By Steve Blankinship, Associate Editor
Condenser units, commonly called hotwells, have been used for decades to cool steam generated by power plants. Essentially a steel box roughly the height of a two-story building with hundreds of copper tubes running throughout, a hotwell usually sits on four concrete pedestals buffered by steel shear plates. These plates allow the unit to slide back and forth as it vibrates, expands and contracts. Over time, the steel shear plates may rust and corrode. What’s more, the concrete pedestals are stressed, resulting in cracking and spalling.
When the steel plates are corroded, plant owners either replace the hotwell or fix the problem by dismantling the unit, repairing the base and rebuilding the hotwell. Either way, a boiler is off-line for extended periods and replacement and repair costs can be substantial.
Florida Power & Light (FPL) had a better idea for replacing steel shear plates supporting two 1.5 millionpound hotwells. Under extreme pressure, the steel plates that had acted as a buffer had disintegrated to the point that the hotwell’s steel legs had melded into their pedestals. Tom Joseph and Gurudas Pai of FPL, along with Ernie Kabath, a contract civil engineer from Foster Wheeler, proposed lifting the hotwells less than 0.5 inch by transferring their loads to hydraulic lifts. After the units were raised, 0.25-inch-thick Teflon pads were to be inserted between the hotwell and the pedestals. The pads offered more cushioning and are designed to be more sympathetic to movement from vibration. They were also designed to be less expensive than original plates. Additional repairs to the concrete pedestals would be made after the hotwell was lifted.
 A 3/8-inch Teflon pad was inserted when the hotwell was lifted 0.5 inch. Photo courtesy of Innovative Engineering Technologies |
The solution was devised and implemented by Innovative Engineering Technologies (IET), a Stuart, Florida-based engineering company. IET faced numerous challenges. The hotwells were 40 years old and had several large piping connections, some of which were 30 inches in diameter. All of them had bellows joints to allow for expansion and contraction.
“Doing research, we were told by the hotwell manufacturer that the joints could tolerate a half-inch out of center alignment, but FPL was more cautious,” said Fred Shaffer, vice president of IET. “We figured that if we could lift the hotwell just a quarter of an inch, it would be enough to use a high-pressure water hose to blast out the old debris, slide in the new Teflon pads, set the hotwell back down and the system would function as originally intended.”
IET used 12 hydraulic jacks, each capable of a one-million-pound lift. There was one pump, but all hydraulic jacks were independently operated.
“The trick to the lift was keeping the unit level,” said Shaffer. “Each jack had a separate valve so the amount of pressure could be varied. By monitoring and measuring the four corners, we were able to keep the lift level.”
FPL’s balance of plant fleet team also added support to assure that the condenser equipment would remain undamaged during the lift and repair.
The first issue IET dealt with was using enough pressure to break away the hotwell’s feet from the base plates, which had welded together from corrosion.
“When the hotwell separated from its base there was an extremely loud bang that scared the bejeebers out of us,” said Shaffer. “But once the unit popped loose, the hotwell began lifting.” Because one side of the hotwell was heavier, control had to be maintained to keep the unit as level as possible. Field measurements were continuously taken at the corners and the lift constantly monitored.
The first lift took about four hours because the lifting was done with small increments of pressure. About two months later a second lift on another unit was done. That operation took only an hour. According to Shaffer, “By then we knew what to expect. We knew at about what pressures the hotwell legs would break loose from the pedestals, and what it would take to actually get it to break loose. We were able to work from higher increments, use fewer steps, and speed the process.” He adds that everything in both lifts went according to plan. “FPL is very pleased with the project,” said Shaffer. “It was successfully completed on time and within budget.”