WO2009153427A2 - Method for liquefying natural gas with pre-cooling of the coolant mixture - Google Patents

Method for liquefying natural gas with pre-cooling of the coolant mixture Download PDF

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Publication number
WO2009153427A2
WO2009153427A2 PCT/FR2009/000572 FR2009000572W WO2009153427A2 WO 2009153427 A2 WO2009153427 A2 WO 2009153427A2 FR 2009000572 W FR2009000572 W FR 2009000572W WO 2009153427 A2 WO2009153427 A2 WO 2009153427A2
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WO
WIPO (PCT)
Prior art keywords
mixture
heat exchange
natural gas
refrigerant mixture
refrigerant
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PCT/FR2009/000572
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French (fr)
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WO2009153427A3 (en
Inventor
Béatrice Fischer
Anne-Claire Lucquin
Gilles Ferschneider
Amandine Teillet De Wit
Jérôme PIGOURIER
Pierre-Yves Martin
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Ifp
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Priority to RU2011101884/06A priority Critical patent/RU2509967C2/en
Publication of WO2009153427A2 publication Critical patent/WO2009153427A2/en
Publication of WO2009153427A3 publication Critical patent/WO2009153427A3/en

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Classifications

    • 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
    • F25J1/0047—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
    • F25J1/0214—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
    • F25J1/0265—Arrangement of heat exchanger cores in parallel with different functions, e.g. different cooling streams comprising cores associated exclusively with the cooling of a refrigerant stream, e.g. for auto-refrigeration or economizer
    • 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
    • F25J1/0279—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
    • 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.
    • F25J1/0294—Multiple compressor casings/strings in parallel, e.g. split arrangement
    • 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
    • F25J1/0279—Compression of refrigerant or internal recycle fluid, e.g. kind of compressor, accumulator, suction drum etc.
    • F25J1/0296—Removal of the heat of compression, e.g. within an inter- or afterstage-cooler against an ambient heat sink
    • 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
    • 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
    • F25J2290/00—Other details not covered by groups F25J2200/00 - F25J2280/00
    • F25J2290/12—Particular process parameters like pressure, temperature, ratios

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 tankers.
  • LNG liquid natural gas
  • US 6,105,389 proposes a liquefaction process comprising two refrigerant mixtures flowing in two closed and independent circuits. Each of these circuits operates through a compressor communicating to the refrigerant mixture the power required to cool the natural gas.
  • the present invention proposes to improve the process disclosed by US 6 105 389 in order to improve the operation and energy yields, thus to produce more by emitting less CO 2 and keeping substantially identical equipment.
  • the present invention relates to a process for liquefying a natural gas, in which the following steps are carried out: a) a refrigerant mixture is compressed, b) the compressed refrigerant mixture is condensed by heat exchange, c the condensed refrigerant mixture is stored in a storage tank, the tank containing in equilibrium a liquid phase of a refrigerant mixture and a gaseous phase of a refrigerant mixture, d) the refrigerant mixture is withdrawn in the liquid phase from the storage tank, e) a step is carried out in which only the refrigerant mixture withdrawn in step d) is subcooled by heat exchange, f) the natural gas is cooled; at least by heat exchange with the subcooled refrigerant mixture obtained in step e).
  • the cooling mixture in step e), can be subcooled by heat exchange with an external fluid chosen from air and water.
  • the cooling mixture in step e), can be sub-cooled by exchanging heat with a portion of the cooling mixture, said portion being expanded before heat exchange.
  • said portion of refrigerant mixture can be taken from said withdrawn refrigerant mixture before performing the heat exchange of step e).
  • said portion of refrigerant mixture can be taken from the refrigerant mixture obtained after performing the heat exchange of step e) and before performing the heat exchange of step f).
  • step e) can be performed in a first heat exchanger
  • step f) can be performed in at least a second heat exchanger, the first heat exchanger being separate from the second heat exchanger
  • the cooling mixture may comprise, in molar percentage: between 0 and 5% of methane, between 30 and 70% of ethane, between 30 and 70% of propane and between 0 and 20% of butane.
  • step f) the natural gas can be cooled to a liquid natural gas.
  • the natural gas in step f), can be cooled and simultaneously a second refrigerant mixture by heat exchange with the subcooled refrigerant mixture obtained in step e) and after step f) it is possible to liquefying and subcooling the natural gas by exchanging heat with the second refrigerant mixture until a liquid natural gas is obtained.
  • the second refrigerant mixture may comprise, in molar percentage: between 0 and 12% of nitrogen, between 20 and 80% of methane and between 20 and 80% of ethane and between 0 and 10% of propane.
  • FIG. 1 represents a method according to the invention
  • FIG. 1 represents a liquefaction process using a first refrigerant circuit appearing in the dashed line frame referenced (I) and a second refrigerant circuit indicated by reference (II).
  • the first refrigerant circuit (I) uses a first refrigerant mixture, hereinafter referred to as MR1, which may be composed of a mixture of hydrocarbons such as a mixture of ethane and propane, but may also contain methane. and / or butane.
  • MR1 first refrigerant mixture
  • the proportions in molar percentages of the components of MR1 may be:
  • the second refrigerant circuit (II) uses a second refrigerant mixture, hereinafter referred to as MR2, which may be composed for example of a mixture of hydrocarbons and nitrogen such as a mixture of methane, ethane, propane and nitrogen but may also contain butane.
  • MR2 second refrigerant mixture
  • the proportions in molar percentages of the components of MR2 may be:
  • the natural gas arrives via the pipe 10 in general at a pressure of between 4 MPa and 7 MPa and at a temperature which may be between 0 ° C. and 60 ° C.
  • the natural gas flowing in the pipe 10, the first refrigerant mixture MR1 circulating in the conduit 23, and the second refrigerant mixture MR2 circulating in the conduit 31 enter successively into the exchangers Ei, E 2 and E 3 to circulate in parallel directions and co-current.
  • the natural gas exits the heat exchanger train formed by E 1 , E 2 and E 3 through line 11 at a temperature which can be between -30 ° C. and -75 ° C.
  • the second refrigerant mixture MR2 arriving via the duct 31 passes successively through the heat exchangers Ei, E 2 and E 3 and is discharged through the duct 32 which is completely condensed and preferably sub-cooled to a temperature which may be between -30 ° C. and -75 ° C.
  • MR1 from Ei is separated into two fractions, a fraction sent via line 24 to valve V 1 and a fraction sent via line 26 to exchanger E 2 .
  • MR1 from E 2 is separated into two fractions, a fraction sent via line 27 to valve V 2 and a fraction sent via line 29 to exchanger E 3 .
  • MR1 from E 3 is sent through line 29b to valve V 3 .
  • the MR1 fractions are respectively expanded through expansion valves Vi, V 2 , V 3 at three different pressure levels, and then vaporized respectively in the exchangers E 1 , E 2 , E 3 by heat exchange with the natural gas, the second refrigerant mixture MR2 and a part of the first refrigerant mixture MR1.
  • the three fractions were vaporized respectively sent via lines 25, 28 and 30 in the compressor K 1 to be compressed.
  • the first refrigerant mixture MR1 compressed is condensed in the condenser C 1 by heat exchange with an external cooling fluid, for example water or air. Then the MR1 is introduced into the recipe balloon D. In the method described in FIG.
  • the MR1 is split into three separate fractions to optimize the approach in the E 1 -E 2 -E 3 exchange train.
  • the refrigerant mixture MR1 may also not be split or split into two or four fractions, for the sake of thermal optimization of the process.
  • the recipe balloon D acts as a buffer storage to balance, especially in terms of pressure, temperature and volume, the refrigerant mixture MR1 in the circuit (I).
  • the balloon D contains in equilibrium a portion of MR1 in the liquid phase and a portion of MR1 in the gas phase.
  • the level of the liquid in the balloon D varies depending on the total amount of refrigerant mixture present in the circuit.
  • the presence of the balloon D makes it possible to balance the pressures in the circuit (I).
  • the MR1 is introduced in liquid form into the flask D at a pressure and a temperature close to the equilibrium of the liquid and vapor phases of the MR1.
  • the MR1 was directly sent from the balloon D in the exchanger, as proposed in the prior art, it could be partially vaporized, due to pressure losses, heat exchange and possible differences in static height in the circulation ducts, before being introduced into the heat exchanger train E 1 -E 2 -E 3 .
  • the heat exchanger C 2 can only cool the MR1 so without compromising the refrigeration of natural gas.
  • the heat exchanger C 2 may be independent of the exchanger train ErE 2 -E 3 and can therefore be placed near the recipe balloon D to reduce the risk of vaporization of the MR1 withdrawn from the balloon D.
  • the refrigerant mixture MR1 is withdrawn in the liquid phase from the recipe flask D and is sub-cooled by a few degrees (a temperature drop that can range from 2 ° C. to 10 ° C.) through the exchanger C 2 so as to ensure that the refrigerant melamine MR1 enters the Ei exchanger in completely complete form. liquid at a temperature well below the MR1 bubble point temperature. Thus, it optimizes the distribution in the different passes of the exchanger.
  • the natural gas from the heat exchanger train ErE 2 -E 3 through line 11 can be fractionated, that is to say a portion of C2 + hydrocarbons containing at least two carbon atoms is separated from natural gas, following a device known to those skilled in the art.
  • the optionally fractionated natural gas is sent through the pipe 11b into the exchanger E 4 , where the MR2 arriving via the conduit 32 circulates in parallel and co-current.
  • the MR2 leaving the exchanger E 4 via the conduit 33 is expanded in the valve V 4 .
  • the expanded MR2 from V 4 is returned to E 4 in countercurrent to be vaporized by countercurrently cooling the natural gas and MR2.
  • the subcooled natural gas is discharged from the exchanger E 4 through the conduit 12.
  • the vaporized MR2 is sent via the conduit 35 into the compressor K 2 and then cooled in the exchanger C 3 by exchanging heat with an external cooling fluid, for example water or air.
  • MR2 pressure of the output of K 2 may be between 2 MPa and 7 MPa. If necessary, the refrigerant mixture MR2 can be withdrawn from the compressor K 2 to be cooled in the exchanger C 4 , then introduced through the conduit 36 into K 2 to be compressed.
  • the member K 2 may consist of several compressors arranged in series or in parallel.
  • the MR 2 is not split into separate fractions, but, in order to optimize the energy efficiency in the exchanger E 4 , the MR 2 can also be split into two or three fractions, each fraction being relaxed at a different pressure level and then sent to different stages of the compressor K 2 .
  • the variants of the invention described with reference to Figures 2 and 3 propose to use a fraction of MR1 to perform the subcooling of the MR1 before entering the train of heat exchangers ErE 2 -E 3 .
  • the MR1 coming out of the recipe flask via the conduit 20 is introduced into the exchanger E 2 i in order to lower the temperature of the MR1, a drop of between 5 0 C and 30 0 C relative to the MR1 temperature before entering E 2 i.
  • the MR1 is sub-cooled E 2 i by the conduit 21.
  • the MR1 is then split into two parts.
  • the first fraction FMR1 flowing in the duct 22 is expanded through the expansion valve V 5 and is vaporized in E 2 i by exchange with MR1.
  • FMR1 is completely steam and is returned to the compressor Ki at the most appropriate pressure level.
  • the other fraction of MR1 from E 2 i is sent through line 23 to the exchanger E i.
  • a variant of the invention is represented in FIG. 3.
  • the MR1 coming out of the recipe balloon D via line 20 is separated into at least two fractions 21b and 22b.
  • the fraction 21b enters the exchanger E 21 to lower the temperature of the MR1, a drop of between 5 ° C. and 30 ° C. relative to the temperature of the MR1 before entering E 2 i.
  • the MR1 exits sub-cooled E 2 i through the conduit 23.
  • the fraction 22b is expanded through the expansion valve V 5 and vaporized in E 2 i by exchange with the fraction 21 b. At the outlet of E 2 i, the fraction 22b is completely vaporized and is returned to the compressor K 1 at the most appropriate pressure level.
  • FIGS. 1 and 2 are illustrated by the following numerical example, which makes it possible to apprehend the benefit provided by the process of FIG. 2 with respect to the method of FIG.
  • Natural gas arrives via line 10 at a pressure of 6.8 MPa and at a temperature of 20 ° C.
  • the composition of this gas in molar percentages is as follows:
  • the heat exchanger train ErE 2 -E 3 uses a first refrigerant mixture whose composition is in molar percentages:
  • the second refrigerant mixture MR2 leaving the exchanger train ErE 2 -E 3 through the conduit 32 is at a temperature of -59.5 ° C.
  • the exchanger E 4 uses the second refrigerant mixture whose composition in molar percentages is as follows:
  • the natural gas is liquefied at a temperature of -152.8 ° C.
  • the first refrigerant mixture MR1 is compressed in the gas phase in the multi-stage compressor Ki to a pressure of 3.06 MPa.
  • the compressed MR1 is condensed at a temperature of 36 ° C by heat exchange with water at 26 ° C in C 1, for which an approach of 10 0 C was considered. He is then at the point of bubble. It is the temperature of 36 ° C which imposes to compress the MR1 up to a pressure of 3.06 MPa.
  • the MR1 is subcooled to a temperature of 31 ° C. by heat exchange with water at 26 ° C. in C 2 , for which an approach of 5 ° C. been considered. Cooling temperatures in Ci and C 2 are limited by the temperature of the water that is available.
  • the MR1 therefore enters the Ei-E 2 -E 3 exchanger train at a temperature of 31 ° C., which is 5 ° C. lower than the bubble point temperature at the pressure of 3.06 MPa.
  • the method described with reference to Figure 2 lowers the MR1 inlet temperature in the exchangers being EnEd 2 -E 3. As the subcooling is no longer done with water in C2, but by the MR1 itself in E 2 - I , one can carry out cooling at lower temperature in Ci.
  • the MR1 is cooled to a temperature of 31 0 C by heat exchange with water at 26 ° C in Ci, for which we can consider a thermal approach in the condenser Ci of 5 ° C only.
  • the compression pressure of Ki can be lowered: at the output of the compressor Ki, the MR1 is compressed at 2.80 MPa only.
  • the MR1 After passing through the recipe flask D where it is at the bubble point, the MR1 is subcooled in E 21 to a temperature of 25 ° C. To reach this temperature, the fraction FMR1 is relaxed in V 5 to 1.43 MPa, then it cools the MR1 counter-current. FMR1 comes out of E 2 i completely vapor, and at a temperature of 29 ° C. FMR1 is then redirected to the high pressure suction of the compressor Ki. In FIG. 2, the MR1 therefore enters the ErE 2 -E 3 exchange train at a temperature of 25 ° C., which is 6 ° C. lower than the bubble point temperature at the pressure of 2.80 MPa.
  • the energy consumptions of the compressors are as follows:
  • the output of LNG at the end of E 4 is 5.3 MTPA (million tonnes per year).
  • the efficiency of the refrigerant cycles is therefore 35.70 MW / (MTPA).
  • FIGS. 1 and 3 are illustrated by the following numerical example, which makes it possible to apprehend the benefit provided by the process of FIG. 3 with respect to the process of FIG.
  • Natural gas arrives via line 10 at a pressure of 6.8 MPa and at a temperature of 20 ° C.
  • the composition of this gas in molar percentages is as follows:
  • the heat exchange train E 1 -E 2 -E 3 uses a first refrigerant mixture whose composition is in molar percentages:
  • the natural gas leaving the exchanger train ErE 2 -E 3 through line 11 is at a temperature of -52 ° C.
  • the second refrigerant mixture MR2 leaving the exchanger train E 1 -E 2 -E 3 through line 32 is at a temperature of -59.5 ° C.
  • the exchanger E 4 uses the second refrigerant mixture whose composition in molar percentages is as follows:
  • the natural gas is liquefied at a temperature of -152.8 ° C.
  • the first refrigerant mixture MR1 is compressed in the gas phase in the multi-stage compressor Ki to a pressure of 3.06 MPa.
  • the compressed MR1 is condensed at a temperature of 36 ° C by heat exchange with water at 26 ° C in C 1, for which an approach of 10 0 C was considered. He is then at the point of bubble. It is the temperature of 36 ° C which imposes to compress the MR1 up to a pressure of 3.06 MPa.
  • MR1 After passing through the receiving flask D, MR1 is subcooled i ⁇ 10/11 I'o nn ⁇ tomn ⁇ rati go Ho ⁇ 1 0 P.
  • the MR1 therefore enters the ErE 2 -E 3 exchanger train at a temperature of 31 ° C., which is 5 ° C. lower than the bubble point temperature at the pressure of 3.06 MPa.
  • the method described with reference to FIG. 3 makes it possible to lower the inlet temperature of the MR1 in the Ei-E 2 -E 3 exchanger train. As the subcooling is no longer done with water in C 2 but by the MR1 itself in E 21 , it is possible to carry out cooling at a lower temperature in Ci.
  • the MR1 is cooled to a temperature of 31 ° C. C by heat exchange with water at 26 ° C in Ci, for which a thermal approach in the condenser Ci of 5 ° C can be considered.
  • the compression pressure of Ki can be lowered: at the outlet of the compressor K 1 , the MR1 is compressed at 2.80 MPa only.
  • the MR1 After passing through the recipe flask D where it is at the bubble point, the MR1 is subcooled in E 2 i to a temperature of 25 ° C. To reach this temperature, a fraction FMR1 of the MR1 leaving the balloon D is expanded in V 5 at 1.39 MPa, then it cools the remaining fraction of the MR1 counter-current. FMR1 comes out of E 2 -I completely vapor, and at a temperature of 28 ° C. FMR1 is then redirected to the high-pressure suction of compressor K 1 .
  • the MR1 thus enters the heat exchanger train E 1 -E 2 -E 3 at a temperature of 25 ° C., which is 6 ° C. lower than the temperature of the bubble point at the pressure of 2.80 MPa.
  • the energy consumptions of the compressors are as follows:
  • the output of LNG at the end of E 4 is 5.3 MTPA (million tonnes per year).
  • the efficiency of the refrigerant cycles is therefore 35.70 MW / (MTPA).
  • the energy consumption of the compressors are as follows:

Abstract

The invention relates to a method for liquefying a natural gas, in which the natural gas is cooled, condensed and sub-cooled by indirect heat-exchange with two coolant mixtures flowing in circuits (I) and (II). The first coolant mixture is compressed in K1, and cooled and at least partially condensed by heat exchange in C1 with an external fluid (water, air). The first coolant mixture is sub-cooled by heat exchange in C2 so that the first coolant mixture is in a liquid phase in order to ensure a good distribution of the coolant mixture in the exchanger line E1-E2-E3.

Description

PROCÉDÉ DE LIQUÉFACTION D'UN QAZ NATUREL AVEC PRÉ-REFROIDISSEMENT DU MÉLANGE RÉFRIGÉRANT METHOD FOR LIQUEFACTING A NATURAL QAZ WITH PRE-COOLING THE REFRIGERANT MIXTURE
La présente invention concerne le domaine de la liquéfaction du gaz naturel.The present invention relates to the field of liquefaction of natural gas.
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 bateaux méthaniers.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 tankers.
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, et réduire la facture énergétique (et donc environnementale) liée à la production de GNL est un objectif prioritaire.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, and reducing the energy (and therefore environmental) bill related to LNG production is a priority objective.
Le document US 6 105 389 propose un procédé de liquéfaction comportant deux mélanges réfrigérants circulant dans deux circuits fermés et indépendants. Chacun de ces circuits fonctionne grâce à un compresseur communicant au mélange réfrigérant la puissance nécessaire pour refroidir le gaz naturel.US 6,105,389 proposes a liquefaction process comprising two refrigerant mixtures flowing in two closed and independent circuits. Each of these circuits operates through a compressor communicating to the refrigerant mixture the power required to cool the natural gas.
La présente invention propose de perfectionner le procédé divulgué par le document US 6 105 389 afin d'améliorer le fonctionnement et les rendements énergétiques, donc de produire plus en émettant moins de CO2 et en conservant des équipements sensiblement identiques.The present invention proposes to improve the process disclosed by US 6 105 389 in order to improve the operation and energy yields, thus to produce more by emitting less CO 2 and keeping substantially identical equipment.
De manière générale, la présente invention concerne un procédé de liquéfaction d'un gaz naturel, dans lequel on effectue les étapes suivantes : a) on comprime un mélange réfrigérant, b) on condense, par échange de chaleur, le mélange réfrigérant comprimé, c) on stocke le mélange réfrigérant condensé dans un ballon de stockage, le ballon contenant en équilibre une phase liquide de mélange réfrigérant et une phase gazeuse de mélange réfrigérant, d) on soutire du mélange réfrigérant en phase liquide du ballon de stockage, e) on effectue une étape dans laquelle seul le mélange réfrigérant soutiré à l'étape d) est sous-refroidi par échange de chaleur, f) on refroidit le gaz naturel au moins par échange de chaleur avec le mélange réfrigérant sous-refroidi obtenu à l'étape e).In general, the present invention relates to a process for liquefying a natural gas, in which the following steps are carried out: a) a refrigerant mixture is compressed, b) the compressed refrigerant mixture is condensed by heat exchange, c the condensed refrigerant mixture is stored in a storage tank, the tank containing in equilibrium a liquid phase of a refrigerant mixture and a gaseous phase of a refrigerant mixture, d) the refrigerant mixture is withdrawn in the liquid phase from the storage tank, e) a step is carried out in which only the refrigerant mixture withdrawn in step d) is subcooled by heat exchange, f) the natural gas is cooled; at least by heat exchange with the subcooled refrigerant mixture obtained in step e).
Selon l'invention, à l'étape e), on peut sous-refroidir le mélange réfrigérant par échange de chaleur avec un fluide extérieur choisi parmi l'air et l'eau.According to the invention, in step e), the cooling mixture can be subcooled by heat exchange with an external fluid chosen from air and water.
Alternativement, à l'étape e), on peut sous-refroidir le mélange réfrigérant par échange de chaleur avec une portion du mélange réfrigérant, ladite portion étant détendue avant échange de chaleur. Par exemple, ladite portion de mélange réfrigérant peut être prélevée dudit mélange réfrigérant soutiré avant d'effectuer l'échange de chaleur de l'étape e). Alternativement, ladite portion de mélange réfrigérant peut être prélevée du mélange réfrigérant obtenu après avoir effectué l'échange de chaleur de l'étape e) et avant d'effectuer l'échange de chaleur de l'étape f).Alternatively, in step e), the cooling mixture can be sub-cooled by exchanging heat with a portion of the cooling mixture, said portion being expanded before heat exchange. For example, said portion of refrigerant mixture can be taken from said withdrawn refrigerant mixture before performing the heat exchange of step e). Alternatively, said portion of refrigerant mixture can be taken from the refrigerant mixture obtained after performing the heat exchange of step e) and before performing the heat exchange of step f).
Selon l'invention, l'étape e) peut être effectuée dans un premier échangeur de chaleur, l'étape f) peut être effectuée dans au moins un deuxième échangeur de chaleur, le premier échangeur de chaleur étant distinct du deuxième échangeur de chaleur.According to the invention, step e) can be performed in a first heat exchanger, step f) can be performed in at least a second heat exchanger, the first heat exchanger being separate from the second heat exchanger.
Le mélange réfrigérant peut comporter en pourcentage molaire : entre 0 et 5% de méthane, entre 30 et 70% d'éthane, entre 30 et 70% de propane et entre 0 et 20% de butane.The cooling mixture may comprise, in molar percentage: between 0 and 5% of methane, between 30 and 70% of ethane, between 30 and 70% of propane and between 0 and 20% of butane.
A l'étape f), on peut refroidir le gaz naturel jusqu'à obtenir un gaz naturel liquide.In step f), the natural gas can be cooled to a liquid natural gas.
Alternativement, à l'étape f), on peut refroidir le gaz naturel et, simultanément, un deuxième mélange réfrigérant par échange de chaleur avec le mélange réfrigérant sous-refroidi obtenu à l'étape e) et après l'étape f) on peut liquéfier et on peut sous-refroidir le gaz naturel par échange de chaleur avec le deuxième mélange réfrigérant jusqu'à obtenir un gaz naturel liquide. Le deuxième mélange réfrigérant peut comporter en pourcentage molaire : entre 0 et 12% d'azote, entre 20 et 80% de méthane et entre 20 et 80% d'éthane et entre 0 et 10% de propane.Alternatively, in step f), the natural gas can be cooled and simultaneously a second refrigerant mixture by heat exchange with the subcooled refrigerant mixture obtained in step e) and after step f) it is possible to liquefying and subcooling the natural gas by exchanging heat with the second refrigerant mixture until a liquid natural gas is obtained. The second refrigerant mixture may comprise, in molar percentage: between 0 and 12% of nitrogen, between 20 and 80% of methane and between 20 and 80% of ethane and between 0 and 10% of propane.
D'autres caractéristiques et avantages de l'invention seront mieux compris et apparaîtront clairement à la lecture de la description faite ci-après en se référant aux dessins parmi lesquels :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 drawings among which:
- la figure 1 représente un procédé selon l'invention,FIG. 1 represents a method according to the invention,
- les figures 2 et 3 schématisent d'autres modes de réalisation de l'invention.- Figures 2 and 3 show schematically other embodiments of the invention.
La figure 1 représente un procédé de liquéfaction mettant en oeuvre un premier circuit réfrigérant figurant dans le cadre en trait pointillé référencé (I) et un deuxième circuit réfrigérant indiqué par la référence (II).FIG. 1 represents a liquefaction process using a first refrigerant circuit appearing in the dashed line frame referenced (I) and a second refrigerant circuit indicated by reference (II).
Le premier circuit réfrigérant (I) met en oeuvre un premier mélange réfrigérant, nommé ci-après MR1 , qui peut être composé d'un mélange d'hydrocarbures tels qu'un mélange d'éthane et de propane, mais peut également contenir du méthane et/ou du butane. Les proportions en pourcentages molaires des composants de MR1 peuvent être :The first refrigerant circuit (I) uses a first refrigerant mixture, hereinafter referred to as MR1, which may be composed of a mixture of hydrocarbons such as a mixture of ethane and propane, but may also contain methane. and / or butane. The proportions in molar percentages of the components of MR1 may be:
- Méthane : 0 à 5%- Methane: 0 to 5%
- Ethane : 30 à 70%- Ethane: 30 to 70%
- Propane : 30 à 70%- Propane: 30 to 70%
- Butane : 0 à 20%- Butane: 0 to 20%
Le deuxième circuit réfrigérant (II) met en oeuvre un deuxième mélange réfrigérant, nommé ci-après MR2, qui peut être composé par exemple par un mélange d'hydrocarbures et d'azote tels qu'un mélange de méthane, éthane, propane et azote, mais peut également contenir du butane. Les proportions en pourcentages molaires des composants de MR2 peuvent être :The second refrigerant circuit (II) uses a second refrigerant mixture, hereinafter referred to as MR2, which may be composed for example of a mixture of hydrocarbons and nitrogen such as a mixture of methane, ethane, propane and nitrogen but may also contain butane. The proportions in molar percentages of the components of MR2 may be:
- Azote : 0 à 12%- Nitrogen: 0 to 12%
- Méthane : 20 à 80%- Methane: 20 to 80%
- Fthanft • 9Ω à Rf) % - Propane : O à 10 %- Fthanft • 9Ω to Rf)% - Propane: 0 to 10%
Le gaz naturel arrive par le conduit 10 en général à une pression comprise entre 4 MPa et 7 MPa et à une température qui peut être comprise entre 00C et 600C. Le gaz naturel circulant dans le conduit 10, le premier mélange réfrigérant MR1 circulant dans le conduit 23, et le deuxième mélange réfrigérant MR2 circulant dans le conduit 31 entrent successivement dans les échangeurs Ei, E2 et E3 pour y circuler selon des directions parallèles et à co-courant. Le gaz naturel sort du train d'échangeurs de chaleur formé par Ei, E2 et E3 par le conduit 11 à une température qui peut être comprise entre -300C et -75°C. Le deuxième mélange réfrigérant MR2 arrivant par le conduit 31 traverse successivement les échangeurs de chaleur Ei, E2 et E3 et est évacué par le conduit 32 totalement condensé et de préférence sous-refroidi à une température qui peut être comprise entre -30°C et -75°C.The natural gas arrives via the pipe 10 in general at a pressure of between 4 MPa and 7 MPa and at a temperature which may be between 0 ° C. and 60 ° C. The natural gas flowing in the pipe 10, the first refrigerant mixture MR1 circulating in the conduit 23, and the second refrigerant mixture MR2 circulating in the conduit 31 enter successively into the exchangers Ei, E 2 and E 3 to circulate in parallel directions and co-current. The natural gas exits the heat exchanger train formed by E 1 , E 2 and E 3 through line 11 at a temperature which can be between -30 ° C. and -75 ° C. The second refrigerant mixture MR2 arriving via the duct 31 passes successively through the heat exchangers Ei, E 2 and E 3 and is discharged through the duct 32 which is completely condensed and preferably sub-cooled to a temperature which may be between -30 ° C. and -75 ° C.
Dans le train d'échangeurs de chaleur E1-E2-E3, trois fractions du premier mélange réfrigérant MR1 en phase liquide sont successivement soutirées. Le MR1 issu de Ei est séparé en deux fractions, une fraction envoyée par le conduit 24 à la vanne V1 et une fraction envoyée par le conduit 26 à l'échangeur E2. Le MR1 issu de E2 est séparé en deux fractions, une fraction envoyée par le conduit 27 à la vanne V2 et une fraction envoyée par le conduit 29 à l'échangeur E3. Le MR1 issu de E3 est envoyé par le conduit 29b à la vanne V3. Les fractions de MR1 sont respectivement détendues à travers des vannes de détente V-i, V2, V3 à trois niveaux de pression différents, puis vaporisées respectivement dans les échangeurs E1, E2, E3 par échange de chaleur avec le gaz naturel, le deuxième mélange réfrigérant MR2 et une partie du premier mélange réfrigérant MR1. Les trois fractions vaporisées sont respectivement envoyées par les conduits 25, 28 et 30 dans le compresseur K1 pour être comprimées. Le premier mélange réfrigérant MR1 comprimé est condensé dans le condenseur C1 par échange de chaleur avec un fluide extérieur de refroidissement, par exemple de l'eau ou de l'air. Puis le MR1 est introduit dans le ballon de recette D. Dans le procédé décrit par la figure 1 , le MR1 est scindé en trois fractions séparées pour optimiser l'approche dans le train d'échange E1-E2-E3. Selon l'invention, le mélange réfrigérant MR1 peut également ne pas être scindé ou être scindé en deux ou quatre fractions, dans un souci d'optimisation thermique du procédé.In the train of heat exchangers E 1 -E 2 -E 3 , three fractions of the first refrigerant mixture MR1 in the liquid phase are successively withdrawn. MR1 from Ei is separated into two fractions, a fraction sent via line 24 to valve V 1 and a fraction sent via line 26 to exchanger E 2 . MR1 from E 2 is separated into two fractions, a fraction sent via line 27 to valve V 2 and a fraction sent via line 29 to exchanger E 3 . MR1 from E 3 is sent through line 29b to valve V 3 . The MR1 fractions are respectively expanded through expansion valves Vi, V 2 , V 3 at three different pressure levels, and then vaporized respectively in the exchangers E 1 , E 2 , E 3 by heat exchange with the natural gas, the second refrigerant mixture MR2 and a part of the first refrigerant mixture MR1. The three fractions were vaporized respectively sent via lines 25, 28 and 30 in the compressor K 1 to be compressed. The first refrigerant mixture MR1 compressed is condensed in the condenser C 1 by heat exchange with an external cooling fluid, for example water or air. Then the MR1 is introduced into the recipe balloon D. In the method described in FIG. 1, the MR1 is split into three separate fractions to optimize the approach in the E 1 -E 2 -E 3 exchange train. According to the invention, the refrigerant mixture MR1 may also not be split or split into two or four fractions, for the sake of thermal optimization of the process.
Le ballon de recette D joue un rôle de stockage tampon pour équilibrer, notamment en terme de pression, température et volume, le mélange réfrigérant MR1 dans le circuit (I). Le ballon D contient en équilibre une portion de MR1 en phase liquide et une portion de MR1 en phase gazeuse. Le niveau du liquide dans le ballon D varie en fonction de la quantité totale de mélange réfrigérant présent dans le circuit. La présence du ballon D permet d'équilibrer les pressions dans le circuit (I). Le MR1 est introduit sous forme liquide dans le ballon D à une pression et une température proche de l'équilibre des phases liquide et vapeur du MR1.The recipe balloon D acts as a buffer storage to balance, especially in terms of pressure, temperature and volume, the refrigerant mixture MR1 in the circuit (I). The balloon D contains in equilibrium a portion of MR1 in the liquid phase and a portion of MR1 in the gas phase. The level of the liquid in the balloon D varies depending on the total amount of refrigerant mixture present in the circuit. The presence of the balloon D makes it possible to balance the pressures in the circuit (I). The MR1 is introduced in liquid form into the flask D at a pressure and a temperature close to the equilibrium of the liquid and vapor phases of the MR1.
Si le MR1 était directement envoyé du ballon D dans l'échangeur, comme proposé dans l'art antérieur, il risquerait d'être partiellement vaporisé, du fait des pertes de charge, d'échanges thermiques et de différences éventuelles de hauteur statique dans les conduits de circulation, avant d'être introduit dans le train d'échangeurs de chaleur E1-E2-E3. Or il est difficile de répartir de manière homogène un mélange de gaz et de liquide dans les différentes passes d'un échangeur de chaleur. De ce fait, l'échange de chaleur dans ErE2-E3 ne serait pas optimisé. L'échangeur de chaleur C2 permet de refroidir uniquement le MR1 donc sans compromettre la réfrigération du gaz naturel. De plus, l'échangeur de chaleur C2 peut être indépendant du train d'échangeurs ErE2-E3 et de ce fait peut être disposé à proximité du ballon de recette D pour réduire les risques de vaporisation du MR1 soutiré du ballon D.If the MR1 was directly sent from the balloon D in the exchanger, as proposed in the prior art, it could be partially vaporized, due to pressure losses, heat exchange and possible differences in static height in the circulation ducts, before being introduced into the heat exchanger train E 1 -E 2 -E 3 . However it is difficult to distribute homogeneously a mixture of gas and liquid in the different passes of a heat exchanger. As a result, the heat exchange in ErE 2 -E 3 would not be optimized. The heat exchanger C 2 can only cool the MR1 so without compromising the refrigeration of natural gas. In addition, the heat exchanger C 2 may be independent of the exchanger train ErE 2 -E 3 and can therefore be placed near the recipe balloon D to reduce the risk of vaporization of the MR1 withdrawn from the balloon D.
Selon l'invention, représenté par la figure 1 , après passage par le ballon de recette D, le mélange réfrigérant MR1 est soutiré en phase liquide du ballon de recette D et est sous-refroidi de quelques degrés (une baisse de température pouvant aller de 2°C jusqu'à 100C) par l'échangeur C2 de façon à garantir que le mélanαe réfriαérant MR1 entre dans l'échanqeur Ei sous forme complètement liquide à une température bien inférieure à la température du point de bulle du MR1. Ainsi, on optimise la distribution dans les différentes passes de l'échangeur.According to the invention, represented by FIG. 1, after passing through the recipe flask D, the refrigerant mixture MR1 is withdrawn in the liquid phase from the recipe flask D and is sub-cooled by a few degrees (a temperature drop that can range from 2 ° C. to 10 ° C.) through the exchanger C 2 so as to ensure that the refrigerant melamine MR1 enters the Ei exchanger in completely complete form. liquid at a temperature well below the MR1 bubble point temperature. Thus, it optimizes the distribution in the different passes of the exchanger.
Le gaz naturel issu du train d'échangeurs de chaleur ErE2-E3 par le conduit 11 peut être fractionné c'est-à-dire qu'une partie des hydrocarbures C2+ contenant au moins deux atomes de carbone est séparée du gaz naturel, suivant un dispositif connu de l'homme de l'art.The natural gas from the heat exchanger train ErE 2 -E 3 through line 11 can be fractionated, that is to say a portion of C2 + hydrocarbons containing at least two carbon atoms is separated from natural gas, following a device known to those skilled in the art.
Le gaz naturel éventuellement fractionné est envoyé par la conduite 11b dans l'échangeur E4, où le MR2 arrivant par le conduit 32 circule en parallèle et à co-courant. Le MR2 sortant de l'échangeur E4 par le conduit 33 est détendu dans la vanne V4. A noter qu'il est possible d'utiliser en amont de la vanne V4, ou en remplacement de celle-ci, une turbine de détente. Le MR2 détendu issu de V4 est renvoyé dans E4 à contre-courant pour être vaporisé en réfrigérant à contre- courant le gaz naturel et le MR2. Le gaz naturel sous-refroidi est évacué de l'échangeur E4 par le conduit 12. En sortie de E4, le MR2 vaporisé est envoyé par le conduit 35 dans le compresseur K2 puis refroidi dans l'échangeur C3 par échange de chaleur avec un fluide extérieur de refroidissement, par exemple de l'eau ou de l'air. La pression du MR2 en sortie de K2 peut être comprise entre 2 MPa et 7 MPa. Si nécessaire, le mélange réfrigérant MR2 peut être soutiré du compresseur K2 pour être refroidi dans l'échangeur C4, puis introduit par le conduit 36 dans K2 pour être comprimé. Selon un mode de réalisation, l'organe K2 peut être constitué de plusieurs compresseurs arrangés en série ou en parallèle.The optionally fractionated natural gas is sent through the pipe 11b into the exchanger E 4 , where the MR2 arriving via the conduit 32 circulates in parallel and co-current. The MR2 leaving the exchanger E 4 via the conduit 33 is expanded in the valve V 4 . Note that it is possible to use upstream of the valve V 4 , or in replacement thereof, an expansion turbine. The expanded MR2 from V 4 is returned to E 4 in countercurrent to be vaporized by countercurrently cooling the natural gas and MR2. The subcooled natural gas is discharged from the exchanger E 4 through the conduit 12. At the outlet of E 4 , the vaporized MR2 is sent via the conduit 35 into the compressor K 2 and then cooled in the exchanger C 3 by exchanging heat with an external cooling fluid, for example water or air. MR2 pressure of the output of K 2 may be between 2 MPa and 7 MPa. If necessary, the refrigerant mixture MR2 can be withdrawn from the compressor K 2 to be cooled in the exchanger C 4 , then introduced through the conduit 36 into K 2 to be compressed. According to one embodiment, the member K 2 may consist of several compressors arranged in series or in parallel.
Dans le procédé décrit par la figure 1 , le MR2 n'est pas scindé en fractions séparées, mais, pour optimiser l'efficacité énergétique dans l'échangeur E4, le MR2 peut également être scindé en deux ou trois fractions, chaque fraction étant détendue à un niveau de pression différent puis envoyée à différents étages du compresseur K2. Les variantes de l'invention décrites en référence aux figures 2 et 3 proposent d'utiliser une fraction de MR1 pour effectuer le sous-refroidissement du MR1 avant d'entrer dans le train d'échangeurs de chaleur ErE2-E3.In the process described in FIG. 1, the MR 2 is not split into separate fractions, but, in order to optimize the energy efficiency in the exchanger E 4 , the MR 2 can also be split into two or three fractions, each fraction being relaxed at a different pressure level and then sent to different stages of the compressor K 2 . The variants of the invention described with reference to Figures 2 and 3 propose to use a fraction of MR1 to perform the subcooling of the MR1 before entering the train of heat exchangers ErE 2 -E 3 .
Les références des figures 2 et 3 identiques à celles de la figure 1 désignent les mêmes éléments.The references of Figures 2 and 3 identical to those of Figure 1 designate the same elements.
En référence à la figure 2, le MR1 sortant du ballon de recette par le conduit 20, est introduit dans l'échangeur E2i pour baisser la température du MR1 , une baisse comprise entre 50C et 300C par rapport à la température du MR1 avant entrée dans E2i. Le MR1 ressort sous-refroidi de E2i par le conduit 21. Le MR1 est alors scindé en deux parties. La première fraction FMR1 circulant dans le conduit 22 est détendue à travers la vanne de détente V5 et est vaporisée dans E2i par échange avec MR1. En sortie de E2-I, FMR1 est complètement vapeur et est retournée au compresseur Ki au niveau de pression le plus approprié. L'autre fraction de MR1 issu de E2i est envoyée par le conduit 23 à l'échangeur Ei.With reference to FIG. 2, the MR1 coming out of the recipe flask via the conduit 20 is introduced into the exchanger E 2 i in order to lower the temperature of the MR1, a drop of between 5 0 C and 30 0 C relative to the MR1 temperature before entering E 2 i. The MR1 is sub-cooled E 2 i by the conduit 21. The MR1 is then split into two parts. The first fraction FMR1 flowing in the duct 22 is expanded through the expansion valve V 5 and is vaporized in E 2 i by exchange with MR1. At the output of E 2 - I , FMR1 is completely steam and is returned to the compressor Ki at the most appropriate pressure level. The other fraction of MR1 from E 2 i is sent through line 23 to the exchanger E i.
Une variante de l'invention est représentée par la figure 3. Le MR1 sortant du ballon de recette D par le conduit 20 est séparé en au moins deux fractions 21b et 22b. La fraction 21 b pénètre dans l'échangeur E21 pour baisser la température du MR1 , une baisse comprise entre 5°C et 300C par rapport à la température du MR1 avant entrée dans E2i. Le MR1 sort sous-refroidi de E2i par le conduit 23. La fraction 22b est détendue à travers la vanne de détente V5 et vaporisée dans E2i par échange avec la fraction 21 b. En sortie de E2i, la fraction 22b est complètement vapeur et est retournée au compresseur K1 au niveau de pression le plus approprié.A variant of the invention is represented in FIG. 3. The MR1 coming out of the recipe balloon D via line 20 is separated into at least two fractions 21b and 22b. The fraction 21b enters the exchanger E 21 to lower the temperature of the MR1, a drop of between 5 ° C. and 30 ° C. relative to the temperature of the MR1 before entering E 2 i. The MR1 exits sub-cooled E 2 i through the conduit 23. The fraction 22b is expanded through the expansion valve V 5 and vaporized in E 2 i by exchange with the fraction 21 b. At the outlet of E 2 i, the fraction 22b is completely vaporized and is returned to the compressor K 1 at the most appropriate pressure level.
Le fait de sous-refroidir le MR1 par une fraction dudit MR1 permet, comme le montre ci-après les exemples numériques 1 et 2 de réduire la consommation des circuits réfrigérants. Exemple 1Subcooling the MR1 with a fraction of said MR1 makes it possible, as shown below in numerical examples 1 and 2, to reduce the consumption of the refrigerant circuits. Example 1
Les procédés décrits par les figures 1 et 2 sont illustrés par l'exemple numérique suivant, qui permet d'appréhender le bénéfice apporté par le procédé de la figure 2 par rapport au procédé de la figure 1.The processes described in FIGS. 1 and 2 are illustrated by the following numerical example, which makes it possible to apprehend the benefit provided by the process of FIG. 2 with respect to the method of FIG.
Le gaz naturel arrive par la ligne 10 à une pression de 6.8 MPa et à une température de 200C. La composition de ce gaz en pourcentages molaires est la suivante :Natural gas arrives via line 10 at a pressure of 6.8 MPa and at a temperature of 20 ° C. The composition of this gas in molar percentages is as follows:
- azote : 1.80%- nitrogen: 1.80%
- méthane : 94.00%- methane: 94.00%
- éthane : 3.28%- ethane: 3.28%
- propane : 1.23%- propane: 1.23%
- i-butane : 0.25%- i-butane: 0.25%
- n-butane : 0.16%n-butane: 0.16%
Le train d'échangeurs de chaleur ErE2-E3 met en œuvre un premier mélange réfrigérant dont la composition est en pourcentages molaires :The heat exchanger train ErE 2 -E 3 uses a first refrigerant mixture whose composition is in molar percentages:
- méthane : 0.5%- methane: 0.5%
- éthane : 49.5%- ethane: 49.5%
- propane : 49.5%- propane: 49.5%
- i-butane : 0.5%- i-butane: 0.5%
Le gaz naturel sortant du train d'échangeurs ErE2-E3 par le conduit 11 , il est à une température de -520C. Le deuxième mélange réfrigérant MR2 sortant du train d'échangeurs ErE2-E3 par le conduit 32 est à une température de -59.5°C.The natural gas leaving the exchanger train ErE 2 -E 3 through the conduit 11, it is at a temperature of -52 ° C. The second refrigerant mixture MR2 leaving the exchanger train ErE 2 -E 3 through the conduit 32 is at a temperature of -59.5 ° C.
L'échangeur E4 met en œuvre le second mélange réfrigérant dont la composition en pourcentages molaires est la suivante :The exchanger E 4 uses the second refrigerant mixture whose composition in molar percentages is as follows:
- azote : 9%- nitrogen: 9%
- méthane : 38%- methane: 38%
- éthane : 52%- ethane: 52%
- propane : 1 %- propane: 1%
En sortie de l'échangeur E4, le gaz naturel est liquéfié à une température de -152.8°C. Dans le procédé de la figure 1 , le premier mélange réfrigérant MR1 est comprimé en phase gazeuse dans le compresseur multi-étagés Ki jusqu'à une pression de 3.06 MPa. Le MR1 comprimé est condensé à une température de 36°C par l'échange de chaleur avec de l'eau à 26°C dans C-i, pour lequel une approche de 100C a été considérée. Il est alors au point de bulle. C'est la température de 36°C qui impose de comprimer le MR1 jusqu'à une pression de 3.06 MPa. Après passage dans le ballon de recette D, le MR1 est sous-refroidi jusqu'à une température de 310C par échange de chaleur avec de l'eau à 26°C dans C2, pour lequel une approche de 5°C a été considérée. Les températures de refroidissement dans Ci et C2 sont limitées par la température de l'eau qui est disponible.At the outlet of the exchanger E 4 , the natural gas is liquefied at a temperature of -152.8 ° C. In the process of FIG. 1, the first refrigerant mixture MR1 is compressed in the gas phase in the multi-stage compressor Ki to a pressure of 3.06 MPa. The compressed MR1 is condensed at a temperature of 36 ° C by heat exchange with water at 26 ° C in C 1, for which an approach of 10 0 C was considered. He is then at the point of bubble. It is the temperature of 36 ° C which imposes to compress the MR1 up to a pressure of 3.06 MPa. After passing through the recipe flask D, the MR1 is subcooled to a temperature of 31 ° C. by heat exchange with water at 26 ° C. in C 2 , for which an approach of 5 ° C. been considered. Cooling temperatures in Ci and C 2 are limited by the temperature of the water that is available.
Dans la figure 1 , le MR1 rentre donc dans le train d'échangeurs Ei-E2-E3 à une température de 310C, inférieure de 5°C à la température du point de bulle à la pression de 3.06 MPa.In FIG. 1, the MR1 therefore enters the Ei-E 2 -E 3 exchanger train at a temperature of 31 ° C., which is 5 ° C. lower than the bubble point temperature at the pressure of 3.06 MPa.
Le procédé décrit en référence à la figure 2 permet de baisser la température d'entrée du MR1 dans le train d'échangeurs ErE2-E3. Comme le sous-refroidissement n'est plus fait à l'eau dans C2, mais par le MR1 lui-même dans E2-I, on peut effectuer un refroidissement à plus basse température dans Ci. Le MR1 est refroidi à une température de 310C par échange de chaleur avec de l'eau à 26°C dans Ci, pour lequel on peut considérer une approche thermique dans le condenseur Ci de 5°C seulement. De ce fait, on peut baisser la pression de compression de Ki : à la sortie du compresseur K-i, le MR1 est comprimé à 2.80 MPa seulement. Après passage dans le ballon de recette D où il est au point de bulle, le MR1 est sous-refroidi dans E21 jusqu'à une température de 25°C. Pour arriver à cette température, la fraction FMR1 est détendue dans V5 à 1.43 MPa, puis elle refroidit à contre-courant le MR1. FMR1 sort de E2i complètement vapeur, et à une température de 29°C. FMR1 est alors redirigée vers l'aspiration haute pression du compresseur Ki. Dans la figure 2, le MR1 rentre donc dans le train d'échange ErE2-E3 à une température de 25°C, inférieure de 6°C à la température du point de bulle à la pression de 2.80 MPa.The method described with reference to Figure 2 lowers the MR1 inlet temperature in the exchangers being EnEd 2 -E 3. As the subcooling is no longer done with water in C2, but by the MR1 itself in E 2 - I , one can carry out cooling at lower temperature in Ci. The MR1 is cooled to a temperature of 31 0 C by heat exchange with water at 26 ° C in Ci, for which we can consider a thermal approach in the condenser Ci of 5 ° C only. As a result, the compression pressure of Ki can be lowered: at the output of the compressor Ki, the MR1 is compressed at 2.80 MPa only. After passing through the recipe flask D where it is at the bubble point, the MR1 is subcooled in E 21 to a temperature of 25 ° C. To reach this temperature, the fraction FMR1 is relaxed in V 5 to 1.43 MPa, then it cools the MR1 counter-current. FMR1 comes out of E 2 i completely vapor, and at a temperature of 29 ° C. FMR1 is then redirected to the high pressure suction of the compressor Ki. In FIG. 2, the MR1 therefore enters the ErE 2 -E 3 exchange train at a temperature of 25 ° C., which is 6 ° C. lower than the bubble point temperature at the pressure of 2.80 MPa.
Dans les conditions mentionnées ci-dessus, selon le procédé décrit en référence à la figure 1 , les consommations énergétiques des compresseurs sont les suivantes :Under the conditions mentioned above, according to the method described with reference to FIG. 1, the energy consumptions of the compressors are as follows:
K1 : 81.0 MW K2 : 108.2 MWK1: 81.0 MW K2: 108.2 MW
La production de GNL en sortie de E4 est de 5.3 MTPA (million de tonnes par an).The output of LNG at the end of E 4 is 5.3 MTPA (million tonnes per year).
L'efficacité des cycles réfrigérants est donc de 35.70 MW/(MTPA).The efficiency of the refrigerant cycles is therefore 35.70 MW / (MTPA).
Dans les conditions mentionnées ci-dessus, avec le procédé comme décrit par la figure 2 qui bénéficie de l'invention, les consommations énergétiques des compresseurs sont les suivantes :Under the conditions mentioned above, with the method as described in Figure 2 which benefits from the invention, the energy consumption of the compressors are as follows:
K1 : 76.4 MW K2 : 108.2 MWK1: 76.4 MW K2: 108.2 MW
La production de GNL en sortie de E4 est toujours de 5.3 MTPA (million de tonnes par an).LNG production at the output of E 4 is still 5.3 MTPA (million tonnes per year).
L'efficacité des cycles réfrigérants améliorée de 0.87 MW/(MTPA) est donc de 34.83 MW/(MTPA).The efficiency of the improved refrigerant cycles of 0.87 MW / (MTPA) is therefore 34.83 MW / (MTPA).
Exemple 2Example 2
Les procédés décrits par les figures 1 et 3 sont illustrés par l'exemple numérique suivant, qui permet d'appréhender le bénéfice apporté par le procédé de la figure 3 par rapport au procédé de la figure 1.The methods described in FIGS. 1 and 3 are illustrated by the following numerical example, which makes it possible to apprehend the benefit provided by the process of FIG. 3 with respect to the process of FIG.
Le gaz naturel arrive par la ligne 10 à une pression de 6.8 MPa et à une température de 200C. La composition de ce gaz en pourcentages molaires est la suivante :Natural gas arrives via line 10 at a pressure of 6.8 MPa and at a temperature of 20 ° C. The composition of this gas in molar percentages is as follows:
- azote • 1 80% - méthane : 94.00%- nitrogen • 1 80% - methane: 94.00%
- éthane : 3.28%- ethane: 3.28%
- propane : 1.23%- propane: 1.23%
- i-butane : 0.25%- i-butane: 0.25%
- n-butane : 0.16%n-butane: 0.16%
Le train d'échange de chaleur E1-E2-E3 met en œuvre un premier mélange réfrigérant dont la composition est en pourcentages molaires :The heat exchange train E 1 -E 2 -E 3 uses a first refrigerant mixture whose composition is in molar percentages:
- méthane : 0.5%- methane: 0.5%
- éthane : 49.5%- ethane: 49.5%
- propane : 49.5%- propane: 49.5%
- i-butane : 0.5%- i-butane: 0.5%
Le gaz naturel sortant du train d'échangeurs ErE2-E3 par le conduit 11 est à une température de -52°C. Le deuxième mélange réfrigérant MR2 sortant du train d'échangeurs E1-E2-E3 par le conduit 32 est à une température de -59.5°C.The natural gas leaving the exchanger train ErE 2 -E 3 through line 11 is at a temperature of -52 ° C. The second refrigerant mixture MR2 leaving the exchanger train E 1 -E 2 -E 3 through line 32 is at a temperature of -59.5 ° C.
L'échangeur E4 met en œuvre le second mélange réfrigérant dont la composition en pourcentages molaires est la suivante :The exchanger E 4 uses the second refrigerant mixture whose composition in molar percentages is as follows:
- azote : 9%- nitrogen: 9%
- méthane : 38%- methane: 38%
- éthane : 52%- ethane: 52%
- propane : 1 %- propane: 1%
En sortie de l'échangeur E4, le gaz naturel est liquéfié à une température de -152.8°C.At the outlet of the exchanger E 4 , the natural gas is liquefied at a temperature of -152.8 ° C.
Dans le procédé de la figure 1 , le premier mélange réfrigérant MR1 est comprimé en phase gazeuse dans le compresseur multi-étagés Ki jusqu'à une pression de 3.06 MPa. Le MR1 comprimé est condensé à une température de 36°C par l'échange de chaleur avec de l'eau à 26°C dans Ci, pour lequel une approche de 100C a été considérée. Il est alors au point de bulle. C'est la température de 36°C qui impose de comprimer le MR1 jusqu'à une pression de 3.06 MPa. Après passage dans le ballon de recette D, le MR1 est sous-refroidi iι 10/11 I'O nnα tomnόrati ira Ho ^1 0P. nar όrhanπo Ho rhalonr avpr Ho l'oai i à 9R0H dans C2, pour lequel une approche de 5CC a été considérée. Les températures de refroidissement dans Ci et C2 sont limitées par la température de l'eau qui est disponible.In the process of FIG. 1, the first refrigerant mixture MR1 is compressed in the gas phase in the multi-stage compressor Ki to a pressure of 3.06 MPa. The compressed MR1 is condensed at a temperature of 36 ° C by heat exchange with water at 26 ° C in C 1, for which an approach of 10 0 C was considered. He is then at the point of bubble. It is the temperature of 36 ° C which imposes to compress the MR1 up to a pressure of 3.06 MPa. After passing through the receiving flask D, MR1 is subcooled iι 10/11 I'o nnα tomnόrati go Ho ^ 1 0 P. nar όrhanπo Ho Ho rhalonr AVPR OAI i 9R 0 H in C 2 , for which an approach of 5 C C was considered. Cooling temperatures in Ci and C 2 are limited by the temperature of the water that is available.
Dans la figure 1 , le MR1 rentre donc dans le train d'échangeurs ErE2-E3 à une température de 310C, inférieure de 5°C à la température du point de bulle à la pression de 3.06 MPa.In FIG. 1, the MR1 therefore enters the ErE 2 -E 3 exchanger train at a temperature of 31 ° C., which is 5 ° C. lower than the bubble point temperature at the pressure of 3.06 MPa.
Le procédé décrit en référence à la figure 3 permet de baisser la température d'entrée du MR1 dans le train d'échangeurs Ei-E2-E3. Comme le sous-refroidissement n'est plus fait à l'eau dans C2 mais par le MR1 lui-même dans E21, on peut effectuer un refroidissement à plus basse température dans Ci. Le MR1 est refroidi à une température de 31 °C par échange de chaleur avec de l'eau à 26°C dans Ci, pour lequel on peut considérer une approche thermique dans le condenseur Ci de 5°C seulement. De ce fait, on peut baisser la pression de compression de Ki : à la sortie du compresseur K1, le MR1 est comprimé à 2.80 MPa seulement. Après passage dans le ballon de recette D où il est au point de bulle, le MR1 est sous-refroidi dans E2i jusqu'à une température de 25°C. Pour arriver à cette température, une fraction FMR1 du MR1 sortant du ballon D est détendue dans V5 à 1.39 MPa, puis elle refroidit à contre-courant la fraction restante du MR1. FMR1 sort de E2-I complètement vapeur, et à une température de 28°C. FMR1 est alors redirigée vers l'aspiration haute pression du compresseur K1.The method described with reference to FIG. 3 makes it possible to lower the inlet temperature of the MR1 in the Ei-E 2 -E 3 exchanger train. As the subcooling is no longer done with water in C 2 but by the MR1 itself in E 21 , it is possible to carry out cooling at a lower temperature in Ci. The MR1 is cooled to a temperature of 31 ° C. C by heat exchange with water at 26 ° C in Ci, for which a thermal approach in the condenser Ci of 5 ° C can be considered. As a result, the compression pressure of Ki can be lowered: at the outlet of the compressor K 1 , the MR1 is compressed at 2.80 MPa only. After passing through the recipe flask D where it is at the bubble point, the MR1 is subcooled in E 2 i to a temperature of 25 ° C. To reach this temperature, a fraction FMR1 of the MR1 leaving the balloon D is expanded in V 5 at 1.39 MPa, then it cools the remaining fraction of the MR1 counter-current. FMR1 comes out of E 2 -I completely vapor, and at a temperature of 28 ° C. FMR1 is then redirected to the high-pressure suction of compressor K 1 .
Dans la figure 3, le MR1 rentre donc dans le train d'échangeurs E1-E2-E3 à une température de 25°C, inférieure de 6°C à la température du point de bulle à la pression de 2.80 MPa.In FIG. 3, the MR1 thus enters the heat exchanger train E 1 -E 2 -E 3 at a temperature of 25 ° C., which is 6 ° C. lower than the temperature of the bubble point at the pressure of 2.80 MPa.
Dans les conditions mentionnées ci-dessus, selon le procédé décrit en référence à la figure 1 , les consommations énergétiques des compresseurs sont les suivantes :Under the conditions mentioned above, according to the method described with reference to FIG. 1, the energy consumptions of the compressors are as follows:
K1 : 81.0 MW K2 : 108.2 MW La production de GNL en sortie de E4 est de 5.3 MTPA (million de tonnes par an).K1: 81.0 MW K2: 108.2 MW The output of LNG at the end of E 4 is 5.3 MTPA (million tonnes per year).
L'efficacité des cycles réfrigérants est donc de 35.70 MW/(MTPA).The efficiency of the refrigerant cycles is therefore 35.70 MW / (MTPA).
Avec le procédé comme décrit par la figure 3 qui bénéficie de la variante de l'invention, les consommations énergétiques des compresseurs sont les suivantes :With the method as described in FIG. 3 which benefits from the variant of the invention, the energy consumption of the compressors are as follows:
K1 : 76.4 MW K2 : 108.2 MWK1: 76.4 MW K2: 108.2 MW
La production de GNL en sortie de E4 est toujours de 5.3 MTPA (million de tonnes par an).LNG production at the output of E 4 is still 5.3 MTPA (million tonnes per year).
L'efficacité des cycles réfrigérants, améliorée de 0.87 MW/(MTPA), est donc de 34.83 MW/(MTPA). The efficiency of the refrigerant cycles, improved by 0.87 MW / (MTPA), is therefore 34.83 MW / (MTPA).

Claims

REVENDICATIONS
1) Procédé de liquéfaction d'un gaz naturel dans lequel on effectue les étapes suivantes : a) on comprime un mélange réfrigérant, b) on condense, par échange de chaleur, le mélange réfrigérant comprimé, c) on stocke le mélange réfrigérant condensé dans un ballon de stockage, le ballon contenant en équilibre une phase liquide de mélange réfrigérant et une phase gazeuse de mélange réfrigérant, d) on soutire du mélange réfrigérant en phase liquide du ballon de stockage, e) on effectue une étape dans laquelle seul le mélange réfrigérant soutiré à l'étape d) est sous-refroidi par échange de chaleur, f) on refroidit le gaz naturel au moins par échange de chaleur avec le mélange réfrigérant sous-refroidi obtenu à l'étape e).1) Process for liquefying a natural gas in which the following steps are carried out: a) a cooling mixture is compressed, b) the compressed refrigerant mixture is condensed by heat exchange, c) the condensed refrigerant mixture is stored in a storage flask, the flask containing in equilibrium a liquid phase of a refrigerant mixture and a gaseous phase of a refrigerant mixture, d) the refrigerant mixture is withdrawn in the liquid phase from the storage flask, e) a step is carried out in which only the mixture refrigerant withdrawn in step d) is subcooled by heat exchange, f) the natural gas is cooled at least by heat exchange with the subcooled refrigerant mixture obtained in step e).
2) Procédé selon la revendication 1 , dans lequel à l'étape e) on sous-refroidit le mélange réfrigérant par échange de chaleur avec un fluide extérieur choisi parmi l'air et l'eau.2) Process according to claim 1, wherein in step e) the cooling mixture is subcooled by heat exchange with an external fluid selected from air and water.
3) Procédé selon la revendication 1 , dans lequel à l'étape e) on sous-refroidit le mélange réfrigérant par échange de chaleur avec une portion du mélange réfrigérant, ladite portion étant détendue avant échange de chaleur.3) Process according to claim 1, wherein in step e) the cooling mixture is subcooled by heat exchange with a portion of the refrigerant mixture, said portion being expanded before heat exchange.
4) Procédé selon la revendication 3, dans lequel ladite portion de mélange réfrigérant est prélevée dudit mélange réfrigérant soutiré avant d'effectuer l'échange de chaleur de l'étape e).4) Process according to claim 3, wherein said refrigerant mixture portion is taken from said withdrawn refrigerant mixture before performing the heat exchange of step e).
5) Procédé selon la revendication 3, dans lequel ladite portion de mélange rά-frinάront αet nrάl-H/άû HI I mόlsinπc- rόfrinόrαnt nhtp»nι ι nnrpxs offrarti ι£ l'échange de chaleur de l'étape e) et avant d'effectuer l'échange de chaleur de l'étape f).5) A method according to claim 3, wherein said portion of mixture rά-frinάront αet nrάl-H / άû HI I mόlsinπc- rόfrinόrαnt nhtp »nιnlpxs offrarti ι £ the heat exchange of step e) and before performing the heat exchange of step f).
6) Procédé selon l'une des revendications précédentes, dans lequel l'étape e) est effectuée dans un premier échangeur de chaleur, dans lequel l'étape f) est effectuée dans au moins un deuxième échangeur de chaleur, et dans lequel le premier échangeur de chaleur est distinct du deuxième échangeur de chaleur.6) Method according to one of the preceding claims, wherein step e) is performed in a first heat exchanger, wherein step f) is performed in at least a second heat exchanger, and wherein the first Heat exchanger is separate from the second heat exchanger.
7) Procédé selon l'une des revendications précédentes, dans lequel le mélange réfrigérant comporte en pourcentage molaire : entre 0 et 5% de méthane, entre 30 et 70% d'éthane, entre 30 et 70% de propane et entre 0 et 20% de butane.7) Method according to one of the preceding claims, wherein the coolant mixture comprises molar percentage: between 0 and 5% methane, between 30 and 70% ethane, between 30 and 70% propane and between 0 and 20 % butane.
8) Procédé selon l'une des revendications précédentes, dans lequel à l'étape f), on refroidit le gaz naturel jusqu'à obtenir un gaz naturel liquide.8) Method according to one of the preceding claims, wherein in step f), the natural gas is cooled to obtain a liquid natural gas.
9) Procédé selon l'une des revendications 1 à 7, dans lequel à l'étape f), on refroidit le gaz naturel et, simultanément, un deuxième mélange réfrigérant par échange de chaleur avec le mélange réfrigérant sous-refroidi obtenu à l'étape e) et dans lequel après l'étape f) on liquéfie et on sous-refroidit le gaz naturel par échange de chaleur avec le deuxième mélange réfrigérant jusqu'à obtenir un gaz naturel liquide.9) Method according to one of claims 1 to 7, wherein in step f), the natural gas is cooled and, simultaneously, a second refrigerant mixture by heat exchange with the cooling mixture subcooled obtained at step e) and wherein after step f) the natural gas is liquefied and subcooled by heat exchange with the second refrigerant mixture until a liquid natural gas is obtained.
10) Procédé selon la revendication 9, dans lequel le deuxième mélange réfrigérant comporte en pourcentage molaire : entre 0 et 12% d'azote, entre 20 et 80% de méthane et entre 20 et 80% d'éthane et entre 0 et 10% de propane. 10) Process according to claim 9, wherein the second refrigerant mixture comprises in molar percentage: between 0 and 12% of nitrogen, between 20 and 80% of methane and between 20 and 80% of ethane and between 0 and 10% of propane.
PCT/FR2009/000572 2008-06-20 2009-05-15 Method for liquefying natural gas with pre-cooling of the coolant mixture WO2009153427A2 (en)

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