Page 248 - Distillation theory

P1: JPJ/FFX P2: JMT/FFX QC: FCH/FFX T1: FCH
0521820928c07 CB644-Petlyuk-v1 June 11, 2004 20:18

222 Trajectories of the Finite Columns and Their Design Calculation

x x
a) D 2 b) D 2
x F S 1 r x F
x x
B min B
x f−1
x
f−1
+
N
2 x ∞ r
S f−1
1 r 4 1 4
2
3 x 3
c) D
S 2 s
x F
∞
x
f
x B

1 4
x min
+ f
N
s
S 1 s
3
Figure 7.1. Rectifying trajectories at sharp intermediate split and different x f −1 (K 1 >
K 2 > K 3 ) (a); rectifying trajectories at quasisharp intermediate split and different x f −1
3,4 1,2
(b); section bundles (separatrix sharp spilt regions Reg R and Reg R ) (c). Separatrix
sep,r sep,s
sharp split section regions are shaded. 1,2 3,4

one composition point at the first tray below the feed cross-section x f . These points
min,R 2
lie at the separatrix min-reflux regions of sections trajectories Reg sep,r (S − N )
+
r
r
2
and Reg min,R (S − N ), respectively.
+
sep,s s s
At reflux bigger than minimum, the sizes of working trajectory bundles of the
sections increase and, at the condition of validity of material balance in feed cross-
section (Eq. [5.18]), points x f −1 and x f can be located not only at these separatrix
1
2
+
regions, but also inside separatrix sharp split regions Reg sh,R (S − S − N ) and
r
r
r
sep,r
2
1
+
Reg sh,R (S − S − N ) (Fig. 7.1a,b). Figure 7.1a,b for clarity’s sake shows only
sep,s s s s
the working trajectories and the separatrix sharp split region of the top section at
3,4
the sharp and quasisharp intermediate split Reg sh,R of four-component mixture.
sep,r
1,2
The intermediate split is chosen as illustrating the most general case of separating
multicomponent mixtures. To determine the set of composition points at the first
trays above and below the feed cross-section at given reflux larger than minimum,
1
2
+
we examine first sharp separation and linear regions Reg sh,R (S − S − N ) and
r
r
sep,r
r
1
2
Reg sh,R (S − S − N ). We designate possible compositions in the feed cross-
+
sep,s s s s
sh
section at these assumptions (x f −1 ) sh and (x f ) .
lin lin