By Steve Blankinship, Associate Editor
NV Energy’s Clark station in Las Vegas, Nev. is a large and unique natural gas-fired generating facility. Located in an area that was once miles from the heart of Las Vegas, the city and its fast-growing suburbs have since spread out and engulfed the plant. NV Energy, the local utility, has experienced an annual load growth of 3 to 4 percent, more than twice the U.S. average. Formerly Nevada Power Co. and Sierra Pacific Power, NV Energy has a summer peak in excess of 7,500 MW. The Las Vegas Strip alone accounts for about 1,000 MW of load. The utility’s generating capacity has doubled in the past three years, from about 2,500 MW to more than 6,000 MW. And the summertime load swing between day and night ranges from 3,000 MW to 6,000 MW.
Clark consists of two 2 x 1 combined cycle units that produce 462 MW and 13 simple cycle units. Total plant output is 1,115 MW. Units 1, 2 and 3built in the 1950s and 1960swere decommissioned in 2007 and removed to make room for new peaking units. Units 5, 6, 7 and 8 are receiving major combustion section retrofits to reduce NOX emissions.
Clark has two 2 x 1 combined cycle units that produce 462 MW and 13 simple cycle units. Shown here are four peaking units.
About 70 percent of NV Energy’s generation is from natural gas. Coal represents 21 percent. Nine percent comes from renewables. In addition to having one of the largest blocks of geothermal power production in the world (210 MW in operation and another 308 MW slated to be on line by 2012), NV Energy’s renewable energy portfolio includes a share of the 64 MW Nevada Solar One thermal solar project and a handful of photovoltaic solar installations. NV Energy also plans to add 200 MW to 400 MW of wind capacity. The company’s goal is to have 20 percent of its generation from renewables and conservation by 2015.
Clark has 51 full time employees13 in management and 38 operating personnel. Operations and maintenance personnel also run the nearby Sunrise Station, which has one simple-cycle Westinghouse 501B2 and one older gas-fired boiler/steam turbine unit. Since it was built, Clark has gone from baseload status to intermediate duty to a peaking plant, despite the fact that it produces some power all the time.
Plant Manager Dariusz Rekowski says that before 2006, Clark’s capacity factor ranged from 55 to 60 percent, with minimum load at night and maximum load during the hottest days. Adding peaking gas plants to the system in 2006 meant Clark dropped to a fairly steady 40 percent annual capacity factor. By 2010, Clark is expected to drop below 20 percent, making it a full-fledged peaking facility.
Recent upgrades, peaking expansion and additions to plant controls and combustion systems, including dry low NOX, have doubled output while cutting per-kilowatt emissions by about 50 percent.
“The combined cycle units were designed to follow load pretty well” says Rekowski. “With the PSM combustion system retrofit, we will be able to get down to 40 MW, which is 55 percent of maximum, and go right back up to 100 percent.” The plant can ramp at a rate of 10 MW a minute. And because the plant has bypass stacks, operators can run the combined cycle units in simple cycle mode or open the dampers to produce steam for combined cycle operation.
The plant uses standard maintenance schedules recommended by the original equipment manufacturers: 8,000 operating hours for combustion inspection, 16,000 operating hours for hot gas and 32,000 for major inspection. “With the combustion system enhancements, we can eliminate combustion inspections and go to hot gas and major inspections only,” says Rekowski. That reduces O&M costs and provides higher availability because of reduced maintenance outages.
Clark is a zero water discharge plant. As its capacity factor falls, so does water consumption for the combined cycle units. That water is now used for emissions control and inlet air cooling of the simple cycle units.
Clark’s ability to supply large blocks of power on short notice provides substantial load support and spinning/fast response reserve for NV Energy. The plant can provide 600 MW to the grid in 10 minutes. Additionally, Clark’s location means it can be brought to full load within minutes and allow importation of additional megawatts when needed.
Clark can also produce power at 69 kV, 138 kV and 230 kV, further enhancing its voltage support capabilities. Its 69 kV capability will soon be eliminated. Two hundred MW will continue to produce power at 230 kV while the rest of the units will generate at 138 kV.
Despite the fact that the plant had to get by with the same number of personnel while modifications were being made, Clark maintained its safety record, which currently stands at 15 years without a lost time accident (2.7 million man-hours) and more than three years without an OSHA recordable injury.
“That’s amazing when you consider we have 21 units at Clark and Sunrise to operate and maintain,” Rekowski says.