Study of combustion behaviour and kinetics modelling of Chinese Gongwusu coal gangue: Model-fitting and model-free approaches

Abstract

Coal gangue (CG) is the predominant solid waste produced in the mining industry. Understanding the combustion thermokinetics is essential for the effective management of environmental hazards caused by the spontaneous combustion of CG. In the present study, the combustion behaviour and kinetics modelling of CG were investigated through thermogravimetric analysis at heating rates of 10, 20, and 30 °C/min under air atmosphere. The kinetic behaviour of CG was established using common model-free (the Flynn-Wall-Ozawa, Tang, and and Vyazovkin methods) and model-fitting (the Coats-Redfern and Kennedy-Clark methods). The mass loss of CG in combustion experiments was mainly divided into three phases based on the thermogravimetry curves (stages 1–3). It was determined that prompt combustion and organic matter decomposition occur in the second stage at a temperature of 310–760 °C; this is critical for the utilization of CG in combustion. Results indicated that the increasing rates of heating would improve the oxidation reaction rate of CG. The apparent activation energies of the two samples were 291.41–364.09 and 71.63–147.99 kJ/mol. In addition, the nucleation-growth model A1/3 (n = 1/3, g(α) = [−ln(1 − α)]3) and the reaction order model F1.5 (n = 1.5, g(α) = 2[(1 − α) − 1/2–1]) were identified as the optimal real mechanism for each sample. The compensation effect was affirmed by identification. Furthermore, the analysis also indicated that fire risk control management of accumulated CG was improved by the avoidance of the mixture of other combustible impurities such as wood, paper, and coal with CG.