An in-situ forced oxidation wet flue gas desulfurization apparatus, method and arrangement for utilization with oxy-fuel combustion power plants. The apparatus is a tower-like structure having a flue gas scrubbing zone and a reaction zone located subjacent to the gas scrubbing zone. A sulfur oxide absorbing liquid slurry is supplied to the gas scrubbing zone to react with and scrub the sulfur oxides from the flue gas. The partially reacted liquid slurry reagent and the scrubbed products drain into the reaction zone, rising to a set level. Oxidation air is introduced into the liquid slurry in the reaction zone to force the in-situ oxidation of sulfur compounds collected in the reaction zone. A wall separates and communicates the gas scrubbing zone and the reaction zone, the wall prevents the oxidation air from entering the gas scrubbing zone and extends into the liquid slurry below a nominal depth required to establish and maintain a liquid slurry seal thereby substantially precluding the leakage of flue gas into the reaction zone while allowing the partially reacted liquid slurry reagent and scrubbed products to drain into the reaction zone.