Air Pollution Control Equipment Services, Coal

First & Last: The Ultra-Supercritical Coal-Fired Turk

Issue 6 and Volume 117.

AEP's Turk is one of the most efficient, least polluting coal-fired power plants on the planet.
AEP’s Turk is one of the most efficient, least polluting coal-fired power plants on the planet.

By Denver Nicks, Associate Editor

Firsts are rare-by definition they come only once-and lasts are rare for the same reason. But rarest of all is that which is the first and last of its kind, like Doctor Frankenstein’s hero-monster, doomed to be forever alone on the day it was born. AEP’s ultra-supercritical coal-fired Turk power plant may prove to be one such rarity: a great technological leap forward unlikely to ever be repeated again in the United States.

The Turk project was announced in August 2006 but didn’t go online until seven years later. AEP spent those intervening years securing the necessary regulatory permits and fighting a battle in the Arkansas Supreme Court. AEP ultimately lost that battle, requiring a late-in-the-game reconfiguration of where all the plant’s power output would be sold, but bringing a new coal plant online in the late 2000s was never going to be easy. “I would think there was always some concern,” said Tim Riordan, vice president of engineering services for AEP, “because much of this was going to have to be decided in the court system or with commissions or other federal agencies and of course we don’t have control over that.”

Still, it wasn’t just a regulatory victory when the plant finally went into service on December 20, 2012. The event was also a technological victory: AEP had succeeded in bringing online the most efficient coal-fired commercial power plant ever built.

The 600 MW Turk Power Plant is situated in Hempstead County, in the southwestern corner of Arkansas, where it employs 109 people on a total payroll of $9 million and pumps $6 million in school and county property tax revenues every year, according to AEP. Through its subsidiary the Southwestern Electric Power Co., or SWEPCO, which operates the facility, AEP invested $1.3 billion of the $1.8 billion required to build the plant and the company now owns 73 percent of its output. The remaining ownership is divided between the Arkansas Electric Cooperative Corp., the East Texas Electric Cooperative, and the Oklahoma Municipal Power Authority.

The attribute that makes Turk unique among power plants-that gives cause to append the word “ultra” to the preexisting and more familiar “supercritical”-is that it works just like a supercritical power plant, only better. As an ultra-supercritical coal-fired power plant, Turk operates at extraordinarily high pressures and temperatures, well above typical supercritical pressures of around 4,500 psi and hotter than 1050 degrees Fahrenheit.

“As you increase temperature you increase your efficiencies,” Riordan explained. By working at such a high temperature and pressure, Turk achieves the highest efficiencies around in coal power generation today; according to AEP, between 39 and 40 percent of the thermal energy available in the fuel comes out as electric power. This level of efficiency in extracting energy from coal allows Turk to use less of the stuff to produce the same amount of power. Less coal burned means less emissions of sulfur dioxide, nitrogen oxide, mercury, carbon dioxide and particulate matter. It also means fewer waste products and less fly ash, and decreased need for the commodities used in environmental control activities, like activated carbon and ammonia. The reduction in pollutants is combined with the latest emission-control technologies, like catalytic reduction systems, dry flue gas desulfurization, baghouse technology to combat particulate releases and activated carbon injection to reduce Hg emissions. The end result is one of the most efficient, least polluting coal-fired power plants on the planet.

Joey White, machinist, works to move some of the Turk Plant's emissions control equipment into place.
Joey White, machinist, works to move some of the Turk Plant’s emissions control equipment into place.

Achieving super-high temperatures and pressures wasn’t as easy as just dialing up the heat. Special materials had to be tested to withstand the pressure and temperature of an ultra-supercritical power plant. For use in the facility materials need to have high creep rupture strength, resistance against embrittlement, and low oxidation growth in addition to ease of manufacture and availability. “High chrome, creep strength enhanced ferritic steels (CSEF), and nickel based alloys meet these needs,” Riordan said.

Working with both the original equipment manufacturers and with EPRI (the Electric Power Research Institute), and other research groups, AEP worked “to understand these components”-like boiler headers, main steam lines, and blade components-“for their weldability and long term creep strength,” Riordan said. “There was quite a bit of R&D work.”

In constructing Turk, AEP bought the major components, like the boiler turbine and environmental control equipment, before its EPC agreement with Shaw was completed. Afterwards, however, Shaw led construction on everything but the boiler, in addition to completing engineering details and integration of the facility. The boiler, along with the baghouse, dry scrubber, and selective catalytic reduction unit, were all provided by Babcock & Wilcox, while Alstom provided the main turbine and generator in addition to the feed pump turbine.

In designing and constructing Turk, AEP included input from operating staff to ensure the innovative facility didn’t just make sense from an economic and regulatory perspective, but from an ergonomical perspective too. Design plans gave consideration to something as simple as making sure thaTheadroom was sufficient to safely remove motors or maintain equipment. “Many times with an EPC contract the footprints get smaller and smaller because of cost concerns,” Riordan said. “We spent a lot of time with our engineer of record, Shaw, to make sure that we had a very safe and maintainable facility.

“You really don’t want people standing on hand rails to operate a valve, right?”

As to whether or not there will ever be another American plant like Turk, Riordan isn’t optimistic.

Drew Smith, machinist, performs maintenance on one of the Turk Plant's six coal pulverizers.
Drew Smith, machinist, performs maintenance on one of the Turk Plant’s six coal pulverizers.

“I would hope so. Unfortunately with the new environmental rules for new generating facilities, the proposed CO2 limits are probably going to prevent that from happening in the near term,” he said.

“This could very well be one of the last conventional coal burning facilities built in the country.”

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