Large Gas Turbine

8/11/2019 Large Gas Turbine

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ARGE GAS TURBINE

Gas Turbine Functional Description

1. INTRODUCTION

1.1. General

The gas turbine designed for operation as a simple-cycle unit or in a combined steam and gas turbine cycle(STAG). The gas turbine assembly contains six majorsections or groups:. Air inlet!. "ompressor

#. "ombustion System$. Turbine%. &xhaust'. Support systemsThis section briey describes ho the gas turbineoperates and the interrelationship of the majorcomponents.

1.2. Gas Path Description

The gas path is the path by hich gases o throughthe gas turbine from the air inlet through thecompressor* combustion section and turbine* to theturbine exhaust.+hen the turbine starting system is actuated and theclutch is engaged* ambient air is dran through the airinlet plenum assembly* ,ltered and compressed in themulti-stage* axial-o compressor. or pulsation

protection during startup* compressor bleed ales areopen and the ariable inlet guide anes are in the

Chapter

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closed position. +hen the high-speed relay actuates*the bleed ales begin operation automatically and the

ariable inlet guide ane actuator energi/es to positionthe inlet guide anes for normal turbine operation.

"ompressed air from the compressor os into theannular space surrounding the combustion chambers*from hich it os into the spaces beteen the outercombustion casings and the combustion liners* andenters the combustion /one through metering holes ineach of the combustion liners.uel from an o0-base source is proided to o lines*each terminating at the primary and secondary fuelno//les in the end coer of the separate combustion

chambers.

Options:

1 2n li3uid fueled machines* the fuel is controlled priorto being distributed to the no//les to proide an e3ualo into each li3uid fuel distributor ale mounted oneach end coer and each li3uid fuel line on eachsecondary no//le assembly.

1 2n gas fueled machines* the fuel no//les are themetering ori,ces hich proide the proper o intothe combustion /ones in the chambers.The no//les introduce the fuel into the combustion/one ithin each chamber here it mixes ith thecombustion air and is ignited by one or more of thespar4 plugs. At the instant hen fuel is ignited in onecombustion chamber ame is propagated* throughconnecting cross,re tubes* to all other combustionchambers here it is detected by four primary amedetectors* each mounted on a ange proided on thecombustion casings.The hot gases from the combustion chambers o intoseparate transition pieces attached to the aft end of thecombustion chamber liners and o from there to thethree-stage turbine section. &ach stage consists of aro of ,xed no//les and a ro of turbine buc4ets. 5neach no//le ro* the 4inetic energy of the jet isincreased* ith an associated pressure drop* hich isabsorbed as useful or4 by the turbine rotor buc4ets*


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resulting in shaft rotation used to turn the generatorrotor to generate electrical poer.

After passing through the third-stage buc4ets* thegases are directed into the exhaust di0user. The gases

then pass into the exhaust plenum and are introducedto atmosphere through the exhaust stac4.

2. B!" ND !UPPORT!

2.1. Turbine Base

The base that supports the gas turbine is a structuralsteel fabrication of elded steel beams and plate.

5ts prime function is to proide a support upon hichto mount the gas turbine.6ifting trunnions and supports are proided* to oneach side of the base in line ith the to structuralcross members of the base frame. 7achined pads oneach side on the bottom of the base facilitate itsmounting to the site foundation. To machined pads*atop the base frame are proided for mounting the aftturbine supports.

2.2. Turbine !upports

8igid leg-type supports at the compressor end andsupports ith top and bottom piots at the turbine end.2n the inner surface of each support leg a ater jac4etis proided* through hich cooling ater is circulatedto minimi/e thermal expansion and to assist inmaintaining alignment beteen the turbine and the

load e3uipment. The support legs maintain the axialand ertical positions of the turbine* hile to gib 4eyscoupled ith the turbine support legs maintain itslateral position. 2ne gib 4ey is machined on the loerhalf of the exhaust frame. The other gib 4ey ismachined on the loer half of the forard compressorcasing. The 4eys ,t into guide bloc4s hich are eldedto the cross beams of the turbine base. The 4eys areheld securely in place in the guide bloc4s ith boltsthat bear against the 4eys on each side. This 4ey-and-bloc4 arrangement preents lateral or rotational


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moement of the turbine hile permitting axial andradial moement resulting from thermal expansion.

#. CO$PR"!!OR !"CTION

#.1. General

The axial-o compressor section consists of thecompressor rotor and the compressor casing. +ithinthe compressor casing are the ariable inlet guide

anes* the arious stages of rotor and stator blading*and the exit guide anes. 5n the compressor* air iscon,ned to the space beteen the rotor and stator

here it is compressed in stages by a series ofalternate rotating (rotor) and stationary (stator) airfoil-shaped blades. The rotor blades supply the forceneeded to compress the air in each stage and the statorblades guide the air so that it enters the folloing rotorstage at the proper angle. The compressed air exitsthrough the compressor discharge casing to thecombustion chambers. Air is extracted from thecompressor for turbine cooling and for pulsation

control during startup.

Option:

1 Air may also be extracted from the compressor henthe combustion turbine is operating for use in the plantcompressed air system.

#.2. Rotor

The compressor portion of the gas turbine rotor is anassembly of heels9 a speed ring* tie bolts* thecompressor rotor blades* and a forard stub shaft (seeigure ).&ach heel has slots broached around its periphery.The rotor blades and spacers are inserted into theseslots and held in axial position by sta4ing at each endof the slot. The heels are assembled to each otherith mating rabbets for concentricity control and areheld together ith tie bolts. Selectie positioning of the


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heels is made during assembly to reduce balancecorrection. After assembly* the rotor is dynamicallybalanced.

The forard stubshaft is machined to proide thethrust collar* hich carries the forard and aft thrustloads. The stubshaft also proides the journal for theo. bearing* the sealing surface for the o. bearingoil seals and the compressor lo-pressure air seal.The stage ; heel carries the rotor blades and alsoproides the sealing surface for the high-pressure airseal and the compressor-to-turbine marriage ange.

#.#. !tator

#.#.. General


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The casing area of the compressor section iscomposed of three major sections. These are the:a. 5nlet casingb. "ompressor casing

c. "ompressor discharge casingThese casings* in conjunction ith the turbine casing*form the primary structure of the gas turbine.They support the rotor at the bearing points andconstitute the outer all of the gas-path annulus. Allof these casings are split hori/ontally to facilitatesericing.

#.#.!. Inlet Casin%

The inlet casing (see igure !) is located at theforard end of the gas turbine. 5ts prime function isto uniformly direct air into the compressor. The inletcasing also supports the o. bearing assembly. Theo. bearing loer half housing is integrally castith the inner bellmouth. The upper half bearinghousing is a separate casting* anged and bolted tothe loer half. The inner bellmouth is positioned to

the outer bellmouth by nine airfoil-shaped radialstruts. The struts are cast into the bellmouth alls.They also transfer the structural loads from theadjoining casing to the forard support hich isbolted and doeled to this inlet casing.


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The aft compressor casing contains stage % throughstage ! compressor stator stages. &xtraction ports inaft casing permit remoal of #th-stage compressorair. This air is used for cooling functions and is also

used for pulsation control during startup andshutdon.

#.#.$. Co&pressor Dischar%e Casin%

The compressor discharge casing is the ,nal portionof the compressor section. 5t is the longest singlecasting* is situated at midpoint - beteen the forardand aft supports - and is* in e0ect* the 4eystone of

the gas turbine structure. The compressor dischargecasing contains the ,nal compressor stages* formsboth the inner and outer alls of the compressordi0user* and joins the compressor and turbinecasings. The discharge casing also proides supportfor the combustion outer casings and the innersupport of the ,rst-stage turbine no//le.


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The compressor discharge casing consists of tocylinders* one being a continuation of the compressorcasing and the other being an inner cylinder thatsurrounds the compressor rotor. The to cylinders are

concentrically positioned by fourteen radial struts.A di0user is formed by the tapered annulus beteen theouter cylinder and inner cylinder of the discharge casing.The di0user conerts some of the compressor exit

elocity into added static pressure for the combustion airsupply.

#.#.%. Bla'in%

The compressor rotor and stator blades are airfoil shapedand designed to compress air e0iciently at high blade tip


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elocities. The blades are attached to the compressorheels by doetail arrangements.The doetail is ery precise in si/e and position tomaintain each blade in the desired

position and location on the heel.The compressor stator blades are airfoil shaped and aremounted by similar doetails into ring segments in the,rst ,e stages. The ring segments are inserted intocircumferential grooes in the casing and are held inplace ith loc4ing 4eys. The stator blades of theremaining stages hae a s3uare base doetail and areinserted directly into circumferential grooes in thecasing.

6oc4ing 4eys hold them in place.

(. D)N*2 CO$BU!TION !+!T"$

(.1. General

The combustion system is of the reerse-o type iththe > combustion chambers arranged around theperiphery of the compressor discharge casing as shon

on igure #. "ombustion chambers are numberedcountercloc4ise hen ieed loo4ing donstream andstarting from the top left of the machine. This system alsoincludes the fuel no//les* a spar4 plug ignition system*ame detectors* and cross,re tubes. ?ot gases*generated from burning fuel in the combustion chambers*o through the impingement cooled transition pieces tothe turbine.?igh pressure air from the compressor discharge isdirected around the transition pieces. Some of the airenters the holes in the impingement sleee to cool thetransition pieces and os into the o sleee. The restenters the annulus beteen the o sleee and thecombustion liner through holes in the donstream end ofthe o sleee. (See igure $ and igure %). This airenters the combustion /one through the cap assembly forproper fuel combustion. uel is supplied to eachcombustion chamber through ,e no//les designed todisperse and mix the fuel ith the proper amount ofcombustion air.


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Fi%ure #: Co&bustion !,ste&rran%e&ent


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Options:

@ual fuel-The @6-! combustion system shon in igure$ is a single stage* dual mode combustor capable of

operation on both gaseous and li3uid fuel.2n gas* the combustor operates in a di0usion mode at loloads (%=B load)* and a pre-mixed mode at high loads(C%=B load). +hile the combustor is capable of operatingin the di0usion mode across the load range* diluentinjection ould be re3uired for 2x abatement.2il operation on this combustor is in the di0usion modeacross the entire load range* ith diluent injection usedfor 2x .

Gas uel only-2n gas* the combustor operates in adi0usion mode at lo loads (%=B load)* and a pre-mixedmode at high loads (C%=B load). +hile the combustor iscapable of operating in the di0usion mode across the loadrange* diluent injection ould be re3uired for 2xabatement.6i3uid fuel only- 2n oil operation* this combustor is in thedi0usion mode across the entire load range* ith diluentinjection used for ox.

(.2. Outer Co&bustion Cha&bers an' Flo- !leees

The outer combustion chambers act as the pressureshells for the combustors. They also proide anges forthe fuel no//le-end coer assemblies* cross,re tubeanges* and* here called for* spar4 plugs* amedetectors and false start drains. The o sleees (igure%) form an annular space around the cap and linerassemblies that directs the combustion and cooling airos into the reaction region. To maintain theimpingement sleee pressure drop* the openings forcross,re tubes* spar4 plugs* and ame detectors aresealed ith sliding grommets.

(.#. Cross/re Tubes

All combustion chambers are interconnected by means ofcross,re tubes. The outer chambers are connected ith


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an outer cross,re tube and the combustion liner primary/ones are connected by the inner cross,re tubes.

(.(. Fuel No00le "n' Coers

There are ,e fuel no//le assemblies in each combustor.igure ' and igure ; shos a typical cross-section of a@6-! fuel no//le. The no//le shon is for the dual fueloption and shos the passages for di0usion gas*premixed gas* oil* and ater. +hen mounted on the endcoer* as shon in igure '* the di0usion passages of fourof the fuel no//les are fed from a common manifold*called the primary that is built into the end coer. The

premixed passage of the same four no//les is fed fromanother internal manifold called the secondary. Thepremixed passages of the remaining no//le are suppliedby the tertiary fuel system9 the di0usion passage of thatno//le is alays purged ith compressor discharge airand passes no fuel.

(.. Cap an' )iner sse&blies

The combustion liners (igure >) use external ridges andconentional cooling slots for cooling. 5nterior surfaces ofthe liner and the cap are thermal barrier coated to reducemetal temperatures and thermal gradients. The cap(igure D and igure =) has ,e premixer tubes thatengage each of the ,e fuel no//le. 5t is cooled by acombination of ,lm cooling and impingement cooling andhas thermal barrier coating on the inner surfaces (igureD and igure =).

(.. !par3 Plu%s

"ombustion is initiated by means of the discharge fromspar4 plugs hich are bolted to anges on thecombustion cans and centered ithin the liner and osleee in adjacent combustion chambers.

A typical spar4 plug arrangement is shon in igure .These plugs receie their energy from high energy-capacitor discharge poer supplies. At the time of ,ring*a spar4 at one or more of these plugs ignites the gases in


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a chamber9 the remaining chambers are ignited bycross,re through the tubes that interconnect the reaction/one of the remaining chambers.

(.4. Ultraiolet Fla&e Detectors

@uring the starting se3uence* it is essential that anindication of the presence or absence of ame betransmitted to the control system. or this reason* a amemonitoring system is used consisting of multiple amedetectors located as shon on igure #. The amedetectors (igure and igure !) hae ater cooled

jac4ets to maintain acceptable temperatures.

The ultraiolet ame sensor contains a gas ,lled detector.The gas ithin this detector is sensitie to the presenceof ultraiolet radiation hich is emitted by a hydrocarboname. A @" oltage* supplied by the ampli,er* isimpressed across the detector terminals. 5f ame ispresent* the ioni/ation of the gas in the detector allosconduction in the circuit hich actiates the electronicsto gie an output indicating ame. "onersely* theabsence of ame ill generate an output indicating no

ame.The signals from the four ame detectors are sent to thecontrol system hich uses an internal logic system todetermine hether a ame or loss of ame conditionexists.


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Fi%ure . Fuel No00le Cross*!ection


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igure = Spar4 lag


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. TURBIN" !"CTION

.1. General

The three-stage turbine section is the area in hichenergy in the form of high temperature pressuri/ed gas*produced by the compressor and combustion sections* isconerted to mechanical energy.

gas turbine hardare includes the turbine rotor* turbinecasing* exhaust frame* exhaust di0user* no//les* andshrouds.

.2. Turbine Rotor

%.!.. !tructureThe turbine rotor assembly* shon in igure $* consistsof the forard and aft turbine heel shafts and the ,rst-*

second- and third-stage turbine heel assemblies ithspacers and turbine buc4ets. "oncentricity control is


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achieed ith mating rabbets on the turbine heels*heel shafts* and spacers. The heels are held togetherith through bolts mating up ith bolting anges on theheel shafts and spacers. Selectie positioning of rotor

members is performed to minimi/e balance corrections.

.2.2. 5heel !ha6ts

The turbine rotor distance piece extends from the ,rst-stage turbine heel to the aft ange of the compressorrotor assembly.The turbine rotor aft shaft includes the o. ! bearing

journal.

.2.#.5heel sse&blies

Spacers beteen the ,rst and second* and beteen thesecond and third-stage turbine heels determine theaxial position of the indiidual heels. These spacerscarry the diaphragm sealing lands. The -! spacerforard and aft faces include radial slots for cooling airpassages.

Turbine buc4ets are assembled in the heels ith ,r-tree-shaped doetails that ,t into matching cut-outs in theturbine heel rims. All three turbine stages haeprecision inestment-cast* long shan4 buc4ets. The long-shan4 buc4et design e0ectiely shields the heel rimsand buc4et root fastenings from the high temperatures inthe hot gas path hile proiding mechanical damping ofbuc4et ibrations. As a further aid in ibration damping*the stage-to and stage-three buc4ets hae interloc4ingshrouds at the buc4et tips. These shrouds also increasethe turbine e0iciency by minimi/ing tip lea4age. 8adialteeth on the buc4et shrouds combine ith steppedsurfaces on the stator to proide a labyrinth seal againstgas lea4age past the buc4et tips.igure ! shos typical ,rst-* second-* and third-stageturbine buc4ets for the gas turbine. The increase in thesi/e of the buc4ets from the ,rst to the third stage isnecessitated by the pressure reduction resulting fromenergy conersion in each stage* re3uiring an increasedannulus area to accommodate the gas o.


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The ,rst-stage forard heelspace is cooled bycompressor discharge air. A labyrinth seal is installed atthe aft end of the compressor rotor beteen the rotor and

inner barrel of the compressor discharge casing. Thelea4age through this labyrinth furnishes the air othrough the ,rst-stage forard heelspace. This coolingair o discharges into the main gas stream aft of the,rst-stage no//le.The ,rst-stage aft heelspace is cooled by #th stageextraction air ported through the !nd stage no//le. Thisair returns to the gas path forard of the !nd stageno//le.

.2.. !econ'*!ta%e 5heelspaces

The second-stage forard heelspace is cooled bylea4age from the ,rst-stage aft heelspace through theinterstage labyrinth. This air returns to the gas path atthe entrance of the second-stage buc4ets.The second-stage aft heelspace is cooled by #th stageextraction air ported through the #rdstage no//le. Air

from this heelspace returns to the gas path at the third-stage no//le entrance.

.2.4. Thir'*!ta%e 5heelspaces

The third-stage forard heelspace is cooled by lea4agefrom the second-stage aft heelspace through theinterstage labyrinth. This air reenters the gas path at thethird-stage buc4et entrance.The third-stage aft heelspace obtains its cooling airfrom the discharge of the exhaust frame cooling airannulus. This air os through the third-stage aftheelspace* and into the gas path at the entrance to theexhaust di0user.

.2.7. Buc3ets

Air is introduced into each ,rst-stage buc4et through aplenum at the base of the buc4et doetail (igure #). 5tos through serpentine cooling holes extending the


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length of the buc4et and exits at the trailing edge and thebuc4et tip. The holes are spaced and si/ed to obtainoptimum cooling of the airfoil ith minimum compressorextraction air. igure $ shos the ,rst-stage buc4et

design.Enli4e the ,rst-stage buc4ets* the second-stage buc4etsare cooled by spanise air passages the length of theairfoil. Air is introduced li4e the ,rst-stage* ith a plenumat the base of the buc4et doetail. Again airfoil cooling isaccomplished ith minimum penalty to thethermodynamic cycle. See igure %.The third-stage buc4ets are not internally air cooled9 thetips of these buc4ets* li4e the second stage buc4ets* are

enclosed by a shroud hich is a part of the tip seal. Theseshrouds interloc4 from buc4et to buc4et to proideibration damping.

.#. Turbine !tator

.#.1. !tructure

The turbine casing and the exhaust frame constitute the

major portion of the 7SD==A gas turbine statorstructure. The turbine no//les* shrouds* and turbineexhaust di0user are internally supported from thesecomponents.

.#.2. Turbine Casin%

The turbine casing controls the axial and radial positionsof the shrouds and no//les. 5t determines turbineclearances and the relatie positions of the no//les to theturbine buc4ets. This positioning is critical to gas turbineperformance.?ot gases contained by the turbine casing are a source ofheat o into the casing. To control the casing diameter*it is important to reduce the heat o into the casing andto limit its temperature.?eat o limitations incorporate insulation* cooling* andmulti-layered structures. #th stage extraction air ispiped into the turbine casing annular spaces around the!nd and #rd stage no//les.


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rom there the air is ported through the no//le partitionsand into the heel spaces.Structurally* the turbine casing forard ange is bolted tothe bul4head ange at the aft end of the compressor

discharge casing. The turbine casing aft ange is boltedto the forard ange of the exhaust frame

.#.#. No00les

5n the turbine section there are three stages of stationaryno//les (igure #) hich direct the high-elocity o ofthe expanded hot combustion gas against the turbinebuc4ets causing the turbine rotor to rotate. Fecause of

the high pressure drop across these no//les* there areseals at both the inside and the outside diameters topreent loss of system energy by lea4age. Since theseno//les operate in the hot combustion gas o* they aresubjected to thermal stresses in addition to gas pressureloadings.

.#.(. First*!ta%e No00le

The ,rst-stage no//le receies the hot combustion gasesfrom the combustion system ia the transition pieces. Thetransition pieces are sealed to both the outer and innersidealls on the entrance side of the no//le9 thisminimi/es lea4age of compressor discharge air into theno//les.The 7odel D==A gas turbine ,rst-stage no//le (igure') contains a forard and aft caity in the ane and iscooled by a combination of ,lm* impingement andconection techni3ues in both the ane and sideallregions.The no//le segments* each ith to partitions or airfoils*are contained by a hori/ontally split retaining ring hichis centerline supported to the turbine casing on lugs atthe sides and guided by pins at the top and bottom

ertical centerlines. This permits radial groth of theretaining ring* resulting from changes in temperature*hile the ring remains centered in the casing.The aft outer diameter of the retaining ring is loadedagainst the forard face of the ,rst-stage turbine shroud


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and acts as the air seal to preent lea4age of compressordischarge air beteen the no//le and turbine casing.2n the inner sideall* the no//le is sealed by a angecast on the inner diameter of the sideall that rests

against a mating face on the ,rst-stage no//le supportring. "ircumferential rotation of the segment innersideall is preented by an eccentric bushing and alocating doel that engages a lug on the inner sideall.The no//le is preented from moing forard by the lugselded to the aft outside diameter of the retaining ring at$% degrees from ertical and hori/ontal centerlines.These lugs ,t in a grooe machined in the turbine shell

just forard of the ,rst-stage shroud T hoo4. Fy moing

the hori/ontal joint support bloc4 and the bottomcenterline guide pin and then remoing the inner sidealllocating doels* the loer half of the no//le can be rolledout ith the turbine rotor in place.

.#.. !econ'*!ta%e No00le

"ombustion air exiting from the ,rst stage buc4ets isagain expanded and redirected against the second- stage

turbine buc4ets by the second-stage no//le. This no//le ismade of cast segments each ith to partitions orairfoils. The male hoo4s on the entrance and exit sides ofthe outer sideall ,t into female grooes on the aft sideof the ,rst-stage shrouds and on the forard side of thesecond-stage shrouds to maintain the no//le concentricith the turbine shell and rotor.This close ,tting tongue-and-grooe ,t beteen no//leand shrouds acts as an outside diameter air seal. Theno//le segments are held in a circumferential position byradial pins from the shell into axial slots in the no//leouter sideall.The second-stage no//le is cooled ith #th stageextraction air


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Fi%ure 1( First*!ta%e Buc3et Coolin% Passa%es

gure 13. Turbine Sections-ue!"a# $ie" Sho"ing ooling Air Flo"s


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Fi%ure 1

Fi%ure 1 First*!ta%e No00les Coolin%


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%.#.'. Thir'*!ta%e No00le

The third-stage no//le receies the hot gas as it leaes

the second-stage buc4ets* increases its elocity bypressure drop* and directs this o against the third-stage buc4ets. The no//le consists of cast segments* eachith three partitions or airfoils. 5t is held at the outersideall forard and aft sides in grooes in the turbineshrouds in a manner similar to that used on the secondstage no//le. The third-stage no//le is circumferentiallypositioned by radial pins from the shell.#th stage extraction air os through the no//le

partitions for no//le conection cooling and foraugmenting heelspace cooling air o.

%.#.;. Diaphra%&

Attached to the inside diameters of both the second andthird-stage no//le segments are the no//le diaphragms.These diaphragms preent air lea4age past the innersideall of the no//les and the turbine rotor. The

highlo* labyrinth seal teeth are machined into the insidediameter of the diaphragm. They mate ith opposingsealing lands on the turbine rotor. 7inimal radialclearance beteen stationary parts (diaphragm andno//les) and the moing rotor are essential formaintaining lo interstage lea4age9 this results in higherturbine e0iciency.

%.#.>. !hrou's

Enli4e the compressor blading* the turbine buc4et tips donot run directly against an integral machined surface ofthe casing but against annular cured segments calledturbine shrouds. The shroudsH primary function is toproide a cylindrical surface for minimi/ing buc4et tipclearance lea4age.The turbine shroudsH secondary function is to proide ahigh thermal resistance beteen the hot gases and thecomparatiely cool turbine casing. Fy accomplishing thisfunction* the turbine casing cooling load is drastically


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reduced* the turbine casing diameter is controlled* theturbine casing roundness is maintained* and importantturbine clearances are assured.The ,rst and second-stage stationary shroud segments

are in to pieces9 the gas-side inner shroud is separatedfrom the supporting outer shroud to allo for expansionand contraction* and thereby improe lo-cycle fatiguelife. The ,rst-stage shroud is cooled by impingement* ,lm*and conection.The shroud segments are maintained in thecircumferential position by radial pins from the turbinecasing. Ioints beteen shroud segments are sealed byinterconnecting tongues and grooes.

%.#.D. "8haust Fra&eThe exhaust frame is bolted to the aft ange of theturbine casing. Structurally* the frame consists of anouter cylinder and an inner cylinder interconnected bythe radial struts. The o. ! bearing is supported from theinner cylinder.The exhaust di0user located at the aft end of the turbineis bolted to the exhaust frame. Gases exhausted from the

third turbine stage enter the di0user here elocity isreduced by di0usion and pressure is recoered. At theexit of the di0user* the gases are directed into theexhaust plenum.&xhaust frame radial struts cross the exhaust gas stream.These struts position the inner cylinder and o. ! bearingin relation to the outer casing of the gas turbine. Thestruts must be maintained at a constant temperature inorder to control the center position of the rotor in relationto the stator.This temperature stabili/ation is accomplished byprotecting the struts from exhaust gases ith a metalfairing that forms an air space around each strut andproides a rotated* combined airfoil shape.20-base bloers proide cooling air o through thespace beteen the struts and the rapper to maintainuniform temperature of the struts. This air is thendirected to the third-stage aft heelspace.


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Trunnions on the sides of the exhaust frame are used ithsimilar trunnions on the forard compressor casing to liftthe gas turbine hen it is separated from its base.

. B"RING!

.1. General

The 7SD==A gas turbine unit has to four-element*tilting pad journal bearings hich support the gas turbinerotor. The unit also includes a thrust bearing to maintainthe rotor-to-stator axial position. Thrust is absorbed by a

tilting pad thrust bearing ith eight shoes on both sidesof the thrust bearing runner. These bearings and seals areincorporated in to housings: one at the inlet casing* onein the exhaust frame. These main bearings are pressure-lubricated by oil supplied from the main lubricating oilsystem. The oil os through branch lines to an inlet ineach bearing housing.


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'... )ubrication

The main turbine bearings are pressure-lubricated ithoil supplied* from the oil reseroir. 2il feed piping* here

practical* is run ithin the lube oil drain lines* or drainchannels* as a protectie measure. 5n the eent of asupply line lea4* oil ill not be sprayed on nearbye3uipment* thus eliminating a potential safety ha/ard.+hen the oil enters the housing inlet* it os into anannulus around the bearing. rom the annulus* the oilos through machined holes or slots to the bearingrotor interface.

'..!. )ubricant !ealin%

2il on the surface of the turbine shaft is preented frombeing spun along the shaft by oil seals in each of thebearing housings. These labyrinth seals are assembled atthe extremities of the bearing assemblies here oilcontrol is re3uired. A smooth surface is machined on theshaft and the seals are assembled so that only a smallclearance exists beteen the oil seal and the shaft. The

oil seals are designed ith tandem ros of teeth and anannular space beteen them. Jressuri/ed sealing air is


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admitted into this space to preent lubricating oil aporfrom exiting the bearing housing.The air that returns ith the oil to the main lubricating oilreseroir is ented to atmosphere after passing through

an oil apor extractor.


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Flo- !leee sse&bl,

6iner

Large Gas Turbine

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