Dominion Energy Brayton Point Power Station
The Brayton Point Cooling Towers had its beginnings with the Environmental Protection Agency’s (EPA) New England office in 2003. They issued the permit that required the Dominion Energy to reduce the amount of water used and the lower the temperature of water discharged into the Mount Hope Bay. The temperature of the bay is an environmental concern because of the negative effect of the warm water on native fish populations. The EPA requirements are met with two closed-cycle cooling towers that will be used by four coal and oil fired electricity generators, reducing the amount of water used by 95%, from 1,300 million gallons a day to 70 million gallons and then significantly lowering the temperature of the water that re-enters the bay.
Power for the plant is produced by using pressurized water for steam-electric generating units that spin turbines to generate electricity. That water then is cooled by spraying it into the bottom third of the cooling tower where the heat in the water dissipates upward and the remaining cooled water is re-circulated back into the power plant.
Each cooling tower is 500 ft. tall, about 360 ft. wide, and 21-in. at the bottom standing atop 44 columns with lintels 40 ft. tall that allow for air circulation. The remaining shell of the towers is cast-in-place. The massive towers stand on top of 1,600 precast concrete piles that were specially designed and produced. The 500 ft. height of the towers allows for the steam which ranges between 5,000 and 10,000 gallons a day to dissipate into the open air rather then settle as a perpetual fog on the ground.
In early 2009 Vynorius Prestress joined with Kiewit Construction the lead engineer of the project, to produce piles for the cooling towers. They discovered soils at the site where not suitable for a conventional footing forcing the engineers to utilize a deep foundation system. The engineers chose Precast Prestressed Concrete Piles (PPCP) to fulfill their deep foundation requirement. The proposed foundation would be situated on 20 in. x 20 in. PPCP’s designed by LEAP Associates with lengths ranging from 60 ft. to 80 ft. Michael Barth, Vice President of Vynorius Prestress, proposed a 6500 psi mix design including Type II Cement, Newcem and the corrosion inhibitor DCI adding both strength and longevity to the critical first phase of the project. Design strength was reached within 48 hours with 28 day strengths of 10,000 psi being routine. Kiewit Construction reported that this part of the job was completed ahead of schedule.
The site of the power station is located next to the ocean and possible corrosion from the salt water is a big concern. Unistress, the projects precast concrete producer, added fly ash, a corrosion inhibitor and metakalin a newer additive that boosts compressive strength to the concrete mix increasing the density to prevent the corrosive salt water from penetrating and doing damage.
The two tower shells are now complete and Unistress is working on phase II with Dominion Energy. Delivery and erection of the 98 total (49 in each tower) precast “A-Frames” for inside each tower is underway. The legs on each A-Frame are 1 ft. 8-in. square and range from 33 ft. 2-in. to 39 ft. 3-in. long. These A-Frames, which support flumes for water were originally designed as cast-in-place structures and later redesigned as precast. This redesign saved time and allowed the heads to be match cast eliminating the cast-in-place sections. The frames are delivered to the job site in two halves that are than post tensioned together. Once stressed and grouted on site, the frames are lifted, tipped and installed.
Unistress is also producing the 96 precast concrete flumes, 48 for each tower. Several different sizes and types of flumes are needed. These flumes will help move the over 70 million gallons of water a day. Precast concrete also holds up to the brutal force of 360,000 gallons of water per minute traveling into the towers.
This kind of project requires the long-term strength that comes from precast concrete. These cooling towers will be in service for generations and ready to take on the ever-increasing demands for energy.
Precaster for A-frames, columns, flumes and lintel beams:
Precaster for piles:
Structural Precast Elements:
• Precast distribution channels (flumes)
• Precast columns
• Precast lintels beams
• Precast prestressed concrete piles