Fly Ash Reactivation for the Desulfurization of Coal-Fired Utility Station's Flue Gas

Abstract

Fly ash hydration in the liquid phase has been studied by employing temperature, hydration time, and water/fly ash weight ratio as variables. The results show that temperature and hydration time have a large positive effect in surface area development of the hydrated ashes (due to the formation of hydrated tetracalcium aluminate) whereas the water/fly ash weight ratio effect seems to be negative but its influence is very small. Desulfurization tests have been carried out with some of these hydrated fly ashes. Tests consisted of exposing the solid for 1 h to an N₂/SO₂ gas stream containing 500 ppm SO₂. The variables employed were temperature and relative humidity. The results show that SO₂ capture rises with temperature and, particularly, with an increase in relative humidity. A correlation between surface area and SO₂ capture was found. The greater the surface area, the greater the amount of SO₂ captured. This fact shows that hydrated tetracalcium aluminate is a highly reactive substance against SO₂.