Gas desorption and diffusion model driven by density gradient in coal particle and its experimental study

In order to solve the fick diffusion model in coal particle gas desorption process has the problem of larger deviation, better explain the desorption diffusion mechanism in the gas in coal grains, first of all, gas desorption experiment in closed space was conducted, the different initial desorption gas desorption data under the pressure of coal samples, the accuracy of the empirical formula and compares four kinds of desorption; then the Fick diffusion model driven by concentration gradient is reviewed and a new diffusion model driven by free gas density is proposed. At the same time, the related equations of desorption and diffusion are established and solved numerically based on the finite difference numerical method. Finally, the results of the new gas diffusion model are compared with the Fick model and the experimental data, and the advantages of the new gas diffusion model are discussed. The results show that the different desorption empirical formulas have great differences in the accuracy of fitting experimental data, and the empirical formulas which can fit well in the whole experimental time scale are screened out. The numerical prediction results of the new diffusion model under four different initial desorption pressures are basically consistent with the experimental data in the whole experimental time scale. Relatively speaking, the numerical calculation results based on Fick diffusion model are not accurate. Under the premise of ensuring the prediction accuracy of the theory, the diffusion coefficient of the micro channel in the new diffusion model does not change with time and pressure. Compared with the analytical and numerical solutions of the classical Fick diffusion model which is based on the assumption of constant diffusion coefficient, the new model can describe the gas desorption diffusion behavior more reasonably and accurately. The research content is expected to provide some new ideas and references for understanding of mechanism of gas desorption and diffusion,index of gas outburst desorption and the calibration of coal seam gas content.