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Based on a prototype presented in a prior publication, this research investigates the operational characteristics of a methane-fueled solid oxide fuel cell (SOFC) system with anode off-gas recirculation (AOGR) for electrical energy supply on sea-going vessels. The proposed first-principle system model utilizes a spatially segmented SOFC stack and lumped balance of plant components validated on the component level to accurately depict the steady-state and transient operating behavior. Five operational limitations are chosen to highlight permissible operating conditions with regard to stack and pre-reformer degradation. Steady-state operating maps are presented, emphasizing efficient operating conditions at maximum stack fuel utilization and minimal permissible oxygen-to-carbon ratio. Exemplary transient load changes illustrate increasing system control complexity caused by gas flow delays due to the spatially distributed plant layout. Actuation strategies are presented and underline the need for a top-level model predictive system controller to assure a dynamic and efficient operation within the defined constraints. [ABSTRACT FROM AUTHOR]

A laboratory-scale solid oxide fuel cell (SOFC) system using liquefied natural gas (LNG) as a fuel is designed to be used as an energy converter on seagoing vessels (MultiSchIBZ project). The presented system design phase is supported by thermodynamic system simulation. As heat integration plays a crucial role with regard to fuel recirculation and endothermic pre-reforming, the heat exchanger and pre-reforming component models need to exhibit a high degree of accuracy throughout the entire operating range. Compact additively manufactured tube-bundle and plate-fin heat exchangers are designed to achieve high heat exchange efficiencies at low pressure losses. Their heat transfer correlations are derived from experimental component tests under operating conditions. A simulation study utilizing these heat exchanger characteristics is carried out for four configuration variants of pre-reforming and heat integration. Their system behaviour is analyzed with regard to the degree of pre-reforming and the outlet temperature of the fuel processing module. The combination of allothermal pre-reforming with additively manufactured plate-fin heat exchangers exhibits the best heat integration performance at nominal full load and yields a partial load capability to up to 60% electrical load at net electrical efficiencies of 58 to 60% (LHV). [ABSTRACT FROM AUTHOR]

Electrolyte-supported solid oxide cells are often used for steam electrolysis. Advantages are high mechanical stability and a low degradation rate. The aim of this proof of concept study was to use a femtosecond laser to process the electrolyte of an electrolyte-supported solid oxide cell and evaluate the effect of this laser treatment on the electrochemical performance. The femtosecond laser treatment induces a macroscopic and a superimposed microscopic structure. It can be proven that the electrolyte remains gas tight and the electrochemical performance increases independently of the laser parameters. The initial area-specific resistance degradation during a constant current measurement of 200 h was reduced from 7.9% for a non-treated reference cell to 3.2% for one of the laser-treated cells. Based on electrochemical impedance measurements, it was found that the high frequency resistance of the laser-treated cells was reduced by up to 20% with respect to the reference cell. The impedance spectra were evaluated by calculating the distribution of relaxation times, and in advance, a novel approach was used to approximate the gas concentration resistance, which was related to the test setup and not to the cell. It was found that the low frequency polarization resistance was increased for the laser-treated cells. In total, the area-specific resistance of the laser-treated cells was reduced by up to 14%. [ABSTRACT FROM AUTHOR]