Performance of a Solid Oxide Fuel Cell short-stack with biogas feeding

In this study, the main sections required to produce electricity in an SOFC short stack starting from biogas were studied and tested at a lab-scale level. A test-rig including a cleaning unit, a reformer and an SOFC stack was built and used to run a test of 500h. In the plant, an in-house planar SOFC short stack (composed of three nickel based anode-supported cells) was fed by a simulated biogas mixture (60vol.% CH4, 40vol.% CO2) contaminated by 30ppmv of H2S (the main contaminant found in biogas, and deleterious for both the reformer and fuel cells). In the plant, H2S is first removed from the gas stream by adsorption in a fixed bed reactor packed with Na–X zeolites. The mixture was also passed on a ZnO guard bed (heated at 300°C) before feeding the reformer unit in order to guarantee a durable and stable operation of the same. The reformer uses a Ni-based catalyst, and was operated at ∼700°C in a mixed steam-/dry-reforming condition to produce a gas mixture suitable for the Ni-based SOFC with CH4 converted almost entirely to H2 and CO. The 3-cells short stack was operated at 800°C and 0.1Acm−2 for more than 500h. The gas analysis was performed, via a mass spectrometer, in several points of the plant. These measurements indicated that no sulfur breakthrough takes place from the zeolites bed, and furthermore that the catalyst has a quite stable behavior.