Abstract: For extracting argon, air is separated in a rectifying system comprising at least one air separating column and one crude argon column. An argon-containing oxygen fraction is taken from the air separating column and is introduced into a crude argon column. In the upper area of the crude argon column, a crude argon fraction is removed and a first reflux liquid is charged. A first residual fraction is taken from the lower area of the crude argon column. The crude argon fraction is introduced into the lower area of a semipure column. In the upper area of the semipure column, an argon fraction is taken which has reduced oxygen, and a second reflux liquid is charged. From the lower area of the semipure column, a second residual fraction is taken which forms the first reflux liquid for the crude argon column.

Abstract: A process and apparatus for air separation by low temperature rectification are described in which argon is obtained exclusively by rectification. A crude argon column (24) is equipped with at least 150 theoretical plates in the form of low pressure drop packing so that, in it, a substantially complete separation of the oxygen is possible, e.g., less than about 10 ppm, preferably less than 1 ppm oxygen.

Abstract: In a system for air fractionation by low-temperature rectification, refrigeration is produced in a cooling stage by compression and expansion of the feed air or of nitrogen from rectification. By using the work gained during expansion for compressing only a partial stream of the gas passed through the cooling stage, the system according to this invention operates with increased efficiency and lower operating costs.

Abstract: In a process and apparatus for air separation by rectification air 1 is preliminarily separated in a first rectification stage 2 of a two-stage rectification column to obtain a nitrogen-rich fraction 4 and an oxygen-rich fraction 8. These two fractions are fed to the second rectification stage 6 and separated into oxygen and nitrogen fractions. An argon-enriched fraction, containing essentially oxygen and argon, is removed from the second rectification stage at an intermediate point and is separated in a raw argon column 10 by rectification into an argon-rich fraction 18 and a liquid fraction 19 containing essentially oxygen. The liquid fraction 19 is fed back into the second rectification stage. Another fraction 22 is removed from the raw argon column above the bottom thereof and is separated in a high-purity oxygen column 23 to produce a high-purity oxygen fraction 25, 26 and a lighter residual fraction 24.