2. Application Domain The Energy Problem: Growing world demand and diminishing supply –Efficient, large scale (> 1MW) power production is a necessity –Environmentally responsible solutions are also a necessity. Potential Solutions –Renewable resources and technologies (wind, solar, bio-mass, etc.) –Efficiency/conservation measures Demand Side: End use conservation Supply Side: Exploitation of by-product heat –Advanced power cycles Cogeneration of Steam (by-product heat used for process heating) Combined Cycle (gas turbine topping cycle, steam bottoming cycle) Integrated Gasification Combined Cycle Solid Oxide Fuel Cell/Gas Turbine (SOFC/GT) Hybrids

3. SOFC Basics SOFC Operation: Electrochemical oxidation of hydrogen and reduction of oxygen generates electrical current for an external load. SOFC General Benefits –Direct conversion of chemical energy to electrical –High temperature operation (800-1000°C) High quality by-product heat, and enhanced chemical kinetics Reduces the need for expensive catalysts. –Reduced greenhouse gas emissions and criteria pollutants (e.g. NO x or SO x ) –Internal reformation at high temperatures allows for broader fuel options.

4. SOFC/GT Hybrids Operational Basics –Air stream to SOFC pressurized by compressor and preheated by recuperative heat exchanger –High temperature SOFC exhaust expanded through turbine for power generation –Combustion of unutilized fuel in exhaust can boost power produced by turbine Benefits –High efficiency (η > 60%) Common combined cycle plants η ~ 50% maximum –Lowered emissions for criteria pollutants –Depending on fuel carbon dioxide can be eliminated or at least sequestered

5. Design Decision By-product heat provides cogeneration/bottoming cycle opportunities Recuperative heat exchanger enhances SOFC/GT cycle performance The Catch: Increasing recuperator heat transfer decreases the quantity and quality of by-product heat. –Quality is used in the thermodynamic sense, i.e. the “usefulness” of heat. Primary Questions –How much recuperator heat transfer? –How large of a fuel cell? –What are the priorities? Total power? Cogeneration?

6. Heat Rejected Size of Fuel Cell Total Power Turbine Power Turbine Inlet Temp Recuperator Heat Transfer SOFC Power Additional Power Potential Influence Diagram

7. SOFC/GT Dymola Model

8. Brayton Cycle Performance Results of increasing heat exchanger heat transfer –Higher turbine work output –Lower recuperator exit enthalpy, i.e. lower quality heat –Lower heat rejection Trade-off between SOFC/GT power and cogeneration

9. SOFC/GT performance under uncertainty Mass flow rate dominates turbine output power Turbine output normally distributed Main Effects: Turbine Power (W) m_fuel Heat_xfer Anode_Temp Turbine output distribution

10. Challenges Dymola –Understanding ThermoTech files –Building components Building the model –High Level doesn’t work –Use of Examples Model Center –Arena –Maximum Estimation Likelihood

11. Dymola TechThermo –Not completely developed –Doesn’t follow exact thermodynamic properties –Thermodynamic logic of library convoluted –Lots of Component-Icon-Models (CIM) Empty containers Can require extensive coding

12. Dymola Building Components –Finding relevant equations –Learning the code –Debugging

13. Model Building Started at a High Level –Too much too fast –Singularity problems –Needed to target specific areas

14. Model Building Success –Started small –Evaluated each individual component –Combined smaller “blocks” –Built components as needed Standard Brayton Cycle Recuperated Brayton Cycle Recuperator (built from CIM)

15. Model Center Arena –Limited knowledge of software –Not sure how to fit it in Elicitation of Beliefs –Hard to grasp the mathematical concept –ZunZun to the rescue