Enhanced effects of ash and slag on SO formation in the post-flame region.

The effects of slag, fly ash (formed in boiler above 1500 °C), and experimental ash (formed in muffle furnace at 815 °C) on the formation of sulfur trioxide (SO) were studied in a fixed bed rector. The results showed that the slag had the best catalytic effect on SO formation, the effect of fly ash was second, and the effect of experimental ash was the worst. The reason may be that the forms of iron in different samples were different. Iron in the experimental ash all existed in the form of FeO. Iron in the fly ash mainly existed in the form of composite iron oxides, such as FeMgSiO, CaFe(SiO), and MgFeO. Iron in the slag also mainly existed in the form of composite iron oxides, such as CaFeO, MgFeO, and CaMgOFeSiO. The different forms of iron had different effects on SO formation. Composite iron oxides could produce more oxygen vacancies owing to lattice defects. This likely promoted the migration and regeneration of lattice oxygen and thus better promoted the formation of SO than FeO. Moreover, MgFeO and CaFe(SiO) could better promote SO formation than CaMgOFeSiO and FeMgSiO. In addition, increasing the SO concentration and O concentration increased the SO concentration but increasing the SO concentration decreased the SO formation ratio.