(124e) Energy Efficiency of Hybrid Processes for Olefin / Paraffin Separation

A new thermodynamically guided methodology (TGM) is proposed for the structural and parametric optimization of hybrid processes used for energy intensive separations, such as olefin/paraffin blends. The approach addresses energy savings through the retrofit of existing distillation columns with a fixed size separator, e.g. a PSA or membrane unit. A superstructure representation of the various solutions is first developed where the additional separator feed stream is taken as a side draw from the column, and the raffinate and extract streams are fed back into the column. Since the distillation column is a heat driven separation while the additional separator is a work driven separation, the chosen objective thermodynamic function is the total exergy consumption of the hybrid process. The thermodynamically based mathematical formulation is of the nonlinear programming (NLP) type, which is solved using the Generalized Reduced Gradient Method. The results of the optimization show a potential for exergy reduction compared to conventional distillation columns. Preliminary evaluation of a couple of case studies, including an analysis of a C3 column, will be presented.