Page 273 - Distillation theory

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

7.4 Design Calculation of Extractive Distillation Columns 247

column contains only one impurity component (component 1), its composition
can be set quite exactly. The calculation of trajectories of the sections is carried
out by method “tray by tray” in an upward direction. The trajectory of the bottom
1
1
+
+
section is attracted to separatrix sharp region S − N (Reg sh,R ) and to node N .
s
s
s
sep,s
2,3,4
The calculation is carried out until the achievement of chosen point x f at segment
∞
[x min , x ]. To determine x opt , this calculation is carried out many times, finishing in
f f f
different points. The composition in point x f −1 is determined from the conditions
of material balance in the feed cross-section. After that, the calculation of the in-
termediate section from point x f−1 to point x e is carried out. The trajectory of the
2,3
2
1
intermediate section is attracted to separatrix bundle S − S − N (Reg sh,R ) and
+
m
sep,e
m
m
1,4
to node point N . The composition in point x e−1 is determined from the conditions
+
m
of material balance in the cross-section of entrainer input, and the calculation of
the top section from point x e−1 to point x D is carried out. The trajectory of the
top section is attracted to node point N of edge of the concentration simplex
−
r
2
1 − 4(Reg sh,R ). The whole calculation is quite stable and it does not require iter-
sep,r
1
ations by product composition. The distillation trajectory for the column under
consideration may be presented as follows:
1
x B → qS → x f ⇐⇓ x f −1 → x e ⇐⇓ x e−1 → x D
s
Reg Reg t [x f ] ∈ Reg qsh,R [x f −1 ] ∈ Reg qsh,R Reg t Reg Reg
B s sep,s sep,e e att D
The way it is presented here is the same we used for three-component mixtures,
1
but here the number of components in points x B and qS is 3, not 2, and that in
s
points x f and x f −1 is 4, not 3.
7.4.3. The Multicomponent Mixtures: The Top Product Is a Binary Mixture, the
Entrainer Is a Pure Component (m r = 2, m e > 2)
According to Section 6.5, in this case the joining of trajectories of the bottom
and the intermediate sections is similar to the intermediate split in two-section
columns, and the joining of trajectories of the top and the intermediate sections
takes place according to the split with one distributed component. Therefore, the
calculation of section trajectories should be carried out according to the general
algorithm described in Section 7.3 for two-section columns at the intermediate
split and at the split with a distributed component (Fig. 7.13b). The distillation
trajectory for the column under consideration may be presented as follows:
1 1
x B → qS → x f ⇐⇓ x f −1 → x e ⇐⇓ x e−1 ← qS ← x D
s r
Reg Reg t [x f ] ∈ Reg qsh,R [x f −1 ] ∈ Reg qsh,R Reg t Reg qsh,R Reg t Reg
B s sep,s sep,e e sep,r r D
7.4.4. The Multicomponent Mixtures: The Top Product Is Pure Component, the
Entrainer Is a Mixture (m r = 1, m e > 2)
According to Section 6.5, in this case the joining of trajectories of the bottom and
intermediate sections is similar to joining of sections of two-section column with a