| Fire in mines is one of the main obstacles to the high-quality development of the coal industry.When the roof is cut along the gob to retain the entry,the side of the entry is directly connected with the caving zone of the gob,which completely changes the risk of spontaneous fire in the gob,and the risk of spontaneous fire in the gob is significantly increased.The balance relationship between oxygen,gas and temperature in the area is also changing constantly,so it is urgent to explore the dynamic evolution law of the spontaneous combustion danger zone in the gob of the gob-cutting and gob-retaining mine.In view of the current domestic and foreign research on the fire,gas,and temperature coupling disaster mechanism in the goaf,the following research is carried out.According to the theory of “roof cutting and broken wall beam”,the caving situation of overlying strata in goaf of S2173 first mining face is simulated and explored by using discrete element analysis software 3DEC.The caving and deformation laws of overlying strata in goaf are obtained: the overlying strata of goaf on the side of roof cutting and retaining roadway directly caves,and the caving rock in the caving zone in this area has strong integrity,so the porosity and permeability in goaf near retaining roadway are less than those in goaf on the return air side.With the advance of the working face,the vertical stress of the caving rock in the deep caving zone of goaf gradually increases,and it is gradually compacted.Combined with the simulation results and adding time term,the four-dimensional porosity and permeability distribution model of surrounding rock caving in goaf is derived,which is compiled into UDF for subsequent Fluent simulation.The heating and oxygen consumption characteristics of coal samples were studied.The oxidative spontaneous combustion process and ignition temperature of coal were studied by synchronous thermal analyzer.According to the characteristic temperature or weight ratio change,the TG curve was divided into four stages:preheating weight loss stage,oxidation weight gain stage,combustion stage and burnout stage.The kinetic parameter equation of coal sample oxidation spontaneous combustion ignition stage;the closed oxygen consumption experiment measures the continuous oxygen consumption rate,suffocation(critical)oxygen volume fraction and the risk of spontaneous combustion in the goaf under mining conditions.Provide a basis for the division of suffocation zone and spontaneous combustion oxidation heating zone;coal sample heating program and measurement of spontaneous combustion landmark gas,the relationship between the concentration of each gas produced by coal spontaneous combustion and temperature,build prediction and forecast model,establish the prevention of spontaneous combustion disasters and early prediction and identification of mines Early warning system of coal spontaneous combustion fire;combined with the above research,the equation system for the dynamic simultaneous solution of multiphase gas and temperature is obtained.Field measurement,laboratory smoke experiment of similar model and temperature experiment of similar model confirmed the linkage law of air leakage and working face ventilation in the gob-cut gob-retaining gob,and the complex boundary conditions of the flow field in the gob-cut gob-retention gob According to the distribution characteristics of air leakage at the boundary of the working face,the interaction between ventilation,air leakage in the gob flow field and the spontaneous combustion of the gob “three zones” is analyzed.The results show that the air leakage of the gob-cut entryway at the opening of the cutout has a great influence on the distribution shape,location and size of the spontaneous combustion area in the goaf,and the gob-side entry retention is within 100 m close to the working face due to the influence of the air leakage and airflow of the working face.The phenomenon of air leakage inside is more obvious.In order to study the distribution law of gas,oxygen concentration and temperature in the gob of gob cut and gob entry retention,the sliding grid technology and the dynamic grid technology in the dynamic grid were used in Fluent software at the same time,and the ambient temperature was 298 K respectively Simulates the flow field coupled with oxygen,gas and temperature in the gob at 305 K,and explores the evolution law of the spontaneous combustion danger zone in the gob with time and space changes,and verifies the end entry by simulation.Feasibility of nitrogen injection for fire-fighting measures.The results show that the spontaneous combustion danger area of goaf along goaf retaining roadway with cutting roof changes continuously with the advance of working face.The spontaneous combustion oxidation zone of the goaf is distributed along the side of the retaining roadway and behind the working face.The high temperature area is close to the lower corner of the working face and presents a long and narrow shape with the advance of the working face.The gas concentration gradually increases with the advance of the working face and is mainly distributed near the upper corner of the open-cut.With the increase of ambient temperature,the oxygen,gas and temperature field in the goaf also change.Nitrogen injection in the tail roadway can eliminate the spontaneous combustion oxidation area distributed along the cutting top and goaf staying lane,reduce the temperature in the goaf,reduce the width of the spontaneous combustion oxidation zone behind the working face from 240 m to 200 m before nitrogen injection,and reduce the minimum safe fire advance speed of the working face from 3.6 m/d to 3.0m/d.There are 62 panels,13 tables,and 175 references in the paper. |
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