A dry or semi-dry scrubbing system, unlike the wet scrubber, does not saturate the flue gas stream that is being treated with moisture. In some cases no moisture is added, while in others only the amount of moisture that can be evaporated in the flue gas without condensing is added. Therefore, dry scrubbers generally do not have a stack steam plume or waste water handling/disposal requirements. Dry scrubbing systems are used to remove acid gases (such as SO2 and HCL) primarily from combustion sources.