Lost Gas and Desorption Kinetics of Coal at Different Pressures, Exposure Times, and Sampling Intervals

The content of coalbed methane (CBM) is an important parameter that affects the performance of coal extraction and the safety of coal mines. The importance of this parameter is especially more pronounced when using the direct method to determine CBM content, in which the measuring accuracy of the lost gas affects the results. The loss is affected by the gas pressure and exposure time. In this article, the influence of gas pressure and exposure time on the estimation results and loss rate was investigated. Moreover, the influence of the sampling interval and observation time on the accuracy of the kinetic model in simulating the desorption process was analyzed. The obtained results demonstrated that the lost gas is positively associated with pressure and exposure time, and the lost gas rate is proportional to the exposure time. It was found that although the Barrer method outperforms the power function method, in terms of calculation accuracy, both methods have large errors. In terms of physical sense and model accuracy, the pore diffusion (IDM) model best fits the desorption kinetics of this coal. In the stable desorption stage, the desorption process is more consistent with Henry's law. When the desorption changes violently, the desorption process is more consistent with Fick's diffusion law. In order to ensure the consistency between the model and the experiment (95% confidence interval), the sampling interval of IDM model at 1 MPa should be more than 30 s.