Grid diagram

Figure 16.1 The grid diagram for the data from Table 6.2.

Figure 16.4a shows the grid diagram with a CP table for design above the pinch. Cold utility must not be used above the pinch, which means that hot streams must be cooled to pinch temperature by recovery. Hot utility can be used, if necessary, on the cold streams above the pinch. Thus it is essential to match hot streams above the pinch with a cold partner. In addition, if the hot stream is at pinch conditions, the cold stream it is to be matched with must also be at... 

Figure B.l shows a pair of composite curves divided into vertical enthalpy intervals. Also shown in Fig. B.l is a heat exchanger network for one of the enthalpy intervals which will satisfy all the heating and cooling requirements. The network shown in Fig. B.l for the enthalpy interval is in grid diagram form. The network arrangement in Fig. B.l has been placed such that each match experiences the ATlm of the interval. The network also uses the minimum number of matches (S - 1). Such a network can be developed for any interval, providing each match within the interval (1) satisfies completely the enthalpy change of a strearh in the interval and (2) achieves the same ratio of CP values as exists between the composite curves (by stream splitting if necessary).

The streams (including utilities) are drawn in a grid diagram which shows the intervals, their Nk values, and the pinch location. 

Figure 18.4b shows the grid diagram with CP-table for the design below the pinch. Hot utility must not be used below the pinch, which means that cold streams must be heated to pinch temperature by heat recovery. Cold utility... 

It is now seen why the grid diagram contains the column at j = —1 that value of R is needed in order to get the four coefficients from U DERIV at R = 0 A concentration value on this column need never be referred to. 

Figure 10.2 Targeting of energy and capital costs before HEN design Grid Diagram...

Figure 10.3 The Grid Diagram enables to develop the Heat Exchanger Network Appropriate Placement...

Balanced composite curves are similar with those discussed above, with the difference that now the utilities are considered as streams. Since the utilities covers any imbalance between the streams selected for integration, the enthalpy balance is closed. Moreover, the design of the heat exchangers is done in the balanced grid diagram. 

The design of the Heat Exchanger Network takes place in the balanced grid diagram. This means that the utilities have been placed on the Grand Composite Curve. As illustrated by the Fig. 10.3, the hot streams run from left to right at the top, and cold streams run counter-currently at the bottom. 

Consider the streams given in the Table 10.1. Develop the Heat Exchanger Network in a grid diagram for Minimum Energy Requirements. 

Solution. Figure 10.27 presents the grid diagram, on which stream supply and target temperatures, as well as the CP s are marked. In Example 10.2 the Pinch was located at 130-140 °C for ATC = 10 °C. We recall that the heat loads of streams were ... 

Solution. Figure 10.34 presents the grid diagram. We notice that there is only a cold stream, but three hot streams including the hot utility. There is no process Pinch. However, we may consider a utility Pinch on the cold side. In this case we select =15 C, a lower value that the threshold of 20 °C, as calculated in the Example 10.2. Hence, we are at the left of the cold utility Pinch. 

Another application is the split of streams at Pinch in order to fulfil the feasibility criteria of matches. Some insights can be obtained from the grid diagram. However, the exact split fraction is a typical optimisation problem. The same is valid for splitting streams far from Pinch. Note that bypasses of streams around heat exchangers can be used for temperature control. 

Pinch analysis is a method of assessing the works infrastructure of production plants and supply systems with respect to energy consumption, quantities of waste products, quantities of emissions, and capital costs. The fundamental elements of pinch analysis are the composite curves, the grid diagram, and the pinch itself. 

The pinch represents the boundary between the balanced heat sources (system below the pinch) and heat sinks (system above the pinch). In the optimum case, no heat transfer occurs across the pinch. The grid diagram (Fig. 59) is used in the development of economical heat recovery systems using the pinch technology. 

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