Air separation method and apparatus

An apparatus for separating air comprising:

• one or more main air compressors configured for producing a stream of compressed and purified air, wherein the stream of compressed and purified air is split into a first part of the stream of compressed and purified air, a second part of the stream of compressed and purified air that is further compressed in a first booster compressor to produce a first boosted pressure air stream, and a third part of the stream of compressed and purified air that is further compressed in a second booster compressor to produce a second boosted pressure air stream;
• a main heat exchange system configured to cool the first part of the stream of compressed and purified air, to partially cool the first boosted pressure air stream, and to partially cool the second boosted pressure air stream;
• a cold compressor configured to further compress the partially cooled first boosted pressure air stream and form a cold compressed stream, wherein the cold compressed stream is further cooled in the main heat exchange system to form a cold compressed liquid air stream;
• a turboexpander configured to expand the partially cooled second boosted pressure air stream and form an exhaust stream;
• a liquid expander disposed downstream of the main heat exchange system and configured to expand the cold compressed liquid air stream to form a subsidiary air stream;
• a distillation column system having a higher pressure column and a lower pressure column linked in a heat transfer relationship via a condenser reboiler and configured to receive the subsidiary air stream, the exhaust stream, and the first part of the compressed and purified air and produce an oxygen-rich liquid from the lower pressure column;
• and
• a pump connected to the lower pressure column to pump the oxygen-rich liquid to produce a pumped liquid oxygen stream;
• wherein the exhaust stream is introduced into the lower pressure column and the subsidiary air stream is introduced into at least one of the lower pressure column or higher pressure column;
• and
• wherein at least part of the pumped liquid oxygen stream is warmed in the main heat exchange system to form an oxygen-rich product through indirect heat exchange with the first boosted pressure air stream, the second boosted pressure air stream and the cold compressed stream;
• wherein the cold compressor is driven by a variable speed motor controlled by a variable speed drive and speed of the motor and therefore, the cold compressor is reduced during a turndown operation of the cryogenic rectification process when production of the oxygen product stream is reduced;
• and
• wherein the liquid expander is a liquid turboexpander coupled to an electrical generator or oil-brake system to compensate for the work of compression added by the cold compressor.

A method for separating air comprising the steps of:

• producing a stream of compressed and purified air in one or more main air compressors;
• splitting the stream of compressed and purified air into a first part of the stream of compressed and purified air, a second part of the stream of compressed and purified air, and a third part of the stream of compressed and purified air;
• further compressing the second part of the stream of compressed and purified air in a first booster compressor to produce a first boosted pressure air stream, and further compressing the third part of the stream of compressed and purified air in a second booster compressor to produce a second boosted pressure air stream;
• cooling the first part of the stream of compressed and purified air and the first boosted pressure air stream in a main heat exchange system and partially cooling the second boosted pressure air stream in the main heat exchange system;
• further compressing the partially cooled first boosted pressure air stream in a cold compressor to form a cold compressed stream;
• further cooling the cold compressed stream in the main heat exchange system to form a cold compressed liquid air stream;
• expanding the partially cooled second boosted pressure air stream in a turboexpander to form an exhaust stream;
• expanding the cold compressed liquid air stream in a liquid expander disposed downstream of the main heat exchange system to form a subsidiary air stream;
• rectifying the subsidiary air stream, the exhaust stream, and the first part of the compressed and purified air in a distillation column system comprising a higher pressure column and a lower pressure column linked in a heat transfer relationship via a condenser reboiler to produce an oxygen-rich liquid from the lower pressure column;
• pumping the oxygen-rich liquid from the lower pressure column to produce a pumped liquid oxygen stream;
• and
• warming at least part of the pumped liquid oxygen stream in the main heat exchange system to form an oxygen-rich gaseous product through indirect heat exchange with the first boosted pressure air stream, the second boosted pressure air stream and the cold compressed stream;
• wherein the exhaust stream is introduced into the lower pressure column and the subsidiary air stream is introduced into at least one of the lower pressure column or higher pressure column;
• wherein the cold compressor is driven by a variable speed motor controlled by a variable speed drive and speed of the motor and therefore, the cold compressor is reduced during a turndown operation of the cryogenic rectification process when production of the oxygen product stream is reduced;
• and
• wherein the liquid expander is a liquid turboexpander coupled to an electrical generator or oil-brake system to compensate for the work of compression added by the cold compressor.