Research On Prevention And Control Of Spontaneous Combustion Of Gob In Goaf Of Zhengwang Coal Fully Mechanized Caving Face

With the popularization of fully mechanized top coal caving technology in coal mine production in recent years,the mining height and output of the working face have increased,but at the same time the amount of residual coal left in the goaf has also increased,and the cracks in the rock formation have further expanded and become toxic and harmful.With the massive outflow of gas,there is a high probability of spontaneous combustion during the mining process.In particular,the mining of close coal seams is different from the mining of ordinary coal seams.Due to the small distance between the coal seams,the overlying strata are affected by repeated mining.The damage to the rock strata is relatively high and there are many fissures.The influence of the negative pressure of mine ventilation has led to a large influx of air leakage in the goaf,which has caused great difficulties for the safe mining of fully mechanized caving face and fire prevention and extinguishing work in the goaf.There is a large old goaf near the 11103 working face of Zhengwang Coal Industry.The leftover coal in the hidden old goaf accelerates oxidation and spontaneous combustion under the action of air leakage and air flow,which leads to the CO content in the upper corners of the working face and the combined roadway.Exceeding the limit seriously affects the safe mining of the fully mechanized caving face.Based on the analysis of the spontaneous combustion mechanism of the coal left in the goaf and the actual problems in the working face,the law of spontaneous combustion in the goaf is now studied through theoretical analysis,numerical simulation and the beam tube monitoring system,and the air leakage and work in the goaf are comprehensively considered.Based on indicators such as CO content in the upper corners of the surface,a comprehensive fire-fighting technical plan for pressure equalization and inert gas fire-fighting technology+pressure-equalizing and inert gas coupling research is proposed.The main research contents of the thesis are as follows:(1)Establish a model based on the rock mechanics characteristics of the 11103 working face of Zhengwang Coal Industry,and use FLAC^3Dsimulation software to analyze the failure characteristics and stress distribution of the adjacent mined-out areas at a short distance.First,analyze the damage of the coal pillar roof and floor after the mining of the overlying 9^#coal seam to determine the degree and scope of the rock layer damage.Then analyze the overburden failure characteristics of the lower 10+11^#coal seam under continuous mining,and determine the distribution range of the"three vertical zones"in the goaf and related simulation parameters to provide a basis for subsequent research.(2)Using Fluent software to simulate the flow field distribution and the change of each gas concentration in the adjacent goaf before and after the implementation of pressure equalization ventilation technology in the fully mechanized caving face,and analyze the relationship between the air leakage pressure difference and the air leakage in the goaf.Furthermore,the flow field distribution and the three-zone changes in the goaf under different air supply rates of the working face under equal pressure ventilation are analyzed to determine the optimal ventilation volume and daily advancing distance of the fully mechanized caving face under equal pressure ventilation.The analysis shows that:the pressure equalization simulation has effectively solved the problem of over-limit CO at the upper corner of the working face,and the air leakage and the intensity of the air leakage in the goaf are significantly reduced,and the air leakage pressure difference in the goaf is about 15Pa.When the air supply of the working face is 700m³/min,the spontaneous combustion area in the goaf is the smallest,but the problem of spontaneous combustion of coal in the goaf still poses a great threat,and further fire-fighting measures are required in the goaf.(3)When implementing inert gas fire prevention technology in the goaf,in order to achieve the best prevention effect,Fluent software is used to simulate the prevention and control effect of the working face stope(including the goaf)at different gas injection positions and different gas injection rates.Quantitative results are given,and then the coupling study of equalizing pressure fire prevention and inert gas fire prevention is carried out to provide a basis for the prevention and control of spontaneous combustion of coal remaining in the goaf of the working face.The analysis shows that:adding a percentage of liquid CO₂to N₂can better improve the fire prevention and extinguishing effect of the goaf.When the gas injection ratio of N₂to CO₂is 3:1,the dangerous area of the goaf is the smallest.Compare the fire prevention and extinguishing effects of the goaf under different gas injection positions and gas injection rates in the area to determine the best gas injection parameters for the goaf.When pressure equalization and inert gas fire suppression are combined,the gas injection volume in the goaf can be reduced to 7.5m3/h,which greatly reduces the cost of fire fighting.(4)Research on pressure equalization parameters of 11103 fully mechanized caving face.Calculate and verify the minimum required air volume at the working face and the minimum air pressure of the equalizing fan to determine the control range and model of the equalizing fan.Furthermore,the wind window area is optimized and adjusted by the working face wind measurement method to ensure the stability of the pressure equalization system.Under the real-time monitoring of the on-site beam tube monitoring system,real-time monitoring and analysis of various index gases after pressure equalization ventilation on the working face and inert gas injection in the goaf are carried out.The results show that:pressure equalization ventilation has effectively treated the problem of over-limit CO in the upper corner of the working face.After the inert gas is injected,the gas concentration monitoring results in the goaf and working face meet the safety production standards,ensuring the safe mining of the working face.