4Q2005 7EA UsersGrp

� COMBINED CYCLEJOURNAL,FourthQuarter�005

7EA UsErs GroUp

Las Vegas has some com-pellingqualitiesasameet-ing location:plentyofhotelrooms, quality restaurants,and direct flights to mostUS locations. However, italsohasmanydistractions.One might expect thesedistractions to adverselyimpactattendanceataseri-ous technical meeting asthey do the availability of

knowledgeable booth personnel atlargetradeshows.Butthatcertainlywas not the case at the 7EA UsersGroup’s annual meeting in earlyNovemberattheRivieraHotel.

Each day Chairman Mike Hoy([email protected]),managerof techni-calsupportforTVA’scombustiontur-binesanddistributedresourcesgroup,called themeeting toorderall seatswere occupied. More than 80 usersattended;59 companies exhibitedatthe vendor fair after the first day’ssessionsconcluded.Vendorpersonnelwereinvitedtoparticipateinthecon-ferenceprogramonthesecondday.

Therewasplentytolearn from 10 formalpresentations cover-ing user experienceand problem-solving,vendor solutions, andtechnologyinnovation.Sandwiched betweenthe formal presenta-tionswere11so-called“hot-topic”discussionsthat invited partici-

pation of all user attendees. Groupmeals, a stage show, and trip toHoover Dam rounded out the pro-gram and allowed a more relaxedenvironment for follow-on discus-sions. The �005 annual meetingwas managed by Lockwood Greene,Charlotte,NC,underthedirectionofDougVandergriff.

Hoy’sfirstmeetingaschairmanofthe7EAUserswasbigsuccessjudgingfromthepaucityofemptyseatsduringthedayand the engaging conversa-tionduringthediscussionperiods.Hereplaced PaulBruningas chairmanearly this year.Recall thatBruning([email protected]), who man-agestheSumasplant inWashingtonstateforthird-partyoperator,CalpineCorp,chairedthegroup’smeetingsforthepreviousthreeyears.Heremainsonthesteeringcommittee.

Other members of the steeringcommitteeare:n Dave Ulozas (dwuloza@nppd.

com), plant manager, NebraskaPublicPowerDistrict.

n Paul Beatty ([email protected]), O&M superinten-dent for Duke Energy’s Lincoln,

Mill Creek, and Buzzard Roostpeakingstations.

n Kris Edmondson ([email protected]), ProgressEnergyFloridaInc.

n GeorgeDavies([email protected]),manager, CT department, Tur-lockIrrigationDistrict.

n Lane Watson ([email protected]),engineer,chemicaloperations,FMGlobal.The 7EA Users serves owner/

operatorsofthemorethan 1000 7B, 7E,and7EAgasturbines(GTs) worldwide—oraboutone-thirdofGEEnergy’s (Atlanta)frame fleet. Since itsinception 10 yearsago, the user grouphasgrowntoover300individuals who rep-resentmorethan100companies. An active

e-mailforumisextremelyusefulforsharingcommonproblems/solutions.

However,thereisnosubstitutefora face-to-facemeeting thatpromotesopendiscussionamongparticipants.Keep in mind as you read throughthissectionthattheinformationpro-videdismerely“thetipoftheiceberg”in terms of content delivered. Theeditorshavefocusedonmeetinghigh-lightstomanagetheoveralllengthofthe7EAconferencereport.Toextractmaximumvalue fromanyuser con-ference,youmustattendinperson.

User experience and problem-solving

Internal misalignment probable source of bearing problemsThetechnicalportionofthemeetingbegan immediately after the morn-ingcoffeebreakonthefirstdaywith

Problem-solvingfocusofmostpresentations,interactive

‘hot-topic’discussions

Hoy

Beatty Edmondson Davies WatsonUlozas

To receive information on the 2006 7EA Usersconference. . . .. . . .as it becomes available, con-tact Wickey Elmo today ([email protected], 704-753-5377). Goose Creek Systems Inc, Indian Trail, NC, has been selected by the 7EA Users Group Steering Committee to administer the 2006 meeting.

� COMBINED CYCLEJOURNAL,FourthQuarter�005

7EA UsErs GroUp

asessiononbearingproblemsofcon-cerntoatleastseveralusers. Dis-cussion focused on a control groupof 7EA GTs that had the followingexperiencewithNo.1bearingsoverthelastfiveyears:n Increasing temperature of bear-

ingmetal.n High bearing-metal tempera-

tures.n BearingsreplacedonthreeGTs.

Internalmisalignmentoftherotorwassuspectastheprimarysourceofthe No. 1 bearing problem, for thefollowingreasons:

1.Bearing-wear patterns andseal-clearance data were indicativeofmisalignment.

�.No. 1 bearings exhibitedincreasing temperature trends onnearly70%oftheunitssurveyed.

3.Specifiedangularitychecksarenotconductedatthefactory.Factoryclearancedata on the control groupindicated that a majority were outofspec.

�.Rail rubs (Fig 1) and honey-comb-seal wear (Fig �) often wereobserved on turbine third-stagebuckets; tip rubs on compressorbladesinstagesfivethrough10(Fig3).

Specificdetailsonthreeindividu-almachineswereofferedbyattend-eestoprovideinsightsnecessaryforproblemevaluationandtheformula-tionofasolution:

Machine 1. Bearing metal tem-perature(BMT)was�75Fonrestartfollowing a unit trip at 99 MWcaused by fuel interruption. Lessthan a week later, temperaturereached300Fonanotherrestart,butsettled at 165F during steady-stateoperation. Operations personnelcarefully tracked BMT for the nextthree months; an outage was takenafter bearing temperature spikedabovethe�65FlimitspecifiedbytheOEM.ThemachinewasopenedandplantpersonnelfoundtheNo.1bear-ing damaged (Fig �). The bearingfailedwithonly1�07firedhoursonthemachine.

A root-cause analysis (RCA) wasperformed by the OEM. The com-pany checked external alignmentdata,analyzedbearingbabbittmate-rial,andconductedametallographicexamination. Regarding alignment(turbinetoaccessorygear),horizon-talreadingswere7milsoutofspec;face readings were 1.5 mils out ofspec in the horizontal plane. Find-ings were dramatically different onthe generator end of the machine,with vertical alignment 50 mils outofspec,horizontal8mils;faceread-ings were closed � mils at the bot-tom.

Chemical analysis of the upperbearing half, which was in goodcondition, indicated a high contentof lead—at least 50% higher than

the specification called for. Leaddecreases the melting point of bab-bitt.Whiletheaverageleadcontentwas in spec for the damaged lowerhalf(somesectionswerehigh,otherslow), coppercontentwashighbyatleast�5%.Copper,whichraisesthemeltingpointofbabbitt,wasparticu-larlyvisiblealongthegrainboundar-iesofsomecracks.

Metallographic examinationshowed good bonding of babbittmaterial. But it also revealed thatbabbittformedtothecontourofthebacking-materials arrangement,indicating that it was under highstress.

ConclusionsoftheRCAwerethatNo.1bearingfailurewasaresultof(1) reduced fatigue strength of thebabbittmaterialbecauseofthehighleadcontent (even though thedam-agedbottomhalfwashighincopper)and (�) possible internal misalign-ment. The OEM recommended thatbearingsbecheckediftheirtempera-turesexceed�30F.

At another 7EA in the control group, operators noted that thetemperature of the No. 1 bearingwastrendingupwardoveraperiodofweeksandthemachinewasremovedfromserviceforinspectionafteronly188�firedhours.Asforthepreviouscase,damagewasfoundonthelowerhalfof thisbearingwhiletheupperhalfremainedingoodcondition.

Data gathered on this machineindicatedthatontheaccessory-gearend, horizontal alignment was 3�mils out of spec, with face readings1miloutinthehorizontalplane;onthegeneratorend,verticalreadingswere55milsoutofspec,horizontal�0mils,andthefaceclosed�milsatthebottom.

Babbittanalysisshowedhighlev-els of copper, lead, and iron in thetophalfofthebearing;copperatthehigh end of the spec limit (possiblyslightlyhigheraccordingtoonetest)andleaddoublethespeclimitinthelowerhalf. High concentrationsoflead were found in babbitt cracksaswellas inareassurroundingthecracks. Lead precipitated along thegrain boundaries. Metallographicinspection revealed cracks in thebabbitt approximately four-thou-sandthsofaninchbelowthesurface;bondingwassatisfactory.

Investigatorsofferedthefollowingconclusionsaftercarefulanalysis:n External misalignment was not

considered a contributor to bear-ing failure,eventhoughthegen-eratorwassittinglowerthantheGT. Reason: Such a conditionwouldhaveincreasedtheloadontheNo.3bearingandreduced the

2. Internal misalignment also is con-ducive to honeycomb seal wear

1. rail wear on turbine third-stage buckets is one indicator of possible internal misalignment

4. Lower bearing half shows consid-erable damage after only 1407 hours of fired operation

3. rubbing of compressor-blade tips against the casing in the area of rows five to 10 is yet another sign of possible internal misalignment of the 7EA machine

6 COMBINED CYCLEJOURNAL,FourthQuarter�005

7EA UsErs GroUp

loadontheNo.1bearing.n Internalmisalignmentwasapos-

siblecauseofthebearingfailure.n Oilconditionwassatisfactoryand

bearingsurfacesexhibitednofor-eign-objectwear.

n Analysis of subsurface cracksrevealedleadcontentthatexceed-ed�5%insomeareas.Leadpar-ticleswereobservedsurroundingthecracks.TheOEMwassaidtohaverecom-

mended that bearing temperaturesbemonitoredcloselywithanalarmifthebabbittreaches��0F.Shutdownwas recommended at �50F; bearingreplacementifthebabbitthits�65F.

Operators responsible for a third 7EA in the control groupobserved a step change in bearingtemperature from 185F to �30Fduring one run and the unit wasremoved from service for inspec-tion. Visual examination after �177firedhoursofoperationrevealednophysical damage to either bear-inghalf,butwearatbottomdeadcenter indicated a low-speedwearcondition.

This unit had only slighthorizontal misalignment on theaccessory-gear end—nothingsignificantenoughtoexplainthetemperature step change. Bab-bitt analysis revealed a metalchemistryconsistentwithASMEB�3 Type 3 babbitt, which isharder and more wear resis-tant than the Type � materialspecified.Thewearpatternwasindicative of low-speed (turninggear/ratchet)operation.

Another important observation:spalling and subsurface crackingwith iron contamination. Possiblecause of this condition is lubricat-ing-oilfilmlossduringturninggear/ratchetoperation,allowingtheshaftto directly contact babbitt material.Keepinmindthatirondoesalterthebabbitt material and cause prema-turespallingandcracking.However,the degree of spalling and crackingpresentforthismachinewasnotsuf-ficient to have caused the dramatictemperature step change observed,investigatorssaid.

Investigators concluded that thetemperature step change recordedwas caused by either (1) internalmisalignment or (�) the thermo-couple short identified during labo-ratory examination. Regarding thesecond possible cause, operatorsquestioned why both thermocoupleswere reading temperatures over��5F. Possibly, the shorted ther-mocouple was damaged in bearingremovalorshipment.

Another conclusion was that

the jerky operation of the ratchetinstalledonthisunitisconducivetolow-speedwear.Ownerhalvedratch-etuseto30minutesevery��hourstheunitisidletominimizeitsimpacton bearing wear. Voith Turbo Inc,York, Pa, which supplies ratchetstold the editors of the COMBINEDCYCLEJournalthatratchetsshouldprovidesmoothshaftrotation.Ifthisis not the case, adjustment and/ormaintenanceisnecessary.

profiling a 100,000-hr outage

Many large frame machines areapproaching100,000hoursofserviceand there is widespread interest inthe experience of owner/operatorsthat have conducted their second“major” inspection/overhaul, whichusuallyisdoneataboutthe96,000-hrmark.

Obviousquestionsaboutmachinereliability arise at this point, withO&Mpersonnelwonderingaboutthelong-termhealthofspecificpartsandofmaterialsingeneral.

Perhaps there’s something com-pelling about the number 100. Thehumanbody,ifitsurvives,isprettywellwornoutafteracenturyofser-vice.Thereliabilityofanautomobileon long trips typically is debatedat 100,000 miles, etc. Is 100,000

hoursofGToperationathresholdofconcern?Shoulditbe?

Certainly,thereare“hard”hours(cycling service) and “easy” hours(baseloadoperation) forGTs justasautoshavetheirhard(city)andeasy(highway) miles. Most well-engi-neered vehicles should get around�00,000 miles today with normalmaintenance. Why shouldn’t GTsrun for �00-, 300-, or �00-thousandhours when operated on gas andmaintainedproperly?

Bruning, the former chairmanofthe7EAUsersGroupisproactivewhen it comes to sharing GT O&Mexperience. “Weall learn fromeachother,”hesays,“andallbenefitfromopen collaboration.” Having com-pleted in June the second major atSumas, the Washington-state planthemanages,Bruningwasprimedfora speaking engagement at the LasVegasmeeting.HewasaccompaniedbyOperationsSupervisorStuKeck.

Sumasisagas-only,135-MW,1 × 1 combined cycle owned byNational Energy Systems Co(NESCO), Kirkland, Wash, andoperated by Calpine Corp, SanJose, Calif. It supplies base-load power under a long-termpurchase agreement to PugetEnergyInc(PSE);processsteamtoSOCCOForestProducts.Theplant operates under an LTSA/CSA (long-term service agree-ment/continuing service agree-ment)withGEEnergy,Atlanta,for“major”parts,technicalassis-tance,andoutagelabor.

Thescopeofworkandsched-ule for a Sumas major are dictatedby the GT’s maintenance cycle. Itrequires rotor removal and inspec-tion every six years, based on unitoperating time and starting fre-quency. Primary goal of the outagewas to complete the work requiredin a manner that supports anoth-er six years of reliable, base-loadoperation. A four-week outage wasplanned,Bruningsaid.

He credited Keck and Mainte-nance Supervisor Rob Bertschingerwith having done most of the plan-ning. They relied on an MS Projectdatabase to communicate schedul-ing, procurement, and manpowerrequirements. This electronic toolsummarizes outage results andincludes a record of pictures takenand provides a basis for planningfuture outages. The combined cyclereturnedtoservicewithin�8days.

The preliminaries. Immedi-atelypriortotheoutage,contractorswere mobilized and briefed on sitesafety requirements. GE assistedwith generator testing at this time.Bruning Keck

5. Gas-turbine rotor is lifted out of the casing for inspection and refur-bishment

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7EA UsErs GroUp

ItisrequiredeveryfiveyearsbytheWestern Electricity CoordinatingCouncil(WECC)—apartoftheNorthAmerican Electric Reliability Coun-cil.Thefirsteveningaftershutdownwas spent preparing componentsforsafedisassemblyandinspection.TheauxiliaryboilerwasputinservicetosupportSOCCOanda temporary diesel generatorstartedtosupplypowerduringtheoutage.

The gas turbine deter-mined the critical path forthe outage. Work includedremoval of the rotor (Fig 5)and replacement of turbinefirst-andsecond-stagenozzles,buckets, and shroud blockswith new parts to improvereliability and efficiency. Thesecond-stage nozzles wereprovidedwiththeOEM’snewinner-diameter brush seals,which also contributed to theefficiency increase. Note that theseals force combustion gases thatpreviouslybypassedthesecondstagetoflowthroughthenozzles,boostingoutput. Turbine components gener-allywerefoundin“asexpected”con-dition,accordingtoBruning,andthemachine was reassembled with noknownproblems.

The compressor section (Fig 6)exhibited problems both expectedand unexpected. The IGV (inletguide vane) blades and 17th-stagerotatingbladeswerechangedassug-gestedinoneoftheOEM’stechnicalinformationletters(TILs).Integrityofthecompletecompressorrotorwasverified by NDE (nondestructiveexamination).Radialcracksfoundinfirst-stagebladeswererepairedandother minor damage was blended.Someofthe16th-stagestatorbladesweredamagedduring reinstallationandwerereplaced.

Bruningsaidhewaspleasedwith

theOEM’sonsiteinspectionofcom-ponentsandrepairwork.

Crackswerefoundintheinletple-num’sbirdscreenanditwasreplacedwith one fabricated of a more suit-able material. Brush seals betweenstationary and rotating components

also were replaced to improve effi-ciency.Bearings,bearingseals,andinstrumentationwereinspectedandrepaired or replaced as necessary.Accessory-gearbox bearings andhydraulic pump were changed out;otheroilpumps,coolers,filterswerecleanedandinspected.

Combustion system componentswere replaced new or repaired (Fig7). Excessive wear of flow-sleevestops,whichcontributedtoproblemswithsomeothercombustionsystemcomponents,werereplacedwithnewparts.

The steam turbine’s (ST) steam path—throughthestopvalve(MSV),controlvalves,andshell—wasdisas-sembled, inspected,andrepairedasnecessary.Thiswasonlythesecondtime since initial startup in 1993that these components had beeninspected.

Bruning said that rotor bladesand stationary diaphragms were in

good condition and required onlyminorweldrepairs.Diaphragmspillstrips were not reconditioned inspiteofminorwear indications,butthe rotor packing was replaced toreducesteamleakage.TheMSVwasinspectedanditsstrokechecked.The

controlvalveshadnomechani-cal problems, but a hydraulicactuator leaked following theoverhaul and was replaced bytheOEMduringaplannedfol-low-upoutageinAugust.

Journalandthrustbearingswere inspected and repairedas needed. The generator wasrealignedtotheturbine.Controlsystemsandsupervisoryinstru-mentation was repaired andupgraded. Lube and hydraulicoilwasreplacedonboththeGTandST.

Both generators werescheduled for maintenancealong with their respective

turbines. The GT generator had itsrotatingfieldreplacedwitharebuiltrotor supplied by GE . This wasplanned because the original partshowed indications of misalignedfieldendwindingsunder its retain-ingrings(Fig8).

A TIL had suggested carefulinspection of the rotating fieldbecause, in some generators, theadhesive used under the retainingringsdidnotsetupproperlyandthewindings moved. Such a conditiongets worse over time, according toBruning,andthatcoil-to-coiland/orcoil-to-frameshortsareapossibilityatsomepoint.Machinesthatcycledfrequentlyweremost likely tohavethisproblem.

The Sumas staff consideredreplacement of the rotating fieldappropriateduringamajorbecauseoftherelativelylongoutage.TheGEexchange program (Figs 9, 10) wasviewed positively by Bruning and

8. rotating field for the GT generator is eased out of the machine

6. Compressor section in almost-new condition is reinstalled

7. Transition pieces are reinstalled as reassembly nears completion


his colleagues for several reasons,including:n Refurbishment included a high-

speed balance and tight qual-ity control characteristic of theOEM’swork.

n Less risk than hiring a third-partycontractor to fixyourrotorbecause you’re really not sure ofwhat’s wrong with it when the

rotorisremovedfromthegenera-torandyoudon’tknowhowlongrepairswilltake.TherotorintheSTgeneratorwas

notremovedforinspectionbecauseithad shown no evidence of problemssincelastremovedin1999.

HRSG and SCR. Little workwas conductedon theheat-recoverysteamgenerator (HRSG)inthesec-

ondmajorbecauseroutinecleaning,inspection,andrepairshadbeencon-ducted during the last annual out-age. The largest task in the HRSGareawasreplacementofthecatalystfor the selective catalytic reduction(SCR) system responsible for NOxcontrol.Alsoaccomplishedwasmodi-fication of the flow pattern for theammonia (catalyst) injectiongrid toenablemoreefficientreagentuse.

Steam side of the HRSG wasfound in good condition; no degra-dation was identified. The gas pathexhibited minor cracks, insulationgapsinsomeareas,andtubefouling.Theseconditionsallwerecorrected.

The SCR catalyst was replaced

9. reconditioned rotor certified by the OEM replaces one removed

10. proper fit-up of reconditioned rotor in the generator is verified

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with one requiring less ammonia,having a lower pressure drop, andlesslikelytocausedownstreamfoul-ing.Repairsweremadetotheammo-niastoragetankaswell.

High-voltage electrical sys-tem. Bruning said that preventivemaintenance of high-voltage (HV)electrical gear was conducted dur-ing the outageand the13.8-kVbusenclosure was replaced because itshowedsignsofoverheating.Clean-ing and inspection of transformers,insulators,breakers,backupbatterysystems, and protective relays wasroutine, he continued; no problemswereidentified.

The electrical scope of work wasexpandedwhenproblemswerefoundwith the interconnecting cable andbus. Specifically, cable connectionshad been overheated and a sectionof bus between the GT generatorand its accessory compartment wasmisaligned. The misalignment wascorrected.

However,only temporaryrepairswere made to the cable insulationand plans prepared for thoroughtesting after the major was com-pleted. Bruning and his staff alsodecided topostpone fixingproblemswithcablesupports inthetraytoalatter date. Finally, a reactor wasordered for future installation to

allow parallel generator operationthrough transformers serving boththeGTandST.Theinterconnectingcablesrequired forthereactorwereinstalledduringtheoutage.

Valves, instruments, and con-trols. Independent outside contrac-torsplayedamajorroleintheinspec-tion and adjusting of valves andI&C components. A specialty valvecontractor inspected internally andadjustedmostmajorvalves,extensiveinstrumentation checks were con-ductedbyanother service firmwithplant staff assisting. Maintenanceandmodificationstotheplantdistrib-uted control system (DCS) and theMark V turbine/generator controlswere performed by GE and a Port-land-basedengineeringfirm.

Valves, pressure regulators, andfilters for the gas supply line werecleaned and inspected as well. Fil-ters were found in good conditionandlinepiggingwasnotconsiderednecessaryforatleastanotheryear.

Makeup and circ water. Themakeup water treatment systemwasoverhauledandreverse-osmosismembranesreplaced.Resultsofthiswork were particularly rewarding,accordingtoBruning.Waterqualityandsystemreliabilitywereimprovedandthesystemisnoweasiertooper-ateandmaintain.

Activitiesinthecirculatingwatersystemfocusedoninspectionoffans,gearboxes,andsystempiping.Avari-able-frequency drive for one of thefanswasreplaced.Cooling-towerfillhadbeenreplacedduringapreviousoutage and the basin cleaned. Themaincondenserandheatexchangersforbothlube-oilandgeneratorcool-ingwereinspectedandcleaned.

Pumps and motors. Criticalpumpsandmotors—includingthosefor the circ-water and lube-oil sys-tems—were cleaned and inspected.MostlargemotorswereremovedtoaGEshopforthiswork.

The rewards and pitfalls of restart. Bruningratedthemajorasuccessintermsofpersonnelsafetyand post-outage operations. Therewere no reportable injuries and nolosttime.Allcomponentsinspectedeitherwerefoundingoodconditionorrepairedtoaconditionthatwouldallow them to operate reliabilityat least until the next scheduledmaintenance outage. Cleaning of,and repairs on, the GT producedimmediate results: Plant outputincreased by more than �% follow-ingrestart.

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1� COMBINED CYCLEJOURNAL,FourthQuarter�005

exactly the way you want it to. AtSumas, the plant was ready forrestart �6 days after the outagestarted, but a few of the seeminglyinevitable glitches required correc-tionanddelayedsynchronizationbyaday.Forexample:n A faulty solenoid on a compres-

sorbleedvalvestuckintheclosedposition, causing the compressorto surge before it reached fullspeed. When full speed finallywas achieved, air leakage fromthe wrapper joints and bearingdrainflangewasexcessive.

n ST vibration levels were higherthannormalonrestart.Thiswasattributedtothetightclearancesassociated with new packing.Vibrationpersistedonrestartsforthenextmonth, butdisappearedafterthat.

n SToutputwaslessthanexpected.Theshortfallwastracedtovalveproblemsattributedtoage,duty,and contractor errors. High- andlow-pressuresteamdump,steam-seal dump, and steam-letdownvalves all were leaking. A planwasdevelopedtocorrectproblemsduring planned “clean-up” out-agesinJulyandAugust.Bruningand his staff also agreed to hireanother specialty valve contrac-tortomeasureleakageremaining

after field fixeswere complete toguide work necessary in futureoutages and to minimize plantthermal-efficiencylosses.

n An alignment problem with thebreakerfortheGTgeneratorwasidentified on restart and correct-ed.

n NOxdistributionacrossthestackrevealed that adjustments madeto the SCR’s ammonia injectiongrid required some correction.Thishassincebeendoneandthesystemisworkingasplanned.

n One circ-pump motor failed onrestart. Itwasremovedandsentoutforrewind.

n The starting motor for the GTdeveloped signs of bearing wear.This was corrected during theAugustfollow-onoutage.End notes. Valve repairs made

afterthemajoroutageincreasedSToutputasmallamountoverthepre-outage capability. Remaining areasof concern are the reliability of theHV cable between the generatorsandtransformers,installationofthereactor, and losses through turbinecontrol valves. Valve recondition-ingwillbeafocusoftheplantstaff,Bruning said in wrapping up, toassuremaximumelectricalandther-maloutputat thehighestefficiencypossible.

Find any chunks of green plastic material in your turbine oil?

Hard to believe that some owner/operators do not participate in oneor more of the user groups servingtheGT-basedgenerationsector.Thenetworking is invaluable, akin tofree consulting from experts. Con-sider the following question postedto the7EAUsersGrouponlinebul-letin board last May by one plantmanager:

While performing a routine main lube-oil filter change, we were unable to completely pump down the filter housing. The unit was not operating at the time and the transfer valve was cycled one time to see if the valve would seat off. Leakage into the housing was too great to open the filter. After the transfer valve was cycled, chunks of plastic-type material started coming through the drain on the inlet side of the filter housing. The material apparently is from the transfer-valve sealing shoe. It appears that the material has chemically degraded to the point that its mechanical properties have been compromised.

I am very concerned that the shoes also have degraded on the down-

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stream side of the filter. The unit was installed in 2001 and all oil tests have been good. Has anyone else experienced this problem?

Two replies were posted to thebulletinboardlessthanthreehours.Wouldanyoneotherthanaplantcol-leaguehaverespondedsoquickly?

Reply 1: We have experienced the same problem on one of our units. We noticed a high differential across our filters and were going to do a filter change-out. When we got started, we noticed that we were get-ting flow through both of our filters. We were able to drain about 100 gallons of oil, which was enough to open one of the filter hous-ings. We are due for a combustor can inspection this fall and are going to pull the transfer valve as well. We think that it is sealing-shoe mate-rial. This unit also was installed in 2001.

Reply 2: Our company has four 7EAs that were installed between 2002 and 2004. The transfer valves for the lube-oil coolers and filters have the same GE part number that you have. Our original problem was the inability to isolate a lube-oil cooler for inspection. The original

valve seals were urethane and they have been changed to a Viton mate-rial and are performing well: No deterioration noted upon inspection of the shoe that had been in ser-vice the longest. The urethane seals swelled, cracked, and eventually large chunks came off the valve seat. On one unit, we had to contract with

a borescope retrieval com-pany to locate and remove the chunks from the piping downstream of the filter dis-charge transfer valve.

Thedialogcontinuedfromwhen the question was firstasked publicly in May �005until an outreach session,moderatedbyPatMyers,theplant manager at ReliantEnergy’s Ceredo Generating

Station, was conducted at the LasVegas meeting. By the time Myersconvened the session, much hadbeen accomplished by users work-ing collaboratively, including thefollowing:n The transfer-valve manufacturer

andtheGTOEMwerecontactedin May; both said they wereunawareoftheproblem.

n Thetwovendorsweresentfailedshoesandsamplesof lubeoil foranalysisandRCA.Aftertheusernetworkidentified

severalmorefailures,GEwasaskedto issue a TIL. No TIL had beenreleasedbythetimethe7EAUsersGroup met in Las Vegas; however,the OEM recommended that theshoes be replaced with ones madeofVitonA.Note that the issue isagenericone,alsoimpactingmachinesmade by Siemens Power Genera-tion Inc, Orlando, as well as otherOEMs.

Information gathered by 7EAusers revealed that every plantreporting failures had lube-oiltransfer valves with shoes madeof polyurethane (Figs 11, 1�); alsothathundredsofunitswereatrisk.Initially, the problem was thoughtto be limited to GTs installed in�000 or later, but problems havebeenreportedon1999machinesaswell. The response from the plantcommunity on this issue has beensignificant.

Symptoms. Representatives ofplantsimpactedbytheissuereportedthatthefirstindicationofaproblemusually was that the filter housingcouldnotbecompletelydraineddur-ing a routine filter-element change-out. Another indicator: A visible oilstream impinging on the bulls-eyesight glasses installed in both theonline and offline filter housing. Inmost cases, the transfer valve was

Myers

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7EA UsErs GroUp

cycled to see if it would seat. Aftercycling,chunksofgreenplastic-typematerialflowedthroughthedrainonthefilterhousings.

Once the 7EA users began col-laborating, other interesting factscameintolight:n Someusershad“quietly”replaced

theirshoeswithanothermaterialthinking that the original mate-rial may have been overheatedduringoilflushingofthesystem.

n Othershadnoticedthesymptomsofdeterioration,butwerenotsureofthecause.

n The OEM had replaced transfer-valve shoes on some machinesunder warranty as early as Sep-tember�00�.There was much discussion of

polyurethaneshoedeteriorationdur-ing theannualmeeting.Plantman-agerswereveryconcernedaboutthepossibility ofdamage resulting fromthe restriction or interruption of oilflowtobearings,servos,valveactua-tors,etc,causedbypiecesofentrainedshoematerial(Figs13,1�).

Root-cause theories abound,

butunanimityhadnotbeenachievedpriortotheLasVegassession.Herearethethoughtsofsomeexperts:n Glycol contamination of the oil

caused a chemical reaction withthepolyurethane.

n Oil temperature exceeded thematerial’s thermal rating (�00Ffor polyurethane, 350F for VitonA, the recommended replace-ment)

n Lube oil was chemically incom-patiblewithpolyurethane.

n Glue/epoxy used in manufactur-ing filter elements reacted withtheoil.

n Transfervalvewasinstalledpriortochemicalcleaningofthesystematthefactory.

n Chemicals from pipe fabricationweren’t completely flushed fromthesystem.Formal research suggested that

the valve shoes most likely failedbecause of “stress overload.” Mate-

rialanalysisrevealedboththermaldegradation (discoloration) andchemical incompatibility (volumeswell).Thesemechanismsactinginconcert would accelerate failure bybreaking down the polymer chainsthatgivethematerialitsstrength.

RCA aside, the bottom line isthatthe7EAuserscollectivelyhaveidentifiedwhatappearstobeaverypractical and immediate solution totheshoedeteriorationproblem.

First recommendation is that ifyou findshoesealmaterial inyourtransfer valves, do not switch the valve position untilyou inspect thetransfer valve. Next, completelyflush the lube/hydraulic oil systemas you would a new installation—this to ensure that hideout loca-tionsaresweptcleanandalldebrisis removed. Finally, replace thedegraded shoes with ones of VitonA.Infact,itprobablyisappropriate

to switch to Viton A as soonas convenient. Replacementshoes only cost about $300each.

Shoe removal and replace-mentisarelativelyeasytask.Herearethesimplesteps:n Remove plugs at the lubeoilpumps.n Pump oil from filter com-partments into the mainsump.n Remove the valve from its

body.n Replace“O”rings.n Installnewshoes.n Reinstallvalve.

Locking in rocking vanes, blades

Itwasn’tlongagothatRodgerAnder-sonandhiscolleaguesatDRS-PowerTechnology Inc (PTI), Schenectady,NY,revealedto7EAowner/operators(andlaterto7FAusers)acost-effec-tive method for solving the “looseblade” problem adversely impactingtheoperationofmanycompressorsinthe7EAfleet.Anderson([email protected], 978-353-5318) specifi-callyaddressedtheuseofPTI’s“fix”(patentpending)tofifth-stagestatorvanes at the �00� annual meeting.At that time the solution had beenapplied to a dozen machines; nowthe total exceeds �0. Plus, nearlyhalfadozen7FAshaveapplied thetechnique—successfully, accordingtoAnderson.

Of particular interest at the�005meetingwasashortreportbyHeatherRegnier,PE,aGTengineerin TransAlta’s technical servicesgroup,Calgary,Alta,onthesuccess-

Shoe

Shoe Port

Port

Material recovered from screen serving No. 1 bearing

11. shoe locations are identified in simplified sketch of a transfer valve

12. Deterioration of polyurethane shoe material illustrates that this valve has lost its ability to prevent fluid flow between online and offline filter com-partments

13. pieces of polyurethane were collected in the screen protecting the No. 1 bearing on one machine

14. Where has all the seat material gone? Answer is obvious: every-where. At left are particles found in the main tank, in the center is debris from the generator tank, at right are large chunks removed from the lube-oil filter


ful implementation of the PTI solu-tionbyqualifiedpersonnelemployedbytheenergycompany.

But before summariz-ing Regnier’s presentation,here’s somebackground forthoseunfamiliarwithPTI’spinning technique. Ander-son offers this explanationforwhyvanesmayrockovertime:n During operation, indi-

vidual vanes are loadedby pressure forces andreactagainstthecase.

n Loading is dynamic, aspressurefluctuatesaboutthemean.

n When the machine isshut down, the load isremoved.

n Loading/unloading/fluc-tuationresultinrelativemotion.

n The sliding and ham-mering that result frommotion wear the vanebaseandcasinggroove.Wear and blade motion allow

shims installed between adjacentvanes to work their way into theflowpath—eveninthelowerhalfofthecompressor.Performancesuffersas the shimsprotrude into the flowpath. Shims have been observed to

migrate1/8in.ormoreintotheflowstream, which can initiate a flowdisturbance that produces a strong

once-per-revolution stimu-lus at the tips of down-streamrotorblades.

In the extreme, whensufficient wear occurs atshim tabs—often referredto as “ears”—because ofblade movement and thesharpcornersinthecasinggroove, shims can releaseintotheflowstream.Resultis downstream foreign-objectdamage(FOD).

ThePTIsolutionrecentlyimplemented by TransAltainvolved machining holespartway into the base ofeach vane (Fig 15). HolesweredrilledonthetwosidesofthebaseperpendiculartothedirectionofairflowsuchthatPTI’sengineeredspringdowelpincouldbe insertedinto adjacent blades pre-

venting their movement. Of course,anyshimsweredrilledsotheytooareretainedbythedowel.

Regnier reported that inSeptem-ber and October of �005 TransAltacompletedmajors on two7EAunits(one in Alberta, the other in Sas-katchewan) that had been commis-

sionedin1999andhadaccumulatedabout�8,000hoursofoperation.Bothoperate base-load on natural gaswithout steam or water injection.Turbineinlettemperatureatthetwoplantsis�035F.

Inspection revealed evidence ofthe classicStage5vane rock (dam-age to both the slot and vane plat-forms) and shim migration. Trans-Alta considered the PTI fix as wellas the OEM’s patch-ring repair toeliminaterocking—bothviablesolu-tions. Pinning was selected for tworeasons: It could be accomplishedwithinthetimeallocatedfortheout-ageanditwasaboutone-quarterthecostofthepatch-ringrepair.Trans-Altaimplementedthefixitselfwithlong-distance direction by PTI—thefirstendusertoso.

The TransAlta inspection teamalso founddamageon thebackendofonecompressor.

Specifically, there was a crackcompletely though the shroud (Fig16) on the first row of exit guidevanes(EGV)—therowclosesttotherotor.Thecompleterowofvaneswasreplaced. Inaddition, a vane in thesecond row of EGVs was found dis-placed (Figs 17, 18). Investigatorsconcluded that ithadbeen “rocked”out of position. The vane segmentwasreplaced.

Anderson

Regnier


To add rigidity to vanes at theback end of the compressor—row17, and the two rows of exit guidevanes—TransAlta selected theOEM’s “set-screw mod.” It involves

locking-in vanes by inserting a setscrewthroughthebaseringandupinto the center of the each vane’sbase.Anotherpartof theprocedureistodoublestakeandpeenthevanes

ineachslot(R17,EGV1,andEGV�).Olaf Barth, an engineer in

Dominion Resources Services Inc’scombustion-turbineoperationservic-esunit,GlenAllen,Va, tookaturn

at the podium toaddress bucketrock. He spokeof severe bucketrock on at leastoneofDominion’sG T s e q u i p p e dwith a turninggear.Ithadoper-ated for about75,000hoursataslowroll(about30rpm). Wear was

sosignificantthatsealpinswerelib-erated.Thequestionheposedtothegroup:Whatdoyoufix,andhow?

Barth said he knew of instanceswhere owner/operators replacedwheels inaneffort to eliminate theproblem.Alsomentionedwasswitch-ingfromaconventionalturninggearthat typically is operated continu-ouslytoaratchet.Someusershavedonethismodificationtogettocur-rentdesign.

He suggested as an interim fixthemetalsprayingofbucketrootstolockthemintothewheel.Buteven-tually, Barth continued, the wheelmustbefixed.Build-uponthewheelof a very hard material is another

15. Addition of pin retains both shim and vane. Shim’s retaining ears are maintained in mint condition because vane movement is stopped

16. Crack in EGV1 shroud extends through weld

17, 18. Displaced blade in EGV2 was thought to have been “rocked” loose

Barth

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7EA UsErs GroUp

possiblealternativetoreplacement.Barthsaidheandcolleagueswere

still trying to determine the rootcauseofthespecificcondition.Indus-tryexperienceisthatthesofter(thanthe buckets) wheels usually take80%-90% of the wear; buckets theremainder.However,datafromthisrecentcaseshowtheopposite!

Vendor solutionsImprovements in fuel-system valves

SchuylerMcElrathofJansen’sAir-craft Systems Controls Inc (JASC),Tempe, Ariz, was behind the podi-um at the 7EA meeting updatingthe industry on user experiencewith the company’s water-cooledliquid-fuel check valve, which hasgotten considerable attention oflate. Cited advantage of this prod-uct is itsability tooperate reliablyin dual-fuel service without thecoking that can cause spurious GTtrips and other operational upsets.Agoodbackgrounderonthevalveisavailableinthe3Q/�005issueoftheCOMBINEDCYCLEJournal(p�7)as part of the magazine’s coverageoftheCTOTF(CombustionTurbineOperations Task Force) meeting(available at www.psimedia.info/ccjarchives.htm).

McElrath discussed the past,present, and future offuel control, includinga historical perspectiveon why liquid-fuel checkvalves have failed andhow past deficienciescanbeovercomethroughinnovative design (Figs19-�1). He then updatedthe experience with thewater-cooled valve (Fig��)attheValeroEnergybetasitedescribedinthearticle cited above. By the end ofOctober, theDelaware facilityhadaccumulatedmorethan8000actualoperating hours on both gas andliquidfuel—6500gasand1500oil.This represents more than 96,000totalhourswithoutafailureofanykind.

Based on the Valero experience,McElrath said designers expect thecheck valve to have a reliable life-timeof,perhaps,aslongas�0years.He reported that there has been a�500%improvementinValero’sabil-ity to transferbetweengasand liq-uidfuelsandthatallofthefacility’sturbine starts on liquid fuel havebeen successful since installation of

thenewvalve.McElrath said this performance

shows that by eliminating coking,the check valves seal properly andpreventevacuationoftheliquidfuellines.TheValeroretrofitprovesthepoint conclusively, he suggested:After running on gas for as long as��consecutivedays,Valerostillwasabletotransfertoandstartonliquidfuelwithoutaproblem.

Next, he discussed the future ofactivelycooledfuelcontrols,some-thing that had not been articulatedin a public forum before the LasVegasmeeting.McElrathintroducedthe company’s so-called activelycooledcombiningvalvewhichreplac-esinasinglehousingpurge-air,liq-uid-fuel,andfueldistributionvalves(Figs�3,��).

By eliminating coking and con-tamination-relatedfailures(aninte-gral fuel strainer removes particu-

lates that could cause sealfailures), he claimed thatthenewvalvewouldrequireserviceonlyduringregularlyscheduled outages. Specifi-cally, valve maintenancewould be conducted whencombustor-can end covers

were replaced—regardless of theusagefrequencybetweenintervals.

In wrapping-up, McElrath saidthatbothvalvesareeasilyinstalled

Conventional liquidfuel check valve

23, 24. Combining valve easily bolts on to the engine

21. Coking is the primary cause of failures that occur when attempting to transfer from gas to oil

22. production water-cooled liq-uid-fuel check valve exhibits robust design

19. standard installation for a liq-uid-fuel check valve shows close proximity of valve to high-temperature surfaces

20. Example of coking in a ball-and-spring check valve that can cause operational problems

McElrath


7EA UsErs GroUp

oEM upgrades and mods for the 7E product line

GE Energy’s J R (Bob) Johnston, Atlanta, is a walking encyclope-dia on performance and reliability improvements for GE frames. The 25+ year GT veteran recently told the editors of the COMBINED CYCLE Journal that the manufacturer is continually updating/upgrading/uprating its designs and that tech-nology advancements generally are available for application on older machines in various model series.

By way of example, he concen-trated on the 7EA. The 7Es, John-ston said, first shipped in 1977, but design improvements have been ongoing and the engine has a well-defined market niche. You may hear most discussion of GE frames revolving around the 7F model series, but the OEM expected to ship more 7Es in 2005 than 7Fs.

So what does all this mean to owner/operators? Simply put, there are many avenues to capacity and efficiency improvements, if the mar-ket you serve can support the invest-ment. Depending on the vintage of your MS7001E, an uprate to a firing temperature of 2055F could increase output anywhere from about 5% to nearly 19% and reduce heat rate by up to 4.6% (figure).

One of the first things you have to consider with regard to an uprate is the capability of the generator and electrical auxiliaries. GE is respected for sizing its generators conserva-tively so uprates generally are pos-sible, but an engineering review is required. Analysis of the GT compo-nents and accessories also is neces-sary to determine their compatibility with the enhancement being consid-ered. And don’t forget to review your duty cycle—annual service hours and starts. What upgrades make most sense on a cost/benefit basis for your business case?

The optimum time to uprate or upgrade units generally is during a major overhaul when new parts or significant refurbishment of exist-ing parts is already necessary. Most users get started by selecting one or two upgrades that offer fastest pay-back; then add other upgrade mod-ules later, when appropriate.

The manager of one 7E-based cogeneration plant in California recently told the editors of the COMBINED CYCLE Journal that he believed his facility could remain competitive, even in such a difficult electricity market, if equipment was

continually upgraded to be at the leading edge of technology. This plant had already benefited from being the first to complete a 2055F upgrade. Previously it had converted to DLN (dry low-NOx) combustors, switched to state-of-the-art gas con-trol valves, and completed several other enhancements.

Early this year the facility became the first to retrofit third-stage tur-bine buckets and nozzles, an aero-dynamic enhancement described by Johnston as being particularly beneficial. The upgrade was made possible by internal collaboration between frame and aero designers, who promised a 1% increase in out-put and a 1% decrease in heat rate at ISO conditions. The plant con-firmed that these expectations had been achieved.

Compressor upgrades. John-ston also talked about the benefits of compressor upgrades. Approxi-mately 20% of the inlet air is lost to the thermal cycle because of losses associated with cooling hot-gas-path parts and with excessive clearances between rotating and stationary components. Thus there are two main avenues available to get better performance from the compressor:n Increase air flow.n Reduce air-flow losses.

In the late 1990s, GE invested heavily in reducing losses, and sig-nificant savings were achieved. For example, use of brush seals in place of labyrinth seals can boost output by up to 1% and decrease heat rate by 0.5%.

More recently, the 7EA compres-sor has been redesigned for retrofit to existing units—the first major

redesign of this component ever. The greater air flow associated with this enhancement allows an increase in output of up to 11% and an efficien-cy increase of up to 2.5% compared to the early 1970s base design. The OEM announced that this upgrade is available for quotation now, with deliveries beginning in spring 2007.

Johnston said that the compa-ny’s track record in performance upgrades has been excellent. One metric he cites to support this claim: GE has done more than 500 firing-temperature uprates and met project targets more than 99% of the time.

IGV (inlet guide vane) perfor-mance improvements have also been very popular, with 700 to 800 units opting for this upgrade. Extending the interval between combustor inspections is another way to reduce O&M costs. The company’s Extendor™ system for the combustion system (wear-resistant coatings and materials, enhanced clearances, and mechani-cal design improvements) was implemented with this in mind.

How to get started. Generally speaking, the further away you are, the better things look. To get closer to what performance improvement options might benefit your facility, access on the company’s website GER-3571H, “Performance and Reli-ability Improvements for Heavy-Duty Gas Turbines,” www.gepower.com/prod_serv/products/tech_docs /en/ downloads/ger3571h.pdf. Although the publication is several years old, it is good for preliminary work. Next step would be to access more detailed and more current information through your regular GE channels.

Extendor™ combustion system

Improved cooling in first-stage nozzle

Improved sealsfor first-stage shrouds

Honeycomb seal

Better materials, second-stage nozzle Better

materials, third-stage nozzle

Better materials, first-stage bucket

Third-stage buckets with improved scalloped shrouds

Second-stage buckets with improved cooling

Nimonic transition pieces (TBC coated)

Brush seals (optional)

Thermal-barrier coating for combustion liners


7EA UsErs GroUp

on dual- fuel frame machines,regardlessofmakeormodel,wherewater is available at between �0and 80 psig (typical for GTs thatusecoolingwatersystemsfortheiratomizing air and lube-oil heatexchangers). Depending on themachine’s rated output, anywherefrom5to18gpmofwaterwouldberequired.

Parker Hannifin Corp’s solu-tion to problems experienced withconventional OEM-supplied fuel-system valves was different fromJASC’s. Mike Doutt ([email protected]), senior product engineerin the company’s InstrumentationProducts Div, Huntsville, Ala, fol-lowed McElrath at the podium andpresentedanewcheck-valvedesignfor liquid fuel,purgeair,andwaterinjection.

Performance goals for Parker’snewvalveinliquid-fuelservice(Fig�5) include the following: reliablebubble-tight shutoff, resistance tofailure from coking effects, easilyreplaceablesealparts,easyremovalofcokedeposits.

The design of choice relies on afloating ball valve and ahigh-performance Teflonseatwithasphericalseal-ingsurface.Essentially,itcombinesaballvalveanda check valve, with theself-centeringfloatingballserving as the seal ele-ment.AccordingtoDoutt,the flexible seat adjuststhesealareatobackpres-sureloading,therebyopti-mizing sealing forces. Ball cagemisalignment, he said, does notadverselyimpacttheseal.

Douttadded that theapplicationtemperatures and pressures in GTfuel-systemserviceareverycompat-iblewithParker’snewdesign:300Ftypical maximum temperature; 300psig (max)/150 psig (typical) purge-air pressure; 11�5 psig (max)/500psig(typical)liquid-fuelpressure.

Getting into more detail, Douttsaid that the advanced carbon-graphite (for liquid fuel service)and “hard” carbon-reinforced Tefloncopolymerseatmaterialswereflexi-bleandforgiving(theseatdeformstoperfectly match the ball’s sphericalsurface),chemicallyinert,capableofsustained500Foperation,andresis-tanttocokebuildup.

Doutt demonstrated the ease ofvalve maintenance and repair. A“five-minutejob,”hesaid,onerequir-ingnospecialtools;easyclean-outofanycokedepositsthatmightform.

Demonstration valves have beenin liquid-fuel, purge-air, and water-

injection service for as long as twoyears, mostly on peakers—includ-ing GE 9E, 7FA, 7EA, and 7B (Fig�6) and some Siemens and Pratt &Whitney models. Doutt added thatproductionvalvesnowareavailableforawiderangeofmachines.

QC check for inlet air filters

Inletairfiltersareupfordis-cussion at almost every GTuser-group meeting becausecompressor health and per-formance depend on theireffectiveness. At the 7EAannualmeeting,RonTroxell([email protected]), engineer-ing manager, Greenlees Fil-terLLC,ForestPark,Ill,ledthediscussion.

Troxellreviewedfiltrationbasics, manufacturing processes,andtheneedforcarefulevaluationof competing products before pur-chasingreplacementfilters.Mostofthismaterialhadbeencoveredpre-viously in theCOMBINEDCYCLEJournal(referto“SelectingGTinletairsystemsfornew,retrofitapplica-tions,”Spring�00�;“Life-cyclecostanalysis key toidentifying opti-mumreplacementfilters,” Summer�00�; “Selectingthe proper inletair filter foryourGT,”�Q/�005).Toaccess these arti-cles, please visitthe CCJ onlinearchivesatwww.psimedia.info/ccjarchives.htm.

But you learn something newalmosteverytimeyourevisitasub-ject—no matter how familiar youare with it. A practical takeawayfrom Troxell’s presentation was aseries of sketches that can assist

25. reliable, bubble-tight shutoff and resistance to failure from coking effects are among the attributes of Parker’s new valve for GT fuel sys-tems

26. one of a series of valves engi-neered specifically for GE machines

Doutt

Troxell

Straight pleats

Curled pleats

Uneven pleats

Leaning pleats

Secondary pleats

27. Cut through a sample filter before making a purchasing decision to be sure the supplier is capable of making the straight pleats needed to maximize filtration effectiveness

�0 COMBINED CYCLEJOURNAL,FourthQuarter�005

7EA UsErs GroUp

in evaluating the quality of filtersbefore making your next purchase(Fig�7).

Troxellfocusedpartofhispresen-tationontheimpactpleatshapehason performance. He said that whilegood filter media obviously is veryimportant,poorpleatingwillnegateits effectiveness. Recall that mostfiltermanufacturersbuymediafroma paper mill—usuallyoff the shelf. The largesuppliers, by contrast,often have media madetotheirspecifications.

Mediaissentthrougha pleater that makespleats of nominal � in.depth. Pleats must bestraight,asshowninthetopsketch in the figure,orperformancewill suf-fer. With curled pleats and leaningpleats,onlyabout30%ofthemediaisusedeffectively;secondarypleatsalsorestrictflowthroughthefilter.Whenpleatsareuneven,dustdoesn’t evengetintothenarrowpleats.

Troxellsuggestedthatbeforemak-ingapurchasingdecision,youshouldcutapartoneormoresample filtersfromeachprospectivevendortovisu-allyinspectpleatconfiguration.

Third-party parts: Better than the originals?

Bucketsandvanes,likeairfiltersandotherparts,wearovertimeandmustbe refurbishedor replaced.The for-merispreferredtotheextentpossiblebecauseofthecostadvantageitusu-ally offers over replacement. Wherereplacement parts are the economicchoice, owner/operators are findingthe marketplace for replacementparts extremely competitive today.Third-partysuppliersoftenarecapa-bleofchallengingtheOEM’srelation-ship with its customers by offeringupgradeddesignsatlowercost.

KevinJPallos,managerofopera-tions for Pratt & Whitney PowerSystems Inc’s industrial GT partsand services group, discussed hiscompany’s capabilities as an alter-nativetotheOEMand,byexample,describeditsreplacementfirst-stagebucketforthe7EA.

PallosbeganbyreviewingP&W’sprocesses for design, measurement,parts validation, etc. He also dis-cussedtheproprietarymaterialsandcoatings it can offer to improve thedurability of hot-gas-path compo-nentswhilemaintainingengineper-formance on-spec. Field experienceofitsnewbucketdesignwascoveredalongwithguarantees.

A look aheadTheplantmanagerswhoattenduser-group meetings are focused on thepractical aspects of operating theirfacilities efficiently, reliably, andsafely—afterall,that’swhatthey’repaidtodo.Butthey’realsoreceptiveto receiving, on occasion, an objec-

tiveviewpointoftheindustry’sdirection and to learning ofnewdevelopments.Ithelpsputthingsinperspective.

Consider DLN (dry, lowNOx) combustion. It repre-sentedasignificanttechnologi-calleapforward,enablingGTsto operate at the lowest NOxemissions levels of any firedgenerating resource. Today’smost advanced DLN systems

produce less than 5 ppm, withoutpost-combustion cleanup. How-ever, depending on the location ofyour plant, that might not be goodenough. SCRs are one way to driveNOx emissions to near zero. But isthere a better way to reduce evenfurther the formationofNOx in thecombustionchamber?

To look ahead, the 7EA steeringcommitteeinvitedapresentationbyMartin Kalin ([email protected]),CEO,ALMTurbineInc,Wash-ington, DC, on the trapped vortexcombustor (TVC) that his companyexpects to soon commercialize. TheoriginalTVCconceptwasdevelopedbytheairforce.

TVCpromisestobeastepaheadofDLN.Kalinviewsitasalesscom-plex solution to high-efficiency/low-emissions combustion thanDLN. Based on test-standdata collected while burn-ingnaturalgas,heexpects7EA (1) NOx levels of lessthan�ppmfromno load tofull load and (�) CO emis-sions of from 0 to 5 ppmfrom half load to full loadand from 7.5 to 1� ppmfrom10%to50%ofthefull-load rating (Fig �8). Thenewcombustorismulti-fuelcapable(liquidfuel,syngas,etc).

Kalin next pointed to the highpressure-drop losses that charac-terize the DLN, but not the TVC.Benefit is an increase in turbineefficiency that promises a 1.5% to�.5% reduction in fuel consump-tion.Fora7EAoperating8000hr/yron gas at $9/million Btu, the TVCwouldreducetheannualfuelcostbyabout$1.5million,Kalincontinued.TheTVC alsohas fewerparts thanDLN (Fig �9), a feature conducivetohigherreliabilityandlowerO&M

costs.NotethemuchsmallersizeoftheTVCcomparedtoaconventionalcombustor.ATVCretrofitfora7EAwould be sized appropriately toaccommodatetheengine.

Key to the TVC’s performance,noted Kalin, is a combustor design

that enables low-turbu-lence mixing, flame stabil-ity, and complete combus-tionat��00F in�millisec.Recall that conventionalGT combustors typicallyoperate above 3000F andthey require about threetimestheresidencetimetoachievecompletefuelburn-ing. Temperature of thegasesexitingthecombustor

neverexceed��80FforaTVCretro-fitofa7EA,accordingtoKalin.

Tounderstandjusthowdifferentthe TVC is from a DLN combustor,consider these design characteris-tics: Ithasnopilotnozzles, second-ary fuel nozzles, dilution zone, orfilmorback-sidecooling.

As�005drewtoaclose,ALMwasintheprocessoftestingacombustorthatcouldberetrofittedintoa7EA.Kalinsaidthecompanywasclosetoidentifyingabeta test siteandwasinterested in identifying other testpartners.ccj

Pallos

Kalin

28. Ultra-low Nox and Co emis-sions characteristic of the trapped vortex combustor will eliminate the need for post-combustion pollutant removal

2250 2600 2960 3320

25

20

15

10

5

0

100

80

60

40

20

Car

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mon

oxid

e, p

pm

v

Oxi

des

of n

itrog

en, p

pm

Combustor exit temperature, F

CO

NOx

Temperature range for low emissions with the ALM combustor

ALM liner and transition piece

OEM’s combustor liner

Transition piece

Liner

Igniter

29. Conventional can and TVC com-bustors are compared for a 25-MW aero engine. The TVC has no pilot nozzles, secondary-fuel nozzles, dilu-tion zone, or film cooling

Documents

4Q2005 7EA UsersGrp