Production of ammonium sulfate

A process for simultaneously producing ammonium sulfate and removing sulfur dioxide from a sulfur dioxide-containing gas in a distillation column comprised of an upper ammonia scrubbing zone, a central reaction zone, and a lower stripping and crystallization zone that contains at least one vapor-liquid contact tray which comprises:

• (a) introducing a sulfur dioxide-containing gas and ammonia into said central reaction zone wherein sulfur dioxide, ammonia, water and oxygen react to form an ammonium sulfate-containing solution which flows downward into said lower stripping and crystallization zone;
• (b) introducing water into the upper ammonia scrubbing zone of said distillation column, said water scrubbing the ascending gases as it flows downward into said central reaction zone;
• (c) withdrawing a substantially ammonia and sulfur dioxide-free gas overhead from said distillation column;
• (d) introducing an oxygen-containing gas into the bottom of the lower stripping and crystallization zone of said distillation column;
• (e) supplying heat to said distillation column;
• (f) withdrawing a slurry stream of liquid and ammonium sulfate solids from each vapor-liquid contact tray on which such a slurry exists in said lower stripping and crystallization zone;
• (g) separating a substantial portion of said ammonium sulfate solids from each slurry stream withdrawn from each vapor-liquid contact tray to produce a liquid stream depleted in ammonium sulfate solids;
• and
• (h) returning each liquid stream produced from each slurry stream in step (g) to the vapor-liquid contact tray from which the slurry stream was originally withdrawn.