Patent ID: 7179438

Claim:
A method for recovering gypsum product and magnesium hydroxide product from flue gas containing sulfur dioxide, the method comprising: treating the flue gas containing sulfur dioxide with a magnesium hydroxide slurry to produce magnesium sulfite and magnesium bisulfite; oxidizing the magnesium sulfite and magnesium bisulfite by reaction with air; producing magnesium sulfate blowdown from the oxidized magnesium sulfite and magnesium bisulfite; reacting the magnesium sulfate blowdown with calcium chloride to produce a gypsum slurry; removing gypsum fines from the gypsum slurry; washing the gypsum slurry after the gypsum fines are removed to produce gypsum product, a magnesium chloride filtrate, and a residual stream; reacting the magnesium chloride filtrate with calcium hydroxide to produce a magnesium hydroxide slurry; removing grit and unreacted calcium hydroxide from the magnesium hydroxide slurry to form a treated magnesium hydroxide slurry; and purifying the treated magnesium hydroxide slurry to produce a magnesium hydroxide product and a calcium chloride solution.