Two-phase Bubble Column Research Articles

Computational Fluid Dynamics Modelling of Two-Phase Bubble Columns: A Comprehensive Review

Bubble columns are used in many different industrial applications, and their design and characterisation have always been very complex. In recent years, the use of Computational Fluid Dynamics (CFD) has become very popular in the field of multiphase flows, with the final goal of developing a predictive tool that can track the complex dynamic phenomena occurring in these types of reactors. For this reason, we present a detailed literature review on the numerical simulation of two-phase bubble columns. First, after a brief introduction to bubble column technology and flow regimes, we discuss the state-of-the-art modelling approaches, presenting the models describing the momentum exchange between the phases (i.e., drag, lift, turbulent dispersion, wall lubrication, and virtual mass forces), Bubble-Induced Turbulence (BIT), and bubble coalescence and breakup, along with an overview of the Population Balance Model (PBM). Second, we present different numerical studies from the literature highlighting different model settings, performance levels, and limitations. In addition, we provide the errors between numerical predictions and experimental results concerning global (gas holdup) and local (void fraction and liquid velocity) flow properties. Finally, we outline the major issues to be solved in future studies.

Biodesulfurization of Dibenzothiophene and Its Alkylated Derivatives in a Two-Phase Bubble Column Bioreactor by Resting Cells of Rhodococcus erythropolis IGTS8

Biodesulfurization (BDS) is considered a complementary technology to the traditional hydrodesulfurization treatment for the removal of recalcitrant sulfur compounds from petroleum products. BDS was investigated in a bubble column bioreactor using two-phase media. The effects of various process parameters, such as biocatalyst age and concentration, organic fraction percentage (OFP), and type of sulfur compound—namely, dibenzothiophene (DBT), 4-methyldibenzothiophene (4-MDBT), 4,6-dimethyldibenzothiophene (4,6-DMDBT), and 4,6-diethyldibenzothiophene (4,6-DEDBT)—were evaluated, using resting cells of Rhodococcus erythropolis IGTS8. Cells derived from the beginning of the exponential growth phase of the bacterium exhibited the highest biodesulfurization efficiency and rate. The biocatalyst performed better in an OFP of 50% v/v. The extent of DBT desulfurization was dependent on cell concentration, with the desulfurization rate reaching its maximum at intermediate cell concentrations. A new semi-empirical model for the biphasic BDS was developed, based on the overall Michaelis-Menten kinetics and taking into consideration the deactivation of the biocatalyst over time, as well as the underlying mass transfer phenomena. The model fitted experimental data on DBT consumption and 2-hydroxibyphenyl (2-HBP) accumulation in the organic phase for various initial DBT concentrations and different organosulfur compounds. For constant OFP and biocatalyst concentration, the most important parameter that affects BDS efficiency seems to be biocatalyst deactivation, while the phenomenon is controlled by the affinities of biodesulfurizing enzymes for the different organosulfur compounds. Thus, desulfurization efficiency decreased with increasing initial DBT concentration, and in inverse proportion to increases in the carbon number of alkyl substituent groups.

The effect of operating and design parameter on bubble column performance: The LOPROX case study

It is known that the performances of multi-phase reactors depend on the operating parameters (the temperature and the pressure of the system), the phase properties, and the design parameters (the aspect ratio (AR), the bubble column diameter, and the gas sparger design). Hence, the precise design and the correct operation of multi-phase reactors depends on the understanding and prediction of the fluid dynamics parameters. This paper contributes to the existing discussion on the effect of operating and design parameter on multi-phase reactors and, in particular, it considers an industrial process (e.g., the LOPROX (low pressure oxidation) case study, which is typical example of two-phase bubble columns). Based on a previously-validated set of correlations, the influence of operating and design parameter on system performances is studied and critically analyzed. First, we studied the effects of the design parameter on the liquid–gas interfacial area, by keeping constant the fluid physical–chemical properties as well as the operating conditions; subsequently, we discussed for a fixed system design, the influence of the liquid phase properties and the operating pressure. In conclusion, this paper is intended to provide guidelines for the design and scale-up of multi-phase reactors.

High-performance hybrid modeling chemical reactors using differential evolution based fuzzy inference system

Bubbly flow behavior simulation in two-phase chemical reactors such bubble column type reactors is widely employed for chemical industry purposes. The computational fluid dynamics (CFD) approach has been employed by engineers and researchers for modeling these types of chemical reactors. In spite of the CFD robustness for simulating transport phenomena and chemical reactions in these reactors, this approach has been known as expensive for modeling such turbulent complex flows. Artificial intelligence (AI) algorithm of the adaptive network-based fuzzy inference system (ANFIS) are largely understood and utilized for the CFD approach optimization. In this hybrid approach, the CFD findings are learned by AI algorithms like ANFIS to save computational time and expenses. Once the pattern of the CFD results have been captured by the AI model, this hybrid model can be then used for process simulation and optimization. As such, there is no need for further simulations of new conditions. The objective of this paper is to obviate the need for expensive CFD computations for two-phase flows in chemical reactors via coupling CFD data to an AI algorithm, i.e., differential evolution based fuzzy inference system (DEFIS). To do so, air velocity as the output and the values of the x, and y coordinates, water velocity, and time step as the inputs are inputted the AI model for learning the flow pattern. The effects of cross over as the DE parameter and also the number of inputs on the best intelligence are investigated. Indeed, DEFIS correlates the air velocity to the nodes coordinates, time, and liquid velocity and then after the CFD modeling could be replaced with the simple correlation. For the first time, a comparison is made between the ANFIS and the DEFIS performances in terms of the prediction capability of the gas (air) velocity. The results released that both ANFIS and DEFIS could accurately predict the CFD pattern. The prediction times of both methods were obtained to be equal. However, the learning time of the DEFIS was fourfold of ANFIS.

Eulerian-Eulerian Approach to CFD Simulation of Two-Phase Bubble Column

Calculation work is carried out in the present project to study the effect of different parameters on hydrodynamics of gas-liquid flow by using CFD. The steady state and transient, three dimensional simulations are performed of the whole bubble column for various inlet gas and sparger designs. A standard k-ε is used to describe turbulence occurring in the continuous fluid. Results show he asymmetric recirculation stronger with an increase in the number of holes giving better mixing. The gas hold-up increased with superficial gas velocity but independent of the sparger design at high velocity. Comparison of simulation results with the previous experimental work data has provided a successful validation of the model.

In sito galanthamine extraction during the cultivation of Leucojum aestivum L. shoot culture in two-phase bubble column cultivation system.

Two‐phase bioreactor cultivation system was developed and applied for in sito recovery of extracellular galanthamine during the cultivation of Leucojum aestivum L. shoot culture in a modified column bioreactor system. The inclusion of an external circulation column with adsorbent resin Amberlite XAD‐4 as a second phase, on the 21st day of the beginning of cultivation resulted in 1.25 folds increase in biomass accumulation and maximal amounts of accumulated galanthamine of 6 mg/L (3.1 mg/L intracellular and 2.9 mg/L extracellular). It was demonstrated that the inclusion of a second phase at the cultivation of the L. aestivum shoot culture in a bubble column bioreactor with internal sections redirected the alkaloid metabolism to galanthamine synthesis and inhibits the synthesis of hemanthamine and lycorine type alkaloids. Our research demonstrated that the application of the two‐phase cultivation systems could be an important tool to increase the yields of valuable secondary metabolites in plant tissue culture‐based bioprocess.

Simulation of carbon dioxide absorption by amino acids in two-phase batch and bubble column reactors

ABSTRACTThe absorption of carbon dioxide (CO2) is an important process in many practical applications. The use of amino acid solutions as absorption solvents has the potential to reduce the amount of energy required by the regeneration process. The goal of this research project is to develop dynamic models to simulate CO2 absorption by using amino acid solutions as absorption solvents. A reaction scheme is proposed to represent the chemical reactions between the amino acid and CO2. Two reaction models, for a two-phase batch reactor and a bubble column, based upon transient mass and energy balances for the chemical species found in CO2 gas-liquid absorption are presented. Computer codes have been written to implement the proposed models. Simulation results are presented and discussed. The proposed models can be used to optimize and control CO2 absorption in practical applications.

Two-Phase Bubble Columns: A Comprehensive Review

We present a comprehensive literature review on the two-phase bubble column; in this review we deeply analyze the flow regimes, the flow regime transitions, the local and global fluid dynamics parameters, and the mass transfer phenomena. First, we discuss the flow regimes, the flow regime transitions, the local and global fluid dynamics parameters, and the mass transfer. We also discuss how the operating parameters (i.e., pressure, temperature, and gas and liquid flow rates), the operating modes (i.e., the co-current, the counter-current and the batch modes), the liquid and gas phase properties, and the design parameters (i.e., gas sparger design, column diameter and aspect ratio) influence the flow regime transitions and the fluid dynamics parameters. Secondly, we present the experimental techniques for studying the global and local fluid dynamic properties. Finally, we present the modeling approaches to study the global and local bubble column fluid dynamics, and we outline the major issues to be solved in future studies.

Computational fluid-dynamic modeling of the mono-dispersed homogeneous flow regime in bubble columns

Two-phase bubble columns are equipment used to bring one or several gases into contact with a liquid phase. Despite the simple system design, bubble columns are characterized by complex fluid dynamic phenomena at different scales; for this reason, their correct design, operation and scale-up rely on the precise estimation of global and local fluid dynamics properties. In this respect, multi-phase Computational Fluid Dynamics (CFD), in the Eulerian multi-fluid framework, is particularly useful to study the fluid dynamics in multi-phase reactors. Within this approach, the accurate prediction of the fluid dynamics depends on the correct modeling of (a) the momentum exchange between the phases, (b) the effects of the dispersed phase on the turbulence of the continuous phase, and (c) the bubble coalescence and break-up phenomena. Furthermore, the global and the local fluid dynamic properties are related to the prevailing flow regime, i.e., the homogeneous flow regime and the heterogeneous flow regime. This paper mainly focuses on the homogeneous flow regime, which can be classified as “pseudo-homogeneous” or “mono-dispersed homogeneous”, depending on the prevailing bubble size distribution. The numerical modeling of the “pseudo-homogeneous” flow regime has been discussed in our previous papers (i.e., modeling closures and suitable boundary conditions); conversely, this paper contributes to the existing discussion on the modeling closures by investigating the “mono-dispersed homogeneous” flow regime in “small-scale” and “large-scale” bubble columns. To this end, two test cases have been considered: (a) a “small-scale” bubble column (a test case taken from the previous literature); (b) a large-scale bubble column (a test case experimentally studied within this paper by image analysis, optical probe and gas holdup techniques). In particular, this paper studies the effects of the interfacial forces and bubble induced turbulence modeling within the Eulerian two-fluid approach. Three-dimensional transient simulations have been performed and the numerical results were compared with experimental data (both local and global fluid dynamics parameters). The results have been critically analyzed and the reasons for the discrepancies between the numerical results and the experimental data have been identified and may serve as a basis for future studies. Likewise, recommendations on suitable closures as well as guidelines for future studies have been provided. In conclusion, this paper extends the validation of a previously proposed set of closure relations (validated for the “pseudo-homogeneous” flow regime in a “large-scale” annular gap bubble column) to the “mono-dispersed homogeneous” flow regime in “small-scale” and large-scale bubble columns.

Comparison of void fraction measurements using different techniques in two-phase flow bubble column reactors

Local, area and volume average void fraction measurements have been conducted in gas-liquid two-phase flow through vertical pipes of different diameters under different modes of operation covering up-flow, down-flow and batch bubble column. The measurement techniques used include gamma ray densitometry, electrical resistance tomography (ERT), wire mesh sensor (WMS), optical void probe, and pressure transducers. The consistency among different measurement techniques has been examined by comparing the local, area and volume-average void fraction measurements made using the above methods in the same test section under the same flow conditions. The accuracy of the measurement techniques has been found to depend significantly on the mode of two-phase flow operation. The results show that the gamma densitometry and the pressure transducers can produce highly reliable measurements independent of the mode of operation. However, the optical void probe was found to underestimate the local values of void fractions, particularly, in the case of a co-current down-flow with sub-millimeter sized bubbles. Also, the electrical resistance tomography technique was found to be the least reliable method, as it underestimated the void fraction in the co-current up-flow as well as co-current down-flow operation. The accuracy of the wire mesh sensor was strongly dependent on the size of the bubbles relative to the wire mesh spacing.

Novel gas holdup and regime transition correlation for two-phase bubble columns

The gas holdup is dimensionless parameter of fundamental and practical importance in the operation, design and scale-up of bubble columns. Unfortunately, the many relationships between the bubble column fluid dynamic parameters and the various variables characterizing the system make it difficult to find general correlations for the precise estimation of the gas holdup. Wilkinson et al. (1992), in their pioneering paper, proposed a correlation to predict the gas holdup in industrial-scale bubble columns, based on the physical properties of the phases and the operating conditions. However, this correlation lacks in generality, as it does not take in account the bubble column design. In this paper, we propose a generalization of the Wilkinson et al. (1992) gas holdup correlation to take into also the bubble column design parameters. Starting from considerations concerning the flow regime transition, corrective parameters are included to account for the effects introduced by the gas sparger openings, the bubble column aspect ratio and the bubble column diameter. The proposed correlation has been found to predict fairly well previously published gas holdup and flow regime transition data.

Gas holdup and flow regime transition in spider-sparger bubble column: effect of liquid phase properties

This paper discusses the effects of the liquid velocity and the liquid phase properties on the gas holdup and the flow regime transition in a large-diameter and large-scale counter-current two-phase bubble column. In particular, we compared and analysed the experimental data obtained in our previous experimental studies. The bubble column is 5.3 m in height, has an inner diameter of 0.24 m, it was operated with gas superficial velocities in the range of 0.004–0.20 m/s and, in the counter-current mode, the liquid was recirculated up to a superficial velocity of -0.09 m/s. Air was used as the dispersed phase and various fluids (tap water, aqueous solutions of sodium chloride, ethanol and monoethylene glycol) were employed as liquid phases. The experimental dataset consist in gas holdup measurements and was used to investigate the global fluid dynamics and the flow regime transition between the homogeneous flow regime and the transition flow regime. We found that the liquid velocity and the liquid phase properties significantly affect the gas holdup and the flow regime transition. In this respect, a possible relationship (based on the lift force) between the flow regime transition and the gas holdup was proposed.

Estimation of bubble size distributions and shapes in two-phase bubble column using image analysis and optical probes

A precise estimation of bubble size distributions and shapes is required to characterize the bubble column fluid dynamics at the “bubble-scale”, and to evaluate the heat and mass transfer rate in bubble column reactors. Image analysis methods can be used to measure the bubble size distributions and shapes; unfortunately, these experimental techniques are limited to resolve bubble clusters and large void fractions, and can not be applied under relevant operating conditions (e.g., high temperature and pressure). On the other hand, needle probes (i.e, optical and conductive probes) can be used to measure bubble sizes in dense bubbly flows and under relevant operating conditions; however, needle probes measure chord length distributions, which should be converted into bubble size distributions by using statistical algorithms. These algorithms rely on correlations—generally obtained for single droplets/bubbles—that predicts the bubble shapes, by relating the bubble equivalent diameter to the bubble aspect ratio. In this paper, we contribute to the existing discussion through an experimental study regarding the bubble sizes and aspect ratio in a large air-water bubble column. The experimental investigation has consisted in gas holdup, image analysis and optical probe measurements. First, the gas holdup measurements have been used to identify the flow regime transition between the homogeneous flow regime and the transition flow regime. Secondly, the homogeneous flow regime has been described at the “bubble-scale”: chord length distributions and bubble size distributions have been obtained by using an optical probe and image analysis, respectively. Based on the experimental data from the image analysis, a correlation between the bubble equivalent diameter and the bubble aspect ratio has been proposed and has been compared with existing correlations. Finally, the chord length distributions have been converted into bubble size distributions using a statistical method, supported by the aspect ratio obtained through image analysis. The proposed approach has been able to estimate correctly the bubble size distributions at the center of the column then near the wall. We have also demonstrated that the correlations used to predicts the bubble shapes are the main point of improvement in the method.

A Combined Multifluid-Population Balance Model Applied to Dispersed Gas–Liquid Flows

The two-phase bubble columns are widely used for carrying out gas–liquid reactions in a variety of industrial applications. The optimal operation of many of the processes carried out in the bubble columns depends on the bubble size distribution, which determines the interfacial momentum, mass, and heat transfer fluxes through the contact area between the liquid and gas phases. In this context, the population balance equation is relevant as it can be used to quantify the amount of bubbles of different sizes present at different locations in the bubble column. The combined multifluid-population balance models use mass and momentum equations coupled with population balances for the dispersed phase, whereas the continuum mechanical equations of the two-fluid or multifluid models are used for the liquid phase. The most rigorous description is based on a kinetic theory approach with size resolution (KTAWSR). In this study, the KTAWSR model is applied to simulate bubbly flows under complex conditions, that is, significant change in the Sauter mean diameter along the axial direction of the bubble column. The model is solved using the spectral orthogonal collocation method. Both sensitivity analyzes and comparison to experimental data from the literature are used to assess the potential of the model. Fair agreement between the experimental data and model prediction is achieved. It is concluded that the model adds as a valuable tool with good potentials for the population balance community, considering both the level of details resolved with this model and its possible use in developing future breakage and coalescence models.

Wall-to-bulk Mass Transfer in a Two-phase Upflow Bubble Column with a Composite Promoter

Experiments were conducted to investigate the effect of pertinent dynamic and geometric variables on wall-to-bulk mass transfer coefficient in two-phase upflow bubble column in the presence of a composite promoter. The liquid phase is an electrolyte consisting of equimolal solution of potassium ferrocyanide and ferricyanide of 0.01 N with 0.5 N sodium hydroxide. The gas phase is nitrogen and a 6.73 cm i.d. acrylic column was employed as the test section. Helical tapes of four different widths wound on central rods of three different diameters with five varying pitches were used as composite promoter elements along with annular rods of four different diameters. Measurement of limiting currents at point electrodes fixed flush with the inner surface of the test section facilitated the computation of wall-to-bulk mass transfer coefficients. The wall-to-bulk mass transfer coefficient was found to increase with increase in liquid and gas velocities in the presence of the promoter. The effect of rod diameter, tape width and tape pitch yielded improvements upto 40% at lower liquid and gas velocities. The entire data were correlated with the equation j D = 110.3 (Re)–0.8424 (Fr g )0.089.

Heat transfer metrology issues in two-phase bubble column reactors

The metrology and the impact of various parameters and operating conditions on the bulk-to-tube heat transfer coefficients in two-phase bubble columns are investigated on a small-scale mock-up. It is shown that (1) quasi-adiabatic conditions can be reached in the column; (2) the bulk-to-tube heat transfer coefficients for each U-tube downward and upward sections may or may not differ significantly, depending on the way uncertainty of the measurements is estimated; (3) using the different measurements and uncertainty estimates for given conditions, a mean heat transfer coefficient over all tubes is estimated within ±5%. The consequences for bulk-to-tube heat transfer coefficient prediction in a larger column are discussed.

On the Coupled Solution of a Combined Population Balance Model Using the Least-Squares Spectral Element Method

In this work, a cross-sectional averaged two-fluid model combined with a population balance model is applied to simulate the flow field and the bubble size distributions in a two-phase bubble column. The Martinez-Bazan breakage kernel and a modified Prince and Blanch coalescence kernel have been chosen to describe bubble breakage and bubble coalescence, respectively. In the present study, we discuss the use of a higher-order spectral element method—the least-squares method—to compute the system of equations in a coupled manner. The least-squares method is highly accurate and has a number of advantages over the conventional numerical methods like the finite difference and finite volume methods. In contrast to the finite volume method, when desinging an overall solution algorithm, this least-squares method ensures that all the continuity equations are satisfied individually and it deals with both the convective and diffusive terms stably and accurately. The novel iterative algorithm solves the flow and the ...

Influence of structured packing on gas holdup in a three-phase bubble column

In this work, the influence of structured packing on gas holdup in gas–liquid–solid dispersions has been studied. The experiments were carried out in an empty column and in column containing structured packing operating under identical conditions. Glass beads and silicon carbide particles were used as the solid material and the volumetric fraction of solids was varied from 0% to around 10%. The liquid viscosity was strongly modified using water, CMC solution and glycerol. The experimental results obtained with both columns were compared with previous results obtained in two-phase bubble columns. The influence of structured packing on the total gas holdup for different superficial gas velocities was found to be similar with and without suspended solids. Therefore, the results obtained in this work were analysed on the basis of correlations derived earlier for gas–liquid dispersions. Excepting the results obtained with glycerol, these correlations can predict the gas holdup of three-phase bubble columns with reasonable accuracy.

The investigation of gas holdup distribution in a two-phase bubble column using ultrasonic computed tomography

Abstract In this study, time-averaged gas holdup distributions were investigated in a 16 cm diameter bubble column for two-phase dispersed system of air–water and air–glycerol solution of 10 wt% by using ultrasonic computed tomography (UCT). A quantitative result of UCT – as a coupling of the ultrasonic transmission method and the iterative filtered backprojection (IFBP) image reconstruction technique – is presented. The UCT results are in a good agreement with those by the bed expansion method. A higher gas holdup in the air–glycerol 10 wt% solution than in the air–water system was observed. The distribution of gas holdup in the column with an attached baffle is also investigated by UCT.

Evaluations of Euler–Euler Simulations of Bubble Columns Based on Numerical Tracer Experiments

This paper considers the question of how to evaluate Euler–Euler simulations of macro-mixing in two-phase bubble columns. Here, the idea is to perform tracer experiments (jump responses) both experimentally and also numerically. In both cases the resulting data is then analysed on the basis of the convection–dispersion model. Given that the integral quantities gas hold-up, axial dispersion coefficient (i.e., Bodenstein number) and mean residence time show sensitivity with respect to the physical phenomena, the applied turbulence models (i.e., k– ɛ and SST) and the boundary conditions, respectively to their numerical consequences, this approach provides a means to evaluate the quality of sophisticated mathematical models and their numerical realization.