Effect of gas injection in underground coal combustion on kinetic of water-containing coal

NIE Baisheng; BAI Kaidan; HE Hengyi; LIU Peng

doi:10.12438/cst.2024-0647

Abstract：In-situ combustion for energy recovery from underground coal seams is a potential way for green and safe mining of coal re-sources in the future.In order to explore the combustion and kinetic characteristics of water-bearing coal under different gas injection rates,lignite with typical moisture content(11％-32％)was taken as the research object.The parameters such as characteristic temperatures,comprehensive combustion performance indices,and maximum exothermic rate of the coal samples were analyzed by the thermogravimet-ric analyzer and differential Scanning Calorimetry(TG-DSC),and the Coats-Redfern method was used to calculate the activation energy of the coal samples.The results show that the moisture content has a significant impact on the combustion and exothermic properties of coal.With the increase of moisture content,the ignition temperature and the maximum combustion rate temperature of the experimental coal samples first decrease and then increase,while the comprehensive combustion performance index and the maximum exothermic rate first increase and then decrease.When the moisture content is 22.8％,the ignition temperature of the coal is the lowest,and the comprehensive combustion performance index and the exothermic intensity are the largest,which shows that the moderate water content is conducive to the rapid ignition and combustion of the coal.The air flow rate exerts a significant influence on the combustion rate and the exothermic strength of coal.The combustion rate will be improved by increasing air flow rate,but when the air flow rate increases by 80 mL/min,the exothermic intensity will be significantly reduced,because the flow rate is too large to take away more heat,which is not conducive to the oxidation of the coal itself.The kinetic analysis shows that with the increase of moisture content,the activation energy decreases first and then increases.The lowest values of activation energy are 54.55,54.18 and 57.97 kJ/mol for the coal with 22.8％moisture content under the three air flow rates,The activation energy of coal with 11.6％and 22.8％moisture content is the smallest at 50 mL/min,and the activa-tion energy of coal with remaining moisture content is the smallest at 20 mL/min.When the air flow rate is 80 mL/min,the activation en-ergy value of coal sample is significantly increased,which further confirms that coal with 22.8％moisture content is easy to fire at 50 mL/min.High air flow is not conducive to the ignition of water-containing coal.The research results can lay a theoretical foundation for coal combustion mechanism,and provide theoretical guidance for in-situ ignition and stable combustion of underground coal seams.