Insights into the transformation mechanism of Se in sized ash particles arising from coal combustion: Model vs. experiment

One major challenge on Se emission control in power plants is the relatively low capture efficiency of the fly ash while with large fluctuations in the proportion of unstable physically adsorbed Se. In this study, a comprehensive transformation model of Se during coal combustion is developed and compared to field tests for validation. Results show three transformation stages of Se: remain SeO2 vapor (> 750 ?), chemical adsorption dominates (350-750 ?) and physical adsorption dominates (< 350 ?). The condensation of Se is hardly occurred in each stage due to the low partial pressure of SeO2(g). Se enrichment in small particles is reflected both by physical and chemical adsorption, and the particles of size < 1 mu m are the major host for the physically adsorbed Se. The gas -to-solid transformation of Se would be enhanced with increased fly ash particles and the inherent Ca/Fe fraction. The promotion effect of Fe is stronger than Ca partly due to the competition of SO2 in flue gas that leads to the fast consumption of CaO at > 800 ?. These findings help better understand the partitioning mechanism of Se in sized ash particles and provide guidance on strengthened Se removal in power plants.

Automated summary

This study develops a comprehensive transformation model of selenium during coal combustion and validates it through field tests. The results reveal different transformation stages of selenium and identify the enrichment of selenium in small particles. Additionally, the study uncovers factors influencing the gas-to-solid transformation of selenium.