Anodic Side
The anodic recirculation system, designed on the basis of a hybrid system power of about 450 kW and a system efficiency of 59%, is composed of a fuel line (for fuel cell fuel flow emulation), an anodic single stage ejector, and the anodic volume. The fuel line has been designed to supply the ejector primary duct with an air mass flow rate (for fuel cell fuel flow emulation) up to 20 g/s. It consists of a 15 kW air compressor, an air dryer, and the flow (MP), pressure (PEjP1), and temperature (TEjP1) sensors. The anodic ejector generates the recirculation flow rate through this system as in a typical SOFC hybrid system. The anodic volume is a nominal diameter pipe (U pipe) of 350 millimetres for a volume of about 0.8 m3. The anodic volume dimension has been designed on the basis of a reference system and a fuel cell dimension consistent with the micro gas turbine mass flow rate. The Rolls-Royce fuel cell stack has been considered. Starting from the RRFCS plant layout some calculations have been carried out taking into account the different system layout and operating parameters. With a simulation tool, already developed, the size and performance of the fuel cell stack coupled with the T100 micro gas turbine have been defined.
Cathodic Side
The test rig designed for hybrid system emulation is composed of a commercial recuperated microturbine package (see Micro Gas Turbine Test Rig) modified for the fuel cell emulator connection, a set of pipes designed for measurement reasons and to widen the operative range of the machine with a bleed, five valves to control the flow rates during start-up phases and a high temperature modular volume for the fuel cell stack physical simulation.
The fuel cell physical emulator, designed with thorough CFD support presented in a previous work, is a thermally insulated modular vessel connected between the recuperator outlet and the combustor inlet, as in a real pressurized hybrid system. This vessel, designed for a maximum temperature of about 630°C (903.15 K), is composed of two collector pipes, connected to the recuperator outlet and the combustor inlet respectively, and five module pipes connected to both collectors. These last pipes are mounted on seams for easy removal, i.e. easy volume dimension change. Both collectors and module pipes have a nominal diameter of 350 millimeters and their total length is around 43 meters for a maximum volume of about 4 m3 (the Greitzer parameter of the compressor is between about 1.0 with the minimum volume and 8.0 in maximum volume configuration, while in the original commercial layout of the machine the Greitzer parameter of the compressor is between about 0.4 and 0.7).
