Split column multiple condenser-reboiler air separation process

A process for the production of nitrogen gas at greater than atmospheric pressure by the separation of air by rectification comprising:

• (A) introducing cleaned, cooled feed air at greater than atmospheric pressure into a high pressure column operating at a pressure of from about 80 to 300 psia;
• (B) separating said feed air by rectification in said high pressure column into a first nitrogen-rich vapor fraction and a first oxygen-enriched liquid fraction;
• (C) recovering from about 0 to 60 percent of said first nitrogen-rich vapor fraction as high pressure nitrogen gas at a purity exceeding about 99 percent;
• (D) condensing at least a portion of said first nitrogen-rich vapor fraction by indirect heat exchange with said first oxygen-enriched liquid fraction thereby producing a first nitrogen-rich liquid portion and a first oxygen-enriched vapor fraction;
• (E) employing at least some of said first nitrogen-rich liquid portion as liquid reflux for said high pressure column;
• (F) introducing said first oxygen-enriched vapor fraction into a medium pressure column operating at a pressure, lower than that of said high pressure column, of from about 40 to 150 psia;
• (G) separating said first oxygen-enriched vapor fraction by rectification in said medium pressure column into a second nitrogen-rich vapor fraction and at least some oxygen in the form of a second oxygen-enriched liquid fraction;
• (H) vaporizing a portion of said second oxygen-enriched liquid fraction by indirect heat exchange with cleaned, cooled feed air at a pressure of from about 80 to 350 psia, thereby producing a first oxygen-enriched vapor portion, for use as vapor reflux in said medium pressure column, and liquid air;
• (I) dividing said liquid air into a first part which is introduced into said high pressure column wherein it is separated by rectification into parts which comprise the first nitrogen-rich vapor fraction and the first oxygen-enriched liquid fraction, and into a second part, which is introduced into said medium pressure column wherein it is separated by rectification into parts which comprise the second nitrogen-rich vapor fraction and the second oxygen-enriched liquid fraction;
• (J) recovering up to 60 percent of said second nitrogen-rich vapor fraction as medium pressure nitrogen gas at a purity exceeding about 99 percent;
• (K) condensing at least a portion of said second nitrogen-rich vapor fraction by indirect heat exchange with a portion of said second oxygen-enriched liquid fraction thereby producing a second oxygen-enriched vapor portion and a second nitrogen-rich liquid portion;
• (L) employing said second nitrogen-rich liquid portion as liquid reflux for said medium pressure column;
• (M) employing said first nitrogen-rich liquid portion as additional liquid reflux for said medium pressure column in an amount equivalent to that of from about 0 to 60 percent of said first nitrogen-rich vapor fraction such that the sum of said amount and of the high pressure nitrogen gas recovered in step (C) is from about 0 to 60 percent of said first nitrogen-rich vapor fraction;
• and
• (N) removing from the process said second oxygen-enriched vapor portion having an oxygen purity of from 57 to 97 percent.