Enhanced effects of ash and slag on SO3 formation in the post-flame region.

Abstract

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 (SO3) were studied in a fixed bed rector. The results showed that the slag had the best catalytic effect on SO3 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 Fe2O3. Iron in the fly ash mainly existed in the form of composite iron oxides, such as Fe0.3Mg0.7SiO3, Ca3Fe2(SiO4)3, and MgFe2O4. Iron in the slag also mainly existed in the form of composite iron oxides, such as CaFe2O4, MgFe2O4, and CaMgO0.88Fe0.12SiO4. The different forms of iron had different effects on SO3 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 SO3 than Fe2O3. Moreover, MgFe2O4 and Ca3Fe2(SiO4)3 could better promote SO3 formation than CaMgO0.88Fe0.12SiO4 and Fe0.3Mg0.7SiO3. In addition, increasing the SO2 concentration and O2 concentration increased the SO3 concentration but increasing the SO2 concentration decreased the SO3 formation ratio.