A detailed exergy analysis of a distillation system has been conducted. This analysis is divided in four parts: (1) adiabatic rectification column; (2) adiabatic stripping column: (3) diabatic rectification column; and (4) diabatic stripping column. The results of all cases are presented in this paper, This analysis concerns the mixture water-ethanol working at 1 bar. The main objective is to determine the distribution of exergy losses inside the column and the optimal distribution of heat to be transferred inside the column in order to produce the minimum overall exergy losses.