TW333521B - Magnesium-enhanced sulfur dioxide scrubbing with gypsum formation - Google Patents

Abstract

A method of removing sulfur dioxide from a gaseous stream with a magnesium-enhanced lime scrubbing medium so as to produce a gypsum by-product comprising: passing the gaseous stream through a wet scrubbing unit while contacting the gaseous stream with an aqueous slurry of magnesium-enhanced lime, where the aqueous slurry contains between 13-20 percent by weight calcium sulfite solids, and with magnesium sulfite and magnesium sulfate dissolved therein; directing the aqueous slurry, after contact with the gaseous stream, to a hold tank and adding lime and magnesium thereto to replenish reacted lime and magnesium; recycling the replenished aqueous slurry to the wet scrubbing unit for further contact with the gaseous stream passing therethrough; removing a bleed stream of the aqueous slurry, containing calcium sulfite, magnesium sulfite and magnesium sulfate, and having a pH of between 4.5-5.6, from the wet scrubbing unit, after contact with the gaseous stream and prior to directing the same to the hold tank; passing the removed aqueous slurry directly to an oxidizing unit, without separation of calcium sulfite solids, magnesium sulfite and magnesium sulfate therefrom; oxidizing the calcium sulfite and magnesium sulfite to produce gypsum and magnesium sulfate, the gypsum precipitating as a solid and the magnesium sulfate dissolving in the aqueous medium; removing any residual solids and the gypsum from the aqueous slurry to produce a clarified solution; separating the gypsum from residual aqueous medium and returning the separated aqueous medium to the wet scrubbing unit; and returning the clarified solution along with the separated aqueous medium to the wet scrubbing unit for admixture with the aqueous slurry.