Planar and Tubular Solid Oxide Fuel Cells

 

Dynamic Simulation Approach

Modular Approach:

Individual simulation modules for each fuel cell type

• Tubular SOFC
  
• Planar SOFC
  
• MCFC
  
• PEM
  

Reformer module
Gas turbine module (compressor and turbine sub-modules)
Combustor module
Catalytic oxidizer module
Heat exchanger module
Humidifier module
Condenser module
Pumps, valves, regulators, plumbing, and other balance of plant (BOP)

Standardized Framework For Dynamic Modeling & Controls

• Collaboration between Control group (Prof. F. Jabbari) and Dynamic Simulation (Prof. S. Samuelsen, J. Brouwer, …)
• MATLAB and SimulinkTM Framework Chosen
• User friendly package by MathWorks (Matlab)
• Flexibility
  • Prepackaged modules
  • Object oriented
  • Easy to learn and use
  • Hardware extensible
  • Transferable to other software
• Natural for adding controls development and power electronics

Previous Module Development

Reformer, SOFC, MCFC, PEM, Gas Turbine

General Model Assumptions

• 1D process flow
  
• Well-stirred within nodal volume
  
• Slow pressure transients

Fuel Cell Assumptions

• H2 electrochemically oxidized only
  
• CO consumed via water-gas shift
  
• Shift always at equilibrium (constraint)
  
• Equipotential: V_cell = V_{node 1} = V_{node n}

Dynamic Model Basic Equations

Equation of State       

• Calculates changes in mole fraction based on inlet molar flows and reaction rates

Dynamic Model Basic Equations

Energy Conservation

• Gaseous     
  
  
  
  
  
• Solid        

 

Heat Transfer

• Conduction
  
• Axially from node to node through solids
  
• Between nodal materials (bipolar plates, electrodes, …)

Convection

• Between surfaces and gases
  
• Based on Nusselt number

Radiation

• From surface to surface
  
• Geometry is an issue
  
• Concentric cylinders: TSOFC
  
• Parallel planes: PSOFC
  
• Other: combustor, reformer

Solid Oxide Fuel Cell Electrochemistry

Cell Reactions     

Nerst Potential     

• Ideal operating voltage with respect to partial pressures of cell reactants
  

Steam Reformation – Occurs in Reformer and Fuel Cells

Methane reformation reaction        

• Reaction rates on nickel based catalysts:
                 Lee et al. (1990) and Ross et al. (1972)

Water Gas Shift – Occurs in Reformers and in Fuel Cells

Shift reaction

• Reaction proceeds fast enough at elevated temperatures to assume equilibrium
  
• Algebraic constraint at exit of each node

Fuel Cell Operation

Actual operating voltage         

• Polarization losses are due to kinetics, mass transport and electrical resistances

 

PSOFC DISCRETIZATION
10 Discrete Computational Nodes

• Anode Gas
  
• Cathode Gas
• Cell Solid
  
• Bi-Polar Plates

 

Sample TSOFC Outputs: 10% Load Increase

 

Progress and Current Status

Jet Fuel Equilibrium Results

• Various Jet Fuel thermodynamic data acquired
• Commercial Aviation Fuel, Jet-A
  • C11H21
  • MW: 153 g/mol
  • Heat of formation (DHfo): -249 kJ/mol
• Traditional Air Force Military Aviation Fuel, JP-4
  • C10H19.4
  • MW: 139 g/mol
  • Heat of formation (DHfo): -227 kJ/mol
• Traditional Navy Military Aviation Fuel, JP-5
  • C10H19.2
  • MW: 139 g/mol
  • Heat of formation (DHfo): -222 kJ/mol
• Standard Military Aviation Fuel, JP-8
  • C12H23
  • MW: 167 g/mo
  • Heat of formation (DHfo): -319 kJ/mol

Jet Fuel Equilibrium Results

Jet Fuel Equilibrium Results – Effects of O/C

Jet Fuel Equilibrium Results – Partial Oxidation

New Module Development

Reaction Mechanism Need and Approaches

• Use Equilibrium results in look-up tables with discretized dynamic model for heat transfer, mass and momentum conservation
  
• Use Chemical Kinetics from a simpler hydrocarbon set
  
• Obtain data and/or develop simple chemical kinetic mechanism for JP-5

Must incorporate dynamic equations

• Heat transfer (conduction, convection, radiation)
  
• Mass (or species) conservation
  
• Momentum conservation
  
• Energy conservation

Main module development need is for the overall geometry of the NuElement Module

Dynamic JP-5 Reformer Module

Concentric Cylinders

• Combustor
  
• Catalyst Bed
  
• Preheat
  
• Anode off-gas recycle (option)
  

Reformation Kinetics

New Module Development

• Reformer Geometry (5 nodes)

• Six Step Reaction Mechanism

• Arrhenius Rate Expressions

 

• Reaction Equilibrium Constants

 

• Reformer Dynamic Simulation Results – S/C 1.0 à 1.5

• Reformer Dynamic Simulation Results – S/C 1.0 à 1.5

• Reformer Dynamic Simulation Results – O/C 0.25 à 0.5

• Reformer Dynamic Simulation Results – Catalyst “light off”

Personnel

Investigators:  J. Brouwer, F. Jabbari, and G.S. Samuelsen,
Students: Li Yuan, Fabian Mueller, Anh-Tuan Do

Sponsors

U.S. Department of Energy
California Energy Commission
Siemens Power Corporation

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