Fuel Processors

Project Goals

•  Develop detailed dynamic models of fuel processor   (FEMLAB) and fuel cell components (Simulink) for aeronautical applications
• Integrate models into a common framework for dynamic simulation and analysis using Simulink
•  Evaluate and refine approach for reusability, rapid development and assessment of complete system, and design improvement from simulation results

Background

• Fuel cell based power systems are becoming increasingly important in aeronautical applications
• Reformer based fuel cell systems make the technology amenable to logistic fuels such as diesel, JP5 and JP8
• A fundamental analysis of the dynamic system response is a critical factor in the overall design process.
• Detailed dynamic models of the fuel reformer – fuel cell system will become a key tool for carrying out design analyses. 

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)
Catalytic oxidizer Combustor 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

Mass Conservation Equations

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: PSOF
• Other: combustor, reformer

Planar Nodal SOFC Heat Transfer Resistances

 

 

Solid Oxide Fuel Cell Electrochemistry

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

Steam Reformation – Occurs in Reformer and Fuel Cells

Methane reformation reaction

Water Gas Shift – Occurs in Reformers and in Fuel Cells

Shift reaction

Fuel Cell Operation

Actual operating voltage

PSOFC DISCRETIZATION

• 10 Discrete Computational Nodes
  
• Anode Gas
  
• Cathode Gas
• Cell Solid
• Bi-Polar Plate

Sample TSOFC Outputs: 10% Load Increase

Progress & 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/mol
  • Heat of formation (DHfo): -319 kJ/mol

 

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

• Reformer Geometry (5 nodes)

• Six Step Reaction Mechanism

• Arrhenius Rate Expressions

• Reaction Equilibrium Constants

• Reformer Dynamic Simulation Results – S/C 1.0 1.5

• Reformer Dynamic Simulation Results – S/C 1.0 1.5

• Reformer Dynamic Simulation Results – O/C 0.25 0.5

• Reformer Dynamic Simulation Results – O/C 0.25 0.5

• Reformer Dynamic Simulation Results – Catalyst “light off”

 

Conclusions

• Simulink interface critical  to the development of system-wide dynamic models.
• Modular approach compatible with several implementation techniques for component models, including user-written programs (FORTRAN / C) as well as commercial simulation software.

Personnel

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

Sponsors

Nu Element, Inc.

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