Page 218 - Design of Simple and Robust Process Plants

5.7 Simplification and Ranking per Unit Operation 203

(3)
(1)

F (2)
HEAT HEAT
(4)

(1)
(2)
F (2)
(3)
HEAT
HEAT
(4)

(2) (3)
(1)
F
HEAT
HEAT HEAT
(4)

Fig. 5.39. Four component separation with; one DWCand a
sequential column, two DWC's or three sequential columns.

6. Two divided wall columns where product 2 is removed as a side stream of the
DWC and at the top of the second column. This application is chosen when
the temperature range over the first DWC would be too large; then, some
product 2 is left in the bottom to lower the temperature. A similar approach
was applied for the installation of a partial condenser (see Figure 5.33).
7. A sequence of three distillation columns.

An overview is given of the one-, two-, three-, and four-component separations in
order of complexity in Table 5.9. It is clear that the conventional approach of distilla-
tion columns in series is more complex and more expensive as an increasing num-
ber of columns becomes involved.
Most absorption units are based on chemical absorption versus physical absorp-
tion. The standard physical absorption unit is a packed or tray column. The chemic-
al absorption units were discussed in the section on G/L reactors.
The above illustrates that many options exist for multi-component distillation
separations before a selection ends in a conventional approach with standard distil-
lation columns in sequence. It might be considered surprising that, despite these