Technical Solutions for Emissions Reduction

Genera 2015

Technical Solutions for Emissions Reduction

Juan Nogales GE Power & Water Madrid, February 24, 2015

© 2015 General Electric Company. All rights reserved.

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

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Flame Types

Combustion Principles

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

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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

f Flame

Temperature

ø = 1

Lean Blow Out

Rich Blow Out Diffusion

Lean Premixed

Diffusion Flame Temp. Range

Premixed Flame Temp. Range

Combustion Principles

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

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

NO

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 NOx

Flame Temperature

Rich Lean

ø = 1

Lean Blow Out

Rich Blow Out

Standard Combustor

DLN Comb Diffusion

Lean Premixed

Diffusion NOx

Lean Premixed Standard

Combustor

Premixer example

•Fuel is injected into airstream

•Turning vanes swirl air to increase turbulence.

DLN1 Combustor

Combustion Principles

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

Diffusion NOx

Lean Premixed

Fuel

Air

Comparison of Diffusion & DLN

Temperature

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

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

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











Examples







Flame Types

Combustion Principles

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

f Flame

Temperature

ø = 1

Lean Blow Out

Rich Blow Out Diffusion

Lean Premixed

Diffusion Flame Temp. Range

Premixed Flame Temp. Range

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 (NO_x) usually refers to NO and NO₂. Since NO in contact with O₂ is quickly converted into NO₂, NO_x measurements mainly consider NO₂ only.

NO_X Gas Characteristics

NO: odorless and colorless gas.

NO₂: red-brown gas with strong odor, highly toxic and corrosive.

NO_x production is caused by 3 main mechanism:

1. Thermal NO 2. Prompt NO 3. Fuel bound NO

Combustion Principles

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 NO_x 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

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

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

Temperature, 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

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.

Typical emission trend for conventional gas turbine

combustor

Combustion Principles

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

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

Droplet size

Combustion Principles

Pollutants: summary

Modern combustors show many characteristics in order to reduce pollutant emissions and match nowadays restrictions.

NO

•air injection

•steam/water injection

•premixed burner

CO

•catalytic reduction

UHC & VOC

SO

Smoke

&Particulate

•combustor design

•fuel composition

•liquid fuel atomization

Combustion Principles

NO_x 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