抄録
Solid oxide fuel cells (SOFC) are expected to become highly efficient power generation equipments in distributed energy systems. The fuel flexibility of SOFC is attractive for the small-scale power generation driven with the fuel derived from biomass. In general, biomass fuel is composed of some different chemical species. In this paper, the effects of fuel composition on a 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-fueled hybrid system are estimated as the reference case. At the SOFC operating temperature of 800℃ and the pressure ratio of 3.0, the efficiency values of the methane-fueled system is 59% (LHV). The four different fuel compositions, i.e., H_2O/CH_4, H_2/CH_4, CO/CH_4 and CO_2/CH_4, are taken up, and methane content values are changed in the range from 100% to 20% (volume ratio) in the cycle analyses. Throughout the simulation, it is found that the decrease of methane content leads to the performance degradation. In particular, in the cases of CO/CH_4 and CO_2/CH_4, the power generation efficiency values greatly decrease together with the decrease of methane content. Because, increasing carbon monoxide or carbon dioxide content has the decline of hydrogen molar ratio at the anode inlet gas, and then the cell voltage decreases. In contrast to this, steam and hydrogen have less influence on the performance degradation, for steam and hydrogen contribute increasing the mole fraction of hydrogen in the reformed gas. However, higher concentration of steam and hydrogen causes the remarkable efficiency decrease.
