Degree of Freedom Analysis and Variable Selection

Let us first treat the three internal flow variables required to be specified in the Petlyuk. Satisfying this requirement essentially means setting the reflux ratios in three CSs. Again it is useful to specify a reference reflux. For this purpose it is useful to specify the reflux ratio in either CSj or CSe, but we will choose to set / ai throughout this chapter. The two remaining flow variables are thus associated with the internal CSs (2 5), and therefore require that the reflux ratios in any two of these CSs be set. This is not an easy task, because refluxes can be positive or negative, and their magnitudes are not bound. Thus, just as with side-rectifiers and 

The parameter I governs the amount of liquid in CS i that is directed toward CS2 at the thermally coupled junction at the top of the column. The liquid flowrate then directed toward CS3 is simply equal to (1 — The parameter I v dictates how 

We have now established a convenient way of specifying and representing the internal flow variables in the column. As mentioned previously, the designer is still required to specify an internal composition variable in the column. The choice of the compositional variable will be discussed in greater detail later, but for now it will suffice to state that we will specify the difference point of CS3 (X s). The reason behind choosing this specific variable and making an intelligent choice for it will become clear in the discussions in Section 7.3.3. 

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