Process synthesis hierarchical approaches

The flowsheet synthesis of continuous chemical-like process can be performed following a systematic strategy known as the hierarchical approach. The procedure, initially proposed by Jim Douglas and coworkers in the decade 1980-90 [1, 2], describes the conceptual design process as a logical sequence of analysis and synthesis steps grouped in levels. Each level involves a flowsheet development mechanism based on design decisions. The result is not a unique solution but a collection of alternative flowsheets from which an evaluation procedure eliminates the less attractive ones. 

Process Synthesis by Hierarchical Approach (c) Formation of byproducts and impurities... 

Process Synthesis by Hierarchical Approach Table 2.1 Heuristics at input/output level. 

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). 

Consider the following industrial example of a process for the production of methyl acetate, first synthesized in the conventional conceptual process design manner, then modified using evolutionary approaches, and finally resynthesized using the lessons from the hierarchical process synthesis procedure experience. For simplicity here, only identity, amount, and composition differences are resolved (that is, temperature and pressure changers will be ignored). 

II. Hierarchical Approach to the Synthesis of Chemical Processing Schemes A Computational Model... 

Siirola, J.J. Strategic process synthesis advances in the hierarchical approach. Comput. Chem. Engng 1996, 20, S1637-SI643. 

Hierarchical Approach is a methodological frame for the conceptual synthesis of process systems. The overall strategy is organised in a number of levels, each level being decomposed in a number of tasks. The approach presented below is organised in eight levels as follows (Douglas and Stephanopoulos, 1995) ... 

Hierarchical Approach is a simple but powerful methodology for the synthesis of process flowsheets. It consists of a top-down analysis organised as a clearly defined sequence of tasks grouped in levels. Each level solves a fundamental problem as, number of plants, input/output structure, reactor design and recycle structure, separation system, energy integration, environmental analysis, safety and hazard analysis, and plantwide control. At each level, systematic methods can be applied for the synthesis of subsystems, as chemical reaction, separations, or heat exchangers network. 

Ogunnaike, B., W. H. Ray, 1998, Modelling and Process Control, Academic Press Ponton, J. W., D. M. Liang, 1993, Hierarchical approach to the design of process control system, Chem. Eng. Res. Des., 70, 181 Seider, W. D., J. D. Seader, D. R. Lewin, 1999, Process Design Principles Synthesis, Analysis and Evaluation, Wiley... 

As mentioned, the process synthesis section should retrace the rationale of flowsheet development by applying the Hierarchical Approach, as explained in Chapter 7. Deviations from the standard flowsheet are encouraged. This is necessary because often the flowsheets described in the open literature are either oversimplified or being based design decisions that could be not longer valid in the context of the actual design. 

---