Replacement of a piece of major equipment can take a big bite out of a powerplant’s revenue, as the plant must be offline for the work to be done. But a Midwest utility completed demolition and replacement of one electrostatic precipitator in 10 weeks this spring and plans to repeat the operation next year.

"The key driver for (replacing) the precipitators was the physical degradation from 35 years of operating experience," says Terry Ward, project manager for Cincinnati-based Cinergy Corp., the parent of PSI Energy Inc., which owns and operates Cayuga Generating Station, Cayuga, Ind. Ward anticipates stricter federal or state opacity regulations. The new precipitators remove 99% of particulate matter and exceed state permit opacity requirements by 50%, he says.

Moving Day. Roll-in of Unit 1 precipitator (above) released crew to start assembly of Unit 2’s (top right). (Photos Courtesy of Cinergy Corp.)

PSI operates two 535-MW coal-fired boilers at Cayuga. In early 2003, Cinergy took bids for the precipitators. Wheelabrator Air Pollution Control Inc., Pittsburgh, won the lump-sum contract to replace the equipment during the plant’s scheduled spring maintenance outage. The owner will not divulge costs.

"We’ve done it a number of times," says Lou Rettura, Wheelabrator project manager. "We used a technique where we assembled in a separate location. It limits the downtime." Under Wheelabrator’s plan, workers construct each precipitator’s two boxes in a staging area, then perform functional tests on components before mounting the boxes on huge dollies and rolling them into position.

Ward liked the approach. "Repairing or rebuilding the current ESPs would have required significantly longer outages for two of our low-cost baseload units," he says. Richard Jerch, project manager for Chicago-based Sargent & Lundy, Cinergy’s architect-engineer, says he had heard of the technique, but had not seen it before. "Roll-in seemed a pretty attractive way," he says. "It’s becoming more common as older units require more retrofit. There must be space available (for assembly) with relatively clear space to roll in."

Last summer Wheelabrator began assembly of the precipitator for Unit 1 on temporary steel baseplates in a parking lot. The 40 x 80-ft footprint of the new boxes is larger than the old 26 x 83-ft footprint, so workers in 2003 had added caissons for an extended foundation. The roll-in path was prepared by moving a large condensate storage tank and placing crushed limestone and some steel plates to enable it to bear 2,000 lb per sq ft.

When the plant’s spring maintenance outage began March 5, Wheelabrator demolished the existing Unit 1 precipitator. Grand Ridge, Fla.-based subcontractor Ducky Johnson’s House Moving Inc. jacked the 100-ft-tall, 1,000-ton precipitator boxes onto 24 self-propelled modular transporters, with eight swivel-steered wheels each. "We did not have a direct shot into this precipitator location," says Jerch. "We had to make some 90° turns." Roll-in of the first box began on March 27 and was completed the next day. The second box was in place March 30. "We actually had clearances on the front and back side of 1Ú2 in.," says Wheelabrator’s Rettura. "It was as slick as putting a plug in a receptacle."

The first precipitator’s collecting electrodes were damaged in transit and had to be refabricated. The problem delayed Wheelabrator’s schedule, but the contractor was ready when the outage began, says Ward. As the powerplant started up again in May, Wheelabrator began assembling the Unit 2 precipitator boxes on the other side of the plant in preparation for next March’s outage. There have been no significant cost or schedule changes, Ward says.