Conventional Bubble Column Research Articles

Simulation of Hydrodynamic Conditions of a Photobioreactor for Microalgae Cultivation

Under optimum environmental conditions, microalgae are able to accumulate significant amounts of lipids within diminutive span. They are therefore established as promising candidates for the production of biodiesel. In order to develop this, and also to cut down the cost parameter involving the production of biodiesel from algae, the growth rate of algae has to be enhanced. To maintain the proper condition for their growth, closed cultivation is the best option for which different types of reactor are used. Bubble column reactor, is one among them, where the mixing rate of algae with nutrients, growth rate increases. This paper reported the design modification of spiral column reactor which will have better mixing rate than conventional bubble column reactor in turn more mass transfer due to more turbulence which can be seen by analyzing the turbulence kinetic energy against radius for both the reactors, for that CFX solver is been used.

Effect of Vibrating Sparger on Mass Transfer, Gas Holdup, and Bubble Size in a Bubble Column Reactor

Abstract Bubble size has a key role in gas holdup and mass transfer in bubble column reactors. In order to have small and uniform bubbles, a new structure was designed; the reactor operates in two modes, with vibrating sparger and conventional bubble column in which sparger is fixed. In vibrating mode, the sparger vibrates gently during gas entering. The vibrating sparger performs like a paddle, resulting in a forced recirculation of gas–liquid inside the reactor; moreover, the bubble detachment is accelerated. The superficial gas velocity was between 0.003 and 0.013 ms− 1, and the vibration frequency was changed between 0 and 10.3 Hz. The bubble size was measured at three various positions of the reactor height by photographic method and using MATLAB 7.0.1 software. The mass transfer coefficient was determined by means of the dynamic gassing-out method. The results show that the bubbles were bigger in vibrating mode than those working without vibration. The bubble size decreases with increase in height from sparger. Gas holdup increased with increase in superficial gas velocity and vibration frequency. The effect of vibration increased the gas holdup with an average of 70% for all superficial gas velocities. Volumetric mass transfer coefficient was almost stable as vibration frequency increased.

Influence Parameters in the Ozonation of Clofibric Acid Using a Cascade Bubble Column

Ozonation of clofibric acid (CA) in aqueous solution was carried out under continuous operation in a cascade bubble column. The influence of operation parameters including initial CA concentration, gas flow rate, liquid flow rate and pH on the removal of CA and TOC was investigated. The results indicated that ozonation could be used to effectively remove CA from water. Increasing the initial CA concentration resulted in a decrease of the CA and TOC removal efficiency. A comparison of CA removal efficiency and ozone utilization between cascade and conventional bubble column indicated that cascade bubble column was an effective way for increasing the solubility ozone in the reactor.

Distribution characteristics of holdups in a multi-stage bubble column using electrical resistance tomography

Based on the principle of chemical reaction engineering, the addition of perforated plates can improve the performance of conventional bubble column and decrease the backmixing behaviors. The distribution characteristics of gas holdup in a multi-stage bubble column embedded with five types of sieve plates and three types of tongue plates were studied using electrical resistance tomography (ERT). The effects of superficial gas velocity and the geometric design of perforated plates on the gas holdup and its radial distribution above and below the plates of the bubble column were discussed. Experimental results show ERT is suitable as an online monitoring tool to provide useful information on the hydrodynamic parameters of multi-stage bubble columns. With increasing superficial gas velocity, local gas holdup increases, and gas holdup below the plate increases with decrease of free area (%FA), hole diameters or angle of tongue plates. ERT technique facilitates noninvasive and nonintrusive visualization of cross-sectional distribution of gas holdup in a bubble column.

Enantioseparation of α-cyclohexylmandelic acid by solvent sublation

Herein we focused on using a novel separation technology, solvent sublation, for the enantioseparation of α-cyclohexylmandelic acid (CHMA). The experiment was carried out in a conventional bubble column using d-iso-butyl tartrate (d-IBTA) and sodium dodecyl sulfate (SDS) as a chiral selector and surfactant, respectively (Fig. 7). Several important parameters influencing the separation performance, such as the type of organic phase, the pH in the aqueous phase, and the concentrations of CHMA, d-IBTA, and SDS were investigated. Under the optimal operating conditions, the enantiomeric excess and separation factor were 54.85% and 4.5, respectively. The yields of d-enantiomer and l-enantiomer were 82.20% and 38.94%, respectively. Finally, the thermodynamic properties of the separation were investigated, which indicated an enthalpy-controlled process. This technique is an efficient chiral separation method, with many advantages, such as low amounts of organic solvent and chiral selector required and easier realization of the multi-stage operation.

Liquid circulation hydrodynamics in an external loop airlift reactor

AbstractThe radial profiles of axial liquid velocity and gas hold‐ups are investigated in the riser of a pilot plant scale external loop airlift reactor (ELAR) using a modified Pavlov tube and differential pressure technique. The experimental investigation reveals that there exist two different kinds of liquid circulation structures in an ELAR, which has rarely been reported in the literature, namely internal liquid circulation, which exists only in the riser and external liquid circulation, which circulates through the downcomer. A power–law relationship is used to correlate the gas hold‐up and superficial gas velocity, which gives good agreement with experimental data. Experiments for axial liquid velocity profiles are analysed in analogy to a model described for a conventional bubble column. The results predicted by the model are in excellent agreement with the experimental data obtained under various operating conditions. © 2011 Canadian Society for Chemical Engineering

Hydrodynamics of a Tapered Bubble Column

AbstractThe hydrodynamic behavior of a single‐stage tapered bubble column using an air‐water two‐phase system has been studied. The experimental results indicate that the holdup increases with increasing superficial gas velocity and bubble slip velocity, while it remains constant with increasing superficial liquid velocity. The gas flow rate has a subtle effect on pressure drop owing to the dynamic pressure recovery stemming from the increase in flow area in the axial direction. The results further suggest that the tapered bubble column shows higher holdup with lower energy dissipation than the conventional bubble columns under similar hydrodynamic conditions. The experimental values of the holdup are in excellent agreement with the well‐known Akita and Yoshida correlation available in the existing literature. Also, the performance of the tapered system has been shown to be much better than that of conventional columns under similar conditions in water/alkaline scrubbing of fly ash and SO2 either alone or in combination.

Dynamics and oxygen transfer of a novel vertical tubular biological reactor for wastewater treatment

Dynamics and oxygen transfer of a novel vertical tubular biological reactor (VTBR) for wastewater treatment were investigated in this paper. It was showed that the dissolved oxygen concentration (DO) in VTBR is higher than that in the conventional bubble column. When the ratio of gas and liquid flow rates was greater than 6.44, there were no phenomena of deficiency oxygen in all reactors. The volume oxygen transfer coefficient ( k L a) was between 0.005 and 0.025 1/s. The multi-stage series CSTR and PFR model were developed to describe the dynamics of VTBR. It was revealed that the PFR model was proper to describe the dynamics of VTBR of which maximum error was only 25%. The industrial effluents from Dalian Bangchui Island Beer Company were utilized to verify the two models. It was suggested that when the ratio of gas–liquid was greater than 6.44, the removal efficiency of COD could be obtained more than 80%.

Effects of natural organic matter (NOM) character and removal on ozonation for maximizing disinfection with minimum bromate and AOC formation

The objective of this study was to evaluate the effects of the character and the removal of natural organic matter (NOM) on the formation of assimilable organic carbon (AOC) and bromate during ozone disinfection. Natural waters from two locations with different dissolved organic carbon (DOC) concentrations were tested. In addition, the DOC concentration of one of the natural waters was reduced either by ion exchange (IEX) or by granular activated carbon (GAC) filtration. The resulting four water types were tested in conventional pilot-scale ozone bubble column reactors and in a bench-scale plug flow reactor with dissolved ozone dosing. For the tested waters NOM fractions were determined with size exclusion chromatography using DOC and UVA254 detection. As expected, it was observed that for the same ozone dosages the CT is higher when NOM is removed by IEX or GAC compared to the situation without NOM removal. It is concluded that, for the waters tested, removal of the humic compounds with a molecular weight of approximately 1,000 g/mol by using IEX led to less AOC formation and less bromate formation as compared to the removal of humic compounds with a molecular weight of 300–500 g/mol by using GAC.

Solid–liquid mass transfer analysis in a multi-phase tank reactor containing submerged coated inclined-plates: A computational fluid dynamics approach

Although there is a voluminous literature on the estimation of interphase transport parameters in conventional slurry bubble column reactors, these correlations are inadequate in photoreactors equipped with specialized internals to facilitate light harvesting efficiency of the photocatalyst. This is particularly germane to the present externally illuminated bubble column reactor containing titania-coated plates immersed in the liquid column at different angles of inclination. Thus, a computational fluid dynamics (CFD) procedure utilizing the Eulerian–Eulerian approach has been used to solve the governing differential equations for the solid liquid mass transport problem based on the standard k – ε model incorporating additional terms that take account of the interfacial turbulent momentum transfer. Mass transfer from the surface of the coated-quartz plates to the liquid phase was modeled using the Launder–Spalding wall functions. The plates were coated with benzoic acid as solid substrate with water and air as the liquid and gas phases, respectively. The increase in mass transfer due to reduction of the boundary layer thickness during air-induced liquid recirculation on either side of the submerged inclined plates was correlated with difference between turbulent and molecular Schmidt numbers via an adjustable parameter, A. CFD simulation using the Launder–Spalding wall function (with A = 1.08 ) gave better agreement with experimental transient concentration profiles than calculations based on FLUENT's enhanced wall function for the plate orientations ( θ = 0 ∘ , 22 . 5 ∘ , and 45 ∘ ) studied. The solid-to-liquid mass transfer was higher on the lower-side of the plate than the upper-side. In particular, mass transfer coefficient was higher with the inclined plate than with the vertical or horizontal orientation suggesting an added advantage for the application of the system as a solar photoreactor.

Particulate‐laden‐SO2 scrubbing in a tapered bubble column

AbstractThe performance of a tapered bubble column that generates higher fractional gas hold up with least power consumption than existing systems under similar hydrodynamic conditions is reported in this article for particulate‐laden‐SO2 scrubbing. Firstly, quiescent batch studies were carried out to analyze SO2 removal at various initial particle concentrations. Results revealed that presence of particles improved the SO2 removal efficiency to about 14–27% that was elucidated by the facilitated adsorptive mass transport. The performance of the system was analyzed in subsequent experimentation operating it under continuous mode for particulate‐laden‐SO2 scrubbing using water and dilute NaOH. Results indicated that the removal efficiency of SO2 was improved to about 25%/(W/m3) due to change in the column geometry and to about 16.7%/(W/m3) due to presence of particles (fly‐ash) within the range of variables studied. The enhancement of removal of SO2 due to presence of particulate matter and that due to alkali scrubbing were quantified and compared. Operating regimes of maximum removal efficiencies (∼100%) of SO2 and particulates either alone or in combination were determined from experimental results. Empirical and semi‐empirical correlations were developed for predicting the scrubbing performances of the tapered column in water and dilute NaOH, respectively. Experimental values fitted excellently well with the predicted values. The superiority of the tapered bubble column over a conventional bubble column for scrubbing of particulates and SO2 either alone or in combination was described. © 2008 American Institute of Chemical Engineers Environ Prog, 2009

Bubble size in a forced circulation loop reactor

AbstractBACKGROUND:The bubble size distribution in gas‐liquid reactors influences gas holdup, residence time distribution, and gas‐liquid interfacial area for mass transfer. This work reports on the effects of independently varied gas and liquid flow rates on steady‐state bubble size distributions in a new design of forced circulation loop reactor operated with an air–water system. The reactor consisted of a cylindrical vessel (∼26 L nominal volume, gas‐free aspect ratio ≈ 6, downcomer‐to‐riser cross‐sectional area ratio of 0.493) with a concentric draft tube and an annular riser zone. Both gas and liquid were in forced flow through a sparger that had been designed for minimizing the bubble size.RESULTS:Photographically measured bubble size distributions in the riser zone could be approximated as normal distributions for the combinations of gas and liquid flow rates used. This contrasted with other kinds of size distributions (e.g. bimodal, Gaussian) that have been reported for other types of gas‐liquid reactors. Most of the bubbles were in the 3 to 5 mm diameter range. At any fixed low value of aeration rate (≤1.8 × 10−4 m3s−1), increase in the liquid flow rate caused earlier detachment of bubbles from the sparger holes to reduce the Sauter mean bubble size in the riser region.CONCLUSION:Unlike in conventional bubble columns where bimodal and Gaussian bubble size distributions have been reported, a normal bubble size distribution is attained in forced circulation loop reactors with an air–water system over the entire range of operation. Copyright © 2007 Society of Chemical Industry

Gas holdup and mixing characteristics of a novel forced circulation loop reactor

Gas holdup and mixing time were characterized in a forced circulation internal loop draft-tube reactor (unaerated aspect ratio ≈ 6, downcomerto-riser cross-sectional area ratio = 0.493) as functions of the forced liquid superficial velocity in the riser (ULr) and the gas superficial velocity in the riser (UGr). Data were obtained in air–water system. The operation ranges were 0 ≤ ULr ≤ 0.051 m/s and 7.8 × 10 −3 ≤ UGr ≤ 3.9 × 10 −2 m/s for the liquid and gas velocities, respectively. Under forced flow conditions the reactor always operated in the bubble flow regimen, but operation as an airlift reactor (i.e. no forced flow of liquid) produced a heterogeneous churn-turbulent flow regimen. Forced flow of liquid enhanced gas holdup in comparison with the airlift mode of operation. Mixing time generally declined with increased flow rates of gas and liquid. The ability to maintain a bubble flow regimen through forced flow of liquid allowed the reactor to attain gas holdup values of >0.12 that are difficult to achieve in air–water in conventional bubble columns and airlift reactors. © 2007 Elsevier B.V. All rights reserved.

Gas–liquid interfacial area and mass transfer coefficient in a co‐current down flow contacting column

AbstractThe gas–liquid interfacial area and mass transfer coefficient for absorption of oxygen from air into water, aqueous glycerol solutions up to 1.5% (w/w) and fermentation medium containing glucose up to a 3% concentration were determined in a co‐current down flow contacting column (CDCC; 0.05 m i.d. and 0.8 m length). Experimental studies were conducted using various nozzle diameters at different gas and re‐circulation liquid rates. Specific interfacial area (a) is determined from the fractional gas hold‐up (εG) and the average bubble diameter (db). Once the interfacial area is determined, the volumetric mass transfer coefficient (kLa) is then used to evaluate the film mass transfer coefficient in the CDCC. The effects of operating conditions and liquid properties on the specific interfacial area were investigated. The values of interfacial area in air–aqueous glycerol solutions and fermentation media were found to be lower than those in the air–water system. As far as experimental conditions were concerned, the values of interfacial area obtained from this study were found to be considerably higher than those of the literature values of conventional bubble columns. The penetration theory is used to interpret the film mass transfer coefficient and results match the experimental kL data reasonably well. Copyright © 2006 Society of Chemical Industry

Enhanced productivity of Chaetoceros calcitrans in airlift photobioreactors

The various modes of cultivation of Chaetoceros calcitrans in airlift photobioreactors (ALPBRs) were examined. The batch system illustrated that the airlift configuration was superior to the bubble column as the airlift supported the circulation of the cell within the system, leading to a better light utilization. The cultivations in both semi-continuous and continuous systems resulted in a high cell productivity, although the steady state cell concentrations in both systems were lower than that obtained from the batch system. The behavior of the large-scale airlift system was not significantly different from the conventional bubble column where the diatom could only be produced at low cell density. Despite this, among all of the systems investigated in this work, the large-scale system gave the highest productivity. The main limiting factor for the large-scale airlift culture was the availability of light. Based on economical analysis, the continuous cultivation in the 2.8 L ALPBR with a medium feed rate of 3 mL min −1 was most attractive where the operation cost could be maintained at a minimum of approx. 7.95 × 10 −4 THB L −1 h −1. However, this continuous small-scale system still suffered from relatively low cell productivity (8.10 × 10 4 cells s −1).

Gas Holdup in Trayed Bubble Column Reactors

The sectionalization of conventional bubble columns by perforated trays into trayed bubble columns (TBCs) has much potential in biochemical and petroleum refining processes, as an effective way to ...

Liquid phase mixing in trayed bubble column reactors

The compartmentalization of conventional bubble columns by perforated trays constitutes a very effective method to reduce the liquid backmixing. The effect of tray design and operating conditions on the overall liquid mixing was studied in a bench-scale trayed bubble column. The extent of liquid backmixing in the column was investigated in light of liquid-phase tracer response experiments. In average, a three fold reduction in the liquid backmixing was achieved in the trayed column as compared to the column without the trays. Moreover, the tray open area and the superficial liquid velocity were found to have the strongest effects on the liquid backmixing. The N-CSTR with Backmixing Model was found to match the experimental tracer response curves better than the Axial Dispersion Model.

Mass transfer studies in flat-sheet membrane contactor with ozonation

Ozone mass transport in the flat-sheet membrane contactor with chemical reaction in the liquid phase has been investigated. The ozone mass transfer coefficients without reaction in the liquid phase were indirectly determined by the oxygen transfer measurement with the steady state method. The oxidation of nitrite to nitrate was utilized to study mass transfer with ozonation. The ozone fluxes and the enhancement factors ( E) were predicted by the facilitation of the resistance-in-series model together with the film and surface renewal models. The performance of the designed membrane modules was assessed by the decolorization of NOM solutions and indigo reagent I. The ozone mass transfer coefficients from oxygen transport experiments were considerably higher than those calculated from the available correlations but provided good predictions for ozone fluxes for pure water. The ozonation accelerated mass transfer in membrane contactor by 6–100 times in this study. The experimental results validated the proposed methods for the predictions of the ozone fluxes and the enhancement factors. The average discrepancies between the experimental and calculated results were 6% for the ozone flux predictions and 3% for the enhancement factor predictions. The resistances to the ozone mass transfer with and without chemical reaction were controlled by the liquid film. The ozone consumption for the NOM decolouriration in the membrane contactor was considerably lower than that in a conventional bubble column.

Hydrodynamics and mass transfer in an upflow monolith loop reactor: influence of vibration excitement

The hydrodynamics and mass-transfer characteristics of monolith loop reactors, with upflow of gas and liquid phases through the channels, have been investigated and compared with conventional internal airlift reactor and bubble column configurations. The volumetric mass-transfer-coefficient per unit volume of dispersed gas bubbles, k L a / ε G , is significantly higher for monolith reactors than for airlift and bubble columns. This improvement is due to the superior mass-transfer characteristics of Taylor flow in narrow capillaries. Application of low-frequency vibrations has the effect of significantly improving k L a / ε G for all reactor configurations studied. For monoliths, vibrations also have the additional beneficial effect of improving the gas–liquid distribution through the channels.

Hydrodynamics and mass transfer in an upflow monolith loop reactor

The hydrodynamics and mass transfer characteristics of a monolith loop reactor, with upflow of gas and liquid phases through the channels, have been investigated and compared with conventional internal airlift reactor and bubble column configurations. The volumetric mass transfer coefficient, k L a, is higher for monolith reactors than for airlift and bubble columns. This improvement is due to the superior mass transfer characteristics of Taylor flow in narrow capillaries. In order to gain further insight into the mass transfer from Taylor bubbles, experimental results are presented on the unit cell lengths and the Taylor bubble rise velocity.