Fuel Cell Program

Diesel Reforming for Fuel Cell Auxiliary Power Units

SECA Core Technology Program ReviewAlbany NY, Sept 30 – Oct 1.

Rod Borup, W. Jerry Parkinson, Michael Inbody, Jose Tafoya, Will J. Vigil, and Dennis R. Guidry

Los Alamos National Laboratory

DOE Program ManagersSECA – Daniel Driscoll/Wayne Surdoval

POC: Rod Borup:Borup@lanl.gov - (505) 667 - 2823

Fuel Cell Program

Potential Applications of Diesel Reformers in Transportation Systems

Diesel Exhaust

POx/SRLean NOxCatalyst

Fuel TankNOx Reductant

SOFCEngineEGR

SOFC Fuel

ReducedNOx ExhaustDiesel Engine

The reforming of diesel fuel potentially has simultaneous on-board vehicle applications:• SECA application: reforming of diesel fuel for SOFC / APU• reductant to catalyze NOx reduction• Hydrogen addition for high engine EGR • fast light-off of catalytic convertor

Fuel Cell Program

Diesel Reforming Tasks and Activities • Objectives: Develop technology suitable for on-board reforming of diesel fuel for transportation SOFC auxiliary power units

• Develop fundamentals (kinetics ….), models, examine components• Approach: Examine Catalytic partial oxidation and steam reforming• Modeling

• Carbon formation equilibrium modeling• Reformer operation with anode recycle

• Experimental• Development of direct diesel fuel injection• Adiabatic reformer operation

• Catalyst evaluation, activity measurements• Hydrocarbon breakthrough speciation

• Anode recycle simulation• Iso-thermal reforming and carbon formation measurements

• Carbon formation rate development• Catalyst regeneration due to carbon formation

Fuel Cell Program

Diesel Reforming MeasurementsAdiabatic Reactor with nozzle

ModelingEquilibrium

KineticCompositionIso-thermal Microcatalyst

Iso-thermal system• Measure kinetics• Steam reforming / POx• Light-off• Carbon formation

NozzleAir / anode recycle Catalyst(Pt/Rh)

Furnace

Window for Catalyst Reaction Zone Observation

Windows forlaser diagnostics

Fuel Cell Program

Relative Carbon Formation from Fuel Vaporization

-0.02

0

0.02

0.04

0.06

0.08

0.1

Diesel(commercial)

Diesel (low - S)

Kerosene(commercial)

Kerosene(low-S)

Hexadecane Dodecane

Rel

ativ

e C

arbo

n Fo

rmat

ion

Dur

ing

Fuel

Ref

luxi

ng

• Saturated pure diesel components do not show pyrolysis• S removal, decreases carbon formation (removes PAHCs)• Diesel fuel injection require technology to avoid carbon formation

during vaporization

Fuel Cell Program

Direct Fuel Nozzle Operation

Simulated Anode ExhaustRecycle (H2, CO, CO2, N2, H2O, HCs)

POx/SR

Noble metalReticulated foam

Supported Catalyst

Fuel Tank

Air

Fuel PressureRegulator

P

Nozzle

• Directly inject fuel to reforming catalyst• Commercial nozzle, control fuel pressure for fuel flow (~ 80 psi)• Air / anode recycle (H2 / N2) distribute in annulus around fuel line / nozzle

• Experimental results• Operated successfully at steady state

• Minimum fuel flow dictated by fuel distribution from nozzle• Requires control of fuel/air preheat, limiting preheat (~ < 180 oC)

• Prevents fuel vaporization/particulate formation

Flowmeter

Fuel Cell Program

SOFC Anode Recycle to Reformer! Water Addition

POx/SR

Fuel Tank

SOFC

Anode RecycleStream

Exhaust

AirReformate

• Methods for water introduction and availability:• Separate water tank (tank, freezing)• Anode water recovery by condensation (heat ex., cond., tank, pump freezing)• Anode recycle to reformer (blower)

Currently simulating anode recycle with N2/H2 mixture

Fuel Cell Program

SOFC Anode Recycle Modeling

Green – Fractional increase in flow due to increasing gas volume due torecycle ratio, leads to larger reformer

800

820

840

860

880

900

920

940

960

0 10 20 30 40 50 60

Recycle Rate / %

Out

let T

empe

ratu

re /

o C

0

0.2

0.4

0.6

0.8

1

1.2

S/C

and

Ref

orm

er O

utle

t Flo

wra

te

Frac

tiona

l Inc

reas

e

Outlet Temp at O/C = 1

S/C

Reformer Outlet FlowrateFractional Increase

Fuel Cell Program

Hydrogen / CO production

Pt / Rh supported catalystResidence time ~ 20 msecAnode recycle simulated with H2, N2, H2O

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.8 0.9 1 1.1 1.2 1.3 1.4

Oxygen / Carbon Ratio

Con

cent

ratio

n / %

H2 (40% Recycle)CO (40% Recycle)H2 + CO (40% Recycle)H2 (30% Recycle)CO (30% Recycle)H2 + CO (30% Recycle)

CO

H2

H2 + CO

30 % Recycle

30 % Recycle

30 % Recycle

40 % Recycle

40 % Recycle

40 % Recycle

Fuel Cell Program

760

780

800

820

840

860

880

900

920

940

0.8 0.9 1 1.1 1.2 1.3 1.4

Oxygen / carbon ratio

Ref

orm

er O

utle

t Tem

pera

ture

/ o C

40 % Recycle30 % Recycle

Reformer temperature during diesel reforming

• Higher recycle reduces operating temperature• Operation with recycle < 30 % difficult due to high operating

temperatures and catalyst sintering

Model Pts

Fuel Cell Program

Reformer Outlet Hydrocarbon Speciation

• Complete hydrocarbon conversion:• Higher O/C reduces HCs• Higher residence and catalyst loading reduces HCs

• Gasoline/PEM reforming durability work shows HCbreakthrough at ~ 500 – 750 hours

0

0.2

0.4

0.6

0.8

1

1.2

0.8 0.9 1 1.1 1.2 1.3

Oxygen / Carbon Ratio

Hyd

roca

rbon

Con

cent

ratio

n / %

.

C1C2C3C4

Fuel Cell Program

Light-off of Reformer with Diesel

• Light-off requires preheating of catalyst • Degree of preheat depends upon fuel• Higher HCs and aromatics require higher

Preheat temperatures for light-off

Repeated light-offs show an increase in temperature required to achieve light-off

100

120

140

160

180

200

220

240

260

280

iso-

octa

ne

Isoo

ctan

e X

ylen

e

Isoo

ctan

e an

thra

cene

Isoo

ctan

e n

apth

alen

e

RFG

Kero

sene

Low

S D

iese

l

Die

sel

Ligh

t-off

Tem

pera

ture

/ o C

150

175

200

225

250

275

300

1 2 3 4 5 6 7 8 9 10

Run #

Tem

pera

ture

/ o C

Low Sulfur Diesel Fuel - CatalystDiesel Fuel (Set #2) - Catalyst T

Fuel Cell Program

Carbon Formation Equilibrium Modeling• Various forms of carbon exist

• (different forms of carbon exist in the literature, and different forms have been observed during reforming)• Commercial codes handle vapor, liquids

• Difficult to deal with solids as 3rd phase • Difficult to input of thermodynamics components

• Different carbon forms have different thermodynamic characteristics

• Developed chemical equilibria code to analyze conditions for carbon formation• Includes 3 types of amorphous carbon

• Dent Carbon (C1)• Boudart Carbon (C2)• Water gas carbon (C3) – (limited thermodynamic data)

• Operation of model in iso-thermal modes (adding adiabatic)• C++ Code operates on Windows PC

Fuel Cell Program

Model Operation & Availability• Specify:

• Isothermal• Adiabatic (needs improvement for amorphous Carbon)

• Gas phase components & concentrations• Equilibrium temperature• Pressure• Types of solid phase

• Output yields (code works where carbon formation is observed)• gas phase concentration• solid phase quantities• (Delta H reaction, outlet temperature – for adiabatic case)

•Model is (will be) available • no-cost (or nominal), non-exclusive to SECA industry teams

Fuel Cell Program

Carbon Disappearance Temperature with Recycle Ratio

500

600

700

800

900

1000

1100

1200

1300

0 10 20 30 40 50 60Recycle Rate / %

Car

bon

Dis

appe

aran

ce T

empe

ratu

re /

o C

Disappearance of all types of amorphous carbon

Fuel Cell Program

Carbon Formation Dependence on Recycle Ratio

• Dent Carbon (C1)• Boudart Carbon (C2)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

600 700 800 900 1000 1100 1200 1300

Temperature / oC

Rel

ativ

e C

arbo

n Fo

rmat

ion

/ Mas

s

C12 - 0% RecycleC12 - 10% RecycleC12 - 20% RecycleC12 - 30% RecycleC12 - 40% RecycleC12 - 50% Recycle

Fuel Cell Program

Carbon Formation:Competing effects kinetics vs. equilibrium

0

0.05

0.1

0.15

0.2

0.25

500 550 600 650 700 750 800 850

Reforming Temperature / oC

Rel

ativ

e C

arbo

n fo

rmat

ion

/ g

Low Sulfur DieselCommercial Diesel

Conditions:Iso-thermal operationTotal O/C = 1.0Pt/Rh support catalystResidence Time = ~ 30 msec

Low temperature – high equilibrium / low kineticsHigh temperature – low equilibrium / high kinetics

Fuel Cell Program

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.00088 0.00092 0.00096 0.001 0.00104

1/Temperature (K)

Car

bon

Form

atio

n

Carbon Formation MeasurementsIso-thermal operationCarbon formation trends with equilibrium at high temperatures

Trends with T (kinetic effect) at lower temperaturesCarbon Formation linear vs. 1/T

Adiabatic operationCarbon formation trends with equilibrium

Carbon decreases with increasing temperatureCarbon Formation linear vs. T

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

950 1000 1050 1100 1150Temperature / K

Car

bon

Form

atio

n

0

0.1

0.2

0.3

0.4

0.5

0.6

0.001 0.00104 0.00108 0.00112 0.00116 0.00121/Temperature (K)

Car

bon

Form

atio

n

Commercial DieselLow Sulfur Diesel

Fuel Cell Program

Carbon AnalysisThermal Gravimetric analysis of catalyst post-carbon forming measurements

Carbon is not typically ‘bound’ to catalyst surface (for noble metal catalysts)

Carbon removal is about 0.4 % catalyst weight

90

92

94

96

98

100

102

0 200 400 600 800 1000 1200

Temperature / oC

Cat

alys

t wei

ght /

%

Fuel Cell Program

Summary/Findings• Direct fuel injection via fuel nozzle

• Control of fuel temperature critical• Prevent fuel vaporization, fuel pyrolysis / clogging of nozzle• Potentially limited turn-down with nozzle

• Reformer operation with SOFC anode recycle• High adiabatic temperatures at low recycle rates

• Leads to catalyst sintering• Limits light-off of reformer

• High recycle increases reformer size, parasitic losses• Operation at 30 – 40 % recycle rate reasonably successful

• Limited success at lower (<20 % recycle rates due to high adiabatic T)• Carbon Formation

• Equilibrium carbon formation modeling• Equilibrium code available for iso-thermal carbon formation cases

• Experimental carbon formation measurements show kinetic effects and equilibrium effects

Fuel Cell Program

Future Activities - Modeling

• Modeling • Make model available for SECA industrial teams (Beta version)

• (no or nominal cost , non-exclusive license)• Model improvements

• Incorporate other carbon species enthalpies (CH0.2)• Incorporate sulfur into equilibrium code• Improve code robustness & make ‘user friendly’

• Examine system effects of anode recycle (efficiency and parasitics)

Fuel Cell Program

Future Activities - Experimental• Experimental

• Examine reformate effect on SOFC• Effect of hydrocarbon ‘breakthrough’ on SOFC

• incorporate SOFC ‘button’ cell operating on reformate• Sulfur effect on reforming kinetics• Carbon formation as function of catalyst, recycle ratio

• Reformer design considerations• Durability – catalyst sintering• Turndown – fuel / air feed preparation• Stand-alone start-up & consideration to avoid C formation• Recycle ratios – evaluate various anode recycle ratios

• ‘real’ recycle – incorporate major/minor constituents