Abstract:
Underground coal fres (UCFs) cause remarkable loss of energy resources and signifcant environmental pollution. Due to the
limited capacity of oxygen transport, the inception and development of UCFs represent a very unique mode of coal–oxygen
reactions. Therefore, a high-volatile fammable coal sample is thermally analyzed with the combined TGA–DSC approach
under four oxygen concentrations (21%, 15%, 9% and 3%) and three heating rates (1 °C min−1, 2 °C min−1 and 5 °C min−1).
It is found that the oxygen concentration does not signifcantly infuence the early (low-temperature) stage of coal–oxygen
reactions. With the decrease in oxygen concentration, the intensity of the exothermic reactions is reduced and the duration
of reactions is extended. Based on the experimental results, the apparent activation energy is calculated. The variation of the
apparent activation energy refects the diferent reaction stages: volatiles burning and char oxidation, which is verifed by the
TGA–DSC results. Under the extreme condition of 3% oxygen concentration, a very distinct macroscopic thermochemical
behavior is observed, and the limited oxygen supply controls the reaction rate throughout the entire process, which qualitatively explains the persistency of the burning phenomena in most UCFs.
