Gas time-dependent diffusion in pores of deformed coal particles: Model development and analysis

Deformed coal provides favorable conditions for the occurrence of gas outburst disasters. The existing gas diffusion model cannot accurately calculate the lost gas amount during the sampling period of deformed coal. In order to solve the above problems, a new mathematical time-dependent diffusivity model (NMTDM) and its simplified model (SNMTDM) of deformed coal have been established and validated. At the same time, the performance and engineering application of models were also discussed. The results show that the fitting accuracy of NMTDM and SNMTDM to gas diffusion data is greater than that of unipore diffusion model (UDM) and simplified unipore diffusion model (SUDM), respectively, which indicates that it is reasonable to regard the diffusion coefficient of deformed coal as a time-dependent variable. The diffusion coefficient of adsorbed gas, diffusion coefficient of free gas and total diffusion coefficient of gas decrease with the increase of time, and SNMTDM can realize the accurate calculation of lost gas amount. However, when the application of SNMTDM extends beyond its applicable range, the calculating results of the model may deviate seriously from the actual values. The gas diffusion models established in this paper can improve the calculation accuracy of lost gas amount and gas content of deformed coal.