Study on the segmented inhibition mechanism of coal spontaneous combustion under the action of low concentration CO2

To elucidate the inhibition mechanism of low-concentration CO 2 (2%-16%) on coal spontaneous combustion, TG-DSC, programmed-temperature oxidation and in-situ FTIR were applied to spontaneously combustible coal at fixed 20% O 2 . Rising CO 2 delayed characteristic temperatures T 1 -T 5 , reduced peak heat release from 8.61 to 7.13 mW·mg -1 , cut peak oxygen consumption by up to 62.9%, and decreased peak CO, CO 2 and hydrocarbon generation by up to 73.3%, 68.7% and 60.9%-91.1%; apparent activation energy rose by 172.3%, 61.0% and 24.8% in the three oxidation stages of coal spontaneous combustion. It revealed that adsorbed CO 2 filled micropores and occupied preferential sites, reducing oxygen adsorption and inhibiting alkyl side-chain oxidation; this weakened with temperature as CO 2 desorbed. Desorption endotherm suppressed coal temperature rise, while free CO 2 inhibited gas-phase oxidation of pyrolysis products and radicals, weakening combustion heat release. Overall, the inhibition weakened with rising temperature, while the marginal benefit of increasing CO 2 concentration diminished progressively.