| dc.description.abstract | The high operating temperature enables solid oxide fuel cell hybrid system to obtain high efficiencies from integration with gas turbines for large scale stationary applications. High temperature solid oxide fuel cell means that the components of the stack need to be made of expensive materials. For smaller scale applications, there is a trend to move to lower temperatures of operation into the so-called intermediate temperature solid oxide fuel cell. Biofuel such as methanol, ethanol and isooctane can be considered to be a favorable biofuel because they are the most environmentally friendly and renewable energy sources. These fuels are easy to be used for solid oxide fuel cell hybrid system and safe in storage and handling.
In this thesis, the hybrid system consists of a proton solid oxide fuel cell (pSOFC) stack, a micro gas turbine, a combustor, compressors, heat exchangers and external steam reformer. The effect of operating parameters such as compressor pressure, fuel utilization, steam-to-carbon ratio (S/C) and bypass ratio are investigated for each fuels. Then, several case studies conducted in this system model are presented. Finally, the performances of the system using different fuels are compared in terms of pSOFC power output, turbine power output, H2 production, pSOFC efficiency, power system efficiency and combine heat and power (CHP) efficiency.
The simulation is based on the thermodynamic analysis and developed using Matlab Version 7.6 / Simulink Version 7.1 / Thermolib 5.1.1.5353 and validated using the published data in the literature. The results from the thermodynamic model showed that the increasing of the compressor pressure can result in the decrease in the pSOFC efficiency but power system and CHP efficiency are enhanced. The increasing of the fuel utilization can result in the increasing of the pSOFC efficiency. However, power system efficiency decreases for methanol fuel but increases for ethanol and isooctane fuels. CHP efficiency increases when fueled by ethanol and isooctane but reduces when fueled by methanol. The variation of the S/C has an impact on the hybrid system. A minimum S/C for each fuel is required to prevent carbon formation but increase S/C will decrease the power system and CHP efficiency. Practically in hybrid system, the value of S/C is usually below the optimum value. From the effect of bypass ratio, it was found that the minimum bypass ratio is 0.05, 0.15 and 0.2 for methanol, ethanol and isooctane. Below those values, steam reformer has insufficient heat to reform the fuel to hydrogen. From the comparison between fuels, it was found that methanol is more attractive than ethanol and isooctane. Finally, due to the new design system configuration of solid oxide fuel cell hybrid system, it is possible to use higher molecular weights fuel such as ethanol and isooctane in external steam reforming. | zh_TW |