Natural gas-fired combined-cycle power plant
Loudoun County, Virginia, US
Siemens and Bechtel
Stonewall Power Project is a 778MW gas-fired combined-cycle power plant built in Loudoun County, Virginia, US, by Texas-based private equity firm Panda Power Funds.
Commissioned in May 2017, it is one of the cleanest natural gas-fuelled power plants in the country, meeting the new carbon emissions standards set by the US Environmental Protection Agency.
The main construction work started in November 2014 after Panda Power Funds secured financing for the project. The power plant has the capacity to fulfil the electricity needs of up to 778,000 homes in Northern Virginia and the District of Columbia (DC) metropolitan area.
The project generated more than 600 jobs during the construction phase and 27 long-term jobs in the operation phase.
Stonewall power project background
Limited liability company Green Energy Partners / Stonewall was the original developer of the project, whereas engineering firm Bechtel Corporation was the development partner. Panda Power Funds acquired a majority stake in the Stonewall project in May 2013, when the project was in the planning stage.
The Virginia Department of Environmental Quality granted an air permit for the project in April 2013, and the Certificate of Public Convenience and Necessity (CPCN) from the regulators was received in May 2014.
Panda Power Funds secured debt funding totalling $571m for the project in November 2014. The lead arrangers for the senior debt financing included Goldman Sachs, Credit Suisse, ICBC, Investec, MUFG Union Bank and Ares.
Siemens Financial Services provided a $75m equity investment for the project.
Stonewall plant and turbine details
The Stonewall power generating station is built on a 101-acre site in a wooded area located nearly four miles south of Leesburg, Virginia.
The multi-shaft combined-cycle power plant consists of two SGT6-5000F gas turbines, one SST6-5000 steam turbine with a SCon-4000 condenser, two SGen6-1000A generators, one SGen6-2000H generator and two duct-fired heat recovery steam generators (HRSGs). All the equipment for the power island was provided by Siemens.
Each of the four-stage SGT6-5000F gas turbines have a rated capacity of 232MW and generate power at 60Hz frequency with single-digit CO and NOx emissions. The SST6-5000 steam turbine has an output ranging from 120MW to 600MW and consists of a combined high-pressure/intermediate-pressure reverse-flow (HI) cylinder and a double-flow low-pressure (L) cylinder. Each gas turbine and steam turbine drives its own generator.
The power island is integrated with Siemens’ SPPA-T3000 instrumentation and control system. It is also equipped with Siemens Flex-Plant technology, which allows for a faster start-up with considerably low emissions and fuel costs.
The plant uses modern emissions-control technology and only pipeline-quality natural gas in order to reduce particulate matter and air emissions. As the plant is built near the existing transmission lines, it eliminates the need to erect additional power lines and minimises disruption to the local community.
Reclaimed municipal wastewater from Leesburg town that would usually be diverted to the Potomac River is used to cool the plant. It ensures conservation of the region’s natural supply of drinking water and also prevents the discharge of toxic substances into the environmentally sensitive Chesapeake Bay watershed.
The Stonewall power facility is a zero-liquid-discharge plant with all its wastewater being purified in a treatment facility and then recycled.
Key players involved with the project
A consortium consisting of Siemens and Bechtel was awarded the turnkey contract to build the Stonewall Energy Project in November 2014. It is the fourth plant being delivered by the Bechtel-Siemens consortium for Panda Power Funds after the Temple I, Sherman and Temple II power projects.
Bechtel was responsible for the project management, engineering, procurement, installation, construction and commissioning of the facility, while Siemens provided the power-island package.
The gas turbines, steam turbines and generators were manufactured at Siemens’ factory in Charlotte, North Carolina.
Power market in Loudoun County
Loudoun County witnessed population growth of nearly 84% between 2000 and 2010, becoming one of the fastest-growing counties in the US.
The Dulles Technology Corridor, a national hub for defence, data storage and technology firms, is located in the county. As a result, nearly 70% of the world’s internet traffic flows through the region. The county imports all of its power requirements from the neighbouring regions.
Electricity supply to Virginia and Washington DC is coordinated by Pennsylvania-New Jersey-Maryland Interconnection (PJM), the largest grid operator in the US. Natural gas-fired combined-cycle and combustion turbine plants account for nearly 26% of PJM’s total installed capacity. Six new combined-cycle gas turbine plants with a total capacity of 4,800MW are expected to come online by 2018.