Positioning heat exchangers in binary tray distillation using isoforce operation

The best way of adding two interstage heat exchangers to a binary distillation column is studied using irreversible thermodynamics. A distillation column is simulated with a computer program using the tray-to-tray calculation method. The purpose of the analysis is to find the locations of the two interstage heat exchangers which give the minimum entropy production rate in the column. According to the isoforce principle, minimum entropy production rate is obtained in distillation when the driving forces are uniformly distributed over the trays. This implies that the entropy production rate, in the optimum case, varies according to the value of the phenomenological coefficient. Therefore, locations with the largest deviations from this behavior are good locations for additional heat exchangers. A column separating n-pentane and n-heptane is used to demonstrate how the optimum variation in the coefficient may be used in practice. (C) 2002 Elsevier Science Ltd. All rights reserved.