Fuel Processing of Diesel for Fuel Cells

National Energy Technology Laboratory

June 19, 2002

David A. Berry, Todd H. Gardner, Robert James, William Rogers, and Dushyant

Shekhawat

2002 SECA CORE REVIEW

Descriptor - include initials /org#/date

Diesel Fuel ProcessingTechnical Issues Addressed

• Diesel fuel is complex and difficult to reform :• Diesel fuel is a complex, multi-component (>100 compounds) sulfur-

containing fuel that exhibits varying reaction pathways and kinetic rates for differing fuels and catalyst types.

• Deactivation of fuel reforming catalysts and fuel cell components via carbon deposition and sulfur poisoning are the principle technology barriers.

• System integration can be a significant challenge:• Reformer integration with fuel cell system requires desulfurization,

water management, and thermal considerations. • Certain FC applications may require high power density design with

“fast” response and high efficiency for both steady-state and transient operations.

• Hydrocarbon slip must be avoided to provide fuel cell with a clean synthesis gas.

Descriptor - include initials /org#/date

Diesel Fuel ProcessingR&D Objectives

• Develop fundamental understanding of diesel fuel processing and provide necessary tools and information to fuel cell/fuel process developers and system integrators for technology development, performance optimization, and system control.

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Diesel Fuel ProcessingTechnical Approach

• Utilize CFD Models to Understand and Address Heat and Mass Transfer Issues and Reactor Performance for Steady State and Transient Analysis

• Conduct Systems Analysis to Understand Reformer Integration and Operational Requirements

• Conduct Kinetic Rate Determination Studies in the Laboratory to Allow for Predictive Modeling and Design

ATR Reactor

Combustor

Fuel CellStack

ZnOSorbent

Bed

HeatExchanger

HeatExchanger

250 C

300 C800 C

650 C

Recycle

Air In

Fuel In

Exhaust

Descriptor - include initials /org#/date

Combustor

AutoThermalReformer

DesulfurizerSorbent Bed

ExhaustCondenser

SteamGenerator

Air Preheater

Air Compressor

Fuel Pump

Water Pump

800 C SECA APU

FuelCell

StackCathode

Anode800 C800 C

800 C

800 C

650 C

Diesel Fuel ProcessingSystems Analysis Results - High Efficiency Diesel Fuel Processor

Descriptor - include initials /org#/date

Combustor

AutoThermalReformer

DesulfurizerSorbent Bed

ExhaustCondenser

SteamGenerator

Air Preheater

Air Compressor

Fuel Pump

Water Pump

800°C NETL APU

FuelCell

Stack Cathode

Anode800 C800 C

800 C

800 C

700 C

650 C

Goals:- Maximize Thermal Integration- Flexible System Startup

Diesel Fuel ProcessingSystems Analysis Results - Integral Combustor/Reformer

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Diesel Fuel ProcessingSystems Analysis Results - Effect of Heat Integration

Shared Heat Non-Shared Heat

Fuel (kg/hr) 0.834 0.834

Air – Stoichs In 5.5 5.2

ATR F/A Ratio 9 3.5

Steam/C Ratio 0.8 0.8

Efficiency 49.8 42.39

Net Power 5.0 4.221

ATR Temperature 800 800

FC Temperature 845 813

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Diesel Fuel ProcessingSystems Analysis - Effect of Heat Integration

Shared Heat Non-Shared Heat

Fuel (kg/hr) 0.834 0.834

Air – Stoichs In 5.5 5.5

ATR F/A Ratio 9 9

Steam/C Ratio 0.8 0.8

Efficiency 49.8 47.16

Net Power 5.0 4.734

ATR Temperature 800 565

FC Temperature 845 745

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Diesel Fuel ProcessingSystems Analysis - Effect of Heat Integration

800 C SECA APUNon-Shared Heat Concept

564 C

745 C

855 C

564 C

650 C

277 C

307 C

272 C

25 C

Air Inlet

Fuel Inlet

Steam

25 C

Combustor

AutoThermalReformer

DesulfurizerSorbent Bed

ExhaustCondenser

SteamGenerator

Air Preheater

Air Compressor

Fuel Pump

Water Pump

FuelCell

Stack

Descriptor - include initials /org#/date

0.00

00

0.15

00

0.30

00

0.45

01

0.60

01

0.75

01

0.90

01

03.5

70

2

4

6

8

10

12

14

16

CO Molar Flow

(kmol/hr)

O2/C Ratio

Steam/C Ratio

CO Molar Flow vs. O2/Steam/C Ratio

0.00

00

0.15

00

0.30

00

0.45

01

0.60

01

0.75

01

0.90

010

4

8

0

5

10

15

20

25

30

35

H2 Molar Flow

(kmol/hr)

O2/C Ratio

Steam/C Ratio

H2 Molar Flow vs. O2/Steam/C Ratio

Diesel Fuel ProcessingSystems Analysis - ATR Oxygen & Steam Sensitivity

Descriptor - include initials /org#/date

• Develop a ATR model in Fluent− Fuel atomization and vaporization− Partial oxidation of diesel fuel− Steam reforming of diesel fuel− Combustion of anode exhaust gas

• Obtain reaction kinetic expressions from− Catalyst manufacturer− Literature− Experiments

• Conduct steady state simulations and validate model with ATR experimental data

• Conduct transient simulations− Use the simulation results to study reformer performance− Export temperature fields into ANSYS and calculate the

thermal stresses

Diesel Fuel ProcessingCFD Modeling - Approach

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ATR Region

Anode Exhaust Combustor

Outer Diameter = 6 in.

Inner Diameter = 2 in.

Length = 12 in.

Diesel Fuel ProcessingCFD Modeling Results - ATR Model Prototype Geometry

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Diesel Fuel ProcessingCFD Modeling Results - Reaction Zones

Anode Exhaust Combustor

Catalytic Steam Reforming

Fuel Spray Vaporization and POX

Length = 6 in.

Length = 6 in.

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ATR Model Inlet Conditions

Fuel Spray

C8H18

0.2 g/s

Nozzle Air

21% Vol. O279% Vol. N2

0.2g/s

650C/923K

Steam

0.18g/s

Anode Exhaust

5%Vol. H23%Vol. CO 21% Vol. CO236% Vol. H2O 35% Vol. N2

1.6g/s

800C/1073K

Cathode Exhaust

18% Vol. O282% Vol. N20.2g/s 650C/923K

Descriptor - include initials /org#/date

ATR Model Results

CO Mole Fraction

H2 Mole Fraction

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Diesel Fuel ProcessingReaction Rate Determination - Modeling Approaches

Level 1Intuitative Lumping

Level 2Mechanism Based

Lumping

Level 3Structure Oriented

Lumping

Level 4Mechanistic

• Lumps derived fromintuition (grossidentification oflumping groups), e.g.paraffins, aromatics,etc.

• Little is knownregarding the exactmechanism

• Psuedo-1st order

• Psuedo-homogeneous phase

• Easy to develop,inexpensive

• Suitable for processsimulators, e.g.ASPEN, ChemCad

• Predicts transientresponse andhydrocarbon slip

• Psuedo-homogeneous phase

• Based on psuedo-species lumpedtogether based onthe elucidation of adetailed mechanism

• Requires aknowledge ofprocess chemistry

• Must possess theanalytical ability tomeasure thepsuedo-species only

• Suitable for processsimulators, e.g.ASPEN, ChemCad

• Predicts transientresponse,hydrocarbon slip,coking and catalystdeactivation

• State of the art incomplex mixturemodeling

• Closely resemblespure mechanisticapproach

• Involves lumpingisomers only

• Detailed knowledgeof process chemistryneeded, expensiveanalytically

• Detailed kineticstudies needed forthe development oflumps

• Suitable for CFDpackages, e.g.Fluent

• Pure mechanisticapproach

• Detailed kineticstudies of singlecomponents andtheir mixtures

• Development ofexperimentalprocedures toevaluate processchemistry

• Knowledge ofcatalyst propertiesneeded

• Requiresspectroscopicmethod

• Predicts transientresponse,hydrocarbon slip,coking and catalystdeactivation basedon fundamentals

Descriptor - include initials /org#/date

C {-R}n

{-R}n

{-R}n

C {-R}n H2 + CO + CO2

O2/H2O

O2/H2OO2/H2O

O2/H2O

AromaticsAromatics

ParaffinsParaffins

NaphthenesNaphthenesOlefinsOlefins

Diesel Fuel ProcessingReaction Rate Determination - Complex Reaction Network

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Product Distribution from ATR of Diesel(T=850 C, O2/C=0.3, S/C=1.5)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

15 25 35 45 55 65 75Residence Time (10-3 sec)

(Mol

e of

H2/C

O fo

rmed

per

mol

e of

C in

fe

ed)

H2 (Ru)CO (Ru)H2 (Pt)CO (Pt)H2 (Pd)CO (Pd)

Descriptor - include initials /org#/date

Diesel Fuel ProcessingExperimental Vs Predicted Values for Diesel ATR on Pt/Al2O3

R2 = 0.91

0.0015

0.0025

0.0035

0.0045

0.0055

0.0015 0.0025 0.0035 0.0045 0.0055

Experimental, [-dCHC/dt]

Pred

icte

d, [-

dCH

C/d

t]

-rHC=k0exp(-8315/T)CHC0.87CH2O

-1.02CO2-0.13

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Diesel Fuel ProcessingExperimental Vs Predicted Values for Diesel ATR on Pd/Al2O3

R2 = 0.90

0.0015

0.0025

0.0035

0.0045

0.0015 0.0025 0.0035 0.0045

Experimental, [-dCHC/dt]

Pred

icte

d, [-

dCH

C/d

t]

-rHC=k0exp(-8260/T)CHC0.74CH2O

-1.07CO20.10

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Diesel Fuel ProcessingExperimental Vs Predicted Values for Diesel ATR on Ru/Al2O3

R2 = 0.72

0.0025

0.0035

0.0045

0.0055

0.0065

0.0075

0.0085

0.0095

0.0025 0.0035 0.0045 0.0055 0.0065 0.0075 0.0085 0.0095

Experimental, [-dCHC/dt]

Pred

icte

d, [-

dCH

C/d

t]

-rHC=k*exp(-4860/T)CHC0.50CH2O

-1.39CO2-0.03

Descriptor - include initials /org#/date

• Diesel-based 5-kWe fuel cell APU system with 45% -50% electrical conversion efficiency identified

• A prototype CFD model including all the key elements of ATR has been developed− Developed a model that accounts for fuel atomization and

vaporization, partial oxidation, steam gasification, and anode exhaust gas combustion

− Tested the convergence behavior of the model

• Laboratory Kinetic Experiments Conducted− Tested Pt, Pd, and Ru catalysts− Initial rate measurements made for hexadecane and diesel fuel

Diesel Fuel Processing2002 Results Accomplishments

Descriptor - include initials /org#/date

• Diesel-based 5-kWe fuel cell APUs are considered a significant high volume market for SOFC’s.

• Fundamental understanding of diesel reforming and general methodology for kinetic rate determination would be very beneficial to catalyst developers. May extend to hydrocarbon fuels in general.

• A validated CFD model would be useful to fuel reforming developers and system integrators to predict steady-state and transient performance, develop control strategies, maximize efficiency, and minimize cost.

Diesel Fuel ProcessingApplicability to SOFC Commercialization

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Diesel Fuel ProcessingFuture Plan

2002 2003 20062004 2005

PREDICTIVE CFD MODEL DEVELOPMENT FOR PREDICTIVE CFD MODEL DEVELOPMENT FOR DIESEL REFORMINGDIESEL REFORMING

- ValidateLEVEL 1 KINETIC MODELLEVEL 1 KINETIC MODELDEVELOPMENTDEVELOPMENT

LEVEL 2 KINETIC MODELLEVEL 2 KINETIC MODELDEVELOPMENTDEVELOPMENT - Validate

LEVEL 3 KINETIC MODELLEVEL 3 KINETIC MODELDEVELOPMENTDEVELOPMENT

DEVELOP KINETIC RATEDEVELOP KINETIC RATEMETHODOLOGYMETHODOLOGY

CONDUCT DESIGN & EVALUATION OF DIESEL REFORMING TECHNOLOGYCONDUCT DESIGN & EVALUATION OF DIESEL REFORMING TECHNOLOGY