Page 208 - Distillation theory

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

182 Distillation Trajectories in Infinite Complex Columns and Complexes

and composition of the entrainer E can be chosen so the separation of main feed
is best conducted.
This allows us to actively influence the location of the pseudoproduct point x
D
of the intermediate section in order to maintain sharp separation (i.e., separation
at which the intermediate section trajectory ends at some boundary element of
the concentration simplex). This is feasible in the case when inside concentration
simplex there is one trajectory of reversible distillation for pseudoproduct point
x that ends at mentioned boundary element, and there is the second trajectory

D
inside this boundary element. To maintain these conditions, pseudoproduct point
x of the intermediate section should be located at the continuation of the men-

D
tioned boundary element, because only in this case can liquid–vapor tie–lines in
points of reversible distillation trajectory located in this boundary element lie at
the lines passing through the pseudoproduct point x . We discuss these conditions

D
in Chapter 4. It was shown that in reversible distillation trajectory tear-off point
x t from the boundary element the component absent in it should be intermedi-
rev,e
ate at the value of the phase equilibrium coefficient between the components of
the top product and of the entrainer (K t > K t > K t ). This condition is
rev,D rev, j rev,E
the structural condition of reversible distillation trajectory tear-off for the inter-
mediate section. Mode condition of tear-off as for other kinds of sections consists
of the fact that in tear-off point the value of the parameter (L/V) m should be
equal to the value of phase equilibrium coefficient of the component absent at the
boundary element in tear-off point of reversible distillation trajectory ((L/V) m =
t
K j (x )).
rev
At sharp adiabatic distillation in the intermediate section, several components
may be absent at the pseudoproduct boundary element at which section trajectory
ends, and the structural conditions of reversible distillation trajectory tear-off into
all the adjacent boundary elements having dimensionality bigger by one should
t
be valid in the trajectory tear-off point x from the boundary element (K t rev,D >
e
D
E
K t > K t ) for all the components of top product i , entrainer i , and the
rev, j rev,E
components, absent at the pseudoproduct boundary element, j. This condition is
similar to the corresponding condition for the top and bottom sections. It should
be valid not only in trajectory tear-off point, but in all its points (i.e., intermediate
section trajectory can be located only in the region, where K Di > K DEj > K Ei
i: j(E)
[sharp split region of the intermediate section Reg sh,e ]).
t
The condition (L/V) m > K j (x ) (mode condition of section trajectory tear-
e
t
off) should be valid in trajectory tear-off point x instead of the condition for
e
t
reversible distillation (L/V) m = K j (x ). Therefore, the minimum value of the
rev
parameter (L/V) m at which intermediate section trajectory bundle can arise is
t
(L/V) min > max K j (x ).
m e
j
t
Intermediate section trajectory tear-off point x should lie on the reversible
e
t
distillation trajectory in the boundary element Reg i: j(E) (x ∈ Reg i: j(E) ) farther
sh,e e sh,e
from pseudoproduct point x than all tear-off points x t from it of reversible

D rev,e
distillation trajectories into adjacent boundary elements.
These conditions are also similar to the corresponding conditions for the top
and bottom sections.