Study On The Effect Of Moisture On Reaction Process Of Coal Spontaneous Combustion Of Using Isotope Tracer Method

Coal spontaneous combustion seriously threatens mine safety production.As one of the important factors affecting the coal spontaneous combustion process,moisture affects the development direction and reaction process of coal spontaneous combustion.At present,people's cognition of the effect of moisture on coal spontaneous combustion is more focused on the physical mechanism of action.Some studies infer that moisture may play a chemical mechanism through catalysis or directly participating in the coal-oxygen reaction process.However,there is currently no exact mechanism.Experimental methods and conclusions support this hypothesis.In particular,how moisture acts on the spontaneous combustion process of coal from the atomic level and then participates in the coal-oxygen reaction process,and the key issues that affect the generation and release of index gases are still unclear.The isotope tracing technology,as a characterization technology of tracing the composition of atoms or molecules,can provide an effective method for studying the spontaneous combustion reaction of water on coal at the atomic level.This paper selects Shaping Changyan coal(SP)and Ximeng lignite(XM)coal samples with different degrees of metamorphism as the research object.Distilled water,²H₂O,and H₂¹⁸O three isotopic waters are used to prepare coal samples for various experiments.Measure the changes of CO and CO₂ concentration during coal spontaneous combustion through programmed temperature experiment,and study the influence of different forms of moisture on the formation of CO and CO₂during coal spontaneous combustion;use thermal analysis experiments to determine the quality changes of SP and XM raw coal and water-immersed coal samples during coal spontaneous combustion Study the influence of morphological moisture on coal mass changes at different stages of coal spontaneous combustion reaction;in-situ infrared oxidation experiment is used to determine various functional group components during coal spontaneous combustion reaction,and to study the influence of morphological moisture on the change of functional group components;through TG-MS Combined experiments are used to determine the ion current intensity of ²H atoms and ¹⁸O atoms in ²H₂O and H₂¹⁸O participating in the generation of various index gases,and to study the migration law and generation mechanism of hydrogen and oxygen atoms in the water generated by the index gases.The main conclusions are as follows:(1)Through the isotopic labeling of hydrogen and oxygen atoms in the water,the isotopic gases of CO₂,CO,H₂ and CH₄ were detected by the mass spectrometer in the airflow at different temperatures during the spontaneous combustion process of coal at 30?220?,which shows that the hydrogen in the water,The oxygen atoms are transferred to the hydrogen-containing gas and the oxygen-containing gas.(2)The mechanism of water participation in the spontaneous combustion process of coal is reflected in two aspects:macroscopically,it is reflected in the formation of a water film by combining with pores and cracks on the surface of the coal body,blocking the entry of external airflow to affect the physical adsorption of oxygen by the coal body,and SP Due to dehydration and chemical reactions,the mass reduction rate of XM and XM immersed coal samples is greater than that of raw coal.Microscopically,water combines with coal-oxygen-temperature to form hydrogen peroxide complexes.The reaction of hydroxyl radicals in the water with exposed active sites will generate carbonyl compounds,hydrogen peroxide complexes and carbonyl groups.The aldehyde compounds react in the direction of aldehydes and carboxylic acid compounds.The CO₂ and CO gas produced by the decomposition of carboxylic acid compounds are the main sources in the spontaneous combustion reaction of coal.Part of the aldehyde compounds will be converted into CO gas.Reacts with oxygen and water to produce carboxylic acid compounds that are easier to decompose.(3)The ways in which hydrogen atoms and oxygen atoms in water participate in coal oxidation reactions are different.Hydrogen atoms in water are mainly involved in the formation and transformation of aliphatic CH components and product water,and the methine and methylene groups will be transformed in the direction of the methyl group.The hydrogen in the water will interact with the methyl group in the process of OH-H cleavage.The radicals combine to generate methane.A part of the hydrogen atoms in the water is derived from hydroxyl radicals.The intensity of the hydroxyl radicals is consistent with H₂O.The aldehyde compounds generated by the combination of hydroxyl radicals will react with hydroxyl compounds to generate hydrogen.In addition,the hydroxyl radicals will generate hydrogen.Combining with the material in coal,it becomes a hydroxyl-containing compound and reacts with aldehyde compound to generate hydrogen.Oxygen atoms in water mainly participate in the formation of various carbonyl compounds,and the migration of oxygen atoms in CO₂ and CO gases is realized through various carbonyl compounds.Hydrogen radicals and hydroxide radicals in water participate in the production process of product water.(4)The overall level of water and oxygen atoms converted into CO₂ and CO gas through chemical reaction is relatively low.The CO and CO₂gas generated by external action water take up 0.46%?3.3%and 0.76%?5.5%of the total CO and CO₂ respectively.,The content of CO and CO₂ gas generated by the coal body's own water content is less than 0.6%;compared with the previous data,the hydrogen atoms in the water have a more obvious role,and the content of hydrogen atoms in the water to generate methane accounts for 9.56%?12.48 of the total content.%,the content of hydrogen atoms participating in the generation of hydrogen in the water accounts for 2.41%to 4.19%of the total content.The original stored moisture of coal is still lower than the externally acting moisture as a whole.The external moisture has an obvious effect at 70?100?,and the internal moisture at 110?150?Moisture participates in chemical reactions strongly.The hydrogen and oxygen atoms in the water have a certain effect on the formation of product water during the spontaneous combustion reaction of coal.At 50?150?,the hydrogen and oxygen atoms in the water jointly participate in the formation of structural water in the coal body.After 150?,the hydrogen atoms and the reaction of hydroxyl-containing compounds in coal is more obvious,and the source of product water is hydrogen atoms in the water.