Operating limitation and degradation modeling of micro solid oxide fuel cell-combined heat and power system

• Published in: Applied energy Vol. 252; p. 113444
• Main Authors: Shi, Wangying, Zhu, Jianzhong, Han, Minfang, Sun, Zaihong, Guo, Yaming
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15.10.2019
• Subjects: Combined heat and power; Degradation model; Operating limitation; Solid oxide fuel cell; Combined heat and power; Solid oxide fuel cell; Operating limitation; Degradation model
• ISSN: 0306-2619; 1872-9118
• DOI: 10.1016/j.apenergy.2019.113444

•A 5 kW micro SOFC-CHP system was simulated combined with a SOFC degradation model.•A real SOFC stack was tested under CH4&H2 showing 262 W output and 600 h lifetime.•The most appropriate parameter range was illustrated to be limited in a shape of a small triangle.•The calculated system electrical efficiency could reach 44.9% (HHV) at 120 A.•The constant current operating pattern had the longest lifetime and constant power followed. The micro Solid Oxide Fuel Cell-Combined Heat and Power (SOFC-CHP) System is one of the most promising technologies of distributed generation and has been commercialized in Japan and Europe. However, the performance degradation of an SOFC stack still exists, causing the ratio of power and heat to change and the Joule heat to increase in the stack. This phenomenon should not have been neglected. A zero-dimension SOFC model including basic Nernst, ohmic, activation and concentration voltage loss was used to simulate the micro SOFC-CHP system, and a degradation model was also applied to modeling the power change with respect to operating time in different situations. Both of the models were verified by real stacks experiment data and the effectiveness was proved in system-level modeling. Three key operating parameters of the system were promoted: stack current I, excess air factor α and fuel utilization Uf. Given the safe temperature ranges of an SOFC stack, combustor and reformer, the most appropriate parameter range was illustrated to be limited in a shape of a small triangle. Within the safe parameter range, while the excess air factor α was fixed at 2.64, the electrical efficiency reached a maximum 44.9% (HHV) at 120 A, while the electric power output of SOFC and hot water were both 5.58 kW. As for the dynamic modeling, by comparing constant current, constant voltage and constant power three operating patterns, results showed that the constant current pattern had the longest lifetime and the constant power pattern followed.