With these scrubbers, acid gases are captured by impaction of the acid gas molecules onto an alkaline slurry, such as lime. Here, the evaporation water from the scrubbing liquid is carefully controlled so that when the material reaches the bottom of the tower, it is a dry powder (a dry fly ash and lime mixture). This method eliminates the scrubber water that must be treated or disposed; additionally, the power requirements and corrosion potential are reduced. Emission tests have demonstrated control efficiencies of 99% or better for hydrogen chloride and sulfur dioxide removal under optimal conditions (temperatures below 300°F, sufficiently high lime/acid ratios, and sufficiently long gas residence time in the scrubber). Dioxins were also considerably reduced (Hershkowitz 1986).
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