Flooding in packed towers

FIG. 15-34 Flooding in packed towers, Use only customary units in the vari-ahles, [Crawford and Wilke, Chem, Eng, Prog, 47, 423 (1951), with petmis-... 

Kaiser [140] presents a correlation analysis for flooding in packed towers that is more analytical in the performance approach. It is based on single phase hydraulics. It would have been helpful for the article to present a comparison of results tvith the other more conventional techniques. 

Copigneaux, R, Flooding in Packed Towers, Hydro. Processing Feb. (1981) p. 99. 

Liquid holdup and flooding in.packed towers. Ind. Eng. Chem., 31 435-445. 

A child s brightly colored pinwheel spinning in the wind creates an irresistible urge to discourse on steam turbines. A pot of pasta boiling over on our stove is the perfect incentive to deliver a lecture, which no one wants to hear, detailing foam-induced flooding in packed towers. Suntanned skin is the perfect example illustrating the power of radiant heat transfer. 

Figure 4.17. Generalised correlation for flooding rates in packed towers(6l)...

The derivation of equations 13.34 and 13.35 has been carried out assuming that u0 is constant and independent of the flowrates, up to and including the flooding-point. This in turn assumes that the droplet size is constant and that no coalescence occurs as the hold-up increases. Whilst this assumption is essentially valid in properly designed spray towers, this is certainly not the case with packed towers. Equations 13.34 and 13.35 cannot therefore be used to predict the flooding-point in packed towers and a more empirical procedure must be adopted. 

Up to the present time, work has been done which allows prediction of the onset of large waves (H2), and of formation of other types of waves (VI, HI), but only on flat uniform liquid surfaces. The extent to which these results can be applied to pipe line flow is uncertain. Apparently, Gazley s papers are still the only basic reports of stratified and wave flow in horizontal pipe incidentally they also show a parallel between liquid instability in pipe flow as evidenced by wave formation, and that evidenced in packed towers by flooding. 

Pressure drop at flooding point in packed towers... 

For additional information and methods for estimating pressure drop and flooding velocities in packed towers, see R. H. Perry and D. Green, Chemical Engineers Handbook, 6th ed., Sect. 18, McGraw-Hill Book Company, New York, 1984. 

Correlation for estimating flooding rate in packed towers. 

The possibility of causing flooding in the tower at the redistribution point must not be overlooked, as too much restriction by a wall wiper, or by packing on a plate can be the focal point for poor tower performance. The velocity conditions should be checked for the smallest crosfrsection. 

Flooding velocities in packed towers. If the flow rate of either the dispersed phase or the continuous phase is held constant and that of the other phase gradually increased, a point is reached where the dispersed phase coalesces, the holdup of that phase increases, and finally both phases leave together through the continuous-phase outlet. The effect, like the corresponding action in an absorption column,... 

The exact definition of the flood point in packed towers is uncertain. Silvey and Keller (367) list ten different flood point definitions which were used by different investigators. Perhaps the most popular definition is (51, 319) "the vapor velocity above which liquid accumulates uncontrollably in the packed bed and continued operation becomes impossible. ... 

Pich4 S., Larachi, F., and Grandjean, B.P.A. (2001a), Flooding capacity in packed towers Database, correlations, and analysis, /wdasfn a/ <6 Engineering Chemistry Research, 40(1) 476-487. 

Pressure drop of 2 in. H20/ftof packed height—fully developed flooding. In a tower with multiple packed sections, observing a 2 in. H2O pressure drop is not particularly informative. An upper section may be flooding because it is overloaded or because a lower section has flooded and backed liquid up the column. 

Liquid hold up in a tower represents the liquid held in the void spaces of the packing during operating conditions. At flooding, essentially all of the voids are filled with liquid. 

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