Study On Microstructure Evolution And Spontaneous Combustion Mechanism Of Coal Induced By Fault Tectonism

Coal spontaneous combustion or strong oxidation of coal seams often occurs in the fault-tectonic area during the coal mining,which seriously threatens the safety production of coal production.In this thesis,five pairs of primary and fault-tectonic coals with different degrees of metamorphism were studied,and simultaneous thermal analysis（TG-DSC）,infrared spectroscopy（FT-IR）experiments,X-ray diffraction（XRD）experiments,mercury-pressure experiments（MIP）,low-temperature（77K）adsorption experiments of N₂,and closed coal oxidation experiments,combined with the method of gray correlation analysis,the mechanism of coal spontaneous combustion characteristics differentiation induced by fault structures was revealed from both macro and micro perspectives.The spontaneous combustion tendency of coal was determined by the simultaneous thermal analysis（TG-DSC）experiment,and the exothermic characteristics of coal combustion were analyzed.The fault tectonism decreased the characteristic temperature of coal,and the percentage decrease of ignition activation energy of coal was 2.66%～16.56%,which increased the spontaneous combustion tendency of coal;the fault tectonism caused the decrease of heat absorption of coal during the heat absorption and evaporation stage,and the increase of exothermic intensity during the oxidation exothermic peak and combustion exothermic stage.The content of active functional groups and the characteristics of microcrystalline structure in coal were analyzed,and the oxidation activity of coal was compared through the infrared spectroscopy and X-ray diffraction experiments.The percentage decreased of-C=C-stretching vibration,-COOH-stretching vibration and-CH₂ content in the fault structure coals were 0.14%to 33.81%,1.62%to 41.07%and 1.52%to 30.18%,respectively;the fault structure promoted the shedding of fatty chains in coal,reduced the spacing of aromatic lamellae,increased the height of microcrystal stacking,increased the aromaticity of coal and decreased the oxidation activity of coal.The pore structure characteristics of the coal were analyzed and the pore complexity was calculated by the mercury-pressure experiments and the low-temperature N₂ adsorption experiments.The percentage increase of total pore volume of the fault structure coal was 1.51%to 90.10%,the percentage increase of specific surface area was 2.78%to 43.96%,the percentage increase of porosity was 1.43%to 19.59%,and the percentage increase of integrated fractal dimension of coal was 0.53%to 15.24%.The fault structure increased the contact area of the oxidation reaction between the coal and oxygen.The heat release characteristics of coal low-temperature oxidation were analyzed through the closed coal oxidation experiments.The percentage increase of oxygen consumption rate,CO release rate and CO₂ release rate of coal after the fault tectonism were 0 to 120.00%,6.07%to100.00%and 0 to 36.67%,respectively,and the percentage increase of oxidative heat release intensity of coal was 4.85%to 38.40%.Based on the gray correlation analysis,it was clear that the main factors affecting the spontaneous combustion of coal were the degree of coal metamorphism,the main internal influencing factor was the volatile fraction,the main external influencing factor was the temperature,and the evolution of coal pore structure was the main factor leading to the differences of spontaneous combustion differentiation of coal in fault structures;the fault tectonism changed the internal structure of coal and external environmental factors,induced the differentiation of coal spontaneous combustion characteristics and increased the risk of spontaneous combustion of coal.The dissertation has 66 figures,68 tables and 211 references.