Award of Merit: Industrial Category
Silo Strengthening at the PPL Brunner Island Steam Electric Station
York Haven, Pennsylvania
Submitted by PULLMAN
D’Huy Engineering, Inc.
Kansas City, MO
The PPL Brunner Island Steam Electric Station is a coal-fired power plant. The 1490-megawatt generating facility provides reliable and affordable electricity to about 1 million homes in the region. In addition to possible new operation loading scenarios, the age and condition of the silos, new and more stringent concrete silo design criteria, and the consideration of alternative coal products were reasons for PPL to pursue a capital project to enhance the silos and extend their life.
Each unit consists of two conjoined reinforced concrete silos constructed in the 1960s. The two conjoined silos share a common wall, forming a figure-eight shape. Each silo is 41 ft (12.5 m) in diameter and 80 ft (24 m) tall, with 8 in. (200 mm) thick exterior walls. Following a comprehensive condition assessment, it was concluded that insufficient reinforcing of silo walls, wall cracking and bulging due to eccentric loading, and the age of the concrete would need to be addressed in the repair program.
With the configuration of the silos and a desire by PPL to attain a 20+-year life extension, innovative repair methods and materials were necessary. Access to the structure was challenging given one side of the silo was open, while the other was directly built adjacent to the boiler structure.
Three different strengthening options were considered and developed with details and cost estimates: carbon fiber-reinforced polymer (CFRP), post-tensioning, and section enlargement. Ultimately, the decision was made to use a combination of near-surface-mounted (NSM) carbon fiber rods for the silos’ interior and CFRP wrap for the exterior. The strengthening project at PPL was completed on schedule over a period of 3.5 months. Because the interior work was performed during an 11-week outage, there was minimal disruption for the facility.