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AU2010213188B2 - Method for liquefying a hydrocarbon-rich stream - Google Patents

Method for liquefying a hydrocarbon-rich stream Download PDF

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Publication number
AU2010213188B2
AU2010213188B2 AU2010213188A AU2010213188A AU2010213188B2 AU 2010213188 B2 AU2010213188 B2 AU 2010213188B2 AU 2010213188 A AU2010213188 A AU 2010213188A AU 2010213188 A AU2010213188 A AU 2010213188A AU 2010213188 B2 AU2010213188 B2 AU 2010213188B2
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Australia
Prior art keywords
fraction
mixed refrigerant
rich fraction
hydrocarbon
liquefied
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AU2010213188A
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AU2010213188A1 (en
Inventor
Heinz Bauer
Daniel Garthe
Rainer Sapper
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Linde GmbH
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Linde GmbH
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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
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B9/00—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point
    • F25B9/002—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point characterised by the refrigerant
    • F25B9/006—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point characterised by the refrigerant the refrigerant containing more than one component
    • 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
    • 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
    • F25J1/02—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
    • F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
    • F25J1/0244—Operation; Control and regulation; Instrumentation
    • 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.
    • F25J1/0291—Refrigerant compression by combined gas compression and liquid pumping
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/0204—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the feed stream
    • F25J3/0209—Natural gas or substitute natural gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/0228—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
    • F25J3/0233—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of CnHm with 1 carbon atom or more
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/0228—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
    • F25J3/0238—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 2 carbon atoms 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
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B1/00—Compression machines, plants or systems with non-reversible cycle
    • F25B1/10—Compression machines, plants or systems with non-reversible cycle with multi-stage compression
    • 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
    • F25J2245/00—Processes or apparatus involving steps for recycling of process streams
    • F25J2245/02—Recycle of a stream in general, e.g. a by-pass stream
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/18—External refrigeration with incorporated cascade loop
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/66—Closed external refrigeration cycle with multi component refrigerant [MCR], e.g. mixture of hydrocarbons
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/90—External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration
    • F25J2270/902—Details about the refrigeration cycle used, e.g. composition of refrigerant, arrangement of compressors or cascade, make up sources, use of reflux exchangers etc.
    • 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
    • F25J2280/00—Control of the process or apparatus
    • F25J2280/02—Control in general, load changes, different modes ("runs"), measurements

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Separation By Low-Temperature Treatments (AREA)
  • Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)

Abstract

A method for liquefying a hydrocarbon-rich fraction and simultaneously separating a C

Description

WO 2010/091804 PCT/EP2010/000614 11 Description Method for liquefying a hydrocarbon-rich stream 5 The invention relates to a process for liquefying a hydrocarbon-rich fraction with simultaneous removal of a C 2 +-rich fraction, wherein the cooling and liquefaction of the hydrocarbon-rich fraction proceed in indirect heat exchange against the mixed refrigerant 10 of a mixed-refrigerant cycle in which the mixed refrigerant is compressed in at least two stages, and the C 2 +-rich fraction is removed at an adjustable temperature level, wherein the mixed refrigerant is separated into a gaseous fraction and a liquid 15 fraction, both fractions are subcooled, expanded essentially to the suction pressure of the first compressor stage and at least in part vaporized. A process of the type in question for liquefying a 20 hydrocarbon-rich fraction is known, for example from DE-A 19722490. Such liquefaction processes are used, for example in natural gas liquefaction. In liquefaction processes of the type in question it is generally necessary to remove certain components, since 25 these would precipitate out in the solid stage at the required low temperatures and/or harm the specified product quality. In the simplest case, it is sufficient to provide only one separator which serves to remove the unwanted components from the hydrocarbon-rich 30 fraction which is to be liquefied. The selective removal of lighter natural gas components, such as ethane for example, in contrast makes considerably higher demands, both of the process procedure and also the controllability under changeable boundary 35 conditions. In natural gas liquefaction processes of small to medium capacity - these are taken to include production 2 rates from 30 000 to 1 million tons/year of LNG - mixed cycles having only one cycle compressor - these are also called Single Mixed Refrigerant (SMR) processes are frequently used. These have the disadvantage that 5 the liquid refrigerant phase can only be vaporized at one pressure level. The targeted setting and controlling of a desired temperature profile therefore is difficult, since the number of possibilities for intervention and/or degrees of freedom in such 10 processes is restricted. Corresponding temperature profiles are required, for example, in order to speed up the partial condensation of the hydrocarbon-rich fraction which is to be liquefied exactly up to a defined temperature which is required for the sought 15 after removal of the unwanted components. Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms 20 part of common general knowledge in the field. It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative. 25 An object of the present invention in a preferred form is to provide a process for liquefying a hydrocarbon rich fraction with simultaneous removal of a C 2 ,-rich fraction which avoids the above-described 30 disadvantages. In particular a process of the type in question for liquefying a hydrocarbon-rich fraction should be specified which is firstly robust and secondly makes possible efficient and controllable removal of ethane and higher hydrocarbons in the course 35 of a natural gas liquefaction process. Therefore, the vaporization of a mixed refrigerant stream must be arranged in such a manner that it can be used directly for controlling a removal of ethane and higher hydrocarbons.
3 For achieving this preferred object, a process of the type in question is proposed for liquefying a hydrocarbon-rich fraction with simultaneous removal of 5 a C 2 +-rich fraction, which is characterized in that at least occasionally, at least one substream of the liquefied previously gaseous fraction of the mixed refrigerant is expanded and added to the expanded liquid fraction of the mixed refrigerant. 10 According to a first aspect of the invention there is provided a process for liquefying a hydrocarbon-rich fraction with simultaneous removal of a C 2 +-rich fraction, wherein the cooling and liquefaction of the 15 hydrocarbon-rich fraction proceed in indirect heat exchange against the mixed refrigerant of a mixed refrigerant cycle in which the mixed refrigerant is compressed in at least two stages, and the C 2 +-rich fraction is removed at an adjustable temperature level, 20 wherein the mixed refrigerant is separated into a gaseous fraction and a liquid fraction, both fractions are subcooled, expanded essentially to the suction pressure of the first compressor stage and at least in part vaporized, wherein at least occasionally, at least 25 one substream, which is liquefied against itself, of the liquefied previously gaseous fraction of the mixed refrigerant is expanded and added to the expanded liquid fraction of the mixed refrigerant. 30 Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the 35 sense of "including, but not limited to". By means of varying the quantitative ratios of the liquid fraction and the liquefied previously gaseous fraction, the temperature profile can be influenced 3a during the vaporization of the mixed refrigerant from the two abovementioned fractions in such a manner that in accordance with the object the temperature of the mixed refrigerant in the upper region of the heat 5 exchanger or heat exchangers which serve for cooling and partial condensation of the hydrocarbon-rich fraction to be liquefied is always below the temperature of the fraction to be liquefied. The procedure according to the invention enables sufficient 10 controllability of the temperature of the hydrocarbon rich fraction to be liquefied on entry into the separation device or separation column to be provided for removing the C 2 +-rich fraction, and so setting a desired concentration of the C 2 +-hydrocarbons in the 15 liquefaction product or Liquefied Natural Gas (LNG) is possible. Further advantageous embodiments of the process according to the invention for liquefying a 20 hydrocarbon-rich fraction with simultaneous removal of a C 2 +-rich fraction which are subjects of the dependent claims are characterized in that - the substream of the liquefied previously gaseous 25 fraction of the mixed refrigerant is taken off at the cold end of the heat exchanger between the hydrocarbon-rich fraction to be liquefied and the mixed refrigerant and/or at a suitable intermediate temperature, expanded and added to 30 the expanded liquid fraction of the mixed refrigerant, wherein a suitable intermediate temperature is then present when the mixed WO 2010/091804 PCT/EP2010/000614 4 refrigerant has a subcooling of at least 50C, preferably of at least 100C, compared with the boiling state, 5 - the heat exchange between the hydrocarbon-rich fraction to be liquefied and the mixed refrigerant proceeds in a multistream heat exchanger, which is preferably constructed as a plate heat exchanger or helically coiled heat exchanger, 10 - if the C 2 +-rich fraction is removed in at least one separation column, at least occasionally, a substream of the hydrocarbon-rich fraction to be liquefied is fed to the top region and/or the 15 bottom region of the separation column, - if the C 2 +-rich fraction is removed in at least one separation column, the separation column bottom temperature is adjusted by means of a reboiler 20 assigned to the separation column. The process according to the invention for liquefying a hydrocarbon-rich fraction with simultaneous removal of a C 2 +-rich fraction and also further advantageous 25 embodiments thereof which are subjects of the dependant claims will be described in more detail hereinafter with reference to the illustrative embodiments shown in Figures 1 and 2. 30 Hereinafter in the explanation of the exemplary embodiment shown in Figure 2, only the differences from the procedure shown in Figure 1 will be considered. The exemplary embodiments of the process according to 35 the invention which are shown in Figures 1 and 2 for liquefying a hydrocarbon-rich fraction have a separation column T which serves for removing a C 2 +-rich fraction from the hydrocarbon-rich fraction to be WO 2010/091804 PCT/EP2010/000614 5 liquefied. The fraction to be liquefied which is subsequently termed natural gas stream, is fed via line 1 to a multistream heat exchanger E3. 5 This heat exchanger is preferably constructed as a soldered aluminium plate heat exchanger. Depending on the system size, preferably 1 to 6 parallel heat exchanger units are provided. Alternatively, the multistream heat exchanger E3 can be constructed as a 10 helically coiled heat exchanger. In this case aluminium plate heat exchangers are preferably used for a liquefaction capacity of 30 000 to 500 000 tons/year of LNG, helically coiled heat exchangers are preferably used for a liquefaction capacity of 100 000 to 15 1 000 000 tons/year of LNG. The natural gas stream is cooled in the heat exchanger E3, partially condensed and subsequently expanded via valve a into the top region of the separation column T. 20 At the top of the separation column T a methane-rich gas fraction is taken off via line 2, liquefied and also subcooled in the heat exchanger E3 and subsequently, via line 3, in which a control valve e is provided, taken off and supplied to further use thereof 25 or intermediate storage. This fraction is the liquefaction product (LNG) . A C 2 +-rich liquid fraction is taken off from the bottom of the separation column T via line 4, which likewise has a control valve d, and supplied to further use thereof. 30 By means of a feed of a substream of the natural gas stream via line 5 and control valve b, the top temperature of the separation column T and therefore the composition of the methane-rich gas fraction taken 35 off via line 2 are influenced. The bottom temperature of the separation column T also, and also the composition of the liquid fraction taken off via line 4 can be influenced by the reboiler E4 and/or the WO 2010/091804 PCT/EP2010/000614 6 addition of a substream of the natural gas stream via line 6 and expansion valve c. The mixed-refrigerant cycle consists of a two-stage 5 compressor unit consisting of a first compressor stage and a second compressor stage, Cl and C2, respectively. Downstream of both compressor stages is connected in each case one cooler, El and E2, respectively. In addition, a low-pressure separator Dl, a medium 10 pressure separator D2, and also a high-pressure separator D3 are provided. From the top of the low-pressure separator Dl which serves for safety of the first compressor stage Cl, the 15 mixed refrigerant circulating in the refrigeration cycle is fed via line 11 to the first compressor stage Cl. Therein, the mixed refrigerant is compressed to a desired intermediate pressure - this is customarily between 7 and 35 bar, preferably between 10 and 25 bar 20 - subsequently cooled in the cooler El, partially condensed and fed via line 12 to the medium-pressure separator D2. While a liquid fraction is taken off therefrom via line 20, which liquid fraction will be considered in more detail hereinafter, the gas phase of 25 the mixed refrigerant which is taken off via line 13 from the top of the separator D2 is fed to the second compressor stage C2 and therein compressed to the desired final pressure - this is customarily between 30 and 80 bar, preferably between 40 and 60 bar. 30 Subsequently, the mixed refrigerant is cooled in the cooler E2, partially condensed and fed via line 14 to the high-pressure separator D3. The liquid fraction occurring in the bottom of the separator D3 is recirculated via line 16, in which an expansion valve k 35 is provided, upstream of the medium-pressure separator D2.
WO 2010/091804 PCT/EP2010/000614 7 At the top of the separator D3, the gaseous refrigerant fraction is taken off via line 15, liquefied and also subcooled in the heat exchanger E3 and taken off therefrom via line 17. This fraction or a substream of 5 this fraction is expanded in the expansion valve g to the lowest cycle pressure before it is fed via line 18 through the heat exchanger E3 and being completely vaporized. Via line 10, the completely vaporized fraction is subsequently fed to the separator Dl. 10 In the procedure shown in Figure 1, the liquid refrigerant fraction is taken off via line 20 from the bottom of the separator D2, fed to the heat exchanger E3 and subcooled therein. Via line 21, the subcooled liquid 15 fraction is taken off from the heat exchanger E3, expanded in the valve f to the lowest cycle pressure and subsequently fed via line 22 back to the heat exchanger E3. The fraction vaporized therein is added via line 23 to the abovementioned vaporized fraction in the line 10. 20 In the valves f and g, customarily an expansion proceeds to a pressure which corresponds, apart from unavoidable pressure drops, to the suction pressure of the first compression stage C1. By means of suitable choice of the 25 composition, amount and/or vaporization pressure of the mixed refrigerant, not only the final temperature but also the flow rate of the hydrocarbon-rich fraction to be liquefied or of the natural gas stream to be liquefied can be adjusted. 30 In contrast to the procedure shown in Figure 1, in the exemplary embodiment shown in Figure 2, the liquid fraction of the mixed refrigerant to be fed to the heat exchanger E3 is not already taken off from the separator D2, but from the 35 separator D3 via line 20' . The liquid fraction occurring in the bottom of the separator D2 is therefore fed via line 16', in which a pump P is arranged, to the separator D3.
WO 2010/091804 PCT/EP2010/000614 8 The process procedure shown in Figure 2 is somewhat more efficient compared with the process procedure shown in Figure 1 - it makes possible an improvement in efficiency of 1 to 5% - but requires a pump which gives rise to increased 5 capital costs and a greater expenditure on maintenance. The process procedure according to Figure 1 is therefore preferably used in relatively small system capacities (30 000 to 500 000 tons/year of LNG) whereas the process procedure shown in Figure 2 is preferably implemented in 10 relatively large system capacities (100 000 to 1 000 000 tons/year of LNG). Owing to the above-described expansion of the liquid subcooled and also liquefied previously gaseous fraction of 15 the mixed refrigerant in the valves f and g to an essentially identical vaporization pressure, the temperature course of the refrigerant stream in the heat exchanger E3 downstream of valve f is not freely selectable. The compositions of the gaseous and liquid refrigerant fractions 20 in turn are coupled by the equilibria in the separators D2 and D3. Therefore, the valve setting of the valve f cannot influence to a sufficient extent the temperature profile in the upper or warmer part of the heat exchanger E3. According to the invention, therefore, at least 25 occasionally, at least one substream of the liquid previously gaseous fraction of the mixed refrigerant 15 is expanded and added to the expanded liquid fraction of the mixed refrigerant in the line 22. In the figures, two possible mixed refrigerant substreams 19 and 24 are shown 30 which, after expansion in valve h or j, respectively, can be added to the expanded mixed refrigerant in the line 22. In practice, in most cases, either valve h or j are provided. In principle, however, the mixed-refrigerant substreams 19 and 24 can be used separately or jointly for controlling the 35 temperature or the temperature profile.
WO 2010/091804 PCT/EP2010/000614 9 In this case the mixed refrigerant substreams 19 and/or 24 is or are taken off at the cold end of the heat exchanger E3 and/or at a suitable intermediate temperature via line 19 or 24, expanded in valve h or j and added to the expanded 5 liquid fraction of the mixed refrigerant 22. A suitable intermediate temperature is present when the mixed refrigerant 15 has a subcooling of at least 5 0 C, preferably at least 10 *C, compared with the boiling state. 10 By means of the procedure according to the invention, a sufficient controllability of the temperature of the hydrocarbon-rich fraction or the natural gas stream 1 which is to be liquefied on entry into the separation column T is provided, as is required for setting a desired concentration 15 of the C 2 .- hydrocarbons in the liquefaction product or LNG.

Claims (7)

1. Process for liquefying a hydrocarbon-rich fraction with simultaneous removal of a C 2 +-rich fraction, 5 wherein the cooling and liquefaction of the hydrocarbon-rich fraction proceed in indirect heat exchange against the mixed refrigerant of a mixed refrigerant cycle in which the mixed refrigerant is compressed in at least two stages, and the 10 C 2 +-rich fraction is removed at an adjustable temperature level, wherein the mixed refrigerant is separated into a gaseous fraction and a liquid fraction, both fractions are subcooled, expanded essentially to the suction pressure of the first 15 compressor stage and at least in part vaporized, wherein at least occasionally, at least one substream, which is liquefied against itself, of the liquefied previously gaseous fraction of the mixed refrigerant is expanded and added to the 20 expanded liquid fraction of the mixed refrigerant.
2. Process according to Claim 1, wherein the substream of the liquefied previously gaseous fraction of the mixed refrigerant is taken off at 25 the cold end of the heat exchanger between the hydrocarbon-rich fraction to be liquefied and the mixed refrigerant and/or at a suitable intermediate temperature, expanded and added to the expanded liquid fraction of the mixed 30 refrigerant, wherein a suitable intermediate temperature is then present when the mixed refrigerant has a subcooling of at least 5 0 C, compared with the boiling state. 35
3. Process according to claim 2 wherein the mixed refrigerant has a subcooling of at least 10 0 C compared with the boiling state. 11
4. Process according to any one of the preceding claims, wherein the heat exchange between the hydrocarbon-rich fraction to be liquefied and the mixed refrigerant proceeds in a multistream heat 5 exchanger, which is constructed as a plate heat exchanger or helically coiled heat exchanger.
5. Process according to any one of the preceding claims, wherein the C 2 +-rich fraction is removed in 10 at least one separation column, wherein, at least occasionally, a substream of the hydrocarbon-rich fraction to be liquefied is fed to the top region of the separation column. 15
6. Process according to any one of the preceding claims, wherein the C 2 +-rich fraction is removed in at least one separation column, wherein, at least occasionally, a substream of the hydrocarbon-rich fraction to be liquefied is fed to the bottom 20 region of the separation column.
7. Process according to any one of the preceding claims, wherein the C 2 +-rich fraction is removed in at least one separation column, wherein the 25 separation column bottom temperature is adjusted by means of a reboiler assigned to the separation column.
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