Hydrodynamics of Simple Bubble Columns

In its most simple form a bubble column reactor basically consists of a vertical cylinder with a gas distributor at the inlet, as sketched in Fig 8.1. Simple construction and lack of any mechanically operated parts are two characteristic aspects of the reactor. In general, the bubble column is an adaptable type of reactor which is reasonable in price and can be built in large sizes. The ratio between length and diameter may vary, but ratios between 3 and 10 are most common [28]. Units of 100 — 200 (m ) are regarded as very large in the chemical industry. 

The liquid phase may be operated in batch mode or it may move co-currently or counter-currently to the flow of the gas phase. The gas usually enters at the bottom of the column through a gas distributor which may vary in design. The gas phase is dispersed by the distributor into bubbles entering a continuous liquid phase. In addition, reactive or catalytic particles may be suspended in the liquid phase. 

The liquid flow rate passing through a bubble column is usually very low. The gas throughput on the other hand may vary widely according to the specified conversion level. The normal ranges of liquid and gas superficial velocities, based on empty reactor cross-sectional area, are in the region of 0 to 3 cm/s) and 3 to 25 cm/s), respectively. 

The reactor may be cooled or heated by means of internal heat exchanges. One of the main features is very high heat transfer coefficients [68], thus ensuring a fairly uniform temperature throughout the reactor even with strong 

Jakobsen, Chemical Reactor Modeling, doi 10.1007/978-3-540-68622-4 8, Springer-Verlag Berlin Heidelberg 2008 

Jakobsen, Chemical Reactor Modeling, DOI tO. 1007/978-3-319-05092-8 8, Springer International Publishing Switzerland 2014 

Bubble columns have been found to work well when the gas throughput is high even in the case of the simple type shown in Fig. 8.1, since the high rate of liquid 

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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. 

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. 

Bubble column Simple construction Mixing because of sparged gas - requires low energy Very complex hydrodynamics Applicable only for slow reactions... 

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