By Douglas J. Smith, IEng
Tube Sleeving Less Expensive than Tube Replacement
The common practice for pitted, cracked or corroded tubes in condensers has been to plug them. However, as more tubes are plugged, the condenser efficiency is lowered. When this happens, the condenser requires a long outage for tube replacement.
Re-sleeving condenser tubes at Calvert Cliffs nuclear power plant. Photograph courtesy of Framatome Technologies
Framatome Technologies has developed a patented heat exchanger sleeving process for re-sleeving tubes rather than plugging or replacing them. According to Framatome, the cost of re-sleeving a tube is substantially less than replacing the tube.
Constellation Energy has recently re-sleeved the plugged tubes in the condenser on Unit 1 at their Calvert Cliffs nuclear plant. The plant official name is Calvert Cliffs Nuclear Inc. Of the six condenser water boxes of the condenser, one had 8.9 percent of its tubes plugged while another had 5.4 percent of the tubes plugged. Because of the plugged tubes, the condenser’s cooling capacity was marginal. To rectify the problem, the plant awarded a contract to Framatome to re-sleeve the plugged tubes during the scheduled outage in March 2000.
Before beginning the re-sleeving, Framatome analyzed the tube material, types of damage, wall thickness, operating pressure and temperature conditions within the condenser and its tubes. An initial inspection also revealed that the working space within the water box was restricted and thus limited the length of the new sleeves. Depending on the location of the tube, the sleeve lengths ranged from 14 inches to 84 inches. Since most of the tube damage was near the inlet of the tubes, Framatome and the plant management determined that most of the tubes could be sleeved.
Before installation in the condenser, the sleeves, which are custom designed for each application, were tested in spare condenser tubes in Framatome’s laboratory. Results of this test ensured the plant personnel that the sleeving would be completed within the three days allocated for the re-sleeving.
After removing the plugs, technicians inspected the tubes to determine if additional damage had occurred since they were plugged. The sleeves were then inserted and expanded to fit snugly against the inside of the tube. Both ends of the sleeves were then expanded, one end to the tube sheet and the other end into the existing tube. Expanding into the existing tube provides a leak-proof sleeve-to-tube joint. A total of 993 sleeves were installed in the two water boxes.
Testing conducted after the unit was returned to service indicated improved flow rates and no leakage problems. Calvert Cliffs management are considering additional re-sleeving for the 2002 unit outage.
Ultra Low-NOx Burner Reduces Emissions Below 9 Ppm
IN 1998, THE STATE of California was experiencing problems in controlling NOx when operating their General Services Heating and Cooling plant in Sacramento at full load. To rectify the problem, the plant installed a “QLA Ultra-Low NOx Water Boiler Burner” to one of the boilers. The burner was supplied by Coen Company, Inc., Burlingame, Calif.
Since installing the new burner, the plant has achieved full compliance. NOx emissions from the natural gas-fired boiler have been reduced from 30 ppm to less than 9 ppm, a drop of more than 70 percent.
In addition to achieving low NOx emissions, the boiler is now operating at maximum efficiency with fuel cost savings of more than $75,000 annually. These savings do not include the avoided costs associated with other more costly NOx reduction options.
According to GRI, which developed the burner with Coen, the capital cost of an equivalent standard low-NOx burner, with selective catalytic reduction (SCR), is approximately $6,000. In addition, the operating cost of the SCR is $1,300/ton of NOx removed. QLA burners, on the other hand, have a capital cost of $2,800 and no SCR operating costs, says GRI.
GRI and Coen are working on the next generation of ultra-low NOx burners which are expected to reduce NOx emissions further. The new burner will include an optical flame management scanner. Coen expects the scanner to be available within the next 18 months.
Big Equipment Demands Big Rigs
SOUTH TEXAS PROJECT, a two-unit, 1,250 MW nuclear power plant, recently replaced the four original steam generators on Unit 1. Rigging International (RI), Alameda, Calif. was awarded the contract to remove and replace the old steam generators. In addition to the challenge of restricted space, the removal and re-installation of the steam generators was part of the tight critical path schedule.
Transportation of GE 7FA gas turbine from rail siding to Elwood energy project. Photograph courtesy Rigging International.
The first two steam generators were shipped from Florida to Texas by barge. When they arrived in Texas, a packaged ballast system was used to ground the barge. The steam generators were then jacked-up and placed on a platform trailer, prior to being transported three miles to a storage area inside of the plant.
Removal of the old steam generators required them to be raised in a vertical position and then rolled through the equipment hatch of the containment structure. Once outside the containment building, the steam generators were lowered 40 feet onto hydraulic trailers for transportation to a holding area on-site. The new steam generators, each weighing 525 tons, were installed by reversing the procedure.
Another lifting project carried out by RI was the transportation of a GE 7FA gas turbine for the Elwood Energy project in Illinois. A specially designed “temporary lifting device” was used to offload the gas turbines from a rail car onto a hydraulic trailer for transport to the plant. At the power plant, the turbines were lifted onto foundations with an engineered trolley gantry.
In total, three gas turbines, three generators, transformers and other electrical equipment were unloaded from the rail cars and transported to the site.