Development of a 10/40kW-Class Reversible Solid Oxide Cell System at Forschungszentrum Jülich

Abstract

The Forschungszentrum Jülich GmbH has successfully developed a 5/15 kW-class reversible Solid Oxide Cell (rSOC) system in recent years, promising a high system efficiency in fuel cell and electrolysis mode [1]. The core element of the system is the well-known Integrated Module developed, which has been adapted from fuel cell to the rSOC operation. This Module consisted of four 10-layer sub stacks, in which each layer had an active cell area of 320 cm². It also contained fuel and air heat exchangers, arranged on top and underneath the stacks, to bring the incoming gases to the operating temperature. In addition, three electrically operated heating plates were implemented to heat up the system at the beginning of the operation and to adjust the stack temperature during the endothermic electrolysis operation. Other components necessary for the system operation such as the evaporator, blowers, condenser and control system are attached near the Integrated Module in a compact and suitable manner. This system was extensively examined after its completion. A maximum power of 5.3 kWDC at a current density of 0.5 A cm-2 and a fuel utilization of 97.3% could be achieved in fuel cell mode. Under these conditions, an electrical efficiency of 62.7% (LHV, DC) was reached. Furthermore, a maximum electrical input power of - 14.3 kWDC could be achieved in electrolysis mode with a current density of -0.89 A cm-2 at a steam conversion rate of 85%. An electrical efficiency of 70% (LHV, DC) was measured for this operating point. In the further course of the tests, the switching between the operating modes was investigated and optimized. The change from fuel cell to electrolysis mode took approximately 13 minutes limited by steam generation and the opposite direction took less than 3 minutes [2]. In the fuel cell mode, a maximum system fuel utilization of more than 99% was achieved through the use of an off-gas recirculation. Such a high utilization could be realized because the steam content has been removed from the recirculated gas stream by condensation before feeding back to the stack inlet. Furthermore, the system behavior during load variation was examined. With this system design, a minimum part load of 0.1 A cm-2 in the fuel cell and - 0.05 A cm-2 in the electrolysis mode could be demonstrated [3]. Based on these experiences, a new rSOC system with a power of 10 kW in fuel cell and 40 kW electrolysis mode will be constructed. For this purpose, the stacks used and the supporting components have to be adapted. In addition, the efficiency in the electrolysis mode will be increased by using a more effective steam generation process. The new developed system as well as its test results will be presented at the conference for the first time.[1] M. Frank, R. Deja, R. Peters, L. Blum, D. Stolten, Applied Energy, 217 (2018) 101-112.[2] R. Peters, M. Frank, W. Tiedemann, I. Hoven, R. Deja, V.N. Nguyen, L. Blum, D. Stolten, ECS Transactions, 91 (2019) 2495-2506.[3] R. Peters, M. Frank, W. Tiedemann, I. Hoven, R. Deja, N. Kruse, Q. Fang, L. Blum, R. Peters, Journal of the Electrochemical Society, (2021).