Investigation On The Mechanism And Genetic Model Of Coal Spontaneous Combustion

The geology,structural geology,coalfield geology,petrology,mineralogy,geochemistry and coal chemistry are used to study the mechanism and genetic model of coal spontaneous combustion,which are discussed from the perspective of microscopic mechanism and macroscopic model.The following results:(1)Predecessors have made a lot of discussions on the distribution law of coal burning in mainland China and the evolution of coal burning quantity with the age.Through the systematic and comprehensive determination and research on the spontaneous combustion of coal in different years and the evolution process of coal combustion,it is concluded that the spontaneous combustion coal fire is mainly distributed in the north and south sides of the Tianshan-Yinshan belt in North China and Northwest China.Guizhou and other places in South China have only found limited coal fire areas.The Carboniferous-Permian spontaneous combustion coal fire in North China is basically the ground coal fire caused by coal fire after underground mining.In terms of times,the Jurassic coal in the new geochronology produced more coal spontaneous combustion zones than the Carboniferous-Permian coal distribution zone produced in the older geochronology,and the Carboniferous-Permian spontaneous combustion coal fire zone was mainly caused by underground mining.Combing and clarify the combing and clarification of the burning area of coal spontaneous combustion in China is 2998.4×104 m2,and the loss of resources is 4146.94x 104t.According to the statistics of coal fire burning area,full consideration is given to the conditions of coal rank and thickness of coal seams.The emission of coal spontaneous combustion CO2 from coal in China is calculated to be 8728.28×104t.(2)The influence of the content of the maceral composition on coal spontaneous combustion has been the main problem discussed by many scholars.Therefore,two inertinite-rich lignites of Xinjiang were selected,and their structures were analyzed from the physical and chemical point of view.The microscopic pore structure characteristics of coal were revealed by low temperature liquid nitrogen and CO2 gas adsorption experiments;X-ray diffraction(by X-ray diffraction(XRD)characterizes the structural characteristics of coal microcrystals;characterizes chemical structure was characterized by solid-state nuclear magnetic resonance(13C NMR);laser desorption ionization time-of-flight mass spectrometry(LDIMS)was used to determine the molecular mass of coal;high-resolution transmission electron microscopy(HRTEM)was used to obtain lattice fringes information,including length,angle,directionality,stacking and curvature information,provides an omnidirectional analysis of the structural characteristics of the inertinite-rich coals.Subsequently,the physical and chemical structural characteristics of the coal were linked with the coal spontaneous combustion propensity index.The characteristics of the pore structure show that the two samples with inertinite-rich have similar changes in the microporous structure.However,the pores measured by the liquid nitrogen experiment showed that the pore volume and specific surface area of SEH were larger than the pore volume and specific surface area of PLQ,while the pore structure obtained by CO2 found that the pores of PLQ sample were higher than those of SEH.The higher micropore volume corresponds to the lower cross point temperature,indicating that the micropore volume plays an important role in promoting coal spontaneous combustion,that is,the higher the proportion of micropore volume,the lower the self-ignition tendency.By comparing the characteristics of the microcrystalline structure parameters of the same coal rank,it is found that the inertinite usually has a higher degree of structural order and lower lattice spacing than the vitrinite/huminite group(the brown coal is called the huminite).Therefore,it is considered that the inertinite-rich coal is more stable than the vitrinite/huminite-rich coal,and is less prone to spontaneous combustion.It was found by 13C NMR that the two samples had similar aromatic structural characteristics.From the comparison of chemical structure,it is found that the two samples with different content of inertinite have little difference in molecular weight distribution,stacking and curvature,but there are some differences in the yield of volatile matter,the orientation of crystallites and the orientation of lattice fringes..Therefore,it is concluded that the microporous structure is quite different in thet inertinite-rich coal,which is the main reason for the difference in coal spontaneous combustion tendency between the two samples.(3)The relationship between coal rank and cross-point temperature(CPT)can be found to have a good linear relationship between coal rank and cross-point temperature.As the coal rank increases,the cross-point temperature increases,and the self-ignition tendency of the coal is higher.The vitrinite reflectance of the sample of 2.13%is an important turning point in pore volume change.When the reflectance is less than 2.13%,average pore volume of coal increases with the increasing coal rank.After that,the average pore volume of coal begins to decrease with the increase of coal rank,and the average specific surface area changes with the pore volume.The influence of coal rank on multi-fractal parameters is relatively obvious,indicating that the more uniform the pore distribution with the increase of coal rank,the less obvious the agglomeration phenomenon of pores,and the more complicated the pore structure.The ash and total sulfur content of coal and CPT show an inverted "U" shape nonlinear relationship curve,while the volatile matter,oxygen content,and fixed carbon content of coal have a good correlation with CPT value.The ash,volatile matter and fixed carbon of coal quality have a good linear or nonlinear relationship with the fractal dimension calculated by Sierpinski and Menger model and the fractal parameters of multifractal calculation.The total pore volume has a good linear positive correlation with CPT.There is a linear or nonlinear relationship between the cumulative pore volume of V2 and V3 and CPT,indicating that the pore size above 100 nm is one of the main causes of coal spontaneous combustion.(4)XRD was used to analyze the microcrystalline structure of the Early Jurassic and Shanxi Carboniferous Permian coals in Xinjiang,and the index of coal spontaneous combustion tendency obtained by CPT experiment.It was found that d002 decreased with the increase of coal rank,coal rank and layer spacing(d002)is one of the main factors affecting coal spontaneous combustion.With the increase of coal rank,the oxygen consumption is lagging.The oxygen consumption of the Jurassic coal samples is stronger than that of the Carboniferous coal samples.As the coal rank increases,the C=O structure in the coal gradually decreases and the aromatic structure increases.The values of structural parameters I and f increased with the deepening of coalification degree,indicating that with the increase of coal rank,the substitution of aromatic structure and the degree of condensing increased,and the aromaticity increased.For low rank coals,phenolic hydroxyl groups and alcoholic hydroxyl groups account for a large proportion,while high-order coals account for a large proportion of aromatic hydroxyl groups and alcoholic hydroxyl groups.Temperature has a significant effect on the aromatic structure of low rank coal and relatively little on high rank coal.The effect of temperature on the hydroxyl group is very obvious in low rank coal,and the peak area of low rank coal gradually decreases with increasing temperature.The total peak area of the hydroxyl groups of the high rank coal fluctuates with increasing temperature.At 120 or 140℃ it is an important node for changes in fat(methyl and methylene),functional groups and hydroxyl groups.(5)Using theoretical knowledge such as structural geology and coalfield geology,it summarizes and summarizes the research results of predecessors on Xinjiang’s geological conditions,and finds that geological tectonic movements,especially the Himalayan period,not only provide heat to contribute to the formation of higher rank coals.The buried deep coal seam will be lifted to the near surface and even some coal seams exposed and the surface,which provides good conditions for the contact of coal and oxygen,which is beneficial to the low temperature oxidation of coal.Through the analysis of the climatic conditions in Xinjiang,including rainfall,sunshine,vegetation,surface temperature and other conditions,it is found that the climatic conditions of drought,lack of sunshine,sufficient sunshine and sparse vegetation provide good thermal storage conditions for Xinjiang coal spontaneous combustion and contribute to low temperature oxidation.The article selects the factors affecting coal spontaneous combustion discussed above,namely the influencing factors of micro-physical properties,namely coal rank,microscopic composition,pore structure,microcrystalline structure,chemical structure;macroscopic characteristics,ie climatic conditions,geological conditions,deterioration Angles such as action and mining effect are used as factors to evaluate the natural influence of coal.The main causes of spontaneous combustion of coal are analyzed quantitatively by analytic hierarchy process(AHP).It is found that coal rank and climatic conditions are the main reasons leading to large-scale spontaneous combustion in Xinjiang,and coal rank and mining effect were the main causes of coal spontaneous combustion in Shanxi.