Gas adsorption isotherms of Akabira coals were established for pure carbon dioxide (CO2), methane (CH4), and nitrogen (N2). Experimental data fit well into the Langmuir model. The ratio of sorption capacity of CO2, CH4, and N2 is 8.5:3.5:1 at a lower pressure (1.2 MPa) regime and becomes 5.5:2:1 when gas pressure increases to 6.0 MPa. The difference in sorption capacity of these three gases is explained by differences in the density of the three gases with increasing pressure. A coal–methane system partially saturated with CH4 at 2.4 MPa adsorption pressure was experimentally studied. Desorption behavior of CH4 by injecting pure CO2 (at 3.0, 4.0, 5.0, and 6.0 MPa), and by injecting the CO2–N2 mixture and pure N2 (at 3.0 and 6.0 MPa) were evaluated. Results indicate that the preferential sorption property of coal for CO2 is significantly higher than that for CH4 or N2. CO2 injection can displace almost all of the CH4 adsorbed on coal. When modeling the CH4–CO2 binary and CH2–CO2–N2 ternary adsorption system by using the extended Langmuir (EL) equation, the EL model always over-predicted the sorbed CO2 value with a lower error, while under-predicting the sorbed CH4 with a higher error. A part of CO2 may dissolve into the solid organic structure of coal, besides its competitive adsorption with other gases. According to this explanation, the EL coefficients of CO2 in EL equation were revised. The revised EL model proved to be very accurate in predicting sorbed ratio of multi-component gases on coals.
[1]
P. J. Reucroft,et al.
Effect of pressure on carbon dioxide induced coal swelling
,
1987
.
[2]
Maria Mastalerz,et al.
Carbon dioxide and methane sorption in high volatile bituminous coals from Indiana, USA
,
2004
.
[3]
R. Marc Bustin,et al.
Selective transport of CO2, CH4, and N2 in coals: insights from modeling of experimental gas adsorption data
,
2004
.
[4]
Sohei Shimada,et al.
Anisotropy of gas permeability associated with cleat pattern in a coal seam of the Kushiro coalfield in Japan
,
2004
.
[5]
Y. Ogawa,et al.
Pore structure of sheared coals and related coalbed methane
,
2001
.
[6]
R. Bustin,et al.
Binary gas adsorption/desorption isotherms: effect of moisture and coal composition upon carbon dioxide selectivity over methane
,
2000
.
[7]
Jan T. Duda,et al.
Absorption and Adsorption of Methane and Carbon Dioxide in Hard Coal and Active Carbon
,
2000
.
[8]
John W. Larsen,et al.
The effects of dissolved CO2 on coal structure and properties
,
2004
.