Josefin Meusinger

Modelling of gas transport phenomena in SOFC anodes

Internal steam reforming in SOFC cells leads to inhomogeneous temperature distributions according to the fast reforming reaction kinetics. This results in thermal induced stresses and may lead therefor to mechanical failure of the material. A one-dimensional numerical simulation program has been developed to describe the transport of gases inside the SOFC anode due to diffusion and permeation as well as the kinetic of the reforming reaction and the electrochemistry. Simulations with experimentally determined reaction rates and structural properties of the anode materials have been performed. In order to reduce the methane conversion rate, a sensitivity analysis has been performed. It can be shown, e.g., that a reduction of the structural parameter ψ which is the ratio of porosity e to tortuosity δ of 26.28% compared to standard material leads to a lowering of the methane conversion rate of 12.24%. Finally, produced cermets are screened in view of a conversion lowering effect.

Optimization of a 200 kW SOFC cogeneration power plant. Part II: variation of the flowsheet

An energetic and economic analysis of a decentralized natural gas-fuelled solid oxide fuel cell (SOFC) power plant in the range of 200 kW capacity is carried out. All calculations start from a basic plant concept with a simple flowsheet and a basic parameter set of SOFC operation and economic data. Changes in costs of electricity and plant efficiencies are determined for variations of the plant concept. Flowsheets with gas recycling by blowers or jet boosters are described. Cathode gas recycling by jet boosters turns out to be more advantageous with respect to the costs of electricity than gas recycling by hot gas fans. The influence of pressure drop in the cathode gas circuit is analyzed. In case of anode gas recycling an internal steam circuit exists. This has the advantage that the external steam generator is eliminated and that the steam concentration in the exhaust gas is reduced. Therefore, a higher amount of excess heat can be used. Removal of useful heat at higher temperature levels diminishes the driving temperature differences and enlarges the heat exchange area of the recuperative heat exchangers located downstream.

Process analysis of a liquid-feed direct methanol fuel cell system

Abstract Recently, a greatly increasing interest in solid polymer electrolyte fuel cells (PEFC) for a range of applications has been observed. The direct methanol fuel cell (DMFC) based on a PEFC uses methanol directly for electric power generation and promises technical advantages, for example, for power trains. This study analyses the interaction between a DMFC stack fed with a liquid aqueous methanol solution and the peripheral system equipment. A simulation model of a DMFC system for mobile applications (from methanol to net electricity) is presented to calculate system efficiencies on the basis of thermodynamic engineering calculations. Based on the simulation calculations, useful operating requirements can be specified. To optimise the performance of DMFC systems, it is necessary to consider the operational characteristics of all the components required in the system. There are worldwide activities to improve the performance of a DMFC stack, which depends on numerous operating parameters. But it is not sufficient to optimise only the current/potential curves of the fuel cell without taking all the consequences for the system into consideration. The results of the computer simulation presented here emphasise the difficulties in improving fuel cell performance without decreasing system efficiency and describes the consequences for the systems operation conditions. Priorities are additionally set concerning the heat management of the fuel cell stack. In the case of liquid fuel supply, the water crossover through the membrane and the ensuing vapourisation at the cathode side impairs the thermal balance. Key operating parameters, which influence these effects, are pressure, temperature, air flow and methanol permeation rate.