GAS TURBINES

P.MAHADEVAN

Objective

• Comprehend the thermodynamic processes occurring in a gas turbine

• Comprehend the basic components of gas turbines and their basic operation

• Comprehend the support systems associated with gas turbines

What is Gas Turbine?

• Energy converter• Chemical Energy to Mechanical EnergyFUNCTION

Prime Mover - Provide Power for movement / transportation

• Mechanical drive (Compressors, Pumps, Blowers)

• Electricity Generation (Generator)

What is Gas Turbine?

It’s an high technology engine It’ an high speed rotating machine (3.000-30.000 rpm) In industrial application may drive generators(GD =

Generator Drive) or pumps and compressors (MD = Mechanical Drive)

It’s used for mobile application as aircraft ships etc. Power range of gas turbine is between 100 kW and 350 MW It’s efficiency is between 25% and 40% High specific power (light and powerful machine) May use a large typology of fuels (gas and liquid types) It may operate continuously without stop also for one year

WHY GAS TURBINE ?

High efficiency Low emissions Low installed cost Low cost power generation Short lead time, modular Multi-fuel capabilities

HISTORICAL PERSPECTIVE

Man tried to develop some turbo machine right from BC days

Claude Burdin (1790-1873) was the first to use the word “turbine” derived from the Latin word “turbo” (spins)

Stolze developed the first gas turbine in 1872 First successful stationary gas turbine operation in 1940

HISTORICAL PERSPECTIVE (Contd)

150 BC - Hero - earliest example of jet propulsion 1500 AD - Leonardo da Vinci – sketch 1629 - Giovanni Branca - first practical application of a

steam turbine 1765 - Reciprocating Steam Engine invented by James Watt 1791 - John Barber - first patent for a turbine engine 1827 -1840 - Hydraulic Turbine 1872 - Stolze - first true gas turbine 1883 - Steam Turbine by De laval 1939 - Heinkel Aircraft Co. - credited for the first flight of a

gas turbine powered jet propelled aircraft 1959 - Gas turbines first used as emergency power

generation

Gas Turbines in Oil and Gas Applications

Principal GT Application Areas:Upstream a) Oil Field and Offshore Power Generation b) Gas Lift (Enhanced Oil Recovery -EOR) c) Water Injection f) Export Compression g) Gas Gathering h) Gas Plant and Gas Boost i) Gas Storage/Withdrawal

Gas Turbines in Oil and Gas Applications (Contd)

Midstream a) Pipeline Compression b) Oil Pipeline Pumping c) LNG Plant (refrigeration,

compression, power)

Gas Turbines in Oil and Gas Applications (Contd)

Downstream a) Refinery power (Steam and Power

Cogeneration) b) Refinery Integrated Gasification

Combined Cycle c) Methanol / Fischer-Tropsch /

Ethanol Fueled Plants

Brayton CycleOpen cycle, unheated engine 1-2: Adiabatic compression of air in compressor 2-3: Constant pressure burning (Combustion) in a combustor 3-4: Adiabatic Expansion through Turbine and Exhaust Nozzle (4-1: Atmospheric Pressure)

Basic Components

Basic Components

Basic Components Compressor

– Draws in air & compresses it Combustion Chamber

– Fuel pumped in and ignited to burn with compressed air

Turbine– Hot gases converted to work– Can drive compressor & external load

Basic Components Compressor

– Draws in air & compresses it Combustion Chamber

– Fuel pumped in and ignited to burn with compressed air

Turbine– Hot gases converted to work– Can drive compressor & external load

Basic Components Compressor

– Draws in air & compresses it Combustion Chamber

– Fuel pumped in and ignited to burn with compressed air

Turbine– Hot gases converted to work– Can drive compressor & external load

CompressorSupplies high pressure air for combustion processCompressor types–Radial/centrifugal flow compressor–Axial flow compressor

Compressor Types Radial/centrifugal flow

– Adv: simple design, good for low compression ratios (5:1)

– Disadv: Difficult to stage, less efficient

Axial flow – Good for high

compression ratios (20:1)

– Most commonly used

Axial Compressor Operation

COMPRESSOR

is the part of theengine where air iscompressed

Compressor Discharge:(1) 30% for primary air (combustion air)(2) 5% operation of gas turbine accessories:

-bleed air and seal air-gas turbine start and motor air-gas turbine anti-icing

(3) remaining air is used as secondary air to:- cool combustion gases- Provide film cooling of the gas generator turbine

Use of Compressed Air

Primary Air (30%)– Passes directly to combustor for combustion

process Secondary Air (65%)

– Passes through holes in perforated inner shell & mixes with combustion gases

Film Cooling Air (5%)– Insulates/cools turbine blades

COMPRESSED AIR

Combustion Chambers Where air & fuel are mixed, ignited, and burned Spark plugs used to ignite fuel Types

Tubular (Single Can)Preferred by European manufacturersSimple design, long life

Annular: for larger, axial compressors Popular in aircraft designs

Can-annular: for really large turbinesPreferred by American manufacturersMost common type, ease of maintenance

TUBULAR TYPES

SINGLE CAN COMBUSTOR

CAN ANNULAR COMBUSTOR

Combustor Types

Another Classification Standard Combustor Dry Low Nox (DLN)

Combustor

Combustion Chamber(s) Operation

is the part of the engine where air is mixed with fuel and burned

COMBUSTOR(s)

Typical Gas Turbine Combustor

Conventional GT Fuel Nozzle

Gas Fuel

Liquid FuelAtomizing Air

Primary Air

Primary Air

Dual Fuel Nozzle Assembly

Turbine Operation

TURBINE

The turbine extract kinetic energy from the expanding gases as the gases comefrom the burner, converting this energy into shaft power to drive the compressorand the engine accessory.Nearly three fourths of all energy available from the product of combustion isneeded to drive the compressors.The turbine is composed from a ring of stator vanes called NOZZLE and a ring ofrotor blades called BUCKETS

Turbines

Consists of one or more stages designed to develop rotational energy

Uses sets of nozzles & blades

Single Shaft Gas TurbinesSingle Shaft Gas Turbine

(with Shaft Coupling):Power Turbine and Gas Generator Turbine on Same ShaftFixed Speed Applications (Range: 90%-100% Full Speed)Mostly used for Electric Power Generation; i.e., Generator Drive via Gearbox (1500 rpm –50 Hz, 1800 rpm – 60 Hz)

SINGLE SHAFT GAS TURBINE

COMBUSTIBILE

AIR

LOAD

COMBUSTORS

EXHAUST GAS

4

3

2

1

TURBINE

AXIAL

COMPRESSOR

AUXILIARY GEARBOX

STARTING MOTOR

60 MW 120 MW 60 MW(50%) (100%) (50%)

1-2 AIR COMPRESSION2-3 COMBUSTION3-4 EXPANSION

LOAD = ELECTRIC GENERATOR (OFTEN) COMPRESSOR, PUMP(NOT COMMON)AUXILARY GEAR BOX= DRIVES OIL PUMPS AND TRANSMITSTORQUE FROM STARTING MOTOR

Single Shaft Gas Turbines

Two-Shaft Gas Turbines

Two-Shaft Gas Turbine (no Shaft Coupling):Power Turbine Independently Supported on its Own Shaft and BearingsVariable Speed Applications (Range 25%-100% Full Speed)Used for Compressor, Pump and Blower Applications

Gas Generator Power Turbine

Types of Couplings

Gear Couplings

Grid-type

Pin-type

Coupling Guards – Non sparking

GEARS

Power Transmission System–Reduction gears used to transfer torque–With split shaft, turbines can run @

different speedsLoad Gear

–Between driver GT and driven equipment

Accessory Gear–For pumps and / or starter

GAS TURBINE TYPES

Industrial Heavy-Duty Aero Derivative Medium Range Small

Industrial Heavy Duty Gas Turbines

Designed shortly after World War II and introduced to the market in early 1950s

Design Characteristics; Heavy wall horizontally split casing, sleeve bearings, large dia combustors, thick airfoil sections for blades and stators

Advantages: Long life, high availability, slightly higher overall efficiencies, Comparatively low noise level

Primarily used in Power plants. Ideal for base load operation

Aero Derivative Gas Turbines

An aircraft-derivative gas generator and a free-power turbine

The gas generator is an aircraft engine modified to burn industrial fuel

Mostly used by gas transmission companies and on gas reinjection platforms

Advantages: favourable installation cost, Adaptation to remote control

Medium Range Gas Turbines

Ratings between 5000-15000 hp Design similar to Heavy Duty GTs Mainly used on offshore platforms and

petrochemical plants

SIMPLE CYCLE

Gas Turbine exhaust gas heat is wasted to the atmosphere

COMBINED CYCLE

Use Gas Turbine Exhaust Heat to Generate Steam in HRSG Use Steam from HRSG to drive steam

turbine generator

COMBINED CYCLE

COMBINED CYCLE

COMBINED CYCLE

Gas Turbine Generator

Stack Bypass Stack

Boiler

Economizer

Supplementary Duct Firing

CLOSED CYCLE APPLICATION

FACTORS AFFECTING GT PERFORMANCE

PRIMARY FACTORS- ambient temperature - ambient pressure (site elevation)

SECONDARY FACTORS- humidity - inlet system pressure drop - exhaust system pressure drop - power losses in the driven equipment (gear, pipeline

compressor or electric generator)

EFFECT OF AIR INLET TEMPERATURE

EFFECT OF AIR INLET TEMPERATURE

EFFECT OF ELEVATION

EFFECT OF INLET LOSS

EFFECT OF EXHAUST LOSS

EFFECT OF INLET LOSS

-100 -75 -50 -25 0 25 50 75 100Change in Inlet Ducting Loss mmH2O

0.98

0.99

1.00

1.01

1.02

Par

amet

er/P

aram

eter

@ G

/Tee

Con

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n

Power Output

Heat Input

Exhaust Temperature

Datum conditions of:Engine inlet temperature 15 °CAmbient pressure 101.3 kPaRelative humidity 60 %Inlet duct loss 100 mmH2OExhaust duct loss 200 mmH2OBased on 'dry' operation in full base load region

EFFECT OF EXHAUST LOSS

-200 -150 -100 -50 0 50 100 150 200Change in Exhaust Ducting Loss mmH2O

0.98

0.99

1.00

1.01

1.02

Para

met

er/P

aram

eter

@ G

/Tee

Con

ditio

n

Power Output

Heat Input

Exhaust Temperature

Datum conditions of:Engine inlet temperature 15 °CAmbient pressure 101.3 kPaRelative humidity 60 %Inlet duct loss 100 mmH20Exhaust duct loss 200 mmH2OBased on 'dry' operation in full base load region

5/11/97 21/08/02

EFFECT OF INLET & EXHAUST LOSS

EFFECT OF ELEVATION

Effect of Relative humidity

-40 -30 -20 -10 0 10 20 30 40Change in Relative Humidity %

0.997

0.998

0.999

1.000

1.001

1.002

1.003

Par

amet

er/P

aram

eter

@ G

/Tee

Con

ditio

n

Exhaust Temperature

Power Output Datum conditions of:Engine inlet temperature 15 °CAmbient pressure 101.3 kPaRelative humidity 60 %Inlet Ducting Loss 100 mmH2OExhaust Ducting Loss 200 mmH2O

Heat Input

GAS TURBINE RATING

ISO RATINGPower rating at design speed and at sea level i.e. Ambient pressure is 14.7

psia (1.0 bar) with an ambient temperature of 59ºF (15ºC) and ambient relative humidity of 60% The ISO rating considers inlet and outlet losses to

be zero.

GAS TURBINE PACKAGE

Gas Turbine Package Components

Gas Turbine Package Components

INSIDE THE PACKAGE Fuel System

- Natural Gas- Liquid (pumped)

Lube Oil System - Supply bearings and gears with oil- Tank- Filter-Pumps (main, pre/post, backup)

Starter (pneumatic, hydraulic, AC motor, diesel engine) Controls (on-skid, off-skid) Seal Gas System (compressors)

Gas Turbine Package ComponentsOUTSIDE THE PACKAGE Enclosure

Fire ProtectionVentilation air inletVentilation exhaustVentilation Fans

Air Inlet System – combustion air Air-filter (self-cleaning, barrier,

inertial)Silencer

Exhaust SystemSilencerStack

Lube Oil Cooler (water, air) Motor Control Center Switchgear, Neutral Ground

Resistor Inlet Fogger/Cooler Fire Protection cabinet

FUEL SYSTEM

The purpose of the fuel system is to deliver fuel to the individual combustors of the turbine under the following conditions:At the required pressure and temperatureIn the right quantity to meet the load demandFree of contaminants, which may be harmful to the turbine

FUEL SYSTEM (Contd)

The fuel system may beGaseous fuelLiquid fuelDual fuel

FUEL SYSTEM (Contd)

The fuel system can be divided into:The combustion control system

located on base at the turbineThe fuel receiving, storage and

forwarding system

TYPICAL FUEL GAS SYSTEM

TYPICAL LIQUID FUEL STORAGE & FORWARDING SYSTEM

TYPICAL TURBINE LIQUID FUEL SYSTEM

DUAL FUEL SYSTEM

DUAL FUEL NOZZLE

TYPICAL ATOMIZING & PURGE AIIR SYSTEM

Wobbe Index

It is customary to give a Wobbe number without units–even though it has the dimensions Btu per scf–because to do so would lead to confusion with the volumetric heating value of the gas.

The usefulness of the Wobbe number is that for any given orifice, all gas mixtures that have the same Wobbe number will deliver the same amount of heat.

The Wobbe Index (WI) is the main indicator of the interchangeability of fuel gases

It is used to compare the combustion energy output of different composition fuel gases

Less than 5% deviation is desired

LUBRICATING & HYDRAULIC OIL SYSTEMS

The purpose of the lube oil system is to supply the lubricant to the bearings and gear box At the right pressure At the right temperature Clean and free from dirt, dust or material particles

The lube oil system works on a closed cycle

TYPICAL LUBE OIL SYSTEM

LUBE OIL SUMP

TURBINE GENERATOR

TYPICAL GTG LUBE OIL SYSTEM

TYPICAL CONTROL (TRIP) OIL SYSTEM

TYPICAL HYDRAULIC OIL SYSTEM

Starting System

Purpose– To get compressor initially rotated– Once at certain RPM, fuel injected and spark

ignited Types

– Electric motor– Diesel engine– Gas Expander/ pneumatic starter

STARTER ARRANGEMENT

Air Intake & Exhaust

Must minimize space and weight Must keep air inlet losses to a

minimum to ensure maximum performance Intake has screens/filters to ensure

clean, filtered air at all times

INLET AIR FILTER TYPES

Self Cleaning Filter

Air Intake Filter

Exhaust Exhaust generates thermal and

acoustic problems– Possible damage to personnel &

equipment Silencers and eductor nozzles used to

silence and cool exhaust Exhaust orientation – axial or

transverse

TYPICAL COOLING WATER SYSTEM

GT ENCLOSURE

TYPICAL GT ENCLOSURE

GT ENCLOSURE (Contd)

Requirements: Acoustic Weatherproof Fire protection Ventilation Lighting Doors

TYPICAL GT COMPARTMENT VENTILATION

FIRE PROTECTION

Fire DetectionTypes of Detectors Ultraviolet (UV) Infrared (IR) Rate Compensated ThermalFire SuppressionTypes of agents Halon CO2 – High Pressure or Low Pressure Inergen Water MistGas detection Infrared (IR) Electro catalytic

Typical CO2 Fire Protection System

TYPICAL CONTROL PANEL

HOT END DRIVE

GENERATORGEARBOX

Air Inlet

Compressor

Combustor

TurbineExhaust

BASE FRAME

MATERIALS OF CONSTRUCTION

Alloy steels for compressor & turbine Nickel or Cobalt based alloys for combustor Stainless Steel for Combustion Air Intake and

Lube Oil Systems.

HOT END DRIVE

COLD END DRIVE LAYOUT

TYPICAL TURBINE START UP CURVE

TYPICAL GT LOADING CURVE

ABNORMAL CONDITIONS THAT REQUIRE GAS TURBINE TRIP

– Over speed. – Low lube oil pressure. – High turbine exhaust temperature. – Excess vibration. – Flame failure in combustor. – Inlet air filter having high differential pressure.– Any initiation of fire protection around the unit.– Gas leak detection

Service life of Gas Turbine Components

Factors that may determine the service life of gas turbine components:

– starts and stops – load and temperature swings – running hours – whether components have protective coatings – material creep strength – endurance limit for fatigue strength evaluation – method of blade cooling – effect of steam injection– erosion wear noted during inspections

PERFORMANCE DEGRADATION

All turbomachinery experiences losses in performance with time.

RecoverableUsually associated with compressor fouling and can be partially rectified by water washing or by mechanically cleaning the compressor blades and vanes after opening the unit

Non-recoverable lossis due primarily to increased turbine and compressor clearances and changes in surface finish and airfoil contour

TYPICAL MAINTENANCE

INSPECTION TYPE

INTERVAL (EOH) DOWNTIME

COMBUSTION INSPECTION 16,000 7 DAYS

HOT GAS PATH INSPECTION

32,000 16 DAYS

MAJOR INSPECTION 64,000 25 DAYS

Turbine Performance Degradation Curves*

Turbine Performance Degradation Curves*

WATER WASH SYSTEM

On Line Wash Off line Wash With or Without detergent Water quality Fixed or mobile

EMISSIONS

EMISSIONS CONTROL – ON ENGINE

Temperature Effects on CO/NOx

AIRFLOW

60%

40%AIRFLOW

30%

70%

FUEL

FUEL

Conventional

Lean Pre-mixed

Same Turbine Inlet Temp.

Diffusion vs. Pre-Mixed

©Solar Turbines Incorporated

2900°F1870 K

4100°F2530 K

Catalytic Combustor

EMISSIONS CONTROL – OFF ENGINE

– Inlet Fogging & “Wet Compression”– Selective Catalytic Reduction (SCR)– Oxidation Catalysts for CO removal– SCONOx

Inlet Fogging & “Wet Compression”

SCONOx

SCR UNITS

GT APPLICATION CONSIDERATIONSOil & Gas Requirements:– Availability / Reliability– Ruggedness– High Power/Weight ratio– Efficiency not Critical

Industrial Power GenerationRequirements:– Cost of Electricity– Efficiency– Cost of O&M

INDUSTRY STANDARDS

STANDARD TITLEAPI 616 Gas Turbines for the Petroleum, Chemical, and Gas

Industry Services

ASME PTC 22 Performance Test Code on Gas Turbines

API 613 Special Purpose Gear Units for Petroleum, Chemical and Gas Industry Services

API 614 Lubrication, Shaft Sealing And Control Oil Systems For Special Purpose Applications

API 670 Non-contacting Vibration And Axial Position Monitoring System

API 671 Special-purpose Couplings For Refinery Services

FURTHER READINGBOOKS Gas Turbine Theory - HIH Saravanamuttoo, G. Rogers and H.

Cohen Sawyer’s Gas Turbine Engineering Handbook Gas Turbine Engineering Handbook – Meherwan P.Boye The Gas Turbine Handbook: Principles and Practices - Tony

GiampaoloJOURNALS Gas Turbine World Hydrocarbon Processing Power EngineeringINTERNET Vendor Websites

GAS TURBINE VENDORS

GE SOLAR ROLLS ROYCE SIEMENS MAN TURBO

GE GAS TURBINE RATINGS

SOLAR TURBINES

ROLLS-ROYCE