Pareto front of ideal Petlyuk sequences using a multiobjective genetic algorithm with constraints

Petlyuk sequences are a very promissory option to reduce energy consumption and capital costs in distillation. The optimal design of Petlyuk sequence implies determining 8 integers and 3 continuous variables with the minor heat duty and number of stages possible, but reaching the specified purities. Note that the heat duty and the number of stages are variable in competition, since we cannot decrease indefinitely one without increasing the other. In other words, we have a multiobjective problem with constraints. In contrast with other numerical strategies proposed, we consider the search of optimal designs set, from minimum reflux ratio to minimum number of stages and all designs between them. This set of optimal designs can be achieved by means of Pareto front, which represents a set of optimal solutions not dominated for a multiobjective problem. In this work, we implemented a multiobjective genetic algorithm with constraints to obtain the Pareto front of Petlyuk sequences. This algorithm is coupled to Aspen Plus simulator, so the complete MESH equations and rigorous phase equilibrium calculations are used. Results show clear tendencies in the design of Petlyuk sequence, and can be used to develop a short design method. In addition, the tool developed can be used to optimize not only the distillation columns but also complete chemical and petrochemical plants. (C) 2008 Elsevier Ltd. All rights reserved.