Electrochemical Air Separation and Emergency Power Fuel Cell for Aircraft

Abstract

The crash of TWA Flight 800 in July 1996 was attributed to an explosion in the center fuel tank. Since then, commercial airliners have been equipped with inerting systems to prevent explosive mixtures of air and kerosene vapor from forming in fuel tanks. The incumbent technology is based on hollow-fiber membrane (HFM) separation modules that split air into an oxygen-enriched air (OEA) stream and a nitrogen- enriched air (NEA) stream. The nitrogen enriched air used to inert kerosene contains less than 12% oxygen. Other methods for separating air like cryogenic distillation and pressure swing absorption producer purer oxygen than HFM, but they do not scale down well. Another alternative is electrochemical air separation. High-temperature air separation units using solid oxide cells have been investigated for large-scale applications like oxy-combustion to facilitate carbon dioxide sequestration. However, high-temperature technologies may be less suitable for transportation applications. Electrochemical air separation at low temperatures can be accomplished with relatively compact polymer-electrolyte cells that evolve oxygen at the anode and reduce oxygen at the cathode. The effluent from the cathode is nitrogen enriched. This presentation discusses proof of concept tests and uses these to explore the relative merits of this approach versus incumbent HFM. The electrochemical air separation stack can be fed hydrogen to provide power during emergencies, potentially performing the functions of two components on commercial aircraft.