Study On Spontaneous Combustion Characteristics Of Low Temperature Oxidation Of Coal Under Buried Depth In Jining Mining Area

In the process of deep coal seam formation,the coal quality changes under the influence of geological environment.The exposed coal body in the production process is affected by the temperature of plateau rock and the surrounding thermal storage conditions.The coal-oxygen composite ability is enhanced,and the risk of coal spontaneous combustion is enhanced.Aiming at the characteristics of spontaneous combustion of coal in deep high temperature thermal environment,based on the industrial analysis,correlation analysis and scanning electron microscopy analysis of coal samples with different buried depth in Jining mining area,the variation of functional groups of coal with different buried depth in Jining mining area and the changes of index gases and oxidation activity during low temperature oxidation were studied by infrared spectroscopy,thermogravimetric analysis and gas chromatography experiments.The characteristics of coal spontaneous combustion are further studied from macro and micro perspectives.Industrial analysis and correlation analysis show that the buried depth of coal samples in this area is significantly correlated with water content.With the increase of buried depth,water content decreases,and there is a significant negative correlation with fixed carbon.With the increase of buried depth,fixed carbon content increases,and volatile content is also closely related.Scanning electron microscopy(SEM)experiments show that with the increase of buried depth,the structure of coal is loose,the pore size is increased,the fracture is fully developed,the connectivity between pore and fracture is enhanced,the contact area of coal and oxygen is increased,and the physical oxygen adsorption capacity is enhanced.Infrared spectroscopy analysis shows that with the increase of buried depth,the content of aliphatic hydrocarbons such as CH3 and CH2 in coal decreases gradually,while C=C in aromatics is more likely to react with oxygen to produce C=O,which increases the activity of oxygen-containing functional groups such as C=O and-OH in coal samples and increases the oxidation activity of coal;with the increase of temperature,the activity of some oxidizable functional groups increases in the process of low-temperature oxidation of coal.Additionally,with the decrease of particle size under the influence of buried depth,the contact area of coal sample increases,CH3 and CH2 of naphthene or aliphatic group are easier to react,C=C consumes more,oxidation activity increases,and spontaneous combustion tendency increases.Gas chromatographic experiments show that coal produces CO,CO2,CH4,C2H6,C2H4,C2H2,and other gases in the process of low temperature oxidation,and increases exponentially after a certain temperature.Among them,CO is the most obvious.In the stage of slow oxidation at low temperature,CO and other index gases generate less.In the stage of accelerated oxidation,with the increase of temperature,the formation rate of CO in deep coal samples accelerates and the amount of CO increases.C2H2 gas is released from the coal sample at 200? but only in depth,which indicates that with the increase of buried depth,the tendency of spontaneous combustion of coal increases and the rate of spontaneous combustion of coal accelerates.The results of thermogravimetric analysis show that physical adsorption is the main factor in the initial stage.With the increase of temperature,physical adsorption reaches saturation,physical adsorption decreases,chemical adsorption increases,and chemical adsorption gradually occupies the dominant position.With the increase of burial depth and the decrease of particle size,the low-temperature oxidation of coal is promoted,the intensity of combustion increases,and the higher the temperature,the more obvious the law is.In the process of heating and oxidation of coal,there is a phenomenon of weight loss.Physical and chemical adsorption rates are different at different temperatures,and the factors of coal sample body also affect the cracking or depolymerization of alkyl side chains,oxygen functional groups and other small molecules around the dense ring aromatic system in the molecular structure of coal samples.With the decrease of particle size under the influence of burial depth,the activity of functional groups in coal increases and the ability to combine with oxygen increases,which is conducive to releasing accumulated heat and promoting the reaction.This rule has certain guiding significance for judging the tendency of spontaneous combustion of coal.