Air separation

An apparatus for separating air comprising:

• a first compressor for compressing the air;
• purification means for purifying the air;
• a main heat exchanger having a first pass in communication with the purification means for reducing the temperature of the air to a temperature suitable for its separation by rectification;
• a rectification column comprising a single stage connected to the main heat exchanger for separating the air into oxygen and nitrogen fractions and having an inlet in communication with the first pass of the main heat exchanger for receiving the air after having been cooled and a first outlet for discharging a liquid oxygen stream;
• a pump in communication with said first outlet of the rectification column and a second pass of the main heat exchanger in heat exchange relationship with the first pass thereof so as to be operable to pump the liquid oxygen stream through the second pass of the main heat exchanger in countercurrent heat exchange with the air passing through the first pass of the main heat exchanger;
• the rectification column also having a second outlet for discharging a stream of a nitrogen vapor;
• means associated with the main heat exchanger and in communication with the second outlet of the rectification column for dividing the stream of the nitrogen vapor into first and second subsidiary streams so that the first subsidiary stream passes from the main heat exchanger intermediate its cold and warm ends and the second subsidiary stream passes from the warm end of the main heat exchanger;
• an expansion turbine in communication with the dividing means so that the first subsidiary stream is expanded after having passed from the main heat exchanger;
• a second compressor connected to the dividing means for compressing the second subsidiary stream after it has passed from the warm end of the main heat exchanger;
• the compresser also being connected to a third pass of the main heat exchanger so that after the compression of the first subsidiary stream, it passes through the main heat exchanger countercurrently to the liquid oxygen stream;
• means connected to the third pass of the main heat exchanger for condensing the second subsidiary stream after passage through the main heat exchanger thereby to form a liquid nitrogen stream;
• and a further heat exchanger for sub-cooling the liquid nitrogen stream;
• said further heat exchanger in communication with said rectification column so that the liquid nitrogen stream after sub-cooling passes into the rectification column as reflux;
• and said further heat exchanger having a passage in communication, at opposite ends thereof with the expansion tubine and a forth pass of the main heat exchanger so that the second first stream passes through the further heat exchanger and then in countercurrent heat exchange with the compressed air stream within the main heat exchanger.