Page 275 - Distillation theory

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7.5 Design Calculation of “Petlyuk Columns” 249

out design calculation at several values of parameter E/D and, for each value of
E/D, at several values of parameter L/D.
The general algorithm of design calculation includes the following steps:
1. Calculation of minimum flow rate of the entrainer or autoentrainer
(E/D) min (see Section 6.6).
2. Determination of the average calculated value of the rate of the entrainer
or autoentrainer (E/D) mean = 3(E/D) min according to the heuristic rule
(Knapp & Doherty, 1994) and of a number of other calculated values of
E/D in the set interval.
3. Calculation of minimum reflux number (L/D) min at (E/D) mean (see Section
6.5).
4. Determination of the average calculated value of reflux number
(L/D) mean = 1,5(L/D) min according to heuristic rule (Knight & Doherty,
1989) and of a number of other calculated values of L/D in the set interval.
5. Calculation of necessary trays number at their optimal distribution in sec-
tions at different set values of parameters E/D and L/D and choice of
design values of these parameters.

We note that there is but a slight dependence between the values of (L/D) min
and E/D. This allows us to confine ourselves to the single-stage calculation of
(L/D) min and to use the same series of values of L/D at different values of
E/D.
The final choice of design and mode parameters is carried out taking into con-
sideration expenditures on separation not only in the column of autoextractive
distillation, but also in that of the entrainer or autoentrainer recovery and in the
intermediate columns, if there are any.

7.5. Design Calculation of “Petlyuk Columns” and of Columns
with Side Sections

7.5.1. Design Calculation of “Petlyuk Columns”
Imperfections of application of simulating software for the purposes of designing
distillation complexes sharply grow compared with those of two-section columns
because of the dramatic increase in the number of degrees of freedom of design-
ing. Therefore, the application of algorithms of design calculation to distillation
complexes is of especially great importance. In connection with this, a number of
simplified methods of design calculation of Petlyuk columns that should precede
rigoroussimulationweredeveloped.Simplifiedmethodswerebasedonlimitations
and assumptions such as ternary mixtures, sharp separation, liquid feeding, con-
stant molar flows, and constant relative volatilities of components (Fonyo, Scabo,
& Foldes, 1974; Tedder & Rudd, 1978; Nikolaides & Malone, 1987; Cerda & West-
erberg, 1981; Triantafyllou & Smith, 1992). A great number of assumptions and
empirical ratios used in these simplified methods do not meet set requirements