THE SYNTHESIS AND EVOLUTION OF NETWORKS OF HEAT EXCHANGE THAT FEATURE THE MINIMUM NUMBER OF UNITS

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Abstract
An important problem in the design of chemical processes is that of bringing process streams from their temperatures of availability to the temperatures at which they are needed without undue cost. An important strategy for reducing the cost of doing this is heat recovery: Using the heat available from streams to be cooled to service streams to be heated. In the absence of nonthermodynamic constraints, it is not difficult to assess the amount of heal recovery possible; and methods have been proposed (Linnhoff and Flower, 1978) that allow full heat recovery to be systematically obtained. The networks to which these methods lead are, however, more complex than necessary. Typically, therefore, those methods have been augmented with techniques for the evolutionary development of the initial network in order to simplify its structure, usually by minimizing the number of “matches” between streams. The present work proposes a simple method for exploiting features of maximally simple networks (those that have as few “matches” as possible) in order to design, with greatly reduced effort, such a network that features a high (typically complete) degree of heat recovery. Further exploitation of those features allows a simple method of evolutionary development that makes it possible, in a very few evolutions, to improve the initial network as much as the data allow. Unlike the other methods offered, the present ones are not hindered by the presence of nonthermodynamic constraints (practicality, safety, operability). Their generality and enhanced simplicity make them, more than any others, applicable in an industrial context. Although intended for application by hand, they lend themselves admirably to computer implementation, especially in an interactive mode. These methods are demonstrated on the standard test examples and prove themselves powerful.