Heating 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. 

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

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. 

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 ... 

Galvanic corrosion can be controlled by the use of sacrificial anodes. This is a common method of controlling corrosion in heat exchangers with Admiralty tube bundles and carbon steel tube sheets and channel heads. The anodes are bolted direcdy to the steel and protect a limited area around the anode. Proper placement of sacrificial anodes is a precise science. 

Operating Temperature and Pressure Arresters are certified subject to maximum operating temperatures and absolute pressures normally seen at the arrester location. Arrester placement in relation to heat sources, such as incinerators, must be selected so that the allowable temperature is not exceeded, with due consideration for the detonation potential as run-up distance is increased. 

Incorrect information can result if the probe is made of the wrong material and is not heat treated in the same way as the process equipment (as well as because of other problems). The probe must be as close as possible to the material from which the equipment of interest is made. Existence of a critical condition, such as weldments or galvanic couples or occluded cells in the eqmpment of concern, makes the fabrication, placement, and maintenance of the probes and monitoring system or critical importance, if accurate and useful data are to be obtained. 

Incoming radiation from the sun is dependent on the size, type, placement, and shading of windows (and placement of the building), and the subsequent heating or cooling of surfaces can change the air distribution in the room. 

Equipment and supplies should be placed in the enclosure before a contaminant-generating procedure commences. Unnecessary equipment should be removed. High-input heat sources within an enclosure will cause convection currents that can disturb the flow and should be avoided, if possible, or accounted for with correct placement of baffles and/or exhaust connections. 

Figure 10-167. Tracer placement on pipe using heat transfer cement. (Used by permission Bui T-109M 1994. Thermon Co./Cellex Div.)...

P-plastomers are semicrystalline, elastomeric copolymers composed predominantly of propylene with limited amounts of ethylene [21]. The concentration of ethylene is typicaUy less than 20 wt%. The placement of the propylene residues is predominantly in a stereoregular isotactic manner. This leads to the crystallinity (which is critical) in the copolymer. The extent of the crystallinity is attenuated by errors in the placement of the propylene and by the incorporation of ethylene. These two strucmral feamres contribute to lower the crystallinity, as measured by the heat of fusion, to less than 40 J g . Copolymers of propylene and ethylene, which have higher levels of crystallinity are... 

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