Page 15 - Distillation theory

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Preface

This book is devoted to distillation theory and its application. Distillation is the
most universal separation technique. Industrial distillation consumes a consid-
erable part of the world power output. The distillation theory enables one to
minimize power and capital costs and thus opens up new ways of designing eco-
nomical separation units. The most important constituent of the distillation theory
is the geometric approach, which reveals general rules governing the variation of
component concentrations along the distillation column. In other words, it pro-
vides general rules for the arrangement of distillation trajectories in the so-called
concentration space, in which every point represents some mixture composition.
A considerable part of the book is concerned with these general rules, which are
used as the basis in developing new methods and algorithms for the optimal design
of separation units.
The geometric approach to distillation was put forward by the German sci-
entists Ostwald and Schreinemakers in the early twentieth century. During the
years that followed, it has been developed by scientists from various countries.
However, until recently, the geometric approach found little use in the design
of distillation units. The progress in this field was made by developing the pure
computational approach, more specifically, ways of describing the liquid–vapor
equilibrium and algorithms for solving sets of distillation equations. This approach
has been fruitful: it has resulted in universal computer programs that enable one
to design a distillation column (system) of any type for separation of any kind of
mixture. However, the pure computational approach gives no answer to a number
of fundamental questions that arise in the optimal design of distillation processes,
particularly in the case of azeotropic distillation. These questions are the follow-
ing: (1) What are the feasible separation products for a given mixture? In other
words, what components can be present in or absent from the separation products?
(2) What minimum power is required to separate a given mixture into the desired
components? (3) What minimum number of trays is necessary to separate a given
mixture into the desired components at a fixed-power input? Answers to these
questions have been provided only by a general geometric theory of distillation.

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