Study on Fire Extinguishing Effect of Liquid Nitrogen Injection in Overlying Goaf of Close Distance Coal Seams

Under the condition of occurrence of close coal seams in the process of mining and the effect of negative pressure ventilation, the high concentration of CO and other harmful gases in the overlying goaf temperature abnormal area intrude into the working face through mining-induced fractures. In order to effectively control the abnormal area temperature and the concentration of harmful gases, the measures of preventive dynamic alternating liquid nitrogen injection were adopted to control the drilling hole along the working face inclination in the high temperature area. The results showed that after nitrogen injection, the temperature of all boreholes showed a significant downward trend, and the concentration of CO gas increased first and then decreased continuously. The effect of regional treatment was obvious, and there was no obvious rebound sign in the short term, which could ensure the safe production of the working face.