Process synthesis problem

See Hooker and Grossman (1999) for more details on occurrence of disjunctions in process synthesis problems. 

This chapter provides an introduction to Process Synthesis. Sections 7.1 and 7.2 discuss the components of a chemical process system and define the process synthesis problem. Section 7.3 presents the different approaches in the area of process synthesis. Section 7.4 focuses on the optimization approach and discusses modeling issues. Finally, Section 7.5 outlines application areas which are the subject of discussion in chapters 8, 9 and 10. 

Process Synthesis, an important research area within chemical process design, has triggered during the last three decades a significant amount of academic research work and industrial interest. Extensive reviews exist for the process synthesis area as well as for special classes of problems (e.g., separation systems, heat recovery systems) and for particular approaches (e.g., insights-based approach, optimization approach) applied to process synthesis problems. These are summarized in the following ... 

Prior to providing the definition of the process synthesis problem we will describe first the overall process system and its important subsystems. This description can be addressed to the overall process system or individual subsystems and will be discussed in the subsequent sections. 

Having described the overall process system, its three main interactive components (i.e., the chemical plant, the heat recovery system and the utility system), as well as the three subsystems of the chemical plant (i.e., the reactor system, the separation system, and the recycle system) we can now define the process synthesis problem. 

The performance criteria are multiple ranging from economic to thermodynamic to operability considerations. As a result, the process synthesis problem can be classified mathematically as a... 

The nature of the multi-objective process synthesis problem is depicted in Figure 7.4 where it is shown that the optimal structure/topology of the process and the operating conditions of the process units result from the trade-offs of (Gundersen 1991) ... 

The mixed discrete-continuous nonlinear nature of the process synthesis problem implies two major challenges which are due to its ... 

To meet the objectives of the process synthesis problem, three main approaches have been proposed, which are based on... 

In the following chapters we will discuss the optimization approach as applied to several classes of process synthesis problems, and we will present optimization models for the targets (i.e., decomposition of process synthesis tasks) as well as for the overall nondecomposed mathematical representation of the alternatives. Prior to doing this, however, we will discuss the basic elements of the optimization approach (iii) in the next section. 

In the following chapters we will discuss the application of the optimization MILP and MINLP approaches to Process Synthesis problems arising in central chemical engineering process systems, sub-systems, and overall process systems. These include... 

V. Visweswaran and C. A. Floudas. Application of the GOP algorithm to process synthesis problems, in preparation, 1995. 

A process-synthesis problem can be formulated as a combination of tasks whose goal is the optimization of an economic objective function subject to constraints. Two types of mathematical techniques are the most used mixed-integer linear programming (MILP), and mixed-integer nonlinear programming (MINLP). 

The next example will revisit the plantwide problem of HDA plant, this time viewed as a process synthesis problem where flowsheet design and controllability are examined at the same levels of the hierarchical methodology. 

Figure 9.4 Parameters of a process synthesis problem in software PNS Studio.

During the last few years process synthesis by algorithm methods have made considerable progress. The problem of chemical process synthesis can be stated as follows given a set of reactants with amounts specified, determine both the cost-optimal structure and the optimal design variables of each process unit that can produce a set of specified products. In general, the process synthesis problem can be expressed as a MINLP problem where the integer and continuous variables occur nonlinearly in the performance index. The mathematical form is ... 

The main contributions of this chapter are reflected in the process synthesis problem analyzed in the second example. The implementation of the optimization model takes the concept of separation to the limit, by separating the structure of the flow sheet from the equations of the model. This separation is extremely useful for more complex process synthesis problems using superstructures. 

Szitkai, Z., Lelkes, Z., Rev, E., Fonyo, Z. (2002b). Handling of removable discontinuities in MINLP models for process synthesis problems, formulations of the Kremser equation. Computers Chem. Engng., in press. 

The mathematical formulation of the process synthesis problem for continuous plants can be stated as follows [7,10]... 

In the second stage, p-strands, p-sheets, and disulfide bridges are identified through a novel superstructure-based mathematical framework originally established for chemical process synthesis problems [121]. Two types of superstructure are introduced, both of which emanate from the principle that hydrophobic interactions drive the formation of p-stmcture. The first one, denoted as hydrophobic residue-based superstructure, encompasses all potential contacts between pairs of hydrophobic residues (i.e., a contact between two hydrophobic residues may or may not exist) that are not contained in helices (except cystines that are allowed to have cystine-cystine contacts even though they may be in hehces). The second one, denoted as -strand-based superstructure, includes all possible p-strand arrangements of interest (i.e., a p-strand may or may not exist) in addition to the potential contacts between hydrophobic residues. The hydrophobic residue-based and p-strand-based superstructures are... 

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