The Morphology of Trickle Flow Liquid Holdup

Gravity driven trickle flow of a liquid over a fixed bed in the presence of a gaseous phase is widely encountered throughout the process industry. It is one of the most common ways of contacting multi-phase fluids for reaction or mass transfer purposes. The presence of three phases greatly complicates the mathematical modelling of trickle-bed reactors and makes a description from first principles difficult. Trickle flow performance is usually characterized in terms of hydrodynamic parameters. One such parameter is the liquid holdup. The value and morphology (shape or texture) of the holdup influences the catalyst contacting, wetting, mass transfer characteristics and ultimately the performance of the trickle flow unit. This study is limited to the air-water-glass spheres system with no gas flow. It is partitioned into three sections. An investigation into the nature of the residual liquid holdup in beds of spherical particles revealed that the general assumption that all residual liquid is held in the form of pendular rings at particle contact points proves to be untrue. Instead, indication is that 48 % of the residual holdup is present in the form of agglomerated liquid globules in interstices of low local porosity. Theoretical residual liquid holdup models and residual liquid holdup-based mass transfer models should include this phenomenon. In a subsequent section, the influence of the prewetting procedure on the operating holdup is investigated. Three distinct limiting cases are identified: Kan-wetted, Levec-wetted and non-wetted. A volumetric utilization coefficient that describes the extent to which the bed is irrigated is developed. It indicates that large fractions of the bed remain non-irrigated in the Levec- and non-wetted modes. A momentum balance-based model is adopted to predict the Kan-wetted mode holdup. This model was successfully extended to predicting the holdup in the Levec- and non-wetted modes by simple incorporation of the volumetric utilization coefficient. The predictive capability of this model is highly satisfactory, especially in light of it using only the classical Ergun constants and no fitted parameters (AARE = 9.6 %). The differences in the hysteresis behaviour of holdup and pressure drop in the different modes are attributed to differences in the morphology of the operating holdup. The existence of the three limiting prewetted modes is confirmed by residence time distribution (RTD) analysis of the stimulus-response behaviour of the system. This behaviour was quantified using a NaCl tracer and conductivity measurements at both the inlet and outlet of a bench scale bed. The analyses show that: · There are large fractions of the holdup that is inaccessible to the tracer in the Levec-wetted and non-wetted modes. · The mixedness in the three prewetted modes differ appreciably, with the Kan-wetted mode clearly less mixed than the Levec-wetted mode. The RTD analyses also confirm the existence of the three prewetting modes in a porous system (spherical a-alumina), with a large fraction of the holdup being inaccessible to the tracer in the Levec-wetted mode. This study emphasizes the role of the morphology of the various types of liquid holdup on the hydrodynamic performance of a trickle flow unit. It is apparent that aspects of the morphology depend strongly on phenomena like globule formation, hysteresis and flow and prewetting history that have not been adequately recognized to date. The visualization of the various modes of trickle flow is an intellectual platform from which future studies may be directed.Dissertation (MEng)--University of Pretoria, 2004.Chemical EngineeringUnrestricte

Investigation of the Hydrodynamics of Fixed Bed Reactor: Co-current Upflow

The main objective ofthis project is to investigate the hydrodynamic characteristics of co-current upflow of gas and liquid in a fixed bed reactor. This is an experimental based project utilizing the packed bed reactor for residence time distribution (RTD) studies. In this project, the RTD of a bench-scale multiphase was studied using air as a gaseous phase and water as a liquid phase. The ranges of air and water velocities are kept at such levels as to simulate the hydrogen/oil ratios of typical bench-scale hydroprocessing units. The experiments are conductedin upflowmode of operationin the reactor, with increasing gas/liquid ratio. The effects of gas and liquid velocities on different hydrodynamic parameters such as pressure drop and operating liquid holdup are investigated. Three moments analysis, which are mean residence time, variance, and skewness, are evaluated in order to characterize the RTD. Other parameters such as bed Peclet number of liquid and stagnant zone volume were also investigated with variation of gas and liquid velocities as to measure the efficiency of the reactor. The discrepancies in experimental results suggested that there are conditions to be altered in order to eliminate the inconsistency

Modelling of CO2 absorption in a rotating packed bed using an Eulerian porous media approach

The rotating packed bed (RPB) is a promising reactor for CO2 capture with liquid amine because of its high mass transfer rate and energy and space savings. The CFD simulations of RPBs generally use the volume of fluid (VOF) method, but this method is prohibitively expensive for 3D simulations, in particular for large-scale reactors. The Eulerian method is a promising and effective method; however, there are still several difficulties, such as the settings for the porous media models in the gas-liquid counter-current flow and the interfacial area between the gas and liquid. To overcome these difficulties in the Eulerian method, this paper uses a new porous media model, a novel liquid generation-elimination model for numerically investigating the gas-liquid counter-current flow in RPBs and a new interfacial area model derived from the VOF simulation. These new models, incorporating the two-film reaction-enhancement mass transfer model, have successfully simulated the CO2 capture process with monoethanolamine (MEA) solutions in a RPB under both low (30 wt%) and high (90 wt%) concentration conditions. The results show that the overall gas phase mass transfer coefficient (KGa) increases with increasing the rotation speeds and the liquid to gas mass flow rate (L/G ratio). The simulations were validated by the experimental data and the results were analysed and discussed

Intensification of polyester synthesis by continuous reactive distillation

The thesis starts with a brief overview of unsaturated polyesters. In particular, the usage of raw materials, the application of unsaturated polyester resins, and, the worldwide supply and demand of the unsaturated polyester resins are discussed. Unsaturated polyester is traditionally produced in a batch-wise-operating reaction vessel connected to a distillation unit. The total production time is around 12 hours and often leads to batch-to-batch inconsistency. Process intensification is required for the unsaturated polyester process to reduce the production time and to achieve a better quality of the product. An attractive alternative to batch-wise polyester production is reactive distillation. In chapter 1, the attractiveness of reactive distillation for the synthesis of unsaturated polyester is discussed. The goal of the thesis is to develop and evaluate a reactive distillation process for the production of unsaturated polyester from anhydrides and glycols. To accurately predict the behavior of reactive distillation process, reliable kinetic and thermodynamic models are required. Therefore, in chapter 2 a dynamic model for a batch-wise operating reaction vessel connected to a flash separation unit is developed in order to validate the kinetic and thermodynamic models and their parameters. This model includes kinetics, description of the change of rate order during the reaction, the polymer NRTL non-ideal thermodynamic model based on non-random theory of liquid (NRTL) and mass balances. The reaction between maleic anhydride and propylene glycol has been taken as a case study. The reaction scheme is complex and the proposed model takes four types of reactions into account; ring opening, polyesterfication, isomerization and saturation reactions. The acid value of the polyester, number-average molecular weight, distilled mass and glycol concentration in the distillate have been subsequently used to validate the model and the model predicts these important variables reliably. The process description is improved by using the vapor liquid equilibrium data predicted from the polymer NRTL model. After successful validation of the kinetic and thermodynamic models, the feasibility of the reactive distillation process for the unsaturated polyester is presented in chapter 3. Moreover, the simulation results of reactive distillation model are compared with the batch reactor model simulation results to determine advantages gained by the reactive distillation over the traditional batch process. The simulation study shows that the total production time of polyester in a continuous reactive distillation system is reduced to 1.8-2 hours compared to the12 hours of the industrial batch reactor process. The model demonstrated that reactive distillation has the potential to intensify the process by factor of 6 to 8 in comparison to the batch reactor process. After finding that reactive distillation is an attractive alternative for the polyesters synthesis, a more in depth analysis is performed. Particularly, the influence of the liquid back mixing on the description of the reactive distillation process, product transition time, the amount of undesired product formation during the product changeover is investigated. Since the current state of the art modelling approach does not account for liquid back mixing, the rate-based model is extended to account for liquid back mixing. The simulation results of extended rate-based model demonstrated that axial dispersion significantly influences the reactive distillation process and cannot be neglected. On the basis of current research work and literature review, a novel design methodology for the economical and technical evaluation of reactive distillation is proposed in chapter 4. Moreover, the applicability of various design methods for reactive distillation is discussed. The proposed framework for the economical evaluation determines the boundary conditions (e.g. relative volatilities, target purities, equilibrium conversion and equipment restriction), checks the integrated process constrains, evaluates economical feasibility, and provides guidelines to any potential reactive distillation process application. Providing that a reactive distillation process is economically attractive, a technical evaluation is performed afterward in order to determine the technical feasibility, the process limitations, working regime and requirements for internals as well as the models needed for reactive distillation. This approach is based on dimensionless numbers such as Damkohler and Hatta numbers, as well as the kinetic, thermodynamic and mass transfer limits. The proposed framework for economical and technical evaluation of reactive distillation allows a quick and easy feasibility analysis for a wide range of chemical processes. Several industrial relevant case studies (synthesis of di-methyl carbonate (DMC), methyl acetate hydrolysis, toluene hydro-dealkylation (HDA) process, fatty acid methyl esters (FAME) process and unsaturated polyesters synthesis) are used to illustrate the validity of the proposed framework. In chapter 4, it is found that the bubble column is the potential device for producing unsaturated polyesters by the reactive distillation. Moreover, the introduction of packing or partition trays in the bubble column significantly improves the unsaturated polyester process because packing or partition trays provide a better mass transfer and the multi-stage effect in the column. But considering the lack of information about the behavior of counter-currently operated bubble columns in the presence of structured packing or partition trays and in a viscous system, a systematic investigation on the gas holdup, axial dispersion and mass transfer in the packed bubble column and the trayed bubble column is undertaken in chapter 5. Four different types of structured packings (Super-Pak, Flexipac, Mellapak and Gauze) and two types of perforated partition trays (with 25% and 40% tray open area) are used to characterize the packed and trayed bubble column, respectively. It is observed that the packed and trayed bubble columns improve the gas holdup and mass transfer compared to the empty bubble column and reduces the axial dispersion significantly. Particularly, the Gauze packing improves the gas holdup and mass transfer and, sufficiently reduces the axial dispersion. In contrast, Super-Pak offers only a modest improvement because of its open structure. Comparison of the experimental data of the packed and trayed bubble column indicates that the partition trays improve the bubble column in the same order as packing. The gas holdup, axial dispersion and mass transfer depend more strongly on the gas velocity compared to the liquid velocity. The liquid viscosity also significantly influences these parameters and therefore the empirical correlations obtained from the air-water system cannot be applied for the viscous system. Moreover, experimental data of the packed, trayed and empty bubble column are correlated by dimensionless numbers. Empirical correlations for the gas holdup, Bodenstein number (for the axial dispersion coefficient) and Stanton number (for the volumetric mass transfer coefficient) as a function of the Froude and Gallilei dimensionless numbers are proposed. In chapter 6, an experimental pilot plant validation of the reactive distillation process for the polyester synthesis is presented. Two different configurations are investigated: 1) a reactive distillation column and 2) a reactive distillation column coupled with a pre-reactor. Due to a relatively short residence time of 0.32 hours and an operating temperature of 190oC in case of the first configuration, a maximum conversion of 37% was achieved; which indicates monoester formation in the reactive distillation column. In the case of the second configuration, a 90% conversion is achieved within 0.55 hours at a temperature of 250oC in the reactive distillation column coupled with a pre-reactor; which confirms the polyester formation in the reactive distillation column. The extended rate-based model developed in chapter 3 is used to simulate the pilot reactive distillation column. The model predicted the experimental data (acid value, conversion, isomerization and saturation fraction, number-average molecular weight, the degree of polymerization and water fraction in the distillate) adequately (5-22%). Moreover, the product specifications of the polyester produced at 250oC in the reactive distillation column is in the range of polyesters produced in the traditional industrial batch reactor setup. Furthermore, discoloration of the polyester was hardly noticed even though the column was operated at 250oC. Finally in chapter 7, the validated model is used to find the best suitable internal and feed configurations of the reactive distillation process for unsaturated polyester synthesis. Moreover, multi-product simulations are performed to find the operational parameters for producing two different grades of polyester in the same equipment. Finally, the product transition time during product changeover is determined. The criteria to select the best configuration are minimum volume and energy requirement to produce 100 ktonnes/year polyester. First the best suitable internal for the column is identified and then the best suitable feed configuration is identified. From simulations, we concluded that the configuration which contains the reactive stripping section as a packed bubble column and the reactive rectifying section as a packed column requires minimum volume and energy to produce 100 ktonnes/year polyester. With respect to the feed configuration, we concluded that the feeding of monoesters to the reactive distillation column significantly intensifies the polyester process compared to an anhydrous reactant fed to the column. Moreover, the product transition time in this configuration is also significantly lower compared to the other configurations. In conclusion, a reactive distillation column coupled with a pre-reactor is the most promising alternative to continuously produce unsaturated polyesters. It requires a factor 10 (90%) lower volume, a factor 15 (93%) lower production time and a factor 3 (66%) lower energy as compared to the traditional batch reactor process to produce 100 ktonnes/year of polyester. Hence, the reactive distillation process improves the unsaturated polyester synthesis in all domains of structure, energy and time compared to the traditional batch reactor process coupled with a distillation column

Performance of multiphase packed-bed reactors and scrubbers on offshore floating platforms: hydrodynamics, chemical reaction, CFD modeling and simulation

Les systèmes flottants de production, stockage et de déchargement (FPSO) ont été introduits dans les secteurs d'exploitation des hydrocarbures offshore en tant qu'outils facilement déplaçables pour l’exploitation de champs de pétrole et de gaz de petites ‘a moyenne tailles ou lorsque ceux-ci sont éloignés des côtes ou en eaux profondes. Ces systèmes sont de plus en plus envisagés pour les opérations de traitement et de raffinage des hydrocarbures à proximité des sites d'extraction des réservoirs sous-marins en utilisant des laveurs et des réacteurs à lit fixe embarqués. De nombreuses études dans la littérature pour découvrir l'hydrodynamique de l'écoulement polyphasiques dans des lits garnis ont révélé que la maîtrise de tels réacteurs continue d’être un défi quant à leur conception /mise à l'échelle ou à leur fonctionnement. De plus, lorsque de tels réacteurs sont soumis à des conditions fluctuantes propres au contexte marin, l'interaction des phases devient encore plus complexe, ce qui entraîne encore plus de défis dans leur conception. Les travaux de recherche proposés visent à fournir des informations cruciales sur les performances des réacteurs à lit fixes à deux phases dans le cadre d'applications industrielles flottantes. Pour atteindre cet objectif, un simulateur de mouvement de navire de type hexapode avec des mouvements à six degrés de liberté a été utilisé pour simuler les mouvements des FPSO tandis que des capteurs à maillage capacitif (WMS) et un tomographe à capacitance électrique (ECT) couplés avec le lit garni ont permis de suivre en ligne les caractéristiques dynamiques locales des écoulements diphasiques. L'effet des inclinaisons et des oscillations de la colonne sur le comportement hydrodynamique des lits garnis biphasiques a été étudié, puis les résultats ont été comparés à leurs analogues terrestres correspondants (colonne verticale immobile). De plus, des stratégies opérationnelles potentielles ont été proposées pour atténuer la maldistribution des fluides résultant des oscillations du lit ainsi que pour intensifier le processus de réactions dans les réacteurs à lit fixe. Parallèlement aux études expérimentales, un modèle Eulérien CFD transitoire 3D a été développé pour simuler le comportement hydrodynamique de lits garnis polyphasiques sous des inclinaisons et des oscillations de colonnes. Enfin, pour compléter le travail expérimental, une étude systématique a été réalisée pour étudier les performances de capture de CO2 à base d'amines d’un laveur à garnissage (en vrac et structuré) émulant une colonne à bord des ...Floating production storage and offloading (FPSO) systems have been introduced to offshore hydrocarbon exploitation sectors as readily movable tools for development of small or remote oil and gas fields in deeper water. These systems are increasingly contemplated for onboard treatment and refining operations of hydrocarbons extracted from undersea reservoirs near extraction sites using embarked packed-bed scrubbers and reactors. Numerous efforts in the literature to uncover the hydrodynamics of multiphase flow in packed beds have disclosed that such reactors continue to challenge us either in their design/scale-up or their operation. Furthermore, when such reactors are subjected to marine conditions, the interaction of phases becomes even more complex, resulting in further challenges for design and scale-up. The proposed research aims at providing important insights into the performance of two-phase flow packed-bed reactors in the context of floating industrial applications. To achieve this aim, a hexapod ship motion simulator with six-degree-of-freedom motions was employed to emulate FPSO movements while capacitance wire mesh sensors (WMS) and electrical capacitance tomography (ECT) coupled with the packed bed scrutinized on-line and locally the two-phase flow dynamic features. The effect of column tilts and oscillations on the hydrodynamic behavior of multiphase packed beds was investigated and then the results were compared with their corresponding onshore analogs. Moreover, potential operational strategies were proposed to diminish fluid maldistribution resulting from bed oscillations as well as for process intensification of heterogeneous catalytic reactions in packed-bed reactors. In parallel with the experiment studies, a 3D transient Eulerian CFD model was developed to simulate the hydrodynamic behavior of multiphase packed beds under column tilts and oscillations. Ultimately, a systematic experimental study was performed to address the amine-based CO2 capture performance of packed-bed scrubbers on board offshore floating vessels/platforms. Apart from gaining a comprehensive knowledge on the influence of translational and rotational movements on multiphase flows in porous media, oil and gas sectors and ship industry would benefit from the results of this work for design and scale-up of industrial reactors and scrubbers.Unité flottante de production, de stockage et de déchargemen

Hydrodynamic and mass transfer study of micro-packed beds in sigle-and two-phase flow

Les micros-lit fixes sont des milieux poreux miniaturisés ralliant les avantages à la fois des microréacteurs et des lits fixes, comme par exemple en terme de rapport surface/volume très élevé conduisant à des taux de transfert de chaleur et de matière intensifiés. Par conséquent, la caractérisation hydrodynamique des micro-lits fixes est nécessaire afin d’appréhender de manière objective les phénomènes de transfert et les modes de contact entre phases. Ensuite l'importance des micro-lits fixes est mise en évidence tandis que les approches pour construire des bases de recherche sur les micro-lits fixes y sont explicitées. Notre recherche commence par l'étude des régimes d'écoulement, des transitions de régime d'écoulement de la multiplicité de l’hydrodynamique et du transfert de matière liquide-solide dans les micro-lits fixes. Cette étude est réalisée au moyen d’une méthode de visualisation par microscopie optique à la paroi et le traitement d’image qui s’en suit pour la partie hydrodynamique et d’une méthode électrochimique basée sur l’oxydoréduction du couple complexes ferri/ferreux hexacyanure pour la partir sur le transfert de matière. Les résultats de perte de charge et de rétention de liquide ont été discutés par rapport aux régimes d’écoulement mis en place et des observations pariétales rendues possibles par microscopie optique. L'effet de la taille des particules et de la géométrie du canal sur les transitions de régimes d’écoulement, le comportement transitoire et le phénomène d'hystérèse ont également été abordés. Finalement, les résultats des expériences hydrodynamiques ont été obtenus en faisant face à de nombreux défis pour lesquels nous avons formulé de nombreuses recommandations en vue d’investigations futures. La détermination expérimentale du coefficient de transfert de masse liquide-solide (kLS) par la technique électrochimique a été effectuée dans un micro-lit fixe rempli de couches de particules de graphite non-sphériques servant de cathode et d'anode. Les expériences ont été réalisées pour un écoulement monophasique en régime de diffusion limitée. Finalement, la correspondance de valeurs de kLS avec les corrélations construites sur la base d’études sur les lits fixes à l’échelle macroscopique a été discutée.Micro-packed beds are miniaturized packed beds having the advantages of both microreactors (high surface-to-volume ratios leading to intensified heat and mass transfer rates, increased safety, etc.) and packed beds (effective contact between the phases) that have the potential to be successfully employed for purposes such as catalyst screening and production of hazardous materials. To assess this potential, hydrodynamic characterization of micro-packed beds is necessary as they address the actual flow phenomena and provide suggestions to improve the contacting patterns between phases for enhanced performances. This work starts with a brief review on process intensification via microreactors. Then the importance of micro-packed beds is highlighted while the approaches to build research foundations on micro-packed beds are discussed. Our research begins by studying the flow regimes, transitions in flow regime and hydrodynamic multiplicity in micro-packed beds mostly by means of microscopic wall visualization and image processing. Results on pressure drop and liquid holdup have been obtained and discussed in terms of flow regimes and wall-flow image analyses. In addition, residence time distributions of the liquid in micro-packed beds have been obtained according to two techniques, by an impulse tracing method (electrolyte tracer injection) and wall visualization with optical microscopy. The effect of particle size and channel geometry (circular vs. square) has also been investigated in terms of flow regime transitions, transient behavior and hysteresis. Finally, challenges and recommendations thereof to surpass the many difficulties encountered are methodically explained to facilitate future investigations. Experimental determination of liquid-solid mass transfer coefficient (kLS) via a linear polarization method was also carried out in a micro-packed bed filled with layers of non-spherical graphite particles serving as cathode and anode for the Redox ferri/ferrocyanide electrochemical reaction. Experiments concerned single-phase liquid flow within the diffusion-limited regime. Particle size analysis and image processing were used to evaluate deviations from spherical geometry of the graphite particles to determine liquid-solid mass transfer coefficient. Finally, the correspondence of kLS values with macro-scale packed bed correlations was discussed

Hydrodynamics of trickle bed reactors : steady- and nonsteady-state operations

Parmi les réacteurs triphasiques gaz-liquide-solide utilisés dans la pratique industrielle, les réacteurs catalytiques à lit fixe arrosé à cocourant de gaz et de liquide vers le bas, i.e., trickle bed reactors (TBR), sont très répandus en particulier dans divers processus de transformation à hautes température et pression. Les travaux expérimentaux se poursuivent depuis plus de quatre décennies sur la quantification des paramètres hydrodynamiques (transition des régimes d'écoulement, perte de pression biphasique, rétention liquide, efficacité de mouillage, etc.) pour cette configuration de réacteurs. Différentes approches ont été mises en œuvre par un grand nombre d’équipes de recherche pour mesurer ces paramètres hydrodynamiques dans le but de construire des outils de prédiction et de description par rapport aux conditions réelles d’opération des processus à l’échelle industrielle. La présente contribution se propose de répondre à la question suivante : Dans quelle mesure les connaissances accumulées à partir d’observations à l’échelle laboratoire dans les conditions ambiantes sont-elles fiables pour opérer un TBR à pression et température élevées? Une question sous-jacente à la précédente concerne le comportement hydrodynamique avec la température lorsque le réacteur est alimenté par un liquide non-newtonien. L'intensification des procédés est une approche en vogue et prometteuse pour continuer à apporter des perfectionnements (gains en économie et en efficacité) au réacteur TBR. Aussi, l’induction artificielle d’impulsions est-elle envisagée dans cette étude en tant que méthode d'intensification de processus pour des températures et pressions non-ambiantes. Le présent travail tentera de démontrer les avantages de plusieurs variantes de l'opération périodique sur l'hydrodynamique des TBR pour des systèmes coalescent, non-newtonien et moussant à des températures et pressions augmentées.Trickle bed reactor (TBR) is one of the most widely used three-phase reactors in various processes mostly operated at high temperature and high pressure. The ongoing experimental work on the hydrodynamic parameters (flow regime transition, pressure drop, liquid holdup, wetting efficiency etc.) of this packed bed reactor configuration goes to early 1960’s. Different techniques were applied by different researchers for the measurement of these hydrodynamic parameters which let the comparison and the decision of more convenient method by means of doing investigations at conditions near to that of industrial processes. Process intensification is considered to be a leading approach for the ongoing research on the economic reduction and reactor efficiency enhancement. Artificial induction of pulses is pronounced as one of the methods for the process intensification in TBRs. As trickle bed reactor is also used in biochemical processes, and the initial liquid behaving like a Newtonian fluid could turn into a non-Newtonian fluid after various biochemical processes; it is emphatic to study TBR hydrodynamics with non-Newtonian systems. Despite large amount of work exists in the literature for steady state hydrodynamics of TBR operating at high pressure; the hydrodynamic behavior of TBR at high temperature has been left as a concealed issue. Additionally none of the experimental work performed to demonstrate the advantages of periodic operation on TBR hydrodynamics dealt with the effects of increased temperature and pressure. This study illustrates the hydrodynamics of TBR at increased temperature and pressure under constant throughput flow and cyclic operation

Investigations in Hydrodynamics and Mixing Pattern in the Bubble Column Equipped with Internals

Bubble column reactors, with or without solid particles, have a number of applications in the chemical, petrochemical, biochemical and environmental industries. A number of these industrial applications require internals such as baffles, heat transfer surfaces and special distributors to meet demands. Proper selection and design of these internals can lead to the improved performance and efficiency of a bubble column reactor. Several experiments are carried out in a bubble column equipped with a concentric tube bundle (CT) and an internal combination consisting of a concentric tube bundle and concentric baffle (or static mixer) (CTB) respectively. Neutrally buoyant particles are used to determine the effect of the CT and CTB internals on the local flow structures in the equipped column respectively. More upward, near-linear particle movements are observed with the CTB internal over the CT internal. Several non-linear particle movements are also observed. Overall bulk liquid circulation flow patterns are proposed for the intermediate to high gas velocity range based on the observed local flow structures for both internals. Comparisons are made between the gas holdups obtained during internal equipment and that of a comparable hollow bubble column from the literature. Both internals increase the gas holdup of a hollow bubble column. However, the increases with the CT internal are higher by more than 25% of that obtained with the CTB internal on average. The effect of the internals on average bubble size is investigated for the small bubble class. Smaller average diameters are obtained when the CT internal is used. The interfacial area in the presence of the two internals is determined respectively. Higher interfacial areas are obtained with the CT internal. The average difference in interfacial area is 54.0 m2/m3. The effect of the internals on mixing time is determined through dye and aqueous salt tracer studies. In both instances, higher mixing times are obtained with the CTB internal. Liquid backmixing is quantified through the axial dispersion coefficients obtained from the salt tracer studies. The axial dispersion coefficients obtained with the CT internal are higher than that of the CTB internal by about 15% on average