Onion diagram

All too often safety and health (and environmental) considerations are left to the final stages of the design. Returning to the hierarchy of design illustrated by the onion diagram in Fig. 1.6, such considerations would add another layer in the diagram outside the utilities layer. This approach leaves much to be desired. 

The two inner layers of the onion diagram in Fig. 1.6 (the reaction and separation and recycle systems) produce process waste. The process waste is waste byproducts, purges, etc. 

This hierarchy can be represented symbolically by the layers of the onion diagram shown in Figure 1.76. The diagram emphasizes the sequential, or hierarchical, nature of process design. Other ways to represent the hierarchy have also been suggested4. 

A number of experimental chemical process synthesis procedures have been developed with a hierarchical architecture based on both the hierarchical structure of the chemical innovation process and the physical property hierarchy. Examples include PIP (Kirkwood et al, 1988) and BALTAZAR (Mahalec and Motard, 1977). This hierarchical approach is also evident in the Pinch Technology Onion Diagram (Linnhoff and Ahmad, 1983). The hierarchical approach is also the foundation for the two early textbooks on process synthesis methodology (Rudd et al, 1973 Douglas, 1988). 

Figure 1.9 Hierachical description of process design by the Onion diagram...

The traditional process design approach can be described by the so called Onion Diagram as shown in Figure 11.1, which provides an overall view of energy considerations throughout the traditional design procedure. 

In short, the traditional design approach adopts a sequential design approach. In contrast, the process integration methodology for process design takes a different approach in that process design aspects in the inner part of the onion diagram are... 

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