WO2019122656A1 - Method for liquefying a natural gas stream containing nitrogen - Google Patents

Method for liquefying a natural gas stream containing nitrogen Download PDF

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Publication number
WO2019122656A1
WO2019122656A1 PCT/FR2018/053334 FR2018053334W WO2019122656A1 WO 2019122656 A1 WO2019122656 A1 WO 2019122656A1 FR 2018053334 W FR2018053334 W FR 2018053334W WO 2019122656 A1 WO2019122656 A1 WO 2019122656A1
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WO
WIPO (PCT)
Prior art keywords
stream
natural gas
cooled
gas
nitrogen
Prior art date
Application number
PCT/FR2018/053334
Other languages
French (fr)
Inventor
Henri Paradowski
Sébastien LICHTLE
Marie MUHR
Original Assignee
L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude filed Critical L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude
Priority to AU2018392161A priority Critical patent/AU2018392161A1/en
Priority to RU2020121187A priority patent/RU2797474C2/en
Publication of WO2019122656A1 publication Critical patent/WO2019122656A1/en

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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/0002—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the fluid to be liquefied
    • F25J1/0022—Hydrocarbons, e.g. natural gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/003—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production
    • F25J1/0032—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration"
    • F25J1/004—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration" by flash gas recovery
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/003—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production
    • F25J1/0032—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration"
    • F25J1/0045—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration" by vaporising a liquid return stream
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/003—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production
    • F25J1/0047—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle
    • F25J1/0052—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle by vaporising a liquid refrigerant stream
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0211—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a multi-component refrigerant [MCR] fluid in a closed vapor compression cycle
    • F25J1/0219—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a multi-component refrigerant [MCR] fluid in a closed vapor compression cycle in combination with an internal quasi-closed refrigeration loop, e.g. using a deep flash recycle loop
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0228—Coupling of the liquefaction unit to other units or processes, so-called integrated processes
    • F25J1/0235—Heat exchange integration
    • F25J1/0237—Heat exchange integration integrating refrigeration provided for liquefaction and purification/treatment of the gas to be liquefied, e.g. heavy hydrocarbon removal from natural gas
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    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
    • F25J1/0279—Compression of refrigerant or internal recycle fluid, e.g. kind of compressor, accumulator, suction drum etc.
    • F25J1/0292—Refrigerant compression by cold or cryogenic suction of the refrigerant gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/0204—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the feed stream
    • F25J3/0209—Natural gas or substitute natural gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/0228—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
    • F25J3/0233—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of CnHm with 1 carbon atom or more
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/0228—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
    • F25J3/0257—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of nitrogen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2200/00—Processes or apparatus using separation by rectification
    • F25J2200/02—Processes or apparatus using separation by rectification in a single pressure main column system
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2200/00—Processes or apparatus using separation by rectification
    • F25J2200/30—Processes or apparatus using separation by rectification using a side column in a single pressure column system
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2200/00—Processes or apparatus using separation by rectification
    • F25J2200/74—Refluxing the column with at least a part of the partially condensed overhead gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2205/00—Processes or apparatus using other separation and/or other processing means
    • F25J2205/02—Processes or apparatus using other separation and/or other processing means using simple phase separation in a vessel or drum
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2210/00—Processes characterised by the type or other details of the feed stream
    • F25J2210/04—Mixing or blending of fluids with the feed stream
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2215/00—Processes characterised by the type or other details of the product stream
    • F25J2215/04—Recovery of liquid products
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
    • F25J2230/08—Cold compressor, i.e. suction of the gas at cryogenic temperature and generally without afterstage-cooler
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
    • F25J2230/32—Compression of the product stream
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2245/00—Processes or apparatus involving steps for recycling of process streams
    • F25J2245/02—Recycle of a stream in general, e.g. a by-pass stream
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/02—Internal refrigeration with liquid vaporising loop
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/08—Internal refrigeration by flash gas recovery loop
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/12—External refrigeration with liquid vaporising loop
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/66—Closed external refrigeration cycle with multi component refrigerant [MCR], e.g. mixture of hydrocarbons
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    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/88—Quasi-closed internal refrigeration or heat pump cycle, if not otherwise provided

Definitions

  • the present invention relates to the field of liquefaction of natural gas.
  • the liquefaction of natural gas consists of condensing the natural gas and subcooling it to a temperature sufficiently low that it can remain liquid at atmospheric pressure. It is then transported in LNG carriers.
  • US 6,105,389 proposes a liquefaction process comprising two refrigerant mixtures flowing in two closed and independent circuits. Each of the circuits operates through a compressor communicating to the refrigerant mixture the power required to cool the natural gas. Each compressor is driven by a gas turbine which is selected from the standard ranges proposed in the trade. However, the power of currently available gas turbines is limited.
  • US 6,763,680 discloses a liquefaction process in which the pressurized liquefied natural gas is expanded in at least two stages so as to obtain at least two gaseous fractions.
  • the pressurized liquefied natural gas is cooled by reboiling a denitrogenation column.
  • a first liquid fraction depleted of nitrogen and a first gas fraction enriched in nitrogen are obtained.
  • This liquid fraction is expanded again to give a liquefied natural gas low in nitrogen and a second gaseous fraction. At least one gaseous fraction is re-compressed and then mixed with the natural gas before condensation.
  • a liquefaction process for natural gas as described in the prior art is not suitable when said natural gas to be liquefied comprises too high a nitrogen level, that is to say greater than 4%.
  • the present invention proposes to improve the process disclosed by US 6,763,680.
  • One of the objects of the present invention is to allow a reduction in the investment cost required for a liquefaction plant.
  • Another object of the The present invention is to achieve, under better conditions, a separation of nitrogen that can be contained in the gas.
  • the inventors of the present invention have developed a solution for producing, from a fixed amount of natural gas, liquefied natural gas low in nitrogen whose flow is increased and while minimizing the costs required for deployment. of this type of process.
  • the present invention relates to a method of liquefying a natural gas feed stream comprising the following steps:
  • step b) characterized in that at least a portion of the liquid stream from step b) is used during step c) to cool the vapor stream from step b) in said heat exchanger.
  • the subject of the invention is also:
  • step a) said natural gas supply stream is cooled and a second refrigerant mixture by indirect heat exchange with at least a first refrigerant mixture for cooling. obtain a cooled natural gas and a cooled second cooling mixture, then the cooled natural gas is condensed and cooled by indirect heat exchange with the cooled second cooling mixture and with at least a portion of the gas stream obtained in step d) for obtain a liquefied natural gas.
  • step b) the stream from step a) is cooled in a means for reboiling said denitrogenation column to the temperature T2.
  • a process as defined above characterized in that the stream cooled to the temperature T2 is expanded in an expansion means prior to introduction into the denitrogenation column.
  • a process as defined above characterized in that at least a portion of the liquid stream from step d) is used as reflux at the top of the denitrogenation column.
  • a method as defined above characterized in that it comprises the following steps:
  • T1 is between - 140 ° C and -120 ° C.
  • a process as defined above characterized in that P2 is between 3 bar abs and 10 bar abs, P1 is between 4 MPa and 7 MPa.
  • step b) the mixture of natural gas and the second refrigerant mixture are cooled to a temperature between -70 ° C and -35 ° C by heat exchange with the first refrigerant mixture.
  • the method according to the invention makes it possible to substantially increase the production capacity by adding a limited number of additional equipment.
  • the method according to the invention is particularly advantageous when each of the refrigeration circuits uses a refrigerant mixture which is completely condensed, expanded and vaporized.
  • feed stream refers to any composition containing hydrocarbons including at least methane.
  • the heat exchanger may be any heat exchanger, unit or other arrangement adapted to allow the passage of a number of flows, and thus allow a direct or indirect heat exchange between one or more lines of refrigerant, and a or multiple feed streams.
  • a natural gas feed stream 1 is introduced into a heat exchange unit E1 at a temperature T1.
  • the feed stream 1 may contain methane, ethane, propane, hydrocarbons having at least four carbon atoms. This stream may contain traces of contaminants eg H2O 0-1 ppm, H2S 4 ppm, CO2 50 ppm.
  • the natural gas feed stream comprises strictly more than 1 mol% of nitrogen, but the specifications impose a maximum content of 1 mol% nitrogen in the LNG.
  • the unit E1 can contain several heat exchangers (2, 3, 1 12).
  • the stream 1 natural gas arrives via the pipe 51 for example at a pressure of between 4 MPa and 7 MPa and at a temperature between 0 ° C and 60 ° C.
  • the natural gas flowing in the duct 51 is combined with the gas 50 to form a mixture of natural gas circulating in the duct 51.
  • the gas flowing in the duct 51, a first refrigerant mixture 201 and a second refrigerant mixture 109 enter the exchanger E1 to circulate in parallel directions and co-current.
  • the natural gas exits the exchanger E1 through line 4, for example at a temperature between -35 ° C and -70 ° C.
  • the second refrigerant mixture exits completely condensed from the exchanger E1 through the duct 100, for example at a temperature of between -35 ° C. and -70 ° C.
  • the exchanger E1 three fractions (202, 212, 222) of the first refrigerant mixture in the liquid phase are successively withdrawn.
  • the fractions are expanded (207, 217 and 227) through the expansion valves 21 1, 221 and 231 at three different pressure levels, and then vaporized in the exchanger E 1 by heat exchange with the natural gas stream circulating in the conduit. 51, the second refrigerant mixture and a portion of the first refrigerant mixture.
  • the three vaporized fractions (208, 218, 228) are sent to different stages (257, 253, 250) of the compressor K1.
  • the vaporized fractions are compressed in the compressor K1 and then condensed in the condenser E101 by heat exchange with an external cooling fluid, for example water or air.
  • the first refrigerant mixture 201 from the condenser E101 is sent into the exchanger E1.
  • the pressure of the first refrigerant mixture at the outlet of the compressor K1 may be between 2 MPa and 6 MPa.
  • the temperature of the first refrigerant mixture at the outlet of the condenser E101 can be between 10 ° C. and 55 ° C.
  • the first refrigerant mixture may be formed by a mixture of hydrocarbons such as a mixture of ethane and propane, but may also contain methane, butane and / or pentane.
  • the proportions in molar fraction (%) of the components of the first refrigerant mixture may be:
  • the natural gas flowing in the duct 4 can be fractionated, that is to say that a portion of the hydrocarbons containing at least two carbon atoms is separated from the natural gas, using a device known from the state of the art.
  • the fractionated natural gas is sent into an E2 heat exchanger.
  • the C2 + hydrocarbons collected are sent to fractionation columns comprising a deethanizer.
  • the light fraction collected at the top of the deethanizer can be mixed with the natural gas circulating in the conduit 4.
  • the liquid fraction collected at the bottom of the deethanizer is sent to a depropanizer.
  • the gas flowing in the duct 4 and the second refrigerant mixture flowing in the duct 100 enter the exchanger E2 to circulate in parallel directions and co-current.
  • the second refrigerant mixture leaving the exchanger E2 through the conduit 101 is expanded by the expansion member T3.
  • the expansion member T3 may be a turbine, a valve or a combination of a turbine and a valve.
  • the second refrigerated mixture expanded from the turbine T3 is sent through the conduit 102 in the exchanger E2 to be vaporized by countercurrently cooling the natural gas and the second refrigerant mixture.
  • the second vaporized refrigerant mixture 103 is compressed by the compressor K2 and then cooled in the indirect heat exchanger C2 by heat exchange with an external cooling fluid, for example water or water. 'air.
  • the second refrigerant mixture 109 from the exchanger C2 is sent into the exchanger.
  • the pressure of the second refrigerant mixture at the outlet of the compressor K2 may be between 2 MPa and 8 MPa.
  • the temperature of the second refrigerant mixture at the outlet of exchanger C2 may be between 10 ° C. and 55 ° C.
  • the second refrigerant mixture is not split into separate fractions, but, to optimize the approach in the exchanger E2, the second refrigerant mixture can also be used. be separated into two or three fractions, each fraction being expanded to a different pressure level and then sent to different stages of the compressor K2.
  • the second refrigerant mixture is formed for example by a mixture of hydrocarbons and nitrogen such as a mixture of methane, ethane and nitrogen but may also contain propane and / or butane.
  • the proportions in mole fraction (%) of the components of the second refrigerant mixture may be:
  • the natural gas comes out of the heat exchanger E2 through line 10 at a temperature which is preferably at least 10 ° C. higher than the bubble temperature of the liquefied natural gas produced at atmospheric pressure (bubble temperature means the temperature at which the first vapor bubbles are formed in a liquid natural gas at a given pressure) and at a pressure P1b identical to the inlet pressure P1 of the natural gas, with the pressure drops close to it.
  • bubble temperature means the temperature at which the first vapor bubbles are formed in a liquid natural gas at a given pressure
  • P1b identical to the inlet pressure P1 of the natural gas
  • the natural gas flowing in the pipe 10 is cooled in the reboiler E4 of a denitrogenation column C0.
  • the natural gas 12 is cooled by heating the bottom (25, 26) of the column C0 by indirect heat exchange, then is expanded in the expansion member V1.
  • the diphasic mixture 13 obtained at the outlet of the member V1 is introduced into the column C0 at a level N1.
  • a gas fraction 38 enriched in nitrogen is recovered. It is sent to be cooled in a heat exchanger E5 and then separated in a phase separator pot B2 in the form of a gaseous fraction 21 and a liquid fraction 21 '.
  • the gaseous fraction 21 discharged from the pot B2 is introduced into the exchanger E2.
  • the gaseous fraction countercurrently cools the stream 4 of natural gas, then is directed via the conduit 22 into the compressor K4.
  • the liquid fraction 21 'discharged from the pot B2 is used as reflux at the top of the column CO.
  • the liquid fraction 31, depleted in nitrogen, discharged in the column tank CO is separated into two parts 32 and 34.
  • a first part 32 is cooled in a heat exchanger E3, then is expanded in an expansion member 33 'at a pressure between 0.05MPa and 0.5MPa.
  • the second portion 34 of the liquid fraction 31 is expanded in an expansion member 34 'and then fed to a heat exchanger E5.
  • the vaporization of this stream 35 gives a current 36 and represents the majority of the refrigeration necessary for cooling the gas stream 38 from the head of the column CO in the heat exchanger E5.
  • the expansion members such as V1, 33 'and 34' may be an expansion turbine, an expansion valve or a combination of a turbine and a valve.
  • the two-phase mixture obtained at the outlet of the expansion element 33 ' is mixed with the flow 36 to give the two-phase mixture 37.
  • the flow 37 is separated in a phase separator pot B1 in the form of a gas fraction 41 and a liquid fraction 61.
  • the gaseous fraction 41 is introduced into the exchanger E3.
  • the gaseous fraction 41 cools the liquid fraction 32 coming from the liquid stream 31 recovered in the vat of the column C1, then is directed by the duct 42 into the compressor K3.
  • the gaseous mixture 49 leaving the compressor K3 is sent to a heat exchanger C3 to be cooled by air or water.
  • the gaseous mixture 50 leaving the exchanger C3 is then mixed with the stream 1 of natural gas flowing in the pipe 51.
  • the liquid fraction 61 discharged from the flask B1 forms the liquefied natural gas (LNG) produced.
  • the gas 28 flowing through the conduit 27 may serve as fuel gas, energy source for the operation of a liquefaction plant.
  • the denitrogenated LNG stream 31 produced at the bottom of the column CO is divided into two parts:
  • stream 32 is countercurrently cooled with the flash gas, stream 41, to give the stream 33 which is expanded to the pressure P3 to be mixed with the stream 36 and to give the stream 37 which feeds the flash balloon LNG B1.
  • Natural gas arrives via line 01 at a pressure of 60 bar and a temperature of 15 ° C.
  • the composition of this gas in molar fraction is as follows:
  • the mixed refrigerant of the pre-cooling cycle (PR) is the same for both processes: 50% ethane and 50% propane. It is implemented in the same way, only flows are adapted to the needs.
  • LR the refrigerant performing the subcooling of natural gas.
  • the new process makes it possible to produce LNG that is low in nitrogen while saving energy.

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Abstract

A method for liquefying a natural gas feed stream comprising the following steps: Step a): Cooling the feed gas stream in order to obtain a liquefied natural gas stream at a temperature T1 and a pressure P1b; Step b): Introducing the stream from step a) into a denitrogenation column at a pressure P2 and a temperature T2 lower than T1 in order to produce, at the bottom, a denitrogenated liquefied natural gas stream and, at the head, a nitrogen-enriched vapour stream; Step c): Condensing the nitrogen-enriched vapour stream from step b) in a heat exchanger in order to produce a two-phase stream; Step d): Introducing the two-phase stream from step c) into a phase separator vessel in order to produce a liquid stream and a nitrogen-enriched gas stream; characterised in that at least part of the liquid stream from step b) is used during step c) to cool the vapour stream from step b) in said heat exchanger.

Description

Procédé de liquéfaction d’un courant de gaz naturel contenant de l’azote  Process for liquefying a stream of natural gas containing nitrogen
La présente invention a trait au domaine de la liquéfaction du gaz naturel. La liquéfaction du gaz naturel consiste à condenser le gaz naturel et à le sous refroidir jusqu'à une température suffisamment basse pour qu'il puisse rester liquide à la pression atmosphérique. Il est alors transporté dans des méthaniers. The present invention relates to the field of liquefaction of natural gas. The liquefaction of natural gas consists of condensing the natural gas and subcooling it to a temperature sufficiently low that it can remain liquid at atmospheric pressure. It is then transported in LNG carriers.
A l'heure actuelle, le commerce international du gaz naturel liquide (GNL) se développe rapidement, mais l'ensemble de la chaîne de production du GNL requiert des investissements considérables. Réduire le niveau de ces investissements par tonne de GNL produit est donc un objectif prioritaire. Il est également important de réduire l’empreinte carbone en diminuant la consommation de combustible.  At present, international trade in liquid natural gas (LNG) is growing rapidly, but the entire LNG production chain requires considerable investment. Reducing the level of these investments per tonne of LNG produced is therefore a priority objective. It is also important to reduce the carbon footprint by reducing fuel consumption.
Le document US 6 105 389 propose un procédé de liquéfaction comportant deux mélanges réfrigérants circulant dans deux circuits fermés et indépendants. Chacun des circuits fonctionne grâce à un compresseur communiquant au mélange réfrigérant la puissance nécessaire pour refroidir le gaz naturel. Chaque compresseur est entraîné par une turbine à gaz qui est choisie parmi les gammes standards proposées dans le commerce. Cependant la puissance des turbines à gaz actuellement disponibles est limitée.  US 6,105,389 proposes a liquefaction process comprising two refrigerant mixtures flowing in two closed and independent circuits. Each of the circuits operates through a compressor communicating to the refrigerant mixture the power required to cool the natural gas. Each compressor is driven by a gas turbine which is selected from the standard ranges proposed in the trade. However, the power of currently available gas turbines is limited.
Le document US 6 763 680 décrit un procédé de liquéfaction où le gaz naturel liquéfié sous pression est détendu en au moins deux étapes de façon à obtenir au moins deux fractions gazeuses. Le gaz naturel liquéfié sous pression est refroidi en assurant le rebouillage d’une colonne de déazotation.  US 6,763,680 discloses a liquefaction process in which the pressurized liquefied natural gas is expanded in at least two stages so as to obtain at least two gaseous fractions. The pressurized liquefied natural gas is cooled by reboiling a denitrogenation column.
En sortie de colonne, on obtient une première fraction liquide appauvrie en azote et une première fraction gazeuse enrichie en azote. Cette fraction liquide est détendue à nouveau pour donner un gaz naturel liquéfié pauvre en azote et une seconde fraction gazeuse. Au moins une fraction gazeuse est re-comprimée puis mélangée avec le gaz naturel avant condensation.  At the outlet of the column, a first liquid fraction depleted of nitrogen and a first gas fraction enriched in nitrogen are obtained. This liquid fraction is expanded again to give a liquefied natural gas low in nitrogen and a second gaseous fraction. At least one gaseous fraction is re-compressed and then mixed with the natural gas before condensation.
Par ailleurs, un procédé de liquéfaction de gaz naturel tel que décrit dans l’art antérieur ne convient pas lorsque ledit gaz naturel à liquéfier comprend un taux d’azote trop important, c’est-à-dire supérieur à 4%. La présente invention propose de perfectionner le procédé divulgué par le document US 6 763 680.  Furthermore, a liquefaction process for natural gas as described in the prior art is not suitable when said natural gas to be liquefied comprises too high a nitrogen level, that is to say greater than 4%. The present invention proposes to improve the process disclosed by US 6,763,680.
Un des objets de la présente invention est de permettre une réduction du coût d'investissement requis pour une usine de liquéfaction. Un autre objet de la présente invention est de réaliser, dans de meilleures conditions, une séparation de l'azote pouvant être contenu dans le gaz. One of the objects of the present invention is to allow a reduction in the investment cost required for a liquefaction plant. Another object of the The present invention is to achieve, under better conditions, a separation of nitrogen that can be contained in the gas.
Ainsi, les inventeurs de la présente invention ont mis au point une solution permettant de produire, à partir d’une quantité fixe de gaz naturel, du gaz naturel liquéfié pauvre en azote dont le débit est augmenté et tout en minimisant les coûts nécessaires au déploiement de ce type de procédés.  Thus, the inventors of the present invention have developed a solution for producing, from a fixed amount of natural gas, liquefied natural gas low in nitrogen whose flow is increased and while minimizing the costs required for deployment. of this type of process.
La présente invention a pour objet un procédé de liquéfaction d’un courant d’alimentation de gaz naturel comprenant les étapes suivantes :  The present invention relates to a method of liquefying a natural gas feed stream comprising the following steps:
Etape a) : Refroidissement du courant gazeux d’alimentation pour obtenir un courant de gaz naturel liquéfié à une température T1 et une pression P1 b ;  Step a): cooling of the feed gas stream to obtain a stream of liquefied natural gas at a temperature T1 and a pressure P1 b;
Etape b) : Introduction du courant issu de l’étape a) dans une colonne de déazotation à une pression P2 et une température T2 inférieure à T1 pour produire, en cuve de ladite colonne, un courant de gaz naturel liquéfié déazoté et, en tête de ladite colonne, un courant de vapeur enrichi en azote ;  Step b): Introduction of the stream from step a) into a denitrogenation column at a pressure P2 and a temperature T2 less than T1 to produce, in the tank of said column, a denitrogenated liquefied natural gas stream and at the top of said column, a vapor stream enriched in nitrogen;
Etape c) : Condensation au moins partielle du courant de vapeur enrichi en azote issu de l’étape b) dans un échangeur de chaleur pour produire un courant diphasique ;  Step c): At least partial condensation of the nitrogen-enriched vapor stream from step b) in a heat exchanger to produce a two-phase current;
Etape d) : Introduction du courant diphasique issu de l’étape c) dans un pot séparateur de phases pour produire au moins deux phases dont un courant liquide et un courant gazeux enrichi en azote ;  Step d): Introduction of the two-phase current from step c) into a phase separator pot to produce at least two phases including a liquid stream and a nitrogen-enriched gas stream;
caractérisé en ce qu’au moins une partie du courant liquide issu de l’étape b) est utilisée durant l’étape c) pour refroidir le courant de vapeur issu de l’étape b) dans ledit échangeur de chaleur. characterized in that at least a portion of the liquid stream from step b) is used during step c) to cool the vapor stream from step b) in said heat exchanger.
Selon d’autres modes de réalisation, l’invention a aussi pour objet :  According to other embodiments, the subject of the invention is also:
- Un procédé tel que défini ci-dessus, caractérisé en ce que lors de l’étape a), on refroidit ledit courant d’alimentation de gaz naturel et un deuxième mélange réfrigérant par échange de chaleur indirect avec au moins un premier mélange réfrigérant pour obtenir un gaz naturel refroidi et un deuxième mélange réfrigérant refroidi, puis on condense et on refroidit le gaz naturel refroidi par échange de chaleur indirect avec le deuxième mélange réfrigérant refroidi et avec au moins une partie du courant gazeux obtenu à l'étape d) pour obtenir un gaz naturel liquéfié.  - A process as defined above, characterized in that during step a), said natural gas supply stream is cooled and a second refrigerant mixture by indirect heat exchange with at least a first refrigerant mixture for cooling. obtain a cooled natural gas and a cooled second cooling mixture, then the cooled natural gas is condensed and cooled by indirect heat exchange with the cooled second cooling mixture and with at least a portion of the gas stream obtained in step d) for obtain a liquefied natural gas.
Un procédé tel que défini ci-dessus, précédentes, caractérisé en ce que préalablement à l’étape b), le courant issu de l’étape a) est refroidi dans un moyen de rebouillage de ladite colonne de déazotation jusqu’à la température T2. A process as defined above, characterized in that prior to step b), the stream from step a) is cooled in a means for reboiling said denitrogenation column to the temperature T2.
Un procédé tel que défini ci-dessus, caractérisé en ce que le courant refroidi à la température T2 est détendu dans un moyen de détente avant son introduction dans la colonne de déazotation.  A process as defined above, characterized in that the stream cooled to the temperature T2 is expanded in an expansion means prior to introduction into the denitrogenation column.
Un procédé tel que défini ci-dessus, caractérisé en ce qu’au moins une partie du courant liquide issu de l’étape d) est utilisée comme reflux en tête de la colonne de déazotation.  A process as defined above, characterized in that at least a portion of the liquid stream from step d) is used as reflux at the top of the denitrogenation column.
Un procédé tel que défini ci-dessus, caractérisé en ce qu’il comprend les étapes suivantes :  A method as defined above, characterized in that it comprises the following steps:
Etape e) : on refroidit la partie du courant liquide issu de l’étape b) non utilisée durant l’étape c) par échange de chaleur indirect avec une deuxième fraction gazeuse obtenue à l'étape f) pour obtenir une fraction liquide refroidie et une deuxième fraction gazeuse réchauffée,  Step e): the part of the liquid stream resulting from step b) not used during step c) is cooled by indirect heat exchange with a second gaseous fraction obtained in step f) to obtain a cooled liquid fraction and a second gaseous fraction heated,
Etape f) : on détend la fraction liquide refroidie obtenue à l'étape, puis on l’introduit dans un deuxième pot séparateur de phases, pour obtenir un gaz naturel liquéfié et la deuxième fraction gazeuse,  Step f): the cooled liquid fraction obtained in the step is expanded and then introduced into a second phase separator pot to obtain a liquefied natural gas and the second gaseous fraction,
Etape g) : on comprime jusqu’à une pression P1 , au moins une partie de ladite deuxième fraction gazeuse réchauffée.  Step g): at least a portion of said second heated gas fraction is compressed to a pressure P1.
Un procédé tel que défini ci-dessus, caractérisé en ce que la teneur en azote du courant gazeux enrichi en azote issu de l’étape d) est supérieure à 30% molaire.  A process as defined above, characterized in that the nitrogen content of the nitrogen-enriched gas stream from step d) is greater than 30 mol%.
Un procédé tel que défini ci-dessus, caractérisé en ce que T1 est comprise entre - 140°C et -120°C.  A process as defined above, characterized in that T1 is between - 140 ° C and -120 ° C.
Un procédé tel que défini ci-dessus, caractérisé en ce que P2 est comprise entre 3 bar abs et 10 bar abs, P1 est comprise entre 4 MPa et 7 MPa.  A process as defined above, characterized in that P2 is between 3 bar abs and 10 bar abs, P1 is between 4 MPa and 7 MPa.
Un procédé tel que défini ci-dessus, dans lequel à l'étape b) le mélange de gaz naturel et le deuxième mélange réfrigérant sont refroidis à une température comprise entre -70°C et -35°C par échange de chaleur avec le premier mélange réfrigérant.  A process as defined above, wherein in step b) the mixture of natural gas and the second refrigerant mixture are cooled to a temperature between -70 ° C and -35 ° C by heat exchange with the first refrigerant mixture.
Un procédé tel que défini ci-dessus, dans lequel le premier mélange réfrigérant comporte en fraction molaire les composants suivants :  A process as defined above, wherein the first refrigerant mixture comprises in molar fraction the following components:
o Ethane : 30% à 70 %  o Ethane: 30% to 70%
O Propane : 30 % à 70 % o Butane : 0 % à 20 %. O Propane: 30% to 70% o Butane: 0% to 20%.
Un procédé tel que défini ci-dessus, dans lequel le deuxième mélange réfrigérant comporte en fraction molaire les composants suivants :  A process as defined above, in which the second refrigerant mixture comprises in molar fraction the following components:
o Azote : 0 % à 20 %  o Nitrogen: 0% to 20%
o Méthane : 30 % à 70 %  o Methane: 30% to 70%
o Ethane : 30 % à 70 %  o Ethane: 30% to 70%
o Propane : 0 % à 10 %.  o Propane: 0% to 10%.
Le procédé selon l'invention permet en effet d'augmenter sensiblement la capacité de production en ajoutant un nombre limité d'équipements supplémentaires.  The method according to the invention makes it possible to substantially increase the production capacity by adding a limited number of additional equipment.
Le procédé selon l'invention est particulièrement avantageux lorsque chacun des circuits de réfrigération met en œuvre un mélange réfrigérant qui est entièrement condensé, détendu et vaporisé.  The method according to the invention is particularly advantageous when each of the refrigeration circuits uses a refrigerant mixture which is completely condensed, expanded and vaporized.
L'expression "courant d’alimentation" telle qu'utilisée dans la présente demande se rapporte à toute composition contenant des hydrocarbures dont au moins du méthane.  The term "feed stream" as used in this application refers to any composition containing hydrocarbons including at least methane.
L'échangeur de chaleur peut être tout échangeur thermique, toute unité ou autre agencement adapté pour permettre le passage d'un certain nombre de flux, et ainsi permettre un échange de chaleur direct ou indirect entre une ou plusieurs lignes de fluide réfrigérant, et un ou plusieurs flux d'alimentation.  The heat exchanger may be any heat exchanger, unit or other arrangement adapted to allow the passage of a number of flows, and thus allow a direct or indirect heat exchange between one or more lines of refrigerant, and a or multiple feed streams.
D'autres caractéristiques et avantages de l'invention seront mieux compris et apparaîtront clairement à la lecture de la description faites ci-après en se référant à la figure représentant schématiquement un procédé de liquéfaction selon l'invention.  Other features and advantages of the invention will be better understood and will become clear from reading the description given below with reference to the figure schematically showing a liquefaction process according to the invention.
Sur la figure, un courant d’alimentation de gaz naturel 1 est introduit dans une unité d’échange de chaleur E1 à une température T1.  In the figure, a natural gas feed stream 1 is introduced into a heat exchange unit E1 at a temperature T1.
Typiquement le courant d’alimentation 1 peut contenir du méthane, de l’éthane, du propane, des hydrocarbures ayant au moins quatre atomes de carbone. Ce courant peut contenir des traces de contaminants par exemple H2O 0-1 ppm, H2S 4 ppm, CO2 50 ppm.  Typically the feed stream 1 may contain methane, ethane, propane, hydrocarbons having at least four carbon atoms. This stream may contain traces of contaminants eg H2O 0-1 ppm, H2S 4 ppm, CO2 50 ppm.
Le courant d’alimentation de gaz naturel comprend strictement plus de 1 % molaire d’azote, or les spécifications imposent une teneur maximum de 1 % molaire d’azote dans le LNG. Typiquement l’unité E1 peut contenir plusieurs échangeurs de chaleur (2, 3, 1 12). The natural gas feed stream comprises strictly more than 1 mol% of nitrogen, but the specifications impose a maximum content of 1 mol% nitrogen in the LNG. Typically the unit E1 can contain several heat exchangers (2, 3, 1 12).
Selon le procédé de liquéfaction de gaz naturel schématisé par la figure, le courant 1 gaz naturel arrive par le conduit 51 par exemple à une pression comprise entre 4 MPa et 7 MPa et à une température comprise entre 0°C et 60°C. Le gaz naturel circulant dans le conduit 51 est réuni avec le gaz 50 pour former un mélange de gaz naturel circulant dans le conduit 51 . Le gaz circulant dans le conduit 51 , un premier mélange réfrigérant 201 et un deuxième mélange réfrigérant 109 entrent dans l'échangeur E1 pour y circuler selon des directions parallèles et à co-courant.  According to the natural gas liquefaction process shown schematically in the figure, the stream 1 natural gas arrives via the pipe 51 for example at a pressure of between 4 MPa and 7 MPa and at a temperature between 0 ° C and 60 ° C. The natural gas flowing in the duct 51 is combined with the gas 50 to form a mixture of natural gas circulating in the duct 51. The gas flowing in the duct 51, a first refrigerant mixture 201 and a second refrigerant mixture 109 enter the exchanger E1 to circulate in parallel directions and co-current.
Le gaz naturel sort de l'échangeur E1 par le conduit 4, par exemple à une température comprise entre - 35°C et - 70°C. Le deuxième mélange réfrigérant sort totalement condensé de l'échangeur E1 par le conduit 100, par exemple à une température comprise entre - 35°C et - 70°C.  The natural gas exits the exchanger E1 through line 4, for example at a temperature between -35 ° C and -70 ° C. The second refrigerant mixture exits completely condensed from the exchanger E1 through the duct 100, for example at a temperature of between -35 ° C. and -70 ° C.
Dans l'échangeur E1 , trois fractions (202, 212, 222) du premier mélange réfrigérant en phase liquide sont successivement soutirées. Les fractions sont détendues (207, 217 et 227) à travers les vannes de détente 21 1 , 221 et 231 à trois niveaux de pression différents, puis vaporisées dans l'échangeur E1 par échange de chaleur avec le courant gaz naturel circulant dans le conduit 51 , le deuxième mélange réfrigérant et une partie du premier mélange réfrigérant. Les trois fractions vaporisées (208, 218, 228) sont envoyées à différents étages (257, 253, 250) du compresseur K1 . Les fractions vaporisées sont comprimées dans le compresseur K1 puis condensées dans le condenseur E101 par échange de chaleur avec un fluide extérieur de refroidissement, par exemple de l'eau ou de l'air. Le premier mélange réfrigérant 201 issu du condenseur E101 est envoyé dans l'échangeur E1 . La pression du premier mélange réfrigérant à la sortie du compresseur K1 peut être comprise entre 2 MPa et 6 MPa. La température du premier mélange réfrigérant à la sortie du condenseur E101 peut être comprise entre 10°C et 55°C.  In the exchanger E1, three fractions (202, 212, 222) of the first refrigerant mixture in the liquid phase are successively withdrawn. The fractions are expanded (207, 217 and 227) through the expansion valves 21 1, 221 and 231 at three different pressure levels, and then vaporized in the exchanger E 1 by heat exchange with the natural gas stream circulating in the conduit. 51, the second refrigerant mixture and a portion of the first refrigerant mixture. The three vaporized fractions (208, 218, 228) are sent to different stages (257, 253, 250) of the compressor K1. The vaporized fractions are compressed in the compressor K1 and then condensed in the condenser E101 by heat exchange with an external cooling fluid, for example water or air. The first refrigerant mixture 201 from the condenser E101 is sent into the exchanger E1. The pressure of the first refrigerant mixture at the outlet of the compressor K1 may be between 2 MPa and 6 MPa. The temperature of the first refrigerant mixture at the outlet of the condenser E101 can be between 10 ° C. and 55 ° C.
Le premier mélange réfrigérant peut-être formé par un mélange d'hydrocarbures tels qu'un mélange d'éthane et de propane, mais peut également contenir du méthane, du butane et/ou du pentane. Les proportions en fraction molaires (%) des composants du premier mélange réfrigérant peuvent être : The first refrigerant mixture may be formed by a mixture of hydrocarbons such as a mixture of ethane and propane, but may also contain methane, butane and / or pentane. The proportions in molar fraction (%) of the components of the first refrigerant mixture may be:
o Ethane : 30 % à 70 %  o Ethane: 30% to 70%
o Propane : 30 % à 70 %  o Propane: 30% to 70%
o Butane : 0 % à 20 %.  o Butane: 0% to 20%.
Le gaz naturel circulant dans le conduit 4 peut être fractionné, c'est à dire qu'une partie des hydrocarbures contenant au moins deux atomes de carbone est séparée du gaz naturel, en utilisant un dispositif connu de l'état de l'art. Le gaz naturel fractionné est envoyé dans un échangeur de chaleur E2. Les hydrocarbures C2+ recueillis sont envoyés dans des colonnes de fractionnement comportant un deéthaniseur. La fraction légère recueillie en tête du deéthaniseur peut être mélangée avec le gaz naturel circulant dans le conduit 4. La fraction liquide recueillie en fond du deéthaniseur est envoyée à un dépropaniseur.  The natural gas flowing in the duct 4 can be fractionated, that is to say that a portion of the hydrocarbons containing at least two carbon atoms is separated from the natural gas, using a device known from the state of the art. The fractionated natural gas is sent into an E2 heat exchanger. The C2 + hydrocarbons collected are sent to fractionation columns comprising a deethanizer. The light fraction collected at the top of the deethanizer can be mixed with the natural gas circulating in the conduit 4. The liquid fraction collected at the bottom of the deethanizer is sent to a depropanizer.
Le gaz circulant dans le conduit 4 et le deuxième mélange réfrigérant circulant dans le conduit 100 entrent dans l'échangeur E2 pour y circuler selon des directions parallèles et à co-courant.  The gas flowing in the duct 4 and the second refrigerant mixture flowing in the duct 100 enter the exchanger E2 to circulate in parallel directions and co-current.
Le deuxième mélange réfrigérant sortant de l'échangeur E2 par le conduit 101 est détendu par l'organe de détente T3. L'organe de détente T3 peut être une turbine, une vanne ou une combinaison d'une turbine et d'une vanne. Le deuxième mélange réfrigérant détendu issu de la turbine T3 est envoyé par le conduit 102 dans l'échangeur E2 pour être vaporisé en réfrigérant à contre- courant le gaz naturel et le deuxième mélange réfrigérant.  The second refrigerant mixture leaving the exchanger E2 through the conduit 101 is expanded by the expansion member T3. The expansion member T3 may be a turbine, a valve or a combination of a turbine and a valve. The second refrigerated mixture expanded from the turbine T3 is sent through the conduit 102 in the exchanger E2 to be vaporized by countercurrently cooling the natural gas and the second refrigerant mixture.
En sortie de l'échangeur E2, le deuxième mélange réfrigérant vaporisé 103 est comprimé par le compresseur K2 puis refroidi dans l'échangeur de chaleur indirecte C2 par échange de chaleur avec un fluide extérieur de refroidissement, par exemple de l'eau ou de l'air. Le deuxième mélange réfrigérant 109 issu de l'échangeur C2 est envoyé dans l'échangeur. La pression du deuxième mélange réfrigérant en sortie du compresseur K2 peut être comprise entre 2 MPa et 8 MPa. La température du deuxième mélange réfrigérant à la sortie de l'échangeur C2 peut être comprise entre 10°C et 55°C.  At the outlet of the exchanger E2, the second vaporized refrigerant mixture 103 is compressed by the compressor K2 and then cooled in the indirect heat exchanger C2 by heat exchange with an external cooling fluid, for example water or water. 'air. The second refrigerant mixture 109 from the exchanger C2 is sent into the exchanger. The pressure of the second refrigerant mixture at the outlet of the compressor K2 may be between 2 MPa and 8 MPa. The temperature of the second refrigerant mixture at the outlet of exchanger C2 may be between 10 ° C. and 55 ° C.
Dans le procédé décrit en référence à la figure, le deuxième mélange réfrigérant n'est pas scindé en fractions séparées, mais, pour optimiser l'approche dans l'échangeur E2, le deuxième mélange réfrigérant peut également être séparé en deux ou trois fractions, chaque fraction étant détendue à un niveau de pression différent puis envoyée à différents étages du compresseur K2. In the method described with reference to the figure, the second refrigerant mixture is not split into separate fractions, but, to optimize the approach in the exchanger E2, the second refrigerant mixture can also be used. be separated into two or three fractions, each fraction being expanded to a different pressure level and then sent to different stages of the compressor K2.
Le deuxième mélange réfrigérant est formé par exemple par un mélange d'hydrocarbures et d'azote tels qu'un mélange de méthane, d'éthane et d'azote mais peut également contenir du propane et/ou du butane. Les proportions en fraction molaires (%) des composants du deuxième mélange réfrigérant peuvent être :  The second refrigerant mixture is formed for example by a mixture of hydrocarbons and nitrogen such as a mixture of methane, ethane and nitrogen but may also contain propane and / or butane. The proportions in mole fraction (%) of the components of the second refrigerant mixture may be:
o Azote : 0 % à 20 %  o Nitrogen: 0% to 20%
o Méthane : 30 % à 70 %  o Methane: 30% to 70%
o Ethane : 30 % à 70 %  o Ethane: 30% to 70%
o Propane : 0 % à 10 %.  o Propane: 0% to 10%.
Le gaz naturel sort liquéfié de l'échangeur de chaleur E2 par le conduit 10 à une température de préférence supérieure d'au moins 10°C par rapport à la température de bulle du gaz naturel liquéfié produit à pression atmosphérique (la température de bulle désigne la température à laquelle les premières bulles de vapeurs se forme dans un gaz naturel liquide à une pression donnée) et à une pression P1 b identique à la pression d'entrée P1 du gaz naturel, aux pertes de charge près. Par exemple le gaz naturel sort de l'échangeur E2 à une température comprise entre -105°C et -145°C et à une pression comprise entre 4 MPa à 7 MPa. Dans ces conditions de température et de pression, le gaz naturel ne reste pas entièrement liquide après une détente jusqu'à la pression atmosphérique.  The natural gas comes out of the heat exchanger E2 through line 10 at a temperature which is preferably at least 10 ° C. higher than the bubble temperature of the liquefied natural gas produced at atmospheric pressure (bubble temperature means the temperature at which the first vapor bubbles are formed in a liquid natural gas at a given pressure) and at a pressure P1b identical to the inlet pressure P1 of the natural gas, with the pressure drops close to it. For example, natural gas leaves the exchanger E2 at a temperature of between -105 ° C. and -145 ° C. and at a pressure of between 4 MPa and 7 MPa. Under these conditions of temperature and pressure, the natural gas does not remain completely liquid after expansion to atmospheric pressure.
Le gaz naturel circulant dans le conduit 10 est refroidi dans le rebouilleur E4 d’une colonne de déazotation C0. Le gaz naturel 12 est refroidi en chauffant le fond (25, 26) de la colonne C0 par échange de chaleur indirecte, puis est détendu dans l'organe de détente V1 . Le mélange diphasique 13 obtenu en sortie de l'organe V1 est introduit dans la colonne C0 à un niveau N1 . En tête de la colonne C0, on récupère une fraction gazeuse 38 enrichie en azote. Elle est envoyée pour être refroidie 39 dans un échangeur de chaleur E5 puis séparée dans un pot séparateur de phases B2 sous forme d'une fraction gazeuse 21 et d'une fraction liquide 21’.  The natural gas flowing in the pipe 10 is cooled in the reboiler E4 of a denitrogenation column C0. The natural gas 12 is cooled by heating the bottom (25, 26) of the column C0 by indirect heat exchange, then is expanded in the expansion member V1. The diphasic mixture 13 obtained at the outlet of the member V1 is introduced into the column C0 at a level N1. At the top of the column C0, a gas fraction 38 enriched in nitrogen is recovered. It is sent to be cooled in a heat exchanger E5 and then separated in a phase separator pot B2 in the form of a gaseous fraction 21 and a liquid fraction 21 '.
La fraction gazeuse 21 évacuée du pot B2 est introduite dans l'échangeur E2. Dans l'échangeur E2, la fraction gazeuse refroidit à contre-courant le courant 4 de gaz naturel, puis est dirigée via le conduit 22 dans le compresseur K4. La fraction liquide 21’ évacuée du pot B2 est utilisée comme reflux en tête de colonne CO. The gaseous fraction 21 discharged from the pot B2 is introduced into the exchanger E2. In the exchanger E2, the gaseous fraction countercurrently cools the stream 4 of natural gas, then is directed via the conduit 22 into the compressor K4. The The liquid fraction 21 'discharged from the pot B2 is used as reflux at the top of the column CO.
La fraction liquide 31 , appauvrie en azote, évacuée en cuve de colonne CO est séparée en deux parties 32 et 34. Une première partie 32 est refroidie dans un échangeur de chaleur E3, puis est détendue dans un organe de détente 33’ à une pression comprise entre 0,05MPa et 0,5MPa. La deuxième partie 34 de la fraction liquide 31 est détendue 35 dans un organe de détente 34’ puis alimente un échangeur de chaleur E5. La vaporisation de ce courant 35 donne un courant 36 et représente la plus grande partie de la réfrigération nécessaire au refroidissement du courant gazeux 38 issu de la tête de la colonne CO dans l’échangeur de chaleur E5.  The liquid fraction 31, depleted in nitrogen, discharged in the column tank CO is separated into two parts 32 and 34. A first part 32 is cooled in a heat exchanger E3, then is expanded in an expansion member 33 'at a pressure between 0.05MPa and 0.5MPa. The second portion 34 of the liquid fraction 31 is expanded in an expansion member 34 'and then fed to a heat exchanger E5. The vaporization of this stream 35 gives a current 36 and represents the majority of the refrigeration necessary for cooling the gas stream 38 from the head of the column CO in the heat exchanger E5.
Les organes de détente tels que V1 , 33’ et 34’ peuvent être une turbine de détente, une vanne de détente ou une combinaison d'une turbine et d'une vanne. Le mélange diphasique obtenu en sortie de l'organe de détente 33’ est mélangé au flux 36 pour donner le mélange diphasique 37. Le flux 37 est séparé dans un pot séparateur de phases B1 sous forme d'une fraction gazeuse 41 et d'une fraction liquide 61 . La fraction gazeuse 41 est introduite dans l'échangeur E3. Dans l'échangeur E3, la fraction gazeuse 41 refroidit la fraction liquide 32 issu du courant liquide 31 récupéré en cuve de la colonne C1 , puis est dirigée par le conduit 42 dans le compresseur K3. Le mélange gazeux 49 sortant du compresseur K3 est envoyé à un échangeur de chaleur C3 pour être refroidi par de l'air ou de l'eau. Le mélange gazeux 50 sortant de l'échangeur C3 est ensuite mélangé avec le courant 1 de gaz naturel circulant dans le conduit 51 .  The expansion members such as V1, 33 'and 34' may be an expansion turbine, an expansion valve or a combination of a turbine and a valve. The two-phase mixture obtained at the outlet of the expansion element 33 'is mixed with the flow 36 to give the two-phase mixture 37. The flow 37 is separated in a phase separator pot B1 in the form of a gas fraction 41 and a liquid fraction 61. The gaseous fraction 41 is introduced into the exchanger E3. In the exchanger E3, the gaseous fraction 41 cools the liquid fraction 32 coming from the liquid stream 31 recovered in the vat of the column C1, then is directed by the duct 42 into the compressor K3. The gaseous mixture 49 leaving the compressor K3 is sent to a heat exchanger C3 to be cooled by air or water. The gaseous mixture 50 leaving the exchanger C3 is then mixed with the stream 1 of natural gas flowing in the pipe 51.
La fraction liquide 61 évacuée du ballon B1 forme le gaz naturel liquéfié (GNL) produit. Le gaz 28 circulant par le conduit 27 peut servir de gaz combustible, source d'énergie pour le fonctionnement d'une usine de liquéfaction.  The liquid fraction 61 discharged from the flask B1 forms the liquefied natural gas (LNG) produced. The gas 28 flowing through the conduit 27 may serve as fuel gas, energy source for the operation of a liquefaction plant.
Plus particulièrement, le flux GNL déazoté 31 produit en pied de la colonne C0 est divisé en deux parties :  More particularly, the denitrogenated LNG stream 31 produced at the bottom of the column CO is divided into two parts:
• Une première partie minoritaire, flux 34 est détendue dans la vanne 34’ jusqu’à une basse pression P3 de telle sorte que le flux 36 et que le mélange diphasique en sortie de sortie de l’organe de détente 33’ soient à des pressions proches avant mélange. Cette pression P3 est donc comprise entre 0,05MPa et 0,5MPa aux pertes de charge près. • Le flux 35 est obtenu et alimente l’échangeur E5. La vaporisation de ce flux qui donne le flux 36 fourni la plus grande partie de la réfrigération nécessaire au refroidissement de la vapeur de tête dans l’échangeur E5. • A first minority part, flow 34 is expanded in the valve 34 'to a low pressure P3 so that the flow 36 and the two-phase mixture output of the expansion member 33' are at pressures close before mixing. This pressure P3 is therefore between 0.05 MPa and 0.5 MPa at the pressure losses close. • The stream 35 is obtained and feeds the exchanger E5. The vaporization of this flux which gives the flow 36 provided the greater part of the refrigeration necessary for the cooling of the overhead vapor in the exchanger E5.
• Une seconde partie majoritaire, flux 32 est refroidie à contre-courant du gaz de flash, flux 41 , pour donner le flux 33 qui est détendu jusqu’à la pression P3 pour être mélangé au courant 36 et donner le flux 37 qui alimente le ballon de flash du GNL B1 .  A second majority part, stream 32, is countercurrently cooled with the flash gas, stream 41, to give the stream 33 which is expanded to the pressure P3 to be mixed with the stream 36 and to give the stream 37 which feeds the flash balloon LNG B1.
Afin d’illustrer davantage la mise en œuvre d’un procédé tel que schématisé sur la figure et tel que décrit précédemment, les données de mises en œuvre dudit procédé selon l’invention ont été comparées à celles correspondant à la mise en œuvre d’un procédé selon l’invention décrite dans l’art antérieur et illustrée par la figure 2 du brevet US 6 763 680.  To further illustrate the implementation of a method as schematized in the figure and as described above, the implementation data of said method according to the invention were compared with those corresponding to the implementation of a method according to the invention described in the prior art and illustrated in Figure 2 of US Patent 6,763,680.
Ces données ont été rassemblées dans le tableau suivant.  These data have been collated in the following table.
Les deux procédés ont été mis en œuvre avec la même méthodologie de façon à ce que l’avantage du procédé selon la présente invention soit mis en évidence clairement.  Both methods have been implemented with the same methodology so that the advantage of the method according to the present invention is clearly demonstrated.
Le gaz naturel arrive par la ligne 01 à une pression de 60 bar et une température de 15°C. La composition de ce gaz en fraction molaire est la suivante :  Natural gas arrives via line 01 at a pressure of 60 bar and a temperature of 15 ° C. The composition of this gas in molar fraction is as follows:
o Méthane : 91 %  o Methane: 91%
o Ethane : 2.5%  o Ethane: 2.5%
o Propane : 1 %  o Propane: 1%
o Isobutane : 0.3%  o Isobutane: 0.3%
o n-butane : 0.2%  o n-butane: 0.2%
o Azote : 5%  o Nitrogen: 5%
Le réfrigérant en mélange du cycle de pré refroidissement (PR) est le même pour les deux procédés : 50% d’éthane et 50% de propane. Il est mis en œuvre de la même façon, seuls les débits sont adaptés aux besoins. On note (LR) le réfrigérant réalisant le sous-refroidissement du gaz naturel. The mixed refrigerant of the pre-cooling cycle (PR) is the same for both processes: 50% ethane and 50% propane. It is implemented in the same way, only flows are adapted to the needs. We denote (LR) the refrigerant performing the subcooling of natural gas.
Figure imgf000012_0001
Figure imgf000012_0001
Le nouveau procédé permet de produire un GNL pauvre en azote en économisant de l’énergie. The new process makes it possible to produce LNG that is low in nitrogen while saving energy.

Claims

REVENDICATIONS
1. Procédé de liquéfaction d’un courant d’alimentation (1 ) de gaz naturel comprenant les étapes suivantes : A method of liquefying a feed stream (1) of natural gas comprising the steps of:
Etape a) : Refroidissement du courant gazeux d’alimentation (1 ) pour obtenir un courant de gaz naturel liquéfié (10) à une température T1 et une pression P1 b ;  Step a): Cooling the feed gas stream (1) to obtain a stream of liquefied natural gas (10) at a temperature T1 and a pressure P1b;
Etape b) : Introduction du courant issu de l’étape a) dans une colonne de déazotation (CO) à une pression P2 et une température T2 inférieure à T1 pour produire, en cuve de ladite colonne, un courant de gaz naturel liquéfié déazoté (31 ) et, en tête de ladite colonne, un courant (38) de vapeur enrichi en azote ;  Step b): introduction of the stream from step a) into a denitrogenation column (CO) at a pressure P2 and a temperature T2 less than T1 to produce, in the tank of said column, a denitrogenated liquefied natural gas stream ( 31) and, at the top of said column, a stream (38) of nitrogen-enriched vapor;
Etape c) : Condensation au moins partielle du courant (38) de vapeur enrichi en azote issu de l’étape b) dans un échangeur de chaleur (E5) pour produire un courant diphasique (39) ;  Step c): At least partial condensation of the stream (38) of nitrogen-enriched vapor from step b) in a heat exchanger (E5) to produce a two-phase current (39);
Etape d) : Introduction du courant diphasique (39) issu de l’étape c) dans un pot séparateur de phases (B2) pour produire au moins deux phases dont un courant liquide (2T) et un courant gazeux enrichi en azote (21 ) ;  Step d): Introduction of the two-phase current (39) from step c) into a phase separator pot (B2) to produce at least two phases including a liquid stream (2T) and a nitrogen-enriched gas stream (21) ;
caractérisé en ce qu’au moins une partie du courant liquide (31 ) issu de l’étape b) est utilisée durant l’étape c) pour refroidir le courant de vapeur issu de l’étape b) dans ledit échangeur de chaleur (E5). characterized in that at least a portion of the liquid stream (31) from step b) is used during step c) to cool the vapor stream from step b) in said heat exchanger (E5 ).
2. Procédé selon la revendication précédente caractérisé en ce que lors de l’étape a), on refroidit ledit courant d’alimentation de gaz naturel et un deuxième mélange réfrigérant par échange de chaleur indirect avec au moins un premier mélange réfrigérant pour obtenir un gaz naturel refroidi et un deuxième mélange réfrigérant refroidi, puis on condense et on refroidit le gaz naturel refroidi par échange de chaleur indirect avec le deuxième mélange réfrigérant refroidi et avec au moins une partie du courant gazeux obtenu à l'étape d) pour obtenir un gaz naturel liquéfié. 2. Method according to the preceding claim characterized in that during step a), said natural gas feed stream is cooled and a second refrigerant mixture by indirect heat exchange with at least a first refrigerant mixture to obtain a gas. cooled natural gas and a cooled second refrigerant mixture, and then condensing and cooling the cooled natural gas by indirect heat exchange with the cooled second cooling mixture and with at least a portion of the gas stream obtained in step d) to obtain a gas liquefied natural.
3. Procédé selon l’une des revendications précédentes, caractérisé en ce que préalablement à l’étape b), le courant issu de l’étape a) est refroidi dans un moyen de rebouillage de ladite colonne de déazotation jusqu’à la température T2. 3. Method according to one of the preceding claims, characterized in that prior to step b), the stream from step a) is cooled in a reboiling means of said denitrogenation column to the temperature T2 .
4. Procédé selon la revendication précédente, caractérisé en ce que le courant refroidi à la température T2 est détendu dans un moyen de détente avant son introduction dans la colonne de déazotation. 4. Method according to the preceding claim, characterized in that the stream cooled to the temperature T2 is expanded in an expansion means before introduction into the denitrogenation column.
5. Procédé selon l’une des revendications précédentes caractérisé en ce qu’au moins une partie du courant liquide (21’) issu de l’étape d) est utilisée comme reflux en tête de la colonne de déazotation. 5. Method according to one of the preceding claims characterized in that at least a portion of the liquid stream (21 ') from step d) is used as reflux at the head of the denitrogenation column.
6. Procédé selon l’une des revendications précédentes, caractérisé en ce qu’il comprend les étapes suivantes : 6. Method according to one of the preceding claims, characterized in that it comprises the following steps:
Etape e) : on refroidit la partie (32) du courant liquide (34) issu de l’étape b) non utilisée durant l’étape c) par échange de chaleur indirect avec une deuxième fraction gazeuse (41 ) obtenue à l'étape f) pour obtenir une fraction liquide refroidie (33) et une deuxième fraction gazeuse réchauffée (42),  Step e): the portion (32) of the liquid stream (34) resulting from step b) not used during step c) is cooled by indirect heat exchange with a second gaseous fraction (41) obtained in step f) to obtain a cooled liquid fraction (33) and a second heated gas fraction (42),
Etape f) : on détend la fraction liquide (33) refroidie obtenue à l'étape e), puis on l’introduit dans un deuxième pot séparateur de phases (B1 ), pour obtenir un gaz naturel liquéfié et la deuxième fraction gazeuse (41 ),  Step f): the cooled liquid fraction (33) obtained in step e) is expanded, then introduced into a second phase separator pot (B1) to obtain a liquefied natural gas and the second gas fraction (41 )
Etape g) : on comprime jusqu’à une pression P1 , au moins une partie de ladite deuxième fraction gazeuse réchauffée (42).  Step g): at least a portion of said second heated gas fraction (42) is compressed to a pressure P1.
7. Procédé selon l’une des revendications précédentes, caractérisé en ce que la teneur en azote du courant gazeux enrichi en azote issu de l’étape d) est supérieure à 30% molaire. 7. Method according to one of the preceding claims, characterized in that the nitrogen content of the gas stream enriched in nitrogen from step d) is greater than 30 mol%.
8. Procédé selon l’une des revendications précédentes, caractérisé en ce que T1 est comprise entre - 140°C et -120°C. 8. Method according to one of the preceding claims, characterized in that T1 is between - 140 ° C and -120 ° C.
9. Procédé selon l’une des revendications 6 à 8, caractérisé en ce que P2 est comprise entre 3 bar abs et 10 bar abs, P1 est comprise entre 4 MPa et 7 MPa. 9. Method according to one of claims 6 to 8, characterized in that P2 is between 3 bar abs and 10 bar abs, P1 is between 4 MPa and 7 MPa.
10. Procédé selon l'une des revendications 2 à 9, dans lequel à l'étape b) le mélange de gaz naturel et le deuxième mélange réfrigérant sont refroidis à une température comprise entre -70°C et -35°C par échange de chaleur avec le premier mélange réfrigérant. The method according to one of claims 2 to 9, wherein in step b) the mixture of natural gas and the second cooling mixture are cooled to a temperature of temperature between -70 ° C and -35 ° C by heat exchange with the first refrigerant mixture.
11. Procédé selon la revendication précédente, dans lequel le premier mélange réfrigérant comporte en fraction molaire les composants suivants : o Ethane : 30% à 70 % 11. Process according to the preceding claim, in which the first refrigerant mixture comprises in mole fraction the following components: Ethane: 30% to 70%
o Propane : 30 % à 70 %  o Propane: 30% to 70%
o Butane : 0 % à 20 %.  o Butane: 0% to 20%.
12. Procédé selon l’une des revendications 10 et 11 , dans lequel le deuxième mélange réfrigérant comporte en fraction molaire les composants suivants : 12. Method according to one of claims 10 and 11, wherein the second refrigerant mixture comprises in molar fraction the following components:
o Azote : 0 % à 20 %  o Nitrogen: 0% to 20%
o Méthane : 30 % à 70 %  o Methane: 30% to 70%
o Ethane : 30 % à 70 %  o Ethane: 30% to 70%
o Propane : 0 % à 10 %.  o Propane: 0% to 10%.
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Citations (5)

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Publication number Priority date Publication date Assignee Title
US6105389A (en) 1998-04-29 2000-08-22 Institut Francais Du Petrole Method and device for liquefying a natural gas without phase separation of the coolant mixtures
US6449984B1 (en) * 2001-07-04 2002-09-17 Technip Process for liquefaction of and nitrogen extraction from natural gas, apparatus for implementation of the process, and gases obtained by the process
US6763680B2 (en) 2002-06-21 2004-07-20 Institut Francais Du Petrole Liquefaction of natural gas with natural gas recycling
US20110239701A1 (en) * 2008-11-03 2011-10-06 Sander Kaart Method of rejecting nitrogen from a hydrocarbon stream to provide a fuel gas stream and an apparatus therefor
US20120090355A1 (en) * 2009-03-25 2012-04-19 Costain Oil, Gas & Process Limited Process and apparatus for separation of hydrocarbons and nitrogen

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6105389A (en) 1998-04-29 2000-08-22 Institut Francais Du Petrole Method and device for liquefying a natural gas without phase separation of the coolant mixtures
US6449984B1 (en) * 2001-07-04 2002-09-17 Technip Process for liquefaction of and nitrogen extraction from natural gas, apparatus for implementation of the process, and gases obtained by the process
US6763680B2 (en) 2002-06-21 2004-07-20 Institut Francais Du Petrole Liquefaction of natural gas with natural gas recycling
US20110239701A1 (en) * 2008-11-03 2011-10-06 Sander Kaart Method of rejecting nitrogen from a hydrocarbon stream to provide a fuel gas stream and an apparatus therefor
US20120090355A1 (en) * 2009-03-25 2012-04-19 Costain Oil, Gas & Process Limited Process and apparatus for separation of hydrocarbons and nitrogen

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