Keeping it cool on the New England coast
Dominion Energy / Mount Hope Bay, Massachusetts
The 1.6-gigawatt Brayton Point plant sits on Mount Hope Bay in southern Massachusetts. Built in the 1960s, its four generating units burn coal, oil, and natural gas. The plant was built with an “open loop” cooling system: water drawn from nearby rivers was circulated through the condensers to pick up and remove excess heat, before being discharged into the bay.
To comply with new EPA standards governing water quality and biodiversity, Dominion Energy was required to reduce its hot water releases. It faced the challenge of either scaling back power generation at Brayton Point to reduce cooling demand, or finding an alternative method of cooling the facility. The station had to remain operational throughout, adding to the complexity of the project.
Dominion Energy embarked on a fast-track program. According to Mott MacDonald project engineer Doug Bondar, “We were appointed in 2008 to design and deliver two new cooling towers, which had to be up and running by May 2012. Industry convention dictated the towers should have been constructed consecutively — but that would have added another year to the project timeframe.”
The new towers provide “closed loop” cooling. A fixed volume of water is repeatedly circulated through the towers, allowing heat from the power plant to be released to the atmosphere through evaporation. Hot water from the turbine condensers is pumped to the towers and sprayed from 7,600 nozzles.
Brayton Point’s conversion from open- to closed-loop cooling is thought to be the first such retrofit ever completed. The project was aided by a 3D CAD model that included data on all existing underground structures, such as piping and foundations. Prospective bidders were able to use this when writing their tenders. As Bondar noted, “This allowed them to develop more reasonable construction cost estimates.”
Mott MacDonald assisted Dominion Energy and contractor Kiewit during construction of the towers, basins, and pipework, delivering them for $550 million — $100 million below budget.
“We achieved this through meticulous due diligence and continuously striving to make sure engineering, design and construction were as efficient as possible,” Bondar said.
By bringing Brayton Point into line with environmental requirements, the project has enabled the plant to operate at its maximum capacity of 450 megawatts in all seasons — while protecting the surrounding waters.