Gas Sparger Design Research Articles

Interface mass transfer and properties of bubbly flows in a column with Newtonian and non-Newtonian liquids

The mass transfer of gas–liquid systems is commonly reported through the volumetric mass transfer coefficient, kLa, which is a function of several complex phenomena. To optimize the rate of mass transfer, increased knowledge about the individual effects of the interfacial area, a, and the liquid-side mass transfer coefficient, kL, on kLa is necessary. In this study, kLa was measured by monitoring the dissolved oxygen concentration in a bubble column. The bubble flows were recorded by a photographic method and the images were analyzed by means of artificial neural network to determine the bubble size. The effects of rheology, superficial gas velocity, and gas sparger design were analyzed. kL decreased with an increase in the superficial gas velocity and with an increase in the viscosity. The relative change in a was much larger compared to the relative change in kL, and hence, for the investigated operational conditions and liquid solutions, the change in kLa was mainly attributed to the change in a. Bubble clusters were formed in the non-Newtonian solutions but for the given operating conditions and liquid solutions, the bubble cluster formation did not have a prominent effect on the mass transfer.

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.

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.

Effect of gas sparger design on bubble column hydrodynamics using pure and binary liquid phases

It is known that the fluid dynamics and transport phenomena in bubble columns depend mainly on the bubble column design (i.e., the column diameter, aspect ratio, and gas sparger openings) and the liquid phase properties. In this communication, we contribute to present-day discussion through an experimental study concerning the combined effects of the gas sparger design and liquid phase properties on both the gas holdup and the main flow regime transition. The experimental study concerning gas holdup measurements was conducted in a large-diameter and large-scale bubble column (with a height of 5.3 m and inner diameter of 0.24 m) operated in the batch mode. Air was used as the dispersed phase (using gas superficial velocities in the range 0.004–0.20 m/s), and various water–monoethylene glycol (MEG) solutions were employed as binary liquid phases. The water–MEG solutions tested have viscosities between 0.9 mPa·s and 7.97 mPa·s, densities between 997.086 kg/m3 and 1094.801 kg/m3, and surface tension between 0.0715 N/m and 0.0502 N/m. Two gas spargers were tested: (a) a spider sparger (“coarse gas sparger”) and (b) a needle sparger (“fine gas sparger”). The former produced a poly-dispersed homogeneous flow regime resulting in a concave gas holdup curve, whereas the latter produced a mono-dispersed homogeneous flow regime resulting in an S-shaped gas holdup curve. It was observed that the mono-dispersed bubble size distribution stabilized the homogeneous flow regime. The addition of MEG produced different effects depending on the gas sparger design. The addition of MEG in the “coarse gas sparger” configuration produced what is usually referred to as “dual effect of viscosity”: depending on the MEG concentration, the homogeneous flow regime was stabilized/destabilized, and thus, the gas holdup increased/decreased. Conversely, the addition of MEG in the “fine gas sparger” changed the shape of the gas holdup curve from an S-shape to concave, thus rendering it similar to the ones produced by “coarse gas sparger”. We speculate that viscous solutions reduce the influence of the inlet conditions in large-diameter and large-scale bubble columns; this is a matter of future research.

The effect of aspect ratio in counter-current gas-liquid bubble columns: Experimental results and gas holdup correlations

It is generally admitted that the gas holdup is independent of the column dimensions and gas sparger design if three criteria are satisfied: the diameter of the bubble column is larger than 0.15m, gas sparger openings are larger than 1–2mm and the aspect ratio is larger than 5. This paper contributes to the existing discussion; in particular, the effect of the aspect ratio (within the range 1–15) in a counter-current gas-liquid bubble column has been experimentally studied and a new gas holdup correlation to estimate the influence of aspect ratio, operation mode and working fluid on the gas holdup has been proposed. The bubble column, equipped with a spider gas sparger, is 5.3m in height, has an inner diameter of 0.24m; gas superficial velocities in the range of 0.004–0.23m/s have been considered, and, for the runs with water moving counter-currently to the gas phase, the liquid has been recirculated at a superficial velocity of −0.0846m/s. Filtered air has been used as the gaseous phase in all the experiments, while the liquid phase has included tap water and different aqueous solutions of sodium chloride as electrolyte. Gas holdup measurements have been used to investigate the flow regime transitions and the global bubble column hydrodynamics. The counter-current mode has turned out to increase the gas holdup and destabilize the homogeneous flow regime; the presence of electrolytes has resulted in increasing the gas holdup and stabilizing the homogeneous flow regime; the aspect ratio, up to a critical value, has turned out to decrease the gas holdup and destabilize the homogeneous flow regime. The critical value of the aspect ratio ranged between 5 and 10, depending on the bubble column operation (i.e., batch or counter-current modes) and liquid phase properties. Since no correlation has been found in the literature that can correctly predict the gas holdup under the investigated conditions, a new scheme of gas holdup correlation has been proposed. Starting from considerations concerning the flow regime transition, corrective parameters are included in the gas holdup correlation to account for the effect of the changes introduced by the aspect ratio, operation mode and working fluid. The proposed correlation has been found to predict fairly well the present experimental data as well as previously published gas holdup data.

Computed Tomographic Investigation of the Influence of Gas Sparger Design on Gas Holdup Distribution in a Bubble Column

The effect of gas sparger design on the gas holdup radial profile in a bubble column (with a diameter of 0.162 m) has been studied using γ-ray computed tomography (CT). Six different configurations of gas spargers were examined, using an air−water system for selected superficial gas velocities from 2 cm/s to 30 cm/s, covering the homogeneous and heterogeneous (churn-turbulent) flow regimes. Two operating pressures were used: 1 and 4 atm. Differences were found between the gas holdup distributions produced by different spargers at dimensionless radii of r/R < 0.8 in the central region of the column. The cross and single nozzle spargers produced closely similar gas holdup distributions, while the perforated plate sparger produced a higher gas holdup when compared to other spargers with the same percentage open area (POA). At 4 atm, the sparger design did not have a significant effect on the gas holdup profiles, compared to atmospheric pressure, except for the case of the single-hole sparger, which was found to yield a higher gas holdup.

NS0 cell damage by high gas velocity sparging in protein‐free and cholesterol‐free cultures

Recent developments in high cell density and high productivity fed-batch animal cell cultures have placed a high demand on oxygenation and carbon dioxide removal in bioreactors. The high oxygen demand is often met by increasing agitation and sparging rates of air/O2 in the bioreactors. However, as we demonstrate in this study, an increase of gas sparging can result in cell damage at the sparger site due to high gas entrance velocities. Previous studies have showed that gas bubble breakup at the culture surface was primarily responsible for cell damage in sparged bioreactors. Such cell damage can be reduced by use of surfactants such as Pluronic F-68 in the culture. In our results, where NS0 cells were grown in a protein-free and cholesterol-free medium containing 0.5 g/L Pluronic F-68, high gas entrance velocity at the sparger site was observed as the second mechanism for cell damage. Experiments were performed in scaled-down spinners to model the effect of hydrodynamic force resulting from high gas velocities on antibody-producing NS0 cells. Cell growth and cell death were described by first-order kinetics. Cell death rate constant increased significantly from 0.04 to 0.18 day(-1) with increasing gas entrance velocity from 2.3 to 82.9 m/s at the sparger site. The critical gas entrance velocity for the NS0 cell line studied was found to be approximately 30 m/s; velocities greater than 30 m/s caused cell damage which resulted in reduced viability and consequently reduced antibody production. Observations from a second cholesterol-independent NS0 cell line confirmed the occurrence of cell damage due to high gas velocities. Increasing the concentration of Pluronic F-68 from 0.5 to 2 g/L had no additional protective effect on cell damage associated with high gas velocity at the sparger. The results of gas velocity analysis for cell damage have been applied in two case studies of large-scale antibody manufacturing. The first is a troubleshooting study for antibody production carried out in a 600 L bioreactor, and the second is the development of a gas sparger design for a large bioreactor scale (e.g., 10,000 L) for antibody manufacturing.

Bubble Column Reactors for Wastewater Treatment. 3. Pilot-Scale Solvent Sublation of Pyrene and Pentachlorophenol from Simulated Wastewater

Removal efficiencies from a three-phase continuous, countercurrent solvent sublation of pyrene and pentachlorophenol from water are presented and compare well with Series CSTR Model predictions. The effects of the air-to-water flow ratio, the solvent flow rate, and the gas sparger design are discussed. Steady-state efficiencies as high as 96% for pyrene and 94% for pentachlorophenol are reported for an annular shear gas sparger. These results demonstrate the superiority of solvent sublation over bubble fractionation which is shown to be limited to a removal efficiency of 68% or less for these compounds. Moreover, analyses of the solvent (mineral oil) phase show that the separation factor (ratio of the solvent effluent concentration to the water effluent concentration) in solvent sublation can be as high as 300, which is distinctly greater than that observed in solvent extraction.

EFFECTS OF GEOMETRY ON HYDRODYNAMICS IN EXTERNAL-LOOP AIRLIFT REACTORS

Experimental investigations were carried out in model external-loop airlift reactors. Two reactors of laboratory scale (riser liquid height ranged between 1.16-1.56 m, riser diameter 0.03 m, AD/AR ratio between 0.111-1,000, total liquid volume VT = (1.189-2.446).10−3m3) and pilot-plant scale (riser liquid height of 4.4 and 4.7 m, respectively, riser diameter 0.200 m, AD/AR ratio of 0.1225 and 0.040 m, total liquid volume, VT = (0.144-0.170) m3) were used. The influences of reactor geometry characterized by some parameter as: AD/AR ratio, liquid height in riser and downcomer and liquid height in gas separator, together with the amount of introduced air, on the basic hydrodynamic design parameters: gas holdup and liquid circulation velocity were analysed. The influence of gas sparger design on gas holdup and liquid velocity was found to be negligible. The experimental liquid circulation velocity was correlated using a simplified form of the energy balance in airlift reactors, valid for external-loop airlift reactors with almost complete phase separation at the top. An original dimensionless correlation for gas holdup prediction involving superficial velocities of gas and liquid, cross sectional areas, dispersion height, riser diameter, as well as Froude number, was obtained.

An average gas hold-up and liquid circulation velocity in airlift reactors with external loop

Experimental investigations were carried out in model airlift reactors with external loops. Two reactors of laboratory scale (height 1.95 m, internal diameter 0.1 m, volume 0.08 m 3) and pilot-plant scale (height 7.18 m, internal diameter 0.2 m, volume 0.7 m 3) were used. The influence of reactor geometry, gas sparger design, liquid properties (both Newtonian and non-Newtonian) and the amount of introduced air was investigated. The influence of gas sparger design on gas hold-up and liquid velocity was found to be negligible. A modified method for the prediction of liquid circulation velocity—based on the energy balance of the reactor—was proposed. An original dimensionless correlation for gas hold-up prediction involving superficial velocities of gas and liquid, cross-sectgional areas, as well as Froude and Morton numbers, was obtained.

Optimum gas sparger design for bubble columns with a low height-to-diameter ratio

The mixing time and fractional gas hold-up have been measured in a bubble column 1 m in diameter using nine sparger designs. It has been shown that an optimum design of sparger (for either mixing time or gas hold-up) is possible for columns having a low height-to-diameter ratio and at low superficial gas velocities. The optimum design also depends on the physical properties of the system. The optimum design of the sparger has been shown to be different for mixing time and gas hold-up.