Combined Cycle Gas Turbine.ppt

Combined Cycle Gas Turbine

Combined Cycle Gas Turbine. CCGT Power Plant Abbas A M Al Fardan

Natural Gas Fueled Combution Turbine Combined Cycle Electricity Generator.flv

Combined Cycle Gas Turbine

What is the CCGT? A combined cycle gas turbine power plant, frequently identified by CCGT shortcut, is essentially an electrical power plant in which a gas turbine and a steam turbine are used in combination to achieve greater efficiency than would be possible independently. The gas turbine drives an electrical generator. The gas turbine exhaust is then used to produce steam in a heat exchanger (steam generator) to supply a steam turbine whose output provides the means to generate more electricity. However the Steam Turbine is not necessarily, in that case the plant produce electricity and industrial steam which can be used for heating or

Combined Cycle Gas Turbine

Basic Gas Turbine Information •Main Gas Turbine Manufactures: General Electrics, Simens Westinghouse & Alstom •Approximately Cost per MW – 0.7mln E •Efficiency approx 40% for gas turbine however in the CCGT plant the efficiency is 50-60% (even higher for cogenerated plant) •Low Green Gas Emission C02, NOx & SOx •Chepear comparing to other technology e.g. CCS •Lifetime 30-40 years

Combined Cycle Gas Turbine

How it works?

220kV Tabert Substation

110kV Clahane Substation

Combined Cycle Gas Turbine

CCGT Fuel Available in KSA Natural Gas. Resources available in KSA Synthetic Gas from coal. Resources not available in KSA

Fuel Oil. Resources available in KSA

Biogas from forestry, domestic and agricultural waste. Resources not available in KSA

Combined Cycle Gas Turbine

CCGT Plants Conventional or Cogeneration Variable

CCGT

High Efficiency Cogeneration

Transmission Network

Lower Impact

Higher Impact

Power Losses

Less power losses

Higher Power Losses

Heat Market

Required

Not Required

Fuel consumption

-33%

+33%

CO2 Emission

-67%

+67%

Water Consumption

-30%

+30%

Capital Cost per kW delivered

630

1200

Combined Cycle Gas Turbine

grid Grid Code Grid Code contains general conditions and rules for general application. The specification and conditions for each application are adjust individually. Those information are included in Grid Connection Offer & Agreement between developer and Transmission Operator TSO. •Client (Requires connection) and TSO must implement Grid Code specification during each stages of the project, for project above 10MW •TSO may be disconnected or terminated the Grid Connection Agreement if the Grid Code is not implemented by client. •The Implementation of the Grid Code may have significant impact on the cost of the Grid Connection

Combined Cycle Gas Turbine

Grid Constraints •Capacity of the transmission lines • Small Infrastructures of the High Voltage Lines •Distance from Energy Load Centres (West Coast) • High Cost of Design and planning permission for Shallow Connection, significantly for OHL 220kV •Planning Restrictions regarding OHL Construction

Combined Cycle Gas Turbine

Grid Connection Costs Variable

Cost

Gas & Steam Turbine Generator

210’000’000

2 bay 110kV/220kV Substation

4’420’000

220kV OHL

710’000/km (12km)

110kV OHL

320’000/km (15km)

Buried Cable 500MVA (optional)

2’150’000/km

Total Cost

227’740’000

Combined Cycle Gas Turbine

Gas Turbine Basics • Gas Turbines – Types – How They Work – Applications – Components of Plant – Flow Paths – Operation

10

Combined Cycle Gas Turbine

Gas Turbine Applications • Simple Cycle • Combined Cycle • Cogeneration

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Combined Cycle Gas Turbine

Types of Gas Turbine Plants • Simple Cycle – Operate When Demand is High – Peak Demand – Operate for Short / Variable Times – Designed for Quick Start-Up – Not designed to be Efficient but Reliable • Not Cost Effective to Build for Efficiency • Combined Cycle – Operate for Peak and Economic Dispatch – Designed for Quick Start-Up – Designed to Efficient, Cost-Effective Operation – Typically Has Ability to Operate in SC Mode

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Combined Cycle Gas Turbine

Principles of Operation • Open Cycle Also referred to as simple cycle)

 

The energy contained in a flowing ideal gas is the sum of enthalpy and kinetic energy. Pressurized gas can store or release energy. As it expands the pressure is converted to kinetic energy. Link to picture

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Combined Cycle Gas Turbine

Brayton Cycle – Gas Turbine Cycle

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Combined Cycle Gas Turbine

Thermodynamic Fundamentals •

Pressure Ratio & CT Components

15

Combined Cycle Gas Turbine

Combustion or Gas Turbine

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Combined Cycle Gas Turbine

Principles of Operation Compressor • As air flows into the compressor, energy is transferred from its rotating blades to the air. Pressure and temperature of the air increase. • Most compressors operate in the range of 75% to 85% efficiency. Combustor • The purpose of the combustor is to increase the energy stored in the compressor exhaust by raising its temperature. Turbine • The turbine acts like the compressor in reverse with respect to energy transformation. • Most turbines operate in the range of 80% to 90% efficiency.

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Combined Cycle Gas Turbine

Principles of Operation Overall Energy Transformations (Thermal Efficiency) • Useful Work = Energy released in turbine minus energy absorbed by compressor. The compressor requires typically approximately 50% of the energy released by the turbine. • Overall Thermal Efficiency = Useful Work/Fuel Chemical Energy *100 Typical overall thermal efficiencies of a combustion turbine are 20% - 40%.

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Combined Cycle Gas Turbine

Gas Turbine Applications • Simple Cycle

COMBUSTOR

COMPRESSOR

INLET AIR

TURBINE

GENERATOR

EXHAUST GAS

19

Combined Cycle Gas Turbine

Simple Cycle Power Plant Westinghouse 501D5 – 340 MW

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Combined Cycle Gas Turbine

Combined Cycle Power Plant

21

GT PRO 13.0 Drew Wozniak 12.54 p 90 T 30 %RH 944 m 4327 ft elev.

Net Power 95959 kW LHV Heat Rate 7705 BTU/kWh 967.3 m

1X GE 6581B 149.2 p 684 T

Fogger 4.717 m

143.2 p 2072 T

2 X GT

73.85 %N2 13.53 %O2 3.233 %CO2+SO2 8.497 %H2O 0.8894 %Ar

12.93 p 1034 T 1934.6 M

33781 kW

12.39 p 68 T 948.7 m 30813 kW Natural gas 18.58 m LHV 369671 kBTU/h 77 T

122 T 292.6 M 122 T

850 p 950 T 248.6 M

96 T

1.694 p 120 T 222.1 M

17.19 p 220 T

292.6 M 29.65 M 29.58 M

0.1296 M

26.36 M

6.89 M V8

195.8 p 597 T

V4

183 p 375 T 70 M

879.8 p 954 T

Combined Cycle Gas Turbine

Combined Cycle Plant Design

120 T

6.89 M FW

LPB

IPE2

IPB

HPE2

IPS1

HPE3

IPS2

HPB1

HPS3

268 T 1934.6 M

1031 T 1934.6 M 17.19 p 220 T 29.65 M 268

203.6 p 373 T 292.6 M 326

p[psia], T[F], M[kpph], Steam Properties: Thermoflow - STQUIK 1512 10-13-2004 23:27:31 file=C:\Tflow13\MYFILES\3P 0 70.gtp

203.6 p 924.2 p 383 T 472 T 36.75 M 251.1 M 419

481

534

199.7 p 910.5 p 460 T 523 T 36.75 M 251.1 M 538

568

195.8 p 910.5 p 500 T 533 T 36.75 M 248.6 M 569

879.8 p 954 T 248.6 M 897

1031 Natural gas 0M

22

Combined Cycle Gas Turbine

Gas Turbine Components Compressor – Combustor - Turbine

23

Combined Cycle Gas Turbine

Gas Turbine Components & Systems (cont’d) • Combustion System – Silo, Cannular, Annular – Water, Steam, DLN

• Turbine – Multiple Shaft, Single Shaft – Number of Stages – Material and Manufacturing Processes

 Exhaust

System

Simple Cycle Stack  Transition to HRSG 

 Generator

Open-Air cooled  TEWAC  Hydrogen Cooled 

 Starting

Systems

Diesel  Motor  Static 

24

Combined Cycle Gas Turbine

Combustion Turbine Fuels • Conventional Fuels – Natural Gas – Liquid Fuel Oil

• Nonconventional Fuels – Crude Oil – Refinery Gas – Propane

• Synthetic Fuels – Chemical Process – Physical Process 25

Combined Cycle Gas Turbine

GE Combustion Turbine Comparisons

26

Combined Cycle Gas Turbine

Gas Turbine Types  

Advanced Heavy-Duty Units Advanced Aero derivative Units

27

Combined Cycle Gas Turbine

Gas Turbine Major Sections • • • • • •

Air Inlet Compressor Combustion System Turbine Exhaust Support Systems

28

Combined Cycle Gas Turbine

Gas Turbine Barrier Inlet Filter Systems

29

Combined Cycle Gas Turbine

Gas Turbine Pulse Inlet Filter System

30

Combined Cycle Gas Turbine

Inlet Guide Vanes

31

Combined Cycle Gas Turbine

Inlet Guide Vanes

32

Combined Cycle Gas Turbine

Gas Turbine Compressor Rotor Assembly

33

Combined Cycle Gas Turbine

6B Gas Turbine

34

Combined Cycle Gas Turbine

Gas Turbine Cut Away Side View

35

Combined Cycle Gas Turbine

Gas Turbine Combustor Arrangement

36

Combined Cycle Gas Turbine

Frame 5 GT

37

Combined Cycle Gas Turbine

GE LM2500 Aero-derivative Gas Turbine

Compressor

Compressor Turbine Section

Power Turbine Section

38

Combined Cycle Gas Turbine

FT4 Gas Turbine

39

Combined Cycle Gas Turbine

FT4 Gas Turbine – Gas Generator Compressor)

40

Combined Cycle Gas Turbine

FT4 Gas Turbine – Gas Generator (Compressor)

41

Combined Cycle Gas Turbine

FT4 Gas Turbine – Free Turbine

42

Combined Cycle Gas Turbine

FT4 Gas Turbine – Free Turbine Gas Path

43

Combined Cycle Gas Turbine

FT4 Gas Generator Performance

44

Combined Cycle Gas Turbine

FT4 Free Turbine Performance

45

Combined Cycle Gas Turbine

Aero-derivative Versus Heavy Duty Combustion Turbines • Aero-derivatives – Higher Pressure Ratios and Firing Temperatures Result in Higher Power Output per Pound of Air Flow – Smaller Chilling/Cooling Systems Required – Compressor Inlet Temperature Has a Greater Impact on Output and Heat Rate – Benefits of Chilling/Cooling Systems are More Pronounced

46

Combined Cycle Gas Turbine

Typical Simple Cycle CT Plant Components • Prime Mover (Combustion Turbine) • Fuel Supply & Preparation • Emissions Control Equipment • Generator • Electrical Switchgear • Generator Step Up Transformer • Starting System (Combustion Turbines) • Auxiliary Cooling • Fire Protection • Lubrication System 47

Combined Cycle Gas Turbine

Typical Peaking Plant Components

Lube Oil System

Switchgear / MCC

GSU

Generator

Starting Engine

Fire Protection

48

Combined Cycle Gas Turbine

Combining the Brayton and Rankine Cycles • Gas Turbine Exhaust used as the heat source for the Steam Turbine cycle • Utilizes the major efficiency loss from the Brayton cycle • Advantages: – – – – – –

Relatively short cycle to design, construct & commission Higher overall efficiency Good cycling capabilities Fast starting and loading Lower installed costs No issues with ash disposal or coal storage

• Disadvantages – High fuel costs – Uncertain long term fuel source – Output dependent on ambient temperature

49

Combined Cycle Gas Turbine

How does a Combined Cycle Plant Work?

Picture courtesy of Nooter/Eriksen

50

Combined Cycle Gas Turbine

Combined Cycle Heat Balance

51

Combined Cycle Gas Turbine

Combined Cycles Today • Plant Efficiency ~ 58-60 percent – Biggest losses are mechanical input to the compressor and heat in the exhaust

• Steam Turbine output – Typically 50% of the gas turbine output – More with duct-firing

• Net Plant Output (Using Frame size gas turbines) – up to 750 MW for 3 on 1 configuration – Up to 520 MW for 2 on 1 configuration

• • • • •

Construction time about 24 months Engineering time 80k to 130k labor hours Engineering duration about 12 months Capital Cost ($900-$1100/kW) Two (2) versus Three (3) Pressure Designs – Larger capacity units utilize the additional drums to gain efficiency at the expense of higher capital costs

52

Combined Cycle Gas Turbine

Combined Cycle Efficiency • • •

•

•

Simple cycle efficiency (max ~ 44%*) Combined cycle efficiency (max ~58-60%*) Correlating Efficiency to Heat Rate (British Units) = 3412/(Heat Rate) --> 3412/ = Heat Rate* – Simple cycle – 3412/.44 = 7,757 Btu/Kwh* – Combined cycle – 3412/.58 = 5,884 Btu/Kwh* Correlating Efficiency to Heat Rate (SI Units) = 3600/(Heat Rate) --> 3600/ = Heat Rate* – Simple cycle – 3600/.44 = 8,182 KJ/Kwh* – Combined cycle – 3600/.58 = 6,207 KJ/Kwh* Practical Values – HHV basis, net output basis – Simple cycle 7FA (new and clean) 10,860 Btu/Kwh (11,457 KJ/Kwh) – Combined cycle 2x1 7FA (new and clean) 6,218 Btu/Kwh (6,560 KJ/Kwh)

*Gross LHV basis

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Combined Cycle Gas Turbine

Gas Turbine Generator Performance Factors that Influence Performance – Fuel Type, Composition, and Heating Value – Load (Base, Peak, or Part) – Compressor Inlet Temperature – Atmospheric Pressure – Inlet Pressure Drop • Varies significantly with types of air cleaning/cooling – Exhaust Pressure Drop • Affected by addition of HRSG, SCR, CO catalysts – Steam or Water Injection Rate • Used for either power augmentation or NOx control – Relative Humidity

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Combined Cycle Gas Turbine

Altitude Correction

55

Combined Cycle Gas Turbine

Humidity Correction

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Combined Cycle Gas Turbine

Cogeneration Plant • A Cogeneration Plant – Power generation facility that also provides thermal energy (steam) to a thermal host. • Typical thermal hosts – paper mills, – chemical plants, – refineries, etc… – potentially any user that uses large quantities of steam on a continuous basis. • Good applications for combined cycle plants – Require both steam and electrical power

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Combined Cycle Gas Turbine

Major Combined Cycle Plant Equipment • • • • •

Combustion Turbine (CT/CTG) Steam Generator (Boiler/HRSG) Steam Turbine (ST/STG) Heat Rejection Equipment Air Quality Control System (AQCS) Equipment • Electrical Equipment

58

Combined Cycle Gas Turbine

Heat Recovery Steam Generator (HRSG)

59

Combined Cycle Gas Turbine Steam Turbine

GE D11

60

Combined Cycle Gas Turbine

Primary to Secondary to End-Use Energy

P r im a r y E n e rg y

Losses

Losses

T r a n s fo r m a tio n T r a n s p o r ta tio n D is tr ib u tio n

U tiliz a tio n D e v ic e o r S y s te m

S e c o n d a ry E n e rg y

F in a l U s e fu l E n e rg y

Combined Cycle Gas Turbine

Outline • • • •

Electricity Basics Electricity from Fossil Fuels Co-generation and Tri-generation Economics

Combined Cycle Gas Turbine

Electricity Basics • Electricity can be either direct current (DC) or alternating current (AC) • In AC current, the voltage and current fluctuate up and down 60 times per second in North America and 50 times per second in the rest of the world • The power (W) in a DC current is equal to current (amps) x voltage (volts): P=VI • The power in an AC current is equal to the product of the root mean square (RMS) of the fluctuating current and voltage if the current and voltage are exactly in phase (exactly tracking each other): P=Vrms x Irms • The standard electricity distribution system consists of 3 wires with the current in each wire offset by 1/3 of a cycle from the others, as shown in the next figure

Combined Cycle Gas Turbine Three-phase AC Current

Combined Cycle Gas Turbine

Two Pole Synchronous Generator

Source: EWEA

Combined Cycle Gas Turbine

• Electricity demand continuously varies, and power utilities have to match this variation as closely as they can by varying their power production. The following distinctions are made: • Base_load power plants: these are plants that run steadily at full load, with output equal to the typical minimum electricity demand during the year. Plants (such as coal or nuclear) that cost a lot to build but are cheap to operate (having low fuel costs) are good choices • Peaking powerp lants: these are plants that can go from an off state to full power within an hour or so, and which can be scheduled based on anticipated variation in demand (natural gas turbines or diesel engines would be a common choice) • Spinning reserve: these are plants that are on but running at part load – this permits them to rapidly (within a minute) vary their output, but at the cost of lower efficiency (and so requires greater fuel use in the case of fossil fuel power plants).

Combined Cycle Gas Turbine

Electricity from Fossil Fuels • Pulverized coal • Integrated Gasification/Combined Cycle (IGCC) • Natural gas turbines and combined cycle • Diesel and natural gas reciprocating engines • Fuel cells

Combined Cycle Gas Turbine

Technical issues related to electricity from fossil fuels • • • • •

Full load efficiency Part-load efficiency Rates of increase of output Impact of temperature on output Auxiliary energy use

Combined Cycle Gas Turbine

Generation of electricity from a conventional, pulverized-coal power plant G e n e ra to r

s te a m

H ig h - P r e s s u r e B o ile r

e le c tr ic ity o u t

fo s s il fu e l in

S te a m T u r b in e

a ir ( O 2 ) CO

to c o o lin g t o w e r o r c o ld riv e r w a te r

2

w a te r c o n d e n s a te CO

2

a n d /o r c o g e n e r a tio n

u p th e s ta c k s e q u e s te r e d C O out

2

C ondenser P um p

Source: Hoffert et al (2002, Science 298, 981-987)

c o o lin g w a t e r r e t u r n f lo w

Combined Cycle Gas Turbine

The upper limit to the possible efficiency of a power plant is given by the Carnot efficiency: η = (Tin-Tout)/Tin So, the hotter the steam supplied to the steam turbine, the greater the efficiency. Hotter steam requires greater pressure, which requires stronger steel and thicker walls. so there is a practical limit to the achievable Carnot efficiency (and actual efficiencies are even lower)

Combined Cycle Gas Turbine

Coal power plant operating temperatures and efficiencies • Typical: 590ºC, 35% efficiency • Best today: > 600ºC, 42-44% efficiency • Projected by 2020: 720ºC, 48-50% efficiency

Combined Cycle Gas Turbine

Integrated Gasification Combined Cycle (IGCC) • This is an alternative advanced coal power plant concept • Rather than burning pulverized solid coal, the coal is heated to 1000ºC or so at high pressure in (ideally) pure oxygen • This turns the coal into a gas that is then used in a gas turbine, with heat in the turbine exhaust used to make steam that is then used in a steam turbine • Efficiencies of ~ 50% are expected, but are much lower at present

Combined Cycle Gas Turbine

Generation of electricity with natural gas • • • •

Simple-cycle power generation Combined-cycle power generation Simple-cycle cogeneration Combined-cycle cogeneration

Combined Cycle Gas Turbine

Simple-cycle turbine • Has a compressor, combustor, and turbine proper • Because hot gases rather than steam are produced, it is not restricted in temperature by the rapid increase in steam pressure with temperature • Thus, the operating temperature is around 1200ºC

Combined Cycle Gas Turbine

Simple-cycle gas turbine and electric generator EXHAUST FUEL C O M B U STO R

SHAFT

E L E C T R I C IT Y G EN ERATO R

CO M PRESSO R

T U R B IN E

IN T A K E A IR

Source: Williams (1989, Electricity: Efficient End-Use and New Generation Technologies and Their Planning Implications, Lund University Press)

Combined Cycle Gas Turbine

Efficiency of generating electricity using natural gas • One might expect a high efficiency from the gas turbine, due to the high input temperature (and the resulting looser Carnot limit) • However, about half the output from the turbine has to be used to compress the air that is fed into it • Thus, the overall efficiency is only about 35% in modern gas turbines

Combined Cycle Gas Turbine

Turbine efficiency vs turbine size (power)

Combined Cycle Gas Turbine

Efficiency and cost of a simple-cycle gas turbine with and without water injection

Combined Cycle Gas Turbine

Due to the afore-mentioned high operating temperature of the gas turbine, the temperature of the exhaust gases is sufficiently hot that it can be used to either: Make steam and generate more electricity in a steam turbine (this gives combined cycle power generation). Or: provide steam for some industrial process that can use the heat, or to supply steam for district heating (this gives simple cycle cogeneration)

Combined Cycle Gas Turbine

Combined-cycle power generation using natural gas C O O L IN G T O W E R

C O ND EN S ER

EX H AU ST

E L E C T R I C IT Y W ATER P U M P

S T E A M T U R B IN E

STEA M

FU EL H EAT RE CO V ERY STEA M G E NE RATO R

CO M BUSTO R

SH A FT

E L E C T R I C IT Y G EN ER ATO R

C O M PR ES SO R

T U R B IN E

IN T A K E A IR

Source: Williams (1989, Electricity: Efficient End-Use and New Generation Technologies and Their Planning Implications, Lund University Press)

Combined Cycle Gas Turbine

Simple-cycle cogeneration EXHAUST

W ATER PU M P PR O CESS STEA M FUEL H EAT RECO VERY STEAM G ENERATO R

C O M B U STO R

SHAFT

E L E C T R I C IT Y G EN ERATO R

CO M PRESSO R

T U R B IN E

IN T A K E A IR

Source: Williams (1989, Electricity: Efficient End-Use and New Generation Technologies and Their Planning Implications, Lund University Press)

Combined Cycle Gas Turbine

The energy can be cascaded even further, as follows: • Gas turbine → steam turbine → useful heat as steam from the steam turbine (combined cycle cogeneration), or • Gas turbine → steam turbine → steam → hot water (also combined cycle cogeneration), or • Gas turbine → steam → hot water

Combined Cycle Gas Turbine

Combined-cycle cogeneration C O O L IN G T O W E R PR O C ES S S TEA M EX H A U ST

C O N D EN S ER E L E C T R I C IT Y S T E A M T U R B IN E

W ATER P U M P ST EA M

FU EL H EAT R E C O V ER Y ST EA M G E N E R ATO R

C O M B U STO R

SH A FT

E L E C T R I C IT Y G EN E R ATO R

C O M PR ES SO R

T U R B IN E

IN T A K E A IR

Source: Williams (1989, Electricity: Efficient End-Use and New Generation Technologies and Their Planning Implications, Lund University Press)

Combined Cycle Gas Turbine

Cogeneration system with production of steam and hot water E L E C T R IC IT Y

FU E L

G A S T U R B IN E

G E N E R ATO R S T E A M

E X H A U S T G A S

H E AT R E C O V E R Y S T E A M G E N E R ATO R

H E AT E X C H A N G E R

E X H A U S T G A S

H O T W AT E R

Source: Malik (1997, M. Eng Thesis, U of Toronto)

Combined Cycle Gas Turbine

• State-of-the-art natural gas combined-cycle (NGCC) systems have electricity generation efficiencies of 55-60%, compared to a typical efficiency of 35% for single-cycle turbines • However, NGCC systems are economical only in sizes of 25-30 MW or greater, so for smaller applications, only the less efficient simple-cycle systems are used • Thus, a number of techniques are being developed to boost the electrical efficiency of simple gas turbines to 42-43%, with one technique maybe reaching 54-57%

Combined Cycle Gas Turbine

In cogeneration applications, the overall efficiency (counting both electricity and useful heat) depends on how much of the waste heat can be put to use. However, overall efficiencies of 90% or better have been achieved

Combined Cycle Gas Turbine

Reciprocating engines • These have pistons that go back and forth (reciprocate) • Normally they use diesel fuel – so these are the diesel generators normally used for backup or emergency purposes • However, they can also be fuelled with natural gas, with efficiencies as high as 45%

Combined Cycle Gas Turbine

Fuel cells • These are electrochemical devices – they generate electricity through chemical reactions at two metal plates – an anode and a cathode • Thus, they are not limited to the Carnot efficiency • Operating temperatures range from 120ºC to 1000ºC, depending on the type of fuel cell • All fuel cells require a hydrogen-rich gas as input, which can be made by processing natural gas or (in the case of hightemperature fuel cells) coal inside the fuel cells

Combined Cycle Gas Turbine

Fuel cells (continued) • Electricity generation efficiencies using natural gas of 40-50% are possible, and 90% overall efficiency can be obtained if there is a use for waste heat • In the high-T fuel cells, the exhaust is hot enough that it can be used to make steam that can be used in a steam turbine to make more electricity • An electrical efficiency of 70% should be possible in this way – about twice that of a typical coal-fired.

Combined Cycle Gas Turbine

F u e l (H 2 )

A ir (M o s tly N 2 + O 2) D C P ow er

Cross section of a single fuel cell.

E e le c tr o n flo w N e g a tiv e io n s or P o s itiv e io n s

F uel d is tr ib u tio n p la te

Several such cells would be placed next to each other to form a fuel cell stack. O x id iz e d F u e l (H 2 O )

N itr o g e n

Combined Cycle Gas Turbine

United Technologies Company 200-kW phosphoric acid fuel cell that uses natural gas as a fuel. 1=fuel processor, 2=cell stack, 3=power conditioner, 4=electronics and controls

Source: www.utcfuelcells.com

Combined Cycle Gas Turbine

Solid Oxide Fuel Cell / Gas Turbine System Fuel

Air o

o

25 C

25 C

FC

AC

o

236 C

o

847 C

SOFC = Solid Oxide Fuel cell AC,FC = Air & Fuel compressor CB = Catalytic burner GT = Gas turbine HRSG = Heat recovery steam generator HE = Heat exchanger

GT-2 o

1079 C GT-1

o

301 C

HE-1

o

738 C o

448 C

o

526 C HE-2

SOFC

o

985 C CB

M 468 C

Turbine Exhaust

o

Pump

o

440 C HRSG o

509 C

o

1290 C

o

HE-3

224 C o

25 C

To heat load From heat load

Combined Cycle Gas Turbine

Electrical efficiency vs. load

Combined Cycle Gas Turbine

Figure 3.11b Relative electrical efficiency vs. load

Combined Cycle Gas Turbine

Summarizing the preceding slides and other information,

• Natural gas combined-cycle has the highest full-load efficiency (55-60%) and holds its efficiency well at part load • Reciprocating engines have intermediate full-load efficiencies (40-45%) and load their efficiencies well at part load • Gas turbines and micro-turbines have low full-load efficiencies (typically 25-35%, but ranging from 16% to 43%) and experience a substantial drop at part load • Fuel cells using natural gas have intermediate full-load efficiency (40-45%) but this efficiency increases at part load

Combined Cycle Gas Turbine

Capital Costs Today • Pulverized coal power plant with state-ofthe-art pollution controls: $1200-1400/kW • Natural gas combined cycle: $400-600/kW in mature markets, $600-900/kW in most developing countries • Reciprocating engines: $600-1200/kW • Fuel cells: $3000-5000/kW

Combined Cycle Gas Turbine

Cogeneration

Combined Cycle Gas Turbine

Cogeneration is the simultaneous production of electricity and useful heat – basically, take the waste heat from electricity generation and put it to some useful purpose. Two possible uses are to feed the heat into a district heating system, and to supply it to an industrial process

Combined Cycle Gas Turbine

Figure 3.12 Proportion of electricity produced decentrally (overwhelmingly as cogeneration)

Combined Cycle Gas Turbine

Technical issues • Impact of withdrawing useful heat on the production of electricity • Ratio of electricity to heat production • Temperature at which heat is supplied • Electrical, thermal and overall efficiencies • Marginal efficiency of electricity generation

Combined Cycle Gas Turbine

Four efficiencies for cogeneration:

• The electrical efficiency – the amount of electricity produced divided by the fuel use (later I’ll need to call this the direct electrical efficiency) • The thermal efficiency – the amount of useful heat provided divided __by the fuel use • The overall efficiency – the sum of the of two • The effective or marginal efficiency of electricity generation – explained later

Combined Cycle Gas Turbine

Impact of withdrawing heat • In simple-cycle cogeneration, capturing some of the heat in the hot gas exhaust does not reduce the production of electricity, but the electrical production is already low • In cogeneration with steam turbines, the withdrawal of steam from the turbine at a higher temperature than would otherwise be the case reduces the electricity production • The higher the temperature at which we want to take heat, the more that electricity production is reduced

Combined Cycle Gas Turbine

Example of the tradeoff between production of useful heat and loss of electricity production using steam turbine cogeneration

Source: Bolland and Undrum (1999, Greenhouse Gas Control Technologies, 125-130, Elsevier Science, New York)

Combined Cycle Gas Turbine

Thus, to maximize the electricity production, we want to be able to make use of heat at the lowest possible temperature. If the heat is to be provided to buildings, that means having well insulated buildings that can be kept warm with radiators that are not very hot

Combined Cycle Gas Turbine

The alternative to cogeneration is the separate production of heat and electricity. The effective efficiency in generating electricity is the amount of electrical energy produced divided by the extra fuel used to produce electricity along with heat compared to the amount of fuel that would be used in producing heat alone. The extra amount of fuel required in turn depends on the efficiency with which we would have otherwise have produced heat with a boiler or furnace.

Combined Cycle Gas Turbine

For example, suppose that we have a cogeneration system with an electrical efficiency of 25% and an overall efficiency of 80%. Then, the thermal efficiency is 80%-25%=55% - we get 55 units of useful heat from the 100 units of fuel. If the alternative for heating is a furnace at 80% efficiency, we would have required 68.75 units of fuel to produce the 55 units of heat. Thus, the extra fuel use in cogeneration is 100-68.75=31.25 units, and the effective electricity generation efficiency is 25/31.25=80%. I call this the marginal efficiency, because it is based on looking at things on the margin (this is a concept from economics).

Combined Cycle Gas Turbine

With a little algebra, it can be shown that the marginal efficiency is given by nmarginal = nel/(1-nth/nb) where nel and nth are the electrical and thermal efficiencies of the cogeneration system, and nb is the efficiency of the boiler or furnace that would otherwise be used for heating

Combined Cycle Gas Turbine

Marginal efficiency of electricity generation in cogeneration (ηel = efficiency of the alternative, central power plant for electricity generation)

Combined Cycle Gas Turbine

Key points • For a given thermal efficiency, the effective electrical efficiency is higher the higher the direct electrical efficiency • However, very high effective electrical efficiencies can be achieved even with low direct electrical efficiencies if the thermal efficiency is high – that is, if we can make use of most of the waste heat • To get a high thermal efficiency requires being able to make use of lowtemperature heat (at 50-60ºC), as well as making use of higher temperature heat

Combined Cycle Gas Turbine

Electricity:heat ratio

• Because the marginal electricity generation efficiency in cogeneration is generally much higher than the efficiency of a dedicated central powerplant, there is a substantial reduction in the amount of fuel used to generate electricity when cogeneration is used • Thus, we would like to displace as much inefficient central electricity generation as possible when cogeneration is used to supply a given heating requirement • This in turn requires that the electricity-to-heat production ratio in cogeneration be as large as possible • (Remember – none of the gains that we’ve talked about occur if we can’t use the waste heat produced by cogeneration)

Combined Cycle Gas Turbine

Electricity : heat output ratio in cogeneration

Combined Cycle Gas Turbine

Figure 3.17 Dependence of overall savings through cogeneration on the electricity:heat ratio and on the central powerplant efficiency, assuming a 90% overall efficiency for cogeneration and 90% efficiency for the alternative heating system

Combined Cycle Gas Turbine

Cost of Electricity

Combined Cycle Gas Turbine

Issues related to the cost of electricity: • Capital cost, interest rate, lifespan • Fuel cost (impact of depends on efficiency) • Fixed and variable operation & maintenance costs • Baseload vs peaking costs • Transmission line costs and transmission losses • Amount of backup capacity

Combined Cycle Gas Turbine

Capital cost of natural gas combined cycle cogeneration plants

Combined Cycle Gas Turbine

Amortization of capital cost: CRF x Ccap / (8760 x CF) units: $/kWh where CRF = i /(1-(1+i)-N) is the cost recovery factor _i = interest rate _N = financing time period Ccap = capital cost ($/kW) 8760 is the number of hours in a year CF= capacity factor (annual average output as a fraction of capacity)

Combined Cycle Gas Turbine

Fuel contribution to the final cost: Cfuel ($/GJ) x 0.0036 (GJ/kWh) / efficiency The cost of electricity from less efficient power plants will be more sensitive to the cost of fuel than the cost of electricity from efficient power plants, but more efficient power plants will tend to have greater capital cost

Combined Cycle Gas Turbine

Typical overnight capital costs and best efficiencies • Pulverized coal: $1200-1400/kW,η= 0.45-0.48 • IGCC: $1400-2600/kW today, η= 0.41-0.55 $1150-1400/kW hoped for, future • NGCC: $400-600/kW, η = 0.55-0.60 • Reciprocating engine: $600-1200/kW,η=0.40-0.46 • Micro-turbine: $1800-2600/kW, η= 0.23-0.27 • Fuel cells: $3000-5000/kW, η= 0.35-0.45 $1000-1500/kW hoped for, future • NGCC/FC hybrid: $2000-3000/kW, η= 0.70-0.80

Combined Cycle Gas Turbine

Cost of electricity from coal and natural gas

Combined Cycle Gas Turbine

Cost of heat from boilers, electricity with or without cogeneration, and heat from cogeneration

Combined Cycle Gas Turbine

Cost of electricity from central coal (at $2/GJ) and from natural gas (at $10/GJ)

Combined Cycle Gas Turbine

Water requirements • Most thermal power plants use water to cool the condenser of a steam turbine and for other, minor, purposes • There are two approaches: a once-through cooling system a recirculating system in a cooling tower • Water use by power generation represents the largest or second largest use of water in most countries (with irrigation sometimes being a larger use)

Combined Cycle Gas Turbine

• In once-through systems, the water is returned to the source (but at a warmer temperature). Large volumes of water are needed – not available in arid regions • In a recirculating systems, water that has removed heat from the condenser is sprayed through a cooling tower, where it is cooled by evaporation, then returns to the condenser • This consumes water, but the amount that is withdrawn from the water source (lakes, rivers or groundwater) is smaller than in oncethrough systems

Combined Cycle Gas Turbine

Typical water requirements • Steam turbines (as in coal power plants) Once through: 80-190 liters withdrawn per kWh of __generated electricity, ~ 1 liter / kWh consumed Recirculating: 1-3 liters/kWh withdrawn 1-2 liters/kWh consumed • Natural gas combined cycle Once through: 30 liters/kWh withdrawn ~ 0.4 liters/kWh consumed Recirculating: 0.9 liters/kWh withdrawn 0.7 liters/kWh consumed

Combined Cycle Gas Turbine

Bottom line: • More efficient power plants, such as natural gas combined cycle power plants, use less water per kWh of generated electricity than less efficient power plants • The water requirements can be a constraining factor in arid regions • It is possible to use air rather than water to cool the condenser, but then the efficiency drops

Combined Cycle Gas Turbine

Section 3.1 – Steam Turbine Fundamentals

Overview • Hero Reaction Turbine – 120 B.C. • First Practical Turbine – 1884, C. Parsons • First Power Plant – 7.5 kw – 1890 • Reaction, Impulse and Velocity-Compounded • Reheat Steam – 1930’s • Last 100 years Turbine is the key element in generating electricity • Turbines run Generators, Pumps, Fans, etc. • Today up to 1,500 MW 126

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Steam Turbine Fundamentals Overview

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Steam Turbine Fundamentals Fundamentals

Energy Transfer Coal, Natural Gas, Nuclear, Biofuel, Waste Fuel 128

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Steam Turbine Fundamentals Section 3.1 – Steam Turbine Fundamentals Reaction Turbines Newton’s third law of motion – For every action there is an equal and opposite reaction.

Narrowing Steam Path

Narrowing Steam Path

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Steam Turbine Fundamentals Section 3.1 – Steam Turbine Fundamentals Impulse Turbines Steam / Gas Flow Fixed Vanes

Moving Blades

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Section 3.1 – Steam Turbine Fundamentals

Reaction – Impulse Comparison

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Steam Turbine Fundamentals Section 3.1 – Steam Turbine Fundamentals Velocity-Compounded Turbine Velocity compounding is a form of staging which by dividing the work load over several stages results in improved efficiency and a smaller diameter for the blade wheels due to a reduction in Ideal blade speed per stage.

Inlet Pressure

1 P= V

Inlet Velocity

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Steam Turbine Fundamentals Section 3.1 – Steam Turbine Fundamentals Turbine Components - Blades Impulse

Reaction 133

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Steam Turbine Fundamentals Section 3.1 – Steam Turbine Fundamentals Turbine Diaphragms

Diaphragms contain the fixed blades

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Steam Turbine Fundamentals Section 3.1 – Steam Turbine Fundamentals Steam Turbine Casing

135

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Steam Turbine Fundamentals Section 3.1 – Steam Turbine Fundamentals Turbine Rotor

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Section 3.1 – Steam Turbine Fundamentals

Turbine Shaft and Casing Seals

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Steam Turbine Fundamentals Section 3.1 – Steam Turbine Fundamentals Turbine Types

Straight HP Tandem HP Tandem LP

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Steam Turbine Fundamentals Section 3.1 – Steam Turbine Fundamentals Turbine – Multiple Sets

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Steam Turbine Fundamentals Section 3.2 – Steam Turbine Design Overview Classification by; • Type – Reaction or Impulse • Steam Temperature and Pressure • Configuration – Compound, Tandem Compound, Cross Compound • Reheat • Output – MW • Structural Elements

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Steam Turbine Fundamentals Section 3.2 – Steam Turbine Design Turbine Design - Basics

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Steam Turbine Fundamentals Section 3.2 – Steam Turbine Design Materials • Blades • Stainless Steel – 403 & 422 (+Cr) • 17-4 PH steel (+ Ti) • Super Alloys • Rotor • High “Chrome – Moley” Steel – Cr-Mo-V • Low “Ni Chrome Steel – Ni-Cr-Mo-V

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A steam turbine is a device that extracts thermal energy from pressurized steam and uses it to do mechanical work on a rotating output shaft. Its modern manifestation was invented by Sir Charles Parsons in 1884. Steam Turbine may also be define as a device which converts heat energy of to the steam to the mechanical energy which finally converted into electrical energy.

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Because the turbine generates rotary motion, it is particularly suited to be used to drive an electrical generator – about 90% of all electricity generation in the United States, is by use of steam turbines. The steam turbine is a form of heat engine that derives much of its improvement in thermodynamic efficiency through the use of multiple stages in the expansion of the steam, which results in a closer approach to the ideal reversible process.

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The modern steam turbine was invented in 1884 by Sir Charles Parsons, whose first model was connected to a dynamo that generated 7.5 kW (10 hp) of electricity. The Parsons turbine also turned out to be easy to scale up. Parsons had the satisfaction of seeing his invention adopted for all major world power stations, and the size of generators had increased from his first 7.5 kW set up to units of 500MW capacity.

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Steam turbines are made in a variety of sizes ranging from small