Experimental Study on the Effect of the Degassing Vacuum Degree on the Adsorption Performance of Gas in Coal

To study the characteristics of the effect of the degassing vacuum degree on the gas adsorption performance of coal, gas adsorption experiments were performed on raw and particle coal under different degassing vacuum degree conditions. The degassing vacuum degree is measured in real time during the whole vacuum degassing experiment. The experimental results demonstrate that the higher the degassing vacuum degree, the greater the gas adsorption capacity of coal and the greater the growth rate of gas adsorption capacity. With the elevation of the degassing vacuum degree, the free energy of the pore surface in the coal body increases under vacuum conditions and the ability of the coal body to adsorb gas increases, which shows that the gas adsorption capacity rises. By comparing the difference in gas adsorption capacity of raw coal and particle coal under the identical degassing vacuum, it can be derived that the internal pore length of particle coal is shortened, the gas migration resistance reduces, and the adsorption potential of the micropore throat decreases. In the process of vacuum degassing, the binding capacity of coal pores to gas decreases and the residual gas capacity decreases. Therefore, compared with raw coal, the gas adsorption capacity of particle coal is significantly increased and the gas adsorption capacity of the coal sample is nearly doubled after the first crushing. The study of the effect of the degassing vacuum degree on the gas adsorption performance of coal is helpful to understanding the influence of residual gas in the coal before adsorption on the accuracy of gas adsorption capacity measurement so that the experimental measurement of gas adsorption is closer to the actual gas content of the coal seam.