WO2013087569A2 - Procédé et appareil pour retirer l'azote d'une composition d'hydrocarbures cryogéniques - Google Patents

Procédé et appareil pour retirer l'azote d'une composition d'hydrocarbures cryogéniques Download PDF

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Publication number
WO2013087569A2
WO2013087569A2 PCT/EP2012/074957 EP2012074957W WO2013087569A2 WO 2013087569 A2 WO2013087569 A2 WO 2013087569A2 EP 2012074957 W EP2012074957 W EP 2012074957W WO 2013087569 A2 WO2013087569 A2 WO 2013087569A2
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WIPO (PCT)
Prior art keywords
vapour
nitrogen
stripping
liquid
stripper column
Prior art date
Application number
PCT/EP2012/074957
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English (en)
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WO2013087569A3 (fr
Inventor
Alexandre M. C. R. SANTOS
Original Assignee
Shell Internationale Research Maatschappij B.V.
Shell Oil Company
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Shell Internationale Research Maatschappij B.V., Shell Oil Company filed Critical Shell Internationale Research Maatschappij B.V.
Priority to CN201280061161.0A priority Critical patent/CN103988035A/zh
Priority to KR1020147019092A priority patent/KR20140103144A/ko
Priority to EP12799178.4A priority patent/EP2791601B1/fr
Priority to JP2014546441A priority patent/JP2015501917A/ja
Priority to RU2014128669A priority patent/RU2607198C2/ru
Priority to CA2858152A priority patent/CA2858152C/fr
Priority to AU2012350742A priority patent/AU2012350742B2/en
Publication of WO2013087569A2 publication Critical patent/WO2013087569A2/fr
Publication of WO2013087569A3 publication Critical patent/WO2013087569A3/fr

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    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25JLIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/0002Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the fluid to be liquefied
    • F25J1/0022Hydrocarbons, e.g. natural gas
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25JLIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02Processes 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
    • F25J3/0204Processes 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
    • F25J3/0209Natural gas or substitute natural gas
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    • F25J1/0032Processes 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"
    • F25J1/004Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration" by flash gas recovery
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    • F25J1/0214Processes 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
    • F25J1/0215Processes 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
    • F25J1/0216Processes 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
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    • F25JLIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2245/00Processes or apparatus involving steps for recycling of process streams
    • F25J2245/02Recycle of a stream in general, e.g. a by-pass stream
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25JLIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2245/00Processes or apparatus involving steps for recycling of process streams
    • F25J2245/90Processes or apparatus involving steps for recycling of process streams the recycled stream being boil-off gas from storage
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25JLIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2280/00Control of the process or apparatus
    • F25J2280/02Control in general, load changes, different modes ("runs"), measurements

Definitions

  • the present invention relates to a method and
  • Liquefied natural gas forms an economically important example of such a cryogenic hydrocarbon
  • Natural gas is a useful fuel source, as well as a source of various hydrocarbon compounds. It is often desirable to liquefy natural gas in a liquefied natural gas plant at or near the source of a natural gas 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 because it occupies a smaller volume and does not need to be stored at high pressure.
  • WO 2011/009832 describes a method for treating a multi-phase hydrocarbon stream produced from natural gas, wherein lower boiling point components, such as nitrogen, are separated from the multi-phase hydrocarbon stream, to produce a liquefied natural gas stream with a lower content of such lower boiling point components. It employs two subsequent gas/liquid separators operating at different pressures.
  • the multi-phase hydrocarbon stream is fed into the first gas/liquid separator at a first pressure.
  • the bottom stream of the first gas/liquid separator is passed to the second gas/liquid separator, which provides vapour at a second pressure that is lower than the first pressure.
  • the vapour is compressed in an overhead stream compressor, and returned to the first gas/liquid separator as a stripping vapour stream.
  • Compressed boil-off gas from a cryogenic storage tank may be added to the stripping vapour stream.
  • the first gas/liquid separator comprises a contacting zone, with contact enhancing means such as trays or packing, arranged gravitationally between the inlet for the multiphase hydrocarbon stream into the first gas/liquid separator and the inlet for the stripping vapour stream.
  • a low pressure fuel gas stream is prepared from the overhead vapour stream discharged from the first
  • a drawback of the method and apparatus as described in WO 2011/009832 is that the equilibrium in the first gas/liquid separator can be disturbed if the amount of stripping vapour changes substantially, which could be the case when the plant transits between holding mode and loading mode operation.
  • the present invention provides a method of removing nitrogen from a cryogenic hydrocarbon composition
  • the present invention provides an apparatus for removing nitrogen from a cryogenic
  • hydrocarbon composition comprising a nitrogen- and methane-containing liquid phase
  • cryogenic feed line connected to a source of a cryogenic hydrocarbon composition comprising nitrogen and a methane-containing liquid phase
  • nitrogen stripper column in fluid communication with the cryogenic feed line, said nitrogen stripper column comprising at least one internal stripping section positioned within the nitrogen stripper column and a sump space defined gravitationally below the stripping
  • a nitrogen-stripped liquid discharge line comprising an intermediate depressurizer , in fluid communication with the sump space of the nitrogen stripper column arranged to receive a nitrogen-stripped liquid from the sump space and to depressurize the nitrogen-stripped liquid, said intermediate depressurizer located on an interface between a stripping pressure side comprising the nitrogen stripper column and a flash pressure side; - a liquid hydrocarbon product line arranged on the flash pressure side in communication with the
  • process compressor arranged in the process vapour line arranged to receive the process vapour and compress the process vapour to provide a compressed vapour at a process compressor discharge outlet of the process compressor, said process compressor being on said
  • bypass splitter whereby an upstream side thereof is in fluid communication with the discharge outlet of the process compressor to receive the compressed vapour, and of which bypass splitter a first discharge side is in fluid communication with the nitrogen stripper column via a stripping vapour line and a second inlet system
  • discharge side is in fluid communication with a vapour bypass line containing a non-stripping portion of the compressed vapour; a condenser arranged in fluid communication with the vapour bypass line to bring an intermediate vapour that comprises at least the non-stripping portion from the vapour bypass line, which condenser comprises a heat exchanging surface providing indirect heat exchange contact between the intermediate vapour and an auxiliary refrigerant stream;
  • a discharge line in communication with both the condenser and with an overhead space of the nitrogen stripper column, and arranged to discharge a vapour fraction as off gas comprising an overhead vapour
  • liquid recycle line on its upstream side in fluid communication with the condenser and on its downstream side in liquid communication with the liquid hydrocarbon product line;
  • bypass path extends between the bypass splitter and the discharge line, wherein the bypass path bypasses the at least one internal stripping section.
  • Fig. 1 schematically represents a process flow scheme representing a method and apparatus incorporating an embodiment of the invention.
  • Fig. 2 schematically represents a process flow scheme representing a method and apparatus incorporating another embodiment of the invention.
  • the present description concerns removal of nitrogen from a cryogenic hydrocarbon composition comprising a nitrogen- and methane-containing liquid phase.
  • a least a first portion of the cryogenic hydrocarbon composition is fed to a nitrogen stripper column as a first nitrogen stripper feed stream.
  • a nitrogen-stripped liquid is drawn from the nitrogen stripper column.
  • a liquid hydrocarbon product stream and a process vapour are produced comprising at least a step of depressurizing the nitrogen-stripped liquid to a flash pressure.
  • the process vapour is compressed, and selectively split into a stripping portion and a non-stripping portion.
  • a stripping vapour stream comprising at least the stripping portion is passed into the nitrogen stripper column gravitationally below a stripping section positioned therein.
  • An intermediate vapour comprising at least the non-stripping portion of the compressed process vapour, is passed through a condenser whereby an excess liquid is formed from the intermediate vapour and whereby at least a bypass portion from the compressed vapour remains in vapour phase.
  • a vapour fraction is discharged as off gas, comprising a discharge fraction of overhead vapour from the nitrogen stripper column and comprising at least the bypass portion from the compressed vapour which bypasses the stripping section positioned in the nitrogen stripper column.
  • a liquid recycle portion comprises at least part of the excess liquid. At least part of the liquid recycle portion is returned to the liquid
  • An advantage of splitting off the non-stripping portion, which contains the bypass portion from the compressed process vapour, and passing at least the bypass portion to the off gas whereby bypassing at least the stripping section positioned within the nitrogen stripper column, is that the nitrogen stripper column can be protected against excess flow of stripping vapour flowing through the stripping section. Such excess flow may cause disturbance of the equilibrium conditions.
  • the vapour fraction in the off gas generally has a heating value.
  • the cooling duty in the condenser is adjusted to regulate the heating value of the vapour fraction being discharged.
  • the ability to regulate the heating value is advantagous allows to stabilize the heating value of the vapour fraction in the off gas against variation or fluctuations in the flow rate and/or the composition of the bypass portion from the compressed process vapour compared to the flow rate and/or composition of the overhead vapour from the nitrogen stripper column. Variations in both flow rate and compositions can be expected in an LNG plant when transiting from holding mode operation to loading mode operation. Not only is the vapour flow rate higher during loading mode, the composition is leaner as well (particularly containing more nitrogen) .
  • the process vapour may comprise vaporous methane that has previously formed part of the raw liquefied product. Vaporous methane that has previously formed part of the raw liquefied product can be formed in an LNG
  • methane containing vapour is formed from the (raw) liquefied product in the form of:
  • loading mode operation The operation mode of an LNG plant while there are ongoing transporter loading operations (typically ship loading operations) is known as loading mode operation.
  • boil-off gas is
  • the proposed solution may facilitate the handling of these vapours both during holding mode and loading mode operations. It combines the removal of nitrogen from the cryogenic hydrocarbon composition with re-condensation of excess vaporous methane. This forms an elegant solution in situations where little plant fuel is demanded, such as could be the case in an electrically driven plant using electric power from an external power grid.
  • the process vapour may comprise one or both of flash vapour and boil-off gas, it is particularly suited for boil-off gas.
  • the flow rate of boil-off gas is the most subject to variation in a typical LNG plant. Since the proposed solution allows for selectively stripping of the compressed vapour into stripping and non-stripping portions, it allows to selectively bypass the stripping section in the nitrogen stripper column with any process vapour in excess of what is needed as stripping vapour.
  • FIG. 1 illustrates an apparatus comprising an embodiment of the invention.
  • a cryogenic feed line 8 is in fluid communication with a nitrogen stripper column
  • a first feed line 10 connects the cryogenic feed line 8 with the first inlet system 21 of the nitrogen stripper column 20, optionally via an initial stream splitter 9 arranged between the cryogenic feed line 8 and the first feed line 10.
  • a liquefaction system 100 may be provided upstream of the cryogenic feed line 8.
  • the liquefaction system 100 functions as a source of a cryogenic hydrocarbon
  • the liquefaction system 100 is in fluid communication with the cryogenic feed line 8 via a main depressurizing system 5, which communicates with the liquefaction system 100 via a raw liquefied product line 1.
  • the main depressurizing system 5 consists of a dynamic unit, such as an expander turbine 6, and a static unit, such as a Joule Thomson valve 6, but other variants are possible.
  • any compressor forming part of the hydrocarbon liquefaction process in the liquefaction system is driven by one or more electric motors, without being mechanically driven by any steam- and/or gas turbine.
  • Such compressor may be driven exclusively by one or more electric motors.
  • the nitrogen stripper column 20 comprises an internal stripping section 24 positioned within the nitrogen stripper column 20.
  • An overhead vapour discharge line 30 communicates with the nitrogen stripper column 20 via an overhead space 26 within the nitrogen stripper column 20.
  • a nitrogen-stripped liquid discharge line 40 communicates with the nitrogen stripper column 20 via a sump space 28 within the nitrogen stripper column 20 gravitationally below the stripping section 24.
  • the nitrogen stripper column 20 may comprise
  • vapour/liquid contact-enhancing means to enhance
  • cryogenic feed line 8 between 2 and 8 theoretical stages may typically be needed in total. In one particular embodiment, 4 theoretical stages were required.
  • Such contact-enhancing means may be provided in the form of trays and/or packing, in the form of either structured or non-structured packing. At least part of the
  • vapour/liquid contact-enhancing means suitably forms part of the internal stripping section 24.
  • An intermediate depressurizer 45 is arranged in the nitrogen-stripped liquid discharge line 40, and thereby fluidly connected to the nitrogen stripper column 20.
  • the intermediate depressurizer 45 is functionally coupled to a level controller LC, which cooperates with the sump space 28 of the nitrogen stripper column 20.
  • the intermediate depressurizer 45 is located on an interface between a stripping pressure side comprising the nitrogen stripper column 20, and a flash pressure side.
  • the flash pressure side comprises a liquid
  • the flash pressure side furthermore comprises a cryogenic storage tank 210 connected to the liquid hydrocarbon product line 90 for storing the liquid hydrocarbon product stream, an optional boil-off gas supply line 230, and an optional end flash separator 50.
  • end flash separator 50 may be configured in fluid communication with the nitrogen stripper column 20 via the intermediate depressurizer 45 and the nitrogen-stripped liquid discharge line 40.
  • the end flash separator 50 may then be connected to the cryogenic storage tank 210 via the liquid hydrocarbon product line 90.
  • a cryogenic pump 95 may be present in the liquid hydrocarbon product line 90 to assist the transport of the liquid hydrocarbon product to the cryogenic storage tank 210.
  • cryogenic feed line 8 is also connected to at least one of the group consisting of: the nitrogen-stripped liquid discharge line 40, the liquid hydrocarbon product line 90 and the process vapour line 60.
  • a second feed line 11 is connected at an upstream side thereof to the optional initial splitter 9. This second feed line
  • a bypass stream flow control valve 15 is arranged in the second feed line 11.
  • the bypass stream flow control valve is functionally connected to a flow controller FC provided in the first feed line 10.
  • the second feed line 11 feeds into the optional end flash separator 50.
  • a benefit of the optional second feed line 11 and the optional initial splitter 9 is that the nitrogen stripper column 20 can be sized smaller than in the case that the cryogenic feed line 8 and the first feed line 10 are directly connected without a splitter such that all of the cryogenic hydrocarbon composition is let into the nitrogen stripper column 20 via the first inlet system 21.
  • the process vapour line 60 as shown in the
  • Fig. 1 may be connected to the optional end flash separator 50 via a flash vapour line 64 and flash vapour flow control valve 65, as well as to the cryogenic storage tank 210 via the optional boil-off gas supply line 230.
  • An advantage of the latter connection is that it allows for re-condensing of at least part of the boil-off gas from the cryogenic storage tank 210 by means of a condenser, which will be further discussed herein below.
  • stripping pressure side and the flash pressure side is a process compressor 260.
  • the process is a process compressor 260.
  • the compressor 260 is driven by an electric motor.
  • the process compressor 260 is arranged in the process vapour line 60 to receive the process vapour and to compress the process vapour.
  • a compressed vapour discharge line 70 is fluidly connected with a process compressor discharge outlet 261 of the process compressor 260.
  • the process compressor 260 is provided with anti-surge control and a recycle cooler which is used when the process compressor is on recycle and during start-up (not shown in the drawing) .
  • a stripping vapour line 71 is in fluid communication with the nitrogen stripper column 20 via a second inlet system 23 configured at a level gravitationally below the stripping section 24 and preferably above the sump space 28.
  • the stripping vapour line 71 is connected to the compressed vapour discharge line 70 via a bypass splitter
  • a stripping vapour valve 75 is provided in the stripping vapour line 71.
  • an external stripping vapour supply line 74 is provided in fluid communication with the second inlet system 23 of the nitrogen stripper column 20.
  • the optional external stripping vapour supply line 74 connects to the
  • stripping vapour flow control valve 73 is provided in the optional external stripping vapour supply line 74.
  • the optional external stripping vapour supply line 74 is suitably connected to a hydrocarbon vapour line in, or upstream of, the liquefaction system 100.
  • the bypass splitter 79 is also in fluid communication with a condenser via at least a vapour bypass line 76.
  • a vapour bypass control valve 77 is preferably provided in the vapour bypass line 76.
  • the vapour bypass line 76 contains a non-stripping portion of the compressed vapour from the compressed vapour discharge line 70.
  • the condenser can be any type of indirect heat exchanger in fluid communication with the bypass splitter 79 via the vapour bypass line 76. Such condenser is advantageously utilized to re-condense at least part of compressed process vapour from the compressed vapour discharge line 70.
  • FIG. 1 shows a convenient embodiment wherein the condenser is provided in the form of an overhead
  • the condenser 35 external to the nitrogen stripper column 20.
  • the overhead condenser 35 is arranged in fluid
  • the condenser comprises a heat exchanging surface that provides indirect heat exchange contact between the intermediate vapour and the auxiliary refrigerant stream 132, whereby heat can pass from the intermediate vapour to the auxiliary refrigerant stream 132 at a cooling duty.
  • An auxiliary refrigerant stream flow control valve 135 is provided in the
  • auxiliary refrigerant line 132 auxiliary refrigerant line 132.
  • the vapour bypass line 76 suitably extends along a bypass path extending between the bypass splitter 79 and the overhead vapour discharge line 30 on an upstream side of the overhead condenser 35.
  • the bypass path extends between the bypass splitter 79 and the overhead vapour discharge line 30 and/or the vapour fraction discharge line 80.
  • the bypass path does not pass through the internal stripping section 24 in the nitrogen stripper column 20. This way it can be avoided that the non-stripping portion passes through the
  • an overhead separator 33 is arranged on a downstream side of the overhead vapour discharge line 30.
  • the overhead vapour discharge line 30 discharges into the overhead separator 33.
  • the overhead separator 33 is arranged to separate any, non-condensed, vapour fraction from any condensed fraction of the overhead vapour.
  • a vapour fraction discharge line 80 is arranged to discharge the vapour fraction mentioned above.
  • the vapour fraction discharge line 80 is in fluid
  • vapour fraction discharge line 80 is inherently in communication with both the condenser and with the overhead space 26 of the nitrogen stripper column 20.
  • the bypass path in this embodiment extends to the vapour fraction discharge line 80.
  • vapour bypass line 76 A benefit of the vapour bypass line 76 is that at times when there is an excess of process vapour, this can be processed together with the off gas in the vapour fraction discharge line 80 without upsetting the material balance in the nitrogen stripper column 20.
  • the condenser is also in fluid communication with a liquid recycle line 13.
  • the liquid recycle line 13 is in liquid communication with the liquid hydrocarbon product line 90.
  • Liquid communication means that the liquid recycle line 13 is connected to any suitable location from where at least a part of a liquid recycle portion can flow into the liquid hydrocarbon product line 90 while staying in the liquid phase.
  • the liquid recycle line 13 may for instance be connected directly to one or more selected from the group consisting of: the nitrogen stripper column 20, the cryogenic feed line 8, the first feed line 10, the optional second feed line 11, the nitrogen-stripped liquid discharge line 40, the optional end flash separator 50 and the liquid
  • hydrocarbon product line 90 hydrocarbon product line 90.
  • a recycle valve 14 is configured in the liquid recycle line 13.
  • the nitrogen stripper column 20 comprises an internal rectifying section 22 in addition to the internal stripping section 24.
  • the internal rectifying section 22 is positioned within the nitrogen stripper column 20, gravitationally higher than the stripping section 24.
  • the overhead space 26 is preferably defined gravitationally above the rectifying section 22.
  • the first inlet system 21 is provided gravitationally between the internal rectifying section 22 and the internal stripping section 24.
  • the overhead space 26 is
  • the optional internal rectifying section 22 may comprise vapour/liquid contact-enhancing means similar to the internal stripping section 24, to further enhance component separation and nitrogen rejection.
  • a reflux system may be arranged to allow at least a reflux portion 36 of the condensed fraction into the nitrogen stripper column 20 at a level above the
  • the reflux system comprises a condensed fraction
  • the condensed fraction splitter 39 fluidly connects the condensed fraction discharge line 37 with the nitrogen stripper column 20, via a reflux portion line 36 and a reflux inlet system 25, and with the liquid recycle line 13.
  • An optional reflux flow valve 32 functionally controlled by a reflux flow controller may preferably be provided in the reflux portion line 36.
  • the liquid recycle line 13 is preferably in liquid communication with the liquid hydrocarbon product line 90 via a recycle path that does not pass through the
  • the liquid recycle line 13 helps to avoid feeding too much liquid onto the rectifying section 22 and to avoid passing the recycle liquid through the rectifying section 22. This is beneficial to avoid disturbing the
  • a cooling duty controller 34 may be provided to control the cooling duty, being the rate at which heat passes from the intermediate vapour to the auxiliary refrigerant stream.
  • the cooling duty being the rate at which heat passes from the intermediate vapour to the auxiliary refrigerant stream.
  • the cooling duty controller 34 is configured to control the cooling duty in response to an indicator of heating value of the off gas relative to a demand for heating power.
  • the cooling duty controller 34 is embodied in the form of a pressure controller PC and the auxiliary refrigerant stream flow control valve 135, which are functionally coupled to each other.
  • a combustion device 220 is suitably arranged on a downstream end of the vapour fraction discharge line 80, to receive at least a fuel portion of the vapour fraction in the vapour fraction discharge line 80.
  • the combustion device may comprise multiple combustion units, and/or it may include for example one or more of a furnace, a boiler, an incinerator, a dual fuel diesel engine, or combinations thereof.
  • a boiler and a duel fuel diesel engine may be coupled to an electric power generator.
  • the amount of methane in the off gas can be any amount of methane in the off gas.
  • a vapour recycle line 87 is optionally configured to receive at least a vaporous recycle portion of the vapour from the overhead discharge line 30.
  • the vapour recycle line 87 bypasses the nitrogen stripper column 20, and feeds back into at least one of the group consisting of: the liquid hydrocarbon product line 90 and the process vapour line 60.
  • a vapour recycle flow control valve 88 is preferably provided in the vapour recycle line 87.
  • a benefit of the proposed vapour recycle line 87 is that it allows for selectively increasing of the nitrogen content in the liquid hydrocarbon product stream 90. If the optional end flash separator 50 is provided, the vapour recycle line 87 suitably feeds into the end flash
  • the configuration of the optional vapour recycle line 87 comprises an optional vapour fraction splitter 89, which may be provided in the vapour fraction line 80, allowing controlled fluid communication between the vapour fraction line 80 and the vapour recycle line 87.
  • a cold recovery heat exchanger 85 may be provided in the vapour fraction discharge line 80, to preserve the cold vested in the vapour fraction 80 by heat exchanging against a cold recovery stream 86 prior to feeding the vapour fraction 80 to any combustion device.
  • the cold recovery stream 86 may comprise or consist of a side stream sourced from the hydrocarbon feed stream in the hydrocarbon feed line 110 of the liquefaction system 100.
  • the resulting cooled side stream may for instance be combined with the
  • the cold recovery stream 86 may comprise or consist of the overhead vapour in the
  • overhead vapour discharge line 30 preferably in the part of the overhead vapour discharge line 30 where through the overhead vapour is passed from the nitrogen stripper column 20 to the overhead condenser 35.
  • the duty required from the auxiliary refrigerant stream 132 in the overhead condenser 35 would be reduced.
  • suitable liquefaction systems can represent any suitable hydrocarbon liquefaction system and/or process, in particular any natural gas liquefaction process producing liquefied natural gas, and the invention is not limited by the specific choice of liquefaction system.
  • suitable liquefaction systems employ single refrigerant cycle processes (usually single mixed refrigerant - SMR - processes, such as PRICO described in the paper "LNG Production on floating platforms” by K R Johnsen and P Christiansen, presented at Gastech 1998 (Dubai), but also possible is a single component refrigerant such as for instance the BHP-cLNG process also described in the afore-mentioned paper by Johnsen and Christiansen) ;
  • C3MR such as described in for instance US Patent 4,404,008, or for instance double mixed
  • refrigerant - DMR - processes of which an example is described in US Patent 6,658,891, or for instance two- cycle processes wherein each refrigerant cycle contains a single component refrigerant); and processes based on three or more compressor trains for three or more
  • any compressor forming part of the hydrocarbon liquefaction process in the liquefaction system is driven by one or more electric motors, without being mechanically driven by any steam- and/or gas turbine.
  • Such compressor may be driven exclusively by one or more electric motors.
  • electric motors as refrigerant compressor drivers. It will be clear that any drivers other than electric motors can be replaced for an electric motor to enjoy the most benefit of the present invention.
  • cryogenic heat exchanger 180 in this case in the form of a coil wound heat exchanger comprising lower and upper hydrocarbon product tube bundles (181 and 182, respectively), lower and upper LMR tube bundles (183 and 184, respectively) and an HMR tube bundle 185.
  • At least one refrigerated hydrocarbon pre-cooling heat exchanger 115 may be provided in the hydrocarbon feed line 110 upstream of the cryogenic heat exchanger 180.
  • a main refrigerant in the form of a mixed
  • the main refrigerant circuit 101 comprises a spent refrigerant line 150, connecting the cryogenic heat exchanger 180 (in this case a shell side 186 of the cryogenic heat exchanger 180) with a main suction end of a main refrigerant compressor 160, and a compressed refrigerant line 120 connecting a main refrigerant compressor 160 discharge outlet with an MR separator 128.
  • One or more heat exchangers are provided in the
  • compressed refrigerant line 120 including in the present example at least one ambient heat exchanger 124 and at least one refrigerated main refrigerant pre-cooling heat exchanger 125.
  • the MR separator 128 is in fluid
  • the at least one refrigerated hydrocarbon pre-cooling heat exchanger 115 and the at least one refrigerated main refrigerant pre-cooling heat exchanger 125 are
  • pre-cooling refrigerant via lines 127 and 126, respectively.
  • the same pre-cooling refrigerant may be shared from the same pre-cooling refrigerant cycle.
  • the at least one refrigerated refrigerant via lines 127 and 126, respectively.
  • hydrocarbon pre-cooling heat exchanger 115 and the at least one refrigerated main refrigerant pre-cooling heat exchanger 125 may be combined into one pre-cooling heat exchanger unit (not shown) .
  • the optional external stripping vapour supply line 74 (if provided) may suitably be connected to the
  • hydrocarbon feed line 110 either at a point upstream of the at least one refrigerated hydrocarbon pre-cooling heat exchanger 115, downstream of the at least one refrigerated hydrocarbon pre-cooling heat exchanger 115, or (for instance possible if two or more refrigerated hydrocarbon pre-cooling heat exchangers are provided) between two consecutive refrigerated hydrocarbon pre- cooling heat exchangers, to be sourced with a part of the hydrocarbon feed stream from the hydrocarbon feed line 110.
  • the HMR tube bundle At a transition point between the upper (182, 184) and lower (181, 183) tube bundles, the HMR tube bundle
  • HMR line 141 is in fluid connection with an HMR line 141 in which an HMR control valve 144 is configured.
  • the HMR line 141 is in fluid communication with the shell side 186 of the cryogenic heat exchanger 180 and, via said shell side 186 and in heat exchanging arrangement with each of one of the lower hydrocarbon product tube bundle 181 and the lower LMR tube bundle 183 and the HMR tube bundle 185, with the spent refrigerant line 150.
  • the LMR tube bundle 184 is in fluid connection with an LMR line 131.
  • a first LMR return line 133 establishes fluid
  • An LMR control valve 134 is configured in the first LMR return line 133.
  • the first LMR return line 133 is in fluid communication with the spent refrigerant line 150, via said shell side 186 and in heat exchanging arrangement with each of one of the upper and lower hydrocarbon product tube bundles 182 and 181, and each one of the LMR tube bundles 183 and 184, and the HMR tube bundle 185.
  • FIG. 2 reveals one possible source of the auxiliary refrigerant.
  • the LMR line 131 is split into the
  • a second LMR return line 138 on an upstream end thereof fluidly connects with the auxiliary refrigerant line 132 via the overhead condenser (for example the overhead condenser 35 of Figure 1, or an integrated internal overhead condenser 235 as depicted in Figure 2), and on a downstream end the second LMR return line 138 ultimately connects with the spent refrigerant line 150, suitably via the first HMR line 141.
  • the overhead condenser for example the overhead condenser 35 of Figure 1, or an integrated internal overhead condenser 235 as depicted in Figure 2
  • vapour recycle line 87 may be provided but have not been reproduced in Figure 2 for purpose of clarity.
  • the overhead condenser 35, the overhead separator 33 and the reflux system have been embodied in the form of the integrated internal overhead condenser 235, which is internally configured within the overhead space 26 in the nitrogen stripper column 20.
  • Such internal overhead condenser 235 is known in the art.
  • the liquid recycle line 13 is provided in liquid communication with a partial liquid draw off tray 27 provided inside the nitrogen stripper column 20 gravitationally above the rectifying section 22 and below the internal overhead condenser 235.
  • the partial liquid draw off tray 27 functions equivalently to the condensed fraction splitter 39 of Figure 1.
  • the condenser is preferably arranged in fluid communication with both the vapour bypass line 76 and the overhead space 26 of the nitrogen stripper column 20, whereby the intermediate vapour passing through the condenser preferably comprises both the non-stripping portion from the vapour bypass line 76 and the overhead vapour obtained from the overhead space 26 of the
  • the apparatus and method for removing nitrogen from a cryogenic hydrocarbon composition comprising a nitrogen- and methane-containing liquid phase may be operated as follows .
  • a cryogenic hydrocarbon composition 8 comprising a nitrogen- and methane-containing liquid phase is
  • the cryogenic hydrocarbon composition 8 may be obtained from natural gas or petroleum reservoirs or coal beds. As an alternative the cryogenic hydrocarbon composition 8 may also be obtained from another source, including as an example a synthetic source such as a Fischer-Tropsch process. Preferably the cryogenic hydrocarbon composition 8 comprises at least 50 mol% methane, more preferably at least 80 mol% methane.
  • the temperature of lower than -130 °C can be achieved by passing a hydrocarbon feed stream 110 through the liquefaction system 100.
  • the hydrocarbon feed stream 110 comprising a hydrocarbon-containing feed vapour may be heat exchanged, for example in the cryogenic heat
  • the desired cryogenic hydrocarbon composition 8 may then be obtained from the raw liquefied stream 1.
  • the main refrigerant stream may be generated by cycling the main refrigerant in the main refrigerant circuit 101, whereby spent refrigerant 150 is compressed in the main refrigerant compressor 160 to form a
  • the light refrigerant fraction 121 is passed via successively the lower LMR bundle 183 and the upper LMR bundle 184 through the cryogenic heat exchanger 180, while the heavy refrigerant fraction 122 is passed via the HMR bundle 185 through the cryogenic heat exchanger 180 to the transition point. While passing through these respective tube bundles, the respective light- and heavy refrigerant fractions are cooled against the light and heavy refrigerant fractions that are evaporating in the shell side 186 again producing spent refrigerant 150 which completes the cycle. Simultaneously, the
  • hydrocarbon feed stream 110 passes through the cryogenic heat exchanger 180 via successively the lower hydrocarbon bundle 181 and the upper hydrocarbon bundle 182 and is being liquefied and sub-cooled against the same
  • the hydrocarbon feed stream 110 may contain varying amounts of components other than methane and nitrogen, including one or more non- hydrocarbon components other than water, such as CO 2 , Hg, H 2 S and other sulphur compounds; and one or more
  • hydrocarbons heavier than methane such as in particular ethane, propane and butanes, and, possibly lesser amounts of pentanes and aromatic hydrocarbons.
  • Hydrocarbons with a molecular mass of at least that of propane may herein be referred to as C3+ hydrocarbons
  • hydrocarbons with a molecular mass of at least that of ethane may herein be referred to as C2+ hydrocarbons.
  • the hydrocarbon feed stream 110 may have been pre-treated to reduce and/or remove one or more of undesired components such as CO 2 and H 2 S, or have
  • composition of the hydrocarbon feed stream 110 thus varies depending upon the type and location of the gas and the applied pre-treatment ( s ) .
  • the raw liquefied stream 1 may comprise between from 1 mol% to 5 mol% nitrogen, be at a raw temperature of between from -165 °C to -120 °C and typically at a liquefaction pressure of between from 15 bara to 120 bara. In many cases, the raw temperature may be between from -155 °C to -140 °C. Within this more narrow range the cooling duty needed in the liquefaction system 100 is lower than when lower temperatures are desired, while the amount of sub-cooling at the pressure of above 15 bara is sufficiently high to avoid excessive production of flash vapours upon depressurizing to between 1 and 2 bara.
  • the cryogenic hydrocarbon composition 8 may be obtained from the raw liquefied stream 1 by main
  • a first nitrogen stripper feed stream 10 is derived from the cryogenic hydrocarbon composition 8, and fed into the nitrogen stripper column 20 at a stripping pressure via the first inlet system 21.
  • the stripping pressure is usually equal to or lower than the initial pressure.
  • the stripping pressure in preferred embodiments is selected in a range of between 2 and 15 bar absolute.
  • the stripping pressure is at least 4 bara, because with a somewhat higher stripping pressure the stripping vapour in stripping vapour line 71 can benefit from some additional enthalpy
  • the stripping pressure is at most 8 bara in order to facilitate the separation efficiency in the nitrogen stripper column 20. Moreover, if the stripping pressure is within a range of between from 4 to 8 bara, the off gas in the vapour fraction line 80 can readily be used as so-called low pressure fuel stream without a need to further compress.
  • the raw temperature of the raw liquefied stream 1 was -161 °C while the liquefaction pressure was 55 bara.
  • the main depressurization may be effected in two stages: first a dynamic stage using the expansion turbine 6 to reduce the pressure from 55 bara to about 10 bara, followed by a further depressurization in a static stage using the Joule Thomson valve 7 to a pressure of 7 bara.
  • the stripping pressure in this case was assumed to be 6 bara.
  • An overhead vapour stream 30 is obtained from the overhead space 26 of the nitrogen stripping column 20.
  • a vapour fraction 80 obtained from the overhead vapour stream 30, and comprising a discharge fraction of the overhead vapour 30, is discharged as off gas.
  • at least a fuel portion of the vapour fraction 80 is passed to the combustion device 220 at a fuel gas pressure that is not higher than the stripping pressure.
  • a nitrogen-stripped liquid 40 is drawn from the sump space 26 of the nitrogen stripper column 20.
  • temperature of the nitrogen-stripped liquid 40 is typically higher than that of the first nitrogen stripper feed stream 10. Typically, it is envisaged that the temperature of the nitrogen-stripped liquid 40 is higher than that of the first nitrogen stripper feed stream 10 and between -140 °C and -80 °C, preferably between
  • the flash pressure that is lower than the stripping pressure, suitably in a range of between from 1 and 2 bar absolute.
  • the flash pressure suitably in a range of between from 1 and 2 bar absolute.
  • stripping vapour in stripping vapour line 71 can benefit from some additional heat of compression that is added to the process stream 60 in the process compressor 260.
  • the intermediate depressurizer 45 may be controlled by the level controller LC, set to increase the flow rate through the intermediate depressurizer if the level of liquid accumulated in the sump space 26 of the nitrogen stripper column 20 increases above a target level. As a result of the depressurization, the temperature is generally lowered to below -160 °C.
  • hydrocarbon product stream 90 that is produced hereby can typically be kept at an atmospheric pressure in an open insulated cryogenic storage tank.
  • Process vapour 60 is produced as well.
  • the process vapour 60 may comprise flash vapour 64 that is often generated upon the depressurization of the nitrogen- stripped liquid 40 and/or depressurization of a bypass feed stream 11 (further discussed later herein below) .
  • the first nitrogen stripper feed stream 10 comprises a first portion of the cryogenic hydrocarbon composition 8. It may contain all of the cryogenic hydrocarbon composition 8, but in practice it is preferred to split the cryogenic hydrocarbon composition 8 into the first portion 10 and a second portion 11 having the same composition and phase as the first portion 10.
  • the second portion is preferably diverted, in form of the bypass feed stream, from the stripping pressure side to a suitable location on the flash pressure side.
  • the split ratio defined as the flow rate of the second portion relative to the flow rate of the cryogenic hydrocarbon composition in the cryogenic hydrocarbon composition line 8, may be controlled using the bypass stream flow control valve 15.
  • This bypass stream flow control valve 15 may be controlled by the flow controller FC to maintain a predetermined target flow rate of the first nitrogen stripper feed stream 10 into the nitrogen stripper column 20.
  • the flow controller FC will increase the open fraction of the bypass stream flow control valve
  • the split ratio may
  • the cryogenic hydrocarbon composition 8 advantageously be selected between 50 % and 95 %.
  • the lower values are typically recommended for higher content of nitrogen in the cryogenic hydrocarbon composition, while higher values are preferred for lower content of nitrogen.
  • the content of nitrogen in the cryogenic hydrocarbon composition 8 was 3.0 mol% whereby the selected split ratio was 75%.
  • the second portion originating from the initial stream splitter 9 is also be depressurized to said flash pressure, before subsequently feeding it into at least one of the group consisting of: the nitrogen-stripped liquid discharge line 40, the liquid hydrocarbon product line 90 and the process vapour line 60; while bypassing the nitrogen stripper column 20.
  • the optional second portion is passed into the optional end flash separator 50.
  • the process vapour 60 may comprise boil-off gas.
  • Boil-off gas 230 typically results from adding of heat to the liquid hydrocarbon product stream 90 whereby a part of the liquid hydrocarbon product stream 90 evaporates to form the boil-off gas.
  • the generation of boil-gas can exceed the flow rate of flash vapour by multiple times, particularly during operating the plant in so-called loading mode, and hence it is an important benefit to not only re-condense the flash vapour but to re-condense the boil-off gas as well, if there is not enough on-site demand for heating power to use all of the methane contained in the boil-off gas.
  • the optional boil-off gas supply line 230 connects a vapour space in the cryogenic storage tank 210 with the process vapour line 60.
  • the nitrogen-stripped liquid after its depressurization is fed into the optional end flash separator where it is phase separated at a flash
  • the flash separation pressure is equal to or lower than the flash pressure, and suitably lies in the range of between from 1 to 2 bar absolute into the liquid hydrocarbon product stream 90 and the flash vapour 64. In one embodiment the flash separation pressure is envisaged to be 1.05 bara.
  • the process vapour 60 is compressed to at least the stripping pressure, thereby obtaining a compressed vapour stream 70.
  • a stripping vapour stream 71 is obtained from the compressed vapour stream 70, and passed into the nitrogen stripper column 20 via the second inlet system 23. This stripping vapour can percolate upward through the stripping section 23 in contacting counter current with liquids percolating downward through the stripping section 23.
  • an external stripping vapour may selectively be fed into the nitrogen stripper column 20 via the second inlet system 23.
  • major disruption of the nitrogen stripper column 20 may be avoided, for instance, in case the process compressor 260 is not functioning to provide the compressed vapour stream 70 in sufficient amounts .
  • Obtaining of the stripping vapour stream 71 from the compressed vapour stream 70 involves selectively splitting the compressed vapour stream 70 into a
  • the non- stripping portion comprises a bypass portion of the compressed vapour, which bypass portion may herein below also be referred to as vapour bypass portion. It does not contain the stripping portion.
  • the stripping vapour stream 71 contains at least the stripping portion.
  • the selective injection may be controlled using the vapour bypass control valve 77.
  • the vapour bypass control valve 77 is controlled by a pressure controller on the compressed vapour line 70, which is set to increase the open fraction of the vapour bypass control valve 77 in response to an increasing pressure in the compressed vapour line 70.
  • the flow rate of the vapour bypass portion that is allowed to flow through the vapour bypass line 76 into the overhead vapour stream 30 is particularly high during so-called loading mode at which time usually the amount of boil-off gas is much higher than in is usually the case during so- called holding mode.
  • the vapour bypass control valve 77 is fully closed during normal operation in holding mode.
  • a partially condensed intermediate stream is formed from an intermediate vapour by passing the intermediate vapour through the condenser.
  • the intermediate vapour also contains the overhead vapour 30. This may be achieved by selectively injecting the non-stripping portion of the compressed vapour into the overhead vapour stream 30, thereby forming the intermediate vapour.
  • the forming of the partially condensed intermediate stream suitably involves indirectly heat exchanging the intermediate vapour against the auxiliary refrigerant stream 132 and partially condensing the intermediate vapour, whereby heat is passed from the intermediate vapour to the auxiliary refrigerant stream 132 at a selected cooling duty.
  • the resulting partially condensed intermediate stream comprises a condensed fraction containing an excess liquid, and a vapour fraction.
  • fraction contains the bypass portion from the compressed vapour, which remains in the vapour phase throughout the partially condensing.
  • the condensed fraction is separated from the vapour fraction in the overhead separator 33, at a separation pressure that may be lower than the stripping pressure, and preferably lies in a range of between 2 and 15 bar absolute.
  • the vapour fraction is discharged via the vapour fraction discharge line 80 as off gas.
  • the condensed fraction is discharged from the overhead separator 33 into a reflux system, for instance via the condensed fraction discharge line 37.
  • the bypass portion bypasses the at least one internal stripping section 24.
  • the bypass portion does not pass through the at least one internal stripping section 24.
  • bypass portion bypasses not only the stripping section 24 but the entire nitrogen stripper column 20, such as is shown in the embodiment of Figure 1.
  • At least part of the condensed fraction discharged from the overhead separator 33 is led into the liquid recycle line 13 to form a liquid recycle portion.
  • the recycle valve 14 may suitably be controlled using a flow controller provided in the condensed fraction discharge line 37 and/or a level controller provided on the
  • the liquid recycle portion contains at least part of the excess liquid. At least part of liquid recycle portion is returned to the liquid hydrocarbon product stream, while keeping this at least part in liquid phase. This may be done by feeding the liquid recycle portion into at least one of the group consisting of: the nitrogen stripper column 20, the cryogenic hydrocarbon composition 8, the first nitrogen stripper feed stream 10, the optional bypass feed stream
  • the condenser which in the embodiment of Figure 1 is embodied in the form of the overhead condenser 35, thus allows for re-condensation of vaporous methane that has previously formed part of the raw liquefied product 1 (or the cryogenic hydrocarbon composition 8), by adding any such vaporous methane containing stream to the
  • the methane is condensed to the extent that it is in excess of a target amount of methane in the discharged vapour fraction 80.
  • the vaporous methane can find its way to the heat exchanging with the auxiliary refrigerant 132 by which it is selectively condensed out of the overhead vapour 30 from the nitrogen stripper column 20, while allowing the majority of the nitrogen to be discharged with the off gas.
  • the vapour fraction 80 in the off gas generally has a heating value.
  • the heating value of the vapour fraction 80 being discharged is suitably regulated by adjusting the cooling duty in the overhead condenser 35. This may be done by the cooling duty controller 34. By adjusting the cooling duty at which heat is passed from the
  • the relative amount of methane in the off gas can be
  • discharged vapour fraction can be regulated to match with a specific demand of heating power. This renders the off gas suitable for use as fuel gas stream, even in
  • the heating value may be regulated to match with an actual demand of heating power by the combustion device 220.
  • the heating value being regulated may be selected in accordance with the appropriate circumstances of the intended use of the off gas as fuel gas.
  • the heating value may be determined in accordance with DIN 51857 standards.
  • the heating value being regulated may be proportional to the lower heating value (LHV; sometimes referred to as net calorific value) , which may be defined as the amount of heat released by combusting a specified quantity (initially at 25°C) and returning the temperature of the combustion products to 150°C. This assumes the latent heat of vaporization of water in the reaction products is not recovered.
  • LHV lower heating value
  • cooling duty reflects the rate at which heat is exchanged in the condenser, which can be expressed in units of power (e.g. Watt or MWatt) .
  • the cooling duty is related to the flow rate of the auxiliary refrigerant being subjected to the heat exchanging against the overhead vapour.
  • the cooling duty is automatically
  • vapour fraction is passed to one or more selective consumers of methane, such as for instance the combustion device 220 shown in Figure 1, the controlling can be done in response to the demanded heating power, whereby the partial flow rate of methane is controlled to achieve a heating value that matches the demand.
  • auxiliary refrigerant stream flow control valve 135 may be controlled by the pressure controller PC to maintain a predetermined target flow rate of auxiliary refrigerant stream 132 through the overhead condenser 35.
  • the pressure controller PC will be set to decrease the open fraction of the auxiliary refrigerant stream flow control valve 135 when the pressure drops below a pre-determined target level, which is indicative of a higher consumption rate of methane than supply rate in the vapour fraction 80. Conversely, the pressure controller PC will be set to increase the open fraction of the auxiliary refrigerant stream flow control valve 135 when the pressure exceeds the pre-determined target level .
  • the vapour fraction 80 is envisaged to contain between from 50 mol% to 95 mol% of nitrogen, preferably between from 70 mol% to 95 mol% of nitrogen or between from 50 mol% to 90 mol% of nitrogen, more preferably between from 70 mol% to 90 mol% of nitrogen, still more preferably from 75 mol% to 95 mol% of nitrogen, most preferably from 75 mol% to 90 mol% of nitrogen.
  • the condensed fraction 37 is contemplated to contain less than 35 mol% of nitrogen.
  • the auxiliary refrigerant 132 stream preferably has a bubble point under standard conditions at a lower
  • the auxiliary refrigerant may contain between from 5 mol% to 75 mol% of nitrogen.
  • the auxiliary refrigerant stream is formed by a slip stream of the main refrigerant stream, more preferably by a slip stream of the light refrigerant fraction. This latter case is illustrated in Figure 2 but may also be applied in the embodiment of Figure 1.
  • Such a slip stream may conveniently be passed back into the main refrigerant circuit via the shell side 186 of the cryogenic heat exchanger 180, where it may still assist in withdrawing heat from the stream in the upper and/or lower tube bundles .
  • a contemplated composition of the auxiliary refrigerant contains between 25 mol% and
  • auxiliary refrigerant contains at least 95% of these constituents and/or the total of nitrogen and methane is at least 65 mol%.
  • a composition within these ranges is may be readily available from the main
  • refrigerant circuit if a mixed refrigerant is employed for sub-cooling of the liquefied hydrocarbon stream.
  • the overhead vapour stream 30 is preferably obtained from an overhead space of the nitrogen stripping column 20 above the rectifying section 22.
  • the condensed fraction may pass through into the nitrogen stripper column 20 via the reflux inlet system 25.
  • the reflux portion is suitably obtained from the condensed fraction and charged into the nitrogen stripper column 20 via the optional reflux pump 38
  • the reflux portion may contain all of the condensed fraction, but optionally, the condensed fraction is split in the optionally provided condensed fraction splitter 39 into a liquid recycle portion which is charged via liquid recycle line 13 into, for instance, the first feed stream 10, and the reflux portion which is charged into the nitrogen stripper column 20 via reflux inlet system 25 and reflux portion line 36.
  • the capability of splitting the condensed fraction into the reflux portion 36 and the liquid recycle portion 13 is beneficial to divert any excess liquid of the condensed fraction around the rectifying section 22 as a liquid recycle, such as not to upset the operation of the rectifying section 22.
  • the liquid recycle portion is recycled into the nitrogen stripper column 20, bypassing of the internal rectifying section
  • the partially condensing may also involve direct and/or indirect heat exchanging with other streams in other consecutively arranged overhead heat exchangers.
  • the cold recovery heat exchanger 85 may be such an overhead heat exchanger whereby the partially condensing of the overhead stream further comprises indirect heat exchanging against the vapour fraction 80.
  • the optional vapour recycle line 87 may be
  • the target amount of nitrogen dissolved in the liquid hydrocarbon product stream 90 is between 0.5 and 1 mol%, preferably as close to 1.0 mol% as possible yet not exceeding 1.1 mol%.
  • the vapour recycle flow control valve 88 regulates the amount of the vapour fraction stream 80 that is fed back into, for instance, the end flash separator 50 while bypassing the nitrogen stripper column 20.
  • the amount of nitrogen in the liquid hydrocarbon product stream 90 can be influenced.
  • the vapour recycle flow control valve 88 may be controlled in response to a signal from a quality measurement instrument QMI that is optionally provided in the liquid hydrocarbon product line 90.
  • the proposed method and apparatus are specifically suitable for application in combination with a
  • hydrocarbon liquefaction system such as a natural gas liquefaction system, in order to remove nitrogen from the raw liquefied product. It has been found that even when the raw liquefied product - or the cryogenic hydrocarbon composition - contains a fairly high amount of from 1 mol% (or from about 1 mol%) up to 5 mol% (or up to about 5 mol%) of nitrogen, the resulting liquid hydrocarbon product can meet a nitrogen content within a
  • the remainder of the nitrogen is discharged as part of the vapour fraction in the off gas, together with a controlled amount of methane.
  • the presently proposed method and apparatus are most beneficial when the raw liquefied product, or the cryogenic hydrocarbon composition, contains from 1.5 mol%, preferably from 1.8 mol%, up to 5 mol% of nitrogen.
  • Existing alternative approaches may also work adequately when the nitrogen content is below about 1.8 mol% and/or below about 1.5 mol%.
  • cryogenic hydrocarbon composition 8 was assumed to consist for more than 90 mol% of a mixture of nitrogen and methane
  • the amount of nitrogen (1.654 mol%) and methane (98.204 mol%) is more than
  • the amount of methane in the discharged vapour fraction 80 could be kept at about 80 mol% and well within the range of between 10 mol% and 25 mol% while at the same time the nitrogen content in the liquid
  • hydrocarbon product stream 90 was kept within the target of close to 1.0 mol% and not exceeding 1.1 mol%.
  • boil-off gas consisting of about 17 mol% nitrogen and 83 mol% methane was added to the process via the boil-off gas supply line 230, while in loading mode this was about 4.4 kg/s.
  • the liquefaction system 100 in the calculation used a line up as shown in Figure 2 with a mixed refrigerant in the compressed refrigerant line 120 with a composition as listed in Table 3 in the column labelled "120".
  • mixed refrigerant composition
  • the pressure in the compressed refrigerant line 120 was 58 bara, in loading mode higher, 61 bara.
  • the aggregated pressure drop in the lower and upper LMR tube bundles (183 and 184, respectively) of the cryogenic heat exchanger is 13 bar in both cases.
  • the pressure drop imposed by the auxiliary refrigerant stream flow control valve 135 was 39 bar in the holding mode case and 42 bar in the loading mode operation so that the shell pressure in shell side 186 of the cryogenic heat exchanger 180 was the same for both the holding mode as the loading mode.
  • the relative flow rate of the auxiliary refrigerant stream 132 consisted of 11 % of the total LMR flow rate in LMR line 131. In loading mode this was 18 %. Also the actual flow rate was 1.6x higher than in the holding mode case, but the separation between HMR and LMR in MR separator 128 was made to favour HMR a little bit more in the loading mode operation than in the holding mode operation .
  • cryogenic hydrocarbon composition was assumed to contain no hydrocarbons heavier than methane (C2+ hydrocarbons), such as could be the case if the cryogenic hydrocarbon composition is derived from non-conventional gas sources, such as coal bed methane, shale gas, or perhaps certain synthetic sources.
  • non-conventional gas sources such as coal bed methane, shale gas, or perhaps certain synthetic sources.
  • the proposed methods and apparatus may also be applied where the cryogenic hydrocarbon
  • composition would contain up to about 15 mol% of C2+ hydrocarbons, including one or more selected from the group consisting of ethane, propane, i-butane, n-butane, and pentane. In essence these additional C2+

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Abstract

De l'azote est retiré d'une composition d'hydrocarbures cryogéniques. Au moins une première partie de la composition d'hydrocarbures cryogéniques est introduite dans une colonne de strippage d'azote en tant que premier courant de strippage d'azote. Un liquide qui a subi un strippage d'azote est soutiré de la colonne de strippage d'azote. Un courant de produit d'hydrocarbures liquides et une vapeur de traitement sont produits comprenant au moins une étape de dépressurisation du liquide qui a subi un strippage d'azote à une pression éclair. La vapeur de traitement est comprimée, et séparée de manière sélective en une partie de strippage et une partie de non-strippage. Un courant de vapeur de strippage comprenant au moins la partie de strippage est amené à passer à travers la colonne de strippage d'azote. Une fraction de vapeur est déchargée en tant que gaz d'échappement, comprenant une fraction de décharge de la vapeur de tête provenant de la colonne de strippage d'azote et comprenant au moins la partie de dérivation provenant de la partie de non-strippage de la vapeur compressée, qui contourne une section de strippage positionnée dans la colonne de strippage d'azote.
PCT/EP2012/074957 2011-12-12 2012-12-10 Procédé et appareil pour retirer l'azote d'une composition d'hydrocarbures cryogéniques WO2013087569A2 (fr)

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CN201280061161.0A CN103988035A (zh) 2011-12-12 2012-12-10 用于从低温烃类组合物中去除氮气的方法和装置
KR1020147019092A KR20140103144A (ko) 2011-12-12 2012-12-10 극저온 탄화수소 조성물로부터 질소를 제거하기 위한 방법 및 장치
EP12799178.4A EP2791601B1 (fr) 2011-12-12 2012-12-10 Procédé et appareil pour retirer l'azote d'une composition d'hydrocarbures cryogéniques
JP2014546441A JP2015501917A (ja) 2011-12-12 2012-12-10 極低温の炭化水素組成物から窒素を除去するための方法と装置
RU2014128669A RU2607198C2 (ru) 2011-12-12 2012-12-10 Способ и устройство для удаления азота из криогенной углеводородной композиции
CA2858152A CA2858152C (fr) 2011-12-12 2012-12-10 Procede et appareil pour retirer l'azote d'une composition d'hydrocarbures cryogeniques
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JP2015210077A (ja) * 2014-04-24 2015-11-24 エア プロダクツ アンド ケミカルズ インコーポレイテッドAir Products And Chemicals Incorporated 中間供給ガス分離を使用した液化された天然ガスの生産における統合された窒素除去
JP2015210078A (ja) * 2014-04-24 2015-11-24 エア プロダクツ アンド ケミカルズ インコーポレイテッドAir Products And Chemicals Incorporated 貢献する再注入回路を使用した液化天然ガスの生成における統合された窒素除去
JP2015210079A (ja) * 2014-04-24 2015-11-24 エア プロダクツ アンド ケミカルズ インコーポレイテッドAir Products And Chemicals Incorporated 冷却ヒートポンプを使用する液化された天然ガスの生産における統合された窒素の除去
EP3611454A1 (fr) * 2018-08-14 2020-02-19 Air Products And Chemicals, Inc. Liquéfaction de gaz naturel à élimination d'azote intégré

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AU2012350742B2 (en) 2015-08-20
MY172968A (en) 2019-12-16
RU2014128669A (ru) 2016-02-10
JP2015501917A (ja) 2015-01-19
EP2791601A2 (fr) 2014-10-22
KR20140103144A (ko) 2014-08-25
EP2791601B1 (fr) 2020-06-24
WO2013087569A3 (fr) 2014-05-01
RU2607198C2 (ru) 2017-01-10
AU2012350742A1 (en) 2014-05-22
CN103988035A (zh) 2014-08-13
CA2858152A1 (fr) 2013-06-20

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