Study On Characteristics And Risk Discrimination Of Gas Explosion Induced By Coal Spontaneous Combustion In Goaf

Coal spontaneous combustion is an important ignition source for gas explosion in goaf.The flame shock wave generated by the explosion may also roll up the accumulated coal dust and cause gas/coal dust two-phase coupling explosion accident in addition to causing casualties and equipment damage.The secondary or even multiple explosions may occur due to the continuous emission of gas through the coal spontaneous combustion area.The secondary disaster caused by the uncertainty of its occurrence will expand the serious consequences of the primary explosion.Based on this,this dissertation independently develops an explosion equipment which is consistent with the similarity and unity between the gas and/or coal dust explosion process induced by coal spontaneous combustion in goaf and the environment considering the geometry,heat source and gas flow.The characteristics of primary and multiple gas and gas/coal dust explosion induced by coal spontaneous combustion in goaf and the propagation characteristics of combustion and explosion flame wave were studied systematically.The numerical model of the experimental equipment was established.The process of gas explosion induced by coal spontaneous combustion in goaf was simulated through the combination of experimental results and numerical simulation.The discriminant characteristic parameters of secondary explosion in goaf were obtained.Different ignition modes were used to detonate gas in the study of flame wave propagation characteristics of gas combustion and explosion.The propagation process of spherical flame wave and irregular flame wave caused by gas explosion induced by two ignition modes was recorded by high-speed camera.The flame wave image was processed by MATLAB to optimize the traditional calculation method and verify its correctness.The propagation velocity of irregular folded tensile flame wave generated by gas explosion induced by high-temperature surface was calculated based on image processing and fractal interpolation method.The propagation velocity of each point of flame wave front was obtained after two iterations.This dissertation reveals the propagation law of tensile flame of gas explosion triggered by high-temperature surface.The flame wave of gas explosion induced by high-temperature surface propagates in the form of fold turbulence.The large-scale vortex on the surface of irregular flame wave leads to additional turbulence,which promotes the key characteristic parameters of gas explosion.The flame propagation velocity of gas explosion induced by high-temperature surface is greater than that of electric spark.The characteristics of primary and multiple gas explosions induced by coal spontaneous combustion in goaf were studied.Two ignition modes,spontaneous combustion high-temperature surface and electric spark,were used to carry out experiments on different concentrations of gas.The explosion limit,explosion pressure(P),pressure rise rate(dP/dt),explosion temperature(T)and other key characteristic parameters after primary explosion and secondary explosion were obtained.The formation law of carbon oxygen compounds and hydrocarbon gases after primary explosion was obtained.Spontaneous combustion high-temperature surface is more difficult to detonate gas than electric spark.But once the gas is detonated,its explosion risk is higher than electric spark.The influencing factors of secondary explosion were studied based on the formation gas of primary explosion.The chemical kinetic micro mechanism of secondary explosion was revealed.The dangerous concentration of gas primary and secondary explosion induced by spontaneous combustion high-temperature surface is 11.5%,which is higher than 9.5%of electric spark due to the different ignition mechanism.The key characteristic parameters of gas explosion induced by high-temperature surface are higher than that of electric spark.The key characteristic parameters of explosion increase with the increase of high-temperature surface temperature.The risk of secondary explosion is less than that of primary explosion based on the explosion limit and key explosion parameters.But the harm caused by secondary disaster of secondary explosion can not be ignored.This is related to the gas generation after the primary explosion.The chemical kinetic mechanism affecting the secondary explosion limit and the key characteristic parameters is different in the two stages from the lower explosion limit to 11.5%and11.5%to the upper explosion limit.The main influencing reactions are R156 and R158.The spontaneous combustion high-temperature surface ignition mode was used to detonate the gas/coal dust mixture in the study of gas/coal dust two-phase coupling explosion.The process and mechanism of gas/coal dust explosion induced by coal spontaneous combustion in goaf were simulated.The characteristic parameters of gas/coal dust gas-solid two-phase explosion were obtained,and its risk was evaluated.The role of volatile matter of coal dust in homogeneous and heterogeneous reactions was revealed.The most dangerous explosion combination concentration of the selected gas/coal dust mixture is(9.5%,500g/m~3),(9.5%,400g/m~3),(8.5%,500g/m~3)under the condition that the high-temperature surface temperature is 1073K.The lower limit of gas explosion and the turning concentration of three key characteristic parameters(P,dP/d T,T)decreased from 11.5%to 9.5%,10.5%and 9.5%respectively due to the participation of coal dust.The peak values of three key explosion characteristic parameters increased by 0.8%,6.9%and 0.8%respectively.The greater the volatile content of coal dust,the greater the explosion characteristic parameters of gas/coal dust.Jiang model can predict the lower explosion limit of gas/coal dust induced by high-temperature surface.The numerical model was verified by the key characteristic parameters of gas explosion induced by spontaneous combustion high-temperature surface and the propagation velocity of combustion and explosion flame wave.The explosion characteristic parameters which are difficult to obtain by experiment were obtained through numerical simulation.The explosion characteristic parameters can be used to evaluate the risk of goaf.The established model can simulate the gas explosion and migration law induced by coal spontaneous combustion in goaf.The formation process of disasters was further revealed.The discriminant characteristic parameters for judging the occurrence conditions of secondary explosion of gas explosion induced by coal spontaneous combustion in goaf were obtained,which provides monitoring characteristics and discriminant methods for the risk early warning of secondary explosion in goaf.