NO329177B1 - Process and system for forming liquid LNG - Google Patents

Process and system for forming liquid LNG Download PDF

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Publication number
NO329177B1
NO329177B1 NO20073245A NO20073245A NO329177B1 NO 329177 B1 NO329177 B1 NO 329177B1 NO 20073245 A NO20073245 A NO 20073245A NO 20073245 A NO20073245 A NO 20073245A NO 329177 B1 NO329177 B1 NO 329177B1
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NO
Norway
Prior art keywords
gas
cooling
heat exchanger
fractionation column
accordance
Prior art date
Application number
NO20073245A
Other languages
Norwegian (no)
Other versions
NO20073245L (en
Inventor
Inge Sverre Lund Nilsen
Original Assignee
Kanfa Aragon As
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 Kanfa Aragon As filed Critical Kanfa Aragon As
Priority to NO20073245A priority Critical patent/NO329177B1/en
Priority to KR1020107001622A priority patent/KR101568763B1/en
Priority to EP08779082A priority patent/EP2165140A1/en
Priority to CN200880021514.8A priority patent/CN101711335B/en
Priority to US12/665,329 priority patent/US20100132405A1/en
Priority to AU2008283102A priority patent/AU2008283102B2/en
Priority to CA002692213A priority patent/CA2692213A1/en
Priority to PCT/NO2008/000229 priority patent/WO2009017414A1/en
Priority to MYPI20095466A priority patent/MY163902A/en
Priority to BRPI0813297-6A2A priority patent/BRPI0813297A2/en
Publication of NO20073245L publication Critical patent/NO20073245L/en
Publication of NO329177B1 publication Critical patent/NO329177B1/en

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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
    • F25J1/02—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.
    • F25J1/0285—Combination of different types of drivers mechanically coupled to the same refrigerant compressor, possibly split on multiple compressor casings
    • F25J1/0288—Combination of different types of drivers mechanically coupled to the same refrigerant compressor, possibly split on multiple compressor casings using work extraction by mechanical coupling of compression and expansion of the refrigerant, so-called companders
    • 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
    • B01D3/14—Fractional distillation or use of a fractionation or rectification column
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
    • C10L3/00—Gaseous fuels; Natural gas; Synthetic natural gas obtained by processes not covered by subclass C10G, C10K; Liquefied petroleum gas
    • C10L3/06—Natural gas; Synthetic natural gas obtained by processes not covered by C10G, C10K3/02 or C10K3/04
    • C10L3/08—Production of synthetic natural gas
    • 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
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    • 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
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    • 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"
    • F25J1/0035—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 gas expansion with extraction of work
    • F25J1/0037—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 gas expansion with extraction of work of a return stream
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    • 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
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    • 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
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    • 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
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/006—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the refrigerant fluid used
    • F25J1/007—Primary atmospheric gases, mixtures thereof
    • F25J1/0072—Nitrogen
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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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    • F25J1/006—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the refrigerant fluid used
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    • F25J1/0082—Methane
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    • F25J1/0092—Mixtures of hydrocarbons comprising possibly also minor amounts of nitrogen
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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
    • F25J1/0238—Purification or treatment step is integrated within one refrigeration cycle only, i.e. the same or single refrigeration cycle provides feed gas cooling (if present) and overhead gas cooling
    • 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
    • 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
    • F25J1/0241—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 wherein the overhead cooling comprises providing reflux for a fractionation step
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
    • F25J1/0257—Construction and layout of liquefaction equipments, e.g. valves, machines
    • F25J1/0275—Construction and layout of liquefaction equipments, e.g. valves, machines adapted for special use of the liquefaction unit, e.g. portable or transportable devices
    • F25J1/0277—Offshore use, e.g. during shipping
    • F25J1/0278—Unit being stationary, e.g. on floating barge or fixed platform
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
    • F25J1/0279—Compression of refrigerant or internal recycle fluid, e.g. kind of compressor, accumulator, suction drum etc.
    • F25J1/0294—Multiple compressor casings/strings in parallel, e.g. split arrangement
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • 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
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2210/00—Processes characterised by the type or other details of the feed stream
    • F25J2210/06—Splitting of the feed stream, e.g. for treating or cooling in different ways
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2220/00—Processes or apparatus involving steps for the removal of impurities
    • F25J2220/60—Separating impurities from natural gas, e.g. mercury, cyclic hydrocarbons
    • F25J2220/64—Separating heavy hydrocarbons, e.g. NGL, LPG, C4+ hydrocarbons or heavy condensates in general
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/14—External refrigeration with work-producing gas expansion loop
    • F25J2270/16—External refrigeration with work-producing gas expansion loop with mutliple gas expansion loops of the same refrigerant
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/90—External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration

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Description

Den foreliggende oppfinnelse vedrører en fremgangsmåte til fremstilling av LNG fra en inngående fødegass på en onshore eller offshore installasjon slik det framgår av innledningen i det selvstendige krav 1. The present invention relates to a method for the production of LNG from an incoming feed gas on an onshore or offshore installation as is apparent from the introduction in the independent claim 1.

Oppfinnelsen vedrører også et system for utførelse av fremgangsmåten omfattende en fraksjoneringskolonne for innføring av en fødegass, et varmevekslersystem for nedkjøling og delvis kondensering av fraksjoneringskolonnens overhead gasstrøm, en separator for å separere tofasestrømmen fra varmeveksiersystemet, innretning for tilbakeføring av væske fra separatoren til fraksjoneringskolonnen og innføring av denne væsken i kolonnens øver del som refluks, og innretning for å føre gassen fra separatoren tilbake til varmeveksiersystemet for videre nedkjøling og flytendegjøring til LNG. Jfr. slik det framgår av innledningen i det selvstendige systemkrav 11. The invention also relates to a system for carrying out the method comprising a fractionation column for the introduction of a feed gas, a heat exchanger system for cooling and partial condensation of the overhead gas flow of the fractionation column, a separator for separating the two-phase flow from the heat exchange system, device for returning liquid from the separator to the fractionation column and introduction of this liquid in the upper part of the column as reflux, and equipment to lead the gas from the separator back to the heat exchanger system for further cooling and liquefaction into LNG. Cf. as can be seen from the introduction in the independent system requirement 11.

Med oppfinnelsen tar man sikte på å anvende en lukket gassekspansjonsprosess for å flytendegjøre naturgassen, og ved at gassen først føres gjennom en fraksjoneringskolonne hvor gassen kjøles og separeres til en overheadfraksjon med redusert innhold av pentan (C5) og tyngre komponenter, og en bunnfraksjon anriket med de tyngre hydrokarbonene, videre ved at fraksjoneringskolonnens refluks genereres som en integrert del av systemet for flytendegjøring ved at overheadgassen kondenseres delvis. Ved å utføre flytendegjøringen i samsvar med oppfinnelsen oppnås produksjon av flytende gass med maksimalt innhold av etan og LPG (flytende petroleumsgass) samtidig som virkningsgraden til gassekspansjonsprosessen økes, og bi-produksjon av ustabil/flyktig væske med høyt innhold av etan, LPG og pentan minimeres. The invention aims to use a closed gas expansion process to liquefy the natural gas, and by first passing the gas through a fractionation column where the gas is cooled and separated into an overhead fraction with a reduced content of pentane (C5) and heavier components, and a bottom fraction enriched with the heavier hydrocarbons, further by the fractionation column reflux being generated as an integral part of the liquefaction system by partially condensing the overhead gas. By performing the liquefaction in accordance with the invention, the production of liquefied gas with a maximum content of ethane and LPG (liquefied petroleum gas) is achieved at the same time as the efficiency of the gas expansion process is increased, and by-production of unstable/volatile liquid with a high content of ethane, LPG and pentane is minimized .

Oppfinnelsen omfatter spesielt en fremgangsmåte og et system for flytendegjøring av naturgass eller annen hydrokarbongass fra gassfelt eller fra gass/oljefelt, hvor det er hensiktsmessig å flytendegjøre gassen for å muliggjøre transport av gassen fra kilden til markedet. Dette er spesielt relevant for olje/gassfelt til havs. The invention includes in particular a method and a system for liquefying natural gas or other hydrocarbon gas from gas fields or from gas/oil fields, where it is appropriate to liquefy the gas to enable transport of the gas from the source to the market. This is particularly relevant for offshore oil/gas fields.

Med naturgass menes her en blanding av hydrokarboner der en vesentlig andel består av metan. Naturgass flytendegjøres vanligvis ved at gassen blir kraftig nedkjølt slik at den kondenserer og blir til væske. Med LPG menes flytende petroleumsgass som omfatter propan og butaner (C4, C4 komponenter). By natural gas is meant here a mixture of hydrocarbons in which a significant proportion consists of methane. Natural gas is usually liquefied by the gas being greatly cooled so that it condenses and becomes a liquid. LPG means liquefied petroleum gas which includes propane and butanes (C4, C4 components).

Formålet med oppfinnelsen er å gjøre flytendegjøring av gassen energieffektiv samtidig som: -prosessen beholdes enkel slik at utstyret kan benyttes offshore, og da spesielt på flytende installasjoner -bi-produksjonen av kondensat under flytendegjøringen minimeres effektiviteten maksimeres, og slik at brenngassbehovet minimeres. The purpose of the invention is to make liquefaction of the gas energy efficient while: - the process is kept simple so that the equipment can be used offshore, and then especially on floating installations - the by-production of condensate during liquefaction is minimized, the efficiency is maximized, and so that the need for fuel gas is minimized.

Fremgangsmåten ifølge karakteristikken i krav 1, er kjennetegnet ved de følgende trinn: 1) at fødegassen ledes gjennom en fraksjoneringskolonne (150) hvor den kjøles og separeres i en overheadfraksjon med redusert innhold av pentan (C5) og tyngre komponenter, og en bunnfraksjon anriket med tyngre hydrokarboner, 2) at fraksjoneringskolonnens overheadfraksjon ledes inn i et varmevekslersystem (110) og underkastes en delvis kondensering til dannelse av et tofasefluid, og i en egnet separator (160) separeres tofasefluidet til en væske (5) rik på LPG og pentan (C3-C5) som resirkuleres som kald refluks til fraksjoneringskolonnen (150), mens gassen (6) inneholdende lavere mengder av C5-hydrokarbon og hydrokarboner tyngre enn C5, avledes for videre behandling i varmeveksiersystemet (110) for flytendegjøring til LNG med maksimalt innhold av etan og LPG, og 3) at kjølekretsen for flytendegjøring av gass i varmeveksiersystemet omfatter en åpen eller lukket gassekspansjonsprosess med minst ett gassekspansjonstrinn. The method according to the characteristic in claim 1 is characterized by the following steps: 1) that the feed gas is led through a fractionation column (150) where it is cooled and separated into an overhead fraction with a reduced content of pentane (C5) and heavier components, and a bottom fraction enriched with heavier hydrocarbons, 2) that the overhead fraction of the fractionation column is fed into a heat exchanger system (110) and subjected to a partial condensation to form a two-phase fluid, and in a suitable separator (160) the two-phase fluid is separated into a liquid (5) rich in LPG and pentane (C3 -C5) which is recycled as cold reflux to the fractionation column (150), while the gas (6) containing lower amounts of C5 hydrocarbon and hydrocarbons heavier than C5, is diverted for further treatment in the heat exchanger system (110) for liquefaction into LNG with a maximum content of ethane and LPG, and 3) that the cooling circuit for gas liquefaction in the heat exchanger system includes an open or closed gas expansion process with at least one gas sexpantion step.

De foretrukne utførelsene av fremgangsmåten er definert i de uselvstendige kravene 2-10. The preferred embodiments of the method are defined in the independent claims 2-10.

Systemet ifølge oppfinnelsen er kjennetegnet ved at kjølesystemet som benyttes for nedkjøling, kondensering og flytendegjøring av gass i varmeveksiersystemet omfatter en åpen eller lukket gassekspansjonsprosess med minst ett gassekspansjonstrinn, slik det fremgår av karakteristikken i krav 11. The system according to the invention is characterized by the fact that the cooling system used for cooling, condensing and liquefaction of gas in the heat exchanger system includes an open or closed gas expansion process with at least one gas expansion stage, as is evident from the characteristic in claim 11.

De foretrukne utførelsene av systemet er definert i de uselvstendige kravene 12-16. The preferred embodiments of the system are defined in the independent claims 12-16.

Fortrinnsvis er systemet designet og konfigurert for å separere fødegassen slik at systemets overhead gasstrøm vil være anriket med det aller meste av butan (C4) og hydrokarboner med lavere normalkokepunkt enn butan, og fraksjoneringskolonnens bunnprodukt vil være anriket med det aller meste av C6 og komponenter med normalkokepunkt høyere enn C6. Preferably, the system is designed and configured to separate the feed gas so that the overhead gas stream of the system will be enriched with the vast majority of butane (C4) and hydrocarbons with a lower normal boiling point than butane, and the bottom product of the fractionation column will be enriched with the vast majority of C6 and components with normal boiling point higher than C6.

Bakgrunn: Background:

Flytendegjøring av naturgass kan gjøres ved bruk av en gassekspansjonsprosess, hvor et kjølemedium gjennomgår en arbeidskrets basert på kompresjon, kjøling, ekspansjon og deretter varmeveksling med fluidet som skal nedkjøles. F.eks. kan man for flytendegjøring av naturgass benytte et komprimert kjølemedium i gassfase, vanligvis nitrogen eller metan, som forkjøles og deretter ekspanderes over en ekspansjonsventil eller en turboekspander. Gassekspansjonen medfører at det genereres meget kald gass, eller en blanding av gass og væske, som så blir benyttet til å flytendegjøre naturgass og til å forkjøle den komprimerte kjølegassen. Gassekspansjonsprosessene er relativt enkle og derfor godt egnet for offshore installasjon. Prosessene har imidlertid noe lavere virkningsgrad enn de mer avanserte prosessene, som f.eks. blandet kjølemediumprosesser, og krever således mye kompresjonsutstyr og mye energi. Liquefaction of natural gas can be done using a gas expansion process, where a refrigerant undergoes a working cycle based on compression, cooling, expansion and then heat exchange with the fluid to be cooled. E.g. for the liquefaction of natural gas, a compressed refrigerant in gas phase, usually nitrogen or methane, can be used, which is pre-cooled and then expanded via an expansion valve or a turboexpander. The gas expansion means that very cold gas, or a mixture of gas and liquid, is generated, which is then used to liquefy natural gas and to pre-cool the compressed refrigerant gas. The gas expansion processes are relatively simple and therefore well suited for offshore installation. However, the processes have a somewhat lower degree of efficiency than the more advanced processes, such as e.g. mixed refrigerant processes, and thus require a lot of compression equipment and a lot of energy.

For å produsere LNG kreves det vanligvis at gassen har relativt høyt innhold av metan. De aller fleste fødegasser vil imidlertid også inneholde en del tyngre hydrokarboner, så som etan, propan, butan, pentan, etc. Det stilles vanligvis en del krav til den flytende gassens innhold av tyngre hydrokarboner: -Den flytende gassens spesifikke energiinnhold pr. kubikkmeter må vanligvis ikke overskride gitte salgsspesifikasjoner. -Den flytende gassens innhold av pentan (C5) og oppover, samt aromatiske forbindeleser, må holdes under definerte grenser for å unngå utfrysing i nedkjølingsprosessen. In order to produce LNG, it is usually required that the gas has a relatively high content of methane. However, the vast majority of feed gases will also contain some heavier hydrocarbons, such as ethane, propane, butane, pentane, etc. There are usually a number of requirements for the content of heavier hydrocarbons in the liquefied gas: -The specific energy content of the liquefied gas per cubic meters must not normally exceed given sales specifications. -The liquid gas's content of pentane (C5) and above, as well as aromatic compounds, must be kept below defined limits to avoid freezing during the cooling process.

Den enkleste måten for å begrense den flytende gassens innhold av tyngre hydrokarboner, er å kondensere gassen delvis for så å separere den kondenserte væsken fra gassen, som kjøles videre for flytendegjøring. Separasjonen utføres vanligvis som en integrert del av nedkjølingsprosessen, ved typisk temperatur mellom 0°C og -60°C. Utskilt kondensat kan varmes opp igjen som en del av kjøleprosessen for å utnytte kjølepotensialet. The simplest way to limit the liquefied gas' content of heavier hydrocarbons is to partially condense the gas and then separate the condensed liquid from the gas, which is further cooled for liquefaction. The separation is usually carried out as an integral part of the cooling process, at typical temperatures between 0°C and -60°C. Separated condensate can be reheated as part of the cooling process to utilize the cooling potential.

Ved store landbaserte LNG-anlegg (såkalte "base load" anlegg) fjernes vanligvis det meste av propan og tyngre hydrokarboner, og i mange tilfeller også en vesentlig del av etan, før eller som en del av flytendegjøringen. Dette gjøres for å møte salgsspesifikasjonene og for å kunne produsere og selge verdifull etan, LPG og kondensat/nafta. Det benyttes vanligvis omfattende prosesser med lavtemperatur fraksjoneringskolonner både som del av nedkjølingsprosessen og som separate enheter utenfor kjølesystemet. At large land-based LNG plants (so-called "base load" plants), most of the propane and heavier hydrocarbons, and in many cases also a significant part of the ethane, are usually removed before or as part of the liquefaction. This is done to meet sales specifications and to be able to produce and sell valuable ethane, LPG and condensate/naphtha. Extensive processes with low-temperature fractionation columns are usually used both as part of the cooling process and as separate units outside the cooling system.

For offshore LNG-produksjon er det derimot lite ønskelig å håndtere andre produkter enn den flytende naturgassen. Der hvor det også produseres olje eller kondensat, kan man imidlertid tillate å skille ut kondensat for stabilisering og eksport sammen med annen olje og/eller kondensat. Stabilisert kondensat vil imidlertid hovedsakelig bestå av C6+ med relativt lavt innhold av pentan og lettere komponenter. Hydrokarboner lettere enn C6 kan stort sett ikke lagres eller transporteres sikkert uten å være nedkjølt eller under trykk. Noe utskilte hydrokarboner eller kondensat kan benyttes som brensel, men utover det ønsker man å kunne beholde disse komponentene i LNG-produktet. Som følge av mindre LNG-volumer og muligheten for senere innblanding i store LNG volumer, kan det offshore være hensiktsmessig å produsere en flytende naturgass med et vesentlig høyere eller gjerne maksimalt innhold av tyngre hydrokarboner. For offshore LNG production, however, it is not desirable to handle products other than the liquefied natural gas. However, where oil or condensate is also produced, condensate may be allowed to be separated for stabilization and export together with other oil and/or condensate. However, stabilized condensate will mainly consist of C6+ with a relatively low content of pentane and lighter components. Hydrocarbons lighter than C6 generally cannot be stored or transported safely without being refrigerated or under pressure. Some separated hydrocarbons or condensate can be used as fuel, but beyond that, you want to be able to keep these components in the LNG product. As a result of smaller LNG volumes and the possibility of later mixing in large LNG volumes, offshore it may be appropriate to produce a liquefied natural gas with a significantly higher or preferably maximum content of heavier hydrocarbons.

Den foreliggende oppfinnelse representerer en vesentlig optimalisering for anvendelse offshore, og spesielt på en flytende enhet, ved at en relativt enkel og robust gassekspansjonsprosess benyttes for flytendegjøring av naturgass, og ved at energieffektiviteten til denne prosessen økes samtidig som mengden flytende gass maksimeres ved å maksimere innholdet av etan og LPG, samtidig som mengden hydrokarboner tyngre enn metan som skilles ut som bi-produkt under flytendegjøringen, minimeres. The present invention represents a significant optimization for use offshore, and especially on a floating unit, in that a relatively simple and robust gas expansion process is used for the liquefaction of natural gas, and in that the energy efficiency of this process is increased at the same time as the amount of liquefied gas is maximized by maximizing the content of ethane and LPG, while minimizing the amount of hydrocarbons heavier than methane that are separated as a by-product during liquefaction.

Et anlegg som omfatter systemet ifølge oppfinnelsen kan derved enkelt tilpasses og installeres eksempelvis om bord på flytende offshore installasjoner hvor plass ofte er en minimumsfaktor. A plant comprising the system according to the invention can thereby be easily adapted and installed, for example, on board floating offshore installations where space is often a minimum factor.

Referanser til kjent teknologi og andre publikasjoner, og sammenligning med foreliggende oppfinnelse. : I patentpublikasjonene US 2006/0260355 A1 og US 6,662,589 er det omtalt systemer som tilsynelatende er like foreliggende oppfinnelser, men som i realiteten skiller seg vesentlig fra foreliggende oppfinnelse. Systemene i de refererte publikasjonene omfatter prosesser for samtidig flytendegjøring av naturgass og gjenvinning / utskilling av komponenter tyngre enn metan, dvs. etan og tyngre komponenter, der etan, LPG og tyngre komponenter fraksjoneres til salgsprodukter, og hvor den flytende gassen har vesentlig redusert innhold av etan og tyngre komponenter. Dette oppnås ved føre fødegassen til en fraksjoneringskolonne der den kontaktes med en etan-rik refluks slik at fraksjoneringskolonnen skiller føden til en overhead gassfraksjon med vesentlig redusert innhold av komponenter tyngre enn metan, og en væskestrøm fra bunnen vesentlig anriket med komponenter tyngre enn metan. Den etan-rike refluksen genereres ved at gassen fra fraksjoneringskolonnen delvis kondenseres, samt ved å nedkjøle og kondensere en etan-rik strøm som er resirkulert fra et fraksjoneringstog for fraksjonering av fraksjoneringskolonnens bunnfraksjon, References to known technology and other publications, and comparison with the present invention. : In the patent publications US 2006/0260355 A1 and US 6,662,589 systems are mentioned which are apparently similar to the present invention, but which in reality differ significantly from the present invention. The systems in the referenced publications include processes for simultaneous liquefaction of natural gas and recovery/separation of components heavier than methane, i.e. ethane and heavier components, where ethane, LPG and heavier components are fractionated into sales products, and where the liquefied gas has a significantly reduced content of ethane and heavier components. This is achieved by feeding the feed gas to a fractionation column where it is contacted with an ethane-rich reflux so that the fractionation column separates the feed into an overhead gas fraction with a substantially reduced content of components heavier than methane, and a liquid stream from the bottom substantially enriched with components heavier than methane. The ethane-rich reflux is generated by partially condensing the gas from the fractionation column, as well as by cooling and condensing an ethane-rich stream that is recycled from a fractionation train for fractionation of the fractionation column's bottom fraction,

I patentpublikasjonene US 6,401,486 , US 6,742,358 og WO2006/115597A2 omtales det systemer for samtidig flytendegjøring av naturgass og gjenvinning / utskilling av komponenter tyngre enn metan, dvs. etan og tyngre komponenter. Selve prosessene er også vesentlig ulik og mer omfattende enn foreliggende oppfinnelse i og med fødegassen først gjennomgår nedkjøling i bl.a. varmeveksleren(e) forflytendegjøring av gass samt ved varmeveksling med en flash-ekspandert utskilt væske og med fluid fra kolonnens bunn. Videre ekspanderes hele eller deler av fødegasstrømmen gjennom en turboekspander eller Joule-Thomson ekspansjonsventil før den ledes til fraksjoneringskolonnen. In the patent publications US 6,401,486, US 6,742,358 and WO2006/115597A2, systems are mentioned for the simultaneous liquefaction of natural gas and recovery/separation of components heavier than methane, i.e. ethane and heavier components. The processes themselves are also significantly different and more extensive than the present invention in that the feed gas first undergoes cooling in, among other things the heat exchanger(s) liquefaction of gas as well as by heat exchange with a flash-expanded separated liquid and with fluid from the bottom of the column. Furthermore, all or part of the feed gas stream is expanded through a turboexpander or Joule-Thomson expansion valve before it is led to the fractionation column.

Patentpublikasjonene US 2006/0260355 A1, US-patentskrift 6,662,589, US-patentskrift 6,401,486 samt US-patentskrift 6,742,358 omhandler følgelig prosesser for å minimere den flytende gassens innhold av etan, LPG, samt de tyngre hydrokarboner, mens foreliggende oppfinnelse omfatter et system og fremgangsmåte for å maksimere den flytende gassens innhold av metan, etan og LPG. Men verken US patentsøknad 2006/0260355 A1, US-patentskrift 6,662,589, US-patentskrift 6,401,486 eller US-patentskrift 6,742,358 beskriver den energieffektiviseringen som kan oppnås for en gassekspansjonsprosess med integrerte separasjonskolonnen som mottar refluks rik på C3 - C5 fra flytendegjørings-varmeveksleren(e) for produksjon av LNG The patent publications US 2006/0260355 A1, US patent 6,662,589, US patent 6,401,486 and US patent 6,742,358 consequently deal with processes for minimizing the liquid gas's content of ethane, LPG, as well as the heavier hydrocarbons, while the present invention comprises a system and method for to maximize the liquefied gas content of methane, ethane and LPG. However, neither US Patent Application 2006/0260355 A1, US Patent 6,662,589, US Patent 6,401,486 nor US Patent 6,742,358 describe the energy efficiency that can be achieved for a gas expansion process with integrated separation column receiving reflux rich in C3 - C5 from the liquefaction heat exchanger(s). for the production of LNG

I DE-patentskrift 10205366 omtales det en prosess for samtidig flytendegjøring av naturgass og gjenvinning / utskilling av komponenter tyngre enn etan, og hvor utskilt LPG og tyngre komponenter fraksjoneres til salgsprodukter, Dette oppnås ved å først delvis kjøle ned fødegassen i kondenseringsanlegget for flytendegjøring av naturgass, videre ved å føre den nedkjølt fødegassen til en fraksjoneringskolonne der den kontaktes med en etan-rik refluks slik at fraksjoneringskolonnen skiller føden til en overhead gassfraksjon med vesentlig redusert innhold av komponenter tyngre enn etan, og en væskestrøm fra bunnen vesentlig anriket med komponenter tyngre enn etan. Den etan-rike refluksen genereres ved at gassen fra fraksjoneringskolonnen delvis kondenseres og deretter kontaktes med en C4/C5 strøm i en andre fraksjoneringskolonne, og hvor C4/C5 fraksjonen er resirkulert fra et fraksjoneringstog for fraksjonering av bunnproduktet fra den første fraksjoneringskolonnen. DE-patentskrift 10205366 omfatter med andre ord en prosess for å minimere den flytende gassens innhold av LPG, samt de tyngre hydrokarboner, mens foreliggende oppfinnelse omfatter et system og fremgangsmåte for å maksimere den flytende gassens innhold av LPG. Publikasjonen DE 10205366 beskriver heller ikke energieffektivisering som kan oppnås for en gassekspansjonsprosess med integrerte separasjonskolonnen som mottar refluks rik på C3 - C5 fra flytendegjørings-varmeveksleren(e) for produksjon av LNG. DE patent 10205366 describes a process for simultaneous liquefaction of natural gas and recovery/separation of components heavier than ethane, and where separated LPG and heavier components are fractionated into products for sale. This is achieved by first partially cooling down the feed gas in the condensing plant for liquefaction of natural gas , further by passing the cooled feed gas to a fractionation column where it is contacted with an ethane-rich reflux so that the fractionation column separates the feed into an overhead gas fraction with a substantially reduced content of components heavier than ethane, and a liquid stream from the bottom substantially enriched with components heavier than ethane. The ethane-rich reflux is generated by the gas from the fractionation column being partially condensed and then contacted with a C4/C5 stream in a second fractionation column, and where the C4/C5 fraction is recycled from a fractionation train for fractionation of the bottom product from the first fractionation column. In other words, DE patent 10205366 includes a process for minimizing the liquid gas's content of LPG, as well as the heavier hydrocarbons, while the present invention includes a system and method for maximizing the liquid gas's content of LPG. The publication DE 10205366 also does not describe energy efficiency that can be achieved for a gas expansion process with integrated separation column receiving reflux rich in C3 - C5 from the liquefaction heat exchanger(s) for the production of LNG.

I US-patentskrift 4,690,702 omtales det en LNG prosess hvor fødegassen først forkjøles i kjøleanlegget for LNG-produksjon, for deretter å føres til en første fraksjoneringskolonne hvor den kontaktes med en nedkjølt etan-rik refluks som er resirkulert fra en andre fraksjoneringskolonne for fraksjonering av bunnstrømmen fra den første kolonnen. Publikasjonen omfatter ikke et system hvor en C3-C5-rik refluks for en fraksjoneringskolonne oppnås ved å delvis kondensere overhead gassprodukt fra fraksjoneringskolonnen som en integrert del av en LNG-prosess. US patent 4,690,702 describes an LNG process where the feed gas is first pre-cooled in the refrigeration plant for LNG production, and is then led to a first fractionation column where it is contacted with a cooled ethane-rich reflux that is recycled from a second fractionation column for fractionation of the bottom stream from the first column. The publication does not include a system where a C3-C5 rich reflux for a fractionation column is achieved by partially condensing overhead gas product from the fractionation column as an integral part of an LNG process.

US-patentskrift 7,010,937 viser et system for samtidig flytendegjøring av naturgass og gjenvinning / utskilling av komponenter tyngre enn metan. I følge denne publikasjonen forkjøles og delvis kondenseres gassføden slik at en væskestrøm kan separeres i en separator, og hvor denne væskestrøm fraksjoneres i en første fraksjoneringskolonne for å generer en overhead gass som nedkjøles for å lage refluks for en andre fraksjoneringskolonne. Gasstrømmen fra separatoren ekspanderes over en gassekspander og ledes til den andre fraksjoneringskolonnen. Dette US-patentet har derfor lite til felles med foreliggende oppfinnelse slik den er definert i de etterfølgende patentkrav. US patent 7,010,937 shows a system for simultaneous liquefaction of natural gas and recovery/separation of components heavier than methane. According to this publication, the gas feed is precooled and partially condensed so that a liquid stream can be separated in a separator, and where this liquid stream is fractionated in a first fractionation column to generate an overhead gas that is cooled to create reflux for a second fractionation column. The gas stream from the separator is expanded over a gas expander and led to the second fractionation column. This US patent therefore has little in common with the present invention as defined in the subsequent patent claims.

I tillegg til ovennevnte publikasjoner skal det refereres til EP-1.715.267 og WO2005/071333. In addition to the above-mentioned publications, reference should be made to EP-1,715,267 and WO2005/071333.

Beskrivelse av oppfinnelsen: Description of the invention:

Oppfinnelsen vil nå beskrives mer detaljert med referanse til vedlagte figurer, hvori: Figur 1 viser oppfinnelsen i en prinsipiell utførelse med hovedkomponenter og hoved virkemåte. The invention will now be described in more detail with reference to the attached figures, in which: Figure 1 shows the invention in a principle embodiment with main components and main mode of operation.

Figur 2 viser oppfinnelsen med alternativ utførelse. Figure 2 shows the invention with an alternative embodiment.

Figur 3 viser oppfinnelsen med alternativ utførelse som inkluderer ytterligere stabilisering av de tyngre hydrokarboner som skilles ut (kondensat). Figur 4 viser detaljert oppfinnelsen utført ved å benytte en dobbel gassekspansjonsprosess. Figur 5 viser oppfinnelsen utført ved å benytte en hybrid kjølekrets med en gassekspansjonssløyfe og en væskeekspansjonssløyfe. Figur 6 viser eksempel på varm og kald temperaturkurve (komposittkurve) for en konvensjonell nitrogenekspanderkrets. Figur 7 viser eksempel på varm og kald temperaturkurve (komposittkurve) for en nitrogenekspanderkrets utført ved bruk av foreliggende oppfinnelse. Figure 3 shows the invention with an alternative embodiment which includes further stabilization of the heavier hydrocarbons that are separated (condensate). Figure 4 shows in detail the invention carried out by using a double gas expansion process. Figure 5 shows the invention implemented by using a hybrid cooling circuit with a gas expansion loop and a liquid expansion loop. Figure 6 shows an example of a hot and cold temperature curve (composite curve) for a conventional nitrogen expander circuit. Figure 7 shows an example of a hot and cold temperature curve (composite curve) for a nitrogen expander circuit carried out using the present invention.

Figur 8 viser en sammenligning av kurvene vist i figurene 6 og 7. Figure 8 shows a comparison of the curves shown in figures 6 and 7.

Med referanse til figur 1, omfatter systemet for optimalisert flytendegjøring av gass som minimum de følgende prinsipielle komponenter: With reference to figure 1, the system for optimized liquefaction of gas comprises as a minimum the following principal components:

-En innkommende gasstrøm 1 som skal kjøles ned og gjøres flytende. -An incoming gas stream 1 to be cooled and liquefied.

-En fraksjoneringskolonne 150, hvori den innkommende gassen kjøles og separeres til en overheadfraksjon 2 med redusert innhold av pentan og tyngre komponenter, og en bunnfraksjon 3 anriket med de tyngre hydrokarbon-komponentene. -Et system av varmevekslere 110, hvori den innkommende gassen nedkjøles og delvis kondenseres for separasjon av tyngre hydrokarboner, for videre å nedkjøles og flytendegjøres. -A fractionation column 150, in which the incoming gas is cooled and separated into an overhead fraction 2 with a reduced content of pentane and heavier components, and a bottom fraction 3 enriched with the heavier hydrocarbon components. -A system of heat exchangers 110, in which the incoming gas is cooled and partially condensed for separation of heavier hydrocarbons, to be further cooled and liquefied.

-En produktstrøm 11 som består av nedkjølt og flytendegjort gass. -A product stream 11 which consists of cooled and liquefied gas.

-En produktstrøm 3 som hovedsakelig består av pentan og tyngre hydrokarboner. -Et kjølesystem for nedkjøling og flytendegjøring av gassen bestående av en gassformig kjølemiddelstrøm 20, minst en sirkulasjonskompressor 100, minst en etterkjøler 130, minst en gassekspander 120. -A product stream 3 which mainly consists of pentane and heavier hydrocarbons. -A cooling system for cooling and liquefying the gas consisting of a gaseous refrigerant stream 20, at least one circulating compressor 100, at least one aftercooler 130, at least one gas expander 120.

Innkommende og renset fødegass 1, f.eks. en metanrik hydrokarbongass, føres først til en fraksjoneringskolonne 150, hvor gassen kjøles ned i møtet med en kaldere refluks-væske. Under nedkjøling og motstrøms kontakt med den kaldere væsken, separeres fødegassen til en overheadfraksjon 2 med redusert innhold av hydrokarbonene som har molekylvekt høyere enn pentan (C5), og en bunnfraksjon 3 anriket med C6 og hydrokarboner som har høyere molekylvekt enn C6. Fraksjoneringskolonnens overheadfraksjon 2 ledes så til varmeveksiersystemet 110, hvor gassen nedkjøles og kondenseres delvis, slik at resulterende tofasefluid 4 kan separeres i en egnet separator 160. En væske 5 rik på LPG og pentan (C3 - C5) som separeres i separatoren 160 resirkuleres som kald refluks til fraksjoneringskolonnen 150. Siden denne væsken er generert ved kondensering ved nedkjøling, vil refluksvæsken 5 ha lavere temperatur enn fødegassen 1. Gassen 6 fra separatoren 160 har nå fått ytterligere redusert sitt innhold av C5 hydrokarbon og hydrokarboner tyngre enn C5. Denne gassen ledes så tilbake til varmeveksiersystemet 110 for videre nedkjøling, kondensering og underkjøling. Den flytende gassen 11 ledes eventuelt gjennom en kontrollventil 140 som kontrollerer driftstrykk og strømning gjennom systemet. Incoming and purified feed gas 1, e.g. a methane-rich hydrocarbon gas, is first fed to a fractionation column 150, where the gas is cooled in the encounter with a colder reflux liquid. During cooling and countercurrent contact with the colder liquid, the feed gas is separated into an overhead fraction 2 with a reduced content of the hydrocarbons that have a molecular weight higher than pentane (C5), and a bottom fraction 3 enriched with C6 and hydrocarbons that have a higher molecular weight than C6. The overhead fraction 2 of the fractionation column is then led to the heat exchange system 110, where the gas is cooled and partially condensed, so that the resulting two-phase fluid 4 can be separated in a suitable separator 160. A liquid 5 rich in LPG and pentane (C3 - C5) that is separated in the separator 160 is recycled as cold reflux to the fractionation column 150. Since this liquid is generated by condensation during cooling, the reflux liquid 5 will have a lower temperature than the feed gas 1. The gas 6 from the separator 160 has now had its content of C5 hydrocarbon and hydrocarbons heavier than C5 further reduced. This gas is then led back to the heat exchanger system 110 for further cooling, condensation and subcooling. The liquid gas 11 is optionally led through a control valve 140 which controls the operating pressure and flow through the system.

I foretrukket utførelse er gassfødestrømmen 1 på forhånd nedkjølt ved egnet eksternt kjølemiddel, så som tilgjengelig luft, vann, sjøvann eller et separat egnet kjøleaggregat / forkjølingssystem. For sistnevnte eksterne kjølemetode benyttes ofte et eget lukket mekanisk kjølesystem med propan, ammoniakk eller annet egnet kjølemiddel. In a preferred embodiment, the gas feed stream 1 is previously cooled by a suitable external coolant, such as available air, water, seawater or a separately suitable cooling unit / pre-cooling system. For the latter external cooling method, a separate closed mechanical cooling system with propane, ammonia or another suitable cooling agent is often used.

I foretrukket utførelse opereres fraksjoneringskolonnen 150 og separatoren 160 ved trykk og temperaturer som medfører at det samlede systemet (fraksjoneringskolonnen 150 og refluksseparator 160) genererer en komponentsplitt / separasjonspunkt i normalkokepunktområdet (NBP) mellom -12°C og 60°C. Dette kan f.eks. tilsvarer at lett nøkkelkomponent for separasjonen er butan (C4) med normalkokepunkt mellom -12°C og 0°C, og tung nøkkelkomponent er en C6 komponent med kokepunkt mellom 50°C og 70°C. Systemets overhead gasstrøm 6 vil da være anriket med det aller meste av butan (C4) og hydrokarboner med lavere normalkokepunkt enn butan. Fraksjoneringskolonnens bunnprodukt 3 vil være anriket med det aller meste av C6 og komponenter med normalkokepunkt høyere enn C6, mens pentan (C5, NBP=28 - 36°C) er en overgangskomponent som fordeler seg i systemets gassprodukt og fraksjoneringskolonnens bunnprodukt. In the preferred embodiment, the fractionation column 150 and the separator 160 are operated at pressures and temperatures which result in the overall system (fractionation column 150 and reflux separator 160) generating a component split / separation point in the normal boiling point range (NBP) between -12°C and 60°C. This can e.g. corresponds to the light key component for the separation being butane (C4) with a normal boiling point between -12°C and 0°C, and the heavy key component being a C6 component with a boiling point between 50°C and 70°C. The system's overhead gas stream 6 will then be enriched with the vast majority of butane (C4) and hydrocarbons with a lower normal boiling point than butane. The fractionation column's bottom product 3 will be enriched with the vast majority of C6 and components with a normal boiling point higher than C6, while pentane (C5, NBP=28 - 36°C) is a transitional component that is distributed in the system's gas product and the fractionation column's bottom product.

Nedkjøling og kondensering av fødegassen i varmeveksiersystemet 110 besørges av en åpen eller lukket gassekspansjonsprosess. Kjøleprosessen starter med at et kjølemiddel 21 bestående av gass eller blanding av gasser (så som ren nitrogen, metan, en hydrokarbonblanding, eller en blanding av nitrogen og hydrokarboner), ved et høyere trykk fortrinnsvis mellom 3 og 10 MPa, ledes til varmeveksiersystemet 110 og kjøles til en temperatur mellom 0°C og -120°C, men slik at kjølemiddelstrømmen hovedsakelig er gass ved gjeldende trykk og temperatur 31. Forkjølt kjølemiddel 31 blir så ledet inn på en gassekspander 121, hvor gassen ekspanderes til et lavere trykk mellom 5% - 40% av innløpstrykket, men fortrinnsvis til mellom 10% og 30 % av innløpstrykket, og slik at kjølemiddelet hovedsakelig er i gassfase. Gassekspanderen er normalt en ekspansjonsturbin, også kalt turboekspander, men andre typer ekspansjonsutstyr for gass kan benyttes, så som en ventil. I gassekspanderen 121 ekspanderes den forkjølte kjølemiddelstrømmen med høy isentropisk virkningsgrad, slik at temperaturen synker kraftig. I enkelte utførelser av oppfinnelsen kan det skilles ut noe væske i denne ekspansjonen, men dette er ikke nødvendig for prosessen. Den kalde kjølemiddelstrømmen 32 ledes så tilbake til varmevekslerne 110 der den benyttes for nedkjøling og eventuelt kondensering av de andre innkommende varme kjølemiddelstrømmene og gassen som skal nedkjøles, kondenseres og underkjøles. Cooling and condensation of the feed gas in the heat exchanger system 110 is provided by an open or closed gas expansion process. The cooling process starts with a coolant 21 consisting of gas or a mixture of gases (such as pure nitrogen, methane, a hydrocarbon mixture, or a mixture of nitrogen and hydrocarbons), at a higher pressure preferably between 3 and 10 MPa, being led to the heat exchanger system 110 and is cooled to a temperature between 0°C and -120°C, but so that the coolant flow is mainly gas at the current pressure and temperature 31. Precooled coolant 31 is then led into a gas expander 121, where the gas is expanded to a lower pressure between 5% - 40% of the inlet pressure, but preferably to between 10% and 30% of the inlet pressure, and so that the refrigerant is mainly in the gas phase. The gas expander is normally an expansion turbine, also called a turboexpander, but other types of expansion equipment for gas can be used, such as a valve. In the gas expander 121, the precooled refrigerant flow is expanded with a high isentropic efficiency, so that the temperature drops sharply. In some embodiments of the invention, some liquid may be separated in this expansion, but this is not necessary for the process. The cold coolant stream 32 is then led back to the heat exchangers 110 where it is used for cooling and possibly condensation of the other incoming hot coolant streams and the gas to be cooled, condensed and subcooled.

Etter at den kalde kjølemiddelstrømmene 32 er oppvarmet i varmeveksiersystemet 110 vil kjølemiddelet forelige som gasstrømmen 51, som i en lukket sløyfe utførelse på en hensiktsmessig måte re-komprimeres for gjenbruk og kjøles med eksternt kjølemiddel, så som luft, vann, sjøvann eller et egnet kjøleaggregat. After the cold coolant stream 32 has been heated in the heat exchange system 110, the coolant will appear as the gas stream 51, which in a closed loop design is suitably re-compressed for reuse and cooled with an external coolant, such as air, water, seawater or a suitable cooling unit .

Alternativt vil kjølesystemet i en åpen utførelse benytte et kjølemiddel 21 bestående av gass eller blanding av gasser ved et høyere trykk oppdrevet fra en hensiktsmessig kilde, f.eks. fra fødegassen som skal behandles og nedkjøles. Videre vil den åpne utførelsen omfatte at lavtrykks kjølemiddelstrøm 51 benyttes til annet formål eller på en hensiktsmessig måte rekomprimeres for å blandes med fødegassen som skal behandles og nedkjøles. Alternatively, the cooling system in an open design will use a coolant 21 consisting of gas or a mixture of gases at a higher pressure generated from a suitable source, e.g. from the feed gas to be treated and cooled. Furthermore, the open design will include that the low-pressure coolant stream 51 is used for another purpose or recompressed in an appropriate manner to be mixed with the feed gas to be treated and cooled.

I en foretrukket utførelse føres den returnerende kjølemiddlestrømmen 51 fra varmeveksleren 110 til en egen kompressor 101 drevet av ekspansjonsturbinen 121. På denne måten utnyttes ekspansjonsarbeidet, og prosessens energieffektivitet økes. Etter kompressoren 101 etterkjøles kjølemiddelet i en varmeveksler 131, før strømmen komprimeres ytterligere i sirkulasjonskompressorene 100. Sirkulasjonskompressorene 100 kan være en eller flere enheter, eventuelt ett eller flere trinn pr. enhet. Sirkulasjonskompressoren kan også være utstyrt med mellomkjøling 132 mellom kompresjonstrinnene. Det komprimerte kjølemiddelet 20 kjøles så ved varmeveksling i en etterkjøler 130 ved hjelp av egnet eksternt kjølemedium, så som så som luft, vann, sjøvann eller en egnet separat kjølekrets, for så å bli gjenbrukt som komprimert kjølemedium 21 i en lukket sløyfe. In a preferred embodiment, the returning refrigerant stream 51 is led from the heat exchanger 110 to a separate compressor 101 driven by the expansion turbine 121. In this way, the expansion work is utilized, and the energy efficiency of the process is increased. After the compressor 101, the refrigerant is cooled in a heat exchanger 131, before the flow is further compressed in the circulation compressors 100. The circulation compressors 100 can be one or more units, possibly one or more stages per unit. The circulation compressor can also be equipped with intercooling 132 between the compression stages. The compressed coolant 20 is then cooled by heat exchange in an aftercooler 130 using a suitable external coolant, such as air, water, seawater or a suitable separate cooling circuit, and then reused as compressed coolant 21 in a closed loop.

I foretrukket utførelse er systemet av varmevekslerne 110 en varmeveksler som omfatter mange forskjellige "varme" og "kalde" strømmer i samme enhet (en såkalt multistrøms varmeveksler). Figur 2 vises en alternativ utførelse der flere multistrøms varmevekslere kobles sammen på en slik måte at nødvendig varmeoverføring mellom de varme og kalde strømmene kan utføres. I figur 2 vises et varmevekslersystem 110 bestående av flere varmevekslere i serie. Oppfinnelsen er imidlertid ikke relatert til en spesifikk type varmeveksler eller antall vekslere, men kan utføres i flere forskjellige typer varmevekslersystemer som kan håndtere det nødvendige antall varme og kalde prosesstrømmer. Figur 3 viser en alternativ utførelse der fraksjoneringskolonnen 150 utstyres med en koker (reboiler) 135 for å forbedre separasjonen ytterligere (skarpere splitt mellom lette og tunge komponenter), samt å redusere flyktigheten kolonnens bunnfraksjon. Dette kan utnyttes til å direkte produsere kondensat som er stabilt ved omgivelsestemperatur og atmosfærisk trykk. Figur 4 viser detaljert oppfinnelsen utført i en mer avansert utførelse der det benyttes en dobbel gassekspansjonsprosess. I denne utførelsen blir den komprimerte kjølemiddelstrømmen 21 først nedkjølt til en mellomtemperatur. Ved denne temperaturen splittes kjølemiddelstrømmen i to deler, hvor den ene delen 31 tas ut av varmeveksleren og ekspanderes i gassekspander 121, til en lavtrykks gasstrøm 32. Den andre delen 41 forkjøles ytterligere for så å bli ekspandert i gassekspander 122, til et trykk vesentlig likt trykket i strøm 32. De ekspanderte kalde kjølemiddelstrømmene 32, 42, returneres til forskjellige innløpslokasjoner på varmeveksiersystemet 110, og kombineres til en strøm i denne veksleren. Oppvarmet kjølemiddel 51 returneres så til re-kompresjon. I alternativ utførelse til systemet i figur 3 kan den komprimerte kjølemiddelstrømmen 20 i den doble gassekspansjonskretsen splittes i to strømmer før varmeveksleren 110, for så å bli nedkjølt til forskjellige temperaturer i egne strøningskanaler i varmeveksleren 110. Det samme gjelder oppvarmingen av returnerende kalde kjølemiddelstrømmer 32, 42. Utførelsen er forøvrig i samsvar med figur 3. Figur 5 viser detaljert oppfinnelsen utført ved bruk av en hybrid kjølesløyfe, der ett og samme kjølemiddel benyttes både i en ren gassfase og i en ren væskefase. In a preferred embodiment, the system of heat exchangers 110 is a heat exchanger comprising many different "hot" and "cold" streams in the same unit (a so-called multi-stream heat exchanger). Figure 2 shows an alternative design where several multi-stream heat exchangers are connected together in such a way that the necessary heat transfer between the hot and cold streams can be carried out. Figure 2 shows a heat exchanger system 110 consisting of several heat exchangers in series. However, the invention is not related to a specific type of heat exchanger or the number of exchangers, but can be implemented in several different types of heat exchanger systems that can handle the required number of hot and cold process streams. Figure 3 shows an alternative embodiment where the fractionation column 150 is equipped with a boiler (reboiler) 135 to further improve the separation (sharper split between light and heavy components), as well as to reduce the volatility of the column's bottom fraction. This can be used to directly produce condensate that is stable at ambient temperature and atmospheric pressure. Figure 4 shows in detail the invention carried out in a more advanced embodiment where a double gas expansion process is used. In this embodiment, the compressed refrigerant stream 21 is first cooled to an intermediate temperature. At this temperature, the coolant flow is split into two parts, where one part 31 is taken out of the heat exchanger and expanded in gas expander 121, to a low-pressure gas flow 32. The other part 41 is further precooled and then expanded in gas expander 122, to a pressure substantially equal to the pressure in stream 32. The expanded cold refrigerant streams 32, 42 are returned to different inlet locations on the heat exchanger system 110, and are combined into a stream in this exchanger. Heated refrigerant 51 is then returned to re-compression. In an alternative embodiment to the system in Figure 3, the compressed refrigerant stream 20 in the double gas expansion circuit can be split into two streams before the heat exchanger 110, and then be cooled to different temperatures in separate distribution channels in the heat exchanger 110. The same applies to the heating of returning cold refrigerant streams 32, 42. The design is otherwise in accordance with figure 3. Figure 5 shows in detail the invention carried out using a hybrid cooling loop, where one and the same coolant is used both in a pure gas phase and in a pure liquid phase.

I denne utførelsen besørger en lukket kjølesløyfe nedkjølingen av fødegassen i varmeveksiersystemet 110. Den nevnte kjølesløyfen starter med at metan eller en blanding av metan og nitrogen, hvor metan utgjør minst 50% volum, komprimeres og etterkjøles til en komprimert kjølemiddelstrøm 21, og hvor denne kjølemiddelstrømmen forkjøles, og minst en del 31 av kjølemiddelstrømmen benyttes i gassfase ved at den ekspanderes over en gassekspander 121, og at minst en del 41 av kjølemiddelstrømmen kondenseres til væske og ekspanders over en ventil eller væskeekspander 141. In this embodiment, a closed cooling loop takes care of the cooling of the feed gas in the heat exchanger system 110. The said cooling loop starts with methane or a mixture of methane and nitrogen, where methane makes up at least 50% volume, compressed and recooled into a compressed refrigerant flow 21, and where this refrigerant flow is precooled, and at least a part 31 of the refrigerant flow is used in gas phase by expanding it over a gas expander 121, and that at least a part 41 of the refrigerant flow is condensed to liquid and expanded over a valve or liquid expander 141.

Det presiseres at utførelsen av oppfinnelsen ikke er begrenset til kun kjøleprosessene beskrevet over, men kan benyttes ved enhver gassekspansjonskjøleprosess for flytendegjøring av naturgass eller annen hydrokarbongass, der nedkjølingen hovedsakelig oppnås ved å benytte en eller flere ekspanderende gasstrømmer. It is specified that the implementation of the invention is not limited to only the cooling processes described above, but can be used in any gas expansion cooling process for the liquefaction of natural gas or other hydrocarbon gas, where the cooling is mainly achieved by using one or more expanding gas streams.

Ved å utføre flytendegjøringen av naturgassen i henhold til oppfinnelsen, oppnås et produkt av flytende gass som har maksimalt innhold av metan, etan og LPG, men som samtidig ikke inneholder mer enn tillatt av pentan og tyngre hydrokarboner med normalkokepunkt over 50 - 60°C. Samtidig minimeres eller elimineres bi-produksjon av flyktige hydrokarboner med vesentlig innhold av etan, propan og butan, som vil være vanskelig å håndtere på en offshore installasjon for LNG produksjon. Samtidig vil det også produseres mer flytende naturgass med lavere energiforbruk enn for tilsvarende kjølekrets konfigurert uten fraksjoneringskolonnen som mottar kald LPG-rik refluks fra nedkjølingsprosessen. By carrying out the liquefaction of the natural gas according to the invention, a product of liquefied gas is obtained which has a maximum content of methane, ethane and LPG, but which at the same time does not contain more than permitted of pentane and heavier hydrocarbons with a normal boiling point above 50 - 60°C. At the same time, by-production of volatile hydrocarbons with a significant content of ethane, propane and butane, which would be difficult to handle on an offshore installation for LNG production, is minimized or eliminated. At the same time, more liquefied natural gas will also be produced with lower energy consumption than for a corresponding cooling circuit configured without the fractionation column that receives cold LPG-rich reflux from the cooling process.

Årsaken til at energiforbruket for gassekspansjonsprosessene for flytendegjøring av naturgassen reduseres ved bruk av oppfinnelsen, sammenlignet med en tilsvarende kjøleprosess uten den integrerte separasjonskolonnen, har flere sammenhenger: De tyngre hydrokarbonene som det er helt nødvendig å skille ut for å hindre frysing under flytendegjøring, vil kondenseres og separeres ut ved vesentlig høyere temperatur enn ved konvensjonell fremgangsmåte, i og med at mye av kondenseringen skjer i fraksjoneringskolonnen. Dette reduserer eksergitapet i kjøleprosessen ved at en nedkjølingslast flyttes til et høyere temperaturområde. The reason why the energy consumption for the gas expansion processes for the liquefaction of the natural gas is reduced when using the invention, compared to a corresponding cooling process without the integrated separation column, has several connections: The heavier hydrocarbons, which it is absolutely necessary to separate out in order to prevent freezing during liquefaction, will be condensed and is separated out at a significantly higher temperature than with conventional methods, as much of the condensation takes place in the fractionation column. This reduces the exergy loss in the cooling process by moving a cooling load to a higher temperature range.

Nedkjølingsprosessens varmevekslersystem 100 mottar gassen som skal flytendegjøres som strøm 2 (fraksjoneringskolonnes overhead gasstrøm), som har en redusert temperatur i forhold til den reelle gassfødestrømmen 1. En gassekspansjonsprosess er karakterisert ved at varme- og kjølekurvene domineres av den store gassmengden som benyttes som kjølemiddel. Disse gasstrømmene danner lineære (rettlinjede) kjølekurver. Den reduserte fødetemperaturen inn på varmeveksleren medfører ett "knekkpunkt" på varm kjølekurve (summen av strømmer som er under nedkjøling), slik at det er mulig å oppnå en generell reduksjon av avstanden mellom de varme- og kalde kjølekurvene. Dette gir bedre temperaturtilpassing, lavere eksergitap, og dermed redusert energiforbruk for å drive kjøleprosessen. The cooling process's heat exchanger system 100 receives the gas to be liquefied as stream 2 (fractionation column overhead gas stream), which has a reduced temperature in relation to the real gas feed stream 1. A gas expansion process is characterized by the fact that the heating and cooling curves are dominated by the large amount of gas used as coolant. These gas flows form linear (straight-lined) cooling curves. The reduced feed temperature into the heat exchanger causes a "break point" on the hot cooling curve (the sum of flows that are under cooling), so that it is possible to achieve a general reduction of the distance between the hot and cold cooling curves. This provides better temperature adaptation, lower exergy loss, and thus reduced energy consumption to drive the cooling process.

Foreløpige analyser og sammenligninger viser at nødvendig kompressorarbeid pr. kg flytende naturgass som blir produsert, kan reduseres med 5 - 15 % for en gassekspansjonskrets utført i henhold til oppfinnelsen, sammenlignet med konvensjonelle metoder. Preliminary analyzes and comparisons show that the necessary compressor work per kg of liquefied natural gas that is produced can be reduced by 5 - 15% for a gas expansion circuit carried out according to the invention, compared to conventional methods.

Figur 6 viser varme- og kalde kjølekurver (varme og kalde komposittkurver, dvs. summen av henholdsvis alle varme strømmer som skal kjøles ned, og summen av alle kalde strømmer som skal varmes opp) for varmeveksiersystemet 110 utført i henhold til foreliggende oppfinnelse, og med en dobbel nitrogenekspansjonsprosess som kjølesystem. Figur 7 viser tilsvarende varme- og kalde kjølekurver for en tilsvarende kjøleprosess med samme føde, men utført på konvensjonell måte uten integrert fraksjoneringskolonne. Kurvene ser tilsynelatende like ut, men ved å betrakte figur 8 som viser et utsnitt og begge systemene i samme kurve, kan "knekkpunktet" og den bedre tilpassingen tydelig observeres. Figure 6 shows heat and cold cooling curves (hot and cold composite curves, i.e. respectively the sum of all hot streams to be cooled, and the sum of all cold streams to be heated) for the heat exchange system 110 carried out according to the present invention, and with a double nitrogen expansion process as a cooling system. Figure 7 shows corresponding heat and cold cooling curves for a corresponding cooling process with the same feed, but carried out in a conventional manner without an integrated fractionation column. The curves apparently look the same, but by looking at figure 8 which shows a section and both systems in the same curve, the "break point" and the better fit can be clearly observed.

Eksempel Example

Eksempelet under viser naturgass med 90.4 vol% metan som skal flytendegjøre der oppfinnelsen benyttes for å maksimere mengden flytende gass, og samtidig minimere bi-produksjon av ustabil hydrokarbon væske med høyt innhold av etan, propan og butan. Strømdataene refererer til figur 1, 2, 4 eller 5. The example below shows natural gas with 90.4 vol% methane to be liquefied where the invention is used to maximize the amount of liquefied gas, and at the same time minimize by-production of unstable hydrocarbon liquid with a high content of ethane, propane and butane. The current data refers to figure 1, 2, 4 or 5.

Claims (16)

1. Fremgangsmåte til fremstilling av LNG fra en inngående fødegass (1) på en onshore eller offshore installasjon, karakterisert ved de følgende trinn: 1) fødegassen ledes gjennom en fraksjoneringskolonne (150) hvor den kjøles og separeres i en overheadfraksjon (2) med redusert innhold av pentan (C5) og tyngre komponenter, og en bunnfraksjon anriket med tyngre hydrokarboner, 2) fraksjoneringskolonnens overheadfraksjon (2) ledes inn i et varmevekslersystem (110) og underkastes en delvis kondensering til dannelse av et tofasefluid, og i en egnet separator (160) separeres tofasefluidet til en væske (5) rik på LPG og pentan (C3-C5) som resirkuleres som kald refluks til fraksjoneringskolonnen (150), mens gassen (6) inneholdende lavere mengder av C5-hydrokarbon og hydrokarboner tyngre enn C5, avledes for videre behandling i varmeveksiersystemet (110) forflytendegjøring til LNG med maksimalt innhold av etan og LPG, 3) kjølekretsen for flytendegjøring av gass i varmeveksiersystemet omfatter en åpen eller lukket gassekspansjonsprosess med minst ett gassekspansjonstrinn. 1. Method for producing LNG from an incoming feed gas (1) on an onshore or offshore installation, characterized by the following steps: 1) the feed gas is led through a fractionation column (150) where it is cooled and separated into an overhead fraction (2) with reduced content of pentane (C5) and heavier components, and a bottoms fraction enriched with heavier hydrocarbons, 2) the fractionation column's overhead fraction (2) is fed into a heat exchanger system (110) and subjected to a partial condensation to form a two-phase fluid, and in a suitable separator ( 160), the two-phase fluid is separated into a liquid (5) rich in LPG and pentane (C3-C5) which is recycled as cold reflux to the fractionation column (150), while the gas (6) containing lower amounts of C5 hydrocarbon and hydrocarbons heavier than C5 is diverted for further treatment in the heat exchanger system (110) liquefaction to LNG with a maximum content of ethane and LPG, 3) the cooling circuit for gas liquefaction in the heat exchanger system includes a open or closed gas expansion process with at least one gas expansion stage. 2. Fremgangsmåte i samsvar med krav 1, karakterisert ved at under trinn 1) ledes fødegassen gjennom en fraksjoneringskolonne (150) hvor den kjøles og separeres i en overheadfraksjon med redusert innhold av hydrokarboner med molekylvekt høyere enn pentan (C5), og en bunnfraksjon (3) anriket med (C6) og hydrokarboner med molekylvekt høyere enn C6. 2. Method in accordance with claim 1, characterized in that during step 1) the feed gas is passed through a fractionation column (150) where it is cooled and separated into an overhead fraction with a reduced content of hydrocarbons with a molecular weight higher than pentane (C5), and a bottom fraction ( 3) enriched with (C6) and hydrocarbons with a molecular weight higher than C6. 3. Fremgangsmåte i samsvar med krav 1-2 karakterisert ved at fraksjoneringskolonnen (150) og separatoren 160 drives slik at pentan (C5, NBP=28 til -36°C) er en overgangskomponent som fordeler seg både i systemets overhead gasstrøm (6) og i systemets rejektstrøm (3). 3. Method in accordance with claims 1-2, characterized in that the fractionation column (150) and the separator 160 are operated so that pentane (C5, NBP=28 to -36°C) is a transition component that is distributed both in the system's overhead gas stream (6) and in the system's reject current (3). 4. Fremgangsmåte i samsvar med krav 1-3, karakterisert ved at fraksjoneringskolonnen (150) og separatoren 160 drives ved trykk og temperaturer som medfører at det samlede systemet (fraksjoneringskolonnen 150 og refluksseparator 160) genererer en komponentsplitt/separasjonspunkt i normalkokepunktområdet (NBP) mellom -12°C og 60°C. 4. Method in accordance with claims 1-3, characterized in that the fractionation column (150) and the separator 160 are operated at pressures and temperatures which cause the overall system (fractionation column 150 and reflux separator 160) to generate a component split/separation point in the normal boiling point range (NBP) between -12°C and 60°C. 5. Fremgangsmåte i samsvar med krav 1-4 karakterisert ved at den lette nøkkelkomponent for separasjonen er butan (C4) med normalkokepunkt mellom -12°C og 0°C, og tung nøkkelkomponent er en C6 komponent med kokepunkt mellom 50°C og 70°C, hvorved systemets overhead gasstrøm (6) da vil inneholde det meste av n-butan og hydrokarboner med lavere normalkokepunkt enn n-butan, og systemets rejektstrøm (3) omfatter mesteparten av C6 og komponenter med normalkokepunkt høyere enn C6. 5. Method in accordance with claims 1-4 characterized in that the light key component for the separation is butane (C4) with a normal boiling point between -12°C and 0°C, and the heavy key component is a C6 component with a boiling point between 50°C and 70 °C, whereby the system's overhead gas stream (6) will then contain most of n-butane and hydrocarbons with a lower normal boiling point than n-butane, and the system's reject stream (3) includes most of C6 and components with a normal boiling point higher than C6. 6. Fremgangsmåte i samsvar med et av de foregående krav, karakterisert ved at fødegassens temperatur reduseres gjennom fraksjoneringskolonnen (150) slik at gassens temperatur når den innføres i varmeveksiersystemet (110) er lavere enn kjølegasstrømmenes temperatur i varm ende av varmeveksiersystemet (varmt pinch point temperatur) 6. Method in accordance with one of the preceding claims, characterized in that the temperature of the feed gas is reduced through the fractionation column (150) so that the temperature of the gas when it is introduced into the heat exchanger system (110) is lower than the temperature of the cooling gas streams at the hot end of the heat exchanger system (hot pinch point temperature ) 7. Fremgangsmåte i samsvar med et av de foregående krav, karakterisert ved at det anvendes en reboiler (135) tilkoblet til fraksjoneringskolonnen (150) for å redusere bunnproduktets damptrykk. 7. Method in accordance with one of the preceding claims, characterized in that a reboiler (135) connected to the fractionation column (150) is used to reduce the vapor pressure of the bottom product. 8. Fremgangsmåte i samsvar med et av de foregående krav, karakterisert ved at den anvendte varmeveksleren for flytendegjøring (LNG produksjon) omfatter en eller flere multistrøms varmevekslere. 8. Method in accordance with one of the preceding claims, characterized in that the used heat exchanger for liquefaction (LNG production) comprises one or more multi-flow heat exchangers. 9. Fremgangsmåte i samsvar med et av de foregående krav, karakterisert ved at den utføres med en lukket gassekspansjonsprosess med minst en nitrogen-ekspander 9. Method in accordance with one of the preceding claims, characterized in that it is carried out with a closed gas expansion process with at least one nitrogen expander 10. Fremgangsmåte i samsvar med et av de foregående krav, karakterisert ved at den utføres med en åpen gassekspansjonsprosess med minst en gassekspander, hvori egnet gass ved et høyere trykk benyttes som kjølegass, og hvor den ekspanderte gassen ved et lavere trykk ikke rekomprimeres for gjenbruk men benyttes til et annet formål. 10. Method in accordance with one of the preceding claims, characterized in that it is carried out with an open gas expansion process with at least one gas expander, in which suitable gas at a higher pressure is used as cooling gas, and where the expanded gas at a lower pressure is not recompressed for reuse but used for another purpose. 11. System for utførelse av fremgangsmåte i henhold til krav 1-10 bestående av en fraksjoneringskolonne (150) for innføring av en fødegass, et varmevekslersystem (110) for nedkjøling og delvis kondensering av fraksjoneringskolonnens overhead gasstrøm, en separator (160) for å separere tofasestrømmen fra varmeveksiersystemet, innretning for tilbakeføring av væske fra separatoren til fraksjoneringskolonnen og innføring av denne væsken i kolonnens øver del som refluks, og innretning for å føre gassen fra separatoren tilbake til varmeveksiersystemet for videre nedkjøling og flytendegjøring til LNG, karakterisert ved at kjølesystemet som benyttes for nedkjøling, kondensering og flytendegjøring av gass i varmeveksiersystemet omfatter en åpen eller lukket gassekspansjonsprosess med minst ett gassekspansjonstrinn. 11. System for carrying out the method according to claims 1-10 consisting of a fractionation column (150) for introducing a feed gas, a heat exchanger system (110) for cooling and partial condensation of the overhead gas stream of the fractionation column, a separator (160) for separating the two-phase flow from the heat exchanger system, device for returning liquid from the separator to the fractionation column and introducing this liquid into the upper part of the column as reflux, and device for returning the gas from the separator to the heat exchanger system for further cooling and liquefaction into LNG, characterized in that the cooling system used for cooling, condensing and liquefaction of gas in the heat exchanger system comprises an open or closed gas expansion process with at least one gas expansion stage. 12. System i samsvar med krav 11, karakterisert ved at en reboiler (135) er koblet til fraksjoneringskolonnen (150), hvilken reboiler er innrettet til å redusere bunnproduktets (3) damptrykk. 12. System in accordance with claim 11, characterized in that a reboiler (135) is connected to the fractionation column (150), which reboiler is designed to reduce the vapor pressure of the bottom product (3). 13. System i samsvar med krav 11, karakterisert ved at varmeveksleren for flytendegjøring (LNG produksjon) omfatter en eller flere multistrøms varmevekslere. 13. System in accordance with claim 11, characterized in that the heat exchanger for liquefaction (LNG production) comprises one or more multi-flow heat exchangers. 14. System i samsvar med krav 11, karakterisert ved at kjøleprosessen er en lukket gassekspansjonsprosess med minst en nitrogenekspanderfor kjøling. 14. System in accordance with claim 11, characterized in that the cooling process is a closed gas expansion process with at least one nitrogen expander for cooling. 15. System i samsvar med krav 11, karakterisert ved at gassekspansjonsprosessen omfatter et gassformig kjølemiddel ved et trykk på mellom 3 og 10 MPa og som ledes til varmeveksiersystemet 110 og kjøles til en temperatur mellom 0°C og -120°, og hvor den avkjølte gassen ekspanderes til et trykk mellom 5% - 40% av innløpstrykket, ledes så tilbake til varmevekslerne 110 der den benyttes for nedkjøling. 15. System in accordance with claim 11, characterized in that the gas expansion process comprises a gaseous coolant at a pressure of between 3 and 10 MPa and which is led to the heat exchange system 110 and cooled to a temperature between 0°C and -120°, and where the cooled the gas is expanded to a pressure between 5% - 40% of the inlet pressure, then led back to the heat exchangers 110 where it is used for cooling. 16. System i samsvar med krav 11, karakterisert ved at kjølekretsen omfatter to ekspansjonstrinn, hvor det gassformige kjølemiddel ved et trykk på mellom 3 og 10 MPa kan splittes i to deler enten før eller etter forkjøling i varmeveksiersystemet, og hvor de to delene forkjøles til forskjellige temperaturer i varmeveksiersystemet, og de to delene ekspanderes til vesentlig det samme trykket før de ledes tilbake til forskjellige lokasjoner på varmeveksiersystemet for å utføre kjøling.16. System in accordance with claim 11, characterized in that the cooling circuit comprises two expansion stages, where the gaseous coolant at a pressure of between 3 and 10 MPa can be split into two parts either before or after precooling in the heat exchanger system, and where the two parts are precooled to different temperatures in the heat exchanger system, and the two parts are expanded to substantially the same pressure before being returned to different locations on the heat exchanger system to perform cooling.
NO20073245A 2007-06-22 2007-06-22 Process and system for forming liquid LNG NO329177B1 (en)

Priority Applications (10)

Application Number Priority Date Filing Date Title
NO20073245A NO329177B1 (en) 2007-06-22 2007-06-22 Process and system for forming liquid LNG
KR1020107001622A KR101568763B1 (en) 2007-06-22 2008-06-20 Method and system for producing lng
EP08779082A EP2165140A1 (en) 2007-06-22 2008-06-20 Method and system for producing lng
CN200880021514.8A CN101711335B (en) 2007-06-22 2008-06-20 method and system for producing LNG
US12/665,329 US20100132405A1 (en) 2007-06-22 2008-06-20 Method and system for producing LNG
AU2008283102A AU2008283102B2 (en) 2007-06-22 2008-06-20 Method and system for producing LNG
CA002692213A CA2692213A1 (en) 2007-06-22 2008-06-20 Method and system for producing lng
PCT/NO2008/000229 WO2009017414A1 (en) 2007-06-22 2008-06-20 Method and system for producing lng
MYPI20095466A MY163902A (en) 2007-06-22 2008-06-20 Method and system for producing lng.
BRPI0813297-6A2A BRPI0813297A2 (en) 2007-06-22 2008-06-20 METHOD AND SYSTEM FOR LIQUID NATURAL GAS (LNG) PRODUCTION

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AU2008283102B2 (en) 2013-02-07
MY163902A (en) 2017-11-15
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US20100132405A1 (en) 2010-06-03
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BRPI0813297A2 (en) 2014-12-30
NO20073245L (en) 2008-12-23

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