Reactive Scrubbing for Mercury Removal and Stabilization

Mercury emissions from incinerators have long been recognized as an environmental issue. Current U.S. Environmental Protection Agency regulations call for the reduction of mercury emission by 85 percent for municipal, hazardous, and medical waste incineration sources. The most common approach for mercury control from these sources is the use of activated carbon, either injected as a powder into the gas upstream of particulate control equipment or as a fixed bed of granular carbon. In both cases, large volumes of mercury-contaminated carbon are generated that could create a disposal problem posed by the leachability of mercury from the carbon material. ADA Technologies, Inc., has investigated reactive scrubbing as an alternate technology for gas-phase mercury control that features a significant advantage over the use of carbon. The reactive scrubbing design developed by ADA removes elemental and speciated forms of mercury from gas streams and in a secondary process converts the captured mercury to mercuric sulfide, a granular solid that is extremely insoluble and eligible for disposal as a nonhazardous waste. During the past 2 years, ADA has been engineering a system using reactive scrubbing for the treatment of an industrial process gas stream saturated with mercury vapor. The reactive scrubber is able to reduce mercury concentrations greater than 95 percent. For the application of reactive scrubbing to incinerators, design guidelines must be defined to optimize the scrubber operation. In this Phase I research project, gas-to-liquid ratio and scrubber reagent concentration will be investigated as a function of feed gas composition to optimize the scrubber operating parameters for efficient and cost-effective mercury capture. The stabilization process used to treat captured mercury in the scrubber liquor also will be investigated to identify alternate chemistries that can make the process more economical. As a final activity, a credible cost estimate for a reactive scrubber system for a commercial-scale incinerator will be prepared. A commercialization path for the proposed reactive scrubber technology has been identified that follows a progression used in the commercialization of other ADA technologies. The basic design of the industrial reactive scrubber has been licensed to a company that sells environmental control equipment to a range of industrial customers. The commercial potential of the developed technology is promising, with a large market based on the number of medical and municipal incinerators currently in use.