Abstract: A flue-gas scrubbing-liquor regeneration process that is based on contacting N-S compounds contained in a flue-gas scrubbing liquor with a lime/limestone solution in a double draw-off crystallizer under suitable pH conditions for precipitating calcium salts of N-S compounds. The precipitated crop is filtered and then hydrolyzed in a sulfuric acid environment to produce gypsum and ammonium sulfate in solution. The hydrolyzed slurry is filtered and the filtrate is neutralized with lime to liberate ammonia gas that is then sparged through a sulfuric acid solution to cause the precipitation of commercial-grade ammonium sulfate.