Numerical Investigation of the Evolution of Gas and Coal Spontaneously Burned Composite Disaster in the Goaf of Steeply Inclined Coal Seam

As the coal mine gets deeper and the stopes' structures become more complex, gas and coal spontaneously burned composite disaster seriously threatens the efficient operation of coal mines. To study the interaction process and disaster-causing mechanism of gas and coal spontaneous combustion (GCSC), this paper establishes a numerical model to study the influence of drilling location/pressure and N-2 injection on the evolution of gas and coal spontaneously burned composite disaster in the goaf. The simulation shows that in the central part of the goaf, a combined area of gas and coal combustion poses a possibility of spontaneous combustion calamity, and the length of the compound disaster area is about 20 m. The methane (CH4) explosion zone and the dioxygen(O-2) temperature rise zone do not overlap in the air entrance roadway and return air roadway, indicating that there is no risk of compound disasters. The optimal nitrogen (N-2) injection rate for this working face is 2000 m(3)/h, and the N-2 port should be located 25 m profound into the goaf, which can effectively drive the diffusion of N-2 and narrow the O-2 zone's breadth. The findings have considerable engineering applications for revealing the evolution process, risk assessment and control for GCSC compound disasters in coal mines.