Type Of Gas Sparger Research Articles

Design of bubble columns equipped with porous sparger

Bubble columns are gas-liquid conductors that are widely used in chemical and biochemical process industries, due to their simple construction, low operating cost and high energy efficiency. In all these processes gas holdup and bubble size are important design parameters, since they define the gas-liquid interfacial area available for mass transfer. In turn, bubble size distribution and gas holdup depend largely on column geometry, operating conditions, physico-chemical properties of the two phases and type of gas sparger. This paper is a review of the work conducted in our Lab and concerns the design of bubble columns equipped with metal porous sparger. The effect of the liquid phase properties, the gas flow rate and the geometrical characteristics of the device on the performance the bubble column has been experimentally investigated. Based on the experimental data obtained using several Newtonian and non-Newtonian liquids generalized correlations were formulated, which can predict with reasonable accuracy the transition point from homogenous to heterogeneous regime as well as the gas hold up and the mean bubble size at the homogenous regime given the liquid properties, the gas flow rate and the geometrical parameters of the device.

Volumetric gas-liquid mass transfer coefficient in an external-loop airlift reactor with inserted membrane

The effects of the inserted membrane in the downcomer of an external-loop airlift reactor, the gas sparger type (single orifice and sinter plate) and added alcohol (ethanol, n-butanol, or n-hexanol) on the volumetric gas-liquid mass transfer coefficient (kLa) were studied. Due to the presence of the membrane in the downcomer, kLa did not change significantly; the differences were smaller than 10%. The highest values of the kLa were obtained using the sinter plate. It was found that the addition of small amounts of alcohol increased the mass transfer. Using our experimental results and the data of other authors, the feed-forward back propagation neural network for prediction of kLa in external-loop airlift reactors with alcohol solutions was proposed.

Sparger Type Influence on the Volumetric Mass Transfer Coefficient in the Draft Tube Airlift Reactor with Diluted Alcohol Solutions

In this work, the influence of addition of normal aliphatic alcohols (from methanol to n-octanol) and the gas sparger type (single orifice, perforated plate, and sinter plate) on the volumetric mass transfer coefficient in a draft tube airlift reactor was investigated. The results showed that the addition of alcohols from methanol to n-hexanol led to an increase in the volumetric mass transfer coefficient, in comparison to water, while n-heptanol and n-octanol had the opposite effect. The influence of the gas sparger was dominant at low superficial gas velocities. At higher gas velocities, the liquid-phaseproperties and the sparger type, being opposite in effect on mass transfer, annulled one another’s influence. Also, simple correlation was proposed to predict the volumetric mass transfer coefficient. The analysis of the parameters in the proposed correlation showed that the liquid-phaseproperties, expressed through the surface tension gradient, and the gas sparger type, mainly through initial bubble size, had a marked influence on the mass transfer.

Statistical tool combined with image analysis to characterize hydrodynamics and mass transfer in a bubble column

Image analysis technique has been proved to be very effective in the quantification of particles size and morphology distributions in different work areas. In the present work this technique was combined with the discriminant factorial analysis (DFA) in order to allow the automatic identification of single bubbles (isolated bubbles without influence of surrounded bubbles) in multiphase systems. With the previous methodology it has been possible to distinguish online and automatically among three different classes of bubbles (single bubbles and medium complexity and large complexity bubbles groups), allowing for the first time the computation of the local bubble population complexity in the system. The automatic and correct characterization of the single bubbles allowed the correct determination of bubble size and, consequently, the specific interfacial area a at different experimental conditions. Agreement between automated and manual classification, measured in terms of a performance index, is 98% for single bubbles identification. Further, the present work describes the application of such methodology to the study of temperature, type of gas sparger, and liquid phase properties (viscosity and surface tension) influence on the individual components of volumetric liquid side mass transfer coefficient, k L a. The results show that the different experimental parameters and liquid properties act by a particular way on k L and a.

Sparger Type Influence on the Hydrodynamics of the Draft Tube Airlift Reactor with Diluted Alcohol Solutions

The objective of this work was to investigate the influence of normal aliphatic alcohols (from methanol to n-octanol) and the gas sparger type (single orifice, perforated plate, and sinter plate) on the hydrodynamics of a draft tube airlift reactor. The results showed that the presence of alcohols led to both an increase in the gas holdup and reduction of the downcomer liquid velocity, in comparison to the values obtained in water. The type of gas sparger also changed the hydrodynamic behavior—the gas holdup increased with dispersion effectiveness, from single orifice to sinter plate, while the effect on the downcomer liquid velocity was in conjunction with the liquid phase properties. Simple correlations were developed to predict the gas holdup and the downcomer liquid velocity. Beside the gas superficial velocity, the proposed correlations include the surface tension gradient, as a unique parameter which represents the liquid phase properties, and sparger related variables: the ratio of the sparger’s to...

Characterization of a gas‐liquid OBC: Bubble size and gas holdup

AbstractA fundamental experimental study of gas‐liquid contacting in an oscillatory baffled column is presented focusing on the effect of fluid oscillation on gas holdup and bubble size. The results show that beyond a critical level of fluid oscillation the Sauter mean diameter of the dispersion is substantially reduced, while the gas holdup (and, thus, the residence time of the gas phase) increases significantly. The reduction of bubble size was described in terms of bubble breakage, caused by the interaction of the bubbles with eddies. The experimental results were modeled by applying Kolmogoroff's theory of isotropic turbulence. The steep increase in the gas holdup with oscillation was mainly due to bubble entrainment by large vortices, formed by the oscillatory flow in the presence of baffles. A semi‐theoretical expression, based on the forces acting on a bubble, was proposed, and was able to accurately match the experimental trends. The results also show that the gas‐liquid hydrodynamics are mainly governed by the oscillatory operating conditions, and independent of the type of gas sparger. © 2004 American Institute of Chemical Engineers AIChE J, 50: 3019–3033, 2004

Effect of hydrodynamics on mass transfer in a gas–liquid oscillatory baffled column

In this paper, we present an experimental study on mass transfer of oxygen into water in an oscillatory baffled column (OBC). The objective of this work is to establish the contribution of individual parameters, such as the size of bubbles and the gas holdup, to the overall volumetric mass transfer coefficient ( k L a). Our results show that the gas holdup is the most important factor. The liquid-side mass transfer coefficient ( k L) is calculated directly from the experimental measurements of gas holdup, Sauter mean diameter and k L a, and an increase of k L with D 32 is observed. The results also show that, above a critical level of fluid oscillation, the mass transfer coefficients are mainly governed by the oscillatory operating conditions, while independent of the type of gas sparger.

Performance characteristics of novel mechanical foam breakers in a stirred tank reactor

Unlimited foam formation and insufficient foam collapse can have serious effects in an aerated system such as a fermentation process. Mechanical foam breakers are used in foam control to avoid the drawbacks associated with the use of chemical antifoams and defoaming agents. In this paper, two new foam breakers consisting of a two-blade paddle with three slits, and a two-blade paddle with 168 thin needles have been tested. They gave significantly reduced critical speeds and power consumption for foam control in a stirred vessel, compared with some conventional foam breakers. The effects of various parameters, namely the physical properties of the foaming solution, type of gas sparger, surfactant concentration, and foam-breaker clearance above liquid level, have been investigated. The degree of difficulty of controlling dynamic foams generated continuously in a stirred vessel is found to be a function of the nature of the foam, ie its bubble size, its liquid holdup, and the degree of foamability of the system. © 1999 Society of Chemical Industry

Characterization of axial liquid dispersion in gas–liquid and gas–liquid–solid reactors

Axial liquid mixing was studied in gas–liquid systems (bubble columns) and two types of gas–liquid–solid system (the turbulent and inverse turbulent beds) for different types of gas sparger (membrane and perforated plate). In the turbulent and inverse turbulent beds, solids, larger and lighter than water and of large diameter (3–4 mm) are fluidized only by an upward gas flow. In two-phase systems, the type of gas sparger has a strong effect on the gas flow regime and consequently on the axial liquid mixing. A general diagram with co-ordinates Pe versus Fr (1/3) has been established in order to explain all the results. It allows the hydrodynamic characteristics to be predicted by a simple measurement of the axial liquid dispersion coefficient E zl . In the gas–liquid–solid reactors tested, the effect of the gas sparger on axial liquid mixing can be pronounced. A flow regime diagram is proposed, which shows a heterogeneous flow behaviour independent of the gas sparger when the solid content of the column is sufficiently high.

Effect of Gas Sparger Type on Operational Characteristics of a Bubble Column under Mechanical Foam Control

The effects of gas sparger types on the operational characteristics of a bubble column (BC) with a rotating-disk mechanical foam-breaker (MFRD), such as foam-breaking, foaming, flow and mass transfer characteristics, were studied. The required critical disk rotational speed, N c , and liquid hold-up in the foam, Φ L , reflected the foam-breaking behaviour of the MFRD and the foaming behaviour of the BC respectively, which changed depending on the gas sparger type. The dependence of the gas sparger type on the gas hold-up, e g , was similar to that observed for the volumetric mass transfer coefficient, k L a. A comparative investigation of k L a with various gas spargers, in terms of the specific power input, also demonstrated the usefulness of the porous sintered glass bead filter as a gas sparger.

Interfacial areas in agitated gas-liquid contactors

Chemical reactions with known chemical and physical properties were used for the determination of integral values of the interfacial areas created with an agitator in a gas-liquid contactor. The reactions between oxygen and a sulphite solution and between carbon dioxide and sodium hydroxide solutions were chosen. For the first system the chemical reaction in the liquid boundary layer is proved to be rate determining under our experimental conditions. The existence of two regions is demonstrated: 1. (a) A region without agitation effect. At agitation rates below a minimum agitation rate n 0 D interfacial areas are not affected by the stirring; they only depend on the gas load v s and the type of gas sparger. 2. (b) A region with agitation effect. At agitation rates above n 0 D the interfacial areas are linearly dependent on the agitation rate and independent of the gas load and type of gas inlet. The value of n 0 D depends on the tank to agitator diameter ratio and probably is independent of the liquid viscosity. Generally valid correlations for the minimum agitation rates and the interfacial area under fully baffled conditions could be derived for a great number of geometrically similar impellers of different sizes in vessels with diameters ranging from 0.14 to 0.90 m. Although vessels with a diameter larger than 1 m were not investigated the method of correlation seems to give good results for scaling-up. The influence of the physical properties of the liquid remains uncertain.

Gas holdup in a three-phase fluidized-bed bioreactor

The effects of system parameters on the gas holdup in a three-phase fluidized-bed bioreactor were examined. A valve technique was used to measure the average gas holdup in the reactor. Gas holdup was found to be strongly affected by fluid superficial velocities, bead size and density, electrolyte concentration, type of gas sparger, and temperature. Quantitative and qualitative observations were made regarding the differences between conventional glass-particle systems and low-density gel-particle systems. Most notably, the degree of bubble coalescence and mode of fluidization were highly dependent on each system.

Sectionalised bubble column: Gas hold‐up and wall side solid—Liquid mass transfer coefficient

AbstractThe effect of gas sparger type, clear liquid height, liquid viscosity and addition of electrolyte on fractional gas hold‐up in a 0.38 m i.d. sectionalised bubble column (SBC) was studied for superficial gas velocities ranging from 0.03 to 0.15 m s−1. A study of the wall side solid–liquid mass transfer coefficient, kSL, has been made by considering the dissolution of copper in acidic dichromate solutions. The variation of kSL with axial distance in a section for different gas velocities has been explained. A comparison between the performance of sectionalised bubble columns and conventional bubble columns has been presented. In some cases, the SBC may prove to be superior to bubble columns in practice.

Interfacial areas in agitated gas-liquid contactors

Chemical reactions with known chemical and physical properties were used for the determination of integral values of the interfacial areas created with an agitator in a gas-liquid contactor. The reactions between oxygen and a sulphite solution and between carbon dioxide and sodium hydroxide solutions were chosen. For the first system the chemical reaction in the liquid boundary layer is proved to be rate determining under our experimental conditions. The existence of two regions is demonstrated: (a) A region without agitation effect. At agitation rates below a minimum agitation rate n 0 D interfacial areas are not affected by the stirring; they only depend on the gas load v s and the type of gas sparger. (b) A region with agitation effect. At agitation rates above n 0 D the interfacial areas are linearly dependent on the agitation rate and independent of the gas load and type of gas inlet. The value of n 0 D depends on the tank to agitator diameter ratio and probably is independent of the liquid viscosity. Generally valid correlations for the minimum agitation rates and the interfacial area under fully baffled conditions could be derived for a great number of geometrically similar impellers of different sizes in vessels with diameters ranging from 0·14 to 0·90 m. Although vessels with a daimeter larger than 1 m were not investigated the method of correlation seems to give good results for scaling-up. The influence of the physical properties of the liquid remains uncertain.