Sensitivity analysis of a solid oxide co-electrolysis cell system with respect to its key operating parameters and optimization with its performance map

• Published in: Energy conversion and management 2021-12, Vol.249, p.114848, Article 114848
• Main Authors: Min, Gyubin, Park, Young Joon, Choi, Saeyoung, Hong, Jongsup
• Format: Article
• Language: English
• Subjects: Carbon monoxide; Co-electrolysis; Conversion; Current density; Efficiency; Electrolysis; Empirical analysis; High current; Low currents; Optimal operation; Optimization; Parameter sensitivity; Performance evaluation; Performance indices; Performance map; Sensitivity analysis; Solid oxide electrolysis cell system; System simulation; Temperature gradients
• ISSN: 0196-8904; 1879-2227
• DOI: 10.1016/j.enconman.2021.114848

•Optimal operation for a solid oxide co-electrolysis cell system is investigated.•The effect of key operating parameters and system performance map is explained.•High system efficiency and reactant conversion is obtained at high current density.•High current-to-reactant ratio allows high efficiency and high reactant conversion.•Air ratio should rather be chosen to support the thermal stability of the stack. This study performs thermodynamic optimization of solid oxide co-electrolysis cell system’s key operating parameters (current density, current-to-reactant ratio, and air ratio) by using high-fidelity and empirical-based system component models. For each operating parameter, a sensitivity analysis is conducted to elucidate optimal operating points for high system performance evaluated by indices such as system efficiency, reactant conversion, and H2:CO ratio. At a high current density of 1.2 A/cm2, the highest system efficiency of 58.21%, the highest reactant conversion of 63.84%, and the lowest H2:CO ratio of 1.258 are obtained. Likewise, a high current-to-reactant ratio of 0.9 allows obtaining the high system efficiency of 58.26%, the high reactant conversion of 83.79%, and the lowest H2:CO ratio of 1.230. Contrary to the two parameters, at the lowest air ratio of 3, the maximum system efficiency of 63.38% and the maximum H2:CO ratio of 1.516 are obtained, whereas the highest reactant conversion of 62.78% is obtained at the highest air ratio. Based on the single parameter analysis, a performance map for each system performance index is derived as a function of current density and current-to-reactant ratio under the fixed air ratio given that the air ratio is more related to the thermal inertia of the stack. To gain high system efficiency and high reactant conversion, a high current-to-reactant ratio of 0.75 ∼ 0.90 is necessary. The high current density of 1.2A/cm2 is also recommended for obtaining high performance, a small temperature gradient inside the SOEC stack, and small temperature variation with the change of the current-to-reactant ratio. However, if the system aims to obtain a low H2:CO ratio, low current-to-reactant ratio and low current density are suggested at the expense of system efficiency and reactant conversion. The maximum system efficiency is obtained at 1.2A/cm2 and the current-to-reactant ratio of 0.75, and the maximum reactant conversion of 88.91% is obtained at 1.2A/cm2 and the current-to-reactant ratio of 0.90. On the other hand