combustion principles
TRANSCRIPT
Genera 2015
Technical Solutions for Emissions Reduction
Juan Nogales
GE Power & Water
Madrid, February 24, 2015
© 2015 General Electric Company. All rights reserved.
This material may not be copied or distributed in whole or in part without prior permission of the copyright owner.
LM1600®, LM2500®, LM6000®, LMS100® and LM5000® are registered trademarks of the General Electric Company (USA)
DIFFUSION FLAME
(Yellow & Sooty)
Fuel and air (reactants) are not mixed, fuel and air are
injected separately into the combustion environment.
Air and fuel diffuse together at the boundaries.
Application
Examples
candle flame
torch
diesel engine
all types of
furnaces
standard
combustors
Flame Types
Combustion Principles
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PREMIXED FLAME
(Blue)
Fuel and air (reactants) are uniformly mixed
to a molecular scale upstream of the flame.
Flame occurs downstream of premixing.
Application
Examples
spark ignition
engine
oxy-acetylene
welding torch
Dry Low NOx
combustor
Diffusion vs. Premixed Flame
DIFFUSION Very Robust and Stable Flame
Typically Operable Over a 1100°C (2000°F)
Temp. Rise Range
High NOx Emissions Without Diluent
Low CO Emissions
PREMIXED Very Narrow Operating Window
Typically Operable Over a 110-165°C
(200-300°F) Temp. Rise Range
Can Achieve Very Low NOx Emissions
Without Diluent
Low CO Emissions Can Be Difficult
Fuel/Air ratio (f)
Flame
Temperature
Rich Lean
ø = 1 Lean Blow
Out
Rich Blow
Out
Diffusion
Lean
Premixed
Diffusion Flame
Temp. Range
Premixed Flame
Temp. Range
Combustion Principles
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Combustion Chambers
ANNULAR CHAMBER
CAN SYSTEM CHAMBER
Axial development
Low Aerodynamic
resistance
Radial developement
Reverse Flow
Easier Maintenance
Direct Flow
Heavy Duty
Primary Purpose
Jet Derivative
To Ensure Flame Stability Througout All Operating
Phases
Combustion Principles
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Fuel Nozzle
Liner
Cross Fire Tubes
Spark Plug
Casing
Cover
Main Components
Can System Design
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Aeroderivative combustors Single-Annular Combustor (SAC) Dry-Low-Emissions (DLE) Combustor
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NOx Reduction: premixing
Premixed combustors operate with lean mixture reducing the flame temperature down to the
lower flammability limit (Lean Blow Out).
Fuel/Air ratio (f) Flame Temperature
NO
x
Fla
me
Te
mp
era
ture
Rich Lean
ø = 1 Lean Blow
Out
Rich Blow
Out
Standard
Combustor
DLN Comb
Diffusion
Lean
Premixed
NOx Diffusion
Lean Premixed
Standard
Combustor
Premixer example •Fuel is injected into airstream
•Turning vanes swirl air to
increase turbulence.
DLN1 Combustor
Combustion Principles
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Combustor Evolution: DLN
Fuel/Air Flame Temperature
NOx
CO
Flame
Temperature
Rich Lean
ø = 1
R
R
R L L
L
Homogeneous
Lean Premixed
Flame
Standard Combustor
Regions of Rich and Lean
Reactions
Dry Low NOx
Lean Premixed Combustor Fuel/Air
Premixer
Lean Blow
Out
Rich Blow
Out
Turbine Inlet
Standard Comb
DLN Comb
Diffusion
Lean
Premixed
CO
NOx Diffusion
Lean Premixed
Fuel
Air
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Comparison of Diffusion & DLN Te
mp
era
ture
Tflame
Dilution Air
Seal leakage
Diffusion Flame
High Tflame
High NOx
Tfire
Tflame Seal leakage
Lean Premixed
Flame
Homogeneous F/A
Low Tflame
Low NOx
Tfire CO Burnout
Tcd Tcd
Premixer Example
Turning vanes swirl air
Fuel injected into airstream
Fuel and air mix before
Entering flame zone
Fuel/Air
Premixers
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Standard combustors (Diffusion) -water/steam: NOx ~50 mg/Nm3 CO ~ 30 mg/Nm3 +5% heat rate increase vs dry, lower exhaust temp. -Combustor/HS wear/thermal stress -Water source ~0.25 tons/hr/MWe
DLE/DLN Combustors (Premix) -1.0/1.5/2.X: Nox 50-10 mg/Nm3 CO 30 mg/Nm3 -DLE Commercial op.: 1995 / operating hours: ~15 MM -DLN Commercial op.: 1991 / operating hours: ~150 MM
Technological Summary
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DLE upgrades examples
LM2500 SAC (diffusion): NOx: 383 mg/Nm3 CO: 7 mg/Nm3
LM2500 DLE (Premix): NOx: 50 mg/Nm3 CO: 30 mg/Nm3
2011 - GT hardware upgrade - Fuel System upgrade - Control systems upgrade - Engineering package - Installation
- 12 months lead time (Order to
Delivery) - Outage time: 28 days, 7 days start
up
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DLN upgrades examples
Frame 6B (diffusion): NOx: 400 mg/Nm3 CO: 7 mg/Nm3
Frame 6B DLN (Premix): NOx: 50 mg/Nm3 CO: 30 mg/Nm3
2011 - GT hardware upgrade - Fuel System upgrade - Control systems upgrade - Engineering package - Installation
- 12 months lead time (Order to
Delivery) - Outage time: 49 days
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Genera 2015
Technical Back up slides
Juan Nogales
GE Power & Water
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DLN Fuel Staging DLN Operational Modes:
Transfer Mode Diffusion Flame
100% Secondary Fuel
50% Load
Premixed Mode Premixed Flame / Diffusion Pilot
81% Primary / 19% Secondary Fuel
50% - 100% Load
F/A
Mixing
Lean-Lean Mode Diffusion Flame
~60% Primary / 40% Secondary Fuel
19% - 50% Load
Primary Mode Diffusion Flame
100% Primary Fuel
Ignition - 19% Load
Diffusion
Diffusion
Diffusion/Premix
Diff /Premix
Premix
Primary Zone Dual Purpose: 1. Low Load Diffusion Flame 2. High Load Premixing Chamber
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Starting configuration
B reaction zone (30 cups)
25 - 35% load
BC + 2A reaction zone
(57 – LM6000 only)
5 - 25% load
BC reaction zone (45)
50% to full load
ABC reaction zone (75)
Idle - 5% load
BC/2 reaction zone (39)
35 - 50% load
AB reaction zone (60)
Typical DLE Burner Modes
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PREMIXED FLAME
(Blue)
Fuel and air (reactants) are uniformly mixed
to a molecular scale upstream of the flame.
Flame occurs downstream of premixing.
DIFFUSION FLAME
(Yellow & Sooty)
Fuel and air (reactants) are not mixed, fuel and air are
injected separately into the combustion environment.
Air and fuel diffuse together at the boundaries.
Application
Examples
candle flame
torch
diesel engine
all types of
furnaces
standard
combustors
Application
Examples
spark ignition
engine
oxy-acetylene
welding torch
Dry Low NOx
combustor
Flame Types
Combustion Principles
© 2015 General Electric Company. All rights reserved. Subject to the restrictions on cover page
Diffusion vs. Premixed Flame
DIFFUSION Very Robust and Stable Flame
Typically Operable Over a 1100°C (2000°F)
Temp. Rise Range
High NOx Emissions Without Diluent
Low CO Emissions
PREMIXED Very Narrow Operating Window
Typically Operable Over a 110-165°C
(200-300°F) Temp. Rise Range
Can Achieve Very Low NOx Emissions
Without Diluent
Low CO Emissions Can Be Difficult
Fuel/Air ratio (f)
Flame
Temperature
Rich Lean
ø = 1 Lean Blow
Out
Rich Blow
Out
Diffusion
Lean
Premixed
Diffusion Flame
Temp. Range
Premixed Flame
Temp. Range
Combustion Principles
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Pollutants: Nitrogen Oxides Nitrogen oxides are to be limited by laws because their polluting effects include: lungs
affecting and lower resistance to respiratory infections, greenhouse effect, photochemical
smog, acid rains, depletion of stratospheric ozone.
Nitrogen oxides (NOx) usually refers to NO and NO2. Since NO in contact with O2 is quickly
converted into NO2, NOx measurements mainly consider NO2 only.
NOX Gas Characteristics
NO: odorless and colorless gas.
NO2: red-brown gas with strong odor,
highly toxic and corrosive.
NOx production is caused by 3 main
mechanism:
1. Thermal NO
2. Prompt NO
3. Fuel bound NO
Combustion Principles
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The major part of NO produced during combustion processes belongs to the Thermal NO,
produced by the Zeldovich mechanism.
Temperature, K
Equivalence ratio
Temperature, K
NOx production rate
Thermal NO increases exponentially with the flame
temperature and proportionally to the residence time.
Solutions to reduce NOx content include:
1. premixed burner/combustor to assure lean
combustion -> lower temperature;
2. steam/water/air injection to cool down combustion
primary zone -> lower temperature;
3. short combustor -> lower residence time.
f=1
Pollutants: Nitrogen Oxides
Combustion Principles
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Pollutants: Carbon Monoxides Carbon monoxide (CO) gas is a by-product of combustion systems; cars and trucks are the
source of nearly two-thirds of this pollutant.
When inhaled, CO blocks the transport of oxygen to the brain, heart, and other vital organs in
the human body. Symptoms of mild poisoning include headaches and dizziness at
concentrations less than 100 ppm. In the United States, OSHA limits long-term workplace
exposure levels to 50 ppm. CO Gasses Characteristics
CO : odorless and colorless gas.
CO production is caused by 3 main mechanism:
1. Inadequate burning rates due to too low
f/a ratio and/or insufficient residence time.
2. Inadequate mixing of fuel and air, which
produce local rich regions that generate
high local concentrations of CO.
3. Quenching of post flame products by
entrainment with liner cooling air.
Combustion Principles
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CO main zones of production are located:
•at high f (rich mixture) where lack of oxygen leads to incomplete reaction from CO to CO2.
•at very low f (very lean mixture) combustion processes reaction rate is limited by low
temperature and consequent no development from CO to CO2.
•at stoichiometric condition the high temperature activates the equilibrium CO reactions.
CO NOx
0
500
1000
1500
2000
2500
3000
0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00
Equivalence Ratio
Tem
pe
ratu
re,
K
1.00E-06
1.00E-05
1.00E-04
1.00E-03
1.00E-02
1.00E-01
1.00E+00
CO NOx
T,degrees K
Relative NOx
Production Rate
Relative CO
Production Rate Solution to reduce CO include:
1. reducing of cold spots in the
combustion chamber (film
cooling, water injection).
2. use of mixing devices to
reduce rich regions.
3. operation at adequate
burning rates.
Pollutants: Carbon Monoxides
Combustion Principles
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Pollutants: UHC and VOC Un-burned HydroCarbons (UHCs) and Volatile Organic Compounds (VOCs) result from incomplete
combustion, then some fuel and fuel derived compounds are present into combustion products. UHCs are
toxic and react with NO to generate ozone (O3) which, at ground level, is a pollutant element, causing eyes
and respiratory issues and large ageing problems to plants.
VOCs effect on environment is highly dependent on the type of compound, the most known and dangerous
is benzene, which is carcinogenic.
UHCs production is normally associated
with:
1. poor atomization of fuel
2. inadequate burning rate
3. chilling effects of film cooling.
Then UHC production trend is
similar
to that of CO.
Note: power is proportional to flame temperature
Typical emission trend for
conventional gas turbine
combustor
Combustion Principles
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Sulfur dioxide (SO2) is caused mainly by the combustion of fuel containing sulfur
compounds, like diesel, sour gas, etc.
SO2 acts as an acid. Inhalation results in laboured breathing, coughing, and/or a sore throat
and may cause permanent pulmonary damage. When mixed with water and contacted by skin,
frostbite may occur. When it makes contact with eyes, redness and pain will occur. SO2 is also
responsible for acid rains.
Solutions to reduce SO2
emission include:
•fuel desulfurization
•flue gas desulfurization
Combustion reactions
S8 + 8 O2 → 8 SO2
2 H2S(g) + 3 O2(g) → 2 H2O(g) + 2 SO2(g)
Typical desulfurization reaction
SO2 + 2 NaOH → Na2SO3 + H2O
Pollutants: Sulfure Dioxide
Combustion Principles
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Pollutants: Smoke and Particulate
Smoke is a general term that refers to the black, impure carbon particles resulting from the
incomplete combustion of a hydrocarbon fuels.
Smoke is a product of incomplete combustion processes, it is primarily produced in region of
high fuel concentration (f > 1) and high temperature which promotes pyrolysis and growth
processes.
Most of the smoke produced in the flame zone is destroyed in downstream zones with high
oxygen unless some rich regions remain unmixed or are cooled prematurely. Liquid fuels
If liquid fuel is not pre-
vaporized, sprays tend to
produce local zone of rich
combustion, and consequent
high production of smoke and
particulate.
Solutions include sprays with
smaller droplet size in order to
enhance vaporization and
mixing. Equivalence ratio (f)
Droplet
size
Combustion Principles
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Pollutants: summary
Modern combustors show many characteristics in order to reduce pollutant emissions and
match nowadays restrictions.
NOx
•air injection
•steam/water injection
•premixed burner
CO •combustor design
•catalytic reduction
UHC & VOC •combustor design
SOx •control fuel sulfur content
Smoke &Particulate
•combustor design
•fuel composition
•liquid fuel atomization
Combustion Principles
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NOx and CO production trends versus equivalent ratio sets the operative window between
0.40 and 0.50-0.60. A control of the effective flame fuel/air ratio can be obtained by use of
premixed flame, where air/fuel proportion are set upstream combustion zone.
Object of premixing is to maximize the
amount of fuel burned at lean
equivalence ratios where NOx is low, but
flame is not cold enough to “freeze” the
CO to CO2 reaction
Pollutants: summary
Combustion Principles
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