Bubble size distribution in the sparger region of bubble columns

doi:10.1016/S0009-2509(01)00301-3

Chemical Engineering Science

Volume 57, Issue 1, January 2002, Pages 197-205

https://doi.org/10.1016/S0009-2509(01)00301-3 Get rights and content

Abstract

It is well known that the gas distributor can play an important role on the evolution of the bubble size distribution (BSD) in gas–liquid reactors, strippers and absorbers. Therefore, the main subject of the present work was to study the influence of sparger design and process parameters on the BSD in the sparger region of the considered apparatus. For this purpose, both detailed measurements and prediction of the size of bubbles produced at the sparger were carried out in three different experimental apparatuses.

The unique set of BSD curves were obtained by analyzing a large amount of bubbles with a measurement based on image analysis technique.

Additionally, Colella's model of BSD evolution in bubble columns was further developed by implementing a detailed physical model for predicting the initial BSD at the sparger where the model input is only based on design/process parameters. A validation of the model was carried out using data from two different columns. The comparison between calculated and experimental BSD shows good agreement.

Introduction

In chemical engineering operations and practice, gas–liquid contactors are widely used for carrying out reactions and mass transfer operations such as stripping and absorption. The presence of a gas phase dispersed in a continuous liquid is the reason why such kind of reactors can provide high interfacial area for mass and heat exchange, good mixing and high thermal stability.

The dispersion of the gas into the column is a critical aspect determining the performance of gas–liquid systems. Small bubbles and a uniform distribution over the cross section of the equipment are desired to maximize the interfacial area and improve transport phenomena.

In a recent work by Colella, Vinci, Bagatin, Masi, and Abu Bakr (1999), the interfacial mechanisms focussing on coalescence and breakage in three bubble columns (with different L/D and geometry) was investigated analyzing more than 500 bubbles for each BSD. One of the main conclusions of that investigation was that the global hydrodynamics of the three columns is strongly dependent on the gas distributor. Therefore, a correct estimation of the influence of sparger design and process parameters on BSD, which is the subject of the present work, is essential.

The formation of bubbles at orifices submerged in a liquid has been the subject of many theoretical and experimental works. The main review publications in this field were presented by Kumar and Kuloor (1970), Rabiger and Vogelphol (1986, Chapter 4), and Tsuge (1986, Chapter 9). In the above cited publications, the research was meanly focussed on the bubble formation at a single orifice. As a consequence, the interaction between the neighbouring bubbles was hardly investigated. However, Miyahara, Matsuha, and Takahashi (1983) studied experimentally the influence of the distance between the holes and of the number of holes on the bubble diameter in the perforated plates measuring bubbles at 25 and $45 cm$ from the sparger in a column $70 cm$ high. They concluded that the volume of the gas chamber does not influence the bubble diameter when the number of holes of the perforated plate is above ∼15. For conditions in which the gas chamber volume has no effect, decreasing the pitch the bubble diameter increases due to coalescence when the ratio of the pitch to the hole diameter (P/d_H) is less than ∼8.

The added value of the present work in comparison to literature is the detailed measurement of bubble sizes close to the sparger (from 0 to $16 cm$ ) using 600 bubbles for each distribution. The experiments were carried out in different bubble columns (EniChem and POLIMI) and airlifts (EniChem) using different perforated ring and perforated plate spargers. The evolution of BSD is investigated as function of height and gas superficial velocity and as function of the sparger design (i.e., number of holes, hole diameter and pitch) and process parameters (i.e., gas flow rate).

From the modeling point of view, Colella's model of BSD evolution in bubble columns was further developed by implementing a detailed physical model for predicting the initial BSD at the sparger where the model input is only based on design/process parameters. A validation of the model was carried out using data from two different columns. The comparison between calculated and experimental BSD shows good agreement.

Section snippets

Experimental procedure

The experiments were carried out in three different vessels located in Politecnico di Milano (briefly indicated in the following with the acronym POLIMI) and in EniChem using different spargers. The measurements include the evolution of BSD as function of sparger design (i.e., hole diameter, number of holes, distance between the holes) and process parameters (i.e., gas flow rate) and also as function of height and gas superficial velocity in the sparger region.

All the main features of the

Experimental results and discussion

In this section, the main experimental trends as a function of the experimental conditions and apparatus examined, are analyzed in terms of the arithmetic average bubble size. That value gives us a useful compact way to describe the main experimental features. Accordingly, in all the following tables, we will refer only to that value. In particular, the whole picture of the experiments is summarized in Table 4, where for each apparatus and operating condition that average value is reported.

From

Prediction of bubble size at sparger

A population balance equation model, which computes BSD evolution in bubble columns, was already developed by Colella et al. (1999). However, the input distribution of this model is obtained from measured BSD. Therefore, the main aim of this part of the investigation is exploring the possibilities to simulate an initial size distribution at the sparger for the prediction of BSD evolution in bubble columns. As a first step to obtain a description of the evolution of BSD in bubble columns without

Concluding remarks

To understand the interfacial mechanisms in the sparger region of bubble columns, which play an important role in the reactor hydrodynamics, detailed sets of data of bubble size distribution were investigated. The bubble size distribution measurements were carried out in different bubble columns (EniChem and Politecnico di Milano) and airlifts (EniChem) using different spargers. In order to obtain the distribution curves about 600 bubbles for each distribution were analyzed. The measurements

Notation

$〈d_{CALC} 〉$	calculated average diameter of bubble size, (cm)
$〈d_{EXP} 〉$	experimental mean diameter of bubble, (cm)
$d_{H}$	hole diameter, (cm)
$d_{w} =〈d_{EXP} 〉 gρ_{L} d_{H} σ^{1/3}$	dimensionless mean diameter
$Fr= U_{th}^{2} gd_{H}$	Froude number
$g$	gravity, $(cm / s^{2})$
$G$	gas flow rate, $(cm^{3} / s)$
$G_{H}$	gas flow rate through the orifice, $(cm^{3} / s)$
$h$	height from the sparger, (cm)
$N_{holes}$	number of holes
$N_{w} = We Fr^{1/2}$	dimensionless velocity
$P$	distance between the holes (pitch), (mm)
$Re_{th} = ρ_{G} U_{th} d_{H} μ_{G}$	Reynolds number through the hole
$U_{g}$	gas superficial velocity, (cm/s)
$U_{th}$	gas velocity

Acknowledgements

The presented work was carried out for the ADMIRE project (Advanced Design Methods for Improved performance of Industrial gas–liquid Reactors) under the Brite/Euram 3 program, Project Number BE95-2039.

The original bubble size distribution experimental data are available upon request.

References (18)

R Kumar et al.
The formation of the bubbles and drops
Advances in Chemical Engineering
(1970)
R.D La Nauze et al.
A note on gas bubble formation models
Chemical Engineering Science
(1974)
T Otake et al.
Coalescence and breakup of bubbles in liquids
Chemical Engineering Science
(1977)
W.V Pinczewski
The formation of bubbles at a submerged orifice
Chemical Engineering Science
(1981)
T Akita et al.
Bubble size, interfacial area and liquid-phase mass transfer coefficent in bubble column
Industrial Engineering Chemistry
(1974)
A.H.S Ang et al.
Probability concepts in engineering planning and design. Vol. 1 — Basic Principles
(1975)
D Colella et al.
A study on coalescence and breakage mechanisms in three different bubble columns
Chemical Engineering Science
(1999)
R.L Datta et al.
The properties and behaviour of gas bubbles formed at circular orifice
Transactions of the Institute of Chemical Engineers
(1950)
Di Stanislao, M. (1999). Study of bubble size distribution in the sparger region of different bubble column. MS Thesis...

There are more references available in the full text version of this article.

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View full text

Bubble size distribution in the sparger region of bubble columns

Abstract

Introduction

Section snippets

Experimental procedure

Experimental results and discussion

Prediction of bubble size at sparger

Concluding remarks

Notation

Acknowledgements

Advances in Chemical Engineering

Chemical Engineering Science

Chemical Engineering Science

Chemical Engineering Science

Bubble size, interfacial area and liquid-phase mass transfer coefficent in bubble column

Industrial Engineering Chemistry

Probability concepts in engineering planning and design. Vol. 1 — Basic Principles

A study on coalescence and breakage mechanisms in three different bubble columns

Chemical Engineering Science

The properties and behaviour of gas bubbles formed at circular orifice

Transactions of the Institute of Chemical Engineers