Research on Self-Ignition Characteristics and Prediction Indices of Pulverized Low-Rank Coal Under Different Oxygen Concentrations

Abstract

Self-ignition frequently takes place during transportation, storage, and application of low-rank coal dust, which may engender severe hazard issues. Grasping the self-ignition features of pulverized coal with a low maturity degree and effects of the thermostatic environment is indispensable for forestalling fires and explosions. Both minimum ignition temperature (MIT) and ignition delay time (t_i) are beneficial for estimating the self-ignition difficulty of accumulated pulverized coal. Accordingly, this study explored both pulverized coal samples of low rank and tested them by a hot oven device under various limited oxygen concentration ($X_{{{\text{O}}_{{2}} }}$) conditions (≤ 21 vol%). The results revealed that the MIT of the Yanzhou (YZ) sample was higher than that of the Zhangjiamao (ZJM) sample under the same $X_{{{\text{O}}_{{2}} }}$ condition. Furthermore, an increase in ambient temperature markedly curtailed the t_i. The MITs were all increased by roughly 50 °C for the two samples when the $X_{{{\text{O}}_{{2}} }}$ decreased from 21 to 5 vol%. The CO and C₂H₄ production, along with oxygen consumption rates, increased first and then tended to be stable with the extension of reaction time. The analysis result of the gas ratio suggested that the CO/CO₂ and C₂H₄/C₂H₆ ratios could be considered as secondary indices for the prevention and control of pulverized coal self-ignition. Furthermore, with the decrease in the $X_{{{\text{O}}_{{2}} }}$, both the apparent activation energies and pre-exponential factors of the two samples all showed a stage increase propensity. The reaction rates of the two samples decreased dramatically when the $X_{{{\text{O}}_{{2}} }}$ decreased from 21 to 5 vol%. These results suggested that reducing $X_{{{\text{O}}_{{2}} }}$ is an effective means for the prevention of pulverized coal self-ignition.