Experimental Study On Surface Thermal Anomaly And Characteristics Of Gas Release During Low Temperature Oxidation Of Coal

Because of human activities and natural factors,worldwide underground coal fires problem becomes more and more serious.Underground coal fires have become one of the major disasters endangering coal resources,mining safety and environmental protection.Detection and control of underground coal fire disasters are important to energy security,social and economic development of China and many other countries.Identifying the relationship between the surface thermal anomaly and coal oxidation is important in the understanding of the evolution of underground coal fires.However,most lab-scale studies could not simulate the essential physical and chemical processes involved in underground coal fires because of oversimplification,and insufficient attention has been paid to surface thermal anomaly.In view of the problem,focusing on the thermodynamic evolution of underground coal fires,an experimental apparatus was built up to simulate heat transfer,mass transfer and infiltration of oxygen and combustion products occurring in underground coal fires.The overburden of coal seams was simulated using ceramic foams,and by applying external heating to the bottom of the coal layer,the surface temperature of the ceramic foam and gas concentrations were measured.The experimental results indicate:under different conditions,the variations of coal temperature with time are similar,under the condition of the single-point fracture,the increase of ceramic foam thickness accelerates the process of low temperature oxidation of coal,thus reducing the time needed to reach the fast-oxidation critical point.The variation of gas temperature,temperature at typical points and coal temperature with time are consistent,based on which the variation of coal temperature can be inferred.The gas temperature and the temperature at typical points can be used to derive the coal temperature.The concentration of CO and the ratio of CO/CO₂ rise rapidly when the coal temperature reaches the critical temperature for fast-oxidation.The CO concentration is nearly in an exponential relationship with the coal temperature,and the correlation between the CO concentration and the coal temperature could be used to judge the progress of low-temperature oxidation of coal,which could provide some guidance to the early-stage detection of underground coal fires.