Basic study on electric load following operation of small distributed solid oxide fuel cell system

固体氧化物燃料电池（SOFC）采用氧化钇稳定氧化锆（YSZ）等氧离子导电陶瓷材料作为电解液，其工作温度高达1200-1300 K，其优势是与一些合适的底循环（如燃气轮机）相结合，可以实现非常高的综合效率，可以利用其废气。因此，在中大型电源中，其研究与开发得到了积极的推进。此外，它现在也有望作为小型分布式热电联产系统的动力源，因为它利用燃料的蒸汽转化反应的内部产热，其效率有望达到50%左右，而不需要底部循环。然而，SOFC在用作电池材料的陶瓷的耐久性方面存在问题，因为它的工作温度非常高，电池温度波动会对电池产生热应力。因此，其中的电池温度分布应尽可能保持恒定。然而，在小型分布式热电联产系统中，通过控制电池内平均电流密度进行变负荷运行是必要的，这种运行通常会引起电池温度波动。考虑到这一点，针对SOFC变负荷运行模式的建立，通过数值模拟研究了共流和逆流型平面SOFC单体电池内平均电流密度与温度分布的关系。模拟结果表明，通过适当调节空气利用率，可以将温度分布的变化抑制到足够低的水平，实现两种电池的变负荷运行。为了补偿负载的快速变化和平滑功率波动，我们提出在SOFC和负载之间安装双电层电容器，并通过数值模拟验证了其效果。此外，还设计了一种双电层电容的实验电路，并将实验结果与仿真结果进行了比较。结果表明，虽然实验电路在瞬态响应上存在一些差异，但实验电路的工作原理与仿真结果基本一致。这表明了本文所提出的电容控制方法的有效性。少

The solid oxide fuel cell (SOFC) adopts oxygen ion conducting ceramic materials, such as yttria-stabilized zirconia (YSZ), as the electrolyte, and its operating temperature is very high as 1200-1300 K, leading to an advantage that very high overall efficiency can be achieved by combining it with some suitable bottoming cycle, such as the gas turbine, that can utilize its exhaust gas. Its research and development, therefore, have been actively promoted for middle to large-scale electric power sources. In addition, it is now also expected as the power source for the small distributed co-generation systems, because its efficiency is expected to reach about 50% by itself without the bottoming cycle by utilizing the internal heat generation for the steam reforming reaction of the fuel. The SOFC, however, has a problem in durability of the ceramics used as its cell materials, because its operating temperature is very high and cell temperature fluctuation induces the thermal stress to the cer … More amics. The cell temperature distribution in it, therefore, should be kept as constant as possible. In the case of the small distributed co-generation systems, however, the variable load operation through the control of the average current density in the cell is necessary, and this operation usually causes the cell temperature fluctuation. Considering this fact, aiming at the establishment of the variable load operation of the SOFC, we investigate the relation between the average current density and the temperature distribution in the co-flow and counter-flow type planar SOFC single cells by numerical simulations. It is made clear from the simulations that the change of the temperature distribution can be suppressed to sufficiently low level and the variable load operation can be realized for both types of cells by properly regulating the air utilization. To compensate the very fast load change and to smoothen the power fluctuation, we propose to install an electric double layer capacitor between the SOFC and the load, and its effect is confirmed through numerical simulations. In addition, an experimental circuit using an electric double layer capacitor is composed, and the experimental results are compared with the simulation results. As a result, although there exists a little difference on the transient response, it is made clear that the experimental circuit operates almost according to the simulation. This indicates the validity of the capacitor control method proposed in this study. Less