A TGA–DSC‑based study on macroscopic behaviors of coal–oxygen reactions in context of underground coal fres

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.