IMPROVING HEAT INTEGRATION OF DISTILLATION COLUMNS IN A CRYOGENIC AIR SEPARATION UNIT

The distillation columns of a cryogenic ASU (air separation unit) are responsible for a considerable part of the total ASU inefficiencies. The efficiency of a conventional distillation column can be increased by distributing the reboiler and condenser duties over a larger part of its length. In an ASU, this can be realized by moving the LPC (low pressure column) down along the HPC (high pressure column), thus increasing the number of HI-stages (heat integrated stages). We present an assessment of the effect that such an intensification of the heat integration has on the performance of the ASU distillation section, using the entropy production as performance criterion. Increasing both the number of HI-stages and the pressure in the LPC is found to yield a decrease of 21% in the total entropy production. Decreasing the pressure in the HPC instead of increasing the pressure in the LPC yields a decrease of 23%.