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DOE - Fossil Energy Techline - Issued on: February 18, 2002 Advanced Mercury Control System's Performance is on Track, Test ShowsCould Apply to 90 Percent of all Coal Plants in U.S.Kenosha, WI - Preliminary results of a Department of Energy-sponsored mercury-control technology show the technology is living up to its design potential. More mercury from coal plants burning subbituminous coal and using an electrostatic precipitator (ESP) to collect fine particles and fly ash can be removed with a carbon-sorbent-injection system even when less carbon is used. This finding is significant because subbituminous coal, especially that of the Powder River Basin in Wyoming, typically generates a high amount of elemental mercury. A large-scale demonstration conducted by ADA Elemental Solutions of Littleton, Colo. indicates that injecting a dry carbon sorbent into the gas stream may provide an effective solution for those PRB plants equipped with ESP's for particulate control. The market is certainly sizable. Approximately 90 percent of all coal plants in the United States use ESPs, notes Mike Durham, president of ADA-ES. Carbon injection is the simplest and most mature mercury-control technology being field tested (today)," he said. With the Environmental Protection Agency developing regulations that could require large mercury reductions at the nation's 1,100-plus coal units by 2007, a viable, economic technology would play a very promising role in future power generation. After two weeks of testing a carbon sorbent for mercury control at a coal plant operated by Wisconsin Electric-Wisconsin Gas (WE-WG) near Kenosha, Wis., ADA-ES reported that mercury-removal rates range from 40 to 70 percent while carbon-injection rates vary from 2-10 lbs/hr of carbon injected for every 1 million cubic feet of gas that was treated. Previous modeling indicated that carbon injected upstream of an ESP would require injection rates exceeding 30 lbs/hr to remove 50% of mercury. Although this level of mercury removal is certainly encouraging, other issues, such as an increased carbon content in the fly ash, may cause significant economic losses to a plant that sells 100 percent of its flyash for concrete applications. Even at the lowest activated carbon-injection rates, the carbon content in flyash was too great for buyers to accept. One possible solution is to install a fabric filter downstream of the ESP. This way, the carbon would be injected after the ESP and collected by the fabric filter. Because mercury adheres to activated carbon or fly ash that is injected into a plant's gas stream, ESPs or fabric filters capture more of the pollutant. In ADA's technology, a fine water mist may also be sprayed into the flue gas to cool its temperature (if it exceeds about 300o F) to the range where the dry sorbent is more effective. DOE selected ADA-ES to perform large-scale sorbent-injection for mercury removal at four different coal plants in the United States in the fall of 2000. The first test site was Alabama Power's Gaston plant, Wilsonville, Ala., which fires low-sulfur Eastern bituminous coal and uses fabric filters to reduce particulate matter emissions. Fabric filters are capable of removing at least 80 percent of mercury by injecting 1/10th the amount of carbon needed for an ESP. Results from the Gaston site indicate that as much as 90 percent of all mercury was removed at the highest performing periods during two weeks of testing. WE-WG was the second site to be tested. Two species of mercury, elemental and oxidized, are produced from coal-fired power plants. The oxidized form of mercury can be removed by a conventional wet scrubber if it is part of a plant's configuration. If not, then a carbon-injection system such as ADA's is required to remove both species. Because contact between the gas and carbon is not as good in plants using ESPs rather than fabric filters, mercury removal rates aren't as high. Nonetheless, the WE-WG results are encouraging because mercury emissions from low-sulfur Western coals is one of the most difficult to control, and the plant is representative of a number of large power stations across the country. A next step in sorbent-injection development and commercialization, Durham said, could be to test the system on different coals for longer periods of time and to use it in concert with a scrubber. Past tests have been significantly smaller (1-megawatt pilot tests). Competing methods such as non-carbon-based sorbents or oxidation catalysts have not been field tested at this scale and, as a result, could lag a few years behind in the development cycle, Durham estimates. Because mercury control is now being discussed in several bills before Congress, it is taking on greater importance as time goes by, said Durham, who added that Massachusetts, New Hampshire and Wisconsin have all announced plans to regulate mercury in the next few years, and several utilities have vowed to install mercury controls by 2006. ADA will also test its injection system at two PG&E Generating's plants, both of which fire low-sulfur bituminous coals and are equipped with ESPs and carbon/ash separation systems. The technology will be demonstrated at the Brayton Point power station, Somerset, Mass. this spring and Salem Harbor, Salem, Mass. in the fall. The project is receiving $4.5 million from the Energy Department. ADA-ES and an 11-organization support team is providing an additional $2.2 million. -End of TechLine - Technical contact: |