Comparative Analysis of Gas Adsorption and Diffusion Characteristics of the Coal Matrix under Constant Pressure and Constant Volume Conditions

Abstract

Research coal particle gas diffusion law is of great significance for coal and gas comining, while the coal particle adsorption diffusion experiment is divided into two models: constant pressure and constant volume. It is worth exploring which model is more scientific in engineering applications. In this work, two diffusion models of constant pressure and constant volume were proposed based on the theory of the density gradient of free gas. Four coal samples were subjected to isothermal adsorption experiments under two experimental conditions: constant volume and constant pressure, and the results of the simulation and experiment were compared. The results show that (i) the equilibrium cumulative adsorption amounts were basically the same when comparing the adsorption curves of the coal samples under two different experimental conditions; (ii) the two experimental conditions of constant volume and constant pressure have almost no effect on the maximum gas adsorption amount but have a greater effect on the adsorption rate; (iii) the microchannel diffusion coefficients under constant pressure conditions are 1.5−2.5 times higher than those under constant capacity conditions, and based on the differences between the constant pressure diffusion model and the constant volume diffusion model, the application of the two diffusion models in engineering was determined.