Page 225 - Distillation theory

P1: FCH/FFX P2: FCH/FFX QC: FCH/FFX T1: FCH
0521820928c06 CB644-Petlyuk-v1 June 11, 2004 20:17

6.7 Distillation Complexes with Thermal Coupling Flows 199

1
1
1,2
1,2
a) b)
1,2,3 1,2,3
2
2
2,3 1,2,3,4
1,2,3,4 2,3

3 2,3,4
3
2,4,3
34
,
3,4
4
4
1 1
c) 2 d)
1,2,3,4
3
1,2
4
1 2
1,2,3,4
3

2 3,4
1,2,3,4
3
4

4
Figure 6.13. Some Petlyuk columns for four-component mixtures: (a) sequential column ar-
rangement; (b) more operable arrangement; (c) with two divided walls; and (d) in two columns
(with intermediate split in first column).

Columns with thermal coupling flows, but with sharp intermediate separation
between components with average volatilities, were introduced to decrease the
number of sections (Cahn et al., 1962; Petlyuk, Platonov, & Avet’an, 1966; Chris-
tiansen et al., 1997a; Kaibel, 1987) (Fig. 6.13d). Such sequences require bigger
energy expenditures for separation and contain exchange sections between point
of withdrawal of products with average volatilities. Flow rates of liquid and vapor
in exchange sections are equal.
In Fig. 6.13a ÷ c, the number of components at the exit from each section
is smaller by one than at the entrance. It was shown in the work (Christiansen,
Scogestad, & Lien, 1997b), that the complete separation of four-component mix-
tures into pure components in such sequences requires energy expenditures bigger
only by 10% ÷ 15% than the separation of two-component mixture.