Causes of oxygen deficiency in upper corners of working face in shallow-buried and short-distance coal seams and comprehensive prevention technology

Shendong, Pingshuo, Datong coalfield in China have a large of shallow-buried and close-distance coal seams, shallow buried and close-distance coal seams have the characteristics of shallow coal seams and close seam spacing. Under mining disturbance, cracks are likely to form air leakage channels. Surface air entering the overlying gob can easily cause spontaneous combustion of the remaining coal in the overlying gob, which indirectly affects the oxygen concentration in the upper corners of the working face during the mining of the underlying coal, resulting in oxygen depletion. In order to explore the causes of oxygen deficiency in the corner of the working face and put forward the measures to prevent oxygen deficiency, taking 91103 fully-mechanized working face of Daheng coal mine as the research background, theoretical analysis, CDEM numerical simulation and SF6 air leakage test methods were used for the study. The results show that there are obvious cracks and sedimentation on the ground. By simulating the process of coal and rock damage, fracture process and cracks development, the ground surface and the overlying gob and working face are connected. Using continuous quantitative release of SF6 tracer gas in the working face for air leakage measurement, the measurement results verify the numerical simulation of the surface, overlying gob and working face through model. The oxygen deficiency in upper corner is due to the low oxygen gas released from the crushing of shallow-buried coal, the oxidation derived gas from gob and the inert gas injected into fire prevention. Under the dual effects of ventilation negative pressure and atmospheric pressure, low oxygen gas by the air leakage channel enters the working face as well as the ventilation characteristics of U-type ventilation mode, resulting in oxygen deficiency. Among them, the serious air leakage caused by the connection between the working face and the ground surface is the main cause of oxygen deficiency in the upper corner. Based on the research on the causes of poor oxygen, Daheng Coal Mine adopted comprehensive prevention and control measures, such as plugging up and down the well, installing air curtains, buried pipe drainage, fans with air duct, etc., which effectively solved the problem of poor oxygen at the upper corners of the working surface, and the oxygen concentration in the upper corner of the working face was always at the normal level.