Semester

Fall

Date of Graduation

2010

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Ismaili Celik.

Abstract

Solid Oxide Fuel Cells (SOFCs) offer great promise as a clean and efficient alternative to conventional power generation technologies. A major advantage of SOFCs in comparison to other fuel cell types is that they can be operated directly on a wide variety of fuels including biogas, hydrocarbon fuels and coal-derived synthesis gas (syngas). SOFC operating on coal syngas is an especially attractive prospect given the abundant coal resources in the world. However, coal syngas usually contains various impurities such as phosphorus, arsenic, zinc, sulfur, mercury, selenium, and vanadium which affect the performance and durability of SOFCs. At low impurity concentrations, degradation rates are quite slow and long term experiments (more than 1000 h) are required in order to determine the cell degradation rates accurately. Theoretical models that can predict the degradation behavior of SOFCs operating on syngas with very low levels of impurities could substantially reduce the time and effort involved in durability experiments.;In an attempt to predict the typical degradation patterns observed in Solid Oxide Fuel Cell (SOFC) anodes due to coal syngas contaminants such as arsenic (As) and phosphorous (P), a new phenomenological model is formulated. The model includes gas phase diffusion including Knudsen diffusion and surface diffusion within the anode and the adsorption reactions on the surface of the Ni-YSZ based anode. Model parameters such as reaction rate constants for the adsorption reactions are obtained through indirect calibration to match the degradation rates reported in the literature for arsine (AsH3), phosphine (PH3), hydrogen sulfide (H2S) and hydrogen selenide (H2Se) under accelerated testing conditions. Current simulation results from implementation of the model demonstrated that the deposition of the impurity on the Ni catalyst starts near the fuel channel/anode interface and slowly moves toward the active anode/electrolyte interface which is in good agreement with the experimental data. Parametric studies performed at different impurity concentrations and operating temperatures showed that the coverage rate increases with increasing temperature and impurity concentration, as expected.;The calibrated model was then used for prediction of the performance curves at different impurity concentrations and operating temperatures. Encouraging agreement was obtained between the predicted results and the experimental data reported in the literature. Synergistic effect of various impurities including AsH3, PH3 and H2S was also examined and it was concluded that the mixture of impurities leads to faster degradation and thus shorter lifetime of the cell when compared to that of a single impurity.

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