Abstract:

To reveal the impact of coal metamorphism on the self-ignition process,experimental and quantitative analysis methods was combined to analyze the pyrolysis characteristics, microstructural changes, and their correlations during coal self-ignition. First, Fourier-transform infrared spectroscopy (FTIR) was employed to determine changes in the content of active functional groups in coal samples. Then, thermogravimetric analysis (TGA) was conducted to obtain pyrolysis characteristic parameters for coal samples with varying degrees of metamorphism. Finally, Pearson correlation coefficient method was applied to quantify the relationship between microstructure and characteristic temperatures during coal self-ignition. The results indicate that as the degree of coal metamorphism increases, the content of aromatic and aliphatic hydrocarbons(Ar-CH) rises, while oxygen-containing functional groups(C-O-C) significantly decrease. Low-rank coal samples exhibit the highest proportion of oxygen-containing functional groups, whereas high-rank coal samples contain more than 50% aromatic hydrocarbons. Increased metamorphism delays weight loss curves and shifts them to higher temperature regions, leading to an increase in characteristic temperatures. Ar-CH show a significant positive correlation with characteristic temperatures, while C-O-C exhibit a negative correlation. Overall, the increase in Ar-CH and the decrease in C-O-C in coal samples are identified as the primary microstructural factors responsible for the rise in characteristic temperatures and the reduction in self-ignition propensity.

Key words: metamorphic degree, microstructur, pyrolysis parameters, correlation, spontaneous combustion of coal, functional groups