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System and Method to Supply Gaseous Nitrogen from a LNG-based Liquefier Associated with Air Separation

IP.com Disclosure Number: IPCOM000202753D
Publication Date: 2010-Dec-28

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The IP.com Prior Art Database

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System and Method to Supply Gaseous Nitrogen from a LNG-based Liquefier Associated with Air Separation

               A system is set forth to increase the capacity of an LNG-based liquefier in a cryogenic air separation unit where, in a low production mode, the nitrogen that is fed to the LNG-based liquefier consists only of at least a portion of the high pressure nitrogen from the distillation column system while in a high production mode, a supplemental compressor is used to boost the pressure of at least a portion of the low pressure nitrogen from the distillation column system to create additional (or replacement) feed to the LNG-based liquefier or gaseous nitrogen co-product.  The necessary additions are also described for situations when the air feed to the air separation unit has excess nitrogen due to the composition of air and the desired liquid products and there is demand for on-site gaseous nitrogen at or near the LNG receiving terminal.

The system is best understood when read in connection with the drawings.

               Figure 1a is a schematic diagram showing one example of the prior art to which the system pertains.  Referring now to Figure 1a, the facility includes an LNG-based liquefier (2) and a cryogenic ASU (1).  In this example, the cryogenic ASU includes a higher pressure column (114), lower pressure column (116), and main exchanger (110).  Feed air 100 is compressed in 102 and dried in 104 to produce stream 108.  Stream 108 is cooled in main exchanger 110 against returning gaseous product streams, to produce cooled air feed 112.  Stream 112 is distilled in the double column system to produce liquid oxygen 158, high pressure nitrogen gas (stream 174) and low pressure nitrogen gas (stream 180).  The nitrogen gases 174 and 180 are warmed in main exchanger 110 to produce streams 176 and 182.  Stream 182 is ultimately rejected to the atmosphere.  Stream 176 is processed in the LNG-based liquefier (2) to create liquefied nitrogen product stream 188 and liquid nitrogen refrigerant stream 186.  Liquid nitrogen refrigerant stream 186 is introduced into the distillation columns through valves 136 and 140.  Refrigeration for LNG-based liquefier is provided from LNG stream 194, which is vaporized and heated to produce stream 198.  In Figure 1a, the only nitrogen feed to the LNG-based liquefier is stream 176, which originates from the higher pressure column 114.

               Figure 1b is a schematic diagram showing the basic concept of the system in relation to Figure 1a.  Referring now to Figure 1b, feed air 100 is compressed in 102 and dried in 104 to produce stream 108.  Stream 108 is cooled in main exchanger 110 against returning gaseous product streams, to produce cooled air feed 112.  Stream 112 is distilled in the double column system to produce liquid oxygen 158, high pressure nitrogen gas (stream 174) and low pressure nitrogen gas (stream 180).  The nitrogen ga...