Page 20 - Academic Press Encyclopedia of Physical Science and Technology 3rd Chemical Engineering

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Encyclopedia of Physical Science and Technology EN001H-01 May 7, 2001 16:18

Absorption (Chemical Engineering) 17

its own packings. Perry’s text contains a more extensive
tabulation of packing factors.
Maximum capacity of a packed bed is usually limited by
the onset of flooding. During normal operation, gas flows
up while liquid drains freely along the packing surfaces.
As gas rate is increased, it begins to interfere with free
draining, causing some liquid accumulation in the bed.
When this interference is so high that liquid fills the tower,
the column is said to be flooded.
The condition of flooding is predicted from generalized
charts such as that in Fig. 16. The abscissa shows a scale of
a dimensionless term called the flow parameter. This pa-
rameter represents a ratio of the kinetic energy of the liquid
to the kinetic energy of the gas; thus very low values of
the parameter are associated with low-pressure absorbers
where the volumetric ratio of gas to liquid may be very
high. The ordinate scale shows values of a capacity pa-
rameter, generalized through the packing factor(Table II)
Each curve in Fig. 16 represents a constant pressure
drop value. Packed absorbers are usually sized to give
a pressure drop of 0.25 to 0.50 in. H2O per foot (200–
2
400 N/m per meter) of packed depth. Figure 16 is used
to determine the column cross sectional area to achieve

FIGURE 15 Common types of random packings (Parts e and f,
courtesy of Norton Co.; part g, courtesy of Glitsch, Inc.; part h,
FIGURE 14 Packed column. courtesy of Nutter Engineering Corp.)