Versatile thermodynamic design of a solid oxide electrolysis cell system and its sensitivity to operating conditions

A solid oxide electrolysis cell (SOEC) is the most efficient electrolysis method, owing to the high operating temperature. Although high temperature electrolysis has lower electricity consumption, it also requires an amount of thermal energy. Thermal energy is supplied to the SOEC systems through internal heat recuperation and external heat integration. Thus, thermal integration is an important part of SOEC system design and operation. However, most SOEC system studies have focused on the electric performance of the stack, neglecting thermal energy consumption. This study presents a design procedure for system thermal integration. The SOEC system operable under all stack operating conditions (endothermic, thermoneutral, and exothermic) is designed. The internal heat recuperation is maximized by branching the cathode inlet and anode outlet streams. Then, an operating condition analysis is performed to analyze the effect of operating conditions on the proposed system. The system-level effect of operating parameters (stack voltage, stack inlet temperature, steam conversion, air ratio, hydrogen fraction) on the system’s performance and thermal aspects is examined. The results of this study provide guidelines for designing SOEC systems and selecting operating conditions.