AU2013211458A1 - Process for liquefying a hydrocarbon-rich fraction - Google Patents

Process for liquefying a hydrocarbon-rich fraction Download PDF

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Publication number
AU2013211458A1
AU2013211458A1 AU2013211458A AU2013211458A AU2013211458A1 AU 2013211458 A1 AU2013211458 A1 AU 2013211458A1 AU 2013211458 A AU2013211458 A AU 2013211458A AU 2013211458 A AU2013211458 A AU 2013211458A AU 2013211458 A1 AU2013211458 A1 AU 2013211458A1
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Australia
Prior art keywords
hydrocarbon
rich fraction
liquefied
process according
pressure
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Abandoned
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AU2013211458A
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Heinz Bauer
Claudia Gollwitzer
Martin Gwinner
Ana-Maria Lamuela Calvo
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Linde GmbH
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Linde GmbH
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Classifications

    • 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
    • F25J1/0047—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle
    • F25J1/0052—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle by vaporising a liquid refrigerant stream
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/003—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production
    • F25J1/0047—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle
    • F25J1/0052—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle by vaporising a liquid refrigerant stream
    • F25J1/0055—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle by vaporising a liquid refrigerant stream originating from an incorporated cascade
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • 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
    • F25J1/008—Hydrocarbons
    • F25J1/0092—Mixtures of hydrocarbons comprising possibly also minor amounts 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
    • 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
    • F25J1/0095—Oxides of carbon, e.g. CO2
    • 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
    • F25J1/0211—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a multi-component refrigerant [MCR] fluid in a closed vapor compression cycle
    • F25J1/0214—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a multi-component refrigerant [MCR] fluid in a closed vapor compression cycle as a dual level refrigeration cascade with at least one MCR cycle
    • F25J1/0215—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a multi-component refrigerant [MCR] fluid in a closed vapor compression cycle as a dual level refrigeration cascade with at least one MCR cycle with one SCR cycle
    • 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.
    • 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.
    • F25J1/0281—Compression of refrigerant or internal recycle fluid, e.g. kind of compressor, accumulator, suction drum etc. characterised by the type of prime driver, e.g. hot gas expander
    • F25J1/0283—Gas turbine as the prime mechanical driver
    • 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.
    • F25J1/0292—Refrigerant compression by cold or cryogenic suction of the refrigerant 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
    • F25J2290/00—Other details not covered by groups F25J2200/00 - F25J2280/00
    • F25J2290/12—Particular process parameters like pressure, temperature, ratios

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Ocean & Marine Engineering (AREA)
  • Separation By Low-Temperature Treatments (AREA)

Abstract

Abstract Process for liquefying a hydrocarbon-rich fraction Process for liquefying a hydrocarbon-rich fraction, in particular natural gas, is described, in which 5 - the hydrocarbon-rich fraction that is to be liquefied (A - B) is cooled (ElB - E4B) in indirect heat exchange against a multistage precooling circuit (1 9, 30 -37, 40 - 47), - the refrigerant of the precooling circuit is at least 10 95% by volume carbon dioxide, - the cooled hydrocarbon-rich fraction (C) is liquefied and subcooled (E7, E8, E10) in indirect heat exchange against a mixed cycle (10 - 19), and - the mixed refrigerant of the mixed cycle comprises 15 exclusively the component(s) nitrogen, methane and/or ethane. (Figure 1 is associated therewith) iT,

Description

-1 Description Process for liquefying a hydrocarbon-rich fraction The invention relates to a process for liquefying a hydrocarbon-rich fraction, in particular natural gas. 5 Classical natural gas liquefaction systems of the capacity range from 1 to 5 million tons per annum (mtpa) of LNG (Liquefied Natural Gas) are predominantly based on a process having a propane precooling and a mixed cycle for liquefaction and subcooling of the natural gas. Such a 10 liquefaction process is described, for example, in US Patent 3 763 658. It is additionally known to use carbon dioxide as refrigerant for precooling in natural gas liquefaction. The lowest easily reachable temperature, however, is limited by 15 the triple point of carbon dioxide to about -56'C, since carbon dioxide is present in solid form below this temperature and makes difficult a continuous process procedure. The previously described liquefaction process which is 20 outstandingly suitable for land systems contains higher hydrocarbons, in particular propane, not only in the precooling of the pure substance but also in the mixed cycle. These higher hydrocarbons, in the event of leaks in the system, form gas clouds having a density greater than 25 air. As a result, under some circumstances, hazardous, explosive air-hydrocarbon mixtures can form, which are categorized as a considerable safety hazard.
-2 In the case of floating natural gas liquefaction systems (FLNG), therefore, attempts are made to avoid flammable refrigerant entirely - for example, by using nitrogen, carbon dioxide or HCFCs or to limit the spread of local 5 system faults by suitable safety distances between potential hazardous sources. In all cases, however, the space requirement for the liquefaction system increases, and therefore also the capital costs owing to the required enlargement of the relatively expensive ship's hull. This 10 is due, for example, in the case of what are termed N 2 expander processes, to the relatively low thermodynamic efficiency, which requires larger compressors and drives for a given liquefaction output. It is an object of a preferred form of the present 15 invention to specify a process of the type in question for liquefying a hydrocarbon-rich fraction which, owing to a more compact structure, has a smaller space requirement compared with the liquefaction processes currently realized in FLNG systems. In addition, the process should satisfy 20 the prescribed safety requirements. 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. 25 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. According to a first aspect of the invention, there is provided a process for liquefying a hydrocarbon-rich 30 fraction, wherein -3 - the hydrocarbon-rich fraction that is to be liquefied is cooled in indirect heat exchange against a multistage precooling circuit, - the refrigerant of the precooling circuit is at least 5 95% by volume carbon dioxide, - the cooled hydrocarbon-rich fraction is liquefied and subcooled in indirect heat exchange against a mixed cycle, and - the mixed refrigerant of the mixed cycle comprises 10 exclusively the component(s) nitrogen, methane and/or ethane. According to a second aspect of the invention, there is provided a hydrocarbon-rich fraction when liquefied by a process according to the invention. 15 In a related aspect, the present invention provides process for liquefying a hydrocarbon- rich fraction, in particular natural gas, wherein - the hydrocarbon-rich fraction that is to be liquefied (A - B) is cooled (ElB - E4B) in indirect heat 20 exchange against a multistage precooling circuit (1 9, 30-37, 40-47), - the refrigerant of the precooling circuit is at least 95% by volume carbon dioxide , - the cooled hydrocarbon- rich fraction (C) is liquefied 25 and subcooled (E7, E8, E10) in indirect heat exchange against a mixed cycle (10-19), and -4 - the mixed refrigerant of the mixed cycle comprises exclusively the component(s) nitrogen, methane and/or ethane . Preferably the carbon dioxide circulating in the pre 5 cooling circuit (1-9, 30-37, 40-47) is compressed in two separate compressor casings (C1A, C1B) , wherein the exit pressure of the low pressure casing (ClA) is below the critical pressure of carbon dioxide. Preferably the exit pressure of the high-pressure casing 10 (ClB) is operated at a final pressure of at least 90 bar, preferably at least 100 bar. Preferably the mixed refrigerant circulating in the mixed cycle (10 -19) is compressed to a pressure above the critical pressure thereof (C2). 15 Preferably the temperature(s) of the hydrocarbon- rich fraction that is to be liquefied, of the carbon dioxide and/or of the mixed refrigerant is/are adjusted in such a manner that the drive powers of the compressors ( C1A, C1B) of the precooling circuit (1 - 9, 30 - 37, 40 - 47) and of 20 the compressor or compressors (C2) of the mixed cycle differ by a maximum of 10%, preferably by a maximum of 5% . Preferably the hydrocarbon-rich fraction that is to be liquefied, before the cooling and liquefaction thereof , is subjected to an adsorptive water removal , characterized in 25 that the liquefied hydrocarbon- rich fraction (D , D' ) is expanded (V2) , the resulting gaseous fraction is compressed to the pressure of the hydrocarbon- rich fraction that is to be liquefied (A, A' ) and fed thereto, wherein the compressed gaseous fraction , before the -5 feeding thereof, serves for regenerating the dryer or dryers of the adsorptive water removal (Y) . Preferably the refrigerant of the precooling circuit is at least 99% by volume carbon dioxide. 5 Preferably higher hydrocarbons and optionally hydrocarbons at risk of freezing, such as, for example , benzene , are removed from the precooled hydrocarbon- rich fraction that is to be liquefied (C) . To achieve the preferred object, a process for liquefying a 10 hydrocarbon-rich fraction is proposed, in which - the hydrocarbon-rich fraction that is to be liquefied is cooled in indirect heat exchange against a multistage precooling circuit, - the refrigerant of the precooling circuit is at least 15 95% by volume carbon dioxide, - the cooled hydrocarbon-rich fraction is liquefied and subcooled in indirect heat exchange against a mixed cycle, and - the mixed refrigerant of the mixed cycle comprises 20 exclusively the component(s) nitrogen, methane and/or ethane. The process according to the invention for liquefying a hydrocarbon-rich fraction is distinguished in that a multistage single-component precooling circuit and a mixed 25 cycle which serves for liquefying and subcooling the hydrocarbon-rich fraction are combined, wherein the refrigerant of the precooling circuit is at least 95% by -6 volume, preferably at least 99% by volume, carbon dioxide, while the mixed refrigerant of the mixed cycle comprises exclusively the component(s) nitrogen, methane and/or ethane. The use of higher hydrocarbons - these are taken to 5 mean C 3 +-hydrocarbons - is dispensed with completely. Using the procedure according to the invention, FLNG systems can - without having to accept reductions in safety - be implemented in a more compact and thus cheaper form. Compared with optimized liquefaction processes which are 10 customarily used in land-based systems, the process according to the invention for liquefying a hydrocarbon rich fraction has a higher energy consumption. The excess energy consumption is approximately 7%, in unfavourable applications, a maximum of 10%. 15 Further advantageous embodiments of the process according to the invention for liquefying a hydrocarbon-rich fraction are characterized in that - the carbon dioxide circulating in the precooling circuit is compressed in two separate compressor 20 casings, wherein the exit pressure of the low-pressure casing is below the critical pressure of carbon dioxide, - the exit pressure of the high-pressure casing is operated at a final pressure of at least 90 bar, 25 preferably at least 100 bar, - the mixed refrigerant circulating in the mixed cycle is compressed to a pressure above the critical pressure thereof, -7 - the temperature (s) of the hydrocarbon-rich fraction that is to be liquefied, of the carbon dioxide and/or of the mixed refrigerant is/are adjusted in such a manner that the drive powers of the compressors of the 5 precooling circuit and of the compressor or compressors of the mixed cycle differ by a maximum of 10%, preferably by a maximum of 5%, - if the hydrocarbon-rich fraction that is to be liquefied, before the cooling and liquefaction 10 thereof, is subjected to an adsorptive water removal, the liquefied hydrocarbon-rich fraction is expanded, the resulting gaseous fraction is compressed to the pressure of the hydrocarbon-rich fraction that is to be liquefied and fed thereto, wherein the compressed 15 gaseous fraction, before the feeding thereof, serves for regenerating the dryer or dryers of the adsorptive water removal, - the refrigerant of the precooling circuit is at least 99% by volume carbon dioxide, and 20 - higher hydrocarbons and optionally hydrocarbons at risk of freezing, such as, for example, benzene, are removed from the precooled hydrocarbon-rich fraction that is to be liquefied. The process according to the invention for liquefying a 25 hydrocarbon-rich fraction and further advantageous embodiments of the same will be described in more detail hereinafter with reference to the exemplary embodiments shown in Figures 1 and 2.
-8 In the embodiment shown in Figure 1 of the process according to the invention, the hydrocarbon-rich fraction A that is to be liquefied is first fed to an amine scrubber X and therein freed from components, in particular carbon 5 dioxide and sulphur compounds, that interfere in the subsequent liquefaction. Then, the hydrocarbon-rich fraction A' is cooled in the heat exchanger ElC, which will be considered in more detail hereinafter, and then fed to an adsorptive water removal unit Y. 10 The hydrocarbon-rich fraction B pretreated in this manner is then cooled in the heat exchangers ElB to E4B against the refrigerant of the precooling circuit, which will be considered in more detail hereinafter. In the heat exchanger E7/EB, the cooled hydrocarbon-rich fraction C is 15 liquefied (heat exchanger section E7) and subcooled (heat exchanger section EB) in indirect heat exchange against the mixed refrigerant of the mixed cycle, which will be considered in more detail hereinafter. At the cold end of the heat exchanger E7/E8, the liquefied and subcooled 20 hydrocarbon-rich fraction D is withdrawn and fed, for example, to an atmospheric storage tank which is not shown in Figure 1. For this purpose, the hydrocarbon-rich fraction D is expanded in valve V2 to the desired storage pressure. The resultant gaseous fraction can, according to 25 an advantageous embodiment of the process according to the invention, be compressed to the pressure of the hydrocarbon-rich fraction A that is to be liquefied, and fed thereto, wherein the compressed gaseous fraction, before the feeding thereof, preferably serves for 30 regenerating the dryer or dryers of the adsorptive water removal unit Y.
-9 The previously mentioned precooling circuit in which carbon dioxide circulates according to the invention as refrigerant, in the embodiment shown in Figure 1, has a compressor unit which consists of two separate compressor 5 casings C1A and CiB. In this case the carbon dioxide streams 6, 7 and 8 that are fed to the low-pressure casing CiA are preferably only compressed to a pressure which is below the critical pressure of carbon dioxide. The carbon dioxide 9 compressed in this manner is cooled in the 10 aftercooler E5A against a suitable medium and fed to the high-pressure casing CiB of the compressor unit. Therein, the carbon dioxide is compressed to the desired final pressure. Advantageously, this is at least 90 bar, preferably at least 100 bar, and is therefore markedly 15 above the critical pressure of carbon dioxide. The carbon dioxide 1 that is compressed to the desired final pressure is cooled in the aftercoolers E5B and E6 against a suitable external medium or against itself, expanded in the valve V1 to a subcritical pressure, similar 20 to the pressure of the carbon dioxide 9 present at the exit of the low-pressure casing CiA and fed via conduit 2 to the separator D1. The separator D1 serves, inter alia, as buffer container which compensates for inventory fluctuations due to various operating states or else 25 refrigerant losses. The gaseous carbon dioxide 3' arising at the top of the separator Di is fed to the precompressed carbon dioxide 9. The liquid carbon dioxide arising in the separator Di is withdrawn via conduit 3. A substream of the carbon dioxide is expanded in the valve V3 and, in the heat 30 exchanger ElC, serves for cooling the hydrocarbon-rich fraction A' that is to be liquefied before said carbon dioxide substream is fed via the conduit sections 4 and 5 -10 to the compressor unit ClA/ClB at an intermediate pressure level. The majority of the liquid carbon dioxide 3 is divided into two substreams 30 and 40. While the first substream 30 5 serves for cooling the mixed refrigerant 11 of the mixed cycle, the second substream 30 serves for cooling the hydrocarbon-rich fraction B that is to be liquefied. In the embodiment of the process according to the invention shown in Figure 1, these cooling operations each proceed in four 10 heat exchangers ElA - E4A and ElB - E4B, respectively. For this purpose, the two substreams are expanded into the respective heat exchangers ElA - E4A and ElB - E4B via the conduit sections 30 and 40, 32 and 42, 34 and 44, and also 36 and 46, into each of which is arranged an expansion 15 valve a - h. The resultant gaseous carbon dioxide is withdrawn from the above-mentioned heat exchangers via the conduit sections 31 and 41, 33 and 43, 35 and 45, and also 37 and 47, and fed via the conduit sections 5 - 8 back to the compressor unit ClA/C1B at a suitable pressure level. 20 The mixed refrigerant of the mixed cycle 10 that is compressed by the compressor or the compressor unit C2 to the desired cycle pressure is cooled against a suitable external medium in the aftercooler E9 and then fed via conduit 11 through the heat exchangers ElA to E4A and 25 cooled against the refrigerant of the precooling circuit. The mixed refrigerant 12 present in two phases at the exit of the heat exchanger E4A is separated in the separator D2 into a liquid fraction 13 and a gaseous fraction 16. The liquid fraction 13 is further cooled in the heat exchanger 30 section E7 of the heat exchanger E7/E8, cold-producingly expanded in the expansion valve V4 and then again fed to -11 the heat exchanger section E7 via conduit 14. In this heat exchanger section E7, the mixed refrigerant is completely vaporized against the hydrocarbon-rich fraction C that is to be liquefied and then fed via conduit 15 to the above 5 mentioned compressor C2. The gaseous fraction of the mixed refrigerant 16 arising in the separator D2 is cooled, completely liquefied and subcooled in the heat exchanger sections E7 and EB, then cold-producingly expanded in the valve V5 and again fed via 10 conduit 17 to the heat exchanger E7/E8 at the cold end thereof. Therein, the mixed refrigerant is completely vaporized against the hydrocarbon-rich fraction C that is to be liquefied and subcooled, and then likewise fed to the compressor C2 via conduit 15. 15 The inventory of liquid hydrocarbons in the mixed cycle is restricted substantially to the separator D2, the conduits 13, 14 and 17 between the separator D2 and the heat exchanger section E7, and also the liquids situated in the heat exchanger sections E7 and EB. Owing to the 20 considerable reduction of the inventory of liquid hydrocarbons in the mixed cycle and the avoidance of higher or C3+ hydrocarbons categorized as particularly hazardous, the liquefaction system can be implemented in a more compact and thus cheaper form without reductions in safety. 25 In a development of the process according to the invention for liquefying a hydrocarbon-rich fraction, it is proposed that the temperature(s) of the hydrocarbon-rich fraction that is to be liquefied, of the carbon dioxide and/or of the mixed refrigerant is or are to be adjusted in such a 30 manner that the drive powers of the compressors of the precooling circuit and of the compressor or compressors of -12 the mixed cycle differ by a maximum of 10%, preferably by a maximum of 5%. By way of this advantageous procedure, the drives GT required for operating the compressors or compressor units ClA/C1B and C2 can be identical. 5 According to a further advantageous embodiment of the process according to the invention for liquefying a hydrocarbon-rich fraction, the mixed refrigerant circulating in the mixed cycle is compressed to a pressure above its critical pressure. Unwanted distribution problems 10 of the gas and liquid phases can be avoided thereby, which can occur, in particular in a floating system (FLNG), owing to swell. On account of the above-described advantageous procedure, the separator D2 shown in Figure 1 is unnecessary, since 15 the mixed refrigerant is not in two phases, but one phase, at the exit of the heat exchanger E4A. Figure 2 shows an embodiment of the process according to the invention in which the mixed refrigerant 10'/11' circulating in the mixed cycle is compressed by the 20 compressor C2 to a pressure above the critical pressure thereof. Cooling of the mixed refrigerant of the mixed cycle and pretreatment and cooling of the hydrocarbon-rich fraction that is to be liquefied are not shown in Figure 2. These process steps run identically to those explained with 25 reference to Figure 1. The mixed refrigerant 12' cooled against the refrigerant of the precooling circuit can now be fed directly to the heat exchanger E10 and be cooled therein against itself. The heat exchanger E10 in this case replaces the heat exchanger 30 E7/E8 shown in Figure 1. The cooled mixed refrigerant is -13 cold-producingly expanded in the expansion valve V6 and fed via conduit 18 back to the heat exchanger E10 at the cold end thereof. Therein, the mixed refrigerant is completely vaporized against the hydrocarbon-rich fraction C that is 5 to be liquefied and subcooled and then fed via conduit 19 to the above-mentioned compressor C2. At the cold end of the heat exchanger E10, the liquefied and subcooled hydrocarbon-rich fraction D' is withdrawn.

Claims (14)

1. Process for liquefying a hydrocarbon-rich fraction, wherein - the hydrocarbon-rich fraction that is to be liquefied 5 is cooled in indirect heat exchange against a multistage precooling circuit, - the refrigerant of the precooling circuit is at least 95% by volume carbon dioxide, - the cooled hydrocarbon-rich fraction is liquefied and 10 subcooled in indirect heat exchange against a mixed cycle, and - the mixed refrigerant of the mixed cycle comprises exclusively the component(s) nitrogen, methane and/or ethane. 15
2. Process according to claim 1, wherein the hydrogen rich fraction is natural gas.
3. Process according to claim 1 or claim 2, wherein the carbon dioxide circulating in the procooling circuit is compressed in two separate compressor casings, 20 wherein the exit pressure of the low-pressure casing is below the critical pressure of carbon dioxide.
4. Process according to any one of the preceding claims, wherein the exit pressure of the high-pressure casing is operated at a final pressure of at least 90 bar. 25
5. Process according to claim 4, wherein the final pressure is at least 100 bar.
6. Process according to any one of the preceding claims, wherein the mixed refrigerant circulating in the mixed -15 cycle is compressed to a pressure above the critical pressure thereof.
7. Process according to any one of the preceding claims, wherein the temperature(s) of the hydrocarbon-rich 5 fraction that is to be liquefied, of the carbon dioxide and/or of the mixed refrigerant is/are adjusted in such a manner that the drive powers of the compressors of the precooling circuit and of the compressor or compressors of the mixed cycle differ by 10 a maximum of 10%.
8. Process according to claim 7, wherein the drive powers of the compressors differ by a maximum of 5%.
9. Process according to any one of the preceding claims, wherein the hydrocarbon-rich fraction that is to be 15 liquefied, before the cooling and liquefaction thereof, is subjected to an adsorptive water removal, wherein the liquefied hydrocarbon-rich fraction is expanded, the resulting gaseous fraction is compressed to the pressure of the hydrocarbon-rich fraction that 20 is to be liquefied and fed thereto, wherein the compressed gaseous fraction, before the feeding thereof, serves for regenerating the dryer or dryers of the adsorptive water removal.
10. Process according to any one of the preceding claims, 25 wherein the refrigerant of the precooling circuit is at least 99% by volume carbon dioxide.
11. Process according to any one of the preceding claims, wherein higher hydrocarbons and optionally hydrocarbons at risk of freezing, are removed from the -16 precooled hydrocarbon-rich fraction that is to be liquefied.
12. Process according to claim 11, wherein said hydrocarbons are selected from benzene. 5
13. A hydrocarbon-rich fraction when liquefied by a process according to any one of the preceding claims.
14. Process for liquefying a hydrocarbon-rich fraction or a hydrocarbon-rich fraction when liquefied by the process substantially as herein described with 10 reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples.
AU2013211458A 2012-09-06 2013-07-30 Process for liquefying a hydrocarbon-rich fraction Abandoned AU2013211458A1 (en)

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CA3000821A1 (en) * 2015-10-06 2017-04-13 Exxonmobil Upstream Research Company Consolidated refrigeration and liquefaction module in a hydrocarbon processing plant
US20190162469A1 (en) * 2017-11-27 2019-05-30 Air Products And Chemicals, Inc. Method and system for cooling a hydrocarbon stream
US20190162468A1 (en) * 2017-11-27 2019-05-30 Air Products And Chemicals, Inc. Method and system for cooling a hydrocarbon stream
CN110173959B (en) * 2019-05-15 2021-04-02 挪威极地航运公司 Boil-off gas reliquefaction recovery system
US11827317B1 (en) * 2022-05-04 2023-11-28 Storeco2 Uk Limited Carbon dioxide transport and sequestration marine vessel

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