AU2008229702B2 - Process for helium enrichment - Google Patents

Process for helium enrichment Download PDF

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AU2008229702B2
AU2008229702B2 AU2008229702A AU2008229702A AU2008229702B2 AU 2008229702 B2 AU2008229702 B2 AU 2008229702B2 AU 2008229702 A AU2008229702 A AU 2008229702A AU 2008229702 A AU2008229702 A AU 2008229702A AU 2008229702 B2 AU2008229702 B2 AU 2008229702B2
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fraction
helium
nitrogen
methane
enriched
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AU2008229702A1 (en
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Heinz Bauer
Martin Gwinner
Rainer Sapper
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Linde GmbH
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Linde GmbH
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • 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"
    • F25J1/004—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 flash gas recovery
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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"
    • F25J1/0045—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration" by vaporising a liquid return stream
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    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0228—Coupling of the liquefaction unit to other units or processes, so-called integrated processes
    • F25J1/0229—Integration with a unit for using hydrocarbons, e.g. consuming hydrocarbons as feed stock
    • F25J1/023—Integration with a unit for using hydrocarbons, e.g. consuming hydrocarbons as feed stock for the combustion as fuels, i.e. integration with the fuel gas system
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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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    • F25J1/02—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
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    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/06—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation
    • F25J3/0605—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation characterised by the feed stream
    • F25J3/061—Natural gas or substitute natural gas
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    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/06—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation
    • F25J3/063—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation characterised by the separated product stream
    • F25J3/0635—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation characterised by the separated product stream separation of CnHm with 1 carbon atom or more
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    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/06—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation
    • F25J3/063—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation characterised by the separated product stream
    • F25J3/066—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation characterised by the separated product stream separation of nitrogen
    • 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
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/06—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation
    • F25J3/063—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation characterised by the separated product stream
    • F25J3/0685—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation characterised by the separated product stream separation of noble gases
    • F25J3/069—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation characterised by the separated product stream separation of noble gases of helium
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    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/06—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation
    • F25J3/0695—Start-up or control of the process; Details of the apparatus used
    • 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
    • F25J2205/02—Processes or apparatus using other separation and/or other processing means using simple phase separation in a vessel or drum
    • 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
    • F25J2205/40—Processes or apparatus using other separation and/or other processing means using hybrid system, i.e. combining cryogenic and non-cryogenic separation techniques
    • 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
    • F25J2205/60—Processes or apparatus using other separation and/or other processing means using adsorption on solid adsorbents, e.g. by temperature-swing adsorption [TSA] at the hot or cold end
    • 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
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    • F25J2215/00—Processes characterised by the type or other details of the product stream
    • F25J2215/04—Recovery of liquid products
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    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2220/00—Processes or apparatus involving steps for the removal of impurities
    • F25J2220/60—Separating impurities from natural gas, e.g. mercury, cyclic hydrocarbons
    • F25J2220/62—Separating low boiling components, e.g. He, H2, N2, Air
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    • F25J2290/00—Other details not covered by groups F25J2200/00 - F25J2280/00
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  • Engineering & Computer Science (AREA)
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  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
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Abstract

Abstract A process is described for obtaining a helium-enriched fraction (16) from a fraction (1) comprising essentially 5 methane, nitrogen and helium, for example an LNG fraction. According to the invention, this process comprises the following process steps: 10 a) decompressing (a) and separating (D3) the fraction (1) comprising essentially methane, nitrogen and helium into a helium-richer gas fraction (6) comprising methane and nitrogen and a liquid fraction (7) comprising methane and nitrogen, b) decompressing (d) and separating (D4) the liquid fraction (7) comprising methane and nitrogen into a nitrogen-rich gas fraction (8) and a methane-rich liquid fraction (17), c) cooling and partially condensing (E) the helium-richer gas fraction (6) comprising methane and nitrogen, d) separating (D7) the partially condensed helium-richer 25 fraction (6) comprising methane and nitrogen into a helium-enriched gas fraction (13) and a nitrogen/methane-rich liquid fraction (14), and e) decompressing (k) and evaporating the nitrogen/ 30 methane-rich liquid fraction (14) in indirect heat exchange (E) with the helium-richer fraction (6) which comprises methane and nitrogen and is to be partially condensed.

Description

- 1 AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT ORIGINAL Name of Applicant/s: Linde Aktiengesellschaft Actual Inventor/s: Heinz Bauer and Rainer Sapper and Martin Gwinner Address for Service is: SHELSTON IP 60 Margaret Street Telephone No: (02) 9777 1111 SYDNEY NSW 2000 Facsimile No. (02) 9241 4666 CCN: 3710000352 Attorney Code: SW Invention Title: PROCESS FOR HELIUM ENRICHMENT The following statement is a full description of this invention, including the best method of performing it known to me/us: File: 59588AUP00 - la Description Process for helium enrichment 5 The invention relates to a process for obtaining a helium enriched fraction from a fraction comprising essentially methane, nitrogen and helium, for example an LNG fraction.'' 10 Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field. 15 At present, helium is obtained predominantly from natural gas, in which it is present, however, only in a highly dilute state - typically the helium content is a few 100 ppmv or less. In order to be able to obtain helium in an economically viable manner, hydrocarbons and nitrogen 20 have to be removed in a very efficient manner. It is therefore customary to integrate the obtaining of helium into a natural gas liquefaction process or to connect it thereto. Since the hydrocarbons are naturally liquefied here, but nitrogen is permissible only up to a certain 25 limit in the liquefied natural gas product (LNG), almost every natural gas liquefaction plant includes a process step in which a gaseous, nitrogen-rich fraction is removed from the LNG. This process step is typically referred to as the end flash. 30 The helium enrichment by means of a one-stage gas-liquid separation is, however, not considered to be optimal, since the helium is still present "contaminated" with a large amount of nitrogen and light hydrocarbons, especially 35 methane. After the liquefaction, the LNG is therefore generally decompressed to an elevated pressure in a first stage, and a helium-rich gas stream is drawn off in a first separator. The methane- and nitrogen-rich liquid fraction obtained in the first separator is then decompressed to a - 2 lower pressure and separated in a second separator into a nitrogen-rich gas fraction - which typically forms the combustion gas fraction - and a methane-rich liquid fraction. The majority of the nitrogen outgassing thus does 5 not take place until the decompression upstream of or in the second separator. In the case of such a procedure, the helium concentration in the gas phase of the first separator is increased 10 compared to a one-stage decompression and phase separation. The helium-enriched gas stream is generally purified in a downstream purification process to such an extent that it liquefies and can be marketed as an on-spec liquid helium product. 15 The helium concentration in this gas stream drawn off from the first separator is, however, relatively low. It is between 2 and 20 mol%, typically between 3 and 10 mol%. This has the consequence that a considerable level of 20 apparatus complexity and energy expenditure is required in the subsequent fine purification. Furthermore, the content of combustible components, especially of methane, in the gas stream drawn off from the first separator is still sufficiently high that these combustible components which 25 are removed together with the nitrogen to be removed in the fine purification cannot or should not be released to the atmosphere owing to undesired product losses and/or owing to environmental considerations. 30 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. Unless the context clearly requires otherwise, throughout 35 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 - 3 sense; that is to say, in the sense of "including, but not limited to". Although the invention will be described with reference to 5 specific examples it will be appreciated by those skilled in the art that the invention may be embodied in many other forms. According to a first aspect, the present invention provides 10 a process for obtaining a helium-enriched fraction is proposed, which has the following process steps: a) decompressing and separating the fraction comprising essentially methane, nitrogen and helium into a 15 helium-richer gas fraction comprising methane and nitrogen and a liquid fraction comprising methane and nitrogen, b) decompressing and separating the liquid fraction 20 comprising methane and nitrogen into a nitrogen-rich gas fraction and a methane-rich liquid fraction, c) cooling and partially condensing the helium-richer gas 25 fraction comprising methane and nitrogen, d) separating the partially condensed helium-richer fraction comprising methane and nitrogen into a helium-enriched gas fraction and a nitrogen/ methane-rich liquid fraction, and 30 e) decompressing and evaporating the nitrogen/ methane-rich liquid fraction in indirect heat exchange with the helium-richer fraction which comprises methane and nitrogen and is to be partially condensed. 35 According to a second aspect, the present invention provides a helium-enriched fraction from a fraction comprising essentially methane, nitrogen and helium, said - 4 helium-enriched fraction obtained by a process according to the first aspect. Further advantageous embodiments of the process according 5 to the invention for obtaining a helium-enriched fraction, which constitute the subject-matter of the dependent claims, are characterized in that - process steps a), c), d) and e) are implemented in at 10 least two decompression and separation apparatuses arranged in series, the pressure of each separation apparatus being lower in each case than the pressure of the upstream separation apparatus, 15 - the helium-enriched fraction has a helium content of at least 40% by volume, preferably of at least 60% by volume, and - the helium-enriched fraction is subjected to a 20 subsequent purification, preferably to an adsorptive subsequent purification. The process according to the invention for obtaining a helium-enriched fraction and further embodiments thereof, 25 which constitute the subject-matter of the dependent claims, will be explained in detail hereinafter with reference to the working example shown in the figure. By means of the process according to the invention, 30 essentially two gaseous fractions are obtained. This is a combustion gas fraction which is drawn off via line 8 at the top of the separator D4. This comprises the majority of the nitrogen, which is not permissible in the methane-rich product fraction drawn off from the bottom of the separator 35 D4 via line 17. The combustion gas fraction in line 8 typically has a pressure between 1.05 and 2.0 bara, preferably between 1.1 and 1.5 bara.
- 5 At the top of the separator D3, a helium-richer, methane and nitrogen-containing gas fraction is drawn off via line 6 and forms the second gaseous fraction, specifically the so-called crude helium fraction. This fraction is present 5 at a pressure between 2 and 10 bara, preferably 3 and 6 bara. Higher pressures are advantageous because the downstream fine purification, which may be provided, of the helium-enriched stream drawn off from the process via line 16 can thus be conducted less expensively. 10 According to the invention, the crude helium fraction drawn off via line 6 at the top of the separator D3 is now cooled and partially condensed in the heat exchanger E. In the separator D7, a separation into a helium-enriched gas 15 fraction and a nitrogen/methane-rich liquid fraction is then effected. This liquid fraction is drawn off from the bottom of the separator D7 via line 14, decompressed in the valve k to the desired release pressure of the combustion gas fraction in line 8, and evaporated against process 20 streams to be cooled before being mixed with the combustion gas fraction in the heat exchanger E. The helium-enriched gas fraction drawn off via line 13 at the top of the separator D7, after incipient heating in the 25 heat exchanger E, is sent via line 16 to its further use or further treatment, such as a fine purification. Under favourable conditions, the helium-enriched gas fraction drawn off from the top of the separator D7 via 30 line 13 already satisfies the requirements of any downstream helium fine purification process. Since, however, increasingly high demands are being made on emissions, it is advantageous to lower the methane content in this helium-enriched gas fraction as far as possible, 35 since the methane remaining in this fraction should preferably be removed with the nitrogen in the fine purification and be released to the atmosphere.
- 6 In order to achieve a very low methane concentration in the helium-enriched stream, in an advantageous embodiment of the process according to the invention, decompression, removal of the helium crude fraction in the separator D3 5 and methane discharge in the separator D7 are conducted in several stages. Similarly to a rectification column, the associated increase in the number of equilibrium stages enables a 10 sharper methane-helium separation. In contrast to rectification columns, the equilibrium stages are, however, operated here at different pressures (PD1 > PD 2 > PD3 > PD 4 ) In general, a number of three pressure stages - achieved by the three separators Dl, D3 and D4 - is sufficient to 15 achieve the desired helium purity and yield. If required, it is, however, possible to provide one or more additional equilibrium stages until the required purities are achieved. In the figure, an additional equilibrium stage is shown by the separators D2 and D6 drawn with dotted lines. 20 The figure shows a procedure in which four equilibrium stages, achieved by the separators Dl to D4, are provided. The fraction comprising essentially methane, nitrogen and 25 helium, which stems, for example, from a natural gas liquefaction process, is decompressed in valve a and separated in a first separator Dl into a helium-enriched gas fraction and an essentially methane- and nitrogen containing liquid fraction. The liquid fraction is drawn 30 off from the separator Dl via line 3, decompressed in valve b and separated again in a second separator D2 into a helium-enriched gas fraction and an essentially methane and nitrogen-containing liquid fraction. The latter is drawn off from the bottom of the separator D2 via line 5, 35 decompressed in valve c and separated in the third separator D3 into a helium-enriched gas fraction and an essentially methane- and nitrogen-containing, liquid fraction. The latter is drawn off from the bottom of the separator D2 via line 5, decompressed in valve c and -7 separated in the third separator D3 into a helium-enriched gas fraction and an essentially methane- and nitrogen containing liquid fraction. The latter is drawn off from the separator D3 via line 7, decompressed in valve d and 5 separated in the fourth separator D4 into the combustion gas fraction already mentioned and a methane-rich liquid fraction. While the methane-rich liquid fraction is fed via line 17 10 to its further use and/or intermediate storage, the combustion gas fraction is drawn off via line 8 and, after addition of the methane-rich fractions from separators D5 to D7 via line 15, sent to its further use. 15 The helium-enriched gas fractions drawn off from the separators Dl to D3 via lines 2, 4 and 6 are in each case cooled in the heat exchanger E, partially condensed at the same time and then separated in the separators D5, D6 and D7 into a helium-enriched gas fraction and a methane-rich 20 liquid fraction. The helium-enriched gas fractions are drawn off from the separators D5 to D7 via lines 9, 11 and 13 and decompressed in the valves e and g to the desired release pressure existing in line 16. 25 The methane-rich liquid fractions obtained in the separators D5 to D7 are drawn off via lines 10, 12 and 14, decompressed in valves f, h and k to the release pressure of the combustion gas in the line 15, and evaporated in the heat exchanger E upstream of the mixing into the combustion 30 gas stream. By virtue of the above-described staged decompression of the fraction which is present under pressure and comprises essentially methane, nitrogen and helium, virtually full 35 recovery of the helium dissolved in this fraction is enabled. In this case, the achievable yields are 96 to 99.9%, preferably 98 to 99.5%. At the same time, mixing of the crude helium with undesired components, such as -8 nitrogen and especially methane, is substantially prevented. While a one-stage methane discharge, as achievable by means 5 of the separators D3 and D7, enables a crude helium concentration of 30 to 60% by volume, preferably 40 to 50% by volume, addition of a second stage - achieved through the separators Dl and D5 - can already achieve a crude helium concentration of 40 to 85% by volume, preferably 60 10 to 80% by volume. The integration of further removal stages - symbolized in the figure by the separators D2 and D6 shown with dotted lines - enables the crude helium concentration to be raised to more than 90% by volume. However, an economic optimum is achieved when the methane 15 content remaining in the helium-enriched fraction is sufficiently low to allow release of the methane together with the nitrogen to the atmosphere within the regulations which apply. 20 Any final fine purification of the crude helium to virtually 100% which is to be provided is generally effected by means of an adsorption process, preferably of a pressure swing adsorption process. 25 The separators Dl to D4 may be designed as sections of a common, vertical pressure vessel, in which case the section with the highest pressure (Dl) is arranged at the top and the section with the lowest pressure (D4) at the bottom and all other sections between them in the sequence of 30 pressure. The same design in terms of construction is achievable mutatis mutandis for the separators D5 to D7.

Claims (10)

1. Process for obtaining a helium-enriched fraction from a fraction comprising essentially methane, nitrogen and 5 helium, for example an LNG fraction, having the following process steps: a) decompressing and separating the fraction comprising essentially methane, nitrogen and helium into a 10 helium-richer gas fraction comprising methane and nitrogen and a liquid fraction comprising methane and nitrogen, b) decompressing and separating the liquid fraction 15 comprising methane and nitrogen into a nitrogen-rich gas fraction and a methane-rich liquid fraction, c) cooling and partially condensing the helium-richer gas fraction comprising methane and nitrogen, 20 d) separating the partially condensed helium-richer fraction comprising methane and nitrogen into a helium-enriched gas fraction and a nitrogen/methane rich liquid fraction, and 25 e) decompressing and evaporating the nitrogen/ methane-rich liquid fraction in indirect heat exchange with the helium-richer fraction which comprises methane and nitrogen and is to be partially condensed. 30
2. Process according to Claim 1, wherein the fraction comprising essentially methane, nitrogen and helium comprises an LNG fraction. 35
3. Process according to Claim 1 or Claim 2, wherein process steps a), c), d) and e) are implemented in at least two decompression and separation apparatuses arranged in series, the pressure of each separation apparatus being - 10 lower in each case than the pressure of the upstream separation apparatus.
4. Process according to any one of the preceding claims, 5 wherein the helium-enriched fraction has a helium content of at least 40% by volume.
5. Process according to Claim 4, wherein the helium enriched fraction has a helium content of at least 60% by 10 volume.
6. Process according to any one of the preceding claims, wherein the helium-enriched fraction is subjected to a subsequent purification, preferably to an adsorptive 15 subsequent purification.
7. Process according to Claim 6, wherein the subsequent purification is an adsorptive subsequent purification. 20
8. A helium-enriched fraction from a fraction comprising essentially methane, nitrogen and helium, said helium enriched fraction obtained by a process according to any one of the preceding claims. 25
9. Process for obtaining a helium-enriched fraction from a fraction comprising essentially methane, nitrogen and helium, substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples. 30
10. A helium-enriched fraction from a fraction comprising essentially methane, nitrogen and helium, said helium enriched fraction obtained by a process, substantially as herein described with reference to any one of the 35 embodiments of the invention illustrated in the accompanying drawings and/or examples.
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Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3805537A (en) * 1970-08-13 1974-04-23 Linde Ag Helium-enriched helium-hydrogen mixture using methane to scrub out residual nitrogen

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3805537A (en) * 1970-08-13 1974-04-23 Linde Ag Helium-enriched helium-hydrogen mixture using methane to scrub out residual nitrogen

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