Study On The Reaction Characteristics Of Coal Surface Active Molecular Structure In The Heating Process Of Aerobic And Anaerobic Atmosphere

Coal spontaneous combustion is a complex physicochemical process,and the physical changes and chemical reactions involved in its non-linear self-acceleration process vary at different temperature stages,while the active molecular structure of the coal body undergoes thermal decomposition reactions due to heat accumulation during the oxidation process of coal spontaneous combustion,and the differences in the microstructure of coal samples lead to the complexity of its oxidation and pyrolysis behaviour at different temperature stages.Based on the oxidation and pyrolysis mechanisms in the process of coal spontaneous combustion,this thesis investigates the macroscopic gas and heat production characteristics,microscopic radical properties and functional group evolution of the oxidation and pyrolysis behaviour of the reactive molecular structure of coal samples during the warming process in aerobic(air)and anaerobic(nitrogen)atmospheres,using theoretical analysis and experimental tests.The main findings are as follows:Based on the TG-DTG curves,the characteristic temperature stages of the spontaneous combustion process of coal samples with different degrees of metamorphism were determined.The characteristic temperature points of the coal samples increased with the degree of metamorphism,and the temperature points of the heat loss curves and the maximum heat loss rate during the warming process of oxidation and pyrolysis were shifted towards the high temperature point as the degree of coalification increased,the heat loss ratio and the maximum heat loss rate at the end temperature of the oxidation reaction of the coal samples were significantly larger than those of the pyrolysis process.The results of the integration of the DSC curves by stages show that the evaporation and heat absorption of water in the evaporation and desorption stages of the oxidation process of XLT lignite and ZC bituminous coal play a dominant role,while the oxidation and pyrolysis processes of YQ anthracite show exothermic reactions in all stages.The oxidation of reactive groups is the main source of heat release in the process.The relationship between the oxygen consumption and oxygen consumption rate of different coal samples was generally XLT lignite>ZC bituminous coal>YQ anthracite.The initial temperatures of the different gases produced by the coal samples during the aerobic and anaerobic warming processes were the same,but the concentration of the gases produced by the anaerobic pyrolysis process was much smaller than that of the oxidation process,indicating that the intermediate products of the coal-oxygen complex reaction would promote the production of hydrocarbon gases.Based on electron paramagnetic resonance spectroscopy experiments,it was found that the participation of oxygen enhanced the free radical chain reaction.The changes in free radical parameters during aerobic and anaerobic warming were generally consistent for different coal grades,but the changes in pyrolysis reactions were smaller.The line width ΔH of XLT lignite is positively correlated with temperature,the line width ΔH of ZC bituminous coal and YQ anthracite is negatively correlated with temperature.The range of variation of g values for the coal samples under anaerobic conditions was smaller than that of the aerobic environment,and the oxidation reaction produced a large number of secondary free radicals.The maximum growth rate of free radical concentration during oxidation:XLT lignite 710.42%>ZC bituminous coal 285.54%YQ anthracite>146.98%,and the maximum growth rate of free radical concentration during pyrolysis:XLT lignite 1230.59%>ZC bituminous coal 242.48%>YQ anthracite 168.8%.Based on in situ FTIR experiments,it was found that the hydroxyl-OH content decreased continuously with increasing temperature during aerobic and anaerobic warming,the C-O structures of XLT lignite and ZC bituminous coal mainly acted as generators in the early stage of oxidation,and the C-O structures of higher-order coal samples mainly acted as reactants during pyrolysis.The carbonyl C=O structures increased rapidly in the early stage of oxidation and pyrolysis,and the ZC bituminous coal and YQ anthracite increased in the oxidative pyrolysis the rate of C=O production accelerates during the oxidation stage.The-COOH structure of XLT lignite decreases again at 400℃.The aromatic hydrocarbon structure of the coal samples decreases continuously during oxidation and pyrolysis.The changes in aliphatic hydrocarbon content during pyrolysis of coal samples of different coal grades generally tended to be in an aerobic environment,with lower-grade coal aliphatic groups having stronger reactivity with increasing temperature.This thesis investigates the macroscopic characteristics and microscopic properties of the warming process of coal reactive molecular structures in aerobic and anaerobic atmospheres,and obtains the differences in gas production characteristics,radical phasing characteristics and functional group evolution patterns during coal oxidation and pyrolysis,which are important for understanding the reaction mechanisms of the oxidation and pyrolysis mechanisms in the process of coal spontaneous combustion.The thesis has 53 figures,8 tables and 106 references.