Performance Evaluation of a SOFC-GT Hybrid System With Ejectors for the Anode and Cathode Recirculations

Abstract

The recirculation of the anode and cathode exhaust has huge benefits on the fuel cell system, for instance, keeping proper operating conditions of the reformer and preheating the inlet air which reduces the recuperator size. Furthermore, the ejectors used for the fuel cell recirculation are more reliable and low-cost in maintenance than high temperature blowers. In this paper, an anode and cathode recirculation scheme, both equipped with ejectors, was designed in a Solid Oxide Fuel Cell-Gas Turbine (SOFC-GT) hybrid system. Additionally, a blower was added between the compressor and the heat exchanger to overcome the significant pressure loss caused by the cathode ejector. This configuration separates the compressor from the fuel cell and turbine components, introducing more flexibility in system modification. The investigations were conducted to analyze the performance of the hybrid system with anode and cathode ejectors in this paper. Firstly, the ejector model was established based on the energy, mass and momentum balance equations. Furthermore, it was validated that the ejector model was consistent with the reference data. Secondly, the stand-alone performance of the anode and cathode ejectors was analyzed. The geometry parameters of the ejectors were determined based on the design conditions. Then the off-design performance was analyzed based on the designed ejectors geometry. The results show that the performance of the ejectors is greatly influenced by the inlet conditions of the primary and secondary fluid mass flow rate. Finally, the anode and cathode ejectors were integrated into the SOFC-GT hybrid system. Meanwhile, the off-design and dynamic behaviors of the whole SOFC-GT hybrid system with anode and cathode ejectors for recirculation loops were analyzed. In the end, the results show that the designed ejectors can effectively satisfy the demands of the SOFC-GT system with anode and cathode recirculation loops. And the safety range of relative fuel flow rate is from 0.42 to 1.22 when the rotator speed is constant.