Performance analysis of a MCFC & supercritical carbon dioxide hybrid cycle under part load operation

Abstract

The authors have previously presented a proposal for hybrid cycles comprising a high temperature fuel cell, either MCFC or SOFC, and a bottoming closed supercritical Brayton cycle working on carbon dioxide, whose expected performance has already been reported. As a continuation, this work presents an assessment on the expected part load performance of such a hybrid system where a simple recuperative carbon dioxide cycle has been considered, instead of the more complicated recompression cycle usually adopted for heavy duty power plants – fast nuclear reactors. Different control strategies for part load operation have been considered and incorporated into the previous model: inventory control, by-pass control and temperature control. Then, a performance analysis of the bottoming system under similar part load operating conditions at the fuel cell has been carried out. Results show the excellent part load performance of the system proposed and, more specifically, the interest of a mixed control instead of using a single technique, which is not feasible in practice due to operational limits. Finally, the very important effect of heat exchanger effectiveness on system efficiency is reported, especially when temperature control is adopted.