Mixing characteristics and gas hold‐up of a bubble column

Abstract

The hydrodynamic behavior of a bubble column has been studied for various Newtonian and non-Newtonian liquids (water, glycerol, carboxymethylcellulose and polyacrylamide solutions). The mixing time, the power consumption, the circulation time and the gas hold-up have been measured in a cylindrical column (diameter: 0.254 m, height: 0.9 m) for three air sparger plates with different numbers and distributions of I mm diameter orifices. It is shown that the mixing efficiency decreases as the viscosity or the shear-thinning and clastic properties of the liquid increase. The viscosity of the liquid has little influence on the gas hold-up which is, however, strongly affected by the sparger plate characteristics and increases as the liquid phase becomes more elastic. A model for predicting gas hold-up is proposed.Le comportement hydrodynamique d'une colonne a bulles utilisant diffcrents liquides newtoniens et non-newtoniens (eau, glycerol, solutions de carboxymCthylcellulose et de polyacrylarnide) a ete CtudiC. Le temps dc rndange, la puissance dissipte, le temps de circulation et le taux de vide ont Ct6 determinks dans une colonne cylindrique (diametre: 0.254 m, hauteur: 0.9 m). Trois differents types de distributeur d'air ont Cte utilises. Tous possedent des orifices de 1 mm de diametre, mais le nombre et la repartition des orifices different de I'un i I'autre. On constate que I'efficacite de I'action de melange decroit lorsque la viscositt du liquide augmente ou lorsque ses propriktds rhkofluidisantes et elastiques deviennent plus importantes. La viscositi du liquide a peu d'influence sur le taux de vide observe qui, par contre, varie beaucoup selon le type de plaque distributrice utilisk ct augmente avec le caractere Clastique du liquide. Un mod& pour la prediction du taux de vide est propose. ubble columns are more and more used in the chemical B industry for applications such as reactors, absorbers and extractors. They are flexible and present economic advantages over mechanically stirred columns: low investment and low operating costs. They are particularly attractive for applications in biotechnology where a strong mixing action has to be avoided. However, their use is not as widespread as could be expected (Schugerl et a]., 1977). It seems that the long industrial tradition of using mechanically stirred reactors is still strongly entrenched. Furthermore, well established design criteria are not yet available. Valuable efforts have been made in order to improve the knowledge of bubble column operation and design characteristics. Shah et al. (1982) have presented a thorough review of the recent work in this field.Most reactants in biochemical engineering show a non-Newtonian behavior, sometimes coupled with an elastic behavior. However, few studies have been conducted on bubble columns with non-Newtonian liquids. Chemical reactions, mass or heat transfer processes may be controlled by the hydrodynamics in a bubble column. Hence it is important to determine how the hydrodynamics is affected by the operating condit...

Gas-Liquid Direct-Contact Evaporation: A Review

“…High intensities of turbulence are thus obtained. In view of the high gas flow rates associated with many industrial applications, most commercial bubble columns operate in the heterogeneous bubbling regime [51,53,55,58].…”

“…3 is related to a sparger with small, evenly distributed orifices which enables radially homogeneous bubbling. Large orifices and/or uneven gas bubbling will always lead to the heterogeneous regime, regardless of the gas superficial velocity [58,60,61]. Other existing methods for identifying the operating regime are discussed by Vial et al [62].…”

“…Using a total of 378 experimental data from six different sources [58,76,137,141,154], Almeida and Lage [155] …”

A New Approach for the Prediction of Gas Holdup in Bubble Columns Operated under Various Pressures in the Homogeneous Regime

“…The gas holdup ε G can be estimated also as the superficial gas velocity u G divided by the bubble rise velocity u B (Guy et al, 1986). This illustrates that the ε G value determines the gas residence time in the bubble bed.…”

On the estimation of the regime transition point in bubble columns

“…In the case of most industrial units, operation at the heterogeneous regime is desired [1,[8][9][10], but for some bioreactors the homogeneous regime is preferred [2,11]. Therefore, the prediction of the regime transition point acquires considerable importance.…”