Hidden and pseudo pinch phenomena and relaxation in the synthesis of heat-exchange networks

Abstract

Based on the pinch point method and a modification of the fast algorithm a new combined strategy is proposed for completing the synthesis of heat-exchange networks. To avoid the violation of minimum energy consumption and the assignment of overcomplicated structures, two new types of pinch situation (hidden and pseudo pinches) are distinguished and two new rules suggested. The total allowable heat load, determined iteratively, assures minimum energy consumption. The minimum heat load, as an arbitrary parameter, limits the exchangers' size and thus avoids the synthesis of overparcelled countercurrent cascades (too many, small, exchangers). The synthesis of heat-exchange networks is further improved by applying direct relaxation of the pinch principle (neglecting the pinch temperature) when the heating or cooling demand of the residue of a stream after a match is less than the minimum heat load. The structures and results of the computer program elaborated according to the new strategy proved to be quite reasonable for industrial problems.