Development of the Base-Case Design

Finally, before leaving this section on preliminary process synthesis, the limitations of the heuristic approaches should not be overlooked. Many algorithmic methods are very effective for the synthesis of alternative flowsheets, their analysis, and optimization. These methods are usually used by design teams in parallel with their work on the development of the base-case design, which is the subject of the next section. The algorithmic methods are easily implemented and are illustrated with many examples in Part Two of this text (Chapters 6-12). 

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Throughout Chapters 1 and 3, the role of die process simulators is deemphasized. Rather, emphasis is placed on the steps in process synthesis and the development of the base-case design. Although from time to time these chapters refer to simulation results, a formal discussion of the role of process simulators during process creation is not attempted until Chapter 4 (and the accompanying multimedia CD-ROM). Chapter 3 introduces the steps in process synthesis without discussing many of the key heuristics used in making decisions. A more formal treatment is reserved for Chapter 5. 

As mentioned in Section 3.5, Development of the Base-Case Design, the simulatioi model prepared for the complete process is often the source of the stream conditions in thi PFD (e.g.. Figure 3.19). Furthermore, as the design team completes the process integratioi step, the model can be improved to represent the more complete PFD. 

The user can use the mechanism in the following way. First, he or she develops the base-case design which does not violate any process constraints. Then, the user improves the base-case design in the evolutionary manner by relaxing the decisions that look relatively promising in terms of contribution to the economic potential of the process flowsheet. Suppose we are working on the recycle structure level and we find one design... 

As shown in Figure 1.2, in developing a base-case design, the design team checks regularly to confirm that the process remains promising. When this is not the case, the team often returns to one of the steps in process creation or redevelops the base-case design. 

Hydrodealkylation of toluene is a process where toluene is converted into benzene by reaction with hydrogen, forming Diphenyl as a byproduct. This is a well known process, which has been studied in numerous publications. The reference design and flowsheet considered in this paper are taken from Seider et al. (1999), where further details can be found. The necessary steady state simulations have been performed with a commercial process simulator, from where the results have been transferred to a software developed for this work to calculate the indicator values. The steady state simulation results are also transferred to ICAS (ICAS Documentation, 2002) to determine the environmental impact factors, the sustainability metrics and the safety factors. Table 1 shows the most important indicator-values from the base case design. A detailed calculation results document can be obtained from the corresponding author. 

Often, chemical plant design is informed by laboratory and pilot-scale experimentation. While the initial chapters in this book will inform the reader of the most important design parameters that need to be measured and determined from such experiments, how to then ensure that these parameters perform in the same way in a large-scale plant is the subject of Chapter 6. Although it is desirable to conduct the experimental work in the system for which the results are required, this is not always easy. The system of interest may be hazardous or expensive to build and run, while the fluids involved may be corrosive or toxic. In this case scale models are used, which overcome the above problems and allow extensive experimentation. In the majority of cases the model will be smaller in size than the actual, desired plant, but sometimes, due to the nature of the materials to be handled, the fluids involved may also be different. Scale-up is only possible if the model and plant are physically similar and, hence, the procedure is based on dimensionless groups. How to develop and use these groups is described in Chapter 6. 

The case studies cover key applications in chemical process industries, from petrochemistry to polymers and biofuels. The selection of processes was confronted with the problem of availability of sufficient design and technology data. The development of the flowsheet and its integration is based on employing a systems viewpoint and systematic process synthesis techniques, amply explained over three chapters. In consequence, the solution contains elements of originality, but in each case this is compared to schemes and economic indices reported in the literature. 

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