CPFD flow pattern simulation in downer reactors

Abstract

This study contributes with a computational fluid dynamic simulation based on the numerical solution of continuity and momentum balance equations in a three‐dimensional (3‐D) framework. The proposed down flow gas–solid suspension model includes a unit configuration and CD drag coefficients recommended for these units. Computational particle fluid dynamics (CPFD) calculations using suitable boundary conditions and a Barracuda (version: 14.5.2) software allow predicting local solid densification and asymmetric “wavy flows.” In addition, this model forecasts for the conditions of this study higher particle velocity than gas velocity, once the flow reaches 1 m from the gas injector. These findings are accompanied with observations about the intrinsic rotational character of the flow. CPFD numerical 3‐D calculations show that both gas and particle velocities involve the following: (a) an axial velocity component, (b) a radial velocity component (about 5% of axial velocity component), and (c) an angular velocity component. The calculated velocity components and the rotational flow pattern are established for a wide range of solid flux/gas flux ratios. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1635–1647, 2013

Effects of the riser exit geometries on the hydrodynamics and solids back-mixing in CFB risers: 3D simulation using CPFD approach

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CFD Approaches for Modeling Gas-Solids Multiphase Flows - A Review

“…In the Eulerian-Eulerian approach, fluid and particles both are considered as continuous phases which are fully inter-penetrating (Zhang et al, 2012) i.e. solid phase is treated as a pseudo-fluid (Abbasi et al, 2013).…”

“…The averaging procedure leads to many unclosed terms, which must be modeled (Snider et al, 2011). Constitutive relationships that are obtained from empirical information and/or kinetic theory are used for this purpose (Abbasi et al, 2013). Eulerian-Eulerian model for granular flows (Euler-granular model) is an example for Eulerian-Eulerian approach.…”

Hydrodynamics and reactor performance evaluation of a high flux gas‐solids circulating fluidized bed downer: Experimental study

“…The downer reactor, where gas and solids move downward in a concurrent fashion, has drawn much attention in recent years due to its unique features such as insignificant solids backmixing, shorter residence time, and narrow residence time distribution . These features of downer reactors can potentially lead to its application for ultrarapid reactions such as the highly selective and fast catalytic conversion of residual oil or other hydrocarbons, biomass, and coal pyrolysis, where narrower RTD is critical.…”

“…The design, optimization, and scale‐up of a downer reactor require more precise and quantitative understanding of both the flow behavior and the chemical reaction. Considering the numerous studies on hydrodynamics and hot model reactions in CFB riser reactors, not much efforts devoted to hydrodynamics and especially to reactor performance in downers in recent years . Previous studies using catalytic ozone decomposition as a model reaction to evaluate reactor performance were mainly focused on gas ‐ solids contacting in CFB risers .…”