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Fuel cell gas turbine hybrids – akey part of a clean futureThe Rolls-Royce development programmefor pressurised hybrid fuel cell systemsRobert Cunningham – Fuel Cells Group

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Team

GD Agnew1, CN Berns1, SA Ali2, RR Moritz2, P Butler1, E Dean1

C Burrows1, RD Collins1, RH Cunningham1, N Hart1, MJ Oakley1,M Pashley1, N Lapeña-Rey1, R Scholes1, O Tarnowski1,D Wastie1, R Woodburn1 , G Wright1

� Rolls-Royce Strategic Research Centre, Derby, UK� Rolls-Royce, Indianapolis, USA

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Overview

The Rolls-Royce vision of pressurised hybrids� Pressurised hybrids� Reducing $/kW for SOFC in general� Benefits of pressurised operation at high temperature� Comparison of atmospheric and pressurised systems

Progress towards the vision� System and turbogenerator development� Stack module development� Internal reforming

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High temperature fuel cell hybrids� Air side of fuel cell enclosed in gas

turbine– Fuel cell at pressure but separate

flow� Recuperator (Heat exchanger)

allows air in to be heated by air out� Heat from fuel cell provides

compression for free� High efficiency (60-70%)

– Supports capital cost differencefrom conventional plant (GTs etc)

Simple pressurised SOFC/GT hybridshowing air side flows only

OUT

IN

PowerElectronicsSOFC

Recuperator(HX)

AlternatorAir in Exhaust

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Two ways to reduce $/kW

Reduce $� Improve system integration

– Purpose-designed andintegrated components can bespec’d to suit fuel cell

� Early fuel cell demonstratorshave used process industryplant

– General purpose componentsare over-spec’d for specific fuelcell application

� Reduce stack size and weight– Reduces overall system size,

weight and cost

Increase kW� Increase stack efficiency� Increase stack power

– Increasing cell current densityrequires greater flows

– Increased current also incursgreater I2R losses andreduces efficiency

� Increase system power andefficiency

– Pressurised hybrid has higherpower and efficiency than rawstack

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Cost reduction with SOFC systems in general� SOFC can use cheap electrode

materials– High temperature chemistry has

fast kinetics� Anode exhaust provides water

for reforming– No need for elaborate water

management/humidification� Easy to use heat output from

stack– 800+°C difference with ambient

makes thermal managementsimple

� Hard to poison high temp stack– System simplified – no need to

backup fuel processingcomponents

– Thrives on CO– Happy with CO2, NH3

� Simple fuel processing -Internal reforming benefits

– No need for water gas shiftreactors or selective oxidiser

– Close integration of fuelprocessing cuts cost

– Internal reforming providessignificant portion of stackcooling

� Affordable fuel flexibility– Can accommodate wide range

of CO / H2 mixtures

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Pressurised and atmospheric compared

� Identical stack in pressurisedand atmospheric configurations

– Near term SOFC stack– Underlying stack efficiency 50%– System efficiency exceeds

stack efficiency for pressurisedcase

� $/kW better by 680/1050 = 0.65at pressure if $ cost identical

– Atmospheric recuperator mustbe exotic material

– Pressurised recuperator can bestainless steel

576871Recuperator

hot inlettemp °C

1051684Net powerkW

67%44%EfficiencyNet AC LHV

Press’dAtm

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Turbomachinery cheaper than heat exchanger

� Incoming flows can beheated by

– Heat exchanger– Compression in

turbomachinery� Fuel cell exhaust can be

brought down in temperatureby

– Heat exchanger– Expansion in turbine

� Heat exchange is lowvelocity process (m/s)

– Large amounts of metal perunit massflow

� Turbomachinery uses highvelocities (300+m/s)

– Very small amounts of metalper unit massflow

– Lower cost than heatexchange especially for hightemperatures

– Materials used in turbinesare unaffordable in heatexchanger quantities

� Turbocharging of fuel cellprovides blower function

– Work for compressor comesfrom fuel cell waste heat

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Progress towards the vision

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System and turbogenerator development

� EU IM-SOFC-GT project– Integrated modelling– Concept definition– Started Feb 2001

� Specialised turbomachineryconcept development beingpursued at Indianapolis

– Oil-free turbogeneratorconcepts

– Interim results from USDOE funded hybrid turbinedevelopment reported inASME Turbo 2001†

Two-stageaxial turbineMagnetic

radialbearing

High speedDirect drivealternator

Aeroderivativeradial

compressor

MagneticThrust bearing

† S.A. Ali and R.R Moritz, A Turbogenerator for Fuel Cell/Gas Turbine Hybrid Power Plant

Novel oil-free turbogenerator conceptfrom DOE hybrid turbine programme

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� RR established IP-SOFC stackprogramme 9 years ago

– World leading stack concept– Strong on manufacturing cost

� Focus now on stacks and systems– Optimise for overall performance– Results are for stacks

– Not just cells� Leading EU programmes

– MF-SOFC– Stack development

– IM-SOFC-GT– Integrated modeling and concept

design of hybrids� Participating in EU programme

– CORE– Component Reliability

IP-SOFC stack modules

Integrated Planar SOFC (IP-SOFC)

SingleIP-SOFC

cell

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1 kW class stack operated in August 2000

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1 kW stack on test at Derby (August 2000)

� 828W output achieved on 97% hydrogen� Total power from individual elements operated individually 960W

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European Union MF-SOFC project

� Stack development to 20kW� Atmospheric demonstration� Largest SOFC stack

development programme in EUFramework 5

– €9M gross funding to 2003

� Partners:RisøGaz de FranceImperial CollegeACLUK DTI support

� DG Research– Gilles Lequeux

� 5th Framework Programme� Energy, environment and

sustainable development

� Only short selection ofinterim results presentedhere focussing onRolls-Royce contribution

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Revised stack design� Addresses issues raised in 1kW

stack� Uses novel Rolls-Royce concept for

a pressurised stack� Thin tubes

– x3 on kW/litre – improves systemcost significantly

– Improved heat and mass transfer� New manifolding design based on

bundles– Much improved compliance and

potential leakage– Improved flexibility on internal

reforming– x10 reduction in manifolding 40 cell modules (new design)

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Improved mass transfer

� No mass transfer tail-off seen– Down to limiting 0.5V– With dilute H2 and low flows

� Analysis indicates 75% utilisation achieved in correspondinganode recirculation scheme down to current under 300mA/cm2

Effect of Flowrate 40% H2 60% N2 3% H2O

0

1

2

3

4

5

6

7

8

0 1 2 3 4 5

Module Current /A

Mod

ule

Volta

ge /V

2 N l /min

3 N l /min

4 N l /min

5 N l /min

Effect of Flowrate 40% H2 60% CO2 3% H2O

0

1

2

3

4

5

6

7

0 1 2 3 4

Module Current /A

Mod

ule

Volta

ge /V

2 N l /min

3 N l /min

4 N l /min

5 N l /min

Results shown for short 14 cell modules with7 cells in series at 900°C (June ’01)

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Successful operation on methane

� DTI internal reformingproject

� Reformer based on flat tubein flow-series with short MF-SOFC module

� Module run on methanemixture corresponding tooperation with re-circulatinganode stream

14 cell short module with internalreforming unit (behind)

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Conclusions 1

� Pressurised fuel cell hybrid costs benefit directly andindirectly from pressurisation

� $/kW potential for hybrids exceeds that of atmospheric units– Cost of GT and pressure vessel paid for by other savings

� Pressurised hybrids have greater potential to exploit benefitsof mature fuel cell technology

– Can fully exploit increases in power density (kW/litre) to reduceoverall system cost

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Conclusions 2� World-class results from Rolls-Royce stack development

programme– 1kW stack operation– Operation of new Rolls-Royce stack design– 300W/litre at $300/kW (100MW pa)– At intended operating current:

– 75% fuel utilisation– Under 2%/1000hrs degradation

– Operation on methane mixture� Funding from the following sources is gratefully

acknowledged– European Union– US Department Of Energy– UK Department of Trade and Industry