Fuel flexibility for a turbocharged SOFC system

The aim of this paper is the analysis of a turbocharged Solid Oxide Fuel Cell (SOFC) system considering the influence of fuel composition variation. This is an innovative system layout based on the coupling of an SOFC stack with a turbocharger. The SOFC pressurization carried out with a turbocharger instead of a microturbine is a solution to combine high efficiency with reduced-cost plant layout. Moreover, the fuel flexibility is an essential issue to operate the system with different fuel compositions ranging from natural gas to biogas (considering also the CO2 removal option). This research activity started from the development of a steady-state system model using previously validated tools. The software was implemented in Matlab®-Simulink® environment considering the coupling of the different plant components. The analysis was started considering design conditions for a system fed by biogas (50% CH4 and 50% CO2 molar composition). Then, to reach fuel flexibility performance (as required for applications with renewable sources), the anodic ejector was re-designed to satisfy the related constraint for the Steam-to-Carbon ratio. The mentioned change in fuel composition involved also the control valves (bypass and/or bleed) to maintain the SOFC temperature at its set-point value, taking into account all the system constraints.