Experimental Study On Inhibiting Coal Spontaneous Combustion By Injecting Flue Gas Into Goaf

Coal-fired power plants are a concentrated source of CO2 emissions,and reducing CO2 emissions is an important part of the green development of power plants.The inert gas content of flue gas is above 80%,and injecting flue gas into the underground mining area can not only sequester CO2 and other gases,but also prevent the spontaneous combustion of coal left in the goaf.In order to investigate the spontaneous combustion characteristics of coal under flue gas conditions,four types of coal with low degree of metamorphism were selected,and the characteristic temperature points of TG-DTG curves and activation energy changes,changes of gas products and concentrations,and changes of characteristic functional groups in coal under simulated flue gas conditions with air and CO2 concentrations of 4%,8%,12%,and 16%respectively,were compared and analyzed for the injection of flue gas into the goaf.This paper provides theoretical references for coal spontaneous combustion suppression technology.The weight loss characteristics of coal spontaneous combustion process under flue gas conditions were investigated by thermogravimetric experiments.The results showed that the power plant flue gas delayed the coal oxygen reaction time,and the flue gas played an obvious effect of inhibiting coal spontaneous combustion when φ(CO2)≥12%.With the increase of CO2 concentration in the flue gas,the characteristic temperature points of coal spontaneous combustion all increase,and the higher the CO2 concentration,the greater the corresponding temperatures increase.The effect of flue gas on the five characteristic temperature points was T1>T3>Twmax>T2>Ti.The kinetics of coal spontaneous combustion reaction was studied by Coats-Redfern method,and the results showed that the activation energy of coal ignition was significantly increased by flue gas,and the activation energy of coal ignition under flue gas conditions increased with the increase of CO2 concentration in flue gas.The activation energy of coal samples increased by 20%～43%under 16%CO2 concentration flue gas condition.The concentration changes of indicator gases generated from coal spontaneous combustion under flue gas conditions were studied by adiabatic warming and gas chromatography coupled experiments.The results showed that the maximum concentrations of CO,CH4,C2H4 and C2H6 from coal spontaneous combustion decreased continuously with the increase of CO2 concentration in the flue gas,and the decreases were 31%～94%,2%～8 3%,13%～96%and 16%～91%respectively.The flue gas significantly suppressed the generation of coal spontaneous combustion process gas products and had the best suppression effect on DNH and XDT generated gases.The analysis of the composite gas index of coal spontaneous combustion process showed that the inhibition of C2H4,C2H6 and CH4 generation from XLGL and XDT by flue gas at temperatures above 210℃ was ranked from strong to weak as CH4>C2H6>C2H4.The changes of characteristic functional groups in the low temperature oxidation process of coal under the flue gas conditions were investigated by in situ diffuse reflectance infrared spectroscopy experiments.The results showed that the hydroxyl absorption peaks of lignite at room temperature showed a trend of increasing and then decreasing with the increase of CO2 concentration of flue gas,and the highest hydroxyl absorption peaks were observed at 8%CO2 concentration of flue gas.The average consumption rate of hydroxyl groups in bituminous coal decreased with the increase of CO2 concentration in flue gas when the temperature was lower than 155℃.Power plant flue gas suppressed the consumption of aliphatic hydrocarbons,oxygen-containing functional groups and substituted benzene in coal.With the increase of CO2 concentration in flue gas,the consumption rate of aliphatic hydrocarbons in lignite keeps decreasing and the inflection point temperature of aliphatic hydrocarbon content in bituminous coal keeps increasing.With the increase of CO2 concentration in flue gas,the inflection point temperature of absorption peaks of carboxyl,carbonyl and substituted benzene in coal kept increasing,and the inflection point temperature of absorption peaks of corresponding functional groups in coal increased by 10 ℃～30 ℃,30℃～50℃ and 20℃～60℃ respectively under 16%CO2 concentration flue gas condition.