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Gas Turbine Combustion Systems

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About me

• 2007-Present Solar Turbines Inc., Caterpillar Company

• 2002-2007 Ph.D. Combustion Science, MAE, UCSD

• 2000-2002 General Electric Global Research Center

• 1998-2000 M.S., Aerospace Engineering, Indian Institute of Technology & University of Stuttgart

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• Motivation to study about Industrial Gas Turbines

• What does combustor do?

• Types of combustors

• Design requirements

• Introduction to combustion chemistry

• Alternative fuels, pollutants, oscillations

• Challenges related with variable load conditions

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Energy Outlook ReportUS DOE

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Trend of world’s energy consumption (Data from US Department of Energy)

1 Quadrillion = 1015, 1 BTU = 1.055x103 J

World’s energy requirement can largely be classified into Electric power, transportation energy

1 Quadrillion BTU = 45M Tons Coal or 1T ft3 Natural Gas or 170M Barrels of crude oil1 Barrel crude oil = 42 gallon = 6.1 GJ of energy

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*Organization of economic cooperation and development

Trend of world’s electricity consumption (Data from US Department of Energy)

Fossil fuels: Coal, gasoline, diesel, natural gas and other petroleum products

Alternative sources of energy: Wind turbines, solar panels, hydroelectric, nuclear, geothermal, tidal, and list goes on…Alternative fuels: Ethanol, bio-diesel, biomass, coke oven gas, syngas, municipal waste, landfill gases, anything rotting…

Major sources of electricity production

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There is a very well established energy infrastructure based on fossil fuels in US and across the globe.

Fuel Reserves (Q)Lifetime (y) No Growth

Lifetime (y) w/ Growth

Coal 24,000 258 140Oil 9280 60 50Gas 6966 90 50

The world’s proven fossil fuel reserves and lifetimes

The advantage of alternative fuels is that the existing infrastructure can be used.

Gas turbines industry is going to stay in business for a long time

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About Solar’s Gas Turbines

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How does this story relate with Gas Turbines Combustion systems?

Types of engines- Power generation: Gas Turbines, Steam Turbines, Nuclear, Hydro-Transportation : diesel, gasoline, aircraft engines (based on gas turbine cycles)

“Strictly speaking, energy is not “consumed”, but rather is converted into different forms.”

Various types of engines are used to achieve this objective.

Steam turbines are similar to gas turbines but they have different principles of operation. Nuclear power plants use nuclear energy to make steam which rotates the steam turbines.

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Gas Turbines find their applications in

- electric power generation, mechanical drive systems, supply of process heat and compressed air, pump drives for gas or liquid pipelines

- jet propulsion, land and sea transport (infancy state)

Industrial turbines or prime movers

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• Solar Turbines Incorporated, a subsidiary of Caterpillar Company is a world leading producer of mid-range (1 MW – 25 MW) industrial gas turbines for use in power generation, natural gas compression, and pumping systems.

• There are 12,500+ engines installed in 102 countries

• Solar ranks as one of the 50 largest exporters in the United States

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Our units are used for power generation, gas compression, and mechanical drive applications

-Power generation is the production of electrical energy whether for stand-by or base load power applications.

- Gas compression applications include gathering (at the well head), transmission (pipeline), re-injection (storage), and pressure boost (compression).

- Mechanical drive applications are units sold as prime-movers for non-Solar packaged driven equipment, whether generators, compressors, or pumps

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Harbor Drive Facility

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Gas Turbines OEMs

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Output 1.2 MW Thermal Eff. 24.5%

Output 4.6 MW Thermal Eff. 29.9%

Output 7.7 MW Thermal Eff. 34.8%

Output 11.2 MW Thermal Eff. 33.9%

Output 15.3 MW Thermal Eff. 35.7%

Output 4.6 MW Thermal Eff. 39.5%

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Latest addition…

Output 22.3 MW Thermal Eff. 40%

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1) Compression

2) Combustion

3)Expansion (Turbine)

Output Shaft Power

Output Shaft Power

Two ShaftTurbine Engine

Single ShaftSingle ShaftTurbine EngineTurbine Engine

Power Generation

Mechanical Drive

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Simplistic Gas Turbines working principles

1-2 Isentropic compression (in a compressor)2-3 Constant pressure heat addition (in a combustor)3-4 Isentropic expansion (in a turbine)4-1 Constant pressure heat rejection

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Petrobras, offshore Brazil, Power generation and crude oil production

Power generation for gas fields in Siberia

Natural gas transmission, Desert environment

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Solar’s presence in San Diego- two, soon to be three, Titan 130's at UCSD- two Taurus 60's at SDSU- some recuperated Saturns at landfills in San Marcos and Santee - a Saturn genset at the Hotel Del- a Mercury 50 at the VA hospital- two Mercurys at Qualcomm- two Centaur 40s at the Balboa Naval Hospital- a Taurus 60 at the Children's Hospital

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List of companies and their products

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Industrial Aero-derivativesOverhaul Life 48,000 hours 30,000 hoursHot section inspection 8000 hours 6000 hoursOverhaul Life On-site Gas generator removalEngine weight Heavy Duty LightFast start capability No YesTolerance to poor fuel Fair PoorEase of automation Good GoodSuitable for off-shore Fair GoodPower Up to 325 MW Up to 55 MWThermal Efficiency 25-39% 25-42%

Difference between Heavy Duty and Aeroderivative Turbines

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Evolution of products : Uprates

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Performance of Gas Turbines is limited by1. Component efficiencies2. Turbine working temperature

Current state of the artPr = 35/1components = 85-90%TIT = 1650 K

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What makes Gas Turbines attractive for Industrial prime movers?Advantages• Very high power-to-weight ratio, compared to reciprocating engines• Smaller than most reciprocating engines of the same power rating• Fewer moving parts than reciprocating engines• Low operating pressures• High operation speeds• Low lubricating oil cost and consumption• High reliability• Goes for 30-50K hours before first overhaul. Usually runs for 100K-300K hours (10+ years) life cycle

Disadvantages• Cost is much greater than for a similar-sized reciprocating engine since the material must be stronger and more heat resistant. Machining operations are more complex• Usually less efficient than reciprocating engines, especially at idle• Delayed response to changes in power settingsThese make GT less suitable for road transport and helicopters

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Some Basics

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Gas Turbine componentsInlet system Collects and directs air into the gas turbine. Often, an air cleaner and silencer are part of the inlet system. It is designated for a minimum pressure drop while maximizing clean airflow into the gas turbine.

Compressor Provides compression, and, thus, increases the air density for the combustion process. The higher the compression ratio, the higher the total gas turbine efficiency . Low compressor efficiencies result in high compressor discharge temperatures, therefore, lower gas turbine output power.

Combustor Adds heat energy to the airflow. The output power of the gas turbine is directly proportional to the combustor firing temperature; i.e., the combustor is designed to increase the air temperature up to the material limits of the gas turbine while maintaining a reasonable pressure drop.

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Gas Producer Turbine Expands the air and absorbs just enough energy from the flow to drive the compressor. The higher the gas producer discharge temperature and pressure, the more energy is available to drive the power turbine, therefore, creating shaft work.

Power Turbine Converts the remaining flow energy from the gas producer into useful shaft output work. The higher the temperature difference across the power turbine, the more shaft output power is available.

Exhaust System Directs exhaust flow away from the gas turbine inlet. Often a silencer is part of the exhaust system. Similar to the inlet system, the exhaust system is designed for minimum pressure losses.

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What drives Research and Development work in Gas Turbines?

• In 1950’s component efficiencies• In 1990’s emissions• In 21st century it is emissions and alternative fuels• Nature of application and location are always the factors

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Simplistic Gas Turbines working principles

1-2 Isentropic compression (in a compressor); h2-h1 = mCp(T2-T1)2-3 Constant pressure heat addition (in a combustor); h3-h2 = mCp(T3-T2)3-4 Isentropic expansion (in a turbine); h3-h4 = mCp(T3-T4)4-1 Constant pressure heat rejection

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Gas TurbineminCpTin(min+mF)CpTout

Shaft power

mFqRcomb

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Consider Centaur and Mercury

Known P ratio = 10TIT = 1350 KCompressor Eff. = 0.86Turbine Eff. = 0.89Heat exchanger effectiveness = 0.8Ambient temperature and pressure, 300 K, 1 barSpecific heat Cp = 1.005 kJ/Kg-KSpecific heat ratio = 1.4

Calculate (a) Compressor outlet temperature (b) Turbine out temperature (c) Compressor work (d) Turbine work (e) back work ratio (f) Efficiency for ideal, actual, and recuperator engine

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First Law: WVVhhQ 21

2212 2

1

2

2

0Vhh Stagnation enthalpy

Compressor work )( 1212 TTchh p

Turbine work )( 4343 TTchh p

Heat input )( 2323 TTchh p

For isentropic process 4

3

1

1

2

1

2

1

TT

rPP

TT

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Thermal Efficiency )()()(

inputenergy outputnet work

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1243

TTcTTcTTc

p

pp

1

11r

Net work out )( 1243 TTcTTcW ppnet

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1

2’2

3

44’

Equipment efficiencies

0102

01'

02

TTTT

C

1

1

01

02010102

PPT

TTC

1

0403030403 /

11PP

TTT T

'0403

0403

TTTT

T

T

S

Process 1-2’ and 3-4’ idealProcess 1-2 and 3-4 actual

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1

2’2

3

44’

T

S

Recuperator

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Heat exchanger effectiveness

0204

0205

TTTT

)()()(

inputenergy outputnet work

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1243

TTcTTcTTc

p

pp

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Variation of Cp with temperature