St. Johns River Power Plant: A Powerful, Towerful Reinvigoration
ST. JOHNS RIVER POWER PLANT
Location: Jacksonville, FL
Owner: Jacksonville Electric Authority (JEA)
Size: Two 458-tall cooling towers
Expertise: Restoration & Renovation
The St. Johns River Power Plant (SJRPP) is an electric-generating plant whose twin turbine-generators add a total of approximately 1.3 million kW to the power transmission grid. Two 458-foot tall, hyperbolic cooling towers provide essential natural-draft cooling to the plant. In service since the late 1980s, the reinforced concrete towers were experiencing significant deterioration due to corrosion of their reinforcing steel. Their concrete veil (shell) was spalling and cracking, threatening the towers’ structural integrity.
Walter P Moore was engaged by Jacksonville Electric Authority (JEA) to determine the cause and extent of the deterioration, develop remediation solutions, study repair phasing, prepare construction documents for contractors for use in repairing and preventing further damage, and provide construction administration services to oversee the implementation of repairs. Extending the towers’ lives by 25 years, roughly doubling their life-cycle, was the goal. Replacing them would have cost an estimated $500 million.
Straightforward, yes. Simple, no. The math was complicated.
Big, Tall, Long, & Detailed
The size and height of the twin towers precluded a quick solution. Equivalent to a 36-story building, their combined surface area totaled 540,000 SF, of which approximately 200,000 SF needed remediation. And that would have to be done in phases given the sensitivity of the towers to buckling during extensive concrete removal. Furthermore, the towers would have to continue to operate throughout the construction phase, in spite of potentially loose and falling concrete.
Frequent gusting winds and the curved geometry of the towers (317-foot base diameter, tapering to 183-feet at the throat, and ending at 205-feet at the top) meant that traditional, suspended scaffolding couldn’t be efficiently used to perform the 88 lifts needed per tower for the 11-foot wide by 5-foot high concrete panels forming the new veil. Instead, a unique mast-climber technology was implemented to follow the curvature of the towers. Equipped with a pivoting work platform, workers not only have close-in access to the surface they are repairing, they can move about more freely. And this saves time.
No Power Interruptions.
Walter P Moore conducted numerous analyses, before and during the project. Among them geographic-specific wind-load studies (this is hurricane territory) and studies to ensure the towers’ structural integrity during repair and after. From this, constraints were developed for concrete removal and phasing the work.
A significant portion of the existing reinforcement was either supplemented or replaced. This was due to the aggressive corrosive environment from chloride-rich cooling water pulled from wells near the Atlantic Ocean. To safeguard against future deterioration, we specified a customized impressed current cathodic protection system to protect the existing reinforcing steel in the towers.
This project required meticulous attention to detail over an extended period of time and through multiple hurricane seasons. Close coordination was essential to maintain compatibility of materials and proper steel encasement.
After 12 months in design, construction began March, 2011, with a completion timeframe estimated at three years. As of the summer, 2015, the towers were undergoing their commissioning phase, as per our design criteria – four years, start-to-finish, without interruption of the power grid, as per the client.