Domestic gas product from an lng facility

Abstract

An LNG facility capable of producing a domestic gas product from an intermediate stream in the LNG facility. Withdrawing the domestic gas product from a location within the LNG facility can minimize operational disturbances typically caused by extracting a domestic gas product stream upstream of the liquefaction portion of the LNG facility. In addition, withdrawing the domestic gas product from this location can provide increased control of light contaminants (e.g., nitrogen) in open-loop refrigeration cycles and can ultimately result in incremental LNG and/or NGL production.

1 . A process for liquefying a natural gas stream in an LNG facility, said process comprising:
 (a) cooling at least a portion of said natural gas stream in a first refrigeration cycle via indirect heat exchange with a predominantly methane refrigerant;   (b) flashing at least a portion of the cooled natural gas stream to thereby provide a predominantly liquid product stream and a predominantly vapor refrigerant stream;   (c) compressing at least a portion of said predominantly vapor refrigerant stream to thereby provide a compressed refrigerant stream; and   (d) separating at least a portion of said compressed refrigerant stream into a domestic gas fraction and a compressed refrigerant fraction.   
     
     
         2 . The process of  claim 1 , further comprising, prior to step (a), cooling at least a portion of said natural gas stream in an upstream refrigeration cycle via indirect heat exchange with an upstream refrigerant. 
     
     
         3 . The process of  claim 2 , further comprising cooling at least a portion of said compressed refrigerant fraction in said upstream refrigeration cycle. 
     
     
         4 . The process of  claim 3 , wherein said upstream refrigeration cycle comprises a closed-loop refrigeration cycle. 
     
     
         5 . The process of  claim 3 , wherein said upstream refrigerant comprises a pure component refrigerant. 
     
     
         6 . The process of  claim 3 , wherein said upstream refrigerant comprises propane and/or ethylene. 
     
     
         7 . The process of  claim 1 , further comprising, prior to step (d) and subsequent to step (c), cooling at least a portion of said compressed refrigerant stream. 
     
     
         8 . The process of  claim 1 , wherein the mass flow rate of said domestic gas fraction is at least about 2 percent of the mass flow rate of said compressed refrigerant stream. 
     
     
         9 . The process of  claim 1 , further comprising, optionally, withdrawing a fuel gas stream from said compressed refrigerant fraction and/or said domestic gas fraction. 
     
     
         10 . The process of  claim 1 , wherein said vapor refrigerant stream provides at least a portion of said cooling of step (a). 
     
     
         11 . The process of  claim 1 , further comprising producing liquefied natural gas (LNG) that comprises at least a portion of said predominantly liquid product stream. 
     
     
         12 . The process of  claim 11 , wherein the produced LNG is at about atmospheric pressure. 
     
     
         13 . The process of  claim 1 , further comprising routing said domestic gas fraction to a location outside of said LNG facility, wherein said routing does not require the use of a compressor other than the compressor or compressors used to carry out step (d). 
     
     
         14 . The process of  claim 1 , wherein said domestic gas fraction has a pressure in the range of from about 35 to about 75 barg. 
     
     
         15 . The process of  claim 1 , further comprising vaporizing LNG produced via steps (a)-(d). 
     
     
         16 . A computer simulation process comprising utilizing a computer to simulate the process of  claim 1 . 
     
     
         17 . A process for liquefying a natural gas stream in an LNG facility, said process comprising:
 (a) cooling at least a portion of said natural gas stream in an upstream refrigeration cycle of said LNG facility via indirect heat exchange with an upstream refrigerant to thereby provide a cooled natural gas stream;   (b) further cooling at least a portion of said cooled natural gas stream via indirect heat exchange with a predominantly methane refrigerant stream in a methane refrigeration cycle to thereby produce a further cooled natural gas stream and a warmed refrigerant stream;   (c) separating at least a portion of said warmed refrigerant stream into a domestic gas fraction and a refrigerant fraction; and   (d) cooling at least a portion of said refrigerant fraction in said upstream refrigeration cycle via indirect heat exchange with said upstream refrigerant.   
     
     
         18 . The process of  claim 17 , further comprising, prior to step (c), flashing at least a portion of said further cooled natural gas stream to thereby produce a vapor refrigerant stream and a liquid product stream. 
     
     
         19 . The process of  claim 17 , further comprising, prior to step (c), compressing at least a portion of said warmed refrigerant stream, wherein said domestic gas fraction comprises at least a portion of the compressed warmed refrigerant. 
     
     
         20 . The process of  claim 19 , further comprising, prior to step (c), cooling at least a portion of said compressed warmed refrigerant to thereby produce a compressed cooled refrigerant, wherein said domestic gas fraction comprises at least a portion of said compressed cooled refrigerant. 
     
     
         21 . The process of  claim 17 , wherein the mass flow rate of said domestic gas fraction is at least about 2 percent of the mass flow rate of said warmed refrigerant stream. 
     
     
         22 . The process of  claim 17 , further comprising, optionally, withdrawing a fuel gas stream from said refrigerant fraction and/or said domestic gas fraction. 
     
     
         23 . The process of  claim 17 , wherein said upstream refrigeration cycle comprises a closed-loop refrigeration cycle. 
     
     
         24 . The process of  claim 17 , wherein said methane refrigeration cycle comprises an open-loop refrigeration cycle. 
     
     
         25 . The process of  claim 17 , wherein said upstream refrigerant comprises ethylene and/or ethane. 
     
     
         26 . The process of  claim 17 , wherein said upstream refrigerant comprises propylene and/or propane. 
     
     
         27 . The process of  claim 17 , wherein said domestic gas fraction has a pressure in the range of from about 35 to about 75 barg. 
     
     
         28 . The process of  claim 17 , further comprising, vaporizing LNG produced via steps (a)-(d). 
     
     
         29 . A computer simulation process comprising utilizing a computer to simulate the process of  claim 17 . 
     
     
         30 . A process for liquefying a natural gas stream in an LNG facility, said process comprising:
 (a) cooling at least a portion of said natural gas stream in a first refrigeration cycle via indirect heat exchange with a first refrigerant to thereby produce a cooled predominantly methane stream;   (b) separating at least a portion of said cooled predominantly methane stream in a distillation column to thereby provide a heavies-rich stream and a heavies-depleted stream;   (c) subjecting at least a portion of said heavies-depleted stream to expansion cooling to thereby produce LNG having a pressure in the range of from about 0 to about 40 psia; and   (d) prior to at least a portion of said expansion cooling of step (c), withdrawing a domestic gas fraction from said heavies-depleted stream.   
     
     
         31 . The process of  claim 30 , wherein said expansion cooling includes flashing at least a portion of said heavies-depleted stream to thereby produce a predominantly vapor stream and a predominantly liquid stream, wherein said domestic gas fraction comprises at least a portion of said predominantly vapor stream, wherein said LNG comprises at least a portion of said predominantly liquid stream. 
     
     
         32 . The process of  claim 31 , further comprising using at least a portion of said predominantly vapor stream to cool at least a portion of said heavies-depleted stream via indirect heat exchange in a second refrigeration cycle to thereby produce a warmed predominantly vapor stream, wherein said domestic gas product comprises at least a portion of said warmed predominantly vapor stream. 
     
     
         33 . The process of  claim 32 , further comprising compressing at least a portion of said warmed predominantly vapor stream to thereby produce a compressed warmed predominantly vapor stream, wherein said domestic gas product comprises at least a portion of said compressed warmed predominantly vapor stream. 
     
     
         34 . The process of  claim 30 , further comprising, prior to step (c), cooling at least a portion of said heavies-depleted stream in a second refrigeration cycle via indirect heat exchange with a second refrigerant. 
     
     
         35 . The process of  claim 34 , wherein said second refrigeration cycle comprises an open-loop methane refrigeration cycle. 
     
     
         36 . An LNG facility for liquefying a natural gas stream, said LNG facility comprising: an open-loop refrigeration cycle operable to cool at least a portion of said natural gas stream via indirect heat exchange with a first refrigerant, wherein said open-loop refrigeration cycle comprises—
 a first heat exchanger defining a first cooling pass and a first refrigerant pass, wherein said first heat exchanger is operable to cool at least a portion of said natural gas stream in said first cooling pass via indirect heat exchange with said first refrigerant in said first refrigerant pass;   an expander defining an expander inlet and an expander outlet, wherein said expander inlet is coupled in fluid communication with said first cooling pass;   a vapor-liquid separator defining a separator inlet, a lower liquid outlet, and an upper vapor outlet, wherein said separator inlet is coupled in fluid flow communication with said expander outlet, wherein said upper vapor outlet is coupled in fluid flow communication with said first refrigerant pass;   a first refrigerant compressor defining an inlet port and an outlet port, wherein said inlet port is coupled in fluid flow communication with said first refrigerant pass;   a compressed refrigerant conduit for routing fluid flow from said outlet port of said compressor to a location within said LNG facility; and   a domestic gas conduit for routing fluid flow from said outlet port of said compressor and/or said compressed refrigerant conduit to a location outside said LNG facility.   
     
     
         37 . The facility of  claim 36 , further comprising a closed-loop refrigeration cycle located upstream of said open-loop refrigeration cycle, wherein said closed-loop refrigeration cycle is operable to cool at least a portion of said natural gas stream via indirect heat exchange with a second refrigerant. 
     
     
         38 . The facility of  claim 36 , wherein said location within said LNG facility is in said closed-loop refrigeration cycle. 
     
     
         39 . The facility of  claim 37 , wherein said closed-loop refrigeration cycle is operable to cool the fluid routed thereto by said compressed refrigerant conduit via indirect heat exchange with said second refrigerant. 
     
     
         40 . The facility of  claim 37 , wherein said closed-loop refrigeration cycle comprises a second heat exchanger defining a second cooling pass and a second refrigerant pass, wherein said second heat exchanger is operable to cool at least a portion of said natural gas stream in said second cooling pass via indirect heat exchange with said second refrigerant in said second refrigerant pass. 
     
     
         41 . The facility of  claim 40 , wherein said second heat exchanger further comprises a third cooling pass, wherein said location inside said LNG facility is said third cooling pass, wherein said second heat exchanger is operable to cool fluid routed to said third cooling pass by said compressed refrigerant conduit via indirect heat exchange with said second refrigerant in said second refrigerant pass. 
     
     
         42 . The facility of  claim 36 , wherein said LNG facility comprises a plurality of gas turbines each defining a fuel gas inlet, wherein said domestic gas conduit does not route fluid flow to any of said fuel gas inlets. 
     
     
         43 . The facility of  claim 36 , further comprising at least two downstream expanders coupled in fluid communication with said expander outlet. 
     
     
         44 . The facility of  claim 43 , further comprising a downstream vapor-liquid separator coupled between and in fluid flow communication with said at least two downstream expanders. 
     
     
         45 . The facility of  claim 44 , wherein said first heat exchanger further comprises an additional refrigerant pass coupled in fluid flow communication with said downstream vapor-liquid separator. 
     
     
         46 . The facility of  claim 45 , wherein said first refrigerant compressor further defines an additional inlet port coupled in fluid flow communication with said additional refrigerant pass. 
     
     
         47 . The facility of  claim 36 , further comprising a third heat exchanger interposed in said compressed refrigerant conduit and operable to cool fluids flowing through said compressed refrigerant conduit, wherein said domestic gas conduit is coupled in fluid flow communication with said compressed refrigerant conduit downstream of said third heat exchanger. 
     
     
         48 . The facility of  claim 36 , wherein said LNG facility is a cascade-type LNG facility.