Thermodynamic design and analysis of SOFC/PEMFC hybrid systems with cascade effects: A perspective on complete carbon dioxide capture and high efficiency

To capture as much carbon dioxide as possible while minimizing the performance degradation, this study proposes two solid oxide fuel cell (SOFC)/polymer electrolyte membrane fuel cell (PEMFC) hybrid systems. One is a hybrid system in which the PEMFC not only generates power, but also performs the role of CC (hybrid system 1). The other is a hybrid system in which pressure swing adaption (PSA) is incorporated to capture carbon dioxide, and consumption of hydrogen in the PEMFC is maximized (hybrid system 2). In addition, an organic Rankine cycle (ORC) was added to further improve the performance of the hybrid systems by utilizing the waste heat of exhaust gas. The cascade effects between SOFC and PEMFC contribute to achieving nearly complete CC and high efficiency. Especially, hybrid system 2 achieved 10% and 5%p improvements over the stand-alone SOFC system in net power and efficiency. It is promising in that the proposed systems utilizing cascade effects can achieve nearly zero carbon emission and high efficiency despite the use of natural gas without hydrogen supply. In other words, the proposed systems are expected to contribute to the realization of carbon neutrality without waiting for the technological maturation associated with hydrogen.