The 4th International Symposium on Mine Safety Science and Engineering (ISMSSE2018)

248 / 2018-05-09 07:54:37

Research on the air leakage mechanism and the suitable gas drainage volume with the upper tunnel gas extraction

gas extrction,upper tunnel,air leakage,coal self-heating,gob

Mine occupational health and environmental safety > Fire protection

Gas drainage using the upper tunnel is an effective way to prevent the gas overrun of the working face. However, the negative pressure of the gas drainage and the fracture arising from the layout of the upper tunnel result in more air leakage in the gob, consequently increasing the risk of coal self-heating. Despite extensive studies focusing on the influences of the negative pressure, only a handful of papers have placed attention on the location of the effective drainage section and air leakage flow fields under the gas drainage of the upper tunnel. Furthermore, increasing the drainage volume can improve the gas control effects but leads to an intensification of air leakage, which is adverse to the prevention of coal self-heating, yet existing studies have not proposed a theoretical model to determine the suitable gas drainage volume for solving this contradiction. In this paper, the formation of an air leakage channel was studied along with the advance of the working face, including the breaking process of the upper tunnel and the expansion of the caving zone. The location of the effective drainage section of upper tunnel was obtained and applied in the CFD model to solve the air leakage flow fields in the gob. Based on the air leakage mechanism of the upper tunnel, a theoretical model of the suitable gas drainage volume was proposed. The results indicated that the effective drainage section of the upper tunnel was behind the working face within a certain distance. The flow patterns of air leakage were influenced by the gas drainage of the upper tunnel and presented the characteristics of spatial distribution. The oxygen volume fraction of the upper tunnel increased gradually with an increase in the gas drainage volume. Through the theoretical model, a suitable range of the gas drainage volume was obtained to administer the coal mine methane level and lower the risk of coal self-heating. Finally, compared with the measured data, the reliability of the simulation results and the correctness of the theoretical model are both verified.