Study On Adsorption And Spontaneous Combustion Characteristics Of Water-immersed Air-dried Coal In Methane Atmosphere

The soaked and air-dried coal body in the goaf is subjected to different levels of multi-component mixed gas dynamic competitive adsorption and desorption processes on the inner and outer surfaces of the coal body.The pore structure of the coal body,the types and quantities of the contained material components have varying degrees of change.This has a great impact on the coal body spontaneous combustion oxidation process.In particular,air-dried coal bodies with different immersion time have different effects on the opening and expansion of pores,which affects the adhesion and competitive adsorption of gas on the surface of the coal body.In this paper,raw coal that has not been immersed and one month,three months,or five months of soaked and air-dried coal samples are selected.Based on the high-temperature and high-pressure gas adsorption platform and the normal temperature and pressure adsorption instrument,the adsorption law of methane,oxygen,nitrogen,and mixed gas is studied Based on the simulation experiment platform of coal spontaneous oxidation under different methane oxidation atmospheres,ESR and FTIR were used to analyze the changes of free radical concentration,aliphatic hydrocarbons,aromatic hydrocarbons and oxygen-containing functional groups during spontaneous combustion oxidation under different methane oxidation atmospheres.The following main conclusions are obtained:With the increase of immersion time,the adsorption capacity of air-dried coal soaked in water to methane,oxygen,nitrogen and mixed gas increases gradually.At the same time,it is found that the effect of immersion time on methane adsorption is greater than that of oxygen and nitrogen.The adsorption capacity of the mixed gas with different methane concentration increases with the increase of the methane concentration in the mixed gas.It is inferred that because the competitive adsorption of methane and oxygen/nitrogen has more advantages,the higher the concentration of methane is,the more the amount of adsorbed mixed gas is.The g factor value of water-immersed air-dried coal increases gradually with the increase of oxidation temperature.The g factor values of the three kinds of long air-dried coal all change steadily at the methane concentration of 0%-15%,and increase rapidly at 15%of the 35%methane concentration.However,after the methane concentration reaches 35%,the change of the g factor value remains slow.The increasing rate of g factor with methane concentration at 40?,130?and 220?is higher than that of water-soaked air-dried coal in five months.The free radical concentration of soaked and air-dried coal in one month shows phased characteristics with the change of methane concentration:the methane concentration is less than 35%,the free radical concentration decreases rapidly with the increase of methane concentration,and the decreasing range increases with the increase of oxidation temperature.when the methane concentration is higher than 35%,the decreasing trend of free radical concentration slows down,and the change of free radical concentration shows that methane has a certain effect on the formation of free radicals.For three-month and five-month soaked air-dried coal,the critical methane concentration point is earlier than 35%in one month,and almost 25%in five months.For a month of immersion in air-dried coal,with the increase of methane concentration,the initial reduction stage of-CH₂-,-CH₃ gradually weakens until disappears.The aliphatic hydrocarbons immersed in water for three months and air-dried coal have similar changes to the aliphatic hydrocarbons for one month.The five-month soaked air-dried coal starts at 25%,and the percentage of aliphatic hydrocarbons starts to rise from the beginning of oxidation.Under one month of immersion in air-dried coal,the area percentage of aromatic hydrocarbon-CH peaks gradually decreased with the increase of oxidation temperature under different methane atmospheres,but the rate of decline gradually slowed down with the increase of methane concentration.Observe that the three-month and five-month immersed air-dried coals have a similar pattern to the one-month immersed air-dried coals,and the three long-term immersed coals have maintained a downward trend.-OH decreases rapidly after it begins to oxidize,and as methane concentration increases,the decrease in-OH decreases.Comparing the decline rates of these three types of immersed air-dried coal at 40?-85?and 85?-130?,the decline rate of-OH in the initial oxidation of one-month immersed air-dried coal is significantly greater than three and five months.When oxidizing in dry air,the-CO content remains basically unchanged before 120?,and the oxidation temperature begins to increase rapidly after 120?.With the increase of methane concentration,the rapid increase of-CO content is greatly advanced,which can be explained by The formation of-CO functional group has a certain relationship with methane.The percentage of ether oxygen bond peak area in five months of immersed water-dried coal is greater than three months and one month,but the growth is not significant.The-COOH of a month of immersed in air-dried coal decreases rapidly at 40?-120?.As the concentration of methane increases,the rate of decrease slows down significantly.The rate of decrease in the initial period of three months relative to one month was further slowed.The slowing down of the initial rate of coal drying after five months of immersion and air-drying was more obvious,and there was no increase in-COOH content.In this paper,a system based on the study of physical and chemical properties such as multicomponent gas adsorption,free radicals and functional groups is constructed,which provides a new research idea for the interaction between gas adsorption and coal spontaneous combustion oxidation.At the same time,it is of great significance for the prevention and control of long-term soaked and air-dried coal spontaneous combustion disaster.There are 32 pictures,12 tables and 95 references in this paper.