Study On Risk Identification And Early Warning Of Coal Spontaneous Combustion In Goaf Based On Multi-field Coupling

In recent years,the phenomenon of Coal Spontaneous Combustion（CSC）in goaf becomes more and more common,and spontaneous combustion of coal in goaf leads to gas explosion and other major events,which seriously threatens the safety production of coal mine,CSC in goaf is the early disaster of coupling disaster of gas and CSC,and also one of the necessary conditions for later disaster and the top priority of disaster prevention and control,effective measures must be taken to early identify the disaster risk of CSC in goaf and prevent accidents in advance to prevent accidents in the bud,before the disaster,but CSC in goaf is the result of multi factor and multi field coupling evolution of complex system,Accurate identification and accurate warning are difficult.Therefore,In this paper,the method of theoretical analysis,experimental research,numerical simulation,intelligent calculation and system development are combined adoption,a similar simulation experimental platform is built to study the gas migration law affected by goaf gas concentration,oxygen concentration,air leakage intensity and coal surrounding rock temperature.The multi field coupling model of gas solid oxidation heat of coal in goaf is established,the mutual influence,dynamic change and correlation characteristics of inducing factors in CSC are analyzed,and the spatio-temporal coupling mechanism of inducing variables in the evolution process of CSC is revealed;Based on the multi-field coupling mechanism and risk identification index of CSC,the risk prediction model under the influence of multiple factors of CSC is established,and the prediction system of dynamic identification and advance warning of CSC is constructed.The conclusions are as follows:1)According to the research needs,Tiejishan Coal mine is selected as the research object.Through experimental research,field test and statistical analysis,it is determined that CO is the symbol gas of coal spontaneous combustion in goaf of 4427 working face of Tiejishan Coal Mine,The critical value of carbon monoxide concentration in goaf is 140ppm,and the critical value of carbon monoxide concentration in return air corner is 12ppm,the carbon monoxide concentration at the corner of return air is taken as a index to judge the spontaneous combustion state of abandoned coal in goaf.The main influencing factors of coal spontaneous combustion in goaf of 4427 face are coal body temperature,coal and rock porosity,gas concentration,oxygen concentration and air leakage speed.2)Based on the similarity analysis,a similar model test bench was built according to1:50 to test and analyze the law of gas migration in the goaf of 4427 working face.In the goaf,under the normal temperature environment and the high temperature heating environment of the heating source,simulate and test the gas concentration of each measuring point at different air inlet speeds in the air inlet roadway.When the heating source in the goaf is heated at high temperature,the CH₄concentration is basically the same as that in the normal temperature environment,but the gas concentration near the heat source is higher than that in the normal temperature environment.The wind speed of air inlet roadway has a great influence on the distribution law of gas concentration in goaf.The greater the wind speed is,the more significant the influence is.As 1.1m/s air leakage wind speed,the gas accumulates near the heating source in the first layer,and the contour mutation of local area is formed here,that is,the concentration of gas is about 5%.The closer the boundary line of high concentration gas is to the working face,the larger concentration gas（the greater the dangerous area of gas explosion）.With the increase of leakage wind speed,the farther the high gas concentration zone is from the working face,that is,the area of high concentration gas gradually becomes smaller.3)Based on the goaf gas migration law simulation test device,the goaf coal spontaneous combustion multi-field coupling physical model is established,which is the same as the test system.Under different conditions gas concentration in goaf is numerically analyzed for the temporal and spatial variation law,and compared with the test data to determine the reliability of the physical model.At a certain distance from the air inlet roadway,the relative error of gas concentration is greater near the working face.With the increase of the height and length of the goaf,the gas concentration also increases.Above the high temperature point,different ranges of gas accumulation areas appear.Compared with the gas concentration in the same plane with the same air leakage speed and height from the bottom at normal temperature,the gas concentration at high temperature is larger4)The gas-solid-thermal-oxidation multifield coupling orthogonal numerical simulation of coal spontaneous combustion in goaf was carried out by constructing 3125 different working conditions including gas concentration,oxygen（concentration）mass fraction,air leakage speed,high temperature point temperature and porosity of goaf,and the change rule of CO concentration at the corner of goaf return air was obtained.CO concentration near the working face along the longitudinal direction of the goaf is low,while in the middle of the goaf it is significantly higher,and the CO concentration in the deep part of the goaf appears a vortex distribution.When the gas concentration,oxygen concentration,air flow velocity and high temperature point temperature are fixed,the change of CO concentration at the return air corner increases with the increase of porosity.Methane concentration,high temperature point temperature and porosity have a great influence on the CO concentration at the corner of the return air roadway,while oxygen concentration and air flow velocity have little influence.5)The model of CSC is established based on the comparison of coal porosity and CO concentration,and the calculation model of CSC rate is established based on the calculation of CSC temperature and CO concentration in goaf.The correlation between velocity and CO concentration is the smallest,and the correlation between CH4 concentration and CO concentration is the highest.Velocity,temperature,O2 concentration and porosity were negatively correlated with CO concentration,while CH4 was positively correlated with CO concentration.For the prediction of CSC,cs-rf algorithm is more accurate than RF and ANN algorithm;At the same time,through the comparison of iterative processes under different CS parameters,it can be seen that PA and n parameters only affect the calculation efficiency,but do not affect the prediction accuracy.The calculation results further illustrate the superiority of this algorithm.6)The time series prediction model of CSC based on Grey Markov algorithm is established,and the relevant early warning system is compiled.After Markov modification,the grey prediction model can accurately predict the CO concentration in the future;The CSC early warning system based on the algorithm proposed in this paper can conveniently and quickly realize the storage and retrieval of on-site monitoring data,the calculation and prediction of CO concentration,and give the early warning level,which is of great significance to resolve risks in advance and ensure safe production.