Performance Investigation of a Pilot-Scale Integrated Anaerobic Digestion-Solid-Oxide Fuel Cell System Calibrated to Experimental Stack Data

Abstract

Biogas is a renewable-energy by-product produced at many wastewater treatment plants (WWTPs) by anaerobic digestion. Unfortunately, biogas is currently underutilized at smaller facilities because of the capital and maintenance capital costs associated with combined heat and power (CHP) technologies and biogas purification. Solid oxide fuel cell (SOFC) systems are a CHP technology currently entering commercial markets that could lead to a rise in biogas utilization at WWTPs because they are the CHP technology with the highest electrical efficiencies and most environmentally-friendly emissions profiles.

A 2kWe biogas-fed SOFC pilot plant has been proposed for construction at the Ravensview wastewater treatment plant in Kingston, ON, that is to be directly integrated with one of the on-site digesters. Importantly, the pilot plant will include a biogas purification system comprised of inexpensive adsorbents that selectively targets the two most detrimental contaminant species, hydrogen sulphide and siloxanes.

This work began with an experimental component in which a prospective SOFC stack for the pilot plant was operated on processed biogas. Subsequently, a process model of the pilot plant was developed using the UniSim Design simulation software. The process model is enhanced by the inclusion of a tunable empirical cell model that was calibrated to the prospective stack performance. A series of sensitivity analyses were performed on the pilot plant model which revealed that the system could be operated on the expected range of biogas compositions generated at WWTPs. The maximum feasible gross electrical and CHP efficiencies were estimated to be 62 and 77 % for operation on Ravensview biogas.