Air separation process and system utilizing pressure-swing driers

A cryogenic air separation system comprising compressor means for compressing a feed air stream, a plurality of pressure swing adsorption driers connected through switch valve means to alternately receive said compressed feed air stream and remove the moisture contained in said feed air stream, a reversing heat exchanger having at least two reversing passages connected through switch valve means to cool said dried feed air stream and freeze out the carbon dioxide contained in said dried feed air stream, dual pressure distillation means connected to receive said cooled air stream and separate said air stream into at least one low pressure nitrogen stream having a nitrogen purity above 98% and at least one other low pressure stream, switch valve means for alternately passing at least a portion of said nitrogen stream through said reversing heat exchanger passages countercurrent to said feed air stream to cool said feed air stream and sublime the carbon dioxide from said reversing passages, means for withdrawing said nitrogen stream containing said sublimed carbon dioxide from said reversing exchanger passages as a product nitrogen stream, means for passing said other low pressure stream through non-reversing heat exchanger passage means to cool said feed air stream and warm said other low pressure stream, and switch valve means for alternately passing at least a portion of said other low pressure stream through said adsorption driers to remove the moisture from said driers.

A cryogenic air separation system comprising:

• a. pressure-swing adsorption means for removing moisture from a compressed air stream,
• b. reversing heat exchanger means for cooling said dried air stream and freezing out CO.sub.2 from said dried feed air stream,
• c. cryogenic distillation means for separating said cooled air stream into at least one low pressure nitrogen product stream and an additional low pressure stream,
• d. passage means for passing at least a portion of said additional low pressure stream through said pressure-swing adsorption means for removing moisture adsorbed in said adsorption means at a pressure less than the pressure of said compressed air stream,
• e. passage means for passing at least a portion of said nitrogen product stream through said reversing heat exchanger means for removing said frozen CO.sub.2 from said reversing heat exchanger means, and
• f. passage means for withdrawing said nitrogen product stream from said reversing heat exchanger means as a product stream comprising at least 99.5% nitrogen.