A process and system for removing sulfur oxide, other gases, and particulate from a flue gas. The process includes treating flue gas with a slurry formed from water, an alkaline reagent, and the purge stream from a wet scrubber in a spray dryer, thereby producing a dry by-product. The process further includes filtering the flue gas to remove at least a portion of the dry by-product, wet scrubbing the flue gas exiting the filter in a wet scrubber, adding a lime or limestone reagent to the wet scrubber, and producing gypsum. Activated carbon may be injected into the flue gas upstream of the filtering step and particulate may be removed from the flue gas upstream of the spray dryer.