Experimental Study On Coal Microscopic Properties And Spontaneous Combustion Limit Parameters For Different Soaking Time

Western China is rich in fossil energy reserves and is one of the major regions of China’s energy supply,and coal resources are a supporting energy source for the country’s industrial production.Coal spontaneous combustion is one of the main causes of mine disasters,and most of the coal seams in the west are flammable coal seams.In the process of mining the lower coal seam,water is extracted from the overlying mining area by water detection or hydrophobic extraction,and when the water is extracted,it causes the phenomenon of"water-gas replacement",which leads to the increased tendency of spontaneous combustion of the coal left in the overlying waterlogged mining area and poses a great threat to the safety production of coal mines.In order to have a deeper understanding of the microscopic physicochemical properties of water-soaked coal and the relevant limit parameters of water-soaked coal seam,this paper adopts the coal sample of No.2 water-rich coal seam of Ningxia Hongliu coal mine for experimental study,which is of great significance to provide theoretical support for mine fire prevention and control.In order to investigate the microscopic characteristics of long-term water immersion coal samples and the nature of coal spontaneous combustion and oxidation,the experimental coal samples in this paper were transported directly from the site after mining to the laboratory for processing,and the coal samples were divided into raw coal and water immersion samples with 30,60,90,120 and 150 days of water immersion,which were subjected to industrial analysis,scanning electron microscopy experiment,nitrogen adsorption and desorption experiment,Fourier infrared spectroscopy experiment and coal The relevant parameters of the long-term waterlogged coal samples were further investigated to develop corresponding countermeasures for the prevention and control of fires in the mining area.The surface changes and pore morphology of the long-term immersed coal samples were characterized by scanning electron microscopy and nitrogen adsorption and desorption experiments.With the increase of water immersion time,the number of pores on the surface of coal samples increased significantly and larger fissures appeared;after water immersion and air-drying,the pore volume and specific surface area gradually decreased compared with the original coal,and the pore diameter showed an overall increase compared with the original coal samples,which is due to the phenomenon of water immersion and swelling of coal samples after water immersion,and the pore diameter will be changed as a result.The pore volume and specific surface area will be reduced.Through the Fourier infrared spectroscopy experiments on the long-term leached coal samples,the main functional groups and the contents of various functional groups of different leached coal samples were obtained by the peak fitting and peak determination of each peak position of the peak spectra,which consisted of aliphatic hydrocarbons,aromatic hydrocarbons and oxygen-containing functional groups,and the proportion of oxygen-containing functional groups was the largest,among which the content of hydroxyl groups was the largest;the effect of leaching on the contents of structurally stable C=C and C=O functional groups was also observed.The influence of leaching on the content of C=C and C=O functional groups with stable structure is relatively small,and the influence on the content of methyl groups and methylene groups is large.Through the programmed temperature rise experiments on the long-term submerged coal samples,we analyzed the changes of gas components with the experimental temperature during the low-temperature oxidation of long-term submerged coal samples,and the gas indexes were selected to show that the CO/△O₂ and CO/CO₂ ratios can be used as indicator gases for coal spontaneous combustion;the oxygen consumption rate of coal samples increases with the length of submergence time,and the exothermic intensity also increases with the growth of submergence time.The oxygen consumption rate of coal samples will increase with the length of water immersion,and the exothermic intensity will increase.The oxygen consumption rate,CO production rate and CO₂ production rate were calculated for the limit parameters of the relic coal,and the minimum coal pile thickness,lower limit oxygen concentration and upper limit air leakage intensity changed more compared with the original coal samples,and the coal samples were more likely to reach the minimum requirement of coal oxidation spontaneous combustion with the growth of the submersion time,then the submerged air-drying was more likely to lead to coal spontaneous combustion,and the D₁₂₀ coal sample had the tendency of coal spontaneous combustion than other submerged air-drying coal samples After the statistical study of the apparent activation energy of coal samples in the overall warming stage and the accelerated warming stage,the apparent activation energy of coal samples after water immersion was significantly smaller than that of the original coal samples,the I value of the immersed air-dried coal samples was larger than that of the original coal samples,and the cross-point temperature of the immersed air-dried coal samples was lower than that of the original coal,which indicated that the immersed air-drying was more favorable to the heat storage of coal samples for spontaneous combustion,and the possibility of coal spontaneous combustion increased.