Measurements and Modeling of Excess Adsorption of Pure and Mixed Gases on Wet Coals

Abstract

Pure-gas excess adsorption isotherms were measured for methane, nitrogen, and CO2 on two water-moistened coals at 319.3 K and pressures up to 12.4 MPa. The coals were lower basin Fruitland (LBF) coal, from the San Juan basin, and Illinois #6 coal, from the Illinois basin. Furthermore, gas-mixture adsorption measurements were made on the Illinois #6 coal for the three binary mixtures formed by methane, nitrogen, and CO2. The rationale for this study was (a) to provide data useful for development and testing of models for the competitive adsorption of mixed gases on coals and (b) to assess the ability of the simplified local-density model to describe the data. The pure gas measurements revealed that CO2 excess adsorption on both coals exhibited distinct maxima near the CO2 critical pressure. At a pressure of 7 MPa, the ratio of excess adsorptions for N2:CH4:CO2 was 1:2.8:4.4 for LBF coal and 1:2.7:6.3 for Illinois #6 coal. The LBF coal showed low levels of adsorption, which can be attributed to the high ash...