A multi-function duct for a dry scrubber system useful for processing a gas stream, such as a flue gas stream produced by a fossil fuel fired boiler, a combustion process or the like, is provided. The multi-function duct is useful for a circulating dry scrubber (CDS) dry flue gas desulfurization (DFGD) system operable for dry or moistened reducing agent distribution into a flue gas stream flowing therethrough. As such, the distributed dry or moistened reducing agent reacts with acid gas in the flue gas to produce a dry reaction product.