(449i) Rapid Evaluation of Distillation Process Alternatives Involving Complex Column Configurations for the Separation of Multicomponent Azeotropic Mixtures

The synthesis of the optimal distillation process design for the separation of multicomponent azeotropic mixtures is until today a challenging task, particularly if complex column configurations are involved. We present in this work the application of a recently developed generalized design approach [1] for rapid and efficient evaluation of several distillation process alternatives for the separation of multicomponent highly nonideal azeotropic mixtures into three products, with respect to the minimum energy requirement and the thermodynamic efficiency of the process. The investigated distillation process designs in this work comprise direct sequence, indirect sequence, column with prefractionator and thermally coupled configurations [1, 2].

The applied design approach is based on the distillation theory of ideal behaving mixtures and on the decomposition of the whole distillation process into all constituting mass transfer sections. At pinch conditions, all possible constant composition zones in the process including those around the feed sections and those around the side stream sections are identified, so that no conceptual splitting of a thermally coupled distillation process design into a sequence of simple columns is needed. Furthermore, each set of constant composition zones is characterized by the relevant mass transfer sections along with the respective Eigenfunctions and split. Based on this approach, simple design methods valid for arbitrary feed thermal condition, for any number of components and for different types of splits have been applied for the determination of all relevant design parameters at pinch conditions of the previously mentioned column configurations separating multicomponent highly nonideal azeotropic mixtures approximated by equivalent multicomponent pseudo-ideal mixtures [1, 3].

Two illustrative examples are presented for the synthesis of the optimal distillation process design separating ternary and quaternary highly nonideal azeotropic mixtures. In each case, it is shown that for all investigated complex column configurations, the design tools presented in this work, have been successfully validated using appropriate RadFrac (Aspen Plus ®) models; providing thereby good design estimates for fast and reliable screening of all considered process alternatives by means of rigorous simulation, thus leading to the establishment of the optimal distillation process design.

 

References

(1) Adiche, C. and Ait Aissa, B., 2016. A Generalized Approach for the Conceptual Design of Distillation Columns with Complex Configurations, Chem. Eng. Res. Des., Part A, 109, 150-170

(2) Agrawal, R., 2003. Synthesis of Multicomponent Distillation Columns Configurations, AIChE J., Vol.49, No.2, 379-401.

(3) Adiche, C. and Vogelpohl A., 2011. Short-cut Methods for the Optimal Design of Simple and Complex Distillation Columns, Chem. Eng. Res. Des. Part A. , 89, 1321-1332.