GER-4206 - Combined-Cycle Development Evolution and Future · Combined-cycle systems utilizing the Brayton Cycle gas turbine and the Rankine Cycle steam system with air and water

GE Power Systems

Combined-CycleDevelopmentEvolution and Future

David L. ChaseGE Power SystemsSchenectady, NY

GER-4206

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Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Gas Turbine Combined-Cycle Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Gas Turbine Combined-Cycle Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

First Generation Combined-Cycle Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Second Generation Combined-Cycle Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Third Generation Combined-Cycle Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Fourth Generation Combined-Cycle Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Combined-Cycle Development Evolution and Future

GE Power Systems ■ GER-4206 ■ (04/01) i


GE Power Systems ■ GER-4206 ■ (04/01) ii

IntroductionCombined-cycle systems utilizing the BraytonCycle gas turbine and the Rankine Cycle steamsystem with air and water as working fluidsachieve efficient, reliable, and economic powergeneration. Flexibility provided by these sys-tems satisfies both utility-power generation andindustrial-cogeneration applications.

Current commercially available power-genera-tion combined-cycle plants achieve net plantthermal efficiency typically in the 50–55% LHVrange. Further development of gas turbine,high-temperature materials and hot gas path,metal surface cooling technology show promisefor near-term future power generation com-bined-cycle systems capable of reaching 60% orgreater plant thermal efficiency. Additional gasturbine technological development, as well asincreases in steam-cycle pressure and tempera-ture and steam-turbine stage-design enhance-ment, is expected to achieve further STAG™combined-cycle efficiency improvement.

Current General Electric STAG™ (trade namedesignation for the GE product line of com-bined-cycle systems) product line offerings,combined-cycle experience, and advanced sys-tem development are used to demonstrate theevolution of combined-cycle system technology.

Gas Turbine Combined-Cycle FeaturesThe combination of the gas turbine BraytonCycle and the steam power system RankineCycle complement each other to form efficientcombined-cycles. The Brayton Cycle has highsource temperature and rejects heat at a tem-perature that is conveniently used as the energysource for the Rankine Cycle. The most com-monly used working fluids for combined cyclesare air and steam. Other working fluids (organ-ic fluids, potassium vapor, mercury vapor, andothers) have been applied on a limited scale.

Combined-cycle systems that utilize steam andair-working fluids have achieved widespreadcommercial application due to:

1. High thermal efficiency throughapplication of two complementarythermodynamic cycles.

2. Heat rejection from the Brayton Cycle(gas turbine) at a temperature that canbe utilized in a simple and efficientmanner.

3. Working fluids (water and air) that arereadily available, inexpensive, and non-toxic.

These combined-cycle systems provide flexibili-ty with features that include:

1. High Thermal Efficiency - Combined-cycle thermal efficiency is higher thanthat of other conventional powergeneration systems.

2. Low Installed Cost - Combined-cycleequipment is pre-engineered and factory-packaged to minimize installation timeand cost. All major equipment (gasturbine generator, heat recovery steamgenerator [HRSG], and steam turbinegenerator) is shipped to the field asassembled and tested components.Auxiliary equipment, such as condensers,can be shipped factory-tubed and hydro-tested. This greatly reduces the inventoryof parts that must be managed in thefield and minimizes installation cost.Combined-cycle equipment cost is higherthan that for conventional steam plantsdue to pre-engineering; however,combined-cycle plant installation costsare significantly lower, resulting from thereduced installation cycle.

3. Fuel Flexibility - Combined-cycle plantsoperate efficiently by burning a wide


GE Power Systems ■ GER-4206 ■ ( 04/01) 1

range of fuels, ranging from cleannatural gas and distillate oil fuels to ash-bearing crude oil and residual oil fuels.Operation with coal-derived gas fuels hasbeen applied in many commercial-size,combined-cycle systems.

4. Flexible Duty Cycle - Combined-cyclesystems provide flexibility in operationfor both baseload and mid-range dutywith daily startup. Gas turbines in multi-shaft, combined-cycle configuration canbe started quickly, bringing about two-thirds of plant power on-line, typically in

less than 60 minutes. Combined-cycleplants also provide efficient operation atpart load, particularly for multiple gasturbine combined-cycle systems. This is il-lustrated by the variation in plant outputwith variation in plant heat rate curveshown for a General Electric STAG 200system. (See Figure 1.) Modulatingcompressor inlet guide vanes arestandard features of many gas turbine

models, enabling high efficiencyoperation at part load through reductionin turbine airflow. This is accomplishedat nearly constant turbine exhausttemperature, so that design steamconditions and low stack loss can bemaintained to provide excellent part-loadefficiency.

5. Short-Installation Cycle - Combined-cycle plants can be installed andoperated in less time than that requiredfor conventional steam plants. Again, thisis primarily due to the pre-engineering

and packaging of major components inthe factory. Phased installation of theplant, when gas turbines are installed andoperated in the simple-cycle modeduring the steam-cycle equipmentinstallation, enables the user to generatepower and revenue in as little as a yearfrom order date. (See Figures 2–4.) Atypical combined-cycle plant installationschedule is presented in Figure 5.



Figure 1. STAG 209E combined-cycle part load performance

6. High Reliability/Availability - Highreliability operation results fromevolutionary design development thatimproves parts and components, andquality manufacturing programs thatoffer operational factory testing. Highavailability is achieved through

development of sound operation andmaintenance practices, which resideprincipally with the user. Manufacturerexperience and recommendations alsocontribute to this feature.

7. Low Operation and Maintenance Costs - Low operation and maintenance



Figure 2. Six MS7001B gas turbines

Figure 3. Two STAG 407B combined-cycle steam system installation

costs are achieved through quality de-sign, prudent operation, and equipmentdesign that allow convenient access forcomponent inspection.

8. High Efficiency in Small CapacityIncrements - Gas turbine generators aredesigned and manufactured in discreteframe sizes. For example, the General

Electric heavy-duty, gas turbine-packagedpower plant product line includes theMS6001B (50 Hz and 60 Hz), MS7001FA(60 Hz), MS7001B (60 Hz) and theMS9001FA (50 Hz) units, which cover anoutput range of approximately 37 MW to250 MW. Application of these gas turbinemodels in combined-cycle systems as



Figure 4. Two STAG 407B combined cycle

Figure 5. Typical project schedule

single or multiple gas turbine and HRSGinstallations can provide from about 50MW to several thousand megawatts ofpower generation at essentially constantplant thermal efficiency.

Gas Turbine Combined-CycleDevelopmentThe commercial development of combined-cy-cle systems has proceeded in parallel with gasturbine development. We are presently in thethird generation technology of combined-cyclesystems and are at the launch point of thefourth generation.

First Generation Combined-Cycle Plants The first gas turbine installed in an electric util-ity in the United States was applied in a com-bined cycle. This was a 3.5 MW gas turbine thatused the energy from the exhaust gas to heatfeedwater for a 35 MW conventional steam unit.The gas turbine is shown in Figure 6. A schemat-ic showing the combined-cycle system is shownin Figure 7. This system entered service in June1949, and a similar system was added to this sta-tion in 1952. The heat recovery economizers

applied in these systems used bare tubes, as wastypical of heat exchangers in combined-cyclesystems installed prior to 1959.

Most combined-cycle power generation systemsinstalled during the 1950s and early 1960s in-cluded conventionally-fired boilers. These sys-tems were basically adaptations of conventionalsteam plants with the gas turbine exhaust gasserving as combustion air for the boiler. Theefficiency of this type of combined cycle wasapproximately 5–6% higher than that of a simi-lar conventional steam plant. These systemscould economically utilize bare tubes in theboiler because of the high mean temperaturedifference between the combustion productsand the water/steam.

The repowering of steam power plants with gasturbine generators and HRSGs is still attractivein many applications today as evidenced by therecent Colorado Public Service, Fort St. Vraininstallation, which was placed in commercialoperation in 1999.

The summary presented in Table 1 characterizesthe first generation combined-cyle systems.



Figure 6. Gas turbine in first power generation combined cycle

Second Generation Combined-CyclePlants Equipment that made it economically feasibleto weld continuous spiral fins to tubes was intro-duced to boiler manufacturers in 1958. Heatrecovery combined cycles, using the sensibleheat in the gas turbine exhaust gas, were madefeasible by the enhanced gas-side heat transferusing finned tubes. Combined-cycle systemswith finned tube boilers entered service in1959.

During the 1960s the application of the heatrecovery type of combined-cycle systemsbecame more prevalent. Its initial applicationwas in power and heat applications where itspower-to-heat ratio was more favorable. Also, asmall number of the heat recovery type com-bined cycles were installed in utility power gen-eration applications during the 1960s.Application of these systems in the 1970s and1980s established the heat recovery feedwaterheating combined-cycle as a mature technologyfor baseload and mid-range service.

The summary presented in Table 1 characterizesthe first generation systems. Table 2 and Table 3

represent second generation characteristics andexperience.

The requirements for stack gas NOx emissioncontrol was initially legislated during the late1970s. The first systems utilized gas turbinewater or steam injection to meet new sourceperformance standards of 75 ppmvd at 15%oxygen with efficiency and fuel-bound nitrogenadjustments. Combined-cycle plants utilizedsteam from the steam cycle for NOx controlbecause this had the least impact on plant effi-ciency. As emission requirements became morestringent, it was necessary to apply SCR to aug-ment NOx abatement (TEPCO Groups I andII). Application of SCR systems became com-mon in Japan and in the USA in the mid-1980s.

Third Generation Combined-Cycle Plants The first and second generation combined-cy-cles were configured using gas turbine designsthat were optimized for simple-cycle output andefficiency. Gas turbine design optimization forsimple-cycle and for combined-cycle output andthermal efficiency is illustrated in Figure 8 per-formance maps as a function of firing tempera-ture and pressure ratio parameters.



Figure 7. OG&E Belle Isle feedwater heating repowering system cycle diagram

Specific power (i.e., output per pound of air-flow) is important since the higher the value,the smaller the gas turbine required for designpower output. The importance of thermal effi-ciency is obvious since it directly impacts theoperating fuel cost. Figure 8 illustrates a numberof significant points.

1. Where simple-cycle efficiency is thegoal, high pressure ratio is desirable.

2. Where combined-cycle efficiency is theobjective, more modest pressure ratiosare selected.

3. Firing temperature has a greaterimpact on combined-cycle efficiencythan simple-cycle efficiency.

Fuel price escalation in the 1970s and 1980s fur-ther increased the need for more efficientpower plants for base- and mid-range service.



Gas Turbine Small Size ( Frame 3000 & 5000)

Application Repowering & Cogeneration from 1949 - 1968

Steam Cycle Non-reheat, Single or Two Pressure

Emission Control None

Fuel Distillate Oil / Natural Gas

Table 1. Gas turbine in first power generation combined cycle

Gas Turbine 50-90 MW Capacity (MS6000B, MS7000B/C/E and MS9000B/E

Application Heat Recovery Feedwater Heating CC from 1968-1999

Steam Cycle Non-reheat, Single, Two & Three Pressure

Emission Control GT Water and Steam Injection plus Selective Catalytic Reduction System (SCR) Installed inthe HRSG Gas Path for NOx Control

Fuel Natural Gas / Distillate Oil / Low Btu Gas /Heavy Oils

Table 2. Second generation combined-cycle system characteristics



This led to gas turbine designs in the late 1980sthat were optimized specifically for combined-cycle efficiency.

The GE “F” Technology gas turbine designed inthe 1980s, with pressure ratio of about 14:1 and2400°F firing temperature was the result of adesign effort aimed at optimization for com-

bined-cycle peak efficiency rather than simple-cycle peak efficiency.

The fleet leader “F” Technology gas turbineentered commercial operation in 1990 in acombined-cycle installation at the VirginiaPower Chesterfield site and launched the thirdgeneration of combined-cycle systems.

Table 3. Second generation combined-cycle experience



The third generation “F” Technology com-bined-cycle experience is summarized in Table 4and system characteristics are defined in Table 5.

The trend of combined-cycle plant efficiencyimprovement is illustrated by Figure 9, whichshows the performance of selected STAG plantinstallations as a function of commercial oper-ating date. Gas turbine development has hadthe greatest impact on improved combined-cycle efficiency due primarily to the increase infiring temperature made possible through thedevelopment of high-temperature oxidation/corrosion-resistant metals and coatings, andadvanced metal surface cooling techniques.Another important factor is that the gas turbinecontributes about two-thirds of the combined-cycle plant’s power.

Advances in steam system technology have alsocontributed to improved combined-cycle effi-ciency. The significant steam-cycle develop-ments include:

1. Technology to weld continuous spiralfins on HRSG heat transfer tubes(1959).

2. Application of larger annulus areasteam turbine designs for low exhaustpressure applications.

3. Application of reheat steam cycle with“F” Technology gas turbines.

The current STAG product line ratings, whichrepresent third generation combined-cyclecapability, is summarized in Figure 10.

Fourth Generation Combined-Cycle Plants Further gas turbine materials development and

hot gas path cooling technology advances, as

well as higher temperature and pressure steam

cycles, will continue the trend for more efficient

combined-cycle systems in the future.

Gas turbines installed in the first, second andthird generation combined-cycle plants are con-figured with open-loop cooling of the turbinehot gas path and cooling air supplied from thecompressor. Hot gas path components are inlarge part cooled by film cooling. As a result,there is significant exhaust gas temperaturedrop across the first stage nozzle, and signifi-cant “chargeable air” required to cool down thesteam turbine stages. The drop in exhaust gastemperature across the first stage nozzle andthe increase in chargeable cooling loss due toincreases in turbine firing temperature maydiminish efficiency gains to the point of being

Figure 8. Gas turbine performance thermodynamics



Table 4. Third generation combined-cycle experience

Gas Turbines 70-250 MW (MS6001FA, MS7001FA, MS9001ECand MS9001FA)

Application Heat Recovery Feedwater Heating CC in the 1990s

Steam Cycle Reheat, Three Pressure

Emission Control DLN Combustion with Natural Gas and Water /Steam Injection with Oil Fuels plus SCR Installed in the HRSG

Fuel Natural Gas / Distillate Oil / Low Btu Gas

Table 5. Third generation combined-cycle system characteristics

60 Hz. STAG Combined Cycle Experience with ìF î Te chnology Gas Turbine Country Installation Configuration COD Output (MW) USA Virginia Power #7 S107F 1990 214USA Virginia Power #8 S107F 1992 218Korea KEPCO Seo-Inchon #1 & #2 8 x S107F 1992 1887USA Sithe Independence 2 x S207FA 1995 1062USA Tampa Electric, Polk Co. S107FA 1996 313Korea KEPCO Seo-Inchon #3 & #4 2 x S207FA 1996 1004USA US Gen. Co., Hermiston 2 x S107FA 1996 425USA Crockett Cogen S107FA * 1996 202/248Mexico CFE Samalayuca 3 x S107FA * 1998 506USA Cogentrix, Clark Co. S107FA * 1998 254USA Ft. St. Vrain S207FA 1999 487Korea KEPCO, POSCO S207FA 1999 498Columbia EPM LaSierra S207FA 2001 478USA Bucksport Energy S107FA 2001 176USA Westbrook S207FA 2001 528USA Santee Cooper S207FA 2001 600Korea Pusan 4 x S207FA 2003/4 2000

Number of gas turbines =Installed Capacity = 12,411 MW

50 Hz. STAG Combined Cycle Experience with ìF î Te chnology Gas Turbine Country Installation Configuration COD Output (MW) Japan TEPCO, Yokahama 8 x S109FA * 1996/7 2800China China Power & Light 8 x S109FA * 1996/72 2731Japan TEPCO, Chiba 4 x S109FA * 1998 1440India Enron, Dabhol I S209FA 1998 698Chile Renca S109FA 1998 370Netherlands AKZO, Delesto S109FA * 1999 364U.K. Sutton Bridge S209FA 1999 800Thailand Ratchaburi 3 x S209FA 2000 2130Argentina Central Puerto S209FA 2000 769Japan Hitachi Zosen S106FA 1999 106U.K. Tri-Energy S209FA 2000 700U.K. Great Yarmouth S109FA * 2001 407India Enron, Dabhol II 2 x S209FA 2001 1600Japan TEPCO, Futtsu 3 4 x S109FA * 2002 1590Spain Castellon S209FA 2002 285* Single-shaft Combined Cycle

Number of gas turbines = 50 units= 17,795 MW

*Single-shaft Combined Cycle45 Units

Installed capacity



uneconomical. For this reason, the GE fourthgeneration plants with “H” Technology gas tur-bines will be configured with an integratedclosed-loop steam cooling system (See Figure 11).This system allows higher turbine firing tempera-ture to be achieved without increasing combus-tion temperature. This is because exhaust gastemperature drop across the first stage nozzle issignificantly reduced as outlined in Figure 12.Another important benefit of the integratedclosed-loop steam cooling system is the elimina-tion of “chargeable cooling air” for the first and

second stage rotating and stationary airfoils. Thistechnology is expected to provide two percent-age points thermal efficiency improvement.

The “H” platform gas turbine combined-cycleplants are expected to achieve 60% LHV thermalefficiency in the first half of this decade. Theapplication of ceramic hot gas path parts andcoatings show promise for further future per-formance gains.

Steam cycle improvements that includeincreased steam pressure and temperature with

2. Houston L&P, Wharton

Combined-Cycle Illustration

1. City of Clarksdale (S105) Station (S407B)

3. Salt River (S107E) 4. Western Farmers (S107E) 5. MMWEC (S307E) 6. CFE Mexico (S307E) 7. Chubu (S107E)

8. VP Chesterfield (S107F)

Plant Commercial Operation Date

Co

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ined

Cyc

le P

lan

t E

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ien

cy (

Per

cen

t)

1980197030

35

40

45

50

55

60

20001990

(11)(12)

(9) (10)

(1)

(3)(2)

(6)

(8)

(7)

(5)(4)

Seo 9. KEPCO, Inchon (S107F) 10. Sithe, Independence (S207FA) 11. Sutton Bridge (S209FA) 12. KEPCO, Seo Inchon (S207FA)

Figure 9. Combined-cycle system efficiency trend

Figure 10. Current STAG product line ratings

supercritical steam cycles have near-term appli-cation. Current economic analysis indicates,however, that the thermodynamic gain associat-ed with steam cycles that have steam tempera-tures and pressures above the current levels(1050°F and 1400 PSIG to 1800 PSIG) cannot

be justified in most cases because of the addedcosts.As in the past, operating cost (fuel price) andthe cost of new technology development willdictate the trend for increased combined-cycleefficiency.



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Figure 11. S107H/S109H cycle diagram

Figure 12. Impact of stage one nozzle cooling method

References

D.L. Chase and P.T. Kehoe, “Combined-Cycle Product Line and Performance,” GER-3574F.

C.E. Maslak and L.O. Tomlinson, “Combined-Cycle Experience,” GER-3651E.

H.E. Miller, “F” Technology - The First Half Million Operating Hours,” GER-3950.

Frank Brooks, “GE Heavy-Duty Gas Turbine Performance Characteristics,” GER-3567G.

P.W. Schilke, “Advanced Gas Turbine Materials and Coatings,” GER-3569F.

J. Cofer, J.K. Reinker and W.J. Sumner, “Advances in Steam Path Technologies,” GER-3713D.

D.L. Chase and L.B. Davis, “Current Review of Combined-Cycle Technology - Pacific Coast ElectricalAssociation,” 1988.

List of FiguresFigure 1. STAG 209E combined-cycle part load performance

Figure 2. Six MS7001B gas turbines

Figure 3. Two STAG 407B combined-cycle steam system installation

Figure 4. Two STAG 407B combined cycle

Figure 5. Typical project schedule

Figure 6. Gas turbine in first power generation combined cycle

Figure 7. OG&E Belle Isle feedwater heating repowering system cycle diagram

Figure 8. Gas turbine performance thermodynamics

Figure 9. Combined-cycle system efficiency trend

Figure 10. Current STAG product line ratings

Figure 11. S107H / S109H cycle diagram

Figure 12. Impact of stage one nozzle cooling method

List of TablesTable 1. Gas turbine in first power generation combined cycle

Table 2. Second generation combined-cycle system characteristics

Table 3. Second generation STAG power generation experience

Table 4. Third generation combined-cycle experience

Table 5. Third generation combined-cycle system characteristics





Documents

GER-4206 - Combined-Cycle Development Evolution and Future · Combined-cycle systems utilizing the Brayton Cycle gas turbine and the Rankine Cycle steam system with air and water