overiew of comb cycle rev 6.0_part 2

7/31/2019 Overiew of Comb Cycle Rev 6.0_Part 2

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Combined Cycle Power Generation

-An Introduction


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Combined

Cycle

PowerGeneration


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One Gas

Turbine andOne SteamTurbine.

[without anyadditionalfuelconsumption]


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Fully firedcombinedcycle


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District

heating andprocess heatfor industry.


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Bypass Stack /

Waste Heat Recovery Systems


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GTHRSG

+

ST

3%

MISC

LOSSES

100% FUEL

INPUT

OUTPUT

30 %

67%

OUTPUT

16 %

3% MISC

LOSSES

34%

CONDENSER

LOSSES

14% TO

STACK

Combined Cycle Heat Flow


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HRSG - Classification

HRSG

VERTICAL HORIZONTAL

DRUMTYPE

ONCETHROUGH

UNFIRED SUPPLEMENTRY FIRED


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Heat Recovery

Steam Generator[HRSG]


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Typical two stage Combined Cycle


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Water Steam Path


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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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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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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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TRIPLE PRESSURE CC PLANT


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Temperature

Profile in aWaste HeatRecoveryBoiler


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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 ofHeat 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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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

Lower pinch point results in linear rise in cycle

efficiency

Lower pinch point results in exponential rise in

boiler heat transfer area


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PINCH POINT:Every 10C decrease in Pinch Point, results inq HP steam flow increases by 4.6 %

q Steam turbine output increases by 3.4 %

q Heat rate improves by 20 kcal/kWHrq Efficiency improves by 0.52 %

Optimum breakeven is 10 C, with regard to

Heat Transfer area of Evaporator

Pinch point at Dadri (HP Ckt) is 11.6C

(LP ckt) is 8.0 C

Combined Cycle Parameters


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Optimum Approach & Pinch Point

Triple Pressure Levels Reduces Irreversibility &


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Triple Pressure Levels Reduces Irreversibility &Increasing Heat Transfer

Triple Pressure CC Plant


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Triple Pressure CC Plant

T i l P HRSG With SCR


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Triple Pressure HRSG With SCR

SCR


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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 sophisticatedcontrol system for controlling injection.

Excessive Size and Weight.

Costly as compared to primary methods.

Sensitive to fuels containing more than 1000 ppm of

sulfur.

P i i l f D NO th SCR


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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 injecting

ammonia in presence of a catalyst.

SCONOx: Single catalyst for removal

of CO, NOx, VOCs, SO2 and requires

no chemical injection.

Energy balance in diff scenario


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Energy balance in diff scenario

Config GTOutput

GTLosses

HRSGLossesStacklossesCondenser losses STLossesSToutput

Single

pr.

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

Triple

pr.

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

Fi d T b


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Finned Tubes


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Single Shaft CC Plant


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Single Shaft CC Plant

Single Shaft Plant Arrangement


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Single Shaft Plant Arrangement

Multi-shaft Arrangement


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Multi-shaft Arrangement

Single-shaft Arrangement


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Single-shaft Arrangement

Si l Sh f C bi d C l Pl


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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.

Si l Sh ft CC U it D t N d


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Single Shaft CC Units Dont 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

C t R d ti i Si l Sh ft U it lt f


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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.

Si l Sh ft U it C fi ti


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Single Shaft Unit Configuration

GT- Generator Clutch ST

GT ST Generator

GT Generator Clutch ST config


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GT-GeneratorClutchST config.

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

Startup of gas Turbine is independent of Steamturbine

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

Gas turbine and steam turbines have their ownthrust and journal bearings

GTSTGenerator Configuration


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GT ST Generator Configuration

Axial steam turbine exhaust is not

possible Steam turbine shares the cold end

thrust / journal bearing of Gas Turbine

Auxiliary steam is required for cooling ofsteam turbine during startup

Outage of ST necessarily lads to outage of the

whole power train.

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


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C bi d C l O ti


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Combined Cycle Options

STEAM CYCLE:

Single pressureTwo pressure

Three pressure

Reheat

Non-reheat

DEAERATION:

Deaerating condenser

Deaerator/evaporatorintegral with WHRB

HRSG DESIGN:

Natural circulationevaporator

Forced circulationevaporator

Unfired

Supplementary fired

NOx CONTROL:

Water InjectionSteam Injection

SCR ( NOx and/or CO)

Dry Low NOx

Combustion

C bi d C l O i


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CONDENSER:

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

Cost Distribution for a CC Power Plant


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(2GTs + 2HRSGs + 1ST)

bine, Aux equipment : 26piping + auxiliary equipment: 1urbine + generator+piping+condenser:

and supervisory equipment+transformeineering: 6 %+ supervision: 18 %

Cost Distribution for a CC Power Plant

Bypass Stack /


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Bypass Stack /Waste Heat Recovery Systems

Power Enhancement Methods


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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

Owners own economic evaluation factors

for plant output, heatrate, O&M costs.

Power Enhancement Methods

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

ostofInstallation

O&MCost

O&MStaff

FuelRequirement

Landrequirement

WaterRequirement

GestationPeriod

PlantEfficency

Thermal

Comb. Cycle

Comparison of Availability Reliability


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Comparison of Availability, ReliabilityAvailability = [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


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overiew of comb cycle rev 6.0_part 2

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