Operational behavior and reforming kinetics over Ni/YSZ of a planar type pre-reformer for SOFC systems

Abstract

At Forschungszentrum Jülich GmbH, a multi-component SOFC design based on planar stacks has been developed, in which all hot system components are scaled to a nominal SOFC stack power of 5 kW. To optimize the SOFC system it is necessary to investigate the effects of design and operating parameters on the system components like pre-reformer and afterburner. A special designed 5-layer planar type steam pre-reformer on basis of Ni/YSZ has been built and tested for operational behavior and kinetics of steam reforming with methane. This paper summarizes and discusses the experimental results on the global reaction kinetics of a Jülich planar pre-reformer in the temperature range between 350 °C and 620 °C at ambient pressure (1 bar). The species compositions of product gas at different feed compositions, flow rates and temperatures are determined by using gas-chromatographic methods and dew-point measurements. The reproducibility of experiments in the low temperature range (especially less than 430 °C) was only assured, when the catalyst has been reduced before every kinetic experiment. The proposed kinetic expression of Arrhenius type (second order with respect to mole fraction of methane and first order with respect to mole fraction of water) gives a good agreement with the experimental results of the methane steam reforming. It is general effective for different steam to carbon ratios. The temperature distribution in the pre-reformer and the loss of heat are also discussed.