Air separation method and apparatus

Abstract

A method and apparatus for separating air in which an oxygen-rich liquid stream is pumped and then heated within a heat exchanger to produce an oxygen product through indirect heat exchange with first and second boosted pressure air streams. The first boosted pressure air stream is cold compressed at an intermediate temperature of the heat exchanger, reintroduced into the heat exchanger at a warmer temperature and then fully cooled and liquefied. The second boosted pressure air stream, after having been partially cooled, is expanded to produce an exhaust stream that is in turn introduced into a lower pressure column producing the oxygen-rich liquid. The second boosted pressure air stream is partially cooled to a temperature no greater than the intermediate temperature at which the cold compression occurs so that both the first and second boosted pressure air streams are able to take part in the heating of the oxygen-rich stream.

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         29 . 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 between the main heat exchange system of the distillation column 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 produce an oxygen-rich liquid from the lower pressure column through cryogenic rectification of the subsidiary air stream, the exhaust stream, and the first part of the compressed and purified air; 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 to impart refrigeration and the subsidiary air stream is introduced into at least one of the lower pressure column or higher pressure column to impart additional refrigeration; 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.   
     
     
         30 . The apparatus of  claim 29 , wherein the main heat exchange system further comprises:
 a higher pressure heat exchanger configured to warm the pumped liquid oxygen stream through indirect heat exchange with the first boosted pressure air stream and the second boosted pressure air stream; and   a lower pressure heat exchanger configured to cool the first part of the compressed and purified air to a temperature suitable for rectification via indirect heat exchange with a stream of waste nitrogen from the distillation column system.   
     
     
         31 . The apparatus of  claim 30 , wherein the higher pressure heat exchanger is further configured to further cool the cold compressed stream. 
     
     
         32 . The apparatus of  claim 30 , wherein the higher pressure heat exchanger is further configured to warm a stream of pumped nitrogen from the higher pressure column to produce a high pressure gaseous nitrogen product stream. 
     
     
         33 . The apparatus of  claim 30 , wherein the distillation column system is configured to produce a stream of gaseous nitrogen and the lower pressure heat exchanger is further configured to warm the stream of gaseous nitrogen to produce a low pressure gaseous nitrogen product stream. 
     
     
         34 . The apparatus of  claim 33 , wherein the stream of gaseous nitrogen is a stream of overhead nitrogen or shelf nitrogen from the lower pressure column. 
     
     
         35 . The apparatus of  claim 30 , wherein the higher pressure heat exchanger further comprises:
 a first intermediate outlet positioned to discharge the first boosted pressure air stream at an intermediate temperature about equal to a vaporization or pseudo-vaporization temperature of the oxygen-rich liquid stream;   a first intermediate inlet to introduce the cold compressed air stream into the higher pressure heat exchanger at a warmer temperature than the intermediate temperature; and   a second intermediate outlet positioned to discharge the second boosted pressure air stream at a temperature no greater than the intermediate temperature so that both the first and second boosted pressure air stream thereby assist in heating the oxygen-rich liquid stream at temperatures within the main heat exchange system above the intermediate temperature.   
     
     
         36 . The apparatus of  claim 29 , wherein the first part of the compressed and purified stream constitutes between about 50 percent to 65 percent of the compressed and purified air stream on a volume basis. 
     
     
         37 . The apparatus of  claim 36 , wherein the second part of the compressed and purified stream constitutes between about 27 percent to 35 percent of the compressed and purified air stream on a volume basis. 
     
     
         38 . The apparatus of  claim 29 , further comprising:
 a motor coupled to the cold compressor and configured to independently drive the cold compressor; and   a variable speed drive connected to the motor to control speed of the motor and therefore, the cold compressor.   
     
     
         39 . The apparatus of  claim 38  wherein the speed of the cold compressor is reduced during a turndown operation of the apparatus when production of the oxygen-rich product is reduced. 
     
     
         40 . 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 cool 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 between the main heat exchange system and the distillation column 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 to impart refrigeration and the subsidiary air stream is introduced into at least one of the lower pressure column or higher pressure column to impart additional refrigeration.   
     
     
         41 . The method of  claim 40 , wherein the main heat exchange system comprises a higher pressure heat exchanger and a lower pressure heat exchanger and the step of warming at least part of the pumped liquid oxygen stream further comprises warming at least part of the pumped liquid oxygen stream in a higher pressure heat exchanger via indirect heat exchange with the first boosted pressure air stream and the second boosted pressure air stream. 
     
     
         42 . The method of  claim 40 , wherein the main heat exchange system comprises a higher pressure heat exchanger and a lower pressure heat exchanger and the step of cooling the first part of the stream of compressed and purified air, the first boosted pressure air stream, and the second boosted pressure air stream further comprises;
 cooling the first part of the stream of compressed and purified air in the lower pressure heat exchanger via indirect heat exchange with a stream of waste nitrogen from the distillation column system; and   cooling the first boosted pressure air stream and the second boosted pressure air stream in the higher pressure heat exchanger; and   further cooling the cold compressed stream in the higher pressure heat exchanger to form the cold compressed liquid air stream;   
     
     
         43 . The apparatus of  claim 41 , wherein the higher pressure heat exchanger is further configured to further cool the cold compressed stream. 
     
     
         44 . The method of  claim 41 , wherein the higher pressure heat exchanger is further configured to warm a stream of pumped nitrogen from the higher pressure column to produce a high pressure gaseous nitrogen product stream. 
     
     
         45 . The method of  claim 42 , wherein the distillation column system is configured to produce a stream of gaseous nitrogen and the lower pressure heat exchanger is further configured to warm the stream of gaseous nitrogen to produce a low pressure gaseous nitrogen product stream. 
     
     
         46 . The method of  claim 45 , wherein the stream of gaseous nitrogen is a stream of overhead nitrogen or shelf nitrogen from the lower pressure column. 
     
     
         47 . The method of  claim 40 , wherein the first part of the compressed and purified stream constitutes between about 50 percent to 65 percent of the compressed and purified air stream on a volume basis wherein the second part of the compressed and purified stream constitutes between about 27 percent to 35 percent of the compressed and purified air stream on a volume basis. 
     
     
         48 . The method of  claim 40 , wherein the cold compressor is coupled to a variable speed motor and a variable speed drive configured to independently drive the cold compressor.