Analysis means-ends

Heuristic based approaches are more relevant for structured products. The most well known heuristic based approach is the hierarchical decomposition method developed by Douglas (Douglas, 1988). In the first level of this method one only looks at the input-output structure of the process. In subsequent levels more detail is added, finally ending with the entire flowsheet. Design decisions are made by using heuristics and short-cut models. An alternative method is due to Siirola (1996) means end analysis. In this method the properties of the feedstock and the desired products are compared. Tasks are defined to eliminate the property differences between the feedstock and the desired product. 

The method we are using is a combination of the hierarchical decomposition (Douglas, 1988) and means end analysis (Siirola, 1996). The three first stages of... 

One complication is that often property-changing operators can only be applied to a stream when certain other properties of the stream are within specified values, which may not be true at the time. For example, a method to select only crystals greater than a given size can be applied only if a stream contains solids. Similarly, a separation method expected to exploit relative volatility differences can be applied only if enthalpy conditions permit simultaneous liquid and vapor phases. If the preconditions for the immediate application of an operator believed to be useful are not met, a new design subproblem may be formulated whose objective is to reduce property differences between the initial stream and the conditions necessary for the application of the operator. This recursive strategy is a common feature of the means-ends analysis paradigm. 

If the hierarchical means-ends analysis synthesis procedure is applied to the methyl acetate problem, the task identification, task integration, and equipment design stages are kept completely separate. Following the property-difference hierarchy, an identity-changing reaction task (Task A) is identified first, as before. When examining the differences between the result of this reaction task application and the product methyl acetate and by-product water destinations,... 

Branch and bound algorithms Best-first search algorithms Branch-and-cut algorithms Means-ends analysis... 

A different approach to process synthesis is offered by means-ends method. It is based on the observation that the purpose of material processing is to apply various operations in such a sequence that the differences in properties between the raw materials and the products are systematically eliminated. As a result, the raw materials are transformed into the desired products. The means-ends method starts with an initial state and successively applies transformation operators to produce intermediate states with fewer differences until the goal state is reached. The hierarchy for the reduction of property differences is as follows identity, amount, concentration, temperature, pressure, and finally form. This property changing method has its limitations, as it ignores the influences and the impacts on other properties. Moreover, the search method takes an opportrmistic approach, which cannot guarantee the generation of a feasible flowsheet. The means-ends analysis approach has been used as a systematic process synthesis method for overall process flowsheet synthesis, as well as for the more detailed case of a separation system to resolve the concentration differences in nonideal systems that include azeotropes. 

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