1 GER-3582E ABSTRACT A broad steam turbine product line is avail- able for the wide range of STAG combined cycle systems, depending upon the number of gas tur- bines employed, gas turbine characteristics, steam cycle/HRSG selection, and site specific space, cooling and operating considerations. The addition of the H technology to the STAG combined cycle systems is described. Thermodynamic design aspects are discussed, and useful screening tables are presented for steam turbine selection. Application considera- tions of reheat versus nonreheat, multi-shaft ver- sus single shaft and axial exhaust versus down exhaust are reviewed. Unique design features for sliding pressure, boiler following operation are described, as well as GE steam turbine prod- uct line design features which enhance installa- tion, maintainability and reliability. INTRODUCTION GE has built over 200 steam turbine-genera- tor units totaling more than 15,000 MW of capacity for application in both reheat and non- reheat combined-cycle power plants. Last-stage buckets up to 40 inches/1016 mm at 3600 rpm and 42 inches/1067 mm at 3000 rpm have been applied, allowing for compact High Power Density ™ (HPD) arrangements which comple- ment recent increases in GE gas turbine sizes. The use of longer last-stage buckets permits a more cost-effective, compact HPD design with a minimum number of casings, while still provid- ing ample exhaust annulus area for optimal thermal efficiency. GE offers a complete line of STAG ™ (Steam And Gas) combined-cycle steam turbines which are matched to the exhaust energy of one or more GE gas turbines and Heat Recovery Steam Generator(s) (HRSGs). HRSGs are used to con- vert the gas turbine exhaust into useful steam for the bottoming portion of the combined- cycle. Flexibility is incorporated to allow the steam turbine design to be optimized for site- related parameters such as process extractions and condenser pressure. The trend toward higher gas turbine firing and exhaust temperatures has made reheat com- bined-cycles common. These reheat steam cycles, with advanced gas turbine designs, are termed Advanced Combined-Cycles (ACC). A structured, modular approach to the combined- cycle steam turbine product line allows applica- tion of nonreheat steam cycles with advanced gas turbines as well. GE STAG steam turbine designs can accommodate one, two and three pressure steam cycles. The data in this paper is presented based on three pressure nonreheat cycles for gas turbines with approximately 1000 F/538 C or lower exhaust temperature, and three pressure reheat steam cycles for ACCs uti- lizing the 6FA, 7EC, 7FA, 9EC, and 9FA gas tur- bines. The latest addition to the GE STAG product line involves a platform for the 7G, 9G, 7H and 9H STAG systems. These machines are com- bined-cycle technology that integrate the gas turbine, steam turbine and generator into a seamless system, where each component is opti- mized for the highest level of performance. The data in this paper describes the advance machine platform based on a three pressure reheat steam cycle. The 7H and 9H STAG advanced machines are additionally integrated with steam cooling in the gas turbine. STAG combined-cycle systems are designated with a code system to capture key system param- eters: the first digit is the number of gas turbines per steam turbine, the second is not significant for heavy-duty gas turbines, and the third, fourth, and fifth places contain the gas turbine frame size and model letter(s). An example is a STAG 207FA, where two model 7FA gas turbines are applied in a “two-on-one” configuration with a single steam turbine. One-on-one configura- tions are further qualified as being multi-shaft (MS), or single shaft (SS). An example is a STAG 109E MS, indicating that the combined- cycle contains a single frame 9E gas turbine gen- erator and a separate GE steam turbine genera- tor on two different shafts. Two or more steam turbine choices are avail- able for each STAG system. Units with different STEAM TURBINES FOR STAG ™ COMBINED-CYCLE POWER SYSTEMS M. Boss GE Power Systems Schenectady, NY
Transcript
1
GER-3582E
ABSTRACTA broad steam turbine product line is avail-
able for the wide range of STAG combined cyclesystems, depending upon the number of gas tur-bines employed, gas turbine characteristics,steam cycle/HRSG selection, and site specificspace, cooling and operating considerations.The addition of the H technology to the STAGcombined cycle systems is described.Thermodynamic design aspects are discussed,and useful screening tables are presented forsteam turbine selection. Application considera-tions of reheat versus nonreheat, multi-shaft ver-sus single shaft and axial exhaust versus downexhaust are reviewed. Unique design featuresfor sliding pressure, boiler following operationare described, as well as GE steam turbine prod-uct line design features which enhance installa-tion, maintainability and reliability.
INTRODUCTIONGE has built over 200 steam turbine-genera-
tor units totaling more than 15,000 MW ofcapacity for application in both reheat and non-reheat combined-cycle power plants. Last-stagebuckets up to 40 inches/1016 mm at 3600 rpmand 42 inches/1067 mm at 3000 rpm have beenapplied, allowing for compact High PowerDensity™ (HPD) arrangements which comple-ment recent increases in GE gas turbine sizes.The use of longer last-stage buckets permits amore cost-effective, compact HPD design with aminimum number of casings, while still provid-ing ample exhaust annulus area for optimalthermal efficiency.
GE offers a complete line of STAG™ (SteamAnd Gas) combined-cycle steam turbines whichare matched to the exhaust energy of one ormore GE gas turbines and Heat Recovery SteamGenerator(s) (HRSGs). HRSGs are used to con-vert the gas turbine exhaust into useful steamfor the bottoming portion of the combined-cycle. Flexibility is incorporated to allow thesteam turbine design to be optimized for site-related parameters such as process extractions
and condenser pressure.The trend toward higher gas turbine firing
and exhaust temperatures has made reheat com-bined-cycles common. These reheat steamcycles, with advanced gas turbine designs, aretermed Advanced Combined-Cycles (ACC). Astructured, modular approach to the combined-cycle steam turbine product line allows applica-tion of nonreheat steam cycles with advancedgas turbines as well. GE STAG steam turbinedesigns can accommodate one, two and threepressure steam cycles. The data in this paper ispresented based on three pressure nonreheatcycles for gas turbines with approximately 1000F/538 C or lower exhaust temperature, andthree pressure reheat steam cycles for ACCs uti-lizing the 6FA, 7EC, 7FA, 9EC, and 9FA gas tur-bines.
The latest addition to the GE STAG productline involves a platform for the 7G, 9G, 7H and9H STAG systems. These machines are com-bined-cycle technology that integrate the gasturbine, steam turbine and generator into aseamless system, where each component is opti-mized for the highest level of performance. Thedata in this paper describes the advancemachine platform based on a three pressurereheat steam cycle. The 7H and 9H STAGadvanced machines are additionally integratedwith steam cooling in the gas turbine.
STAG combined-cycle systems are designatedwith a code system to capture key system param-eters: the first digit is the number of gas turbinesper steam turbine, the second is not significantfor heavy-duty gas turbines, and the third,fourth, and fifth places contain the gas turbineframe size and model letter(s). An example is aSTAG 207FA, where two model 7FA gas turbinesare applied in a “two-on-one” configuration witha single steam turbine. One-on-one configura-tions are further qualified as being multi-shaft(MS), or single shaft (SS). An example is aSTAG 109E MS, indicating that the combined-cycle contains a single frame 9E gas turbine gen-erator and a separate GE steam turbine genera-tor on two different shafts.
Two or more steam turbine choices are avail-able for each STAG system. Units with different
STEAM TURBINES FOR STAG™ COMBINED-CYCLEPOWER SYSTEMS
M. BossGE Power SystemsSchenectady, NY
exhaust annulus areas are offered to permitoptimization to site-specific cooling conditionsand project specific economic evaluation crite-ria.
GE steam turbines for STAG plants are avail-able for a wide range of applications up to 1800psig/124 bar and 1050 F/566 C for both reheatand nonreheat cycles. Automatic extractionmodules are available for nonreheat units incogeneration combined-cycles. Each unit isspecifically designed for combined-cycle, slidingpressure operation. Numerous features areincluded for optimum performance and highestreliability with minimum installation, operationand maintenance costs. Recognizing the fre-quent and rapid starting-and-loading dutyrequired of many combined-cycle units, STAGturbines incorporate design geometries thatenhance suitability for high cyclic life withoutcompromise of base load capability. STAG steamturbines benefit from GE’s large operating fleetexperience. Design tools and features developedfor fossil, nuclear and industrial applications allcontribute in unique ways to the STAG steamturbine product line. The result is GE’s leader-ship in sustained efficiency, reliability, maintain-ability and extended life for combined-cyclesteam turbines.
STEAM TURBINE APPLICATIONTO STAG PLANTS
STAG StructureGE has established a structured line of steam
turbines to meet the requirements of the com-bined-cycle market. Principally focused on cur-rent GE gas turbine models, an array of steamturbine components have been developed toform a comprehensive product line. Sufficientflexibility has been retained to allow variationsin product offerings to accommodate cogenera-tion applications, STAG “add-ons” (conversionsof simple cycle plants to combined-cycle), ormatch the equipment of other gas turbine sup-pliers.
Table 1 lists the GE gas turbines commonlyapplied in combined-cycle applications. Models6B and 6FA utilize gear-driven generators andare applied at both 50 and 60 Hz. LM6000 desig-nates an aircraft derivative gas turbine which isalso applied at both 50 and 60 Hz. The exhaustcharacteristics and approximate output are list-ed for ISO standard conditions, with an indica-tion of the steam cycles available. Gas turbineswith exhaust temperatures of approximately1000 F/538 C or lower are applied in nonreheatcycles. Gas turbines with exhaust temperaturesabove 1000 F/538 C are routinely applied inreheat cycles; however, steam turbines for non-reheat cycles are also available for these applica-tions.
Table 2 presents approximate gross poweravailable from combined-cycles based on the gasturbines listed in Table 1. Gas turbine outputdiffers from the power listed in Table 1, due tothe effect of increased exhaust pressure dropassociated with the HRSG. A three-pressureHRSG is used for both reheat and nonreheatsteam cycles. The steam turbine output variesconsiderably depending upon the exhaust pres-
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Table 1GE GAS TURBINE EXHAUST CHARACTERISTICS
Hz GT MODEL EXH TEMP EXH TEMP FLOW FLOW GTG STAG CYCLEDEG F DEG C K LB/HR KG/HR
sure and the selected steam turbine configura-tion. More detailed information is provided inTables 4 through 8.
Steam Turbine Exhaust Size SelectionThe steam leaving the last stage of a condens-
ing steam turbine can carry considerably usefulpower to the condenser as kinetic energy. Theturbine designer needs to select an exhaust areafor a particular application that provides a bal-ance between exhaust loss and capital invest-ment in turbine equipment. For an optimumselection to be made, the turbine designerneeds to understand the present worth value ofoutput and efficiency. Efficiency may beexpressed in terms of fuel cost, steam turbineheat rate, or combined-cycle heat rate. Anyother relevant data, such as anticipated capacityfactor, or a weighting of various anticipated load
points, should be specified to the turbinedesigner in requests for quotations.
Figure 1 is an illustrative exhaust loss curvefor a condensing steam turbine. Exhaust loss,expressed in specific energy terms, is plottedversus the velocity of the steam passing throughthe exhaust annulus (VAN). The dashed curve isleaving loss, the kinetic energy carried by theexhaust flow assuming uniform axial flowthrough the annulus. At low velocities, the totalexhaust loss is much greater than the axial leav-ing loss component, due to internal off-designinefficiency and off-angle effects. Most applica-tions are selected to operate at intermediateannulus velocities, about 500 to 1000 ft/s (150to 300 m/s). Other losses come into play at highvelocities - above 1000 ft/s (300 m/s).
Annulus velocity is approximated by the conti-nuity equation, VAN=Q/A; where Q is the vol-ume flow and A is the exhaust annulus area.
Volume flow, Q, is also the product of mass flowand the specific volume. Velocity is then directlyproportional to the specific volume for a con-stant mass flow. For convenience, specific vol-ume can be approximated as the reciprocal ofexhaust pressure. Annulus velocity is theninversely proportional to both exhaust pressureand exhaust annulus area, as indicated in Figure1.
The thermodynamic optimum value of annu-lus velocity, VAN, is the lowest point on theexhaust loss curve. The band labeled “economicoptimum” reflects that, historically, it has notbeen economically justifiable to invest in suffi-cient exhaust area to operate at full load at thebottom of the curve. Sizing the turbine in thisway also may cause excessively low VAN, and con-sequently high exhaust loss, at part load. Asthermal efficiencies have been continuouslydriven upward by economic and environmentalconsiderations, this “economic band” has in factshifted closer toward the thermodynamic opti-mum.
Exhaust sizing considerations are critical forany condensing steam turbine, but particularlyso for combined-cycle applications. There areusually no extractions from the steam turbine,since feedwater heating is generally accom-plished within the HRSG. Generation of steamat multiple pressure levels (intermediate pres-sure and/or low pressure admissions to the tur-bine downstream of the throttle) increases themass flow as the steam expands through the tur-bine. Mass flow at the exhaust of a combined-cycle unit in a three-pressure system can be asmuch as 30% greater than the throttle flow. Thisis in direct contrast to most units with fired boil-ers, where exhaust flow is about 25% to 30% lessthan the throttle mass flow, because of extrac-tions from the turbine for multiple stages of
feedwater heating. The last turbine stage of acombined-cycle unit can generate up to 15% ofthe unit’s power, compared to 10% or less forthe last stage of a typical unit with feedwaterheating extractions.
Combined-cycles are influenced by ambientconditions. Steam turbine exhaust volume flowand annulus velocity are affected in two ways:both directly in mass flow to the condenser(GT/HRSG steam production) and volume flowas influenced by exhaust pressure. For example,at low ambient temperatures, gas turbine outputand HRSG steam production can be consider-ably increased above plant rating point.Condenser (exhaust) pressure, is directly relat-ed to ambient air or cooling water temperature.Condenser pressure is expected to be lowest atlow ambient air/cooling water temperature, andexhaust annulus velocity will be the highest.
Provisions need to be considered in design ofthe plant’s control philosophy to maintain anexhaust pressure/exhaust velocity within reason-able limits.
At high ambients, gas turbine airflow andHRSG steam production may be reduced, there-by lowering mass flow to the steam turbine, anddecreasing VAN. At the same time, high ambientair temperature and/or high circulating watertemperature increases exhaust pressure, whichfurther reduces VAN because of decreased specif-ic volume. This may be somewhat offset by alower exhaust pressure, resulting from thereduced condenser duty, associated with lowersteam flow to the condenser. These aspectsshould underscore the importance for the tur-bine designer to have an understanding of thecombined-cycle operation envelope, such thatthe steam turbine is designed for satisfactoryoperation throughout the required range.Other variables such as supplementary exhaustfiring in the HRSG, and variations in processsteam flow for cogeneration applications mustalso be considered in exhaust sizing.
Table 3 lists the current family of GE last-stagebuckets (LSB) for use in 50 and 60 Hz com-bined-cycle steam turbines. Of note are severalbuckets suitable for high back pressure opera-tion. Capability for full load operation at 15inches HgA/381 mm HgA is achieved with the20H and 22H buckets, and up to 20 inchesHgA/508 mm HgA with the 13H LSB. The avail-ability of these designs provides flexibility in sta-tion siting. Plants using air-cooled condensersmay require the additional operational flexibili-ty afforded by these rugged high back pressuredesigns.
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Figure 1. Illustrative exhaust loss curve
Figure 2 illustrates six representative configu-rations and the effect of exhaust end selectionon steam turbine output for a range of exhaustpressures. It is clear from these curves that theunits with largest annulus area have the best per-formance at low back pressures. The curvescross over around 2 inches HgA/51 mm HgA.The units with smaller exhaust ends have betterperformance at high back pressure. Steam tur-bine selection must balance output across theexpected operating range against the equip-ment investment.
It should be apparent that the best steam tur-bine choice for any combined-cycle is stronglyinfluenced by the site exhaust pressure, which,in turn, is largely determined by the tempera-ture of the cooling media.
Nonreheat Cycle Steam ConditionsThe exhaust temperature of the 6B, 7EA and
9E gas turbines listed in Table 2 is approximate-
ly 1000 F/538 C and supports a main steamthrottle temperature of about 950 F/510 C. Thelower exhaust temperature of the aero-derivativeLM6000 supports a main steam throttle temper-ature of about 850 F/454 C.
Throttle pressure is selected based upon thesize of the steam turbine, in conjunction witheconomic considerations. Higher throttle pres-sures provide superior thermodynamic perfor-mance for multiple pressure HRSGs. However,higher pressure reduces steam turbine inlet vol-ume flow, which makes the nozzles and bucketsshorter, and increases stage leakage losses as afraction of total flow. The result is that practicalbenefits of increased throttle pressure aregreater for larger units than smaller STAGplants with multi pressure steam cycles.Detailed studies of pressure optimization haveresulted in selection of 850 psig/59 bar forsmaller STAG plants with multiple pressuresteam cycles. Units in the intermediate rangefrom 40 MW to 60 MW utilize a throttle pressure
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Table 3LAST STAGES AVAILABLE FOR COMBINED-CYCLE STEAM TURBINES
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Figure 2. Steam turbine wheel output as a function of exhaust pressure and exhaust size, reheatSTAG1400 psig 1000F/1000F (96 BAR 538C/538C) steam conditions
Figure 2a 107FTA 60 Hz Steam Turbine
Figure 2c 207FA 60 Hz Steam Turbine
Figure 2e 206FA 60 Hz Steam Turbine
Figure 2b 109FA 50 Hz Steam Turbine
Figure 2d 207FA 50 Hz Steam Turbine
Figure 2f 206FA 50 Hz Steam Turbine
of approximately 1000 psig/69 bar. 1250psig/86 bar is typical for steam turbine ratingsgreater than 60 MW.
Since sliding pressure operation with full arcadmission is employed, the design point throttleflow and pressure must be set with considerationof the maximum throttle flow to be seen by thesteam turbine. This ensures that the casing inletis not subjected to pressure greater than themaximum allowable. For example, the designthrottle pressure may be set to 1200 psig/83 barfor a 120 MW unit, so that the throttle pressurefor flows greater than design flow falls within the1250 psig/86 bar nominal limit for the casinginlet.
The nonreheat cycles employ IntermediatePressure (IP) and Low Pressure (LP) admissionsto the steam turbine, downstream of the throt-tle. Typically, no extractions are taken for feed-water heating. If site conditions require a steamturbine extraction due to HRSG/stack mini-mum temperature requirements, provisions aremade within the low pressure turbine design toaccommodate feedwater heating extraction(s).In general, the design approach for combined-cycles is to achieve an HRSG stack temperaturewhich is as low as possible, extracting as muchgas turbine exhaust energy as possible to maxi-mize cycle efficiency. Occasionally, a concernwith high sulfur gas turbine fuels is acid conden-sation on low temperature heat transfer sur-faces. In these cases, an LP turbine extractionmay be used to heat feedwater above the aciddew point prior to feedwater supply to theHRSG economizer.
Reheat Cycle Steam ConditionsThe exhaust temperatures of the 6FA, 7EC,
7FA, 9EC, 9FA 7G, 7H, 9G and 9H gas turbinesare sufficiently high to justify the use of a reheatcycle. Figure 3 compares reheat and nonreheatexpansions for initial conditions of 1450 psigand 1000F (100 bar and 538C). The first portionof both expansions, A-B, is the same. In the non-reheat case, the expansion continues unbrokento the condenser, B-C, with a relatively highmoisture content in the low pressure turbinesection. In the reheat case, the steam exhaustfrom the high pressure turbine, B, is returned tothe HRSG, where it is reheated back to the ini-tial temperature, D. The remaining expansion,D-E, is therefore hotter and drier than the non-reheat case.
The reheat cycle benefits thermodynamic per-formance by adding heat to the steam cycle at ahigher average temperature than the nonreheat
cycle, and by reducing moisture loss in the lowpressure section. The drier low pressure sectionexpansion reduces the potential for last-stagemoisture erosion. The gain from the reheatcycle is seen as greater steam turbine output forthe same heat to the HRSG. Reduced heatrejected to the condenser reduces the size of thecooling system and the amount of cooling flowrequired.
Analysis has shown that initial steam condi-tions of 1450 psig, 1000F with reheat to 1000F(100 bar, 538C with reheat to 538C) are an eco-nomical design, based on moderate economicevaluation parameters. 1800 psig, 1000F, withreheat to 1000F (124 bar, 538C with reheat to538C) is attractive for some of the larger STAGcycles, when the steam turbine rating is 125 MWor greater. Like nonreheat cycles, the actualdesign point pressure should be set with consid-eration of the maximum throttle flow/throttlepressure for the steam turbine across the operat-ing range.
A three-pressure HRSG permits selection of areheat pressure that optimizes heat addition tothe steam cycle, while also achieving maximumheat recovery within the HRSG. The three-pres-sure reheat combined-cycle is shown schemati-cally in Figure 4. Two secondary admissions (IPand LP) of steam from the HRSG at 350 psig/24bar and 40 psig/3 bar are employed. The IPadmission is usually piped to the cold reheatline, downstream of the high pressure turbine
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Figure 3. Comparison of nonreheat andreheat expansions
section. This IP admission steam then flowsthrough the reheater and is seen by the steamturbine as an increased mass flow, compared tothe high pressure turbine section flow. Since theIP steam cannot reach the condenser withoutpassing through the combined reheat valves, noadditional protective valving is required for thesteam turbine. The LP admission is piped intothe steam turbine casing at an appropriate stagelocation in the steam path, which sets the LPdrum pressure in the HRSG. Two separatehydraulically-operated butter fly valves areinstalled in the LP admission steam line nearthe turbine to provide redundant lines ofdefense against overspeed. A similar approach isused for IP admissions on nonreheat units withthree pressure steam cycles.
The H technology use a three pressure reheatsteam cycle with initial steam conditions ofeither 2400 psig 1050F/1050F (583 C/583 C) or1800 psig/124 bar 1050F/1050F (583 C/583 C).The higher initial pressure steam system givesthe higher performance and results in a multi-casing design with a short inner shell over thefirst few HP stages. The 1800 psig/124 bar initialpressure allows for an optimized system withlower fuel cost or a mid-range peaking dutycycle.
The 7H and 9H gas turbines utilize theadvanced technology, closed-circuit steam-cool-ing systems. The gas turbine cooling system isintegrated in two key areas as follows:
• Steam is supplied from the high pressure(HP) steam turbine exhaust and the HRSGintermediate pressure (IP) evaporator tothe closed circuit system that cools the gasturbine stage 1 and 2 nozzles and buckets.
The cooling steam is returned to the steamcycle in the hot reheat line. Thus, the cool-ing system operates in parallel with thereheater.
• Air extracted from the gas turbine com-pressor discharge is cooled externally priorto readmission to cool the wheels in thehigh-pressure stages of the compressor.Water from the discharge of the IP econo-mizer in the HRSG cools the cooling airand subsequently heats the natural gasfuel.
STAG STEAM TURBINEPRODUCT STRUCTURE
PerformanceTables 4 through 9 present the performance
of the structured product line of steam turbinesfor use in the STAG systems listed in Table 2.Approximate steam turbine output is listed forvarious combinations of steam turbine configu-rations and exhaust pressures. Table 4 listsSTAG plants with steam turbines less than 60MW, with relatively low steam conditions, forboth 50 and 60 Hz units.
Table 5 covers the STAG plants whose steamturbines have ratings between 40 MW and 60MW, while Table 6 considers the larger nonre-heat units greater than 60 MW.
Tables 7 and 8 provide data for advancedcombined-cycles. 50 Hz reheat steam turbineswith the advanced 6FA, 9EC and 9FA gas tur-bines are listed in Table 7. Table 8 lists 60 Hzreheat steam turbines with the advanced 6FA,7EC and 7FA.
Tables 4 through 8 give a suggested turbinetype in terms of last-stage bucket size and num-ber of low pressure turbine flows for differentcondenser (exhaust) pressures. The relationbetween exhaust annulus area and exhaust pres-sure can be clearly seen by following across arow for a particular STAG model. In most cases,more than one steam turbine design is suggest-ed for a combination of STAG model andexhaust pressure. The units with larger annulusareas yield additional output. In these cases, thechoice requires consideration of the annual vari-ation in exhaust pressure level, the anticipatedcapacity factor of the plant and the difference inthe capital cost of the units.
The H combined cycle power generation sys-tems are designed to achieve 60% net plant effi-ciency. The operational and performance char-
acteristics for the H technology gasturbine/combined cycle products are summa-rized in Table 9. The significant efficiencyincreases over the F technology product line areachieved by advancing the operational condi-tions — pressure ratio and firing temperature.These advantages are achieved with the STAG109H and STAG 107H systems, while maintain-
ing single-digit NOx and CO capability.
Casing ArrangementsSchematics of available STAG steam turbine
casing arrangements are shown in Figures 5through 7.
Nonreheat Multi-shaftFigure 5 shows nonreheat configurations for
multi-shaft STAG applications. The steam tur-bine generator is completely independent of thegas turbine generators(s). Axial flow exhaustsare available for single flow applications. Shownin Figure 5A, the axial arrangement permitslocating the condenser near the same level as
the turbine, reducing foundation height andpermitting slab type construction of the founda-tion. With the condenser at the turbine exhaust,the generator is driven from the high pressureend of the turbine. A flexible expansion jointbetween the turbine exhaust and the condensercan accept the axial thermal growth, permittingflexible support of the turbine exhaust. Thehigh pressure end of the turbine is fixed to thefoundation. The thrust bearing is located withinthe turbine front standard (high pressure endsupport), which allows for maintenance of closeaxial clearances in the high pressure stages.Figure 6 illustrates a cross section drawing of asingle casing unit with an axial exhaust.
Large axial exhaust units utilizing last-stagebuckets (LSB) greater than 30 inches (762 mm)are fixed to the foundation at the exhaust end.The turbine front standard accommodates axialexpansion of the stationary parts with either aflexible support arrangement or a sliding baseplate support. With single casing axial exhaustunits, the thrust bearing is located in the frontstandard, close to the high pressure stages.
Figures 5B and 5C illustrate single flow anddouble flow down exhaust arrangements. Inthese cases, the exhaust must be keyed to thefoundation to minimize the shear which wouldotherwise occur in the condenser expansionjoint. The generator is driven in the traditionalarrangement from the low pressure end of the
Figure 5. Nonreheat steam turbine arrange-ments for multi-shaft STAGA. Single-casing, axial exhaustB. Single-casing, down exhaustC. Two-casing, down exhaust
turbine. The condenser is directly below the tur-bine exhaust. The turbine front standard is sup-ported with either a flex leg support or a slidingsupport arrangement. The thrust bearing islocated in the turbine front standard. The dou-ble flow configuration is illustrated in cross sec-tion in Figure 7.
Nonreheat Single ShaftIn single shaft STAG configurations, one
steam turbine and one gas turbine drive a com-mon generator. Nonreheat single shaft arrange-ments are shown in Figure 8. The gas turbine iscoupled to the main generator coupling, whilethe steam turbine drives the generator from theopposite (collector) end. Each turbine has itsown thrust bearing and overspeed protection. Aflexible coupling, which accepts limited axialmotion, is located between the generator andthe steam turbine. Keying and expansionarrangements differ in some cases, from multi-shaft arrangements, due to limitations in theamount of axial expansion which can be accom-modated by the flexible coupling.
Nonreheat single shaft STAG steam turbinesare designed for removal when the generatorrotor is pulled from the stator for inspection ormaintenance. Piping connections are flanged,rather than welded, to facilitate removal.
Reheat Multi-shaftFigure 9 shows arrangements for multi-shaft
reheat STAG units, where the steam turbinedrives its own generator. Figure 9A illustrates acompact single casing configuration, used withmoderate steam conditions and megawatt rat-ings. GE’s experience with this configurationdates to the 1950s. It has most recently beenapplied to multi-shaft 107FA units at an air-
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Figure 8. Nonreheat steam turbine arrange-ments for single shaft STAGA. Single-casing, axial exhaustB. Single-casing, down exhaustC. Two-casing, down exhaust
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Figure 7. Nonreheat, double flow down exhaust unit
cooled condenser site. A cross section of a singlecasing reheat unit for STAG application isshown in Figure 10.
The single flow units with two casings, Figures9B and Figure 9C, are built with a separate highpressure (HP) section and a combined interme-diate pressure and low pressure (IP/LP) section.This arrangement is compact and clean, with noneed for crossover or cross-around pipingbetween the two turbine casings. This arrange-ment is shown in cross section in Figure 11.
The multi-shaft double flow exhaust arrange-ment is shown in Figure 9D. Conventionalreheat design practice is followed with the lowpressure turbine section keyed to the founda-tion near its center, and accommodation of thethermal expansion at the turbine front stan-dard.
Reheat Single ShaftFigure 12 shows arrangement sketches for sin-
gle shaft reheat STAG units in which the gas andsteam turbines drive a common generator.These advanced machines are much more high-ly integrated than earlier generations of nonre-heat single shaft STAG units. The flexible cou-pling of the steam turbine to the generator iseliminated, and a single thrust bearing servesthe entire turbomachine. The generator is driv-en from one end only, which allows easy accessfor generator rotor removal. The commonthrust bearing is located in the gas turbine com-pressor inlet, which is rigidly keyed to the foun-dation, as are the steam turbine front bearingstandards and exhaust hoods. With completemechanical integration, coordinated startingand loading of the gas turbine and steam tur-bine are facilitated, and operation is simplified.Single shaft configurations also offer maximumreliability and compact plant arrangements.
Figure 12A shows the single flow arrange-
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Figure 10. Single-casing reheat turbine with axial exhaust
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Figure 9. Reheat steam turbine arrangementsfor multi-shaft STAGA. Single-casing, axial exhaustB. Two-casing, axial exhaustC. Two-casing, single flow down
exhaustD. Two-casing, double flow down
exhaust
ment, consisting of an HP section and a com-bined IP and LP section. There is no need forcrossover or cross-around piping, since the twocasings are interconnected by the HRSGreheater and reheat steam piping. The HP cas-ing and the rotor expand away from the frontstandard, maintaining close axial clearances,while the IP casing grows from the fixed exhaustcasing. Special care is exercised in the design to
accommodate the relatively large differentialexpansion between the hot and cold conditionsin the IP section, and to provide for axial move-ment between the HP exhaust and LP turbine,since both are independently keyed to the foun-dation.
Figure 12B illustrates the design for a singleshaft reheat STAG unit with a double flow LPturbine section. Here the two casings are anopposed-flow HP/IP section and a double flowLP. As with the single flow unit, both casings areanchored to the foundation. Provision is madefor relatively large movement between the twosteam turbine casings and between the rotatingand stationary parts in the LP.
The single shaft reheat STAG unit’s uniqueintegration has the benefit of not requiringcombined reheat valves to protect the combinedgas/steam turbine-generator from overspeed.The large rotor inertia of the combinedmachine and the power required to drive thegas turbine compressor act as an energy sink,allowing the full volume of the steam in thereheater and the hot and cold reheat piping toexpand through the reheat turbine to the con-denser without causing speed to rise above theemergency overspeed set point. Safety reliefvalves are not required for the reheater, simplify-ing plant piping and reducing cost.
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Figure 12. Reheat steam turbine arrangementsfor single shaft STAGA. Two-casing, down exhaust,
single flowB. Two-casing, down exhaust,
double flow
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Figure 11. Two-casing reheat turbine with single flow down exhaust
A single shaft reheat STAG arrangement witha double flow low pressure section is shown inFigure 13. Figure 13 corresponds to the arrange-ment of Figure 12B. The steam turbine compo-nents to the right of the gas turbine inletplenum are the front standard, the opposed-flow HP/IP section, mid-standard, crossoverpipe to the LP section, LP turbine section andgenerator. Eight of these units are presentlyoperating for TEPCO in Japan in a 2800 MW,109FA STAG installation.
FEATURES FOR REDUCED INSTALLATION AND
MAINTENANCE COSTSGE steam turbines for STAG plants have been
specifically designed for combined-cycle applica-tions. They incorporate a number of special fea-tures for optimum installation, operation andmaintenance costs.
Stop-and-Control Valve ArrangementSteam is admitted to the turbine through one
or two combined stop-and-control valves, whichare piped to the lower half of the turbine casing.These combined valves, specifically designed forcombined-cycle applications, are similar to com-bined reheat stop-and-intercept valves oftenused with traditional units. The control valveand main stop valve are contained within thesame valve casing, and the valve disks share thesame seat. The actuators, stems and disks areotherwise completely independent for controland overspeed protection. Each valve is testableon-line via an operator command from the con-trol room. Normal operating mode is controlvalve full open, with the throttle pressure slidingup or down as HRSG steam production varies.The control valve is used for speed/load andinlet pressure control during start-up and shut-
down. A combined stop-and-control valve isshown in Figure 14.
Low-Profile InstallationThe steam turbines applied in the nonreheat
single shaft STAG systems and small-to-mediumsize multi-shaft STAG systems can be configuredin single casing, single flow axial exhaust units.The location of the condenser at the end of thesteam turbine can reduce the foundationheight, with possible savings in the foundation,the crane support structure, and the steam tur-bine building (for indoor installations).
The round axial exhaust connection is a bolt-ed flange, which is typically connected to atransverse condenser via a flexible expansionjoint. The axial exhaust portion of the turbinecasing carries a cone assembly, which containsthe exhaust end turbine bearing. The bearing isaccessed via a hatch in the upper half exhaustcasing. The bearing housing is vented to theatmosphere by an inlet pipe in the lower halfexhaust casing and a discharge pipe in theupper half. A recent STAG 107EA multi-shaftinstallation is shown in Figure 15. The axial
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Figure 14. Combined stop-and-control valveoutline
GT19644
Figure 13. Reheat single shaft gas and steamturbine-generator
exhaust steam turbine at the right of the photo-graph is shown with the condenser expansionjoint at center. The large steam ductwork at cen-ter and left connects the axial exhaust to an aircondenser. The steam turbine auxiliaries are inthe foreground.
Support and axial alignment of the turbineare accomplished by one of two means. Anexhaust end flex leg and a foundation-keyedfront standard may be used. Alternatively, a flexleg or sliding front standard may be required forunits with LSB greater than 30 inches (762mm), in conjunction with a foundation-keyedexhaust casing. A condenser expansion joint isrecommended both for units with flexibleexhaust supports and units which are keyed atthe exhaust end.
Assembled ShipmentSTAG steam turbines are designed to meet
the objectives of low installation and mainte-nance costs, short shipment cycles, compact size,high efficiency and modular construction.Wherever possible they are shipped assembled,complete with rotor, diaphragms and front stan-dard, so that site work is minimized. Piping isfactory-fitted on packaged units, reducing instal-lation cycle time and field piping work.
Axial exhaust, single flow nonreheat unitswith last-stage buckets up through 30 inch-es/762 mm are shipped assembled. Smallerdown exhaust units, up through 20-inch/508mm LSB, can be shipped assembled as well.High pressure and combined HP/IP sections fortandem compound units can be shipped assem-bled, with the steam path completely installed.
Assembled shipment reduces the number ofparts to be handled on-site. Inventory require-
ments and lost or damaged parts are minimized.The units are assembled by trained factory per-sonnel who are thoroughly familiar with steamturbine assembly. Critical, time-consuming taskssuch as fit-up and clearance checks are per-formed in the controlled environment of thefactory, where ready access is available to toolingand engineering support. A recent 207FA instal-lation significantly reduced the steam turbine-generator centerline installation cycle by order-ing the HP/IP sections as factory-assembledmodules.
MaintainabilitySince no shell-mounted valves are used,
removal of the turbine upper half is facilitated.With the combined stop-and-control valvearrangement, a minimum number of valve cas-ings need to be opened for valve inspections.
A traditional GE design feature for maintain-ability is vertical orientation of the main steamvalves. This approach allows for rapid disassem-bly and assembly of these important valves dur-ing routine inspections, utilizing the stationcrane.
Since STAG inlet conditions are typically lessthan or equal to 1800 psig/124 bar, single shellconstruction is used, simplifying disassembly,alignment and reassembly. With the exceptionof crossover piping connections on some twocasing units, all main steam piping connectionsare made to the lower half casings.
CYCLIC DUTY FEATURESRecognizing the unique ability of gas turbines
to be stopped and started easily and quickly,STAG steam turbines incorporate a number ofspecial features which ensure compatibility withcyclic duty without compromise of base loadcapability.
The use of wheel-and-diaphragm constructionallows use of relatively small shaft diameters inthe vicinity of high temperature stages, minimiz-ing thermal stresses in this most critical rotorsection during startup, load changes and shut-down. Large fillets are employed between thewheels and the rotor body to reduce thermalstress concentrations.
Axial clearances are carefully selected to allowfor large differential expansions between rotorand casing during rapid start-up and shutdowns,without compromising interstage leakage. Eachstage is individually aligned to set clearances.
Coupling spans are designed with sufficientlength to avoid bearing unloading, which can
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Figure15. Axial exhaust steam turbine in aircondenser application
occur when bearing support elevation changesdue to rapid steam temperature swings orchanges in exhaust pressure. Bearings are fre-quently fitted with tilting pad designs to maxi-mize misalignment tolerance, ensuring stableoperation and minimal shaft vibration.
Shells are designed with optimum propor-tions between flange and wall thicknesses.Surface geometries are controlled to permit uni-form heat transfer and reduce stress concentra-tions during cyclic changes in critical areas.Thermal gradients between first-stage nozzlearcs are eliminated with full arc admission. Sincea governing stage is not required with full arcadmission, the first-stage wheel is reduced insize, reducing the thermal inertia of the rotor.
GE DESIGN FEATURESAll GE steam turbines incorporate design fea-
tures developed from across GE’s broad steamturbine product line. This contributes to theiroutstanding record of reliability, sustained effi-ciency and long life.
Combined-cycle steam turbines have inherentreliability advantages compared to more tradi-tional applications. STAG steam turbines oper-ate at modest steam conditions which permitsimpler designs, are smaller in size with less ther-mal expansion, and many drive simple air-cooled generators. The result is a distinct advan-tage leading to outstanding reliability - greaterthan 97%.
Wheel-and-Diaphragm ImpulseDesign
GE uses an impulse stage design whichrequires fewer stages than would be used for areaction steam path. This permits the use ofwheel-and-diaphragm construction. The movingbuckets are carried in the rims of wheelsmachined from a solid rotor forging. The highcentrifugal stress of the bucket attachment areais away from the rotor surface, where thermalstress is highest. The result is separation of theareas with highest thermal and centrifugalstresses. The fixed nozzles are carried in weldednozzle diaphragms, which seal on the shaft atthe minimum diameter, using a rub tolerantspring-backed packing design
The alternative reaction design is usually exe-cuted in drum rotor construction, in which themoving blades are inserted in the surface of thedrum, concurrent with the high thermal stressfield. The fixed blades seal on the drum surfacenear the steam path diameter.
The wheel-and-diaphragm construction pro-vides the benefit of minimal interstage loss. Therelatively small shaft diameters minimize tran-sient thermal stresses and enhance starting andloading characteristics.
Steam Turbine AdmissionArrangement
Steam turbines for power-generation-onlySTAG applications are designed for operation inthe boiler (HRSG) following mode, where thesteam pressure varies with load. The off-shellcombined stop-and-control valve is normally fullopen. Figure 16 shows a cross section of a com-bined stop-and-control valve. The control valveis used for start-up, inlet (HRSG) pressure con-trol at light loads, and as the first line of defenseagainst overspeed. This sliding pressure modedoes not require multiple inlet valves for partload efficiency. Since the steam cycle is onlyapproximately one-third of the STAG plant’spower output, operators can use the gas tur-bines to contribute to grid frequency control.This simple, single admission inlet is shown for acombined HP/IP section in Figure 17. Heatingand cooling of the admission parts are uniform,thermal stresses are minimized, and rapid start-ing, loading and unloading are facilitated.
For cogeneration applications, it may bedesirable to use a more conventional inletarrangement with shell-mounted control valves.
This allows operation across the steam turbineload range at rated pressure with good part loadefficiency. Considerations for application of aconventional inlet arrangement are the expect-ed variations in steam turbine high pressure sec-tion flow, and any interconnection of the STAGmain steam header with the steam host. Forexample, a STAG main steam header may betied to multiple paper mill boilers, precludingsliding throttle pressure operation.
A full arc admission design for sliding pres-sure operation can, however, be used in cogen-eration STAG units with automaticextraction(s), provided two parameters are care-fully considered. The anticipated variation inhigh pressure section flow must be within a rea-sonable range, and the HRSG floor pressuremust be set high enough such that low throttleflow/throttle pressure conditions do not causeoverheating of the high pressure stages. If HPsection flow variations are large, then a conven-tional partial arc admission arrangement withmultiple control valves may be preferable. Notethat a unit with a conventional inlet arrange-ment may also be operated in sliding pressuremode with all control valves wide open.
An example of a packaged unit with multipleinlet control valves and an automatic extractionfor a cogeneration STAG application is shown inFigure 18.
Figure 18. Packaged cogeneration unit with multiple inlet control valves and automatic extraction
To CrossoverTo LP
HP IP
HotReheat
ColdReheat
MainStream
Centerline SupportAll main structural turbine parts and station-
ary steam path parts are supported at or nearthe turbine centerline. This arrangement mini-mizes the effect of distortion and misalignmentcaused by temperature changes and maintainsradial clearances. During start-ups or rapid loadswings, turbine shells are free to expand axiallyand radially, while the diaphragms remain con-centric with the shaft. Since alignment adjust-ment is straightforward with centerline support,time spent in installation is minimized.
Horizontal Joint FlangeThe horizontal joint flanges are designed with
optimum proportions, confirmed by extensivefinite element modeling. Shell support and bolt-ing flange requirements are integrated into thecasing design. The horizontal joint faces are pre-cision machined to ensure uniform contact andsealing surfaces between upper and lowerhalves. In general, the entire shell is supportednear the flange level. The internal componentsare supported very close to the flange level tominimize distortion and alignment changeeffects.
Moisture RemovalMoisture separation features are applied
throughout the wet regions of the steam path toimprove efficiency and to reduce the potentialfor moisture erosion. GE’s extensive designexperience with wet stage designs benefitstoday’s combined-cycle turbines. Several designfeatures applied to latter stages such as groovedbuckets, flame hardening, and collectiongrooves in the stationary steam path allow GE to
confidently apply long last-stage buckets in non-reheat STAG applications. Figure 19 illustrateskey moisture removal design features.
Steam PathFor effective resistance to corrosion and ero-
sion, the steam path is constructed largely of 12chrome steels. Rugged, impulse-type turbinebuckets utilize external dovetails for attachmentto the rotor wheels and protection of the wheelrims. In order to attain maximum thermal effi-ciency, steam paths are constructed in conicalform (progressively increasing stage inner ringdiameters). This permits the use of slant root-and-tip buckets, and maximizes the bucketactive lengths in the high pressure stages.Three-dimensional flow analysis is used fordesign of the low pressure stages.
Buckets and nozzles utilize carefully selectedaerodynamic profiles throughout the steampath. Each stage design is individually stress-ana-lyzed to ensure conformity to allowable stressesand specific factors of safety. Most importantly,each stage is dynamically analyzed and tuned toavoid incidence of major frequency resonancesduring operation. Vibratory stresses are calculat-ed for each bucket stage and reviewed relative toaccepted stress limits.
Last-Stage BucketsGE STAG steam turbines benefit from the use
of continuously-coupled, last-stage bucketdesigns, originally developed for large fossil-fired central station units. These buckets featurefull coupling at the tip and mid-vane, supersonictip steam passages, and self-shielding erosionprotection. These designs are available for 3000rpm and 3600 rpm units with last-stage bucketsgreater than 23 inches/584 mm.
The continuously-coupled construction joinseach bucket at its tip and at the mid-vane posi-tion such that no bucket or group of bucketscan move independently. The first benefit is thehigh tolerance of buffeting conditions found atlow loads. The second benefit is that the con-verging-diverging steam path geometry near thetip, where the flow is supersonic, is controlled sothat efficiency losses due to shock waves are min-imized. Figure 20 illustrates a representativeselection of last-stage buckets. The mid-vaneconnection is made with small nubs machinedfrom the bucket forging. An aerodynamicallyshaped sleeve is inserted between adjacent buck-ets during installation, and captured betweenbucket nubs. This loose coupling, without weld-
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Figure 19. Moisture removal provisions
ed connections or tie-wire holes through thebucket vane, readily accommodates bucketuntwist. As the rotor reaches running speed,centrifugal force provides a continuous cou-pling effect via the aerodynamic sleeves.
Self-shielding is an important erosion-resist-ing feature of GE’s longer last-stage buckets. Analloy steel is used for the entire vane that pro-vides erosion resistance comparable to Stellite™
shields, without the maintenance and inspectionrequirements associated with welded shields.The problem of loss or erosion of a separateshield and subsequent rapid erosion of a softerunderlying material is eliminated.
The ability of long buckets to tolerate thehigh moisture level found in nonreheat applica-tions has been improved by a redesign of LSBtip seals. Since much of the moisture in thesteam path forms a water film on the outer wallof the diaphragm, the bucket-tip sealingarrangement has been designed to allow thefilm to pass over the tip without creation of adroplet spray which would impact on the bucketvane.
RotorsTurbine rotors are machined from alloy steel
forgings which have passed extensive testing,including magnetic particle, ultrasonic and ther-mal stability checks. Modern turbine rotor forg-ings reflect decades of close cooperationbetween steel mills and GE engineers. The quali-ty of forgings is evaluated using the latest ultra-sonic techniques. GE has been a world leader inthe development of forging chemistry, produc-tion and quality evaluation.Large single flowrotors require different properties at each end.These are referred to as HP/LP or IP/LP rotors.The high pressure or intermediate pressure end
requires good high temperature properties,while the low pressure end requires higher duc-tility and toughness, to handle the large cen-trifugal stresses encountered with long last-stagebuckets. This design challenge is handled in twoways. Differential heat treatment processes havebeen developed which allow single forgings tobe produced with different properties at eachend. Alternatively, a solid bolted connection isused, in which separate forgings of differentmaterials are joined with a precision rabbet cou-pling in the factory to provide a rotor with therequisite high and low temperature properties.This coupling is not required to be disassembledfor maintenance. GE has over forty years of suc-cessful experience with bolted rotor construc-tion. Bolted rotor construction is seen in theIP/LP section of Figure 11.
DiaphragmsThe diaphragm and outer rings are construct-
ed of various steels, depending upon themechanical design requirements of the particu-lar stage location. The aerodynamically shapednozzles and side walls which form the steampath passages are made from 12 chrome steels.
Spring-backed packings are mounted in thebore of all diaphragms. Large back clearancesprovide a high degree of rub tolerance. Packingrings are made from soft leaded bronze or duc-tile iron materials. The packing rings aredesigned for optimum clearance/leakage con-trol, prevention of shaft damage in the event ofrubs, and minimal wear for sustained efficiency.
CONCLUSIONThe special features and designs discussed
here for matching the steam turbine to the char-acteristics of the gas turbine, HRSG, and site-related conditions have been highly successfulin both reheat and nonreheat, single shaft, andmulti-shaft applications. GE steam turbines forSTAG combined-cycle plants have been highlyreliable since their inception in the mid-1960s.Operating modes have varied from daily start-and-stop service to full base load applications.Reliability of GE steam turbines in STAG serviceexceeds 97%.
GE has a structured STAG product line foraero-derivative, conventional heavy-duty, andadvanced heavy-duty gas turbines. Steam turbinedesign flexibility is allowed for cogenerationapplications, and optimization to project-relatedsite and economic considerations. The ultimatein compact, efficient advanced combined-cycle
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Figure 20. 3600 RPM last-stage bucket family
units is available in GE’s 107FA, 107G, 109FA,109G, 109H and 109FA single shaft gas/steamturbines.
REFERENCES1. Baily, F.G., “Steam Turbines For Advanced
Combined-Cycles,” GE Power GenerationTurbine Technology Reference Library PaperNo. GER-3702B, 1993.
2. Brooks, F.J., “GE Gas Turbine PerformanceCharacteristics,” GE Power GenerationTurbine Technology Reference Library PaperNo. GER-3567D, 1993.
3. Tomlinson, L.O., Chase, D. L., Davidson, T.L.,and Smith, R.W., “GE Combined-CycleProduct Line and Performance,” GE PowerGeneration Turbine Technology ReferenceLibrary Paper No. GER-3574D, 1993.
4. Cofer, J.I., Reinker, J.K., and Sumner, W.J.,“Advances in Steam Path Technology,” GEPower Generation Turbine TechnologyReference Library Paper No. GER-3713B,1993.
5. Tomlinson, L.O. “Single Shaft Combined-Cycle Power Generation System,” GE PowerGeneration Turbine Technology ReferenceLibrary Paper No. GER-3767, 1993.
6. Bievenue, R.T., Ruegger, W. A., and Stoll,H.G., “Features Enhancing Reliability andMaintainability of GE Steam Turbines,” GEPower Generation Turbine TechnologyReference Library Paper No. GER-3741A,1993.
7. Schofield, P., “Steam Turbine SustainedEfficiency,” GE Power Generation TurbineTechnology Reference Library Paper No.GER-3750A, 1993.
Figure 1. Illustrative exhaust loss curveFigure 2. Steam turbine wheel output as a function of exhaust pressure and exhaust size, reheat STAG
1400 psig 1000 F/1000 F (96 bar 538 C/538 C) steam conditionsFigure 3. Comparison of nonreheat and reheat expansionsFigure 4. Three pressure level reheat cycle diagramFigure 5. Nonreheat steam turbine arrangements for multi-shaft STAG
A. Single-casing, axial exhaustB. Single-casing, down exhaustC. Two-casing, down exhaust
Figure 6. Nonreheat, single-casing, axial exhaust steam turbineFigure 7. Nonreheat, double flow down exhaust unitFigure 8. Nonreheat steam turbine arrangements for single shaft STAG
A. Single-casing, axial exhaustB. Single-casing, down exhaustC. Two-casing, down exhaust
Figure 9. Reheat steam turbine arrangements for multi-shaft STAGA. Single-casing, axial exhaustB. Two-casing, axial exhaustC. Two-casing, single flow down exhaustD. Two-casing, double flow down exhaust
Figure 10. Single-casing reheat turbine with axial exhaustFigure 11. Two-casing reheat turbine with single flow down exhaustFigure 12. Reheat steam turbine arrangements for single shaft STAG
A. Two-casing, single flow down exhaustB. Two-casing, double flow down exhaust
Figure 13. Reheat single shaft gas and steam turbine-generatorFigure 14. Combined stop-and-control valve cross sectionFigure 15. Axial exhaust steam turbine in air condenser applicationFigure 16. Combined stop-and-control valve cross sectionFigure 17. STAG admission design - opposed-flow HP/IP sectionFigure 18. Package cogeneration unit with multiple inlet control valves and automatic extractionFigure 19. Moisture removal provisionsFigure 20. 3600 RPM last-stage bucket family
LIST OF TABLES
Table 1. GE gas turbine exhaust characteristicsTable 2. STAG power plants - approximate outputsTable 3. Last stages available for combined-cycle steam turbinesTable 4. STAG steam turbine selection chart: nonreheat steam turbines less than 40 MW
1400 psig (96 bar) 1000 F/1000 F (538 C/538 C)Table 9. G & H vs. FA Characteristics and Performance
GER-3682E
Michael J. BossMr. Boss is presently a Product design engineer in Advance Design,
for Steam Turbine Design and Development Engineering. In this posi-tion he is responsible for the overall design and performance of theAdvanced Steam Turbine designs.
Mr. Boss previously was Technical Leader of the Automated SteamPath Layout Program (ASPL), where he established the method for thecomputerized steam turbine designs. Prior to that assignment he wasTechnical Leader in Thermodynamics and Application Engineering.
Mr. Boss is a lecturer for the ASME Fundamentals Course andAdvanced Course in Steam Turbine Design, Operation andMaintenance.
