Steam-side systems
Hitachi's nomenclature for the 890-MW steam turbine is TCDF-40—a tandem-compound, four-flow, single-shaft, 3,600-rpm machine with 40-inch last-stage titanium blades. Those blades have the same length as Genesee Unit 3, and the turbine is much like the one that powers the 700-MW Unit 2 of Chubu Electric Power Co.'s Hekinan plant. The WSEC unit is also the largest Hitachi steam turbine installed outside of Japan.
The steam turbine-generator, rated at 1,025 MVA, is also among the largest two-pole generators manufactured by Hitachi. Its 0.52-MPa·g hydrogen cooling system for the rotor windings is the same used in large four-pole generators of 1,500-MVA class. The design makes the stator frame structure more compact. The stator windings are water-cooled.
Critical components in the turbine system—the bodies of the main stop, main steam control, and combined reheat valves, and main and reheat steam lead piping—are made of 9-Cr forged steel; 12-Cr steel was used in the high-pressure/low-pressure (HP/IP) rotors, HP/IP internal casings, and diaphragm for the HP/IP sections. To improve efficiency and reliability, a continuous cover blade was applied to the moving blades of the HP and LP sections. To further raise efficiency, an advanced vortex nozzle was mated to the nozzle blades in all sections.
Sliding-pressure operation of the boiler is controlled as a function of steam turbine power, with the turbine governing valves wide open. This minimizes throttling losses and allows the steam pressure at the turbine inlet to change to maintain flow at a constant volume. Sliding-pressure operation also improves the thermal efficiency of the steam turbine at partial loads, by decreasing thermodynamic losses.
The feedwater system has an HP heater above the reheat port, two 50% turbine-driven boiler feedpumps, and a motor-driven start-up feedpump supplied by Ebara Corp. (www.ebara.co.jp). Feedwater heating is done in eight stages, via seven closed-cycle feedwater heaters from Thermal Engineering International (www.babcockpower.com) and one deaerating heater from Kansas City Deaerator Co. (www.kansascitydeaerator.com). A little domestic content never hurts.
The condenser was designed by Hitachi Ltd. and fabricated in Canada. ITT Goulds Pumps (www.goulds.com) provided the three 50% vertical condensate pumps, while U.S. Filter Corp. (now Siemens Water Technologies, www.water.siemens.com) supplied the full-flow condensate polisher that keeps the working fluids in spec for the once-through supercritical steam generator. A 22-cell mechanical-draft, fiberglass cooling tower supplied by GEA Power Cooling Inc. (www.geaict.com) tempers the cooling water moved by three 50% vertical, wet pit circulating water pumps, also supplied by Ebara.
Makeup water is produced by six wells located at the plant. Well water is cleaned up by clarifiers and a reverse osmosis (RO) demineralization system from U.S. Filter and then stored in a 500,000-gallon tank. The demin water is used for main cycle makeup and for regenerating the condensate polishers and the RO system's mixed-bed resins.
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