Comparative Analysis for Active Functional Groups and Spontaneous Combustion Characteristics of Weakly Caking Coal Under Oxygen-Limited Atmospheres

Oxygen concentration is a critical determinant in the spontaneous combustion of weakly caking coal. To analyze the correlation between active functional groups in coal and its spontaneous combustion characteristics under oxygen-limited atmospheres, the weakly caking coal was selected, and the TG analyzer and FTIR were adopted to obtain the mass change and active functional groups in coal. Meanwhile, the comprehensive combustion parameters and apparent activation energy of coal were calculated, and the main factors affecting spontaneous combustion characteristics of coal were obtained by a gray correlation method. The results illustrated that, with an increase in the oxygen concentration, the average apparent activation energy gradually enlarged, the dominant active functional groups driving this change switched in an oxygen-dependent manner. The aromatics -CH and -C=C- in aromatic ring were the major factors affecting apparent activation energy at 5 vol.%. The C-O structure became the foremost influencing factor at 13 vol.%, followed by intermolecular hydrogen bonding, -COOH structure, -C=C- in aromatic ring, and free hydroxyl, indicating a strong chemical reaction at this oxygen concentration. Meanwhile, -C=C- in aromatic ring and -COOH structure became key contributors at 21 vol.%. Moreover, the reduction of the oxygen concentration alleviated comprehensive combustion ability of coal. These findings can provide a basis for efficient control of coal spontaneous combustion in goaf.