Spontaneous oxidation kinetics of weathered coal based upon thermogravimetric characteristics

Coal spontaneous combustion (CSC) is a major hazard in energy and mining. Weathered and fresh coal may have different propensities to CSC and combustion-related behaviours. In this study, the combustion of fresh and weathered coal samples was directly compared at four heating rates, and the characteristics were measured using a synchronous thermal analyser. The Kissinger–Akahira–Sunose, Flynn–Wall–Ozawa, and Friedman methods were used to determine the most likely reaction mechanism function and perform a complete thermokinetic analysis. The combustion of the fresh sample was more intense than that of the weathered sample, and its combustion characteristic index was greater. The distribution of the apparent activation energy revealed that the weathered sample was more prone to thermal decomposition and reacted more readily in the early combustion stages; by contrast, the fresh sample reacted more readily in the later combustion stages. The mechanisms of combustion in the fresh and weathered coal were found to be best represented by the Jander and Avrami–Erofeev equations, respectively. The combustion process of the weathered samples was more complex than that of the fresh sample. It consisted of two stages: first, organic matter decomposed and combusted, and then, inorganic matter, such as CaCO3, did so.