REACTIVATION OF FLY-ASH AND CA(OH)2 MIXTURES FOR SO2 REMOVAL OF FLUE-GAS

Mixtures of fly ash and Ca(OH)2 were hydrated, characterized, and tested in laboratory-scale experiments. Hydrated mixtures developed a high total surface area, greater than the arithmetical addition of surface areas of initial solids before hydration. The relative surface area increment increased with temperature, time of hydration, and fly ash/Ca(OH)2 ratio, the temperature effect being the most important. Tetracalcium aluminate monosulfate and tetracalcium aluminate were assumed to be responsible for these area increments. Only 5% SO2 removal was observed with untreated fly ash after 1 h of contact and at high humidity. High SO2 capture occurred with hydrated mixtures. SO2 removal correlates well with the relative surface area increment. The amount of SO2 capture increases strongly with the increasing relative humidity of the gas.