Cryogenic rectification method

A method of rectifying a feed stream containing oxygen, nitrogen and argon comprising:

• rectifying the feed stream in a cryogenic rectification process employing a high pressure column operatively associated with a low pressure column in a heat transfer relationship to condense a nitrogen-rich vapor formed in the high pressure column through indirect heat exchange with an oxygen-rich liquid column bottoms formed in the low pressure column and an argon column connected to the low pressure column to separate the argon from the oxygen;
• the high pressure column and the low pressure column each being configured to separate the nitrogen from the oxygen by contacting an ascending vapor phase becoming evermore rich in nitrogen as the ascending vapor phase ascends with a descending liquid phase becoming evermore rich in oxygen as it descends, the ascending vapor phase being contacted with the descending liquid phase, in each of the high pressure column and the low pressure column, within mass transfer contacting elements peripherally bounded by a column diameter selected such that a maximum superficial vapor velocity produced by the ascending vapor phase results in a vapor capacity factor below an operational limit at which flooding would otherwise occur within the mass transfer contacting elements in which the maximum superficial vapor velocity occurs and the column diameter of the low pressure column is substantially equal to or less than the diameter of the high pressure column;
• the argon column being connected to the low pressure column such that the argon is separated from the oxygen contained in an argon and oxygen containing vapor stream that is withdrawn from the low pressure column and an oxygen-rich liquid stream resulting from the separation of the argon from the oxygen is returned to the low pressure column, thereby to increase recovery of oxygen within the oxygen-rich liquid column bottoms;
• imparting refrigeration to the cryogenic rectification process with an exhaust stream produced by expanding a nitrogen-rich vapor stream composed of the nitrogen-rich vapor of the high pressure column within a turboexpander also employed within the air separation process;
• the nitrogen-rich vapor stream having a vapor flow rate such that vaporization of the oxygen-rich liquid column bottoms produces the maximum superficial vapor velocity within the low pressure column that is below the operational limit at which the flooding would have otherwise occurred within the mass transfer contacting elements in which the maximum superficial vapor velocity occurs;
• and
• forming an oxygen product from an oxygen-rich stream withdrawn from the low pressure column and composed of the oxygen-rich liquid column bottoms.