8. Combined Cycle Power Plants Fluid Techniques in Plants 8. Combined Cycle Power Plants 9 / 80 Gas Turbine Steam Turbine Combustion Internal External Thermodynamic cycle Brayton Rankine

8. Combined Cycle Power Plants 1 / 80Thermal Fluid Techniques in Plants

8. Combined Cycle Power Plants


Cost of Electricity 193

Wide Use of Gas Turbine 735

Introduction to Combined Cycle Power Plants 21

Electricity Demand and Supply 112

Characteristics of Combined Cycle Power Plants 274


Combined Cycle Power Plants

Compressor

Fuel

Combustor

Turbine

Inlet

Air

Steam

Turbine

G

G

Condenser

Deaerator

Condensate

PumpHP Boiler

Feed Pump

LP Boiler

Feed Pump

HP Superheater

HP Evaporator

HP Economizer

LP Superheater

LP Evaporator

LP Economizer

HP

Drum

LP

Drum

Exhaust

Gas

HRSG

In simple cycle mode, the gas turbine is operated alone, without the benefit of recovering any of energy

in the hot exhaust gases. The exhaust gases are sent directly to the atmosphere.

In combined cycle mode, the gas turbine exhaust gases are sent into HRSG. The HRSG generates

steam that is normally used to power a steam turbine.


T

s

Topping Cycle

(Brayton Cycle)

Bottoming Cycle

(Rankine Cycle)

T-s Diagram for a Typical CCPP


TH

TL

QL

W

QH

SteamTurbine

TH

TL

QL

W

QH

Gas Turbine

WSteamTurbine

HRSG

[ Fossil & Nuclear ] [ Combined Cycle]

Thermodynamic Consideration


Gas Turbine Combined Cycle

구분 Topping Cycle Bottoming Cycle

Main Components GT ST/HRSG

Working Fluid Air Water/Steam

Temperature High Medium/Low

Thermodynamic Cycle Brayton Rankine

Coupling Two Cycles Heat Exchanger

Topping Cycle Coupling Bottoming Cycle


CCPP System Options

Items Options Remarks

Steam Cycle

• Single pressure / Two pressure /Three pressure *

• Reheat *

• Non-reheat

• Non-reheat for rated EGT less than

1000°F/538°C

• Reheat for rated EGT higher than

1050°F/566°C and fuel heating

• Heat recovery feedwater heating

Fuel

• Natural gas */ Distillate oil / Ash bearing oil

• Low BTU coal and oil-derived gas

• Multiple fuel systems

NOx Control

• Water injection / Steam injection

• SCR (NOx and/or CO)

• Dry Low NOx combustion *

Condenser• Water cooled (once-through system) *

• Cooling tower /Air-cooled condenser

Deaeration• Deaerating condenser *

• Deaerator/evaporator integral with HRSG

HRSG Design

• Natural circulation evaporators *

• Forced circulation evaporators

• Unfired *

• Supplementary fired

* Base Configuration for Combined Cycle Power Plants


Unfired, 3-pressure steam cycle

• Non-reheat for rated EGT less than 1000°F/538°C

• Reheat for rated EGT higher than 1050°F/566°C and fuel heating

• Heat recovery feedwater heating

• Feedwater dearation on condenser

• Natural circulation HRSG evaporators

GT with DLN combustors

Once-through condenser cooling water system

Multi-shaft systems (2-on-1, or 3-on-1)

Single-shaft systems

• Integrated equipment and control system

Base Configurations for CCPP


Gas Turbine Steam Turbine

Combustion Internal External

Thermodynamic cycle Brayton Rankine

Cycle type Closed (Open) Closed

Working fluid Air Water/Steam

Max. pressure, bar 23 (40 for Aviation) 350 (5050 psig)

Max. temperature, C(F) 1350 (2462) 630 (1166)

Blade cooling Yes No

Shaft cooling No Yes (USC)

Max. cycle efficiency, % 40 49 (USC)

Max. number of reheat 1 2

Power density High Low

Steam conditions of the steam turbines for combined cycle applications are lower than those for

USC steam turbines.

GT vs. ST


Major equipment of combined cycle power plant

• Gas turbine, steam turbine, generator, HRSG

Main advantages of the combined cycle power plant

• Higher thermal efficiency than the others (up to 60%)

- SC steam plants: 35~40%, USC steam plants: 49%

• Shorter construction period

• Lower initial construction cost

- Capital costs of gas fired combined cycle are about 40% of coal fired steam plants

• Lower emission (low NOx burners, SCR, CO catalysts are available)

Current situation

• Construction of CCPP has increased dramatically since 1970s

• Market is governed by GE and Siemens

• It is hard to develop a new competitive model because it requires both advanced technologies and

high cost

CCPP




Introduction to Combined Cycle Power Plants1

Electricity Demand and Supply2



국내 복합발전 설치 현황 - 민자

회사 Site 제작사 GT model MW/Unit GT대수 GT용량 ST용량 총용량 비고

GS EPS 당진 SiemensV84.3A

SGT6-8000H

179.0

276.0

4

1

716.0

276.0

382.0

140.0

1,098

416

2-on-1

1-on-1

GS 파워부천 WH 501D5 105.2 3 315.6 150.0 466 3-on-1 (CHP)

안양 ABB GT11N 79.4 4 317.6 150.0 468 4-on-1 (CHP)

GS 에너지 인천 GE 6F 70.0 2 140.0 60.0 200 (구)인천종합에너지

SK E&S

광양 GE 7FA+e 171.7 4 686.8 394.0 1,081 K-Power

오성 GE 7FA+e 183.0 3 549.0 285.0 834 3-on-1

장문 Siemens SGT6-8000H 274.0 4 1096.0 704.0 1,800 2-on-1 2 (2017 완공)

하남 두중/MHI M501GAC 267.3 1 267.3 131.6 399 CHP

POSCO광양 GE 7FA+e 168.8 2 337.6 165.0 502

포항 GE 7FA+e 168.8 2 337.6 165.0 502

POSCO에너지 인천

WH

Siemens

Siemens

W501D5

SGT6-5000F

SGT6-8000H

102.0

203.0

274.0

12

4

3

1,200.0

812.0

822.0

600.0

440.0

438.0

1,800

1,252

1,260

3-on-1 4

2-on-1 2

1-on-1 3

MPC순천

Siemens

MHI

W501FD2

M501J

185.0

317.0

2

2

370.0

634.0

208.0

312.0

578

946

2-on-1

2-on-1

대산 WH W501D5 102.0 4 408.0 100.0 508 현대중공업 인수

한국지역난방공사판교 GE 7EA 88.0 1 88.0 88

파주 MHI M501F 153.0 2 306.0 175.0 481

동두천드림파워 동두천 MHI M501J 317.0 4 1,268.0 610.0 1,878 2015년 3월완공

대구그린파워 대구 Siemens SGT6-8000H 276.0 1 276.0 144.0 420

포천파워 포천 두중/MHI M501GAC 267.5 4 1,070.0 530.0 1600

S-Power(안산복합) 안산 Siemens SGT6-8000H 274.0 2 548.0 272.0 820

대륜발전(한진중) 양주 두중/MHI M501F 185.0 2 670.0 200.0 870 CHP

합 계 73 13,511.5 6,755.6 20,267


국내 복합발전 설치 현황 - 한전

발전소 Site 제작사 GT model MW/Unit GT 대수 GT용량 ST용량 총용량 비고

남부발전

신인천 GE 7FA+e 165.0 8 1320.0 600.0 1,920 2-on-1

부산 GE 7FA 165.0 8 1320.0 640.0 1,960 2-on-1

한림 GE 6B 38.0 2 76.0 29.0 105

영월 두중/MHI M501F 183.0 3 549.0 299.4 848 3-on-1

안동 Siemens SGT6-8000H 277.0 1 277.0 140.0 417 1-on-1

중부발전

보령 ABB GT24AB 163.0 6 978.0 546.0 1,524 2-on-1

인천

Siemens

Siemens

ABB

V84.3A

V84.3A

GT24AB

179.0

184.0

163.0

2

2

2

358.0

368.0

326.0

195.0

193.0

182.0

553

561

508

2-on-1

2-on-1

2-on-1

세종 두중/MHI M501F 186.5 2 373.0 204.0 577 2-on-1 (CHP)

서부발전

서인천 GE 7FA+e 165.0 8 1320.0 712.0 2,032 1-on-1

평택GE 7EA 87.9 4 351.6 183.0 535 4-on-1

MHI M501J 317.5 2 635.0 311.0 946 2-on-1

군산 MHI M501G 254.0 2 508.0 263.0 771 2-on-1

남동발전 분당 ABB GT11N 79.4 8 635.2 300.0 935

동서발전

일산 WH 501D5 105.2 6 631.2 300.0 931 4-on-1, 2-on-1

울산

WH 501D5 105.2 2 210.4 100.0 310 2-on-1

WH 501F (150) 150 4 600.0 300.0 900 2-on-1

MHI M501J 287.0 2 574.0 299.0 873 2-on-1

합 계 74 11,410.4 5,796.4 17,206


복합화력 4,300 MW (7FA+e x 16 Units)

신인천/서인천복합발전단지


부산복합 (2,000 MW) 분당복합 (960 MW) 일산복합 (900 MW)

보령복합 (1,800 MW) POSCO 광양복합 (500 MW) POSCO 포항복합 (500 MW)

POSCO파워 (3,000 MW) GS EPS (1,000 MW) 현대중대산 (500 MW) 메이야율촌 (500 MW) K-Power(1,074 MW)

울산 (1,200 MW)

담수설비

GS 파워 (1,000 MW)

국내 복합화력발전소 [1/2]


포천복합 (1600 MW) 군산복합 (700 MW) 영월복합 (900 MW)

현대대산복합 (507 MW)분당복합 (960 MW) GS EPS 부곡복합 (1020 MW)

국내 복합화력발전소 [2/2]


2004 2006 2008 2010

Bill

ions

of

Dolla

rs (

2007)

3

6

9

12

15

18

Commercial Aviation

Electrical Generation

Military Aviation

Mechanical Drive

Marine Propulsion

Gas Turbine Production by Sector

Source: Davis Franus, Forecast International






Characteristics of Combined Cycle Power Plants4


2015년 기준

• 석탄: 탄소배출권비용을감안하면발전원가 27.2원상승

• 원자력: 핵폐기물처리비용미반영

원자력

55

단위: 원/kWh

석탄 중유 LNG 풍력 태양광

66

117.0

156

?

?

국내 발전원가 비교


Source: Power Plant Engineering (Black & Veatch)

발전원가 비교 [1/3]



[ Influence of the equivalent utilization time on the cost of electricity ]

1000 2000 3000 4000 5000 6000 7000 8000 9000

220

200

180

160

140

120

100

80

60

40

20

0

Equivalent utilization time, hr/a

Cost o

f e

lectr

icity,

US

$/M

Wh

1250 MW Nuclear

800 MW Steam (coal)

800 MW CCPP (gas)

250 MW GT (gas)

0


In contrast to steam turbine-generators, the manufacturers of gas turbines have a defined product line,

allowing for substantial standardization and assembly line manufacturing.

The modular concept of the package power plants made gas turbines relatively quick and easy to install.

Standardization and modularization combine to provide the product benefits of relatively low capital cost

and fast installation.

The benefits of low capital cost and fast installation were initially offset by higher operating costs when

compared to other installed capacity. Therefore, early utility applications of gas turbine generator were

strictly for peak load operation for a few hundred hours per year.

Improvements in efficiency and reliability and the application of combined cycles have added to the

economic benefits of the technology and now give gas turbine based power plants a wider range of

application on electric systems.



Type of PlantOutput,

MW

Descripti

on

Investment

cost, US$/kW

Average

efficiency

(LHV), %

Fuel price,

US$/MBTu

(LHV)

감가상각

Combined Cycle

Power Plant800

2 x GT

1 x ST750 56.5 8.0 25

Gas Turbine

Plant (gas)250 1 x GT 413 37.5 8.0 25

Steam Power

Plant (coal)800 1 x ST 1716 44.0 3.5 25

Nuclear Power

Plant1250 1 x ST 3500 34.5 0.5 40

< Inputs for the evaluation of the cost of electricity >

No cost for CO2 emissions were included.

Cost of Electricity


Co

st o

f E

lectr

icity (

US

$/M

Wh

)

800 MW

CCPP

(gas)

20

40

60

80

100Capital

O&M

Fuel

Intermediate LoadBase Load

800 MW

Steam

(coal)

250 MW

GT PP

(gas)

1250 MW

Nuclear PP

800 MW

CCPP

(gas)

800 MW

Steam

(coal)

250 MW

GT PP

(gas)

1250 MW

Nuclear PP

Cost of Electricity


GE S109H

: Dry Low NOx Combustors(H System™)

: Combined cycle

: 14 Can-annular lean pre-mix DLN-2.5combustors

: Output 480 MW (Gas turbine power 300 MW)

: Heat rate 6000 kJ/kWh

: $153,500,000 ($320/kW) F15-K : $1억

복합화력발전 가격


NOZZLE BUCKET제작사 MODEL

출력(MW)

TIT (C) 단개수 가격($)/Set MATERIAL 개수 가격($)/Set MATERIAL

1 48 1,180,000 FSX410 92 2,200,000 GTD111

2 48 1,180,000 GTD222 92 1,500,000 GTD1117FA 175 1,260

3 60 1,190,000 GTD222 92 1,450,000 GTD111

1 32 680,000 FSX414 92 670,000 GTD111

2 48 690,000 FSX414 92 680,000 IN7387EA 88 1,104

3 48 740,000 FSX414 92 600,000 U500

1 36 390,000 FSX414 92 430,000 GTD111

2 48 450,000 GTD222 92 330,000 IN738

GE

6B 39 1,104

3 64 420,000 GTD222 92 310,000 U500

1 42 240,000 IN738 115 400,000 IN738LC

2 66 210,000 IN939 115 400,000 IN738LC

3 84 280,000 IN730 97 210,000 IN738LC

4 90 210,000 X45 105 390,000 IN738LC

GT11N 80 1,027

5 40 390,000 20/25/2 59 500,000 ST 16/25MD

1 100 1,170,000 MAR M247LC 197 800,000 DS CM247LC

2 44 656,000 MAR M247LC 88 950,000 DS CM247LC

3 80 948,000 MAR M247LC 86 1,170,000 DS CM247LC

4 78 1,170,000 IN738LC 84 950,000 MAR M247LC

ABB

GT24 150 1,255

5 76 800,000 IN738LC 82 1,240,000 MAR M247LC

1 48 810,000 ECY-768 81 340,000 U520

2 48 700,000 X45 73 300,000 U520

3 56 720,000 ECY-768 55 340,000 U520501D2 105 1,198

4 56 770,000 X45 51 340,000 IN GC-750

1 32 560,000 ECY-768 72 1,400,000 IN738

2 24 410,000 X45 66 1,000,000 IN738

3 16 380,000 ECY-768 112 1,400,000 IN738

WH

501F 150 1,293

4 14 430,000 X45 100 1,100,000 U520

Turbine Blade Prices (1998년기준)








Advantages Disadvantages

1. High thermal efficiency

2. Low initial investment

3. Short construction time

4. Fuel flexibility

Wide range of gas and liquid fuels

5. High reliability and availability

6. Low operation and maintenance cost

7. High efficiency in small capacity increments

Various gas turbine models

8. Operating flexibility

Base, intermediate, peak load

9. Environmental friendliness

10. Reduced plant space

1. Higher fuel costs

2. Uncertain long-term fuel supply

3. Output more dependent on ambient

temperatures

System Features of CCPP


1. High Thermal Efficiency [1/6]

The value of efficiency is very high because fuel spend may be about 70 percent of the total cost.

All major OEMs have developed air-cooled gas turbines for combined cycles with efficiencies around 61

percent.

Siemens proved performance of 60.75% at the Irsching site outside Berlin.

The old paradigm that high performance meant advanced steam cooled gas turbines and slow started

bottoming cycles has definitely proven false.

Both GE and Siemens are able to do a hot-start within 30 minutes to full load.

Steam cooling will most likely only be used for 1,600C firing level since there will be an air shortage for

both dry low emission and turbine cooling.

The key for 61% efficiency is high performance gas turbines having higher pressure ratio and firing

temperature.

In addition, the exhaust gas temperature has to be at a level for maximum bottoming cycle performance.

Currently, most OEMs have capability of steam turbine throttle temperature of 600C(1112F) and the

optimum exhaust gas temperature should therefore be on the order of 25-30C higher.

Both GE and Siemens have presented advanced throttle conditions for their bottoming cycles, 165

bar/600C and 170 bar/600C, respectively.


Fuel Energy

100%

GT 37.6%

ST 21.7%

Co

nd

ense

r

31.0%

Stack8.6%

Loss in HRSG0.3%

Loss

0.5%

Loss

0.3%

Three Pressure

Reheat Cycle T

s

Topping Cycle

(Brayton Cycle)

Bottoming Cycle

(Rankine Cycle)

Combined cycle power plants have a higher thermal efficiency because of the application of two

complementary thermodynamic cycles

[ Heat balance in a typical combined cycle plant ]



10

원자력

열효율

, %

60

50

40

30

20

IGCC가스터빈(SIMPLE)

화력(SC)

화력(USC)

가스터빈(복합)

35

38

49

40

48

60발전유형별성능비교

Comparison of Thermal Efficiency



1967 1972 1979 1990 2000 2008 2012

TIT, C (F) 900 (1650) 1010 (1850) 1120 (2050) 1260 (2300)1426

(2600)

1426

(2600)1500

Press. Ratio 10.5 11 14 14.5 19-23 20-23 20-23

EGT, C (F) 427 (800) 482 (900) 530 (986) 582 (1080) 593 (1100) 623

Cooling 1 vane1&2 vane

1 blade

1&2 vane

1&2 blade

1,2,3 vane

1,2,3 blade

1,2,3 vane

1,2,3

blade

SC Power, MW 50-60 60-80 70-105 165-240 165-280400-480

(CC)

SC Heat Rate,

Btu/kWh11,600 11,180 10,250 9,500 8,850

CC Heat Rate,

Btu/kWh8,000 7,350 7,000 6,400 5,880 5,690

SC Effi., % 29.4 30.5 33.3 35.9 38.6 40

CC Effi., % 42.7 46.4 48.7 53.3 58.0 60 61

Evolution of Heavy Duty Gas Turbine Design Features



Load, %

30 40 50 60 70 80 90 100

65

60

75

70

85

80

95

90

100 The gas turbine equipped with

VIGV or several rows of variable

stator vanes keeps the efficiency

of the combined cycle plant

almost constant down to

approximately 80 to 85% load.

This is because a high exhaust

gas temperature can be

maintained as the air mass flow is

reduced.

Below that level, the turbine inlet

temperature must be reduced,

leading to an increasingly fast

reduction of efficiencies.

The steam turbine is operated with sliding pressure mode down to 50% load. Below that point, the live-

steam pressure is held constant, resulting in throttling losses.

Part Load Efficiency



4 GTs + 1 ST Arrangement

Combined Cycle Load, %

30 40 50 60 70 80 90 100

65

60

75

70

85

80

95

90

100

110

20

4GTs3GTs2GTs1GT

Down to 75%, parallel reduction in load on all 4 GTs.

At 75%, one GT is shut down.

Down to 50%, parallel reduction in load on 3 remaining GTs.

At 50%, a second GT is shut down.

Part Load Efficiency



Type of Plant Output (MW)Specific Price

(US$/kW)

Combined Cycle Power Plant 800 550 - 650

Combined Cycle Power Plant 60 700 - 800

Gas Turbine Plant 250 300 - 400

Gas Turbine Plant 60 500 - 600

Steam Power Plant (coal) 800 1,200 – 1,400

Steam Power Plant (coal) 60 1,000 – 1,200

Nuclear Power Plant 1,250 2,000 – 3,000

Biomass Power Plant 30 2,000 – 2,500

These prices are valid for 2007.

Interest during construction is not included.

Capital costs of gas-fired combined cycle are about 45% of coal-fired steam plants

Comparison of Initial Construction Cost

2. Low Initial Construction Cost [1/4]


Source: Gas Turbine World (1999 Jan/Feb)

Comparison of Gas Turbine Price


1401

17EA

17FA

19FA

1GT11N2

1V84.2

1GT13D

1GT24

1GT26

1501D5A

1701D

1501F

1701F

1V94.2 1V84.3

1V94.3A

GE

Siemens

ABB

WH

100 200 300 400

ISO net combined cycle plant output, MW

Price

le

ve

l fo

r C

CP

P (

Tu

rnke

y b

ase

), U

SD

/kW

550

500

450

400

350

300

1V94.2A


Basis: 350~700MW CC plant with a V94.3A Gas Turbine

Items Portion % CCPP

Integrated

Services15%

4 Project management / Subcontracting

2 Plant and project engineering / Software

8 Plant erection / Commissions / Training

1 Transport / Insurance

Lots 85%

15 Civil works

32 Gas turbine / Steam turbine / Generator set

16 Balance of plants

7 Electrical systems

4 Instrumental and control

11 HRSG island

As a rule of thumb, a 1% increase in the efficiency could mean that 3.3% more capital can be invested.

Cost Breakdown for CCPP



Steam Turbine Set

8%

Power Island

Mechanical System

9%

Heat Recovery

Steam Generator

10%

Gas Turbine Set

32%

Electrical (without high

voltage switchyard)

9%

Control 3%

Mechanical

Systems Outside

Power Island

8%

Civil, Arrangement,

Building Facilities

18%

Site

Infrastructure

3%

Cost Breakdown for a 400 MW CCPP



Type of Plant Time [Months]

Combined Cycle Power Plant 20 - 30

Gas Turbine Plant 12 - 24

Steam Power Plant (coal) 40 - 50

Nuclear Power Plant 60 - 80

Biomass Power Plant 22 - 26

The gas turbine usually can be operated in simple cycle mode while the steam portion of the combined

cycle is erected.

The gas turbine from the 1960s to the late 1980s was used only as peaking power in the countries where

the large steam turbines were used as base load power plants.

However, gas turbine was used as base load mainly in the developing countries where the need of power

was increasing rapidly because the waiting period of three to six years for a steam plant was unacceptable.

Combined cycle plants are relatively quick

to design and erect because all major

equipment is shipped to the field as

assembled and tested components.

The gas turbine is assembled at the

factory and mounted on a structural base

plate or skid, minimizing the need for field

assembly of the turbine.

Other components and support systems

such as cooling water and lubricating oil

are modules that are easily erected and

connected to the gas turbine skid.

Comparison of Construction Time

3. Short Construction Time [1/2]


Pre-engineered solution has the following benefits:

• Time (shorter delivery time)

• Quality (robust design)

• Risk (exchangeable components in case of troubles)

• Cost

Customizationstart from outside to inside

Standardizationstart from inside to outside

1980’s 2000’s

Design Philosophy for Combined Cycle Plants

주문 / 제작 모델 / 표준화

3. Short Construction Time [2/2]


Most gas turbine applications rely on natural gas or No. 2 distillate

oil.

Because of the availability and economics of natural gas, the

majority of new power plants prefer natural gas as a fuel.

Fuel affects CC performance in a variety of ways.

Natural gas containing high hydrogen content has a higher heat

content and therefore output and efficiency increase when the

natural gas is used as a fuel.

Plant output and efficiency can be reduced when the ash bearing

fuels (crude oil, residual oil, blends, or heavy distillate) are used

because of fouling occurred in gas turbine and HRSG.

Plant output and efficiency can be reduced when the fuels

containing higher sulfur content are used. This is because higher

stack gas temperature is required to prevent condensation of

corrosive sulfuric acid.

Heavy fuels normally cannot be ignited for gas turbine startup;

therefore a startup and shutdown fuel, usually light distillate, is

needed with its own storage, forwarding system, and fuel

changeover equipment.

Fuel Units

Natural Gas

Process Gas

Dual Gas

Distillate

Naphtha

Kerosene

Distillate or Gas

Distillate and Gas

Crude

Crude and Distillate

Residual

Residual or Gas

Residual/Distillate/Gas

1408

13

60

783

14

30

964

82

59

32

120

4

1

Total 3570

[Table] GE heavy-duty GT

shipped for fuels (by 1983)

4. Fuel Flexibility


The probability that a unit, which is classified as available, and in ready service, can be started, and

be brought to synchronization within a specific period time is defined as above. An inability to start

within the specified period and synchronize is considered a failure to start. However, repeated

attempts to start without attempting corrective action are not considered additional failures to start.

Starting Reliability =No. of Successful Starts

No. of Attempted Starts

MTBF =Fired Hours

Trips from a state of operation

P = period hours (normally one year, 8,760h)

F = total forced outage hours for unplanned outages and repairs

S = scheduled maintenance hours

Reliability = Availability =P F

P

P S F

P

Definition of Reliability and Availability

5. High Reliability and Availability [1/4]


• SGT6-5000F (W501F): Reliability: 99%, Availability: 95%, Starting reliability: 93% (2010)

Type of Plant

Source A Source B

Availability

(%)

Reliability

(%)

Availability

(%)

Reliability

(%)

Combined Cycle Power Plant 90 - 94 95 - 98 86 - 93 95 - 98

Advanced GT CCPP 84 - 90 94 - 96

Gas Turbine Plant (gas fired) 90 - 95 97 - 99 88 - 95 97 - 99

Steam Power Plant (coal fired) 88 - 92 94 - 98 82 - 89 94 - 97

Nuclear Power Plant 88 - 92 94 - 98 80 - 89 92 - 98

Many analyses show that a 1% drop in the availability needs about 2~3% increase in the efficiency to

offset that loss.

The larger gas turbines, just due to their size, take more time to undergo any of the regular

inspections, such as combustor, hot gas path, and major overall inspections, thus reducing the

availability of these turbines.

Comparison of Reliability and Availability



Source: EPRI CS-3344 pp.1-3

Gas

clean up

Fans (0.6%) Boiler tubes (4.2%) Fouling/slagging (2.8%) Pulverizers (0.6%) Bearings (2.0%)

Pumps (1.7%) Condenser (3.8%) Turbine blades (2.7%) Generator (3.8%)

Stack

Air

heater

Pulverizer

Coal

prepCoal

HP

heater

LP

heater

Water

treatment

Condenser

Water

HP Turbine IP Turbine

LP Turbines

Econ

S.H.R.H.

AshAsh

I.D. fan

F.D. fan

Generator

Availability Reduction in Coal-Fired Power Plant



Reliability is the percentage of the time between planned overhauls where the plant is generating or is

ready to generate electricity, whereas the availability is the percentage of the total time where power could

be produced.

Availability and reliability are very important in terms of plant economy because the power station’s fixed

costs are constant whether the plant is running or not.

A high availability has a positive impact on the cost of electricity.

The major factors affecting plant availability and reliability are:

• Design of the major components

• Engineering of the plant as whole, especially of the interfaces between the systems

• Mode of operation (whether base, intermediate, or peak-load duty)

• Type of fuel

• Qualifications and skill of the operating and maintenance staff

• Adherence to manufacturer’s operating and maintenance instructions (preventive maintenance)



Type of Plant Output (MW)Fixed (Million

US$/year)

Variable

(US$/MWh)

Combined Cycle Power Plant 800 6~8 2~3

Combined Cycle Power Plant 60 3~4 3~4

Gas Turbine Plant 250 2~2.5 3~4

Gas Turbine Plant 60 1~1.5 4~5

Steam Power Plant (coal) 800 12~15 2.5~3.5

Nuclear Power Plant 1250 40~60 2.0

Biomass Power Plant 30 3~4 5~8

Fixed O&M: personnel and insurance costs.

Variable O&M: cost depending upon the operation regime of the plant. Included items are:

• Inspection and overhauls, including labor, parts, and rentals

• Water treatment expenses

• Catalyst replacement

• Major overhaul expences

• Air filter replacements

Comparison of Operating and Maintenance Cost

6. Low O&M Cost [1/4]


ItemsSimple

cycle

Combined

cycleSteam coal IGCC

Fuel type NG NG Coal Coal

Fuel cost ($/MBtu) 2.65 2.65 1.5 1.5

Fixed O&M cost ($/kW/year) 0.7 3.7 28.1 38.8

Variable O&M cost ($/MWh) 7.3 3.3 2.7 3.7

Normalized plant cost 1.14 1 4.40 6.07

Source: GE (1991)

Some estimate that burning residual or crude oil will increase maintenance costs by a factor of 3,

(summing a base of 1 for natural gas, and by a factor of 1.5 for distillate) and that those costs will

be three times higher for the same number of fired hours if the unit is started every fired hour,

instead of once every 1000 fired hours.

Comparison of Operating and Maintenance Cost



O&M costs include operating labor, materials, and tools for plant maintenance on both a routine and

emergency basis.

These expenses are neither a function of plant capital cost nor plant generating capacity.

They vary from year to year and generally become higher as the plant becomes older.

These costs also vary according to the size of plant, type of fuel used, loading schedule, and operating

characteristics (peaking or base load).

In general, O&M costs are approximately equal to one-fourth of the fuel costs.

A good rule of thumb is that the maintenance cost is twice the initial cost during the plant life (normally, 25

years).

The running profile has a profound impact on the O&M cost.

Usually, the first maintenance is scheduled for either 24,000 hours or 1,200 starts (whichever occurs first).

Nowadays, it is common to have a maintenance agreement at some level for risk mitigation.

There are different levels of contractual services ranging from part agreement to full coverage LTSA

services.

One can choose to use either the OEM or another third party service provider.



In many cases, financing organs or insurer requires and LTSA (or better) for risk mitigation to level the

insurance cost at a reasonable level.

There are ways of potentially reducing the maintenance cost and one should always lumped methods with

equivalent hours.

The word lumped is used in a sense that the two different ageing mechanisms, such as creep, oxidation,

regular wear and tear and stresses related to thermal gradients during start and stop, are evaluated as

equivalent time by e.g. assuming that a start consumes time rather being a low cycle.

The total number of gas turbine operated in the world is about 47,000 units and the total value of the gas

turbine after market was 19.3 billion USD in 2009.

The after market is valuable greatly to the manufacturers since all 47,000 units requires maintenance on a

regular basis.

Certain in-house produced parts may be offered with several hundred percent margin. In contrast, the

margin of a complete new turn-key power plant is about 10 percent.

The reward for the user, by having a LTSA, is discounted parts and prioritized treatment by the supplier.



Mode Baseload Plant (1990s)SCC5-4000F cycling plant

(Siemens)

Hot start (8 h) 90 min 45-55 min

Warm start (64 h) 200 min 120 min

Cold start (>120 h) 250 min 150 min

7. Operating Flexibility [1/11]

Operational flexibility is essential in combined cycle power plants for frequency control.

Most OEMs are capable of 30 min hot-start and steep (35-50 MW/minute) ramp-rates.

The steam cooled gas turbine gas a longer start-up time. Thus, is has less flexibility in terms of DSS.


Gas turbines as well as combined cycle power plants have the unique potential to react quickly and with

flexibility to changes in grid, because they have the following characteristics:

• Short startup time

• High-loading gradients

• Possibilities for frequency support

• Good part load behavior

• Additional system for power augmentation

Built for both base-load and peak-load operation

High efficiency to maximize generation opportunities

Lower start-up emissions

Lower demineralized water consumption

• Once-through HRSG

Operational flexibility becomes a

major topic in modern power

markets



[ Start-up procedure ]



Hot start (start after an 8-hour shutdown) of a 400 MW CCPP with optimized steam turbine start-up

technology (Siemens)



Improvement of SGT6-5000F (W501F) Starting Capability

30 MW/min 5 additional minutes to 150 MW

5 minutes to accelerate

30 min. to baseload

13.5 minutes to accelerate

Improved





Gas turbines are capable of relatively quick starts.

Heavy duty gas turbines can achieve starting times as low as 10 minutes but usually no higher than 30

minutes from cold start to 100% load.

Aeroderivative gas turbines can achieve 100% load in 3 minutes or less.

If equipped with bypass systems, the startup of the steam cycle portion of the combined cycle can be

separated from the gas turbine.

The gas turbine can be operated at full load while the steam turbine is warming up.

The HRSG can be warmed up nearly as quickly as the gas turbine, with excess steam produced being

bypassed to the condenser.

The startup time of the gas turbine and the combined cycle plant is significantly less than the time required

for a comparably sized coal-fired power plant.

Supercritical plants require feedwater purity so that tube side deposition will not cause overheating damage.

Condensate polishing with oxygenated water treatment is required to achieve excellent water purity.

Even many natural circulation (drum type) units now use oxygenated water treatment.

The deposition has been greatly reduced so that the requirement for frequent chemical cleaning is almost

eliminated.



Turbine start/stop cycle – firing temperature changes Transient temperature distribution (1st

stage bucket)

For rapid changes in gas temperature, the edges of the bucket or nozzle respond more quickly than

the thicker bulk section.

These gradients, in turn, produce thermal stress that, when cycled, can eventually lead cracking.



Light Off &

Warm-up

maxBase Load

Metal Temperature

Tm

FSNL

Fired

Shutdown

Acceleration

% S

train

Te

nsile

(+

)C

om

pre

ssiv

e ()

Key Parameters• Total strain range

• Max metal temperature

Bucket Low Cycle Fatigue (LCF) – Temperature Strain History



Currently, short start-up and shutdown times are emphasized by customers because of high fuel price.

Especially, fast start-up is important for intermediate load application.

The important parameters should be considered for fast start-up are as follows:

• HRSG ramp capability

• Steam turbine ramp capability

• Piping warm up times

• Steam chemistry

• Steam turbine back-pressure limitations



HRSG

There has also been a debate over the years whether the once-through HRSG technology should be better off

than drum boilers in terms of cycling.

GE

• Detailed transient analysis showed that the majority of fatigue life consumption occurs at

the hottest high pressure superheater and reheater during fast gas turbine loading,

regardless of whether the HRSG uses high pressure drum or once through technology.

• The HRSG stack is equipped with an automatic damper that closes upon plant shutdown to

reduce HRSG heat loss and the time required for next plant start-up, as well as reduce the

cyclic stress of the start.

Siemens

• Once-through HRSG eliminates the thick wall HP drum and allows an unrestricted gas

turbine start-up.

a. gas turbine start-up produces rapid boiling in the evaporator

b. if water level in the drum rises to the separators, water carry over into the superheater

may occur

c. the typical response to this is to either trip or slow gas turbine load ramp

It is hard to conclude that which one is better in terms of operating flexibility.



8. Lower Emissions [1/3]

Pollutants characteristics

Smoke • Smoke is usually formed in small fuel rich regions especially during start-up.

UHC and CO

• The unburned hydrocarbons and CO are formed incomplete combustion typically at idling

conditions.

• Carbon monoxide (CO) emissions are low at gas turbine loads above 50%, typically less

than 5~25 ppmvd (9~43 g/GJ).

• Low CO emissions are the result of highly-efficient combustion.

• Catalytic CO emission abatement systems are also available, if required.

• The CO catalyst is installed in the exhaust gas path, typically upstream of the HRSG

superheater.

CO2

• CO2 production is a direct function of the CHx fuels burned it produces 3.14 times the fuel

burned.

• The only way to reduce the production of CO2 is to use less fuel for the power produced.

NOx

• NOx have been major pollutant in modern gas turbines.

• New units under development have goals which would reduce NOx levels below 9 ppm.

• SCRs have also been used in conjunction with DLN combustors.

• New research of catalytic combustors will give 2 ppm in the future.


Lignite: 980~1,230

Hard coal: 790~1,080

Oil: 890

NG: 640

NG Comb. cycle

Unit: g CO2/kWh

410~430

Solar 80~160

Nuclear: 16~23

Wind: 8~16

Hydro power: 4~13

Electricity generation with CCS

CO2 Emissions from Different Power Plants



The CO2 emissions of the plant are having a more direct impact on the economics of a plant due to the

effort to globally limit these kinds of emissions.

The combined cycle plant emits about 40% of the CO2 of a coal-fired plant. This is driven by the higher

efficiency and the higher hydrogen content in natural gas.

Unfortunately, however, the relative lower CO2 content in the flue gas makes the separation process more

difficult, and may render in high separation tower heights to provide for sufficient residence time.

Another issue is the flue gas flow which is on the order of 1.5 kg/MW, compared to 0.95 kg/MW for than

advanced steam plants.

The cross section of the separation tower should provide for a velocity around 5 m/s. Therefore, a combined

cycle plant requires a higher and wider tower for CO2 capture plant compared to a coal fired plant.

No commercial full-scale technology for CO2 capture exists today and the road-maps towards feasible

solution are still not clear.

It has been expected that the efficiency of combined cycle power plant with CO2 capture plant will drop 8

percent for a GE 9FB.03 with a 3-pressure HRSG. This is because a lot of LP steam is required for solvent

regeneration.

Lower CO2 Emissions



Options for Power EnhancementsTypical Performance Impact

Output Heat Rate

Base configuration Base Base

Evaporative cooling GT inlet air (85% effective cooler) +5.2 % -

Chill GT inlet air to 45F +10.7 % +1.6 %

GT peak load operation +5.2 % 1.0 %

GT steam injection (5% of GT airflow) +3.4 % +4.2 %

GT water injection (2.9% of GT airflow) +5.9 % +4.8 %

HRSG supplementary firing +28 % +9 %

Note: 1. Site conditions = 90F, 30% RH(Relative Humidity)

2. Fuel = NG

3. 3-pressure, reheat steam cycle

Output = m h•

9. Options for Power Enhancements


BoilerFeedwater

Pump

Steam

Turbine

10 Meters

Comparison with Coal-Fired Power Plants

10. Compactness [1/8]


[ Single-Shaft CCPP (107FA) ]

Arrangement of Single-Shaft [GE]



Arrangement of Multi-Shaft [207FA – GE]



Single Shaft (1-on-1 configuration) Multiple Shaft (2-on-1 configuration)

ComponentsLess generator required

One compact lube oil system

One large ST instead of 2 smaller STs

Less auxiliaries (pumps etc) required

Civil Smaller plant area Higher flexibility in plant layout

Costs

Lower capital cost of plant because one

generator and one step-up transformer is

eliminated

Performance Same level in larger plantsSteam turbine has higher efficiency because

of larger steam volume flow

Operating

Flexibility

Suitable for daily start and stop (DSS)

operationSuitable for base load operation

Availability Higher (less complexity)

Operation limit

Operation is limited to concurrent operation of

the gas turbine and steam turbine, unless the

steam turbine can be decoupled from the

generator through a clutch

The gas turbine can be decoupled from the

operation of the steam turbine, allowing for

steam turbine shutdown with continued gas

turbine operation



Arrangement of Single-Shaft [Siemens]



Single-shaft with generator between gas turbine and steam turbine enables installation of a clutch between

steam turbine and generator.

One problem of a Jaw clutch, which was used previously, is that it can only be engaged when the gas turbine

is at rest. This means that in the event of a failed gas turbine start, the operator must wait until the gas

turbine is stationary before engaging the jaw clutch to re-start.

Currently, SSS(Synchronous Self-Shifting) clutch has been employed popularly. The SSS clutch engages in

that moment when the steam turbine speed tries to overrun the rigidly coupled gas turbine generator and

disengages if the torque transmitted from the steam turbine to the generator becomes zero.

The clutch allows startup and operation of gas turbine without driving the steam turbine.

This results in a lower starting power and eliminates certain safety measures for the steam turbine, such as

cooling steam or sealing steam.

The clutch also provides design opportunities for accommodating axial thermal expansion.

However, the clutch is an additional component with a potential impact on availability. Additionally, the

generator located at the end of the line of shafting has advantages during generator overhaul.

Single-shaft units without a clutch definitely need auxiliary steam supply to cool the steam turbine during

startup. This is not necessary in units with a clutch.

Single-Shaft



A gearbox is necessary in applications where

the manufacturer offers the package for both

60 and 50 cycle applications. The gearbox will

use roughly 2 percent of the power produced

by the turbine.

Arrangement of Single-Shaft [GE, 6FA]



Typical Plant Arrangement [GE, S207EA]









Cogeneration means the simultaneous production of electricity and thermal energy in the same plants.

The thermal energy is usually steam or hot water.

The types of cogeneration plants:

① Industrial power stations supplying heat to an industrial process

② District heating power plants

③ Power plants coupled to seawater desalination plants

The supplementary firing in the HRSG gives greater design and operating flexibility, but the cycle efficiency

is normally lower if supplementary firing is used.

Thermal energy in the form of steam can be extracted from HRSG, or from an extraction in the steam

turbine.

The power coefficient (also called the alpha-value) is defined as the ratio between the electrical and the

thermal output.

Fuel utilization is a measure of how much of the fuel supplied is usefully used in the plant. It is equal to the

sum of electrical output and thermal output divided by the fuel input.

Cogeneration [1/3]


Single Pressure

Supplementary Firing

Backpressure Turbine

Heat Balance

Cogeneration [2/3]


In the simplest arrangements, the

gas turbine waste heat is used

directly in an industrial process,

such as for drying in a paper mill,

or cement works.

Adding an HRSG converting

waste heat into steam, gives

greater flexibilities in the process

for chemical industries, or district

heating

CHP; Combined Heat and Power

Cogeneration [3/3]


Seawater Desalination Plant


IGCC


Combined cycle plants are very well suited to rapid load changes because gas turbine react extremely

quickly to frequency variations.

As soon as fuel valve opens, more added power becomes available on the shaft and gas turbine load jumps

of up to 35% are possible, but this is detrimental to the life expectancy of the turbine blades.

To perform a plant load jump while the frequency is falling, it is essential that gas turbine is operating below

the maximum output level.

For frequency support gas turbines are typically operated between 50 and 95% load.

The electrical output of the combined cycle power plants is controlled by means of gas turbine only. This is

because the gas turbine generates two-thirds of the total power output, a solution without control for the

steam turbine power output is generally preferred.

The gas turbine output is controlled by a combination of VIGV and TIT control.

The TIT is controlled by a combination of the fuel flow into the combustor and VIGV setting.

VIGVs allows a high gas turbine exhaust temperature down to approximately 40% GT load. Below this level,

TIT is further reduced because the airflow cannot be further reduced.

The steam turbine will always follow the gas turbine by generating power with whatever steam is available.

Load Control & Frequency Response


질의 및 응답

작성자: 이 병 은 (공학박사)작성일: 2016.02.15 (Ver.1)연락처: [email protected]

Mobile: 010-3122-2262저서: 실무 발전설비 열역학/증기터빈 열유체기술

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