Coal pyrolysis law and mechanism of index gas generation in Linsheng Mine

To provide a theoretical basis for predicting spontaneous combustion in Linsheng coal mine, the pyrolysis characteristics of coal were investigated from both macroscopic laws and microscopic mechanisms. Programmed-temperature gas chromatography was utilised to test the generation and evolution laws of critical indicator gases (CO, C2H4, C2H2). XPS, 13C NMR and FT-IR were employed to elucidate the microscopic compositional and structural changes of coal samples. ReaxFF simulations revealed the product transformations of coal molecules during pyrolysis. The generation mechanisms of indicator gases were examined by FT-IR analysis. The results showed that the detected temperatures for CO, C2H4 and C2H2 generation from coal were approximately 60 °C, 165 °C and 308 °C. Linsheng coal exhibited a low degree of aromatic condensation with the molecular formula of C148H100O11N2S. During pyrolysis, the content of reactive –OH groups in coal increased, while substituted aromatics first increased and then decreased. The carbon content was elevated with a lowered H/C ratio, indicating progressive aromatisation and simplification of the coal structure. Gasification reactions persisted throughout the entire process, leading to continuous cleavage of small molecules to form gases. The formation of indicator gases is closely related to reactive functional groups including ester, ether, alcohol, carbonyl, phenol, alicyclic and substituted aromatics.