Adsorption kinetics of CO2, CH4, and their equimolar mixture on coal from the Black Warrior Basin, West-Central Alabama

Abstract

Abstract Laboratory experiments were conducted to investigate the adsorption kinetic behavior of pure and mixed gases (CO 2, CH 4 , approximately equimolar CO 2 + CH 4 mixtures, and He) on a coal sample obtained from the Black Warrior Basin at the Littleton Mine (Twin Pine Coal Company), Jefferson County, west-central Alabama. The sample was from the Mary Lee coal zone of the Pottsville Formation (Lower Pennsylvanian). Experiments with three size fractions (45–150 µm, 1–2 mm, and 5–10 mm) of crushed coal were performed at 40 °C and 35 °C over a pressure range of 1.4–6.9 MPa to simulate coalbed methane reservoir conditions in the Black Warrior Basin and provide data relevant for enhanced coalbed methane recovery operations. The following key observations were made: (1) CO 2 adsorption on both dry and water-saturated coal is much more rapid than CH 4 adsorption; (2) water saturation decreases the rates of CO 2 and CH 4 adsorption on coal surfaces, but it appears to have minimal effects on the final magnitude of CO 2 or CH 4 adsorption if the coal is not previously exposed to CO 2 ; (3) retention of adsorbed CO 2 on coal surfaces is significant even with extreme pressure cycling; and (4) adsorption is significantly faster for the 45–150 μm size fraction compared to the two coarser fractions.