Study on the effect of moisture on CO2 replacement of methane in coal

Abstract

In order to study the effect of moisture on CO2 displacing methane in coal, a set of isothermal adsorption experiments of CO2, CH4 and their mixed gases were carried, and the adsorption potential energy of coal adsorbed water was calculated by the optimized BET model. In this experiment, two highly metamorphic coal samples of fat coal and anthracite coal with different moisture contents were prepared by the water vapor adsorption partition method. The results show that the adsorption capacity of coal to water vapor can be fitted by the optimized BET model. The first-order and second-order adsorption potential energies of anthracite for water are E1=44.20 kJ/mol and E2=42.27 kJ/mol, respectively, which are larger than the adsorption potential energies of coal for CH4 and CO2, indicating that the water has a displacement effect on gas in coal. The adsorption capacity of CO2 is greater than that of CH4 under the same conditions. The ability of coal to adsorb CO2 and CH4 gradually decreases with the increase of water content, and the displacement effect of H2O on CH4 in coal is significantly enhanced. The displacement of CH4 in coal by CO2 decreases with the increase of water content, and the displacement rate is basically unchanged. Moisture plays an inhibitory role in CO2 displacement.

Keywords

• gas drainage
• co2 replacing ch4
• competitive adsorption
• bet model
• adsorption potential energy