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• 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]

In order to study the variation law of coal spontaneous combustion characteristics, the temperature programming experiment of coal spontaneous combustion was used to research the characteristics of raw coal and pre-oxidized coals. The results showed that, compared with the raw coal, the oxygen consumption rate, CO and CO2 production rate, heat release intensity of pre-oxidized coal to 90° were higher with temperature increased. The variation curves of the oxygen consumption rate, CO production rate, heat release intensity of pre-oxidized coal to 130 170°C with temperature increased had cross points temperature with that of raw coal. The cross point temperature was 80~90 °C to pre-oxidized coal to 130 °C and was 110~120 °C to pre-oxidized coal to 170 °C. The above three parameters values of pre-oxidized coals were higher than that of raw coal when temperature was below the cross point temperature while they became smaller in opposite direction. The CO2 production rate of pre-oxidized coals to 130 °C and 170 °C was bigger than that of raw coal when the temperature was below 80 °C while it became smaller when the temperature was over 80 °C. The minimum float coal thickness and lower limit oxygen concentration extremum of pre-oxidized coals decreased, and upper limit air-leakage intensity increased. With higher degree of oxidation, the variable quantity of critical parameters extremum was greater. [ABSTRACT FROM AUTHOR]

• Variation of atomic ratio and microcrystalline structure with temperature under nitrogen atmosphere were explored. • Abrupts of H/C and O/C occured as rising the temperature of coal samples. • Correlation was established by thermal property with atomic ratio and microcrystalline structure. To explore the main influencing factors of atomic ratio (O/C, N/C, and H/C) as well as microcrystalline structure (d 002 , L a , L c , and M c) on thermal properties (specific heat capacity, thermal conductivity, and thermal diffusivity) at certain temperatures within 30.0–300.0 °C, three coal samples were collected from coal mines of Dafosi, Yangjiaping, and Hujiahe in Binchang coalfield, Shaanxi Province, PR China. Thermal properties of coal samples were determined by laser-flash apparatus in nitrogen atmosphere. After temperature treated at 30.0, 60.0, 90.0, ..., 300.0 °C in nitrogen atmosphere, the atomic ratio and microcrystalline structure of samples were measured by proximate analyser and X-ray diffractometer. The results indicated that with an increment in the temperature, the value of H/C for three coal samples diminished slightly and then promptly, whereas O/C diminished slightly and then increased before 120.0 °C, as well as finally increasing, and the N/C had no obvious change. Concurrently, the microcrystalline structure of coal samples became more orderly and complete. Furthermore, the TD decreased with temperature, the SHC and TC showed an opposite trend with TD. Based upon grey correlation analysis, the major influencing factors of atomic ratio and microcrystalline structure on thermal property were approached. The results provided insight into the physicochemical properties of the coal of interest for predicting the progress of coal spontaneous combustion. [ABSTRACT FROM AUTHOR]