Clear liquid acid flue gas desulfurization system

An efficient and cost-effective flue gas desulfurization process for removing sulfur dioxide from waste gases is provided. The process employs a substantially solids-free clear liquor scrubbing liquid and an organic acid additive capable of maintaining a process pH of 4.5 to 6.0 under inhibited oxidation conditions in the absorber to accomplish sulfur dioxide removal while avoiding scale formation and encrustation. Calcium sulfite relative saturation is controlled to a desired low optimum level by maintaining the circulating calcium ion concentration at a corresponding optimum low level. A smaller thickener unit area is required to produce calcium sulfite crystals with optimum settling and dewatering characteristics. A reactor system that promotes the formation of small, efficiently dewatered calcium sulfite solids is also provided.