Lift Pump Performance Testing
The lift pumps, like most large vertical pumps, were designed as prototypes scaled from preexisting model pumps using the principles of similitude. The prototype design was verified by independent analysis and design reviews using established procedures before manufacture of the pumps began. In addition, full-speed performance testing of each full-size lift pump with its respective gearbox driver was required from ITT.
Performance tests were conducted in the open pit of ITT’s pump factory in Pewaukee, in accordance with HI standards for vertical pump testing to validate the hydraulic and mechanical performance of each pump. The factory test included a temporary suction bell for the pump suction and discharge piping with flow meters and discharge throttling valves for flow measurement and control (Figure 6).
6. Test before shipping. Each of the new lift pumps underwent hydraulic and mechanical testing in the manufacturer’s facility after assembly. Minor problems were quickly corrected prior to shipping the pumps to the project site. Courtesy: Bechtel Power Corp.
Overall, the lift pumps and drives performed well, with the exception of two minor problems. In the end, all four prototype pumps met the mechanical and hydraulic performance design. Full-speed testing of the lift pumps and gearboxes proved beneficial because problems were detected and corrected in the factory, and final quality was validated before the equipment was shipped to the job site.
Field Work Begins
Construction of the new CW system for OCPP began by driving dock sheet pilings with bracing to isolate a portion of the intake channel for new construction (Figure 7). Once the area was isolated and dried, the intake tunnel shaft was completed and the lift pump station foundations were poured. Enough of the open channel remained for ongoing OCPP operations.
7. New water works. The scope of the civil construction work for the lift pump station was extensive. Courtesy: Bechtel Power Corp.
The steel-fabricated FSI forms arrived at the site in individual sections with the curb rings separate. Prior to beginning FSI installation, a survey crew provided elevation benchmarks and two reference lines that were used to locate the four FSIs per the as-designed centerlines of the pumps.
The FSI sections were assembled at grade and lowered down into position as complete subassemblies. Positions of the FSIs were adjusted with the help of porter powers and the leveling screws provided on the subassemblies. The leveling process was started with the jack screws threaded too low, so the FSI sat intentionally too high, because it is easier to lower than to raise a massive object (Figure 8).
8. Bottom-up assembly. Two of four FSIs are shown after being placed in the drywell. Courtesy: Bechtel Power Corp.
Care was taken to install metal jack plates under each and every leveling screw. These jack plates were fixed to the foundation with epoxy in a true level condition. Leveling screws bearing against level jack plates helped maintain the level conditions while the FSIs were shifted to meet their position requirements. This small step reduced installation cycle times and improved final quality of the work.
After the anchor bolt holes were set and tightened, the cavity under each FSI was filled with grout. After that grout cured, subsequent lifts of concrete were poured until the FSIs were fully encapsulated except for "leave-out" areas for curb ring installation. The strength of the FSI fabrications with additional support bracing was utilized to minimize the number of individual pours and thereby maximize civil work efficiency.
Next, the curb rings were positioned and welded onto the FSI outlets. Prior to welding, another survey was performed for elevation benchmarks and centerlines for curb ring positions. The curb rings were cleaned and then hoisted into position over their anchor bolts. Leveling screws were used as construction aids to level and retain the curb rings in final position. A stitch-welding technique was used to connect the curb rings to the FSIs, with two welds placed in unison on opposite sides. This process helped ensure the levelness of the curb ring with minimal welding rework.
When final positions were confirmed with precision survey and leveling instruments, fillet welds were made around the circumference of the curb-ring-to-FSI joints. Then leveling screws were removed and as-built survey results were recorded. These as-built records were later used to determine the as-designed placement of the pumps and their soleplates on the next floor up.
Next, grout was poured around the curb rings to an elevation flush with the lower floor of dry-pit space. Once the grout cured, the curb ring anchor bolts were tightened to torque specification.
Finally, the upper floor and foundations were constructed with leave-outs for pump soleplates (Figure 9).
9. Hold your water. Concrete was placed on the second floor for discharge water piping supports. Courtesy: Bechtel Power Corp.
Locating the anchor bolts for the soleplates was a laborious task because the soleplates must be positioned on the same centerlines as the curb rings down below. Several attempts were made to locate the soleplates on their pre-set anchor bolts and simultaneously on the curb ring as-built centerlines. In the end, the anchor bolt holes in the soleplates were machined oversize so that centerline-to-centerline requirements could be achieved.
Pump Installation Next
A number of alternative construction methods were evaluated for hoisting and installing each 84,000-pound pump subassembly. The challenge was compounded by the confined area around the pump station and by ground with limited bearing pressure capability. Large portable cranes were a viable solution, but their availability was problematic for the project schedule. An innovative solution was finally found: Redeploy an existing gantry crane system, staged on the job site for future lifting of 400-ton turbine generators, to the lift pump station construction area. Figure 10 is a series of photos that illustrate the successful use of the gantry crane to move one of the four lift pumps into place.
10. Vertical limit. This photo sequence illustrates how the plant’s gantry crane was used to move the lift pumps into place. Courtesy: Bechtel Power Corp.
The four-post gantry crane system offered the advantage of improved load distribution over the length of the existing lift pump house footings and fine lift positioning control. A special powered swivel was added to the crane so that pump assemblies could be oriented properly in the confined area. Once assembled, this crane was used to install the four pumps safely and effectively at all four locations in the pump station. This work was completed outdoors during the Wisconsin winter as snow was falling (Figure 11).
11. Freezing for a living. Installation of the new cooling water intake system occurred in the middle of winter as snow was falling. Courtesy: Bechtel Power Corp.
Construction on the OCPP Expansion Project continues, and start-up for Unit 1 is planned for later this year; Unit 2 is scheduled to go online in 2010. In the meantime, the upgraded CW system with new lift pump station for OCPP was commissioned in December 2008 and is currently providing cold water from the bottom of Lake Michigan to the existing CW pumps for the four operating units of Oak Creek Power Plant.
--Paul W. Behnke, PE (pwbehnke@bechtel.com) is senior principal engineer and manager of Rotation Equipment; Yifan Zheng, PE (yzheng@bechtel.com) is principal engineer and Hydraulics & Hydrology Group supervisor; and Brian Delrue was formerly an engineer with Bechtel Power Corp.
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