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Absorption (Chemical Engineering) 19
caused by massive liquid carryover from tray to tray (en-
trainment flood) or when liquid backup in the downcomer
reaches the tray above (downcomer backup flood) or when
the downcomer is unable to handle the total quantity of
descending liquid (downcomer choke flood). At low liq-
uid rates and high gas velocities, entrainment flooding is
the most common limit. At high liquid flow rates and low
gas velocities (e.g., high pressure operation), downcomer
backup and downcomer choke flood are the most common
limits.
FIGURE 17 Tray column.
other performance characteristics at high gas rates; but
valve trays weep less and therefore perform better at low
gas rates.
A third type of tray, once commonly employed but cur-
rently used only for special applications, is the bubble-
cap tray. Its design and operation are discussed by Bolles
(1963).
The maximum capacity of a tray column is usually lim-
ited by the onset of flooding, which occurs when liquid
excessively accumulates inside the column. Flooding is FIGURE 18 Types of dispersion on an absorption tray.
