Geometric optimization of an ejector for a 4 kW SOFC system with anode off-gas recycle

• Published in: International journal of hydrogen energy 2018-05, Vol.43 (19), p.9413-9422
• Main Authors: Genc, Omer, Toros, Serkan, Timurkutluk, Bora
• Format: Article
• Language: English
• Subjects: Anode off-gas recycling; Ejector; Entrainment ratio; Geometric design; Solid oxide fuel cell; Steam to carbon ratio
• ISSN: 0360-3199; 1879-3487
• DOI: 10.1016/j.ijhydene.2018.03.213

One of the important energy saving tools used in solid oxide fuel cell (SOFC) system is the anode off-gas recycling (AGR) via an ejector which allows the recirculation of the unused fuels in the anode exhaust gas including hot steam which is essential for the elimination of the carbon deposition and the initiation of the reactions in the reformer. In an ejector system developed for the SOFCs, the steam to carbon ratio (STCR) and entrainment ratio are the crucial parameters for the determination of the ejector performance. These parameters can be engineered by modifying the geometric dimensions and operation conditions. This study focuses on the determination of the maximum STCR value and entrainment ratio via numerical geometric analyses for a micro combined heat and power (μ-CHP) system based on 4 kW SOFC, utilizing methane. A detailed numerical procedure for designing an ejector is provided and the ejector performance is investigated for different critical dimensions (throat diameter, nozzle exit angle and nozzle position etc.). The results show that the nozzle position and the nozzle exit angle significantly affect STCR and the entrainment ratio. When the nozzle position increases and nozzle exit angle decreases, the entrainment ratio and STCR is found to increase. The entrainment ratio and STCR are determined as around 7.3 and 2.7, respectively for a specific design created in the study. •An ejector design is performed for 4 kW SOFC system.•Critical parameters are numerically studied to determine the ejector performance.•4032 different cases for various ejector geometries are considered.•The maximum entrainment ratio of 7.3 and the maximum STCR of 2.7 are obtained.