Inorganic aerosols and their role in catalyzing sulfuric acid production in furnaces

Submicrometer ash and sulfur oxides are important pollutants formed during pulverized coal combustion. The submicrometer ash contains known catalysts for sulfur dioxide oxidation as well as alkaline species that will react with sulfur oxides. This work was an investigation to determine if submicrometer ash-sulfur oxide interactions can have a significant impact on the fate of sulfur. The submicrometer-ash-sulfur oxide interaction studies were carried out using submicrometer ash of controlled composition generated from the combustion of synthetic chars. The submicrometer ash was either exposed to SO2 in the combustion chamber or immobilized on a quartz-fiber filter for later exposure to SO2. Submicrometer-ash catalysis of SO2 oxidation was found to contribute significantly to the SO3 formed in the convective passes of a utility boiler, depending on the coal, combustion conditions, and temperature profile in the convective section. The calcium within the freshly formed submicrometer ash appears to sulfate more rapidly than would be predicted from rates published in the literature and is expected to sulfate completely in the convective section of a utility boiler.