US20080006053A1 - Natural Gas Liquefaction Process - Google Patents
Natural Gas Liquefaction Process Download PDFInfo
- Publication number
- US20080006053A1 US20080006053A1 US10/573,213 US57321304A US2008006053A1 US 20080006053 A1 US20080006053 A1 US 20080006053A1 US 57321304 A US57321304 A US 57321304A US 2008006053 A1 US2008006053 A1 US 2008006053A1
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- US
- United States
- Prior art keywords
- cooling
- hydrocarbon
- circuit
- liquefaction
- refrigeration
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
- 238000000034 method Methods 0.000 title claims abstract description 90
- 230000008569 process Effects 0.000 title claims abstract description 58
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 title claims description 35
- 239000003345 natural gas Substances 0.000 title claims description 17
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 claims abstract description 98
- 238000001816 cooling Methods 0.000 claims abstract description 81
- 229930195733 hydrocarbon Natural products 0.000 claims abstract description 80
- 150000002430 hydrocarbons Chemical class 0.000 claims abstract description 80
- 239000003507 refrigerant Substances 0.000 claims abstract description 72
- 239000004215 Carbon black (E152) Substances 0.000 claims abstract description 67
- 229910002092 carbon dioxide Inorganic materials 0.000 claims abstract description 58
- 238000005057 refrigeration Methods 0.000 claims abstract description 51
- 239000001569 carbon dioxide Substances 0.000 claims abstract description 38
- 239000007789 gas Substances 0.000 claims description 24
- 238000000926 separation method Methods 0.000 claims description 17
- 238000001704 evaporation Methods 0.000 claims description 14
- 230000008020 evaporation Effects 0.000 claims description 9
- 230000015572 biosynthetic process Effects 0.000 claims description 6
- 239000000498 cooling water Substances 0.000 claims description 4
- 238000009833 condensation Methods 0.000 claims description 3
- 230000005494 condensation Effects 0.000 claims description 3
- 239000013535 sea water Substances 0.000 claims description 3
- 239000000126 substance Substances 0.000 claims 1
- 239000002826 coolant Substances 0.000 abstract description 13
- 239000003949 liquefied natural gas Substances 0.000 description 27
- 239000000203 mixture Substances 0.000 description 19
- ATUOYWHBWRKTHZ-UHFFFAOYSA-N Propane Chemical compound CCC ATUOYWHBWRKTHZ-UHFFFAOYSA-N 0.000 description 7
- UHOVQNZJYSORNB-UHFFFAOYSA-N Benzene Chemical compound C1=CC=CC=C1 UHOVQNZJYSORNB-UHFFFAOYSA-N 0.000 description 6
- 230000006835 compression Effects 0.000 description 5
- 238000007906 compression Methods 0.000 description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 5
- 229910001868 water Inorganic materials 0.000 description 5
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- OTMSDBZUPAUEDD-UHFFFAOYSA-N Ethane Chemical compound CC OTMSDBZUPAUEDD-UHFFFAOYSA-N 0.000 description 4
- 230000009467 reduction Effects 0.000 description 4
- 238000009835 boiling Methods 0.000 description 3
- 235000011089 carbon dioxide Nutrition 0.000 description 3
- 238000009826 distribution Methods 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 239000001294 propane Substances 0.000 description 3
- 230000008859 change Effects 0.000 description 2
- 239000002131 composite material Substances 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000005265 energy consumption Methods 0.000 description 2
- 238000000605 extraction Methods 0.000 description 2
- 238000007667 floating Methods 0.000 description 2
- 239000012530 fluid Substances 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- 238000003860 storage Methods 0.000 description 2
- RWSOTUBLDIXVET-UHFFFAOYSA-N Dihydrogen sulfide Chemical compound S RWSOTUBLDIXVET-UHFFFAOYSA-N 0.000 description 1
- 239000001273 butane Substances 0.000 description 1
- 239000004148 curcumin Substances 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000009977 dual effect Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000002360 explosive Substances 0.000 description 1
- 238000007710 freezing Methods 0.000 description 1
- 230000008014 freezing Effects 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 239000012263 liquid product Substances 0.000 description 1
- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 description 1
- 229910052753 mercury Inorganic materials 0.000 description 1
- 239000000479 mixture part Substances 0.000 description 1
- IJDNQMDRQITEOD-UHFFFAOYSA-N n-butane Chemical compound CCCC IJDNQMDRQITEOD-UHFFFAOYSA-N 0.000 description 1
- OFBQJSOFQDEBGM-UHFFFAOYSA-N n-pentane Natural products CCCCC OFBQJSOFQDEBGM-UHFFFAOYSA-N 0.000 description 1
- 230000002265 prevention Effects 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 238000004088 simulation Methods 0.000 description 1
- 239000007858 starting material Substances 0.000 description 1
- 239000002918 waste heat Substances 0.000 description 1
Images
Classifications
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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
- F25J1/003—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
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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
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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
- F25J1/006—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
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
- F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
- F25J1/0211—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
- F25J1/0217—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 at least a three level refrigeration cascade with at least one MCR cycle
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
- F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
- F25J1/0211—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
- F25J1/0217—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 at least a three level refrigeration cascade with at least one MCR cycle
- F25J1/0218—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 at least a three level refrigeration cascade with at least one MCR cycle with one or more SCR cycles, e.g. with a C3 pre-cooling cycle
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
- F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
- F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
- F25J1/0257—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
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
- F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
- F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
- F25J1/0279—Compression of refrigerant or internal recycle fluid, e.g. kind of compressor, accumulator, suction drum etc.
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
- F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
- F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
- F25J1/0279—Compression of refrigerant or internal recycle fluid, e.g. kind of compressor, accumulator, suction drum etc.
- F25J1/0281—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
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
- F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
- F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
- F25J1/0279—Compression of refrigerant or internal recycle fluid, e.g. kind of compressor, accumulator, suction drum etc.
- F25J1/0292—Refrigerant compression by cold or cryogenic suction of the refrigerant gas
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
- F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
- F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
- F25J1/0279—Compression of refrigerant or internal recycle fluid, e.g. kind of compressor, accumulator, suction drum etc.
- F25J1/0295—Shifting of the compression load between different cooling stages within a refrigerant cycle or within a cascade refrigeration system
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
- F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
- F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
- F25J1/0279—Compression of refrigerant or internal recycle fluid, e.g. kind of compressor, accumulator, suction drum etc.
- F25J1/0296—Removal of the heat of compression, e.g. within an inter- or afterstage-cooler against an ambient heat sink
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- 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
- 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
- F25J1/0297—Removal of the heat of compression, e.g. within an inter- or afterstage-cooler against an ambient heat sink using an externally chilled fluid, e.g. chilled water
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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
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B1/00—Compression machines, plants or systems with non-reversible cycle
- F25B1/10—Compression machines, plants or systems with non-reversible cycle with multi-stage compression
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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
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B2309/00—Gas cycle refrigeration machines
- F25B2309/06—Compression machines, plants or systems characterised by the refrigerant being carbon dioxide
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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
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B2400/00—General features or devices for refrigeration machines, plants or systems, combined heating and refrigeration systems or heat-pump systems, i.e. not limited to a particular subgroup of F25B
- F25B2400/13—Economisers
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
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- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B5/00—Compression machines, plants or systems, with several evaporator circuits, e.g. for varying refrigerating capacity
- F25B5/02—Compression machines, plants or systems, with several evaporator circuits, e.g. for varying refrigerating capacity arranged in parallel
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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
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B9/00—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point
- F25B9/002—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point characterised by the refrigerant
- F25B9/008—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point characterised by the refrigerant the refrigerant being carbon dioxide
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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
- 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
Definitions
- the present invention relates to a method for the liquefaction of a hydrocarbon-rich flow.
- Natural gas can be obtained from the earth to form a natural gas feed which must be processed before it can be used commercially. Normally the gas is first pre-treated to remove or reduce the content of impurities such as carbon dioxide, water, hydrogen sulphide, mercury, etc.
- the gas is often liquefied before being transported to its point of use to provide liquefied natural gas (LNG).
- LNG liquefied natural gas
- natural gas Since natural gas is a mixture of gases, it liquefies over a range of temperatures. At atmospheric pressure, the usual temperature range within which complete liquefaction occurs is ⁇ 165° C. to ⁇ 155° C. However, since the critical temperature of natural gas is about ⁇ 80° C. to ⁇ 90° C., the gas cannot be liquefied purely by compressing it. It is therefore necessary to use refrigeration processes.
- Natural gas liquefaction plants are either designed as what are known as LNG baseload plants, i.e. plants for the liquefaction of natural gas for the supply of natural gas as primary energy, or as what are known as peak-shaving plants, i.e. plants for the liquefaction of natural gas to cover peak demand.
- LNG baseload plants are operated as a rule with coolant circuits consisting of a mixture of hydrocarbons. These mixed refrigerant circuits are more efficient in terms of energy than expander circuits and make it possible, with the high liquefaction capacities of the baseload plants, for correspondingly relatively low energy consumptions to be achieved.
- the Mixed Fluid Cascade process is known, e.g. from the U.S. Pat. No. 6,253,574, and uses three independent refrigeration cycles, which shifts the limit of a real single train concept with proven compressor drivers to above 8 mtpa LNG.
- the first coolant circuit serves to provide pre-cooling
- the second coolant circuit serves to provide the liquefaction
- the third coolant circuit serves to provide the sub-cooling for the hydrocarbon-rich flow or natural gas respectively.
- hydrocarbons with higher boiling points are at least those components of the hydrocarbon-rich flow or natural gas which would freeze out during the following cooling stage, i.e. C 5 + hydrocarbons and aromates.
- hydrocarbons meaning in this situation in particular propane and butane, which would undesirably increase the calorific value of the liquefied natural gas are also separated out before the liquefaction stage.
- C 3 + separation Due to the provision of this separation, designated hereinafter as C 3 + separation, at a given pressure of the raw gas the temperature level of the separation of these components is set within comparatively narrow limits.
- an LNG liquefaction process having first and second refrigeration circuits wherein the second refrigeration circuit is used at least partially for pre-cooling the hydrocarbon-rich stream to be liquefied.
- Part of the refrigerant of the liquefaction cycle may be vaporized under elevated pressure in the precooling section of the process and fed to the LC compressor as a side stream. In this way a substantial load balancing between all the refrigeration cycles can be achieved.
- a method for the liquefaction of a hydrocarbon-rich flow in particular of a natural gas flow, whereby the liquefaction of the hydrocarbon-rich flow is effected against a refrigerant circuit cascade consisting of three refrigeration circuits, whereby the first of the three refrigeration circuits serves to provide preliminary cooling, the second refrigeration circuit serves to provide the actual liquefaction, and the third refrigeration circuit serves the sub-cooling of the liquefied hydrocarbon-rich flow, and whereby each refrigeration circuit comprises at least one single-stage or multi-stage compressor, characterised in that at least one part flow of the refrigerant of the second refrigeration circuit is used for the preliminary cooling of the hydrocarbon-rich flow.
- the invention provides a method of liquefying a hydrocarbon-rich gas, wherein the gas flows through a cascade of three refrigeration stages, each stage comprising a refrigerant circuit and a compressor, wherein at least part of the flow of refrigerant from the second circuit is used for the preliminary cooling of the hydrocarbon rich gas in the first refrigeration stage.
- the part flow of the refrigerant of the second refrigeration (or cooling) circuit, used for the pre-cooling of the hydrocarbon-rich flow is evaporated at a pressure which is higher than the evaporation pressure of the remaining part flow of the refrigerant of the second cooling circuit, and is conducted to the-compressor of the second cooling circuit at an intermediate pressure level.
- the separation of heavier components and/or components of the hydrocarbon-rich flow which freeze out during the liquefaction of the hydrocarbon-rich flow takes place before the actual liquefaction of the hydrocarbon-rich flow.
- the volumes and/or evaporation pressures of the two part flows of the second cooling circuit are changeable.
- At least one part flow of one of the two part flows of the second cooling circuit is used for the provision of cooling in the heavy hydrocarbon separation unit.
- the invention therefore provides a load balanced liquefaction process for LNG in which each compressor may have a substantially equal share of the total load, and preferably an equal share.
- This concept can be applied more widely and hence from another aspect the present invention provides a method of liquefaction comprising a plurality of cooling circuits arranged in a cascade formation, each circuit comprising a compressor, wherein each compressor has a substantially equal share of the total load.
- the benefits of load balancing the refrigeration circuits are not limited to any particular type of refrigerant used.
- mixed refrigerant cascades provide an efficient system and therefore in one preferred embodiment the refrigeration circuits are mixed refrigerant circuits.
- a method for the liquefaction of a hydrocarbon-rich flow in particular of a natural gas flow, whereby the liquefaction of the hydrocarbon-rich flow is effected against a mixed refrigerant circuit cascade consisting of three refrigeration circuits, whereby the first of the three refrigeration circuits serves to provide preliminary cooling, the second refrigeration circuit serves to provide the actual liquefaction, and the third refrigeration circuit serves the sub-cooling of the liquefied hydrocarbon-rich flow, and whereby each refrigeration circuit comprises at least one single-stage or multi-stage compressor, characterised in that at least one part flow of the refrigerant of the second refrigeration circuit is used for the preliminary cooling of the hydrocarbon-rich flow.
- LNG FPSOs Floating LNG production, storage and offloading facilities
- carbon dioxide Another non-flammable and inert refrigerant option is carbon dioxide, which may operate in a vapour compression cycle giving reasonable efficiency. Carbon dioxide has a freezing point of ⁇ 56.6° C., which restricts the minimum possible evaporating temperature due to the risk of dry ice formation. Therefore carbon dioxide is an option for the precooling process only. Since most of the hydrocarbon refrigerant inventory is in the precooling cycle, a change over to CO 2 may still improve the safety of the liquefaction process significantly.
- carbon dioxide is also distinguished from the common hydrocarbon refrigerants for natural gas precooling by its rather low critical temperature (31.1° C.), which is comparable to that of ethane (32.3° C.).
- WO 01/69149 discloses the possibility of providing a carbon dioxide precooling circuit in a cascade arrangement with a main cooling circuit.
- the low critical temperature of CO 2 is a disadvantage since the throttling loss and heat rejection loss in the refrigerating cycle will be larger than for C 3 and C 3 /C 2 mixtures. In addition, the heat transfer loss will be larger than with mixed refrigerant due to constant-temperature evaporation.
- the first refrigeration circuit comprises carbon dioxide.
- the carbon dioxide circuit can be operated to provide a higher minimum evaporation temperature and thus the risk of dry ice formation is reduced.
- the load of the carbon dioxide cycle is reduced the impact of the lower thermodynamic efficiency of CO 2 compared with C 2 /C 3 is alleviated.
- the increase in power consumption caused by using CO 2 can be reduced to only a few percent greater than when using hydrocarbons.
- the carbon dioxide is cooled after condensation to a temperature of 20° C. or less, more preferably to 15° C. or less. This can be achieved using air cooling although preferably cold cooling water is used.
- the water is preferably sea water, preferably extracted from a depth suitable to give the required low temperature.
- the carbon dioxide pre-cooling cycle includes a sub-cooling heat exchanger installed after the condenser.
- the carbon dioxide cooling circuit comprises three pressure levels in order to improve the thermodynamic efficiency of the process.
- the higher operating pressure required when using CO 2 means that it my be preferable to use a high pressure casing with the carbon dioxide compressor. More preferably the compressor can be split into two casings and a barrel type casing used for the high pressure stage.
- a LNG liquefaction process comprising three cascade cycles each driven by a compressor, wherein the compressors are substantially equally loaded and one of the cascade cycles is a carbon dioxide cycle.
- a carbon dioxide pre-cooling circuit for LNG liquefaction wherein the carbon dioxide has a minimum evaporation temperature of no less then ⁇ 50° C., preferably no less than ⁇ 40° C. and most preferably no less than ⁇ 35° C.
- FIG. 1 shows a load balanced liquefaction process in accordance with a preferred embodiment of the invention
- FIG. 2 show an alternative embodiment of a load balanced process
- FIG. 3 shows a graph of overall power demand as a function of a reference temperature
- FIG. 4 shows a load balanced liquefaction process containing a carbon dioxide pre-cooling circuit
- FIG. 5 shows hot/cold composite curves for the processes shown in FIGS. 2 and 4 ;
- FIG. 6 shows a comparison of refrigerant inventories of the processes shown in FIGS. 2 and 4 .
- FIG. 1 the cooling and liquefaction of the hydrocarbon-rich flow, which is conducted via line 1 , are effected against a mixed refrigerant circuit cascade, consisting of three mixed refrigerant circuits.
- a mixed refrigerant circuit cascade consisting of three mixed refrigerant circuits.
- the hydrocarbon-rich flow which is to be liquefied is cooled in the heat exchanger E 1 against the two evaporating mixed refrigerant flows 4 b and 4 d of the first mixture circuit 4 a to 4 e, then cooled by the evaporating mixed refrigerant flow 3 d, and then conducted via line 1 a to a heavy hydrocarbon separation unit S, represented simply as a box.
- At least one part flow of one of the two part flows 3 b and 3 d of the second cooling agent mixture circuit 3 a to 3 e is used for the provision of cooling in the separation unit S.
- the choice of which of the two part flows 3 b and/or 3 d is drawn from for this provision of cooling is determined by the temperature level(s) required in the heavy hydrocarbon separation unit S.
- the hydrocarbon-rich flow to be liquefied is then conducted via line 1 c to a second heat exchanger E 2 , and is liquefied in this against the evaporating mixed refrigerant flow 3 b of the second cooling circuit 3 a to 3 e.
- the hydrocarbon-rich flow is conducted via line 1 d to a third heat exchanger E 3 , and is subcooled here against the mixed refrigerant flow 2 b of the third cooling circuit 2 a to 2 c.
- the subcooled liquid product is then conducted via line le to its further use.
- each of the three cooling circuits 2 a to 2 c, 3 a to 3 e, and 4 a to 4 e has a compressor, V 2 , V 3 , and V 4 respectively. Not shown in the drawing are the corresponding drives for these compressors V 2 , V 3 , and V 4 .
- the coolers or heat exchangers which are located downstream of the compressors V 2 , V 3 , and V 4 respectively are not shown in the drawing, in which the refrigerant mixture is cooled against a cooling medium, such as water.
- the refrigerant mixture of the first refrigerant circuit, compressed in the compressor V 4 , is conducted via line 4 a to the heat exchanger E 1 , and is divided here into two part flows 4 b and 4 d after cooling has taken place.
- the refrigerant mixture in these part flows 4 b and 4 d, after throttling has been effected in the valves d and e or expansion devices, is evaporated to different pressure levels in the heat exchanger E 1 and then conducted via line 4 c or 4 e to the compressor V 4 before the first stage (part flow 4 c ) or to an intermediate pressure level (part flow 4 e ).
- a part flow 3 d of the refrigerant mixture of the second refrigerant mixture circuit 3 a to 3 e is drawn off after the heat exchanger E 1 , expanded in valve c, and then evaporated in heat exchanger E 1 against cooling process flows, before being conducted via line 3 e, at an intermediate pressure level, to the circuit compressor V 3 .
- the refrigerant mixture part flow 3 d makes a contribution to the pre-cooling of the hydrocarbon-rich flow in heat exchanger E 1 .
- the part flow 3 d of the refrigerant mixture of the second mixed refrigerant circuit 3 a to 3 e, used for the pre-cooling of the hydrocarbon-rich flow must be evaporated at a pressure which is higher than the evaporation pressure of the mixed refrigerant part flow 3 b of the second mixed refrigerant circuit 3 a to 3 e.
- the distribution of the cooling capacity of the second refrigerant circuit onto the heat exchangers E 1 and E 2 , and therefore to the pre-cooling and liquefaction of the hydrocarbon-rich flow which is to be liquefied, can be adjusted almost at will.
- one compressor is used in each case with a third of the total drive capacity in the first and third refrigerant mixture circuit, i.e. for the pre-cooling as well as for the subcooling of the hydrocarbon-rich flow which is to be liquefied.
- the compressor of the second refrigerant mixture circuit is operated according to the invention in such a way that it uses 20% of its capacity, and consequently 6.66% of the total capacity, for pre-cooling, while the remaining 80%, i.e. 26.66% of the total capacity, is used for liquefaction.
- the method according to the invention accordingly makes possible the economical exploitation of the available compressors and drive units, because the (circuit) compressors of the three refrigerant circuits obtain approximately the same drive capacity, i.e. a third of total capacity in each case.
- FIG. 2 shows an alternative version of the load balanced process.
- the pre-cooling cycle C 10 comprises a first circuit driven by a first compressor V 10 and one part 22 of the refrigerant stream 21 from the second cycle C 20 .
- Three General Electric MS 7121 EA (Frame 7) gas turbines are used to drive the compressors V 10 , V 20 , V 30 . If highest availability is of the essence, the three refrigeration cycles can be designed with two times 50% gas turbine/compressor trains. In this case six GE MS 6581 B (Frame 6) gas turbines would replace the three Frame 7s.
- All LNG plants require the extraction of at least of those hydrocarbons, which would freeze in the LNG under storage conditions (e.g. aromatics and C 5 +).
- precooling is usually considered as first cooling step between ambient temperature and extraction of the mentioned hydrocarbons.
- the precooling portion of the overall power demand of all refrigeration compressors for the two gases defined in Table 1 is shown in FIG. 3 as a function of a reference temperature. This is the temperature, under which all main process streams (natural gas, refrigerant fluids) enter into the cryogenic heat exchangers.
- a process with three refrigeration cycles offers a much wider field for even load distribution between the cycles. If part of the refrigerant of the liquefaction cycle C 20 is vaporized under elevated pressure in the precooling section C 10 and is fed to the LC compressor V 20 as side stream 22 , a perfect load balancing between all three refrigeration cycles can be achieved. This feature is a major aspect of a cost effective design for large production capacities. As all three (3) cycles are symmetrically driven this arrangement is referred to as MFC*s3.
- the final compressor V 30 of FIG. 2 is split into two casings V 31 , V 32 .
- the second casing V 32 is designed to deal with high pressures at which the multistage compressor operates.
- the precooling circuit C 10 of FIG. 2 has been replaced with a pre-cooling circuit C 100 which comprises a carbon dioxide stream 101 .
- a pre-cooling circuit C 100 which comprises a carbon dioxide stream 101 .
- the stream 101 is split into three separate streams, 102 , 103 , 104 which are then expanded to different pressures. This compensates for the constant temperature evaporation of CO 2 .
- Unlike hydrocarbon streams 201 , 301 only part of the carbon dioxide stream 101 is sub-cooled by the pre-cooling heat exchanger E 100 prior to expansion, in order to reduce the internal heat load of this exchanger.
- the CO 2 precooling compressor V 100 is split into two casings, V 110 , V 120 with a barrel type casing V 120 for the high-pressure stage.
- the carbon dioxide is cooled by a water cooled condenser C 20 and an additional subcooling heat exchanger C 22 , using seawater to subcool the liquid refrigerant after the condenser C 20 , in order to improve process efficiency.
- a desuperheater can also be provided after the compressor, as in many conventional systems.
- load balancing is achieved by allowing the liquefaction compressor V 200 to take over some of the precooling cycle load, leading to a “symmetrical” process.
- Temperature profiles in the form of hot/cold composite curves for the two cases are shown in FIG. 5 .
- the three CO 2 precooling temperature levels are easily observed in the left diagram.
- the highest pressure level to the liquefaction compressor is also considered part of precooling. Changes in the subcooling process are minimal between the two cases.
- the minimization of hydrocarbon refrigerant inventory is very important in terms of safety.
- the HC refrigerant inventory is reduced by about 70% in the CO 2 -precooled process.
- the reduced hydrocarbon charge is positive in relation to loss prevention and to the availability of the three main safety functions of the LNG barge, which are (i) main structural strength, (ii) main escape routes, and (iii) means of evacuation.
Abstract
Description
- The present invention relates to a method for the liquefaction of a hydrocarbon-rich flow.
- Natural gas can be obtained from the earth to form a natural gas feed which must be processed before it can be used commercially. Normally the gas is first pre-treated to remove or reduce the content of impurities such as carbon dioxide, water, hydrogen sulphide, mercury, etc.
- The gas is often liquefied before being transported to its point of use to provide liquefied natural gas (LNG). This enables the volume of gas to be reduced by about 600 fold, which greatly reduces the transportation costs. Since natural gas is a mixture of gases, it liquefies over a range of temperatures. At atmospheric pressure, the usual temperature range within which complete liquefaction occurs is −165° C. to −155° C. However, since the critical temperature of natural gas is about −80° C. to −90° C., the gas cannot be liquefied purely by compressing it. It is therefore necessary to use refrigeration processes.
- Natural gas liquefaction plants are either designed as what are known as LNG baseload plants, i.e. plants for the liquefaction of natural gas for the supply of natural gas as primary energy, or as what are known as peak-shaving plants, i.e. plants for the liquefaction of natural gas to cover peak demand.
- It is known to cool natural gas by using heat exchangers in which a refrigerant or coolant is used. One well-known method comprises a number of coolant or refrigeration cycles in the form of a cascade.
- LNG baseload plants are operated as a rule with coolant circuits consisting of a mixture of hydrocarbons. These mixed refrigerant circuits are more efficient in terms of energy than expander circuits and make it possible, with the high liquefaction capacities of the baseload plants, for correspondingly relatively low energy consumptions to be achieved.
- Conventional liquefaction processes using only two refrigerant cycles are limited to about 5 million tons per annum (mtpa) LNG, unless parallel strings within a single train are considered.
- The Mixed Fluid Cascade process is known, e.g. from the U.S. Pat. No. 6,253,574, and uses three independent refrigeration cycles, which shifts the limit of a real single train concept with proven compressor drivers to above 8 mtpa LNG.
- This method is also known from the German published
application 197 16 415. - With liquefaction methods of this type, in principle the first coolant circuit serves to provide pre-cooling, the second coolant circuit serves to provide the liquefaction, and the third coolant circuit serves to provide the sub-cooling for the hydrocarbon-rich flow or natural gas respectively.
- Between the pre-cooling and the liquefaction, if necessary, the separation of hydrocarbons with higher boiling points takes place. These are at least those components of the hydrocarbon-rich flow or natural gas which would freeze out during the following cooling stage, i.e. C5+ hydrocarbons and aromates. Often, in addition, those hydrocarbons, meaning in this situation in particular propane and butane, which would undesirably increase the calorific value of the liquefied natural gas are also separated out before the liquefaction stage.
- This separation of hydrocarbons with higher boiling points usually takes place by provision being made for what is known as an HHC (Heavy Hydrocarbon) column, which serves to separate the heavy hydrocarbons as well as benzene out of the hydrocarbon-rich flow which is to be liquefied. A process stage of this kind is likewise described in the German published
application 197 16 415 already mentioned. - Due to the provision of this separation, designated hereinafter as C3+ separation, at a given pressure of the raw gas the temperature level of the separation of these components is set within comparatively narrow limits.
- If the first coolant circuit is now used exclusively for the pre-cooling of the hydrocarbon-rich flow which is to be liquefied before this C3+ separation, then a part of the overall compression effect of some 40 to 50% will necessarily be spent on this, while the remaining compression effect of 60 to 50% will be divided over the second and third coolant circuits.
- In the sense of an economical exploitation of the available compressor and drive units, however, the inventors have realised that it is desirable for the (circuit) compressors of the three circuits to retain approximately the same drive capacity, i.e. in each case about a third of the overall drive capacity. This applies in particular to large liquefaction plants with a liquefaction capacity greater than 5 mtpa, because the number of available compressors and drive units for such orders of magnitude is severely restricted. By standardizing the drive units and compressors of the three coolant circuits, it is possible to maximize the attainable liquefaction capacity of the liquefaction process using tried-and-trusted drive units and compressors respectively.
- Thus according to one aspect of the invention there is provided an LNG liquefaction process having first and second refrigeration circuits wherein the second refrigeration circuit is used at least partially for pre-cooling the hydrocarbon-rich stream to be liquefied. Thus the installed power of the gas turbines and starters—at least during normal liquefying operation—can be exploited to the full.
- Part of the refrigerant of the liquefaction cycle (LC) may be vaporized under elevated pressure in the precooling section of the process and fed to the LC compressor as a side stream. In this way a substantial load balancing between all the refrigeration cycles can be achieved.
- Therefore, according to one aspect of the present invention there is provided a method for the liquefaction of a hydrocarbon-rich flow, in particular of a natural gas flow, whereby the liquefaction of the hydrocarbon-rich flow is effected against a refrigerant circuit cascade consisting of three refrigeration circuits, whereby the first of the three refrigeration circuits serves to provide preliminary cooling, the second refrigeration circuit serves to provide the actual liquefaction, and the third refrigeration circuit serves the sub-cooling of the liquefied hydrocarbon-rich flow, and whereby each refrigeration circuit comprises at least one single-stage or multi-stage compressor, characterised in that at least one part flow of the refrigerant of the second refrigeration circuit is used for the preliminary cooling of the hydrocarbon-rich flow.
- From another aspect, the invention provides a method of liquefying a hydrocarbon-rich gas, wherein the gas flows through a cascade of three refrigeration stages, each stage comprising a refrigerant circuit and a compressor, wherein at least part of the flow of refrigerant from the second circuit is used for the preliminary cooling of the hydrocarbon rich gas in the first refrigeration stage.
- Preferably the part flow of the refrigerant of the second refrigeration (or cooling) circuit, used for the pre-cooling of the hydrocarbon-rich flow is evaporated at a pressure which is higher than the evaporation pressure of the remaining part flow of the refrigerant of the second cooling circuit, and is conducted to the-compressor of the second cooling circuit at an intermediate pressure level.
- Preferably the separation of heavier components and/or components of the hydrocarbon-rich flow which freeze out during the liquefaction of the hydrocarbon-rich flow takes place before the actual liquefaction of the hydrocarbon-rich flow.
- Preferably the volumes and/or evaporation pressures of the two part flows of the second cooling circuit are changeable.
- Preferably at least one part flow of one of the two part flows of the second cooling circuit is used for the provision of cooling in the heavy hydrocarbon separation unit.
- The invention therefore provides a load balanced liquefaction process for LNG in which each compressor may have a substantially equal share of the total load, and preferably an equal share. This concept can be applied more widely and hence from another aspect the present invention provides a method of liquefaction comprising a plurality of cooling circuits arranged in a cascade formation, each circuit comprising a compressor, wherein each compressor has a substantially equal share of the total load.
- The benefits of load balancing the refrigeration circuits are not limited to any particular type of refrigerant used. However, as mentioned above mixed refrigerant cascades provide an efficient system and therefore in one preferred embodiment the refrigeration circuits are mixed refrigerant circuits.
- Therefore, according to another aspect of the present invention there is provided a method for the liquefaction of a hydrocarbon-rich flow, in particular of a natural gas flow, whereby the liquefaction of the hydrocarbon-rich flow is effected against a mixed refrigerant circuit cascade consisting of three refrigeration circuits, whereby the first of the three refrigeration circuits serves to provide preliminary cooling, the second refrigeration circuit serves to provide the actual liquefaction, and the third refrigeration circuit serves the sub-cooling of the liquefied hydrocarbon-rich flow, and whereby each refrigeration circuit comprises at least one single-stage or multi-stage compressor, characterised in that at least one part flow of the refrigerant of the second refrigeration circuit is used for the preliminary cooling of the hydrocarbon-rich flow.
- It will be appreciated that the use of hydrocarbons as refrigerants poses a safety issue and this is particularly significant in the offshore environment, where it is highly undesirable to have large liquid hydrocarbon inventories in what is inevitably a confined space.
- Floating LNG production, storage and offloading facilities (LNG FPSOs) are now considered a realistic option for remote offshore gas fields that cannot be economically exploited with conventional onshore technology. A floating concept may soon become the preferred solution for draining deep-water gas reserves.
- Therefore the need to increase the safety of such a system is of great importance.
- One possibility is to use a nitrogen based process, but this has the significant disadvantage that the thermal efficiency is much lower than a hydrocarbon based system. In addition, because nitrogen has a low heat transfer coefficient, a large heat transfer area is required to dissipate the waste heat from the process into a cooling medium. Consequently, despite the safety hazards involved, hydrocarbon-based refrigeration cycles continue to be used.
- Another non-flammable and inert refrigerant option is carbon dioxide, which may operate in a vapour compression cycle giving reasonable efficiency. Carbon dioxide has a freezing point of −56.6° C., which restricts the minimum possible evaporating temperature due to the risk of dry ice formation. Therefore carbon dioxide is an option for the precooling process only. Since most of the hydrocarbon refrigerant inventory is in the precooling cycle, a change over to CO2may still improve the safety of the liquefaction process significantly.
- Apart from being non-flammable and its high triple point, carbon dioxide is also distinguished from the common hydrocarbon refrigerants for natural gas precooling by its rather low critical temperature (31.1° C.), which is comparable to that of ethane (32.3° C.).
- WO 01/69149 discloses the possibility of providing a carbon dioxide precooling circuit in a cascade arrangement with a main cooling circuit.
- The low critical temperature of CO2 is a disadvantage since the throttling loss and heat rejection loss in the refrigerating cycle will be larger than for C3 and C3/C2 mixtures. In addition, the heat transfer loss will be larger than with mixed refrigerant due to constant-temperature evaporation.
- It has been found that replacing a traditional C3/C2 precooling process, for example that disclosed in U.S. Pat. No. 6,253,574, with an equivalent CO2 process increases the total power consumption for liquefaction by about 10%, which is considered unacceptable. This consumption increase is due to the reduction in efficiency of the cycle due to the low critical temperature of carbon dioxide. In addition, the evaporating temperature in the first stage of the CO2 precooling cycle is only a few degrees higher than the CO2 triple point. This leads to operational problems and a danger of dry ice formation.
- There therefore exists a need for an efficient liquefaction process containing a CO2 precooling circuit.
- The applicants of the present invention have realised that a carbon dioxide pre-cooling circuit can be combined with the load balanced liquefaction process described above in order to overcome the above discussed problems with using carbon dioxide.
- Therefore, in a preferred embodiment of the present invention the first refrigeration circuit comprises carbon dioxide.
- This concept is considered inventive in its own right and therefore, according to another aspect of the present invention there is provided a substantially load balanced mixed refrigerant cascade process comprising a carbon dioxide pre-cooling circuit.
- As the liquefaction compressor takes over some of the pre-cooling cycle load, the carbon dioxide circuit can be operated to provide a higher minimum evaporation temperature and thus the risk of dry ice formation is reduced. In addition, as the load of the carbon dioxide cycle is reduced the impact of the lower thermodynamic efficiency of CO2 compared with C2/C3 is alleviated. In a load balanced process where each compressor contributes a third of the total power consumption, the increase in power consumption caused by using CO2 can be reduced to only a few percent greater than when using hydrocarbons.
- In order to achieve maximum efficiency from the carbon dioxide circuit it is preferable that the carbon dioxide is cooled after condensation to a temperature of 20° C. or less, more preferably to 15° C. or less. This can be achieved using air cooling although preferably cold cooling water is used. As the invention is particularly suited for offshore application the water is preferably sea water, preferably extracted from a depth suitable to give the required low temperature.
- Preferably therefore the carbon dioxide pre-cooling cycle includes a sub-cooling heat exchanger installed after the condenser.
- Using this method the reduction in total power consumption is great enough to make using a CO2 pre-cooling circuit a viable option in both on and offshore LNG facilities.
- Preferably the carbon dioxide cooling circuit comprises three pressure levels in order to improve the thermodynamic efficiency of the process.
- In order to reduce the internal heat load of the precooling circuit it is preferable that only a substream of carbon dioxide is subcooled in the pre-cooling circuit. This is unlike the second and third cooling cycle refrigerants, the full sub-cooling of which increases the efficiency of the process.
- The higher operating pressure required when using CO2 means that it my be preferable to use a high pressure casing with the carbon dioxide compressor. More preferably the compressor can be split into two casings and a barrel type casing used for the high pressure stage.
- According to another aspect of the present invention there is provided a LNG liquefaction process comprising three cascade cycles each driven by a compressor, wherein the compressors are substantially equally loaded and one of the cascade cycles is a carbon dioxide cycle.
- According to a further aspect of the present invention there is provided a carbon dioxide pre-cooling circuit for LNG liquefaction wherein the carbon dioxide has a minimum evaporation temperature of no less then −50° C., preferably no less than −40° C. and most preferably no less than −35° C.
- Preferred embodiments of the present invention shall now be described, by way of example only, with reference to the following drawings, in which:
-
FIG. 1 shows a load balanced liquefaction process in accordance with a preferred embodiment of the invention; -
FIG. 2 show an alternative embodiment of a load balanced process; -
FIG. 3 shows a graph of overall power demand as a function of a reference temperature; -
FIG. 4 shows a load balanced liquefaction process containing a carbon dioxide pre-cooling circuit; -
FIG. 5 shows hot/cold composite curves for the processes shown inFIGS. 2 and 4 ; and -
FIG. 6 shows a comparison of refrigerant inventories of the processes shown inFIGS. 2 and 4 . - In
FIG. 1 the cooling and liquefaction of the hydrocarbon-rich flow, which is conducted vialine 1, are effected against a mixed refrigerant circuit cascade, consisting of three mixed refrigerant circuits. These as a rule have different compositions, such as are described, for example, in the aforementioned German publishedapplication 197 16 415. - The hydrocarbon-rich flow which is to be liquefied is cooled in the heat exchanger E1 against the two evaporating mixed refrigerant flows 4 b and 4 d of the
first mixture circuit 4 a to 4 e, then cooled by the evaporating mixedrefrigerant flow 3 d, and then conducted vialine 1 a to a heavy hydrocarbon separation unit S, represented simply as a box. - In this separation unit S the C3+ separation described heretofore takes place, whereby the components separated out of the hydrocarbon-rich flow are drawn off from the heavy hydrocarbon separation unit S via
line 1 b. - According to one advantageous embodiment of the method according to the invention, not shown in the drawing, at least one part flow of one of the two part flows 3 b and 3 d of the second cooling
agent mixture circuit 3 a to 3 e, which will be discussed in greater detail hereinafter, is used for the provision of cooling in the separation unit S. In this situation, the choice of which of the two part flows 3 b and/or 3 d is drawn from for this provision of cooling is determined by the temperature level(s) required in the heavy hydrocarbon separation unit S. - The hydrocarbon-rich flow to be liquefied is then conducted via
line 1 c to a second heat exchanger E2, and is liquefied in this against the evaporating mixedrefrigerant flow 3 b of thesecond cooling circuit 3 a to 3 e. - Once liquefaction has taken place, the hydrocarbon-rich flow is conducted via
line 1 d to a third heat exchanger E3, and is subcooled here against themixed refrigerant flow 2 b of thethird cooling circuit 2 a to 2 c. The subcooled liquid product is then conducted via line le to its further use. - As can be seen from the drawing, each of the three
cooling circuits 2 a to 2 c, 3 a to 3 e, and 4 a to 4 e, has a compressor, V2, V3, and V4 respectively. Not shown in the drawing are the corresponding drives for these compressors V2, V3, and V4. In addition, the coolers or heat exchangers which are located downstream of the compressors V2, V3, and V4 respectively are not shown in the drawing, in which the refrigerant mixture is cooled against a cooling medium, such as water. - The refrigerant mixture of the first refrigerant circuit, compressed in the compressor V4, is conducted via
line 4 a to the heat exchanger E1, and is divided here into two part flows 4 b and 4 d after cooling has taken place. The refrigerant mixture in these part flows 4 b and 4 d, after throttling has been effected in the valves d and e or expansion devices, is evaporated to different pressure levels in the heat exchanger E1 and then conducted vialine part flow 4 c) or to an intermediate pressure level (part flow 4 e). - The refrigerant mixture of the
second cooling circuit 3 a to 3 e, compressed in the compressor V3, is conducted vialine 3 a through heat exchangers E1 and E2, and is cooled in these. Thatpart flow 3 b of this refrigerant mixture flow, which is conducted through heat exchanger E2, after expansion in valve b, is evaporated in heat exchanger E2 against cooling process flows, and is then conducted vialine 3 c to the intake stage of compressor V3. - According to the invention, a
part flow 3 d of the refrigerant mixture of the secondrefrigerant mixture circuit 3 a to 3 e is drawn off after the heat exchanger E1, expanded in valve c, and then evaporated in heat exchanger E1 against cooling process flows, before being conducted vialine 3 e, at an intermediate pressure level, to the circuit compressor V3. Accordingly, the refrigerantmixture part flow 3 d, according to the invention, makes a contribution to the pre-cooling of the hydrocarbon-rich flow in heat exchanger E1. - In order for this to be achieved, the
part flow 3 d of the refrigerant mixture of the second mixedrefrigerant circuit 3 a to 3 e, used for the pre-cooling of the hydrocarbon-rich flow, must be evaporated at a pressure which is higher than the evaporation pressure of the mixedrefrigerant part flow 3 b of the second mixedrefrigerant circuit 3 a to 3 e. - By selecting the intermediate pressure at which the mixed
refrigerant part flow 3 e is evaporated and conducted to the compressor V3, and by regulating the volume distribution of the two mixed refrigerant part flows 3 b and 3 d, the distribution of the cooling capacity of the second refrigerant circuit onto the heat exchangers E1 and E2, and therefore to the pre-cooling and liquefaction of the hydrocarbon-rich flow which is to be liquefied, can be adjusted almost at will. - If, for example, 40% of the total drive capacity is required for the pre-cooling and 60% for the liquefaction and subcooling of the hydrocarbon-rich flow, then, with the concept and method according to the invention, one compressor is used in each case with a third of the total drive capacity in the first and third refrigerant mixture circuit, i.e. for the pre-cooling as well as for the subcooling of the hydrocarbon-rich flow which is to be liquefied. The compressor of the second refrigerant mixture circuit is operated according to the invention in such a way that it uses 20% of its capacity, and consequently 6.66% of the total capacity, for pre-cooling, while the remaining 80%, i.e. 26.66% of the total capacity, is used for liquefaction.
- The method according to the invention accordingly makes possible the economical exploitation of the available compressors and drive units, because the (circuit) compressors of the three refrigerant circuits obtain approximately the same drive capacity, i.e. a third of total capacity in each case.
- Accordingly, large liquefaction plants in particular, with a liquefaction capacity greater than 5 million tonnes LNG per year, can be operated substantially more economically, since, by standardizing the drives and compressors of the three cooling circuits, the achievable liquefaction capacity of the liquefaction process can be maximised with the use of tried-and-trusted drive units and compressors.
-
FIG. 2 shows an alternative version of the load balanced process. As withFIG. 1 the pre-cooling cycle C10 comprises a first circuit driven by a first compressor V10 and onepart 22 of therefrigerant stream 21 from the second cycle C20. Three General Electric MS 7121 EA (Frame 7) gas turbines are used to drive the compressors V10, V20, V30. If highest availability is of the essence, the three refrigeration cycles can be designed with twotimes 50% gas turbine/compressor trains. In this case six GE MS 6581 B (Frame 6) gas turbines would replace the three Frame 7s. - All LNG plants require the extraction of at least of those hydrocarbons, which would freeze in the LNG under storage conditions (e.g. aromatics and C5+). In an LNG plant precooling is usually considered as first cooling step between ambient temperature and extraction of the mentioned hydrocarbons.
- It should be emphasised that the method according to the invention can be combined with all known separation methods considered to be prior art for relatively high-boiling hydrocarbons.
- The precooling portion of the overall power demand of all refrigeration compressors for the two gases defined in Table 1 is shown in
FIG. 3 as a function of a reference temperature. This is the temperature, under which all main process streams (natural gas, refrigerant fluids) enter into the cryogenic heat exchangers. -
TABLE 1 Lean Rich mol % Gas Gas N2 5.00 5.00 CH4 88.93 84.07 C2H6 3.96 5.58 C3H8 1.37 2.73 C4H10 0.48 1.34 C5H12 0.17 0.65 C6H14 0.06 0.32 C7H16 0.02 0.16 C8H18 0.01 0.08 Benzene 0.01 0.08 100.00 100.00 - The lower the reference temperature and the richer the gas the smaller the required compressor power for precooling becomes. This situation can be addressed reasonably well by designers of dual flow liquefaction processes, if the power mismatch between precooling and liquefaction plus subcooling is compensated by helpers for the gas turbines.
- A process with three refrigeration cycles offers a much wider field for even load distribution between the cycles. If part of the refrigerant of the liquefaction cycle C20 is vaporized under elevated pressure in the precooling section C10 and is fed to the LC compressor V20 as
side stream 22, a perfect load balancing between all three refrigeration cycles can be achieved. This feature is a major aspect of a cost effective design for large production capacities. As all three (3) cycles are symmetrically driven this arrangement is referred to as MFC*s3. - Unlike the embodiment of
FIG. 1 , the final compressor V30 ofFIG. 2 is split into two casings V31, V32. The second casing V32 is designed to deal with high pressures at which the multistage compressor operates. - In order to provide actual figures for a realistic process design a large LNG train has been studied. On the basis of the lean gas composition with a pressure of 62 bar and a temperature of 35 deg C. at the inlet to precooling a conceptual process design was made. The refrigeration compressors are driven by Frame 7's with additional 20 MW on each shaft, which have been recruited from the starter/helpers. The resulting LNG rundown amounts to 8.5 mtpa at 333 stream days, which is accompanied by an additional quantity of 0.4 mtpa NGL (C3+ hydrocarbons). The specific energy consumption of the refrigeration compressors is 259 kWh/tLNG.
- In
FIG. 4 the precooling circuit C10 ofFIG. 2 has been replaced with a pre-cooling circuit C100 which comprises acarbon dioxide stream 101. After compression and condensation/subcooling thestream 101 is split into three separate streams, 102, 103, 104 which are then expanded to different pressures. This compensates for the constant temperature evaporation of CO2. Unlike hydrocarbon streams 201, 301 only part of thecarbon dioxide stream 101 is sub-cooled by the pre-cooling heat exchanger E100 prior to expansion, in order to reduce the internal heat load of this exchanger. - Owing to the higher operating pressure, the CO2 precooling compressor V100 is split into two casings, V110, V120 with a barrel type casing V120 for the high-pressure stage. After compression the carbon dioxide is cooled by a water cooled condenser C20 and an additional subcooling heat exchanger C22, using seawater to subcool the liquid refrigerant after the condenser C20, in order to improve process efficiency. In addition a desuperheater can also be provided after the compressor, as in many conventional systems.
- As with the previous embodiments, “load balancing” is achieved by allowing the liquefaction compressor V200 to take over some of the precooling cycle load, leading to a “symmetrical” process.
- Process simulations of the above embodiment as shown in
FIG. 4 andFIG. 2 gave power requirement data as shown in Table 2, using the design data as shown in Table 3. As a result of the load-balanced process, the power input to the CO2-precooled case was only 4.4% higher than the baseline. For a given maximum available power as defined by the hydrocarbon process case, this would correspond to a LNG capacity of 95.6% with CO2 precooling unless more driver capacity is installed. -
TABLE 2 C2/C3 CO2 precooling precooling Total shaft power 162.7 155.8 MW (104%) (100%) Precooling 49.6 47.6 MW compressor Liquefaction 50.5 47.7 MW compressor Subcooling 50.5 48.5 MW compressor Other power 12.1 12.0 MW consumers -
TABLE 3 LNG production capacity 5.8 mtpa Gross calorific value 40 MJ/Sm3 of LNG Feed gas pressure 69 bar (liquefaction inlet) Sea cooling water 5 ° C. temperature - Temperature profiles in the form of hot/cold composite curves for the two cases are shown in
FIG. 5 . The three CO2 precooling temperature levels are easily observed in the left diagram. The highest pressure level to the liquefaction compressor is also considered part of precooling. Changes in the subcooling process are minimal between the two cases. - Layout, size and weight of an offshore LNG liquefaction module with CO2 precooling were compared to the baseline hydrocarbon case (that shown in
FIGS. 1 and 2 ). Among the factors that contributed to reduce the equipment footprints and give smaller dimensions with CO2 were reduced precooling compressor suction drum sizes and smaller precooling piping dimensions. Additional equipment caused by the third precooling pressure level/drum and the installation of a refrigerant subcooler made the net reduction in footprint area marginal, however. The plate-fin heat exchangers were reduced in size due to larger LMTD (Logarithmic Mean Temperature Difference) and less internal duty. While plate fin heat exchangers were used in this instance it is of course also possible to use other types of heat exchangers, which could also be reduced in size. Some of the major pipe sizes in the liquefaction and subcooling circuit did not change much, and it is these pipes that to a large degree set out the deck heights, so no changes were envisaged relative to deck elevations. In total, it was concluded that the liquefaction module size would be no greater when using a CO2 precooling circuit, and indeed a reduction of a few square meters is possible. In addition, the weight of the module dropped by 100 tons. - A major safety concern of the LNG process with hydrocarbon precooling, especially when applied offshore, is the possible formation of a flammable and explosive hydrocarbon/air mixture in case of a major leakage in one of the refrigerant circuits. Thus, the minimization of hydrocarbon refrigerant inventory is very important in terms of safety.
- As may be observed from the
FIG. 6 , the HC refrigerant inventory is reduced by about 70% in the CO2-precooled process. The reduced hydrocarbon charge is positive in relation to loss prevention and to the availability of the three main safety functions of the LNG barge, which are (i) main structural strength, (ii) main escape routes, and (iii) means of evacuation. - If the molecular weight of the hydrocarbon refrigerant is higher than that of air, a flammable cloud can accumulate inside or between the modules, and on the deck surfaces. Thus, in addition to minimizing the total hydrocarbon inventory it is of special importance to eliminate the heavier components, especially propane (52% heavier than air), but also ethane (4% heavier than air). By replacing the hydrocarbon precooling with CO2, all propane is eliminated from the liquefaction module, and even though ethane is present in the liquefaction and subcooling refrigerants, both these mixtures have a molar mass that is lower than air.
- From the above results it has been found that the introduction of CO2 precooling in a load-balanced MFC*s3 process does not give a significant increase in specific power requirement, or equipment size/weight/cost, while the safety of the process can be improved.
Claims (26)
Applications Claiming Priority (5)
Application Number | Priority Date | Filing Date | Title |
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DE10344030.5 | 2003-09-23 | ||
DE2003144030 DE10344030A1 (en) | 2003-09-23 | 2003-09-23 | Liquefying hydrocarbon-rich gas e.g. natural gas involves flowing of gas through three refrigeration stages, each having a circuit and compressor, so that a part flow of refrigerant from the second circuit pre-cools the gas in first stage |
GB0409103.9 | 2004-04-23 | ||
GB0409103A GB0409103D0 (en) | 2003-09-23 | 2004-04-23 | Natural gas liquefaction process |
PCT/GB2004/004047 WO2005028975A2 (en) | 2003-09-23 | 2004-09-23 | Natural gas liquefaction process |
Publications (1)
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US20080006053A1 true US20080006053A1 (en) | 2008-01-10 |
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ID=34379077
Family Applications (1)
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US10/573,213 Abandoned US20080006053A1 (en) | 2003-09-23 | 2004-09-23 | Natural Gas Liquefaction Process |
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US (1) | US20080006053A1 (en) |
AU (1) | AU2004274706B2 (en) |
NO (1) | NO20061751L (en) |
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WO (1) | WO2005028975A2 (en) |
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US20070175240A1 (en) * | 2005-11-24 | 2007-08-02 | Jager Marco D | Method and apparatus for cooling a stream, in particular a hydrocarbon stream such as natural gas |
WO2009153427A2 (en) * | 2008-06-20 | 2009-12-23 | Ifp | Method for liquefying natural gas with pre-cooling of the coolant mixture |
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US20110185767A1 (en) * | 2006-08-17 | 2011-08-04 | Marco Dick Jager | Method and apparatus for liquefying a hydrocarbon-containing feed stream |
US20130125568A1 (en) * | 2011-11-17 | 2013-05-23 | Air Products And Chemicals, Inc. | Compressor Assemblies and Methods to Minimize Venting of a Process Gas During Startup Operations |
US20140060111A1 (en) * | 2012-09-06 | 2014-03-06 | Linde Aktiengesellschaft | Process for liquefying a hydrocarbon-rich fraction |
US20160061517A1 (en) * | 2014-08-29 | 2016-03-03 | Black & Veatch Holding Company | Dual mixed refrigerant system |
US9562717B2 (en) | 2010-03-25 | 2017-02-07 | The University Of Manchester | Refrigeration process |
US20170217051A1 (en) * | 2016-01-28 | 2017-08-03 | Jean-Charles Viancin | Method for manufacturing a flexible mold with peripheral stiffener, and mold resulting from said method |
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US20190195536A1 (en) * | 2016-06-22 | 2019-06-27 | Samsung Heavy Ind. Co., Ltd | Fluid cooling apparatus |
US11359858B2 (en) * | 2019-12-31 | 2022-06-14 | L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude | Method for liquefying ammonia |
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Also Published As
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NO20061751L (en) | 2006-06-22 |
WO2005028975A2 (en) | 2005-03-31 |
AU2004274706A1 (en) | 2005-03-31 |
RU2352877C2 (en) | 2009-04-20 |
RU2006113610A (en) | 2007-10-27 |
WO2005028975A3 (en) | 2005-05-26 |
AU2004274706B2 (en) | 2008-08-07 |
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