Another first: AEP introduces flue gas venting technology in the U.S.

Flue gas from Cardinal Unit 3 is now vented through a 29-foot diameter fiberglass duct to the unit’s cooling tower rather than through a conventional stack. Photo by: Keith Burger

(Story by Rachel Hammer)

BRILLIANT, Ohio — On February 1, 2012, AEP added yet another entry to its list of pioneering technologies.

That day, for the first time in the U.S., the company began venting the flue gas from Cardinal Unit 3 through the hyperbolic-shaped natural draft cooling tower rather than through a conventional stack. The technology has been used in numerous new and retrofit installations in Europe for the past 25 years, but this is the first such installation in the U.S.

AEP installed this technology as part of the unit‘s flue gas desulfurization (FGD or scrubber) retrofit project. The new FGD system will remove up to 98 percent of the unit’s sulfur dioxide (SO₂) emissions.

AEP’s technology partner for this project was Charlotte, N.C., based SPX Cooling Technologies Inc. SPX, formerly Marley Cooling Tower, has been associated with many cooling tower projects across the AEP system.

The technology
The venting equipment is relatively simple. Keith Burger, project manager – Projects & Controls, explained that during the unit’s tie-in outage to connect the new FGD system to the generating unit, the side of the cooling tower concrete shell was reinforced and a hole was cut into it. A 29-foot diameter fiberglass duct was hoisted by crane and set into place to run from the duct leaving the FGD system into the cooling tower. At the center of the cooling tower, the duct makes a 90-degree turn to direct the flue gas upwards to exit through the cooling tower.

While the process itself is relatively simple, associated issues, such as air flow impacts, structural design, environmental permitting and associated air modeling, made it significantly more complex to secure acceptance for the project.

Deciding factors
The unique configuration of the Cardinal Unit 3 site created concerns and challenges that caused AEP to evaluate alternate technologies for venting the flue gas.

Typically, AEP has built new stacks as part of the FGD retrofit projects. At Cardinal Unit 3, the only potential location for a new stack was in close proximity to and in direct line with the flow of the water vapor plume as it exits the top of the cooling tower. In cold weather, the water vapor could freeze to the stack and form potentially hazardous ice accumulations. This ice could pose hazards for workers, equipment and reliable operations.

Alternatives were limited. According to Tim Riordan, vice president – Engineering Services, there were no real viable alternatives for placement of a new stack.

“Applying this technology in this situation is the right thing to do on many levels. First and foremost, it addresses the safety hazard. It’s also a good environmental solution. Both the science and the results from existing installations indicate that the increased mass and flow rates from the combined FGD exhaust and cooling tower water vapor plumes will disperse the flue gas in a manner that is protective of the environment,” he said.

Permitting
AEP worked closely with the Ohio Environmental Protection Agency (Ohio EPA) to understand any potential impacts that application of the new technology might have on ambient air quality. Ohio EPA approved the extensive modeling performed by AEP before modifying the air permit. According to Mark Runyon, senior engineer – Air Quality Services, AEP has installed four ambient sulfur dioxide monitoring stations and three meteorological stations near the plant. In accordance with the Ohio EPA permit, monitoring was performed for one year prior and will continue for a minimum for two years after initial FGD operation.

Runyon pointed out that emissions reduction equipment remains the same. So the content of the combined plume is no different from the content of the two plumes vented separately. Also, continuous emissions monitoring equipment (CEMs) placed inside the duct will monitor the plume constituent.

Construction
Construction Service’s Site Manager Dick Aeberli noted that because this was a first time evolution, there was particular emphasis on making sure everyone had a clear understanding of the execution of the critical lift plan.

Considerable effort and several months of planning were dedicated to developing this unique rigging scheme for placing the 175-ton fiberglass flue duct, which measured 220 feet in length and 29 feet in diameter, into the cooling tower. Wind speed was a major factor in making this critical lift, therefore, even the time of day was significant. In the early morning hours of October 25, the lift was executed.

“Recognizing the magnitude of this undertaking, a collective effort between the building trades, AEP and contractor management, with safety as the number one priority, we were able to complete this monumental feat,” Aeberli said.

Other cooling tower work, other firsts
Removing the cooling tower from service for the FGD project provided an opportunity to perform other cooling tower work.

The original precast concrete hot water distribution support structure for Cardinal 3 was in poor condition, requiring numerous repairs through the years and was reaching the end of its useful life. Planning and approval to replace the hot water distribution components with a more efficient design that would improve thermal efficiency already was underway. So when the FGD project came along, AEP was able to integrate the multiple projects to execute them more efficiently.

This project then became the first in the world to combine retrofitting discharge of flue gas through the cooling tower concrete shell with conversion from a cross-flow hot water distribution system to a more thermally efficient counter-flow system. Previous similar European natural draft cooling tower installations used concrete hot water distribution supports. Cardinal 3’s cooling tower fill system was rebuilt with fiberglass supports.

Technology acceptance
Plant neighbors in the Brilliant area have an ongoing interest in activities at Cardinal Plant. Throughout the construction program to add environmental controls on all three of the plant’s units, plant leaders and the project management team conducted several briefings with community leaders and several public meetings to keep the community informed.

Interest in the construction activity at Cardinal Plant was heightened considerably this fall when the hole in the side of the cooling tower was visible from Ohio Route 7. “The timing was right for another update,” commented Chuck George, plant manager. While attendance wasn’t particularly high, local media covered the meeting. “It was another good opportunity to let our neighbors know about the good things we are doing here at Cardinal, especially since all three units now have state-of-the-art environmental controls,” George added.

Cardinal Plant is located at Brilliant, Ohio, and has total coal-fired generating capacity of 1,830 megawatts. AEP owns Unit 1 and Buckeye Power owns units 2 and 3. AEP operates the facility on behalf of all owners and managed the FGD retrofit project. All three units now are equipped with selective catalytic reduction systems to reduce nitrogen oxide emissions and FGD systems to address SO₂emissions.