Proper attention to the installation and use of bearings and seals at hydro facilities can save time and money, as well as provide confidence in the long-term operation of the plant.
By Elizabeth A. Ingram
Bearings and seals have important jobs to fulfill on various pieces of equipment at hydroelectric facilities, including gates and turbines. Bearings can minimize friction and corrosion, keep the shaft aligned, and eliminate the need for grease. Seals can protect against the intrusion of water and dirt and minimize leakage.
The applications on the following pages showcase innovative materials and approaches designed to provide for reliable long-term operation while minimizing wear and leakage. As a result, the hydro project owners have gained confidence in the operation of their facilities and, in many cases, saved money and/or time.
Installing self-lubricating bearings on miter gates
The downstream navigation lock gates at the 1,780-MW The Dalles Dam project were showing signs of wear. These two miter gates, which began operating in 1957, allow for passage of marine traffic on the Columbia River in Oregon.
In September 2009, U.S. Army Corps of Engineers personnel noticed issues of wear, based on readings from the gate stress and strain monitors. Inspection of the gates revealed that two did not make any contact when closed and the overall load was being transferred to the pintle areas. This resulted in cracking through the skin plate and end post. Emergency repairs were performed to keep the gates operating while the Corps began design and engineering work to replace all the gates.
|The self-lubricated bushings for the miter gates at the 1,780-MW The Dalles Dam project were specified with close running clearances and were installed using a glue-fit method.|
The new gates are 52 feet wide by 106 feet high and weight about 750,000 pounds. For the rotating parts, the Corps specified self-lubricated bushings and thrust plates to eliminate grease and any concerns about corrosion. Columbia Industrial Products (CIP) manufactured CIP Hydro Bearings for the gudgeon pin upper bushing, operating arm bushings, eye bar bushings, flange bushings, and thrust washers. CIP Hydro is a laminated composite material, says Jessica Leamen with CIP. This material is a medium-weave polytetrafluoroethylene and polyester fabric blend. The addition of solid lubricants to the resin reduces friction, extends wear life, and improves performance in wet and dry applications, she says.
To address the Corps’ concern with corrosion in the application, the bearings were designed with a glue-fit installation method. The glue acts as a protection paint for the housing and eliminates the concern with water seeping into the surface between the housing and bearing, Leamen says. The glue-fit process also allows for tighter running clearances and overall dimensions that are similar to the original bearing design. Design with this method eliminates the tolerances of the house and the press/interference fit between the inner diameter of the housing and the outer diameter of the bearing. The internal diameter of the bearing remains unchanged and can more accurately operate based on the final machined tolerances of the composite, therefore accomplishing tighter running clearances.
CIP had previously used this installation method during replacement of the tainter gates at 40-MW Foster Dam.
Installation was completed in March 2011.
For more information, visit www.cipcomposites.com.
Retrofitting butterfly valve seats in-situ
In-situ retrofitting of worn metal seats on butterfly valves with rubber seats can be an economical solution to extend the life cycle of a valve, says Brian Hartman with Hartman Valve.
On non-offset butterfly valves with metal seats split at the hubs, it can be difficult or even impossible to perform in-situ replacement of worn metal seats with new metal seats and achieve the desired leakage rate, he says. These valves had their metal seats factory installed and custom fitted by craftsmen of that era to minimize leakage. Dimensioning and tolerancing for interchangeability did not exist, Hartman says. Problems include matched drilled holes on large quantity bolt patterns, matched bored hub interfaces, distorted bodies, and worn trunnion bearings. By contrast, the in-situ retrofit with rubber seals is not affected by these variances. The time required to convert metal seats to rubber seats is unique to each installation but takes two to three weeks on average, he says. Once the rubber seats are installed, replacement with new rubber seats can be achieved in less than a week.
The efficacy of in-situ retrofitting of worn metal seats with rubber seats first was proven by the U.S. Department of the Interior’s Bureau of Reclamation. This work was performed as a prototype on a 168-inch A-6 turbine isolation butterfly valve at 2,078-MW Hoover Dam. Results from this installation showed a low leakage rate at the hubs that was well within the limits of the downstream drain, as well as tight shutoff across the seats. This work then was performed on an additional 14 168-inch and two 120-inch isolation valves at Hoover and on the 100-inch valves at Reclamation’s 27-MW Anderson Ranch Dam facility.
A variation of this technology was used on four butterfly valves at 3-MW San Gabriel Dam. The Joshua Hendy designed metal seated valves at this dam, owned by the Los Angeles Department of Public Works, had their metal seats retrofitted with rubber seats. These valves consisted of two 123 inch, one 96 inch, and one 51 inch. This retrofit was accomplished by Hartman Valve as part of the modernization of this 75-year-old facility.
The essence of this technology is the locking of the rubber seal to prevent circumferential movement. This locking prevents the seal from pulling away from the hubs, minimizing leakage at the hubs while providing tight shutoff between the disc seat and body seat. The ability to rapidly remove and replace, and adjust in-situ, a newly installed rubber seat is critical to the practicality of the retrofit, Hartman says.
Many large butterfly valves and ball valves installed 50 or more years ago now need seat replacement, Hartman says. Ideal candidates include Joshua Hendy, some Pelton, Reclamation, Allis Chalmers, and S. Morgan Smith designs. The best time to perform this work is during extended facility shutdowns. This retrofit is universal to any valve without integral seats, he says.
For more information, visit www.hartmanvalve.com.
Returning to an old bearing material
Sometimes the best solution for a problem is an old solution, says Bob Shortridge with Lignum-Vitae.
The U.S. Army Corps of Engineers’ Lock and Dam 15 on the Mississippi River between Illinois and Iowa has been operating since 1934. The original lignum vitae bearings installed on the 213 kVa turbine, used to power the lock, lasted until 2001, a lifespan of 67 years. The operators and engineers at many hydroelectric plants using lignum vitae bearings typically speak of 20 to 30 years of service, Shortridge says. Thus, the bearings at Lock and Dam 15 provided a particularly long life.
In 2001, the Corps installed new bearings made of a composite metal. The first set of new bearings lasted for six years; the second set lasted less than two years. As a result of this experience, in its request for quotes the Corps specified that the replacement bearings be manufactured using lignum vitae because “modern composite metal bearing materials … are unacceptable materials due to their inability to match the characteristics of lignum vitae.” The Corps said two aspects make lignum vitae a resource for hydro turbine bearings: hardness and self-lubrication.1
|The existing bearing on one unit at 624-MW Rock Island was modified for installation of a self-equalizing thrust bearing, which can equalize load and center the shaft up to a 1/8-inch out of plumb condition.|
Lignum vitae is a dense tropical hardwood that has been in use for hundreds of years in pumping devices, water wheels, the first Francis turbines, and the water-lubricated bearings for Thomas Edison’s first hydroelectric plant in 1882, Shortridge says. Once believed to be rare, it is now harvested in a sustainable manner that will last into perpetuity, he says.
For this application at Lock and Dam 15, the Corps says lignum vitae provides the strength needed to keep the shaft in place, while also lubricating the shaft and aiding in filtering the raw water of the Mississippi River. This is important because it keeps sediments from embedding in the bearings, which can then score or scratch the shaft. The Corps specified lignum vitae bearings of a minimum thickness of 2.48 inches with a 0.5-inch-thick stainless steel backing plate, fastened together to make one piece. In 2010, the Corps replaced the four bearings.
More than 3,800 hydro plants worldwide rely on lignum vitae, and many are returning to its use, Shortridge says. Lignum vitae also shows promise for use in wave turbines.
For more information, visit www.lignum-vitae.com.
Using “green” grease to lubricate bearings
“Green” grease is an alternative to self-lubricated bearings when hydro project owners are concerned about the environmental effects of a lubricant, says Ken Brown with Eco Fluid Center Ltd.
Using an environmentally friendly grease can save considerable costs associated with the outage time required to replace bearings at a facility, Brown says. In addition, standard bronze bearings typically have a long service life (several decades), while experience shows that self-lubricated bearings may need to be replaced much sooner, especially if the installation was not performed completely correctly.
|Spherical bearings manufactured by DRIE-D are being installed on the Oyster 2 wave energy device being built by Aquamarine Power.|
VSG, supplied by Eco Fluid Center of Toronto, Ontario, Canada, is one example of a green grease. VSG is a canola oil-based, biodegradable, low-toxicity lubricating grease. It is thickened with calcium sulphonate and is 81 percent biodegradable after 21 days.
This grease has been in use for more than 15 years, with applications at hydro facilities in the U.S., Canada, Iceland, and New Zealand, Brown says. It is being used on hydroelectric facilities and for wire ropes and gate slides. At this time, it is the only green grease known to meet the performance requirements of the specifications for wicket gate greases of Ontario Power Generation, Hydro-Quebec, and the Tennessee Valley Authority (TVA), Brown says.
VSG also was tested by the Bureau of Reclamation and performed the best of all greases tested, according to the resulting report. Reclamation has used VSG at one high-head dam since 1999. TVA ran VSG alongside its regular grease and self-lubricating bearings in a three-unit facility for 10 years. Based on the favorable results, VSG is now used in many more TVA facilities.
Brown says a green grease such as VSG also can help federal agencies comply with the requirement of Executive Order 13514, which calls on them to establish an integrated strategy toward sustainability and to prioritize the reduction of greenhouse gas emissions. Among other initiatives, the order requires agencies to advance sustainable acquisition to ensure that 95 percent of federal purchases are “energy-efficient, water-efficient, biobased, environmentally preferable, non-ozone depleting, contain recycled content, or are non-toxic or less-toxic alternatives.”
VSG has better low-temperature mobility than some standard mineral oil-based greases, offers corrosion protection, and does not contain a soap thickener (resulting in fewer distribution block problems), Brown says.
As with any time greases are changed, it is important to check the compatibility. If the two greases are incompatible, the mixture can soften and not provide the required performance, Brown says. If this occurs, an intermediate grease can be used for a few pumping cycles.
The incremental cost to use VSG typically is only a few hundred dollars per year per unit, Brown says. And, in fact, its use sometimes can save money. BC Hydro reports a significant decrease in the amount of grease used at one of its hydro stations. Personnel went from greasing bearings once every four hours to only once a week. VSG has been used at this facility since 1996.
For more information, visit www.fluidcenter.com.
Self-equalizing bearing installed at Rock Island
Chelan County Public Utility District (PUD) employed a self-equalizing thrust bearing on one unit at its 624-MW Rock Island project on the Columbia River in Washington.
Most large, tilting-pad thrust bearings in hydro facilities are equipped with jack screws or other mechanical methods of setting individual bearing shoe heights, says Mike Brawley with Kingsbury Inc. Over time, aggregate migration of the concrete in the powerhouse can cause the station to tilt, changing the vertical orientation of the turbine shaft. Non-equalizing bearings cannot accommodate the resulting misalignment, and adjustable designs require changes over time, Brawley says. An “out of plumb” shaft can eventually lead to damage to the turbine guide bearings and reduce the load capacity of the unit.
This plant, which began operating in 1933, is undergoing a rehabilitation. In upgrading a decades-old plant to be operational for 20 years or more, installation of equalizing bearings is one of many long-term precautions that can be taken to permit the extended life, Brawley says. Chelan County PUD installed a 73-inch bearing designed by Kingsbury. This bearing uses a hydraulically-equalizing design that permits the bearing to equalize the load and center the shaft up to a 1/8-inch out of plumb condition.
The Hydraulically Self Equalizing design can be retrofit into the existing thrust bearing base ring and utilizes the original thrust runner and shoes. The base ring is equipped with hydraulic cylinders to replace the original jack screws. The cylinders operate at more than 2,500 pounds per square inch, constantly equalizing the static and dynamic thrust load across all shoe segments, Brawley says. The bearing also is equipped with load cells to constantly monitor the load, a pressure transducer to monitor the hydraulic pressure, and a proximity probe to monitor position of the cylinder.
The first unit at Rock Island was equipped with this bearing in 2007. The result has been almost perfect equalization of the load on individual thrust shoes, confirmed by load cell measurements, and the hydraulic equalizing bearing has operated with no problems or interruption of service since installation, Brawley says. Five additional units at the plant will be upgraded over the next five to seven years.
For more information, visit www.kingsbury.com.
Using greaseless bearings and seals at Mossyrock
After more than 40 years of service, efficiency of the two propeller units at the 300-MW Mossyrock project on the Cowlitz River in Washington had declined. In addition, repairs and maintenance were becoming more expensive. Owner Tacoma Power determined that, without replacement, failure due to mechanical fatigue eventually would occur, resulting in very costly repairs. As a result, Tacoma Power decided to upgrade the units and install one additional unit.
The utility contracted with Andritz Hydro Canada to upgrade the original Mossyrock units. The two units to be replaced were originally built in 1968 and had a service life of almost 40 billion kWh.
Trelleborg Sealing Solutions Canada is a preferred supplier for Andritz Hydro, with Orkott TXMM hydro bearings being the recommended product for specification on all future projects, says Wendy Sack with Trelleborg.
Thus, as part of this upgrade, Trelleborg specified Orkot TXMM hydro bearing materials. These bearing materials offer a low coefficient of friction, are self-lubricating, and have virtually no swelling in water. The bearings also are well-suited for high-load applications where customers insist on a long bearing life, Sack says. The wicket gate bearings, vertical and horizontal liners, operating rings, and all linkage bearings on the turbines at Mossyrock were fitted with these materials.
In addition, Variseal VR seals were incorporated into all intermediate and lower wicket gate bearing designs. Trelleborg designs these seals specifically for wicket gate bearing applications. They use an EPDM elastomeric energizer encased in a Zurcon Z80 jacket to seal against water and/or dirt.
The upgraded turbines were installed in 2009 and have operated successfully to date. In addition to replacing the wicket gate seals and bearings, Andritz replaced the exciters and generator stator, refurbished the rotors, and modernized the governor with a new digital control system.
As a result of this upgrade, Mossyrock produces enough electricity to supply 78,000 homes, compared with 58,000 before the work.
For more information, visit www.tss.trelleborg.com.
Supplying bearings for a wave energy device
Aquamarine Power chose bearings supplied by DRIE-D for its Oyster 2 wave energy technology.
The technology, which is designed to capture energy from amplified surge forces in near-shore waves, includes an oscillating wave surge converter fitted with double-acting water pistons. Each passing wave activates the pump, delivering high-pressure water by pipeline to shore where it powers conventional hydroelectric generators.
The Oyster 2 is a next-generation device that builds on lessons learned from deployment and testing of the Oyster 1 in August 2009. The 800-kW Oyster 2 is 26 meters wide by 16 meters high. It will deliver 250 percent more power than Oyster 1, Aquamarine says.
For the main hinge bearings on these units, DRIE-D is supplying 1.2-meter spherical plain bearings constructed using D-GLIDE bearing material. These bearings are low friction and low wearing and offer high load capability, says Frank M. Trivieri with DRIE-D. The hydraulic cylinders on the Oyster units feature smaller spherical bearings of the same material. The spherical bearings were integrated with the stainless steel components and precision machined, resulting in bearings that are expected to be in operation for many years, Trivieri says. DRIE-D has supplied D-GLIDE bearings for several offshore oil applications.
The Oyster 2 device is currently being built and will be installed at the European Marine Energy Centre (EMEC) in Scotland this summer. The second Oyster 2 unit is scheduled to be installed in the summer of 2012.
For more information, visit www.drie-d.nl.
Retrofitting a shaft seal to eliminate leakage
Pyrites Associates, a subsidiary of ENEL Green Power North America Inc., was experiencing a relatively severe shaft leakage issue on the two 3.5-MW horizontal Francis turbines at its 7-MW Pyrites project in New York.
These turbines, which were commissioned in 1985, were sealed using compression packing, and they operated satisfactorily for many years. However, as time went on, wear of the packing sleeves got progressively worse until it was obvious that a great deal of money was being lost. The situation was so severe that, if the units were run at 75 to 80 percent gate opening, the volume of “spraying” that occurred risked wiping out the main bearings and/or flooding the generator pit.
|With a Fully-Split E.A.S.-S.E.E. SEAL rotary mechanical face seal installed, the units at Pyrites Associates’ 7-MW Pyrites project are operating with minimal leakage. Generation from the two units has increased 7.5 percent on average.|
Pyrites Associates was faced with the prospect of spending an estimated $200,000 per unit for a teardown and shaft rehabilitation. The company decided to try to find another way to address the problem.
Sealogic Innovations Corp. proposed to custom design and retrofit its Fully-Split E.A.S.-S.E.E. SEAL rotary mechanical face seals, says Kevin Drumm with Sealogic. The design of this seal incorporates two “floating” faces (not subjected to any mechanical stresses) that self-align into the plane that is precisely perpendicular to the shaft’s axis of rotation, Drumm says. This means the seal does not “flex,” or oscillate during revolutions, maintaining face sealing contact while minimizing wear and spring fatigue.
This seal can be used as an external main shaft seal on horizontal or vertical units or as the internal submerged bearing seal upstream of the runner on S-type and bulb turbines. The seal can be designed to accommodate axial movements in both directions, as well as radial movements, of 0.25 inch or more. It also has minimal requirements for micro-filtered flushing water and can run dry.
The cost for this solution at the Pyrites Associates facility was less than 20 percent of that involved in shaft rehabilitation, Drumm says. On one day in December 2009, the seals were retrofitted within a few hours for each turbine. No modification or refurbishment of the turbines was required for this work. The units have run since that time with leakage rates varying from “bone dry” to insignificant drippage, Drumm says. The units can run up to 100 percent gate opening, and ENEL personnel have calculated a corresponding increase in generation of 7.5 percent on average, he says.
For more information, visit seal-ogic.com.
Converting a flat plate Babbitt bearing to PTFE
On one unit at a ten-unit Canadian hydropower station, an aging flat plate Babbitt bearing had caused a generator imbalance. This 68.5-MVa unit was installed in 1925 but had undergone repairs/refurbishment during its 85 years of service. Rebalancing of this type of bearing is difficult because proper alignment requires extraordinary workman skill, says Kjell Nyqvist, general manager of North American PTFE Bearing LLC.
Other difficulties arise from this type of thrust bearing, he says. It typically carries only one-third of the thrust load due to peripheral oil leakage. And the leading rather than the trailing edge of the plate segments carries the majority of the load, which is the opposite of conventional individually segmented Babbitt and polytetrafluoroethylene (PTFE) bearings. As a result of these issues and concerns, the station owner determined that this particular thrust bearing had outlived its life.
Based on previous experience with 33 PTFE-lined thrust bearings installed and operating since 1999, the station owner decided to replace the bearing with individual PTFE-lined pads.
PTFE has a variety of features that make it preferrable to Babbitt, Nyqvist says. These include twice the permissible specific load, a friction coefficient three to five times lower, lower heat transfer coefficient, no high-pressure oil lift, the ability to hot start directly after a stop and start directly after a prolonged stop and lower brake application speed. This results in a bearing that offers reliability, availability, efficiency, and a long life expectancy, he says.
The replacement work at this Canadian plant was undertaken as part of a generator rehabilitation project in 2010. The unit is now operating well with a new, balanced generator and PTFE thrust bearings, Nyqvist says.
The remaining nine units at this plant are scheduled for refurbishment.
For more information, visit www.ptfehydro.com.
Elizabeth Ingram is associate editor of Hydro Review.