Zorka Novak

Publications (2)2.32 Total impact

• Article: Mixed-Integer Nonlinear Programming Problem Process Synthesis under Uncertainty by Reduced Dimensional Stochastic Optimization

  Zorka Novak, Zdravko Kravanja
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  ABSTRACT: This paper presents the developments of a novel simultaneous method for the optimization and the synthesis of complex chemical problems under uncertainty with a fixed degree of flexibility. The approach approximates the stochastic method in using a weighted objective function calculated over a reduced set of the extreme points (vertices). The feasibility of the design is ensured simultaneously by the feasibility constraints at critical vertices. The main part of the proposed method which was called the method for reduced dimensional stochastic optimization (the RDS method) is a special setup procedure for determining the reduced set of vertices and their weights for the approximation of the expected value of the objective function. A very attractive feature of this method is that the sizes of mathematical models and the computational times are reduced by 1 or 2 orders of magnitude when compared to those of the stochastic methods. On the basis of the RDS method, a robust strategy for the synthesis of complex models under uncertainty is proposed (the RDS strategy). The steps of the RDS method and the RDS synthesis strategy are illustrated in detail by one simple and two more extensive example problems, respectively.
  05/1999;
• Article: Simultaneous Optimization Model for Multicomponent Separation

  Zorka Novak, Zdravko Kravanja, Ignacio E. Grossmann
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  ABSTRACT: This paper describes the general optimization model for the simultaneous synthesis of heat integrated separation sequences and their heat exchanger networks (HEN). The model enables an optimal selection of the separation sequence, type of separation units, heat matches, operating conditions and design parameters. The synthesis of the separation sequence can be either homogeneous (the same type of separators) or heterogeneous (different types of separators) allowing sharp and/or nonsharp separations. The synthesis can be carried out either for a separation problem only or for a separation system together with its flowsheet. The model is formulated as a mixed-integer nonlinear problem (MINLP). The approach is illustrated by two examples: one of them presents the homogeneous synthesis of a sharp distillation sequence using a network separation superstructure and a more compact superstructure. The second example presents the application of the general optimization model in the synthesis of the heterogeneous separation system together with its flowsheet when the compact separation superstructure is used.
  Computers & Chemical Engineering 18. · 2.32 Impact Factor