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 biogaswere studied and tested at a lab-scale level. A test-rig including a cleaning unit, a reformer and an SOFCstack was built and used to run a test of 500 h. 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(60 vol.% CH4, 40 vol.% CO2) contaminated by 30 ppmv 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 streamby adsorption in a fixed bed reactor packed with Na–X zeolites. The mixture was also passed on a ZnOguard bed (heated at 300 C) before feeding the reformer unit in order to guarantee a durable and stableoperation of the same. The reformer uses a Ni-based catalyst, and was operated at 700 C in a mixedsteam-/dry-reforming condition to produce a gas mixture suitable for the Ni-based SOFC with CH4converted almost entirely to H2 and CO. The 3-cells short stack was operated at 800 C and 0.1 A cm2for more than 500 h. The gas analysis was performed, via a mass spectrometer, in several points of theplant. These measurements indicated that no sulfur breakthrough takes place from the zeolites bed,and furthermore that the catalyst has a quite stable behavior.Results clearly show how a SOFC stack can be successfully operated with a contaminated biogenous gasmixture as fuel. As a matter of fact the cell stack exhibited a regular behavior, with no signs of degradationin the complete test.