16 - Minimum number of units (MNU) and minimum total surface area (MTA) targets

Abstract

Targeting approaches for a minimum number of units and minimum total surface area have to account for types of heat exchangers applied. In this chapter, problem of minimum number of matches (MNM) target is formulated and solved. Matches with a single residual stream and two residual streams are interpreted graphically. Minimum total area for matches (MTA-m) target is discussed as developed by Townsend and Linnhoff. Bath formula to calculate total minimum surface area is derived and then analyzed. Illustration of diverse pinch concept is given, as adopted in methods for targeting and designing HEN. Minimum number of shells (MNS) target is characterized in terms of first methods from pinch technology. By considering minimum total area for shells (MTA-s) target we proceed toward explaining approaches for the minimum surface area target for multi-shell apparatus (MTA-s). It is concluded that the bath formula with the so-called spaghetti structure gives targets substantially larger than those found from rigorous approaches. Diverse pinch method does not produce reliable results and, in fact, its accuracy is similar to bath approach. The method of Jeżowski et al. (2003e) is shown to give the results that differ less than 1% from rigorous data from Colberg and Morari (1990), and are of similar accuracy as NLP approach.