An exergetic analysis of an ethanol FED SOFC-GT hybrid system

Abstract

A parametric analysis optimization and comparison of the exergetic efficiency (2nd law) of two different Solid Oxide Fuel Cell based power plants (SOFC-GT and SOFC) is carried out in the present work. The fuel with which the solid oxide fuel cell was fed was considered hydrogen produced from ethanol steam reforming. The SOFC power plant consists of the SOFC device, the burner-reformer, the recuperator and the evaporator, while the SOFC-GT power plant apart from the above devices consists also of the gas-turbine and the compressor. The exergy efficiency and the exergy destruction rate of each device and of the entire cycle were calculated applying thermodynamic rules by the aid of a mathematical model [1]. The simulation results of both systems were analysed and compared. Novel materials for SOFCs presenting high performance at relatively low temperature values (400-600oC) have been recently developed [2]. Taking into account the IT-SOFC's electrochemical characteristics, it was estimated that the power plants under consideration can be operated with thermal and exergy efficiencies around 56-62% and 52-60% respectively, depending on the operating conditions (SOFC's inlet temperature, pressure ratio, performance of fuel cell). From the results it was also concluded that for low current densities the SOFC based power plant prevails in terms of exergy efficiency over SOFC-GT hybrid power plant, while at higher current density values the latter is more efficient.