Method for preparing air for separation by rectification

A method for preparing feed air for separation by cryogenic rectification in a double column air separation facility, whereby the preparatory steps of compression, cooling and cleaning of the feed air are carried out by an integrated system, comprising:

• (a) compressing feed air;
• (b) cooling the compressed feed air;
• (c) passing the cooled, compressed feed air through a first purifier containing heat regenerable adsorbent wherein the air is substantially cleaned of impurities by transfer of the impurities to the adsorbent;
• (d) introducing the cleaned, cooled, compressed feed air into an air separation facility wherein a higher pressure column and a lower pressure column are in heat exchange relation;
• (e) separating the feed air by cryogenic rectification in the air separation facility into nitrogen-rich and oxygen-rich components;
• (f) withdrawing a nitrogen-rich portion from the higher pressure column, expanding the withdrawn portion and warming the expanded withdrawn portion by indirect heat exchange with the cleaned, cooled, compressed feed air prior to its introduction into the air separation facility;
• (g) warming the withdrawn expanded portion by indirect heat exchange with at least a portion of the cooling compressed feed air of step (b);
• (h) passing the warmed portion through a second purifier containing heat regenerable adsorbent which contains impurities so as to transfer those impurities to the warmed portion and thus clean the adsorbent;
• (i) expanding the impurity-containing portion through an expansion turbine for the production of external work;
• (j) employing at least a portion of said external work to compress the feed air of step (a);
• and
• (k) periodically switching the first and second purifiers so that during the switched time the cooled compressed feed air passes through the second purifier containing adsorbent which has been cleaned during the previous period, and the warmed portion passes through the first purifier to remove impurities from the adsorbent deposited there during the previous period.