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AU2009216745B2 - Method and apparatus for cooling and separating a hydrocarbon stream - Google Patents

Method and apparatus for cooling and separating a hydrocarbon stream Download PDF

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Publication number
AU2009216745B2
AU2009216745B2 AU2009216745A AU2009216745A AU2009216745B2 AU 2009216745 B2 AU2009216745 B2 AU 2009216745B2 AU 2009216745 A AU2009216745 A AU 2009216745A AU 2009216745 A AU2009216745 A AU 2009216745A AU 2009216745 B2 AU2009216745 B2 AU 2009216745B2
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Australia
Prior art keywords
stream
refrigerant
hydrocarbon
cooling
fraction
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AU2009216745A
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AU2009216745A1 (en
Inventor
Marco Dick Jager
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Shell Internationale Research Maatschappij BV
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SHELL INT RESEARCH
Shell Internationale Research Maatschappij BV
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/003—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
    • F25J1/0002—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the fluid to be liquefied
    • F25J1/0022—Hydrocarbons, e.g. natural gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/003—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production
    • F25J1/0032—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration"
    • F25J1/0045—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration" by vaporising a liquid return stream
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/003—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production
    • F25J1/0047—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle
    • F25J1/0052—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle by vaporising a liquid refrigerant stream
    • 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
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    • 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
    • F25J1/0057—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 after expansion of the liquid refrigerant stream with extraction of work
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    • 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
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    • 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
    • F25J1/0215—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 with one SCR cycle
    • F25J1/0216—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 with one SCR cycle using a C3 pre-cooling 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
    • F25J1/0228—Coupling of the liquefaction unit to other units or processes, so-called integrated processes
    • F25J1/0235—Heat exchange integration
    • F25J1/0237—Heat exchange integration integrating refrigeration provided for liquefaction and purification/treatment of the gas to be liquefied, e.g. heavy hydrocarbon removal from natural gas
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    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0228—Coupling of the liquefaction unit to other units or processes, so-called integrated processes
    • F25J1/0235—Heat exchange integration
    • F25J1/0237—Heat exchange integration integrating refrigeration provided for liquefaction and purification/treatment of the gas to be liquefied, e.g. heavy hydrocarbon removal from natural gas
    • F25J1/0239—Purification or treatment step being integrated between two refrigeration cycles of a refrigeration cascade, i.e. first cycle providing feed gas cooling and second cycle providing overhead gas cooling
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    • 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
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    • 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
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    • 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
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    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
    • F25J1/0279—Compression of refrigerant or internal recycle fluid, e.g. kind of compressor, accumulator, suction drum etc.
    • F25J1/0292—Refrigerant compression by cold or cryogenic suction of the refrigerant gas
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    • 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
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    • 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
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    • F25J2245/00—Processes or apparatus involving steps for recycling of process streams
    • F25J2245/02—Recycle of a stream in general, e.g. a by-pass stream
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/02—Internal refrigeration with liquid vaporising loop
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/12—External refrigeration with liquid vaporising loop
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/60—Closed external refrigeration cycle with single component refrigerant [SCR], e.g. C1-, C2- or C3-hydrocarbons

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

Abstract

A method and apparatus for cooling and separating a hydrocarbon stream such as natural gas. The method comprises at least the steps of: (a) providing a hydrocarbon stream (10); (b) cooling the hydrocarbon stream (10) to provide a partially liquefied hydrocarbon stream (20); (c) passing at least a fraction of the partially liquefied hydrocarbon stream (20) into a distillation column (12) through a first inlet (17); (d) providing a lower feed stream (30); (e) providing a refrigerant circuit (4) comprising at least a refrigerant stream (40); (f) heating the lower feed stream (30) against the refrigerant stream (40) to provide a heated lower feed stream (50) and a cooled refrigerant stream (60); (g) passing the heated lower feed stream (50) into the distillation column (12) through a second inlet (18) lower than the first inlet (17); and (h) separating the partially liquefied hydrocarbon stream (20) in the distillation column (12) to provide at least a first overhead gaseous stream (70) and a first bottom liquid stream (80).

Description

WO 2009/103715 PCT/EP2009/051882 -1 METHOD AND APPARATUS FOR COOLING AND SEPARATING A HYDROCARBON STREAM The present invention relates to a method and apparatus for cooling and separating a hydrocarbon stream, particularly but not exclusively natural gas, and optionally subsequently liquefying the hydrocarbon 5 stream. In another aspect, the present invention relates to a liquefaction plant comprising such an apparatus. Several methods of cooling and liquefying a natural gas stream thereby obtaining liquefied natural gas (LNG) are known. It is desirable to liquefy a natural gas 10 stream for a number of reasons. As an example, natural gas can be stored and transported over long distances more readily as a liquid than in gaseous form, as it occupies a smaller volume and does not need to be stored at high pressure. 15 Liquefying a hydrocarbon stream such as natural gas generally involves two or more cooling stages, and one or more separation stages. At least one separation stage is to reduce the level of hydrocarbons in a natural gas stream heavier than methane, hereinafter termed "heavier 20 hydrocarbons". Conventionally, heavier hydrocarbons are separated from a natural gas stream prior to any significant cooling, and particularly liquefaction, for several reasons, including having different freezing or liquefaction temperatures than methane that may therefore 25 cause them to block parts of a methane liquefaction plant. Separation of heavier hydrocarbons from natural gas can be carried out by cooling the natural gas to partly condense it, and then using a fractionation column.
2 US 5,960,644 describes a method for removing carbon dioxide, ethane and heavier components from a high pressure natural gas stream, wherein the high pressure natural gas stream is partly condensed and passed through first and second separators, before various streams are passed into a fractionation column. In order to supply heat to the lower part of the fractionation column, a s fluid stream is removed from the fractionation column and is heated in a heat exchanger 46 to obtain a re-boiling stream, and the re-boiling stream is introduced into the fractionation column. US 5,960,644 uses an external refrigerant to partly condense the high pressure natural gas stream, and a heating medium to provide heat to the lower part of the fractionation column. The external refrigerant used to partly condense the high pressure natural gas stream is not described, io and the heating medium is a compressed gaseous product stream requiring separate compression to pipeline pressure. It is an object of the present invention to reduce the power that is needed to provide a given cooling duty of a refrigerant around a refrigerant circuit. According to a first aspect of the present invention, there is provided a method of cooling and is separating a hydrocarbon stream comprising at least the steps of: (a) providing the hydrocarbon stream; (b) cooling the hydrocarbon stream to provide a partially liquefied hydrocarbon stream, wherein at least a fraction of the cooling is provided by partially or fully evaporating a cooled refrigerant stream; 20 (c) passing at least a fraction of the partially liquefied hydrocarbon stream into a distillation column through a first inlet; (d) providing a lower feed stream; (e) providing a refrigerant circuit comprising at least a compressed fully liquefied refrigerant stream; 25 (f) heating the lower feed stream against the compressed fully liquefied refrigerant stream to provide a heated lower feed stream and the cooled refrigerant stream; (g) passing the heated lower feed stream into the distillation column through a second inlet that is located gravitationally lower than the first inlet; and (h) separating the partially liquefied hydrocarbon stream in the distillation column to 30 provide at least a first overhead gaseous stream and a first bottom liquid stream. According to a second aspect of the present invention, there is provided an apparatus for cooling and separating a hydrocarbon stream comprising at least: a first cooling stage to cool a hydrocarbon stream and provide a partially liquefied hydrocarbon stream; 2a a distillation column to receive and separate at least a fraction of the partially liquefied hydrocarbon stream provided through a first inlet; a refrigerant circuit comprising at least a compressed fully liquefied refrigerant stream; a first heat exchanger to heat a lower feed stream against the compressed fully liquefied 5 refrigerant stream to provide a cooled refrigerant stream and a heated lower feed stream to be passed into the distillation column through a second inlet that is located gravitationally lower than the first inlet; and a heat exchange system in the first cooling stage arranged in the refrigerant circuit downstream of the first heat exchanger to cool the hydrocarbon stream against at least a fraction of io the cooled refrigerant stream, thereby partially or fully evaporating the at least the fraction of the cooled refrigerant stream. According to a third aspect of the present invention, there is provided a liquefaction plant comprising an apparatus of the second aspect. According to a fourth aspect of the present invention, there is provided a separated is hydrocarbon product resulting from the method of first aspect. The present invention provides a method of cooling and separating a hydrocarbon stream such as natural gas comprising at least the steps of: (a) providing a hydrocarbon stream; (b) cooling the hydrocarbon stream to provide a partially liquefied hydrocarbon stream, 20 wherein at least a fraction of the cooling is provided by partially or fully evaporating a cooled refrigerant stream; (c) passing at least a fraction of the partially liquefied hydrocarbon stream into a distillation column through a first inlet; WO 2009/103715 PCT/EP2009/051882 -3 (d) providing a lower feed stream; (e) providing a refrigerant circuit comprising at least a compressed fully liquefied refrigerant stream; (f) heating the lower feed stream against the 5 refrigerant stream to provide a heated lower feed stream and the cooled refrigerant stream; (g) passing the heated lower feed stream into the distillation column through a second inlet lower than the first inlet; and 10 (h) separating the partially liquefied hydrocarbon stream in the distillation column to provide at least a first overhead gaseous stream and a first bottom liquid stream. The present invention also provides apparatus for 15 cooling and separating a hydrocarbon stream such as natural gas comprising at least: a first cooling stage to cool a hydrocarbon stream and provide a partially liquefied hydrocarbon stream; a distillation column to receive and separate at 20 least a fraction of the partially liquefied hydrocarbon stream provided through a first inlet; a refrigerant circuit comprising at least a compressed fully liquefied refrigerant stream; and a first heat exchanger to heat a lower feed stream 25 against the compressed fully liquefied refrigerant stream to provide a cooled refrigerant stream and a heated lower feed stream to be passed into the distillation column through a second inlet lower than the first inlet; and a heat exchange system in the first cooling stage 30 arranged in the refrigerant circuit downstream of the first heat exchanger to cool the hydrocarbon stream against at least a fraction of the cooled refrigerant WO 2009/103715 PCT/EP2009/051882 -4 stream, thereby partly or fully evaporating the at least the fraction of the cooled refrigerant stream. The present invention also provides a liquefaction plant comprising apparatus as herein defined. 5 Embodiments and examples of the present invention will now be described by way of example only and with reference to the accompanying non-limited drawings in which: Figure 1 is a diagrammatic scheme for a first method 10 of cooling and separating a hydrocarbon stream according to one embodiment of the present invention; Figure 2 is a diagrammatic scheme for a second method of cooling and separating a hydrocarbon stream as part of a liquefaction plant according to a second 15 embodiment of the present invention; Figure 3 is a diagrammatic scheme for a third method of cooling and separating a hydrocarbon stream according to a third embodiment of the present invention; Figure 4 is a diagrammatic scheme for a fourth 20 method of cooling and separating a hydrocarbon stream according to a fourth embodiment of the present invention; and Figure 5 is a diagrammatic scheme for a fifth method of cooling and separating a hydrocarbon stream according 25 to a fifth embodiment of the present invention. Embodiments of the present disclosure employ a refrigerant stream to heat a lower feed stream passing into a distillation column. The thus resulting cooled refrigerant stream is then advantageously employed to 30 cool a hydrocarbon stream, thereby to partially condense or help to partially condense the hydrocarbon stream, before passing at least part of it to the distillation column.
WO 2009/103715 PCT/EP2009/051882 -5 As summarized in for instance Figure 1, there is provided a method of cooling and separating a hydrocarbon stream such as natural gas comprising at least the steps of: 5 (a) providing a hydrocarbon stream 10; (b) cooling the hydrocarbon stream 10 to provide a partially liquefied hydrocarbon stream 20; (c) passing at least a fraction of the partially liquefied hydrocarbon stream 20 into a distillation 10 column 12 through a first inlet 17; (d) providing a lower feed stream 30; (e) providing a refrigerant circuit 4 comprising at least a refrigerant stream 40; (f) heating the lower feed stream 30 against the 15 refrigerant stream 40 to provide a heated lower feed stream and a cooled refrigerant stream 60; (g) passing the heated lower feed stream 50 into the distillation column 12 through a second inlet 18 that is located gravitationally lower than the first inlet 17; 20 and (h) separating the partially liquefied hydrocarbon stream 20 in the distillation column 12 to provide at least a first overhead gaseous stream 70 and a first bottom liquid stream 80. 25 In a preferred embodiment, the cooling in step (b) is carried out by partially or fully evaporating the cooled refrigerant stream 60, such as a sub-cooled liquefied refrigerant stream. In a further preferred embodiment, the refrigerant stream 40 in steps (e) and 30 (f) is a compressed fully liquefied refrigerant stream, such that the cooled refrigerant stream 60 produced in step (f) is a sub-cooled liquefied refrigerant stream.
WO 2009/103715 PCT/EP2009/051882 -6 The use of a compressed fully liquefied refrigerant stream to heat the lower feed stream 30 sub-cools the liquefied refrigerant stream. Such a resulting sub-cooled liquefied refrigerant stream is advantageous because it 5 produces less flash vapour when used for cooling, such as the cooling of the hydrocarbon stream. Again with reference to Fig. 1, an apparatus for cooling and separating a hydrocarbon stream, such as natural gas, is also provided. The apparatus comprises at 10 least: a first cooling stage 14 to cool a hydrocarbon stream 10 and provide a partially liquefied hydrocarbon stream 20; a distillation column 12 to receive and separate at 15 least a fraction of the partially liquefied hydrocarbon stream 20 provided through a first inlet 17; a refrigerant circuit 4 comprising at least a refrigerant stream 40; and a first heat exchanger 16 to heat a lower feed 20 stream 30 against the refrigerant stream 40 to provide a heated lower feed stream 50 to be passed into the distillation column 12 through a second inlet 18 located gravitationally lower than the first inlet 17. In a preferred embodiment, the apparatus further 25 comprises a heat exchange system 34 in the first cooling stage 14 arranged downstream of the first heat exchanger 16 to receive at least a fraction of the cooled refrigerant stream 60 and cool the hydrocarbon stream 10 against the at least the fraction of the cooled 30 refrigerant stream 60, thereby partly or fully evaporating the refrigerant stream 60. The cooled refrigerant stream 60 is preferably a sub-cooled liquefied refrigerant stream. In a further preferred WO 2009/103715 PCT/EP2009/051882 -7 embodiment, the refrigerant stream 40 in the refrigerant circuit 4 is a compressed fully liquefied refrigerant stream. One advantage of cooling the refrigerant stream 5 through the heat exchange with the lower feed stream, is that the refrigerant stream then has more cooling duty to cool the hydrocarbon stream, and optionally other streams. Another advantage of the present invention is that 10 by cooling the refrigerant stream through the heat exchange with the lower feed stream, less compression power is required for the refrigerant circuit to provide the same cooling duty around its circuit, for example to cool the hydrocarbon stream. 15 Thus, the present disclosure can provide a method that requires less power to provide the duty for cooling and separating the same amount of hydrocarbon. Described now in more detail, Figure 1 shows a method of cooling and separating a hydrocarbon stream 10 20 according to one embodiment of the present invention. The hydrocarbon stream 10 may be any suitable hydrocarbon stream such as, but not limited to, a hydrocarbon-containing gas stream able to be cooled. One example is a natural gas stream obtained from a natural 25 gas or petroleum reservoir. As an alternative the natural gas stream may also be obtained from another source, also including a synthetic source such as a Fischer-Tropsch process. Usually such a hydrocarbon stream is comprised 30 substantially of methane. Preferably such a hydrocarbon stream comprises at least 50 mol% methane, more preferably at least 80 mol% methane.
WO 2009/103715 PCT/EP2009/051882 -8 Although the method according to the present invention is applicable to various hydrocarbon streams, it is particularly suitable for natural gas streams to be liquefied. As the skilled person readily understands how 5 to liquefy a hydrocarbon stream, this is not discussed herein in detail. Depending on the source, the hydrocarbon stream 10 may contain one or more non-hydrocarbons such as H 2 0, N 2 , C0 2 , Hg, H 2 S and other sulphur compounds. 10 If desired, the hydrocarbon stream 10 may be pre treated before use either as part of a hydrocarbon cooling process, or separately. This pre-treatment may comprise reduction and/or removal of non-hydrocarbons such as CO 2 and H 2 S or other steps such as early cooling 15 and pre-pressurizing. As these steps are well known to the person skilled in the art, their mechanisms are not further discussed here. Thus, the term "hydrocarbon stream" as used herein also includes a composition prior to any treatment, such 20 treatment including cleaning, dehydration and/or scrubbing, as well as any composition having been partly, substantially or wholly treated for the reduction and/or removal of one or more compounds or substances, including but not limited to sulfur, sulfur compounds, carbon 25 dioxide and water. Preferably, a hydrocarbon stream to be used in the present invention undergoes at least the minimum pre treatment required to subsequently allow liquefaction of the hydrocarbon stream. Such a requirement for liquefying 30 natural gas is known in the art. The hydrocarbon stream 10 may also contain varying amounts of hydrocarbons heavier than methane such as ethane, propane, butanes and pentanes, as well as some WO 2009/103715 PCT/EP2009/051882 -9 aromatic hydrocarbons. The composition varies depending upon the type and location of the hydrocarbon stream such as natural gas. Hydrocarbons heavier than methane generally need to be removed from natural gas for several 5 reasons, such as having different freezing or liquefaction temperatures that may cause them to block parts of a methane liquefaction plant. C 2
-C
4 hydrocarbons can be used as a source of natural gas liquids (NGLs) and/or refrigerant. Removal of hydrocarbons heavier than 10 methane is often termed 'NGL recovery'. Figure 1 shows a hydrocarbon stream 10 containing natural gas, which is cooled in a first cooling stage 14 to provide a cooled and partially liquefied hydrocarbon stream 20. The cooling in the first cooling stage 14 may 15 cause partial condensation of the hydrocarbon stream 10. The first cooling stage 14 may comprise a heat exchange system 34, e.g. in the form of one or more heat exchangers such as kettles, either in parallel, series or both, in a manner known in the art. Cooling in the first 20 cooling stage 14 is provided by a first cooling stage refrigerant stream 15, which is warmed and partially or fully evaporated in the first cooling stage 14 to provide a warmed first cooling stage refrigerant stream 15a. The cooling of the hydrocarbon stream 10 by the 25 first cooling stage refrigerant stream 15 may be part of a liquefaction process, such as a pre-cooling stage, optionally involving a propane refrigerant circuit as described hereinafter with reference to Figure 2, or the cooling may be a separate process. The first cooling 30 stage refrigerant stream 15 may therefore be part of one or more refrigerant circuits hereinafter described, or may be provided separately.
WO 2009/103715 PCT/EP2009/051882 - 10 Cooling of the hydrocarbon stream 10 may involve reducing the temperature of the hydrocarbon stream 10 to below -0 0 C, for example, in the range -10 0 C to -70 0 C. At least a fraction, optionally all, of the 5 partially liquefied hydrocarbon stream 20 from the first cooling stage 14 is passed into a distillation column 12 through a first inlet 17. The distillation column 12 may be of any suitable size and design known in the art. One common distillation 10 column is a scrubber or scrub column, generally operating at an above ambient pressure in a manner known in the art. One purpose of the distillation column 12 is to provide a generally gaseous stream that is methane enriched, and therefore more suitable for subsequent 15 liquefaction. Suitable operating parameters for a distillation column 12 are known in the art, and can be varied to vary the composition of at least one of the major product streams provided therefrom. Commonly, there are two major 20 product streams provided from a distillation column 12, being a partially or fully gaseous overhead stream, and a bottom stream, generally being at least partially, usually fully, liquid. The bottom stream is intended to be enriched in the hydrocarbons heavier than methane in 25 the hydrocarbon stream 10, especially butanes, pentanes and heavier hydrocarbons. In order to reduce the amount of methane that may pass out of the distillation column 12 as part of the bottom stream, it is known in the art to provide a heated 30 stream at or near the bottom of the distillation column 12 so as to encourage methane from the bottom of the distillation column 12 upwards to become or remain gaseous, and therefore pass out of the distillation WO 2009/103715 PCT/EP2009/051882 - 11 column 12 as part of a gaseous overhead stream. Such a stream is conventionally heated by a separate boiler, and is therefore commonly termed a 're-boiling stream'. In this regard, Figure 1 shows a lower feed stream 5 30 intended to provide heat at or near the bottom of distillation column 12 in the manner of a re-boiling stream known in the art. As discussed herein above, conventionally, heat for the re-boiling stream is provided by a separate boiler, which requires a dedicated 10 fuel source, and whose energy is not recoverable. According to the method of the present disclosure, the lower feed stream 30 passes through a first heat exchanger 16 to heat the lower feed stream 30 against a compressed fully liquefied refrigerant stream 40 15 discussed hereinafter in more detail. The heat exchange in the first heat exchange 16 provides a heated lower feed stream 50, which passes into the distillation column 12 through a second inlet 18 lower than the first inlet 17, preferably at or near the bottom of the distillation 20 column. This is to provide heat preferably at or near the bottom of the distillation column 12 to encourage the passage of methane in the partially liquefied hydrocarbon stream in the distillation column 20 to pass out of the distillation column 12 as part of the overhead gaseous 25 stream 70. The distillation column 12 preferably provides a first overhead gaseous stream 70 having a composition greater than 80 mol% methane, and having a temperature below 0®C, more preferably in the range -200C to -400C. 30 The distillation column 12 in Figure 1 also provides a first liquid bottom stream 80, generally being enriched in hydrocarbons heavier than methane.
WO 2009/103715 PCT/EP2009/051882 - 12 The compressed fully liquefied refrigerant stream 40 is part of a first refrigerant circuit 4, several arrangements for which are shown and described in Figures 2, 3 and 4 hereinafter by way of examples only. 5 The first refrigerant circuit 4 comprises at least one refrigerant compressor and at least one refrigerant stream. One or more of the refrigerant streams may be divided and/or combined one or more times in the refrigerant circuit, to provide cooling to one or more 10 other streams, units, fluids, etc. in a manner known in the art, generally by passing through one or more heat exchangers. The cooling by each refrigerant stream (being a full stream or a fraction or part thereof) is provided by the partial or full evaporation of the refrigerant 15 stream at low pressure in a manner known in the art, the low pressure being provided by passage through one or more valves and/or other expanders. Each refrigerant stream used in the present disclosure may be formed from a single component such as 20 propane or nitrogen, or may be a mixed refrigerant formed from a mixture of two or more components selected from a group comprising: nitrogen, methane, ethane, ethylene, propane, propylene, butanes, pentanes, etc. Different stages, sections or steps of any part of a 25 hydrocarbon cooling process may involve the same or different types of refrigerant in a manner known to the person skilled in the art, and the present invention is not therefore limited thereby. The first heat exchanger 16 may comprise one or more 30 heat exchangers in parallel, series or both in a manner known in the art. The compressed fully liquefied refrigerant stream 40 generally has a temperature above OC, such as in the WO 2009/103715 PCT/EP2009/051882 - 13 range 10-700C. The temperature of the cooled refrigerant stream 60, which will be a sub-cooled liquefied refrigerant stream, is less than the refrigerant stream 40. 5 By providing compressed refrigerant stream 40 as a fully liquefied stream, a reduction in the cooling duty required of the lower feed stream 30 is achieved, compared to a corresponding compressed vapour, or only partly liquefied refrigerant stream. In this way, the 10 heat input to the lower feed stream 30, supplied by the compressed fully liquefied refrigerant stream 40 can be controlled, and more particularly lowered, compared to the use of a partly or fully vaporised refrigerant stream, to provide a heated lower feed stream at a 15 temperature suitable to optimise the separation in the distillation column 12. Use of a partly or fully vaporised refrigerant stream may require too much cooling duty of the lower feed stream 30 such that the heated lower feed stream 50 would be too hot, reducing the 20 separation efficiency in the distillation column. Thus, a system is provided in which the cooling duty available from the lower feed stream 30 can be matched with the requirements of the compressed fully liquefied refrigerant stream 40. 25 The cooled, such as sub-cooled liquefied, refrigerant stream 60 is subsequently partially or fully evaporated to provide cooling as part of the first refrigerant circuit 4. At least a fraction of the cooling of the hydrocarbon stream 10 is carried out by partially 30 or fully evaporating the cooled, such as sub-cooled liquefied, refrigerant stream 60. By providing the cooled refrigerant stream 60 as a sub-cooled liquefied refrigerant stream, by cooling compressed fully liquefied WO 2009/103715 PCT/EP2009/051882 - 14 refrigerant stream 40, a reduction in the flash vapour produced by cooling the hydrocarbon stream 10 is achieved. The first refrigerant 4 circuit may be involved with treatment of the hydrocarbon stream 10 and/or with 5 the first overhead gaseous stream 70, or be separate therefrom. Examples of arrangements for the provision of the lower feed stream 30, the compressed fully liquefied refrigerant stream 40, the cooled, such as sub-cooled 10 liquefied, refrigerant stream 60, and the first refrigerant circuit 4, are described hereinafter, but the present invention is not limited thereto. Figure 2 shows the hydrocarbon stream 10 passing through the first cooling stage 14 to provide a partially 15 liquefied hydrocarbon stream 20, which fully passes into the distillation column 12 through the first inlet 17 to provide a first overhead gaseous stream 70 and a first bottom liquid stream 80 as described above. Figure 2 also shows the compressed fully liquefied 20 refrigerant stream 40 passing through a first heat exchanger 16 to provide a cooled, such as sub-cooled liquefied, refrigerant stream 60 as described above. As one possible embodiment of the present invention, Figure 2 shows the first refrigerant circuit 4 comprising 25 one or more first refrigerant compressors 42. The refrigerant passing around the first refrigerant circuit 4 may be any suitable refrigerant being a single component such as propane, or a mixed refrigerant. A refrigerant compressor includes any unit, device or 30 apparatus able to increase the pressure of a refrigerant stream. This includes refrigerant compressors having a single compression process or step, or refrigerant compressors having multi-stage compressions or steps.
WO 2009/103715 PCT/EP2009/051882 - 15 Some stages or steps of a hydrocarbon cooling process may involve two or more refrigerant compressors in parallel, series or both. The present invention is not limited by the type or arrangement or layout of the refrigerant 5 compressor or refrigerant compressors, particularly in any refrigerant circuit. As part of the first refrigerant circuit 4, the first refrigerant compressor 42 provides a first compressed refrigerant stream 44 which passes through one 10 or more coolers such as a water and/or air cooler 46, to provide a cooler compressed stream 48 which passes into an accumulator 52 in a manner known in the art. From the accumulator 52, there is provided an accumulator stream 54, which is fully liquefied. 15 Typically, at least a fraction of the accumulator stream 54 is provided as a first cooling refrigerant stream 56, which is expanded and/or evaporated through a suitable valve 58 to provide an expanded refrigerant stream 62 (which can act as the first cooling stage refrigerant 20 stream 15 in Figure 1) to pass into the first cooling stage 14 to at least partly cool the hydrocarbon stream 10, and to provide a warmed refrigerant stream 75 (like the warmed first cooling stage refrigerant stream 15a shown in Figure 1), which passes back to the first 25 refrigerant compressor 42. Figure 2 also shows the option of dividing the accumulator stream 54 by a stream splitter 64 to provide the compressed fully liquefied refrigerant stream 40. The proportion of the divided streams 56, 40 from the 30 accumulator stream 54 can be calculated in order to provide the desired subsequent heat exchanges. It can be seen from Figure 2 that the compressed fully liquefied refrigerant stream 40 provided by the WO 2009/103715 PCT/EP2009/051882 - 16 stream splitter 64 is a relatively warm stream following the compression in the first refrigerant compressor 42. At least part of this heat can be used to heat the lower feed stream 30 prior to use of the cooled, such as a sub 5 cooled liquefied, lower feed stream refrigerant stream 60 as a normal refrigerant stream. The cooled lower feed stream refrigerant stream 60 may be used as a normal refrigerant stream at any suitable location or locations, and through any suitable 10 heat exchange system including any suitable heat exchangers and/or cooling stages, either as part of the present method cooling and separating a hydrocarbon stream, and/or elsewhere in the liquefaction plant 1, and/or in an independent process or plant. Thus, the 15 refrigerant circuit 4 may comprise a heat exchange system arranged downstream of the first heat exchanger 16, wherein at least a fraction of the cooled, such as a sub cooled liquefied, refrigerant stream 60 may be used to provide cooling to another stream. 20 At least a fraction of the cooled, such as a sub cooled liquefied, refrigerant stream 60 at least partially cools the hydrocarbon stream 10. This may be achieved by passage of the cooled, such as a sub-cooled liquefied, refrigerant stream 60 through a valve 19 to 25 provide an expanded refrigerant stream 60a, and passage thereof into the first cooling stage 14. All of the heated/warmed refrigerant from the first cooling stage 14 can return to the first refrigerant compressor 42 through line 75. 30 In this way, at least a fraction, optionally all, of the cooled, such as a sub-cooled liquefied, refrigerant stream 60 provides at least a part of the cooling of at WO 2009/103715 PCT/EP2009/051882 - 17 least part of or all of the hydrocarbon stream 10 in the first cooling stage 14. Figure 3 shows a number of other and/or alternative embodiments of the present invention using the first 5 refrigerant circuit 4 shown in Figure 2. In a first alternative of the present invention shown in Figure 3, at least a fraction, optionally all, of the first liquid bottom stream 80 provides the lower feed stream 30, which passes through the first heat 10 exchanger 16 to provide the heated lower feed stream 50. Optionally, the heated lower feed stream 50 passes into a lower feed gas/liquid separator 51, which may be external or internal to the distillation column 12, to provide a second overhead gaseous stream 50a for use in the 15 distillation column 12, and a second bottom stream 50b for use as an NGL stream. Figure 3 also shows the cooled, such as a sub-cooled liquefied, refrigerant stream 60 providing, as stream 60a after valve 19, at least a part of the cooling of the 20 hydrocarbon stream 10 in the first cooling stage 14. This could provide a separate warmed refrigerant stream 60b from the first cooling stage 14, which could be returned to the first refrigerant compressor 42 as part of the return stream 75 as described above (along with the 25 expanded refrigerant stream 62 also passing into the first cooling stage 14), or could be separately returned to the first refrigerant compressor 42 at any other suitable location, one example of which is as a return stream 60c upstream of the first refrigerant compressor 30 42 (shown in dashed line in Figure 2 for clarity). Figure 3 also shows the option of dividing the accumulator stream 54 by the stream splitter 64 to provide a usually majority second refrigerant stream 66 WO 2009/103715 PCT/EP2009/051882 - 18 which can be expanded by a valve 68 to provide cooling in a second heat exchanger 72 as described hereinbelow, and to provide a second return stream 74 to the refrigerant compressor 42. The second heat exchanger 72 may be 5 associated, aligned or integral with the first cooling stage 14 in a manner known in the art. Figure 3 also shows non-limiting examples of alternative sources of the compressed fully liquefied refrigerant stream 40 from the first refrigerant circuit 10 4. As an example, the compressed stream 44 from the refrigerant compressor 42 could be divided by a stream splitter to provide a first split stream 76 as the source prior to the cooler 46. 15 Alternatively, the source of the refrigerant stream 40 may be from a separate supply, such as a separate refrigerant circuit. For example, Figure 3 also shows a second refrigerant circuit 6 comprising one or more second 20 refrigerant compressors 82 able to provide a second compressed refrigerant stream 84, which then passes through one or more second coolers 86 and then the second heat exchanger 72 to provide a cooler second compressed stream 92. The cooler second compressed stream 92 is 25 shown in Figure 3 passing through a third separator 94, generally to provide a lighter overhead stream 96 and a heavier bottom stream 98. In a manner known in the art, the lighter overhead stream 96 and the heavier bottom stream 98 pass though a third heat exchanger 102 to be 30 cooled, are separately expanded outside the third heat exchanger 102, and then returned therein to provide cooling to the streams passing through the third heat WO 2009/103715 PCT/EP2009/051882 - 19 exchanger 102. This provides a second return refrigerant stream 104 to the second refrigerant compressor 82. The third heat exchanger 102 may be fully or part of a second cooling stage of a hydrocarbon cooling process. 5 A second cooling stage is preferably separate from the first cooling stage. That is, the second cooling stage comprises one or more separate heat exchangers using a second refrigerant circulating in a second refrigerant circuit, although the refrigerant of the second 10 refrigerant circuit may also pass through one or more heat exchangers of the first cooling stage. Such a second cooling stage is sometimes also termed a 'main cooling' stage. In a manner similar to that described above in 15 relation to the first refrigerant circuit 4, the second refrigerant circuit 6 may provide one or more part or split streams as the source of the compressed fully liquefied refrigerant stream 40. For example, the second compressed refrigerant stream 84 could be divided to 20 provide a third split stream 106, and the second refrigerant stream after the cooler 86 could provide a fourth split stream 108. Similarly, the warmed refrigerant stream 60b from the first cooling stage 14 could be returned into the 25 second refrigerant circuit 6 at any suitable location, such as as a third return stream 60d after the second heat exchanger 72, or as a fourth return stream 60e into the third separator 94. Figure 3 also shows at least a fraction, preferably 30 all, of the first overhead gaseous stream 70 from the distillation column 12 being subsequently liquefied in the third heat exchanger 102 to provide a liquefied hydrocarbon stream 120 such as LNG.
WO 2009/103715 PCT/EP2009/051882 - 20 Figure 4 shows a hydrocarbon stream 10 being cooled in heat exchanger system 34a of first cooling stage 14 similar to Figures 1 to 3, to provide a partially liquefied hydrocarbon stream 20. 5 In another alternative embodiment of the present invention, Figure 4 shows that the hydrocarbon stream 10 can be divided by a stream splitter 21 into at least a first part stream 10a and a second part stream 10b in a manner known in the art. The ratio of the division of the 10 hydrocarbon stream 10 into the first and second part streams 10a, 10b may be any ratio or proportion. Preferably, any part stream to be provided through the first inlet 17 into the distillation column 12 is the majority of the hydrocarbon stream 10, such as described 15 in WO 2006/061400 Al, incorporated herein by way of reference. The first part feed stream 10a passes through the heat exchange system 34a in first cooling stage 14 as described above to provide the partially liquefied 20 hydrocarbon stream 20 which passes into the distillation column 12. The second part stream 10b provides the lower feed stream 30 for passage into first heat exchanger 16 to provide a heated lower feed stream 50, which also passes 25 into the distillation column 12. As shown in Figures 2 and 3, the refrigerant stream 40 can be provided from the first refrigerant circuit 4 after the accumulator 52, optionally as a fraction of the second refrigerant stream 66 being provided to the second 30 heat exchanger 72 (not shown in Figure 4), represented as fraction stream 78. In another alternative embodiment of the present invention, the hydrocarbon stream 10 is provided from an WO 2009/103715 PCT/EP2009/051882 - 21 initial stream 8, which passes through a fourth heat exchanger 112, which may comprise one or more heat exchangers in series, parallel or both. The fourth heat exchanger 112 may form part of the first cooling stage 5 14. Cooling for the fourth heat exchanger 112 can be provided either by use of the cooled, such as a sub cooled liquefied, refrigerant stream 60 after passing through the valve 19 to provide an expanded refrigerant stream 60a, and/or by provision of at least a fraction of 10 the expanded refrigerant stream 62 in the first refrigerant circuit 4 prior to its use as the first cooling stage refrigerant stream 15 in the first cooling stage 14. Dashed line 63 show passage of an optional refrigerant stream into the fourth heat exchanger 112, 15 and return line 63a could also be the path of return of the expanded refrigerant stream 60a and any optional refrigerant stream 63 back into the first refrigerant circuit 4 after use in the fourth heat exchanger 112. An optional second fraction of the expanded refrigerant 20 stream 60g may be passed to heat exchanger system 34a of the first cooling stage 14. Figure 4 shows second fraction expanded refrigerant stream 60g being passed to first cooling stage refrigerant stream 15 which is then passed to heat exchange system 34a of the first cooling 25 stage 14. Optionally, the fourth heat exchanger 112 is a part of the first cooling stage 14. In this way, Figure 4 shows embodiments of the present invention wherein a fraction of the hydrocarbon 30 stream 10 provides at least a fraction of the lower feed stream 30, preferably by division of the hydrocarbon stream 10 into at least first and second part streams 10a, 10b, and wherein the first part stream 10a is cooled WO 2009/103715 PCT/EP2009/051882 - 22 to provide the partially liquefied hydrocarbon stream 20, and the second part stream 10b provides at least a fraction of the lower feed stream 30. Figures 3 and 4 also show various alternatives for 5 the provision of cooling to the first cooling stage 14, and various embodiments for the use of the cooled, such as a sub-cooled liquefied, refrigerant stream 60 to provide cooling, preferably as part of the refrigerant circuit 4 through one or more of the same or different 10 heat exchangers. Figure 5 shows further alternative embodiments of the present invention. In Figure 5, the hydrocarbon stream 10 passes through the first cooling stage 14 as described above to 15 provide a partially liquefied hydrocarbon stream 20 which passes into a feed stream gas/liquid separator 32 to provide a feed stream overhead gaseous stream 100a, and a feed stream liquid bottom stream 100b. At least a fraction, preferably all, of the feed 20 stream liquid bottom stream 100b is provided as the lower feed stream 30 which passes through the first heat exchanger 16 to provide the heated lower feed stream 50, and then passes into the distillation column 12 as described hereinabove. 25 Meanwhile, at least a fraction, preferably all, of the feed stream overhead gaseous stream 100a passes through a fifth heat exchanger 116 to provide a cooled partially liquefied hydrocarbon stream 20a which also passes into the distillation column 12. Cooling for the 30 fifth heat exchanger 116 can be provided by a suitable cooling and/or refrigerant stream 114 from one or more of the sources of a refrigerant stream described herein, or from a separate source, in a manner known in the art, at WO 2009/103715 PCT/EP2009/051882 - 23 least a fraction of which is derived from cooled, such as a sub-cooled liquefied, refrigerant stream 60, to provide a warmed further refrigerant stream 114a. Cooling of the feed stream overhead gaseous stream 5 100a increases the temperature difference between the subsequent cooled partially liquefied hydrocarbon stream 20a and the heated lower feed stream 50 as they enter the distillation column 12, thus increasing the separation, or the efficiency of the separation, of the content of 10 the distillation column 12 into its first overhead gaseous stream 70 and first bottom liquid stream 80, preferably increasing the amount of methane, which passes out of the distillation column 12 as part of the first overhead gaseous stream 70. 15 From the distillation column 12, the first gaseous overhead stream 70 passes through a second cooling stage 22, comprising one or more heat exchangers in parallel, series or both in a manner known in the art. Optionally, the second cooling stage 22 comprises the third heat 20 exchanger 102 and the cooler second compressed stream 92 shown in Figure 3. From the second cooling stage 22, a partially, preferably fully, liquefied hydrocarbon stream 120 passes to a final separator such as an end-flash vessel 24, to 25 provide a final overhead stream such as end flash gas 24a, and a final bottom stream such as an enriched liquefied hydrocarbon stream 90. In another embodiment of the present invention, optionally, at least a fraction 90b of the final bottom 30 stream 90 is split from the main product stream 90a (such as LNG). This fraction 90b is able to provide, via a pump 94, a secondary lower feed 30a which passes through a secondary heat exchanger 16a to provide a secondary WO 2009/103715 PCT/EP2009/051882 - 24 heated lower feed stream 50a, which itself passes into the distillation column 12. Heating for the secondary lower feed stream 30a can be provided by a secondary refrigerant stream 40a, being the same as, a fraction of, 5 or separately derived from, the compressed fully liquefied refrigerant stream 40. The secondary heat exchanger 16a provides a cooled secondary refrigerant stream 60f, which may be combined with or associated with the cooled refrigerant stream 60, or otherwise separately 10 used. Thus, the distillation column 12 may receive more than one heated lower feed stream, either separately or combined into a single stream. The present disclosure provides an advantageous method of using a least a fraction of a refrigerant 15 stream to heat rather than cool another stream, prior to its subsequent use as a refrigerant stream in a refrigerant circuit as medium against which to cool another stream. Such a refrigerant stream can be provided at, by or from a number of locations around a refrigerant 20 circuit, and the heated refrigerant stream cam be returned to the refrigerant circuit at a number of suitable locations. Thus, the present disclosure provides flexibility in the provision and return of the refrigerant stream to and from a refrigerant circuit. 25 Table 1 below gives an overview of phases, mass rates, pressures, temperatures and certain compositions for some of the streams and various parts of an example process of the arrangement shown in Figure 2.
WO 2009/103715 PCT/EP2009/051882 - 25 Table 1. V=Vapour, L=Liquid StreamPhase Total Mass Rate Temp Pressure Cl C2+ Kg/Sec C Bar Mol% 10 V/L 209.3 20.0 60.0 0.825 0.17 10a V/L 146.5 20.0 60.0 0.825 0.17 20 V/L 146.5 -37.0 59.0 0.825 0.17 30 V/L 62.8 20.0 60.0 0.825 0.17 40 L 66.1 52.0 18.5 0.000 1.00 44 V 142.0 83.7 19.0 0.000 1.00 48 L 142.0 52.0 18.5 0.000 1.00 50 V/L 62.8 50.0 59.5 0.825 0.17 54 L 142.0 52.0 18.5 0.000 1.00 56 L 75.8 52.0 18.5 0.00 1.00 60 L 66.1 22.4 18.2 0.000 1.00 60a V/L 66.1 -40.0 1.1 0.000 1.00 62 V/L 75.8 -40.0 1.1 0.000 1.00 70 V 165.5 -25.2 58.0 0.884 0.10 75 V 142.0 -39.9 1.1 0.000 1.00 80 L 43.8 -39.9 1.1 0.000 1.0 The present disclosure also requires less compression power and less cooling in the first refrigerant circuit because of the cooling provided to the refrigerant stream by its use for heating the lower 5 feed stream. Table 2 below provides a comparison for the power duties required by or in the first cooling stage 14, the first heat exchanger 16, the first refrigerant compressor 42 and its subsequent cooler(s) 46, between; WO 2009/103715 PCT/EP2009/051882 - 26 (i) an example of the present disclosure as shown in Figure 2; and (ii) the same arrangement for the first refrigerant circuit, but with separate or external heating being 5 provided to the first heat exchanger to heat the lower feed stream (provided as a fraction of the hydrocarbon stream), and whose heating stream is not subsequently used in the first refrigerant circuit. The first refrigerant circuit of the comparison example is only 10 used to provide same amount of cooling to the first cooling stage. Table 2. Duty (kW) Apparatus Comparison Disclosure Difference (ii) (i) 14 31530 31530 0.0% 16 6130 6130 0.0% 46 61450 49500 -19.4% 42 29920 24110 -19.4% Table 2 confirms that the embodiment of the present disclosure shown in Figure 2 provides a near 20% reduction in the power required for the first refrigerant 15 compressor 42, and a similar near 20% reduction in the cooling required in the first cooler(s) 46. These are significant power and cooling duty reductions in industrial scale of providing a liquefied hydrocarbon stream. 20 Table 2 confirms that the embodiment of the present disclosure shown in Figure 2 requires less compression power for the refrigerant circuit to provide the same cooling duty around its circuit, which reduces the WO 2009/103715 PCT/EP2009/051882 - 27 overall power required to cool and separate the same amount of a hydrocarbon stream as the comparison example, which could equate to that shown in US 5,960,644. The person skilled in the art will understand that 5 the present invention can be carried out in many various ways without departing from the scope of the appended claims.

Claims (18)

1. A method of cooling and separating a hydrocarbon stream comprising at least the steps of: (a) providing the hydrocarbon stream; 5 (b) cooling the hydrocarbon stream to provide a partially liquefied hydrocarbon stream, wherein at least a fraction of the cooling is provided by partially or fully evaporating a cooled refrigerant stream; (c) passing at least a fraction of the partially liquefied hydrocarbon stream into a distillation column through a first inlet; io (d) providing a lower feed stream; (e) providing a refrigerant circuit comprising at least a compressed fully liquefied refrigerant stream; (f) heating the lower feed stream against the compressed fully liquefied refrigerant stream to provide a heated lower feed stream and the cooled refrigerant stream; is (g) passing the heated lower feed stream into the distillation column through a second inlet that is located gravitationally lower than the first inlet; and (h) separating the partially liquefied hydrocarbon stream in the distillation column to provide at least a first overhead gaseous stream and a first bottom liquid stream.
2. A method as claimed in claim 1 wherein the lower feed stream comprises at least a 20 fraction of the first liquid bottom stream.
3. A method as claimed in claim 1 or 2 wherein the lower feed stream comprises a fraction of the hydrocarbon stream.
4. A method as claimed in claim 3 wherein the hydrocarbon stream is divided into at least first and second part-streams, and wherein the first part-stream is cooled to provide the partially 25 liquefied hydrocarbon stream, and the second part-stream forms said fraction of the hydrocarbon stream in the lower feed stream.
5. A method as claimed in claim 1 or claim 2 wherein the lower feed stream comprises a fraction of the partially liquefied hydrocarbon stream.
6. A method as claimed in claim 5 wherein the partially liquefied hydrocarbon stream is 30 passed into a first gas/liquid separator to provide a feed stream overhead gaseous stream and a feed stream liquid bottom stream, and wherein at least a fraction of the feed stream overhead gaseous stream is provided to the first inlet of the distillation column, wherein the lower feed stream comprises at least a fraction of the feed stream liquid bottom stream.
7. A method as claimed in any one of the preceding claims wherein at least a fraction of 3s the first overhead gaseous stream is at least party condensed and passed into a final gas/liquid 29 separator to provide at least a final bottom stream, and wherein at least a fraction of the final bottom stream is a secondary lower feed stream.
8. A method as claimed in any one of the preceding claims wherein at least a fraction of the cooling in step (b) is provided by the refrigerant circuit. s
9. A method as claimed in any one of the preceding claims wherein the refrigerant circuit comprises one or more refrigerant accumulators, and wherein the compressed fully liquefied refrigerant stream is provided from at least one of said refrigerant accumulators.
10. A method as claimed in any one of the preceding claims wherein the compressed fully liquefied refrigerant stream is propane. 10
11. A method as claimed in any one of the preceding claims, wherein the hydrocarbon stream is a natural gas stream.
12. A method as claimed in any one of the preceding claims wherein at least a fraction of the first overhead gaseous stream is subsequently liquefied to provide a liquefied hydrocarbon stream such as LNG. is
13. Apparatus for cooling and separating a hydrocarbon stream comprising at least: a first cooling stage to cool a hydrocarbon stream and provide a partially liquefied hydrocarbon stream; a distillation column to receive and separate at least a fraction of the partially liquefied hydrocarbon stream provided through a first inlet; 20 a refrigerant circuit comprising at least a compressed fully liquefied refrigerant stream; a first heat exchanger to heat a lower feed stream against the compressed fully liquefied refrigerant stream to provide a cooled refrigerant stream and a heated lower feed stream to be passed into the distillation column through a second inlet that is located gravitationally lower than the first inlet; and 25 a heat exchange system in the first cooling stage arranged in the refrigerant circuit downstream of the first heat exchanger to cool the hydrocarbon stream against at least a fraction of the cooled refrigerant stream, thereby partially or fully evaporating the at least the fraction of the cooled refrigerant stream.
14. A liquefaction plant comprising apparatus as claimed in claim 13. 30
15. A method of cooling and separating a hydrocarbon stream, said method as claimed in claims 1 and substantially as hereinbefore with reference to any one of the accompanying drawings.
16. A separated hydrocarbon product resulting from the method of any one of claims 1 to 12 or 15. 30
17. An apparatus for cooling and separating a hydrocarbon steam, substantially as hereinbefore described with reference to any one of the accompanying drawings.
18. A liquefaction plant comprising an apparatus as claimed in claim 17. 5 Dated 20 February 2012 Shell Internationale Research Maatschappij B.V. Patent Attorneys for the Applicant/Nominated Person SPRUSON & FERGUSON 10
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