Appropriate Placement

Thus the appropriate placement of heat pumps is that they should be placed across the pinch. Note that the principle needs careful interpretation if there are utility pinches. In such circumstances, heat pump replacement above the process pinch or below it can be economic, providing that the heat pump is placed across a utility pinch. Such considerations are outside the scope of the present text. 

A refrigeration system is a heat pump in which heat is absorbed below ambient temperature. Thus the appropriate placement principle for heat pumps applies in exactly the same way as for refrigeration cycles. The appropriate placement for refrigeration cycles is that they also should be across the pinch. As with heat pumps, refrigeration cycles also can be appropriately placed across utility pinches. It is common for refrigeration cycles to be placed across a utility pinch caused by maximizing cooling water duty. 

Linnhoff, B., and de Leur, J., Appropriate Placement of Furnaces in the Integrated Process, IChemE Symp. ries No 109, 1988. 

There is no obvious benefit from integrating an exothermic reactor below the pinch. The appropriate placement for exothermic reactors is above the pinch. ... 

The preceding appropriate placement arguments assume that the process has the capacity to accept or give up the reactor heat duties at the given reactor temperature. A quantitative tool is needed to assess the capacity of the background process. For this purpose, the grand composite curve can be used and the reactor profile treated as if it was a utility, as explained in Chap. 6. 

The appropriate placement of reactors, as far as heat integration is concerned, is that exothermic reactors should be integrated above the pinch and endothermic reactors below the pinch. Care should be taken when reactor feeds are preheated by heat of reaction within the reactor for exothermic reactions. This can constitute cross-pinch heat transfer. The feeds should be preheated to pinch temperature by heat recovery before being fed to the reactor. 

Appropriate placement can be assessed quantitatively using the grand composite curve. The streams associated with the reactor can be represented as a grand composite curve for the reactor and then matched against the grand composite curve for the rest of the process. 

Rgure 14.1 The appropriate placement of distillation columns. (From Smith and Linnhoff, Trans. IChemE, ChERD, 66 195, 1988 reproduced by permission of the Institution of Chemical Engineers.)... 

All these arguments can be summarized by a simple statement The appropriate placement for distillation is not across the pinch. ... 

The appropriate placement principle can only be applied if the process has the capacity to give up or accept the required heat... 

The appropriate placement of distillation columns when heat integrated is not across the pinch. The grand composite curve can be used as a quantitative tool to assess integration opportunities. 

The concept of the appropriate placement of distillation columns was developed in the preceding chapter. The principle also clearly applies to evaporators. The heat integration characteristics of distillation columns and evaporators are very similar. Thus evaporator placement should be not across the pinch. ... 

It was noted earlier that dryers are quite difierent in character from both distillation and evaporation. However, heat is still taken in at a high temperature to be rejected in the dryer exhaust. The appropriate placement principle as applied to distillation columns and evaporators also applies to dryers. The plus/minus principle from Chap. 12 provides a general tool that can be used to understand the integration of dryers in the overall process context. If the designer has the freedom to manipulate drying temperature and gas flow rates, then these can be changed in accordance with the plus/minus principle in order to reduce overall utility costs. 

The appropriate placement of the major items of equipment in relation to the heat recovery pinch is as follows ... 

Gases may be added above or below the liquid surface by appropriate placement of a fritted-glass gas delivery tube in a rubber gasketed adapter (Fig. A3.5). 

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