New technology tackles most pollutants emitted by coal-fired power plants
A new technology for removing mercury from the emissions of coal-fired power plants has the added benefit of simultaneously reducing other pollutants.
Tests conducted at three coal-fired power plants show that a new technology can reduce mercury emissions at higher rates and lower costs than current methods, according to its developers, Chem-Mod LLC. But its ability to simultaneously remove the other pollutants associated with burning coal is what really sets the technology apart.
Coal-fired power plants are the largest unregulated source of mercury [708KB PDF] in the U.S. and currently emit about 48 tons of mercury annually. The toxic mercury from the coal released into the atmosphere is in either the elemental (Hg0) or the oxidized (Hg2+) form. However, the two established technologies that show the most potential for controlling the metal—activated carbon injection and flue gas desulfurization, which is also known as the “scrubber technique”—have difficulty capturing Hg0 because of its low reactivity. The Chem-Mod system is able to capture Hg0 by using a liquid sorbent to oxidize it to Hg2+ or trap it on its surface. A second, powder sorbent captures SO2 and heavy metals. The two sorbents combine to trap the emissions in a ceramic-like matrix that is locked into the fly ash.
The technology removed up to 98%, 90%, and 86% of the mercury in week-long tests with different bituminous and subbituminous grades of coals. In addition, the system cut SO2 emissions by 40–75% and those of arsenic, chloride, and heavy metals by 75–90%, estimates Douglas Comrie, vice president of Chem-Mod and the technology’s principal inventor. Because the new system can capture a range of pollutants, it has an advantage over existing mercury-specific systems, which are “one-trick ponies,” he says.
The Chem-Mod technology also costs less than scrubbers, which will be its main commercial competitor, Comrie says. For a 200-megawatt, coal-burning plant, the Chem-Mod system will cost approximately $2–8 million, whereas a scrubber costs $60–80 million. The Chem-Mod price tag is similar to the $2–6 million annual cost estimate that the U.S. Department of Energy made in the mid-1990s for using activated carbon to remove mercury.
Chem-Mod’s encapsulation of multiple pollutants makes the technology fundamentally different from other sorbent approaches, says Thomas Erickson, associate director for research at the University of North Dakota’s Energy and Environmental Research Center (EERC), which independently pilot-tested the technology and provided analytical support for the full-scale tests. Currently, about 25 different technologies are in the works for mercury emissions control, Erickson says, but Chem-Mod is the first to promote a market-ready technology.
However, Michael Holmes, EERC’s deputy associate director for research, warns that consistently achieving 90% mercury removal is not easy. “Everything has to be going in your favor,” he says. “With mercury, there is no one-size-fits-all rule. You can have the same coal performing differently with mercury, for different reasons.”
But Comrie believes that after computer models are used to optimize the Chem-Mod process, something the company is now doing, “the system will [consistently] reduce somewhere around 75% sulfur and at least 90% mercury.” He says that optimization for each plant’s furnace will improve results by providing operators with a variety of information, such as the best location to add the sorbent.
Although Chem-Mod has gone public with its approach, most companies with competing ideas haven’t publicly revealed their technologies because it is not clear when mercury control regulations will go into effect, Erickson says. Currently, legislative debate is under way over three federal proposals for mercury reductions that were laid out in 2003: the Clear Skies Act, the Clean Air Planning Act, and the Clean Power Act.
Amid this debate, the U.S. EPA issued the Clean Air Mercury Rule (CAMR) in March 2005, which promotes a cap-and-trade approach to reduce mercury emissions 21% by 2010 and 70% by 2018. Critics of CAMR argue that it offers a loophole for managers of some coal-fired plants to do little or nothing about their emissions. These critics complain that EPA should have chosen to enforce a “best-technology” solution for all plants, which would have driven the industry to solutions such as Chem-Mod. Comrie points out that the energy industry could meet the 2018 standards today with his technology.
Many states are preparing their own mercury rules, and some, including Connecticut, Massachusetts, and New Jersey, already have more stringent regulations than CAMR, requiring as much as 90% emissions cuts in shorter time frames. If utilities demand a new mercury-reduction technology, many companies would come out with other new techniques, Erickson says.
Comrie points out that Chem-Mod’s technology also offers another advantage: Because the ceramic-bound emissions do not leach from the fly ash, it can be reused. This means that utilities can sell the ash instead of paying for landfill disposal. There is a large market for using fly ash to make concrete, in place of Portland cement. Utilities can also sell fly ash from plants that use scrubbers. Plants that use activated carbon do not have this option because the process contaminates fly ash, rendering it valueless.
Comrie is expecting at least one full-scale commercial facility to start using the Chem-Mod technology in the next 3–4 months, and at least half a dozen others by the end of the year. —PRACHI PATEL-PREDD
