UTILISATION OF BIOGAS FROM AN URBAN SEWAGE TREATMENT PLANT IN A SOLID OXIDE FUEL CELL

摘要

A biogas coming from anaerobic digestion of urban sewage has been used to feed a SOFC planar anode-supported cell. The sewage is produced from the urban area of Torino (IT), and eventually collected and treated by SMAT (the municipal company managing the potable and waste water of the city). The biogas is produced by the thermophilic fermentation of the sludge which remains after the several treatments the sewage goes through in the above-mentioned plant. The biogas is of a high quality: it has on average a a methane content around 65% (the balance being essentially CO_2), and the only significant impurity measured is H_2S in a range of 70-80 ppm. The as-produced biogas has been used for feeding a planar Ni-YSZ anode-supported SOFC with a LSCF cathode. The biogas desulphurization was accomplished flowing the gas in a fixed-bed reactor, filled with activated. The fuel processing with POX has been assessed to avoid carbon deposition into the Ni-YSZ anode and convert the CH_4 into H_2 and CO. Short tests to check for eventual anode degradation were performed under typical operating conditions. The cell voltage was always stable under load with the tested mixtures. A cell electrical efficiency around 45% has been measured at 800°C and 80% FU. System simulations have performed as well to assess the whole system configuration under a biogas feeding. Optimization routines have been implemented to predict the best net AC efficiency achievable by a SOFC system running on biogas. Additional considerations on the management of poor LHV biogas mixture have been also assessed, showing how dry-reforming of CH_4 with the CO_2 already available in the biogas stream would be an excellent option needed to be investigated with further detail in the next future.