Low-temperature exothermic oxidation characteristics and spontaneous combustion risk of pulverised coal
粉煤低温氧化放热特征及自燃危险性
Fuel, Volume 252, 15 September 2019, Pages 238-245
Li-Feng Ren, Jun Deng, Qin-Wei Li, Li Ma, Chi-Min Shu
摘要：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.
Thermokinetic characteristics of coal spontaneous combustion based on thermogravimetric analysis
基于热重分析的煤自燃热动力学特征
Fuel, Volume 250, 15 August 2019, Pages 235-244
Qing-Wei Li, Yang Xiao, Cai-Ping Wang, Jun Deng, Chi-Min Shu
摘要：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.
Determination of the influence of pyrite on coal spontaneous combustion by thermodynamics analysis
通过热力学分析确定黄铁矿硫对煤自燃的影响
Process Safety and Environmental Protection, Volume 129, September 2019, Pages 163-167
Fuqiang Yang, Yong Lai, Yuze Song
摘要：In order to uncover the effect of pyrite on the tendency of coal to spontaneously combust, thermal analysis was carried out to characterize the reaction process of coal with different pyrite contents at four heating rates of 5, 10, 15, and 20 K min−1 in air flow from 25 to 900 °C. The Flynn-Wall-Ozawa method was applied to calculate the activation energy of coal with different pyrite contents. The results show that the thermogravimetric (TG) curve of coal samples can be divided in four stages, being water evaporation, oxygen absorption, thermal decomposition and burnout. As the mass fraction of pyrite content increased, the ignition point of the coal samples decreased and the weight loss rate during the thermal decomposition phase diminished. Meanwhile, the exothermic peak and mass loss peak moved toward lower temperatures. The peak values in the derivative thermogravimetric (DTG) and differential scanning calorimetry (DSC) curves shifted to higher temperatures with higher ignition and burnout temperatures under faster heating rates, but the whole curve shape was not affected. The apparent activation energies of the coal samples declined with higher pyrite contents, so the spontaneous combustion of coal can be promoted by pyrite.
Prediction of gas and coal spontaneous combustion coexisting disaster through the chaotic characteristic analysis of gas indexes in goaf gas extraction
通过瓦斯指数混沌特性分析预测采空区瓦斯抽放过程中的瓦斯与煤自燃并存灾害
Process Safety and Environmental Protection, Volume 129, September 2019, Pages 8-16
Yawei Song, Shengqiang Yang, Xincheng Hu, Wanxin Song, Qin Xu
摘要：The gas and coal spontaneous combustion coexisting disasters have become a common mode of major and extraordinarily serious accident of coal mine, so it has important significance to predict the coexistence disaster for prevention and treatment. This study took the gas samples from gas drainage pipeline in the goaf of 1203 working face of Hongyang No. 2 Coal Mine, and then analyzed the chaotic characteristics of coal gas indexes from gas drainage pipeline by using the R/S analysis method. The results show that the Hurst index of time series of gas indicators related to coal spontaneous combustion shows stable statistical characteristics when the oxygen concentration fluctuates smoothly. However, when the oxidation of coal in goaf accelerates, the Hurst index will be smaller than 0.77025. The Hurst index of time series of gas indicators related to gas in the goaf of 1203 working face is greater than 0.5, which indicates that gas has persistent correlation. The Hurst index can quantitatively reflect the inherent tendency characteristics and persistent intensity of the gas concentration variation process. The Hurst index of time series of gas indicators related to coal spontaneous combustion at the monitoring point can be used to judge the time tendency of coal spontaneous combustion in goaf and further judge the spontaneous combustion state of coal. Therefore, methods for judging whether the coal in goaf is in the dangerous stage of spontaneous combustion and for determining the change trend of gas concentration in the goaf were proposed. On this basis, the coexisting disaster were forecasted, moreover, this kind of prediction method can reduce the misinformation of the coexisting disaster. The study provides a meaningful new idea and method for improving the theory of coexisting disaster prediction.
