Use of wastewater treatment plant biogas for the operation of Solid Oxide Fuel Cells (SOFCs)

Solid Oxide Fuel Cells (SOFCs) perform well on light hydrocarbon fuels, and the use of biogas derived from the anaerobic digestion (AD) of municipal wastewater sludges could provide an opportunity for the CH4 produced to be used as a renewable fuel. Greenhouse gas (GHG), NOx, SOx, and hydrocarbon pollutant emissions would also be reduced. In this study, SOFCs were operated on AD derived biogas. Initially, different H-2 dilutions were tested (N-2, Ar, CO2) to examine the performance of tubular SOFCs. With inert gases as diluents, a decrease in cell performance was observed, however, the use of CO2 led to a higher decrease in performance as it promoted the reverse water-gas shift (WGS) reaction, reducing the H-2 partial pressure in the gas mixture. A model was developed to predict system efficiency and GHG emissions. A higher electrical system efficiency was noted for a steam:carbon ratio of 2 compared to 1 due to the increased H-2 partial pressure in the reformate resulting from higher H2O concentration. Reductions in GHG emissions were estimated at 2400 tonnes CO2, 60 kg CH4 and 18 kg N2O. SOFCs were also tested using a simulated biogas reformate mixture (66.7% H-2, 16.1% CO, 16.5% CO2, 0.7% N2, humidified to 2.3 or 20 mol% H2O). Higher humidification yielded better performance as the WGS reaction produced more H-2 with additional H2O. It was concluded that AD-derived biogas, when cleaned to remove H2S, Si compounds, halides and other contaminants, could be reformed to provide a clean, renewable fuel for SOFCs. (C) 2016 Elsevier Ltd. All rights reserved.