A TGA-DSC-based study on macroscopic behaviors of coal-oxygen reactions in context of underground coal fires

Underground coal fires (UCFs) cause remarkable loss of energy resources and significant 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 flammable 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 degrees C min(-1), 2 degrees C min(-1) and 5 degrees C min(-1)). It is found that the oxygen concentration does not significantly influence 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 reflects the different reaction stages: volatiles burning and char oxidation, which is verified 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.

Automated summary

Underground coal fires cause significant loss of energy resources and pollution. The limited oxygen supply in UCFs results in a unique mode of coal-oxygen reactions. Experimental results show that oxygen concentration does not significantly affect early reaction stages, but influences reaction intensity and duration at low oxygen levels. The variation in apparent activation energy reflects different reaction stages, such as volatiles burning and char oxidation, with limited oxygen supply controlling reaction rate throughout the process.