Study on spontaneous combustion laws and fire prevention measures of coal remains during water drainage in water soaked goaf

Abstract

ABSTRACT After the water release in the waterlogged mining area, the residual coal is prone to spontaneous combustion after being air-dried. To investigate the law of spontaneous combustion of residual coal in water immersed goaf during drainage, experimental studies, field observations and numerical simulations were used to analyze the effect of drainage on the spontaneous combustion characteristics of residual coal. Nitrogen injection parameters were optimized based on the results of the study. The experimental results show that: the spontaneous combustion tendency of soaked coal is enhanced compared with that of raw coal, and the spontaneous combustion tendency of soaked coal in goaf is stronger than that of the laboratory prepared soaked coal, because the immersion time of field-immersed coal is longer than that of laboratory-prepared coal samples. The simulation results of oxygen concentration and pressure distribution during goaf drainage show that: compared with that without drainage, the pressure in goaf decreased by 270 Pa, the air leakage in the goaf increased, the area of oxidation zone expanded by 5.2 times, and the possibility of spontaneous combustion of residual coal increased. Injecting nitrogen during the drainage was proposed to suppress the oxidation of the residual coal. The effect of nitrogen injection was measured on site and numerically simulated. After nitrogen injection were taken, the pressure dropped by 130 Pa after water release and the area of oxidation zone expanded by 1.5 times, indicating that nitrogen injection measures can effectively suppress the water-gas replacement. In addition, for this flooded goaf, the optimized nitrogen injection rate is 600 m3/h. This study provides an important reference for the prevention and control of spontaneous combustion hazards of residual coal in the short-distance composite coal seam during drainage of water immersed goaf.