Multiscale modeling of fixed-bed reactors with porous (open-cell foam) non-spherical particles: Hydrodynamics

Abstract

A B S T R A C TAn accurate numerical model is proposed to simulate flow through cylindrical fixed-bed reactors with randomly packed porous non-spherical particles. The length scale for flow outside the porous particles (made of open-cell foam) is O (10 ) 2 higher than the size of the internal micro-pores of the particles. To capture the flow at these two different length scales, a multiscale modeling approach, derived using volume averaging theory (VAT), is developed. The flow through and around the porous particles is computed as a single hydrodynamic field in a Cartesian computational domain. The flow within the inter-particle space is fully resolved, whereas, flow at the scale of the intra-particle micro-pores is not resolved and instead represented by closure terms. Random packings of cubic and cuboid particles in cylindrical columns of different diameter are generated using a glued-sphere Discrete Element Method (DEM) approach. The packing structures for different particle-column combinations are analysed. The effects of particle size/shape, column diameter and internal porosity of the particles on the overall pressure drop and flow distribution are investigated. The macroscopic Reynolds number (based on the particle equivalent diameter and the superficial velocity of the bed) is varied from 0.1 to 400. The effect of Reynolds number on pressure drop is analyzed, as well as the reduction in pressure drop due to the presence of the intra-particle pores. In addition, our numerical simulations have helped to elucidate the detailed fluid-solid interaction in complex bi-disperse, dual porosity porous media.

Modeling and Validating Fixed‐Bed Reactors: A State‐of‐the‐Art Review

“…A particular challenge in the modelling of heterogeneously catalyzed gas phase reactions lies in the correct mapping of the transport processes within the porous catalyst particle, which take place on much smaller time and length scales than the macroscopic convection of the fluid phase . So far, a detailed understanding of the complex interactions of the physical and chemical relationships on all scales involved is missing, so that diffusion and reaction processes are often simplified .…”

“…A further disadvantage of different approaches, in which attempts are made to calculate the different time and length scales coupled, is that currently no numerical solution methods are available. This means that if the different scales are calculated, usually co‐simulation methods are used , , . In this case, for example, the balances of the convective fluid flow are calculated iteratively up to a defined criterion.…”

Syngas production by chemical-looping gasification of waste activated carbon with iron-based oxygen carrier

“…As illustrated in Fig. 8a, the surface structure of the fresh sample was tough and loose with a porous structure, which was bene cial for the diffusion and reactions of reactants (Das et al 2018). After the 1st cycle, a greater porosity structure was observed than that of fresh sample, which was ascribed to gas escaping from the interior of the OC particles (Deng et al 2019).…”

Modeling and Validating Fixed‐Bed Reactors: A State‐of‐the‐Art Review

“…Ein weiterer Nachteil verschiedener Ansätze, in denen versucht wird, die verschiedenen Zeit‐ und Längenskalen gekoppelt zu berechnen, besteht darin, dass numerisch derzeit keine Lösungsmethoden zur Verfügung stehen. Das bedeutet, wenn die unterschiedlichen Skalen berechnet werden, wird in der Regel auf Co‐Simulationsverfahren zurückgegriffen , , . In diesem Fall werden beispielsweise zunächst die Bilanzen der konvektiven Gasströmung bis zu einem definierten Kriterium iterativ berechnet.…”