Method for the production of liquefied natural gas and nitrogen

Abstract

A method for the production of liquefied natural gas (“LNG”) and nitrogen is provided. The method may include the steps of: a) providing a nitrogen production facility, wherein nitrogen production facility comprises: a main heat exchanger, an air separation unit, a nitrogen recycle compressor, a first nitrogen refrigeration supply configured to provide refrigeration to the main heat exchanger for cooling a main air feed, b) providing a secondary refrigeration supply; c) liquefying a natural gas stream using refrigeration from the secondary refrigeration supply to form an LNG product stream; wherein the secondary refrigeration supply is configured to compress and expand a refrigerant to produce refrigeration, wherein the refrigerant of the secondary refrigeration supply is shared with refrigerant of the first nitrogen refrigeration supply

We claim: 
     
         1 . A method for the production of liquefied natural gas (“LNG”) and nitrogen, the method comprising the steps of:
 a) providing a nitrogen production facility, wherein nitrogen production facility comprises: a main heat exchanger, an air separation unit, a nitrogen recycle compressor, a first nitrogen refrigeration supply configured to provide refrigeration to the main heat exchanger for cooling a main air feed; 
 b) providing a secondary refrigeration supply; 
 c) liquefying a natural gas stream using refrigeration from the secondary refrigeration supply to form an LNG product stream; 
 wherein the secondary refrigeration supply is configured to compress and expand a refrigerant to produce refrigeration, wherein the refrigerant of the secondary refrigeration supply is shared with refrigerant of the first nitrogen refrigeration supply. 
 
     
     
         2 . The method as claimed in  claim 1 , wherein the secondary refrigeration supply comprises a third turbine-booster, wherein the third turbine-booster has a third booster and a third turbine. 
     
     
         3 . The method as claimed in  claim 2 , wherein the natural gas stream is liquefied in a secondary heat exchanger. 
     
     
         4 . The method as claimed in  claim 3 , wherein the main heat exchanger is configured to receive a main air feed comprising purified and compressed air at a pressure of at least 3 bar,
 wherein the air separation unit is in fluid communication with a cool side of the main heat exchanger, the air separation unit being configured to receive cooled air from the main 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,   wherein the nitrogen recycle compressor is in fluid communication with a warm side of the main heat exchanger such that the nitrogen recycle compressor is configured to receive a nitrogen recycle from the main heat exchanger, wherein at least a portion of the nitrogen recycle is made up of gaseous nitrogen from the air separation unit,   wherein the first nitrogen refrigeration supply comprises a first turbine-booster which has 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, and   wherein the second nitrogen refrigeration supply comprises a second turbine-booster which has 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.   
     
     
         5 . The method as claimed in  claim 4 , wherein the third booster is in fluid communication with the outlet of the second booster such that the third booster is configured to receive a portion of the boosted nitrogen from the outlet of the second booster. 
     
     
         6 . The method as claimed in  claim 4 , further comprising the step of compressing the portion of the boosted nitrogen in the third booster, cooling the portion of the boosted nitrogen in the secondary heat exchanger, expanding the portion of the boosted nitrogen to an expanded pressure P E  to form a cold refrigerant, and warming the cold refrigerant in the secondary heat exchanger against the natural gas stream to form a warm refrigerant stream. 
     
     
         7 . The method as claimed in  claim 6 , wherein the expanded pressure P E  is selected based on a first condition within the air separation unit. 
     
     
         8 . The method as claimed in  claim 7 , wherein the first condition includes a pressure of a reboiling fluid configured to provide reboiling duty for the bottom reboiler of the single column. 
     
     
         9 . The method as claimed in  claim 7 , wherein the first condition includes the vaporization temperature of bottom liquids surrounding the bottom reboiler of the single column. 
     
     
         10 . The method as claimed in  claim 6 , further comprising the step of cooling the warm refrigerant stream in the main heat exchanger to form a cooled refrigerant stream. 
     
     
         11 . The method as claimed in  claim 10 , wherein the cooled refrigerant stream, or a portion derived therefrom, is used to provide reboiling duty to the bottom reboiler of the single column. 
     
     
         12 . The method as claimed in  claim 11 , further comprising the steps of withdrawing a fraction of partially compressed nitrogen recycle from an internal stage of the nitrogen recycle compressor; introducing the partially compressed nitrogen recycle to the main heat exchanger for cooling before using the partially compressed nitrogen recycle as the heating fluid for the bottom reboiler; and then flashing the partially compressed nitrogen recycle into a top portion of the single column. 
     
     
         13 . The method as claimed in  claim 12 , wherein the warm refrigerant stream is combined with the partially compressed nitrogen recycle from the internal stage of the nitrogen recycle compressor prior to cooling in the main heat exchanger. 
     
     
         14 . The method as claimed in  claim 4 , wherein the third booster is in fluid communication with the outlet of the first booster such that the third booster is configured to receive a portion of the boosted nitrogen from the outlet of the first booster. 
     
     
         15 . The method as claimed in  claim 4 , wherein the third booster is in fluid communication with the outlet of the nitrogen recycle compressor such that the third booster is configured to receive a portion of the boosted nitrogen from the outlet of the nitrogen recycle compressor. 
     
     
         16 . The method as claimed in  claim 4 , wherein both the first and the second boosters are in fluid communication with the outlet of the nitrogen recycle compressor such that both the first and second boosters are configured to receive a portion of the boosted nitrogen from the outlet of the nitrogen recycle compressor. 
     
     
         17 . The method as claimed in  claim 4 , wherein the second turbine and third turbine are the same turbine. 
     
     
         18 . The method as claimed in  claim 17 , wherein the turbine outlet pressure is thermally linked with the reboiler of the single column. 
     
     
         19 . The method as claimed in  claim 1 , further comprising the step of providing a third refrigeration supply, wherein the third refrigeration supply comprises a natural gas expansion turbine. 
     
     
         20 . The method as claimed in  claim 19 , further comprising the step of expanding a high pressure natural gas stream within the natural gas expansion turbine to produce an expanded natural gas stream, and warming the expanded natural gas stream in a secondary heat exchanger.