Flowsheet integrated process design

Process synthesis by superstructure optimization consists of the identification of the best flowsheet from a superstructure that considers many possible alternatives, including the optimal one. A substantial advantage is that integration and design features may be considered simultaneously. At today s level of software technology the superstructure optimization is still an emerging technique. However, notable success has been achieved in numerous applications. The reference in this field is the book of Biegler et al. [6]. 

In order to support the central role of flowsheets during engineering design, we have implemented a prototypical flowsheet-centered architecture (Fig. 3.7). The central element of this architecture is the VISIO based flowsheet editor that, based on the PRIME process integration mechanism, is operationally linked to other domain-specific tools and acts as the prominent communication medium among developers. 

As a (very simple) example, we consider the flowsheet in Fig. 4.2. The flowsheet has been designed in the process-integrated flowsheet editor that forms part of the PRIME environment (cf. Subsect. 3.1.3). The simulation model for the reactor device (CSTR - continuous stirred tank reactor) is already given. The developer s task is to find a suitable model to represent the separation. The designer can choose between several separation models, including complex combinations with recycle streams (backflows). 

All in all, the flowsheet editor FEW is a promising new approach to chemical process design in the early stages because it offers new, meaningful functions and integrates different tools. However, without improving the interaction-related usability issues, the task-related new concept cannot be evaluated in a realistic scenario with experienced chemical process engineers. 

The current practice has shown that there is a gap between process and control engineers. Filling this gap is a challenge for education. Only very recently plantwide controllability issues have been included in a book dealing with process design (Seider, Seader Lewin, 1999). This chapter aims to give another perspective on the same subject, with emphasis on integrating controllability aspects in flowsheet synthesis. 

Process plants can be represented by means of subsystems, called basic flowsheet structures (BPS). These can interact through material and energy streams. This representation reveals two steps for integrating conceptual design and plantwide control design controllable BFS s, and couple the BFS s in such a way that a controllable system is obtained. 

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