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• Explored the exothermic properties of pulverised coal in various oxygen concentrations. • Determined three stages of low-temperature oxidation of pulverised coal. • Investigated the inhibiting effect of low O 2 concentrations on pulverised coal oxidation. • Proposed an index for evaluating the risk of pulverised coal spontaneous combustion. To investigate the spontaneous combustion risk of pulverised coal, the low-temperature oxidation heat flow of three metamorphic pulverised coals was measured using a C80 microcalorimeter system at various oxygen concentrations to investigate the spontaneous combustion risk of pulverised coal. The results indicated that low-temperature exothermic oxidation of pulverised coal occurred in stages that had distinct characteristics. When the temperature increased, the heat flow curve of RNM and QM pulverised coals first decreased, then increased, and finally decreased, but the heat flow curve of the PSM pulverised coal first decreased and then increased. A considerable lag was observed in the heat flow curves with the decrease in the oxygen concentration, and the characteristic temperature increased. Stage 1 released the least heat, whereas stage 3 released the most heat. A decrease in the oxygen concentration considerably reduced the heat release of pulverised coal. A spontaneous combustion risk index was proposed on the basis of low-temperature oxidation heat release of pulverised coal. Decreased oxygen concentration and high metamorphism of pulverised coal considerably reduced the spontaneous combustion risk index. [ABSTRACT FROM AUTHOR]

• A new index for forecasting spontaneous coal combustion is proposed. • CO/CO 2 ratio increases exponentially as temperature increases. • Multiparameter self-ignition prediction system developed for Huainan mining area. Hazards due to spontaneous combustion of coal seriously threaten coal mining safety. To explore and evaluate the prediction indices and limiting parameters of coal self-ignition, seven samples from the Huainan mining area in Anhui Province, China were tested. Experiments were conducted using an oil-bath temperature-programmed system. The experimental results indicated that the oxygen consumption rates and CO production increased slowly initially and then rapidly with the increase in temperature. The plots of CO/CO 2 ratio versus temperature exhibited an exponential property. The C 2 H 4 /C 2 H 6 ratios exhibited an unstable alternation when the temperature was in the range of 100–130 °C. However, the ratios became steady after the temperature increased above 130 °C. The low-temperature oxidation process was divided into three stages according to the Δ C CO / Δ C O 2 ratios. The oxidation index D O , a new indicator, was used to precisely forecast the point of spontaneous combustion. The limiting parameter analysis indicated that the minimum float coal thicknesses h min and limiting oxygen concentrations C min first increased and then decreased constantly with an increase in temperature. The parameters reached their maximum value at 50 °C. The maximum air leakage intensity Q max followed a trend opposite to that of the two aforementioned parameters. With an increase in temperature, Q max first decreased and then increased. The results provide valuable information for predicting spontaneous combustion of coal, which can help prevent or mitigate risks in industrial mining. [ABSTRACT FROM AUTHOR]

• Gas products during spontaneous combustion of coal were studied. • The significant variation of active groups in spontaneous combustion of coal was studied. • The quantitative relationship between key active groups and gas products was established. • The mechanism of gas release from spontaneous combustion of coal was described. In order to reveal the internal relationship between the active groups and gas products in spontaneous combustion of coal, the correlation between the content of active functional groups and the production of gas products was studied by temperature programmed experiment and in situ infrared spectroscopy analysis experiment. The results show that there are three characteristic temperature points in the gas release curve of Jurassic coal spontaneous combustion in northern Shaanxi, which can be divided into slow oxidation stage, critical temperature stage, rapid oxidation reaction stage and combustion stage. CH 3 , CH 2 , C–H and OH are actively consumed in the spontaneous combustion of coal. C O gradually increased, which is an important oxidation product during Jurassic coal oxidation in northern Shaanxi. The chain length CH 2 /CH 3 is attacked and the fracture shortened, while the oxygen enrichment degree of C O/C C in coal increases gradually. The correlation values of key active groups of CH 3 , CH 2 , C–H, OH, C O, CH 2 /CH 3 , and C O/C C with oxygen, carbon and oxygen gases and alkane and olefin gases in the process of coal oxidation heating in different coal seams in northern Shaanxi during Jurassic period are obtained. The results show that CH 3 , CH 2 and CH 2 /CH 3 , are the main parts of oxygen molecules attacking and binding in the Jurassic coal oxidation process in northern Shaanxi, and the oxygen-rich products of coal decompose into carbon oxygen gas and alkane alkene gas. Due to the different activation energies of various active groups, the spontaneous combustion of coal shows different reaction degrees in each stage. The research results can be used to understand the occurrence and development degree of spontaneous coal combustion, and have important guiding significance for the monitoring and warning of spontaneous coal combustion and the targeted prevention and control of spontaneous coal combustion disasters. [ABSTRACT FROM AUTHOR]