Page 267 - Distillation theory

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

7.3 Design Calculation of Two-Section Columns 241

Let’s examine split 1,2 : 2,3,4 (K 1 > K 2 > K 3 > K 4 ) as an example. The summary
concentration of impurity components 3 and 4 is set in the top product, and the
concentration of component 1 is set in the bottom product. Besides that, the
distribution coefficient β of component 2 or its concentration in the top product
x D,2 is set.
The concentration of the only non-key impurity component in the top product,
that is, component 4, and of tray numbers in the sections are determined with the
help of the described algorithm, and the concentrations of the rest of the com-
ponents in the products are determined from the conditions of material balance
according to the set values x F,i , η D , η B , and β:
F
x D,1 = x F,1 x B,1 = 1 − η B
D
Fβ F
x D,2 = x F,2 x B,2 = x F,2 (7.14)
D(1 + β) B(1 + β)
F D
x D,3 = (1 − η D ) − x D,4 x B,3 = x F,3 − (1 − η D )
B B
F
x B,4 = x F,4
B
3,4 1
Figure 7.11 shows separatrix trajectory bundles Reg R and Reg R of the
sep,r sep,s
1,2 2,3,4
sections and calculation trajectories for equimolar mixture pentane(1)-hexane

x D
2
x F
1
r S
x B

x ÷ x ) 4 ( 1 s S
) 1 (
D D
+
N r
S 2
1 r 4
+
s N
x ÷ x (4)
) 1 (
B
B
3
Figure 7.11. Section trajectories at quasisharp split
with the distributed component 2 for the equimo-
lar pentane(1)-hexane(2)-heptane(3)-octane(4) mixture
((L/V) r = 0.5, x D,2 = 0.336, product purity − 0.999,
0.99, 0.98, 0.95); rectifying separatrix sharp split region
3,4
Reg R is shaded.
sep,r
1,2