AU2005224308A1 - Method for liquefying a hydrocarbon-rich flow - Google Patents

Method for liquefying a hydrocarbon-rich flow Download PDF

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AU2005224308A1
AU2005224308A1 AU2005224308A AU2005224308A AU2005224308A1 AU 2005224308 A1 AU2005224308 A1 AU 2005224308A1 AU 2005224308 A AU2005224308 A AU 2005224308A AU 2005224308 A AU2005224308 A AU 2005224308A AU 2005224308 A1 AU2005224308 A1 AU 2005224308A1
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mixed refrigerant
hydrocarbon
refrigerant cycle
stream
rich flow
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AU2005224308A
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AU2005224308B2 (en
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Heinz Bauer
Hubert Franke
Rainer Sapper
Marc Schier
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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"
    • F25J1/0042—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
    • F25J1/003—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
    • F25J1/0057—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle by vaporising a liquid refrigerant stream after expansion of the liquid refrigerant stream with extraction of work
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—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
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0228—Coupling of the liquefaction unit to other units or processes, so-called integrated processes
    • F25J1/0235—Heat exchange integration
    • F25J1/0237—Heat exchange integration integrating refrigeration provided for liquefaction and purification/treatment of the gas to be liquefied, e.g. heavy hydrocarbon removal from natural gas
    • F25J1/0239—Purification or treatment step being integrated between two refrigeration cycles of a refrigeration cascade, i.e. first cycle providing feed gas cooling and second cycle providing overhead gas cooling
    • 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.
    • F25J1/0285—Combination of different types of drivers mechanically coupled to the same refrigerant compressor, possibly split on multiple compressor casings
    • F25J1/0287—Combination of different types of drivers mechanically coupled to the same refrigerant compressor, possibly split on multiple compressor casings including an electrical motor
    • 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
    • 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.
    • F25J1/0295—Shifting of the compression load between different cooling stages within a refrigerant cycle or within a cascade refrigeration 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
    • 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.
    • F25J1/0296—Removal of the heat of compression, e.g. within an inter- or afterstage-cooler against an ambient heat sink
    • 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.
    • F25J1/0298—Safety aspects and control of the refrigerant compression system, e.g. anti-surge control
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2220/00—Processes or apparatus involving steps for the removal of impurities
    • F25J2220/60—Separating impurities from natural gas, e.g. mercury, cyclic hydrocarbons
    • F25J2220/64—Separating heavy hydrocarbons, e.g. NGL, LPG, C4+ hydrocarbons or heavy condensates in general
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2245/00—Processes or apparatus involving steps for recycling of process streams
    • F25J2245/02—Recycle of a stream in general, e.g. a by-pass stream

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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)
  • Oil, Petroleum & Natural Gas (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Separation By Low-Temperature Treatments (AREA)

Description

CERTIFICATE OF VERIFICATION I, Daniel HANCOCK MA, translator to RWS Group Ltd, of Europa House, Marsham Way, Gerrards Cross, Buckinghamshire, England, state that the attached document is a true and complete translation to the best of my knowledge of International Patent Application No. PCT/EP2005/002019. Dated this 31st day of July 2006 Signature of Translator: . For and on behalf of RWS Group Ltd WO 2005/090886 - 1 - PCT/EP2005/002019 Description Process for liquefying a hydrocarbon-rich flow 5 The invention relates to a process for liquefying a hydrocarbon-rich flow, in particular a natural gas stream, the liquefaction of the hydrocarbon-rich flow taking place against a mixed refrigerant cycle cascade comprising two mixed refrigerant cycles, the first 10 mixed refrigerant cycle being used for precooling and the second mixed refrigerant cycle being used for liquefaction and supercooling of the hydrocarbon-rich flow to be liquefied, and each mixed refrigerant cycle having at least one single-stage or multi-stage 15 compressor driven by at least one gas turbine, the gas turbines being assigned starters which can be used to assist the gas turbines during normal operation. In the following text, the term "precooling" is to be 20 understood to mean cooling the hydrocarbon-rich flow to be liquefied down to a temperature at which the separation of heavy or higher boiling-point hydrocarbons is carried out. The following, further cooling of the hydrocarbon-rich flow to be liquefied 25 falls under the term "liquefaction" in the following text. Natural gas liquefaction processes of the generic type - generally designated the dual-flow LNG process - are 30 sufficiently well known from the prior art to those skilled therein; by way of example, US patent 6,105,389 may be mentioned. If heavy hydrocarbons are contained in the natural gas 35 stream to be liquefied, these are separated out between the precooling and liquefaction and drawn off as what are known as the NGL (Natural Gas Liquid) fraction and, if appropriate, supplied to further processing. Those components of the hydrocarbon-rich flow or natural gas -2 to be liquefied which are designated heavy or higher boiling-point hydrocarbons are those components which would freeze out during the subsequent cooling and liquefaction - that is to say C 5 .- hydrocarbons and 5 aromatics. It is often the case that those hydrocarbons which would undesirably increase the calorific value of the liquefied natural gas - in this case propane and butane, in particular, are meant - are also separated out before the liquefaction. 10 This separation of higher boiling-point hydrocarbons is normally done by an HHC (Heavy HydroCarbon) column or scrub column being provided, which is used to separate out the heavy hydrocarbons and benzene from the 15 hydrocarbon-rich flow to be liquefied. A process management system of this type is described, for example, in DE-A 197 16 415. In dual-flow LNG plants, the cycle compressor is 20 normally driven by gas turbines. These are in turn normally started up by electrical or steam-operated starters. Since such starters often have to provide significant power - 20 to 40% of the gas turbine output - they are used as "helpers" to assist the gas turbines 25 during normal operation. Larger gas turbines are available on the market only in discrete output stages with comparatively large steps in output. The power of the starters or helpers is limited in relation to the gas turbine output, in order to avoid synchronization 30 problems. On account of a large number of process boundary conditions, such as the composition and pressure of the hydrocarbon-rich flow to be liquefied, ambient 35 temperature, etc., and the requirements on the separation of heavy hydrocarbons which may be required, an optimal division of power between the compressor drives of the two mixed refrigerant cycles cannot be reached or can be reached only by accident. Typically, -3 the first or precooling cycle needs about 40 to 55% of the total energy. The power demand of the precooling cycle is additionally often smaller than that of the second or liquefaction cycle. 5 This asymmetry can be compensated for by means of different utilization of the helpers. For instance, if the power distribution between the first and the second mixed refrigerant cycle is 45 to 55% and if both mixed 10 refrigerant cycles each have a gas turbine with an output of 70 MW and a helper with an output of 20 MW, the helper of the first cooling cycle is operated with only 4 instead of with the possible 20 MW. A large part of the investment in this helper thus remains unused 15 during the normal liquefaction operation. The object of the present invention is to specify a generic process for liquefying a hydrocarbon-rich flow in which the installed power of the gas turbines and 20 starters/helpers can be used fully during normal operation. Furthermore, the investment and operating costs of the gas turbines and starters/helpers used are to be reduced and/or optimized, in particular the use of identical gas turbines and starters/helpers is to be 25 made possible. In order to achieve this object, it is proposed that a) the second mixed refrigerant cycle have a cold intake compressor with a pressure ratio of at 30 least 10, and b) the first mixed refrigerant cycle be used at least partly for the intermediate cooling of at least a partial stream of the partially compressed mixed refrigerant stream of the second mixed refrigerant 35 cycle. The process according to the invention and further refinements of the same, which represent subjects of the dependent patent claims, are to be explained in -4 more detail in the following text by using the exemplary embodiment illustrated in the figure. As the figure shows, the hydrocarbon-rich flow to be 5 liquefied is supplied via line a to a heat exchanger El. In the latter, the hydrocarbon-rich flow to be liquefied is cooled down to such an extent that the heavy or higher boiling-point hydrocarbons contained therein condense and can be separated out from the 10 hydrocarbon-rich flow in the separation unit H, which is supplied with the cooled process stream via line b. The separated hydrocarbons are drawn off via line c and, if appropriate, supplied to further use. 15 It should be emphasized that the process according to the invention can be combined with all known separation methods for higher boiling-point hydrocarbons counting as prior art. 20 Via line d, the hydrocarbon-rich flow now freed of higher boiling-point hydrocarbons is supplied to a second heat exchanger E2 and, in the latter, is liquefied and supercooled against the refrigerant mixture of the second mixed refrigerant cycle. The 25 liquefied and supercooled hydrocarbon-rich flow is drawn off from the heat exchanger E2 via line e, optionally expanded in an expansion turbine T1 and then, via valve f and line g, supplied directly to further use or (intermediate) storage. 30 In the procedure illustrated in the figure, the refrigerant mixture compressed in the compressor V1 is supplied via line 10 to a condenser E3 and then via line 11 to the heat exchanger El and supercooled in the 35 latter. In the heat exchanger El, separation into three mixed refrigerant partial streams 12, 15 and 18 takes place. In the valves 13, 16 and 19, these partial streams are expanded to different pressure levels and, after renewed passage through and evaporation in the -5 heat exchanger El, are supplied via the lines 14, 17 and 20 to the compressor V1 at different pressure levels. 5 The compressor V1 is driven by a gas turbine Gl. The starters required for the operation of the gas turbines G1 and G2, as has already been explained at the beginning, are not illustrated in the figure. 10 In a procedure analogous to that described by using the first mixed refrigerant cycle, the compressed refrigerant mixture of the second mixed refrigerant cycle is first supplied via line 30 to a recooler E4 and then via line 31 to the heat exchanger El and 15 cooled down and condensed in the latter. The liquefied mixed refrigerant stream is then supplied via line 32 to the heat exchanger E2, supercooled further in the latter, expanded in the optional expansion turbine T2 after passing through the heat exchanger E2 and then 20 supplied via line 33 to an expansion valve 34 and expanded in the latter. The second mixed refrigerant partial stream, following evaporation in the heat exchanger E2, is than supplied via line 35 to the input stage of the cycle compressor V2. 25 The heat exchanger E2 can be constructed as a spiral heat exchanger or as a plate exchanger. If the liquefaction and supercooling of the hydrocarbon-rich flow to be liquefied takes place in a plate exchanger, 30 then - according to an advantageous refinement of the process according to the invention - the refrigerant mixture 28 of the second mixed refrigerant cycle can be evaporated while rising or falling. 35 The aforementioned cycle compressor V2, which, according to the invention, is a cold-intake compressor which has a pressure ratio of at least 10, is likewise driven by a gas turbine G2, which is assigned a starter/helper not illustrated in the figure.
-6 According to the invention, a partially compressed mixed refrigerant stream is now drawn off from an intermediate stage of the cycle compressor V2 via line 5 36, subjected to recooling E5 and then at least partly supplied via line 39 to the heat exchanger El and cooled intermediately in the latter against the first cooling cycle. The intermediately cooled, partly compressed mixed refrigerant stream is then again 10 supplied via line 40 to a suitable intermediate pressure stage of the compressor V2 and compressed to the desired final pressure. Using the first cooling cycle for the intermediate 15 cooling of the the second cooling cycle relieves the latter at the cost of the first cooling cycle, since the compressor power of the compressor V2 in its high pressure part falls in proportion with the now lowered intake temperature of the intermediately cooled 20 refrigerant stream in line 40. According to the invention, a displacement of the compressor powers as far as power equality between the two compressors V1 and V2 and their associated starters/helpers can now be realized. 25 The optimum choice of the abovedescribed intermediate cooling is determined by the dew point of the refrigerant mixture chosen for the second cooling cycle at the selected intermediate pressure at which the 30 refrigerant mixture is drawn off. Ideally, the entire refrigerant mixture of the second cooling cycle is cooled down by means of the first cooling cycle until power equality of the two cycle drives V1 and V2 is achieved. 35 The fact that the first mixed refrigerant cycle is now used for intermediate cooling of the second mixed refrigerant cycle means that the installed power of -7 identical gas turbines and starters/helpers can be used fully. In view of the already mentioned limiting of the 5 starter or helper power in relation to the gas turbine output, it is obvious that the full utilization of the two helpers which is now achieved leads to maximization of the plant capacity. This will be explained by using the following example. 10 If, on account of the process according to the invention, a power distribution of 50% to 50% between the first and the second mixed refrigerant cycle is now reached, then - assuming identical gas turbines and 15 starters/helpers for the two refrigerant cycles - these and their investments can be used fully. To return to the example given above, the starter/helper of the second cooling cycle can now also be operated with a power of 20 MW. As compared with the initial stage 20 mentioned at the beginning, the useable installed power is increased from 164 MW to 180 MW by the process according to the invention. With a given drive concept, the plant output can therefore be increased by about 10%. 25 As already explained, the precooling of the hydrocarbon-rich flow to be liquefied is carried out at thee different temperature levels (mixed refrigerant streams 12/14, 15/17 and 18/20). The ideal intake 30 temperature of the high-pressure part of the compressor V2 is, however, at best found by accident by this discretization of the temperature levels of the precooling. 35 As a development of the process according to the invention, it is therefore proposed that the temperature of the intermediate cooling El of at least one partial stream of the partially compressed mixed refrigerant stream 36, 39 of the second mixed -8 refrigerant cycle is influenced by the fact that the intermediately cooled partial stream is drawn off from the intermediate cooling El at different temperature levels - illustrated in the figure by the line 21 shown 5 dotted - and/or the partial stream of the partially compressed mixed refrigerant stream 37 which is not supplied to the intermediate cooling El, which is expanded to the inlet pressure in the valve 38, is supplied to the following compressor stage or stages. 10 The desired intake temperature of the high-pressure part of the compressor V2 can now be set by means of this procedure.

Claims (4)

1. A process for liquefying a hydrocarbon-rich flow, 5 in particular a natural gas stream, the liquefaction of the hydrocarbon-rich flow taking place against a mixed refrigerant cycle cascade comprising two mixed refrigerant cycles, the first mixed refrigerant cycle being used for precooling 10 and the second mixed refrigerant cycle being used for liquefaction and supercooling of the hydrocarbon-rich flow to be liquefied, and each mixed refrigerant cycle having at least one single-stage or multi-stage compressor driven by 15 at least one gas turbine, the gas turbines being assigned starters which are used to assist the gas turbines during normal operation, characterized in that a) the second mixed refrigerant cycle has a cold 20 intake compressor (V2) with a pressure ratio of at least 10, and b) the first mixed refrigerant cycle is used at least partly for the intermediate cooling (El) of at least a partial stream of the partially 25 compressed mixed refrigerant stream (36, 39) of the second mixed refrigerant cycle.
2. The process as claimed in claim 1, characterized in that the temperature of the intermediate 30 cooling (El) of at least one partial stream of the partially compressed mixed refrigerant stream (36, 39) of the second mixed refrigerant cycle is influenced by the fact that the intermediately cooled partial stream is drawn off from the 35 intermediate cooling (El) at different temperature levels and/or the partial stream of the partially compressed mixed refrigerant stream (37) which is not supplied to the intermediate cooling (El) is - 10 supplied to the following compressor stage or stages.
3. The process as claimed in claim 1 or 2, 5 characterized in that the liquefaction and supercooling of the hydrocarbon-rich flow to be liquefied takes place in a spiral heat exchanger (E2) or in a plate exchanger (E2). 10
4. The process as claimed in claim 3, the liquefaction and supercooling of the hydrocarbon rich flow to be liquefied taking place in a plate exchanger (E2), characterized in that the refrigerant mixture (28) of the second mixed 15 refrigerant cycle evaporates while rising or falling.
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WO2021023393A1 (en) 2019-08-02 2021-02-11 Linde Gmbh Process and plant for producing liquefied natural gas
DE102020004821A1 (en) 2020-08-07 2022-02-10 Linde Gmbh Process and plant for the production of a liquefied natural gas product

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DE2440215A1 (en) * 1974-08-22 1976-03-04 Linde Ag Liquefaction of low-boiling gases - by partial liquefaction with mixed liquid coolant and further cooling with expanded gas coolant
US4404008A (en) * 1982-02-18 1983-09-13 Air Products And Chemicals, Inc. Combined cascade and multicomponent refrigeration method with refrigerant intercooling
FR2751059B1 (en) * 1996-07-12 1998-09-25 Gaz De France IMPROVED COOLING PROCESS AND INSTALLATION, PARTICULARLY FOR LIQUEFACTION OF NATURAL GAS
US6119479A (en) * 1998-12-09 2000-09-19 Air Products And Chemicals, Inc. Dual mixed refrigerant cycle for gas liquefaction
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