Optimization of Process Flowsheets

After studying this chapter and the multimedia CD-ROM that accompanies this book, the reader should 

Be able to formulate a nonlinear optimization problem (nonlinear program, NLP) to maximize or minimize an objective function by adjusting continuous decision variables in the model of the process. 

Understand the nature of algorithms that optimize the process while simultaneously converging the recycle loops and design specifications associated with the process simulation. 

Begin to understand the advantages and disadvantages of converting design specifications, associated with a simulation model, to equality constraints in the NLP. 

From a mathematictd point of view, chemical engineers deal with three types of problems when solving equations. The first type, which is the subject of most undergraduate text books in chemical engineering and has been the main subject of this book to this point, is the completely specified case where the number of equations, to be solved is equal to the 

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Kocis, G. R., and Grossmann, I. E., A Modeling/Decomposition Strategy for MINLP Optimization of Process Flowsheets, paper no. 76a, AIChE Meeting, Washingtonj D.C., 1988. 

Kocis GR and Grossmann IE (1988) A Modelling and Decomposition Strategy for the MINLP Optimization of Process Flowsheets, Comput Chem Eng, 13 797. 

Cuthrell, J. E., and Biegler, L. T., Simultaneous solution and optimization of process flowsheets with differential equation models, Chem. Eng. Res. Des. 64, 341 (1986). 

Kocis, G. R., and Gro.ssmann, E. E., A modeling and decomposition strategy for the MINLP optimization of process flowsheets, Comp, and Chem. Engr. 13, 797 (1988). 

Yee, T. F., Grossmann, 1. E., and Kravtmja, Z. Simultaneous Optimization Models for Heat Integration. III. Optimization of Process Flowsheets and Heat Exchanger Networks, Comput. Chem. Eng. 14, 1185 (1990c). 

In this work, we develop an algorithm based on fitting response surfaces -using a kriging metamodel- for the optimization of constrained-noise black box models. Besides, an important characteristic is that we deal with constrained problems in which the metamodel can represent either the objective function or some constraints (or both simultaneously). A typical case is the optimization of process flowsheets using modular simulators in which some units are represented by a metamodel. In these systems it is possible to include external constraints and even the result of some calculations could be constraints to the model. 

In all of these alternatives, the design team selects acceptable temperature levels and flow rates of the recirculating fluids. These are usually limited by the rates of reaction, and especially the need to avoid thermal runaway or catalyst deterioration, as well as the materials (rf construction and the temperature levels of the available cold process streams and utilities, such as cooling water. It is common to assign temperatures on the basis of these factors earily in process synthesis. However, as optimization strategies are perfected, temperature levels are varied within bounds. See Chapters 10 and 18 for discussions of the use of optimization in process synthesis and optimization of process flowsheets, as well as Example 6.3 to see how constrained optimization is applied to design an ammonia cold-shot converter. 

GuiUen-Gosalbez G, Caballero JA, Jimenez L. Apphcation of life cycle assessment to the strucmral optimization of process flowsheets. Ind Eng Chem Res 2008 47(3) 777—89. 

Guillen-Gosalbez, G., Caballero, 1. A., limenez, L. (2008). Application of lifecycle assessment to the structural optimization of process flowsheets. Industrial and Engineering Chemistry Research, 47,777-789. 

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