Prevention and control technology of harmful gas intrusion in close-up coal seam under fire area

The mining of the close coal seam under the fire area easily leads to the occurrence of harmful gas intrusion, which seriously threatens the safe mining of the working face. The goaf upon the 30110 mining face of the Sunjiacha coal mine had serious spontaneous combustion problem. Although the nitrogen injection and plugging air technology were taken to control the disaster, the effect was not obvious. To solve this problem, PFC^2D was used to build a mining numerical model for dynamically tracking the change of fracture variation. The result shows that the air leakage channel will occur with the collapse of main roof in lower coal seam, which provides the basis for the monitoring work before the disaster and the application of the pressure equalization system. In order to prevent the invasion of harmful gases and avoid fresh air flowing into the fire area causing an explosion, a pressure balancing ventilation method was applied in the 30110 mining face. It can control the air pressure between upper fire area and lower working face in a safe range. The test safety pressure of 296 Pa and the normal safety adjustment interval (118 Pa, 166 Pa) were determined by calculation. Application results prove that the pressure balancing ventilation can effectively prevent the occurrence of harmful gas intrusion and ensure the safe mining of the mine.