A 5 kWel Solid Oxide Fuel Cell Stack Operating on Biomass Gasification Producer Gas: System Design and Results

Abstract

This paper describes the system setup and presents results from the ongoing BioSOFC project. The project aims at demonstrating integration of atmospheric biomass steam gasification, high temperature gas cleaning and Solid Oxide Fuel Cells (SOFCs). This is done by taking a slipstream from a steam gasification reactor (the Fast Internally Circulating Fluidised Bed (FICFB) gasifier at Biomasse Kraftwerk Gu¨ssing in Gu¨ssing, Austria) as fuel feed for a 5 kWel Solid Oxide Fuel Cell (SOFC) stack. The system also includes a novel high temperature particle filter (the Panel Bed Filter (PBF)) and a high temperature H2S removal unit. The biomass gasifier, using wood chips as fuel, has a dry producer gas consisting of H2 (up to 45 vol%), CO (up to 30 vol%), CO2 (up to 20 vol%), CH4 (8–12 vol%) and N2 (1–2 vol%). This gas composition makes the producer gas highly suitable as fuel for SOFCs. However, the gas has a relatively high particle loading (up to 60 g/Nm3) and a tar content of up to 2 g/Nm3. In addition, it has been reported that the dry producer gas contains 100–200 ppmv H2S and 500–1000 ppmv NH3. Due to otherwise expected fuel cell performance degradation, the particles have to be removed before entering the SOFC stack. In addition, the sulphur (mainly H2S) concentration must be reduced to minimize the performance degradation in the SOFC. The slipstream is taken from the top of the gasifier freeboard, and is then cooled from about 900°C to 550°C before entering the PBF where the particles are removed. The H2S concentration is reduced in a separate fixed-bed reactor with a Zink-oxide based sorbent. The pressure in the producer gas is increased from the somewhat below atmospheric pressure in the filter to the atmospheric pressure required by the SOFC stack. This pressure increase is achieved by means of two high temperature fans operated at about 525°C. The producer gas is then heated again to up to 900°C before entering the fuel cell stack. This paper presents results from component tests carried out at the Norwegian University of Science and Technology (NTNU) as well as results from the field tests of the system in Gu¨ssing. This ongoing project is scheduled to continue until December 2007. The BioSOFC project is carried out in cooperation with TU-Vienna and Austrian and Norwegian technology companies. The project is funded by the Research Council of Norway and six Norwegian companies.