Large-area goaf fires: a numerical method for locating high-temperature zones and assessing the effect of liquid nitrogen fire control

Goaf fires are serious hazards in coal mines, especially in the closely spaced shallow coal seams of northwestern China, where spontaneous combustion of coal occurs frequently. A numerical simulation method was developed for a large-area spontaneous combustion fire in the goaf of the 12306 fully caved face at Bulianta coal mine in the Shendong mining area. Theoretical and geometrical models were developed to rapidly locate the high-temperature zone of the fire by simulating the oxygen concentrations and temperature distributions in the goaf. The effectiveness of liquid nitrogen perfusion was also assessed. Field observations showed that the results from the theoretical study were accurate and reliable. The fire was rapidly extinguished by pouring liquid nitrogen at a high flow rate into the high-temperature region of the fire. CO concentration dropped from >10,000 to <5 ppm in the goaf, and the temperature fell from >160 to about 20 °C. The 22305 face below the 12306 goaf was subsequently safely reopened and quickly returned to production.