Air separation method and apparatus with improved argon recovery

A method of separating air comprising:

• compressing and purifying the air such that a first compressed air stream and a second compressed air stream are produced, the second compressed air stream having a higher pressure than the first compressed air stream;
• cooling at least part of the first compressed air stream and condensing the second compressed air stream through indirect heat exchange with return streams produced by a distillation column system to form a liquid air stream;
• producing a refrigerant stream and imparting refrigeration with the use of the refrigeration stream into the distillation column system;
• introducing the at least part of the first compressed air stream into a higher pressure column of the distillation column system, the distillation column system also having a lower pressure column operatively associated with the higher pressure column in a heat transfer relationship, a crude argon column connected to the lower pressure column to rectify an argon-oxygen containing vapor stream withdrawn from the lower pressure column to thereby, at least in part, produce a crude argon stream and an argon refining column to rectify the crude argon stream and thereby form an argon product stream from an argon-rich liquid column bottoms produced in the argon refining column;
• reboiling the argon refining column with the at least a portion of liquid air stream, thereby subcooling the liquid air stream;
• dividing the liquid air stream after having been subcooled into a first intermediate reflux stream and a second intermediate reflux stream;
• valve expanding the first intermediate reflux stream and the second intermediate reflux stream;
• introducing the first intermediate reflux stream into an intermediate location of the higher pressure column;
• and
• introducing, the second intermediate reflux stream into the lower pressure column at a level thereof above where all or any part of a crude liquid oxygen stream composed of a crude liquid oxygen column bottoms of the higher pressure column is introduced for further refinement;
• wherein a crude liquid oxygen stream composed of the crude liquid oxygen is subcooled and divided into first and second subsidiary crude liquid oxygen streams;
• diverting a portion of the liquid air stream after having been subcooled into a first subsidiary liquid air stream;
• valve expanding the first subsidiary liquid air stream and passing the valve expanded first subsidiary liquid air stream in indirect heat exchange with an argon-rich vapor stream produced as argon refining column overhead in the argon refining column, thereby vaporizing the first subsidiary liquid air stream and condensing the argon-rich vapor stream to produce a first argon-rich reflux stream;
• introducing the first argon reflux stream into the argon refining column;
• valve expanding the first subsidiary crude liquid oxygen stream and partially vaporizing the first subsidiary crude liquid oxygen stream in indirect heat exchange with a crude argon-rich vapor stream produced as a crude argon column overhead in the crude argon column to form a second liquid phase stream and a second vapor phase stream while condensing the crude argon-rich vapor stream;
• introducing part of the crude argon-rich vapor stream after having been condensed in the crude argon column as a second argon-rich reflux stream;
• valve expanding another part of the crude argon-rich stream after having been condensed to form the crude argon stream introduced into the argon refining column;
• introducing the second vapor phase stream and the second liquid phase stream into the lower pressure column;
• and
• valve expanding the second subsidiary crude liquid oxygen stream and introducing the second subsidiary crude liquid oxygen stream into the lower pressure column.