151 Direct Use of Biogas in SOFCs A. Winiwarter DTU Energy, Technical University of Denmark INTRODUCTION Biofuels are among the core sources for sustainable energy. Biogas can be derived from many different sources of residual biomass such as waste, manure, sewage sludge, and agro-industrial residues. It consists mostly of CH4 and CO2 and can be converted to electricity and heat using conventional thermomechanical processes. However, using solid oxide fuel cells (SOFCs) instead, much higher efficiencies can be obtained, as the chemical energy is directly converted to electrical energy, which among others reduces CO2 emissions. A second effect of using SOFCs is that due to the different reaction process, only very low amounts SOx and no NOx are produced. Additionally, a lower methane content is necessary than in conventional processes, making the use of currently discarded gas possible and thereby reduction of overall methane emissions is possible as well. While conventional processes are only sufficiently efficient in large scale, SOFCs could also be used in medium and small scale plants. They are therefore well suited for decentralized electricity production and transport of biomass can be avoided. Biogas is generally seen as high potential sustainable fuel, but most conventional applications require expensive upgrading treatment: after cleaning, the fuel is either converted to syngas (mostly H2 and CO) or CO2 (which accounts for the major part of the gas) is removed to use the remaining CH4 as natural gas substitute. In SOFCs nickel present in the anode serves as catalyst for the reforming reaction of biogas to produce H2 and CO that can be utilized electrochemically. Therefore no external gas conversion is necessary, while at the same time taking advantage of the exothermic electrochemical reactions for supplying heat for the endothermic conversion. METHODS AND RESULTS In this project, biogas from a landfill unit in Denmark was used as direct fuel in SOFCs. CO2 was added as oxygen source to reduce carbon deposition, a well-known problem. The long term effect of the gas on the performance of the cells was determined and compared to a test using synthetically mixed biogas. Very low cell degradation proved the concept applicable and gives way for prototype future development of SOFC technology in combination with biogas. Figure 1 Overview 804 ENERGY CONVERSION POSTER IDEA MASTER THESIS
Grøn Dyst 2016
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