Design of bubble column

Bubble-column slurry operations are usually characterized by zero net liquid flow, and the particles are held suspended by momentum transferred from the gas phase to the solid phase via the liquid medium. The relationships between solids holdup and gas flow rate is of importance for design of bubble-column slurries, and some studies of this aspect will be reviewed prior to the discussion of transport phenomena. 

In this chapter the elementary hydrodynamic characteristics of simple bubble columns are summarized. Different designs of bubble columns are sketched, and examples of their industrial applications are outlined. An overview of the status on Eulerian bubble column modeling is presented. 

Joshi JB (2001) Computational flow modehng and design of bubble column reactors. Chem Eng Sci 56(21-22) 5893-5933... 

Joshi, J.B. (2001), Computational flow modelling and design of bubble column reactors, Chemical Engineering Science, 56 5893-5933. 

Design of bubble slurry column reactors (BSCR)... 

Access of Hydrodynamic Parameters Required in the Design and Scale-Up of Bubble Column Reactors... 

The general difficulties in design and scale-up of bubble column reactors concern reaction specific data, such as solubilities and kinetic parameters as well as hydrodynamic properties. The paper critically reviews correlations and new results which are applicable in estimation of hydrodynamic parameters of two-phase and three-phase (slurry) bubble column reactors. 

In general, the procedure for designing a bubble column reactor (BCR) (1 ) should start with an exact definition of the requirements, i.e. the required production level, the yields and selectivities. These quantities and the special type of reaction under consideration permits a first choice of the so-called adjustable operational conditions which include phase velocities, temperature, pressure, direction of the flows, i.e. cocurrent or countercurrent operation, etc. In addition, process data are needed. They comprise physical properties of the reaction mixture and its components (densities, viscosities, heat and mass diffusivities, surface tension), phase equilibrium data (above all solubilities) as well as the chemical parameters. The latter are particularly important, as they include all the kinetic and thermodynamic (heat of reaction) information. It is understood that these first level quantities (see Fig. 3) are interrelated in various ways. 

The major advantage of the bubble column is the simple design of this type of reactor. Mixing of the liquid is achieved by the upflowing gas bubbles, and, as a consequence, mass transfer rates are limited. Another disadvantage of bubble columns is that they have limited temperature and pressure ranges, while they are also unsuitable for processing viscous fluids. 

After introducing the theoretical basis of gas-liquid contacting, the remainder of this entry focuses on gas-liquid contact through gas bubbles dispersed within a continuous liquid, i.e., the most common mode of gas-liquid contact within the chemical industry. Finally, the gas-liquid contactor design procedure is presented, followed by an example involving an industrial-scale STR. Further discussion of bubble columns, packed beds, thin films, and venturi scrubbers is found in related entries in this encyclopedia. 

Dekwer, W.D., Access of Hydrodynamic Parameters Required in the Design and Scale-Up of Bubble Column Reactors, in Chemical Reactors, ACS Symposium Series, American Chemical Society Washington, DC, 1981, pp. 213-241. 

The split-cylinder IL airlift reactor (not shown in the figure) has a vertical flat partition which divides the column into two halves which act as the riser and downcomer sections. In these IL airlift reactors, as the gas holdup in the downcomer is smaller than that in the riser, the liquid will circulate through the riser and downcomer sections due to differences in the bulk densities of the liquid-gas mixtures in the two sections. The overall values of kLo for a well-designed IL airlift reactor of both the draft tube and split-cylinder types, are approximately equal to those of bubble columns of similar dimensions. 

Tray design encompasses the determination of the column diameter and the tray spacing as well as a number of mechanical considerations. The scope of the material in this chapter is limited primarily to the fundamentals involved in the design of single-pass sieve trays. The fundamentals involved in the design of valve trays are essentially the same as those involved in sieve trays. No attempt is made to treat bubble-cap trays, since valve and sieve trays have been used extensively in new installations since the early 1950s. Up until that time, bubble-cap trays were used almost exclusively. The design of bubble-cap trays has been treated by a number of authors see for example Van Winkle.17... 

Bubble and Film Oxygenators. Numerous designs of bubble oxygenators have been proposed over the past 20 years their history and evolution is reviewed by Galletti (18). All designs rely on introducing bubbles of gas into a column of blood and then removing the residual... 

Scaling up of bubble columns is generally based on the requirement of keeping kiA constant. Since A is proportional to, this imphes keeping the superflcial gas velocity constant. Some design aspects of bubble reactors will be illustrated in an example following the section on stirred vessel reactors. 

Godbole, S.P., and Shah, Y.T. (1986), Design and operation of bubble column reactors, in Encyclopedia ofEluid Mechanics Gas-Liquid Flows, N.P. Cheremisinoff, Editor, Houston, Gulf Publishing Company. 3 1216-1239. 

Most problems in the design and performance prediction of bubble column reactors appear, because it is - up to now - not possible to control the fluid dynamics in such reactors. Especially the parcuneters of the turbulent flow in these reactors are of major importance. 

Liquid-phase back mixing is a serious issue for reactions that have nonzero-order kinetics with respect to the liquid-phase reactant. Sectionalization of bubble column using sieve plates of relatively low free area is an attractive choice in such a case. Although this choice has been mentioned in the literature, its application in solid-catalyzed reactions has not attracted any attention. The sieve plate design must be such that it prevents weeping (Prince 1960). The free area in such sieve plates is... 

Non-Newtonian fluids are frequently encountered in the process industries, especially in biochemical and biotechnological applications. It has been known that the rheological properties of the liquids have profound effects on the performance of bubble columns. The non-Newtonian anomalies create uncertainties in the design, scale-up, and operation of bubble columns. Most analyses and correlations are based on the following two premises, which are not necessarily always applicable ... 

Since gas holdup is one of the important design parameters for the performance of bubble columns, study of gas holdup has been extensively carried out. Gas holdup depends mainly on gas velocity and the physical properties of the liquid. Although a number of correlations have been proposed, no single generalized correlation is available at present. Only a few attempts have been made to predict gas holdup theoretically. 

ANSYS simulation enables engineers to study multiphase distribution, heat and mass transfer calculations, chemical kinetics and reaction of gas-liquid reactions. These include the design of plate columns, packed columns and bubble columns, a loop reactor and bioreactor development, gas-in-liquid dispersion studies and emulsion design. 

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