Available Technology

Catalysts for Oxidation of Mercury in Flue Gas

The Department of Energy’s National Energy Technology Laboratory is seeking licensing partners interested in implementing United States Patent Number7,776,780titled "Catalysts for Oxidation of Mercury in Flue Gas." Disclosed in this patent are catalysts for the oxidation of elemental mercury in flue gas. These novel catalysts include iridium (Ir), platinum/iridium (Pt/Ir), and Thief carbons. The catalyst materials will adsorb the oxidizing agents HCl, Cl2, and other halogen species in the flue gas stream that are produced when fuel is combusted. These adsorbed oxidizing agents can then react with elemental mercury in the stream, which is difficult to capture, and oxidize it to form Hg (II) species, such as mercuric chloride (HgCl2), which is soluble in water and more easily removed from the stream.
Patent Abstract: 
Certain effluent gas streams contain many toxic pollutants, including the heavy metals mercury and cadmium. Much research has been done to develop methods to control mercury emissions from flue gases. These methods employ sorbents, catalysts [including those for selective catalytic reduction (SCR)], scrubbing liquors, flue gas or coal additives, combustion modifications, barrier discharges, and ultraviolet radiation. Existing SCR catalysts are not optimized for selectively oxidizing elemental mercury in effluent streams, and typically achieve only 50 percent oxidation. The Ir and Pt/Ir catalysts described in this patent adsorb mercury and HCl and Cl2at high levels. By doing so, they bring together the oxidizing agents HCl and Cl2with elemental mercury to oxidize most of the mercury to Hg (II) species. Mercury (II) chloride is readily removed by the scrubbing solutions employed for acid gas removal and/or by adsorption on unburned carbon in fly ash captured by ESPs or baghouse filters. These catalysts exhibit superior anti-corrosion and high-temperature resistance characteristics. Furthermore, when using Thief carbon, which is partially combusted coal removed from the combustion chamber of a power plant using a lance (called a "thief"), the catalyst is self-activated (by adsorbing Cl2from the flue gas) and disposable.
They can be used to reduce mercury emissions in coal-burning power plants, incinerators, oil-burning boilers and power plants, and refuse-derived fuel power plants -They can adsorb mercury, HCl, Cl2and other halogen species present in flue gases at high levels for efficient oxidation of elemental mercury -Ir-containing catalysts are more temperature resistant than currently available catalysts for mercury removal -Ir-containing catalysts are more corrosion resistant than existing mercury removal catalysts, thus leading to a longer active lifetime -Thief carbons are far less expensive than conventional gold or palladium catalysts -Thief carbons are inexpensive enough to be disposable
Patent Number: 
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