Study On Disaster Mechanism Of Coal Spontaneous Combustion In The Goaf With Gas Environment

Coal spontaneous combustion disasters with the gas environment in the goaf is a typical disaster form in coal mines with high gas and easy spontaneous combustion.However,due to the difficulty in accurate detection and prediction of coal spontaneous combustion under the gas condition in goaf,in-depth study of the dynamic evolution law of coal spontaneous combustion and gas combined disasters in the goaf,and clarifying the determination method of the dangerous area of coal spontaneous combustion and gas combined disasters has become an important direction for the prevention and control of thermal dynamic disasters in the goaf.Restricted by complex conditions such as coal and rock falling in the goaf and multi-component gas symbiosis in goaf,it is very difficult to study the dynamic evolution law of dangerous area of coal spontaneous combustion and gas combined disasters in goaf.In this dissertation,based on the constructed mesoscale thermal simulation platform in goaf,the combination of theoretical analysis,similar physical test simulation and numerical simulation was used to systematically study the multi-field evolution law in the process of coal spontaneous combustion with gas environment,and a hazard assessment model for the combined disasters of coal spontaneous combustion and gas in the goaf is established.The innovative research results of the dissertation are as follows:(1)The development characteristics of the whole process of coal spontaneous combustion with the gas environment are obtained,and the influence mechanism of gas in different oxidation stages on the coal-oxygen compound reaction process is revealed.Based on the in-situ infrared spectroscopy test technology and the accumulation temperature program test system,the microchemical structure,the evolution law of spontaneous combustion temperature rises and gas production of coal under the condition of gas atmosphere were studied,and the coal spontaneous combustion process can be divided into low-temperature slow oxidation stage,rapid heating oxidation stage and stable exothermic spontaneous combustion stage.The influence of multi-gas environment in the goaf on the development of spontaneous combustion was revealed.The low-temperature oxidation stage is dominated by multi-gas physical adsorption and desorption competition.The chemical reaction and physical adsorption of coal surface active groups and oxygen is affected by gas in the form of reducing the ambient oxygen concentration.In the stage of rapid heating oxidation,O₂ is mainly converted to chemical adsorption process on the coal surface,and aliphatic side chain-CH₃/-CH₂-shows high reactivity with O₂,leading to a significant increase in the rate of coal-oxygen composite reaction.In the stable exothermic stage,the O₂ consumption intensity increases sharply and a large number of gas productions are generated.The oxidation of high temperature coal is affected by slow oxidation of CH₄ and O₂.Based on the generation law of index gas in different stages of coal spontaneous combustion,the the gas index of the whole process of coal spontaneous combustion in goaf is determined.(2)Based on the similar experiments,the multi-field evolution law in the process of coal spontaneous combustion with gas environment in goaf is obtained,and the occurrence conditions of combined disaster under the co-existence of coal spontaneous combustion and gas in the goaf are clarified.The mesoscale thermal simulation platform of goaf was developed.Based on this,the study found that there are two forms of reverse O₂ diffusion and forward air flow diffusion exist simultaneously in the process of coal spontaneous combustion.In the stages of low-temperature slow oxidation and rapid heating oxidation,the coal has low O₂ consumption intensity and low heat production.Part of the heat is transferred to the air return side of the goaf with the leakage air flow,and the development of coal spontaneous combustion spreads along the air flow.In the stable heat release stage,the coal has a high oxygen consumption intensity.Due to the limitation of O₂ supply in the goaf,high temperature area caused by the coal spontaneous combustion migrates to the oxygen-rich working face,and the development of coal spontaneous combustion is dominated by the reverse O₂ diffusion.Meanwhile,the influence law of coal spontaneous combustion on gas migration and accumulation in the goaf is obtained.When spontaneous combustion occurs on the air inlet side,the development process of coal spontaneous combustion and gas accumulation is significantly faster than that on the air return side.The possibility of gas explosion induced by coal spontaneous combustion near the air inlet and return corners due to oxygen enrichment and gas accumulation is discussed theoretically.(3)The gas-solid coupling heat transfer of multi-component gas model and disaster hazard assessment model in the coal spontaneous combustion process under the goaf condition are established,and the distribution law of the coal spontaneous combustion and gas combined disaster hazardous area in the goaf was obtained.Based on the parameters of physical similarity simulation experiment in goaf,the gas migration and gas-solid heat transfer mechanism in the coal spontaneous combustion process are analyzed.The gas-solid coupling heat transfer of multi-component gas model and disaster hazard assessment model in the coal spontaneous combustion process under the condition of coal and rock void structure are established,and the distribution law of the hazardous area of coal spontaneous combustion and gas combined disaster in the goaf is analyzed.The influences of air leakage intensity,gas emission source,and spontaneous combustion location on the hazardous area distribution are studied.It is found that ventilation conditions and the void ratio of coal and rock mass jointly determine the evolution direction of dangerous areas.Increased air leakage intensity significantly increases the hazard degree of coal spontaneous combustion and gas combined disaster areas.The research results provide a reference for revealing the coupling disaster mechanism of gas explosion induced by coal spontaneous combustion in the goaf,and provide a guidance for prevention and control of combined thermal dynamic disaster in the goaf.There are 104 figures,9 tables and 181 references in this dissertation.