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In this paper, the influence of energy recuperation on the efficiency of a solid oxide fuel cell (SOFC) power system is studied with the GCTool software developed by the American Argonne National Laboratory (ANL). The recuperative energies include partial recycled air exhausted from cathode side, recirculated fuel and steam from the anode side of the SOFC, and combustion gases from anode exhaust, individually. The methane is chosen as fuel, air is oxidant, and the pressure drops due to streams transported through the duct and components are taken into account in the power system. Full analysis of the state at each node of the system is conducted. The results show that, under the same setting, with an A/F of 4, a pre-reforming rate of 30%, and fuel utilization of 80%, the overall system efficiency is elevated from 50 to 68% in the case of recirculating partial fuel and steam from the anode exhaust of the SOFC. And, the configuration of diluted fuel recycled entirely from the outlet of the anode side of the SOFC is going to cause the overall efficiency to become the lowest in all cases in spite of reaching the highest electric efficiency of 41%. Recirculating partial air released from the outlet of the cathode side could provide extra heat to preheat inflow air, and the overall efficiency will be raised, apparently, as well.

Transient analyses based on electrochemical and thermal models have been performed for investigating the transient behavior of a planar solid oxide fuel cell ͑SOFC͒. The reference case illustrated in this work is for an anode-supported fuel cell with an active area of 76.2 ϫ 76.2 mm 2 and thickness dimensions of 700, 25, and 20 m, and 3 mm for the anode, electrolyte, cathode, and interconnect, respectively. Typical response time and temperature ramp rate of SOFC under steady operating conditions ascend with increasing current density. Furthermore, a series of step functions of current density were imposed to simulate various start-up operating modes. To avoid the temperature ramp rate being too high during the start-up period, a stepwise increment of current density seems to be most suitable. Finally, an example for optimizing the temperature ramp rate and total response time is illustrated. This example involves a three-step increment series of 300, 500, and 640 mA cm −2 , resulting in a temperature ramp rate that complies with a given specification, e.g., less than 5°C per minute, while the total response time is in the moderate range as well.Fuel cells have recently been regarded as a promising clean energy technology with great potential. Because of this, intensive research and development efforts have been undertaken on this topic. Among the various types of fuel cells, solid oxide fuel cells ͑SOFCs͒ belong to the high-temperature category, for which operating temperatures range from about 600-1000°C. High operating temperature is beneficial for elevated energy conversion efficiency and good quality of available heat ͑or exergy͒ of the device; nevertheless, due to the thermal inertia of ceramic materials in the positive electrode-electrolyte-negative electrode ͑PEN͒, the start-up procedure requires careful attention.The fundamental function unit is a single cell which consists of a PEN and two end plates with fluid piping on each side. Flow channels for fuel and oxidant are integrated on the end plates at the anode and cathode sides. However, in practical applications, multiple cells are piled up to form a stack that corresponds to serial connections of the electric loop on the individual cell. In this case, interconnects with double-sided flow channels lay between the PENs in the middle section of the stack. The reference case illustrated in this work is for a fuel cell of the anode-supported type that has an active area of 76.2 ϫ 76.2 mm 2 with thickness dimensions of 700, 25, and 20 m and 3 mm for the anode, electrolyte, cathode, and interconnect, respectively. A schematic configuration of the cell unit in the repeated parts of the stack is shown in Fig. 1.As specified in previous work, 1 metal would be utilized as the material for the interconnect, effectively reducing the cost and enhancing the mechanical integrity and durability. Hence, it is desirable that the maximum metal temperature should remain near or below 800°C. The steady-state model calculations reported that with an inlet temperature of 640...