Air separation

An air separation process comprising:

• separating in a double rectification column, comprising a higher pressure rectification column and a lower pressure rectification column, a flow of compressed vaporous air into an oxygen-rich fraction and a nitrogen-rich fraction;
• separating in a side rectification column an argon fraction from an argon-enriched oxygen vapour stream withdrawn from an intermediate outlet of the lower pressure rectification column;
• taking an oxygen-rich liquid air stream from the higher pressure rectification column;
• introducing a vaporous oxygen-enriched air stream is introduced into the lower pressure rectification column through an inlet above the said intermediate outlet;
• separating at least part of said oxygen-enriched liquid air stream is separated in an intermediate pressure rectification column at a pressure between the pressure at the bottom of the higher pressure rectification column and that at the said inlet to the lower pressure rectification column to form a liquid air stream further enriched in oxygen and a vapour depleted of oxygen;
• vaporizing at least one stream of the further enriched liquid so as to form part or all of the said vaporous oxygen-enriched air stream;
• condensing a flow of the oxygen-depleted vapour;
• taking at least part of the condensed oxygen-depleted vapour as a product;
• reboiling the intermediate pressure rectification column by a stream of vapour withdrawn either from a section of the lower pressure rectification column extending from said intermediate outlet to said inlet or from the side rectification column;
• and
• withdrawing a liquid stream of a mixture comprising oxygen and nitrogen is withdrawn from an intermediate mass exchange region of the intermediate pressure rectification column and employing said liquid stream in condensing the flow of oxygen-depleted vapour.

An air separation plant comprising:

• a double rectification column, comprising a higher pressure rectification column and a lower pressure rectification column for separating a flow of compressed vaporous air into an oxygen-rich fraction and a nitrogen-rich fraction;
• a side rectification column for separating an argon-enriched vapour stream withdrawn from an intermediate outlet of the lower pressure rectification column;
• the higher pressure rectification column having an outlet for an oxygen-enriched liquid air stream and the lower pressure rectification column having a first inlet for an oxygen-enriched vaporous air stream above said intermediate outlet;
• an intermediate pressure rectification column for separating at least part of said oxygen-enriched liquid air stream at a pressure between the pressure at the bottom of the higher pressure rectification column and that at the said inlet to the lower pressure rectification column to form a liquid air stream further enriched in oxygen and a vapour depleted of oxygen;
• a heat exchanger for vaporising a stream of the further enriched liquid air so as to form a part or all of the vaporous oxygen-enriched air feed to the lower pressure rectification column;
• a condenser for condensing a flow of the oxygen-depleted vapour having an outlet for condensate communicating with a further inlet to the lower pressure rectification column and/or with a product collection vessel;
• and
• a reboiler associated with the intermediate pressure rectification column having condensing passages communicating with an outlet from a section of the lower pressure rectification column extending from said intermediate outlet to said first inlet, or with an outlet from the side rectification column;
• the condenser having boiling passages therein communicating at their inlet end with an intermediate mass exchange region of the intermediate pressure rectification column.