Method and apparatus for producing high purity oxygen

An apparatus for producing high purity oxygen comprising:

• an auxiliary cryogenic rectification plant connected to a plurality of cryogenic air separation plants to receive a combined low purity liquid oxygen stream formed from the low purity liquid oxygen streams produced by the cryogenic air separation plants and a combined gaseous nitrogen stream formed from the gaseous nitrogen streams produced by the cryogenic air separation plants;
• the auxiliary cryogenic rectification plant having a distillation column configured such that nitrogen is separated from the combined low purity oxygen stream and the high purity oxygen is formed from residual liquid produced from reboiling bottoms liquid in a bottom region of the distillation column, a reboiler located in a bottom region of the distillation column and positioned such that the combined gaseous nitrogen stream passes through the reboiler, reboils the bottoms liquid, thereby produces a liquid nitrogen stream and the liquid nitrogen stream is introduced into the top region of the distillation column as reflux, a heat exchanger connected to the reboiler such that the combined gaseous nitrogen stream is cooled prior to passing into the reboiler and a subcooling unit positioned between the reboiler and the top region of the distillation column such that the liquid nitrogen stream is subcooled prior to being introduced into the top region of the distillation column;
• means for imparting refrigeration to the auxiliary cryogenic rectification plant;
• the subcooling unit connected to the top region of the distillation column and the heat exchanger connected to the subcooling unit such that a nitrogen-rich stream produced at the top region of the distillation column passes in indirect heat exchange with the liquid nitrogen stream and thereafter, the combined gaseous nitrogen stream and the refrigeration is thereby recovered in subcooling the liquid nitrogen stream and in cooling the combined gaseous nitrogen stream;
• and
• the distillation column having, at the bottom region thereof, an outlet to discharge the high purity oxygen as a high purity liquid oxygen stream.