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Fuel Cell 101
Don HoffmanDon Hoffman Ship Systems &
Engineering Research Division
March 2011
Distribution Statement A: Approved for public release; distribution is unlimited.
Fuel Cell Operation
• A Fuel Cell is an electrochemical power source
• It supplies electricity by combining hydrogen and oxygen electrochemically without combustion.
• It is configured like a battery with anode and cathode.
• Unlike a battery, it does not run down or require recharging and will produce electricityand will produce electricity, heat and water as long as fuel is supplied.
2H+ + 2e- O2 + 2H+ + 2e- 2H2OH2
Distribution Statement A: Approved for public release; distribution is unlimited. 2
FUELFUEL
CONTROLS
Fuel Cell System
HEAT & WATER CLEANCLEAN EXHAUSTEXHAUST
USEFUL HEAT
POWERPOWER SECTIONSECTION
POWERPOWER CONVERSION /CONVERSION / CONDITIONINGCONDITIONING
HYDROGENHYDROGEN RICH GASRICH GAS
POWER POWER
TO APPLICATION
FUELFUEL PROCESSINGPROCESSING
Distribution Statement A: Approved for public release; distribution is unlimited. 3
Fuel Cell System
HEAT & WATER CLEAN EXHAUSTCLEAN EXHAUST
USEFUL HEAT
POWERPOWER SECTIONSECTION
POWERPOWER CONVERSION /CONVERSION / CONDITIONINGCONDITIONING
HYDROGENHYDROGEN RICH GASRICH GAS
FUELFUEL POWER POWER
TO APPLICATION
FUELFUEL PROCESSINGPROCESSING
CONTROLS
Distribution Statement A: Approved for public release; distribution is unlimited. 4
Fuel Cell Types
Electrolyte Cell Temp
Proton Exchange Membrane (PEM)
Polymer Membrane (Solid)
70-90 C
Phosphoric Acid Phosphoric Acid (PAFC)
Phosphoric Acid Phosphoric Acid (Liquid)
120 180 C 120-180 C
High Temp PEM (HTPEM)(HTPEM)
Phosphoric Acid Polymer (Solid) Polymer (Solid)
120-180 C
Molten Carbonate (MCFC)
Potassium Lithium Carbonate (Liquid)
650 C
Solid Oxide (SOFC) (Tubular, planar)
Solid Zirconium Oxide Ceramic
(Solid)
700-950 C
Distribution Statement A: Approved for public release; distribution is unlimited. 5
e o ate
Fuel Cell Types
Electrolyte Cell Temp Fuel
Proton Exchange Membrane (PEM)
Polymer Membrane (Solid)
70-90 C Pure Hydrogen
Phosphoric Acid Phosphoric Acid (PAFC)
Phosphoric Acid Phosphoric Acid (Liquid)
120 180 C 120-180 C Hydrogen Hydrogen rich
reformate
High Temp PEM (HTPEM)(HTPEM)
Phosphoric Acid Polymer (Solid) Polymer (Solid)
120-180 C Hydrogen richrich
reformate
Molten Carbonate (MCFC)
Potassium Lithium Carbonate (Liquid)
650 C Methane rich
reformate
Solid Oxide (SOFC) (Tubular, planar)
Solid Zirconium Oxide Ceramic
(Solid)
700-900 C Hydrogen rich
reformate
Distribution Statement A: Approved for public release; distribution is unlimited. 6
NC
Y
Polarization Curve Polarization or Operational Voltage, V, Curve
geC
ell V
olta
g
E EF
FIC
IE
C
NC
REA
SEIN
Theoretical EMF or Ideal Voltage Theoretical EMF or Ideal Voltage 1.23
TARGET OPERATION 1.0
Region of Concentration Region of Concentration Polarization (mass transport limited)
0.5 (resistance loss)
Region of Activation Polarization (reaction rate loss)
Region of Ohmic Polarization
Current Density (mA/cm^2)
INCREASE POWER DENSITY
Distribution Statement A: Approved for public release; distribution is unlimited. 7
Fuel Cell System
HEAT & WATER CLEANCLEAN EXHAUSTEXHAUST
USEFUL HEAT
POWERPOWER SECTIONSECTION
POWERPOWER CONVERSION /CONVERSION / CONDITIONINGCONDITIONING
HYDROGENHYDROGEN RICH GASRICH GAS
FUELFUEL POWER POWER
TO APPLICATION
FUELFUEL PROCESSINGPROCESSING
CONTROLS
Distribution Statement A: Approved for public release; distribution is unlimited. 8
Fuel Reforming
• Fuel Reforming refers to processes that change the fuel from a liquid hydrocarbon to a gas-phase, fuel-rich, streamstream – Fuel Reforming is an endothermic process – Heat is required to sustain the reaction
• Several processes exist; most practical ones are: – Partial Oxidation Reforming (with air) – Steam Reforming (with steam) – Autothermal Reforming (with air and steam)
• Water Gas Shift is an equilibrium reaction, used to convert Carbon Monoxide and Steam into Carbon Dioxide and additional Hyydroggen
Distribution Statement A: Approved for public release; distribution is unlimited. 9
t t t
Partial Oxidation Reforming
Delphi POX Reformer
Output CO HH2 N2
• Air reacts with fuel to form Carbon Monoxide and Hydrogen. • Heat is supplied by oxidizing a portion of the fuel inside the reformer.
P Si l di b ti f hi h d i hi h i• Pros: Simple adiabatic reformer, high power density, high contaminant tolerance, no steam required
• Cons: Low efficiency, susceptible to soot formation, low pressure operation, nitroggen dilution of the pproduct fuel
C8H18 + 4 (O2 + 3.8 N2) → 8 CO + 9 H2 + 3.8*4 N2 Distribution Statement A: Approved for public release; distribution is unlimited. 10
Steam Reforming
O t tOutput CO H2
PCI High Density Steam Reformer
• Steam reacts with fuel to form Carbon Monoxide and Hydrogen. • Heat is supplied by burning fuel external to the reformer, through heat exchange
•Pros: High efficiency, capable of high pressure, air compression not required, fuel not diluted by nitrogen •Cons: Higher complexity, low power density, scalability, low contaminant tolerance high steam flow high temperature heat exchange tolerance, high steam flow, high temperature heat exchange
Distribution Statement A: Approved for public release; distribution is unlimited.
C8H18 + 8 H2O → 8 CO + 17 H 2 11
Autothermal Reforming
Output COCO H2 N2
PCI 250kW Autothermal Reformer
• Combines partial oxidation with steam reforming. Air and Steam react with fuel to form Carbon Monoxide and Hydrogen.
• Heat is supplied by oxidizing a portion of the fuel inside the reformer.
• Pros: Adiabatic operation, greater efficiency than POX, high power density,contaminant tolerance
• Cons: Higher complexity control, requires steam and air, nitrogen dilutes the fuel stream
C8H18 + 3.6 (O2 + 3.8 N2) + 0.8 H2O → 8 CO + 9 H2 + 13.7 N2 Distribution Statement A: Approved for public release; distribution is unlimited. 12
Water Gas Shift Reaction
OutpputInpput CO2
CO H2 H2
H2O
Water Gas Shift Reactor
• Steam reacts with Carbon Dioxide to form Carbon Monoxide and increased H d Th ti i li htl th iHydrogen. The reaction is slightly exothermic.
• Hydrogen yield is limited by temperature kinetics and equilibrium
• Pros: Simple adiabatic reactor increases hydrogen yield from all types of • Pros: Simple adiabatic reactor, increases hydrogen yield from all types of reformers, hydrogen yield better at lower temperatures.
• Cons: Low power density, requires additional steam, low contaminant tolerance, poor kinetics at low temperature
Distribution Statement A: Approved for public release; distribution is unlimited.
CO + H2O → CO2 + H2 13
t t
Membrane Separation Output CO2
Inpput Outpput CO2 H2 H2P&E Pd Membrane
• Palladium-alloy membranes can be used to separate pure Hydrogen from a Hydrogen-rich reformate stream M h i i l diff i f h d th h h lid b• Mechanism involves diffusion of hydrogen atoms through the solid membrane metal. Produces high-purity hydrogen
• Hydrogen yield is limited by the difference in hydrogen gas partial pressure across the membrane
• Pros: Simple reactor, no moving parts, makes ultra high purity hydrogen, lowpower requirements C E i t i l hi h f i i ld • Cons: Expensive materials, high pressure reformers increase yield
Distribution Statement A: Approved for public release; distribution is unlimited. 14
Heavy Vehicle Heavy Vehicle
Commercial Commercial MarineSmall Marine
Residential, A i
Electronics Industrial, Dist. Gen
.01 .1 1 10 100 1,000 10,000
, APU Automotive Locomotive
SOFC MCFC
POWER (kWe)
PEM/HT PEMFC
SOFC Multiple Modules
PAFC DMFC
UV/S ll C ft/ Soldier Power
Ship Service , Large MEP
Vehicles, Small MEPPortable
PowerMilitary
UV/Small Craft/ Submersible
Distribution Statement A: Approved for public release; distribution is unlimited. 15
Fuel Cell Benefits
Reduced Acquisition & Life Cycle Costs • Greater System Efficiencies •• Reduced Maintenance CostsReduced Maintenance Costs • Enables Spiral Development
Enhanced Survivability • Reduced IR Signature • Reduced Acoustic Signature • Distributed Power Generation
Design Flexibility • Modular Approach to Ship Power • Multi Platform Applicable
Distribution Statement A: Approved for public release; distribution is unlimited. 16
Power Generation TechnologiesEEl
ectr
iccal
Effi
ccien
cy (%
) 70
60
50
40
30
20
1 10 100 1000 10000
Power (kW)
Fuel Cells MCFC
PAFC
Cells
Even at It’s Infancy, Fuel Cell System Efficiency Starts Where the Other Technologies End
Distribution Statement A: Approved for public release; distribution is unlimited. 17
Airborne Noise Diesels
Gas TurbinesGas Turbines
1st Generation SSFC Module (w minimal isolation)
Airborne noise: Sound intensity level (dB) in engine room corrected to 10 feet distance
Distribution Statement A: Approved for public release; distribution is unlimited. 18
Emission Comparison (gm/kw Hr @ 100% Power) CO2 NOCO2 NOx
17 3 986
8.0
17.3
687 550
<0.001
8.0
SSFC DDG51 AOE 6 SSFC DDG51 AOE 6 GTG SSDG GTG SSDG
• Fuel Cells have higher efficiency, with correspondingly lower CO2 emissions.
• Fuel cells are not a combustion process, so they have greatly reduced NOx, CO, hydrocarbon, and particulate emissions.
• Low SO2 output is a function of higher efficiency and low/no sulfur in fuel
Power Generation Technologies Volumetric Density Comparison
70
60
50
40
30
20
10 1 10 100 1000 10000
X
MULTI MODULE
PA & MCFC
Power (kW) Fuel Cell System Volumetric Density Dependent on Overall
System Design
Volu
met
ric D
eensi
ty ww
/l