Reformering av naturgas för fastoxidbränsleceller

Abstract

This work studies the reforming of natural gas for use in solid oxide fuel cells (SOFC). The aim of the thesis was to construct a reformer feeding reformate gas to a SOFC test station. The reformer should be able to operate in steam reforming, catalytic partial oxidation and anode off-gas recycling mode and in a wide temperature and gas flow range. SOFCs are seen as one of the promising energy conversion technologies. A variety of hydrocarbons are suitable as fuels, but it is often sensible to use a pre-reformer which convert the fuel into a hydrogen-rich gas stream. The thesis literature part gives an detailed overview of fuel cells and reforming methods. The experimental work covers the construction process, including dimensioning of the reformer according to the specifications of the test station and reactor design to optimise heat transfer. A precious metal catalyst was chosen for the reformer. Methods for avoiding carbon formation were studied. In addition, a Comsol Multiphysics computer simulation was constructed to demonstrated the couplings between heat and mass transfer and chemical reactions in the reformer. The performance of the reformer was tested in all reforming modes. The gas composition of product gas was analysed by gas chromatography and compared to calculated equilibrium values. Additionally, the catalyst stability was tested in a 190 hour long test run in steam reforming. All measured gas compositions matched closely with the calculated values. The identified deviations were small and to no harm in practical use. The heat transfer in the reactor was considered optimal and the operator can control the outlet gas temperature by setting the furnace to the targeted temperature. No signs of degradation were seen in the stability test. According to this study, the performance of the reformer is optimal in a wide operation range and this reformer design is suitable to be used in fuel cell research