The Targeting Approach

The targeting approach is based on the identification of performance targets ahead of design and without prior commitment to the final network configuration. In the context of synthesizing MENs, two useful targets can be established  

Minimum number of mass exchanger units. Combinatorics determines the minimum number of mass exchanger units required in the network. This objective attempts to minimize indirectly the fixed cost of the network, since the cost of each mass exchanger is usually a concave function of the unit size. FuithetTnore, in a practical context it is desirable to minimize the number of separators so as to reduce pipework, foundations, maintenance, and instrumentation. Normally, the minimum number of units is related to the total number of streams by the following expression (El-Halwagi and Manousiouthakis, 1989). 

In general, these two targets are incompatible. Later, systematic techniques will be presented to enable the identifying an MOC solution and then minimizing the number of exchangers satisfying the MOC. 

A pmticularly useful concept in synthesizing MENs is the notion of c( tespond-ing composition scales. It is a tool for incorporating diermodynamic constraints 

CHAPTER THREE Synthesis Of mass-exchange networks 

It is important to rive the mathematical expession relating y,- and Xj on the practical-feasibility line. For a given y,, the v ues of xj can be obtained by evaluating x that is in equilibrium with y then subtracting cy, i.e.. 

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The optimization component of process integration drives the iterations between synthesis and analysis toward an optimal closure. In many cases, optimization is also used within the synthesis activities. For instance, in the targeting approach for synthesis, the various objectives are reconciled using optimization. In the structure-based synthesis approach, optimization is typically the main framework for formulating and solving the synthesis task. 

As has been mentioned in Section 3.4, the targeting approach adopted for synthesizing MENs attempts to first minimize the cost of MSAs by identifying the flowrates and outlet compositions of MSAs which yield minimum operating cost MOC . This target has been tackled in Chapter Three as well as in the foregoing sections in this chapter. The second step in the synthe.sis procedure is to minimize... 

Immediately after these responses were noted, the robot was positioned closer to the target, approaching to a distance of approximately one foot downcurrent from the source. The response at this position is indicated in Figure 6.10. 

In this chapter, we will focus on the potential of metabolomics to detect these unintended effects. This method enables the analysis of the overall metabolite composition employing some of the traditional analytical techniques used for the targeted approach. These include GC and... 

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