Abstract
Solid oxide fuel cells (SOFC) are expected to become a primary power supply component in distributed energy systems. In addition, the fuel flexibility of SOFCs is attractive for the small-scale distributed power generation driven with biomass derived fuel. In this paper, the performance evaluation of a biogas fueled micro gas turbine (μGT)-solid oxide fuel cell (SOFC) combined power generation system is investigated by using thermodynamic cycle simulation. The power generation characteristics of methane and hydrogen fueled hybrid systems are performed as reference cases. At the SOFC operating temperature of 800℃ and the pressure ratio of 3.0, the efficiency values of the methane fueled system and the hydrogen fueled system are 59% and 51% (LHV), respectively. The data of biogas compositions are extracted from the previously reported work regarding the fuel cell operation with biogas from farming waste/sewage and a wood gasification process. Throughout the simulation, it is found that the fuel compositions significantly affect the system performance. Higher methane content in biogas causes the higher efficiency of a hybrid system, because an internal steam reforming of methane operates effectively upon the efficiency improvement of a hybrid system. In the case of hydrogen fuel, excess heat of a cell stack is solely used for fuel pre-heating. Consequently, much air is required for cell stack cooling, and the fractional power output of a μGT becomes larger. Higher ratio of μGT power to total power leads lower efficiency. This means that the utilization of hydrogen rich fuel degrades efficiency. The system optimization, which includes biomass fuel production processes, is essential for the development of much highly effective hybrid systems.
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