Study on the Stage Characteristics and Action Mechanism of Low-Concentration CO<sub>2</sub> in Inhibiting Coal Spontaneous Combustion.

Abstract

This study examined the inhibitory mechanism of low-concentration CO₂ on coal spontaneous combustion using adiabatic oxidation experiments, thermogravimetric-differential scanning calorimetry (TG-DSC), and in situ Fourier transform infrared spectroscopy (FTIR). The analysis focused on heat release behavior, gas evolution, and functional group transformations in atmospheres containing 16% O₂ and 2-8% CO₂. The results indicate that CO₂ inhibits coal oxidation by occupying surface-active sites and promoting endothermic desorption during heating, which extends the spontaneous ignition period by 38-110%. During the slow oxidation stage (ambient temperature to 70 °C), CO₂ significantly suppresses O₂ adsorption and aliphatic functional group oxidation, delays gas evolution, and extends the heating duration by 40-121%, accounting for 86-90% of the total ignition delay. In the accelerated oxidation stage (70-150 °C), increased CO₂ desorption partially offsets the exothermic effect; however, the reduced efficiency of active site blocking decreases the inhibition rate to 30-69%. In the intense oxidation stage, CO₂ desorption exceeds 90%. Although radical quenching still reduces the heat release rate by 16-20%, oxygen deficiency becomes the dominant limiting factor, rendering CO₂ inhibition largely ineffective. Overall, the effective suppression of coal oxidation at low temperatures highlights the potential of using flue gas as a cost-effective and environmentally sustainable fire prevention strategy.