Ejector design and performance evaluation for recirculation of anode gas in a micro combined heat and power systems based on solid oxide fuel cell

Abstract In this paper, a theoretical analysis of an ejector for micro combined heat and power systems based on Solid Oxide Fuel Cell (SOFC) for small-scale residential applications is presented. A novel detailed procedure for the ejector designing is provided and its effectiveness is validated through a comparison with testing results. The ejector geometry is analysed in terms of component efficiency. The SOFC system performance with regard the recirculation of anode gas is finally discussed. Results show that fuel inlet temperature and the diameter of the ejector mixing chamber of the ejector largely affect the ejector performance. A large mixing chamber diameter allows a high entrainment ratio but causes a worse ejector efficiency suggesting a highest efficiency still ensuring the required entrainment ratio. At system level, it is shown that the degree of fuel pre-reforming affects the recirculation ratio. Besides, if anode gas recirculation is implemented the system capital cost decreases due to reduction in size of ancillary components. The high electrical efficiency achieved by the system reduces the heat output and makes it more attractive when less heat is demanded.