Research On Evolution Law Of CH₄ Explosion Hazard In Fire Area Of Coal Mine

When fire occurs in coal mine （If can’t directly put out the fire）, especially fire in goaf. The most commonly used method of fire prevention is fire area sealing, but gas explosion often occurs in the process of fire area sealing. Combining research methods of theoretical analysis, experiment research and computer simulation, this dissertation has studied change laws of flow field, concentration field and temperature field in the process of fire area sealing.Analyzing sources and components of gases in fire area, it is concluded that the main gases in fire area are CO, CO₂, CH4 and H2. Through analysis and derivation based on fluid mechanics, heat transfer and other related theories, combustion speed change law, gas distribution law and temperature distribution law of fire area has been obtained.Carrying out an experiment of tunnel fire development process, according to the experimental model, numerical model of tunnel fire has been established and meshed. Numerical simulation of the development at the initial stage of fire has been carried out by the established model. Then in the center vertical section of tunnel, flow field variation of with temperature, temperature distribution law and gas distribution law at the initial stage of fire have been obtained.Conducting an experiment on gas explosion hazard, the influence law of parameters such as temperature, combustible gas concentration and inert gas concentration on gas explosion hazard and explosion intensity have been obtained. Gas explosion hazard increases with the increase of initial temperature, pressure and CO concentration. After injecting N2 and CO₂, gas explosion hazard decreases, critical oxygen concentrations of non-explosion are 13.4% and 15.8%, the inert effect of CO₂ is better than that of N2.Gas explosion pressure decreases with the increase of initial temperature and increases significantly with the increase of CO concentration. Gas explosion pressure of upper limit is higher than that of lower limit.When gas concentration is 9.5%, gas explosion pressure is the highest. The gradient of gas explosion pressure increases with the increase of gas concentration, When initial temperature increases, the gradient of gas explosion pressure increases, but the increase extent is lower, For the increase of CO concentration, the gradient of gas explosion pressure has a significant increase. When the initial pressure varies from 10 to 16MPa, the gradient of gas explosion pressure remain remain largely unchanged, when the initial pressure varies from 16 to 20MPa, the gradient of gas explosion pressure increases with the increase of initial temperature.Analyzing change law of flow field in the process of sealing fire area, numerical simulation of that has been carried out, it can be obtained that back-flow layer forms as average wind speed of the entrance decreases below 1.5 m·s^-1. Thickness of back-flow layer, length of back-flow and maximum current speed rise with the declining of average wind speed at the entrance. Gas concentration and CO concentration rise with the decrease of wind speed. When wind speed decreases to 0.1 m·s^-1, CO will be mixed near the roof at 10.1 m to the weather side of fire source, and its concentration is more than 5%, the temperature of fire area is more than 100℃, the lower limit of gas explosion is less than 2.8%. Gas concentration is 4% in this area and the O₂ concentration is relatively higher, it can be concluded that there is a great possibility for the occurrence of gas explosion.The inert effect and dilution effect of the injection of inert gas have been analyzed, numerical stimulation on inert gas injection in the process of fire area sealing has been carried out. Then the change law of development of back-flow layer and explosive area has been obtained, which determines the optimal direction of injection parameters of inert gas.In this dissertation,the influence parameters of gas explosion and the change law of flow field in the process of fire area sealing has been analyzed, the hazard area of gas explosion in fire area has been judged by numerical simulation, effects of inert gas injection on gas explosion in the process of fire area sealing has been studied, The results are of great significance to prevent the occurrence of gas explosion in the process of fire area sealing and effectively check the outbreak of mine great disaster accidient.