Air separation

A method of separating air in a double distillation column comprising lower and higher pressure distillation columns, including the steps of withdrawing an argon-enriched fluid stream from the lower pressure column and separating an argon product from said fluid stream in a further distillation column provided with liquid argon reflux from a condenser, wherein liquid nitrogen is withdrawn from the higher pressure column and is reboilded in said condenser thereby providing a portion of the refrigeration therefor, the remainder of said refrigeration being provided by a stream of liquid withdrawn from the bottom of the higher pressure column, said stream of liquid being introduced into the lower pressure column downstream of its passage through the condenser, a gaseous stream is formed by mixing in a vapor-liquid contact column said reboiled nitrogen with oxygen taken from the lower pressure column, there being in said vapor-liquid contact column a downward flow of liquid that becomes progressively richer in nitrogen in the direction of its flow and an upward flow of vapor that becomes progressively richer in oxygen in the direction of its flow, said gaseous stream being withdrawn from an intermediate level in said column, at least part of the gaseous stream formed in said vapor-liquid contact column is withdrawn and warmed, said part of the gaseous stream being taken as product or expanded in a turbine to provide refrigeration.