Ammonia as a Contaminant in the Performance of an Integrated SOFC Reformer System

As supply of natural gas (NG) is limited, more attention is being given to operating fuel cells on syngas derived from gasification of feedstocks such as coal and biomass. Ammonia (NH₃) is one of the problematic contaminants contained in syngas produced from these nitrogen containing feedstocks. NH₃ can be easily oxidized to nitric oxide (NO) in a combustion process and thus if present in the anode exhaust gas would be problematic. The potential effects of NH₃ (particularly at low levels) on fuel cell system performance have not been well studied. The former studies on NH₃ have been limited to either the reforming process alone or testing the fuel cell at the cell level with NH₃ containing gases. No studies have been accomplished on a fuel cell system level basis. Objectives of this work are to obtain a comprehensive understanding of fuel cell system performance on syngas containing NH₃ using an integrated SOFC reformer system. Detailed analysis is conducted within the three major reacting components — indirect internal reformer, SOFC stack and combustion zone. Various simulation tools (etc., CHEMKIN, ASPEN, APSAT) are utilized for analysis. Results show that NH₃ conversion (into N₂ and H₂) in the internal reformer is about 50% when temperature is 750° C. NH₃ conversion (into N₂ and H₂) in the SOFC stack can affect NO_x emissions significantly. More than 50% NH₃ left from SOFC stack can convert into NO_x in the combustion zone. Experimental study is also planned to validate the theoretical results.