Field work
As the project's general contractor, Slattery Skanska was responsible for all civil, structural, electrical, and mechanical work as well as for installing, testing, and commissioning all subsystems, including balance-of-plant equipment. Slattery Skanska awarded E-J Electric Installation Co. (Long Island City, N.Y.) a contract for 5-kV temporary power, underground duct banks, conduits, cable trays, and switchgear.
Skanska did the civil, structural, and mechanical work itself, including construction of three buildings on the property: the main building (which houses the two gas turbines, two HRSGs, and the steam turbine), a gas compressor building, and a chiller building. Within the chiller building is equipment that produces chilled water for cooling the gas turbines' intake air (increasing their output), a one-million-gallon water tank, and a 32-module air-cooled condenser (ACC).
The ACC (Figure 4)—from SPX Cooling Technologies of Bridgewater, N.J.—uses twenty-four 200-hp single-speed motors for cooling the 272 primary heat exchanger bundles and eight 200/50-hp dual-speed motors on the 48 secondary heat exchanger bundles that optimize condenser vacuum over the range of normal plant operating conditions. Seven-bladed aluminum fans of 32-ft diameter blow 1.6 million lb/hr of ambient air across the 32 modules, enough to condense the almost 1.1 million lb/hr of exhaust steam that enters the ACC through a 20-ft diameter duct.
4. Compact surfaces. The air-cooled condenser used at NYPA Astoria has 10 million square feet of single-row condenser tubes, enough to condense over 1 million lb/hr of exhaust steam. Courtesy: SPC Cooling Technologies
NYPA Astoria's twin 240-ft exhaust stacks were prefabricated in Bayonne, N.J. in four, 120-ft sections and barged to the job site. Final fabrication was completed off-site, because Con Edison liquefied natural gas (LNG) storage tanks are very close to the site of the new plant. The LNG tanks are equipped with very sensitive flame detectors that had to be secured while welding was done on the Astoria job site. The completed assemblies were then hauled about a quarter-mile to the job site for erection.
Skanska also managed E-J Electric's installation of the plant's electrical systems, comprising a digital control system, three step-up transformers, and switchgear. DMJM Harris and the construction team worked together to push the schedule forward and to mitigate the impact on construction of final engineering design changes, which were being made at the same time. The project team worked closely to prioritize the design sequence to facilitate construction. Meanwhile, the engineering team (GE and Sargent & Lundy) placed design personnel on-site to provide solutions to any problems that arose during construction.
Because soil conditions at the plant site were not sufficient to hold the heaviest equipment securely in place, Sargent & Lundy devised a system of "H" beam piles below all of the facilities, equipment, and building foundations. Skanska installed more than 4,500 "H" beam piles for the foundations.
At one point, almost 200 electricians were working two shifts (from 7 a.m. to 3:30 p.m., and from 4 p.m. to midnight) to complete the project. According to Tony Mann, president of E-J Electric, they started the double shifts in the spring of 2004 in an effort to meet Con Edison's scheduled backfeed date of May 1, 2005, in spite of weather delays and the late arrival of structural steel.
Quid pro quo
NYPA has shown other developers the proper etiquette for developing a power project in Queens. As part of the NYPA Astoria development agreement, the NYPA is investing more than $50 million over five years in energy-efficiency and clean-energy projects in Queens and other boroughs. Statewide, the Authority is investing up to $100 million a year in such initiatives for tax-supported public facilities, with its efforts yielding considerable benefits, including annual savings on electric bills of more than $93 million and reduction in oil use by 1.7 million barrels a year.
A 2002 agreement with the Borough of Queens and environmental groups included a provision limiting operating hours of the existing Poletti project once the new combined-cycle plant began supplying electricity. NYPA will limit Poletti's capacity factor to 30% on a three-year average, with no single year above 35%.
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