Experimental study on accuracy of direct gas content determination

The direct method is important for determining the gas content of coal seams and has a significant effect on the rapid determination of gas content in underground coal mines. The accuracy of the loss has a great impact on the accuracy of the gas content determination. In order to investigate the accuracy of this method,the test conditions of di- rect gas content measurement in coal mines were simulated, and the gas desorption experiments for coal were de- signed. The experiments were carried out according to the current national standards for direct measurement of gas con- tent. Different gas adsorption pressures were set to change the gas content. Different coal exposure times were set to modify the gas desorption loss. The experiments adopted a general coal gas adsorption and desorption experiment sys- tem. The No. 9 coal from Fenghuangshan Coal Mine in Shanxi was crushed into five particle sizes and mixed uniformly. Desorption experiments with different pressures and different exposure times were performed. Based on the experi- mental data,the calculation of the loss was carried out using the method prescribed by the national standard. The cal- culation results show that the method stipulated by the national standard has a large error. The reason for the error is that during the gas desorption process of coal,the gas desorption speed varies with time,but the single t law or power function law does not consider the variation comprehensively. Based on the calculation of the loss and the analysis of the error,combined with the microscopic desorption and diffusion of the gas molecule,the gas desorption in the direct method of determining gas content should be divided into three phases,which are the high-speed release phase confir- ming to the linear law at the beginning stage,the fast desorption phase confirming to the t law at the middle stage and the slow release phase confirming to the power functions law at the late stage. In addition,the paper provides the math- ematical expressions of desorption amount and desorption time corresponding to different stages.