Energy targets

Heat Exchanger Network and Utilities Energy Targets... 

Figure 6.7 The composite curves set the energy target and the location of the pinch.

In other words, to achieve the energy target set by the composite curves, the designer must not transfer heat across the pinch by... 

Flgum 6.9 A design that achieves the energy target. 

This shifting technique can be used to develop a strategy to calculate the energy targets without having to construct composite curves ... 

Most constraints can be evaluated by scoping the problem with different boundaries, as illustrated in Example 6.2. If this approach cannot be applied, then mathematical programming must be used to obtain the energy target. ... 

Although the composite curves can be used to set energy targets, they are not a suitable tool for the selection of utilities. The grand composite curve is a more appropriate tool for understanding the interface between the process and the utility system. It is also, as is shown in later chapters, a useful tool for study of the interaction between heat-integrated reactors and separators and the rest of the process. 

The energy cost of the process can be set without having to design the heat exchanger network and utility system. These energy targets cam be calculated directly from the material and energy balance. Thus... 

In Chap. 10, modification of the process for reducing process waste was considered in detail. It also was concluded that to minimize utility waste, the single most effective measure would be improved heat recovery. The energy-targeting methods presented in Chaps. 6 and 7 maximize heat recovery for a given set of process conditions. However, the process conditions can be changed to improve the heat recovery further. 

Figure 14.9 The composite curves after process modifications shows a much reduced energy target. (From Smith and Linnhoff, Trans. IChemE, ChERD, 66 195, 1988 reproduced by permission of the Institution of Chemical Engineers )...

Having decided that no exchanger should have a temperature difference smaller than ATmi, two rules were deduced. If the energy target set by the composite curves (or the problem table algorithm) is to be achieved, there must be no heat transfer across the pinch by... 

Following this approach, the design is straightforward, and the final design is shown in Fig. 16.176. It achieves the energy targets... 

These rules are both necessary and sufficient for the design to achieve the energy target, given that no individual exchanger should have a temperature difference smaller than ATnin-... 

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