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)

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

© 2015 General Electric Company. All rights reserved. Subject to the restrictions on cover page

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 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



Fuel Nozzle

Liner

Cross Fire Tubes

Spark Plug

Casing

Cover

Main Components

Can System Design


Aeroderivative combustors Single-Annular Combustor (SAC) Dry-Low-Emissions (DLE) Combustor


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



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


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


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


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


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


Genera 2015

Technical Back up slides

Juan Nogales

GE Power & Water


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


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


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



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



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



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



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.



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



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



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



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



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



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



Documents

Combustion Principles