Page 344 - Distillation theory

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318 Synthesis of Separation Flowsheets

In patent literature, a large number of other methods to increase the output of
light oil products is introduced, but they require installation of additional columns.
The purpose of modernization of crude unit can be decrease of expenditures
of heat and cold.
At two-column atmospheric unit, the simple method to decrease expenditures
of heat and cold is application of two feedings with different temperatures in
◦
column of partial recovery of benzine (top feeding is at temperature about 100 C
and bottom feeding is at temperature achieved by means of heating of crude by
hot products and by pumparounds).
Considerable change of main succession of separation with the purpose to de-
crease energy expenditures at the increase of capital costs was offered in patent
(Devos, Gourlia, & Paradowski, 1987). The peculiarity of this flowsheet consists of
consequent partial recovery of light fractions (gases, light benzine, heavy benzine,
kerosene) in several columns of preliminary separation and obtaining of light end
products in several more additional columns. Reboilers of all these columns warm
by hot products and by pumparounds, which ensures good recuperation of heat
at a large number of heat exchangers. Heavier products are obtained in atmo-
spheric and two vacuum columns with furnace heating and with live steam. Ideas
of prefractionation (i.e. split with distributed component) and pinch technologies
are used in this flowsheet. The same idea is used in simplified way in the classical
two-column flowsheet (Fig. 8.32b). In a more advanced way, this idea was used in
the unit recently created in Germany, which contains two prefractionators at pres-
sure three and two atmospheres producing a light naphta with a 80 ÷ 90 C boiling
◦
range and a medium naphta with a 90 ÷ 120 C boiling range. This separation
◦
flowsheet was named “progressive distillation.”

8.8. Conclusion

While designing and reconstructing separation equipment, one can drastically
increase their economy via application of the newest method of scientifically based
presynthesis, automatic sequencing, thermodynamic improving, and the use of the
best distillation complexes.
The software for automatic sequencing for zeotropic mixtures includes auto-
matic identification of possible splits in simple columns and in distillation com-
plexes, and automatic identification of sequences of these simple columns and
complexes, ensuring obtaining from the initial mixture of the prescribed set of
products. The degree of complexity of distillation complexes (number of prod-
ucts, number of sections, number of shells of column) can be different and has
to be set by the user before the task is solved. After identification of possible
sequences, the design calculation by new algorithms of all columns and complexes
of each sequence at minimum reflux flow rates or at set excess reflux factor with
estimation of energy or summary (energy and capital) expenditures for each se-
quence is carried out. The degree of simplification of design calculation and of
estimation of expenditures can be different and can be set by the user before
solution of the task.