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Water and pyrite (FeS2) in coal have great synergistic effect on coal self-ignite. In order to explore the characteristics of spontaneous combustion of high humidity and high sulfur coal, this paper selected different concentrations of water and pyrite to carry out thermogravimetric experiment and oxidation reaction kinetics analysis. The changes of coal samples oxidation under low temperature in mass and characteristic temperatures were studied through thermogravimetric (TG) analysis. The results indicate that the promoting effect of water on coal spontaneous combustion turns to restrain when it reaches 15%, and water and pyrite have substantial synergistic effect on coal oxygen absorption and mass gain stage (T3–T5 in TG temperatures), besides there is a range of water/pyrite contents (10–15 mass% water and 2–4 mass% pyrite) that have the largest effect on coal oxidation reactions. Through the analysis of oxidation reaction kinetics, it was found that the change rule of the apparent activation energy (Ea) in coal oxygen absorption and mass gain stage is similar to that of the thermogravimetric change, and it was the lowest at 2–4 mass% pyrite and 10–15 mass% water content. The reaction process of coal oxidation by water and pyrite conforms to the equation n = 4 Avrami-Erofeev, therefore water and pyrite just can promote coal oxidation externally. This research provides support for further understanding and control the influence of water and associated pyrite on coal self-ignite. [ABSTRACT FROM AUTHOR]

To reduce the hazardous effect of coal fires, gas-heat dynamic characteristics were investigated in the closed fire zone. A temperature-programmed experiment and a C80 microcalorimeter were employed to evaluate the heating and decaying processes of coal spontaneous combustion, CO production and thermal oxidation were compared to analyze the gas-heat dynamic relationship and nonlinear dynamics. The results revealed that CO production and the heat flux exhibited obvious hysteresis in the decaying process, the oxygen concentration linearly increased with the total CO production and cumulative heat release. Moreover, the heat release in the heating process was lower than that in the decaying process under identical oxygen-poor conditions, this mechanism increasingly dominated with increasing oxygen concentration. Additionally, the total CO production exhibited a good linear relationship with the cumulative heat release during the heating process, the decaying process exhibited a nonlinear trend due to the hysteresis effect. Compared with that of the heating process, the apparent activation energy of the decaying process was lower, the coal spontaneous combustion risk was higher and reignition was more likely to occur. These research results are great practical significance for inhibiting coal fire hazards and guiding fire area unsealing in the closed fire zone. [Display omitted] • The heating and decaying processes of coal oxidation were simulated by experiments. • Correlation of CO and heat under various oxygen concentrations were analyzed. • Dynamic relationship of the heating and decaying processes was compared and analyzed. • The CO production and heat flux exhibited obvious hysteresis in the decaying process. • The decaying process of coal oxidation was more dangerous to reignite. [ABSTRACT FROM AUTHOR]

• Mechanisms causing mass variation of combusting coal were separated and evaluated. • Contributions of different mechanisms to mass variation of coal were researched. • Transformation of the kinetic mode in spontaneous coal combustion was explored. • Kinetic compensation effect of variations in E a and A was investigated. Coal spontaneous combustion (CSC) is a severe threat to coal mining operations. Using thermogravimetric experiments, the contributions of different mechanisms to the mass variation during CSC were analysed. Furthermore, the kinetic mode and kinetic compensation processes were investigated. Among the different mechanisms of coal–oxygen reaction, solid-phase combustion contributes least to mass loss; for coals of high rank, gas-phase combustion makes the greatest contribution. Oxidative decomposition contributes most for coals of low rank. Furthermore, the kinetic mode governing CSC is three-dimensional diffusion in the mass gain stage and changes to random nucleation and subsequent growth in the mass loss stage. The apparent activation energy reaches its maximum near the ignition temperature and indicates a kinetic compensation effect with the pre-exponential factor in each stage. These findings are crucial for understanding the processes involved in CSC. [ABSTRACT FROM AUTHOR]

Abstract This study examined the combustion characteristics and kinetics of coal samples treated with imidazole-based ionic liquids (ILs), namely, [Emim][BF 4 ], [Bmim][BF 4 ], [Bmim][NO 3 ], and [Bmim][I], under oxidation. The oxidation of the coal samples was investigated using thermogravimetry (TG) at heating rates of 4.0, 6.0, 8.0, and 10.0 °C·min−1. The results for the IL-treated samples revealed that the composite index S (representing the ignition, combustion, and burnout properties) decreased and H f (representing the rate and intensity of the combustion process) increased with high correlation coefficients. The characteristic temperatures of the maximum oxidization mass gain (T 2), ignition point (T 3), maximum mass loss rate (T 4), and burnout point (T 5) increased by 13.1 ± 0.5, 9.2 ± 0.5, 21.5 ± 0.5, and 35.9 ± 0.5 °C, respectively. At T 3 and the maximum mass loss rate, the release of CO and CO 2 was further altered, suggesting that the C O functional groups were damaged or oxidized. The results of the Ozawa-Flynn-Wall kinetic equation used to determine the apparent activation energy (E a) of coal samples revealed that the E a of the treated samples increased. The reaction rate constant characterizes the effect of E a and pre-exponential factors (A), and the results showed that ILs can weaken the reaction process at low temperatures (<130 °C). Highlights • Changes in the combustion performance occurred in samples treated with ILs. • The S decreased and H f increased with an increase in the amount of ash. • The reaction process of the treated sample is accelerated above 130 °C determined by k. • The difference in gas reveals that C O was destroyed by ILs. [ABSTRACT FROM AUTHOR]