AU2008221073B2 - Method for the separation of nitrogen from liquefied natural gas - Google Patents

Method for the separation of nitrogen from liquefied natural gas Download PDF

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Publication number
AU2008221073B2
AU2008221073B2 AU2008221073A AU2008221073A AU2008221073B2 AU 2008221073 B2 AU2008221073 B2 AU 2008221073B2 AU 2008221073 A AU2008221073 A AU 2008221073A AU 2008221073 A AU2008221073 A AU 2008221073A AU 2008221073 B2 AU2008221073 B2 AU 2008221073B2
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rich fraction
substream
liquefied hydrocarbon
stripping column
liquefied
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AU2008221073A1 (en
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Heinz Bauer
Hubert Franke
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Linde GmbH
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Linde GmbH
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/0204—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the feed stream
    • F25J3/0209—Natural gas or substitute natural gas
    • 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
    • C10L3/10—Working-up natural gas or synthetic natural gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/0002—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the fluid to be liquefied
    • F25J1/0022—Hydrocarbons, e.g. natural gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/003—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production
    • F25J1/0032—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration"
    • F25J1/0042—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 liquid expansion 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
    • F25J1/02—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
    • F25J1/0258—Construction and layout of liquefaction equipments, e.g. valves, machines vertical layout of the equipments within in the cold box
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/0228—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
    • F25J3/0233—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of CnHm with 1 carbon atom or more
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/0228—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
    • F25J3/0257—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of nitrogen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2200/00—Processes or apparatus using separation by rectification
    • F25J2200/02—Processes or apparatus using separation by rectification in a single pressure main column system
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2200/00—Processes or apparatus using separation by rectification
    • F25J2200/40—Features relating to the provision of boil-up in the bottom of a column
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2200/00—Processes or apparatus using separation by rectification
    • F25J2200/70—Refluxing the column with a condensed part of the feed stream, i.e. fractionator top is stripped or self-rectified
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2205/00—Processes or apparatus using other separation and/or other processing means
    • F25J2205/30—Processes or apparatus using other separation and/or other processing means using a washing, e.g. "scrubbing" or bubble column for purification purposes
    • 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
    • F25J2210/00—Processes characterised by the type or other details of the feed stream
    • F25J2210/90—Boil-off gas from storage
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2215/00—Processes characterised by the type or other details of the product stream
    • F25J2215/04—Recovery of liquid products
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
    • F25J2230/08—Cold compressor, i.e. suction of the gas at cryogenic temperature and generally without afterstage-cooler
    • 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
    • F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
    • F25J2230/42—Processes or apparatus involving steps for increasing the pressure of gaseous process streams the fluid being nitrogen
    • 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
    • F25J2240/00—Processes or apparatus involving steps for expanding of process streams
    • F25J2240/30—Dynamic liquid or hydraulic expansion with extraction of work, e.g. single phase or two-phase turbine
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2245/00—Processes or apparatus involving steps for recycling of process streams
    • F25J2245/42—Processes or apparatus involving steps for recycling of process streams the recycled stream being nitrogen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2245/00—Processes or apparatus involving steps for recycling of process streams
    • F25J2245/90—Processes or apparatus involving steps for recycling of process streams the recycled stream being boil-off gas from storage
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/12—External refrigeration with liquid vaporising loop
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2280/00—Control of the process or apparatus
    • F25J2280/02—Control in general, load changes, different modes ("runs"), measurements
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2290/00—Other details not covered by groups F25J2200/00 - F25J2280/00
    • F25J2290/40—Vertical layout or arrangement of cold equipments within in the cold box, e.g. columns, condensers, heat exchangers etc.
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2290/00—Other details not covered by groups F25J2200/00 - F25J2280/00
    • F25J2290/62—Details of storing a fluid in a tank

Abstract

Disclosed is a method for separating an N-rich fraction from a liquefied hydrocarbon-rich fraction, particularly liquefied natural gas. In said method, the liquefied hydrocarbon-rich fraction is fed to a stripping column, which is used for separating the N-rich fraction, after being liquefied and being supercooled. According to the invention, a first partial flow of the liquefied hydrocarbon-rich fraction (2, 2') is fed to the stripping column (S) as reflux while a second partial flow of the liquefied hydrocarbon-rich fraction (3, 3') is fed to the bottom of the stripping column (S). The second partial flow of the liquefied hydrocarbon-rich fraction (3, 3') has a higher temperature than the first partial flow of the liquefied hydrocarbon-rich fraction (2, 2').

Description

METHOD OF SEPARATING OFF NITROGEN FROM LIQUEFIED NATURAL GAS Field of the Invention 5 The invention relates to a method of separating off an
N
2 -rich fraction from a liquefied hydrocarbon-rich fraction, in particular from liquefied natural gas, wherein the liquefied hydrocarbon-rich fraction, after its liquefaction and subcooling, is fed to a stripping 10 column which serves for separating off the N 2 -rich fraction. Background of the Invention Any discussion of the prior art throughout the 15 specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field. Methods of the type in question for separating off an 20 N 2 -rich fraction from a liquefied hydrocarbon-rich fraction are used, in particular, in the liquefaction of natural gas. The liquefied natural gas (LNG) obtained by means of the prior art liquefaction method typically is allowed only to have a nitrogen content of a maximum of 25 1% by volume. If the nitrogen content is above this threshold value, generally separating off the impermissible nitrogen amount from the liquefied natural gas is required. 30 This nitrogen separation customarily proceeds via a pressure expansion of the natural gas which was liquefied under pressure, wherein via a suitable choice, with respect to temperature and pressure of the -2 liquefied natural gas, of the initial state before expansion and of the pressure after expansion, a targeted outgassing of the liquefied natural gas is achieved. The nitrogen which is unwanted in the liquid 5 phase, this is the wanted LNG product, is removed via the resultant gas phase. In this procedure, however, there is the problem that, depending on the boiling equilibrium, the amount of 10 methane outgassing together with the nitrogen to be removed is undesirably high. To avoid this disadvantage, methods of the type in question for separating off nitrogen from liquefied natural gas are used, in which, by providing a stripping column, nitrogen can be 15 depleted more selectively, and simultaneously, the unwanted losses of methane to the nitrogen-rich fraction to be depleted can be decreased. Such a method of the type in question for separating off a nitrogen-rich fraction from a liquefied hydrocarbon-rich fraction may 20 be taken, for example, from US-Patent 5,893 274. In the abovementioned procedure, the liquified hydro carbon-rich fraction, after its expansion, is delivered in two phases to the top of the stripping column. The 25 bottom of the stripping column is heated with the liquefied hydrocarbon-rich fraction, before its expansion, in indirect heat exchange via a reboiler. The liquid fraction produced in the bottom of the stripping column is the desired LNG product, whereas the nitrogen 30 rich gas fraction taken off at the top of the stripping column is generally then used as combustion gas.
- 3 However, it is disadvantageous in this procedure that a heat exchanger or reboiler which serves for heating the bottom of the stripping column is required. This is exposed to high thermal stresses, in particular in non 5 steady-state conditions, such as starting up the stripping process or plant stoppage. If there is a failure of this component, this generally leads to a complete plant shutdown, which can extend over an unacceptable long period, up to some weeks. 10 It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative. It is an object of an especially preferred form of the invention 15 to specify a method of the type in question for separating off an N 2 -rich fraction from a liquefied hydrocarbon-rich fraction, which method avoids the abovementioned disadvantages. 20 Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the 25 sense of "including, but not limited to". Although the invention will be described with reference to specific examples it will be appreciated by those skilled in the art that the invention may be embodied in 30 many other forms.
- 3a Summary of the Invention According to a first aspect of the present invention there is provided a method of separating off an N 2 -rich fraction from a liquefied hydrocarbon-rich fraction, 5 wherein the liquefied hydrocarbon-rich fraction, after its liquefaction and subcooling, is fed to a stripping column which serves to separate off the N 2 -rich fraction, wherein a first substream of the liquefied hydrocarbon-rich fraction is applied to the stripping 10 column as reflux, whereas a second substream of the liquefied hydrocarbon-rich fraction is fed to the bottom of the stripping column, wherein the second substream of the liquefied hydrocarbon-rich fraction has a higher temperature than the first substream of the liquefied 15 hydrocarbon-rich fraction. According to a first aspect of the present invention there is provided an N 2 -rich fraction, when separated from a liquefied hydrocarbon-rich fraction by a method 20 as defined according to the first aspect of the present invention. The invention relates to a method of the type in question for separating off an N 2 -rich fraction from a 25 liquefied hydrocarbon-rich fraction is proposed, which is characterized in that a first substream of the liquefied hydrocarbon-rich fraction is applied to the stripping column as reflux, whereas a second substream of the liquefied hydrocarbon-rich fraction is fed to the 30 bottom of the stripping column, wherein the second substream of the liquefied hydrocarbon-rich fraction has a higher temperature than the first substream of the - 3b liquefied hydrocarbon-rich fraction at liquefaction pressure. According to the invention, henceforth a substream of 5 the liquefied hydrocarbon-rich fraction itself serves as bottom heating for the stripping column. This makes the provision of an additional heat exchanger or reboiler, as is required in the prior art, superfluous. All of the disadvantages associated with this component are 10 consequently avoided in the method according to the invention. However, it is disadvantageous in the method according to the invention that the energy consumption of the liquefaction process selected rises slightly. 15 Further advantageous embodiments of the method according to the invention for separating off an N 2 -rich fraction from a liquefied hydrocarbon-rich fraction which are subject matter of the dependent claims are characterized in that 20 - the first substream and/or the second substream of the liquefied hydrocarbon-rich fraction, before being fed into the stripping column is or are subjected to an expansion, preferably an expansion 25 in a liquid expander, P07037-DE/AVA = EM-AVA2811 28.02.2007 - Christoph Zahn/bg -4 - the temperature difference between the first substream and the second substream of the liquefied hydrocarbon-rich fraction before 5 expansion to the pressure of the stripping column is between 40 and 100 0 C, preferably between 60 and 80 0 C, - the first substream of the liquefied hydrocarbon 10 rich fraction which is applied to the stripping column as reflux has a gas fraction of at most 80% by volume, typically has a vapour fraction after expansion of 20% by volume, preferably 10% by volume, 15 - the quantitative ratio between the first substream and second substream of the hydrocarbon-rich fraction which is fed to the stripping column is variable and 20 - in addition to the second substream of the liquefied hydrocarbon-rich fraction, at least one further methane-rich or nitrogen-rich stream is fed to the bottom of the stripping column. 25 The method according to the invention for separating off an N 2 -rich fraction from a liquefied hydrocarbon rich fraction and also further embodiments of the same will be described in more detail hereinafter with 30 reference to the example method shown in the figure. The hydrocarbon-rich stream to be liquefied, hereinafter termed the natural gas (stream), which is at a pressure between 30 and 120 bar, is fed to a 35 liquefaction process via line 1. This liquefaction process is only shown in diagrammatic form in the figure, more precisely in the form of two heat exchanger regions El and E2 and also a black box R P07037-DE/AVA = EM-AVA2811 28.02.2007 - Christoph Zahn/bg - 5 which is meant to represent the components of one or more refrigerant cycles and/or mixed refrigerant cycles. The procedure of the invention can in principle be combined with all known liquefaction methods. 5 In the embodiment of the method according to the invention shown in the figure, in the heat exchanger El there proceeds a liquefaction and also if appropriate a slight subcooling of the natural gas stream to be 10 liquefied against a (mixed) refrigerant stream which is conducted via line 4 through the heat exchanger El. However, if the natural gas is present in supercritical form, this is the case, depending on the composition of the natural gas, from approximately 60 bar, strictly 15 speaking no liquefaction and subcooling any longer proceed, but rather an increase in density by means of cooling. The liquefied and if appropriate slightly subcooled 20 natural gas stream is taken off from the heat exchanger El via line 1' and divided into two substreams 2 and 3. The first substream is subcooled in the heat exchanger E2 against the (mixed) refrigerant stream 5 which is 25 conducted through the heat exchanger E2 via line 5, expanded so as to produce cold in the liquid expander X1 and subsequently applied via line 2' to the stripping column S at the top thereof as reflux. The stripping column S is customarily operated in a 30 pressure range between 1.0 and 2.0 bar, preferably between 1.0 and 1.3 bar. The second substream of the liquefied and if appropriate slightly subcooled natural gas is fed via 35 line 3 to a liquid expander X2, expanded so as to produce cold in this, and subsequently conducted via line 3' to the bottom of the stripping column S. The abovementioned expander X2 can if appropriate be P07037-DE/AVA = EM-AVA2811 28.02.2007 - Christoph Zahn/bg -6 constructed as what is termed a two-phase expander in which the fluid is present in two phases at the outlet. The abovementioned expanders X1 and X2 can be provided 5 optionally. If they are not provided, or if one of these expanders is not provided, generally use is made of expansion valves a and b, by means of which the substreams fed to the stripping column S are expanded to the pressure of the stripping column S, in the lines 10 2 and 3. Omission of these expansion valves a and b, with simultaneous omission of the abovementioned expanders X1 and X2, would be conceivable if the substreams fed to the stripping column S by the lines 2 and 3 were already present at the pressure prevailing 15 in the stripping column S. The temperature difference between the first substream and second substream of the natural gas stream fed to the stripping column S is, before expansion thereof, 20 between 40 and 100 0 C, preferably between 60 and 80 0 C. The parameters pressure and temperature of the second natural gas substream fed to the stripping column S in the bottom thereof must be selected such that this substream, after its expansion to the pressure of the 25 stripping column S, is present in two phases. As a result, the gas phase can be used as stripping vapour for the stripping column S. Via the control of the quantitative ratio between the 30 two natural gas substreams 2/2' and 3/3' and also of their vapour fractions after their expansion to the pressure of the stripping column S, the desired nitrogen stripping from the LNG product produced in the bottom of the stripping column S can be achieved. At 35 the same time, by means of this procedure, as previously, the methane content of the overhead product of the stripping column S can be controlled or set.
P07037-DE/AVA = EM-AVA2811 28.02.2007 - Christoph Zahn/bg - 7 The LNG product is taken off from the bottom of the stripping column S via line 6 and fed, for example, to an LNG store T. From this it can be fed by means of the pump P via line 7 to an LNG carrier C. 5 The nitrogen-rich fraction taken off at the top of the stripping column S via line 9 is customarily compressed in one or more stages to the desired delivery pressure and fed via line 10 to its further use, for example as 10 combustion gas. The compression V is preferably implemented by means of a cold-intake compressor. The use of a cold-intake compressor enables the pressure in the stripping column 15 S to be close to atmospheric pressure without having to risk oxygen ingress into the nitrogen-rich fraction which is taken off via line 9, which would be feared in the event of warming of the nitrogen-rich fraction which is taken off via line 9 owing to a pressure loss. 20 Advantageously, the compressor V which is used for the compression has adjustable inlet blades. These make possible a high load range without a requirement of gas recycling which can be achieved via line 11. The 25 nitrogen-rich fraction fed via line 11 to the bottom of the stripping column S is what is termed the surge protection fraction. The boil-off gas produced during loading of the LNG 30 carrier C can likewise be fed via line 12 to the bottom of the stripping column S and/or be recycled via the lines 12 and 8 to the LNG store T. In addition, the boil-off gas produced in the LNG store T can be fed via the lines 8 and 12 to the bottom of the stripping 35 column S. Via this means, also the abovementioned fractions fed to the bottom of the stripping column S, together with the second substream of the liquefied P07037-DE/AVA = EM-AVA2811 28.02.2007 - Christoph Zahn/bg - 8 natural gas stream, can serve for the stripping process. Customarily, in line 8, a fan G, which is shown dashed 5 in the figure, must be provided, by means of which the boil-off gas produced in the LNG store T is fed to the bottom of the stripping column S. Omission of such a fan is possible when the stripping column S can be mounted sufficiently high above the LNG store T, so 10 that although the pressure in the LNG store T can be higher than in the bottom of the stripping column S, the provision of a pump in line 6 is not necessary.

Claims (13)

1. A method of separating off an N 2 -rich fraction from a liquefied hydrocarbon-rich fraction, wherein the 5 liquefied hydrocarbon-rich fraction, after its liquefaction and subcooling, is fed to a stripping column which serves to separate off the N 2 -rich fraction, wherein a first substream of the liquefied hydrocarbon-rich fraction is applied to 10 the stripping column as reflux, whereas a second substream of the liquefied hydrocarbon-rich fraction is fed to the bottom of the stripping column, wherein the second substream of the liquefied hydrocarbon-rich fraction has a higher 15 temperature than the first substream of the liquefied hydrocarbon-rich fraction.
2. A method according to claim 1, wherein the liquefied hydrocarbon-rich fraction is liquefied 20 natural gas
3. A method according to claim 1 or claim 2, wherein the first substream and/or the second substream of the liquefied hydrocarbon-rich fraction, before 25 being fed into the stripping column is or are subjected to an expansion.
4. A method according to claim 3, wherein the expansion is in a liquid expander. 30
5. A method according to any one of the preceding claims, wherein the temperature difference between the first substream and the second substream of - 10 the liquefied hydrocarbon-rich fraction is between 40 and 100 CC.
6. A method according to any one of the preceding 5 claims, wherein the temperature difference between the first substream and the second substream of the liquefied hydrocarbon-rich fraction is between 60 and 80 0 C. 10
7. A method according to any one of the preceding claims, wherein the first substream of the liquefied hydrocarbon-rich fraction which is applied to the stripping column as reflux has a gas fraction of at most 80% by volume. 15
8. A method according to any one of the preceding claims, wherein the quantitative ratio between the first substream and second substream of the hydrocarbon-rich fraction which is fed to the 20 stripping column is variable.
9. A method according to any one of the preceding claims, wherein in addition to the second substream of the liquefied hydrocarbon-rich 25 fraction, at least one further methane-rich or nitrogen-rich stream is fed to the bottom of the stripping column.
10. A method according to any one of the preceding 30 claims, wherein as the second substream is expanded and at least partly vaporised, said substream acts as a stripping vapour.
- 11 11. An N 2 -rich fraction, when separated from a liquefied hydrocarbon-rich fraction by a method as defined according to any one of the preceding claims. 5
12. A method according to claim 1, said method substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or 10 examples.
13. An N 2 -rich fraction, when separated from a liquefied hydrocarbon-rich fraction by a method substantially as herein described with reference 15 to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples. 20 Dated this 3 rd day of August 2012 Shelston IP Attorneys for: Linde Aktiengesellschaft
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DE102007010032A DE102007010032A1 (en) 2007-03-01 2007-03-01 Procedure for separating a nitrogen-rich fraction from a liquefied natural gas, comprises supplying the natural gas after its liquefaction and super cooling, to a stripping column that serves the separation of the nitrogen-rich fraction
PCT/EP2008/001290 WO2008104308A2 (en) 2007-03-01 2008-02-19 Method for the separation of nitrogen from liquefied natural gas

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KR20120040700A (en) * 2009-07-21 2012-04-27 쉘 인터내셔날 리써취 마트샤피지 비.브이. Method for treating a multi-phase hydrocarbon stream and an apparatus therefor
DE102009038458A1 (en) * 2009-08-21 2011-02-24 Linde Ag Process for separating nitrogen from natural gas
DE102010044646A1 (en) * 2010-09-07 2012-03-08 Linde Aktiengesellschaft Process for separating nitrogen and hydrogen from natural gas
FR2971332B1 (en) 2011-02-09 2017-06-16 Air Liquide METHOD AND APPARATUS FOR CRYOGENIC SEPARATION OF METHANE RICH FLOW
WO2013087570A2 (en) * 2011-12-12 2013-06-20 Shell Internationale Research Maatschappij B.V. Method and apparatus for removing nitrogen from a cryogenic hydrocarbon composition
WO2013087569A2 (en) * 2011-12-12 2013-06-20 Shell Internationale Research Maatschappij B.V. Method and apparatus for removing nitrogen from a cryogenic hydrocarbon composition
AU2012354774B2 (en) * 2011-12-12 2015-09-10 Shell Internationale Research Maatschappij B. V. Method and apparatus for removing nitrogen from a cryogenic hydrocarbon composition
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