GER-4194 - The 7FB: The Next Evolution of the F Gas Turbine

GE Power Systems

The 7FB:The Next Evolutionof the F Gas Turbine

Roberta EldridLynda KaufmanPaul MarksGE Power SystemsSchenectady, NY

GER-4194

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Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Critical Issues in the F Evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Life-Cycle Economics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1The F Series Gas Turbine Experience . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Reliability and Availability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4The Evolution of Cost Improvements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5The FA Compressor Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7The H Gas Turbine Combined Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8The Flowback of H Technology into the F Platform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Applying Six Sigma to Determine the Future Evolution of the F/FA . . . . . . . . . . . . . . . . . . . . 9The Next Step in the F Product Evolution: The 7FB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

The 7FB: The Next Evolution of the F Gas Turbine

GE Power Systems ■ GER-4194 ■ (04/01) i


GE Power Systems ■ GER-4194 ■ (04/01) ii

IntroductionGlobal deregulation of the power generationindustry and the emergence of a merchantplant market have accelerated the demand forhigh-efficiency, lower-cost power plants. Thedrive for efficiency has been reinforced by grow-ing concern over global warming, which hasbeen attributed to the burning of fossil fuels. Inview of these market demands, GE has contin-ued to evolve its F technology, which has beenthe standard setter for economical, clean powergeneration during the last decade. GE intro-duced the MS7001FB in November 1999 atPower-Gen International (Figure 1). The 7FB isbetter by over 1 percentage point in net plantcombined-cycle efficiency and greater by nearly7% in combined-cycle output than its predeces-sor, the MS7001FA.

Some of the many factors that were consideredin advancing the F/FA product line to the FBincluded life-cycle economics, the F/FA operat-ing experience, a comprehensive FA compres-sor test and applicable technologies that weredeveloped under the H System program. The HSystem program was supported by the ATSProgram, which was sponsored by the U.S.Department of Energy. Six Sigma, GE’s statisti-cal process, was used to evaluate these factorsand examine potential next steps in arriving atthe optimal solution – the 7FB.

Critical Issues in the F Evolution

Life-Cycle Economics In the 1950s, when gas turbines were first usedfor power generation in large numbers, theywere applied almost exclusively to peaking duty.Designs were required for this mode of servicethat featured low specific cost and good startingreliability.

Through the 1960s and early 1970s, continuingadvances in efficiency, reliability and availabilityfacilitated a wider range of applications for gasturbines. Today, with the addition of low emis-sions, low overall life-cycle cost and fast installa-tion time, the gas turbine-based power plant hasbecome the most widely used method for powerproduction.

Many gas turbine applications today require thegas turbine to run nearly continuously. Withthis increase in operating hours, the cost of fuelhas assumed greater significance in optimizingmachine design. As operating (or fuel) cost hasbecome more important, technology develop-ment has been focused on improving efficiency,primarily through increasing firing tempera-ture. But higher operating temperatures candrive design engineers to use more expensiveparts that may affect operating and mainte-nance practices.

So, in today’s environment, with gas turbines in


GE Power Systems ■ GER-4194 ■ (04/01) 1

Figure 1. The MS7001FB gas turbine

widespread use in power generation and cogen-eration applications as baseload machines incombined-cycle configurations, optimizing gasturbine design requires balancing multipleobjectives of low first cost, fuel cost, and opera-tion and maintenance costs over the life of amachine.

GE continues to evolve its gas turbine productlines to address the growing challenge of meet-ing multiple objectives. Figure 2 shows the majorelements of the life-cycle cost of a representa-tive combined-cycle power plant. Clearly, thelargest component of life-cycle cost, or cost ofelectricity (COE), is fuel cost, which is a func-tion of fuel price and a power plant’s overall

thermal efficiency. The percent contribution tothe overall COE of each of these elements hasvaried over time. As economies of scale havereduced capital cost and improved efficiencyhas reduced fuel cost, operation and mainte-nance (O&M) costs, which have exhibited littlechange, have become a larger and more signifi-cant fraction of total life-cycle cost.

Designers may select more expensive materialsto achieve higher efficiencies, and their costmust be offset by the power plant’s increased

performance. A look at capital costs (Figure 3)shows the gas turbine flange-to-flange (GT) costis a relatively small portion of the overall powerplant capital cost. However, the gas turbine con-sumable components make up the largest con-tribution to maintenance costs, as shown inFigure 4.

This discussion, thus far, has illustrated trendsfor average plants. GE has made a statisticalassessment of the variations expected in plantcost; efficiency based on plant-to-plant differ-ences, given a single design; and maintenancecosts, based on the differences in experiencefrom one plant to another. Of these variations,O&M variability has the greatest impact on life-cycle cost.



ce

i t a l

CapitalRecovery

Fuel

Operation &Maintenance

7500 hoursper year

Figure 2. Major elements of the life-cycle cost ofownership (present value) for a typicalcombined-cycle power plant

7500 hoursper year

Balance ofPlant - Prime

Labor,Generators,Training,

etc.

PPAccessories

GTAccessories ST GT

Figure 3. Elements of capital cost for typical com-bined-cycle plant

Figure 4. Elements of maintenance costs for a typ-ical combined-cycle power plant

CapitalRecovery

Operation &Maintenance

Fuel

7500 hoursper year

G

SteamTurbine,

Generator,HRSG, BOP

Gas TurbineLabor

GasTurbine

Parts

GasTurbine

Parts

Gas TurbineLabor

SteamTurbine,

Generator,HRSG, BOP

7500 hoursper year

Balance ofPlant-Prime

Labor,Generators,

Training,etc. GT

Accessories STGT

Power PlantAccessories

Figure 5 shows the effect on the probability ofachieving various levelized electricity costs withand without consideration of O&M variation.The expected O&M cost itself is the same inboth cases. Various approaches could be takento compensate for O&M uncertainty (worth, inthis example, 1% in a levelized COE). Forexample, pursuit of higher fuel efficiency wouldrequire a 1.5% improvement in heat rate to off-set the total uncertainty of O&M cost.

This example illustrates the importance of notonly the magnitude of the elements of COE forthe average plant but the variability of these ele-ments. In light of this, designers are obliged tomake design choices that minimize COE and, atthe same time, must consider how to reduce thevariation of design parameters so as to minimizethe resultant variability of COE.

The F Series Gas Turbine Experience The F technology was initially designed in the1980s; it represented a quantum leap in theoperating temperatures, cooling technologyand aerothermal performance of heavy-duty gasturbines. GE’s first F-technology unit entered

commercial service June 6, 1990, at VirginiaElectric & Power Company’s Chesterfield site.Since that time there has been a continuum ofnew units entering service, incremental refine-ments and improvements. As of February 24,2000, there are currently 93 F/FA gas turbinesin service with a cumulative operating ex-perience of 1,695,579 fired hours and 43,437starts.

The F technology has also been scaled upwardto the MS9001F, 50 Hz machines and downwardto the MS6001F, 50/60 Hz machines for a grandtotal of 158 F units now in service with 2,680,497fired hours and 55,872 starts. This experienceincludes operation in duty cycles from peak-shaving to baseload to daily start-stop mode, asshown in Figure 6.

Figure 7 illustrates the rate at which GE is accu-mulating hours on the F/FA fleet. In 1999 theaverage number of fired hours grew at a rate of60,000 per month. The projected rate of growthfor 2000 is about 100,000 per month.

The introduction of the F-class machine in theearly 1990s was impelled by the concurrent



Typical F Technology CC Power PlantTotal Capital Cost = $500/kW57.2% Efficiency & $3.50/MMBtu Fuel

Levelized Cost of Electricity (COE) - US$/kW-hr

Figure 5. Ignoring operation and maintenance (O&M) cost variation would require an additional 1% in levelized cost of electricity (COE) for a given level of confidence

needs to press the limits on aerothermal per-formance, meet drastically lowered emissionsstandards (with new Dry-Low-NOx combustionsystems) and succeed in a fiercely competitivemarket that was paying 20% to 40% less perinstalled kilowatt. The multifront advancesyielded the overall necessary performanceincreases but also led to several shortcomings inequipment design that had a negative impacton availability. These were addressed andresolved by means of extensive root-cause analy-ses (RCA) and have been corrected at the

design level for the current offering of GEMS7001FA gas turbines.

Reliability and Availability In the United States there are two organizationsthat collect reliability-related operating datafrom utility-sized generating plants. The olderand more broadly recognized is the U.S. gov-ernment-sponsored North American ElectricReliability Council (NERC), which has been col-lecting this data under government mandatefrom regulated utilities since the 1970s. NERC



0

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9F/FA

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50 Hours/Start

Cycling Duty

Peaking Duty

Base Load

F/FA Fleet (Machine) Experience

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47

85

Figure 6. F series machines are used in a variety of applications, including baseload, cycling and peaking duties

2,119

2,554

2,963

3,371

3,780

1,396

1,632

1,837

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urs

in

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F/FA Fleet

7F/FA

9F/FA

6FA

Over 2 .6 Million Hours

on F Technology December 16, 1999

Figure 7. F/FA machines have accumulated over 2.6 million operating hours in all operating modes and nowhave an accumulation rate of over 100,000 hours per month

does not currently collect data from GE F-classgas turbines. The second organization isStrategic Power Systems, Inc. (SPS), a privatelyheld firm that focuses on the reliability of gasturbine electrical generation plants, worldwideand application-wide, using their ORAP datasystem to collect data from many heavy-duty gasturbine manufacturers.

Ultimately the quality of any design is measuredin terms of the resulting units’ reliability andavailability as they perform their service. GEuses a sophisticated reliability model for esti-mating reliability, availability and maintainabili-ty performance for equipment guarantees. Datacollected from various sources, including SPS’sORAP, as well as the 7F User’s Group and direct-ly from some customers are used to calibratethe reliability model that can be passed along toGE’s customers and clients. The current modelshows that the typical current-productionMS7001F gas turbine will average about 99.0%reliability and 95.0% availability on a life-cyclebasis. Note that reliability is measured as:

100 x (1 - FOF),

where FOF is the forced outage factor.

Availability is measured as:

100 x (1 - FOF - SOF),

where SOF is the scheduled outage factor.

The 1999 ORAP average of 25 GE units at89.3% availability and the 75-unit-year surveythat averaged 89.35% availability are showinglow averages because of a relatively few numberof units with significantly long scheduled out-ages related to the correction of generic prob-lems. Newer units will not experience thesenow-resolved problems.

Figures 8A and 8B illustrate GE’s competitiveassessment of the independent SPS ORAP data.In 1999 GE’s simple-cycle availability of 89.3%compared most favorably with the industry aver-

age of 84.9%, which includes GE and othermajor gas turbine manufacturers. Simple-cyclereliability of 99.4% compared most favorablywith the industry average of 95.7%. This dataillustrates the GE advantage of the F-class gasturbines’ reliability and availability.

A first look at the 7F/FA reliability figures, inFigure 8B, affirms that the units are now clearlymeeting and exceeding the simple-cycle plantaverage reliability target levels of 99.0%. Thisdemonstrates that the fleet availability numbersare driven by scheduled outage events. Now,recognizing that a significant part of scheduledoutage hours are due to correction of old butsolved issues, this data can be interpreted as aconfirmation of the equipment’s inherent capa-bility to achieve 95.0% average availability.

The Evolution of Cost Improvements Gas turbine designers are obliged to pursueopportunities for improving efficiency, reliabili-ty and maintenance cost to avoid invalidatingthe machine’s experience base. This experiencebase, from whichever gas turbine product itcomes, can benefit multiple product lines.Figure 9 shows the incremental evolution of theE-class machine. As the E class matured, a deci-sion was made to introduce the F-class machines– the 7F and its scaled versions, the 9F and the6F. Many factors drove this decision, but oncethe F machines were introduced, technologicaladvancement or operating experience on the Fproduct line has helped drive further evolutionof the older E-class machines. Likewise, thenext-generation product, the H machine, willhave an impact on the E and F products.

Design improvements in the F/FA product lineare made incrementally and are based onproven materials, extensive laboratory orengine testing and operating experience. Whenthe F technology was announced, its upratepotential was projected and these uprates



began immediately upon completion of theprototype testing at the Greenville factory. Oneprojection made was that the combined-cycleefficiency would be increased from the 50%cited in the introduction paper to 55%. The55% level was achieved in 1994 with the testingof Korea’s first MS7001F unit in combined-cyclemode.

Uprates continue as the technology becomesavailable and as experience on the high-tem-perature components of the F/FA fleet remains

favorable. Table 1 shows the evolution of theMS7001F machine. Each uprate has beenachieved without reducing inspection intervalsbelow those established by the original design.The first uprate of the MS7001F simply tookadvantage of the better-than-expected perform-ance observed in testing. Firing temperatureupgrades involved modifications to componentcooling and pressure ratio. Higher pressureratio prevents the overheating of the last-stagebuckets. Improvements in bucket and nozzle



Sim ple C ycle Plan t:

R eliab ility (% )

99.4

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80

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liab

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)

GE

Industry25

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53

Units

Sim ple C ycle P lant:

Availab ility (% )

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84.9

80.0

85.0

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95.0

100.0

7F/FA

Availability (%)

GE

Industry

25

Units

53

Units

7F/FA

FIG 8BFIG 8A

7F/FA

Figure 8. GE’s 7F/FA availability (Figure 8A) and reliability (Figure 8B) for simple-cycle power plants relativeto the F industry (source: Strategic Power Systems, Inc., ORAP data)

40%

45%

50%

55%

60%

1970 2000

Year of Shipment

2600

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CC Efficiency

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"E"

"F"

"H"

FuturePotentialUpgrades

Co

mb

ined

Cyc

le E

ffic

ien

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Figure 9. Continuous technology development and experience benefits flow across product lines

Simple-Cycle Plant:

Availability (%)

Simple-Cycle Plant:

Reliability (%)

7F/FA

53Units

Avai

labi

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(%)

25Units Re

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53Units

cooling have been achieved by increasing theuse of film cooling. The original MS7001F first-stage bucket cooling system was derived fromthe CF6 aircraft engine bucket’s system, but itdid not employ the CF6’s film-cooled leadingedge. The current buckets now use more of thefull CF6 system.

Other technologies have been imported fromGE Aircraft Engines including improved clear-ance and leakage control. An example of thistechnology is honeycomb seals, which havebeen used for years in the MS9001E andMS7001EA machines. Figure 10 shows the evolu-tion of the PG7231FA to the PG7241FA, illus-trating the incremental enhancements that

were incorporated recently into the 7F productline.

The FA Compressor Test Incremental improvements in the F series com-pressor were incorporated during the F series’evolutionary life. Consequently, in 1998 a FAcompressor test was performed to revalidate thecompressor’s capability (Figure 11).

The objectives of the test were twofold: (1) tothoroughly map the FA compressor’s aerody-namic and aeromechanical behavior and (2) tocharacterize the thermal behavior of a high-radius rabbet (HRR) compressor rotor struc-ture. One significant result of the test was the



Table 1. MS7001F gas turbines

Stage 1 Nozzle, Bucket, Shroud• Thermal Barrier Coating• Reduced Cooling Air

Double Walled Cone• Improved Sealing• Reduced Flow

Tapered Struts

9PPM DLN 2.6 Combustor• Flexible SealsNew EGV Arrangement

Robust CompressorRotor

Honeycomb HPPS• Tie Bolt & Marriage Flange Cooling

3300 Series Bentley Probes#1 & #2 Bearings

Hot Gas PathImproved SealingStage 2 Bucket

• Scalloped Shroud• Mod Cooling

Hole Pattern

Monitoring/Diagnostics• Added Combustor Tuning Kit

Figure 10. The transition from PG7231FA to PG7241FA gas turbine illustrates incremental improvement philosophy

establishment of compressor surge and stallcharacteristics, which demonstrated a compres-sor operating limit that would allow significantpressure ratio growth. Another significant resultwas the empirical determination of rotor ther-mal transients which was used to validate ana-lytical predictions for the HRR rotor structure.

The H Gas Turbine Combined Cycle A key advantage to gas turbine power-genera-tion systems is their ability to continue evolvingto higher firing temperatures (at the inlet tofirst rotational stage) because each increase infiring temperature yields a dual benefit ofincreased efficiency and increased specific workto overall power plant life-cycle cost. This hadled to the step in technology from the E-class toF-class gas turbines and, more recently, to thebeginning of yet another evolutionary path,GE’s H System technology and the GE H-class gasturbine (Figure 12).

The H System is designed to achieve 60% netplant combined-cycle efficiency. The three keycomponents of the H-technology gas turbineare shown in Figure 13: (1) closed-loop steamcooling, which is used for the first and second

stages of its four-stage turbine; (2) a higher-pressure-ratio compressor, derived from the GEAircraft Engines CF6-80C2, optimizes efficiencyand specific work with the 2600°F class of firingtemperatures; and (3) the DLN combustion sys-tem now in service across GE’s commercialproduct lines, which has been adapted to the Hgas turbine.

The Flowback of H Technology into the F Platform The H program took proven aircraft enginematerials and developed the casting and forg-ing processes necessary to scale from aircraftengine-sized components to power system-sizedcomponents. The FB program leveraged Hmaterial process development specifically in theareas of bucket materials and rotor forgings.

As an example, the stage-three and -four buck-ets on the 7H are using GE Aircraft Engines’single-crystal N4 alloy with grain boundarystrengtheners added for use as DSN4 orGTD444. Rapid-prototype tooling facilitatedearly casting trials on both 7H bucket stages inGTD444, producing over 90% casting yields forthe first 7H build. These successful results will



Figure 11. A FA compressor test vehicle (CTV) was constructed to comprehensively determine aerody-namic and structural behavior

be directly applied to the stage-two and -threebuckets on the 7FB.

Another example of technology developed onthe H System that will be incorporated into the7FB is the Mark VI control system. Require-ments of the combined-cycle H System drove theneed for a more capable control system. TheMark VI will also be used to control the nextupgrade of the 7F platform.

The 7FB compressor rotor design will incorpo-rate a high-radius rabbet configuration. This

configuration has significant operating experi-ence in aircraft engines. It was demonstrated onthe FA test in 1998 and is being utilized on theH System.

Applying Six Sigma to Determine theFuture Evolution of the F/FAAs GE looked forward to the continued evolu-tion of the F/FA product line, a range of factorswere considered. Key factors that had to beweighed carefully included the continuingimprovement in F reliability and growing expe-



Figure 12. The first H gas turbine

DLN 2.6 Combustor

– 12 Cans

– GE FA Experience

18 Stage Compressor

– 23:1 Pressure Ratio

– 1230 pps Airflow

– GE Aircraft Engine Derived

4 Stage Turbine

– 2600F Class

– Closed Circuit Steam Cooled

– GEAE/GEPS Materials

Figure 13. Key components of the MS7001H gas turbine

rience base, the development and testing of Hand other technologies and the recent FA com-pressor test results.

The question that remained was how to com-bine the complexities of power plant life-cycleeconomics with the choices that exist to arriveat an optimum design solution. GE PowerSystems used the company’s Six Sigma method-ology to combine these advantages for its cus-tomers’ satisfaction in the development of the7FB. The Six Sigma process permeates GE’sdesign, manufacturing, and operationalprocesses and applies a precise methodology toa complex multivariable situation. Its statisticalcapabilities permit incorporation of the exten-sive database of GE gas turbine operationalexperience to quantify the effect and expectedrange of design modifications under analysis.Where data is not available, the Six Sigmaprocess provides the framework to ensure thatdesign trade-offs are made rigorously andreviewed thoroughly.

One multivariable situation that needed to beevaluated involved looking at all aspects ofincreasing the pressure ratio, which permits anincrease in firing temperature and efficiency.

But this presents challenges involving the tur-bine section and its design. Also, NOx goals canconflict with the pursuit of efficiency. Our cus-tomers’ top priority – achieving the lowest life-cycle cost – was the focal point of our decision-making process.

One Six Sigma tool, Quality FunctionDeployment (QFD) has become the startingpoint for any development task at GE and wasused to kick off the development of the 7FB.While QFD is in itself a powerful analytic tool,its greatest value lies in the debates and innova-tive thought that it informs and fosters.

The QFD process (see Figure 14) begins withidentifying and ranking customers’ require-ments through interviews and discussions.Next, relevant functional requirements areidentified and an analysis is performed to deter-mine the level at which each functional require-ment affects each customer requirement. Pointvalues are assigned to indicate level of effect.Finally, a score is calculated that shows the sig-nificance of each functional requirement to sat-isfying the customer requirements and, thus,identifying where the development effortsshould be focused. It should be noted, the QFD



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27 27 15 15 9Customer Requirements

High Combined Cycle Efficiency 1 = 9 points Low NOx Emissions 2 = 3 Low Specific Cost ($/kW) 3 = 1 High Availability 4 Operating Flexibility 5 High Reliability 6 High Simple Cycle Efficiency 7

Figure 14. An example of Quality Function Deployment analysis

example cited here has been greatly simplifiedfor illustrative purpose.

The QFD process, as applied to the 7FB, gener-ated a series of analyses, or “houses,” beginningat the power plant level and working down tothe gas turbine component level of functionalrequirements. The results of one house flowsinto the next, ensuring the calculated impor-tance of meeting the customers’ requirementsin the first house is retained as one drills downto each of the subsequent levels.

The results of the 7FB QFD indicated life-cyclecost and proven technology were the two func-tional requirements that would most satisfy cus-tomers’ needs. The QFD process was used toweigh internal requirements simultaneouslywith customer requirements.

Many factors influence one or more of the com-ponents of power plant life-cycle cost. (See Figure15.) In turn, each of these factors is influencedby design choices for such things as firing tem-perature, efficiency, material selection, pressureratio and mass flow.

Another Six Sigma tool, Design of Experiment(DOE), was used to quantify the optimal com-bination of these parameters. In terms of thisDOE analysis, these parameters are the input

variables, or x’s, for the response variable, or y,which is COE. Execution of a DOE leads to find-ing the most influential variables and determin-ing their mathematical relationship. Once thisrelationship, or transfer function, is developed,it can be used to determine an optimum com-bination of x’s for a minimum y-COE.

The Next Step in the F Product Evolution:The 7FB The use of Six Sigma tools optimized choicesfor the design teams based on reduced variation(low risk) and minimized COE. As a result, itwas decided not to create a new platform but,rather, to continue the F-series machine’s evo-lution to the next step – the 7FB.

Figure 9 illustrated how the E product line hasbenefited from proven F technology. It alsoillustrated how the F product line could furtherbenefit from the wide variety of technologiesrelated directly to the H machine that havecompleted sufficient proof testing to flow backinto the F product.

Moreover, many of the H components and sys-tems have themselves evolved from F technolo-gy melded with long-term GEAE technology. Asan example, stage-one bucket material technol-ogy has advanced in two ways: from equiaxed



PROJECTEDCOST OFELECTRICITY

PLANT PRICE

GT COST

FINANCING COST

AVAILABILITYFUEL PRICE

PLANT EFFICIENCY

EFFICIENCY DETERIORATION OUTPUT DETERIORATION

PLANNED OUTAGE FREQUENCY

UNPLANNED OUTAGE FREQUENCY

PARTS REPLACEMENT FREQUENCY

PARTS REPLACEMENT COST

UNCERTAINTY - EFFICIENCY UNCERTAINTY - AVAIL.

UNCERTAINTY - REPAIR/ MAINT.

DAILY OPERATION COSTS

OUTAGE DURATION

FUEL COMPOSITION

NOx ABATEMENT

NOx ABATEMENTST, G BOP

FUEL COST

CAPITAL COST

OPERATION &

MAIN

TENANCE COSTS

Figure 15. Factors that influence the components of power plant cost of electricity production

(EA) to directionally solidified (DS) to the cur-rent advanced TBC-coated single-crystal (SC)technology used in the H machine and, con-currently, from radial to serpentine to serpen-tine with advanced film cooling to the currentclosed-loop steam-cooling technology used inthe H. The next logical step in the bucket’sdevelopment is to evolve the F stage-one bucketto an H material (Figure 16), which, as a com-ponent-development plan, illustrates GE’s over-all evolution-based design philosophy.

Other materials developed and implemented atGEAE and for the H machine have been adapt-ed for use in the 7FB to further improve per-formance and reliability. Table 2 defines whichmaterials are being adapted to the 7FB andtheir prior service.

Other technologies such as honeycomb andbrush seals, which have a significant operatinghistory in GEAE engines, GE steam turbinesand GE E-class gas turbines, are being consid-ered for various locations in the 7FB (Figure 17).Rough coatings used to enhance cooling-sideheat transfer, smooth coatings to reduce aero-dynamic drag and reduce hot gas-side heat

transfer, and radiation coatings may also be uti-lized.

Again, with many choices of technologies, thefinal design features were chosen to yield anoptimum configuration to meet all customerrequirements. Some of these features for theresultant 7FB configuration are illustrated inFigure 18.

The resultant performance characteristics ofthe 7FB are compared to its predecessor, the7FA, and the next-generation 7H machine inTable 3. The increase in firing temperature fromthe 7FA to the 7FB has led to higher combus-tion flame temperature for the 7FB and, conse-quently, higher gas turbine NOx. One of theadvantages of the advanced H-technologymachine is its ability to maintain low NOxdespite higher firing temperature by way ofclosed-looped steam cooling of the first-stagenozzle.

Another characteristic of the 7FB is its perform-ance as a function of ambient temperature,shown in Figure 19. This ambient behaviorresults in higher performance for the 7FB rela-tive to the current 7FA for all ambient tempera-



Original 7FFirst-Stage

BucketCurrent 7FAFirst-Stage

Bucket

Tip Cooling Holes

Lead

ing-

Edge

Film

-Coo

ling

Hole

s

ThermalBarrier &CorrosionCoating

Corrosion-ResistantCoating

next step

7FB

• Similar CoolingTechnologywith More Film

• Improved TBC

• Single-CrystalMaterial

• 3D Aero

Figure 16. Evolution of the F series first-stage bucket to allow higher firing temperature and reduce per-formance degradation



Prior Service

Component 7FA (Ref.) 7FB GEAE GEPS

S1B DS GTD111 SX N5 4 4 (H)

S2B & S3B DS GTD111 DS GTD444 4 4 (H)

S1N & S2N FSX414 GTD111 4 4

S3N GTD222 GTD222 4 4

Combustor HastX/N263 HastX/N263 4 4

Transition Pieces N263 N263 4 4

Coating TBC TBC 4 4

Turbine Wheels & Spacers IN706 IN706/IN718 4 4 (H)

Table 2. 7FB materials experience

New 3DAdvanced

AeroTurbineDesign

AdvancedMaterials forHigher FiringTemperature

Enhanced Compressor and TurbineRotor Robustness for Increased

Torque and Temperature

AdvancedTechnology DLN

CombustionSystem

FA CompressorAerodynamics with

Optimized PR

Improved MaterialCompressor Case

Single-CrystalFirst-Stage

Bucket

Advanced Mark VIControl System

AdvancedSeals

Figure 18. FB design features make maximum use of evolutionary designs and extensive operation experience

5” diam. test brush seal

Figure 17. Advanced seals are critical to improved performance

Advanced SealBeing Considered

✓✓✓✓✓✓✓

✓✓✓✓✓

✓

✓

✓

✓

5” diam. test brush seal

tures above 0°F with a maximum benefit forISO and higher ambient temperatures.

The 7FB design is currently in the detaileddesign phase with a scheduled completion atthe end of 2000. First-unit manufacturing,assembly and testing will be completed in 2001with first-unit shipment planned for the end ofthat year. More scheduling details are shown inFigure 20.

The first power plant for the 7FB will be basedon an 800 megawatt, 307FB combined-cycle sys-tem consisting of three gas turbines and onesteam turbine. Commercial operation of thispower plant will begin in 2003. A total of 157FBs have been committed as of this writing,and the next available units are planned forshipment in the first quarter of 2003.

ConclusionFiring temperature is the key to combined-cycleefficiency and, consequently, to minimizing fuelcost. H technology and F experience enable asignificant and vigorous advance in firing tem-perature on the F/FA product. Developmentsat GE Aircraft Engines and GE CorporateResearch and Development continue to pro-vide valuable contributions to product technol-ogy and design and manufacturing techniquesto further enhance performance and reduceoverall power plant costs of the F product.

However, designing gas turbines in today’sderegulated market requires balancing all threemajor elements of life-cycle cost: capital cost,O&M cost and fuel cost. Determining the opti-mum design solution – that is, determining



Characteristics 7FA 7FB 7HFiring Temperature Class, F 2420 2500+ 2600Airflow, Lbs/sec 950 950 1230Pressure Ratio 15.5 18.5 23

EmissionsNOx, ppm 9 25 9

Combined Cycle Performance STAG 107FA STAG 107FB STAG 107HNet Output, MW 263 280 400Net Efficiency, % 56 57.3 60Heat Rate 6095 5956 5690

Table 3. FA, FB and H System™ performance characteristics

Figure 19. The 7FB maintains a performance benefit over all ambient temperatures above 0°F and has amaximum benefit of ISO and above

which advancements to incorporate – is a verycomplex exercise in designing for multipleobjectives.

GE is systematically applying the advanced sta-tistical tools of its corporate-wide Six Sigma ini-tiative to facilitate finding the balance amongthese multiple objectives for satisfying specificcustomer needs. The solution is the 7FB – acombination of proven, robust design optionsthat not only will minimize life-cycle costs but

will minimize the variation of those costs (Figure21). In this way, GE will deliver the next evolu-tionary step in the F product line and signifi-cantly improve on its leadership in low-cost,clean, reliable power generation.

AcknowledgmentsThe ATS Program is sponsored by the U.S.Department of Energy under CooperativeAgreement DE-FC21-93MC31176 with GE



1Q 2Q 3Q1Q 2Q 3Q 4Q1Q 2Q 3Q 4Q1Q 2Q 3Q 4Q20021999 2000 2001

Conceptual Design

Detailed Design

First Unit Assembly & Test

First Unit Shipment

1st Half 2002

1Q 2Q 3Q 4Q1998

FSFL Test

4Q

Figure 20. The 7251FB program schedule

7241

FA

+e

Hea

t Rat

e

Ou

tpu

t -

$/K

WIm

prov

emen

t

Out

put –

Ope

ratio

nsLe

vera

ge

New

Uni

t P

rice

LTS

A P

rice

SC

R7FB

7FA IMPROVED CUSTOMER VALUE

Cos

t of E

lect

ricity

(mils

/kw

-hr)

Elements of COE

• Capital Investment

• Fuel Consumption

• Operations Expense

• Availability

• LTSA Expense

• NOx

• Variation

Figure 21. This waterfall of elements of the COE of the 7FB versus that of the current 7FA+e shows anincrease in customer value

7FA7FB

Power Systems, 1 River Road, Schenectady, NY12345, 518-385-2968. The DOE/FETC Con-tracting Officer’s Representative is Mr. KanwalMahajan, and the period of performance is July1995 to December 31, 2000 (Phase 3R).

ReferencesMiller, Harold, “Engineering Gas Turbines forBest Value over Time,” Power-Gen ‘98 Europe,Milan, Italy, June 1998.



List of FiguresFigure 1. The MS7001FB gas turbine

Figure 2. Major elements of the life-cycle cost of ownership (present value) for a typical combined-cycle power plant

Figure 3. Elements of capital cost for typical combined-cycle plant

Figure 4. Elements of maintenance costs for a typical combined-cycle power plant

Figure 5. Ignoring operation and maintenance (O&M) cost variation would require an additional1% in levelized cost of electricity (COE) for a given level of confidence

Figure 6. F series machines are used in a variety of applications, including baseload, cycling andpeaking duties

Figure 7. F/FA machines have accumulated over 2.6 million operating hours in all operatingmodes and now have an accumulation rate of over 100,000 hours per month

Figure 8. GE’s 7F/FA availability (Figure 8A) and reliability (Figure 2B) for simple-cycle powerplants relative to the F industry (source: Strategic Power Systems, Inc., ORAP data)

Figure 9. Continuous technology development and experience benefits flow across product lines

Figure 10. The transition from PG7231FA to PG7241 gas turbine illustrates incremental improve-ment philosophy

Figure 11. An FA compressor test vehicle (CTV) was constructed to comprehensively determineaerodynamic and structural behavior

Figure 12. The first H gas turbine

Figure 13. Key components of the MS7001H gas turbine

Figure 14. An example of Quality Function Deployment analysis

Figure 15. Factors that influence the components of power plant cost of electricity production

Figure 16. Evolution of the F series first-stage bucket to allow higher firing temperature and reduceperformance degradation

Figure 17. Advanced seals are critical to improved performance

Figure 18. FB design features make maximum use of evolutionary designs and extensive operationexperience

Figure 19. The 7FB maintains a performance benefit over all ambient temperatures above 0°F andhas a maximum benefit of ISO and above

Figure 20. The 7251FB program schedule

Figure 21. This waterfall of elements of the COE of the 7FB versus that of the current 7FA+e showsan increase in customer value

List of TablesTable 1. MS7001F gas turbines

Table 2. 7FB materials experience

Table 3. FA, FB and H System™ performance characteristics



GER-4194 - The 7FB: The Next Evolution of the F Gas Turbine

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