Cryogenic air separation unit with flexible liquid product make

Abstract

A cryogenic air separation unit that provides flexibility in the production of liquid products is disclosed. The present cryogenic air separation unit and associated operating methods involves the use of a dual nozzle arrangement for the main heat exchanger that allows a turbine air stream draw from the main heat exchanger at different temperatures to provide refrigeration to the cryogenic air separation unit which, in turn, enables different production modes for the various liquid products.

What is claimed is: 
     
         1 . An air separation unit having one or more distillation columns for the fractional distillation of a feed air stream and configured to produce one or more liquid products, the air separation unit comprising:
 a main compressor arrangement configured to compress the feed air stream;   an adsorption based pre-purifier configured for removing water vapor, carbon dioxide, nitrous oxide, hydrocarbons or other contaminants from the compressed feed air stream to produce a compressed and purified feed air stream;   a feed air stream circuit configured to divide the compressed and purified feed air stream into at least two streams including a boiler air stream and a turbine air stream;   one or more boiler air stream compressors configured to compress the boiler air stream;   a main heat exchanger configured to receive the compressed boiler air stream and cool the compressed boiler air stream to a cold-end temperature via indirect heat exchange with an oxygen stream from at least one distillation column of the air separation unit;   one or more turbine air stream compressors configured to compress all or a portion of the turbine air stream;   the main heat exchanger further configured to receive the turbine air stream and discharge a first subsidiary stream at a first temperature warmer than the cold-end temperature and a second subsidiary stream at a second temperature colder than the first temperature but warmer than the cold-end temperature;   a turboexpander configured to expand the first subsidiary stream or the second subsidiary stream to produce an exhaust stream having an outlet temperature and wherein the exhaust stream is introduced into the at least one distillation column of the air separation unit;   a first valve disposed between the main heat exchanger and the turboexpander and configured to adjust the flow of the first subsidiary stream and therefore, an inlet temperature to the turboexpander and the outlet temperature;   a second valve disposed between the main heat exchanger and the turboexpander and configured to adjust the flow of the second subsidiary stream and therefore, the inlet temperature to the turboexpander and the outlet temperature; and   the one or more distillation columns configured for fractional distillation of the streams into a plurality of products including the one or more liquid products;   wherein the air separation unit is further configured to operate in a low liquid make mode with the turboexpander configured to expand only the first subsidiary stream:   wherein the air separation unit is configured to operate in a high liquid make mode with the turboexpander configured to expand only the second subsidiary stream.   
     
     
         2 . The air separation unit of  claim 1 , wherein the low liquid make mode produces the liquid products in the amount of about 2.5 percent or less of the total feed air stream. 
     
     
         3 . The air separation unit of  claim 1 , wherein the high liquid make mode produces the liquid products in the amount of about 4.5 percent or more of the total feed air stream. 
     
     
         4 . The air separation unit of  claim 1 , wherein the air separation unit is still further configured to operate in a medium liquid make variable mode with the turboexpander configured to expand a mixture of the first subsidiary stream and the second subsidiary stream. 
     
     
         5 . The air separation unit of  claim 4 , further comprising a third valve disposed between the main heat exchanger and the turboexpander and configured to adjust the mixing of the first subsidiary stream and the second subsidiary stream and therefore, the inlet temperature to the turboexpander and the outlet temperature. 
     
     
         6 . The air separation unit of  claim 4 , wherein the medium liquid make variable mode produces the liquid products in the amount of between about 2 percent and about 8 percent of the total feed air stream. 
     
     
         7 . The air separation unit of  claim 1 , wherein the first temperature is between about 140 Kelvin and about 220 Kelvin. 
     
     
         8 . The air separation unit of  claim 1 , wherein the second temperature is between about 130 Kelvin and about 140 Kelvin. 
     
     
         9 . The air separation unit of  claim 1 , wherein the one or more boiler air stream compressors are configured to compress the boiler air stream to a pressure between about 25 bar(a) and about 70 bar(a). 
     
     
         10 . The air separation unit of  claim 1 , wherein the turbine air stream compressors are configured to compress the turbine air stream to a pressure between about 20 bar(a) and about 60 bar(a). 
     
     
         11 . The air separation unit of  claim 1 , wherein the main heat exchanger is further configured to discharge a third subsidiary stream at the cold-end temperature and at a medium pressure greater than the pressure of the compressed and purified feed air stream and less than the pressure of the compressed boiler air stream, wherein the third subsidiary stream bypasses the turboexpander and is directed to the at least one distillation column of the air separation unit. 
     
     
         12 . The air separation unit of  claim 1 , wherein the feed air stream circuit is further configured to divide the compressed and purified feed air stream such that the turbine air stream is between about 60 percent and 75 percent of the compressed and purified feed air stream. 
     
     
         13 . The air separation unit of  claim 1 , further comprising a first distributor disposed within the main heat exchanger and wherein the first valve is an on-off valve in fluid communication with the first distributor and configured to be in an open position allowing flow of the first subsidiary stream to exit the main heat exchanger or a closed position preventing flow of the first subsidiary stream from exiting the main heat exchanger. 
     
     
         14 . The air separation unit of  claim 13 , further comprising a second distributor disposed within the main heat exchanger and wherein the second valve is an on-off valve in fluid communication with the second distributor and configured to be in an open position allowing flow of the second subsidiary stream to exit the main heat exchanger when the first valve is in the closed position or in a closed position preventing flow of the first subsidiary stream from exiting the main heat exchanger when the first valve is in the open position. 
     
     
         15 . The air separation unit of  claim 1 , wherein the one or more turbine air stream compressors further comprise at least one turbine loaded booster compressor. 
     
     
         16 . An air separation unit having one or more distillation columns for the fractional distillation of a feed air stream and configured to produce one or more liquid products, the air separation unit comprising:
 a main compressor arrangement configured to compress the feed air stream;   an adsorption based pre-purifier configured for removing water vapor, carbon dioxide, nitrous oxide, hydrocarbons or other contaminants from the compressed feed air stream to produce a compressed and purified feed air stream;   a feed air stream circuit configured to divide the compressed and purified feed air stream into at least two streams including a boiler air stream and a turbine air stream;   one or more boiler air stream compressors configured to compress the boiler air stream;   a main heat exchanger configured to receive the compressed boiler air stream and cool the compressed boiler air stream to a cold-end temperature via indirect heat exchange with an oxygen stream from at least one distillation column of the air separation unit;   one or more turbine air stream compressors configured to compress the turbine air stream;   a bypass circuit configured to direct all or a portion of the turbine air stream to bypass at least one of the one or more of compressors;   the main heat exchanger further configured to receive the turbine air stream and discharge a first subsidiary stream at a first temperature warmer than the cold-end temperature and a second subsidiary stream at a second temperature colder than the first temperature but warmer than the cold-end temperature;   a turboexpander configured to expand the first subsidiary stream or the second subsidiary stream to produce an exhaust stream having an outlet temperature and wherein the exhaust stream is introduced into the at least one distillation column of the air separation unit;   a first valve disposed between the main heat exchanger and the turboexpander and configured to adjust the flow of the first subsidiary stream and therefore, an inlet temperature to the turboexpander and the outlet temperature;   a second valve disposed between the main heat exchanger and the turboexpander and configured to adjust the flow of the second subsidiary stream and therefore, the inlet temperature to the turboexpander and the outlet temperature; and   the one or more distillation columns configured for fractional distillation of the streams into a plurality of products including the one or more liquid products;   wherein the air separation unit is configured to operate in a low liquid make mode with all or a portion of the turbine air stream bypassing at least one of the one or more compressors prior to entering the main heat exchanger and the turboexpander configured to expand only the first subsidiary stream;   wherein the air separation unit is configured to operate in a high liquid make mode with none of the turbine air stream bypassing any of the one or more compressors prior to entering the main heat exchanger and the turboexpander configured to expand only the second subsidiary stream;   wherein the air separation unit is configured to operate in a medium liquid make mode with none of the turbine air stream bypassing any of the one or more compressors prior to entering the main heat exchanger and the turboexpander configured to expand only the first subsidiary stream; and   wherein the air separation unit is configured to operate in an alternate medium liquid make mode with all or a portion of the turbine air stream bypassing at least one of the one or more compressors prior to entering the main heat exchanger and the turboexpander configured to expand only the second subsidiary stream.   
     
     
         17 . The air separation unit of  claim 16 , wherein the high liquid make mode produces the liquid products in the amount of about 4.5 percent or more of the total teed air stream. 
     
     
         18 . The air separation unit of  claim 16 , wherein the low liquid make mode produces the liquid products in the amount of about 2.5 percent or less of the total feed air stream. 
     
     
         19 . The air separation unit of  claim 16 , wherein the medium liquid make mode produces the liquid products in the amount of between about 2 percent and about 5 percent of the total feed air stream. 
     
     
         20 . The air separation unit of  claim 16 , wherein the alternate medium liquid make mode produces the liquid products in the amount of between about 2 percent and about 5 percent of the total feed air stream. 
     
     
         21 . The air separation unit of  claim 16 , further comprising a third valve disposed between the main heat exchanger and the turboexpander and configured to adjust the mixing of the first subsidiary stream and the second subsidiary stream and therefore, the inlet temperature to the turboexpander and the outlet temperature. 
     
     
         22 . The air separation unit of  claim 20 , wherein the air separation unit is still further configured to operate in a liquid make variable mode with none of the turbine air stream bypassing any of the one or more compressors prior to entering the main heat exchanger and the turboexpander configured to expand a mixture of the first subsidiary stream and the second subsidiary stream. 
     
     
         23 . The air separation unit of  claim 22 , wherein the liquid make variable mode produces the liquid products in the amount of between about 2 percent and about 8 percent of the total feed air stream. 
     
     
         24 . The air separation unit of  claim 21 , wherein the air separation unit is still further configured to operate in a liquid make variable mode with all or a portion of the turbine air stream bypassing at least one of the one or more compressors prior to entering the main heat exchanger and the turboexpander configured to expand a mixture of the first subsidiary stream and the second subsidiary stream. 
     
     
         25 . The air separation unit of  claim 24 , wherein the liquid make variable mode produces the liquid products in the amount of between about 2 percent and about 5 percent of the total feed air stream. 
     
     
         26 . The air separation unit of  claim 16 , wherein the first temperature is between about 140 Kelvin and about 220 Kelvin. 
     
     
         27 . The air separation unit of  claim 16 , wherein the second temperature is between about 130 Kelvin and about 140 Kelvin. 
     
     
         28 . The air separation unit of  claim 16 , wherein the one or more boiler air stream compressors are configured to compress the boiler air stream to a pressure between about 25 bar(a) and about 70 bar(a). 
     
     
         29 . The air separation unit of  claim 16 , wherein the turbine loaded booster compressor is configured to compress the turbine air stream to a pressure between about 20 bar(a) and about 60 bar(a). 
     
     
         30 . The air separation unit of  claim 16 , wherein the main heat exchanger is further configured to discharge a third subsidiary stream at the cold-end temperature and at a medium pressure greater than the pressure of the compressed and purified feed air stream and less than the pressure of the compressed boiler air stream, wherein the third subsidiary stream bypasses the turboexpander and is directed to the at least one distillation column of the air separation unit. 
     
     
         31 . The air separation unit of  claim 16  wherein the feed air stream circuit is further configured to divide the compressed and purified feed air stream such that the turbine air stream is between about 60 percent and 75 percent of the compressed and purified teed air stream. 
     
     
         32 . The air separation unit of  claim 16 , further comprising a first distributor disposed within the main heat exchanger and wherein the first valve is an on-off valve in fluid communication with the first distributor and configured to be in an open position allowing flow of the first subsidiary stream to exit the main heat exchanger or a closed position preventing flow of the first subsidiary stream from exiting the main heat exchanger. 
     
     
         33 . The air separation unit of  claim 32 , further comprising a second distributor disposed within the main heat exchanger and wherein the second valve is an on-off valve in fluid communication with the second distributor and configured to be in an open position allowing flow of the second subsidiary stream to exit the main heat exchanger when the first valve is in the closed position or in a closed position preventing flow of the first subsidiary stream from exiting the main heat exchanger when the first valve is in the open position. 
     
     
         34 . The air separation unit of  claim 16 , wherein the one or more turbine air stream compressor further comprise at least one turbine loaded booster compressor.