Technology▼Solutions Dramatically improved mercury removal
© 2003 American Chemical Society
Senate Subcommittee on Clean Air, Climate Change, and Nuclear Safety that the results Gore has achieved thus far—assuming further successful field verification—would “allow coalburning facilities to easily comply with the most stringent regulations set forth in the Clear Skies Act of 2003.” The tests indicate that the technology would also allow the utilities to comply with a competing bill, the Clean Air Planning Act of 2003, “and would even approach the control levels required in the Clean Power Act of 2003,” Bucher says. W. L. GORE & ASSOCIATES, INC.
U.S. EPA tests show that a new technology can remove 100 times more mercury from the emissions of coalburning power plants than the best current technologies, according to its developers at W. L. Gore and Associates, Inc., of Elkton, Md. As a result, the “Gore mercury capture technology” has received a great deal of attention since the company unveiled it in late May. The U.S. Department of Energy estimates that power plants emit 48 tons of mercury annually, generating one-third of the country’s total anthropogenic mercury emissions. The Clean Air Trust calls mercury “one of the most prominent toxic problems,” noting that mercury-related fish consumption advisories have been issued for thousands of U.S. water bodies in dozens of states. Gore’s new technology was consistently able to capture more than 90% of the mercury in the EPA tests, which ran 24 hours a day for 7 weeks at the agency’s pilot-scale coal combustion unit in Research Triangle Park, N.C. In addition to capturing such a high percentage of the mercury, the technology is notable for targeting all the different forms of mercury resulting from combustion, says Richard Bucher, Gore’s global business leader. The U.S. electric power industry is facing a looming deadline under the existing Clean Air Act (CAA), which requires EPA to propose MACT (Maximum Achievable Control Technology) standards for mercury by the end of this year, says Frank O’Donnell, executive director of the Clean Air Trust. Whether or not those CAA requirements will go into effect depends on the fate of some of the legislation being debated by the Congress, notably the Clear Skies bill being promoted by the Bush Administration (Environ. Sci. Technol. 2002, 36, 181− 182), O’Donnell says. In early June, Bucher told the U.S.
W. L. Gore has developed a promising technology for removing mercury from coalfired power plant emissions.
The United States is leading the world with mercury regulation, but— as Bucher’s testimony makes clear— exactly what regulations utilities will have to comply with are currently up in the air, O’Donnell says. “I don’t think anyone can tell what EPA will publish as a standard,” he says. Because of this uncertainty, would-be technology providers are faced with a daunting challenge, says Steve Benson, senior research manager at the University of North Dakota’s Energy and Environmental Research Center (EERC), which researches mercury measurement and control technologies. “There’s a tremendous difference if you’re looking at a 60% reduction rather than a 90% reduction,” adds Mike Jones, EERC’s associ-
ate director of industrial relations and technology commercialization. Nonetheless, even though wouldbe technology providers do not yet know how much mercury their technologies will have to eliminate, or when regulations will go into effect, at least 20 different firms are racing to develop and/or perfect technologies to target mercury emissions, Benson says. Although many organizations have announced their intent to develop mercury control technologies, the possibility remains that other companies willlike Gore wait to announce their product until they have promising results to report, he adds. Gore’s new technology is particularly attractive because it appears to work well in testing conducted to date at EPA with the subbituminous and lignite coals mined in the western United States, which account for over 50% of the country’s coal supply, Benson says. “The form of the mercury emitted from a power plant is dependent on the constituents of the coal,” Benson told the U.S. Senate Subcommittee in early June. “Western coals contain low amounts of chlorine and produce mostly elemental mercury. Western coals also contain high levels of calcium and sodium oxides that tie up any available chlorine, further increasing the elemental form of mercury.… The problem with elemental mercury is that it is not very reactive and cannot be readily captured by most existing flue gas pollution control equipment.” To date, there is no cost-effective commercially available technology for power plants that burn these western coals, he adds. Activated carbon is currently one of the two established mercury control technologies with the greatest potential, according to Larry Monroe, program manager of Pollution Control Research for Southern Co., one of the nation’s largest electricity generators. “Conventional activated carbon acts like a great big spongeit [adsorbs] the mercury onto the surface,”
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Bucher says. “It appears that different forms of mercury [adsorb] at different rates. That’s why [activated carbon is] not very efficient at elemental mercury, which is in high quantities in the lignite coals and the subbituminous coals.” In comparison, Gore’s technology is chemically rather than mechanically based, Bucher says. “The mercury is actually chemically reacting and bonding to our material,” he explains. “The data [are] suggesting that that reaction is not dependent upon the
forms. Of course, the particulate form would be captured on our filter bag.” Monroe says that the Gore technology sounds promising, and it compares well to both activated carbon and flue gas desulfurization, the other technology with the most potential for controlling mercury from power plants. Because flue gas desulfurization targets ionic mercury, it is generally more effective for the bituminous coal found in the eastern United States, which typically contains 60% ionic mercury when com-
Irradiating incinerator emissions A heavy dose of electrons can inexpensively remove the dioxins and furans generated by the incineration of municipal solid waste (MSW), according to Koichi Hirota and colleagues at Japan’s Atomic Energy Research Institute (AERI). In research published in ES&T’s July 15 issue (pp 3164–3170), the Japanese scientists described tests of their new technique, which subjected incinerator flue gases to the beam generated by an electron accelerator passed through two titanium foils, at the Takahama Clean Center test facility in central Japan. Hirota’s team reports that a 14-kiloGray dose of irradiation decomposed more than 90% of the polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans in their test system, dechlorinating the gaseous pollutants. The AERI scientists say that the technology could easily meet the Japanese dioxin and furan standards that went into effect in December 2002, which stipulate that large incinerators with the capacity to burn 200 kilograms of garbage and industrial waste daily emit less than 1 nanogram of dioxin per cubic meter of exhaust gas. If the new technology is operated with electricity generated by incineration, the scientists estimate that it could cut the cost of treating MSW incinerator gas by 50% below that of the bag filter systems currently being used to meet the new standards. Although the electron beam technology could also meet the even tougher standards that Japanese environmental activists are calling for, the scientists have not been able to conduct further pilot tests of their technology. “We are looking for local governments (manager[s] of MSW incinerators) having interest in ou[r] technology,” Hirota says.
state of the mercury. It makes the mercury easier to capture, and it also increases the amount of mercury that can be held per gram of material.” Bucher won’t say much more about how his technology works, other than that it doesn’t actually contain any Gore-tex fabric. “We’re still trying to iron out the technology involved,” stresses Bob Rodriguez, a spokesperson for Gore. Gore has focused its testing on western coals, Bucher says. “Elemental mercury is much more difficult to capture, whereas oxidized mercury (HgCl2 and HgO), the predominate forms released from eastern coals (bituminous and anthracite), can be captured fairly effectively in wet scrubbers…. Based on our bench scale tests, we believe that we can capture both vapor-phase mercury
busted, Monroe says. However, it may not work properly in combination with wet SO2 scrubbers, he adds. Gore’s technology compares well to activated carbon because it allows the fly ash from the burned coal to be sold, Monroe says. Activated carbon contaminates fly ash generated by plants that use electrostatic precipitators and fabric filters, which people in the industry refer to as “baghouses”, to control particulate emissions, he explains. “Fly ash produced by many western power plants is a valuable byproduct,” Benson says. Bucher estimates that a 110-megawatt (MW) power plant would give up anywhere from $1.1 to $1.5 million per year (including cost of the activated carbon) because of the lost revenue and cost of disposing of the unsellable fly ash.
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Bucher estimates that Gore’s technology would cost a 110-MW plant upwards of $400,000 year, which he presents as good in light of the $700,000 that the same sized plant would have to spend on activated carbon. But Benson cautions that the Gore product’s lifetime will have the biggest impact on its cost and that lifetime is simply not yet clear. Because the mercury is chemically bound to the material used to capture it, the Gore process will produce a smaller volume of contaminated material than competitive methods and the mercury should be more “stable”. This, says Bucher, means that the resulting material can more easily be landfilled. In the long term, the company envisions that the mercury may even be harvested and recycled, he says. The Gore technology is most appealing to power plants that are using a baghouse to reduce particulate emissions. Somewhere between 15 and 20% of all U.S. coal-fired power plants now have a baghouse, and a larger percentage of European plants use them, Bucher says. Moreover, Bucher says that many of the power plant operators he has talked with “are assuming that they are going to be transitioning to some kind of fabric filter to sequester particulate matter, away from an electrostatic precipitator, because of pending regulations, including tighter constraints on particulate and mercury emissions.” Bucher quotes EPA’s Mercury Study Report to Congress, which estimates that the total capital cost associated with purchasing and installing a fabric filter for a 100-MW coal-fired power plant is approximately $4 million. Benson stresses that the Gore technology needs to go through longer-term, larger-scale testing to demonstrate its efficacy, beginning with a test scheduled to take place at EERC’s pilot facility in late summer or early fall. Assuming all goes well, Bucher says that the company has full-scale field tests planned for 2004: “We have a variety of companies who are very eager to do larger-scale testing in their facilities,” he says. Businesses like Southern Co. need to see that a technology operates dependably for 4−6 months in such a fullscale test, Benson says. Bucher estimates that Gore could begin selling the product commercially in 2005. —KELLYN BETTS
