steam parameters

8/21/2019 Steam Parameters

1/12

by

ohn . alto

A E, y

G E y

Fb,

John S Aalto i Manager of ApplicationEngineering for GE Indutrial and PowerSytem General Electric Coany itchbug Maachuett He ha been engagedin all major apect of rotaing equipmentdeign development and application oerhe pat 20 year During thi period he hahad application eperience with team turbine for Set for US Navy ervice feed

pump turbine for utili applicaion teamurbine for land-baed geerator drive er

vice ce or and mechanical driv team urbinefor indutrial and petrochemical application He ha authoredtechnical paper on eam turbine and centrugal compreor

r Aalto received a BS degree in Mechnical Engineering fromNortheatern Univeri (7)

BRC

The data required by turbine vendors to properly develop adesign for a special purpose stea turbine are discussed in detail.Topics covered include discussion of continuous stea condi-tions, turbine power ratings and sizing, speed ranges, efficincy

definition and calculation, guarantees, and purchaser evaluationcriteria. It will be pointed out how specfication of additional dataduring the proposal phase can result in a turbine design which moreclosely matches the actual requirements of the roject.

Recommedations and proposals w be pointed out and thendiscussed in detail.

NRDCN

The purpose herein is to try to dene all of the design parametersthat are required by a turbine designer during the proposal phase.The addtional definitions proposed ill augment the data usualyfound in customer specications and API 612 data sheets. Wheredefinitions in API 612 and NEMA SM23 are not clear or arenonexistent, definitions are proposed that meet the unwrittenintent of these documents. It will be demonstrated ho a little bit

of extra work during the specification of special puose steamturbines can result in more consistent turbine proposals fromdifferent vendors and turbine designs wich more closely matchall the project requirements.

The turbine designer has many parameters to consider duringthe roposal design. he ones that have te most significant effecton th final design will be discussed in detail.

Recommendaion

Supplementary data sheets (APPENDIX) are proposed whichcan be used by urchasers at the start of each project to specify theadditional data suggested to prospective urbine vendors.

125

The supplementary data sheets can also be used to summarizeand organize this aditional data.

To reiterate, the puose is to supplement the requirements anddenitions of API 612 and NEA S23, not to replace them.

CN EM CNDN

The continuous steam conditions that are specified by thepurchaser probably have a bigger effect on the turbine design thaany other single parameter. Abnormal steam conditions that occurnfrequently and with short duration need to be considered sepa-rately om continuous ones.

RecommendaionNew denitions"maximum continuous and"minimum contin-

uous are proposed. Operation at these steam coditions can be10 percet of the time. "ontinuous replaces "shall averagerom NEMA SM3. New deinitions clear up ambiguity betweendefinitions in API 12 and NEA SM23. Definitions for maxi-mum and minimum continuous extraction pressure, admissionpressure, admission tempeature, and condensing exhaust pres-sure are proposed, since NEMA SM23 does not address them. Itis proposed that pressure"swings be based upon gage pressure. Amodication to "swigs on noncondensing exhaust pressure isproposed. Proposed default values for all steam parameters areindicated in Table 1, and can be specified on the supplementarydata sheet. Actual values should be used instead of default valuesif available.

ble 1 Default Value for Continuou Steam Condiion forMechanical Deign

Maimum

Continuous

Noal

Minimum

Continous

Ie Ie r Eus Eus dss dssPressure eerure Pressure Pressure Pressure Pressure eerure

des des

Normal Normal Normalx1.1 Normalx11 Noal Normal Normal

X 105 + 15 F or+ lOpsi or+ lOpsi + IO"HgA X 105 +!SF

Customer Customer Customr Customer Customer Custoer Customer

pecified pecified pecified pecified pecified pecified peciied

Normal Normal Noalx0.8 Normal x08 OS"HA Normal Nonal

or-lOpsi or-10 psi

When th continuous steam condition requirements of API 612and NEMA SM23 are carefully studied and comared, there areambiguities which an use additional clarification.

NEMA SM23 discusses normal, maximum, and minimumsteam conditions along with variations in steam conitons. Itallows turbine"average inlet pressure of 10 ercet of maximuminlet steam pressure. It also allos oeration at maximum inlettemperature plus 1F, as long as the "inlet steam temperatureshall average not more than maximum temperature over any 2month operating period.

Turbine mechanical designers mut consier the amount of timethat te turbine may be subjcted to any secified steam conditon.


2/12

126 PROCEEDINGS OF THE TWENTY -FIRST TURBO MACHINERY SYMPOSIUM

If the turbine can operate for half its life at a certain pressure ortemperature hile maintaining a specified average, this pressureor temperature must be considered normal and continuous by themechanical designer. To clarify terminology, instead of indicatingthat operation at some maximum plus five percent or plus F isalloed, it is proposed that the pressure or temperature plus thealloable "sing be defined as maximum continuous.

A simple example ill help to explain. A plant has steamconditions of 600 psig and 70F. NEMA SM23 ould allooperation to average 600 psig and average 70F. While maintain-ing this average, operation at 630 (600 x 1.0) psig and 76 (70+ 1)F is alloed; hoever, operation at loer than 600 psig andloer than 70F is required to maintain the average. The pro-posed ne definition of maximum continuous would allo contin-uous operation at 630 psig and 76F, recognizing the fact that theequipment must be designed for these conditions continuouslyanyay.

In a similar manner, NEA SM23 allos operation ith anaverage noncondensing exhaust pressure 10 percent above and 20percent below maximum exhaust pressure. For mechanical designpuoses, these sings must be considered as continuous operat-ing conditions.

NEMA SM23 does not recommend any specic alloable"sings for admission/induction pressure or temperature, extrac-tion pressure, or condensing exhaust pressure. (From this point on,the ord adission ill be used with the same meaning asinduction.)

API 612 lists NEMA S23 as a"Referenced Publication andrequires "operation ith variations rom rated steam conditionsper NEMA M23. It does not, however, define rated steamconditions. API 612 urther states,"Maximum inlet pressure andtemperature refer to the highest inlet steam pressure and temper-ature conditions at hich the turbine is required to operate contin-uously. t does not, however, indicate hether this maximumpressure nd temperature include the five percent pressure marginand/or the F temperature margin noted in NEMA SM23.

The special puose steam turbine data sheets included in API612 allo purchaser specication of minimum, normal, and max-imum steam conditions. Hoever, once again, they do not corre-

late back to NEMA SM23 and also do not specically indicate forhat these steam conditions should be used. It should be pointedout that continuous steam conditions for sizing of steam turbinesmay (and probably should) be different from those used formechanical design considerations. Steam conditions for turbinesizing ill later be discsed in detail.

NEMA SM23 does not specifically state whether pressurevariations indicated are rom gage or absolute pressure. It isproposed that all pressure variations be based upon gage pressureexcept for condensing exaust pressure, hich ill be based uponabsolute pressure.

Default values for continuous steam conditions to be used formechanical design are proposed in Table 1. Maximum and mini-mum continuous values include margins required by NEMASM23. Normal values ill be those hich are expected during

normal operation and must be specifie by the purchaser. For caseshere NEMA SM23 has not suggested alloable variations forcertain parameters, proposed values are indicated here. UsingNEMA S23 as a guide, admissions are treated as inlets, andextractions are treated as noncondensing exhausts.

For normal extraction or noncondensing exhaust pressures be-lo 100 psg, an additional default rule is proposed. A margin of10 psi variation above normal in lieu of 10 percent il be used. Inaddition, for normal extraction or noncondensing exhaust pres-sures belo 0 psig, an additional default rule is proposed. Amargin of 10 psi variation below normal in lieu of 20 percent illbe used; hoever the minimum continuous exhaust pressure ill

never be less than atmospheric. These additional default rulesrecognize normal variations in steam header pressures in manyplants.

For condensing exhausts, a nominal 1.0 in HgA increase inpressure is proposed to recognize normal cooling ater variations.A minimum condensing exhaust pressure of 0. in HgA is pro-posed. This pressure, although extremely lo, will ensure thatturbine last stages ill be suitable for maximum loadings in theevent of unexpectedly cold cooling ater.

Steam admissions are treated the same as an initial inlet. Widevariations in admission temperature can be extremely important tothe turbine designer. Admission temperatures tha t are significant-ly diferent from the "through o temperature require specialdesign consideration."Wet steam at the admission requires veryspecial attention. These conditions must be made knon duringthe proposal phase if they are anticipated.

The turbine mechanical designer must ensure that the turbineil be suitable for continuous operation at these conditions,independent of any other design parameters such as o or poer.Each pertinent parameter should be specified by the purchaserduring the proposal phase unless the default values indicated illcover all expected "sings.

Since it is difficult for the purchaser to predict with certaintyhich combinations of continuous pressure and temperature i

or can occur simultaneously, the turbine designer must assume thatany combination of steam conditions is possible continuously, andaccount for these conditions in the turbine design.

These continuous steam conditions il be used by the mechan-ical designer for numerous purposes. Material selection of theturbine main components and casing design pressure and temper-ature are the most obvious. Each turbine vendor has hardare andmaterial limits hich are solely dependent upon continuous steamconditions A maximum continuous temperature of 78F, forexample, could cause a turbine designer to use alloy steel forturbine inlet parts in lieu of carbon steel, resulting in a significantincrease in cost of the turbine. If, in actuality, temperatures over77F are not envisioned, this must be pointed out to the turbinedesigner.

The possible combinations of continuous steam conditions are

also very important during calculation of maximum bucket stress-es. Maximum continuous temperatures determine the type of bladeattachment to the turbine heel, and variations in pressure are usedto determine maximum stage loadings for calculation of bucketstresses and maximum unbalance pressures for diaphragm design.The entire turbine design must be suitable for continuous operationat these conditions. It can be pointed out that the designer of thepiping to, and piping/exhaust duct from, the steam turbine shouldalso consider these same aspects of steam condition variation.

Abnormal steam conditios (those hich occur only intermit-tently) are also important to consider during the mechanical designof the turbine. It is suggested that the abnormal variations dis-cussed in NEMA SM23 for inlet pressure and temperature beaccounted for in the design as a standard. Other abnormal varia-tions in steam conditions must be made knon to the turbine

designers to allo proper design consideration.The default values of the steam condition variation poposedhere should only be used if the purchaser has not determinedexpected actual variations. Actual values ill result in a lessconservative, but still technically suitable design. In any event,either default or actual values should be indicated on the supple-mentary data sheet to the turbine vendors during the proposalphase.

RBNE WER RNG

Steam turbines designed to API 612 can drive many types ofrotating equipment, including pumps, fans, bloers, generators,


3/12

SPECIFYNG STEM ND RTING CONDITIONS FOR SPECIL PURPOSE STEM TURBINES 127

axial compressors, and centrifugal compressors. For the purposehere, the requirements of API 617 will be used as the basis fordefinition of turbine power ratings.

Recommendation

New definitions and default values for continuous powers formechanical design are proposed in Table 2. New definitions clearup ambiguity between API 617, API 612, and NEMA SM23Turbine rated power includes 10 percent power margin per API617. Minimum power is proposed as compressor normal x 08,since it was previously undefined. It is proposed tat compressorrated point be dened as the point with the"highest power, not the

"highest capacity. Actual values should be used instead of defaultvalues if available.

Table 2 Default Value for Continuou Power for MechanicalDeign

Point Power

Turbine CompressorRated Rated x 1.1

CompressorCustomer

Rated Speciied

Compressor CustomerNormal Specied

Minimum CompressorNormal x 0.8

API 617 Centrifugal Compressors for General Reinery Servicestates,"Steam turbine drivers shall be sized to delver continuously 110 percent of the maximum power (including gear, uidcoupling, or other losses, as applicable) rquired for the purchaser's specified conditions while operating at a coespondingspeed with the specified steam conditions.

API 612 states, "Rated applies to the greatest turbine powerspecified and the corresponding speed. It includes all the powermargins required by the specifications of the driven equipment.

NEMA SM23 states, "Rated power is the maximum specifiedpower output of the turbine.

For the expected operating points of any centrifugal compressor, the point reuiring maximum power may not be coincidentwith the point requiring maximum speed. In this event, a designpoint defined as the "compressor rated point with maximumrequired power and sped is specified. The turbine power rating isbased upon the"compressor rated point. It should be pointed outthat the"compressor rated oint defined here may not be the sameas that define in API 17, where a point with maximum speed and

"at the highest act of ay specified operating point is used.The compressor oeratin oint with the"highest capacity wil

not necessarily ave te ighest required power.The important point to make here is to ensure that the 10 percentmargin specified in API 61 be added to the "compressor ratedpower to determine"trbie rated power.

The minimum required power of any compressor operatingpoint by itself is not important. What is important, however, is therequired torque characteristic of the compressor at speeds andpowers less than maximm. All expected operating oints of thecompressor should be reviewed and made available to the turbinedesigner because the maximum torque required from the steamturbine driver wil l not necessarily be at maximum poer or speed,depending upon the process and gas conditions encountered by the

centrifugal compressor. Minimum power will be discussed furtherwith minimum speed.

A summary of default values for continuous powers for mechanical design is given in Table 2. Actual data should be provided onthe supplementary data sheet if available.

RBNE EED RNGE

API 617 states,"One hundred percent speed is the highest speedrequired for any specified operating point above the normal speed

curve. If there are no specified operating points that require greaterthan normal speed, the 00 percent speed shall be the normalspeed.

NEMA SM23 states,"Rated speed is the speed correspondingto rated power.

API 612 states,"Maximum continuous speed (in revolutions perminute) is the speed at least equal to 10 percent of the highestspeed required by any of the specied operating conditions. API617 has a similar definition for maximum continuous speed.NEMA SM23, however, states, "Maximum continuous speed isthe highest specified operating speed. It is equal to or greater thanrated speed.

Recommendation

New deinitions and default values for continuous speeds for

mechanical design are proposed in Table 3. New deinitions clearup ambiguity between deinitions in API 617, API 612, and NEMASM23. Maximum continuous speed is per API 612. Defaultminimum speed is proposed since it was previously undefined.

Table 3 Default Value for Continuou Speed for MechanicalDeign

Point Speed

Maximum 10%Continuous

100% CustomerSecified

Normal CustomerSpecied

Minimum 80% *

* p 9

The minimum continuous operating speed of the turbine is muchmore important than the minimum power required. NEMA SM23does not address it. API 612 states that the turbine shall be capableof"Continuous operation at the lowest speed at which maximumtorque is required with mnimum inlet and maximum exhaustconditions. The purchaser wi specify oth the speed and torquevalues required. API 617 does not specify how to determineminimum continuous speed, but states,"Minimum allowable speed

(in revolutions per minute) is the lowest speed at which themanufacturer's design will permit continuous operation, which isa result of the design, not a requirement of it.

The important consideration to keep in mind when specifying aminimum continuous speed is to be sure it is low enough to bebelow any specified operating points with a small amount ofmargin, but not with excess margin that will cause undue overdesign of the turbine buckets and rotor. The overall seed range, frommaximum continuous to minimum continuos, is used when calculating bucket vibratory stresses and rotordynamics.

As noted above in the reference to API 612, the turbine must bedesigned for maximum torque down to minimm continuous


4/12

128 PROCEEDINGS OF THE TWENTYFIRST TURBOMACHINERY SYPOSIUM

speed Ths s very portant when calculatng control stage powerloadngs due to the ncrease n energy on them at lower turbneows

It s proposed that the mnmum contnuous speed be defned asthe lower of:

80 percent of 100 percent turbne speed

Fve percent below the actual speed of any requred contnu-ous operatng pont

A speed speced by the purchaser

For the case when the 80 percent default value s used, mnmumpower wll be set at 80 percent, resultng n maxmum torque atmnmum contnuous speed

Proposed default values for contnuous speeds for mechancaldesgn are ndcated n Table 3 axmum contnuous speed wllbe based upon API 612 and 617, 00 percent turbne speed s thesame as 100 percent compressor speed, and te normal speed of thecompressor and turbne may be less than or equal to 1 00 percentspeed nmu s as descrbed above Actual values of speedshould be provded f avalable

RBNE ZNG

Determnng requred ow passng capablty to ensure power

margn for straght through turbnes (no extractons or admssons)s relatvely straghtforward Tryng to ensure adequate powermargn for the whole turbne and ow passng capablty for eachsecton of extracton or admsson turbnes s more complcatedThese two turbne types wll be dscussed separately

API and NEA touch upon turbne szng but further clarca-ton s n order

NEMA S23 states, "nmum steam condtons are thelowest nlet steam pressure and temperature and correspondngexhaust pressure at whch the turbne produces rted power andspeed

API 612 requres that turbnes be capable of "delverng ratedpower at ts correspondng speed wth concdent mnmum nletand maxmum exhaust condtons as specfed on the data sheetsAPI 61 also recognzes that "to prevent overszng nd/or toobtan hgher operatng ecency, t may be desrable to lmt

maxmum turbne capablty by specfyng normal power aselected pecentage of rated power nstead of rated power at thecondtons specfed

Translated, ths eans that the more capablty mrgn that sncluded n the turbne desgn beyond what s requred at thenormal operatng pont, the lower the effcency wll be at thenormal operatng pont

Adequate capablty margn s absolutely essental Excess capalty margn wll result reduced ecenc durng normaloperaton over the ente fe f th turbne and may ncrease thental captal cost of the turbne as well

Straight Through Turbine

Szng (o passng capalty) for straght through turbneswll frst be addressed Parameters requrng defnton are nletand exhaust steam condtons, requred turbne power, and speed

Recommendation

Proposed default values for straght through turbne szngparameters are ndcated n Table 4 The worst case scenaro foreach parameter s default value argn at both 10 percent and00 percent speed s proposed To prevent overszng, purchasershould specfy condtons other than default values f avalable

The contnuous steam condtons dscussed earler are not nec-essarly the ones that should be used to sze the turbne Whendetermnng he steam condtons for szn, the purcaser should

Table 4. Default Sizing Criteria for Stight Through Turbine.

nmum Contnuous Inlet Pressure

nmum Contnuous Inlet Temperature

axmum Contnuous Exhaust Pressure

Turbne Rated Power

100% Speed andaxmum Contnuous Speed

consder each steam parameter separately and determne whchextremes can occur smultaneously and what th power requre-ments of the drven equpment mght be at tat partcular tmeDependng upon the partcular turbne desgn, turbne ow pass-ng capblty can vary wth turbne speed; therefore, the turbnedesgner should ensure ow passng capablt at both 100 percentand urbne maxmum contnuous speeds he ost conservatveapproach for straght through turbnes s ndcated n Table 4

It should be noted that maxmum contnuous nlet temperatures used when sng the turbne for a maxmum ow nstead of a

power, not mnmum contnuous If a maxmum ow s specfednstead of a power, an account must be made of the ncreasedvolume of the steam at the hgher temperature

traction or Admiion Turbine

Both API 612 and NEA S23 requre only that the turbnebe capable of rated power durng operaton at mnmum steacondtons, wth no menton of allowable varaton n extracton oradmsson ows to reach rated power other than"Turbnes shall becapable of contnuous operato at condtons agreed upon be-tween the purchaser and the vendor for extracton or nucton orboth stated n AP 612 When not dscussed pror to the desgn ofthe turne, each vendor can nterpret these requrements to best ths needs, whch may or ay not meet the needs of the purchaserIs reducton n extracton ow, as the route to developng rated

power, acceptable to the proposed process? If not, adtonalpurchaser defnton of turbne operatng characterstcs s requred

Recommendation

API612 and NEA S23 do not adequately address szng ofextracton or admsson turbnes For extracton and admssonturbnes, t s proposed that each turbne secton wll be szd topass a"ow, and the entre turbne wll then be cecked for powercapablty Unless specfed otherwse by the purchaser, t sproposed hat reducton n extracton ow o ncrease n admssonow s the proper route to attanng tubne rated"power

For extracton or admsson turbnes, to ensure power capabltyof the entre turbne, the ow passng capablty of each turbnesecton must be adequate Flow passng capablty must be consd-ered on a secton by secton bass Power marg, on the other hand,s a result of the mode of operaton of the entre turbne Aconsstent approach that can be used for szng these types ofturbnes, and that wll ensure that the turbne szng wll match thepurchaser requrements, wll now be proposed Only sngle auto-matc extracton or admsson turbnes wll be dscussed here,although the approach can be appled for addtonal turbne sectons

Etraction Turbine

For extracton turbnes, there are three varables assocated wtheach operatng pont that determne the approach requred to szethe turbnethrottle flow, extracton ow, and power The pur-chaser specfes two of the three parameters, and the result of the


5/12

SPECIFYING STEAM AND RATING CONDITIONS FOR PECIAL PURPOSE STEAM TURBINES 129

desin is the value of the third arameter There are two basic caseswhich determine the design aroach or these tyes of turbines:Maxium throttle ow secified and extraction flow is the result,and required extraction ow is secified and throttle ow is theresult In all instances, it shall be assued that minimum steamconditions (Table ) will be used unless secified differently bythe urchaser

Table Default Sizing Criteria for Single Automatic EtractionTurbine.

Minimum Continuous Inlet Pressure

Maximum Continuous Inlet emerature

Maximum Cntinuous Extraction Pressure

Minimum Continuous Extraction Pressure

Maximum Continuous Exhaust Pressue

Turbine Rated ower

100% Seed and

Maximum Continuous Seed

z HP 2 z LP

(3)

(3)

(1)

(2)

3 HP LP z

Recommendation

Proosed default values for single automatic extraction turbinesizing parameters are indicated in Table The worst case scenariofor each arameter is default value Maximum inlet temerature isroosed as art of minimum inlet steam conditions (not min) Theuse of normal inlet steam conditions o turbine high ressuresection when sizing low ressure section is roosed Flow andower margin at both 10 ercent and 100 ercent seed isroosed To reent oversizing, the urchaser should specify

conditions other than default values, if aproriateAs an aside, during urcaser secification of extraction oradmission turbines, the secic quantity, or the range in quantityof required extraction or admission ow for each secified comressor oerating oint, should be determined, and this data shouldbe made available o the turbine vendors This rocess can hl touncover all required variations, some of which may be imortantto the sizing of the turbine

There are some secial cases where the igh ressure sectionand/or the low ressure sections of extration turines mus esized at a startu conditio and not holding extaction ressureThis is a secial case which will not be addressed

Herein, HP will be used as an abbreviation for high ressure, andLP will be used for low ressure

ingle Automatic Etraction Turbine Cae (igure )

Maximum throttle ow secified

Normal and rated owes secified

Turbine LP section"sized by:

1 Customer secified oerating oint with maximum LPsection ow, or

2 Secified maximum LP section ow, or

3. LP ow required for rated ower at maximu throttle ow(used nly if 1 and 2 are not secified)

Extraction ow is the result

SHAFT OUTPUT

igure . traction Map Cae .

Step A. Tubine HP section will be sized to ass maximumspecified throttle ow at minimum inlet ressure, maximum inlettemerature, and maxmum extraction pressure

Step B. Turbine LP section will be sized to ass the ow from1 or 2 above (The require ow for 1 above will be determinedwith normal steam conditions and hile holding extraction ressure) The LP section will be sized to ass this required ow atminimum extraction pressure and maximum exhaust ressure andthe temerature at the extraction resulting from running maximumLP section flow through the HP section at normal inlet steam

conditions and minimum extraction ressureStep C. At normal steam conditions, the HP section design from

Ste A will be run with the LP section desin from Ste B If, atmaximum HP section ow and maximum LP sction ow (ointA on Figre 1), the ower develoed is at least equal to turbinerated ower, the design is complete and acceable The ma willbe cut off with a vertical line from maximum throttle ow tmaximum exhaust end ow at rated turbine owe If, however, theresulting ower is less than turbine rated, the LP section owassing caability must be increased (om oint to Point C onFigure 1) above what was required in Ste B (above) until turbinerated ower is develoed (Point D on Figure 1)

It can be noted that even though th LP section ow at Points Cand D is the same, int C is used for LP sizing due to the higherteerature and, therefore, higher steam volume at the extration

Single Automatic Etraction Turbine Cae 2 (igure 2 )

Maximum throttle ow to b e determined

Rated ower secified

Turbine LP section"sized by:

1 Cstomer secified oeratin oit with maximum LPsection flow, or

2 Secified maximum LP section flow, or

3. LP ow required for ratd ower at maximum throttle flow(used only if 1 and 2 are not secified)


6/12

130 PROCEEDINGS OF THE TWENTY-FIRST TURBOMACHINERY SYMPOSIUM

_

w_:

SAT OUPUT

igure 2 Etractin M Case 2

Extrction ow t norml power specified

Step A Turbine HP section will be sized to pss the sum of thespecified extrction ow plus the mximum LP section ow (Forthe first itertion, guess of the LP section ow my be required)Minimum inlet pressure, mximum inlet temperture, nd mxi-mum extrction pressure ill be used r sizing

Step B Turbine LP section will be sized per Step B of Cse 1bove

Step C At norml stem conditions, the HP section design fromStep A will be run with the LP section design from Step B Therere wo possibilities:

Step D If, t mximum HP section o nd mximum LPsection flow (Point A on Figure 2), the poer developed is greterthn rted power, the HP section mximum ow cn be decresed(from Point A to Point B in Figure 2, mintining constntextrction ow) until rted power is developed

Step D2 If, however, the resulting power is less thn turbinerted, both the HP section nd LP section o pssing cpbilitiesmust be incresed (from Point A to Point C for the HP section, nfrom Point D to Point E for the LP section in Figure 2), until rtedpower is developed t the specified extrction o

In summry, for extrction turbines, t minimum stem condi-tions, the HP section is sized t the uppermost right point of the

extrction mp nd the LP section t the loermost rightAdmissin Turbines

As with extrction turbines, there re three vribles ssocitedwith ech operting point tht determine the pproch required tosize n dmission turbinethrottle ow, dmission ow, ndpower The purchser specifies two of the three prmeters, ndthe result of the design is the vlue of the third prmeter There retwo bsic cases which determine the design pproach for thesetypes of turbines: Mximum throttle o specified and dmissionow is the result, nd dmission o is specified and mximumthrottl o is to be determined Once gin, it shall be ssumed

tht minimum stem conditions (Tble 6) will be used unlessspecified differently by the purchser

Table 6 Default Sizing Criteria fr Single Autmatic AdmissinTurbines

Minimum Continuous Inlet Pressure

Mximum Continuous Inlet TempertureMximum Continuous Admission Pressure

Minimum Continuous Admission Pressure

Mximum Continuous Admission Temperature

Mximum Continuous Exhust Pressure

Turbine Rted Power

100 Speed nd

Mximum Continuous Speed

z HP 2 z LP

(3)

(3)(1)

(2)

(2

3 HP

LP z

Recmmendatin

Proposed defult vlues for single automtic dmission turbinesizing prmeters re indicted in Tble . The worst cse scenariofor ech prmeter is defult vlue Mximum inlet temperture isproposed s prt of minimum inlet stem conditions (not min) Theuse of norml inlet stem conditions to turbine HP section whensizing LP section is proposed Flow nd power mrgin t both 10percent nd 00 percent speed is proposed To prevent oversizing,the purchser should specify conditions other thn defult vlues,if pproprite

Single Autmatic Admissin Turbine Case 1 (igure 3)

Mximum throttle flow specified Norml nd rted powers speced

Turbine LP section "sized by:

1 Customer specified operting point with maximum LPsection ow, or

2. Specified mximum LP section ow, or3. LP ow required for rted poer t mximum throttle ow

(used only if 1 nd 2 re not specified) Admission ow is the result

Step A Turbine HP section will be sized to pss mximumspecified throttle ow t minimum inlt pressure, mximum inlettemperture, nd mximum dmission pressure

Step B.For the first itertion, the turbine LP section will besized to pss the sum of mximum throttle ow plus mximum

dmission ow rom 1 or 2 bove The LP section will be sized topss this ow at minimum dmission pressure, mximum dmis-sion temperture, nd mximum exhust pressure The temper-ture (enthlp) t the dmission, resulting from running maximumthrottle ow t norml inlet stem conditions nd minimumdmission pressure, will be used when "mixing the dmissionstem with the throttle ow

Step C At norml stem conditions, the HP section designom Step A will be run ith the LP section design from Step BThere re to possibilities:


7/12

SPECIFYING STEAM AND RATING CONDITIONS FOR SPECIAL PURPOSE STEAM TURBINES 131

2_

w_

SAF OUTU

Figure 3 Admission Map, Case 1

Ste D1 If, at maimum ow through each sectio, the resulig power is greater tha rated, the LP sectio sizig poit ischaged om Poit A to Point B i Figure 3. Step B above will berepeated with the reduce throttle ow from Point B i Figure 3.

Step D2 If, at maimum flow through each sectio, the result-ig power is less tha rate, additional admissio steam is required,ad the LP sectio sizing poit is changed from Point A to Poit Ci Figure 3 util rated power is developed

Single Automaic Admission Turbine Case 2 (Figure 4)

aimum throttle ow to be determied

Rated power specied Turbine LP sectio "sized by:

1 Customer specified operating point with maimum Psection ow, or

2. Specified maimum LP sectio ow, or

3. LP ow required for rated power at maimum throttle ow(used only if 1 ad 2 are not specified)

Admissio ow at oral power specified

Sep A Turbie HP section will be sized to pass the throttle owrequired at the required operating point (For the first iteration, thiswill be a guess) The HP section will be sized at miimum inletpressu, maimum inlet temperature, ad maimum admissionpressure

Step B The turbie LP section will be sized to pass the sum ofthe throttle ow from Step A plus the specified admissio owThe LP sectio will be sized to pass this ow at minimumamissio pressure, maimum admissio temperature, ad mai-mum ehaust pressure The temperature (ethalpy) at the admis-sio, resulting frm runig the throttle ow from Step A atormal inlet steam coditios ad miimum admission pressure,will be used whe"mixig the admissio steam with the throttleow

Step The throttle flow i Step A should be iterated until thepower that results from runig the fow om Step A through theHP section ad the ow from Step B through the LP sectio is

2_

_

SAF OUPU

Figure 4 Admission Map Case 2

equal to normal power (Point D on Figure 4) This becomesthe maimum throttle fow, and the desig procedure becomesthe same as for Admissio Turbie Case 1 above, Steps A, B, C,ad D

traction or Admission Turbine Sizing Summa

The important fact to remember whe sizig etractio oradmissio turbies is that each sectio of the turbie should besized for a o at miimum steam coditios When the turbiesectios have bee sized, the total turbine is checked for powermargin ad the turbie sectios resized, as appropriate, if required

Although ot specifically associated with turbie sizig, for

multisection turbines, minimum sectio ows ca be importatdurig turbie design Turbie sections require miimum ows(the absolute value of the miimum ow will vary, depedigupo steam conditios ad turbie speed) to keep them coolOperation at Poit E i Figure 1 for eample, is a case where theturbie is operating near maimum LP sectio ow, but at consid-erably less tha maximum HP sectio ow If the throttle ow atPoint E is 2 pecet of maimum, for eample, the efficiecy ofthe HP sectio at this ow may be very low or eve negative! Forthe LP section, Point F i Figure 1 is a operating poit that isfunctioning at cosiderably less than LP sctio design ow, andat some fractio of HP sectio desig flow Operation at smallpercetages of desig ows results i high temperatures (orrequires limits in operatig eibility), which must be considereddurig the turbine desig If operatio at"offdesign points such

as these are contemplated, the turbine desiger must be madeaware of this possibiity during the design phase

Turbine Vendor Margin

Durig the maufacture of steam turbines, each vendor hastolerances o the dimensios and ow coefficients of the inletparts that control the ow passing capability of each section of theturbie

Recommendaion

Propose a five percet ow margi be included in the designbeyond what is guaranteed to the purchaser


8/12

132 PROCEEDINGS OF THE TWENTY-FIRST TURBOMACHINERY SYMPOSIUM

To ensure that the"as manufactured turbine does, in fact, havethe o assing cabilities discussed above, it is roosed thatthe turbine be designed ith five ercent additional o marginabove the guaranted o assing caability at the secifiedconditions. This is really the turbine vendor's margin, not theurchaser's. Hoever, it is imortant to have. Assuming normaltoleances, ve ercent o margin ill assure that the exectedo assing caability is attainable.

ZNG EXMLEWhat oversizing can mean to turbine erformance is shon in

Figure 5. I indicates the loss in available energy of steam for agiven turbine section due to one ercent throttling of the steam atthe turine inlet. An inlet throttling loss curve for a tyical turbinedesign is shon in Figure 6. The more margin that has beenincluded in the design beyond th normal oerting oint, the morethrottling; therefore, more loss in available energy.

1

0 . r ,

t-= -

wt +r

--_

-+- /-

-H-

J8 /

nH- --4

/

-

-

2 3 4 7 8 2

iure Percn Bowl Peure vs Percen low

U TO THROTNG LO

/

iure 6 Lo in Available Enery Due o One Percen ThrolinLo.

A sile examle ill illustrte. Assume a noncondensingturbine ith inlet conditions of 1500 sia/950F and exaustpressure of 600 psia. The section pressure ratio is therefore 2.501500/600 = 2.5). It is shon in Figure 5 that for a ressure ratio

of 2.5, the loss in available energy due to one ercent throttling atthe inlet is about 1.0 ercent.Assue that, using only normal steam conditions, 10 ercent

API h argin and five ercen o assing margin are includedin the bae design, resulting in aximum design lo of 115.5ercent 110.0 x 1.05 = 115.5).

Fiure 6 is used to determine the actual aount of throttling. Itis a tyical curve of ercent bol ressure v ercent design o.At 100 ercent o, the bol ressure is 95.2 ercent, a 4.8ercent throttling loss.

If 1,450 si/965F/630 sia"minimum steam conditions areassued, the theoretical steam rate ratio estimate of additional

o required to get the sae outut assuming constant efficiency)results in an added o assing caability requireent of bout 7ercent 22.985/21.466 = 1.07).

If Figure 6 is read at 93.5 ercent design o 100.0/1.07 =93.5), the bol ressure is 93.8 ercent, 6.2 ercent throttlingloss. The difference in bol ressure beteen ith "minimumsteam conditions and ithout is 1.4 ercent 6.2 4.8 = 1.4). A 1.0ercent loss fro Figure 5 times a 1.4 ercent loss from Figure 6results in a 1.4 ercent loss in available energy, just due to the

requirement of"minimum steam. This 1.4 ercent loss is equiv-alent to a 1.4 ercent reduction in efficiency.

It is easy to realize after studying Figure 5 that the throttling lossis ost imortant on turbine, or sections of turbines, ith smallressure ratios such as short energy range noncondensing turbinesor high ressure sections of extraction or admission turbines.Purchasers should kee this in mind hen secifying the sizingcrteria for this tye of turbine.

One final ord on turbine sizing. Oversizing cn cause a re-duction in turbine erformance. Undersizing can lead to situationshere the trbine caability is the limiting facet in the outut of therocess. Take some time during the secification rocess to studythe secific sizing needs and reco them on the sulementarydata sheet.

ZNG EM NGNEMA SM23 gies recommendations for "maximum steam

velocity, in iing, hich are good guidelines. They re rero-duced hee as able 7

ble 7 imum Seam Veloci in Piin

Inlet

ExhaustAdission

Extraction

NoncondeninTurbine/Sec

175

250175

250

CondeninTurbine/Sec

175

450175

250

It is imortant for both the lnt/rocess and the turbine design-ers to consider stea velocities and the associated ressure droshn sizing inlets, extractions, admissions, iing, valves, etc. Allodes of continuous oeration must be considered, not just normaldesign condiion. Maxium extraction or admission flo must bedetermined. It is imortant to oint out, hoever, that higher thnnormal velocities nd ressure dros may be accetable for shorttie oeating oints such as statu or upset conditions.

Recommendaion

Pressure dros in iing and valves external to the turbine mustbe considered by the lant/rocess designers.

Turbine designers ill assume that the inlet or admission res-ures secied are at the inlet ange of the tri throttle valve, andthat exhst and extraction ressures are at the turbine angesunless secied otherise by the urchaser. Pressure dros exter-nal to the turbine ust be considered by the lant/rocess design-ers during turbine design secification. To reiterate, ressuredros to d fro turbine sections ith short energy ranges reost imortant.


9/12

SECIFYIN STEAM AND RATING CONDITIONS FOR SPECIAL PURPOSE STEAM TURBINES 133

RNE ECENCY DENN

It ay s trval to roos dftos of ffccy. AI 612ad NEMA SM23 do ot addrss ffccy. Th truth of thattr s that escally for ultscto turbs dffrt tur-b vdors ay hav dffrt rsoss wh askd to dftur ffccy. Th dscracy s usually foud whchlosss ar ad wch ar ot cludd th ffccy calclato.

Recmmendation

For coarsos th fcecy dfto of trb shaft out-ut dvdd by sta ut s roosd.

Th followg sple dfto s proposd for a straghtthrough turb.

T b

Ef Turb Shaft Output

ur cy = SH

Stea Iut Flow (LB/HR)

TS (LB/HR)

Turb shaft outut s th or avalabl to drv th drvequpt ad stam ut s total throttl ow (FLOW) dvddby th thortcal sta rat TSR) of th stam ro turb ltTTY ag to turb xhaust ag.

For a xtracto turb th followg to s roosd.

Turbe

Efccy

Turbe

Shaft Outut

Stam Iut

SP

FEXTR+

(FTHROTFEXTR)

TSRHE TSROA

Turb shat outut s th owr avalable to drv th drveeqmet ad stam ut s th su of th total xtracto ow(FEXTR) dvdd by th theoretcal sta rat of th stam frotrb lt TTY ag to th turb xtracto ag (TSRHE)lus th total throttl ow (FTHROT) mus th tota xtractoow dvdd by th thoretcal sta rat of th sta fro turblt TTY ag to th turb xhaust age (TSROA).

For a admsso turb th follog dfto s roos.

TurbEffcecy

TurbShaft Out

Sta Iut

SH

FTHROT FADM+

TSROA TSREE

Turb shaft outut s th owr avalabl to drv th rvqut ad sta ut s th su of th total throttl ow(FTROT) dvdd by th thortcal sta rat of th sta froturb lt TTY age to th turb haust ag (TSROA)lus th total adsso o (FAM) dvdd by th thortcalsta rat of th sta ro tub adsso ag to thturb xhaust flag (TSREE).

Ths dtos clud all losss ad thrfor f usd foach dsg udr cosdrato rovd a tru asur that ca

b usd for coarso uoss.

RNE ERRMNCE CLCLNEach vdor has a thod of calculatg arodyac ad

throdyac ffccy ad rforc of th turb staath. Ths thod s usually calbratd basd uo so kd oftst data of slar ty uts. Ths tral ffccy s of thturb stags oly.

Recommendation

roos that ll losss b cludd ffccy calculatos forcoarso uross.

Thr ar rous adtoal losss whch ust b cludd ay ffcc or rforac calculato of a tr turb. Ifth ffccy dftos fro abov ar usd ths losss wll bydfto all b cludd. If howvr scto ffccs arquotd stad of ovrall turb ccs losss assocatdwth th secto ccy calculato ust also b dcatd fora agful rsos.

For forato th followg s a lst of so of th addtoallosss that ust b cosdrd durg turb rforac

calculatos. Tub o args

Cotrol ad TTY valv st lakages

Ilt throttlg losss

TTY

valve chst

cotrol valvs

Barg losses (trust ad joural)

Shaft d lakags

Iteral prssure dros to xtracto ags

Exhast lavg ad throttlg losss

Wh th ouut/ut dto fro abov s usd all losssar cludd th ffccy calculato.

EFF IEN Y GRNEE

AI 612 stats that"Trbs shall be caabl of orato atoral owr ad sd wth oal stam codtos. Th starat (hat rat) crtfd y th aufacturr shall b at thscodtos. NEMA SM23 stats that"Noral owr ad sdad sta codtos are thos codtos oud usual oratod at whch th sta rat wll b guaratd.

Nther rfrc tos ay tolrac o th quotd stacosuto ad hrfor t s assud that ay quotato ofturb rforac s wth o gatv tolrac o ffccy.

Recommendation

roos that turb rforac b quotd wth o gatvtolrac o fccy. Cosdr"avrag guarat ot thrght stuato.

As a ot of t rest AI 617 for Corssors o th othrhad rqures caacty marg (ow assg caablty) th ogatv tolerac but dos allow for a four rct tolrac oowr cosupto. Ths tolrac o rqurd owr s o of thrasos that AI 612 rqurs 10 rct owr arg for steaturb drvrs.

Tstg of sta turbs to rov quted ffccs ca adhas b th toc of sarat ars. As far th uos r scocrd a ortat fact to cosdr wh tryg to akappls-to-appls comparisos of turbin offrigs, is the possibldffrc tolrac o quotd ffccy btw vdors

quoting to ASME PTC-6, and other vendors quoting to DIN.Basically, ASME PTC-6 allows no tolranc on perfomanc,whil DINall ws may tolracs, iludig provisios for agig,strut tolrac ad aufcurg ucrtats.

Although t ay s ovous durg th scfcato of thturb rqurts at th roosal has b sur to scfy allth aratrs of th guarat ot. For a straght throughturb thr s usually o qusto othr tha cofrato thatth"corssor oral ot for xaml s fact th guar-at ot. For xtracto or adsso turs: of throttl owxtracto/adsso ow ad owr two of ths thre ara-trs ust b scfd to fully df a guarat ot. Although


10/12

134 PROCEEDINGS OF TH E TWENTY-FIRST TURBOMACHINERY SYMPOSIUM

o assing caabiliy has he bigges effec on urbine design, heurbine designer has soe exibiliy in seing he design o-ards he o requreens ha wi be used for evaluaion.

One addiional oin o consider in he righ siuaion: here aybe cases hen long op raon a coressor ons ih verydifferen oers and seeds is conelaed. The urchaser ayan o secify an "arifical eciency guaranee oin ha issoe ind of average aong hese long er oeraing oins. Theaoun of ie execed a each oeraing oin ould also be

useful o he urbine vendors during he selecion of he urbined sgn.

ECENCY EVLN

rior o gong ou for equen bids, each urchaser has gonehrough an evaluaion hase ha has indicaed, using some sp cf-ic crieria, ha he roosed proj c is orh ursuing. During hisevaluaion, cos of energ esiaes ere made, and a aybaceriod of soe aoun of e as secied.

Sinceamost all special purpose mechanical drive turbines are

custom designed, thedesigners have a lot of choces to ake tocoe p with a sutabl desgn. The purchaser wants the highest

eciency turbine for the lowest cost. Usually, th s two parae-

ters do not go together. The designer m ust deterinethe aount

ofhardware to incld whilestl having a desgn whose price wll

be ihin he execaions of h urchaser.

ecommendation

rovide sea evaluaion daa o urbine vendors o alo"adeo' evaluaions.

A purchas r can el he urbn desgners deerine he aounof hardare o incude by provding he evalaion cri ra hah

av

already been used to detenine that the project is viabl . If,for exale, he addiion of a sage o he urbne ncr as e

ci ncy by one ercen, bu also inceases he cos by $ 0000s

oud

the addtonalstage be added or not? For some projects the

answer is yes; for others, no. Turbine vendors could or the

optons of a highcost, high efciency desgn, and a low cost, low

eciency d sgn. However, the coectoption ight bea design

soewhere n between. If the valeof stea at eachpressure l v

and the lengthof the vauation period is ade avalable totheturbine vendors pror toquotation, a d sign that best fits the overall

requireens s ore lely o resul.

ER ELN

In addiion o eciency and cos of sea, h r are ofen oherfaces of he overall urbine d sign hich are ioran o heurchaser. In soe cases, hese design cri ra can overide alloher consrains during he selecion of he urbine.

For xamp ,ashort delivery ss ntial to th needsofthe project

sh o

uld be pointedout, including the va lu ation tat willbe asso-

ciated withactual delveries that are short r or longerthan request-

ed. Turbne size and/or weight are parameters that the design

engineer can control f tese are important tothe specfc situaton.

There may be other crit ra, features, or design parametersthat

are important tothe purchaser. Ifso, tese shouldbe pointed outclearly to the turbine vendors during the proposal phase of the

rojec.

DDNL WRK

This is jus a sar in rying o clarify all he esign requireensof secial urose sea urbines during he roosal hase.

Aong he ocs ha could also be addressed are:

Double Auoaic Exracion/Adission Turbnes

Unconrolled Exracion/Adission Turbines

Definiion of Defaul Abnoral Sea Condiions

Suleenary daa shees in eric unis

Many of he conces ha have been resened here can also bealed o hese yes of urbines as ell . For no, hese addiionaloics ill be saved for fure discussions.

MMRY

Many of he ioran design deails required by urbine ven-dors o roose a d sgn ha os closely aches he requre-ens of he rojec have been discussed. Coninuous seacondions, urbine oers and seeds, szing r qur ns, effi-cency consideraions, and cusoer sp ciic requireens all laya significan role in he design proc ss.

The APPENDIX ncludes suleenary daa shees hich canbe us d o sumarize is addiona daa. I is no ioran hahese daa shees be used. I is ioran, hoever, ha henforaion found on he daa shees be rovided o he urbinevendors. Secficaion of his inforaon ih he iniial RFQ ilreduce confusion and also rove urnaround ie beeen RFQand vendor quoaon.

The defaul vau s roosed should be considered as benc-ars from hich o sar. If e defaul values are no appropriafor a paricuar appcaon, his should be so saed. The sule-

menary daa shees rovide an opporuniy o override defaulvau s for eac desin araeer.

Recommendation

Wheher d faul or acual daa are used, is roosed haconnuous sea condions for echancal design, urbine sizngcrieria, vaue of vendor ow argin, connuous oers, andconnuous seeds a ave been sed durng he proposal designbe ncluded in he roosal docuen rovided o he urchaser.

ED

FigreA 1. Straight Throgh Trbine S lementar ata Sheet

Jo No. - [te No.

Purh. Order No. Date

evision

Dae

Maximum

Normal

Minimu

Supplementary SpecialPurposeSteam Turine Dta Sheet

Customary Units

Straight Through Turi'

Continuous Steam Conditions for Mchanical Ds;gnCondensing

nlet Pressure nlet Temperature xhaust Pressure

(Normal+ 5 F) (Normal+ 0"(05 x Normal)

psig deg F "gA

(cs)

(cs)

I

(cs)deg

psig "gA

(Normal) (Normal) (0.5")

psig deg F "gA

cs indicates Customer Specied

Noncondnsingxhaust Pressure

(Normal X l . l o r+ 0 psi)

psig

(cs

psig

(Normal x 0 or- 0 psi)

psig


11/12

SPECIFYING STEAM AND RATING CONDITIONS FOR SPECIAL PURPOSE STEAM TURBINES 35

Turbine Eciency Guarantee PointDeinition

Flow*

Power

Speed

InletPressure

Inlet

lb/h (cs)

hp (c noal)

pm (noal)

psig (noal)

Teperature deg p (noal)ExhaustPressure " HgA (noal)

psig

Specif y Flow or Power ut not oth

Turine Flow Passing CapabilityDesign Point

Flow '

Power

Speed

InletPressure

nlet

lb/hr

hp

rp

psig

(cs)

(t. rated)

( 100% 15%

(min)

Temperature deg p (in)

ExhaustPressure HgA (max)

psig

Flow Passing Margin = --- (5%

Continuous Powers forMechanical Design

Continuous S peeds orMechanical Design Value of Steam:

(hp) - (

pm)

Turbine MaximuRated (C Rated Continuous (05 % $ / lb/hp Throttle Stea

X . 1 Compressor 00% (cs) $ / lb/hr Exhaust SteamRated (cs) (non-cond)

Compressor Noal (cs) Years Evaluation eriodNoal (cs)

Minimum_ (C No Minimum (80 % Site Elevation (Sea Leel)x08

Other Evaluation Criteria:

Data in parentheses indicate default values

Figue A-2 Single Automati xtation Tubine Supplementayata Sheet

Job No

_

Item No

Purch Order No Date

Requisition No

Inquiry No

BY

ev is ion

_ate

Maximum

Supplement Spcial-Purpose

Steam Turbine Data Sheet

Customary Units

Singl Atomatic taction binContino S tam Conition Mchanical Din

Inlet Prssure Inlet Temperture

1.05 x Normal) (Norma] + 15 F

psig deg F(cs) (cs)

Extraction CondensingPressur Exhaust ressure

(Normal x 1 1 or (Noal + 1.0+ O psi

psig HgA

(cs) (cs)

Normal psig psig HgA

Minimum

(Normal) (Normal)

psig deg "cs indcates Customer Specied

(Normal x 0.8 or 0.5 ) ! O p s i)

psig HgA

Noncondensing

Exhaust essur

(Nol x 1 1 or+ !Opsi

psig

(cs)

psig

(Normal x 08 or ! O p s i)

psig

TurbinEfcincyGrntointDnton

Thottl o w

Etcti

Flow lb/h (c)

Por hp (C Norm

s,d rpm (Norml)Inltr p (Noal)

Inltemprtr d (Norml)EtrctionPur pig (Noal)

Trbin Flow n CpblitHh Pur cton Dei$ Point

TholeFlow lbh

"

InletPrse Ji

InltTmpertr d


12/12

136 PROCEEINGS OF THE TWENTY-FIRST TURBOMACHINERY SYMPOSIUM

u n Guat oDenton

Throttle b/hr (c)

donlow lb/hr

owr h C Norl

Sd " Noal

Inltre>ur (Nn1

nleTure d N rmal)

don

AdonTertu de

hautrur " Nol

S onl two o thre

Coninuo us Powers orMechanical Desin

hp)

TurbineRaed

steam parameters

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