Hierarchical design process

Douglas, J. M., A Hierarchical Design Procedure for Process Synthesis, AlChEJ, 31 353, 1985. 

A hierarchical design procedure for process synthesis can be used in conjunction with a flow-sheeting program to analyze, evaluate, and optimize the options (60). The emphasis is on starting with the simplest possible models that will give answers to a particular question quickly so that the questions to be asked at the next decision level can be formulated. At each stage, it is necessary to ensure that the level of detail in the model is sufficient to give rehable information. 

Rossiter and Douglas (1986) state that the first step in process design is to generate a basic structure for the flowsheet i.e. the choice of unit operations and interconnections which can be analysed, refined and costed, and then compared to alternatives. Thus, the generation of an industrial crystallization flowsheet gives rise to a number of optimization problems for which a systematic hierarchical decision process for particulate systems was proposed ... 

Mesoporous silica containers can be used as inhibitor hosts with controlled release properties triggered at the beginning of the corrosion process in response to local pH changes. For instance, mesoporous silica nanoparticles covered with polyelectrolyte layers can be loaded with an inhibitor (2-(benzothiazol-2-ylsulfanyl)-succinic acid) prior to introduction into a hybrid zirconia-silica sol-gel film. This hierarchical design avoids spontaneous release of the inhibitor by the formation of a polyelectrolyte shell over the container s outermost surface. 

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. 

Formally, the hierarchical design procedure can be divided in two steps process synthesis and process integration. The first deals with the synthesis of the process flowsheet and basic material balance. The second step handles the problem of efficient use of energy and helping material resources (water, solvents, hydrogen). Clearly, the two steps are interrelated. 

Stephanopoulos et al., 1994). It provides a well-defined structure of how the synthesis of conceptual processing schemes proceeds from very abstract, vague, and incomplete to fairly detailed, exact, and quite complete flowsheets. However, when it was developed, it was not intended to be a computational model for the design process itself. As a result, it lacks the requisite formalism and representational exactness needed for the construction of a computational process. In this section, we will provide a formalized restatement of the hierarchical procedure, in an effort to cast it more closely to a computational process for its computer-based automation. 

The overall design methodology was modeled as a hierarchical planning process. It starts with project specifications, goes through a predefined set of intermediate design milestones, and ends with a number of design alternatives. 

The Douglas hierarchical design decision procedures for analyzing flowsheets, particularly in the design of new processes ... 

In this chapter, emphasis is placed on the former approach of pinch technology. It is noteworthy that the mass integration concept incorporates the use of both approaches. Also, a notable work that combines the three approaches of hierarchical design via process simulation using the Aspen Plus commercial simulator, pinch technology, and mathematical programming is that of Dantus and High. ° ... 

The most ambitious scientific problem to be solved by IMPROVE - in other words the key topic of this project - is to develop a comprehensive and formal process/product model for design processes. The importance of this model, its appearance across different layers, its hierarchical structure in every layer, and the mapping between different layers were already introduced in Sect. 1.1. 

We already discussed that the PPM should be structured into different layers, from application domain models to platform models (cf. Fig. 1.6). On every layer, there is a complete description of the product, i.e. the result of the design process overall configuration). Trivially, we find hierarchies on every layer. In top-down direction, from layer to layer, the number of details is growing. The model is transformed from layer to layer, from an explicit model to more implicit descriptions (code). The product is complemented by the associated design proce.s.s on every layer. Like the product, the process is hierarchically structured. An abstract process model is transformed into tool commands and corresponding code. 

Smith RL. Hierarchical design and evaluation of processes to generate waste-recycled feeds. Ind Eng Chem Res 2004 43 2508-15. 

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