Patent ID: 8758719
Filing Date: 2014-06-24
Classification: C01C,C01F,C01P,C22B

Abstract:
1. A continuous countercurrent flow process for converting FGD gypsum to ammonium sulfate and calcium carbonate comprising the following steps: separating an aqueous slurry of FGD gypsum to result in a FGD gypsum liquid residue and a FGD gypsum cake; combining the FGD gypsum cake with an ammonium carbonate solution and an ammonium sulfate solution in a first reactor to chemically react and form an ammonium sulfate solution containing a precipitated calcium carbonate and a FGD gypsum remnant and an ammonium carbonate remnant; separating the precipitated calcium carbonate from the ammonium sulfate solution to result in a product ammonium sulfate solution residue and an initial product calcium carbonate cake; employing a part of the product ammonium sulfate solution residue to retain as product ammonium sulfate solution and a remaining part to recycle back into the first reactor; combining the initial product calcium carbonate cake with a portion of the ammonium carbonate solution in a second reactor to chemically react and form an initial product ammonium sulfate solution; separating the initial product ammonium sulfate solution to result in an initial product ammonium sulfate solution residue and a final product calcium carbonate cake and retaining the final product calcium carbonate cake; washing the final product calcium carbonate cake with a portion of the ammonium carbonate solution, then with water to result in an ammonium carbonate wash residue; adding the ammonium carbonate wash residue to the second reactor; and employing part of the initial product ammonium sulfate solution residue to recycle to the first reactor and part of the initial product ammonium sulfate solution residue to recycle to the second reactor.