| Fire is a common thermal disaster in coal mines.Once a fire occurs,under sufficient ventilation and oxygen conditions,the fire will continue to develop and spread rapidly.Not only does it pose a huge threat to the lives and safety of underground workers and rescuers,it also causes major losses to the country and people's resources and property.When the underground fire is difficult to control,it is often necessary to make the fire zone sealed.However,the underground coal mine is in a special posture environment,and more serious secondary disasters such as gas explosions are prone to occur during and after the fire area is sealed.Which would produce the opposite effect to the purpose of firefighting.In order to further deepen the understanding of the special process of underground fire zone sealing,this paper adopts the method of combining similar experimental simulation and numerical simulation to study the underground fire zone closure of coal mines.Use the processed goaf similar experiment platform to obtain a goaf model with a higher degree of similarity,and on this basis,add a U-shaped ventilation roadway and perform similar experiments of fire zone sealing;In contrast to similar experimental results,the FLUENT numerical simulation software loaded with UDF was used to numerically analyze the gas explosion hazard and nitrogen injection fire extinguishing efficiency in the sealed fire area,and the following research results were mainly obtained as follow:(1)With reference to a large number of patents,we independently designed and processed a similar experimental platform for the three-dimensional non-uniform distribution of the goaf voids.According to the similarity theorem,with sand as the skeleton,gypsum powder and calcium carbonate powder as the cementing material,the overlying rock layer of the goaf is laid.A jack was used to push out the trolley at a certain rate to simulate the mining process of the working face,and the stress sensor embedded in the goaf in advance was used to monitor the stress change of the bottom plate,and a similar model of the goaf with a higher degree of reduction was successfully obtained.Similar experiments on the fire zone sealing are conducted.The results of the change law of wind speed,the change trend of temperature field and the movement law of flue gas in the goaf during the process of fire zone closure were obtained.(2)According to the results of similar experiments,combined with the theory of combustible gas explosion,the corresponding geometric model of the working face/goaf is established,and the gas release source term is set in the goaf.Numerical analysis of the gas concentration distribution and the influence of fire smoke on the methane explosion limits during and after the fire zone sealing is obtained;Combining methane concentration,methane explosion limit,minimum explosive oxygen concentration and other parameters,the influence of different fire source positions on the temporal and spatial distribution of methane explosion zone in the fire zone after sealing is obtained.It is concluded that when the fire source is located on the return air side,the possibility of gas explosion in the enclosed fire area is the largest,followed by the fire source on the air inlet side,and the smallest by fire source on the return air side.(3)Based on the temporal and spatial distribution of methane explosion zone in the enclosed fire zone with different fire source positions,numerical simulation analysis was carried out on the influence of the nitrogen injection port position and nitrogen injection flow rate on the inerting efficiency of the fire zone.It is obtained that the minimum nitrogen injection flow rate to prevent explosions when the fire source is on the return air side is 1400m~3/h,the minimum nitrogen injection flow rate to prevent explosions when the fire source is on the air inlet side is 1000m~3/h,the minimum nitrogen injection flow rate to prevent explosions when the fire source is on the middle part of working face is 800m~3/h. |
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