Decision Time for America’s Utilities

Coal-fired utilities in the U.S. weigh the material options for FGD units By Virginia Heffernan

Nickel Magazine, March 2007 -- The race is on for power plants in the United States to meet dramatic reductions in sulphur dioxide (SO₂) and other emissions required by the Clear Skies Act of 2003 and related legislation. Nickel alloys and nickel-containing stainless steels are helping them reach their goal.

Clear Skies legislation designed to reduce power plant emissions of SO₂, nitrogen oxide (NOx) and mercury has yet to pass the U.S. Congress, but in 2005 the Environmental Protection Agency issued the Clear Air Interstate Rule (CAIR), which caps emissions in the eastern U.S. When fully implemented, CAIR will reduce SO2 emissions in these states by more than 70%.

Currently, all fossil fuel-fired stations over 25 megawatts (MW) are limited to emissions of 1.2 pounds of SO₂ per million BTUs (British Thermal Units) of heat input and require an allowance for each ton of SO₂ they emit. The owners of new power plants are required to meet New Source Performance Standards by installing the latest flue gas desulphurization (FGD) technology, and each existing unit must undergo review as a new source if the unit is upgraded to the point where emissions increase significantly.

As a result, U.S. utilities are expected to spend tens of billions of dollars by 2010 to install and upgrade FGD systems, or “scrubbers,” in their power plants. Nickel-containing materials are playing a significant role in these projects.

For example, Ohio-based American Electric Power (AEP), one of the largest electric utilities in the U.S., is spending more than US$3.4 billion to retrofit more than 48% of the company's 25,746 MW of coal-fueled generation by 2010. The program includes both replacement of old scrubbers and new scrubber installations.

The utility chose N06022 and duplex stainless steel S32205 to retrofit the FGD system at Unit 5, a 400-MW generating unit at the Conesville Plant in Ohio, which had previously been lined with rubber. The plant has four operating units capable of generating a total of 1,745 MW of electricity.

“The rubber had been in there for almost 30 years and reached the end of its useful life,” says Ron Balawajder, senior engineer for AEP. “We felt that the alloy technology out there would be a better solution for lining the absorber, rather than trying to install the current generation of rubber that would never last 30 years.”

Although the company is using various materials in its scrubber projects, including fiberglass, the units at Conesville are well-suited to nickel alloys and duplex stainless steels because of a corrosive environment created by high-chloride contents and low pH.

“When we evaluate our upcoming retrofits, we look at what options are out there, and nickel alloys are one,” says Balawajder. “We use them in parts of the system where we feel it would be the best, most cost-effective solution.”

At Unit 5, for instance, AEP replaced carbon steel ducts with 150 tonnes of N06022, as well as 100 tonnes of stainless steel S32205 in the less corrosive areas. The absorber was also sheet-lined, or “wallpapered,” with these nickel-containing materials.

The scrubber at Unit 6 is next in line for a retrofit, followed by the installation of a whole new FGD system at Unit 4 in 2009. The retrofitted wet scrubbers will reduce SO2 emissions by 95%, compared with 92% currently, while the new system at Unit 4 will reduce emissions by up to 98%.

Virginia Heffernan is a Toronto-based freelance science writer.

Photos: iStock

AIRPOL 2007 will be held in Louisville, Kentucky, U.S.A. on June 26-28, 2007. This 3-day event, co-sponsored by NACE International and the Electric Power Research Institute, is designed for the suppliers and users of materials for the construction of flue gas desulphurization systems in coal-fired electric generating stations.  www.nace.org/nace/content/conferences/airpol2/

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