Renewed interest in higher plant efficiency, stable fuel costs, and energy security makes pulverized coal plants very attractive these days. Burning that coal to produce steam at supercritical pressure and temperature, which bumps up efficiency by 3% to 6% and reduces CO2 emissions, made the technology even more compelling for MidAmerican Energy Co. and its partners, who built Walter Scott, Jr. Energy Center Unit 4. If this plant name is unfamiliar, you might recognize it as the former Council Bluffs Energy Center. The facility was dedicated July 10 to Walter Scott Jr., long-time member of the Berkshire-Hathaway and MidAmerican Energy Holdings Co. Boards of Directors.
MidAmerican is the majority owner (61%), developer, and operator of the $1.2 billion project. But it needed the help of dozens of partners: Central Iowa Power Cooperative, Corn Belt Power Cooperative, Lincoln Electric System, Municipal Energy Agency of Nebraska, and the municipal utilities of the Iowa cities of Alta, Cedar Falls, Eldridge, Montezuma, New Hampton, Pella, Spencer, Sumner, Waverly, and West Bend. Combined, these utilities provide electricity to more than 1 million customers. The Walter Scott, Jr. Energy Center (WSEC) is located on the Missouri River, within the city limits of Council Bluffs, Iowa, and across the river from Omaha, Nebraska.
The southwest Iowa site came to life with a single, 45-MW coal-fueled unit in 1954 and since then had been expanded to three units that generate more than 800 MW. Unit 4 doubled the capacity of the site to 1,600 MW when it entered service this June, making it the largest producer in Iowa. The WSEC uses Powder River Basin (PRB) coal, delivered by unit trains as the site's fuel supply. Unit 4 uses the plant's existing coal unloading and storage facilities, but the site's coal crushers and conveyors had to be upgraded to handle the increased throughput that Unit 4 requires. New transfer conveyors also were installed from Unit 3 to the new Unit 4 tripper room.
Wave of the future?
There are about 155 supercritical power stations with a combined capacity of 107 GW currently operating in the U.S. Construction of supercritical-pressure boilers in the U.S. began in the 1950s, peaked in the 1970s, but fell precipitously in the 1980s. "Teething" problems caused by austenitic steel metal fatigue, superheater corrosion, and creep cracking in heavy components operating at high temperatures and pressures were responsible for the technology's fall from grace. The last supercritical project in the U.S. was the 1,300-MW W.H. Zimmer Station, located in Moscow, Ohio, that went commercial in March 1991 under the majority ownership of Duke Energy. Without question, the U.S. has been decidedly slow at adopting the latest supercritical technology; in contrast, over 85% of new European and Asian capacity installed over the past two decades has used it.
Perhaps this project will signal the beginning of a revival of North American interest in supercritical technology as more utilities try to diversify from gas and use more coal. After all, regulated utilities still are required to keep prices low and reliability high. Over the past decade, new coal-fired capacity has represented less than 5% of new generation, but the U.S. Department of Energy predicts a steady rise in its share, possibly to as high as 40%, in the next few decades.
By any account, 16 years has been a long time to wait for the next round of supercritical coal-fired plants to make an appearance, but WSEC Unit 4 (Figure 1) is leading what appears to be a new wave of construction. Following closely on its heels will be several other supercritical plants: Wisconsin Public Service Corp.'s 530-MW Weston Unit 4 (to be built in partnership with Dairyland Power by 2008), Wisconsin Energy's 677-MW Elm Road Generating Station Units 1 and 2 (due on-line in 2009 and 2010, respectively), Kansas City Power & Light's 850-MW Iatan Unit 2 (slated for commercial operation in 2010), and Duke Energy's 900-MW Cliffside Unit 6 (scheduled for 2011 commercial operation). Elm Road and Cliffside are outfitted with Hitachi supercritical boilers closely related to the one powering MidAmerican's Walter Scott, Jr. Energy Center Unit 4.
At the same time, AEP has two ultrasupercritical projects in development: Public Service of Oklahoma's $1.8 billion Red Rock Project (slated for 2012 operation) and SWEPCO's Turk Project (planned for 2011). Both expect their permit approvals this month. There are almost two dozen more supercritical and ultrasupercritical projects in the development queue in the U.S.
Looking back, we see that the last supercritical plant built in North America was the 495-MW Genesee Unit 3, a 2005 POWER Top Plant jointly owned by EPCOR Power Development Corp. and TransAlta. The plant, called G3, is located about 45 miles southwest of Edmonton, Alberta. The owners awarded the design and construction contract for Genesee Unit 3's power island to Hitachi Canada Ltd. (HCL) in December 2001. HCL then called on its parent and Babcock-Hitachi K.K. (BHK) to oversee the engineering and construction phases of the project and provide the plant's major equipment. G3 went commercial on March 1, 2005. This short history lesson is important because the design of WSEC Unit 4 picks up where Genesee Unit 3 leaves off. (More on the technical heredity of this boiler later.)
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