The Application of Nitrogen Curtain Technology to Longwall Goaf to Prevent the Spontaneous Combustion of Coal: A Case Study in Shajihai Coalmine, China

To enhance the inerting effect of nitrogen on large longwall goaf, a novel goaf-inerting method of using a full cross-section nitrogen curtain for a U-shaped ventilation working face is developed. The working principle of the full cross-section nitrogen curtain is elucidated. The design principle and key parameters of the nitrogen curtain needed to achieve an optimum nitrogen injection effect are established. The nitrogen curtain technology is successfully applied to the scenario of fire prevention in the underground goaf. The field study shows that the full cross-section curtain injection of nitrogen exhibits many advantages such as simple operation and homogeneous diffusion. The implementation of the nitrogen curtain reduced the maximum width of the goaf oxidation zone from 70 m to 20 m. And the CO concentration in the upper corner decreased from 21.8 ppm to 11.2 ppm after 18 h of nitrogen injection. After 48 h of injection, the CO concentration in the upper corner remained unchanged and the concentration had reduced to 0 in the lower corner. It was demonstrated that the inerting efficiency of the full cross-section nitrogen curtain reached 86% in the upper corner and 100% in the lower, which is significantly superior to the traditional buried-pipe nitrogen injection method. The effect verifies the effectiveness of the curtain injection method of nitrogen, which can ensure a safe working face production.