Multistage Bubble Column Research Articles

Bubble Columns Staged with Structured Fibrous Catalytic Layers: Residence Time Distribution and Mass Transfer

A new reactor concept for catalyzed three-phase reactions based on the use of woven fibrous materials for bubble columns is suggested. In comparison to conventional multistage bubble columns, the trays are made from woven fibrous catalytic layers. The hydrodynamic parameters such as the residence time distribution (RTD) and the volumetric gas-liquid mass transfer coefficient k(L)a are investigated in an air/water system for different layer structures and different superficial gas (u(g0) < 60 cm/s) and liquid (u(10) < 6 cm/s) velocities. The major reactor design parameters, such as the thread diameter D, the distance between the woven threads w, and the distance between the fibrous layers b, are discussed.

Gas and Liquid Holdups in Multi-Stage Bubble Columns for Gas-Liquid-Liquid-Solid Four-Phase System.

If solvents in the liquid phase are incompatible each other, a gas-liquid-solid three-phase bubble column becomes a gas-liquid-liquid-solid four-phase bubble column. Deprotection of amino acid was carried out in this column. At lower gas velocity, deactivations occur due to the deposit of product on the catalyst. At higher gas velocity, however, the catalytic activity is stable.Gas and liquid holdups in the multi-stage bubble column were measured to investigate the effects of operating conditions on hydrodynamics. Gas and liquid velocities, the height of each stage and the weight of catalyst were varied. The ratio of the organic phase holdup to the aqueous phase holdup changes drastically with the increase in gas velocity. The organic phase becomes continuous at lower gas velocity and the aqueous phase becomes continuous at higher gas velocity. Gas holdup is almost independent of each stage height and the catalyst weight.

Mass transfer in multistage slurry bubble column: analysis by back flow model

Mass transfer in multistage slurry bubble column: analysis by back flow model

Gas holdup-slip velocity relationship in multistage bubble column

Gas holdup data in multistage bubble column is analyzed through slip velocity incorporating pseudo hydrostatic effect, momentum transfer effect, particle-to-particle and particle-to-wall effects and coalescence effects. The bubble size, required for the estimation of single bubble rise velocity, is satisfactorily predicted using the model due to Molerus [9], and the influence of gas throughput, the perforation diameter and the free area of the horizontal plate, as well as the plate spacing on bubble size are examined.

Gas holdup-slip velocity relationship in multistage bubble column

Gas holdup-slip velocity relationship in multistage bubble column

Some aspects of hydrodynamics in multistage bubble columns

Hydrodynamic aspects covering the flow regimes and dispersed phase holdup have been investigated in multistage bubble columns using different geometries for the horizontal perforated plates. Air-water, air-kerosene and air-CMC solutions are investigated to cover a wide range in physical properties of liquids. The data show that the plate perforation diameter, plate spacing and the gas flow rate are the principal variables influencing the flow regimes and the dispersed phase holdup.

Some aspects of hydrodynamics in multistage bubble columns

Some aspects of hydrodynamics in multistage bubble columns

Mathematical model of the process for the oxidation of acetaldehyde to acetic acid

The acetaldehyde oxidation process is one of the important steps of acetic acid production. The reaction takes place in a multistage bubble column and the reaction mechanism is very complicated involving gas-liquid mass transfer, hydrodynamics and other factors, and a set of series-parallel reactions. Based on the reaction kinetics, mass transfer and material balances, a set of nonlinear equations is obtained that can be solved by iteration. The ratio of acetaldehyde to oxygen and the reaction temperature are the main variables which govern the oxidation reaction in the bubble column. Studying the influence of these two variables on the oxidation reaction and comparing the simulation and the experimental data, the results are satisfactory. Finally, a simple control model and the optimal operating conditions are obtained, providing a basis for optimal control of the acetaldehyde oxidation process.

PRESSURE DROP AND MASS TRANSFER COEFFICIENTS IN CONCURRENT SCREEN PLATE BUBBLE COLUMN

Pressure drop and oxygen desorption from water and four other aqueous CMC solutions were determined in a 5 cm diameter multistage bubble column with and without plate reciprocation. The plates were made from stainless steel wire screens of porosities greater than 0.62. The column pressure loss was found to increase with plate agitation, phase velocities and screen mesh number. A modified Reynolds number was proposed to permit a reasonable prediction of the pressure loss, based on the model of Noh and Baird (1984). At a specific power consumption, the present volumetric mass transfer coefficients arc considerably larger than those reported in earlier studies with sieve plates. The coefficients were correlated with specific power input, phase flow velocities and system physical properties.

STEADY-STATE PERFORMANCE OF A MULTI-STAGE BUBBLE COLUMN BIOREACTOR WITH SUBSTRATE LIMITED MICROBIAL GROWTH

The steady-state performance of a multi-stage bubble column bioreactor in which substrate limited microbial growth proceeds is investigated numerically. The back-flow model for representing longitudinal mixing of the liquid phase and the Monod kinetic equation for cell growth are employed here. The influence of the endogenous metabolism of cells is also taken into account. The concentration profiles of substrate and cells, the substrate conversion, the washout condition and the cell productivity are discussed. The effects of various model parameters, especially the back-flow ratio, on such reactor characteristics are presented as equations or figures. Optimal reactor conditions are determined.

向流多段気泡塔におけるＤＢＳ水溶液の逆混合

向流多段気泡塔におけるＤＢＳ水溶液の逆混合

Characteristics of a cocurrent multistage bubble column

Etude des caracteristiques hydrodynamiques et de transfert de masse de telles colonnes contenant 37 plateaux en fonction du diametre de la colonne, de la viscosite du liquide et des debits des deux phases

Frictional loss in multiplate bubble columns

AbstractGas holdup and pressure loss were measured for various gas‐liquid systems in a batch, multistage bubble column. Experimental results show that the use of screen plates (α = 0.64) considerably increases the gas holdup but introduces a significant pressure loss for the two‐phase mixture. The pressure loss was found to be independent of physical properties of the mixture, and predictable either from the modified separated flow model (Chen et al., 1986) or from the kinetic energy loss based on the liquid circulation velocity.

Energy effectiveness and working characteristics of different tower reactors for aerated slurry systems

Decisive hydrodynamic and mass transfer characteristics of different types of tower reactors (rotating disc reactor, single and multistage sieve-tray bubble columns, tower reactor with ejector gas distributor) as well as the energy effectiveness of their performance were compared with the purpose to establish a quantitative basis for the qualified choice of the proper reactor type according to demands of specific reaction processes. Selected design parameters included gas and solid phase holdup, kLaL, liquid phase residence time distribution, and axial distribution of the solid phase, the experiments were carried out in a wide range of solid phase concentration (0-20 wt. %) and particle sizes (2.3-280 μm). The experimental results proved that due to their favourable suspension characteristics and operation stability the rotating disc reactors can be advantageously used for slow reaction processes with low demands on the intensity of interfacial gas-liquid contact which can be carried out at low gas flow rates. On the other hand the multistage bubble column reactors proved to be superior devices for transport–controlled reaction processes regarding both the achievable rate of interfacial mass transfer and the overall energetic efficiency of phase contacting.

Gas holdup and pressure drop for air‐water flow through plate bubble columns

AbstractGas holdup and pressure drop measurements were made in two multistage bubble columns. Plates made from 6 mesh/in screen (α = 0.64) and those of Karr design (α = 0.53) were tested. An improved separated‐flow model was developed for correlating the two‐phase friction losses over the ranges: 0 ≤ VG ≤ 8.22 cm/s and 0 ≤ VL ≤ 6.12 cm/s. This model was also sound for the vibrating disk column introduced by Tojo et al. (1974).Empirical correlations are presented for the gas holdup and the pressure drop due to liquid circulation within these two columns.

Effect of partition plate on dispersion of suspended solid particles in multistage bubble columns.

The movement of solid particles through the partition plate was investigated in a multistage bubble column with continuous flow of liquid containing suspended solid particles. A mathematical model for use in predicting the solid concentration difference through the partition plate was derived on the basis of theoretical consideration of factors controlling the flow of liquid with suspended solid particles through the plate. Using experimentally observed data of solid concentration distribution in gas and slurry cocurrent upflow multistage bubble columns of 10 and 20cm in diameter, model parameters governing the solid concentration difference through the partition plate were correlated with the operating conditions. The transition of solid concentration profile within the column from a stepwise distribution at zero and/or low liquid flow rate, to a sawtoothed one at high liquid flow rate was interpreted by applying the model. From observed values of the gas holdup, the slip velocity of gas against liquid in the multistage bubble column was also correlated with the operating conditions.

Longitudinal dispersion of droplet phase in single- and multi-stage bubble columns for gas-liquid-liquid systems.

The longitudinal dispersion coefficient of droplet phase was measured in 6.6 and 12.2 cm i.d. single- and multistage bubble columns where kerosene was dispersed by air and water flows. Experimental residence time distribution curves of the droplet phase were analyzed by a newly proposed dispersion model, which included the back-flow of droplets through perforated baffle plates and the exchange of dye concentration in the droplet phase at the perforated baffle plates due to dispersion-coalescence phenomena. The exchange coefficient of the dye concentration was obtained by comparing experimental residence time distribution curves with the theoretical ones. The overall longitudinal dispersion coefficient of the droplet phase in multi-stage bubble columns was satisfactorily simulated by the present model, parameters of which were all given as experimental equations. The mean gas holdup in the 12.2cm i.d. column for air-water-solvent (n-hexane, terpentine oil and a mixed oil) systems was increased about 20% by installation of perforated baffl plates.

Longitudinal concentration distribution of droplets in multi-stage bubble columns for gas-liquid-liquid systems.

The longitudinal concentration distribution of droplets dispersed in multi-stage bubble columns was analyzed by the one-dimensional dispersion model with an effective slip velocity of droplets. The variables of the model-mean gas holdup, longitudinal dispersion coefficient of droplet phase and droplet concentration at the top of the column in 4- and 8-stage bubble columns of 6.6 and 12.2 cm i.d.-were measured and correlated. The effective slip velocity was determined by comparing observed mean droplet concentrations with theoretical ones and was correlated in an experimental equation. The concentration distributions of droplets calculated with the above parameters are in good agreement with the observed ones. Mean droplet diameter was also correlated as a function of gas velocity, total liquid velocity and free area of horizontal baffle plates.

Residence time distribution of suspended solid particles in multi-stage bubble column.

Methode de calcul de la distribution des temps de sejour basee sur un modele de sedimentation-diffusion avec ecoulement en retour entre etages. Discussion des resultats de calcul de la distribution des temps de sejour et du coefficient de diffusion longitudinale des particules

Longitudinal concentration distribution of suspended solid particles in multi-stage bubble columns.

The longitudinal concentration distribution of solid particles in 0.122- and 0.214-m i.d. multistage bubble columns was measured and analyzed by using a sedimentation-diffusion model with back-flow and the previously proposed empirical equations for single-stage bubble columns containing suspended solid particles and multi-stage bubble columns. The mean settling velocity of solid particles through the partition plates was correlated with dimensionless groups. The values of concentration of solid particles in multi-stage bubble columns calculated from the proposed correlation and the previously proposed ones agreed with the observed values within ±30%.