Study of gas adsorption characteristics influenced by moisture content, different coal particle sizes, and gas pressures

Abstract

In coal reservoirs, coal, gas, and water coexist. Different moisture conditions may cause different gas storage capacity. In this paper, a series of isothermal adsorption experiments were conducted which consider different coal particle sizes, moisture ratios, and gas adsorption pressures. The Dubinin-Astakhov isothermal model is adopted in our simulations, and some adsorption parameters such as capacity, rate constant, and energy are obtained. Our key results are as follows: (1) the isothermal gas adsorption characteristics of coal are influenced by moisture, where the adsorption capacity decreases as the moisture content increases. The characteristic energy of adsorption decreases both as a function of particle size and as the moisture content increases. (2) The transient adsorption capacity initially increases sharply with time, which later increases slowly and gradually reaches equilibrium. (3) From the viewpoint of moisture content and particle size, the gas adsorption characteristic is inhibited by increased moisture levels and larger sizes. At the same time, the surface area of a coal sample with smaller particle sizes is greater than that of a sample with larger particle sample. This is inferred from our experiments because the sites for adsorption increase for smaller size samples. Our results can be used to ascertain the adsorption mechanism between gas and moisture on coal.