Experienced-Based Rules of Chemical Engineering

[Freeman]

Drum Type Vessels

A. Liquid drums are usually horizontal. Gas/Liquid separators are usually vertical

B. Optimum Length/Diameter ratio is usually 3, range is 2.5 to 5

C. Holdup time is 5 minutes for half full reflux drums and gas/liquid separators

Design for a 5-10 minute holdup for drums feeding another column

D. For drums feeding a furnace, a holdup of 30 minutes is a good estimate

E. Knockout drum in front of compressors should be designed for a holdup of

10 times the liquid volume passing per minute.

F. Liquid/Liquid separators should be designed for settling velocities of 2-3 inches/min

G. Gas velocities in gas/liquid separators, velocity = k (liquid density/(vapor density-1))^0.5,

where k is 0.35 with horizontal mesh deentrainers and 0.167 with vertical mesh deentrainers. k is 0.1 without mesh deentrainers and velocity is in ft/s

H. A six inch mesh pad thickness is very popular for such vessels

I. For positive pressure separations, disengagement spaces of 6-18 inches before the mesh pad and 12 inches after the pad are generally suitable.