Page 188 - Distillation theory

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162 Distillation Trajectories and Conditions of Mixture Separability

calculation of minimum reflux mode, taking into consideration the change of flows
of liquid and vapor in the column sections, do not differ from those described pre-
viously.
As far as the second assumption is concerned, as was mentioned in Section
5.5, it does not influence the compositions in the stationary points. Therefore, it
does not influence the first two stages of the described algorithms of calculation of
minimumrefluxmode.Thisassumptioncouldhavesomeinfluenceonlyatthethird
stage of the algorithms, when curvature of separatrix trajectory bundles should
be taken into consideration. Therefore, the assumption about equilibrium plates
at calculation of minimum reflux mode is even more justified than at calculation
of finite columns.
Therefore, the stated algorithm of calculation of minimum reflux mode, based
on the geometry of the trajectory bundles in concentration space, are potentially
as one likes precise and most general, because they embrace any splits on mixtures
with any components number and any degree of nonideality.

5.6.7. Visualization of Section Trajectories
Visualization is of great importance for understanding calculation results, and
for understanding peculiarities and difficulties in separation of any mixture (it is
especially important for azeotropic mixtures). Geometric approach to the solution
of calculation task is closely connected with visualization of its results. We already
demonstrated it at certain examples of separation of three- and four-component
mixtures. Separation of mixtures with a component number above four does not
allow for such complete visualization. However, less complete and more rough
visualization can be used for such mixtures, considering the components lighter
than light key component as one component, having in each point of the trajectory
the concentration, equal to the sum of concentrations of the components lighter
than the light key component. It should be done similarly with all components
heavier than the heavy key one. The use of such an approach allows to present
separation of mixture with any components number at any intermediate split
without distributed components as separation of the four-component mixture
containing two key components, one pseudocomponent lighter than the light key
component and one pseudocomponent heavier than the heavy key component.
Location of sections trajectories of such conditional mixture in concentration
tetrahedron should follow general described above regularities for usual four-
component mixtures. Therefore, such visualization allows us to understand and to
foresee the designing peculiarities and difficulties of separation of mixtures with
large numbers of component.

5.7. Necessary and Sufficient Conditions of Separability of Mixtures

5.7.1. Adiabatic Columns

We discussed before in Section 5.3 the necessary conditions of separability of
mixtures. The main necessary condition is belonging of product points to possible