Heuristic Rules for the Use of SSCs

The target of most commercial SSCs has focused mainly on the separation of zeotropic mixtures. The criteria for the use of side streams for the separation of ideal mixtures with the expected feed composition regions of SSC arrangements are (Tedder and Rudd, 1978)  

The SSCs can be used in some certain ranges of feed compositions and/or volatilities, and the following list of heuristics provides useful guidelines for SSC application (Glinos and Malone, 1988). 

The purity of the side stream product is restricted by thermodynamics and the nature of the distillation process, which cause these columns to be appropriate either as prefractionators (that is, the side stream is fed to another column for further separation) or to generate recycle streams when there is no strict requirement on the recycle composition (Glinos and Malone, 1985). In addition, SSCs might be useful when the middle-boiling components are trace components or even the main product, as in a pasteurization column (Rooks et al, 1996). Note that the pasteurization column is a side stream column used to remove the light-ends in the vapor phase by using a fiill-reflux condenser. 

In summary, in the ideal case, SSCs can be attractive either when the middle product dominates in the feed and one of the other components is in only minor quantities, or when the middle-boiling components are trace components, or when they are used as prefractionators. Thus, SSCs can only be applied under special circumstances of feed composition and product specification (Smith, 2005). 

Although their application to non-ideal cases is relatively rare, SSCs can also be economical under certain process conditions and design requirements, with some of the criteria that favor the use of SSCs as follows (Rooks et al, 1996)  

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