Comprehensive prevention and control technology of coal spontaneous combustion in compound goaf of close distance coal seam

In China, the occurrence of close distance coal seams accounts for a large proportion, and multiple goaf areas are easily connected to form compound goaf during mining. The compound goaf area is large. There are many air leakage areas and wide distribution range of residual coal, leading to the extremely serious coal spontaneous combustion disaster in compound goaf. In view of the rapid development of coal spontaneous combustion and the abnormal situation of CO and C2H4 pouring out from the compound goaf during the mining, this study comprehensively analyzes the factors such as air leakage source, air leakage sink, geological structure, residual coal during mining and characteristics of spontaneous combustion gas emission of coal, and determines the distribution range and development state of high temperature hidden danger of coal spontaneous combustion in compound goaf. The "two-step" comprehensive control plan for emergency control of hidden dangers and efficient management of hidden dangers is formulated. The combination of pressure equalization and leak plugging to reduce air leakage and nitrogen injection to dilute oxygen in goaf are adopted to achieve the effect of emergency control of hidden dangers. On this basis, effective measure areas of coal spontaneous combustion prevention and control are divided, and compound mud plugging, liquid CO2 cooling and three-phase foam covering oxygen isolation technology are adopted to achieve the goal of highly efficient control of hidden danger. The three-in-one comprehensive prevention and control technology system of "plugging and control velocity-inerting and cooling-covering and oxygen isolation" is constructed to completely eliminate the hidden danger of high temperature in compound goaf. After applying the above techniques, the volume fraction of C2H4 and CO in the compound goaf decreased from 72.1×10-6 and 3 912.6×10-6 to 0 and bellow 20×10-6 respectively. The results show that the proposed technology effectively eliminates the hidden danger of high temperature spontaneous combustion of coal in compound goaf and guarantees the safe and efficient mining of adjacent working face.