Improving the exergy efficiency of a cryogenic air separation unit as part of an integrated gasification combined cycle

The efficiency of a two-column cryogenic ASU (air separation unit) that is part of an IGCC (integrated gasification combined cycle) can be increased significantly by making better use of the heat of compression and by improving the heat integration of the distillation columns. The rational exergy efficiency of the ASU, which is defined as the desired increase in exergy content of the products divided by the amount of work that is added to the process, can be increased from 35% to over 70%. The exergy destruction per amount of feed is reduced with 1.6 kJ/mol air, corresponding to a 0.74% increase in the net electric efficiency of the IGCC. The efficiencies are expected to increase even further because the full potential of using heat-integrated distillation columns is not yet achieved.

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► Cryogenic air separation as part of an integrated gasification combined cycle.
► Considerable improvements in the exergy efficiency of a two-column design.
► Heating the separation products using heat of compression.
► Improving heat integration of the columns using heat-integrated distillation stages.