ABSTRACT
When the industrial application of gas separation began, especially with air separation by
Linde, it initiated an interest in high-pressure reciprocating air compressors with a target of
200 bar. This target was lowered to 40 bar, and even to 25 bar when the expander was
introduced by Claude in 1902. In the 1930s, when air separation plants began to get larger in
capacity, centrifugal machinery began to be used, which did away with the main problem of
oil entrainment by reciprocating units used previously. Since the 1950s, even for small plants,
centrifugal compressors have replaced reciprocating machines almost completely for basic air
separation. Reciprocating machines of the labyrinth, oil-free type, are still being used, but
only for small, high-pressure systems for oxygen compression, or for gases that cannot
tolerate contamination. Subsequently, there has been a perennial tug-of-war between com-
pressor manufacturers and gas separation designers in trying to fit existing compressors to
preset designs and the demands of new process cycles that change ever so quickly.
