Energy balance model of a SOFC cogenerator operated with biogas

• Published in: Journal of power sources 2003-05, Vol.118 (1), p.375-383
• Main Authors: Van herle, Jan, Maréchal, F., Leuenberger, S., Favrat, D.
• Format: Article
• Language: English
• Subjects: Applied sciences; Biogas fuel; Combined power plants; Efficiency; Energy; Energy balance; Energy. Thermal use of fuels; Equipments for energy generation and conversion: thermal, electrical, mechanical energy, etc; Exact sciences and technology; Fuel cells; Installations for energy generation and conversion: thermal and electrical energy; SOFC stack model
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/S0378-7753(03)00103-4

A small cogeneration system based on a Solid Oxide Fuel Cell (SOFC) fed on the renewable energy source biogas is presented. An existing farm biogas production site (35 m 3 per day), currently equipped with a SOFC demonstration stack, is taken for reference. A process flow diagram was defined in a software package allowing to vary system operating parameters like the fuel inlet composition, reforming technology, stack temperature and stack current (or fuel conversion). For system reforming simplicity, a base case parameter set was defined as the fuel inlet of 60% CH 4:40% CO 2 mixed with air in a 1:1 ratio, together with 800 °C operating temperature and 80% fuel conversion. A model stack, consisting of 100 series elements of anode supported electrolyte cells of 100 cm 2 each, was calculated to deliver 3.1 kW el and 5.16 kW th from an input of 1.5 N m 3/h of biogas (8.95 kW LHV), corresponding to 33.8 and 57.6% electrical and thermal efficiencies (Lower Heating Values (LHVs)), respectively. The incidence on the efficiencies of the model system was examined by the variation of a number of parameters such as the CO 2 content in the biogas, the amount of air addition to the biogas stream, the addition of steam to the fuel inlet, the air excess ratio λ and the stack operating temperature, and the results discussed.