Comparative Analyses between Raw and Preoxidized Pulverized Coals: Combustion Behaviors and Thermokinetic and Microcharacteristics

Investigating the difference in the combustion performance and microcharacteristics of oxidized and raw pulverized coal (PC) can contribute to effectively prevent and control the spontaneous combustion of deposited coal dust in high-temperature environment and further help guarantee the safe operation of coal-fired boiler. In this study, the combustion performance and thermokinetic and microcharacteristics of three raw coal samples and their preoxidized forms were explored by a thermogravimetric analyzer (TGA) and Fourier transform infrared spectroscopy (FTIR). According to the characteristic temperatures and variations of the mass loss rate during heating, the entire combustion process of PC was divided into four periods. For each type of coal, the preoxidized PC had relatively lower characteristic temperatures than the corresponding raw PC. The preoxidized samples had larger values of ignition index (Cig) and comprehensive combustibility index (S), but lower values of burnout index (Cb) than raw samples. The values of apparent activation energy (E) for the preoxidized PC were below that of the corresponding raw PC at the same conversion rate (α), which suggested the preoxidized PC required relatively less energy to react and was more prone to spontaneous combustion. In addition, although parts of -OH, C=O, and aliphatic hydrocarbon groups were consumed after the preoxidation treatment, the increase in C-O and -COO- bonds compensated for the adverse effect of the reduction of the aforementioned groups on coal combustion.