Quantitative study on the influence of the difference of the molecular structure on the spontaneous combustion characteristics of the coal metamorphism process

Neimeng lignite, Huajin bituminous coal, Sitai bituminous coal, and Changcun lean coal with different degrees of metamorphism were analyzed via infrared spectrum curve fitting analysis and thermal analysis experiments, and the influence of the change in the active functional groups in the coal structure on the coal spontaneous combustion characteristics was explored. After the spectral curve was fitted, it could be divided into four areas—hydroxyl, C–H stretch band, oxygen-containing functional group, and aromatic structure—and then, the molecular structure content of different functional groups was quantitatively calculated. In the thermal analysis experiment, the characteristic value and the combustion activation energy of the coal were obtained through the thermogravimetric analysis curve, and the calorific value of the coal could be calculated using the differential scanning calorimetry curve. After combining the two experiments to obtain a linear relationship, the results showed that as the degree of coal metamorphism deepened, the activation energy of the coal combustion gradually increased, and the amount of heat released decreased. For the self-associated hydroxyl group in the hydroxyl group, the methylene group in the aliphatic hydrocarbon, the C=C double bond in the oxygen-containing functional group, and the three-substituted aromatic ring in the aromatic structure, the content of these functional groups is the highest for coal, with increases of 11.01%, 31.81%, 14.34%, and 22.9%, respectively, and the effect of inhibiting the spontaneous combustion of coal is more significant.