Annular divided wall column for an air separation unit

An annular column for cryogenic rectification of air or constituents of air, said column comprising:

• a first annular column wall;
• a second annular column wall radially spaced from the first annular column wall and disposed within a first interior space of the first annular column wall to define an annulus column region between the first annular column wall and the second annular column wall and to define an interior core column region as part or all of a second interior space of the second annular column wall;
• a plurality of structured packing elements of a first type disposed within the annulus column region;
• and
• a plurality of structured packing elements of a second type disposed within the interior core column region;
• wherein the first type of structured packing elements and the second type of structured packing elements have different surface area densities and the surface area densities of the first type of structured packing elements are between about 100 m2/m3 to 1200 m2/m3 and the second type of structured packing elements are between about 100 m2/m3 to 1200 m2/m3;
• and
• wherein the first type of structured packing elements have a first nominal inclination angle of corrugations to the horizontal axis of between about 35° to 70° and the second type of structured packing elements have a second nominal inclination angle of corrugations to the horizontal axis of between about 35° to 70° and wherein the first nominal inclination angle of corrugations to the horizontal axis of the first type of structured packing elements is different than the second nominal inclination angle of corrugations to the horizontal axis of the second type of structured packing elements.