In wet limestone gypsum Flue Gas Desulfurizers, flue gas is washed with CaCO3-Water slurry on the wet walls of a vertical absorption tower, where SO2 and O-2 are absorbed to form CaSO3 and CaSO4. Though it is required to capture sulfur into calcium sulfate, which is neutral to the environment as deposited, CaSO3 is not always oxidized completely there to CaSO4 due to insufficient residence time of slurry on the wet walls and the low absorption rate of oxygen. The rest CaSO3 should be oxidized in a bubbling tank just under the tower. Therefore appropriate air bubble injectors are required to supply oxygen, just as much as necessary and enough, into the slurry in the tank. Here is proposed an Air Rotary Sparger (ARS) for the vertically and horizontally uniform distribution of small air bubbles in the tank and its performance is investigated with a small-sized conventional paddle type model with a central air injection hole on the bottom and two ARS models.