overiew of comb cycle rev 7.0_part 2

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Combined Cycle Power Generation

-An Introduction

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Combined Cycle Power Generation

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GTHRSG

+

ST

3%

MISC

LOSSES

100% FUEL

INPUT

OUTPUT30 %

67%

OUTPUT16 %

3% MISC

LOSSES

34%

CONDENSER

LOSSES

14% TO

STACK

Combined Cycle Heat Flow

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Fired ± Unfired HRSG

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District

heating andprocess heatfor industry.

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Classification

HRSG

DRUM TYPE

1/2/3 pr type

ONCE

THR OUGH

UNFIRED SUPPLEMENTRY FIRED

VER TICAL

Natural/ Forced Circulation

HOR IZONTA

N / F Circ.

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VERTICAL HRSG

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VERTICAL HRSG

Flue gas flow -vertical

Water/ steam flow inhorizontal finned tubes

Small foot print area

Added circulation

Good cycling capability

Replacement of tubeseasily possible

Easily access forinspections

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Horizontal HRSG

Flue gas flow-horizontal

Water/ steam flow invertical finned tubes

Large foot print area Natural circulation

In cycling duty problemsin superheater/ reheatersections.

Replacement of tubes notpossible

Access for inspections isdifficult

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Horizontal HRSG

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Horizontal HRSG

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Horizontal types require a 30 % larger footprint area.

More expansion joints are required in horizontal units.

Structural requirements are higher in vertical types.Horizontal types are more difficult for maintenance and

inspections.

Overall cost may be same in both types;

Horizontal Vs Vertical HRSG

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Typical two stage Combined Cycle

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Water ± Steam Path

CEP

HPBFP

LPBFPLP

Drum

LPCCpump

HPTurbine LP Turbine

&Condenser

HPDrum

HPCCpump

Cond.Preheater

LP ECO

HP ECO-I

LP EVA

LP SUP

HP ECO-II

HP EVA

HP SUP-I

HP SUP-II

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Types of Super heater 

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Very popular for small gas

turbines and diesel engines.

Very compact design

Can be shipped totally

assembled.

Types of Evaporator

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This configuration has probably

 been used for more years than any

of the others.

Has the advantage of the upper header being configured as the

steam separation drum.

Types of Evaporator

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Types of Evaporator

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Types of Evaporator

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Optimum Approach & Pinch Point

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Combined Cycle Parameters-PINCH POINT

Difference between flue gas and

water/steam temperature at evaporator

section

It is the minimum differential

temperature between gas and

water/steam in the Boiler

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Lower pinch point results in

linear rise in cycle efficiency

exponential rise in boiler heat transfer area

PINCH POINT

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PINCH POINT:Every 10°C decrease in Pinch Point, results in

HP steam flow increases by 4.6 %

Steam turbine output increases by 3.4 %

Heat rate improves by 20 kcal/kWHr

Efficiency improves by 0.52 %

Optimum 8-15 °C, with regard to Heat Transfer areaof Evaporator

Pinch point at Dadri (HP Ckt) is 11.6°C

(LP ckt) is 8.0 °C

Combined Cycle Parameters

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SINGLE PRESSURE NON REHEAT

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DOUBLE PRESSURE NON REHEAT CYCLE

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DUAL PRESSURE CC PLANT

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Dual Pressure Type

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TRIPLE PRESSURE CC PLANT

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TRIPLE PRESSURE CC PLANT

400MWi CCPP- Castejon (Spain)

Vertical gas path HRSG withnatural circulation and three levels

of pressure and reheat for a gas

turbine of 265MW in local

conditions.It was commissioned in 2002.

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Triple Pressure HRSG With SCR

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Tripple Pressure Type

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Triple Pressure Levels Reduces Irreversibility & Increasing Heat Transfer

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Higher approach point offers stability and compactdesign where as

Narrow approach point results in

Very large economiser surface area

Chances of steaming in economiser water hammer and

fluctuations in drum level

Dadri (HP Ckt) is 2°C

(LP ckt) is 2 °C

HRSG Parameters-Approach Point

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Pressure Stages in WHRB

Criteria :  Maximum available Temperature at WHRB inlet

  Provision of Supplementary firing in WHRB

  Station owners own economic evaluation of 

Heat rate,

Efficiency,

Power output,Extra investment,

Added O& M Cost

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Pressure Stages in WHRB

Output (%) Plant Eff. (%)

Single pr., Non reheat - 4.7 - 4.7

Two pr., Non reheat - 1.0 - 1.0

Three pr., Non reheat Base BaseThree pr., Reheat + 0.7 + 0.7

Limiting Factor:Saturation temperature at particular pressure

Possible degree of Superheat

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WHRB Steam Outlet Conditions

First stage Second Stage Third stage

bar  0C bar  0C bar  0C

Single Pr 40-60 450-520

Dual pr 60-100 480-520 5-15 200-250

Triple Pr 60-120 480-520 20-30 200-300 3-5 150-200

Heat Pick up in 3 Pr System

15-20 %

in Super htr/ Rehtr 

60-70 % in Steaming 20-30 % in

heating water  Originally this picture was super imposition of solar heating to that of HRSG

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Energy balance in diff scenario

Config GT

Output

GT

Losses

HRSG

Losses

Stack

losses

Condenser 

losses

ST

Losses

ST

output

Singlepr.

37.6 0.5 0.2 11.4 29.9 0.3 20.1

Doublepr.

37.6 0.5 0.3 8.2 32.1 0.3 21.0

Triplepr.

37.6 0.5 0.3 8.2 32.0 0.3 21.1

Triple,reheat

37.6 0.5 0.3 8.6 31.0 0.3 21.7

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Temperature Profile

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SCR

Suitable temperature range 300 to 400 oC.

Segments having honeycomb patterns containing

catalyst is arranged within HRSG.

Ammonia slip is a concern, requires sophisticated

control system for controlling injection.

Excessive Size and Weight.

Costly as compared to primary methods.

Sensitive to fuels containing more than 1000 ppm of 

sulfur.

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Principle of DeNOx thru¶ SCR

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Post Combustion Pollution Control

SCR: NOx is converted into nitrogenand water vapour by injectingammonia in presence of a catalyst.

SCONOx: Single catalyst for removal

of CO, NOx, VOCs, SO2 andrequires no chemical injection.

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Finned Tubes

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Module Concept

1 GT + 1 HRSG + 1 ST ]

2 *[ GT + HRSG ] + 1 ST ]

3 *[ GT + HRSG ] + 1 ST ]

4 *[ GT + HRSG ] + 1 ST ]

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2 GT + 1 ST

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2 * [2 GT + 1 ST]

Tamazunchale Combined Cycle Power Station (Mexico)

4 GE 7FA gas turbo-generator units [60

Hz, 183 MW each]

and 2 GE D11S

steam turbines.,totaling 1135 MW

in two modules.

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4 GT + 1 ST

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Single Shaft Arrangements

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Air 

Air 

Fuel

Fuel

Exhaust

gas

Exhaust

gas

GT-

1

GT-2

ST-

1

Steam

G

G

G

106 MW

106 MW

116MW

2 X 106 + 1 X 116 = 328 MW

Combined Cycle Module Configurations

HRS

G

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Combined Module Cycle Configurations

4 X (2 GT + 2 HRSG + 1 ST)

- Four(4)nos.multishaft CC Modules based on

conventional class gas turbine models.- The module shall consist of two (2) nos. Gas

Turbines, two (2) nos. HRSGs, and one (1) no.

Steam Turbine. Each Gas Turbine and Steam

Turbine would drive separate Electric

Generator.

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Air 

Air 

Fuel

Fuel

Exhaust

gas

Exhaust

gas

GT-

1

GT-2

ST-

1

Steam

G

G

G

255

MW

255

MW

276MW

2 X 255 + 1 X 276 = 786 MW

Combined Module Cycle Configurations

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Combined Cycle Module Configurations

2X (2 GT + 2 HRSG + 1 ST)

- Two nos. multishaft CC module based on

advanced (F/FA

) class GT model.- Each module shall consist of two (2) nos. Gas

Turbines, two (2) nos. HRSGs, and one (1) no.

Steam Turbine. Each GT and ST would drive

separate Generator.

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Exhaust

gas

Air 

Fuel

Fuel

Exhaust

gasGT-

1

GT-

2 ST-

1

Stea

m

Air 

Fuel

GT-

3

Air 

Exhaust

gas

3 X 140 + 1 X 230=650 MW

Combined Cycle Module Configurations

G

G

G

G

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Combined Cycle Module Configurations

2X (3 GT + 3 HRSG + 1 ST)

- Two nos. multishaft CC module based on

conventional class gas turbine model.- Each module shall consist of three (3) nos. Gas

Turbines, three (3) nos.HRSGs, and one (1)

no. Steam Turbine. Each GT and ST would

drive separate Generator.

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250 MW GT + 140 MW ST = 390 MW

Combined Cycle Module ConfigurationsCombined Cycle Module Configurations

Configuration ± D

Single Shaft Module

G

Air 

Exhaust

gas

Stea

mGas Turbine

Fuel

Steam Turbine

Si l Sh ft CC Pl t

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Single Shaft CC Plant

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Si l Sh ft Pl t A t

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Single Shaft ± Plant Arrangement

GT 188 MW

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Single Shaft Combined Cycle Plant

Simplified Plant design and operation

Lower initial investment

Unitized design means problems faced inmulti shaft configuration employing Triple

Pressure Reheat ST are absent.

GT ST G t C fi ti

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GT±ST±Generator Configuration

Axial steam turbine exhaust is notpossible

Steam turbine shares the cold endthrust / journal bearing of Gas Turbine

Auxiliary steam is required for coolingof steam turbine during startup

Outage of ST necessarily lads to outage of the

whole power train.

Gas Turbine is accessible formaintenance only after cool-down of complete power train.

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Single Shaft CC Units Don¶t Need

Main steam non return valves

Cold Reheat isolation valves

Cold Reheat Balancing valves

Reheater relief valves

Hot Reheat stop/ control valvesLow pressure Non return valves

Steam headers

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Single Shaft Unit Configuration

GT- Generator ² Clutch ² ST 

GT ² ST ² Generator

GT G t Cl t h ST fi

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GT-Generator±Clutch±ST config.

y Steam turbine must be moved to remove andservice the generator Rotor.

y

Startup of gas Turbine is independent of Steam turbine

y SSS clutch allows load operation of Gas Turbinein case of outage of the ST

y Gas turbine and steam turbines have their ownthrust and journal bearings

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Cost Reduction in Single Shaft Unit results from:

Reduction in number of Electric generators,step up transformers, and high voltagefeeders.

Civil works ± Single building, Reducedbuilding height

Reduction in number of valves and lengthof piping.

Elimination of Bypass stack and diverterdamper.

Limitations of Single Shaft Units

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Limitations of Single Shaft Units

Need for higher starting power

Less Operating Flexibility ;

Option of phased construction and

commissioning not available.

Combined C cle Options

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Combined Cycle Options

  STEAM CYCLE:

Single pressure

Two pressure

Three pressure

Reheat

Non-reheat

  DEAERATION:

Deaerating condenser

Deaerator/evaporatorintegral with WHRB

  HRSGDE

SIGN:

Natural circulationevaporator

Forced circulationevaporator

Unfired

Supplementary fired

  NOx CONTROL:

Water Injection Steam Injection

SCR ( NOx and/or CO)

Dry Low NOx

Combustion

C bi d C l O i

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  CO

NDE

NSE

R:

Water cooled (once through system)

Water cooled (evaporative cooling tower)

Air Cooled condenser)

  FUEL:

Natural gas

Distillate oil

Ash bearing oil

Low Btu coal and oil-derived gas

Multiple fuel system

Combined Cycle Options

C t Di t ib ti f CC P Pl t

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(2GTs + 2HRSGs + 1ST)

Gas turbine, Aux equipment : 26 %HRSG + piping + auxiliary equipment: 17 %

Steam turbine + generator+piping+condenser: 21 %

Electric and supervisory equipment+transformer: 12 %Civil engineering: 6 %

Erection + supervision: 18 %

Cost Distribution for a CC Power Plant 

Bypass Stack /

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Bypass Stack /

Waste Heat Recovery Systems

P E h t M th d

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It is Site specific and dependant on:

Site ambient temperature

Level of desired output enhancement

Anticipated Operational hours

Water availability

Structure of Power Purchase Agreement

Allowable plant emission

Owner¶s own economic evaluation factors

for plant output, heatrate, O& M costs.

Power Enhancement Methods

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Coal fired Vs Combined Cycle

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Coal fired Vs. Combined Cycle

0.6

0.4

0.55

0.73

0.46

0.35

0.65

1.37

0

0.2

0.4

0.6

0.8

1

1.2

1.4

   C  o  s   t   o   f    I  n  s   t  a   l   l  a   t   i  o  n

   O   &   M    C  o  s   t

   O   &   M    S   t  a   f   f

   F  u  e   l    R  e  q   u   i  r  e  m  e  n   t

   L  a  n  d   r  e  q   u   i  r  e  m  e  n   t

   W

  a   t  e  r    R  e  q   u   i  r  e  m  e  n   t

   G  e  s   t  a   t   i  o  n    P  e  r   i  o  d

   P   l  a  n   t    E   f   f   i  c  e  n  c   y

Thermal

Comb. Cycle

Comparison of Availability Reliability

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Comparison of Availability, Reliability

Availability = [Total Operating Hours ± Planned outage-Forced outage]/ Total Operating Hours

Reliability = [Total Operating Hours ± Forced outage]/ Total Operating Hours

Typical Figures

Plant types Availability Reliability

Gas turbine (gas) 88-95 97-99

Steam Turbine (coal) 82-89 94-97

Comb cycle (gas) 86-93 95-98

Nuclear 80-89 92-98

Diesel generator 90-95 96-98

Annexure

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Annexure

Performance Parameters

Annexure

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Annexure

Performance = Actual heat transfer / max possible (ASME PTC 4.4)

valuereferenceaboveinput energy sideGas

water Steambyabsorbed  Energy Efficiency /!

 possiblelossenergy sideGas Max

Gasbylost  Energyess Effectiven !

Which is more ?

Efficiency or effectiveness and Why

Annexure

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Annexure

valuereferenceaboveinput energy sideGas

water Steambyabsorbed  Energy Efficiency

/!

Annexure

8/3/2019 Overiew of Comb Cycle Rev 7.0_Part 2

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Annexure

hh

hh

 possiblelossenergy sideGas MaxGasbylost  Energyess Effectiven

 gas gas

 gas gas

in

out in

min

!!

h gasinis the HRSG inlet enthalpy condition for flue gas;

h gasoutis the HRSG outlet enthalpy condition for flue gas;

h gas minis the minimum possible HRSG outlet enthalpy condition for 

flue gas;

= condensate temperature OR = actual gas temp ± pinch point± (approach point)*(gas temp

fall at eco/ water temp rise at eco)*correction factor of 1.15

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