Spontaneous combustion hazard zone in inclined coal seam goaf and nitrogen injection parameters optimization

This study investigates fire prevention and control in inclined coal seams prone to spontaneous combustion, using the 12020 working face of a Henan mine as a case study. The porosity distribution and spontaneous combustion hazard zones in the goaf were analyzed through on-site observation, theoretical analysis, and numerical simulation. A segmented non-parallel progressive nitrogen injection technique was evaluated and optimized. Results indicate that the non-uniform collapse of the roof rock layer causes the oxidation zone on the return airway side (60.9 m) to extend further than on the intake side (33.6 m), with high-temperature zones concentrated near the return airway and central goaf. Numerical simulations compared nitrogen injection locations and volumes for both monomer and segmented methods, assessing the oxidation zone area, oxygen concentration, and temperature distribution. The segmented non-parallel progressive nitrogen injection method was found to be optimal, with two injection ports: one at the intake airway (35 m, 800 m3/h) and another 20 m below the return airway (80 m, 500 m3/h). This configuration maximizes the superposition effect of nitrogen injection on both sides of the goaf, reducing the oxidation zone by 2831 m2 (71.5%) and lowering the high-temperature point from 38.8 to 32.2 °C. It also rapidly decreases CO concentration to a safe level, effectively preventing spontaneous combustion in the goaf.