Abstract
It is well known that membrane reactors are inherently two-dimensional systems in which species concentrations vary as a consequence of both the reaction and permeation across the membrane, which occurs in the direction perpendicular to that of the main gas flow. Recently, an expression for an enhanced Sherwood number was developed to describe the hydrogen concentration gradients arising in methane steam-reforming membrane reactors as a consequence of the combined effect of hydrogen production, dispersion, and permeation. Here, the analysis is developed in further detail with the aim of (i) assessing the validity of the simplifying assumptions made when developing the 1D model and (ii) identifying the operating conditions under which it is possible to employ the 1D model with the enhanced Sherwood number.
Highlights
The use of membrane reactors has been attracting significant interest as a technology capable of allowing decentralized hydrogen production and coupling with solar heating technologies [1,2]
It is well known that membrane reactors are inherently two-dimensional systems in which species concentrations vary as a consequence of both the reaction and permeation across the membrane, which occurs in the direction perpendicular to that of the main gas flow
In a previous work by some of the same authors [17], it was found that the behaviour of membrane reactors for the production of pure hydrogen can be divided into two main regimes: one in which the transport of hydrogen in the radial direction is limited by the membrane itself and one in which the resistance to mass transport within the packed bed is limiting
Summary
The use of membrane reactors has been attracting significant interest as a technology capable of allowing decentralized hydrogen production and coupling with solar heating technologies [1,2]. Many authors have resorted to 1D models to describe the behaviour of membrane reactors, effectively neglecting the presence of radial gradients [3,4,5]; it has been shown that such a solution often leads to results that are very different from those obtained in reality in terms of integral variables, such as the total amount of hydrogen permeating from the membrane per unit of time [6,7,8]. To the best of our knowledge, at the moment, the attempt to obtain a novel expression for the enhanced Sherwood number has been made a few times for membrane separators [13,14], but only once, by some of the same authors of the present work, for membrane reactors [15]
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