Potential coupled harzard zone of coal spontaneous combustion and gas in goaf under mining condition

Coal spontaneous combustion in goaf often induces gas explosion accidents.To explore the coal spontaneous combustion and gas coupled hazard in goaf under mining condition, the zone of coupled potential harzard in goaf is identified and analyzed based on the method of numerical simulation.Based on the moving mesh which is modified by the method of laplace smoothing, the dynamic model of goaf expansion under the advance of the working face is performed.Then, coupling the solution of seepage field, concentration field and energy field, it is developed that a numerical model of coal spontaneous combustion and emission of gas in goaf during the advance of working face.The distribution of volume fraction, oxygen and gas concentration in goaf under mining condition is obtained.The results show that the gas exploitable zone appears as inclined elongated shape, the gas exploitable zone on the inlet side is located in the deep part of the goaf, and the exploitable area on the return air side is close to the working face.According to the theory of coal spontaneous combustion and gas coupled hazard in goaf, the potential dangerous zone of coal spontaneous combustion and gas coupled hazard in goaf is identified.It is found that the potential dangerous zone primarily located between 15 and 60 m from the working face, and the risk of coupled hazard in the air intake side and the deep of the goaf is lower.Moreover, the quantitative relationship between the potential dangerous area and ventilation flux, the advancing speed of the working surface and the attenuation rate of the gas emission is analyzed.It is found that with the increase of the ventilation, the oxidation zone moves to the deep of the goaf, and the concentration of gas near the working surface is reduced.When the ventilation flux increases from 0.5 m/s to 1.2 m/s, the potential dangerous zone expands gradually, but as the ventilation flux continues to increase, it narrows gradually.As the advancing speed of the working surface is increased, the width of the gas exploitable zone is also increased, and the overlap area between the oxidation zone and the gas exploitable zone is expanded.However, the increase of advancing speed of working face will against the coal spontaneous combustion, so the risk of coupled hazard caused by coal spontaneous combustion and gas will be reduced.The width of gas exploitable zone grows with the increase in gas release attenuation rate of coal which leads to the slowly growth of gas concentration with the increase of distance from working face, so the potential dangerous area of coupled hazard increases.