Hydrogen production from hydrocarbon and ammonia fuels through heat-recirculating “Swiss-roll” reformers

Abstract

The prospects of hydrogen (H<inf>2</inf>) production from hydrocarbons and ammonia (NH<inf>3</inf>) through spiral counterflow “Swiss roll” heat-recirculating combustors were explored. The concept leverages superadiabatic, ultra-rich combustion facilitated by multiple coupled internal counter-flow heat exchanger channels acting to sustain fuel reforming without any need for an external energy source. Zero-dimensional modeling identified favorable conditions (temperature, composition, residence time, etc.) for the highest reforming efficiency and guided the design of heat-recirculating combustors, which were then evaluated computationally through two-dimensional computational fluid dynamics (CFD) calculations. Promising designs were then assessed experimentally through 3D-printed Inconel718 Swiss roll combustors working with hydrocarbon fuels at a 7.5 cm portable scale, showing decent agreements with CFD predictions, demonstrating ≈ 18 % peak hydrogen concentration for methane (CH<inf>4</inf>)-air and ≈ 23 % for propane (C<inf>3</inf>H<inf>8</inf>)-air cases, respectively. For ammonia, sensitivity studies reveal yield favorability with increasing mixture equivalence ratio and temperature. The message is also emphasized by two-dimensional CFD results at a 30 cm scale operating at 10 atm elevated pressure, conducted for high-throughput applications. An improved double-inlet design is also proposed, capable of achieving up to ≈ 32 % hydrogen concentration, corresponding to ≈ 63 % yield. The reformate’s mixture properties that characterize flame stability, such as laminar flame speed ( S<inf>L</inf> ) and ignition delay time ( IDT ), were found to greatly improve as temperature and hydrogen concentration increase post-reforming. The technology can potentially serve either as a stand-alone reformer or augmenter for gas turbines to enable sole ammonia fuel, carbonless operations.