Page 216 - Design of Simple and Robust Process Plants

5.7 Simplification and Ranking per Unit Operation 201
4. An absorber column is used to purify a gas stream by absorption of the least
volatile component in a solvent. Often, the absorption is achieved by chemic-
al reaction compared with physical absorption, such as the removal of CO 2 or
H 2 S.
5. A dephlegmator is a nonadiabatic rectifier, where a vapor stream is purified by
partial condensation of the vapor in a rectification section and refluxed.
6. A rectifier column purifies a vapor stream by partially condensing and reflux-
ing the overhead on the top of the separation column (a specific form of
dephlegmator).
7. Two-component separation in a standard distillation column.

Three-component separations are ranked and presented in Figure 5.37.
1. A distillation column with a vent stream with lights removed at the top, a top
liquid product and a bottom stream (in case the light stream would not be
pure enough, a dephlegmator might be installed at the vent).

DISTILLATION WITH SIDE DRAW
LIGHTS
TOP TOP
SIDE STREAM
F F

HEAT
HEAT
DIVIDED WALL COLUMN
BOTTOM
BOTTOM
TOP

F
MIDDLE
HEAT
BOTTOM

SEQUENTIAL DISTILLATION COLUMN

MIDDLE
TOP
F
HEAT HEAT
BOTTOM

Fig. 5.37. Three component distillation with; side draw, divided
wall column, two sequential columns.