 competitive adsorption in dry and wet coal

Abstract

For further understanding the microcosmic mechanism of CO2 storage and CH4 recovery during coal-fired power plants flue gas injecting into the coal seams, the dry and wet macromolecular models of coal were established. Then Grand Canonical Monte Carlo (GCMC) molecular simulations were performed to state multicomponent (single, binary, ternary and quaternary systems among flue gas and CH4) and competitive adsorption behaviors. The results show that the adsorption amount of individual gas in the mixed components adsorption systems increases with the pressures and bulk mole fractions increasing. While the advantages of selective separation for competitive ones, especially for CO2, decrease. The order of adsorption amount of gases in the mixture depends on not only adsorption ability but also bulk mole fraction. With the same bulk mole fraction of CH4, the selectivities of CO2/CH4 that in the systems injecting flue gas are larger than that injecting pure CO2. With the same 0.99 mmol/g adsorption amount of CO2, injection of flue gas is more beneficial to desorption of CH4 than injection of CO2 due to the large partial pressure of N2. The advantages of competitive adsorption for CO2 can be explained by stronger favorable adsorption sites therefore stronger van der Waals energy and electrostatic energy between CO2 and coal. Water in coal goes against the gases adsorption, especially for CO2, because the preferential adsorption sites are occupied by water. The conclusions of this research lay a theoretical foundation for the application of flue gas-ECBM technology.