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Abstract

Fuel cells allow the efficient conversion of chemically bound primary energy into electrical energy. A stationary fuel cell power plant based on a Molten Carbonate Fuel Cell (MCFC) is developed by the MTU CFC Solution GmbH, in Germany.

The life time and efficiency of a MCFC mainly depends on the spatial temperature profile within the fuel cell stack. The temperature itself is determined by the interaction of the endothermal methane reforming process and the heat releasing electrochemical reactions. The electrochemical reactions take place at the fuel cells' electrodes whereas the reforming reaction takes place in special units within the fuel cell stack - the Indirect Internal Reformer (IIR) units. An improvement of the efficiency and the life time can be achieved by a better adjustment of these heat sources and heat sinks. Detailed multi-scale modelling of the specific parts of the MCFC - the anode and cathode compartment as well as the IIR unit - can help with this task.

In a first step small sections of each part are simulated using the CFD software CFX. In each of this detailed models the coupled heat and mass transport is considered. Additional, the methane reforming and the water gas shift reaction are considered within the IIR unit and the anode compartment. The electrochemical reactions at the anode and cathode electrodes are implemented as wall reactions.

In a second step the entire compartment is modelled. For these simulations the geometry is simplified and quasi-homogenous models are used. An anisotropic permeability as well as a locally distributed catalyst activity incorporate the results of the detailed models.

Major assumptions as well as the structure of the models are discussed and simulation results are presented. Subsequently, possible improvements of the models are proposed and first conclusions for an optimal design and further modelling approaches are drawn.