Thermodynamic considerations of a fuel cell/ gas turbine cycle

Elevated electric efficiencies make fuel cell/ gas turbine cycles attractive energy converters of the near future. This novel arrangement has fuel cell stacks placed on the high pressure side, after the compressor. Judicious operation of the fuel cells minimizes system irreversibility by having them consume a fraction of the fuel and sending the rest to a combustor for thermal energy. Part of this thermal energy is converted to work via expansion. The gas generator (high pressure) turbine compensates the parasitic load, while the power (low pressure) turbine further utilizes flow enthalpy to produce additional power. One of the more promising fuel cells for integration into a gas turbine cycle is the tubular solid oxide fuel cell developed by Siemens/ Westinghouse Electric. Modeling the behavior of conventional gas power cycle components is a mature area, but the cell stacks' dynamics are not as well known. The investigation produced a model of the latest generation of Siemens'/ Westinghouse Electric's cells. The electrochemical dynamics were modeled to within 5% accuracy. Power and thermal energy generation were then calculated from thermodynamic principles. Heat transfer within the cell was also modeled. The cylindrical geometry of the fuel cell and air supply pipe, coupled with themore » isothermal boundary conditions of each, allowed for utilization of well-proven correlations. The annular region between the fuel cell and air supply pipe had mixed mode heat transfer due to radiation and convection. The air flow through the supply pipe was heated via convection. The ability to model the fuel cells and balance-of-plant allowed for thermodynamic analyses and conclusions.« less