Analysis and Design for Hydrogen-Fueled Cascade Solid Oxide Fuel Cell System

Maximizing the total fuel utilization is crucial to improving the electrical efficiency of solid oxide fuel cell (SOFC) systems. Cascade SOFC systems can effectively achieve this goal, but there are fewer studies on hydrogen-fueled cascade SOFC systems. Therefore, further analysis of cascade systems is necessary, especially in determining the optimal cell number ratio, which significantly impacts system efficiency. Because of the characteristics of cascade systems, a model that can quickly predict performance at different flow rates and hydrogen molar fractions is required. Using multiple sets of experimental data, an improved semi-empirical model was developed, which accurately predicted the industrial-sized cell performance at different flow rates and hydrogen molar fractions, and was validated by interpolation and extrapolation. Based on this, a basic system model and a cascade system model were established. The effects of fuel flow rate, cell number ratio, split ratio, and the constraints of cell fuel utilization and voltage on the system performance were investigated and analyzed, and appropriate design and operating parameters for the cascade system were determined. The results indicated that the optimal cell number ratio is between 2 and 3, and the optimal split ratio is 1. In industrial scenarios requiring high fuel utilization operation, the cascade system can significantly improve electrical efficiency while reducing cell fuel utilization compared to the basic system. In the case of a 10-kW rated power system design, the cascade system showed an increase in electrical efficiency from 39.0% to 42.2% up to from 47.6% to 52.7% at rated power compared to the basic system, representing an improvement of 8.6% to 10.5% and a reduction in fuel flow rate of 19.2% to 20.4%. The results obtained provide valuable reference for related research and offer guidance for system design.