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Proanthocyanidin antioxidant was first selected for study, and the inhibitory effect of proanthocyanidin and the optimal mass ratio of 6 mass% were obtained through temperature-programmed experiments. To compensate for the inhibitory effect and action time of a single antioxidant, a composite inhibitor with a physical and chemical synergistic effect was obtained through compounding with sodium polyacrylate, a superabsorbent resin, which improved the inhibitory effect on the spontaneous combustion of long-flame coal. In addition to the temperature-programmed experiments, the spontaneous combustion of long-flame coal was researched through a thermogravimetric (TG)–differential scanning calorimetric (DSC) experiment, and the optimal compound ratio of proanthocyanidins/sodium polyacrylate was determined to be 1:4. Under this ratio, the inhibition rate was close to 88% when the coal temperature ranged from 40 to 130 °C. The TG–derivative TG curve moved to the high-temperature region, and the composite inhibitors improved the characteristic temperature of raw coal and reduced its mass loss. The temperature corresponding to the peak value of the DSC curve increased, and the maximum heat release power was reduced. Fourier-transform infrared spectroscopy experiments revealed that the intensity of the hydroxyl peaks was reduced with the addition of composite inhibitors, and the peak intensity of methyl and methylene was lower than that of the raw coal. The inhibition characteristics of the composite inhibitor were thus obtained through a study of the change pattern of functional groups of coal samples during the heating process. [ABSTRACT FROM AUTHOR]

• 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]

Highlights • Exothermic of pulverized coal on various oxygen concentrations was researched. • Revealing three oxidation stages of low-temperature oxidation of pulverized coal. • Apparent activation energies on various oxygen concentrations were investigated. • Low oxygen concentration had inhibitive effect on exothermic of pulverized coal. Abstract Low-temperature exothermic oxidation characteristics of pulverized sub-bituminous coal was investigated using differential scanning calorimetry system in atmospheres where the oxygen concentrations were 21, 17, 13, 9, and 5 vol. %, respectively. The results indicate that the heat flow gradually decreases after it reaches the maximum value. A decreased oxygen concentration had a delaying effect on the heat flow and derivative of heat flow curves. A low oxygen concentration has typical stage characteristics for inhibiting the exothermic oxidation of pulverized coal. The oxygen concentration has a significant influence on the kinetics characteristics and kinetics parameters. The apparent activation energy increased under different oxygen concentrations with an increase in the conversion rate. The apparent activation energy was less than that in the low oxygen concentration under a high oxygen concentration. When the oxygen concentration less than 9%, the activation energy increases significantly. [ABSTRACT FROM AUTHOR]

Focusing on the problem of unclear ray-traced spots and their distribution rules in the design process of the Herriott cell, first, the characteristics of long-optical-path gas absorption cells were analyzed, and the calculation method of basic cavity length and the effective optical path of Herriott gas absorber cells were studied. Second, according to the transmission characteristics of geometric optics, a physical model of light transmission in Herriott cells was established via the LightTools software. Finally, simulation analysis was performed on Herriott cells with 5- and 14.4-m optical paths separately, determining the quantitative relationship between d/f and the number of spots reflected on the concave mirror, and optimizing the effective optical path and output laser energy of the Herriott cells. Through research analysis, the sizes and distribution positions of concave mirror spots in the Herriott cells were identified, as well as the factors affecting the number of reflections. It was also found that the number of reflected spots gradually decreases as d/f increases, revealing the light-tracing results and its spot distribution rule on the mirror surface, as well as verifying the accuracy of the theory. The findings of this study provide a basis for the optical path system design and optimization for Herriott cells with different optical path lengths. [ABSTRACT FROM AUTHOR]

In order to explore the characteristics of spontaneous combustion of Jurassic coal in northern Shaanxi with low metamorphic degree and high coke content, DSC differential scanning calorimeter and diffuse in situ infrared spectroscopy experiment were used to study and analyze the dynamic evolution law and interaction relationship between macroscopic thermal effect and microstructure in the spontaneous combustion process of different coal seams in northern Shaanxi. The results show that there are three characteristic temperature points in the heat flow curve during the spontaneous combustion of Jurassic coal in northern Shaanxi, which can be divided into four stages according to the characteristic temperature points. It was found that the consumption and production of functional groups in Jurassic coal oxidation process were mainly in the absorption bands of aliphatic hydrocarbon, aromatic hydrocarbon and oxygen-containing functional groups, and CH3, CH2, C–H, OH and C=O were the most active key functional groups in the process of coal oxidation. The dynamic correlation degree between heat flux intensity and key active groups is established by using dynamic grey correlation mathematics method. It is concluded that C=O bond has the highest correlation with heat flow intensity during coal oxidation, and has the greatest influence on heat flow intensity. The correlation values of the active groups CH3 and CH2 are second only to the C=O bond, and they are easy to react with oxygen, accompanied by the reaction heat. Although the correlation degree between C–H and OH bond is lower than that of C=O, CH3 and CH2 bond, the correlation degree value is also high, and has certain contribution to the coal reaction heat. These research results have important guiding significance for the development of targeted inhibitors for Jurassic coal spontaneous combustion disaster in northern Shaanxi. [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]