Experimental Study on Gas Loss Derived from Positive Pressure

Abstract

Positive pressure sampling enables the fixed-point and rapid acquisition of coal samples, but the derivation of loss volume during sampling is usually based on the law of gas desorption from granular coal at atmospheric pressure, which seriously affects the reasonableness of loss amounts under positive pressure and thus leads to errors in gas content determination. The gas loss under positive pressure is the key to the accurate determination of the gas content of coal seams. To obtain reliable loss data, under different positive pressures, we tested the gas desorption process of anthracite coal samples with different adsorption equilibrium pressures, analyzed the effect of positive pressure on gas desorption, studied the changes in the gas desorption rate caused by positive pressure, recorded the fluctuation of the amount of gas loss, and compared the values of loss under different conditions. The results show that the positive pressure is the main factor affecting gas desorption compared to the adsorption equilibrium pressure. The positive pressure has an inhibitory influence on gas desorption. Under the same positive pressure, the gas desorption rate shows a decreasing trend over time, and at the same time, the gas desorption rate gradually decreases accompanied by the increasing positive pressure. The gas loss error rate increases with increasing adsorption pressure under the same positive pressure. However, under the same adsorption pressure, the error rate of loss quantity presents a significant increase with positive pressure. The relative error of gas loss under different positive pressures can reach 63–180%, and the positive pressure has an obvious influence on gas loss. This study has experimentally confirmed that positive pressure has a greater effect on gas desorption than adsorption pressure, which will theoretically improve the method of deriving the amount of gas loss and will provide a basis for the accurate determination of gas content under positive pressure in engineering terms.