Process synthesis systematic approaches

In most chemical processes reactors are sequenced by systems that separate the desired products out of their outlet reactor streams and recycle the unconverted reactants back to the reactor system. Despite the fact that process synthesis has been developed into a very active research area, very few systematic procedures have been proposed for the synthesis of reactor/separator/recycle systems. The proposed evolutionary approaches are always based upon a large number of heuristic rules to eliminate the wide variety of choices. Many of these heuristics are actually extensions of results obtained by separately studying the synthesis problem of reactor networks or separator systems, and therefore the potential trade-offs resulting from the coupling of the reactors with the separators have not been investigated. 

Azeotropic distillation deals with the separation of mixtures involving one or several azeotropes. This problem, which in the past was tackled by means of experience and intuition, is today approached by means of systematic methods based on a deeper thermodynamic analysis. Here, we review the indispensable aspects for process synthesis. More details can be found in recent specialized books [8, 14]. 

Procedures for the actual synthesis of heat-exchanger networks are somewhat less well developed however, all of the standard process synthesis approaches— including systematic generation, evolutionary modification, and superstructure... 

Most of the applications discussed here were based on algorithmic systematic generation approaches to process synthesis. There also exist a number of heuristic rule-based or expert-systems-based approaches including PIP for total flowsheet synthesis, SPLIT for separation schemes (Wahnschafft et ai, 1991),... 

Reviews on earlier developments in the area of process synthesis can be found in Hendry et al. (1973), Hlavacek (1978), and Nishida et al. (1981). In the late sixties, work began to develop a systematic approach to process. synthesis based mostly on the use of decomposition and heuristic rules (Rudd and... 

Today it is recognized that all three approaches (heuristics-based selection, geometric representation, and optimization methods) are useful, and indeed required, for complex process synthesis strategies. This follows because different applications lend themselves to quite different representations. This volume addresses a variety of these synthesis strategies for process subsystems, but represents only a sampling of the state-of-the-art of process synthesis research. The five chapters in this volume address quite different process subsystems and application areas but still combine basic concepts related to a systematic approach. 

To this sense, conceptual process synthesis plays a key role and constitutes a major approach for process intensification to achieve the multifunctional and microstructured devices. In this work, a systematic methodology based on conceptual process synthesis for process intensification is presented. 

A different approach to process synthesis is offered by means-ends method. It is based on the observation that the purpose of material processing is to apply various operations in such a sequence that the differences in properties between the raw materials and the products are systematically eliminated. As a result, the raw materials are transformed into the desired products. The means-ends method starts with an initial state and successively applies transformation operators to produce intermediate states with fewer differences until the goal state is reached. The hierarchy for the reduction of property differences is as follows identity, amount, concentration, temperature, pressure, and finally form. This property changing method has its limitations, as it ignores the influences and the impacts on other properties. Moreover, the search method takes an opportrmistic approach, which cannot guarantee the generation of a feasible flowsheet. The means-ends analysis approach has been used as a systematic process synthesis method for overall process flowsheet synthesis, as well as for the more detailed case of a separation system to resolve the concentration differences in nonideal systems that include azeotropes. 

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