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updates in Kister, Lason, and Gill, Paper presented at the AIChE Spring
National Meeting, Houston, Tex., March 19–23, 1995; and in Kister,
Scherffius, Afshar, and Abkar, in Distillation 2007: Topical Conference
Proceedings, 2007 AIChE Spring National Meeting, Houston, Texas.
The latter reference also discusses correct and incorrect applications of
those interpolation charts.
There are many alternative methods for flood and pressure drop
prediction. The Billet and Schultes [IChemE Symp. Ser. 104, pp.
A171 and B255 (1987)] and the Maćkowiak (“Fluiddynamik von
Kolonnen mit Modernen Füllkorpern und Packungen für Gas/Flussigkeitssysteme,”
Otto Salle Verlag, Frankfurt am Main und Verlag
Sauerländer Aarau, Frankfurt am Main, 1991) correlations are versions
of the GPDC that take the liquid holdup into account. The
Eiden and Bechtel correlation [IChemE Symp. Ser. 142, p. 757
(1997)] is a version of the GPDC in which accuracy is improved by
using constants representative of packing shape instead of packing
factors. The Lockett and Billingham correlation (IChemE Symp.
Ser. 152, p. 400, London, 2006) uses a Wallis correlation
EQUIPMENT FOR DISTILLATION AND GAS ABSORPTION: PACKED COLUMNS 14-59
FIG. 14-56 The Kister and Gill GPDC (SP) chart for structured packings only. Abscissa and ordinate same as in Fig.
14-55. (From Kister, H. Z., and D. R. Gill, IChemE Symp. Ser. 128, p. A109, 1992. Reprinted courtesy of IChemE.)
C G 0.5 + mCL 0.5 = CLG (14-143)
where C L = uL[ρL/(ρL −ρG)] 0.5 (14-144)
and was shown to work well for high-surface-area (>400 m 2 /m 3 ) structured
packings. Here CG is the gas C-factor, Eq. (14-77), based on the
tower superficial cross-sectional area, and m and CLG are constants,
available from the cited reference for some packing.
A drawback of most of these correlations (except that of Eiden and
Bechtel) is the unavailability of constants for many, often most, of the
modern popular packings.
The above methods apply to nonfoaming systems. Foaming systems
can be handled either by applying additional derating (system) factors to
the flood correlation (see Table 14-9) or by limiting the calculated pressure
drop to 0.25 in of water per foot of packing (Hausch, “Distillation
Tools for the Practicing Engineer,” Topical Conference Proceedings, p.
119, AIChE Spring Meeting, New Orleans, March 10–14, 2002).
Pressure Drop The GPDC discussed above (Figs. 14-55 and
14-56) and the Kister and Gill interpolation charts provide popular
methods for calculating packing pressure drops. An alternative popular
method that is particularly suitable for lower liquid loads was presented
by Robbins (below).
For gas flow through dry packings, pressure drop may be estimated
by use of an orifice equation. For irrigated packings, pressure drop
increases because of the presence of liquid, which effectively
decreases the available cross section for gas flow (Fig. 14-53). In principle,
there should be a method for correcting the dry pressure drop
for the presence of liquid. This approach was used by Leva [Chem.
Eng. Progr. Symp. Ser. No. 10, 50, 51 (1954)]. A more recent method
by Robbins [Chem. Eng. Progr., p. 87 (May 1991)] utilizes the same
approach and is described here. The total pressure drop is
∆P t =∆P d +∆P L
(14-145)
where ∆P t = total pressure drop, inches H 2O per foot of packing
∆P d = dry pressure drop = C 3G f 2 10 (C4Lf) (14-146)
∆P L = pressure drop due to liquid presence
= 0.4[L f/20,000] 0.1 [C 3G f 2 10 (C4Lf) ] 4 (14-147)
G f = gas loading factor = 986F s(F pd/20) 0.5 (14-148)
L f = liquid loading factor = L(62.4/ρ L)(F pd/20) 0.5 µ L 0.1 (14-149)
The term F pd is a dry packing factor, specific for a given packing type
and size. Values of F pd are given in Tables 14-13 and 14-14. For operating
pressures above atmospheric, and for certain packing sizes, L f and
G f are calculated differently:
Gf = 986F s(F pd/20) 0.5 10 0.3ρ G (14-150)
L f = L(62.4/ρ L)(F pd/20) 0.5 µ L 0.2 F pd > 200 (14-151a)
L f = L(62.4/ρ L)(20/F pd) 0.5 µ L 0.1 F pd < 15 (14-151b)
The Robbins equations require careful attention to dimensions. However,
use of the equations has been simplified through the introduction of Fig.
14-58. The terms L f and G f are evaluated, and the ∆P L is obtained directly
from the chart. Basic nomenclature for the Robbins method follows:
C3 = 7.4(10) −8
C 4 = 2.7(10) −5
F pd = dry packing factor, ft −1
F s = superficial F-factor for gas, U tρ g 0.5 , ft/s(lb/ft 3 ) 0.5
G = gas mass velocity, lb/hr⋅ft 2
G f = gas loading factor, lb/hr⋅ft 2
L = liquid mass velocity, lb/hr⋅ft 2
L f = liquid loading factor, lb/hr⋅ft 2
∆P = pressure drop, inches H2O/ft packing (× 83.3 =
mm H2O/m packing)