US2017167785A1PendingUtilityA1

Expander-Based LNG Production Processes Enhanced With Liquid Nitrogen

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Assignee: PIERRE JR FRITZPriority: Dec 14, 2015Filed: Nov 10, 2016Published: Jun 15, 2017
Est. expiryDec 14, 2035(~9.4 yrs left)· nominal 20-yr term from priority
Inventors:Fritz Pierre, Jr.Michael W. Miles
F25J 2245/42F25J 1/0283F25J 1/0264F25J 1/0037F25J 1/0254F25J 1/0234F25J 1/0015F25J 2210/42F25J 1/0022F25J 1/0278F25J 2245/90F25J 2210/06F25J 1/0248F25J 1/0025F25J 2230/42F25J 2290/34F25J 2270/16F25J 2270/06F25J 1/0224F25J 1/0265F25J 1/0042F25J 2210/62F25J 2235/60F25J 1/004F25J 1/0288F25J 1/0035F25J 1/0223F25J 1/005
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Claims

Abstract

A method for producing liquefied natural gas (LNG). A natural gas stream is directed to a mechanical refrigeration unit to liquefy the natural gas stream and form a pressurized liquefied natural gas (LNG) stream with a pressure greater than 50 psia (345 kPa) and less than 500 psia (3445 kPa). A liquid refrigerant subcooling unit is provided at a first location. Liquid refrigerant is produced at a second location that is geographically separate from the first location. The produced liquid refrigerant is transported to the first location. The pressurized LNG stream is subcooled in the liquid refrigerant subcooling unit by exchanging heat between the pressurized LNG stream and at least one stream of the liquid refrigerant to thereby produce an LNG stream.

Claims

exact text as granted — not AI-modified
What is claimed is: 
     
         1 . A method for producing liquefied natural gas (LNG), comprising:
 directing a natural gas stream to a mechanical refrigeration unit to liquefy the natural gas stream and form a pressurized liquefied natural gas (LNG) stream with a pressure greater than 50 psia (345 kPa) and less than 500 psia (3445 kPa);   providing a liquid refrigerant subcooling unit at a first location;   producing liquid refrigerant at a second location that is geographically separate from the first location;   transporting the produced liquid refrigerant to the first location; and   subcooling the pressurized LNG stream in the liquid refrigerant subcooling unit by exchanging heat between the pressurized LNG stream and at least one stream of the liquid refrigerant to thereby produce an LNG stream.   
     
     
         2 . The method of  claim 1 , wherein the mechanical refrigeration unit includes an expander-based refrigeration process. 
     
     
         3 . The method of  claim 2 , wherein the expander-based refrigeration process is one of an open loop feed gas expander-based process and a closed loop feed gas expander-based process. 
     
     
         4 . The method of  claim 2 , wherein the expander-based refrigeration process is a feed gas expander-based process that comprises:
 discharging a first cooling stream from a warm-end expander; and   discharging a two-phase stream from a cold-end expander;   wherein a temperature of the first cooling stream is higher than a temperature of the two-phase stream.   
     
     
         5 . The method of  claim 4 , wherein the pressurized LNG stream is a first pressurized LNG stream, and further comprising separating the two-phase stream into a second cooling stream and a second pressurized LNG stream. 
     
     
         6 . The method of  claim 2 , wherein the expander-based refrigeration process is a feed gas expander-based process that comprises:
 discharging a first cooling stream from a warm-end expander; and   location in the dual purpose carrier after the subcooled LNG stream has been offloaded from the dual-purpose carrier.   discharging a second cooling stream from a cool-end expander;   wherein a temperature of the first cooling stream is higher than a temperature of the second cooling stream.   
     
     
         7 . The method of  claim 5 , wherein a pressure of the first cooling stream is the same or substantially the same as a pressure of the second cooling stream. 
     
     
         8 . The method of  claim 7 , further comprising mixing the second pressurized LNG stream with the first pressurized LNG stream prior to directing the pressurized LNG stream to the liquid refrigerant subcooling unit. 
     
     
         9 . The method of  claim 1 , wherein the liquid refrigerant subcooling unit comprises
 at least one heat exchanger, or   at least one compressor and/or expander.   
     
     
         10 . The method of  claim 1 , further comprising:
 using the vaporized liquid refrigerant stream to liquefy a second treated natural gas stream to produce an additional pressurized LNG stream; and   mixing the additional pressurized LNG stream with the pressurized LNG stream prior to the subcooling of the pressurized LNG stream with the liquid refrigerant.   
     
     
         11 . The method of  claim 1 , further comprising locating the mechanical refrigeration unit and the liquid refrigerant subcooling unit on a floating LNG facility. 
     
     
         12 . The method of  claim 1 , further comprising re-liquefying LNG boil-off gas using the liquid refrigerant. 
     
     
         13 . The method of  claim 1 , wherein the liquid refrigerant and/or a liquid refrigerant boil-off gas is used to keep the mechanical refrigeration unit and/or liquid refrigerant subcooling unit equipment cold during turndown and/or shutdown periods of the mechanical refrigeration unit. 
     
     
         14 . The method of  claim 1 , wherein warm liquid refrigerant vapor is used to derime heat exchangers used to exchange heat. 
     
     
         15 . The method of  claim 1 , further comprising:
 transporting the LNG stream from the first location to the second location in a dual-purpose carrier; and   after the LNG stream has been offloaded from the dual-purpose carrier, transporting the liquid refrigerant from the second location to the first location in the dual purpose carrier.   
     
     
         16 . The method of  claim 1 , wherein the mechanical refrigeration unit includes one of a single-mixed refrigerant process, a pure component cascade refrigerant process, or a dual-mixed refrigerant process. 
     
     
         17 . The method of  claim 1 , wherein the pressurized LNG stream has a pressure greater than 100 psia (690 kPa) and less than 400 psia (2758 kPa). 
     
     
         18 . The method of  claim 1 , wherein the pressurized LNG stream has a pressure greater than 200 psia (1379 kPa) and less than 300 psia (2068 kPa). 
     
     
         19 . The method of  claim 1 , wherein the liquid refrigerant comprises liquid nitrogen (LIN), and further comprising producing the LIN by exchanging heat with LNG during LNG regasification. 
     
     
         20 . The method of  claim 1 , wherein the liquid refrigerant comprises liquid nitrogen (LIN), and further comprising:
 pressurizing the LIN to a pressure greater than 400 psia (2758 kPa) to form a high pressure liquid nitrogen stream;   exchanging heat between the high pressure liquid nitrogen stream and the pressurized LNG stream to form a warm nitrogen gas stream; and   reducing, in the liquid refrigerant subcooling unit, a pressure of at least one warmed natural gas stream in at least one expander service, to reduce the pressure of the at least one warmed nitrogen gas stream, and to thereby produce at least one additionally cooled nitrogen gas stream.   
     
     
         21 . The method of  claim 20 , wherein the at least one additionally cooled nitrogen gas stream exchanges heat with the pressurized LNG stream to form warmed nitrogen gas streams. 
     
     
         22 . The method of  claim 20 , further comprising:
 coupling the at least one expander service with   at least one generator to generate electrical power, or   at least one compressor that is used to compress warmed nitrogen gas streams.   
     
     
         23 . The method of  claim 1 , further comprising:
 directing pressurized LNG streams from a plurality of mechanical refrigeration units to the liquid refrigerant subcooling unit to produce at least one LNG stream.   
     
     
         24 . A system for producing liquefied natural gas (LNG), comprising:
 a mechanical refrigeration unit configured to liquefy a natural gas stream using a feed gas expander-based process and form a pressurized liquefied natural gas (LNG) stream with a pressure greater than 50 psia (345 kPa) and less than 500 psia (3445 kPa);   a liquid nitrogen (LIN) subcooling unit located in a first location;   a liquid nitrogen (LIN) stream produced at a second location that is geographically separate from the first location and transported to the LIN subcooling unit;   wherein the LIN subcooling unit is configured to subcool the pressurized LNG stream by exchanging heat between the pressurized LNG stream and at least one stream of the LIN stream to thereby produce an LNG stream and at least one vaporized LIN stream.   
     
     
         25 . The system of  claim 24 , wherein the mechanical refrigeration unit comprises:
 a warm-end expander configured to discharge a first cooling stream therefrom; and   a cold-end expander configured to discharge a two-phase stream therefrom;   wherein a temperature of the first cooling stream is higher than a temperature of the two-phase stream;   wherein the pressurized LNG stream is a first pressurized LNG stream, and   wherein the two-phase stream is configured to be split into a second cooling stream and a second pressurized LNG stream.   
     
     
         26 . The system of  claim 24 , wherein the mechanical refrigeration unit comprises:
 A warm-end expander configured to discharge a first cooling stream therefrom; and   a cool-end expander configured to discharge a second cooling stream therefrom;   wherein a temperature of the first cooling stream is higher than a temperature of the second cooling stream.   
     
     
         27 . The system of  claim 24 , wherein the mechanical refrigeration unit and the liquid refrigerant subcooling unit are located on a floating LNG facility. 
     
     
         28 . The system of  claim 27 , further comprising:
 a dual-purpose carrier configured to transport the LNG stream from the first location to the second location and transport the liquid refrigerant from the second location to the first

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