Kinetic characterization investigation of elemental migration and oxidation in coal spontaneous combustion

Oxidative spontaneous combustion is an inherent property of coal. Coal spontaneous combustion (CSC) occurs mainly in the structure of organic macromolecules, and the substances involved in the reaction are the main elements in coal. At the same time, the thermal effect of the thermal reaction in CSC leads to changes in the elemental content of coal, which is manifested in macroscopic kinetic and thermodynamic processes. Using elementar vario EL–type elemental analyzer to explore the change rule of elements in the coal spontaneous combustion, and found that the elements in the coal change exponentially with the temperature and show obvious staged characteristics, it proposed a functional expression for the temperature point of self-accelerating coal oxidation, which can be used as a key temperature point for suppressing coal spontaneous oxidation; using the thermal analysis kinetic method, obtained the kinetic mechanism function and apparent activation energy of each element in the CSC, which are 4D diffusion model for element C, Avrami–Erofeev equation for element H, n = 2/3, contraction reaction for element O, n = 1/2, Avrami–Erofeev equation for element N, n = 3, and 3D diffusion for element S, Z–L.–T. equation. Revealing the mechanism of the negative apparent activation energy of the O element, that is, the migration of the O element contains two opposing competing reactions; on the basis of the intermediate complex theory, it was determined that the elements migrated from the molecular structure of coal are all non–spontaneous processes, and grasped the thermodynamic action mechanism of the elemental migration reaction, then obtained the key groups –CH₂ and –C = O that promote the occurrence of CSC. The research results provide a theoretical basis for the development of new flame-retardant materials, which is of great significance in achieving the dual-carbon goal.