Regulatory Mechanism of Oxidation Temperature on Secondary Spontaneous Combustion Activity of Coal: Correlation between Functional Group Evolution and Indicator Gas Generation

Understanding the regulatory mechanism of oxidation temperature on the secondary spontaneous combustion activity of coal is crucial for establishing spontaneous combustion warning thresholds. FTIR was employed to study the effect of oxidation temperature on coal functional groups. A programmed-temperature experiment was conducted to analyze changes in gas types and concentrations during the secondary spontaneous combustion of oxidized coal. The results indicate that initial oxidation activates functional groups in coal, such as C-O-C, CO, and -CH3. Therefore, during secondary spontaneous combustion of oxidized coal, as the temperature increases, these functional groups further oxidize and decompose to form gas products. When the oxidation temperature reaches 80 °C, the initial temperature at which coal produces CO and C2H4 during the secondary spontaneous combustion process is 40 °C earlier than that of raw coal, and the initial generation concentrations are 42.45% and 28.83% of raw coal, respectively. Therefore, CO and C2H4 can serve as indicator gases for predicting the spontaneous combustion of oxidized coal. This work provides valuable insights into the spontaneous combustion process of oxidized coal in shallow buried coal seams.