Fuel Cell System Integration

1
Fuel Cell System Integration
2
Synthesis and Design

• Synthesis determine the components to use and
  their relationship to each other
• Design determine the conditions at which the
  various components will operate

3
FC System Synthesis Decisions

• Fuel cell type
• Choices PEMFC, DMFC, PAFC, MCFC, SOFC
• Factors to consider - cost, efficiency, operating
  temperature, available fuel
• Fuel cell stack configuration
• Number and size of cells
• Cooling design
• Assembly of cells into stacks or sub-stacks
• Fuel reformer
• Type of reformer
• Choices - Steam reforming, partial oxidation,
  autothermal
• Factors to consider - Source fuel, desired exit
  gas composition, efficiency vs. complexity,
  weight, cost, etc.
• Reformate clean-up components
• Choices shift reactors, PROX, membrane
  separation, PSA
• Factors to consider cost, efficiency, desired
  composition

4
FC System Synthesis Decisions (continued)

• Integration of stack and reformer external,
  internal indirect, internal direct
• Air compressor - compressor type (screw or
  centrifugal), intercooler
• Heat exchanger network type, location
• Exit gas components condensers, turboexpanders,
  heat exchangers
• Bottoming cycle equipment
• Gas turbine
• Steam power cycle

5
FC Design Decisions - Voltage

• Stack operating voltage

6
FC Design Decisions - Pressure

• Higher operating pressure yields
• Increased reactant concentration increased
  electrochemical kinetics higher Nernst voltage
• Higher efficiency and/or current density
• Reduced system size
• Reduced humidification requirements
• Higher parasitic power requirements
• Higher likelihood of soot formation in reformer
• Reduced degree of reaction for steam reforming
• Higher corrosion rates at cathode (MCFC)

7
FC Design Decisions - Utilization

• Higher fuel utilization (lower equivalence ratio)
  yields
• Reduced fuel use within the stack
• Reduced fuel processing system size, cost
• Lower cell voltage
• Higher stack cost
• Less exit gas for application in bottoming cycle
• Higher oxidant utilization (lower equivalence
  ratio) yields
• Reduced compressor power
• Reduced air system size, cost
• Reduced humidification requirements
• Lower cell voltage
• Higher stack cost

8
FC Design Decisions Temperature

• Higher operating temperature yields
• Increased operating voltage
• More flexible thermal integration
• Less exotic catalyst and resistance to poisoning
• Higher quality rejected heat
• Increased corrosion potential (especially PAFC,
  MCFC)
• Longer warm-up and higher thermal stress
• Increased complexity

9
FC Design Decisions Etc.

• Higher reactant humidification yields
• Higher cell voltage (PEMFC)
• Higher resistance to carbon formation in reformed
  fuels
• Increased cost of water (or equipment to condense
  from exit stream)
• Increased capital cost and complexity
• Potential for flooding
• Increased size (and number) of heat exchangers
  yields
• Improved quality and quantity of thermal energy
  available
• Better system integration possibly improving
  overall electrical efficiency
• Increased cost