Oxidationreaction and kinetics of anthracite infiltrated by liquid CO₂

As one of most important sources on greenhouse effect,the CO₂ recycling and utilization have become a hot spot in research. In the field of mine disaster prevention and control technology,the technologies for controlling spontaneous coal combustion and displacing coal bed methane by liquid CO₂ have achieved a great success. However,the liquid CO₂ with low-temperature (from -56℃ to -20℃) forms a heat transfer after injecting into coal seam,and causes a damaged effect by thermal stress. Specific surface area and volume in coal pore are changed,and then the adsorption capacity of coal-oxygen is transformed and the tendency of spontaneous coal combustion is varied. To study the oxidation characteristics of coal infiltrated by liquid CO₂,a thermo gravimetric analysis was carried out with anthracite in Yongcheng mining area of Henan,China. The characteristic temperatures of original and liquid CO₂ infiltra-ted coal oxidation were analyzed. The oxidation kinetics parameters were calculated by non-isothermal methods (FWO and KAS methods),and the influence of liquid CO₂ on coal oxidation was obtained. The study shows that the critical temperature and crack temperature of anthracite infiltrated by liquid CO₂ were decreased by 2-8℃compared with raw coal. The growth temperature,weight loss temperature,ignition temperature,maximum weight loss rate temperature and burnout temperature were advanced by 100-140℃. The weight loss percentage corresponding to each characteristic temperature was reduced by 0.8%-10.0%. The interval ranges of four oxidation stages (water evaporation and physical adsorption of oxygen,mass gain through oxygen chemisorption,pyrogenic decomposition and combustion)were reduced. The rate and quantity of oxygen adsorption on infiltrated coal were increased,and the combustion reaction speed of was improved. The apparent activation energy of infiltrated coal sample was decreased by 10-30 kJ/mol in four oxidation stages compared with that of raw coal samples. A positive correlation was shown between pre-exponential factor and apparent activation energy. The spontaneous combustion tendency of coal treated by liquid CO₂ was increased,and the process of coal oxidation was accelerated. More stringent measures for preventing spontaneous coal combustion should be carried out after controlling coal fire in gob and displacing coal bed methane by liquid CO₂.