Mesoscopic Devices

Demonstration of a 75 W portable SOFC generator

Jerry Martin—Mesoscopic Devices, LLCTad Armstrong—MSRI

Anil Virkar—Univ. of Utah

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OutlineWhy portable SOFC?System designStack requirementsPerformanceNext generation 250 W generator

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Why portable SOFC’s?Operation on hydrocarbon fuels

High energy density fuel>3X advantage over methanol or hydridesSafe, readily available fuels

Simple fuel reformingCPOX is small, fast, lightweight

Quieter than IC-engine generatorsLighter than batteries

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SOFC advantagesQuiet

<52 dBAUndetectable at 10 m outside

Good fuel efficiencyEstimated 3160 W-hr/kg fuel (~26%)

CompactLunchbox size, ~3 kg

High peak-to-average power ratiosVia battery hybridization.

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SOFC advantages (cont’d.)Common fuels

Propane, kerosene todayGasoline and diesel with development

Operation in wide range of ambient conditionsHigh specific energy compared to batteries

Up to 2000 W-hr/kgBetter than batteries for periods longer than 12 hours

Long periods between maintenance500 hours is a reasonable near-term goalUp to 2000 hours with development

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SOFC challengesSlow startup and shutdown(current generation)

~1 hour to power delivery~1 hour for safe shutdown Not suitable for frequent start-stop cycles

Limited sulfur tolerance Sulfur must be reduced to ppm levels in fuel

Some degradation with thermal cycling

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75W for 5 days

Left: BA-5590’sMiddle: MesoGen 75Right: fuel for MesoGen

Battery weight: 40 kgCost: >$4000Generator + fuel weight: 6 kg

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System configurationFuel options

PropaneDesulfurized keroseneFuel supply subsystem is only change

Optimized for multi-day missions:Direct power for communications equipmentBattery charging

12 or 24 V DC options

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Block diagram

Air blower Stack

+-

Fuel tank(liquid)

fuelpump

Insulation

recuperator

vaporizerpower

conditioning

partialoxidation

tail-gascombustor

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CPOX implicationsSimplest reformerNo water to recover or carryMillisecond contact time design leads to very small reformersFast start, fast response

Leads to dilute anode stream 25% H2, 21% CO47% N2, 6% H2O+CO2

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System integrationBOP components demonstrated to> 1000 hrs between maintenanceControl system

Steady state controlFully automated startup and shutdown

Battery hybridization provides peak power capability

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Integrated 75 W system

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System integration challengesAccurate fuel and air metering at minimum weight, size and power drawAir blower power draw, lifetimeStack performance at high fuel utilization

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Mass breakout: 75W system

Fuel 1.8-6 kg

Stack 0.7 kg

BOP 2.3 kg

3 day mission, 75W 10 day mission, 75W

Weight Distribution (Wet)

fuel71%

stack8%

BOP21%

Weight Distribution (Wet)

fuel42%

stack16%

BOP42%

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Stack requirementsHigh volumetric power densityHigh fuel utilizationHigh cell voltage

Must simultaneously achieve all three for lightweight, efficient system

Critical parameters:Stack power density >400 W/LStack specific power > 100 W/kgLow dP, <0.5 psi (3 kPa)

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Stack performance requirements

High performance on dilute reformate stream (~50% (H2 + CO), 50% N2)Multiple thermal cyclesLight weight (including compression hardware, headers, etc.)

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Planar stacks17 cells16 cm2 active area0.7 kg / 0.2 liters64 x 64 x 47 mm~450 W/liter at operating conditions12 V / 7.5 A / 90 W

1.8 in.

47 mm

2.5 in.

64 mm

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Stack power curve50% H2 in N260% fuel util.40% air util.

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75 W system75 W net for battery charging130 x 180 x 250 mm5 x 7 x 10 inches

3.0 kg dry, 6.6 lb0.8 liters of fuel per day6 kg fuel, 13.2 lb for 10 days~2000 W-hr/kg @ 10 days

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TemperaturesStack temperature ~ 800 CCase temperature ~ 60 CExhaust gas ~ 120 C

250 W dissipation

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System load curve

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propane5-17-2005

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Parasitic loads

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Effect of hybridization

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Heat-up data

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Gross and net power

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stack starts to carry internal loads (42 min)

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load power

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Addressing challengesChanges for future systems

Tubular stacksTighter integration

Leads toShorter startup timesHigher power density

Air supply system changesLengthen maintenance interval

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Hot zone integrationTight integration in the hot zone is critical75 W system

Planar stacksVolume: 700 ml

250 W systemTubular stacksVolume : 1265 ml85% increase inhot zone volumetricpower density

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Tube test resultsSimulated CPOX60% fuel util.Ø10 mm

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AcknowledgementsThis work was supported by

US Defense Advanced Research Projects Agency (contract MDA972-03-C-0060) Office of Naval Research (contract N00014-05-C-0051)