Millisecond Production of Hydrogen from Alternative, High Hydrogen Density Fuels in a Cocurrent Multifunctional Microreactor

Abstract

A pseudo-2-dimensional model is used for modeling a multifunctional microreactor for hydrogen generation by coupling catalytic ammonia decomposition on ruthenium with catalytic propane combustion on platinum. The two reactions are carried out in adjacent parallel plate channels in a cocurrent flow mode. Operating lines defining the attainable region are computed. The high temperatures and fast heat transfer ensure that both reactions go to completion in as low as submillisecond contact times and enable compact hydrogen production for portable and distributed power generation. The ammonia decomposition reaction tends to be limited by the intrinsic rate of reaction, whereas catalytic combustion is also affected by mass and heat diffusion. We have found that moderate and high conductivity materials are preferable because they support a rather wide attainable region. We show that one such device could enable variable hydrogen supply for variable power needs. A simple operating strategy to dial in the desirable power is proposed, which ensures high thermal efficiency (∼75% once-through efficiency of the integrated device and ∼85% reformer efficiency, both without any heat recuperation), wall isothermicity, and high conversions.

Catalytic Combustion for Supplying Energy for Endothermic Reaction

“…Alternative to fossil fuels: As alternative to the use of conventional hydrocarbons and due mainly to its high hydrogen release capacity, some researchers investigated also ammonia [25,94] as a carrier for hydrogen delivery and distribution. Given the ease of liquefying ammonia, these investigations supports the trend [95,96] for the potential use of NH 3 as a carbon-free fuel for the CO-free production of hydrogen to feed portable devices and fuel cells (when NH 3 concentration<0.1ppm).…”

“…Indeed, the percentage ratio between the energy (based on the LHV) obtainable from the produced H 2 and the energy (also based on the LHV) contained in the total amount of NH 3 and H 2 supplied in both channels, did not exceed 10.4%. To overcome the limits imposed by the low power generated by the ammonia combustion and to avoid the introduction of H 2 in the exothermic channel the coupling of NH 3 reforming with hydrocarbon oxidation has been considered in modelling works [31,94]. Indeed, Kaisare et al [94]proposed a pseudo-2-dimensional model for the production of H 2 by coupling the decomposition of NH 3 on ruthenium with the combustion of propane on platinum; there actions occurred in adjacent parallel channels of a micro plate reactor.…”

Flame Stability of Propane-Air Premixed Combustion in Heat-Recirculation Micro-Combustors

“…This is a result of the walls playing a competing role in flame stability: walls transfer heat upstream for ignition of the incoming cold reactants but at the same time are responsible for heat losses. Consequently, there is an optimum wall thermal conductivity in terms of flame stability, which appears to be that of common ceramics such as alumina and silica, maximizing the critical heat loss coefficient (Kaisare and Vlachos, 2007b;Kaisare et al, 2009;Stefanidis and Vlachos, 2009). Low wall thermal conductivity limits the upstream heat transfer along the wall, which limits the preheating of the feed, inhibiting the onset of combustion, and results in blowout.…”

LES of a Meso Combustion Chamber with a Detailed Chemistry Model: Comparison between the Flamelet and EDC Models

“…Previous work in micro/meso-propulsion related to scaling laws issues [3][4][5][6] and focuses predominantly on fluid dynamics and combustion [7][8][9][10][11][12][13][14][15][16][17][18]. Three dimensional numerical simulations of methane-air combustion in swirling micro/meso-combustors are not common: the majority of the references available in the literature investigate the combustion process of propane in micro/meso sized combustor by assuming 2-D axi-symmetrical geometry and reduced kinetic mechanism [7][8][9][10][11][12][13][16][17][18].…”

“…Three dimensional numerical simulations of methane-air combustion in swirling micro/meso-combustors are not common: the majority of the references available in the literature investigate the combustion process of propane in micro/meso sized combustor by assuming 2-D axi-symmetrical geometry and reduced kinetic mechanism [7][8][9][10][11][12][13][16][17][18].…”