Systems of Interconnected Distillation Columns

The particular difficulty associated with the solution of problems involving systems of distillation columns becomes apparent upon close examination of the system shown in Fig. 3-8. First observe that the composition of the recycled bottoms from the second column to the first is not known until a solution to the 

The capital 0 method for systems is introduced by the formulation of the equations for this method for the simple system of two conventional distillation columns shown in Fig. 3-8. In a subsequent section, the formulation is generalized for the case of any number of columns with any number of sidestreams withdrawn. 

As shown in Fig. 3-8, the number of the column from which a stream is withdrawn is denoted by a subscript on D and B. To identify the variables of each column, the column number is carried as the last subscript. For example, d t and dit 2 denote the flow rates of component i in the distillate streams withdrawn from columns 1 and 2, respectively. 

For the system of columns shown in Fig. 3-8, there exists one independent component-material balance per column, namely 

In the interest of simplicity, the subscript co used to identify the corrected flow rates for conventional and complex distillation columns has been omitted in the above expressions and from those which follow. 

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For systems of interconnected distillation columns, the 0 method constitutes an exact solution for certain problems provided that the a, s are constant in each... 

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