Overiew of Comb Cycle Rev 7.0_Part 1

Gas Turbine Power

Generation

-An Introduction

Animated Gas Turbine Parts

Combined Cycle Power Generation

World Electricity Generation by Fuel Source

YEAR - 1995 YEAR - 2020

INTERNATIONAL ENERGY AGENCY

OVER THE YEARS GAS TURBINES AND COMBINED CYCLE PLANTS HAVE BEEN GAINING IN POPOULARITY

Efficiency Of Different Technologies

CC Plants - Preferred Technology• 70 % of post 2000 Generating capacity addition in US has

come from Gas Turbines and CC Plants.

• Last decade has witnessed that majority of UK’s very old coal fired power plants have been replaced by CC Plants.

• For Countries like Japan & Korea with limited fossil fuel resources, preferred technology is combined cycle.

• In India share of GT and CC Plants in total installed capacity is less than 10 % but 80% of the power plants set up by IPPs are combined cycle plants.

• Availability of Natural Gas/ LNG and CC Plants have to play an important role if Short/ Intermediate Term Capacity addition targets are to be met.

LIFE CYCLE COST OF A CC PLANT

1 – 2% INCREASE IN EFFICIENCY JUSTIFIES 3 – 5 % HIGHER INITIAL CAPITAL INVESTMENT.

Combined Cycle Power Generation

Earliest example of harnessing jet propulsion for having Rotary motion.

Invention of Aeolipile in 150 BC

Originator is Hero of Alexandria, Egypt

Initial Concept of Engine

Requirement from a Prime Mover

Less no of Links Vibration free Maintenance free Less complicacy Boost of power Compact High speed Cheap

Improvement over the Years1765 : Reciprocating Steam Engine

by James Watt

1876 : Reciprocating IC Engine by Nikolaus Otto

1883 :Steam Turbine by De Laval

1884 : Steam Turbine by Charls Parson

1908 : First Gas Turbine by Korting AG/BOSCH

1940 : First Stationary Gas Turbine

Turbine as Prime Mover

Most Satisfactory machine:

Absence of Reciprocating & Rubbing Members

Less Balancing problems

Very low Lub Oil consumption

Very high degree of reliability

Most sought after since beginning of the CenturyUse for Moving and Stationary prime movers,

BUT REQUIRES

High Pressure & temperature steamBulky & expensive steam generating equipmentsDifferent working fluid for Boiler & TurbineLengthy/complicated starting & stopping procedures

Necessity of direct working fluid like IC enginesAbsence of Thrust of Power

Steam Turbine as Prime Mover

Developed during World war for aircraft propulsion

Introduced in 1940s to the power generation

By 1960s, established as peak power producer

Initial development for mechanical drives in

Pipeline pumping station

gas compressors

transportation

Gas Turbine as Prime Mover

Simple Gas Turbine

Joule Brayton Cycle

Gas Turbine with Regeneration

Gas Turbine with Intercooling

Gas Turbine with Reheater

GT with Intercooling & Recuperation

Open Cycle Gas Turbine for Power Generation

Where the Generator is Kept?

Industrial Gas Turbine

Industrial Gas Turbine

Gas Turbine Rotor

Gas Turbine Rotor

M501F/M701F Gas Turbine (MHI)

FUEL(100 %)

POWER (30 %)

MISC.(3 %)

EXHAUSTHEAT(67 %)

Heat Balance In Gas Turbine

Gas Turbine Requirements

Factors for a Gas Turbine High efficiency High specific output

Key Parameters affecting above: Firing temperature Pressure Ratio

Higher TIT

• Each 55 oC increase in TIT improves Output by 10-13 % and Efficiency by 2-4 %.

• TIT for Modern Gas Turbines > 1400 oC

• Higher TIT demands : a. Creep Rupture Strength, b. Fatigue Resistance to cyclic loadings,

c. Castability and Machinabilty, d. Phase Stability

GT Blades: Internal Cooling Passage



Turbine Rotor blades

Air for Blade cooling

Air for Blade cooling

The firing temperature is raised from 1104 oC to 1124oC


Interior & Exterior Cooling-air Circulation

Film Cooling & Impingement Convection Cooling

Single And Multipass Cooling



Blade Cooling

• Impingement, Convective, and Film Cooling for First Stage Blades.

• Impingement cooling for rest stages.

• Serpentine passages with turbulence promoters

• Multipass, turbulated, pin fin cooling holes have replaced span wise film cooled design.

• Rotor Air Cooler Heat Utilization

• Cooling by air is detrimental to cycle efficiency because of irreversible pressure losses, reduction in gas path temp.,and internal losses.

• Closed loop steam cooling by convective heat transfer avoids above losses.

• Yields a 2 % power increase in Efficiency.

• In H-class, GT is used as parallel IP reheater for the bottoming cycle.

Closed Loop Steam Cooling


Cooling by air detrimental to cycle efficiency because of irreversible pressure losses, reduction in gas path temp., and internal losses.

Closed loop steam cooling by convective heat transfer avoids losses and yields a 2 % increase in Efficiency.


Firing Temp. Trend & Material Capability

MHI J class has TIT of 1600 0C.



Effect Of Cooling On TIT

MHI J class has TIT of 1600 0C.

Advances in Blade Metallurgy

• Conventional GT Blades - Vacuum precision casting methods, employ segregated hardening by alloying elements.

• Directional Solidification

• Single Crystal Blades

• ODS Ceramics

• Corrosion Resistance Coatings

• Thermal Barrier Coatings

Microstructure of Advance Materials

Directional Solidification

• Grain boundaries reduce creep strength, particularly when traverse the direction of primary stress.

• DS allows the grain-lines to be aligned parallel to the blade axis.

• DS allows blades to operate at 25 K higher temperature than conventionally cast blades.

• Service life in terms of thermal fatigue increases by a factor of 5.

Single Crystal Blades

• SCBs are blades without grain boundaries.

• Further 25 K temp. increase can be gained.

• Molten material is solidified in the form of columnar grains from which a single selected crystal is grown.

• Preferred orientation along the longitudinal axis of the blade.

• Length and weight limitation.

ODS Ceramics

• Oxide Dispersion Strengthened Ceramics

• Strength remains approximately constant upto 1000 °C, though less than Ni based alloys.

• ODS is suitable for Solid and Slightly cooled stationary blades.

• Complex manufacturing methods to produce intricate shapes.

Anti Corrosion Coatings

• Upto 800 °C - Cr based diffusion coatings.• MCrAlY (M-Co and /or Ni) coatings for higher T.• Aluminium forms dense oxide layer on the coating

surface that is thermally very stable.• Other materials control Al activity, hold the oxide

layer in place and adapt the coating to the base.• MCrAlY coatings are applied using the vacuum

plasma spray process. Thickness must not be more than 0.40 mm. Refurbishment after 20-25K hours.

Thermal Barrier Coatings

• TBC allows the operating temperature to be increased by 100 K.

• Outer Ceramic Layer - Zirconia, thickness limited to 0.25 mm.

• Metallic bonding layer - MCrAlY

• Flaking - due to transient stresses between the inner and outer surface of ceramic.

• Peeling - Oxide growth on bonding layer.

• Two principal methods of application -Thermal Spraying (atmospheric plasma) & Physical Vapour Deposition (PVD).

• PVD yields better result but much more costlier.

• Stator blades - Thermal Spraying

• Rotor Blades - PVD

Thermal Barrier Coatings CONTD.

TBC – Working Principle

Firing Temperature & Efficiency in GE Combined-Cycle Plants

(Source: General Electric R&D).

GT-Thermodynamic Fundamentals

• For a given TIT higher Compression Ratio yields higher efficiency.

• Optimum compression ratio for maximum Efficiency and maximum Specific Output are different.

• Optimum r for max. sp. Work Output corresponds to the value for which compressor and turbine outlet temperature are equal.

Performance

Pr. Ratio

1

2

1

11

PP

1 147

Specific Output, MW / kg/sec

Pressure Ratio = 5

10

1520

Max. Shaft O/pMax. Thermal Eff.

Performance

Performance

Efficiency of Simple and Combined-Cycle Gas Turbines

Factors Affecting GT Performance

• Ambient Temperature• Altitude above Mean Sea Level (MSL)• Relative Humidity• Inlet Pressure Loss• Exhaust Pressure Loss• Performance degradation• Steam /Water Injection for NOx Control• Type of Fuel

TYPICAL

Effect of Ambient Temperature

A 28°C results in :• ~ 25 % output reduction and•~ 10 % higher heat rate.

TYPICAL

Effect of Ambient Temperature

A 28°C results in* :• ~ 25 % output reduction and•~ 10 % higher heat rate.

Evaporative Cooling

Base Case 40C, 32% RH, Natural Gas Fuel, LHV 50,047 KJ/KgInlet Pressure loss 10 millibar; Exhaust Pressure Loss 12 millibar

PARAMETER GE 6541B Base Case

GE 6541B with Fog Cooling

GE 9171E Base Case

GE 9171E with Fog Cooling

Output, kW 31,749 35,318 101,510 113,100 Heat Rate, kJ/kWh 12,007 11,674 11,358 11,054

Compressor Inlet Temp, C 40 26 40 26

Pressure Ratio 10.66 11.26 11.1 11.78

Compressor Discharge Pressure, (Bar)

10.64 11.26 11.1 11.78

Air Mass Flow, Kg/sec 122.7 128.9 363.5 382.9 EGT, 557 548 564 553 Fuel Flow Rate, Kg/sec 2.116 2.288 6.399 6.939 Turbine Inlet Temp, C 1100 1100 1124 1123 Axial Compressor Work, kW

42,596 45,286 129,870 137,560

Turbine Section Work, kW 76,564 82,907 234,930 254,44 Thermal Efficiency, % 29.98 30.84 31.7 32.57 GT Specific Power, kW/Kg/sec

15004 15436 15864 16299

Heat Rate for Incremental Power kJ/kWh

- 8,712 - 8,391

Fuel Savings for Incremental Power, %

- 27 - 26

Two Gas Turbines with /Without Fogging

Effect of Altitude

At 1000 meter elevation the gas turbine output is 15 % lower than at sea level

TYPICAL

Effect of Humidity

4 inches H2O inlet drop produces :

• 1.50 % power output loss• 0.50 % heat rate increase• 1.2 °F exhaust temp. Increase

4 inches h2o exhaust drop produces :

• 0.50 % power output loss• 0.50 % heat rate increase• 1.2 °F exhaust temp. Increase

INDICATIVE FIGURES

015

TYPICAL

Effect of Inlet Pressure Drop

TYPICAL

016

Effect of Steam Injection

TYPICAL

Effect of Evaporative Cooling

TYPICAL

018


Self contained power package Units

Provided under supplier under single contract

Stanadardised product line/assembly line

Quick & easy installations

Low capital cost & fast installation

Higher operating costs in Open cycle but high overall efficiency in Combined cycle

Good cycling capability

Lower pollutant emission

Lower pollutant emissionLower installed costMore compact siteClean fuel sourceNo ash disposalNo coal handling costLower O&M costLower manpowerPhase wise construction


Why not have Gas Turbine

everywhere?


Map of

GAIL's

Pipelin

es in

India

HBJ pipe line covers Gujarat, Madhya Pradesh, Rajasthan, Uttar Pradesh, Haryana and Delhi, traversing a total of 2,688 km.

Higher fuel cost

Uncertain long term fuel supply

Output more dependant on Temperature


Gas Turbine Fuels

DISADVANTAGES OF LIQUID FUEL

COMMERCIAL REASON:

Liquid fuels are costlier than gaseous fuels.

Gas Turbine Fuels NCV, Kcal / kg

Price Rs / kg

Heating value/ Price kcal / Rs

Natural Gas 9885 21.70 455.5 HSD 10300 30.2 341.0 Naptha 10500 35.92 292.3 Kerosene 10215 30.94 330.2 Heavy distillate 9832 24.91 394.1 Residual oil 9760 24.91 391.8


• CUMBERSOME ARRANGEMENT: Liquid fuels requires extra arrangement for

transportation.• OPERATIONAL PERSPECTIVE

Requires running of more auxiliaries.Reduced capacity in Open cycle and comb cycleReduced Efficiency.Increased safety risksMore Manpower.


• MAINTENANCE FREQUENCY: More inspection of Hot gas path components.

More equipments to maintain. This translates to costly outages, costly replacements and costlier unscheduled outage hours.

• ENVIRONMENT PERSPECTIVE

More NOxOil spill etc.

MERITS OF LIQUID FUEL

• INCREASED AVAILABILITY

# When Fuel gas is in shortage# Where Power is required, no gas is available.# Increasing power demand Vs availability of Gas

1. M/c doesn’t remain ideal in case of short term gas unavailability and continues ROI.

2. Generating capacity can be enhanced within short time with liquid fuels.

UNDESIRABLE QUALITIES OF LIQUID FUEL ARE BECAUSE OF

INHERENT DEFICIENCY

• Liquid state• High viscosity• Tendency to polymerize• Incompatibility with other

fuel oils• High carbon content

leading to carbon deposits.

CONTAMINATIONS

• Corrosion of hot gas path components due to Vanadium compounds

• Corrosive sulfates with sulfur and alkali metals

• Built up of ash on nozzle blades

Tackling Inherent Deficiencies

• Increased safety precaution

• Heating of Fuel oil pipe lines, storage tank with steam tracing

TACKLING CONTAMINATIONS

• Clean Fuel• Treatment Of Fuels• Additives• Turbine Washing

Major Components Starting system Inlet Air System Compressor Combustion system

Silo typeMultiple CanularAnnular

Turbine Exhaust system Generator Bypass Stack system Waste Heat recovery System

Starting System

1. SFC : Starting Frequency Converter

2. External Motor Driven

Typical power requirement : 2 MW for 150 MW Gas Turbine

Air Intake Filter Housing

Typical Installation

Different Types of Filters

Typical Installation

Inlet SystemIt consists of following parts

1. Filter compartment.

2. Duct.

3. Silencer.

4. Lined elbow.

5. Transition piece.

6. Inlet plenum.

7. Expansion joints.

Filter Cleaning

Erosion Corrosion

Fouling Plugging

Filtration Media

•No of air filters 1144 [ 4 * 132 + 4 * 154 ]•No of solenoid valves 176•Surface area of each cartridge 25 m2

•Filtration efficiency 99. 8 % [3μ], 99 % [1 μ]

•Filter diff pressure Fresh ones 3.5 mbarStart of pulse 7.5 mbarStoppage 5.5 mbarAlarm 30 mbarCollapse 250 mbar

•Duration pulse air flow: 0.1 sec•Interval between two pulses 3.1 sec

Typical Values- Dadri Air filters

• It ingests a huge amount of air - particulate matter, hydrocarbons aerosols and other organic compounds and gases of industrial production eg nitrogen, chlorine and sulphur.

• The fine particulate matter & other compounds are deposited on the compressor blades.

• This alters the aerodynamic profile of the blades and leads to a fall in compressor efficiency (because of thickening of boundary layer air stream)

Why Compressor Cleaning ?

• Thicker boundary layer results in Reduced mass flow through the CompressorReduced compression pressure gain and

therefore lesser pressure ratio.

• Compressor fouling reduces the compressor isentropic efficiency, resulting in more power for compressing the same amount of air

Why Compressor Cleaning ?

Washing restores engine efficiency that would otherwise be lost by fouling.

Effect of Filter Cleaning on GT Output


The compressor blade before cleaning

The compressor blade after cleaning


• The liquid follows the air stream into the compressor, where the mechanical movements and chemical act of the washing liquid releases the deposits.

• Washing can be done off-line and on-line• Off-line washing:

Low air velocities allows washing liquid to move around in the compressor and slowly find its way towards the exhaust end.

The washing result is usually very good (~100 %).

How Compressor Cleaning is Done?

• Washing can be done off-line and on-line• On-line washing:

Centrifugal forces pushes the liquid out to the periphery where it can do no cleaning job.

High air velocity results in a short retention time for the liquid through the compressor.

Strong Air turbulence results in liquid being lost to the duct walls before entering the compressor

Compression results in a temperature increase inside the compressor, and liquid may start to boil off about halfway through the compressor.

Often causes erosion damage to compressor blades


• Washing can be done off-line and on-line

• On-line washing: Way around is to wash with droplets having a

smaller diameter with help of high pressure atomisation (70 bar)

Droplet volume is a function of radius cubed, i.e. a droplet of half the size has only one eighth of the volume and thereby only one eighth of the mass and impact force.

The liquid penetrates into the core air stream and relatively little liquid is lost to the walls.


• Washing can be done off-line and on-line• On-line washing:

Spray droplets will have almost the same velocity as the air entering the compressor and are therefore more likely to penetrate deep into the compressor. This is known as a high droplet-to-air velocity ratio.

The high-pressure system, also referred to as a 'direct injection system', results in fewer nozzles to install as the liquid capacity per nozzle is higher compared to a low-pressure system. This also reduces installation and maintenance costs.


http://www.jxj.com/magsandj/cospp/2004_01/turbine_efficiency.html

Nozzle Spaying Washing Liquid

Nozzles around the Compressor Inlet(Blue Hose)

Compressor Wash Pump Skid

•Mixing Tank•Control system•High pressure pump•Pnuematic 12” tyres

Claims of a Typical Compressor Washing Liquid Producer

30

32

34

36

38

40

Eff

icie

ncy

(%

)

competi

tor

competi

tor

competi

tor

compwas

h

Eff iciency Comparison Between Before and After

Cleaning

Before Cleaning

After Cleaning

150

160

170

180

190

200

210

MW

Out

put

MW Comparison Between Before and After Cleaning

Before Cleaning

After Cleaning

Design



10000

10200

10400

10600

10800

11000

11200

Hea

t R

ate

(KJ/

KW

H)

compe

titor

compe

titor

compe

titor

compw

ash

Heat Rate Comparison Between Before and After Cleaning

Before Cleaning

After Cleaning

Design


10

11

12

13

14

15

Co

mp

ress

or

Ra

tio

competi

tor

competi

tor

competi

tor

compwas

h

Compressor Ratio Comparison Between

Before and After Cleaning

Before Cleaning

After Cleaning

Low-pressure system-offline & on-line washing

typically up to 9 bar atomizing pressure

many nozzles required (low capacity per nozzle

small nozzle orifice may result in clogging

risk for liquid streaking (low liquid exit velocity from nozzle)

separate set of nozzles for on-line and off-line

small risk for nozzle wear

low pump power


High-pressure system -

typically 70 bar atomizing pressure

low installation and maintenance cost (few nozzles to install)

less liquid is used

good on-line liquid penetration (high liquid-to-air velocity ratio)

small risk of erosion damage (less than 100 micron droplet size)

easily retrofittable

same nozzles for off-line and on-line


Combustion -Aims

• CO, UHC, and NOx emission reduction.

• Attaining high inlet temperature

• Flame Stabilization and Combustion Efficiency

• Reducing Pressure losses in CC.

• All above lead to lean premix combustion, reduced resident time, and increased turbulence.

• Annular or Canannular combustors are more suitable than Silo type combustion chambers.

Typical Gas Turbine Installations

Typical section of Combustion Chamber

Typical Silo type combustion chamber

Silo type combustion chamber with Primary and Secondary air

•Primary air: 30 %•Secondary Air:65 %•Blade cooling: 5 %

24 Burners in a Hybrid-Burner-Ring (HBR) Combustor

GAS TURBINE – A SIMPLIFIED SCHEMATIC DIAGRAM

Multiple Canular Combustion System

Siemens 501G Turbine

COMBUSTION -AIMS

• GAS TURBINE COMBUSTION OBJECTIVES - CO, UHC, and NOx emission reduction - Attaining high inlet temperature - Flame Stabilization - High Combustion Efficiency - Minimum Pressure Loss• ABOVE OBJECTIVES ARE ATTAINED BY - Lean premix combustion - Reduced resident time, and - Increased turbulence.• Annular or Canannular combustors are more

suitable for achieving above as compared to Silo type combustion chambers.

Gas Turbine Exhaust Emissions

NOx and SOx Emission Limits

Advances In Combustion

• Dry Low NOx (DLN) Combustion• Lean Premix Prevaporizing (LPP)

Combustion• Rich Burn, Quick Quench, Lean Burn

Combustor (RQL)• Catalytic Combustion

Dry Low NOx Combustion

• Diffusion Combustion - Fuel injection and Air flow separate, burning of heterogeneous mixture.

• A mixture of equivalence ratio less than 0.8 keeps the temperature lower than 1650 oC. Combustion is conducted in multiple locations with precise sequencing and metering of both fuel and air to specific points along the combustion path.

• NOx level achieved is less than 25 ppm (09 ppm also achieved).

Auxiliary Systems

Lub oil system

Hydraulic Oil system

Turbine Cooling air system

Fuel system

NOx Control system

Fire protection system

Compressor wash system

Post Combustion Pollution Control

• SCR: NOx is converted into nitrogen and 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.

Principle of DeNOx thru’ SCR

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.

H-Technology

• The Next generation technology

• Firing temperature raised to 2650 deg F

• Novel features

• Steam Cooling

• CCP efficiency barrier of 60% crossed

• Single shaft CCP configuration 480MW

• Reheat Combined Cycles

• 10% reduction in operating costs

Biggest Gas Turbine – SGT5-8000HGas Turbine: 340 MWWeight 444 tSteam Turbine: 190 MWManufacture: SiemensηGT 39 %ηcc 60 %Fuel N GasAir flow 800 kg/sBlade Air cooled, Ni alloy

Ceramic coatedSingle crystal, approx 15 kg

Exhaust temp 6000C

Country BavariaOperating date: Dec 27, 2007

Typical GE Configuration




M701G2 at TEPCOs Kawasaki Power Plant, Japan GT 334 MW, 21:1 Pr ratio, 14 stage compressorTIT 15000C, Exhaust 5880C1 GT+ 1ST 498 MW ηGT LCV 39.5% ηST LCV 59.3%

MHI Machine

Steam cooled comb liners, stage 1 & 2 stationary blades,Single crystal blades

Alstom Range

Overiew of Comb Cycle Rev 7.0_Part 1

Documents

lean premix

reduced resident

tit of1600

irreversible

gas path temp

nox emission

air velocity

combined cycle