SO2 scrubbing is accomplished using a saturated solution of ammonium sulfate in spray tower absorber. Anhydrous or aqueous ammonia is fed into the absorber recirculation tank under pH control as the reagent for SO2 absorption. Primary reaction products of ammonium sulfate / bisulfite are converted to ammonium sulfate through forced oxidation in the absorber recycle tank. Using the thermal energy of the flue gas, a portion of the byproduct ammonium sulfate is continually crystallized from the saturated absorber liquor forming a suspension of ammonium sulfate. By maintaining high recirculation of absorbing liquor and a relatively low pH, ammonia slip in the outlet flue gas is kept at low levels, which avoids the plume visibility problem that has been a stumbling block of previous ammonia scrubbing processes. A product bleed stream from the absorber is first dewatered in a set of hydroclones followed by a centrifuge to generate an ammonium sulfate cake of approximately 98%+ solids. All the recovered solution is recycled to the absorber. The centrifuge cake is further processed in a dryer/cooler and subsequent compaction granulator to make final ammonium sulfate product with < 0.5% moisture content. The dried ammonium sulfate granules are then stored and shipped for sale in 50 kg standard bags.