impact of fuel composition on efficiency and emissions … · impact of fuel composition on...

Impact of Fuel Composition on Efficiency andEmissions of Prime Movers

Presented by: Don Ferguson, Ph.D.

Gas / Electric Partnership Workshop

February 8 - 9, 2007Houston , TX

Contributions byDoug Straub, Ed Robey, Mark Tucker, Mike Dera,

Eduardo Perez, Rick Addis, Dave Lyons, Dan Maloney, Kent Casleton, Geo Richards

The National Energy Technology Laboratorywww.netl.doe.gov

D. Straub/ESD/October 4, 2006

The Future of Natural Gas(Source: EIA Annual Energy Outlook 2007 – Early Release)

• Demand for NG expected to grow− Based on EIA long-term forecasts, U.S. natural gas consumption is projected to

increase from 22.0 trillion cubic feet in 2005 to 26.1 trillion cubic feet in 2030

• Supply can not keep pace− Total domestic production, including supplemental natural gas supplies, increases from

18.3 trillion cubic feet in 2005 to 21.1 trillion cubic feet in 2022, before declining to 20.6 trillion cubic feet in 2030

US Consumption - Production of Natural Gas (quadrillion Btu)

10

15

20

25

30

1980

1990

2000

2010

2020

2030

ConsumptionProduction

Historical Projection


The Growing Demand for Natural Gas(International Energy Outlook 2006)

• World Natural Gas Consumption− Increased from 95 tcf in 2003 to 182 tcf in 2030.− Higher world oil prices increase the demand for natural gas.

117

9693

73

0

50

100

150

200

1990

2002

2003

2010

2015

2020

2025

2030

Other Non-OECD

Non-OECD Asia

Non-OECD Europe and Eurasia

OECD134

150165

182

Trillion Cubic FeetOECD - Organization for Economic Cooperation and Development

www.lngworldshipping.comWorldnews.com

Iran – India Pipeline

− By 2030 demand for natural gas in developing countries when more than double


What Are The Implications For Power Generation?

• Natural gas usage in the power generation sector continues to grow.


Looking at Alternatives: LNG(Source: EIA Annual Energy Outlook 2006)

• Large natural gas reserves exist that must be liquefied to transport overseas.

• Growth in overseas imports (i.e., LNG)− Net U.S. LNG imports are expected to

rise from 5 percent of net U.S. natural gas imports in 2002 to 39 percent in 2010

− The United States imported 229 Bcf(4.8 million tons) of LNG in 2002 with more than half that volume originating in Trinidad and Tobago.

Russia

Iran

QatarSaudi Arabia

United Arab Emirates

United States

Nigeria

Algeria

Venezuela

Iraq

Indonesia

Norway

Other


Differences Between LNG and NG

• Transportation and storage• Energy content

− LNG typically has a higher heat content per cubic foot.

• Fuel Composition− Low HC, water and CO2 content

compared to domestic natural gas.− High cost of NG compared to NGL’s has

lead to reduced extraction levels• Hydrocarbon Drop-out

− Higher hydrocarbons may influence combustion and physical phenomena

www.panhandleenergy.com


What Are The Implications For Gas Turbine Power Plants?

• LNG fuel composition is different− Higher BTU value− Increase in heavier HC’s− Lower level of inerts

• Effects of sudden changes in gas composition− How will fuels mix in the pipeline?− How to sense changes in fuel composition?

• Gas turbine combustion sensitivity to fuel variations− Emissions− Dynamics− Auto-ignition− Flashback and LBO


DOE Research on Fuel InterchangeabilityOct 2005 – Nov 2006

− Hydrocarbon Dewpoint – Computational simulation could be used to improve dewpointprediction (partnered with West Virginia University).

• FERC requests DOE’s help with a technical assessment of the effect of fuel variability on end-use equipment.− Database & Gap Analysis - gas fuel composition and effects on end-use

equipment.− Pipeline Mixing - Steady-state and transient mixing behavior.− Reciprocating Engines - Effect of gas composition (literature review).− Stationary Gas Turbines – Literature and experimental analysis

of fuel effects on stationary gas turbines.− Sensors for Gas Composition - Rapid gas composition measurement to

assess equipment control options.


Fuel Interchangeability

• Interchangeability (NGC+, Feb 2005)− “The ability to substitute one gaseous fuel

for another in a combustion application without materially changing operational safety, efficiency, performance or materially increasing air pollutant emissions”

• Wobbe Index (Interchangeability Factor)− Single index parameter to measure

interchangeability− Relates the thermal input to a burner

− Does not capture the effects flame speed and combustion chemistry

• Narrower range may limit supply options• Is blending inerts a viable option?

Wobbe Number

US Average 1336

Trinidad 1372

Algeria 1398

Qatar 1417

Abu Dhabi 1417

Malaysia 1434

Oman 1437

GTI Feb 2005

HHVWobbeSG

=


Typical LNG Compositions

Average U.S. Composition1323 Btu/scf

Methane 92.30%

Other 1.50%

Nitrogen 1.80%

Propane 0.80%

Ethane 3.60%

Very Low Btu Content1375 Btu/scf

Methane 96.18%

Other 0.08%

Nitrogen 0.01%

Ethane 3.39%

Propane 0.34%

Low Btu Content1397 Btu/scf

Methane 92.19%

Other 0.43%

Nitrogen 0.00%

Ethane 6.45%

Propane 0.92%

Moderate Btu Content 1408 Btu/scf

Methane 87.14%

Propane 1.34%

Nitrogen 0.49%

Other 0.29%Ethane

10.74%

High Btu Content1421 Btu/scf

Methane88.77%

Ethane7.38%

Propane2.61%

Nitrogen0.03%

Other1.21%

Very High Btu Content1443 Btu/scf

Methane85.98%

Propane3.47%

Ethane 8.69%

Nitrogen 0.02%

Other1.84%


Wobbe Number Control

• Reduce Wobbe number through the addition of inerts− Nitrogen− Air− Carbon Dioxide

Very High BTU Nitrogen AdditionMethane 85.98% 82.49%Ethane 8.69% 8.34%Propane 3.47% 3.33%Butane 1.84% 1.77%Nitrogen 0.02% 4.08%

Wobbe 1443 1400


Effects of Fuel Variability on Gas Turbine Combustion

• In-Use systems can be classified in two categories− Pre-mixed and Diffusion systems

Fuel

D iffu s io nF la m e

CombustionAir

DilutionAir

CoolingAir

Diffusion style• Lean pre-mixed, or DLN, systems

account for > 85% of gas fired capacity built since 19951.

• Diffusion flame systems− Robust, can tolerate fuel variability− Small effect on older diffusion flame systems

(+2ppm/100ppm)• Hung, 1976, 1977; Meier, 1998

• DLN systems are more susceptible to combustion related phenomena− Reduce NOx by lowering flame temperature− But…

• Dynamics?• Flashback and LBO?

Premix style

VariableFuel Impurities

Air

Overheating

W o rnS e a l?

A u to ig n it io n

Flame Relocaton

Air

A ir F lo w L e a k

O s c illa t io n

P re m ix e d F la m e

⎟⎟⎠

⎞⎜⎜⎝

⎛⋅+=

44

ln101CHCH TT

NOxNOx

(1) Personal communications Chuck Linderman , Alliance of Energy Suppliers


Fuel Interchangeability Effects: Emissions

• NOx Emissions: pathways− Thermal NOx / Zeldovich

• Primary NOx pathway with Tf > 1800 K.− Prompt (Fernimore) NOx

• Hydrocarbon driven through oxidation of the HCN moleculeN2 + CH -> HCN + N

− Nitrous Oxide (N2O) MechanismN2O + O -> NO + NO

• Fuel interchangeability concerns− Changes in premixer performance− Changes in flame temperature− Presence of higher hydrocarbons

www.ucsusa.org


Fuel Interchangeability Effects: Flashback / Lean Blow-off

• Flashback− Flame propagates upstream to the premixer through a shear

or boundary layer, or vortex core.− Flame speed exceeds local gas velocity. (primarily driven by

flame speed)− Thermal damage to components.

• Effects of fuel variability?− Changes in flame speed− Lewis number effect (ratio of thermal diffusivity to mass

diffusivity)

• Lean Blow-off− To maintain low flame temperatures, DLN combustor

operate near the lean blow-out limit.− Flame becomes unanchored and can not be held in the

combustor. − Correlated with characteristic combustor (flow) and chemical

(flame speed) time scales.• Effects of fuel variability?

− Changes in flame speed

Result of flashback in DOE experimental combustor


Fuel Interchangeability Effects: Dynamics• What are combustion dynamics

− Damaging pressure oscillations resulting from a coupling between acoustic pressure and heat release perturbations.

• Mechanisms− Equivalence ratio perturbations− Vortex shedding− Changes in the flame surface.

• How fuel variability will effect− Changes in chemical and physical time

scales that effect phase relationship between heat release and acoustic pressure perturbations.

− Changes in fluid medium (gas composition) alter acoustic properties.

Flame u'/q'

Acoustics

VortexShedding

ExternalExcitation

q'u s+u s

'

us'

us

uA'

uV'

uout'Af'

P'

OH'

Air

Fuel

Variable flameanchor, variableflame surface area,vortex collapse,variable flow rate

Flame

Fuel/airratio

disturbance,w/convection

time τ

Acoustic wavesGenerated Reflected

τ


NETL Investigation for Turbine Combustion

• Paper results− Literature, database− Discussion with OEMs, operators− Analytic models− CFD models

• Experimental results− Lab to full scale− Dynamics, blowout, emissions

• Project start: October 2005

Lab Scale15,000 BTUH

AtmosphericPressure DevelopmentCombustor100,000 BTUH

DynamicGas TurbineCombustor5 million BTUH10 atm600 F inlet

Premixer CFD simulation


High Pressure Propane Blending Facility

Meets Req’ts of NFPA-58

Metering runs

270 295 320 345 3700

125

250

375

500

Temperature, (deg K)

Vap

or P

ress

ure,

(psi

)

500

0

VP T plot( )psi

370270 T plot

165F for propane

2x Fluid-bath,controlled-heatpressure vessels

NG

C3H8 FT

FT

On-lineMicro-GC

To Test Rig


NOx Emissions

2

3

4

5

6

7

8

0 1 2 3 4

Fuel Carbon #

NO

x pp

mv,

dry

, 15%

O2

Mixer 1Mixer 2

MethaneEthane

Propane

Fig 6-5 Comparison of NOx emissions from jet-stirred reactor for three fuels (2.3ms residence time, 1790K temperature, 1 atm) 20

0

2

4

6

8

10

12

0 1 2 3 4 5 6

Natural Gas Type

Est

imat

ed N

Ox

(ppm

v); s

ee te

xt

Assumed 5 ppm baseline

NG: 1 2 3 4 5methane 90 85 82 79 77ethane 5 15 0 20 10propane 5 0 14.5 0 9.6n2 0 0 3.5 1 3.4

Figure 6-6. Replot of data presented by Klassen.22 Five natural gas compositions are considered, and an assumed baseline of 5 ppmv NOx is used to scale the normalized data sets; see the text – the actual NOx levels are not reported.

NG: 1 2 3 4 5methane 90 85 82 79 77

ethane 5 15 0 20 10propane 5 0 15.5 0 9.6

N2 0 0 3.5 1 3.4

Fuel: A B C D E F G H I J KCH4 (%) 100 96.2 87.1 86 90 85 87.1 92.2 88.8 86.0 0

C2H6 0 3.4 10.7 9 5 15 10.7 6.5 7.4 8.7 0C3H8 0 0.3 1.3 5 5 0 2.1 0.9 2.6 3.5 100C4H10 0 0.08 0.3 0 0 0 0.0 0.4 1.2 1.8 0CO2 0 0 0 0 0 0 0 0 0 0 0N2 0 0.01 0.5 0 0 0 0 0 0.03 0.02 0

Wobbe# 1360 1377 1409 1435 1419 1420 1420 1398 1424 1443 2023Predicted

NOx 3.5 4.0 4.9 5.5 5.0 5.2 5.1 4.4 4.8 5.1 n/a

Delta NOx(%) 0% 12.6% 40.7% 55.7% 43.0% 47.9% 45.7% 25.1% 36.4% 44.6% n/a

DLN Microturbine Correlation: NOx [15%O2] = 0.0351*C1+0.147*C2+0.225*C3

Table 6-2. Predicted NOx (ppmv @15% O2) and ∆NOx (%) relative to methane for the correlation of microturbine data from Equation 6-4. The correlation was not tested for pure propane fuel, column K, and does not account for butane.

• Literature data (exp and predictions) suggests that NOx will be greater with higher HCs.

• NETL high-pressure tests in progress.

(Top right): Lee, J. C. Y. (2000)., PhD Thesis, University of Washington, Seatle WA.

Hack, R. L., McDonell, V. G. (2005).. ASME GT2005-68777.

(Lower Right) Klassen, M. (2005). White Paper on Natural Gas InterchangeabiliyNGC+


Physical Effects on EmissionsSimplified Analysis for Jet Penetration

• Premixing fuel uses jet penetration to mix fuel/air stream• It is possible to relate the Wobbe index to jet penetration for

comparing two fuel compositions (• Jet penetration is dependent upon the momentum ratio

d

Z

Y

ρjuj2

ρaua2

− r = ρjuj2/ρaua

2

− Assuming a constant heat release independent of fuel composition (QA= QB)

− Fluid mechanics tells us:

− Jet penetration is inversely proportional to Wobbe index 0.5 0.332

2j j

a a

uY Zd u d

ρκ

ρ⎛ ⎞ ⎛ ⎞= ⎜ ⎟ ⎜ ⎟⎜ ⎟ ⎝ ⎠⎝ ⎠

2

2 2

2

A

B A A

BA B B

YWI u d

YWI ud

ρρ

⎛ ⎞⎜ ⎟⎛ ⎞ ⎛ ⎞

= = ⎜ ⎟⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠ ⎜ ⎟

⎝ ⎠

AIR

FUEL

High Wobbe

Low Wobbe

..GSHHVWobbe =


CFD Analysis of Premixer Performance on Various Fuel Compositions

X

Y

0 0.01 0.02 0.03 0.00

0.003

0.006

0.009Wobbe - 1360, Fuel Mass Fraction

100%CH4

Flame Location

X

Y

0 0.01 0.02 0.03 0.00

0.003

0.006

0.009 Wobbe - 1443, Fuel Mass Fraction86% CH4, 8.7% C2H6, 3.5% C3H8, 1.8% C4H10, 0.02% N2

Flame Location

Two- and Three-Dimensional Analysis – agrees with analytical results

100% Methane 100% Propane


Experimental Results: NOx Emissions• NOx emissions

− Only measured in dynamically stable region due to pressure fluctuation bias.

• Two-level factorial design− Equivalence ratio − Propane level

• Premixed system− 5% pilot fuel

13201330134013501360137013801390140014101420

1000 1050 1100 1150

HHV (BTU/scf)

Wob

be In

dex

(BTU

/scf

)Baseline NG 3.5% Propane Blend

5% Propane Blend

~2.5-inches


Preliminary NOx Data(7.5 atm, 600F air preheat, RMS Pressure Levels < 1%)

0 1 2 3 4 5 6%Propane

10

11

12

13

14

15

16

17

18

19

20N

Ox

(ppm

@ 1

5%O

2)

Equivalence Ratio = 0.44-0.45

Standard Deviation = 0.9 ppm

Equivalence Ratio = 0.50-0.51


Preliminary NOx Levels Correlate With Flame Temperature

1550 1575 1600 1625 1650 1675 1700 1725 1750

Adiabatic Flame Temperature (K)

8

10

12

14

16

18

20

NO

x (p

pm @

15%

O2)

Baseline NG

5% Propane

16081.00+ 0.0010.0%

0.453 + 0.0050.44

8

16594.08+ 0.0013.5%

0.478 + 0.0050.48

7

16604.19+ 0.0153.5%

0.479 + 0.0050.48

4

16544.00+ 0.0183.5%

0.474 + 0.0050.48

2

16071.14+ 0.0160.0%

0.453 + 0.0050.44

5

15995.33+ 0.0295.0%

0.445 + 0.0040.44

3

17080.69+ 0.0950.0%

0.503+ 0.0040.52

1

17175.46 + 0.0025.0%

0.510 + 0.0050.52

6

AdiabaticFlameTemp.

(K)

ActualPropane

Level

TargetPropane

Level

ActualEquiv.Ratio

(flows)

TargetEquiv.Ratio

Test Point†

16081.00+ 0.0010.0%

0.453 + 0.0050.44

8

16594.08+ 0.0013.5%

0.478 + 0.0050.48

7

16604.19+ 0.0153.5%

0.479 + 0.0050.48

4

16544.00+ 0.0183.5%

0.474 + 0.0050.48

2

16071.14+ 0.0160.0%

0.453 + 0.0050.44

5

15995.33+ 0.0295.0%

0.445 + 0.0040.44

3

17080.69+ 0.0950.0%

0.503+ 0.0040.52

1

17175.46 + 0.0025.0%

0.510 + 0.0050.52

6

AdiabaticFlameTemp.

(K)

ActualPropane

Level

TargetPropane

Level

ActualEquiv.Ratio

(flows)

TargetEquiv.Ratio

Test Point†


Lean Blowout• Premix combustors operate near lean blowout• If the fuel variability changes the lean blowout,

the engine fuel schedule will need to be changed− Possible emissions or stability compromise− Possible unexpected flameout

• Traditional blowout correlations based on laminar flame speed− Some difference for different hydrocarbons and

methane is slower than propane1

− Note that the turbulent flame speed drops with propane (previous slide)

• Recent NETL studies on H2-CH4 blends:− Stirred reactor models better correlate the blowout

data with wide fuel variability

70

60

50

40

30

20

10

0

70

60

50

40

30

20

10

0

Flame speed Su (cm/sec)

Φ

EkofiskSlochterenWieringermeerMethane


0.5 1.0 1.5

0

20

40

60

80

100

120

140

160

180

0 0.5 1 1.5 2 2.5

Turbulence Intensity u' (m/s)

Bur

ning

Vel

ocity

(cm

/s)

00.20.50.81

Propanemass

fraction

increasingpropane

From previous slide, turbulentFlame speed of CH4 –C3H8 mix

From previousSlide, flame speeds

SimVal LBO Data (8 Aug 2005)Tin=590K V=40 m/s

Effect of Pressure

% H2 in Fuel0 20 40 60 80 100

φ at

Blo

wou

t

0.25

0.30

0.35

0.40

0.45

0.50

0.551 atm4 atm8 atmLutz 1 atm

Flame

No Flame

Appr

oxim

ate

T ad (

K)

1300

1400

1500

1600

1700

Lutz 8 atm

dSU

LL

ref

res

chem2

αττ

==2L

chem Sατ =

Traditional correlations for “loading (L)” define when blowout occurs

Strakey. P., Sidwell, T (2006)Proceedings of Combustion Institute 2006

1Lewis and VonElbe, Cobmustion Flames and Explosions of Gases”, 3rd ed, Academic Press, pp403, Fig 205-206


• Pure propane versus NG: big effect on blowout− Did not follow simple explanations from flame speeds− Did not follow stirred reactor model− Hypothesis is the flame anchor depends on the turbulent

flame speed− More work needed to resolve details

• More realistic fuel blends (up to 10% propane in NG)− Blowout not significantly affected

Natural Gas

20

22.5

25

27.5

30

0.6 0.7 0.8 0.9 1

N.G. Equivalence Ratio

Refe

renc

e V

eloc

ity (m

/sec

)

DetachmentUnstableStable

1833 1987 2121 2235ADIABATIC FLAME TEMP (K)

STABLE

UNSTABLE

STABLE

Lean Blowout: Experimental Results

C3H8/N2

20

22.5

25

27.5

30

0.6 0.7 0.8 0.9 1


Ref

eren

ce V

eloc

ity (m

/sec

)


DE

TAC

HM

EN

T / E

XTI

NC

TIO

N

STA

BLE

UN

STA

BLE

?

C3H8

20

22.5

25

27.5

30

0.6 0.7 0.8 0.9 1


Ref

eren

ce V

eloc

ity (m

/sec

)


DE

TAC

HM

EN

T / E

XTI

NC

TIO

N

STA

BLE

UN

STA

BLE

?

90% Natural Gas / 10% C3H8

20.0

22.5

25.0

27.5

30.0

0.6 0.7 0.8 0.9 1


Refe

renc

e V

eloc

ity (m

/sec

)

DetachmentUnstable

1833 1987 2121 2235

ADIABATIC FLAME TEMP (K)

STABLE

UNSTABLE

UNKNOWN


Flashback• Flame speed is the key issue

− Flame speeds not very different among HCs− Very recent data: turbulent flame speeds change w/HCs

• Lab tests so far do not reveal problems− Not comprehensive− High pressure data still to come− Commercial associated gas applications operate w/o problems (not publicly documented).

Lab flame NG+0% propane

φ = 0.7

0

20

40

60

80

100

120

140

160

180

0 0.5 1 1.5 2 2.5


Bur

ning

Vel

ocity

(cm

/s)

00.20.50.81

Propanemass

fraction

increasingpropane

70

60

50

40

30

20

10

0

70

60

50

40

30

20

10

0

Flame speed Su (cm/sec)

Φ



0.5 1.0 1.5

Figure 6-2. Laminar flame speeds of several natural gas blends and methane. The x-axis is the equivalenceratio (normalized fuel/air ratio).

Figure 6-3 Turbulent flame speeds (Kido et al.10) of methane/propane mixtures having the same laminarflame speed.

φ = 0.7

Lab flame NG+10% propane

φ = 0.74

Lab flame 100% propane


Potential Effects of Fuel Variability on Combustion Instabilities (Dynamics)

• Chemical Effects− Changes in chemical time scales− Changes in the turbulent flame speeds

• Physical Effects− Changes in the acoustic characteristics of the medium


Chemical Effects of Fuel Variability on Dynamic Response

• Effect on dynamic flame response− Changes in chemical time scales

• Damköhler Number• Da >> 1 chemical reactions are

fast in comparison to fluid mixing rates.

• Alters the phase difference between heat release and acoustic pressure

− Changes in the turbulent flame speeds• Changes flame surface area

'flow o

chemical L L

uDaS

ττ δ

= =l

0

20

40

60

80

100

120

140

160

180

0 0.5 1 1.5 2 2.5


Burn

ing

Velo

city

(cm

/s)

00.20.50.81

Propanemass

fraction

increasingpropane


Potential Physical Effects of Fuel Variability on Dynamic Response

AirFuel

Mix

• Changes in fuel system impedance− Measure of the fluids resistance

to propagating acoustic waves− Speed of sound changes with

medium (gas properties).• Alters phase-gain between

components.− Transmission from one fluid into

another• Alters characteristics of reflected

waves.Hot Products

co_air = 343 m/secco_meth = 450 m/secco_prop = 252 m/sec


Lab Burner Tests (14,000 BTUH)

• Tests used to determine any fundamental differences in flame dynamics versus fuel composition?

• Fuel and air fully premixed (no fuel injector impedance effects)

• Most fuels fall within NGC+ Recommended limits

• Nitrogen blending used to reduce Wobbe back to Methane levels

900

1200

1500

1800

2100

2400

2700

0.5 0.7 0.9 1.1 1.3 1.5 1.7

Specific Gravity

High

er H

eatin

g Va

lue (

BTU/

scf)

NGC+ Proposed Max/Min Limits

Constant Wobbe1360

Fuel A Fuel B Fuel C Fuel D Fuel E Fuel F Fuel G

Methane (%) 100 75 70 90 88.25 0 0

Ethane (%) 0 0 0 0 0 0 0

Propane (%) 0 25 20 10 8.25 100 62.3

Nitrogen % 0 0 10 0 3.5 0 37.7

HHV (BTU/scf) 1012 1389 1213 1163 1101 2523 1572

Wobbe(BTU/scf) 1360 1554 1363 1439 1365 2041 1369

Wobbe % Diff 0% 14% 0.2% 6% 0.4% 50% 1%

Microphones

Quartz Main Body

Flow RestrictionPremixedFuel / Air

RingStabilizer


Lab Burner Results (14,000 BTUH)• Fuel D and E most realistic “LNG like” fuel

− Comparable to methane response (no change from baseline)− Additional tests not shown that included ethane produced similar

response• High levels of propane produced a significant change in response.• Nitrogen dilution to reduce Wobbe did not influence dynamic

response.

0

0.25

0.5

0.75

1

1.25

1.5

1600 1700 1800 1900 2000 2100 2200 2300Adiabatic Flame Temp (K)

Norm

alize

d RM

S Pr

essu

re

Fuel A

Fuel B

Fuel C

Fuel D

Fuel E

Fuel F

Fuel G

Nitrogen dilution to reduce W

obbe


Atmospheric Pressure Development Combustor (100,000 BTUH)

Dynamic pressure for various fuel blends

0.00

0.10

0.20

0.30

0.40

0.50

1600 1700 1800 1900 2000 2100 2200Adiabtaic Flame Temperature (K)

RMS

Pres

sure

(psi)

20.0 m/sec22.5 m/sec25.0 m/sec27.5 m/sec30.0 m/sec

Solid Symbols Represent July '06 Repeats

Hollow Symbols Represent Data from Original N.G. Tests in Jan '06

Reference Velocity

0.00

0.10

0.20

0.30

0.40

0.50


RMS

Pres

sure

(psi)


Reference Velocity

0.00

0.10

0.20

0.30

0.40

0.50


RMS

Pres

sure

(psi)


Reference Velocity

0.00

0.10

0.20

0.30

0.40

0.50


RMS

Pres

sure

(psi)

20.0 m/sec22.5 m/sec25.0 m/sec

Hollow Symbols Represent N.G. + 10% C3H8

Solid Symbols Represent July '06 N.G.

Reference Velocity

Natural GasWobbe = 1360 100% Propane

Wobbe = 2041

Propane/NitrogenWobbe = 1369

NG/Propane (90/10%)Wobbe = 1439


Dynamic Gas Turbine Combustor (5 million BTUH, up to 10atm)

• Evaluate change in stability boundary versus fuel− Nominal +4.6% propane to site NG

• Slight change – wider replicate range – minor− Hysteresis loop is larger than fuel effect (component

heating)

0

2

4

6

8

10

12

14

0.45 0.47 0.49 0.51 0.53 0.55 0.57 0.59 0.61Equiv. Ratio (flows)

RM

S Pr

essu

re (p

si)

NG Only - Case 1 NG Only - Case 2NG w/Propane - Case 3 NG w/Propane - Case 4

NGOnly

NG w/PropaneCase 1 Case 2 Case 3 Case 4

Propane (%) 0.5 0.5 4.6 4.6HHV (mBTU/scf) 1.036 1.029 1.094 1.094WOBBE MJ/m^3 50.7 50.7 51.9 51.9WOBBE BTU/scf 1360 1356 1394 1393

Pressure vessel for combustor

~2.5-inches

Fuel injector (looking upstream)Holes are centerbody pilot flow


Summary for Combustion Dynamics• From lab scale to full scale…..

− Modest additions (5-10%) of propane to natural gas didn’t produce a significant change in dynamics amplitude or stability boundary.

• Fuel composition does matter− Pure propane is significantly different than natural gas.− Nitrogen blending for constant Wobbe does not compensate.

• Wobbe does not account for changes in flame speed and combustion chemistry

− Changes in acoustic impedance in fuel injectors and modest changes in flame shape could contribute to changing in the dynamic response in marginally stable combustors.


Overview Summary Turbines (1/2)• Fuel effects on gas turbines

− Limited literature, public data available.− Effects on dry-low NOx system not well-understood.− Emissions

• Uncontrolled NOx emissions will rise with hydrocarbons• Literature: small effect on older, diffusion flame systems

(e.g., +2ppm/100ppm base?)• Literature: small absolute effect in DLN, but may be

significant for machines near permit levels (e.g., +2ppm/4ppm base?)

• NETL analysis: effect not likely due to premixer deterioration

• NETL experimental data shows only a small effect –inconclusive?

• SCR control may be able to accommodate• Did not obtain public report of “brown-plume” exacerbation by

HCs• Link between fuel and brown plume plausible at part-load


Overview Summary (2/2)• Operational issues (DLN systems)

− Autoignition• Actual data on autoignition time scale is NOT in the literature• Experience with premixers in service suggest (but don’t prove) no

problems− Blowout

• Literature correlations: expect little change among HCs• Lab data: noticeable shift in blowout for extreme fuel change

− Flashback• Literature correlations: expect little change among HCs• Lab data did not identify any problems

− Dynamics• Literature: uncertain effects, and physics• NETL analysis: likely effect of fuel impedance + composition on

some engines• Lab data: minor effect for modest fuel change, but significant

effect for extreme fuel change− Key point:

• Wobbe is not a useful parameter to quantify the behavior observed in lab tests (flame speed and combustion chemistry).

• Dilution or fuel heating (to maintain Wobbe) will not negate fuel composition effects.

Full-scale fuel injector(courtesy Woodward)

NETL propane additionsystem added for full-scaleturbine combustion testing

August 1, 2006


Questions?

Contact Info:

Don FergusonNational Energy Technology Laboratory – US DOE

[email protected](304) 285-4192

mailto:[email protected]

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