Study On Gas (Coal Dust) Secondary Explosion Characteristics And Reaction Kinetic Mechanisms

Gas（coal dust）explosion is one of the most serious mine disaster accidents,and the secondary explosion may occur during the disaster relief process,causing the accident to expand.It is extremely important to study secondary explosion conditions,characteristics and mechanisms for preventing secondary explosion disaster accident.Most of the existing studies believe that the cause of the secondary explosion is the re-accumulation of gas to reach the explosion limit,but the fuel-rich conditions of gas（coal dust）explosion produced a lot of flammable gases such as carbon monoxide and hydrogen,and there is lack of research for the explosiblity of the post-explosion gas.At present,the awareness of secondary explosion danger in mines is inadequate.Therefore,laboratory experiments,theoretical analysis and numerical simulation were used to study the composition and generation mechanism of gas（coal dust）post-explosion gas,the explosibility of gas（coal dust）post-explosion gas and its influence law on gas secondary explosion and the reaction kinetic mechanism of gas（coal dust）secondary explosion.The research work and main findings are as follows.The experiments of gas explosion and gas coal dust mixture explosion were carried out,and the gas composition and generation mechanism after the gas（coal dust）explosion were studied.The results show that gas（coal dust）post-explosion gas mainly contains residual oxygen,inert gases such as nitrogen and carbon dioxide,and flammable gases such as produced carbon monoxide,hydrogen and residual methane under fuel-rich conditions.During the gas explosion reaction,the generation of carbon monoxide is mainly associated with HCO,the combination of carbon monoxide with OH and HO₂ radicals,and oxygen with CH₂ is the main way of generating carbon dioxide,the generation of hydrogen is mainly associated with H radicals,and the generation of water is mainly associated with OH radicals.When coal dust is involved in the explosion,reactions of functional groups such as-OH,-CH₂,-CH₃,C=C,Si-O and Ar-C-O of coal dust,the oxidation and gasification reactions of fixed carbon are important factors affecting the post-explosion gas composition characteristics.Secondary explosion experimental research was conducted after gas（coal dust）explosion followed by the introduction of air and ignition.It is found that if the primary explosion fuel-rich state to a certain extent,the post-explosion gas is explosive,and secondary explosion phenomenon occurs when ignited after mixed with the right amount of air.The gas concentration,coal dust mass concentration and deterioration degree in the primary explosion are important factors affecting whether the post-explosion gas is explosive or not.Secondary explosion conditions were studied and the results show that the lower explosion limit of post-explosion gas changes more with the primary explosion gas and coal dust conditions,while the upper explosion limit changes less.The amount of air required for the second explosion can be as low as about 26%.The study of the characteristic law of the secondary explosion of post-explosion gas shows that secondary explosion overpressure peak(P_ex)and pressure rise rate peak(（d P/dt）_ex)first rise and then fall with the increasing volume fraction of mixed air after explosion,but the secondary explosion intensity are lower than the primary explosion.There is a correlation between the primary and secondary explosion parameters.The maximum explosion pressure(P_max)and maximum pressure rise rate(（d P/dt）_max)of the secondary explosion are positively correlated with the gas concentration and coal dust mass concentration of the primary explosion and negatively correlated with the degree of coal dust deterioration.The optimum volume fraction of air required for the secondary explosion is negatively correlated with P_ex and（d P/dt）_ex of the primary explosion.Effects of explosive post-explosion gas on the law of gas secondary explosion were experimentally studied.The results show that explosive post-explosion gas significantly reduces the lower explosion limit of the gas secondary explosion and the minimum amount of air required for the explosion,increasing the risk of secondary explosion.With the increasing concentration of mixed methane after primary explosion,the secondary explosion P_ex and（d P/dt）_ex firstly increase and then decrease.The higher the optimal concentration of mixed methane after primary explosion is,the greater the secondary explosion P_max and（d P/dt）_maxreaches.The destructiveness of gas（coal dust）secondary explosions were analyzed based on the overpressure criterion,and results show that secondary explosions can still cause severe levels of damage.Three possible scenarios for secondary explosions in mines were analyzed and presented:gas explosion,post-explosion gas air mixture explosion and post-explosion gas air mixture explosion.Flammable gases from different sources and the different negative pressure effect after the explosion are the possible causes of the secondary explosion time interval irregularities.Reaction process of the gas（coal dust）secondary explosion was simulated and studed using CHEMKIN software.Key primitive reaction steps affecting the secondary explosion were determine,and the kinetic mechanism of the secondary explosion reaction was revealed.The results show that explosive post-explosion gas,mixed air and gas concentration after the explosion significantly affected the time of pressure and temperature began to rapidly rise during the gas（coal dust）secondary explosion reaction process.When mixed with explosive post-explosion gas,the secondary explosion ignition delay time is shorted with the increasing air amount,and extend with the increasing mixed methane concentration.Due to gas（coal dust）post-explosion gas,mixed methane and mixed air after primary explosion in different proportions,the secondary explosion process of H,O and OH radicals began to generate in different time.Molar fraction of H,O and OH radicals rapidly rises in the early reaction stage,and molar fraction of H and O radicals rapidly destructed in the late reaction stage.When causes of secondary explosion change from gas（coal dust）post-explosion gas to mixed methane,the most critical primitive reaction step to inhibit the secondary explosion reaction changes from CH₄+H=CH₃+H₂ to 2CH₃+M=C₂H₆（+M）.However,in both cases,the most critical primitive reaction step that contributes to the gas（coal dust）secondary explosion reaction is the chain branching reaction H+O₂=O+OH.The results provide a new understanding of the phenomenon and mechanism of secondary explosion in mines.It is of great theoretical and practical significance to the emergency rescue of gas（coal dust）explosion accidents in mines,as well as the prevention and control of secondary explosion accidents.There are 112 figures,17 tables and 171 references in this dissertation.