Heat exchanger network target cold streams

The analysis of the heat exchanger network first identifies sources of heat (termed hot streams) and sinks (termed cold streams) from the material and energy balance. Consider first a very simple problem with just one hot stream (heat source) and one cold stream (heat sink). The initial temperature (termed supply temperature), final temperature (termed target temperature), and enthalpy change of both streams are given in Table 6.1. 

The pinch analysis method provides the targets for the Heat Exchange Network (HEN) designs of the examined process. This HEN design problem is complex and involves combinatorial problems in the pairing between the hot and cold streams to enhance the heat recovery [28]. HEN design is one of the most fundamental activities in the process design procedure as it is considered as sub-synthesis problem of the overall synthesis problem. 

Given a number Nh of process hot streams (to be cooled) and a number Nq of process cold streams (to be heated), it is desired to synthesize a cost effective network of heat exchangers which can transfer heat from the hot streams to the cold streams. Given also are the heat capacity (flowrate x specific heat) of each process hot stream, FCp u, its supply (inlet) temperature, and target (outlet) temper-... 

Masso and Rudd (1969), Lee, Masso and Rudd (1970) and Pho and Lapidus (1973) start a match with the two stream inlet conditions and exchange all the heat possible, terminating when one stream reaches its target outlet temperature or when a temperature pinch occurs. Ponton and Donaldson (1974), Donaldson, Paterson and Ponton (1976) and Grossmann and Sargent (1978) start a match at the hot end of both streams (or as close to the hot end of the cold stream as possible). The idea is to introduce necessary utilities at their least cost level while exchanging as much heat as possible. Rathore and Powers (1975) do both, getting two alternative matches and obviously many more alternative networks. 

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. ... 

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