Gas desorption diffusion behavior in coal particles under constant volume conditions: Experimental research and model development

Understanding gas diffusion characteristics of coal particles is a significant theoretical basis for the exploitation of coalbed methane. Generally, diffusion experiments are performed under constant pressure conditions, and scholars seldom discuss gas desorption experiments with constant volume, but the recognition of this characteristic is also equally important. Based on this, the paper conducted coal particles desorption experiments under conditions of constant volume to explore gas diffusion characteristics under different adsorption equilibrium pressures and initial emission environmental pressures. The experimental data showed that the variation law of desorption amount with time under constant volume conditions conformed to the Langmuir-like equation. Meanwhile, the rising of initial emission environmental pressure reinforced the linear relationship between the limitation desorption amount and the adsorption equilibrium pressure. When the initial emission environmental pressure was 0.10 MPa, the correlation coefficient of linear fitting between them was as high as 0.9826. To better describe the diffusion process of this condition, a dynamic diffusion model of coal particles gas diffusion under constant volume conditions was established. The calculated values of this model had a preferable consistency with the experimental data, and the correlation coefficients were all over 0.99, which verified the reliability of the model. This research makes up for the theory of gas diffusion and provides a theoretical basis for coalbed methane extraction.