Sectionalized bubble column

Some studies13,141 on the liquid-phase axial dispersion in horizontally-sectionalized bubble-columns have also been reported. In these studies, the bubble-column was sectionalized by a series of sieve plates with bubble caps. The data indicated that the axial dispersion in this type of column was considerably less than in an open bubble-column. There was no effect of length-to-diameter ratio up to a ratio of 24 on the axial dispersion. The axial dispersion increased with... 

Contactors in which gas is dispersed into the liquid phase Plate columns (including control cycle reactors) Mechanically agitated reactors (principally stirred tanks) Bubble columns Packed bubble columns Sectionalized bubble columns Two-phase horizontal contactors Cocurrent pipeline reactors Coiled reactors Plunging jet reactors, ejectors Vortex reactors... 

Deen NG, Solberg T, Hjertager BH (2001) Large Eddy Simulation of the Gas-Liquid Flow in a Square Cross-Sectioned Bubble Column. Chem Eng Sci 56(21-22) 6341-6349. 

Been, N. G., Solberg, T. Hjertager, B. H. 2001 Large eddy simulation of the gas-liquid flow in a square cross-sectioned bubble column. Chemical Engineering Science 56, 6341-6349. 

Brief discussion of a total of over 25 reactors of all categories, such as fixed-, fluidized- and moving-bed reactors, bubble columns, sectionalized bubble columns, loop reactors, stirred-tank reactors, film reactors, rotating disk reactors, jet reactors, plunging jet reactors, spray columns, surface aerators... 

Class 1 equipment are also called column-type equipment. Under this category, there are the various multiphase contactors. Gas-liquid contactors include bubble columns, packed bubble columns, internal-loop and external-loop air-lift reactors, sectionalized bubble columns, plate columns, and others. Solid-fluid (liquid or gas) contactors include static mixers, fixed beds, expanded beds, fluidized beds, transport reactors or contactors, and so forth. For instance, fixed-bed geometry is used in unit operations such as ion exchange, adsorptive and chromatographic separations, and drying and in catalytic reactors. Liquid-liquid contactors include spray columns, packed extraction... 

Bubble column, packed bubble column, sectionalized bubble column, plate column, external- and internal-loop air-lift reactors, static mixer, venturi scrubbers... 

FIGURE 11.21 Sectionalized bubble columns (a) flat baffles, (b) conical baffles, and (c) flow pattern. 

FIGURE 11.22 Sectionalized bubble column with sieve plate. 

Liquid-liquid reactors are similar to gas-liquid reactors. In the former case, the dispersed phase is in the form of droplets as against bubbles in the latter. The motion of bubbles and drops can be described using a unified approach. A spray column (or a drop column) is the equivalent of a bubble column but with one difference. The dispersed gas phase is always lighter than the continuous liquid phase (p < Pl)- However, the dispersed liquid phase in spray columns may be lighter or heavier than the continuous immiscible liquid phase. Nevertheless, spray columns can be easily described similar to bubble columns. Furthermore, packed bubble columns and sectionalized bubble columns can be considered equivalent to packed extraction columns and plate extraction columns. External-loop and internal-loop reactors are also possible (for equivalent gas-liquid reactors, refer to Section 11.4.2.1.4). 

For the nth section of the sectionalized bubble column, the relationship between y and y +i can be obtained from Equation (CS7.13) as... 

Let the height of each section be 0.5 m. The above procedure gives the total number of sections as 34.64. We may provide 35 complete sections so that the total height is 17.5 m. The sectionalized bubble column is more attractive than a bubble column, because both the volume and the power consumption are approximately 64% of those in the bubble column. 

Niceno B, Boucker M, Smith BL Euler-Euler large-eddy simulation of a square cross-sectional bubble column using the Neptune CFD code, Sci Technol Nucl Ins, Article ID 410272, 8 pp, 2009. http //dx.doi.org/10.1155/2009/410272. 

Catalytic desulfurization is at present carried out industrially by at least three of the major types of gas-liquid-particle operations referred to in Section I trickle reactors, bubble-column slurry reactors, and gas-liquid fluidized reactors. 

The expression gas-liquid fluidization, as defined in Section III,B,3, is used for operations in which momentum is transferred to suspended solid particles by cocurrent gas and liquid flow. It may be noted that the expression gas-liquid-solid fluidization has been used for bubble-column slurry reactors (K3) with zero net liquid flow (of the type described in Sections III,B,1 and 1II,V,C). The expression gas-liquid fluidization has also been used for dispersed gas-liquid systems with no solid particles present. 

GL 26] [R 3] [P 28] See the discussion of results in the section Reactor model of micro bubble column performance, above [10]. 

Laboratory reactor for studying three-phase processes can be divided in reactors with mobile and immobile catalyst particles. Bubble (suspension) column reactors, mechanically stirred tank reactors, ebullated-bed reactors and gas-lift reactors belong the class of reactors with mobile catalyst particles. Fixed-bed reactors with cocurrent (trickle-bed reactor and bubble columns, see Figs. 5.4-7 and 5.4-8 in Section 5.4.1) or countercurrent (packed column, see Fig. 5.4-8) flow of phases are reactors with immobile catalyst particles. A mobile catalyst is usually of the form of finely powdered particles, while coarser catalysts are studied when placing them in a fixed place (possibly moving as in mechanically agitated basket-type reactors). 

The parameter p (= 7(5 ) in gas-liquid sy.stems plays the same role as V/Aex in catalytic reactions. This parameter amounts to 10-40 for a gas and liquid in film contact, and increases to lO -lO" for gas bubbles dispersed in a liquid. If the Hatta number (see section 5.4.3) is low (below I) this indicates a slow reaction, and high values of p (e.g. bubble columns) should be chosen. For instantaneous reactions Ha > 100, enhancement factor E = 10-50) a low p should be selected with a high degree of gas-phase turbulence. The sulphonation of aromatics with gaseous SO3 is an instantaneous reaction and is controlled by gas-phase mass transfer. In commercial thin-film sulphonators, the liquid reactant flows down as a thin film (low p) in contact with a highly turbulent gas stream (high ka). A thin-film reactor was chosen instead of a liquid droplet system due to the desire to remove heat generated in the liquid phase as a result of the exothermic reaction. Similar considerations are valid for liquid-liquid systems. Sometimes, practical considerations prevail over the decisions dictated from a transport-reaction analysis. Corrosive liquids should always be in the dispersed phase to reduce contact with the reactor walls. Hazardous liquids are usually dispensed to reduce their hold-up, i.e. their inventory inside the reactor. 

The computation performed in this study is based on the model equations developed in this study as presented in Sections II.A, III.A, III.B, and III.C These equations are incorporated into a 3-D hydrodynamic solver, CFDLIB, developed by the Los Alamos National Laboratory (Kashiwa et al., 1994). In what follows, simple cases including a single air bubble rising in water, and bubble formation from a single nozzle in bubble columns are first simulated. To verify the accuracy of the model, experiments are also conducted for these cases and the experimental results are compared with the simulation results. Simulations are performed to account for the bubble-rise phenomena in liquid solid suspensions with single nozzles. Finally, the interactive behavior between bubbles and solid particles is examined. The bubble formation and rise from multiple nozzles is simulated, and the limitation of the applicability of the models is discussed. 

In bubble columns the static head of the fluid is the dominant component of the pressure drop and consequendy it is important to determine the void fraction of the dispersion. All quanuties will be measured as posidve in the upward direction, this being the direction of flow of the dispersed phase. Assuming that the gas bubbles are of uniform size and are uniformly distributed over any cross section of the column, the gas and liquid velocities relative to the column are... 

In most cases the frictional component of the pressure gradient is negligible in bubble columns but if necessary it can be calculated using the homogeneous model discussed in Section 7.5. 

The flow structure in a tall vertical bubble column was analyzed using deterministic techniques. The characterization of the two-phase flow structure was realized in the middle section where the flow is fully developed (measuring section). Three cases under different volume fraction of liquid were shown. The results can be resumed as follows ... 

In a typical slurry bubble column operation, the liquid velocity is one order of magnitude lower than the one of gas, and in general, is very low. This mode of operation can be approximated by a semibatch operation. The semibatch operation is frequently used and is the case where the liquid and the catalyst comprise a stationary phase (sluny) in the reactor. In this case, the material balance, eq. (3.122) is used along with the overall rate based on the bulk gas-phase concentration (see Section 3.4.6). In the following, the semibatch operation is presented. 

Finally, the relationship between the several rate expressions for slurry bubble column reactors is (see Section 3.1.1 for derivation)... 

Now, working these equations and following the method used for sluny bubble columns (see Section 3.4.6), CAS can be eliminated and an overall reaction rate can be written in terms of the gas-phase concentration ... 

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