Sulfur retention in fly ash

The results of the acquisition and analysis of a large body of data on the properties of fly ash from coal fired power plants support the conclusion that sulfur retention by fly ash is mainly controlled by the alkaline metal oxide content of that ash. Investigation of the chemical and physical nature of sulfur retention indicates that although physical adsorption may play a role in retaining a portion of the sulfur, the ultimate amount of sulfur retained is controlled by the percentage of the ash that is available to combine chemically with the sulfur. Nearly all sulfur retained will be in the sulfate form, even though it possibly did not initially condense as a sulfate.

Of the relationships studied relating sulfur retention to alkaline metal oxide content, the best correiations were found using the total alkaline metal oxide values, with the true molar or weighted total providing the best fit. The importance of how the coal was burned, the temperature history of a particle and the method of ash collection were demonstrated to have a very significant impact on reducing data scatter. The particle size and ash surface area data did not show a significant relationship with sulfur retention.