| Models have been developed and validated for the characterization of tubular solid oxide fuel cells (TSOFCs) and a corresponding fuel cell/gas turbine (FC/GT) power cycle. This promising area of technology is expected to attain near-term commercialization (most notably the SiemensWestinghouse “SureCell” initiative). There is a need for continued conceptual design research in order for the full potential of these systems to be realized. Parametric studies were performed to delineate the impact of cell stack operating conditions on power generation, cell stack thermal management, independent cell load-following and performance quality. The diverse operating conditions included variations in physical cell design, stack pressure, operating voltage, stoichiometric number and stack fuel utilization. A number of novel findings are reported throughout the thesis. As an example, it has been shown that lowering cell stack fuel utilization has a number of benefits for both the simple TSOFC arrangement and the hybrid TSOFC/ GT scenario.; The cell stack produces more power at lower fuel utilizations, because fuel supply to the stack actually increases. Additionally, fuel depletion issues (i.e., Nernst potential decrease and smaller limiting currents) are not as influential. A gas turbine bottoming engine would also increase in power production, at lower stack fuel utilizations, because a greater amount of fuel would then fire it. Note that power generation expense is measured per unit rating (e.g., {dollar}/kW). Increasing power capacity may then be a means of lowering cost, which is the key obstacle to commercialization. Another cost reduction may stein from the greater contribution of turbomachinery to system power generation, when stack fuel utilization is lowered. FC/GT system efficiency remains stable across a wide domain of cell stack fuel utilizations. This is a result of both the indirect internally reforming (IIR) fuel processor efficiency and Brayton cycle regeneration increasing at lower stack fuel utilizations.; Engineering thermodynamic design principles were also incorporated within the fuel cell analyses. These considerations revealed insights that would not have been realized if the investigation was limited to traditional indices-of-performance. An example is the unaccounted for thermal exergy that leaves the high temperature cells as by-product heat, when utilizing electrochemical efficiencies. |
