Heat exchanger network utility pinch

Example 16.1 The process stream data for a heat recovery network problem are given in Table 16.1. A problem table analysis on these data reveals that the minimum hot utility requirement for the process is 15 MW and the minimum cold utility requirement is 26 MW for a minimum allowable temperature diflFerence of 20°C. The analysis also reveals that the pinch is located at a temperature of 120°C for hot streams and 100°C for cold streams. Design a heat exchanger network for maximum energy recovery in the minimum number of units. 

Determine the pinch temperatures and the minimum utility requirements for the streams set out in the table below, for a minimum temperature difference between the streams of 20°C. Devise a heat exchanger network to achieve the maximum energy recovery. 

Figure 4.53 shows a possible matching between the hot and cold streams starting from the hot utility above the pinch. Based on these matchings, Figure 4.54 shows a heat exchanger network system. As there are a total of four hot and cold streams and a total of two hot and cold utility streams, from Eq. (4.233) we learn that we need a minimum of five heat exchangers. In the network, hot stream H2 is split into two. H2a has 58.1% of the hot stream H2 and heats the cold stream Cl, while H2b heats the cold stream C2. 

The pinch decomposition is very useful in heat exchanger network design, as it decomposes the problem into two smaller problems. It also indicates the region where heat transfer matches are most constrained, at or near the pinch. When multiple hot or cold utilities are used, there may be other pinches, termed utility pinches, that cause further problem decomposition. Problem decomposition can be exploited in algorithms for automatic heat exchanger network synthesis. 

Composite Curves enable to determine directly the Minimum Energy Requirements (MER) from stream data without ever calculate heat exchangers. These are the minimum hot d minimum cold utility required for driving the heat exchanger network, with a minimum driving force of AT at Pinch. 

III. Heat/Process Integration Study Pinch analysis is well established for finding optimal utilities, heat transfer area, optimal fresh water consumption, minimum cooling water demand, reduced emissions targets and so on (Smith, 2005 Kemp, 2007). One application of pinch analysis to retrofitting the heat exchanger network of a crude... 

It was shown earlier that some problems do not possess a pinch condition. For these cases, only one utility (hot or cold) is required. This situation is illustrated on the tenperature enthalpy diagrams in Figure 15.10. In Figure 15.10ral. the typical heat-exchanger network problem containing a pinch is shown. If the minimum approach temperature is reduced, then the conposite enthalpy curve for the cold streams (at the bottom) moves to the left and becomes closer to the hot stream conposite enthalpy curve. For the problem shown in Figure 15.10(bl. there exists a critical value for the minimum tenperature approach, which the hot utility requirement (Q ) becomes zero and the cold utility... 

The cascade diagram is shown in Figure E15.10(b). Just as in heat-exchange networks, excess mass is cascaded through each interval. In this example, there is no pinch. At the bottom of the cascade diagram, there is excess mass requiring a lean utility (LU). An LU is a different separation unit, such as an adsorber, that removes solute. 

Determine a heat-exchange network below the pinch that has only one utility exchanger. 

AIChE (American Institute of Chemical Engineers) Chemical Professional s Code of Conduct, 831. 832-833 Coffey stills, 92 Colburn equation, 636-639 Cold utilities, HENs (heat-exchanger networks) minimizing, 529-530 minimum approach temperature, 526 multiple utilities, 558 pinch points, 529-530 Cold zones, 712. 714... 

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