Optimization distillation sequence

Know how to determine near-optimal and optimal distillation sequences for neaiiy ideal systems. 

Optimization. Optimi2ation of the design variables is an important yet often neglected step in the design of extractive distillation sequences. The cost of the solvent recovery (qv) step affects the optimi2ation and thus must also be included. Optimi2ation not only yields the most efficient extractive distillation design, it is also a prerequisite for vaUd comparisons with other separation sequences and methods. 

Consider now ways in which the best arrangement of a distillation sequence can be determined more systematically. Given the possibilities for changing the sequence of simple columns or the introduction of prefractionators, side-strippers, side-rectifiers and fully thermally coupled arrangements, the problem is complex with many structural options. The problem can be addressed using the optimization of a superstructure. As discussed in Chapter 1, this approach starts by setting up a grand flowsheet in which all structural features for an optimal solution are embedded. 

HEAT-INTEGRATED DISTILLATION SEQUENCES BASED ON THE OPTIMIZATION OF A SUPERSTRUCTURE... 

Heuristics are reliable, well-established rules for reducing the number of potential alternative sequences with minimum effort, and often lead to near-optimal separation system designs. Most of the heuristics for distillation sequencing were originally formulated from parametric studies. A number of Heuristics have been suggested, some of which contradict each other (5—8). Heuristic methods have also been extended to sequencing nonsharp distillation separations and to combinations of distillation, mixing, and stream bypass operations (9—11). 

Wei-Zhong, A. and Xi-Gang, Y. (2009). A simulated annealing-based approach to the optimal synthesis of heat-integrated distillation sequences. Comput. Chem. 

Caballero, J.A. and Grossmann, I.E. (2014) Optimal synthesis of thermally coupled distillation sequences using a novel MILP approach. Computers Chemical Engineering, 61,118-135. 

Ryan, P.J., and M.F. Doherty, Design/Optimization of Ternary Het-ODgeneous Azeouopic Distillation Sequences, AIChE J., 35, 15K-I60I (1989),... 

Sophos et al. employed an optimal, heat-imegrated distillation sequence. By first identifying favorable unintegrated sequences, feey are able to limit the problem. They assume that the integrated optimum k a member of the set developed in the first screening. These sequences are then looked at for beat integration opportunities given whatever constraints ate appropriate. 

Synthesis of subsystems. The main objective of this approach so far has been the reduction and optimization of energy, including thermal pinch, distillation sequences, and mass and heat exchange networks, which will be described in a Httle more detail later in the chapter (In addition, see chapter 4). 

Bauer, M. H., Stichlmair, J. (1995). Synthesis and Optimization of Distillation Sequences for the Separation of Azeotropic Mixtures. Comput. Chem. Eng., 19, 515-20. 

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