7280590 GE Combined Cycle

GE Power Systems

GE Combined-CycleProduct Line andPerformance

D.L. ChaseP.T. KehoeGE Power SystemsSchenectady, NY

GER-3574G

g

Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1STAG Product Line Designations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1STAG Product Line Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2STAG Power Generation Product Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3STAG Combined-Cycle Major Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Gas Turbines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15HRSG. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Steam Turbine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Generators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24Auxiliaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Plant Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Plant Arrangements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Utility Load Growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Thermal Energy and Power System Product Line. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Engineered Equipment Package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

GE Combined-Cycle Product Line and Performance

GE Power Systems ■ GER-3574G ■ (10/00) i


GE Power Systems ■ GER-3574G ■ (10/00) ii

IntroductionThe development during the past four decadesof larger capacity gas turbine designs (50 MW to380 MW) with increased specific power has ledto the parallel development of highly-efficientand economical combined-cycle systems. TheGE pre-engineered, combined cycle productline is designated STAG™, which is an acronymfor STeam And Gas. Each STAG combinedcycle system is an Engineered EquipmentPackage (EEP) consisting of GE gas turbines,steam turbines, generators, Heat RecoverySteam Generators (HRSGs) and controls. Themost efficient of these STAG systems is config-ured with the GE "H" model gas turbine and isscheduled for commercial operation by the year2003. The “H” combined cycle will achieve 60percent (LHV) thermal efficiency.

The STAG EEP is an optimized and matchedsystem of high technology power generationequipment, software, and services configuredfor convenient integration with the owner's aux-iliaries and balance of plant equipment to forman economical power plant. This single sourcesupply of the EEP enables GE to provide guar-antees of plant thermal and emission perform-ance as well as warrant system operation.

The product line spans a wide range of capabil-ities for both 50 and 60 Hz applications. A widerange of configurations is available with stan-dard options that enable the systems to beadapted to suit the economic requirements ofeach application. The STAG combined-cycleproduct line includes two major categories:

■ Pre-engineered oil- or natural gas-firedsystems for electric power generation

■ Pre-engineered building blocks forcombined-cycle cogeneration systemsand coal- or oil-fired integratedgasification combined-cycle (IGCC)power generation systems.

Economical performance of function is the out-standing characteristic of STAG combined-cyclesystems. The features that contribute to eco-nomical power generation by STAG combined-cycle power generation systems are shown inTable 1 and those for thermal and power systemsare presented in Table 2.

STAG Product Line DesignationsSystem designations that identify STAG com-bined-cycle product line configurations aredefined in Table 3. This example defines thedesignation for the single-shaft and multi-shaftcombined-cycle configurations.


GE Power Systems ■ GER-3574G ■ (10/00) 1

Table 1. STAG combined-cycle power generationsystem features

Table 2. STAG combined-cycle thermal energyand power system features

• High Thermal Efficiency• Low Installed Cost• Fuel Flexibility – Wide Range of Gas and

Liquid Fuels• Low Operation and Maintenance Cost• Operating Flexibility – Base, Mid-range,

Daily Start• High Reliability• High Availability• Short Installation Time• High Efficiency in Small Capacity

Increments

• High Thermal Efficiency• Low Installed Cost• Low Operation and Mainteance Costs

- Steam Generation at Process Conditions- Extraction/Condensing Steam Turbine- Non-Condensing Turbine Exhausting to Process- Unfired/Fired HRSGs- Gas Turbine DLN/Steam Injection

• High Power to Thermal Energy Ratio• High Reliability/Availability• Short Installation Time

STAG Product Line ConfigurationsThe product line includes single-shaft andmulti--shaft configurations. Simplified blockdiagrams of these configurations are presentedin Figure 1. The single-shaft STAG system con-sists of one gas turbine, one steam turbine, onegenerator, and one HRSG with the gas turbineand steam turbine coupled to the single gener-ator in a tandem arrangement on a single shaft.Multi-shaft STAG systems have one or more gas

turbine generators and HRSGs that supplysteam through a common header to a separate,single steam turbine generator.

Single- and multiple-pressure non-reheat steamcycles are applied to STAG systems equippedwith GE gas turbines that have rating pointexhaust gas temperatures of approximately1000°F / 538°C or less. Selection of a single- ormultiple-pressure steam cycle for a specificapplication is determined by economic evalua-



GENGT HRSG

GEN GT HRSG ST GEN

HRSG

GTST GEN

S 2 0 7FA - MSSTAG™ Two GT Model Multi-Shaft

GTs Series Configuration

S 1 0 7FA - SSSTAG™ One GT Model Single-Shaft

GT Series Configuration

STAG IS A REGISTERED TRADEMARK OF GENERAL ELECTRIC(USA)

AND IS AN ACRONYM FOR STeam And Gas

S107FA-SS

S207FA-MS

Table 3. STAG combined-cycle system designations

GT19939

Figure 1. STAG system configurations

tion, which considers plant-installed cost, fuelcost and quality, plant-duty cycle, and operatingand maintenance cost.

Multiple-pressure reheat steam cycles areapplied to STAG systems with GE gas turbinesthat have rating point exhaust gas temperaturesof approximately 1100°F / 593°C or greater.

A generalized combined-cycle, electric powergeneration and thermal energy capability mapis presented in Figure 2. This map is typical of asystem supplying process steam at 150 psig/11.4bars and utilizing a gas turbine with 100 MWrated output.

The vertical axis of Figure 2 with zero thermalenergy shows the power and thermal efficiencyof combined cycles with unfired, supplemen-tary-fired, and fully-fired steam cycles. The mostefficient power generation cycles are those withunfired HRSGs having modular pre-engineeredcomponents. These unfired steam cycles arealso the lowest in cost and are, therefore,applied in the STAG combined-cycle powergeneration product line. Supplementary-firedcombined-cycle systems are provided for cus-

tomer specific applications in which the needfor increased power offsets the correspondingreduction in thermal efficiency.

The most efficient cycles for cogenerationapplications are those with fully-fired HRSGs, asindicated by Figure 2, at maximum thermalenergy output. The fully-fired HRSGs are highin cost because of their water wall constructionand need for field erection. Also, fully-firedHRSGs may add to emission considerations asplant siting requirements are evaluated. Theprimary regions of interest for cogeneration,combined-cycle systems are those with unfired

and supplementary-fired steam cycles. Thesesystems provide a wide range of thermal energyto electric power ratio, 0–12,000 Btu thermalenergy per kW (0–12,660 kJ per kW), and rep-resent the range of thermal energy capabilityand power generation covered by the productline for cogeneration capability.

STAG Power Generation Product LineThe STAG power generation product lineincludes an array of steam cycle options, which



GT21520B

Figure 2. Generalized combined-cycle performance capability

satisfies a wide range of fuels, fuel cost, dutycycle, and other economic considerations. Thisenables selection of a steam cycle for each appli-cation that suits specific economic and opera-tional requirements. Steam cycles utilized in theSTAG product line include:

■ Single-Pressure, Non-Reheat HeatRecovery Feedwater Heating. Thissteam cycle, shown in Figure 3, has anunfired HRSG with finned tubesuperheater, evaporator, and

economizer sections. Energy isrecovered from the exhaust gas byconvective heat transfer. The HRSGschematic diagram is shown in Figure4. This is the simplest steam cycle thatcan be applied in a combined cycleand it has been used extensively. Itresults in a low installed cost.Although it does not produce thehighest combined-cycle thermalefficiency, it is a sound economic



GT16402A

Figure 3. Single-pressure non-reheat cycle diagram

GT1640B

Figure 4. Single-pressure non-reheat HRSG diagram

selection when fuel is inexpensive,when applied in peaking type service,or when burning ash-bearing fuel withhigh sulfur content. This steam cycleis utilized in the STAG product lineprimarily with GE gas turbines havinga baseload exhaust gas temperature ofapproximately 1000°F / 538°C or less.The HRSG stack gas temperature withthis steam cycle is approximately 340°F / 171°C.

■ Multiple-Pressure, Non-Reheat HeatRecovery / Feedwater Heating. Multi-pressure steam generation is used tomaximize energy recovery from gasturbine exhaust. HRSG gas-side andsteam-side temperature profiles forsingle- and multiple-pressure steamcycles are presented in Figures 5 and 6.This illustrates that increasing thenumber of steam pressure levelsreduces the exhaust gas andsteam/water energy difference. Two-or three-pressure steam cycles achievebetter efficiency than the single-pressure systems, but their installed

cost is higher. They are the economicchoice when fuel is expensive or if theduty cycle requires a high load factor.The three-pressure steam cycle isshown in Figure 7 and the HRSGschematic diagram is shown in Figure8. This cycle is similar to the single-pressure cycle with the addition of thelow-pressure and intermediate-pressure sections. Improved plantperformance with multiple-pressuresteam cycles results from additionalheat transfer surface installed in theHRSG. The HRSG stack gas tem-perature is in the range of 200°F / 93°C to 260°F / 127°C.

■ Three-Pressure, Reheat Heat RecoveryFeedwater Heating. The reheat steamcycle matches the characteristics of the“EC,” “F,” and “H” technology gasturbines. The higher exhaust gastemperature of 1100°F / 593°C orgreater provides sufficient hightemperature energy to the HRSG tomake the reheat steam cycle practical.Fuel gas heating to approximately



Tem

pera

ture

Heat Transfer

EconomizerEvaporatorSuperHeater

Pinch

Sub-cool

Approach

Typical Exhaust Gas TemperatureProfile - One Pressure System

Figure 5. Typical exhaust gas/steam cycle temperature profile for single-pressure system



Heat Transfer

Tem

per

atu

re -

°C

HPS

RH

HPS HPB

IPS

HPE

LPS

IPB IPE HPE

LPB LPE

Gas Turbine Exhaust Gas

Low Pressure

High Pressure

Intermediate & Reheat Pressure

Figure 6. Typical exhaust gas/steam cycle temperature profile for three-pressure system

Bypass

DiverterDamper

HRSG

Fuel

GT Gen ST Gen

Deaerating Cond.

Cond.Pump

Legend

Steam

Water

Air, Gas

Fuel

Figure 7. Three-pressure non-reheat cycle diagram

GT16405C

Figure 8. Three-pressure non-reheat HRSG diagram

365°F / 185°C, using water suppliedfrom the HRSG IP economizerdischarge, is also included with the“EC” and “F” technology gas turbines.This steam cycle is shown in Figure 9.The HRSG schematic is presented inFigure 10.

The “H” platform gas turbines, configured withhot gas path components cooled with both a

closed-loop, steam-cooling system and an open-loop, air-cooling system design, are designatedas MS7001H and MS9001H. The reheat steamcycle utilized with these gas turbines is closelyintegrated with the gas turbine steam-cooling

system. This integration provides additionalincentive to select single-shaft STAG configura-tion for these gas turbines. The steam cycleused with the S107H and S109H is shown inFigure 11. The HRSG schematic is shown inFigure 12.

These STAG combined-cycle systems are themost efficient power generation systems cur-rently available. The base configuration for the

STAG power generation combined-cycle prod-uct line is designed for high efficiency when fir-ing natural gas or distillate fuel. A summary ofthe equipment and system configuration is pre-sented in Table 4.

The 60 Hz STAG power generation productline ratings are presented in Table 5. Table 6shows the major equipment in each standardSTAG system. The 50 Hz product line ratingsare presented in Table 7, and Table 8 shows themajor equipment in each of these standardSTAG systems. These ratings are presented forgas turbine base load operation with natural gasfuel. Nominal throttle and reheat steam condi-tions for the non-reheat and reheat STAG prod-uct lines are defined in Table 9.



Figure 9. Three-pressure reheat cycle diagram

Figure 10. Three-pressure reheat HRSG diagram

• Unfired, three-pressure steam cycle- Non-reheat for rated exhaust gas

temperature less than 1000°F/538°C- Reheat for rated exhaust gas temperature

higher than 1050°F/566°C and fuel heating- Heat recovery feedwater heating- Feedwater deaeration in condenser- Natural circulation HRSG evaporators

• Gas turbine with Dry Low NOx combustors

• Once-through condenser cooling water system

• Multi-shaft systems

• Single-shaft systems- Integrated equipment and control system

Table 4. STAG power generation combined-cyclebase configuration

The STAG product line equipment and plantnatural gas fuel ratings defined in Tables 5 and 7represent thermodynamic optimum perform-ance that is expected to be the economic opti-mum configuration for baseload and mid-rangedispatch using clean fuels costing about $2.50per 106 Btu, HHV ($2.64 per 106 Kj, HHV). Awide array of options is available for the STAGpower generation product line to suit specificeconomic criteria as well as the operating andinstallation preferences of the owner. Table 10lists the most commonly-applied options inaddition to the base configuration.

Non-reheat steam cycles with one or two pres-

sures and reheat steam cycles with two pressuresare also available for the STAG product-line sys-tems. Typical performance variation for theseoptional steam cycles is presented in Table 11.HRSGs with forced circulation evaporators areavailable to suit specific installation situationsand owner preferences. Figure 13 shows a two-pressure, non-reheat steam cycle with forcedcirculation HRSG.

Systems can be provided with a deaerator inte-gral to the HRSG that utilizes low-pressure evap-orator energy to perform the feedwater deaera-tion at positive pressure at a small reduction inthermal efficiency. Those systems that include a



C oo lin g

W a te r

C oo lin g A ir

C oo ling

S ystem

To

Stack

Air

Ga s Tu rb in e

Air Tre atment

Co nd en sa te Pu mp

Fue l

IPH P

H e at Re c ov e ry

S team Ge ne rato rFu el

He a tin g

Sys tem

Glan d S eal

Co nd en ser

DeaeratingCondenser

G en era torLPLP

Attemp

Fil te r

L EGE ND

FilterA

FilterB

F e ed wa ter

Pu m p

C on de ns a te Fil te r

Fu el

SteamW aterExhau stAir

S te a m Tu rb in e

Figure 11. STAG 107H/S109H cycle diagram

T O H P TU RB IN E

T o

S ta c k

H e at Re c ov e ry

S te a m Ge ne rato r

Atte mp

LEGEND

Fe e dw ate r

P um p

FR OM C ON D E NS A TE P UM P

Fuel

SteamWaterExhaustAir

TO FUEL HEATING SY STE MTO COOLING AIR COOLING SYSTEM

FROM COOLING AIR COOLINGSYSTEM

FROM GT E XHAUST

T O IP T UR B IN E

TO LP TU RB IN E

FR OM H P T UR B IN E

E X HA U S T

T O G T C OO LIN G

Figure 12. HRSG schematic for S107H/S109H

low-pressure economizer for high thermal effi-ciency will require material that resists corro-sion because feedwater passing through this sec-tion may have a high oxygen concentration,and the external tube surface temperature maybe below the exhaust gas dew point tempera-ture. Figure 14 shows a three-pressure non-reheat HRSG with integral deaerator.

Fuel characteristics affect combined-cycle per-formance in a variety of ways. High hydrogencontent in fuels such as natural gas results in

high water content in the combustion products.Water has a higher heat content than air or othercombustion products, so fuels with high hydro-gen content increase output and efficiency. Ash-bearing fuels foul the gas turbine and HRSG;therefore, equipment and system design consid-erations that accept fouling reduce plant outputand efficiency. Sulfur content in the fuel mayrequire adjustment in the temperature of thestack gas and the water entering the HRSG econ-omizer to prevent condensation of corrosive sul-



Combined cycle Net Plant Net Plant Heat Rate(LHV) ThermalDesignation Power (MW) Btu/ kWhr kJ/ kWhr Efficiency (%, LHV) S106B (4) 64.3 6960 7340 49.0S206B (4) 130.7 6850 7230 49.8S406B (4) 261.3 6850 7230 49.8S106FA (5) 107.1 6440 6795 53.0S206FA (5) 217.0 6355 6705 53.7S107EA (4) 130.2 6800 7175 50.2S207EA (4) 263.6 6700 7070 50.9S107FA (5) 262.6 6090 6425 56.0S207FA (5) 529.9 6040 6375 56.5S107FB (5) 280.3 5950 6280 57.3S207FB (5) 562.5 5940 6260 57.5S107H (6) 400.0 5690 6000 60.0

Notes: 1. Site conditions =59 F, 14.7 psia, 60% RH (15 C, 1.013 bar)2. Steam turbine exhaust pressure = 1.2 inches Hg,A (30.48 mm Hg,A)3. Performance is net plant with allowance for equipment and plant auxiliaries

including those associated with a once-through cooling water system4. Three-pressure, non-reheat, heat-recovery feedwater heating steam cycle5. Three-pressure, reheat, heat-recovery feedwater heating steam cycle with

integrated fuel, gas-heating system6. Three-pressure, reheat, heat-recovery feedwater heating steam cycle with

integrated turbine steam- and air-cooling and fuel-heating systems

Table 5. 60 Hz STAG product line performance

ThermalEfficiency (%, LHV)

Steam TurbineGas Turbine HRSG Exhaust LSB Exhaust

Designation No. Frame No. Type No. Inches mm Config.

• Heavy Duty GT

S106B 1 PG6581 B 1 Non-Reheat, Unfired 1 23 584 AxialS206B 2 PG6581 B 1 Non-Reheat, Unfired 1 33.5 851 AxialS406B 4 PG6581 B 2 Non-Reheat, Unfired 2 33.5 851 DownS106FA 1 PG6101 FA 1 Reheat, Unfired 1 30 762 AxialS206FA 2 PG6101 FA 1 Reheat, Unfired 2 30 762 DownS107EA 1 PG7121 EA 1 Non-Reheat, Unfired 1 33.5 851 AxialS207EA 2 PG7121 EA 2 Non-Reheat, Unfired 2 33.5 851 DownS107FA 1 PG7241 FA 1 Reheat, Unfired 2 30 762 DownS207FA 2 PG7241 FA 2 Reheat, Unfired 4 30 762 DownS107FB 1 PG7251 FB 1 Reheat, Unfired 2 30 762 DownS207FB 2 PG7251 FB 2 Reheat, Unfired 4 30 762 DownS107H 1 PG7001 H 1 Reheat, Unfired 2 40 1016 Down

Table 6. 60 Hz STAG product line equipment

furic acid. The increased stack gas temperaturerequired by higher sulfur content decreases out-put and efficiency. Performance variation withfuel type (hydrogen, ash and sulfur content typi-cal of each) is presented in Table 12.

The STAG product line includes gas turbineswith Dry Low NOx (DLN) combustors that canoperate with stack gas NOx emission concentra-tion as low as 9 ppmvd at 15% oxygen (15.5g/GJ) without water or steam injection, whenoperating on natural gas fuel. Water or steaminjection may be required to meet NOx emis-sion requirements when operating on distillateoil fuel. Also, gas turbines are available with

conventional, diffusion flame combustors oper-ating with water or steam injection to meet NOxemission limits. Table 13 presents stack gas NOxemissions from gas turbines in typical STAGcombined cycle systems for operation with DLNor diffusion flame combustors with natural gasfuel. The effect of water- or steam-injection onNOx abatement and thermal performance isalso presented.

Selective catalytic reduction (SCR) is a stack gasNOx reduction system that uses ammonia toreact with NOx over a catalyst that reduces NOxto nitrogen and water. These systems increasethe plant installation and operating cost, but



Combined cycle Net Plant Net Plant Heat Rate (LHV) ThermalDesignation Power (MW) Btu/kWhr kJ/kWhr Efficiency (%, LHV)S106B (4) 64.3 6950 7340 49.0S206B (4) 130.7 6850 7230 49.8S406B (5) 261.3 6850 7230 49.8S106FA (5) 107.4 6420 6775 53.2S206FA (4) 218.7 6305 6650 54.1S109E (4) 189.2 6570 6935 52.0S209E (4) 383.7 6480 6840 52.7S109EC (5) 259.3 6315 6660 54.0S209EC (5) 522.6 6270 6615 54.4S109FA (5) 390.8 6020 6350 56.7S209FA (5) 786.9 5980 6305 57.1S109H (6) 480.0 5690 6000 60.0

Notes: 1. Site conditions = 59 F, 14.7 psia, 60% RH (15 C), 1.013 bar) 2. Steam turbine exhaust pressure = 1.2 Inches HgA (30.48 mm HgA) 3. Performance is net plant with allowance for equipment and plant auxiliaries including those associated with a once- through cooling water system 4. Three-pressure, non-reheat, heat recovery feedwater heating steam cycle 5. Three-pressure, reheat, heat-recovery feedwater healing steam cycle with integrated fuel gas heating system

6. Three-pressure, reheat, heat-recovery feedwater heating steam cycle with integrated turbine steam and air cooling and fuel heating systems.


Steam Turbine Gas Turbine HRSG Exhaust LSB ExhaustDesignation No. Frame No. Type No. Inches mm Config.

• Heavy Duty GT

S106B 1 PG6581 B 1 Non-Reheat, Unfired 1 17 432 AxialS206B 2 PG6581 B 1 Non-Reheat, Unfired 1 33.5 851 AxialS406B 4 PG6581 B 2 Non-Reheat, Unfired 2 33.5 851 DownS106FA 1 PG6101 FA 1 Reheat, Unfired 1 26 660 AxialS206FA 2 PG6101 FA 2 Reheat, Unfired 1 42 1066 AxialS109E 1 PG9171 E 1 Non-Reheat, Unfired 1 42 1066 DownS209E 2 PG9171 E 2 Non-Reheat, Unfired 2 42 1066 DownS109EC 1 PG9231 EC 1 Reheat, Unfired 1 42 1066 DownS209EC 2 PG9231 EC 2 Reheat, Unfired 2 42 1066 DownS109FA 1 PG9351 FA 1 Reheat, Unfired 2 33.5 851 DownS209FA 2 PG9351 FA 2 Reheat, Unfired 4 33.5 851 DownS109H 1 PG9001 H 1 Reheat, Unfired 2 42 1066 Down


they can reduce NOx to less than 9 ppmvd at15% oxygen (15.5 g/GJ) for all combined-cyclesystems in the product line. The SCR catalysttypically operates in the 570°F/300°C to750°F/400°C temperature range, so the catalystis typically installed within the high-pressureevaporator as shown in Figure 15. The ammoniainjection grid is installed upstream of the evap-orator where the gas temperature is below thetemperature at which ammonia oxidizes toform NOx. This provides intimate mixing of theammonia and NOx as the gas passes throughthe pre-evaporator section.

Carbon monoxide (CO) emissions are low atgas turbine loads above 50%, typically less than



Heat Recovery FeedwaterHeater Steam Cycle

Non-ReheatThree-Pressure

ReheatThree-Pressure

Steam Turbine Size (MW) ≤ 40 > 40 <60 ≥ 60 > 60

Throttle Pressure (psig) 820 960 1200 1400-1800(Kg/cm2,g) (58) (68) (84) (98)

Throttle Temperature (°F) 40 Approach to Gas Turbine 1000-1050(°C) (22) Exhaust Gas Temperature (538-566)

Reheat Pressure (psig) -- -- -- 300-400(Kg/cm2,g) -- -- -- (21-28)

Reheat Temperature (°F) -- -- -- 1000-1050(°C) -- -- -- (538-566)

IP Admission Pressure (psig) 100 120 155 300-400(Kg/cm2,g) (7) (8) (11) (21-28)

IP Admission Temperature (°F) 20 Approach to Exhaust Gas Temperature(°C) (11) Upstream of Superheater

LP Admission Pressure (psig) 25 25 25 40(Kg/cm2,g) (1.8) (1.8) (1.8) (2.8)

LP Admission Temperature (°F) 20 Approach to Exhaust Gas Temperature(°C) (11) Upstream of Superheater

Table 9. STAG product line steam turbine throttleand admission steam conditions

STEAM CYCLE NOX CONTROL• Single pressure • Water injection• Two pressure • Steam injection• Three pressure* • SCR (NOX and/or CO)• Reheat • Dry Low NOx combustion*• Non-reheat CONDENSERDEAERATION • Water cooled (once-through system)*• Deaerating condenser* • Water cooled (evaporative cooling tower)• Deaerator/evaporator integral • Air-cooled condenser

with HRSG FUELHRSG DESIGN • Natural gas*• Natural circulation evaporators* • Distillate oil• Forced circulation evaporators • Ash bearing oil• Unfired* • Low BTU coal and oil-derived gas• Supplementary fired • Multiple fuel systems

* Base configuration

Table 10. Power generation combined-cycle product line system options

STAG 207EA

STEAM CYCLENET PLANTOUTPUT (%)

NET PLANT THERMALEFFICIENCY (%)

THREE PRESSURE, REHEAT +0.7 +0.7THREE PRESSURE, NON-REHEAT BASE BASETWO PRESSURE, NON-REHEAT -1.0 -1.0SINGLE PRESSURE, NON-REHEAT -4.7 -4.7

STAG 107EA

STEAM CYCLENET PLANTOUTPUT (%)


THREE PRESSURE, REHEAT BASE BASETWO PRESSURE, REHEAT -1.1 -1.1THREE PRESSURE, NON-REHEAT -1.2 -1.2TWO PRESSURE, NON-REHEAT -2.0 -2.0

Table 11. Performance variation with steam cycle

5--25 ppmvd (9-43 g/GJ). Low CO emissions arethe result of highly-efficient combustion.Catalytic CO emission abatement systems arealso available, if required, for lower emissionrates. The CO catalyst is installed in the exhaustgas path, typically upstream of the HRSG super-heater.

Options such as compressor inlet cooling,steam or water injection for power augmenta-tion, HRSG supplementary firing and gas tur-bine peak load capabilities are available forcombined-cycle plant power enhancements.They are generally applied primarily for peakperiod capacity additions.



Figure 13. Two-pressure non-reheat steam cyclewith forced circulation HRSG

GT21836A

Figure 14. Three-pressure non-reheat HRSG with integral deaerator

STAG 209E

FUEL NET PLANTOUTPUT (%)


NATURAL GAS BASE BASE

DISTILLATE OIL -3.0 -2.1

RESIDUAL OIL -9.3 -7.6

NOTES 1. OPERATING POINT = BASE LOAD2. TWO PRESSURE, NON-REHEAT

RECOVERY FEEDWATERHEATING SYSTEM CYCLE

Table 12. STAG combined-cycle performance variation with fuel characteristics

Compressor inlet cooling that uses evaporativecooling is an effective means of adding plantcapacity for applications with high ambient airtemperature and low relative humidity. An 85%effectiveness evaporative cooler is expected toincrease plant output by about 5% during oper-ation at 90°F / 32°C and 30% relative humiditysite conditions.

Evaporative and mechanical chiller systems maybe used to cool gas turbine inlet air to as low as45°F / 7°C. These inlet cooling systems can

achieve up to 11% capacity increase duringoperation at site conditions of 90°F / 32°C and30% relative humidity. Evaporative cooling andchilling systems do not improve combined-cycleplant efficiency; however, they may provide eco-nomic peak power addition during warm sum-mer periods.

Supplementary firing of the HRSG can be uti-lized to increase steam turbine capability by asmuch as 100%. This will increase plant capacityby about 25%. Cogeneration of power and



Gas Turbine MS7001EA MS7001FACombustionSystem DLN Diffusion Flame DLN Diffusion FlameNOx PMVD at15% O2 (g/GJ)

9(15.5)

160(275)

42(72)

25(43)

9(15.5)

212(365)

42(72)

Diluent InjectionWater/Fuel byWt

0 0 0.81 - 1.04 - 0 0 0.89 -

Steam/Fuel byWt

0 0 - 1.22 - 1.58 0 0 - 1.62

STAG PlantPerformanceNet Power (∆%) Base Base +3.5 +1.0 +5.0 +1.1 Base Base +5.4 +2.8Net Heat Rate(∆%)

Base Base +3.6 +2.1 +5.2 +3.4 Base Base +3.9 +3.1

Steam Cycle Non-Reheat, Three Pressure Reheat, Three PressureNotes: 1. Site Conditions 59°F, 14.7 psia, 60% RH

(15°C, 1.013 bars)2. Fuel – Natural Gas

Table 13. Effect of NOx control on combined-cycle performance

GT122107B

Figure 15. Three-pressure reheat HRSG with SCR

process energy is usually the incentive forHRSG supplementary firing; however, peakingcapacity credits, or leveling fuel consumptionover the ambient temperature range to accom-modate “take-or-pay” fuel contracts may also jus-tify this option. The incremental efficiency forpower produced by supplemental firing is inthe 34–36% range based on the lower heatingvalue of the fuel.

While gas turbine water or steam injection canbe applied to enhance plant output as well asreduce NOx emissions, plant efficiency isdegraded.

Gas turbine peak load capability is availablewith many gas turbine configurations and canadd 3–10% combined-cycle plant capacity. Thismay be the most economic approach to smallcapacity additions for short periods of timebecause peak load operation significantlyimpacts gas turbine parts life and maintenancecost. Table 14 summarizes the performanceimpact of these combined-cycle power enhance-ment options.

Combined-cycle systems can be integrated withgasification systems to form efficient coal- or oil-

fired power plants with outstanding environ-mental performance. The standard modules inthe STAG combined-cycle product line can bereadily adapted to integrated gasification com-bined cycles (IGCCs).

Figure 16 shows a diagram of an advanced tech-nology “H” platform combined-cycle IGCC sys-tem with oxygen-blown gasifier and integrationof the air separation unit with the gas turbine.This advanced technology IGCC system promis-es to be an economical power generation sys-tem that can fire coal, petroleum coke, heavyresidual oil and other solid or low-grade liquidfuels. The range of ratings for the advancedtechnology IGCC plants is as follows:

Net LHVIGCC Capacity Thermal Eff.Unit Frequency (Hz) Range (MW) Range (LHV)

STAG 107H 60 400-460 49-51 %

STAG 109H 50 480-550 49-51%

The capacities and efficiencies are shown asranges because they vary with the type of gasi-fiers, gas clean-up systems, air and steam cycleintegration, coal or other fuel analysis, and fuelmoisture content.



Typical Performance ImpactPower Enhancement Option ∆ Output ∆ Heat RateBase Configuration Base BaseEvaporative Cooling GT Inlet Air (85%Effective Cooler)

+5.2% -

Chill GT Inlet Air to 45°F +10.7% +1.6%GT Peak Load +5.2% -1.0%GT Steam Injection (5% of GT Air Flow) +3.4% +4.2%GT Water Injection (2.9% of GT Air Flow) +5.9% +4.8%HRSG Supplementary Firing +28% +9%Notes: 1. Site Conditions = 90°F, 30% RH

2. Fuel = Natural Gas3. Three Pressure, Reheat Steam Cycle

Table 14. STAG system power enhancement options

STAG Combined-Cycle MajorEquipmentThe major equipment for STAG combined-cycle electric power generation systems includesthe line of packaged gas turbine power genera-tion units, unfired HRSGs, steam turbine-gen-erators, and controls. This is a line of proven,reliable equipment with excellent performancecharacteristics for combined-cycle systems. Thisequipment includes gas turbine generators andsteam turbine generators manufactured by GEas well as HRSGs and controls selected to forma coordinated combined-cycle system for eachapplication. Features of the major equipmentthat are significant for efficient, reliable com-bined-cycle systems are presented in the follow-ing discussion.

Gas TurbinesThe ratings of GE gas turbines applied in theSTAG combined-cycle product line are present-ed in Table 15. Figure 17 shows a cross-section ofthe PG7121EA gas turbine typical of GE gas tur-bines with 2035°F / 1113°C firing temperature.The PG9171E gas turbine firing temperature is2055°F / 1124°C. A cross-section of the PG9351

FA gas turbine is shown in Figure 18, which istypical of the GE gas turbines with 2420°F /1327°C firing temperature, including thePG7241FA.

The next generation “FB” and “H” platform gasturbines are expected to be in commercial serv-ice in the first half of this decade. The cross-sec-tion of the “H” gas turbine is shown in Figure 19.This new machine features closed-loop steamcooling for the first and second stages of itsfour-stage turbine. In order to optimize per-formance at the 2600°F / 1426°C firing tem-perature, a higher-pressure ratio compressorderived from the GE CF680C2 aircraft engineis utilized.

These gas turbines have the following featuresthat uniquely suit them for combined-cycleapplications:

■ The key performance characteristic ofthe gas turbine that influencescombined-cycle performance isspecific power. Specific power is thepower produced by the gas turbineper unit of airflow (kW output perlb/sec of compressor airflow).Combined-cycle thermal efficiency



GT25099

Figure 16. Advanced technology IGCC system

increases as gas turbine specific powerincreases, as shown in Figure 20. Thisfigure shows that gas turbine firingtemperature is the primary

determinant of specific power.Improvements in combined-cyclethermal efficiency have developedprimarily through the increases in gas



Heavy-Duty Output (kW) Frequency (Hz)

PG6581 B 42,100 50 and 60PG6101 FA 70,140 50 and 60PG7121 EA 85,400 60PG7241 FA 171,700 60PG9171 E 123,400 50PG9231 EC 169,000 50PG7251 FB 184,400 60PG9351 FA 255,600 60MS7001 H * 60MS9001 H * 50

Notes: 1. Fuel = Natural Gas2. Site Conditions = ISO Ambient3. Operating Mode = Base Load, Simple Cycle*Single-Shaft STAG Combined Cycle Configuration Only

Table 15. GE gas turbines applied to STAG product line

Figure 18. MS9001FA heavy-duty gas turbine

Figure 17. MS7001EA heavy-duty gas turbine

turbine firing temperature, which haveresulted from the development ofhigh-temperature / high strengthmaterials, corrosion-resistant coatings,and improved cooling technology.Commercial development ofcombined cycles and improvements incombined-cycle efficiency haveproceeded in parallel with advances ingas turbine technology.

■ STAG systems that utilize the “F”technology gas turbines achieve netthermal efficiencies of 53% (LHV) orgreater. STAG systems that utilize “H”technology gas turbines achieve netthermal efficiencies of 58–60% (LHV).These gas turbines have a rated firingtemperature of 2420°F / 1327°C and2600°F / 1426°C, respectively. The“FA” technology turbine has a 15.5pressure ratio, whereas the “H”technology turbine has a 23.0 pressureratio. These designs provide thehighest gas turbine specific power forthis firing temperature. High specificpower provides the lowest simple-cycleinstalled cost in addition to high

combined-cycle efficiency.

■ The exhaust gas temperature range of1000–1100°F / 538–566°C is uniquelysuited to efficient combined cyclesbecause it enables the transfer of heatfrom exhaust gas to the steam cycle totake place over a minimal temperaturedifference. This temperature rangeresults in the maximum inthermodynamic availability whileoperating with highest temperatureand highest efficiency steam cycles.

■ Multiple can-annular type combustorswith film and impingement coolingmeet the environmental requirementsfor applications throughout the world.They provide reliable operation athigh firing temperatures whileburning fuels that range from naturalgas to residual oil.

■ Turbine materials, coatings andcooling systems enable reliableoperation at high firing temperatures.This achieves high gas turbine specificpower and high efficiency forcombined-cycle systems.



Features

• Closed Loop Steam Cooling

• 4-Stage Turbine

• Compressor Scaled From Proven Design

• Dry Low Nox CombustorGT25129

Figure 19. “H” gas turbine cross-section

■ Most GE current product line gasturbines are configured with open-loop cooling of the turbine hot gaspath. Hot gas path components are inlarge part cooled by film cooling thatuses air supplied from the compressor.This results in a significant exhaust gassteam temperature drop across thefirst stage nozzle, and requiressignificant “chargeable air” to cool theturbine stages. The temperaturedrop across the first stage nozzle andthe chargeable cooling losses increaseas turbine inlet temperature increases.

■ The advanced “H” platform gasturbine is configured with anintegrated closed-loop steam-coolingsystem. The change in strategy to theclosed-loop, steam-cooled systemwithout film cooling allows higherturbine inlet temperatures to beachieved without increasingcombustion temperature. This isbecause the temperature drop acrossthe first stage nozzle is significantlyreduced, as shown in Figure 21. Gasturbine NOx emissions can then bemaintained at low levels at increasedturbine inlet temperature. Anotherimportant benefit of the integratedclosed-loop, steam-cooling system isthe elimination of “chargeable coolingair” for the first- and second-stagerotating and stationary airfoils. Thisresults in two percentage pointsimprovement in combined cyclethermal efficiency.

■ Factory packaging and containerizedshipment of small parts achieve lowinstalled cost and short installationtime.

■ Reliable operation results fromevolutionary design development thatimproves parts and components, ahigh-quality manufacturing programthat includes operational factorytesting of the gas turbine andaccessory systems, follow-up servicesupport by experienced installationand service personnel, and effectivespare parts support.

■ Low maintenance costs are the resultof the combination of the abovefeatures and a design to allowconvenient access. These includeborescope ports to permit inspectionof key parts and components withoutdismantling the equipment.

■ The heavy-duty gas turbine productline has fuel flexibility provided byaccessory systems, combustion systems,and turbine components, whichenable utilization of a wide range ofliquid and gaseous fuels. These include150-400 Btu/scf (6520-16,850 kj/nm3)gaseous fuels, including those derivedfrom coal, coke, or heavy petroleumproducts, and liquid fuels includingnaphtha, light distillates, heavydistillates, crude oil and residual oil.

HRSGHRSGs in the GE STAG product line areunfired and feature modular construction withfinned-tube heat transfer surface and natural orforced-circulation evaporators. Figure 22 illus-trates a natural circulation HRSG with modularconstruction. An installation showing two ofthese HRSGs operating with MS7001EA gas tur-bines is shown in Figure 23. Figure 24 illustratesthe modular-construction, forced-circulationHRSG, and Figure 25 shows an installation of


GE Power Systems ■ GER-3574G ■ (81000) 18

this type HRSG in a STAG 107EA system.

Each gas turbine exhausts to an individualHRSG. For STAG systems with a MS6001B gasturbine, the standard gas ducting is designed sothat two gas turbines exhaust to a single HRSG.These STAG systems are also available with oneHRSG per gas turbine. The HRSG and auxil-

iaries are designed for the specific operatingrequirements of the STAG combined cycle sys-tem. Design features include:

■ Exhaust gas bypass system to provide

fast startup and shutdown andflexibility of operation for multi-shaftSTAG systems. Exhaust gas bypasssystems are not used with single-shaftSTAG units.

■ Flexible tube support system to enablefast startup and load following

capability.

■ Low gas side pressure drop foroptimum gas turbine performance.

■ Large, factory-tested modules that canbe shipped to provide short



GT25454

Figure 20. Gas turbine performance thermodynamics

GT25134

Figure 21. Impact of stage-one nozzle cooling method

installation time and low constructioncost.

■ Fuel flexibility provided by the ability tooperate reliably and efficiently, usingexhaust gas from gas turbines that burnfuels ranging from natural gas toresidual oil.

Steam TurbineGE offers a complete line of steam turbines forcombined-cycle applications. Two or moresteam turbine selections are available for each

STAG product line offering. Steam turbineswith different exhaust annulus areas are avail-able to permit optimization to meet specificcondenser cooling conditions. Steam turbineswith large exhaust annulus areas are moreexpensive, but provide increased capability andmay be the most economic selection for appli-cations with low steam turbine exhaust pres-sure. For applications in which steam turbineexhaust pressures are high, small exhaust annu-lus-area steam turbines provide comparable orhigher capability and low cost, and thereforeare the economic choice. Figure 26 illustrates



GT11717

Figure 22. Natural-circulation HRSG modular construction

Figure 23. Two natural-circulation HRSGs operating with MS7001EA gas turbines

the performance difference for four last-stagebuckets that are available for the STAG 107FAcombined cycle. Steam turbine last-stage buck-et lengths for the STAG product line steam tur-bines range from 14.3 inches / 363 mm to 42inches / 1067 mm.

Because there are no extractions for feedwaterheating, and steam is generated and admittedto the turbine at three pressures, the flow at theexhaust is approximately 30% greater than the

throttle flow. The turbine’s last stage generatesup to 15% of the steam turbine output, so theefficiency of the turbine's last stage and the siz-ing of the exhaust annulus area are particularlyimportant for combined-cycle applications.

As with all modern GE steam turbine last-stagebuckets, the continuously-coupled design isused for high efficiency and reliability.Continuously-coupled designs permit the use ofmany relatively slender blades with narrow,



GT00477C

Figure 24. Forced-circulation HRSG modular construction

Figure 25. Forced-circulation HRSG with PG7111EA gas turbines

closely-controlled flow passages, particularly inthe critical high-velocity tip region. Coversreduce tip leakage losses, provide damping, andhelp to maintain control of the flow passage.

Steam turbine designs for high exhaust pres-sure operation typical of those that are neededfor air-cooled condenser operation at highambient temperature are available. These steamturbine designs are capable of reliable and effi-cient operation at exhaust pressures up to 15inches Hg,a/381mm Hg,a.

Advanced 3D aero packages incorporateadvanced vortex design, contoured inlet sectionsidewalls, and additional radial tip spill strips forsteam turbines larger than 80 MW, which con-tribute to maximum combined cycle thermody-namic efficiency.

The STAG combined-cycle product line steamturbines include axial exhaust and downexhaust configurations. Axial exhaust is pre-ferred for the single-flow steam turbines, typi-cally applied in the small capacity STAG sys-tems. Figure 27 shows a single-flow axial exhauststeam turbine.

A line of reheat steam turbines designed specif-

ically for combined-cycle service is available forSTAG systems employing the “EC,” “F,” and “H”technology gas turbines. The single-shaft STAG107FA, STAG 109FA and STAG 109H aredesigned as integrated machines with a solidturbine/generator coupling and a single-thrustbearing that includes common lubrication andhydraulic and control systems for both gas tur-bine and steam turbine. A two-flow reheatsteam turbine is shown in Figure 28.

Steam turbines specially designed for com-bined-cycle service have features that include:

■ Assembled modules that can beshipped and assembled with a lowprofile installation that reducesinstallation time and cost. (Buildingcost, for indoor installation, also isreduced with the low profile design.)

■ Access for borescopic inspection ofbuckets and nozzles without removalof the turbine upper casing.

■ Fast startup and load-followingcapability provided by minimum shaftdiameter in the vicinity of the firststage, large fillets between wheels androtor, long coupling spans, verticalflexible plate support near thecenterline with keys for maintenanceof alignment, and off-shell valves withfull-arc steam admission.

■ All main steam, cold reheat and hotreheat steam pipes connect to thelower half of the shell. This facilitatesremoval of the upper half shell formaintenance, and eliminates the needfor bolted connections in a hightemperature piping.

■ Sliding pressure operation with thecontrol valves wide open. A controlstage at the inlet is, therefore, not



Figure 26. STAG steam turbine last-stage bucketselection

required.

■ Applications at 1800 psig/124 bar,guse a single wall construction at thehigh-pressure stages as well as thereheat inlet. With 2400 psig/165 bar,gapplications, a short inner shellencloses the early high-pressure stages.This reduces the load on thehorizontal joint bolting and reducesthe thickness of the shell flange.

Generators

Generators for the STAG combined-cycle prod-uct line gas turbines and steam turbines are fac-tory assembled and tested. Air-cooled genera-tors are standard for the smaller STAG systemsusing PG6581B, PG6101FA and PG7121EA gasturbines. They may be open-ventilated or total-ly enclosed water-to-air cooled. If open-ventilat-ed, they are equipped with self-cleaning air fil-ters for desert or other dusty or dirty environ-ments, as shown in Figure 29. Hydrogen-cooledgenerators are standard for the single-shaft andlarger multi-shaft STAG systems. The hydrogen-cooled generators can be cooled by plant-cool-



GT24388

Figure 27. Non-reheat, single casing, axial exhaust steam turbine

Figure 28. Two-flow, reheat steam turbine

ing water or by ambient air with water-to-airheat exchangers. Figure 30 shows a typical pack-aged hydrogen cooled generator for gas turbineapplication.

ControlsThe STAG combined-cycle plant has a distribut-ed digital control system with a redundant datahighway. The station operator consoles provideinteractive color graphic displays of the overallSTAG plant, with sufficient detail to enable theoperator to conveniently operate the plant.

The control systems for multi-shaft and single-shaft STAG combined-cycle system fundamen-tally follow the same principle objectives of sim-plicity, easy starting, automated operation andsuperior load following ability. All main com-ponents of the combined-cycle plant have indi-vidual control panels and interfaces that relayinformation and instructions to and from theplant operator through data highways to theoperator console. The operator console willhave a detailed graphic display with a high levelof detail that enables convenient and informa-tive interaction with the plant as required.

The single-shaft power train is a simple tandemarrangement that does not include an exhaust

bypass system and is solidly coupled to one gen-erator with a common overspeed protectiondevice with less auxiliary equipment. Figures 31and 32 show block diagrams for multi-shaft andsingle-shaft arrangements.

The heat recovery combined cycle is a simplesystem with a minimum of control loops, asshown by the control diagram (Figure 33) for asingle-pressure, multi-shaft STAG system. Thesimplicity of this system, coupled with well-established, automated operation of systemcomponents, enables effective automation of



Figure 29. Air-cooled generator with self-cleaningair filter

Figure 30. Typical packaged hydrogen-cooled generator

the complete power plant. This minimizes thenumber of control room operators. Most STAGsystems operate with only one control roomoperator and one roving operator.

The multi-shaft STAG control is configured toenable automated startup and operation afterremote manual starting of plant auxiliaries,remote manual operation of each major com-ponent, or operation of the gas turbine-genera-tor units from local-control compartments. Thecontrol configuration enables maximum avail-ability because the plant can be operated

remotely with no additional control room oper-ators. The equipment protection system is pro-vided within the unit controls, so normal pro-tection is maintained during all modes of oper-ation, including local or remote manual opera-tion.

The single-shaft STAG unit control system is amicroprocessor-based controller that coordi-nates the operation of the components in eachintegrated combined-cycle unit and communi-cates with the plant control. Because of the sim-ple steam cycle, the tandem coupling of the gas



Figure 31. Distributed control system for plant with multi-shaft STAG combined cycle

Figure 32. Distributed control system for plant with single-shaft STAG combined cycle

and steam turbines to a single generator, andthe elimination of the HRSG exhaust-gas,bypass system, the single-shaft STAG combined-cycle control is very simple. Starting, operation,and shutdown of individual units are automatic.Single-shaft STAG units are controlled by a localunit control system that is coupled to the cen-tral control room operator's console by a datahighway. One control room operator can oper-ate one or more single-shaft STAG combined-cycle units with this type of control system andthe aid of one local operator.

AuxiliariesThe STAG product line ratings are based onplants with once-through systems (seawater orriver water) for steam turbine condenser cool-ing. STAG combined-cycle configurations arealso available for operation with a wide range ofowner-specified auxiliaries, including evapora-tive cooling towers and air-cooled condensers.Plant capability and efficiency with these sys-tems is expected to be lower because steam tur-bine exhaust pressure and cooling system auxil-iary power consumption are increased.

Plant Operation

Typical STAG plant performance variation withambient air temperature is illustrated by theheat rate and power-output capability ambient-temperature effect curves in Figure 34. Low heatrate throughout the ambient-air-temperaturerange is typical of these plants. The low heatrate and increase in output as ambient temper-ature decreases are achieved by the gas turbinecharacteristics and optimum equipment match-ing.

Gas turbine exhaust flow and temperature varywith ambient temperature and barometric pres-sure. Steam production and steam turbine out-put vary with the exhaust gas flow and tempera-ture supply to the HRSG. Steam turbines areselected to suit specific application require-ments. The steam turbines in the standard sys-tems are sized so that their rated flow matchesthe steam production.

Excellent part-load heat rate is achieved onmulti--shaft systems or multiple single-shaftunits by sequentially loading gas turbines tomeet system requirements (Figure 35). Thiscurve also shows that the plant can operate effi-ciently following system load with all gas tur-bines operating. The heat rate increases only1% at approximately 80% of rating.



Figure 33. Multi-shaft STAG control diagram

The modulated, inlet guide vanes (IGV) on thegas turbine compressor contribute significantlyto the excellent part-load performance. Theinlet guide vanes are modulated to control airflow in the power plant between the “hashmark” and the point marked “B.” Varying theair flow maintains nearly constant gas turbinefiring temperature so that the thermodynamicquality of the cycle remains essentially constant.The stack and condenser losses vary almost pro-portionally with output, so that the heat rateremains almost constant. At loads below thehash mark, the gas turbine operates with con-

stant air flow, and firing temperature is reducedas load is reduced.

Fast starting and loading is characteristic ofSTAG combined-cycle generation systems. Thisenables them to operate in mid-range, withdaily start peaking service as well as baseload.Typically, STAG systems can achieve full loadwithin one hour during a hot start and withinapproximately three hours for a cold start.Multi-shaft STAG systems allow the gas turbinesto start independently of the steam cycle andprovide about 65% of the plant capability with-in 15–25 minutes, depending on the size of thegas turbine, for hot, warm, and cold starts, asillustrated in Figure 36. Single-shaft STAG sys-tems are started and loaded to full capacity inabout the same time period as the multi-shaftSTAG systems. The startup sequence and loadprofile for the single-shaft systems differbecause the gas and steam turbines are startedas a single integrated unit and not as two sepa-rate units. Single-shaft STAG startup is illustrat-ed in Figure 37.

Plant ArrangementsThe STAG combined-cycle equipment can beadapted to installation requirements demandedby varying climactic conditions, system configu-



Figure 34. Combined-cycle, ambient air tempera-ture effect curve

Figure 35. STAG 200 part-load performance

rations and owner/operator preferences. Theequipment is suitable for outdoor installations,semi-outdoor installations, or fully-enclosedinstallations. Plant arrangements have beendesigned for each STAG system.

Plan views of STAG combined-cycle arrange-ments are shown in Figure 38 (multi-shaft,S406B), Figure 39 (multi-shaft, S207EA), Figure40 (single-shaft S109E), Figure 41 (multi-shaft,S207FA), and Figure 42 (single-shaft, S107FA).An elevation of the single-shaft S107FA is shownin Figure 43. Figure 44 shows the S107H andS109H plan and elevation views. The S107Hprovides about 58% increase in combined-cyclepower output with only about 10% increase infootprint area.

A 220 MW STAG 207E installation is shown inFigure 45. Figure 46 presents a STAG 109FA com-bined cycle installation. Figure 47 shows a 4000MW installation with eight STAG 107F and fourSTAG 207FA systems at one site. Thesearrangements have indoor turbine-generator

equipment and outdoor HRSGs. Figure 48shows a plant with two STAG multi-shaft com-bined-cycle units in an indoor installation. Foroutdoor installations, the standard gas turbineenclosures are weatherproof, and weatherprooflagging is available for the steam turbines.

InstallationThe short installation time and low installationcost of STAG combined-cycle systems are keyfeatures contributing to economical power gen-eration. This is due to factory packaging of allmajor components and containerized shipmentof small parts. In addition to low direct con-struction cost, the short installation timereduces interest payments during construction.The standard factory modules and standardizeddesigns also reduce plant engineering time andcost.

The time from order to commercial operationfor pre-engineered, standardized STAG designsis typically 24 months, not including permittingtime. The multi-shaft STAG systems can beinstalled in two phases to reduce the timebetween order and initial power production.The gas turbines contribute 65% of the plantcapacity. Typically, the gas turbine can beinstalled in less than 18 months to providepower generation while the steam system isbeing installed. Figure 49 is a typical two-phasemulti-shaft STAG combined-cycle installationschedule.

Utility Load GrowthPower generation economics can be enhancedby the installation of generation capacity insmall increments as utility load grows. STAGcombined-cycle plants fit this economical pat-tern because efficient, low-cost plants are avail-able in small blocks of generating capacity.

Flexibility is also available with the pro-genera-tion approach to capacity addition. Initial natu-ral gas/distillate oil-fired, simple-cycle gas tur-bine installations can be converted to combinedcycle later, when power demands require capac-ity increases. Plot plan area for the steam cycleequipment and transmission line capability arethe main considerations during the initial com-



GT08936B

Figure 36. Multi-shaft STAG starting times



Figure 37. Single-shaft STAG starting times

Figure 38. STAG 406B combined-cycle plan

Figure 39. STAG 207EA combined-cycle plan



Heat Recovery Generator

Generator

Steam Turbine

CondenserGas Turbine

Figure 40. STAG 109E combined-cycle plan

Figure 41. STAG 207FA multi-shaft combined-cycle plan

Figure 42. Four-unit STAG 107FA combined-cycle plan



Figure 43. STAG 107FA single-shaft combined-cycle elevation

GT25050

Figure 44. Single-shaft S107H and S109H plan and elevation

Figure 45. STAG 207E installation

mitment for simple-cycle gas turbines. Futureconversion to coal-derived fuels also is anoption for dealing with the long-range uncer-tainties of conventional fuel availability andprice.

Thermal Energy and Power SystemProduct LineThe product line of thermal energy and powercombined-cycle systems (cogeneration and dis-trict heating systems) are designed with struc-tured flexibility to provide a wide range of

power and thermal energy capacities to suit var-ied application requirements. The most com-monly supplied systems are:

■ Steam generation at processconditions with HRSG (no steamturbine)

- Unfired HRSG

- Supplemental-fired HRSG

■ HRSG and non-condensing steamturbine exhausting to process

- Unfired, one-pressure HRSG

- Unfired, two-pressure HRSG

- Supplemental-fired, one-pressure HRSG

■ HRSG with extraction/condensingsteam turbine

- Unfired, one-pressure HRSG

- Unfired, two-pressure HRSG

- Supplemental-fired, one-pressure HRSG

The capabilities of the thermal energy andpower systems are unique for each gas turbineframe size, as well as each set of process steamconditions for systems with both unfiredprocess HRSGs and unfired HRSGs that havenon-condensing steam turbines. The systems



Figure 46. Indoor S109FA installation

Figure 47. 4000 MW multi-shaft STAG installation

with fired HRSGs and condensing steam tur-bines provide extraordinary flexibility in boththermal energy and power generation capacityfor each gas turbine frame size.

The performance characteristics include thenet plant power, LHV heat content in fuel con-sumed, thermal energy in steam to process, andthermal efficiency and fuel charged to power(FCP). The thermal efficiency for these systemsis calculated by the following equation:

ηTH = 100 x (Qp + QTE)

QFSymbols:

ηTH = Thermal efficiency - LHV (%)QF = LHV heat content of fuel consumption

(Btu/hr, kJ/hr)Qp = Net power output (Btu/hr, kJ/hr)QTE = Thermal energy in process steam

(Btu/hr, kJ/hr)

The fuel charged to power (FCP) is a usefulparameter for comparing an integrated thermalenergy and power system with separate systemsgenerating the same power and thermal energy.For this comparison, the LHV heat content offuel that would be consumed by a conventionalfired boiler in producing the same thermal ener-gy is subtracted from the LHV heat consumptionof the integrated thermal energy and power sys-tem. The resulting FCP can then be comparedwith the heat rate of a separate power generationfacility. This will assess the relative performanceof the integrated thermal energy and power sys-tem with separate thermal energy and powergeneration systems. FCP is calculated by the fol-lowing equation:

FCP = 100 x (Q p - [QTE/ηB])

p

Symbols:FCP = Fuel charged to power = LHV



Figure 48. Two 207FA multi-shaft combined-cycle installation

Figure 49. Typical multi-shaft, combined-cycleproject schedule

(Btu/kWH, kJ/hr)QF = LHV heat content of fuel consumption

(Btu/hr, kJ/hr)QTE = Thermal energy in process steam

(Btu/hr, kJ/hr)ηB = LHV efficiency of fired boiler producing

equivalent thermal energy (%)P = Net electrical output (kW)

Cycle diagrams for thermal energy and powercombined cycle with steam generation atprocess conditions is presented in Figure 50.

These systems include generation of steam atprocess conditions. Figure 50 shows combined-cycle cogeneration systems that produceprocess steam with an unfired or supplemen-tary-fired HRSG. HRSG design for supplemen-tary firing provides the maximum process steamenergy supply. Figure 51 shows combined-cyclecogeneration systems that are equipped withnon-condensing steam turbines.

Many variations of these systems can be fur-nished to satisfy specific process plant energyrequirements, including:

■ Single automatic-extraction steamturbines to efficiently supply steam attwo or three pressures.

■ Multi-pressure HRSGs to supply steam

at multiple-pressure and temperatureconditions. The most flexible thermalenergy and power systems are thosethat include extraction condensingsteam turbines. Simplified cyclediagrams for typical systems with singleautomatic extraction are shown inFigure 52. This system has the capa-bility to operate at lower process steamdemands while using the excess steamgeneration to produce power in thecondensing section of the steamturbine. These systems can befurnished with double automaticextraction steam turbines andmultiple-pressure HRSGs to satisfyspecific process steam requirements.

Engineered Equipment PackageThe GE Combined-Cycle Engineered Equip-ment Package (EEP) is a unique combinationof equipment and services. It provides theowner with a plant performance guarantee andwarranty of operation, and the ability to servicethe complete power generation system, as wellas the capability to customize the plant design,auxiliaries, and structures. This is achieved byincluding in the GE scope the major combined-



Figure 50. Cycle diagrams – thermal energy and power combined cycle with steam generation at processconditions

cycle equipment that requires close coordina-tion for assurance of meeting the performanceand operating objectives. The equipment scopesplit between GE and the owner is shown inTable 16.

The services and software scope split is present-ed in Table 17. Key elements in the GE EEPscope are the combined-cycle system design andthe interface definition that enable the owner

,or the owner’s architect-engineer or engineer-constructor, to design the plant to meet projectspecific requirements.



Figure 51. Cycle diagrams – thermal energy and power combined cycle with non-condensing steam turbine

Figure 52. Cycle diagrams – thermal energy and power combined cycle with extraction/condensing steamturbines

ConclusionThe STAG combined-cycle product line, includ-ing power generation systems and thermalenergy and power systems ranging from 60 MWto 750 MW, are efficient, low-cost systems thatmeet the environmental requirements of allcountries. The GE combined cycle EEP pro-vides assurance of satisfying performance andoperating objectives while allowing a cus-tomized plant that incorporates the owner'spractices and preferences. The attractive eco-

nomics, reliability, and operating flexibility ofthese systems recommend their considerationfor all power generation applications.



GENERAL ELECTRIC

• GAS TURBINE(S)

• STEAM TURBINE(S)

• GENERATOR(S)

• HEAT RECOVERY STEAM GENERATOR(S)

• PLANT CONTROLS

OWNER

• MECHANICAL AUXILIARIES

• ELECTRICAL AUXILIARIES

• MAIN ELECTRICAL CONNECTIONS

• BALANCE OF PLANT

– FOUNDATIONS AND STRUCTURES

– SWITCHYARD

– FUEL HANDLING AND STORAGE

– PLANT COOLING SYSTEM

– CONSTRUCTION MATERIALS

– SITE PREPARATION MATERIALS

Table 16. Equipment scope split with engineeredequipment package

General Electric• Plant performance and environmental guarantee• Combined cycle system design and warranty• Balance of plant equipment functional specifications• Equipment interface drawings• Steady state and dynamic interface definition• Equipment operation and maintenance• Operation and maintenance training• Construction and operation permit support• Performance and environmental test support

Owner• Construction and operation permits• Plant design• Plant construction• Plant start-up, commissioning and operation• Performance and environmental testing• Site preparation• Project administration

Table 17. Services and software split with engi-neered equipment package

List of FiguresFigure 1. STAG system configurations

Figure 2. Generalized combined-cycle performance capability

Figure 3. Single-pressure non-reheat cycle diagram

Figure 4. Single-pressure non-reheat HRSG diagram

Figure 5. Typical exhaust gas/steam cycle temperature profile for single-pressure system

Figure 6. Typical exhaust gas/steam cycle temperature profile for three-pressure system

Figure 7. Three-pressure non-reheat cycle diagram

Figure 8. Three-pressure non-reheat HRSG diagram

Figure 9. Three-pressure reheat cycle diagram

Figure 10. Three-pressure reheat HRSG diagram

Figure 11. STAG 107H/109H cycle diagram

Figure 12. HRSG schematic for S107H/S109H

Figure 13. Two-pressure non-reheat steam cycle with forced circulation HRSG

Figure 14. Three-pressure non-reheat HRSG with integral dearator

Figure 15. Three-pressure reheat HRSG with SCR

Figure 16. Advanced technology IGCC system

Figure 17. MS7001EA heavy-duty gas turbine

Figure 18. MS9001FA heavy-duty gas turbine

Figure 19. “H” gas turbine cross-section

Figure 20. Gas turbine performance thermodynamics

Figure 21. Impact of stage-one nozzle cooling method

Figure 22. Natural-circulation HRSG modular construction

Figure 23. Two natural-circulation HRSGs operating with MS7001EA gas turbines

Figure 24. Forced-circulation HRSG modular construction

Figure 25. Forced-circulation HRSG with PG7111EA gas turbines

Figure 26. STAG steam turbine last-stage bucket selection

Figure 27. Non-reheat, single casing, axial exhaust steam turbine

Figure 28. Two-flow, reheat steam turbine

Figure 29. Air-cooled generator with self-cleaning air filter

Figure 30. Typical packaged hydrogen-cooled generator

Figure 31. Distributed control system for plant with multi-shaft STAG combined cycle

Figure 32. Distributed control system for plant with single-shaft STAG combined cycle



Figure 33. Multi-shaft STAG control diagram

Figure 34. Combined-cycle, ambient air temperature effect curve

Figure 35. STAG 200 part-load performance

Figure 36. Multi-shaft STAG starting times

Figure 37. Single-shaft STAG starting times

Figure 38. STAG 406B combined-cycle plan

Figure 39. STAG 207EA combined-cycle plan

Figure 40. STAG 109E combined-cycle plan

Figure 41. STAG 207FA multi-shaft combined-cycle plan

Figure 42. Four-unit STAG 107FA combined-cycle plan

Figure 43. STAG 107FA single-shaft combined-cycle elevation

Figure 44. Single-shaft S107H and S109H plan and elevation

Figure 45. STAG 207E installation

Figure 46. S109FA indoor installation

Figure 47. 4000 MW multi-shaft STAG installation

Figure 48. Two 207FA multi-shaft combined-cycle installation

Figure 49. Typical multi-shaft, combined-cycle project schedule

Figure 50. Cycle diagrams - thermal energy and power combined cycle with steam generation at process conditions

Figure 51. Cycle diagrams - thermal energy and power combined cycle with non-condensing steam turbine

Figure 52. Cycle diagrams - thermal energy and power combined cycle with extraction/condensing steam turbines



List of TablesTable 1. STAG combined-cycle power generation system features

Table 2. STAG combined-cycle thermal energy and power system features

Table 3. STAG combined-cycle system designations

Table 4. STAG power generation combined-cycle base configuration




Table 8. 50 Hz product line equipment

Table 9. STAG product line nominal steam turbine throttle and admissions steam conditions

Table 10. Power generation combined-cycle product line system options

Table 11. Performance variation with steam cycle

Table 12. STAG combined-cycle performance with fuel characteristics

Table 13. Effect of NOx control on combined-cycle performance

Table 14. STAG system power enhancement options

Table 15. GE gas turbines applied to STAG product line

Table 16. Equipment scope split with engineered equipment package

Table 17. Services and software scope split with engineered equipment package



7280590 GE Combined Cycle

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