Hydrodynamics of trickle-bed reactors involve complex interactions of gas and liquid phases with packed solids. Such complex interactions manifest in different flow regimes occurring in trickle-bed reactors. Knowledge of prevailing flow regime, pressure drop, and liquid holdup is essential for design and performance evaluation of the reactor. Detailed knowledge of fluid dynamics is essential for “a priory” predictions as well as for interpretation of available data. In this study, we have used wall pressure fluctuation measurements to identify prevailing flow regime in trickle beds. Experiments were carried out on two scales of columns (of diameter 10 cm and 20 cm) with two sets of particles (3 mm and 6 mm diameter spherical particles). Effects of prewetted and unwetted bed conditions on pressure drop and liquid holdup were reported for a range of operating conditions (VG = 0.22−0.44 kg/m2s, VL = 2−24 kg/m2s). A comprehensive CFD model was developed to predict measured hydrodynamic parameters. The model w...

Hydrodynamics of Trickle-Bed Reactors: Experiments and CFD Modeling

Trickle-bed reactors (TBRs), which accommodate the flow of gas and liquid phases through packed beds of catalysts, host a variety of gas–liquid–solid catalytic reactions, particularly in the petroleum/petrochemical industry. The multiphase flow hydrodynamics in TBRs are complex and directly affect the overall reactor performance in terms of reactant conversion and product yield and selectivity. Non-ideal flow behaviours, such as flow maldistribution, channelling or partial catalyst wetting may significantly reduce the effectiveness of the reactor. However, conventional TBR modelling approaches cannot properly account for these non-ideal behaviours owing to the complex coupling between fluid dynamics and chemical kinetics. Recent advances in the application of computational fluid dynamics (CFD) to three-phase TBR systems have shown promise of achieving a deeper understanding of the interactions between multiphase fluid dynamics and chemical reactions. This study is intended to give a state-of-the-art overview of the progress achieved in the field of CFD simulation of TBRs over the past two decades. The fundamental modelling framework of multiphase flow in TBRs, advances in important constitutive models, and the application of CFD models are discussed in detail. Directions for future research are suggested.



RESUME Les lits fixes arroses a co-courant descendant de gaz et de liquide sont le siege d'innombrables processus catalytiques triphasiques, en particulier dans le domaine du raffinage petrolier et de la petrochimie. Les caracteres polyphasique et non-ideal de leur hydrodynamique ont des repercussions importantes sur la conversion chimique, la productivite et la selectivite. Ceci se traduit par l'entremise de la maldistribution des fluides, le mouillage partiel du catalyseur ou des ecoulements preferentiels qui peuvent etre determinants en ce qui a trait a l'efficacite du reacteur. La mise en equation rigoureuse de ces non-idealites et des couplages reaction-hydrodynamique a longtemps resiste aux approches de conceptualisation dites « conventionnelles ». Cette revue de synthese s'attarde par consequent a discuter les recentes avancees dans l'utilisation de la mecanique des fluides numerique comme outil « emergent et non-conventionnel » de description quantitative et fine des ecoulements et des reactions catalytiques, et de leur interaction au sein de ces reacteurs. Specifiquement, nous discuterons de la pertinence des differentes approches multi-fluides mises en œuvre, des relations constitutives developpees et de l'utilisation de la mecanique des fluides numerique pour des applications pratiques des lits fixes arroses. Nous suggererons en guise d'epilogue de nouvelles directions de recherche dans ce domaine. © 2011 Canadian Society for Chemical Engineering

Modelling and simulation of trickle‐bed reactors using computational fluid dynamics: A state‐of‐the‐art review

Prediction of pressure drop and liquid holdup in trickle bed reactor using relative permeability concept in CFD

Hydrodynamics of gas–liquid two-phase flow in micropacked beds are studied with a new experimental setup The pressure drop, residence time distribution, and liquid holdup are measured with gas and liquid flow rates varying from 4 to 14 sccm and 01 to 1 mL/min, respectively Key parameters are identified to control the experimentally observed hydrodynamics, including transient start-up procedure, gas and liquid superficial velocities, particle and packed bed diameters, and physical properties of the liquids Contrary to conventional large packed beds, our results demonstrate that in these microsystems, capillary forces have a large effect on pressure drop and liquid holdup, while gravity can be neglected A mathematical model describes the hydrodynamics in the micropacked beds by considering the contribution of capillary forces, and its predictions are in good agreement with experimental data © 2017 American Institute of Chemical Engineers AIChE J, 63: 4694–4704, 2017

Hydrodynamics of gas–liquid flow in micropacked beds: Pressure drop, liquid holdup, and two-phase model

Milli-channel with metal foams under an applied gas–liquid periodic flow: External mass transfer performance and pressure drop

Pressure drop and liquid saturation are two important design parameters in cocurrent gas-liquid downflow through packed beds. A macroscopic model based on momentum balance is formulated for the condition of no radial pressure gradients. The model includes the effect of bubble formation on the pressure drop and holdup and is compared with the experimental data of the earlier investigators and of the present study. The model provides a functional form for correlating pressure drop and liquid saturation but some parameters have to be determined by fitting the experimental data.

Hydrodynamics of two-phase cocurrent downflow through packed beds. Part I. Macroscopic model

Two-phase pressure drop and dynamic and total liquid saturation are experimentally determined for air-water system under cocurrent downflow through packed beds using packing differing widely in geometry The experimental data of the present study as well as that available in literature is satisfactorily correlated in terms of: (a) Lockhart-Martinelli parameters; and (b) the Reynolds numbers defined for the respective phases and the bed porosity, taking into account the flow behavior of the phases through the packed bed

V. G. Rao

Papers

Hydrodynamics of two-phase cocurrent downflow through packed beds. Part I. Macroscopic model

Hydrodynamics of two‐phase cocurrent downflow through packed beds. Part II: Experiment and correlations

A model for the residence time distribution of liquid phase in trickle beds