A real column design exergy optimization of a cryogenic air separation unit

Distillation columns are one of the main methods used for separating air components. Their inconvenient is their high energy consumption. The distillation process is simulated in three types of columns and the exergy losses in the different parts calculated. A sensitivity analysis is realized in order to optimize the geometric and the operational parameters of each type of column. A comparative exergy analysis between the distillation columns considered for cryogenic air separation shows that the exergy efficiency of a double diabatic column, with heat transfer all through the length of the column, is 23% higher than that of the conventional adiabatic double columns.

► In a simple adiabatic distillation column, most of the exergy losses occur in the column itself (57%).
► Operating pressures of 110 kPa and 750 kPa are the optimal values for minimum exergy losses in double adiabatic columns.
► Double diabatic columns show a 23% decrease in the exergy losses compared to double adiabatic columns.