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 Report
US 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
1 Quadrillion BTU = 45M Tons Coal or 1T ft3 Natural Gas or 170M Barrels of crude oil
1 Barrel crude oil = 42 gallon = 6.1 GJ of energy
World’s energy requirement can largely be classified into Electric power, transportation energy
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Trend of world’s electricity consumption (Data from US Department of Energy)
*Organization of economic cooperation and development
Major sources of electricity production
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…
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There is a very well established energy infrastructure based
on fossil fuels in US and across the globe.
The world’s proven fossil fuel reserves and lifetimes
Fuel
Coal
Oil
Gas
Lifetime (y) Lifetime (y)
Reserves (Q) No Growth w/ Growth
24,000
258
140
9280
60
50
6966
90
50
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?
“Strictly speaking, energy is not “consumed”, but rather is converted into different forms.”
Various types of engines are used to achieve this objective.
Types of engines
- Power generation: Gas Turbines, Steam Turbines, Nuclear, Hydro
-Transportation : diesel, gasoline, aircraft engines (based on gas turbine
cycles)
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 primemovers 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 15.3 MW
Thermal Eff. 35.7%
Output 7.7 MW
Thermal Eff. 34.8%
Output 4.6 MW
Thermal Eff. 39.5%
Output 11.2 MW
Thermal Eff. 33.9%
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Latest addition…
Output 22.3 MW
Thermal Eff. 40%
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Power Generation
Single Shaft
Turbine Engine
Output
Shaft Power
3)Expansion
(Turbine)
2) Combustion
1) Compression
Output
Shaft Power
Two Shaft
Turbine Engine
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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Power generation for gas fields in Siberia
Petrobras, offshore Brazil, Power
generation and crude oil production
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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Difference between Heavy Duty and Aeroderivative Turbines
Overhaul Life
Hot section inspection
Overhaul Life
Engine weight
Fast start capability
Tolerance to poor fuel
Ease of automation
Suitable for off-shore
Power
Thermal Efficiency
Industrial
48,000 hours
8000 hours
On-site
Heavy Duty
No
Fair
Good
Fair
Up to 325 MW
25-39%
Aero-derivatives
30,000 hours
6000 hours
Gas generator removal
Light
Yes
Poor
Good
Good
Up to 55 MW
25-42%
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Evolution of products : Uprates
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Performance of Gas Turbines is limited by
1. Component efficiencies
2. Turbine working temperature
Current state of the art
Pr = 35/1
components = 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 settings
These make GT less suitable for road transport and helicopters
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Some Basics
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Gas Turbine components
Inlet 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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mFqRcomb
minCpTin
Gas Turbine
(min+mF)CpTout
Shaft power 
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Consider Centaur and Mercury
Known
P ratio = 10
TIT = 1350 K
Compressor Eff. = 0.86
Turbine Eff. = 0.89
Heat exchanger effectiveness = 0.8
Ambient temperature and pressure, 300 K, 1 bar
Specific heat Cp = 1.005 kJ/Kg-K
Specific 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:
Q  h2  h1  

Stagnation enthalpy
V2
h0  h 
2
Compressor work
h2  h1  c p (T2  T1 )
Turbine work
h3  h4  c p (T3  T4 )
Heat input
For isentropic process

1 2
V2  V12  W
2
h3  h2  c p (T3  T2 )
T2  P2 
  
T1  P1 
  1 


  
 r 
  1 


  

T3
T4
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Thermal Efficiency

net work output cp (T3  T4 )  cp (T2  T1 )

energy input
cp (T3  T2 )
1
 1  
r
Net work out
  1 


  
Wnet  c p T3  T4   c p (T2  T1 )
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Equipment efficiencies
3
T02'  T01
C 
T02  T01
  1 





T01   P02    

T02  T01 
 1
 
 C   P01 



T03  T04
T 
T03  T04'
T
4
2’
4’
2
1
S
Process 1-2’ and 3-4’ ideal
Process 1-2 and 3-4 actual
  1 



  1     

T03  T04  T T03 1  

P
/
P
  03 04 



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Recuperator
3
Heat exchanger effectiveness
T05  T02

T04  T02
T
5
2’
4
4’
2
6
1
S

net work output cp (T3  T4 )  cp (T2  T1 )

energy input
cp (T3  T5 )
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Variation of Cp with temperature
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