Electrical Efficiency of Two-Stage Solid Oxide Fuel Cell Stacks with a Fuel Regenerator

Abstract

Many studies have been conducted for the two-stage solid oxide fuel cell (SOFC) module. Since there are presently no studies for the fuel regenerator's effect on the electrical efficiency of the module to the best of the authors' knowledge, the effect of removing H 2 O and/or CO 2 was investigated. To estimate the electrical efficiency, models of the two-stage SOFC stacks with a fuel regenerator that use hydrocarbon or hydrogen fuel were used. The electrical efficiency was estimated by calculating the maximum fuel utilization rate and the cell voltage. The risk of carbon deposition from the regenerated anode off-gas was estimated by calculating the chemical equilibrium region of the anode gas. The maximum electrical efficiency had a net alternating current (AC) of 71.8% (lower heating value (LHV)) from methane fuel. This was obtained when 100% of the H 2 O and CO 2 were removed by the fuel regenerator. In addition, the net AC efficiency of 60.8% (LHV) was obtained from the 10% humidified hydrogen fuel when 98.0% of H 2 O was removed by the fuel regenerator. These results suggest a high potential to generate a highly efficient power by the two-stage SOFC stacks with a fuel regenerator.

Basic Study of Anode Off-Gas Recycling Solid Oxide Fuel Cell Module with Fuel Regenerator

“…The anode off-gas recycling SOFC module and a two-stage SOFC module with only H 2 O removal by a fuel regenerator were compared. In our previous study, for the twostage SOFC module, the highest net AC efficiency of 68.1% (LHV) was achieved when 88.8% H 2 O was removed by the fuel regenerator (1). In this study, the highest net AC efficiency of 68.1% (LHV) for the anode off-gas recycling SOFC module was realized when 39.5% H 2 O was removed by the fuel regenerator.…”

“…The results showed that the system could be operated at a high fuel utilization rate by removing CO 2 and/or H 2 O from the anode off-gas of the first-stage SOFC stack and reusing the regenerated anode off-gas as the fuel for the second-stage SOFC stack. Consequently, it generated power with high efficiency (1). We also developed an actual two-stage SOFC module with a fuel regenerator and operated it at fuel utilization rate of 91.4% with thermal selfsustainability.…”

“…It was reported that when an anode off-gas is recycled, operation at a high fuel utilization rate is possible because the H 2 and CO contained in it can be reused as a fuel (4). The relationship between the fuel utilization rate and the direct current (DC) efficiency of a fuel cell is as follows: [1] where η DC is the DC efficiency, n is the number of electrons in the electrode reaction, F is Faraday constant, ∆H is the standard enthalpy of combustion, and V cell is the cell voltage. U f is the fuel utilization rate, defined as the ratio of the theoretical amount of fuel required to generate the output current to the amount of total fuel consumption.…”

Study of Operating Conditions for High Efficiency and Anode Safety of Industrial-Size Solid Oxide Fuel Cell

“…最大发电效 率对应的工况如表 1 所示. 此外, 当 SOFC 集成在发电系统中运行时, 合理设 计系统结构, 充分利用高温尾气中的热能 [25] , 能够进一 步提高系统的总体效率 [26][27][28][29] 需要明确的是, 对于不同材料、结构和制备工艺的 电池, 由于其性能水平不同, 其最高效率所对应的燃料 利用率会有所不同, 测试中所选择的燃料流量的数值间 隔也会使结论略有差异. 在世界范围内, 德国 Julich 研 究中心的电堆能够在 85%的燃料利用率下高效运行 [16] ; 日本产业技术综合研究所(Advanced Industrial Science and Technology, AIST)的多个单电池、 电堆在 75%～80% 的燃料利用率下连续运行超过 10000 h, 也有部分电堆 尝试在 85%的燃料利用率下进行稳定性测试, 最长连续 运行 9000 h [8] .…”