Rolls-Royce Fuel Cell systems is developing a hybrid system based on SOFCs (Solide Oxide Fuel Cell) and micro-turbines. The unique and proprietary RRFCS architecture relies on hot gas recycle on both sides of the fuel cell stack; internally to the system an anode recycle loop supplies the proper mixture at the fuel cells stack, while on the cathode side, a second loop is designed to feed the fuel cells stack and to provide the right amount of heat to the reformers. In both cycles ejectors are used to drive the flows through the stack: at the anodic side they provide the steam for the reforming of the fresh fuel stream, acting also as a fuel pre-heater. At the cathode side the recycle is used to heat up the compressed fresh air. In the reformers the fuel is then converted into a reformate mixture in an endothermic reactor fed by the hot stream leaving the stack on the cathode side.The current paper explains how the two cycles have been designed from an aero-thermal point of view and how stress analysis has been conducted on fuel cells tubes to ensure appreciable robustness of the stack.
