Minimum number of heat exchangers in network

Zinin Minimum number of heat exchangers in network —... 

In summary, six heat exchangers is the minimum for this network when it is required that the hot and cold utilities be minimized as well. As discussed in Section 10.4, the minimum number of heat exchangers for this system is five, which can be achieved either by breaking heat loops, usually at the price of exceeding the MER targets, or by stream splitting. ... 

In a more general result, Douglas (1988) shows that the minimum number of heat exchangers is also dependent on the number of independent networks, Nnw that is, the number of sub-networks consisting of linked paths between the connected streams ... 

The final heat-exchanger network is shown in Figure 15.8. The exchangers are represented by single circles, with fluid flowing through both sides. This network has the minimum number of heat exchangers. 

Step (i) was proved in Appendix A of Floudas et al. (1986), and hence the minimum number of matches predicted by the MILP transshipment model can always be represented with an equal number of heat exchanger units in a feasible HEN network. 

To understand the minimum number of matches or units in a heat exchanger network, some basic results oigraph theory can be used. A graph is any collection of points in which some pairs of points are... 

Ahmad, S., and Smith, R., Targets and Design for Minimum Number of Shells in Heat Exchanger Networks, IChemE, ChERD, 67 481, 1989. 

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. 

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).

Figure F.l Within each enthalpy interval it is possible to design a network in (S — 1) matches. (From Ahmad S and Smith R (1989) Targets and Design for Minimum Number of Shells in Heat Exchanger Networks, IChemE, ChERD, 67 481, reproduced by permission of the Institution of Chemical Engineers.)...

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