Study on gas desorption and diffusion kinetic behavior in coal matrix using a modified shrinking core model

Abstract

An accurate model of gas desorption and diffusion is the necessary prerequisite to accurately predict gas transfer and evaluation of gas content in the coal. A new modified shrinking core model was proposed and modified based on the shrinking core model and taking into account the time-depend diffusivity. It was to predict the kinetic process of gas desorption and diffusion including three processes: (1) desorption on the undesorbed core surface, (2) diffusion through the desorbed layer, and (3) diffusion through the gas film. The kinetic data of gas desorption and diffusion was obtained from a series of experimental tests conducted under isothermal conditions. The model showed the best agreement with the experimental data, comparison with the shrinking core model, the simplified unipore diffusion model, and the simplified bidisperse diffusion model. Comparison and validation of simulated curves and experimental data indicated the diffusion through the desorbed layer had a dominant role in the whole process of gas transfer in coal particle. The effect of adsorption equilibrium pressure, temperature, and particle size on the initial diffusivity was discussed by using the modified shrinking core model to model the experimental data. The initial diffusivity was affected slightly by the adsorption pressure and increased with the increase in temperature and the particle size. This research provides a new modified shrinking core model to describe the gas transfer process in coal particles better.