Efficient prevention of coal spontaneous combustion using cooling nitrogen injection in a longwall gob: An application case

Conventional nitrogen injection in longwall gobs often fails to achieve the expected fire protection effect due to the lack of cooling function. To address this issue, a technical solution of cooling nitrogen injection was proposed to prevent the coal spontaneous combustion (CSC) in gobs, and the corresponding deep-cooling equipment system was developed. This system was applied on-site in a coal mine in China and had achieved favorable cooling results. Furthermore, the multi-physics coupling model of CSC in gob was upgraded to be applicable to nitrogen injection conditions. The effects of nitrogen injection parameters were then quantitatively evaluated. The results show that (i) the cooling nitrogen entering the gob can significantly reduce the temperature of the high-temperature zone, about 5 °C, thus effectively reducing the risk of the CSC in gobs; (ii) the simulation results under nitrogen injection are in good agreement with the on-site data, which verifies the accuracy of the nitrogen injection model; (iii) there is an optimal location of the nitrogen injection point in gob, which can suppress the CSC to the maximum extent. This technology of cooling nitrogen injection can be further promoted and applied to other mines with severe spontaneous combustion.