Experimental characterization of a solid oxide fuel cell coupled to a steam-driven micro anode off-gas recirculation fan

[Display omitted] •First realized SOFC system with steam-driven anode off-gas recirculation fan.•Design of a novel oil-free and durable recirculation fan with gas film bearings.•Propulsion with steam turbine leads to explosion-proof and efficient fan operation.•One of the smallest steam turbines tes...

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Veröffentlicht in:Applied energy 2020-03, Vol.262, p.114219, Article 114219
Hauptverfasser: Wagner, Patrick Hubert, Wuillemin, Zacharie, Constantin, David, Diethelm, Stefan, Van herle, Jan, Schiffmann, Jürg
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Sprache:eng
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Zusammenfassung:[Display omitted] •First realized SOFC system with steam-driven anode off-gas recirculation fan.•Design of a novel oil-free and durable recirculation fan with gas film bearings.•Propulsion with steam turbine leads to explosion-proof and efficient fan operation.•One of the smallest steam turbines tested with a tip diameter of 15 mm.•Reliable method of measuring recirculation ratios with a double Venturi nozzle. While the global fuel utilization of solid oxide fuel cells (SOFCs) is limited by the stack aging rate, the fuel excess is typically used in a burner, and thus limiting the system electrical efficiency. Further, natural-gas-fueled SOFCs require treated water for the steam reforming process, which increases operational cost. Here, we introduce a novel micro anode off-gas recirculation fan that is driven by a partial-admission (21%) and low-reaction (15%) steam turbine with a tip diameter of 15 mm. The 30 W turbine is propelled by pressurized steam, which is generated from the excess stack heat. The shaft runs on dynamic steam-lubricated bearings and rotates up to 175 krpm. For a global fuel utilization of 75% and a constant fuel mass flow rate, the electrical gross DC efficiency based on the lower heating value was improved from 52 % to 57 % with the anode off-gas recirculation, while the local fuel utilization decreased from 75% to 61%, which is expected to significantly increase stack lifetime. For a global fuel utilization of 85%, gross efficiencies of 66% in part load (4.5 kWe) and 61% in full load (6.3 kWe) were achieved with the anode off-gas recirculation. The results suggest that the steam-driven anode off-gas recirculation can achieve a neutral water consumption.
ISSN:0306-2619
1872-9118
DOI:10.1016/j.apenergy.2019.114219