The Next Generation
Construction activity at Clark had slowed after the combined-cycle plants entered service, but activity resumed in 2007. The first order of business was demolition of the three original steam units that had been mothballed years earlier to make room for a dozen new peaking combustion turbines.
Twelve Pratt & Whitney SwitftPac packages, each configured with two FT8 aero-derivative combustion turbines coupled to opposite ends of a double-ended generator, were installed during 2008 and early 2009 (Figure 3). Each SwiftPac package is rated at approximately 60 MW at standard conditions, which certainly don’t apply to the Las Vegas area. NV Energy rates the total output of the 24 combustion turbines during the summer at 624 MW, or about 52 MW each for dispatch purposes. The heat rate of a SwiftPac is a touch under 9,600 Btu/kWh at site conditions. Inlet fogging is also used to increase power and flatten out the efficiency curve on hot days.
Today, the entire Clark Generating Station features 19 units with a summer peak rating of 1,102 MW, effectively doubling the site rating from just five years ago while cutting total site emissions in half.
3. Next came the peakers. Twenty-four quick-starting simple-cycle combustion turbines totaling 624 MW were installed from 2008 to 2009 to provide peaking energy to the NV Energy grid. Courtesy: NV Energy
First Responder
A peaking plant must be quick to respond when called upon to immediately quell a grid emergency and must be capable of taming an unexpectedly high peak load on a hot summer day. The 12 SwiftPacs can put more than 600 MW on the grid in about the time it takes me to lose $20 at the nickel slots — 6 minutes to synchronize and 8.5 minutes to reach rated power. The peakers also operate with a tiny emissions footprint by using water injection to reduce NOx emissions and a selective catalytic reduction system to scrub the exhaust to 5 ppm NOx and 2 ppm CO at only 5 ppm of ammonia slip.
The 12 SwiftPacs are arranged in three identical 208-MW load blocks. Block 1 entered commercial service in time for the summer 2008 peak; Block 2 followed in November 2008; Block 3 was added to the dispatch list in time to meet this year’s summer peak. Today, plant operators are kept very busy with one or more blocks of SwiftPac peaking power added to the grid for at least 4 to 6 hours daily to meet the evening peak energy demand. SwiftPac starting reliability has been almost perfect; only twice has a turbine failed to start out of hundreds of starts.
The SwiftPac peakers operate at about a 10% capacity factor, allowing the operation and maintenance (O&M) staff to equalize the wear and tear on them by periodically rotating the lead unit to equalize operating hours and unit starts. The first engine major inspection interval is 25,000 hours, so it will be several years before the first engine overhaul will be required.
Tight Teamwork
The operating tempo at Clark has markedly increased with the addition of the SwiftPacs and the cycling of the combined-cycle plants. Now the plant’s staff of 40 — four operators and a supervisor per shift — must juggle the starts and stops of as many as 19 separate generators in a single day, depending on the system load demand. That’s a far cry from just three years ago, when the same size staff handled just the combined-cycle plants, which weren’t necessarily cycled daily. Today, every unit at Clark is a peaker that may be called to action at a moment’s notice. In addition, Clark’s O&M staff has responsibility for the 501B2 combustion turbine and another aging gas-fired steam plant at the nearby Sunrise Station.
Clark has undergone multiple makeovers during its long life, but perhaps the plant’s most notable accomplishment is its current safety record. There has not been a single lost-time accident over the past 15 years, covering 2.8 million man-hours. The plant has also just finished its third year without an OSHA recordable injury. Given the number and variety of contractors, suppliers, and company employees who have worked on so many upgrade and new construction projects over the years, this is truly a remarkable achievement.
I doubt that anyone knows what Clark’s next evolutionary change will be, but I am sure that whatever new challenges NV Energy faces in the future, somehow Clark will play a critical role in their solution.
—Dr. Robert Peltier, PE is POWER’s editor-in-chief
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