EP0731900B1 - Procede et installation de liquefaction du gaz naturel - Google Patents

Procede et installation de liquefaction du gaz naturel Download PDF

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Publication number
EP0731900B1
EP0731900B1 EP95933471A EP95933471A EP0731900B1 EP 0731900 B1 EP0731900 B1 EP 0731900B1 EP 95933471 A EP95933471 A EP 95933471A EP 95933471 A EP95933471 A EP 95933471A EP 0731900 B1 EP0731900 B1 EP 0731900B1
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EP
European Patent Office
Prior art keywords
mixture
natural gas
cooling
fraction
liquid
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EP95933471A
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German (de)
English (en)
French (fr)
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EP0731900A1 (fr
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Isabelle Prevost
Alexandre Rojey
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IFP Energies Nouvelles IFPEN
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IFP Energies Nouvelles IFPEN
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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
    • 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
    • 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"
    • F25J1/0042—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 liquid expansion with extraction of work
    • 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
    • F25J1/005—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 expansion of a gaseous refrigerant stream with extraction of work
    • 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
    • F25J1/003—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
    • F25J1/0055—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 originating from an incorporated cascade
    • 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
    • F25J1/006—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the refrigerant fluid used
    • F25J1/008—Hydrocarbons
    • F25J1/0092—Mixtures of hydrocarbons comprising possibly also minor amounts 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
    • 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
    • F25J1/0212—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 as a single flow MCR cycle
    • 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
    • F25J1/0214—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 as a dual level refrigeration cascade with at least one MCR cycle
    • 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
    • F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
    • F25J1/0257—Construction and layout of liquefaction equipments, e.g. valves, machines
    • F25J1/0262—Details of the cold heat exchange system
    • F25J1/0264—Arrangement of heat exchanger cores in parallel with different functions, e.g. different cooling streams
    • 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
    • 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
    • F25J2200/70—Refluxing the column with a condensed part of the feed stream, i.e. fractionator top is stripped or self-rectified
    • 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
    • F25J2210/06—Splitting of the feed stream, e.g. for treating or cooling in different ways
    • 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
    • F25J2220/00—Processes or apparatus involving steps for the removal of impurities
    • F25J2220/60—Separating impurities from natural gas, e.g. mercury, cyclic hydrocarbons
    • F25J2220/64—Separating heavy hydrocarbons, e.g. NGL, LPG, C4+ hydrocarbons or heavy condensates in general

Definitions

  • Liquefaction of natural gas is an important industrial operation which allows natural gas to be transported over long distances by LNG carrier, or to store it in liquid form.
  • Natural gas we mean by the then a mixture formed mainly of methane but which may contain also other hydrocarbons and nitrogen, in whatever form found (gaseous, liquid or two-phase). Natural gas at the start mostly in gaseous form, and has pressure values and of temperature such that during the liquefaction stage, it may occur in different forms, for example liquid and gas coexisting at an instant given.
  • an external refrigeration cycle using as refrigerant a mixture of fluids is used.
  • a mixture in vaporizing is likely to refrigerate and liquefy natural gas under pressure. After vaporization, the mixture is compressed, condensed into exchanging heat with an ambient medium such as water or air.
  • the vapor fraction from the separator is liquefied by a cascade effect natural gas refrigeration as well as the necessary refrigeration to ensure the successive stages of condensation of the vapor fraction being ensured by vaporization of the increasingly light liquid fractions from each of the stages of partial condensation of the refrigerant mixture.
  • a method according to the preamble of claim 1 is known from document US-A-3,932,154.
  • the vapor fraction is not condensed into all but only partially condensed so as to present itself to the lowest temperature of the cycle in the form of a mixture comprising a liquid fraction in variable proportion.
  • the mixture refrigerant can be sent to a distillation section, to obtain a fraction M1 enriched in light component (s) and a fraction M2 enriched in heavy constituent (s).
  • the vapor fraction can be expanded during of step b) using a turbine and it is thus possible to recover at least one part of mechanical energy.
  • the refrigerant mixture resulting from heat exchange with natural gas during step d) can be recycled to the compression step a) of the mixture refrigerant.
  • the mixture M1 resulting from the expansion of the vapor fraction coming from the partial condensation of the cooling mixture is, for example, exchanged thermally with natural gas before being mixed with the fraction produced of the expansion of the sub-cooled liquid fraction, originating from the partial condensation of the cooling mixture.
  • the cooling mixture can also be compressed into at least two stages between which a heat exchange cooling stage is performed, for example with an external coolant, water or available air.
  • liquid fraction resulting from the partial condensation of the mixture is, for example, under cooled, before being expanded, by heat exchange with the low temperature mixture from the mixture of relaxed fractions.
  • It can also be sub-cooled, expanded and mixed with the fraction from the recycling of the vapor fraction, so as to ensure, by heat exchange with the mixture thus obtained the cooling step complementary to the mixture from the compression step, as well as a first step in cooling natural gas, for example.
  • the liquid fraction is sub-cooled, for example, to a temperature preferably below its bubble temperature at pressure low of the cycle.
  • Another way to do this is to sub cool, relax and mix the liquid fraction at different temperature levels corresponding to successive stages of heat exchange with natural gas cooled.
  • the liquid fraction is sub-cooled, expanded and vaporized so as to perform the additional cooling step of the vapor fraction of the mixture from the compression and cooling step using the fluid outside cooling, water or air available, as well as a first cooling step of natural gas under pressure, the expanded fraction from the recycling of the vapor fraction being compressed to example an intermediate pressure level between the low pressure and the high cycle pressure and mixed with the fraction from the vaporization of the liquid fraction, said fraction being previously compressed to said intermediate pressure, the resulting mixture being compressed to high cycle pressure.
  • the vapor fraction can undergo at least two stages of condensation partial successive by cooling under pressure, the vapor fraction from of each of these steps being separated and sent to the next, the fraction vapor from the last partial condensation stage being expanded at less partially in a turbine, for example by recovering, preferably at least part of the mechanical power of expansion then mixed with at least one of the liquid fractions, previously relaxed by obtaining a mixture at low temperature which is heat exchanged with natural gas under pressure.
  • a fluid comprising nitrogen can be used as the cooling mixture. and hydrocarbons having a number of carbon atoms between 1 and 5 and preferably at least 10% nitrogen in molar fraction.
  • the refrigerant mixture used in the process has, for example, a pressure equal to at least 200 kPa at the suction of a compressor during the step at).
  • the mixture M1 comprises for example less than 10% of liquid fraction in mole fraction.
  • hydrocarbons other than methane When natural gas contains hydrocarbons other than methane, these hydrocarbons can be separated at least in part by condensation and / or distillation, for example after a first gas cooling step natural under pressure.
  • a natural gas comprising nitrogen and / or helium, these constituents being able to be at least partly separated by vaporization and / or distillation, said vaporization causing additional cooling natural gas cooled under pressure in the liquid state.
  • Natural gas in the liquid state sub-cooled under pressure is, for example, at least partially expanded in a turbine to a pressure close to the atmospheric pressure, producing liquefied natural gas which is then exported.
  • the present invention also relates to an installation for cooling a fluid, in particular for liquefying a natural gas using a refrigerant mixture, comprising a first device for condensing the refrigerant mixture comprising at least one compressor K 1 and one condenser C 1 , a device S 1 making it possible to separate the vapor fraction from the liquid fraction coming from the first condensing device, devices T 1 and V 1 making it possible to relax the separated liquid and vapor fractions respectively and at least one device E 1 , such as an exchanger.
  • a first device for condensing the refrigerant mixture comprising at least one compressor K 1 and one condenser C 1
  • a device S 1 making it possible to separate the vapor fraction from the liquid fraction coming from the first condensing device
  • devices T 1 and V 1 making it possible to relax the separated liquid and vapor fractions respectively
  • at least one device E 1 such as an exchanger.
  • said exchanger is provided with at least one conduit for introducing the mixture of said expanded liquid and vapor fractions and a conduit for introducing said fluid, said mixture being brought into thermal contact with the fluid to be cooled.
  • the expansion device T 1 of the steam fraction and / or the expansion device V 1 is a turbine, so as to recover at least part of the mechanical energy.
  • the installation includes a device for additional cooling of the expanded liquid and / or vapor fractions, natural gas or refrigerant mixture.
  • the present invention offers many advantages over to the methods usually used in the prior art.
  • Partial condensation of the vapor fraction followed by a simple relaxation represents a simpler and more economical method than that which consists in carrying out total cooling leading to total liquefaction of the vapor fraction.
  • the liquid and vapor fractions from a first stage of condensing of the cooling mixture are expanded separately and mixed after expansion to obtain a cooling mixture called low mixing temperature which allows the vaporization temperature of the liquid fraction.
  • the liquefaction process involves a pre-refrigeration cycle which allows the mixture used in the main refrigeration cycle to be condensed. These two cycles use a mixture of fluid as refrigerant which vaporizing liquefies natural gas under pressure. After spraying, the mixture is compressed, condensed by exchanging heat with the medium ambient, such as water or air, available and in most cases recycled to participate in a new liquefaction stage.
  • the principle implemented in the invention described below consists in cool a fluid and in particular to liquefy and sub-cool a natural gas under pressure, for example, by cooling the vapor fraction from a first stage of condensation of a refrigerant mixture by simple expansion and by mixing this partially condensed vapor fraction with a fraction liquid, from the first stage of condensation, expanded to obtain a refrigerant mixture at low temperature.
  • This mixture achieves during a heat exchange, for example liquefaction and subcooling of natural gas under pressure.
  • the pressurized natural gas to be liquefied arrives in an exchanger E 1 by a conduit 1 and leaves this exchanger after liquefaction by a conduit 2.
  • the refrigerant mixture used during the process is first compressed in a compressor K 1 , then sent via a line 3 to a condenser C 1 in which it is cooled and at least partially condensed, for example by means of a fluid cooling exterior, such as water or air.
  • the two-phase mixture obtained after condensation is sent via a line 4 to a separator flask S 1 .
  • the vapor fraction is evacuated for example by a conduit 5 preferably located in the upper part of the separator S 1 and sent to an expansion device, such as a turbine T 1 .
  • This expansion causes the vapor fraction to cool to a temperature, preferably substantially close to the temperature of the final liquefied natural gas produced, for example to a temperature close to 115K.
  • the expanded and cooled vapor fraction is in the form of a fluid M1 called light fluid mainly comprising a vapor phase, sent into a conduit 9 to be mixed with the liquid fraction in the manner described below.
  • the mechanical expansion power can advantageously be recovered to at least partially drive the compressor K 1 .
  • the liquid fraction leaves the separator S 1 through a conduit 6 located for example in the lower part of the separator S 1 and connected to the exchanger E 1 .
  • This liquid fraction is sub-cooled in the exchanger E 1 , from which it emerges through a conduit 7 then it is expanded through an expansion valve V 1 and sent after expansion through a conduit 8.
  • the expanded liquid fraction occurs in the form of a fluid M2 composed mainly of liquid phase or heavy fluid which is discharged through a conduit 8.
  • the fluid M1 coming from the conduit 9 is mixed with the fluid M2 from line 8 to form a low refrigerant mixture temperature, the temperature of which is close to the final gas temperature natural liquefied product.
  • the temperature of this mixture is below the bubble temperature of the liquid fraction M2 for an identical pressure.
  • the low temperature refrigerant mixture is sent to the exchanger E 1 in which it is used to refrigerate the natural gas under pressure, by heat exchange as well as to sub-cool the liquid fraction before expansion.
  • the refrigerant mixture remains at least partially in the vapor state throughout the cycle.
  • the liquid fraction within the mixture is vaporized and the resulting vapor mixture is for example recycled to the compressor K 1 by a conduit 11.
  • the cooling temperature of natural gas and, optionally, any liquid or vapor fraction passing through the exchanger E 1 takes place, for example, up to a temperature substantially close to the temperature obtained by mixing the two fluids M1 and M2.
  • the natural gas leaves liquefied under pressure from the exchanger E 1 through the pipe 2 is expanded through an expansion valve V 2 , for example to a pressure value substantially close to atmospheric pressure, then evacuated to a place storage and / or shipping, for example.
  • the resulting mixture after heat exchange in the exchanger E 1 is evacuated then recycled through a pipe 11 to the compressor K 1 . It is, for example, compressed and then cooled by heat exchange with the external cooling fluid, water or air available.
  • the refrigerant mixture at low temperature can also be used to sub-cool the liquid fraction coming from the separator flask S 1 , the latter then being cooled to a temperature below its bubble temperature at a pressure value substantially equal to the low pressure. of the cycle. Under such conditions, its expansion through the expansion valve does not cause vaporization, which limits mechanical irreversibility and improves the performance of the refrigeration cycle.
  • Part of the steam fraction can nevertheless be cooled and condensed, according to the various methods known in the prior art, the liquid fraction thus obtained being expanded and mixed with the M1 fractions and M2 to form the mixture at low temperature which, by heat exchange, allows liquefying and sub-cooling natural gas under pressure.
  • the fluids M1 and M2 are obtained by simple refrigeration and partial condensation of a mixture initial, the two phases obtained being separated by gravity.
  • FIG. 3 describes a preferred embodiment of the method according to the invention where the refrigerant mixture is formed for example from two fluids obtained by a fractionation stage further than the stage described in Figure 2, for example a distillation step.
  • a M1 light fluid enriched with light constituents making it possible to obtain after mixture of relaxed fluids M1 and M2, a start temperature of vaporization of fluid M1 significantly lower than the bubble temperature that it would have in the absence of the M2 fluid.
  • the refrigerant mixture in the vapor phase under pressure enters through the conduit 61 in the exchanger E61 in which it undergoes a first stage of refrigeration at the same time as the natural gas which enters the duct 69 and leaves via line 70.
  • the partially condensed refrigerant mixture leaves the exchanger E61 via the conduit 62. It is then sent to the section of distillation D60. At the outlet of this distillation section, the fluid is collected light M1 through conduit 63 and heavy fluid M2 through conduit 65. Fluid M2 is sub-cooled in the exchanger E62 from which it emerges through the conduit 66 then is relaxed through the expansion valve V61. Fluid M1 is expanded and cooled by expansion through the turbine T60 from which it emerges through line 64.
  • the following numerical example illustrates how we can make a mixing at low temperature from two fluids M1 and M2 from a fractionation operation by distillation.
  • the refrigerant enters the exchanger E61 through the conduit 61 at a temperature of + 40 ° and at a pressure of 40 bar abs.
  • the material balance for a supply of 200 mol / h is, for example, the following: the distillate flow rate is substantially 100 mol / h and the flow rate residue of 100 mol / h.
  • the gaseous distillate M1 issuing through line 63 is expanded through a T60 expansion turbine up to a pressure of 3 bar.
  • the outlet temperature is -140 ° C and the 0% liquid fraction.
  • This fluid M1 is sent from the turbine to the exchanger E62 via conduit 64.
  • the liquid residue M2 from the distillation through line 65 is introduced into the exchanger E62, from which it emerges via the conduit 66 at a temperature of -85 ° C. It is relaxed through the V61 valve to a pressure of 3 bar so as to obtain an M2 fluid having a temperature by example substantially equal to -140 ° C by isenthalpic expansion, which is evacuated via conduit 67.
  • the two relaxed fluids M1 and M2 are then mixed in the conduit 68 connected to the two conduits 64 and 67, to form a mixture low temperature refrigerant allowing step a) of the process to be carried out liquefaction.
  • the heavy fractions of the fluid the heavier vaporize on contact with the light fractions of the fluid the more lightweight ; this vaporization generates a lowering of temperature.
  • the mixture obtained from the expanded fluids M1 and M2 is at a temperature of -151 ° C in duct 68, which corresponds to a lowering temperature 11 ° C.
  • This low temperature mixture is used, for example, to ensure the liquefaction and final sub-cooling of natural gas in the exchanger E62 and its pre-cooling in the exchanger E61 according to the steps described below.
  • Natural gas to be liquefied enters, for example, through line 69 into the exchanger E61 at a temperature of 40 ° C, and is cooled using the mixture refrigerant from the E62 exchanger up to a temperature of around -36 ° C. It is then sent via line 70 into the fractionation device S60, in which it is purified from the heaviest fractions.
  • the light fraction composed mostly methane and / or nitrogen and / or ethane enters through the pipe 71 in the exchanger E62. Inside this exchanger, this light fraction is condensed and cooled to -148 ° C using the mixture low temperature refrigerant which enters through line 68 with a temperature of -151 ° C flows against the current of the light fraction and comes out of the exchanger at a temperature substantially equal to -40 ° C via line 74.
  • the product obtained is liquefied natural gas (LNG) evacuated through conduit 73.
  • the refrigerant mixture leaving the exchanger via the conduit 74 at a temperature of -40 ° C is sent to the exchanger E61 where it ensures, by example, the precooling of natural gas as described above. he spring from this exchanger through the conduit 75 at a temperature of 35 ° C to be, for example, recompressed, then cooled to room temperature before being recycled into the exchanger E61 via conduit 61.
  • FIGS. 4 to 7 below describe variants for processing the liquid and vapor fractions from the condenser C 1 , as well as natural gas comprising for example an additional cooling step carried out on the mixture or one of the liquid or vapor fractions at the end of a cooling step, for example carried out with an external fluid or else on natural gas.
  • a preferred version of the process according to the invention described in relation with FIG. 4 consists in continuing the condensation of at least part of the refrigerant mixture, up to a temperature below the temperature external coolant, air or water.
  • the refrigerant mixture is sent through a conduit 12 from the condenser C 1 to an additional exchanger E 2 in which it is cooled.
  • the refrigerant mixture thus cooled is sent to the separating flask S 1 through the conduit 4 to then be treated as described above with FIG. 2.
  • This additional cooling step can be carried out at least in part by heat exchange with the recycled refrigerant mixture of the exchanger E 1 , coming from the conduit 11 which passes through the two exchangers E 1 and E 2 , for example.
  • the additional exchanger E 2 makes it possible, for example, to cool the natural gas under pressure during a first cooling step before being sent via a conduit 13 to the exchanger E 1 where it undergoes a second cooling step. Natural gas leaves the exchanger E 1 in liquid form under pressure before being expanded through the valve V 2 and discharged.
  • additional refrigeration can be ensured by heat exchange, using a refrigerant entering the exchanger E 2 by a conduit 15 and leaving the exchanger by a conduit 16.
  • Figure 5 shows schematically a first embodiment in which the fluid passing through the exchanger E 2 comes from the vaporization of at least one liquid fraction of the refrigerant mixture.
  • the at least partially condensed refrigerant mixture is sent from the condenser C 1 to a separator tank S 3 .
  • the vapor fraction is sent via a pipe 17, for example to the exchanger E 2 .
  • the liquid fraction is withdrawn from the tank S 3 by a conduit 18 and sent to the exchanger E 2 from which it emerges sub-cooled by a conduit 19.
  • This sub-cooled liquid fraction is expanded through an expansion valve V 3 , and returned by a conduit 20 to the exchanger E 2 .
  • the expanded liquid fraction is mixed with the recycled vapor mixture coming from the exchanger E 1 , the assembly then being recycled to the exchanger E 2 .
  • Such a mixture makes it possible to sub-cool the liquid fraction, to cool the vapor fraction entering the exchanger E 2 and, optionally, the natural gas during a first cooling step.
  • the vapor fraction thus precooled leaves the exchanger E 2 partially condensed by the conduit 4 before being sent to the stages of the process described in FIG. 2.
  • the liquid fraction from the partial condensation of the cooling mixture obtained by cooling to using the available external cooling fluid, is sub-cooled, relaxed and mixed with the relaxed fraction from the recycling of vapor fraction, so as to ensure, by heat exchange with the mixture thus obtained, the step of additional cooling of the mixture originating from the compression step, as well as a first step of cooling the gas natural under pressure.
  • the liquid fraction of the refrigerant mixture, the vaporization of which provides the necessary cooling power in the exchanger E 2 can also be separated at an intermediate pressure level as illustrated in the diagram in FIG. 6.
  • the refrigerant mixture is compressed in a first compression stage to an intermediate pressure level and then cooled by a cooling fluid available water or air in the exchanger C 10 and partially condensed.
  • the liquid phase obtained is separated in the separator flask S 30 , then sent to the exchanger E 2 in which it is sub-cooled. It is then sent via line 19 to the expansion valve V 3 and then vaporized in the exchanger E 2 from which it emerges through line 11 to be recycled to the compressor K 10 .
  • the vapor phase from the separator S 30 undergoes a complementary compression step in the compressor K 20 , then it is cooled in the exchanger C 20 .
  • the resulting liquid-vapor mixture is then sent to the exchanger E 2 .
  • the liquid and vapor fractions can be sent simultaneously, the flow taking place for example by gravity or separately, the liquid fraction being, for example, pumped.
  • the exchanger E 2 the partial condensation of the mixture is continued and the liquid and vapor phases thus obtained are sent through line 4 to the separator tank S 1 in which they are separated.
  • the two fractions thus obtained are sent to the process steps described in FIG. 2.
  • Another possibility is to avoid mixing the liquid fraction from the condenser under cooled and expanded with the expanded fraction from the recycling of the vapor fraction.
  • Another way to proceed is to perform the pre step cooling or additional cooling step using a first refrigeration cycle closed.
  • Figure 7 shows schematically a way of proceeding according to this diagram using a mixture of refrigerants, consisting for example of ethane, propane and butane, to effect additional cooling of at least minus part of the mixture from the compression step, as well as first stage of cooling natural gas under pressure.
  • a mixture of refrigerants consisting for example of ethane, propane and butane
  • the first refrigeration cycle comprises, for example, compressors K 21 , K 22 , condensers associated with the compressors, respectively C 21 and C 22 and two exchangers E 21 , E 22 .
  • the cycle operates, for example, in the following way: the refrigerant mixture leaves the compressor K 22 at a pressure, for example of 2MPa, and is then cooled in the condenser C 22 for example by heat exchange with an external cooling fluid .
  • the cooled liquid fraction leaving the condenser C 22 is sent via a line 30 to a first exchanger E 21 in which it undergoes a first sub-cooling step. At least part of the cooled liquid fraction leaves the exchanger E 21 through a line 19 and is expanded through the expansion valve V 31 before being recycled to the exchanger E 21 . It is vaporized at an intermediate pressure level preferably between the low pressure and the high pressure of the first refrigeration cycle.
  • the vapor fraction generated during vaporization is evacuated and recycled through a conduit 34 preferably located in the upper part of the exchanger E 21 at the inlet of the compressor K 22 .
  • the remaining liquid fraction is sent to a second exchanger E 22 through a conduit 31 where it undergoes a second cooling step. It is then expanded through the expansion valve V 32 and then vaporized to a value substantially equal to the low pressure value of the first refrigeration cycle at around 0.15 MPa.
  • the vapor fraction obtained during vaporization is sent through a pipe 33 to a compressor K 21 located before the compressor K 22 .
  • the vapor fraction is cooled in the condenser C 21 using, for example, an available external cooling fluid and then mixed with the vapor fraction from the exchanger E 22 by the conduit 34 before the compressor K 22 enters.
  • This procedure advantageously uses the vaporization of the liquid fractions sub-cooled respectively in the exchangers E 21 and E 22 to carry out a first stage of cooling or additional cooling of the vapor fractions from the separator tank S 3 , and / or of the pressurized natural gas. to liquefy passing through the exchanger E 21 via the pipe 1 before being sent to the final exchanger where the final liquefaction operation E 1 takes place (FIG. 2).
  • the refrigerant mixture arriving in the vapor phase from the compression stage is thus precooled in two stages and is in partially condensed form before being sent via line 4 to the separator S 1 to be treated as described above. , for example in Figure 2.
  • the mixture M1 can be used, for example, to cool the natural gas, for example by heat exchange, before being mixed with the mixture M2.
  • the device of FIG. 8 differs from the embodiment of FIG. 2 in particular by the addition of an exchanger E 12 preferably located just after the exchanger E 1 having in particular the function of sub-cooling the mixture M2.
  • the procedure is, for example, as follows: the mixture M1 coming from the turbine T 1 is sent via the pipe 9 to the exchanger E 12 in which it cools the natural gas coming from the exchanger E 1 through the pipe 2.
  • the mixture M1 emerges from the exchanger E 12 by the conduit 9 'and is mixed with the mixture M2 leaving the exchanger E 1 by the conduit 7 expanded in the expansion valve V 1 and returned to the exchanger E 1 by the conduit 8, to obtain the low temperature mixture carrying out the cooling of the natural gas in the exchanger E 1 introduced by the conduit 1 and the sub-cooling of the liquid fraction coming from the separator S 1 entering the exchanger E 1 by the conduit 6.
  • This mixture after heat exchange, emerges from the exchanger E 1 through the conduit 11 in an identical manner to FIG. 2, to possibly be recycled to the compressor K 1 .
  • Part of the vapor phase coming from the separator S 1 can be sent via the line 5 'into the exchanger E 1 .
  • it is mixed with the liquid phase coming from the separator S 1 .
  • the refrigerant mixture used in this embodiment comprises, by example, hydrocarbons whose number of atoms is preferably between 1 and 5, such as methane, ethane, propane butane normal, isobutane, normal pentane or isopentane. It includes preferably at least 10% nitrogen in molar fraction. This condition is by example respected by limiting the content of heavy constituents in the fraction steam and controlling the temperature and pressure conditions at the inlet of the turbine.
  • the pressure of the refrigerant mixture is preferably at least 200 kPa at the inlet of the first compression stage K 1 .
  • the liquid fraction is for example cooled to a temperature substantially close to the temperature obtained by mixing the two relaxed fractions.
  • This liquid fraction being sub-cooled, preferably up to a temperature below its bubble pressure temperature low of the cycle, its expansion through the valve does not cause vaporization, this which allows in particular to limit mechanical irreversibilities and improve cycle performance.
  • the mixture of fluids M1 and M2 can be performed at different temperature levels, corresponding to stages successive heat exchanges with cooled natural gas.
  • FIG. 9 An example of a method according to the invention is described in FIG. 9 in which two successive fractions resulting from the expansion of the liquid fraction are mixed with the fraction resulting from the expansion of the vapor fraction in two step.
  • the exchanger E 1 in FIG. 2 is replaced by a succession of two exchangers E 13 and E 14 .
  • the mixture M1 from the turbine T 1 is sent via line 9 to be mixed with a first fraction from the expansion through the valve V 7 of the liquid fraction leaving under cooled from l exchanger E 14 then is sent to exchanger E 14 in which, it makes it possible to cool, for example, natural gas coming from an exchanger E 13 located before and discharged after cooling by line 2, then is mixed with a second fraction after the expansion of the liquid fraction withdrawn at the outlet of the exchanger E 13 and expanded through the valve V 6 and sent to the exchanger E 13 .
  • the vapor fraction from the cooling step using the external fluid in this embodiment comprises two stages of successive partial condensation by cooling under pressure, the steam fraction from each of these stages being separated and sent to the next, the vapor fraction from the last condensation step partial being at least partially expanded in a turbine with the possibility of at least partially recovering part of the power mechanical expansion, then mixed with at least one of the fractions liquids, previously relaxed by obtaining a mixture at low temperature which is thermally exchanged with natural gas under pressure to liquefy.
  • FIG. 9 shows the use of two successive mixing steps between the relaxed fractions which can without difficulties be extended to a greater number of stages.
  • the choice of number of stages used depends in particular on optimization economic.
  • FIG. 10 shows schematically another way of proceeding, in which the condensation of the vapor fraction resulting from the cooling step in the condenser C 1 of the refrigerant mixture can be carried out in several stages before being sent to the separator S 1 . In this case, it is preferable to separate the liquid fraction obtained after each step.
  • the device comprises for example two condensation exchangers E 23 and E 24 in connection with each other.
  • the refrigerant mixture passes from the condenser C 1 to the separator S 3 .
  • the vapor fraction is sent via line 17 to the exchanger E 23 from which it emerges partially condensed by a line 24 and the mixture resulting from the condensation is separated by a separator tank S 4 .
  • the vapor fraction from the separator flask through a conduit 25 preferably located at the top of the flask is sent to the exchanger E 24 in which it undergoes a new partial condensation stage and emerges in the form of a liquid-vapor mixture through the leads 4 to the steps of the method described in relation to FIG. 2.
  • the liquid fraction coming from the separator S 4 through a conduit 26 is sub-cooled in the exchanger E 24 expanded in a valve V 32 to a pressure around 200 kPa, it is mixed with the recycled vapor fraction of the exchanger E 1 via the conduit 11, this mixture making it possible to provide the required refrigeration in the exchanger E 24 .
  • the vapor fraction from the last partial condensation stage is sent via line 4 to the separator flask before being treated with identical to the process described in relation to FIG. 2 to obtain the mixtures M1 and M2 making up the low temperature refrigerant mixture to liquefy natural gas.
  • hydrocarbons which can form a gas fraction of liquefied petroleum (propane, butane) as well as a light petrol fraction (hydrocarbons with at least five carbon atoms)
  • these hydrocarbons can be at least partially separated by condensation and / or distillation at the end a first step of cooling the natural gas under pressure.
  • Natural gas introduced into the exchanger E 2 via the pipe 1, is available at 6.5 MPa and contains, for example, 88% mole of methane, 4% mole of nitrogen and heavier hydrocarbons such as ethane, propane, butane, pentane and hexane. Partial separation of these heavy fractions can be carried out during the precooling of natural gas in the exchanger E 2 .
  • the natural gas cooled to -20 ° C in the exchanger E 2 feeds via the pipe 40 a distillation device D 1 comprising a column whose reflux is ensured by a liquid fraction arriving through the pipe 43.
  • the natural gas thus rectified in the column is sent via line 41 to the exchanger E 2 in which its cooling is continued down to -80 ° C.
  • the natural gas is successively cooled in the two exchangers E 11 and E 12 to, for example, a temperature of -148 ° C.
  • the ultimate cooling of the natural gas is ensured by the reboiler of a column D 2 located after the exchanger E 12 and its expansion to, for example, a pressure of 0.13 MPa by the turbine T 2 .
  • the liquefied natural gas containing approximately 6% of vapor is introduced at the head of column D 2 , then evacuated at the bottom of column D 2 at a temperature substantially equal to -160 ° C by a conduit 46.
  • the light fraction rich in nitrogen separated in column D 2 is evacuated at the top of the column by line 44 and enters a heat exchanger E 13 in which it makes it possible to liquefy and sub-cool at least a fraction of the natural gas which penetrates in this exchanger by a conduit 49, for example, and exits by a conduit 50 to be mixed with the fraction of sub-cooled natural gas coming from the exchanger E 12 by the conduit 2.
  • the refrigerant used in this example consists, for example, of a mixture of nitrogen, methane, ethane, propane, normal butane and normal pentane.
  • the main constituents are nitrogen and methane with a mole content of 30% and 20% respectively.
  • the refrigerant mixture is cooled to a temperature of 35 ° C in the condenser C 1 , then sent to the separator tank S 3 at the end of which the vapor fraction reaches for example 60% in mass.
  • This vapor fraction is then partially condensed in the exchanger E 2 .
  • the liquid fraction coming from the separator S 3 is sub-cooled in the exchanger E 2 then expanded to a low pressure, for example, 0.18 MPa in the valve V 3 and mixed with the light fraction of the refrigerant coming from the exchanger E 11 via line 14.
  • the refrigerant mixture in the vapor phase, feeds via line 11, the compressor K 1 comprising intermediate cooling exchangers C 41 and C 42 .
  • the partially condensed vapor fraction in the exchanger E 2 is introduced through the conduit 4 into the tank S 1 to obtain a lighter vapor fraction entering the expansion turbine T 1 through the conduit 5 and a heavier liquid fraction sent by the conduit 6 to be sub-cooled in the exchanger E 11 .
  • the temperature of the tank S 1 is, for example, -80 ° C.
  • the expansion operated in the turbine T 1 for example, to 0.2 MPa makes it possible to cool this steam fraction to -150 ° C. which then contains 4% mol of liquid.
  • the heavier liquid fraction sub-cooled in the exchanger E 11 is expanded in the valve V 1 , then mixed at low pressure and at a temperature substantially equal to that of the vapor fraction coming from the turbine T 1 .
  • the temperature of the mixture thus produced before its vaporization against the current of natural gas in the exchanger E 11 makes it possible to maintain a minimum thermal approach of 2 ° C. in this exchanger.
  • the heat exchanges occurring during the refrigeration stages are preferably carried out in heat exchangers operating against the current.
  • These heat exchangers are, for example, pass exchangers multiple and are preferably constituted by plate heat exchangers.
  • These plate heat exchangers can be, for example, heat exchangers brazed aluminum. It is also possible to use steel heat exchangers stainless steel whose plates are welded together.
  • the channels in which circulating fluids participating in heat exchange can be obtained by different means by placing intermediate plates between the plates corrugated, using formed plates, for example by explosion or in using erased plates, for example by chemical etching.
  • the compressor can for example be of the type centrifugal or axial type.
  • the refrigerant mixture is preferably compressed in at least two stages between which a stage of cooling by heat exchange with the external fluid of cooling, water or air, available.
  • natural gas in a liquid state sub-cooled under pressure can be relaxed, as shown in Example 1, at least in part in a turbine, up to a pressure close to atmospheric pressure by producing liquefied natural gas which is exported.
  • the mixture refrigerant used to carry out the liquefaction cycle of a natural gas under pressure includes hydrocarbons whose number of atoms is, from preferably between 1 and 5, such as methane, ethane, propane, normal butane, isobutane, normal pentane, isopentane. It includes, preferably, a nitrogen fraction of less than 10% in molar fraction.
  • the temperature of the mixture obtained from the fractions expanded liquid and vapor is below the bubble temperature of the liquid fraction taken for substantially identical pressure conditions.
  • Subcooling or additional cooling of the liquid fraction is preferably carried out up to a temperature substantially close to the temperature obtained by mixing the two liquid fractions and expanded vapor, which in particular prevents its vaporization through the expansion valve and thus limit mechanical irreversibilities and improve thus the performance of the refrigeration cycle.
  • Part of the steam fraction can be cooled and condensed, the liquid fraction thus obtained being expanded and mixed with the M1 fractions and M2 to form the mixture at low temperature.
  • the variant embodiments relating to FIGS. 4 to 11 can advantageously include separation devices such as that relating to the Figure 3, where the simple gravity separators are replaced by distillation devices for improved separation of the mixture refrigerant.

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EP95933471A 1994-10-05 1995-10-03 Procede et installation de liquefaction du gaz naturel Expired - Lifetime EP0731900B1 (fr)

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FR9412046 1994-10-05
FR9412046A FR2725503B1 (fr) 1994-10-05 1994-10-05 Procede et installation de liquefaction du gaz naturel
PCT/FR1995/001281 WO1996011370A1 (fr) 1994-10-05 1995-10-03 Procede et installation de liquefaction du gaz naturel

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EP0731900A1 (fr) 1996-09-18
NO962314D0 (no) 1996-06-04
JP3965444B2 (ja) 2007-08-29
AU701090B2 (en) 1999-01-21
NO962314L (no) 1996-08-02
MY113403A (en) 2002-02-28
NO307231B1 (no) 2000-02-28
WO1996011370A1 (fr) 1996-04-18
FR2725503B1 (fr) 1996-12-27
AU3611895A (en) 1996-05-02
JPH09506392A (ja) 1997-06-24
US5701761A (en) 1997-12-30
FR2725503A1 (fr) 1996-04-12

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