John Roebel says his latest construction project is every bit the equal of the toughest he's faced: the $1.5 billion conversion of the William Zimmer Generating Station from nuclear to coal power a decade ago.

        Mr. Roebel, vice president of generation resources for Cinergy Corp., is overseeing the utility holding company's $700 million investment in pollution controls at coal-fired generating units at four power plants in Ohio, Kentucky and Indiana.

COSTS & BENEFITS

The cost of the new equipment Cinergy Corp. is installing to control nitrogen oxide emissions won't have an immediate impact on electric rates. That's because under Ohio's electric deregulation plan, residential rates are frozen until 2005. The company has said it's made no decision on seeking cost recovery in Indiana or Kentucky.   The health benefits of reducing nitrogen oxides — and thus, smog — are known, but also difficult to quantify in dollars and cents.   Nitrogen oxide, typically from auto and industrial exhaust, combines with hydrocarbon vapors from gasoline, solvents and other volatile chemicals in the presence of sunlight to make smog. (Smog alerts typically occur in the Tristate during the hottest periods of the summer.)   A key component of smog is ozone. The colorless gas is found in stratospheric belt that helps protect the Earth from ultraviolet radiation. But at ground level, ozone can reduce lung capacity and cause shortness of breath, coughing, headaches, nausea and eye irritation. It's worse for sensitive people children, the elderly, asthmatics and others with lung ailments.   Nationally, air pollution costs an estimated $50 billion a year in health expenses.

        The year-old project, triggered by a 1998 U.S. Environmental Protection Agency order, is designed to reduce emissions of smog-causing nitrogen oxide (NOx) from Cinergy's power plants from about 70,000 tons annually to about 20,000 tons by mid-2004.

        Mr. Roebel, project manager on the Zimmer conversion, said that while that construction project cost twice as much, the NOx control project “construction-wise ... equals that or goes beyond it.”

        The new controls, called selective catalytic reduction (SCR) units, are being installed on up to 11 steam boilers at the power plants. The SCR units, which were made by Siemens Power Generation in Germany, perform the same function as the catalytic converter on your automobile exhaust system.

        Tim Keener, a professor of civil and environmental engineering at the University of Cincinnati, said SCRs are relatively expensive but about the only way to reduce NOx emissions once a utility has installed NOx-reducing burners, something Cinergy has already done.

        "About $5 billion worth of SCRs have been ordered for coal-fired boilers in the United States,” he said.

        So far, Cinergy has begun engineering or construction on nine of the 11 units, which convert the nitrogen oxides to nitrogen and water vapor through a chemical reaction.

        Two control units are planned at the Miami Fort Station near North Bend. Construction is almost complete on one, and testing begins this summer. The erection of steel for the second is just starting.

        Another unit — across the Ohio River at Cinergy's East Bend, Ky., Station near Rabbit Hash — will be tested this summer. Engineering work on a fourth, at the Zimmer station, is just beginning.

        Five more SCR units will be installed on generating units at Gibson Station, Cinergy's power plant near Princeton, Ind. Two of those will be tested this summer with construction and engineering either started or expected to begin soon on the other three.

        Finally, two more SCR units are being planned for Cinergy's Cayuga Station near Terre Haute, Ind.

        “We're studying when put those in now,” Mr. Roebel said depending on different operating scenarios for each unit.

        Under EPA rules, Cinergy has to reduce its systemwide NOx emissions from its 10 coal-fired plants by about 70 percent by the end of May 2004. The current NOx level is about half the amount produced a decade ago.

        The NOx project is complex because each of the SCR units has to be designed for the specific steam boiler it serves.

        “The biggest part of the challenge is fitting them in the existing structure from a construction standpoint,” Mr. Roebel said.

        “We have to situate these things in a retrofit fashion on each of these (generating) units,” he said. “There's probably as much steel going up on some of these as we put up with the original plant.”

Engineering challenges

        Ronald L. Richard, principal engineer, said the project is made more difficult because the units must be placed more than 100 feet in the air alongside the steam boiler units. The placement allows the units to filter the flue gas emissions before they enter a device called an air heater, which reheats gas entering the boiler.

        “We need to be up in the mid-600-degree Fahrenheit range,” he said. “To be able to do that, the (SCRs) have to be between the boiler and the air heater.”

        Before the flue gas containing NOx from the boiler enters the the SCR, it is sprayed with ammonia. Inside the catalyst, which contains ceramic plates made of titanium and vanadium oxide and other alloys, the NOx and ammonia come together creating nitrogen and water vapor.

        The catalyst beds, which look a lot like the inside of a car radiator, are designed to last up to 12,000 hours, depending on the coal burned and other factors. After that, they will be replaced. Replacing each layer of catalysts on the units costs about $3 million.

Adapting technology

        Although SCRs have been used to remove nitrogen oxide from coal plants in Europe and Japan for years, the technology is relatively new in the United States.

        “One problem we had trying to design these units is that it's a new application in this part of the United States and on this kind of coal,” Mr. Roebel said.

        “In Germany, they have extensive data on how SCRs react with German coal, but they don't have a lot of experience with American coal,” Mr. Richard said.

        Each of the SCR modules, which are about the size of a retail chest freezer, weighs about two tons. At each of the 11 generating units, Cinergy will install 384 modules.

        Because of the weight, the SCR modules can't be attached to the boiler structure, but are supported by new steel structures built up and around the existing boilers.

        “We're bridging over the top of equipment that's in service. So you have to be careful not to disrupt that,” Mr. Richard said. “The new steel is very close, within inches of the (boiler) building, and that's all supported by pilings.”

        At Gibson Station, the piling supports for the SCR structures had to be driven 120 feet down to bedrock.

        “In some areas, we had to drive the piles 5 feet at a time because that's all the headroom we had with the piping and everything else above it,” Mr. Richard said.

        “There are all kinds of challenges with this project,” Mr. Roebel said. “At Miami Fort Station, for example, we had to put a crane on the river bank in order to build the SCR structure. The (concrete) pad to set the crane on and excavation to reinforce the river bank cost $1 million. That doesn't include the crane cost.”

Other steps

        While the SCR units account for the bulk of the nitrogen oxide reduction, Cinergy is using other steps to reach its target.

        One technology is called boiler optimization. It uses artificial intelligence installed over the plant's operating system to figure out the best mixture of coal and air being fed into the boiler to reduce NOx.

        In early tests at the Cayuga Station, boiler optimization has reduced nitrogen oxide up to 20 percent — about twice what was expected.

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