To validate and extend previous ideas on the mechanism of displacement of methane (CH4) adsorbed on the internal surface of coal by injecting pure CO2and N2, as well as a mixture of CO2and N2, adsorption and replacement experiments were performed. A coal-methane system partially saturated with CH4 at 2.4MPa adsorption pressure was experimentally studied. Desorption behavior of CH4 by injecting pure CO2(at 3.0MPa, 4.0MPa, 5.0MPa, and 6.0MPa), and by injecting the CO2-N2 mixture and pure N2 (at 3.0MPa, and 6.0MPa) were evaluated. Results indicated that the preferential sorption property of coal for CO2is significantly higher than that for CH4 or N2. CO2injection can displace almost all of the CH4 adsorbed on coal. When modeling the CH4-CO2binary and CH2-CO2-N2 ternary adsorption system by using the Extended Langmuir (EL) equation, the EL model always over-predicted the sorbed CO2value with a lower error, while under-predicting the sorbed CH4 with a higher error. These results were explained that, due to its relatively smaller kinetic diameter, CO2can permeate not only micro-pores but also ultra micro-pores. CH4 and N2 have slightly larger kinetic diameters and may be blocked.
Carbon dioxide (CO2), Methane (CH4), Displacement, Extended Langmuir (EL) model, Akabira coal