Economics hierarchical approach

At each level of the Hierarchical Approach the feasibility of design alternatives are evaluated by means of an Economic Potential (EP). This index is a measure of profitability representing the difference between earnings and expenses on yearly basis. EP must be high enough to accept further reduction at the other levels of flowsheet development. If EP is not positive and high enough, the analysis stops. It is worthy to note that the raw material costs dominate the operation costs in chemical process industries by more than 60%, particularly in commodities. 

The assumption here is that unexamined aspects are neutrally affected by changes in the process described, but if tradeoffs were created a decision maker would have to decide the relative importance of process attributes [4]. An example to show the sustainabdity-based hierarchical approach will be presented next, using chlor-alkali production with a focus on economics and human toxicity potential. 

Heuristic methods were developed by well-experienced engineers and researchers. The first attempt to develop a systematic heuristic approach for the synthesis of multicomponent separation sequences was made by Siirola and Rudd. Common example is hierarchical heuristic approach.Heuristic rules are applied at five design levels to generate and evaluate the alternatives using economic criteria. The hierarchical heuristic method emphasizes the strategy of decomposition and screening. It allows for a quick location of flowsheet structures that are often near ... 

This paper describes an integrated MINLP synthesis of overall process schemes using a combined synthesis / analysis approach. The synthesis is carried out by a multilevel-hierarchical MINLP optimization of the flexible superstructure, whilst the analysis is performed in an economic attainable region (EAR). The role of the MINLP synthesis step is to obtain a feasible and optimal process structure, and the role of the subsequent EAR analysis step is to verify the MINLP solution and to propose in the feedback loop, any profitable superstructure modifications for the next MINLP. The main objective of the integrated synthesis is to exploit interactions between the reactor network, separator network and the remaining part of the heat/energy integrated process scheme. 

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