Elucidation of mean voidage in packed beds

Abstract

Mean voidage is a global structural property of packed beds and its accurate prediction is therefore of great significance in any plug‐flow type model. A general correlation has been developed which enables this parameter to be evaluated. The work reported here deals with mono‐size non‐porous spherical packing, but also tackles related issues such as size distribution and the way in which they influence the mean voidage. In addition, an attempt has been made to discuss the merits of alternative packing arrangements.

A numerical study of fixed bed reactor modelling for steam methane reforming process

“…In this model we have taken the same assumptions for the pseudo-homogeneous reactor model along with one more assumption: all catalyst pellets are of the same size and the voids between are evenly distributed. [44,45] In the present study, a parallel pore model is adopted for the pellet to simplify the complex structure of voids where the fluid may flow; that is, we employ in some respect a general mathematical model of a spherical pellet where reactions take place on active sites within a uniform body. Thus, the mathematical model used in this work assumes a mean pore diameter and the ratio between the porosity and tortuosity is used to characterise a fixed structure of the pellet.…”

A heterogeneous dynamic model for the simulation and optimisation of the steam methane reforming reactor

“…In the present work the following assumptions are made in order to describe the fluid flow within the reactor and the transport of the gaseous components through the porous network: (a) no radial gradients in the bed; this is a valid assumption as long as the reaction scheme is not exothermic. The heat provided at the reactor's walls is simulated by an overall heat transfer coefficient, that depends only on the axial direction of the reactor; (b) pseudo-continuous heterogeneous model; these models rely on the assumption that significant changes in the dependent variables take place at a scale larger than the size of the catalyst particle [55]; (c) isothermal catalytic particle; since solid thermal coefficients are usually one order of magnitude larger than those in the gas phase [3], thermal resistance is mainly imposed by the gas phase; (d) all particles are of the same size and the voids between are evenly distributed [56,57]; (e) no side reaction occurs, such as CH 4 decomposition, Boudouard reaction, or CO reduction to lead to carbon formation; this assumption is valid for steam to methane (S/C) ratio higher than 1.2 [58].…”

Estimation of dispersion coefficients in packed beds

“…In Table 4, the estimates of the axial dispersion coefficient from both the one-dimensional and two-dimensional models are shown side by side. It is obvious from these values that the 2-D values are higher than the 1-D [28] ones over the entire range of operating and physical conditions considered in this study. The reason behind this can be traced to the separation of the transverse part of mixing from the longitudinal element in the 2-D analysis.…”