Placement

ASHRAE 55, Thermal Environmental Conditions for Human Occupancy. This standard covers several areas, including temperature, humidity, and air movement. Important aspects of the standard include the definition of acceptable thermal comfort. It provides information on environmental parameter considerations. The standard makes recommendations for summer and winter comfort zones for humidity and temperature. It also contains guidelines for conducting measurements. 

ASHRAE 62, Ventilation for Acceptable Air Quality This standard can assist professionals in the proper design of building ventilation systems. Important aspects of the standard include the definition of acceptable air quality and information about ventilation effectiveness. It makes a recommendation about using source control through isolation and local exhaust. The standard also contains information on the use of heat recovery ventilation and provides a guideline for allowable carbon dioxide levels. 

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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. 

Now consider the placement of the reactor in terms of the overall heat integration problem. 

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 stream data in Fig. 13.6 include those associated with the reactor and those for the rest of the process. If the placement of the reactor relative to the rest of the process is to be examined, those streams associated with the reactor need to be separated from the rest of the process. Figure 13.7 shows the grand composite curves for the two parts of the process. Figure 13.7b is based on streams 1, 2, 6, and 7 from Table 13.1, and Fig. 13.7c is based on streams 3, 4, 5, 8, 9, 10, and 11. 

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 ... 

Current requirements for vehicles are more pronounced for warm conditions than for cold for many reasons e.g., improved aerodynamics, transversal placement of the motor, generally higher temperatures under the hood, such that the automobile manufacturers prefer a reduction, rather than increase in RVP. 

Plug back cementations, i.e. cement placement inside the casing and across the perforations may be required prior to sidetracking a well or in the course-of abandonment. 

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