Dynamic Liquid Holdup Research Articles

Liquid Holdup in Non-wetting Packing with Lateral Gas Injection

The liquid holdup study has been carried out on a two-dimensional cold model under non-wetting condition with lateral gas injection as it is done in the blast furnace. Non-dimensional numbers for both, cold model and blast furnace have been determined. The measurements of static and dynamic liquid holdups were made under different gas and liquid flow rates using two particulate materials of various diameters. Few experiments were performed under dry and wet bed conditions to ascertain the effect of bed history. Holdups results have been compared with the existing correlations available in the open literature. It is found that existing correlations are unable to predict the correct liquid holdup under the blast furnace conditions.

Liquid Holdup for Two-Phase Countercurrent Flow in the Packed Column with a Novel Internal

In the packed column with a novel internal, which is made of several structured porous passages, gas is divided into two branches which meet liquid in countercurrent and cross-current, respectively, so the excessive pressure drop and “flooding” of conventional gas−liquid countercurrent flow can be avoided. A model for predicting dynamic liquid holdup is presented, and it shows a satisfactory agreement with the experimental results. Below the load point, only the superficial liquid velocity and the volume fraction of the internals have evident effects on the liquid holdup. Above the load point, both superficial gas and liquid velocities have great effects on the liquid holdup and so do the parameters of the internal because they can affect gas-flow behavior.

Reactive distillation with KATAPAK®

KATAPAK-SP and -S are structured catalytic packings for reactive distillation or gas–liquid reactors available from laboratory to industrial scale. Applying the KATAPAK-SP concept, the ratio of catalyst volume fraction to separation efficiency can be varied over a wide range, therefore the design of a reactive distillation column can be further optimized to fit each reaction system best.Pressure drop, separation efficiency, dynamic liquid hold-up and residence time distribution have been investigated for KATAPAK-SP in a diameter of 250mm. Results for different gas and liquid loads are presented. The findings are compared with results for the structured laboratory scale packing KATAPAK-S and the industrial scale packing KATAPAK-S 170.Y.The dehydration of tert-butyl alcohol was selected as a sample reaction to illustrate the influence of different catalytic structures on the performance of the reactive distillation column. The setups are compared with respect to dimensions and economics.

The Rotary Trickle-Bed Reactor– A New Reactor Concept for Biological Gas Purification

A new type of reactor employed to the biological gas purification is presented. The avoidance of clogging in the carrier packing is achieved by i) the use of a structured, rotating carrier packing, ii) a definite liquid irrigation regime during start-up, operation and clean-up time phases, iii) an on-line determination and control of the fixed biofilm mass. A uniform biofilm thickness is generated by an optimized liquid irrigation of the carrier packing with spray nozzles. The detachment of the fixed biomass is accomplished by liquid shear forces generated with jet nozzles. The time-scheduled operation regime of the reactor is founded on the on-line quantification of the immobilized biomass, which results in a new quality of process governing of biotrickling reactors applied to gas purification. This is proved by the experimental results of pressure drop, dynamic liquid holdup as well as the volumetric degradation rates. The degradation of styrene was investigated in laboratory and field experiments showing a maximal volumetric degradation rate of 150 g m–3 h–1 at a pollutant load of 200 g m–3 h–1. The feasibility of this reactor prototype is demonstrated by employing it to the elimination of industrial waste gas.

Multiple-Zone Model for Partially Wetted Trickle Flow Hydrodynamics

This paper describes an implicit 1-D two-fluid hydrodynamic trickle-bed model designed to approximate the actual two-phase flow and bed void using four inclined slits consisting of a dry, a gas-(static)liquid, a (dynamic)liquid-(static)liquid and a gas-(dynamic)liquid slits. Based on the Holub et al.1 mono-slit phenomenological approach, the model can be used to predict the frictional two-phase pressure drop, the external, dynamic and static liquid hold-ups, the pellet-scale external, dynamic and static wetting efficiency in trickle-bed reactors operated under trickle flow regime and partially wetted pellet conditions. In this context, a collection of data relative to the wetting efficiency, liquid hold-up and pressure drop measured under high pressure/high temperature has been compiled from the literature concerning the trickle flow regime in undiluted and diluted beds of catalysts and fines. This useful data provided sufficient and pertinent information to practically implement and successfully validate the model.

Correlations for dynamic liquid holdup under pulsing flow in a trickle-bed reactor

Based on theoretical analysis and experimental results, a new attempt has been made to characterize the dynamics of the fluid flowing under conditions of pulsing flow in a trickle-bed reactor (TBR). Two kinds of correlation are proposed for the dynamic liquid holdup under pulsing flow, which can predict the dynamic liquid holdup for a given packing type and given operating conditions.

An analysis of phase holdup in concurrent gas liquid upflow through packed beds using (I) drift-flux model, and (II) slip ratio

Correlations were developed to predict total and dynamic liquid holdup in terms of drift flux model, hold up ratio, and gas and liquid Reynolds numbers for the experimental data of the present study covering air-water and air-MEA systems for three different packing and a wide range of literature data. These corelations predict the present data and most of the literature data with an RMS deviation less than 0.1. The present static liquid holdup data was found to agree with the correlation due to Saez and Carbonell (1985).

Trickle bed reactor diluted with fine particles and coiled tubular flow-type reactor for kinetic measurements without external effects

Gas and liquid velocities in laboratory scale trickle bed reactors are one or two orders of magnitude lower than those in commercial reactors. Then, the kinetic data may include the external effects. This shortcoming of laboratory scale trickle bed reactor can be resolved by diluting the catalyst bed with fine inert particles. The catalyst bed dilution increases dynamic liquid holdup, pressure drop, gas–liquid mass transfer coefficient. Hydrogenation of 2-phenylpropene on Pd/Al 2O 3 was performed with the trickle bed reactor diluted with fine inert particles and the coiled tubular flow-type reactor to compare the kinetics with that of the basket type batch reactor. The trickle bed reactor diluted with fine inert particles is suitable to obtain the reaction rate without external effects even if the liquid velocity is low. The coiled tubular flow-type reactor should be used at high gas velocities.

Flow regimes, liquid holdups and two-phase pressure drop for two-phase cocurrent downflow and upflow through packed beds: air/Newtonian and non-Newtonian liquid systems

The analysis of the hydrodynamics results of two-phase downflow and upflow through fixed beds with porous particles shows that the flow regimes, two-phase pressure drop and liquid holdups are strongly influenced by the presence of the non-Newtonian liquids. With highly viscous non-Newtonian liquids the hydrodynamic characteristics (pressure drop, dynamic and total liquid holdups) of two-phase downflow are close to those of two-phase upflow—the axial dispersion appears to be an important cause for the possible effects of the hydrodynamics on the reactor performance.

On dynamic liquid holdup determination by the drainage method

A careful examination of the liquid drainage in packed-bed reactors using liquid superficial velocities characteristic of trickle flow regime and no gas velocity is both experimentally and theoretically carried out. True free-flowing or dynamic liquid holdups are determined in two different reactors packed with porous and nonporous particles employing several liquids. Dynamic liquid holdups are shown to be higher than those determined directly from total liquid drained volumes, which are usually reported when the drainage method is applied. It is found that a model of laminar liquid films properly addresses the influence of liquid superficial velocities and of liquid viscosity on the dynamic liquid holdup within the experimental conditions studied. A simple quantitative phenomenological model to describe the drainage kinetics is developed and is independently verified from experimental data. Satisfactory agreement is found for all the examined conditions.

Dynamic liquid holdup and oxygen mass transfer in a cocurrent upflow bioreactor with small packing at low Reynolds numbers

An experimental investigation of dynamic liquid holdup and oxygen absorption mass transfer was carried out in a laboratory bioreactor packed with expanded clay balls. The column was operated with a cocurrent upflow of air and water at low Reynolds numbers. The data obtained for dynamic liquid holdup have been represented by a modified Stiegel-Shah relation with a relative mean error of 0.7%. For prediction of the oxygen mass transfer coefficient, an empirical correlation based on air and water mass superficial velocities has been proposed. It reproduced our experimental results with a relative mean error of 9%. Both correlations proposed in this study are valid for small packing spheres around 2.7 mm in diameter and Reynolds numbers varying for gas and liquid from 0.197 to 0.593 and from 3.875 to 9.315 respectively.

New correlation for liquid hold-up of sodium citrate buffer solution in a Raschig ring packed column

Dynamic liquid hold-up was measured with an air/aqueous sodium citrate buffer solution at 20–40 °C, and an air/water system at 23 °C, in a 0.1 m diameter/1 m high glass column covered by a heat-isolating vacuum jacket and packed with 0.012 m nominal size ceramic Raschig rings. The superficial gas velocity range was extended to 1.2 m s −1. Experimental results of this work were compared with literature data, with different correlations and with a general equation. All expressions were found to be unacceptable for the air/buffer system and useable for the air/water system. In the case of the air/buffer solution a new correlation is recommended on the basis of our measured data and literature values.

Hydrodynamics and mass transfer in a three-phase fixed-bed reactor with cocurrent gas—liquid downflow

The paper presents experimental results concerning dynamic liquid holdup, wetting efficiency and local mass transfer coefficients between the liquid and solid surface in a fixed-bed three-phase reactor, in which both the gas and liquid flow cocurrently downwards. The experiments were conducted for two basic regimes of operation of trickle-bed reactors, namely the gas continuous flow regime and the pulsing flow regime under atmospheric pressure. The measurements of dynamic liquid holdup have been performed for a wide range of gas and liquid flow rates, three different packing diameters, and for two systems of working media of different physical properties. The common correlation developed determines with good accuracy the holdup values in both regimes as well as in the transition region between the two hydrodynamic modes. In experiments concerning the wetting efficiency a dynamic tracer method has been employed, for which an original mathematical model has been formulated. The results are presented in the form of diagrams and appropriate correlating formulae. The experiments concerning local solid—liquid mass transfer coefficients were carried out for two diameters of spherical particles, with the flow rates of both phases and physicochemical properties of the liquid varied over a wide range. The experimental results are correlated and compared with the appropriate literature data. A mathematical model describing the time-varying solid—liquid mass transfer process is formulated for the pulsed flow regime. The time-averaged mass transfer coefficients calculated on the basis of the model developed are compared with the experimental values. A good agreement between these two sets of values fully confirms the assumptions of the model elaborated.

Some experiences with the application of the percolation concept for modelling trickle-bed fluid dynamics

A body-centred cubic lattice has been used to represent the packing in a model of a trickle bed. Liquid distribution has been simulated by a percolation process in this lattice. The liquid flow distribution is governed by a single parameter p which describes the static properties of the packing independent of the liquid load. Simulations of different packings and flow rates describe the experimental results in the low-interaction regime satisfactorily. The simulation results may also be used for the successful estimation of the experimentally determined dynamic liquid hold-up.

A Unified Model for Countercurrent Vapor/Liquid Packed Columns. 2. Equations for the Mass-Transfer Coefficients, Mass-Transfer Area, the HETP, and the Dynamic Liquid Holdup

In part I a model for the two-phase pressure drop in a packed column was derived from an analogy to electrical percolation on a conductor/insulator lattice. In part II we extend that development to include the mass-transfer coefficients, the area available for mass transfer, the height of packing equivalent to a theoretical plate, and the dynamic liquid holdup

Flow dynamics in low height packed column having large fractional void space

A study of the fluid dynamics in low height packed column having very large fractional void space was carried out to investigate pressure drop, liquid holdup and stable operating range. Operation was carried out at high gas velocities using four kinds of liquids. Results provided the possibility operating the column at high gas velocities, which leads to energy conservation. The pressure drop and liquid holdup were found to be useful parameters in checking the performance of the packed column. A model to calculate pressure drop in the packed column with very large fractional void space is presented by taking into account the liquid holdup contribution. Further, empirical correlations for static and dynamic liquid holdup are given.

Statistical hydrodynamics in trickle flow columns

AbstractA stochastic model is proposed for the description of the hydrodynamics in trickle flow columns. The gas‐liquid flow is assumed to be controlled by local packing properties which are represented by random variables. The first (microscopic) level of description corresponds to the smallest volume whose averaged geometrical properties are representative of the whole packing. The hydrodynamics at this level is described by Ergun equations. The second level describes the liquid flow maldistribution induced by the partial wetting of the solid. This is the macroscopic level where the hydrodynamics is described by a probability distribution. This approach is used to develop correlations for predicting the wetting efficiency, the dynamic liquid holdup, and the pressure drop. These correlations give very good results when compared to experimental data over a wide range of operating conditions. In addition, we propose to describe the hysteretic behavior of trickle beds by a modification of the loquid flow texture caused by different values of the apparent solid wettability.

Mass transfer and holdup in gas‐liquid cocurrent flow packed beds containing water‐repellent particles

AbstractWater‐repellent particles were prepared by spraying polytetrafluoroethylene (PTFE) on activated carbon. Gas‐liquid volumetric mass transfer coefficient and holdup were determined in gas‐liquid cocurrent upflow and downflow packed beds from the measurements of gas desorption and volume, respectively. As the PTFE loading increased, the gas‐liquid volumetric mass transfer coefficients in both upflow and downflow modes were enhanced. Gas holdup in the upflow mode increased with the PTFE loading, while the dynamic liquid holdup in the downflow mode decreased. The enhancement of the mass transfer rate from gas to liquid can be explained by the effect of water‐repellency on the surface of activated carbon.

The influence of pressure on the liquid hold-up in a cocurrent gas-liquid trickle-bed reactor operating at low gas velocities

The influence of reactor pressure up to 6.0 MPa on the dynamic liquid hold-up in the trickle-flow regime with superficial gas velocities up to 5.2 cm/s has been investigated for water, ethanol and aqueous 40% ethyleneglycol, with nitrogen as the gas phase. Without gas flow, i.e. single-liquid trickle-flow operation, the reactor pressure has no influence on the dynamic liquid hold-up, which can be well correlated by means of the Reynolds and Galileo numbers. For Rel < 11 the hold-up proportional to Re0.36l and for Rel ⪢ 15 to Re0.55l. This is probably due to a transition between laminar and turbulent film flow. According to the literature the dynamic liquid hold-up is not affected by low gas velocities under atmospheric conditions. The experiments show that in the case of two-phase flow operation at elevated pressures the hold-up decreases at relatively low gas velocities and even more so at higher pressures. This effect has been explained quantitatively by means of the ratio between the pressure gradient and the gravitational force. In addition, the change in the dependence of βdyn on Rel has not been observed anymore: at low Reynolds numbers the hold-up is already proportional to Re0.55l.

The transition between trickle flow and pulse flow in a cocurrent gas—liquid trickle-bed reactor at elevated pressures

The effect of reactor pressure in the range of 0.2–2.0 MPa on the transition between the trickle-flow and the pulse-flow regime has been investigated for the non-foaming water—nitrogen and aqueous 40% ethyleneglycol—nitrogen systems. Most models and flow charts which are all based on atmospheric experiments were able to describe the transition experiments performed at 0.2 MPa reasonably well. However, this is not so at elevated pressures. For both gas—liquid systems it is found that at a constant superficial gas velocity and higher reactor pressures the transition of trickle flow to pulse flow occurs at a relative higher liquid throughput. In the pressure range of 2.5–7.0 MPa the pulse-flow regime could not be obtained for throughputs up to 1.7 cm/s superficial liquid velocity. An explanation for this effect is given based on the dynamic liquid hold-up and pressure drop data determined at the flow regime transition. Finally an empirical equation is proposed, relating the parameters governing the flow regime transition and describing the hydrodynamic conditions at the transition between trickle flow and pulse flow.