Study on the non-uniform melting behavior of ash particles during the combustion process of Zhundong iron-rich coal

The slagging and fouling problems on the heating surfaces during Zhundong iron-rich coal combustion process were extremely serious. Due to the influence of the coal formation environment, the distribution of minerals in the coal was uneven. However, the impact of this uneven distribution on the slagging process remained unclear. In this paper, the melting behavior during the combustion of Zhundong iron-rich coal was investigated using the high-temperature stage optical microscope system (HTSOM). The elemental distribution and mineral composition of the ash particles were analyzed to understand their influence on the melting process. The results showed that three colors of particles were formed after the combustion of Zhundong iron-rich coal, yellow, white and red. The elemental distribution of these particles exhibited significant differences. The yellow particles were more prone to melting, while the red particles were difficult to melt. The Na, S and Si were enriched in the molten zone of the ash particles, whereas Mg, Al and Fe were concentrated in the unmolten zone. The enrichment of Ca was more complex: it was concentrated in the molten zone of the yellow and white particles but enriched in the unmolten zone of the red particles. The main component of the yellow particles was Na2SO4, while the white particles primarily consisted of Ca-Mg-based minerals. The red particles were mainly composed of Fe3O4, Ca3Fe2(SiO4)3, and Fe2O3. These compositional differences were the primary reason for the variations in the melting behaviors of the different colored particles.