Combustion Principles

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)
Combustion Principles
Flame Types
DIFFUSION FLAME
PREMIXED FLAME
(Yellow & Sooty)
(Blue)
Fuel and air (reactants) are not mixed, fuel and air are
Fuel and air (reactants) are uniformly mixed
injected separately into the combustion environment.
to a molecular scale upstream of the flame.
Air and fuel diffuse together at the boundaries.
Flame occurs downstream of premixing.
Application
Examples




candle flame
torch
diesel engine
all types of
furnaces

standard
Application
Examples

spark ignition
engine

oxy-acetylene
welding torch

Dry Low NOx
combustor
combustors
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Combustion Principles
Diffusion vs. Premixed Flame
DIFFUSION
PREMIXED
 Very Robust and Stable Flame
 Very Narrow Operating Window
 Typically Operable Over a 1100°C (2000°F)
 Typically Operable Over a 110-165°C
Temp. Rise Range
(200-300°F) Temp. Rise Range
 High NOx Emissions Without Diluent
 Can Achieve Very Low NOx Emissions
 Low CO Emissions
Without Diluent
 Low CO Emissions Can Be Difficult
Flame
Temperature
Diffusion Flame
Temp. Range
Diffusion
Lean
Premixed
Premixed Flame
Temp. Range
Lean Blow
Out
Lean
ø=1
Fuel/Air ratio (f)
Rich Blow
Out
Rich
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Combustion Principles
Combustion Chambers
Primary Purpose
To Ensure Flame Stability Througout All Operating
Phases
ANNULAR CHAMBER
Axial development
Direct Flow
Low Aerodynamic
Jet Derivative
resistance
CAN SYSTEM CHAMBER
Radial developement
Reverse Flow
Easier Maintenance
Heavy Duty
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Can System Design
Main Components
Casing
Liner
Cover
Cross Fire Tubes
Spark Plug
Fuel Nozzle
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Aeroderivative combustors
Single-Annular Combustor (SAC)
Dry-Low-Emissions (DLE) Combusto
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Combustion Principles
NOx Reduction: premixing
Premixed combustors operate with lean mixture reducing the flame temperature down to the
lower flammability limit (Lean Blow Out).
Diffusion
Standard
Combustor
Diffusion
NOx
NOx
Flame
Temperature
Standard
Combustor
Premixer example
Lean
Premixed
ø
Lean Blow
Out
Lean
DLN Comb
=1
Rich Blow
Out
Fuel/Air ratio (f)
Rich
Lean Premixed
Flame Temperature
DLN1 Combustor
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•Fuel is injected into airstream
•Turning vanes swirl air to
increase turbulence.
Combustor Evolution: DLN
Diffusion
Standard Comb
Diffusion
Flame
Temperature
Lean
Premixed
ø
Lean Blow
Out
Lean
NOx
CO
=1
Rich Blow
Out
Rich
Fuel/Air
L
L
R
R
L
NOx
DLN Comb
Lean Premixed
CO
Flame Temperature
Standard Combustor
Regions of Rich and Lean
Reactions
R
Turbine Inlet
Fuel
Air
Fuel/Air
Premixer
Homogeneous
Lean Premixed
Flame
Dry Low NOx
Lean Premixed Combustor
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Comparison of Diffusion & DLN
Fuel/Air
Premixers
Temperature
Tflame
Lean Premixed
Flame
Homogeneous F/A
Low Tflame
Low NOx
Tflame
Dilution Air
Diffusion Flame
High Tflame
High NOx
Seal leakage
Tfire
Tcd
Seal leakage
CO Burnout
Tfire
Tcd
Premixer Example
Fuel injected into airstream
Turning vanes swirl air
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Fuel and air mix before
Entering flame zone
Technological Summary
Standard combustors (Diffusion)
DLE/DLN Combustors (Premix)
-water/steam:
mg/Nm3
-1.0/1.5/2.X:
NOx ~50
CO  ~ 30
mg/Nm3
Nox  50-10 mg/Nm3
CO  30
mg/Nm3
-DLE Commercial op.: 1995 /
operating hours: ~15 MM
+5% heat rate increase vs dry,
lower exhaust temp.
-DLN Commercial op.: 1991 /
operating hours: ~150 MM
-Combustor/HS wear/thermal stress
-Water source ~0.25 tons/hr/MWe
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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:
Primary Mode
Transfer Mode
Diffusion Flame
100% Secondary Fuel
50% Load
Diffusion Flame
100% Primary Fuel
Ignition - 19% Load
Diffusion
Diff /Premix
Lean-Lean Mode
Premixed Mode
Diffusion Flame
~60% Primary / 40% Secondary Fuel
19% - 50% Load
Premixed Flame / Diffusion Pilot
81% Primary / 19% Secondary Fuel
50% - 100% Load
F/A
Mixing
Diffusion
Diffusion/Premix
Premix
Primary Zone Dual Purpose: 1. Low Load Diffusion Flame 2. High Load Premixing Chamber
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Typical DLE Burner Modes
Starting configuration
B reaction zone (30 cups)
Idle - 5% load
BC/2 reaction zone (39)
5 - 25% load
BC reaction zone (45)
25 - 35% load
BC + 2A reaction zone
(57 – LM6000 only)
35 - 50% load
AB reaction zone (60)
50% to full load
ABC reaction zone (75)
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Combustion Principles
Flame Types
PREMIXED FLAME
DIFFUSION FLAME
(Blue)
(Yellow & Sooty)
Fuel and air (reactants) are uniformly mixed
Fuel and air (reactants) are not mixed, fuel and air are
to a molecular scale upstream of the flame.
injected separately into the combustion environment.
Flame occurs downstream of premixing.
Air and fuel diffuse together at the boundaries.
Application
Application
Examples

spark ignition
engine

oxy-acetylene
welding torch

Examples




Dry Low NOx
combustor
candle flame
torch
diesel engine
all types of
furnaces

standard
combustors
© 2015 General Electric Company. All rights reserved. Subject to the restrictions on cover page
Combustion Principles
Diffusion vs. Premixed Flame
DIFFUSION
PREMIXED
 Very Robust and Stable Flame
 Very Narrow Operating Window
 Typically Operable Over a 1100°C (2000°F)
 Typically Operable Over a 110-165°C
Temp. Rise Range
(200-300°F) Temp. Rise Range
 High NOx Emissions Without Diluent
 Can Achieve Very Low NOx Emissions
 Low CO Emissions
Without Diluent
 Low CO Emissions Can Be Difficult
Flame
Temperature
Diffusion Flame
Temp. Range
Diffusion
Lean
Premixed
Premixed Flame
Temp. Range
Lean Blow
Out
Lean
ø=1
Fuel/Air ratio (f)
Rich Blow
Out
Rich
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Combustion Principles
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
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Combustion Principles
Pollutants: Nitrogen Oxides
The major part of NO produced during combustion processes belongs to the Thermal NO,
produced by the Zeldovich mechanism.
Thermal NO increases exponentially with the flame
temperature and proportionally to the residence time.
Temperature, K
Temperature, K
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.
NOx production rate
f=1
Equivalence ratio
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Combustion Principles
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.
2.
3.
Inadequate burning rates due to too low
f/a ratio and/or insufficient residence time.
Inadequate mixing of fuel and air, which
produce local rich regions that generate
high local concentrations of CO.
Quenching of post flame products by
entrainment with liner cooling air.
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Combustion Principles
Pollutants: Carbon Monoxides
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.
T,degrees K
3000
Relative CO
Production Rate
2500
2000
Temperature, K
1.00E+00
Relative NOx
Production Rate
1.00E-01
1.00E-02
Solution to reduce CO include:
1.
reducing of cold spots in the
combustion
1500
NOx
1000
1.00E-04
(film
cooling, water injection).
1.00E-03
CO
chamber
2.
use of mixing devices to
reduce rich regions.
500
1.00E-05
0
1.00E-06
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1.60
1.80
3.
operation
burning rates.
2.00
Equivalence Ratio
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at
adequate
Combustion Principles
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.
Typical emission trend for
conventional gas turbine
combustor
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
similar
to that of CO.
Note: power is proportional to flame temperature
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is
Combustion Principles
Pollutants: Sulfure Dioxide
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.
Combustion reactions
Solutions
S8 + 8 O2 → 8 SO2
emission include:
2 H2S(g) + 3 O2(g) → 2 H2O(g) + 2 SO2(g)
•fuel desulfurization
to
reduce
•flue gas desulfurization
Typical desulfurization reaction
SO2 + 2 NaOH → Na2SO3 + H2O
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SO2
Combustion Principles
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
vaporized,
is
sprays
not
tend
preto
produce local zone of rich
combustion, and consequent
high production of smoke and
Droplet
size
particulate.
Solutions include sprays with
smaller droplet size in order to
Equivalence ratio
(f)
enhance
mixing.
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vaporization
and
Combustion Principles
Pollutants: summary
Modern combustors show many characteristics in order to reduce pollutant emissions and
match nowadays restrictions.
•air injection
NOx
•steam/water injection
CO
•combustor design
UHC & VOC
•combustor design
SOx
Smoke
&Particulate
•control fuel sulfur content
•premixed burner
•catalytic reduction
•combustor design
•fuel composition
•liquid fuel atomization
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Combustion Principles
Pollutants: summary
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
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