© Fraunhofer IKTS

System Design and Process Layout for a SOFC µCHP-Unit with Reduced Operating TemperaturesThomas Pfeifer, Laura Nousch, Wieland Beckert

Fraunhofer IKTS, Dresden, Germany

European Fuel Cell 2001 – Piero Lunghi Conference & Exhibition

Rome, December 14-16, 2011

© Fraunhofer IKTS - 2 -

The Fraunhofer-Gesellschaft in Germany

60 Institutes more than 18,000 employees

München

Holzkirchen

Freiburg

Efringen-Kirchen

FreisingStuttgart

PfinztalKarlsruheSaarbrücken

St. IngbertKaiserslautern

DarmstadtWürzburg

Erlangen

Nürnberg

Ilmenau

Schkopau

Teltow

Oberhausen

Duisburg

EuskirchenAachenSt. AugustinSchmallenberg

Dortmund

PotsdamBerlin

Rostock

LübeckItzehoe

Braunschweig

Hannover

Bremen

Bremerhaven

Jena

Leipzig

Chemnitz

Dresden

CottbusMagdeburg

Halle

Fürth

Wachtberg

Ettlingen

Kandern

Oldenburg

Freiberg

Paderborn

Kassel

GießenErfurt

Augsburg

Oberpfaffenhofen

Garching

Straubing

Bayreuth

Bronnbach

Prien

Hamburg

Leuna

Fraunhofer-Headquartersin Munich

Fraunhofer-Locations in Germany

© Fraunhofer IKTS - 3 -

Profile of the Fraunhofer IKTS

Regular staff: 400 + student workers

Total budget (2010): € 31,7 m (w/o invest)

Industrial revenues: 38.9 %

Public research revenues: 46.6 %

Core financing: 14.5 %

Research facilities: 140 laboratories and pilot plants of approx. 20.000 m²

Dresden Hermsdorf (since 01/2010)

www.ikts.fraunhofer.de

© Fraunhofer IKTS - 4 -

CeramicMultilayer

BundledMicrotubes (ASC)

PlanarMini-Stack (ESC)

IntegratedStack-Module

IntegratedHotBox-Modules

1 W

Fuel Cell System Development Projects at the Fraunhofer IKTS

H2

PEFC

10 kW1 kW100 W10 W

eneramicby Fraunhofer

â

ButaneSOFC

LPGSOFC

Natural GasSOFC

BiogasSOFC

© Fraunhofer IKTS - 5 -

Level 1Process Layout

Chem. Equilibrium Studies,Stack Performance Maps,Idealized Energy Balances

Basic System Concept

System Specification (SRD)Process Flow Diagram (PFD)Process Design Parameters

Level 2ASystem ModelingMatlab / Simulink,Modelica / Dymola,SimulationX, C++

Level 2BMultiphysics & CFD

FlexPDE, COMSOL, Ansys, Fluent,

DiffPack

Component Design LoopSystem Design Loop

Level 3Controller DesignSimulink / Stateflow,Modelica.StateGraphStatechart Designer

System OperationLevel 4

Data Mining,Model Validation

Sub-Modules Assembly,Successive System Setup

Component Layout,Single Device Testing

Level 1Process Layout

Chem. Equilibrium Studies,Stack Performance Maps,Idealized Energy Balances

Basic System Concept

System Specification (SRD)Process Flow Diagram (PFD)Process Design Parameters

Level 2ASystem ModelingMatlab / Simulink,Modelica / Dymola,SimulationX, C++

Level 2BMultiphysics & CFD

FlexPDE, COMSOL, Ansys, Fluent,

DiffPack

Component Design LoopSystem Design Loop

Level 3Controller DesignSimulink / Stateflow,Modelica.StateGraphStatechart Designer

System OperationLevel 4

Data Mining,Model Validation

Sub-Modules Assembly,Successive System Setup

Component Layout,Single Device Testing

Multi-Level Simulation Supported System Development

Core Modules:sofc.dll prop.dllequi.dll

Development Tools:MS Excel, VBA, C++,Matlab / Simulink, Modelica / SimulationX

FEA:COMSOL Multiphysics,FlexPDE, ANSYS

CFD:Fluent, Ansys CFX

IKTS contributions to LOTUS

IKTS contributions to LOTUS

© Fraunhofer IKTS - 6 -

Preliminary LOTUS Design Studies0-D Stack-Model Parameterization (sofc.dll)

0,0

0,5

1,0

1,5

2,0

2,5

0 100 200 300 400 500 600 700

SOFCPower S-Design Short-Stack Performance

650°C (Test)

650°C (Model)

700°C (Test)

700°C (Model)

750°C (Test)

750°C (Model)

800 °C (Test)

800°C (Model)

Current Density jel / mA cm-2

Cel

l Are

a R

esista

nce

RA

cell/ W

cm2

No. of cells: 5 á 50 cm²Fuel: 100 % H2 (sat. @ 25 °C)Fuel input: 1.5 slm ≈ 270 J/sAir stoich. ratio: 4.2

3,0

3,5

4,0

4,5

5,0

5,5

6,0

0 100 200 300 400 500 600 700

SOFCPower S-Design Short-Stack Performance

650°C (Test)

650°C (Model)

700°C (Test)

700°C (Model)

750°C (Test)

750°C (Model)

800 °C (Test)

800°C (Model)

Current Density jel / mA cm-2

Stac

k Voltag

e U

/ V

No. of cells: 5 á 50 cm²Fuel: 100 % H2 (sat. @ 25 °C)Fuel input: 1.5 slm≈ 270 J/sAir stoich. ratio: 4.2

U/I-Measurements at varying temperature and fuel-input provided by SOFCPower.

Model parameters identified by least squares fit of area specific cell resistance.

© Fraunhofer IKTS - 7 -

Preliminary LOTUS Design StudiesStack Performance Estimation at 650 °C

Available Cell Technology: ASC70066 x 50 cm², CH4-SR Reformate

Fuel Input [J/s]

Sta

ck V

olta

ge |

Ave

rage

Cel

l Vol

tage

[V]

0.15

0.20 0.25 0.30 0.35 0.400.45

el

= 0.50

0.55

FU = 0.2

0.3

0.4

0.5 0.6 0.7 0.8 0.9

VAir,ad

=

100 Nl/min

200 Nl/min

300 Nl/min

PDC

= 400 W

600 W

800 W

1000 W

I = 5 A

10 A

15 A

20 A

25 A

500 1000 1500 2000 2500 3000 3500 4000 4500 5000

39.6 (0.60)

42.9 (0.65)

46.2 (0.70)

49.5 (0.75)

52.8 (0.80)

56.1 (0.85)

59.4 (0.90)

ASC700, S-Design (50 cm²), 66 Cells

Aact

= 66 x 50 cm² / TCell

= 650°C

TFuel

= 650°C / TAir

= 550°C

Fuel: CH

4-SR @ 650 °C, S/C = 1.5, = 0

7.2% CH4 / 60.6% H

2 / 14% H

2O

12.4% CO / 5.9% CO2 / 0% N

2

LHV = 238.98 kJ/mol

650 WDC @ 70% FUUCell = 0.7 V

Fuel Input [J/s]

Sta

ck V

olta

ge |

Ave

rage

Cel

l Vol

tage

[V]

0.20

0.25

0.30

0.35

0.40

0.45

el

= 0.50

0.55

0.60

0.65

FU = 0.2

0.3

0.4

0.5

0.6

0.7

0.8 0.9

VAir,ad

=

100 Nl/min

200 Nl/min

300 Nl/min

400 Nl/min

500 Nl/min

600 Nl/min

700 Nl/min

800 Nl/min

600 W

PDC

=

800 W

1000 W

1200 W

1400 W

1600 W

1800 W

2000 W

I = 10 A

15 A

20 A

25 A

30 A

35 A

40 A

45 A

50 A

400 W

500 1000 1500 2000 2500 3000 3500 4000 4500 5000

39.6 (0.60)

42.9 (0.65)

46.2 (0.70)

49.5 (0.75)

52.8 (0.80)

56.1 (0.85)

59.4 (0.90)

ASC700 +20%, S-Design (80 cm²), 66 Cells

Aact

= 66 x 80 cm² / TCell

= 650°C

TFuel

= 650°C / TAir

= 550°C

Fuel: CH

4-SR @ 650 °C, S/C = 1.5, = 0

7.2% CH4 / 60.6% H

2 / 14% H

2O

12.4% CO / 5.9% CO2 / 0% N

2

LHV = 238.98 kJ/mol

Expected Development: ASC700+20%

66 x 80 cm², CH4-SR Reformate

1550 WDC @ 70% FUUCell = 0.7 V

SOFCPower ASC700+20%

enables LOTUS-developmentSOFCPower ASC700+20%

enables LOTUS-development

© Fraunhofer IKTS - 8 -

Preliminary LOTUS Design StudiesPre-Evaluation of Fuel Reforming Options

Stack-Internal Reforming (IR)

Pre-Reforming

FuelFuelH2OH2O

IR-SOFC

FuelFuel

AirAirPOX SOFC

HeatHeat

FuelFuel

H2OH2OSR SOFC

HeatHeat

FuelFuel

H2OH2OATR SOFC

AirAir

Steam Refor-ming (SR)

AutothermalReforming (ATR)

Partial Oxi-dation (POX)

650 °C

POX

ATR

SR

800 °C

POX

ATR

SR

© Fraunhofer IKTS - 9 -

Preliminary LOTUS Design Studies Comparison of Basic System Concepts

ηel

ηth

No feasible technology for IR with anode off-gas recirculation is available.

SR shows electr. efficiency according to LOTUS development goals.

ATR shows higher total efficiency. RAPH is beneficial for electrical efficiency.

POX is not an option at 650 °C due to the risk of reactor overheating at soot-preventing air ratios.

loss

Steam Reforming (SR) is the best option for LOTUS-developmentSteam Reforming (SR) is the best option for LOTUS-development

mechfuel

CHPth PH

Q

mechfuel

Stackel PH

P

© Fraunhofer IKTS - 10 -

Boundary Conditions for the LOTUS System Design

Stack temperature predetermines reforming temperature 650 °C.

Soot-free reformer operation requires S/C ~ 2 .. 3.

In practical µCHP-operation a lower system S/C is essential.

For start-up and shut-down of ASC a reducing atmosphere > 300 °C is required.

Controlled stack-internal reforming (IR) is beneficial for system efficiency.

Part load operation and independent control of power to heat ratio is beneficial for system economics.

LOTUS system design is governed by the fuel reforming concept and its process integration.

LOTUS system design is governed by the fuel reforming concept and its process integration.

© Fraunhofer IKTS - 11 -

LOTUS System DesignProcess Flow Diagram (PFD)

Implementation of the LOTUS Fuel Reforming Concept

Downscaled steam reformer (SR)

SR directly heated by burner exhaust (AB or SB)

Fuel bypass (FBP) for controlled stack-internal reforming

Optional use of oxidative steam reforming

Air

Fuel

Exhaust

SOFCStack

APHAir Pre-Heater

ABAfter-burner

SRSteam Reformer

CHP-HxHeat Exchanger

WaterEVPEvaporator

Heat

Electricity=

~

SBStart-up-Burner

FBPFuel Bypass

© Fraunhofer IKTS - 12 -

LOTUS System DesignBalance Sheet & Process Layout Calculations

Interactive Process Calculation Sheets in Microsoft Excel

Added Functionality through Visual Basic UDFs and Macros

Parameterized SOFC Stack Model: sofc.dll

Thermophysical Properties: prop.dll

Chemical Equilibrium Calculations: equi.dll

© Fraunhofer IKTS - 13 -

LOTUS System DesignSystem Performance Estimation

Thermal Insulation

3202,9 J/sAir: 22,9 J/s

15

,8 J/s

16

0,4

J/s

Fuel Input

Fuel Bypass

SteamReformer

SOFC Stack

Air Pre-Heater

Evaporator

3023,1 J/s

S/C = 3

ch: 3319,7 J/sth: 249 J/s

Air: 3042,5 J/s

t_Air = 550 °C

7,5 Nl/min

H2O Phase Change

283,9 J/s= 9,3 %

After-burner

ch: 1118,1 J/sth: 393,3 J/sAir: 3541,5 J/s

Inverter

CHP-Hx

10

0,1

J/s

520,3 J/s

Steam: 32,9 J/s

1511,5 J/s

316,8 J/s

H2O-Pump

Air-Fan251,1 Nl/min

366,6 g/h

Water: 0,1 J/s

Exhaust

229,6 J/s = 7,5 %

670,1 J/s

11

3,9

J/s

1467,3 W

Usable Heat

= 20,9 %637 J/s

33

,5 J/s

ch: 1825,3 J/sth: 230,9 J/s

10

,1 J/s

FU = 70 %

Net ElectricalPower

= 42,6 %1296,3 W

AuxiliaryPower= 3,2 %97,6 W

73

,4 J/s

ThermalLosses= 16,7 %507,2 J/s

LOTUS Process LayoutSOFCPower ASC700 + 20% Performance GainExternal Steam Reforming @ 50% Fuel Bypass

Data: LOTUS_ProcCalculation_ASC+20.xlsm, 09/2011Reference Conditions of Enthalpies: p = 101325 Pa, T = 15 °C

Thermal Insulation

3202,9 J/sAir: 22,9 J/s

15

,8 J/s

16

0,4

J/s

Fuel Input

Fuel Bypass

SteamReformer

SOFC Stack

Air Pre-Heater

Evaporator

3023,1 J/s

S/C = 3

ch: 3319,7 J/sth: 249 J/s

Air: 3042,5 J/s

t_Air = 550 °C

7,5 Nl/min

H2O Phase Change

283,9 J/s= 9,3 %

After-burner

ch: 1118,1 J/sth: 393,3 J/sAir: 3541,5 J/s

Inverter

CHP-Hx

10

0,1

J/s

520,3 J/s

Steam: 32,9 J/s

1511,5 J/s

316,8 J/s

H2O-Pump

Air-Fan251,1 Nl/min

366,6 g/h

Water: 0,1 J/s

Exhaust

229,6 J/s = 7,5 %

670,1 J/s

11

3,9

J/s

1467,3 W

Usable Heat

= 20,9 %637 J/s

33

,5 J/s

ch: 1825,3 J/sth: 230,9 J/s

10

,1 J/s

FU = 70 %

Net ElectricalPower

= 42,6 %1296,3 W

AuxiliaryPower= 3,2 %97,6 W

73

,4 J/s

ThermalLosses= 16,7 %507,2 J/s

LOTUS Process LayoutSOFCPower ASC700 + 20% Performance GainExternal Steam Reforming @ 50% Fuel Bypass

Data: LOTUS_ProcCalculation_ASC+20.xlsm, 09/2011Reference Conditions of Enthalpies: p = 101325 Pa, T = 15 °C

Thermal Insulation

3202,9 J/sAir: 22,9 J/s

15

,8 J/s

16

0,4

J/s

Fuel Input

Fuel Bypass

SteamReformer

SOFC Stack

Air Pre-Heater

Evaporator

3023,1 J/s

S/C = 3

ch: 3319,7 J/sth: 249 J/s

Air: 3042,5 J/s

t_Air = 550 °C

7,5 Nl/min

H2O Phase Change

283,9 J/s= 9,3 %

After-burner

ch: 1118,1 J/sth: 393,3 J/sAir: 3541,5 J/s

Inverter

CHP-Hx

10

0,1

J/s

520,3 J/s

Steam: 32,9 J/s

1511,5 J/s

316,8 J/s

H2O-Pump

Air-Fan251,1 Nl/min

366,6 g/h

Water: 0,1 J/s

Exhaust

229,6 J/s = 7,5 %

670,1 J/s

11

3,9

J/s

1467,3 W

Usable Heat

= 20,9 %637 J/s

33

,5 J/s

ch: 1825,3 J/sth: 230,9 J/s

10

,1 J/s

FU = 70 %

Net ElectricalPower

= 42,6 %1296,3 W

AuxiliaryPower= 3,2 %97,6 W

73

,4 J/s

ThermalLosses= 16,7 %507,2 J/s

LOTUS Process LayoutSOFCPower ASC700 + 20% Performance GainExternal Steam Reforming @ 50% Fuel Bypass

Data: LOTUS_ProcCalculation_ASC+20.xlsm, 09/2011Reference Conditions of Enthalpies: p = 101325 Pa, T = 15 °C

© Fraunhofer IKTS - 14 -

LOTUS Parameter StudiesEfficiencies at Varying Fuel Bypass Ratio

Parameter variation:

Bypass Ratio () = 0 .. 1

System-S/C = 1.5 .. 5

Effect of : ηSys

Effect of System-S/C : ηSys

Independent: ηel ~ constant

Fuel

FBP

n

n

© Fraunhofer IKTS - 15 -

LOTUS Parameter StudiesReformate Quality at Varying Fuel Bypass Ratio

FBP-Implications:

Option for controlled stack-internal reforming: x’CH4 = 8 .. 33 Vol.-%

Anode inlet temp. decreases due to mixing and chemical equilibrium.

Recommended Fuel Bypass Ratio: = 0.5 at S/Ctot = 1.5 (S/Cref = 3)

Fuel

FBP

n

n

© Fraunhofer IKTS - 16 -

LOTUS Parameter StudiesProcess Control Options

↓ SR ATR ↓

Efficiency-Shift by oxidative steam reforming:

Reduced reformer heat demand due to partial oxidation of fuel.

Effect of λREF : ηth , ηSys , ηel

At λREF > 0.325: ATR-point

with steam supply, further increase of λREF only with

liquid H2O.

© Fraunhofer IKTS - 17 -

LOTUS Parameter StudiesProcess Control Options

-Control by oxidative steam reforming:

Effects of λREF :

CHP-heat production

Reformer heat demand 0

σ-Shift: 2.2 1

Cell voltage increases due to changed fuel composition.

σ

CHP

net

Q

P

© Fraunhofer IKTS - 18 -

Conclusions & OutlookModelling and Simulation Tasks in the LOTUS-Project

Deliv. Description Status

D 3.1 System Requirements Document as developed during a joint SRD-Workshop, hosted by IKTS

finished06/2011

D 3.2 Prerequisites & Parameter Studies for principal System Design Decisions, presented and discussed at a joint Workshop (MS4)

finished09/2011

D 3.3 Steady State Process Layout with Mass Flow & Energy Balance Sheet (Excel) based on an agreed Process Flow Diagram (PFD)

finished09/2011

D 3.4 Dynamic Process Model in Modelica / SimulationX, first used for detailed recalculation of steady state operation at rated conditions

starting02/1012

D 3.5 Finite State Machine in Modelica StateChart Designer (MiL) for Control Logic Development and Virtual System Start-up

t.b.d.

© Fraunhofer IKTS

Thanks for your attention!

Thomas Pfeiferthomas.pfeifer@ikts.fraunhofer.de

Fraunhofer Institute for Ceramic Technologies and Systems IKTSWinterbergstraße 28, 01277 Dresden, Germany

www.ikts.fraunhofer.dewww.lotus-project.eu