Apparatus for producing liquid nitrogen

Abstract

An apparatus for producing liquid nitrogen is provided. The apparatus includes a heat exchanger, a pair of turbine-boosters, a warm compressor, an air separation unit having a single column, a top condenser and a bottom reboiler, a liquid/gas separator, and an optional subcooler. The apparatus is configured to produce merchant or non-merchant grade liquid nitrogen using the pair of turbine-boosters to provide refrigeration and energy for the process.

I claim: 
     
         1 . An apparatus for producing nitrogen through the cryogenic separation of air, the apparatus comprising:
 a heat exchanger configured to receive a main air feed comprising purified and compressed air at a pressure of at least 5 bar;   an air separation unit in fluid communication with a cool side of the heat exchanger, the air separation unit configured to receive cooled air from the heat exchanger and produce gaseous nitrogen and waste oxygen, wherein the air separation unit comprises a single column having a bottom reboiler and a top condenser;   a recycle compressor in fluid communication with a warm side of the heat exchanger such that the recycle compressor is configured to receive a nitrogen recycle from the heat exchanger, wherein at least a portion of the nitrogen recycle is made up of gaseous nitrogen from the air separation unit;   a first turbine-booster having a first booster and a first turbine, the first booster in fluid communication with the recycle compressor such that the first booster is configured to receive a compressed nitrogen recycle from the recycle compressor;   a second turbine-booster having a second booster and a second turbine, the second booster in fluid communication with the first booster such that the second booster is configured to receive a boosted nitrogen from the first booster, wherein an outlet of the second booster is in fluid communication with the heat exchanger such that the boosted nitrogen from the second booster is cooled within the heat exchanger, wherein the second turbine is in fluid communication with the heat exchanger such that the second turbine is configured to receive a cooled fluid under pressure from the heat exchanger and then expand the cooled fluid to provide refrigeration for the apparatus; and   a liquid/gas separator in fluid communication with the heat exchanger, the liquid/gas separator configured to receive an expanded fluid comprising nitrogen from the second turbine and separate the expanded fluid into a nitrogen-enriched gas and a nitrogen-enriched liquid, the liquid/gas separator in fluid communication with the second booster and the heat exchanger such that the liquid/gas separator is configured to receive a portion of the boosted nitrogen after fully cooling in the heat exchanger, the liquid/gas separator is also configured to send the nitrogen-enriched gas to the cool side of the heat exchanger.   
     
     
         2 . The apparatus as claimed in  claim 1 , wherein the top condenser is in fluid communication with the single column, wherein the bottom reboiler is in fluid communication with the single column, wherein the top condenser is configured to provide condensing duty for the single column, wherein the bottom reboiler configured to provide reboiling duty for the single column. 
     
     
         3 . The apparatus as claimed in  claim 1 , wherein the subcooler is in fluid communication with the single column such that the subcooler is configured to receive a fluid from the single column that is operable to provide subcooling for the subcooler. 
     
     
         4 . The apparatus as claimed in  claim 3 , wherein the fluid received from the single column is an oxygen-rich liquid from a bottom of the single column. 
     
     
         5 . The apparatus as claimed in  claim 3 , wherein the fluid received from the single column is an oxygen-rich liquid from a middle section of the single column. 
     
     
         6 . The apparatus as claimed in  claim 3 , wherein the subcooler is in fluid communication with the liquid/gas separator, the subcooler being configured to subcool the nitrogen-enriched liquid from the liquid/gas separator. 
     
     
         7 . The apparatus as claimed in  claim 1 , wherein the second turbine is mechanically coupled to the second booster. 
     
     
         8 . The apparatus as claimed in  claim 1 , wherein the first turbine is mechanically coupled to the first booster. 
     
     
         9 . The apparatus as claimed in  claim 1 , wherein the recycle compressor is in fluid communication with the heat exchanger, the bottom reboiler and the single column, such that the recycle compressor is configured to have a fraction of partially compressed nitrogen recycle withdrawn from an internal stage of recycle compressor, cooled in the heat exchanger, used by the bottom reboiler as a heating fluid; and then flashed into a top portion of the single column.