Process for cryogenic fractionation of air, air fractionation plant and integrated system composed of at least two air fractionation plants

An air fractionation plant having a rectification column system which has a first rectification column, a second rectification column and a third rectification column, and which is configured to

• operate the first rectification column at a first pressure level, to feed a first feed stream which is formed using cooled compressed air into the first rectification column, and to form a first sump liquid enriched in relation to the first feed stream of oxygen and argon and a nitrogen-rich first top gas in the first rectification column,
• operate the second rectification column at a second pressure level, to feed a second feed stream formed using at least a portion of the first sump liquid into the second rectification column, and to form an oxygen-rich second sump liquid and a nitrogen-rich second top gas in the second rectification column, and
• feed into the third rectification column a third feed stream which is formed using fluid which has a higher argon content than the second sump liquid and the second top gas and is removed from the second rectification column, and to form a third top gas enriched with argon with respect to the third feed stream in the third rectification column,
• wherein the air fractionation plant is configured to be operated such that
• the first pressure level ranges from 9 to 14.5 bar at the top of the first rectification column and the second pressure level ranges from 2 to 5 bar at the top of the second rectification column, and
• it uses the second top gas or a part thereof to form a recirculating stream, and heats, compresses and cools it again, and, after partial or complete liquefaction or in an unliquefied state, feeds it partly or completely or in fractions into the first rectification column and/or into the second rectification column.