Numerical Simulation Research On Spontaneous Combustion Characteristics Of Double-layered Coal And N₂ Fire Extinguishing In Shigang Mine Goaf

When gas extraction is carried out in a high-gas mine,the air leakage in the goaf increases,and the risk of spontaneous ignition of the remaining coal increases.When No.15 coal seam is mined in 15212 fully mechanized caving face of Shigang Mine,the caving of No.14 coal seam located at 4-5m in the roof covers the upper part of No.15 coal seam residual coal in goaf,forming double layer residual coal and increasing the risk of spontaneous combustion.And No.14 coal seam natural ignition period is short,hard roof,not easy to fall,resulting in serious air leakage in goaf,fire prevention is difficult.In order to solve the problem of spontaneous ignition of double-layer coal remaining in the gob of 15212 fully mechanized caving working face in Shigang Mine,this paper adopts the method of combining theoretical analysis,experimental research,field test and numerical simulation to carry out the analysis of No.14 coal and No.15 coal in Shigang Mine.Coal spontaneous combustion temperature-programmed experiment,to study the index gas generation law,spontaneous combustion characteristic parameters,apparent activation energy in the process of coal low-temperature oxidation,and to determine the critical oxygen concentration of coal spontaneous combustion;field test and numerical simulation,to study the“three zones”distribution of spontaneous combustion in goaf.And study the effect of N₂ parameter on the spontaneous combustion danger zone of coal leftover in goaf under gas drainage conditions.Through the experimental study on the characteristics of coal low temperature oxidation,it is concluded that when the temperature remains unchanged,the gas release rate,CO and CO₂ gas generation rate,oxygen consumption rate and heat release intensity during the spontaneous combustion of coal decrease with the decrease of oxygen concentration,and the apparent activation energy and The critical temperature of autoignition increases as the oxygen concentration decreases.When the oxygen concentration is constant,the coal gas release rate,gas production rate（CO and CO₂）,oxygen consumption rate and heat release intensity all show an exponential relationship with the temperature change.The signs of spontaneous combustion of No.14 and No.15 coal seams are CO,C₂H₄ and C₂H₂.The apparent activation energy is used as an index to characterize the spontaneous combustion tendency of coal.The apparent activation energy of No.15 coal is greater than that of No.14 coal,indicating that the spontaneous combustion tendency of No.14 coal is greater than that of No.15 coal.The critical temperature of spontaneous combustion and apparent activation energy change with oxygen concentration were studied,and the critical oxygen concentration of spontaneous combustion of No.14 coal and No.15 coal were determined to be 5.0%and 7.2%,respectively.According to the field test results,it is concluded that the range of the oxidation zone on the inlet side and the return side of the No.15 coal in the gob of the 15212 working face is 53m～131.5m and 31m～62m respectively,and the width is 78.5m and 31m respectively.Numerical simulation shows that the risk of spontaneous combustion of No.14 coal in the gob of 15212 working face is greater than that of No.15 coal.The maximum width of the oxidation zone of No.14 coal and No.15 coal in the gob is 96.6m and 79.7m,respectively,and the area of the oxidation zone is7886.8 m²,6295.1m²,the maximum temperature is 315.81K,312.64K respectively.The minimum advance speed of working face is 4.02m/d.Through numerical simulation study of N₂ injection in goaf shows that N₂ injection in goaf can greatly reduce the width and area of No.14 coal and No.15 coal oxidation zone in goaf,reduce the maximum temperature,and reduce the area of high temperature area.The most suitable position for N₂ injection is that the air inlet side of the goaf is 30m away from the working face,the injection range can be 20～40m,and the reasonable N₂ injection flow rate is2000m³/h～2500m³/h.The lower the N₂ injection temperature,the better the inert cooling effect.The injection of low-temperature N₂ has a better prevention and control effect on the spontaneous combustion of coal left on the air inlet side of the goaf,but the cooling effect of the coal left on the return air side of the goaf is not obvious.The research results provide theoretical basis and method reference for the on-site fire prevention and fire fighting in Shigang Mine,and are of great significance to the management of spontaneous combustion disasters in the goaf of Shigang Mine and to ensure safe production.The paper has 68 pictures,30 tables,and 99 references.