PAG acceptance grows with field experience

COMBINED CYCLE JOURNAL, Fourth Quarter 2014TURBINE LUBRICATIONPowerplant operators, with good reason, are deeply reluctant to make changes in the basic components that their plants depend upon. There is simply too much at stake—system reliability, cost, lost revenue—to tinker with the opera-tion of a plant that functions reason-ably well 98% of the time. “If it ain’t broke, don’t fix it” is the principle that restrains creativity in plant operation. But a growing number of operators have recognized that their turbine fluid systems are, in fact, “broke.” Varnish problems have driven them to look for a non-varnishing lubricant and hydraulic fluid for their power-generation systems.At the 2009 7F Users Group meet-ing, one of the largest US utilities presented its experience with syn-thetic polyalkylene glycol (PAG). At a repowered 2 × 1 combined-cycle plant in Oklahoma, AEP Resources Inc switched one gas turbine (GT) from a hydrocarbon fluid to a PAG during a hot-gas-path inspection in November 2007. The second turbine was converted in March 2008. The senior engineer responsible for the change-over expressed complete sat-isfaction with the ease of the switch. More importantly, the turbines had experienced no varnish deposits since completing the change-over.Calpine Corp also took the plunge in November 2007, converting one of four GTs at Oneta Energy Center, Broken Arrow, Okla, to PAG with equally satisfactory results. Oneta’s two 2 × 1 7FA-powered combined cycles were troubled by varnish and carbon build-up (in servo valves, pencil filters, reservoir interiors, and piping), which was attributed to turbine-oil degrada-tion caused by high heat and friction. The problems with varnish and sludge disappeared after the conversion to PAG (sidebar).Varnish is notoriously difficult to clean out once it has been deposited. Calpine prepared for the lubricant switch with a complete varnish flush using a cleaning formulation in the original oil. Varnish and sludge were removed from system components. Next, 3500 gal of PAG was circulated through the GT and drained. Then the system was refilled with fresh PAG. AEP, by contrast, cut to the chase: To make the switch, the plant simply drained the existing oil and refilled with PAG, bypassing the flush step.In 2009, that was the story for the 7F UG: Three turbines converted—promising, but not enough to start a stampede to PAG. Since then, however, more powerplant owner/operators have used PAG to clean up and protect 82 more units. CCJ recently interviewed several of the engineers in charge of those units, and all spoke positively of their experiences with PAG. We are sharing what we have found for the information of our readers, much like the information exchange at a user-group meeting. Plant managers and engineers considering replacing their turbine fluids with PAG should conduct their own investigation of the alternatives, their pros and their cons, and should not assume this article is the final, authoritative word on the subject.Skidding to a stop NV Energy operates 53 combustion turbines and has converted eight 7FAs units to PAG, said Gary Crisp, senior engineer. The utility typically uses soluble varnish removal (SVR) skids on its turbines, but has taken out of service most of the skids servicing con-verted units. “It varied from plant to plant, but many plugged in the skids, ran them for a period of time, but then saw very little results in the MPC (membrane patch colorimetry) patch PAG acceptance grows with field experienceBy Thomas F Armistead, Consulting EditorWhat causes varnish and how PAG helpsSolving a varnish problem is a matter of basic chemistry. The main elementsare polarity and the principle that inchemistry, “like dissolves like.” This is a rule of thumb that refers to the factthat a material will dissolve in solventsonly when both the material and solvent molecules exhibit similar chemical polarity.Petroleum oil—the traditional base stock used for turbine lubricat-ion and hydraulic systems—is non-polar. The stress of being used as a machine lubricant accelerates the aging of the petroleum oil, resulting in oxidation. This oxidation results in decomposition byproducts that are polar. Because the oxidation byproducts are polar and the base stock non-polar, the byproducts are not soluble and come out of solutionas varnish. Once out of solution,decomposition byproducts are tenacious, will agglomerate, can clog rs, and ultimately plug tight-tolerance servo valves. Turbine trips may result.Polyalkylene glycol (PAG), by contrast, is polar. It is highly oxygen-ated, with every third atom being oxygen. PAG does oxidize; howeverever, the oxidation byproducts are polar and in y soluble in the base stock. To move past varnish problems, some end-users have completely replaced their petro-leum-based turbin uids with PAG. Others have m roleumturbine oil with an oil-soluble PAGlubricant to shift the oil’s polarity.In both cases, the polar nature of the base oil dissolves the polar by-products. Everything remains liquid.That’s the chemical principle: Likedissolves like.To date, end-users have converted51 turbines to PAG from mineral oil.their existing mineral oil lubricant with PAG in 34 additional units. Reports from turbine operators in both cat-egories have been uniformly positive. Some of their stories are told in the main article.COMBINED CYCLE JOURNAL, Fourth Quarter 2014 test, which is your test for varnish,” he said. “Candidly, our filtration and treatment skids that we had in service did not work well and were taken out of service on the units that had been converted to PAG.”Varnish caused a few trips in the year before the conversions. Two gas turbines were converted in December 2012, four in March 2013, and two more in April 2013. But NV Energy’s decision to convert and avoid varnish-ing issues was not driven by the num-ber of trips, Crisp said. It was primar-ily related to the industry experience and obvious benefits of the converted systems. Crisp noted that crews have not had an opportunity to see inside the reservoirs since the fluid conversions were completed, but indications are that varnishing is not a growing prob-lem. He noted that there are 22,000- and 32,000-hr GT parts that have not needed to be accessed. “And, we haven’t had issues with losing control of inlet guide vanes and sticking servo valves,” he added. Pleasants Energy LLC, a sub-sidiary of GDF Suez Energy North America, operates two simple-cycle 7FA turbines in St. Marys, WVa, commissioned in 2002. As peaking units, their run time is low, but their combined lube/hydraulic system is in continuous operation with the units on turning gear, said Gerald Gatti, plant manager. During the past few years they experienced increased varnish issues in the lube oil. “Varnish is accumu-lating in the system and building up, typically on some small servo filters, similar to where other gas-turbine users have experienced problems with varnish,” he said. “Although we did not have any plant trips due to varnish, we did experience failed starts several times. I’m sure if the plant was run-ning a lot more, we would ultimately also have plant trips caused by the varnish buildup in the system.”Gatti arrived at the plant in 2012, and one of his first jobs was to find a solution to the varnish problem. The plant had purchased a varnish removal skid and initially installed it on Unit 1 because the lube oil in that unit had higher varnish levels than Unit 2. The varnish level dropped quickly but then trended up again, “because the origi-nal filter canisters had expired. They get saturated pretty quickly when you have that much varnish in the oil,” Gatti said.The operators went through several sets of filters at a cost of about $4000 each. “After one year, the varnish level in the fluid had been reduced to acceptable levels, but the SVR didn’t remove the varnish that was already plated out within the system or reduce varnish formation,” Gatti said. The plant still had servo filters clogging with varnish throughout the system.Searching for a solution, Gatti found The Dow Chemical Co PAG products. Dow owns the PAG patent and manufactures PAG in the US for global distribution under the name Turbine Fluid TF-25. The exclusive right to sell PAG in North America is held by American Chemical Technologies Inc (ACT), which markets it under the name EcoSafe TF-25. While TF-25 can entirely replace a plant’s turbine fluids, the EcoSafe line of products also includes Revive, a PAG fluid designed to be added at a 10% level to repair a hydrocarbon-based turbine fluid with elevated varnish potential ratings.Gatti talked with other users about their experiences with TF-25. “In all cases we were getting positive feedback from other plants, both within our own company and outside our company on the Revive and the TF-25,” he said. Estimating the cost of replacing the existing turbine fluids with mineral oil or TF-25, he concluded “the cost was not that much different. “What I learned really drives up the cost on mineral oil replacement is the cost of cleaning up the system,” he said. “The cost of the oil itself, let’s say, is half the price of the PAG, but when you add into it the cost of doing a full system flush using 4000 gal of flushing fluid, system cleaner, and several days with the contractor to do it, it can add up to another $80,000 of expense. “When you add those together it’s comparable to the cost of TF-25 and a system cleaning using a PAG-based product (Revive or UltraKlean) in the system for up for 90 days prior to the replacement. You can then just dump the old mineral oil out and put TF-25 in. With that process you minimize the expense and eliminate the need for a complete system flush.”EcoSafe UltraKlean TO is a discontinued ACT product similar to Revive, said Jim Kovanda, ACT vice president. “Although it uses the same base stock as the EcoSafe Revive fluid, it is designed to be circulated for 90 to 120 days, drained, and the system filled with EcoSafe TF-25 or turbine oil,” he said. ACT discontinued the manufac-ture and sale of the product last year because “users were leaving the UltraKlean TO in the systems, well beyond the recommendations, putting the product and system at risk,” he said. Revive, designed for extended use, now is the only PAG base-oil modifier ACT sells.Gatti was hesitant to try PAG fluid, mainly because the company had no experience with it. “It was a big step for us to say we’ll be the corporate guinea pig to try this,” he said. A couple of developments helped push him over the line. In June 2013, GE removed a major barrier to industry acceptance of TF-25 when it revised its gas-turbine lubri-cant recommendations document, GEK 32568h, to explicitly recognize Dow’s PAG-based synthetic turbine fluid as an alternative to mineral oil. Gatti took further comfort in an endorsement by a cogeneration plant manager in Maine he spoke with who had converted his system to TF-25. “They were definitely happy with what they did,” he said. Finally, he asked some oil manufacturing engineers what negatives they saw in it, and lack of long-term experience was the only thing they identified. “They cur-rently don’t have anything to directly compete with it,” he said.Testing the claimsWhile weighing his options, Gatti con-ducted an experiment. In November 2013, he put 660 gal (10%) of Ultra-Klean in Unit 1, with the intention to run it for 90 days, then dumped it and recharged the system with TF-25 (Fig 1). At the same time he moved the SVR skid to Unit 2 and put in 10% Revive (660 gal) to work together with the skid (Fig 2). After 90 days, lab analysis reported that results were good for both systems. “The UltraKlean actually worked similarly to the Revive, even though the difference between the two is spe-cial additive packages that they put in the Revive for long-term use,” Gatti said. Both modifiers dissolved the var-nish that had been plated out and kept it in solution. “That’s the big benefit,” Gatti stressed: keeping the varnish in solution. Revive is twice the price of UltraKlean because of its formula-tion. Gatti has been running both the Revive and the UltraKlean for more than a year now with good results.Having used both the side-stream filter and the PAG, Gatti says the skid “certainly removed the varnish from the fluid. But it didn’t dissolve the varnish that’s already been plated out in the system,” he said. “We continued to see small pencil filters that were plugging up with the varnish. Since we put the UltraKlean and the Revive in, those filters have been COMBINED CYCLE JOURNAL, Fourth Quarter 2014TURBINE LUBRICATIONspotless. We were changing out these little servos every six months, whether we ran the plant or didn’t run the plant, because they were caking up with the varnish. The filtering skid is a good way to prevent varnish from building up, but once you have it built up, it’s difficult for the skid to clean it.”The hydrocarbon-based turbine fluid’s life expectancy is seven years, but no one knows for sure what the life of PAG turbine fluid will be because its field experience dates back only to 2007, he said. “I’m sure it would outlive mineral oil.”Saving a trip Turbine trips were a major problem at another plant with two 7FA units, which the owner asked us not to iden-tify. “Almost every time we’d start we’d have an IGV (inlet guide vane) trip fault,” said Johnathon Drake, pro-cess owner, fleet maintenance. “We’d have to go reset it, stroke the valves, and then we could start up. But we probably have had 12 to 15 trips in the last year.” Trips would occur after the plant had been shut down for several days, Drake said. “Sometimes in a run of several days there could be a trip on day two.” The existing varnish removal skid gave disappointing results, pro-ducing QSA numbers running between 40 and 60, indicating high varnish potential. Skids at some other plants in his company’s system gave good results but required several months to get them.Drake introduced Revive to his system in August last year and has experienced no varnish-caused trips or fail-to-start events since then. Only one thermocouple burned up, he said. “From talking to the user references provided by ACT, we were expecting to see good results. The results we’ve had have exceeded our expectations,” he said. “We’re more than pleased.”Before his plant used Revive, the varnish potential rating was 91. “The last several samples we’ve drawn, the varnish potential is down to 9 and 7, very healthy oil for varnish potential,” Drake said. He has not pulled any pencil filters to check how they are affected, but he has pulled a couple of hydraulic filters just for inspection, JanFebMarAprMayAugSepNovDec JanFebMarApr May Jun Jul Aug Sep Oct Nov Dec Jan Feb MarApr 9Apr 23 Jun 6 Jun 13 Jul 11 Aug 8 Aug 26 Sep 5 Sep 15 Oct 7 Oct 24Sep 6 Sep 13 Sep 18 Sep 24 Oct 1 Oct 10 Oct 31 Nov 5Nov 20 Nov 27 Dec 6 Dec 13 Dec 18 Dec 26 Jan 3 Jan 10 Jan 17 Jan 22 Feb 14 Mar 17 Mar 26 Apr 9 Apr 29 Jun 6 Jun 13 Jul 11 Aug 8 Aug 26 Sep 5 Sep 15Oct 7Oct 242013 20142012 2013 2014Soluble-varnish removal (SVR) skid installed (12-16-11) SVR skid removed (9-6-13)UltraKleen added tolube oil (11-22-13)Sample date Sample date Soluble-varnish removal (SVR) skid installed (9-16-13)Revive added to lube oil (11-22-13)9080706050403020100MPC value9080706050403020100MPC value1, 2. Lube-oil varnish levels on Pleasants Energy Unit 1 (left) and Unit 2 (right)and they looked good. “We put in new filters in the spring time frame of 2014 and we started experiencing a lot of trips again in late July. We pulled some of those filters out and they were really gunked up,” he said (Figs 3 and 4). Drake used Revive to solve a prob-lem, not just as a test. But a major outage is scheduled this year, and he plans to change out the oil. Mineral oil is an option, but the company is using the time until then to evaluate PAG.TF-25 costs $25 to $26 per gal, Drake said, but he sees Revive as a cost saver. “If we’ve got the Revive in there, and it gets the varnish back into solution so it doesn’t plate out, whenever we make the conversion (to TF-25) we’re not going to have to do the high-velocity oil flush. That’s going to save us about $250,000 to not have to complete that rinse-through.” The Revive has resolubilized the varnish, which will be dumped, so the FA shows varnish coating on both end caps and system will not need a flush to clean it for TF-25, he reasons. His plant is designated the fleet’s test site for conversion to PAG. If the conversion continues to deliver the results seen so far, 12 other units could be next in line, he said.Other experiencesIn April 2012, all three of the Frame 6B gas turbines at Atlantic Power Corp’s Morris Cogeneration Plant were in “critical varnish status.” Facing the need to replace the turbine fluid as well as do a varnish flush on each of the three lube systems before recharge, O&M Manager Joe Nichols investigat-ed the EcoSafe Revive base-oil modifier as a possible alternative. Long story short, just 30 days after 10% Revive was added to Unit 1, the unit’s fluid was substantially improved, with a 2-deg-F drop in bearing temperature. The total cost of mineral oil for the plant, including oil, skid and sample analysis, was $48,600 per 6B GT, Nich-ols said, and the fluid had a life expec-tancy of six years. Maintenance to servos and filters per gas turbine was $2100 annually and varnish removal resin cartridges $4700 annually, not counting the cost of downtime required for the maintenance and cleaning. He estimates that the plant had experienced five trips and failed starts total on two of the units in the two or three years before converting to TF-25 lube oil in summer and fall 2013. To the costs of those trips he added costs of downtime for routine servo mainte-nance and cleaning. The total cost of TF-25 for the plant was $66,150, with an anticipated life of 10 to 12 years, and zero cost for opera-tion and maintenance, Nichols said. Since conversion, he has experienced no varnish-caused trips. Unit 2 was charged with 10% Revive at the end of 2014, and Nichols plans to recharge the system with TF-25 at midyear after the Revive cleanse is completed.In using Revive, Nichols was “look-ing to extend the life of the existing COMBINED CYCLE JOURNAL, Fourth Quarter 2014 into solution and releases trapped particulate contamination,” he said. “When the system was restarted the particulate matter quickly plugged up the inline filters at an accelerated rate—twice in 90 days, which was unexpected.” Sources say that is to be expected in a peaking plant that is idled for several days, allowing sus-pended particulate to settle out.Another Atlantic Power plant, Frederickson 1 Station, is using 15% Revive in its 7FA gas turbine and A-11 steam turbine. The plant was constructed in 2002, and the turbine oil is still the original fluid. Richard Chernesky, plant manager, intends to migrate to TF-25 in 2018 and is counting on the Revive to extend the fluid’s life till then. “With the 15% EcoSafe Revive in the system, the varnish will be solubilized and the oxi-dation package to the original Group II oil will be reactivated,” Chernesky said. Frederickson 1 has converted air compressors and hydraulic units and will convert cooling-tower gearboxes to PAG products, he said.Before adding the 15% Revive about three years ago, “we used a combina-tion of cellulose and resin element Fluitec low-flow, high-retention, kid-ney loop systems to handle the quasi-soluble oxidation byproducts with success,” he said. “The Revive basi-cally changes the state of the varnish, solubilizing the agglomeration, so the element filtration resin chemistry has changed to effectively polish the new composition. To date, it’s still effective; with continuous predictive evaluation, in the future the resin element may not be required.”Tales of the pioneersOne of the earliest adopters said he can’t estimate life expectancy of the PAG fluid in his plant, but it is still working well seven years after the change. Jeff Volz, maintenance man-ager for EthosEnergy Group, was one of the presenters at the 7F Users Group meeting in 2009, when his plant was owned by Calpine. He converted one of his four 7FA turbines to TF-25 in 2007, but only recharged a second one with mineral oil and relied on a filtration skid to keep it clean for budgetary reasons. All four had experienced a total of 11 trips in less than a year before that, and the one with PAG has run without a single trip since then. “Varnish will have to be monitored and mitigated as long as we are using mineral oil, which produces varnish. The second round of mineral oil we used has been a lot more successful,” he said.The other early adopter at the 2009 UG meeting said his converted turbines had experienced no varnish deposits in the nearly two years of operation since the conversion. In a recent interview, David Smith, senior engineer at AEP’s Northeastern Sta-tion, confirmed that is still the case after seven years of operation.“Our greatest issue was losing our units unexpectedly,” Smith said. “There were many trips before we knew what was causing the problem, and depending on system demand, we sometimes started back up without replacing a servo.” For an interim fix, plant staff changed out control servos. “I would put a conservative estimate at 50 trips related to varnish,” he said. The plant went through 18 servos before the conversion.The plant also tried other solutions, including filtration skids, but the results were not satisfactory. “We tried electrostatic filters, which removed insoluble varnish, but not the soluble. Right before changeout, we tested a prototype resin filter that seemed to remove soluble particles. Neither did both,” he said. “Had we decided to stay with oil, we’d have had to perform a detergent clean of the system, which at the time was about $50,000 per unit.” Operation and maintenance cost since the conversion has been “just routine changing of filters,” the same mineral oil,” but it didn’t completely satisfy his hope. Based on high soot particulate in the systems, this loca-tion presented a unique case. The EcoSafe Revive “brings varnish back as is required for conventional fluid, he said, and replacement of the PAG fluid is off the radar. “From the sample analysis I’ve seen, there seems to be little to no degradation of the fluid. I thought I saw someone make an esti-mate of 45 years’ longevity, he said.Unit dependability was the princi-pal benefit AEP sought from the fluid change, and it has become even more crucial than it originally was. “Since we made the conversion, the electricity market in our area has changed to a bidding market,” Smith said. “Each day, electricity is bid for the next day and if the bid is accepted, then the gen-erating units are committed to supply power at the day’s price. “If a generating unit should trip during its time of commitment, the lost power has to be replaced at spot market price. Most days this is not catastrophic, but if it’s an exceptionally bad day for electricity prices, it could be. For example, normal electricity prices go on average for around $35 to $45/MWh in our area. On one very cold day last year, the spot market price went to $396/MWh. If we had lost the 460-MW unit we converted on that day, you’re talking more than $182,000/hr to replace. I can’t stress enough how important the dependability is.”Conversion tips Hydrocarbon-based turbine fluid costs $10 to $12/gal; EcoSafe TF-25 costs $25 to $26. Given that price differential, TF-25 has to deliver a lot more value to justify a change. The user experiences described above illustrate how many of the plants have justified the costs of 5, 6. Roof of turbine oil reservoir must be cleaned by hand (left). Nearly completed cleanse with PAG, at right, leaves the reservoir virtually spotlessCOMBINED CYCLE JOURNAL, Fourth Quarter 2014 the change: Some found that avoiding the cost of a high-volume flush and the contractor to perform it made up a large share of the spread, but all cited the complete absence of varnish and the problems it caused in the form of trips and the costs and inconvenience that attend an unplanned system shutdown.NV Energy’s Gary Crisp justified the fluid replacement cost because “we weren’t getting rid of our varnish issue with the treatment skids” and varnish problems were increasingly a high priority for a growing number of the company’s powerplant O&M leaders. Like Gerald Gatti at Pleasants Energy, Crisp took further comfort in the decision to make the conversion because GE now accepts PAG fluids as an alternative lube for its turbines. “Changing something with GE is a pretty significant deal,” he said. After the change-over, he said crews found that, in addition to getting rid of the varnish issue, the viscosity index was a little better and units were experi-encing a 2- to 5-deg-F reduction in bearing metal temperatures.Users may take several different running the Revive system cleanse,see in your reserviors (Fig 7).” The utility also requires that oildeliveries use only ACT tanker trucksto avoid contamination from other fluids.It costs a bit more, but it’s worth it,Crisp said. ACT actually came andwitnessed the deliveries to providetechnical and moral support, he said.Also important is to use a dedicatedflushing contractor (Fig 8). “I don’t thinkyou want the plant to do it. You wantsomebody who has specific experiencein this arena,” Crisp said. -CCJ 7. “Bathtub rings” typically are found in reservoirs holding petroleum-based lube oils (above)8. Flushing best practice: Hire a contractor with the equip- ment and skills required for the job (right) NV Energy drained the system, withspecial attention to all the low po-ints in the system, before refillingwith TF-25. The reservoir was “vir-tually spotless except for the roof,”which the TF-25 had not touched,Crisp said (Figs 5, 6). “It really clean-ed up the bathtub rings that you typicallyapproaches to the change-over. AfterFINALLY ANON-VARNISHINGFLUID TECHNOLOGYTHAT ACTUALLYWORKS.EcoSafe ® Revive ™ is the only fl uid treatment designed to fully solubilize varnish and keep it from ever coming back. Other treatments claim to varnish removal skids. EcoSafe ® Revive ™ shifts the polarity of existing mineral oil-based fl uid throughout your entire system and completely repairs, restores and extends its life. Plus, EcoSafe ® Revive ™ uses the same technology as our non-varnishing PAG-based turbine fl uid EcoSafe ® TF-25, which meets GEK-32568 standards.Learn more and download our free whitepaper “How PAG Turbine Fluid Technology Improves Gas Turbine Protection and Performance” at EcoSafeRevive.comA complete and permanent solution to varnish.?E 3.69after 3 days?E 31.94 ?E 2.8after 45 days 1 2 3 4 5 6