| Coal spontaneous combustion in the mining area is one of the major disasters affecting mine safety production,which not only generates toxic and harmful gases,but also induces secondary disasters such as gas explosion,causing serious casualties and significant economic losses.Along with the rapid development of deep mining,coal spontaneous combustion disaster management is becoming more and more complicated,and the construction of an efficient early warning system is the key to prevent and control coal spontaneous combustion in mines.Gas and temperature are the two parameters carrying the most abundant information about coal spontaneous combustion,which can effectively reflect the state of coal spontaneous combustion in the mining area.However,at present,the distribution law of gas concentration in different areas of the working face is not clearly grasped,which largely weakens the field application effect of gas early warning indicators;limited by technology and engineering,the research on the distribution and evolution characteristics of the temperature field in the mining area is not sufficient,which hinders the understanding of the temperature field in the mining area.In order to supplement,improve and solve the above problems and meet the demand of coal spontaneous combustion early warning in the mining area,this paper carries out the research of coal spontaneous combustion early warning and response mechanism based on the combination of gas and temperature,and develops the coal spontaneous combustion remote monitoring and early warning system,and achieves the following research results.The statistical characteristics of gases in different areas of the working face were analyzed.Firstly,the multi-timescale evolution characteristics of CO and O2concentrations in the upper corner bag wall,outside the bag wall,in the high extraction tunnel and in the mining void area were studied using wavelet analysis,pointing out that CO and O2 have different periodicity in different timescales and their energy density is closely related to the gas change rate.The fluctuation equation of gas wavelet coefficients was fitted,and the highest correlation between the gas in the mining area and the information of coal spontaneous combustion was obtained based on the phase difference and initial amplitude,and the lowest correlation was obtained for the high extraction tunnel.Secondly,based on the kernel density of O2,the characteristic concentration of O2 was obtained and the"three zones"of coal spontaneous combustion in the mining area were subdivided into"first oxidation zone"and"second oxidation zone",which reflects the dynamic change of the mining area.Finally,a short time prediction model of gas was constructed by combining wavelet transform and ARIMA,and the results showed that the model has good accuracy.The mathematical model of the index gases and coal temperature was studied,and the statistical distribution characteristics of the characteristic temperature of the index gases of 88 sets of coal samples were summarized.The relationship between the index gases and coal temperature in the low-temperature oxidation stage of coal conforms to the logistic model,in which the logistic fitting parameters for CO are A1=23.4,A2=14990,p=12,and x0=294;the fitting parameters for C2H4 are A1=0.3,A2=27,p=17,and x0=283.The initial appearance temperature and the inflection point temperature divide the coal spontaneous combustion stage into fluctuation stage,steady growth stage and decay stage.According to the statistical laws,the average initial appearance temperatures of CO,C2H4 and C2H2 are 30°C,120°C and 278°C,the first inflection point temperatures of CO and C2H4 are 158°C and 204°C,and the second inflection point temperatures are 294°C and 283°C.The value of the fitted parameter p was positively correlated with the difficulty of coal low-temperature oxidation gas product generation.According to the mathematical model of CO concentration and coal temperature,the activation energies of the above three stages were obtained as 1.70k J/mol,83.67 k J/mol and 14.27 k J/mol,respectively.A coal spontaneous combustion gas warning index system was constructed.Firstly,it was pointed out that the initial appearance temperature ratios of C2H4 and CO were positively and strongly correlated with the coal spontaneous combustion propensity determination index,and the critical values of initial appearance temperature ratios for coal spontaneous combustion hazard determination were 4.23 and 5.45.There was a state pre-transformation preparation period in the process of coal spontaneous combustion gas release,and the initial oxidation stage had a longer pre-preparation period.Secondly,the coal spontaneous combustion hazard states were classified based on five characteristic temperatures:safe state,low risk,average risk,large risk,significant risk and mega risk state,including CO initial appearance temperature,C2H4initial appearance temperature,CO first inflection temperature,C2H4 first inflection temperature and C2H2 initial appearance temperature.The energy level leap between different states was plotted,and it was pointed out that the coal spontaneous combustion leap occurs only between adjacent states,and its leap energy level is high at both ends and low in the middle.Again,four groups of gas concentration ratios lg(?CO2/?CO)?1/2.1*?C2H6/?C2H4?1/16.2*?CH4/?C2H6and?C3H8/?C2H6 are combined into a set of composite warning indicators:the critical value of warning indicators is greater than1.6 for low risk,between 1 and 1.6 for general risk and low warning level,and less than1 for other risk states and high warning level.Finally,the response countermeasures for different risk levels based on foamed gel fire prevention and suppression technology are constructed.A small experimental bench was built to study the distribution and evolution of temperature field in porous media,and the morphology of temperature field,migration of heat core region and evolution of multi-thermal core region under different particle size,ventilation and wind speed conditions were studied.(1)Under the windless condition,the temperature curves at different points have different concavities,and the larger the distance from the heat source,the longer the temperature response time.(2)The intersection surface of different particle size systems has a significant effect on the transfer of heat flow:when the heat flow passes from small particle size to large particle size,the heat flow appears to contract at the intersection,and conversely,when the heat flow passes from large particle size to small particle size,the heat flow radiates at the intersection.(3)Under different wind speed conditions,the heat core zone has different migration rules.When there is no wind,the heat core zone migrates upward in the longitudinal direction,and the migration displacement of the heat core zone is the largest in the large particle size system,while the migration displacement in the small particle size and mixed II system is not obvious.When the wind speed becomes larger,the thermal core zone starts to migrate in the lateral direction,in which the migration displacement of the thermal core zone in the large particle size system is the largest,the potential thermal core zone appears in the small particle size,and the migration of the thermal core zone in the mixed particle size system is not obvious;in the process of the migration of the thermal core zone,new thermal core zones will be formed,and the new thermal core zones are distributed along the downwind side,and then the phenomenon of multiple thermal core zones coexist.(4)Heat flow extrusion occurs when heat is transferred between multiple thermal core areas,and the vicinity of the extrusion area is the main area for the formation of new thermal core areas,so that the formation of new thermal zones can be effectively prevented by forming a"cut-off"mechanism through the filling of fire prevention materials in the mined area and shortening heat carrying process of wind flow.A comprehensive online monitoring and intelligent early warning system for coal spontaneous combustion was developed.The system can directly read the collected gas and temperature data and automatically generate visual charts,and then provide early warning and grade classification for over-limited gas according to the preset indexes.The system has been applied in 402102 working face of Hujiahe Mine,which has improved the efficiency of coal spontaneous combustion prevention and control.The dissertation includes 173 figures,37 tables and 182 references. |
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