Patent ID: 8479535

Claim:
A method of producing high purity oxygen comprising: withdrawing low purity liquid oxygen streams and gaseous nitrogen streams from a plurality of cryogenic air separation plants; introducing a combined low purity liquid oxygen stream formed from the low purity liquid oxygen streams and a combined gaseous nitrogen stream formed from the gaseous nitrogen streams into an auxiliary cryogenic rectification plant; separating nitrogen from the combined low purity liquid oxygen stream within a distillation column of the auxiliary cryogenic rectification plant such that the high purity oxygen is formed of residual liquid produced by reboiling bottoms liquid in a bottom region of the distillation column, reboiling the bottoms liquid with the combined gaseous nitrogen stream, thereby to condense the combined gaseous nitrogen stream and to form a liquid nitrogen stream and introducing the liquid nitrogen stream into a top region of the distillation column as reflux; imparting refrigeration to the auxiliary cryogenic rectification plant and recovering the refrigeration through subcooling the liquid nitrogen stream and thereafter cooling the combined gaseous nitrogen stream through indirect heat exchange with a nitrogen-rich vapor stream withdrawn from a top region of the distillation column; and withdrawing the high purity oxygen from the bottom region of the distillation column as a high purity liquid oxygen stream.