Development and Simulation of an Innovative Planar Stack Design-Combining a Solid Oxide Fuel Cell (SOFC) With an Allothermal Steam Reformer

摘要

Increasing energy demands, limited resources, pollutants, and CO2-emissions caused bynthe use of fossil fuels require a more efficient and sustainable energy production. Due tontheir high electrical efficiencies as well as fuel and application flexibilities, high temperaturenfuel cells offer great potential to meet the demands of the future energy supply. Thenfuel gases hydrogen and carbon monoxide, which are electrochemically convertible innsolid oxide fuel cells (SOFCs), have to be generated by reformation or gasification ofnhydrocarbons, or in the case of pure hydrogen, as fuel gas, by electrolysis. For thesengenerating processes energy is required. This generally leads to a deterioration of SOFCsystemnefficiencies. At state of the art combined processes, the reformation or gasificationnreactor and the SOFC are usually separated. The heat required for the endothermicnreforming is generated by partial oxidation (POx) of the supplied fuel or by using thenwaste heat of the exhaust gases. At the Institute for Heat- and Fuel-Technology of thenTechnische Universität Braunschweig, an innovative planar SOFC-stack-design with indirectninternal reforming and without bipolar plates was developed. Due to the thermalnand material couplings, the SOFC-waste heat can be directly used to supply the endothermicnreforming process. Additionally, a part of the hot anode off-gas, consistingnmainly of water vapor, is recycled as a reforming agent. Therefore, based on the principlenof the chemical heat pump, depending on the fuel used, system efficiencies of more thann60% can be achieved, even though the SOFC itself reached only an electrical efficiencynof approximately 50%. Additionally, due to the cascaded SOFC structure resulting innhigh fuel utilization, postcombustion of the waste gases is no longer necessary. Becausenof the SOFC membrane allowing only an oxygen-ion flow and thus representing an airnseparation unit and the SOFC design without the mixing of anode and cathode flows, ansimple CO2-separation can be realized by condensing the water vapor out of the anodenoff-gas. Another advantage of the newly developed stack design is its parallel interconnection,nwhich leads to higher reliability concerning single stack levels. The aim of thenwork was a first dimensioning of the new stack design for natural gas as a fuel and itsnenergetical analysis concerning operation and feasibility. With the simulation programndeveloped, the theoretical feasibility of the concept and a high electrical efficiency ofnabout 60% were proven.