A Methodology for Optimizing the Start-Up Scenario of Solid Oxide Fuel Cell Utilizing Transient Analyses

Abstract

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...

Dynamic Modeling of Reversible Solid Oxide Cells

“…Therefore, for a practical application, a maximum tolerable temperature ramp rate, which is allowed during mode switch (∼1 – 2 K min −1 for SOFC start‐ups ), has to be defined. After that, the voltage or rather the current density load change could be applied accordingly to satisfy the design specifications.…”

“…However, the additional time required should be kept in mind. A multi-stepwise increment of cell voltage or current density load could also be used to modulate temperature increases during transients [11,28].…”

The analyses of the start-up process of a planar, anode-supported solid oxide fuel cell using three different start-up procedures

“…There were two approaches reported to estimate the activation polarization [26]. For the first approach, the expressions for activation polarizations of the two electrodes are different [27].…”

Simulation of Dynamic Response of Strontium-Doped Lanthanum Manganite under Cathodic Polarization

“…In recent years, the simulation of the transient behavior of SOFCs became an attractive field, and many models have been proposed based on electrochemical analysis, heat exchange model, and computational fluid dynamics. [21][22][23][24][25] For example, several models have been established regarding the response of SOFC or stacks against the transient current loading. [26][27][28] Among them, however, few simulations dealt with the effect of electrochemical properties of cell components on the dynamic operation, such as polarization effects of LSM cathodes.…”