A System for Control of Aluminum Chloride Fumes

Abstract

During primary aluminum processing the molten aluminum is periodically fluxed with chlorine to separate impurities from the metal. The gaseous effluent from the chlorination process contains submicron particulates and gaseous vapors which produce a dense, white plume. The plume is acidic with hydrogen chloride and chlorine vapors, which cause a variety of corrosion problems. Since the stack discharge temperature can range as low as 200°F-and aluminum chloride sublimates at about 360°F, blockage of ductwork can also occur. For effective removal of both the particulates and chloride gases in the effluent, a sodium hydroxide solution is recommended. However, such a scrubbing liquor produces a flocculent precipitate. Therefore, a nonplugging type of scrubber is required. The solution UOP advanced was a “mobile packing” type of scrubber, utilizing a bed of polypropylene spheres in random, turbulent motion. The motion of the packing prevents plugging. The paper describes the design for such a system, describing the optimum use of ductwork, scrubber placement, gas saturation, and recirculation equipment. Instrumentation requirements, both minimum and optimum are discussed.