West County Energy Center 2,400MW CCGT, United States of America

The West County Energy Center owned by Florida Power & Light Company (FPL) will consist of three 1,250MW natural gas-fired combined-cycle generating units. The plant is located on a 220-acre site in western Palm Beach County, an industrial land that Palm Beach County has already zoned for power plant development.

The 3,750MW West County Energy Center will cost FPL about $1.2bn. Units 1 & 2 of the plant were commissioned in August and November 2009 respectively. Unit 3 is currently under construction and is scheduled to become operational in 2011. The plant will provide electricity to 250,000 homes when fully operational.

The site is located near to a transmission substation and major transmission lines needed to deliver power to urban areas. It will be served by an extension of Gulfstream's natural gas pipeline, with ultra-low sulfur light oil as emergency/back-up fuels. Combustion controls and selective catalytic reduction (SCR) will reduce the carbon emissions.

The new project will supply the equivalent of 466,000 homes and businesses, creating around 350 construction jobs a year (peaking in 2008 at about 1000) and 40 to 50 full-time jobs.

Plant make-up

The West County Energy Center is similar in design to FPL's 2005 Martin and Manatee plant additions and the Turkey Point plant addition. Each combined cycle unit will consist of three 250MW 'G' Class gas turbine-electrical generator sets (Mitsubishi Heavy Industries Model M501G) with evaporative inlet cooling systems.

The units will feed three supplementary-fired Heat Recovery Steam Generators (HRSGs) with SCR reactors and gas-fired duct burners. There will also be four 2250kW emergency generators, two natural gas fired fuel heaters, two diesel fuel storage tanks, and two auxiliary steam boilers. Each gas turbine will fire natural gas as the primary fuel and ultra low sulfur (0.0015% Sulfur) distillate oil as a restricted alternate fuel. Emissions of all pollutants increase with the firing of oil, and oil firing will be limited to a maximum of 500 hours per-year per-gas turbine.

Two 24-cell mechanical draft cooling towers will have hot / cold water temperatures of 40 / 30°C. Cooling water will come from the South Florida Water Management District L-10 / L-12 canal and Floridan aquifer wells.

All the three units will begin using reclaimed water as the primary water source from early 2011. Until then Units 1 and 2 will use the Floridan Aquifer wells as the primary source.

Technology

Ambient air will be drawn into the 17-stage compressor of the M501G where it will be compressed to above 19 atmospheres. The compressed air will be then directed to the combustor section, which consists of 16 separate steam-cooled, can-annular, Dry Low NOx (DLN) combustors. Fuel will be introduced, ignited, and burned. The combustor outlet temperature will be above 1,480°C (2,700°F).

The hot combustion gases routed through the steam-cooled transition pieces will be diluted with additional cool air from the compressor and directed to the turbine (expansion) section. Energy will be recovered in the turbine section in the form of shaft horsepower, of which typically more than 50% will be needed to drive the internal compressor section. The balance of recovered shaft energy will drive the external load. Turbine exhaust gas will be discharged at about 650°C (1,200°F) for extra energy recovery.

Each of the three combustion turbines per unit will drive an electric generator while the exhausted gases from each combustion turbine will raise additional steam in the three HRSGs. This steam will in turn drive a single, separate steam turbine-electrical generator per unit to produce extra electrical power.

Evaporative cooling

Evaporative cooling (injecting fine water droplets into the gas turbine compressor inlet air) will reduce the gas temperature. Lower compressor inlet temperatures will give a higher mass flow rate through the gas turbine, with a boost in electrical power production. The emissions performance will remain within the normal profile of the gas turbine for the lower compressor inlet temperatures. This is typically used at ambient temperatures of 15°C (60°F) or above.

Gas-fired duct burners can be used in the HRSG to provide additional heat to the turbine exhaust gas and produce even more steam-generated electricity. Duct firing is useful during periods of high energy demand.

An SCR system will control NOx emissions from each gas turbine when firing either natural gas or distillate fuel oil. The SCR consists of an ammonia (NH3) injection grid, catalyst, ammonia storage, monitoring and control system, electrical, piping and other ancillary equipment. An oxidation catalyst system may be installed in the future to control CO emissions.