3D simulation of a symmetric MCFC stack model

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 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. After 8 fuel cells an IIR unit is located in the stack. An improvement of the efficiency and the life time can be achieved by a better adjustment of the heat sources and the heat sinks. Mathematical modeling can help with this task. For an understanding of the temperature profile a symmetric model containing 4 fuel cells and one IIR unit is created. Due to the fact that the anode and cathode channels are arranged in a cross flow configuration, a 2D model is used for the cells as well as for the IIR units. Combining several of these to the symmetric stack model, where each cell is thermally coupled to its neighbours, allows to describe temperature gradients along the stack. Thus a three-dimensional temperature profile of the cell stack is provided. Major assumptions and the model structure are discussed and simulation results are presented. Subsequently, possible improvements of the model are proposed and first conclusions for an optimal design of the IIR unit as well as the cell stack are drawn