Cc

20 40 60 80 100 Liquid Flowrate L. M-1 H M Weir Lenglh

Figure 6.15 Plots of entrainment versus liquid flow rate featuring entrainment minima. (H. Z. Kister and J. R. Haas, I. Chem. E. Symp. Ser. 104, p. A483, 1987, reprinted courtesy of the Institution of Chemical Engineers, UK.)

where and

The clear liquid height at the froth-to-spray transition, hct, is calculated using the Jeronimo and Sawistowski (35) correlation, as modified for physical properties by Kister and Haas (36). The relevant equations are Eqs. (6.68) to (6.70). The recommended range of application of the correlation is shown in Table 6,8.

Koziol and Mackowiak (55a) found the Kister and Haas correlation to give good agreement with experimental data. They developed a new dimensionless correlation [thus overcoming the need for a dimensional exponent in Eq. (6.27)] for spray regime entrainment at very low liquid rates (0.1—1.5 gpm/in). Their correlation, however, postulates that entrainment rises with tower diameter at the same steep rate at which it rises with hole diameter. This postulate conflicts with the industry's experience that entrainment does not increase upon tower diameter scale-up.

An early entrainment correlation by Fair (19,34) was recommended by many design publications (5,18,30-33). In the spray regime, Fair's correlation gives reasonable predictions (36), but is less accurate than the Kister and Haas correlation. The same conclusion was reached in-

tablE $.8 Recommended Range of Application for the Kister and Haas (36) Spray Regime Entrainment Correlation

Flow regime

Spray only

Pressure

3-180 psia

Gas velocity

1.3-15 ft/s

Liquid flow rate

0.5-4.5 gpm/in

Gas density

0.03-2 lb/ft3

Liquid density

30-90 lb/ft3

Surface tension

5-80 dyne/cm

Liquid viscosity

0.05-2 cP

Tray spacing

16-36 in

Hole diameter

in

Fractional hole area

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