General Petlyuk Design

Fully thennally coupled columns can be very difficult columns to design because adjusting ont variable may have multiple effects on the operation column. This was not the case in, for instance, simple columns as adjusting a parameter like the reflux ratio will only affect the profile intersection of the two applicable CSs. Thus, we will 

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In the previous examples, a one-to-one correspondence exists between the units and the tasks (e.g., in Fig. 2 each node performs a particular separation task). It is possible, however, to develop more general superstructure representations in which a one-to-many relationship exists between the units and the tasks. An example of a one-to-many relationship is the superstructure for separation shown in Fig. 6 proposed by Sargent and Gaminibandara (1976), this superstructure accommodates sharp splits and has the Petlyuk column embedded as an alternative design. Note, for instance, that column 1 does not have a prespecified separation task. From this example it is clear that superstructures that have one-to-many relationships between units and tasks tend to be richer in terms of embedded alternatives. On the other hand, the more restricted one-to-one superstructures tend to require simpler MINLP models that are quicker to solve. 

This section has thus presented a quick synthesis and analysis method for two simplified infinite reflux cases. Just like simple columns, it can be generally stated that if a design is considered feasible at infinite reflux conditions, then a feasible design can be found at finite reflux too. This fact is particularly useful for nonideal systems. An illustration of a more complex infinite Petlyuk column example is given in the following example for the azeotropic acetone/benzene/chloroform system. 

The general algorithm of design calculation of Petlyuk columns includes the following stages ... 

Methods of the general geometric theory of distillation, encoded in software, provide quick and rehable solutions to problems of flowsheet synthesis and to optimal design calculations. DistillDesigner software allows refinement and confirmation of the algorithms of optimal design. A sample of this software is available at www.petlyuk.com. 

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