| Solid oxide fuel cells (SOFCs) are especially suited for stationary power generation due to their sufficiently high operating temperatures (between 600°C-1000°C), which allow for integration with gas turbines or other bottoming cycles. The turbines and heat exchangers can utilize the heat released from the fuel cell and the fuel can be reformed internally without a catalyst. SOFCs can directly use natural gas, syngas from coal, and various biofuels. Furthermore, with the solid electrolyte, corrosion and electrolyte management problems are somewhat eliminated. For the successful integration of the SOFCs with other power generating technologies, process simulation models that can address system optimization, dynamic power demands and techno-economic evaluation are needed.;The SOFC model and equipment models from AspenPlus(TM) were used to model two hybrid SOFC-GT cycles; one incorporating GT exhaust heat recuperation and SOFC anode exhaust-gas recirculation, and another incorporating GT exhaust heat recuperation and heat recovery steam generation. Parametric analyses were performed investigating the impact of the system pressure, SOFC operating temperature, turbine inlet temperature (TIT), SOFC current density, steam-to-carbon ratio (SCR), SOFC fuel utilization factor and GT isentropic efficiency on the specific work output and efficiency of the two cycles.;This thesis focuses on the first of these requirements by investigating the impact of important system operating parameters on the cycle specific work output and cycle efficiency on SOFC-gas turbine (GT) systems. To be able to carry out the parametric study, a macro-level model of a SOFC stack, written in FORTRAN for implementation in AspenPlus(TM) for the simulation of hybrid SOFC-GT systems, was developed and used in the two hybrid SOFC-GT cycle models of different configurations. The SOFC model, being 0-dimensional, accepts gaseous fuel in any combination of hydrocarbons, with user specified inputs of current density, fuel and air composition, flow rates, temperature, pressure, and fuel utilization factor. The model outputs the composition of the exhaust, work produced, heat available for the fuel reformer, and electrochemical properties of SOFC for model validation. The model was developed considering the activation, concentration, and Ohmic losses to be the main over-potentials within the SOFC. The model was validated using experimental data from Siemens Westinghouse. The results show that the model can capture the operating pressure and temperature dependence of the SOFC performance successfully in a range of 1-15 atm for pressure and 900°--1000°C for temperature, respectively. Additionally, a sensitivity analysis was performed to identify the model constants and input parameters that impact the over-potentials. After validation of the SOFC model, it was implemented in a hybrid SOFC-GT cycle model in AspenPlus(TM) based on an experimental cycle by Siemens Westinghouse. The results show that the SOFC model in combination with built-in equipment models in AspenPlus(TM) is a valid means of modeling hybrid SOFC-GT cycles. |
