Study of the Air Leakage Mechanism and the Suitable Gas Drainage Volume with the Upper Tunnel

Abstract

Gas drainage in an upper tunnel effectively prevents the gas overrun of the working face. However, the upper tunnel gas drainage quickly leads to air leakage and increases the risk of spontaneous coal combustion in the goaf. To reveal the influence of an upper tunnel gas drainage on the spontaneous combustion of coal in the goaf, the formation of an air leakage channel, the gas emission, and the distribution of the intuitive combustion danger area were studied through a numerical simulation and field measurement. The results indicated that the effective drainage section of the upper tunnel was behind the working face within a certain distance, and the air leakage mode presented the stereoscopic air leakage characteristics of high and low positions coexisting in the goaf. The spontaneous combustion danger area distribution increased gradually with the gas drainage volume increasing. However, the gas concentration in the upper corner decreased with the extraction quantity. Then a safe gas drainage volume was determined by comparing and analyzing the coal gas emission and spontaneous combustion with different extraction quantities.