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. Higher first cost Higher efficiency Lower operating cost V Lower first cost Lower efficiency Higher operating cost i 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