Dual heat pump cycles for increased argon recovery

In a cryogenic air distillation process producing argon from feed air using a multiple column distillation system comprising a high pressure column, a low pressure column and a crude argon column wherein the feed air is compressed in a main air compressor, cooled and at least a portion thereof is fed to the high pressure column;

• wherein in the high pressure column, the compressed, cooled feed air is rectified into a crude liquid oxygen bottoms and a high pressure nitrogen overhead;
• wherein the crude liquid oxygen is fed to the low pressure column;
• wherein in the low pressure column, the crude liquid oxygen is distilled into a liquid oxygen bottoms and a gaseous nitrogen overhead;
• wherein the low pressure column and the high pressure column are thermally linked such that a first portion of the high pressure nitrogen overhead is condensed in a reboiler/condenser against a first portion of vaporizing liquid oxygen bottoms;
• wherein an argon containing gaseous side stream is removed from a lower intermediate location of the low pressure column and fed to the crude argon column;
• and finally wherein in the crude argon column, the argon containing gaseous side stream is rectified into an argon-rich vapor overhead and an argon-lean bottoms liquid, and the argon-lean bottoms liquid is returned to the low pressure column;
• the improvement for increasing argon recovery comprising using a first heat pump cycle to transfer refrigeration from the bottom of the low pressure column to the top of the crude argon column and a second heat pump cycle to transfer refrigeration from the bottom of the low pressure column to the top of the low pressure column wherein the first heat pump cycle employs a heat pump fluid selected from the group consisting of nitrogen, argon, oxygen and mixtures thereof and wherein the second heat pump cycle also employs a heat pump fluid selected from the group consisting of nitrogen, argon, oxygen and mixtures thereof and wherein the first heat pump cycle is selected from the group consisting of an indirect reflux first heat pump cycle and a direct reflux first heat pump cycle and wherein the second heat pump cycle is selected from the group consisting of an indirect reflux second heat pump cycle and a direct reflux second heat pump cycle and finally wherein the indirect reflux first heat pump cycle comprises:
• (a) condensing a first heat pump fluid by heat exchange against a second portion of vaporizing liquid oxygen bottoms;
• (b) reducing the pressure of the first heat pump fluid;
• (c) vaporizing the first heat pump fluid by heat exchange against at least a first portion of the argon-rich vapor overhead wherein an adequate temperature difference exists between the argon-rich vapor overhead and the vaporizing first heat pump fluid, thereby condensing said first portion of the argon-rich vapor overhead and returning at least a portion of the condensed argon to the top of the crude argon column to provide at least a first portion of liquid reflux for the crude argon column;
• and
• (d) compressing the first heat pump fluid.