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Optimization of Oxygen Feed Membranes In Autothermal Steam-Reformers

J. Hüppmeier1, S. Barg2, M. Baune1, and J. Thöming1. (1) Centre for Environmental Research and Sustainable Technology – UFT, University of Bremen, Leobener Straße UFT, Bremen, D-28359, Germany, (2) Ceramic Materials and Components - CERAMICS, University of Bremen, IW3 / Am Biologischen Garten 2, Bremen, D-28359, Germany

In conventional concepts for autothermal steam-reformers the spatial temperature distribution is disadvantageous. The different rates of the exothermic oxidation and endothermic reforming reactions lead to the problem of temperature hot-spots, which can damage or even destroy the catalyst or other elements of the reformer. This is especially the case, when the needed oxygen is premixed to the feed gas resulting in a high temperature peak in the entrance region. In the past, some first attempts have been made to solve this hot-spot problem.. One idea is, that the oxygen is not premixed to the feed gas but injected at different positions distributed over the length of the reformer. This leads to more but much smaller temperature peaks. Expanding this idea, one can use also a continuous oxygen injection over the length of the reformer. This can for example be realized by an open porous membrane. By varying the permeability of such a membrane we can adjust the spatial oxygen flux distribution. One of our previous works 1 focused on the optimization procedure of the membrane structure to achieve an isothermal behaviour of the adiabatic autothermal steam-reformer. In the present work we investigate the use of such oxygen feed membranes with varying permeabilities, both in experiments and by simulation analysis. The simulation results show that an optimized membrane can be used for a wide range of operation conditions, i.e. mass fluxes and amounts of oxygen flux without being reduced in efficiency. The experimental results are in good agreement with the simulations and indicate the feasibility of the concept of spatial oxygen feed distribution in autothermal steam-reformers to avoid the hot-spot problem.