(486c) Dynamic Modeling of Thermal Gradients in Solid Oxide Fuel Cells

Authors: 
Spivey, B. J., The University of Texas at Austin
Edgar, T. F., Dept. of Chem. Eng.,The University of Texas at Austin


Stationary hybrid gas turbine-solid oxide fuel cell (SOFC) power plants have demonstrated efficiencies greater than fifty-percent at power levels suitable for distributed power generation near 250 kW. A primary challenge for SOFC plant implementation is the significant impact that temporal and spatial thermal gradients have on stack lifetime. Plants are subject to transient operation due to several uncontrolled disturbances: fuel quality, load-following during emergency shutdowns, and ambient temperature. In addition load-following during normal operation may be a desired control objective. A need exists for dynamic modeling of the radial and longitudinal thermal gradients within the SOFC during changes in operating conditions with the eventual goal being to minimize thermal gradients using advanced control.

This work presents a computational model that characterizes the SOFC thermal gradients that arise due to disturbances and manipulated variable (MV) step changes. The model is based upon a quasi-steady-state conservation model for gas temperature and species mole fractions and dynamic energy conservation for the anode, electrolyte, cathode, and air tube. Model validation is presented using cell performance data from two distinct tubular cell plants available in literature, and a sensitivity analysis illustrates the effect of unknown model parameters. Open-loop MV step changes are performed in preparation for future work in multivariable SOFC control. Cell performance and reliability is characterized by efficiency, power output, and local temperatures and species concentrations.

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