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WO2012050068A1 - Liquefaction method, liquefaction device, and floating liquefied gas production equipment comprising same - Google Patents

Liquefaction method, liquefaction device, and floating liquefied gas production equipment comprising same Download PDF

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Publication number
WO2012050068A1
WO2012050068A1 PCT/JP2011/073255 JP2011073255W WO2012050068A1 WO 2012050068 A1 WO2012050068 A1 WO 2012050068A1 JP 2011073255 W JP2011073255 W JP 2011073255W WO 2012050068 A1 WO2012050068 A1 WO 2012050068A1
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WO
WIPO (PCT)
Prior art keywords
low
pressure
heat medium
temperature side
pressure nitrogen
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.)
Ceased
Application number
PCT/JP2011/073255
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French (fr)
Japanese (ja)
Inventor
岡　勝
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Mitsubishi Heavy Industries Ltd
Original Assignee
Mitsubishi Heavy Industries Ltd
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Filing date
Publication date
Application filed by Mitsubishi Heavy Industries Ltd filed Critical Mitsubishi Heavy Industries Ltd
Priority to EP11832503.4A priority Critical patent/EP2629035B1/en
Priority to KR1020127033255A priority patent/KR101536394B1/en
Priority to CN201180031178.7A priority patent/CN102959351B/en
Publication of WO2012050068A1 publication Critical patent/WO2012050068A1/en
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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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
    • 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
    • B63B35/00—Vessels or similar floating structures specially adapted for specific purposes and not otherwise provided for
    • B63B35/44—Floating buildings, stores, drilling platforms, or workshops, e.g. carrying water-oil separating devices
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G OR C10K; LIQUIFIED PETROLEUM GAS; USE OF ADDITIVES TO FUELS OR FIRES; FIRE-LIGHTERS
    • C10L3/00—Gaseous fuels; Natural gas; Synthetic natural gas obtained by processes not covered by subclass C10G, C10K; Liquefied petroleum gas
    • C10L3/06—Natural gas; Synthetic natural gas obtained by processes not covered by C10G, C10K3/02 or C10K3/04
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/003—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production
    • F25J1/0032—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration"
    • F25J1/004—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration" by flash gas recovery
    • 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
    • F25J1/005—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 expansion of a gaseous 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
    • F25J1/006—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the refrigerant fluid used
    • F25J1/007—Primary atmospheric gases, mixtures thereof
    • F25J1/0072—Nitrogen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—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
    • F25J1/0203—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 single-component refrigerant [SCR] fluid in a closed vapor compression cycle
    • F25J1/0205—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 single-component refrigerant [SCR] fluid in a closed vapor compression cycle as a dual level SCR refrigeration cascade
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—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
    • F25J1/0203—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 single-component refrigerant [SCR] fluid in a closed vapor compression cycle
    • F25J1/0207—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 single-component refrigerant [SCR] fluid in a closed vapor compression cycle as at least a three level SCR refrigeration cascade
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0228—Coupling of the liquefaction unit to other units or processes, so-called integrated processes
    • F25J1/0229—Integration with a unit for using hydrocarbons, e.g. consuming hydrocarbons as feed stock
    • F25J1/023—Integration with a unit for using hydrocarbons, e.g. consuming hydrocarbons as feed stock for the combustion as fuels, i.e. integration with the fuel gas system
    • 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
    • F25J1/0244—Operation; Control and regulation; Instrumentation
    • F25J1/0254—Operation; Control and regulation; Instrumentation controlling particular process parameter, e.g. pressure, temperature
    • 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
    • F25J1/0262—Details of the cold heat exchange system
    • F25J1/0263—Details of the cold heat exchange system using different types of heat exchangers
    • 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
    • F25J1/0262—Details of the cold heat exchange system
    • F25J1/0264—Arrangement of heat exchanger cores in parallel with different functions, e.g. different cooling streams
    • F25J1/0265—Arrangement of heat exchanger cores in parallel with different functions, e.g. different cooling streams comprising cores associated exclusively with the cooling of a refrigerant stream, e.g. for auto-refrigeration or economizer
    • 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
    • F25J1/0262—Details of the cold heat exchange system
    • F25J1/0264—Arrangement of heat exchanger cores in parallel with different functions, e.g. different cooling streams
    • F25J1/0265—Arrangement of heat exchanger cores in parallel with different functions, e.g. different cooling streams comprising cores associated exclusively with the cooling of a refrigerant stream, e.g. for auto-refrigeration or economizer
    • F25J1/0267—Arrangement of heat exchanger cores in parallel with different functions, e.g. different cooling streams comprising cores associated exclusively with the cooling of a refrigerant stream, e.g. for auto-refrigeration or economizer using flash gas as 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
    • F25J1/0257—Construction and layout of liquefaction equipments, e.g. valves, machines
    • F25J1/0275—Construction and layout of liquefaction equipments, e.g. valves, machines adapted for special use of the liquefaction unit, e.g. portable or transportable devices
    • F25J1/0277—Offshore use, e.g. during shipping
    • F25J1/0278—Unit being stationary, e.g. on floating barge or fixed platform
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
    • F25J1/0279—Compression of refrigerant or internal recycle fluid, e.g. kind of compressor, accumulator, suction drum etc.
    • 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
    • F25J1/0282—Steam 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
    • F25J1/0288—Combination of different types of drivers mechanically coupled to the same refrigerant compressor, possibly split on multiple compressor casings using work extraction by mechanical coupling of compression and expansion of the refrigerant, so-called companders
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
    • B63B25/00—Load-accommodating arrangements, e.g. stowing, trimming; Vessels characterised thereby
    • B63B25/02—Load-accommodating arrangements, e.g. stowing, trimming; Vessels characterised thereby for bulk goods
    • B63B25/08—Load-accommodating arrangements, e.g. stowing, trimming; Vessels characterised thereby for bulk goods fluid
    • B63B25/12—Load-accommodating arrangements, e.g. stowing, trimming; Vessels characterised thereby for bulk goods fluid closed
    • B63B25/14—Load-accommodating arrangements, e.g. stowing, trimming; Vessels characterised thereby for bulk goods fluid closed pressurised
    • 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
    • F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
    • F25J2230/20—Integrated compressor and process expander; Gear box arrangement; Multiple compressors on a common shaft
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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
    • F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
    • F25J2230/30—Compression of the feed stream
    • 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
    • F25J2240/00—Processes or apparatus involving steps for expanding of process streams
    • F25J2240/40—Expansion without extracting work, i.e. isenthalpic throttling, e.g. JT valve, regulating valve or venturi, or isentropic nozzle, e.g. Laval
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2245/00—Processes or apparatus involving steps for recycling of process streams
    • F25J2245/90—Processes or apparatus involving steps for recycling of process streams the recycled stream being boil-off gas from storage
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/14—External refrigeration with work-producing gas expansion loop
    • F25J2270/16—External refrigeration with work-producing gas expansion loop with mutliple gas expansion loops of the same refrigerant
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/90—External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration

Definitions

  • the present invention relates to a liquefaction method, a liquefaction apparatus, and a floating liquefied gas production facility including the same, and more particularly to liquefaction of natural gas.
  • liquefied gas is liquefied using a cascade refrigeration cycle or a refrigeration cycle using a mixed refrigerant of several types of refrigerants (for example, Patent Document 1).
  • a mixed refrigerant of several types of refrigerants for example, Patent Document 1.
  • offshore floating bodies have been studied at the place where this liquefaction facility is installed.
  • liquefaction equipment similar to that on land is installed on an offshore floating body, there are requirements for marine use in consideration of anti-sway performance, installation space, ease of liquefaction, and safety. Therefore, although it is used for reliquefaction of boil-off gas of an LNG ship, there is room for application as a liquefaction facility even in a nitrogen expansion cycle of nitrogen refrigerant inferior in liquefaction efficiency.
  • the vertical axis represents temperature (° C.), and the horizontal axis represents heat load (kW).
  • the solid line in FIG. 5 shows the natural gas boosted to 4 Ma
  • the dotted line shows the natural gas boosted to 15 MPa.
  • the alternate long and short dash line in FIG. 5 indicates nitrogen in the case where heat is exchanged with natural gas whose pressure is increased to 4 MPa
  • the alternate long and two short dashes line indicates nitrogen which is heat exchanged with natural gas whose pressure is increased to 15 MPa.
  • the compression circulation of heat medium nitrogen is often driven by a gas turbine because of the nitrogen compressor having a large required power, as in the invention described in Patent Document 2, but is liquefied as fuel consumed by the gas turbine. A part of the raw material gas is assumed.
  • the off-gas generated in the liquefaction process is low in pressure as a fuel for the gas turbine, so that re-pressurization is required and is difficult to use.
  • the off-gas generated in the liquefaction process has a problem that its pressure is almost atmospheric pressure, and there are many nitrogen components, so that it is difficult to use it as a fuel for a gas turbine that drives a nitrogen compressor.
  • the present invention has been made in view of such circumstances, and a liquefaction method, a liquefaction apparatus, and a liquefaction method that are excellent in safety and capable of downsizing equipment while suppressing a decrease in liquefaction efficiency.
  • a floating liquefied gas production facility is provided.
  • the liquefaction method, the liquefaction apparatus, and the floating liquefied gas production facility employ the following means.
  • the liquefied gas heat-exchanged with a single component high-pressure heat medium is depressurized to a predetermined pressure, and then the depressurized liquefied gas is lower in temperature and of the same type as the high-pressure heat medium.
  • It is a liquefaction method characterized by heat-exchanging with a low temperature side heat carrier and liquefying.
  • the liquefied gas is liquefied by exchanging heat with the heat medium.
  • the liquefaction efficiency of the liquefied gas is desirably such that the temperature difference between the liquefied gas and the heat medium is uniformly small over the heat exchange process.
  • the liquefied gas is at a high pressure, the temperature difference with the heat medium is almost uniformly small over the heat exchange process, but the heat exchanger that exchanges heat with the heat medium is enlarged. Also.
  • the liquefied gas is at a low pressure, the liquefied gas is stepped during the heat exchange process.
  • a cascade system in which heat is exchanged between a mixed heat medium such as hydrocarbon and nitrogen or a plurality of single-component heat medium using a plurality of heat exchangers. It has been.
  • a mixed heat medium such as hydrocarbon and nitrogen or a plurality of single-component heat medium using a plurality of heat exchangers.
  • the cascade system there is a problem that the number of devices such as a heat exchanger increases.
  • a mixed heat medium it consists of multiple components, so a plurality of heat mediums are used in accordance with the characteristics of the liquefied gas. There was a problem.
  • the liquefied gas is subjected to heat exchange with the single-component high-temperature side heat medium, and then reduced to a predetermined pressure. Furthermore, the reduced-pressure liquefied gas is of the same type as the high-temperature side heat medium and is subjected to heat exchange with the low-temperature side heat medium at a lower temperature than the high-temperature side heat medium. As a result, the liquefied gas heat-exchanged with the high-temperature side heat medium can be decompressed so as to approximate the temperature change of the low-temperature side heat medium, and then heat-exchanged with the low-temperature side heat medium.
  • the predetermined pressure refers to a pressure corresponding to the critical point of the liquefied gas that exchanges heat with the heat medium.
  • the liquefied gas is a raw material gas before being liquefied, and examples thereof include natural gas (LNG) and liquefied petroleum gas (LPG).
  • a heat exchanger for a high temperature side heat medium that exchanges heat between the liquefied gas and the high temperature side heat medium, and the pressure of the liquefied gas derived from the heat exchanger for the high temperature side heat medium are reduced.
  • a low-temperature side heat medium heat exchanger that exchanges heat between the liquefied gas that has passed through the pressure-reduction valve and the low-temperature side heat medium, and the high-temperature side heat medium and the low-temperature side heat medium include:
  • the liquefaction apparatus is characterized in that it is a single component and of the same type, and the pressure reducing valve reduces the liquefied gas led to the low temperature side heat medium heat exchanger to a predetermined pressure.
  • the single component high-temperature side heat medium is led to the high-temperature side heat medium heat exchanger, and the same type of low-temperature side heat medium as the high-temperature side heat medium is led to the low-temperature side heat medium heat exchanger.
  • a pressure reducing valve for reducing the liquefied gas to a predetermined pressure is provided between the exchanger and the heat exchanger for the low temperature side heat medium.
  • a third aspect of the present invention is a high-pressure turbine that is guided and driven by steam, a high-pressure turbine side shaft that is connected to the high-pressure turbine, and a low-pressure that is guided and driven by steam derived from the high-pressure turbine.
  • a cross-compound turbine having a turbine, a low-pressure turbine side shaft connected to the low-pressure turbine, and a high-temperature side heat medium compressor that compresses the high-temperature side heat medium guided to the high-temperature side heat medium heat exchanger;
  • a low-temperature side heat medium compressor that compresses the low-temperature side heat medium guided to the low-temperature side heat medium heat exchanger, and a steam generation means that generates steam that is guided to the high-pressure turbine.
  • the liquefying apparatus is characterized in that a heat medium compressor is connected to the high pressure turbine side shaft, and the low temperature side heat medium compressor is connected to the low pressure turbine side shaft.
  • the high-temperature side heat medium compressor was connected to the high-pressure turbine side shaft, and the low-temperature side heat medium compressor was connected to the low-pressure turbine side shaft. Since the high-pressure turbine side shaft and the low-pressure turbine side shaft constituting the cross-compound turbine are separated from each other, the high-pressure turbine connected to the high-pressure turbine side shaft and the low-pressure turbine connected to the low-pressure turbine side shaft By controlling each of these, the high temperature side heat medium compressor and the low temperature side heat medium compressor can be independently controlled. Therefore, the high temperature side heat medium and the low temperature side heat medium can be compressed independently of each other, and the refrigeration loads of the high temperature side heat medium and the low temperature side heat medium can be controlled independently.
  • the heat exchanger for the high temperature side heat medium may be a plate type.
  • the plate type is used for the heat exchanger for the high temperature side heat medium in which the liquefied gas and the high temperature side heat medium exchange heat. Therefore, the heat exchanger for high temperature side heat medium can be reduced in size. Therefore, the liquefaction device can be made compact.
  • the steam generating means may be configured to generate steam using off-gas in the liquefied gas as fuel.
  • steam generating means for generating steam by burning off gas in liquefied gas as fuel is used. Therefore, it is possible to drive the steam that drives the cross compound turbine using off-gas in an approximately atmospheric pressure state generated in the liquefaction apparatus. Therefore, the offgas generated from the liquefaction device can be used effectively.
  • a fourth aspect of the present invention is a floating-type liquefied gas production facility including any of the liquefying devices described above.
  • the liquefaction device composed of a cross compound turbine driven by steam was used for the floating liquefied gas production facility. Therefore, the steam turbine currently used for the existing marine main machine can be applied as a cross compound turbine. Therefore, it is not necessary to newly develop a cross-compound turbine for driving the high temperature side heat medium compressor and the low temperature side heat medium compressor, and the existing equipment can be used effectively.
  • nitrogen may be used for the high temperature side heat medium and the low temperature side heat medium.
  • Liquefaction apparatus comprising a high-temperature side heat medium compressor and a low-temperature side heat medium compressor using non-combustible nitrogen as a heat medium, and a high-temperature side heat medium heat exchanger and a low-temperature side heat medium heat exchanger was used in a floating liquefied gas production facility.
  • a steam turbine is used to drive the high temperature side heat medium compressor and the low temperature side heat medium compressor. Accordingly, it is possible to prevent the risk of explosion due to leakage of combustible gas from the heat medium or the like. Therefore, devices such as a high-temperature side heat medium compressor, a low-temperature side heat medium compressor, and a steam turbine can be disposed under the deck. Therefore, the arrangement space of the liquefying device on the deck can be reduced.
  • the liquefied gas is heat-exchanged with a single component high-temperature side heat medium, and then depressurized to a predetermined pressure. Furthermore, the reduced-pressure liquefied gas is of the same type as the high-temperature side heat medium and is subjected to heat exchange with the low-temperature side heat medium at a lower temperature than the high-temperature side heat medium.
  • the liquefied gas heat-exchanged with the high-temperature side heat medium can be decompressed so as to approximate the temperature change of the low-temperature side heat medium, and then heat-exchanged with the low-temperature side heat medium. Therefore, the temperature difference between the liquefied gas, the high temperature side heat medium, and the low temperature side heat medium can be kept substantially constant. Therefore, the liquefied gas can be efficiently liquefied using a single component heat medium.
  • FIG. 4 is a TH diagram showing the relationship between natural gas and nitrogen in the liquefaction apparatus shown in FIGS. 2 and 3.
  • FIG. 4 is a TH diagram showing the relationship between natural gas and nitrogen at a plurality of pressures.
  • a floating liquefied natural gas production facility (Floating LNG: FLNG) 1 includes a plurality of cargo tanks 2 for storing liquefied natural gas (liquefied gas), a pretreatment device 3, a liquefaction device (not shown), a floating type A power supply device (not shown) for supplying power to the liquefied natural gas production facility 1 is provided.
  • Floating liquefied natural gas manufacturing equipment (floating liquefied gas manufacturing equipment) 1 is a product of liquefied natural gas, which is a product obtained by refining and liquefying natural gas (liquefied gas), which is a raw material gas ejected at high pressure from the bottom of the earth or on the seabed Gas (Liquid Natural Gas: LNG) is installed on the ocean.
  • liquefied gas a product obtained by refining and liquefying natural gas
  • LNG Liquid Natural Gas
  • the cargo tank (only three are shown in the figure) 2 stores liquefied natural gas.
  • the cargo tank 2 is a moss independent spherical tank.
  • the pretreatment device 3 removes impurities such as carbon dioxide, hydrogen sulfide, moisture, and heavy components contained in natural gas that is a raw material gas.
  • the liquefaction device liquefies natural gas by heat exchange with a refrigerant (cooling heat medium).
  • the liquefaction device is provided with a cold box 5 in which a high-pressure nitrogen heat exchanger (not shown) and a low-pressure nitrogen heat exchanger (not shown), which will be described later, are stored, and a power supply device that supplies power to the ship.
  • a high-pressure nitrogen heat exchanger not shown
  • a low-pressure nitrogen heat exchanger not shown
  • a steam turbine for driving the compressor (not shown), etc. which will be described later, are stored. It is divided into a power unit section 6 and a storage section 7 provided with an end flash tank (not shown) described later.
  • the cold box 5 is provided on the deck.
  • the cold box 5 is provided with a high-pressure nitrogen heat exchanger (high-temperature side heat medium heat exchanger) and a low-pressure nitrogen heat exchanger (low-temperature side heat medium heat exchanger), which are part of the liquefaction apparatus. .
  • the cold box 5 is heat-insulated to prevent heat from entering and exiting the outside.
  • the power unit section 6 for the liquefier is provided below the deck. In the power unit section 6 for the liquefier, a high-pressure nitrogen compressor (high-temperature side heat medium compressor), a low-pressure nitrogen compressor (low-temperature side heat medium compressor) constituting these liquefaction devices, and these compressors
  • a compressor driving steam turbine cross-compound turbine
  • the storage compartment 7 is provided under the deck and is provided with an end flash tank.
  • the inboard power installation section 4 is provided under the deck and includes a boiler (not shown), a gas-fired diesel engine (not shown), and a gas-fired diesel engine drive generator (not shown). ing.
  • the electric power required in the floating liquefied natural gas production facility 1 is supplied by these devices provided in the inboard power installation section 4.
  • FIG. 2 shows an enlarged configuration diagram on the right side of the liquefying apparatus shown in FIG. 1
  • FIG. 3 shows an enlarged configuration diagram on the left side.
  • the liquefaction apparatus 10 includes a high-pressure nitrogen heat exchanger 11, a low-pressure nitrogen heat exchanger 12, a high-pressure nitrogen compressor 13, a low-pressure nitrogen compressor 14, a compressor driving steam turbine 15, and a Joule-Thomson expansion valve (reduced pressure). Valve) 16, a boiler (not shown), and an end flash tank 30 are mainly provided.
  • the liquefaction apparatus 10 is divided into a refrigeration cycle and a drive unit that drives the liquefaction apparatus 10.
  • high-pressure natural gas for example, 15 MPa to 20 MPa
  • nitrogen as a refrigerant exchange heat with each other
  • relatively low-pressure natural gas for example, 6 MPa or less
  • nitrogen as a refrigerant exchange heat with each other.
  • the high-pressure nitrogen loop 17 mainly includes a high-pressure nitrogen heat exchanger 11, a high-pressure nitrogen compressor 13, and a high-pressure nitrogen expander 19.
  • the high-pressure nitrogen heat exchanger 11 exchanges heat between high-pressure natural gas and nitrogen (hereinafter “high-pressure nitrogen”).
  • high-pressure nitrogen for example, a plate-type stainless steel plate diffusion type (diffusion-bonded heat exchangers) manufactured by Heatlic is preferably used.
  • the high-pressure nitrogen compressor 13 compresses high-pressure nitrogen (high-temperature side heat medium).
  • the high-pressure nitrogen compressor 13 is connected to a high-pressure turbine-side speed reducer 20 connected to a compressor driving steam turbine 15 described later.
  • the high-pressure nitrogen compressor 13 compresses high-pressure nitrogen by driving the high-pressure turbine-side speed reducer 20.
  • the high-pressure nitrogen expander 19 expands high-pressure nitrogen.
  • a high pressure nitrogen booster 21 is connected to the high pressure nitrogen expander 19. The high-pressure nitrogen booster 21 is driven by the high-pressure nitrogen expander 19 expanding and rotating the high-pressure nitrogen. The high-pressure nitrogen booster 21 boosts high-pressure nitrogen by being driven.
  • the low-pressure nitrogen loop 18 mainly includes a low-pressure nitrogen heat exchanger 12, a low-pressure nitrogen compressor 14, and a low-pressure nitrogen expander 22.
  • the low-pressure nitrogen heat exchanger 12 exchanges heat between natural gas and nitrogen (hereinafter referred to as “low-pressure nitrogen”).
  • low-pressure nitrogen a plate fin type heat exchanger with aluminum brazing is used.
  • the low-pressure nitrogen compressor 14 compresses low-pressure nitrogen (low-temperature side heat medium).
  • the low-pressure nitrogen compressor 14 is connected to a low-pressure turbine-side speed reducer 23 that is connected to a compressor driving steam turbine 15 described later.
  • the low-pressure nitrogen compressor 14 compresses the low-pressure nitrogen when the low-pressure turbine-side speed reducer 23 is driven.
  • the low-pressure nitrogen expander 22 expands low-pressure nitrogen.
  • a low pressure nitrogen booster 24 is connected to the low pressure nitrogen expander 22.
  • the low-pressure nitrogen booster 24 is driven by the low-pressure nitrogen expander 22 expanding and rotating the low-pressure nitrogen.
  • the low pressure nitrogen booster 24 boosts the low pressure nitrogen by being driven.
  • the compressor driving steam turbine 15 is a large cross-compound steam turbine used in a main engine of a ship.
  • UST Ultra Steam Turbine
  • the compressor driving steam turbine 15 includes a high pressure turbine 15a, an intermediate pressure turbine (high pressure turbine) 15b, a first low pressure turbine 15c, and a second low pressure turbine 15d.
  • the high-pressure turbine 15a and the intermediate-pressure turbine 15b are provided on the primary shaft 15e (high-pressure turbine side shaft).
  • the first low pressure turbine (low pressure turbine) 15c and the second low pressure turbine (low pressure turbine) 15d are provided on a secondary shaft (low pressure turbine side shaft) 15f.
  • a high-pressure turbine-side speed reducer 20 is connected to the end of the primary shaft 15e, and a low-pressure turbine-side speed reducer 23 is connected to the end of the secondary shaft 15f.
  • the high-pressure turbine-side speed reducer 20 transmits the output transmitted from the primary shaft 15 e to the high-pressure nitrogen compressor 13.
  • the high-pressure nitrogen compressor 13 is driven by the high-pressure turbine 15a or the intermediate-pressure turbine 15b being rotationally driven.
  • the low-pressure turbine-side speed reducer 23 transmits the output transmitted from the secondary shaft 15 f to the low-pressure nitrogen compressor 14.
  • the low-pressure nitrogen compressor 14 is driven by the first low-pressure turbine 15c or the second low-pressure turbine 15d being rotationally driven.
  • the boiler steam generating means
  • the boiler is a co-fired boiler that uses liquefied natural gas such as off-gas and boil-off gas, which will be described later, and heavy oil as fuel.
  • the end flash tank 30 expands the liquefied natural gas that has passed through the high-pressure nitrogen cycle 17 and the low-pressure nitrogen cycle 18 to lower the temperature.
  • the nitrogen component contained in the liquefied natural gas is removed.
  • a pressure reducing valve may be used instead of the end flash tank 30.
  • the Joule-Thompson expansion valve 16 is provided between the high-pressure nitrogen loop 17 and the low-pressure nitrogen loop 18.
  • the Joule-Thompson expansion valve 16 is for expanding Joule-Thompson natural gas that has passed through the high-pressure nitrogen loop 17 by its throttle mechanism.
  • Natural gas which is a raw material gas ejected from onshore or under the seabed, is led to a pretreatment device 3 provided on the deck of the floating liquefied natural gas production facility 1 (see FIG. 1). Natural gas contains carbon dioxide, hydrogen sulfide, moisture, heavy components and the like in the pretreatment device 3.
  • the natural gas purified by the pretreatment device 3 is guided to the cold box 5.
  • the natural gas guided to the cold box 5 is boosted to, for example, 15 MPa or more by a booster compressor 31 (see FIG. 2) or the like.
  • the pressure increase is desirably 10 MPa or more.
  • the natural gas that has been increased in pressure by the booster compressor 31 is guided to the first heat exchanger 32.
  • the natural gas guided to the first heat exchanger 32 is heat-exchanged with seawater, and the temperature is lowered to, for example, 30 ° C.
  • the natural gas whose temperature has been lowered by the first heat exchanger 32 is further guided to the second heat exchanger 33.
  • the natural gas guided to the second heat exchanger 33 is subjected to heat exchange with fresh water which is chiller water, and the temperature is lowered to, for example, ⁇ 20 ° C.
  • the heat exchange efficiency with the high pressure nitrogen in the high pressure nitrogen loop 17 can be improved by heat-exchanging with chiller water and precooling.
  • the natural gas precooled by the second heat exchanger 33 is guided to the high-pressure nitrogen loop 17.
  • the natural gas guided to the high-pressure nitrogen loop 17 is guided to the high-pressure nitrogen heat exchanger 11 constituting the high-pressure nitrogen loop 17.
  • the natural gas guided to the high-pressure nitrogen heat exchanger 11 exchanges heat with high-pressure nitrogen in the first subcooling section K1 provided in the high-pressure nitrogen heat exchanger 11. By exchanging heat with high-pressure nitrogen in the first subcooling section K1, the natural gas is lowered to, for example, ⁇ 80 ° C.
  • the natural gas whose temperature has been lowered is guided to the Joule-Thomson expansion valve 16.
  • the natural gas guided to the Joule-Thomson valve 16 expands (depressurizes) to a pressure of, for example, 10 MPa by passing through the Joule-Thomson expansion valve 16.
  • the temperature of the natural gas that has passed through the Joule-Thompson expansion valve 16 is lowered to, for example, ⁇ 90 ° C.
  • the natural gas is desirably 10 MPa or less due to expansion by the Joule-Thomson expansion valve 16.
  • the natural gas which has been expanded by passing through the Joule-Thomson expansion valve 16 and whose temperature has been lowered is guided to the low-pressure nitrogen loop 18.
  • the natural gas guided to the low pressure nitrogen loop 18 is guided to the low pressure nitrogen heat exchanger 12 constituting the low pressure nitrogen loop 18.
  • the natural gas led to the low-pressure nitrogen heat exchanger 12 exchanges heat with the low-pressure nitrogen in two stages. That is, the temperature of the natural gas is lowered to, for example, ⁇ 135 ° C. in the second subcooling section K2 provided in the low-pressure nitrogen heat exchanger 12, and then the third subcooling provided in the low-pressure nitrogen heat exchanger 12. In the part K3, the temperature is lowered to, for example, ⁇ 160 ° C. to be liquefied.
  • the liquefied natural gas liquefied in this way is guided to the end flash tank 30.
  • the temperature of the liquefied natural gas led to the end flash tank 30 is reduced by expanding in the end flash tank 30, and the nitrogen content in the liquefied natural gas is released.
  • the liquefied natural gas from which the temperature has further decreased and the nitrogen content has been released is led to and stored in the cargo tank 2 shown in FIG.
  • a part of the liquefied natural gas led to the end flash tank 30 is gasified.
  • the amount of gasified liquefied natural gas (hereinafter referred to as “off-gas”) is adjusted such that the flash rate becomes 10% or less by adjusting the temperature of the liquefied natural gas led to the end flash tank 30.
  • Off gas (for example, ⁇ 140 ° C.) is led from the end flash tank 30 to the low pressure nitrogen heat exchanger 12.
  • the off gas guided to the low-pressure nitrogen heat exchanger 12 exchanges heat with the natural gas described above in the second subcooling section K2 provided in the low-pressure nitrogen heat exchanger 12. Thereby, the temperature of the off gas is set to, for example, ⁇ 100 ° C.
  • the off gas is guided to the second condensing part G2 provided in the low-pressure nitrogen heat exchanger 12.
  • the off gas guided to the second condensing part G2 exchanges heat with low-pressure nitrogen described later.
  • the off-gas that has undergone heat exchange in the second condensing unit G2 is heated to, for example, 30 ° C. and is led out from the low-pressure nitrogen heat exchanger 12.
  • the boil-off gas in which a part of the liquefied natural gas is vaporized in the cargo tank 2 (see FIG. 1) is also led to the low-pressure nitrogen heat exchanger 12 in the same manner as the off-gas.
  • the boil-off gas guided to the low-pressure nitrogen heat exchanger 12 is heat-exchanged in the second subcooling section K2 and the second condensing section G2 provided in the low-pressure nitrogen heat exchanger 12, and the temperature thereof becomes, for example, 30 ° C. It is heated and derived from the low pressure nitrogen heat exchanger 12.
  • the high-pressure nitrogen circulating in the high-pressure nitrogen loop 17 is compressed to, for example, 12 MPa and 120 ° C. by the high-pressure nitrogen compressor 13 driven by the high-pressure turbine-side speed reducer 20.
  • the high-pressure nitrogen having a high pressure is led to the third heat exchanger 34.
  • the high-pressure nitrogen guided to the third heat exchanger 34 is heat-exchanged with water supplied from a water supply system (not shown), and the temperature is lowered to 85 ° C.
  • the high-pressure nitrogen that has passed through the third heat exchanger 34 is further guided to the fourth heat exchanger 35.
  • the high-pressure nitrogen led to the fourth heat exchanger 35 is heat-exchanged with fresh water led from a not-shown fresh water system, and the temperature is lowered to 40 ° C.
  • the high-pressure nitrogen whose temperature has decreased to 40 ° C. is led to the high-pressure nitrogen heat exchanger 11.
  • the high-pressure nitrogen led to the high-pressure nitrogen heat exchanger 11 is led to the first condensing part G1 provided in the high-pressure nitrogen heat exchanger 11.
  • the high-pressure nitrogen guided to the first condensing unit G1 exchanges heat with the high-pressure nitrogen expanded through the first subcooling unit K1.
  • the temperature of the high-pressure nitrogen that has passed through the first condensing part G1 falls to, for example, ⁇ 25 ° C.
  • the high-pressure nitrogen whose temperature has decreased due to heat exchange in the first condensing part G ⁇ b> 1 is guided to the high-temperature nitrogen expander 19.
  • the high-pressure nitrogen introduced to the high-temperature nitrogen expander 19 is expanded to, for example, 2 MPa and ⁇ 85 ° C.
  • the high-pressure nitrogen that has expanded and the temperature has decreased is led to the first subcooling section K1 provided in the high-pressure nitrogen heat exchanger 11.
  • the expanded high-pressure nitrogen introduced to the first subcooling section K1 is heated to, for example, ⁇ 30 ° C. by exchanging heat with the natural gas described above.
  • the high-pressure nitrogen heated in the first subcooling unit K1 is heated to, for example, 35 ° C. by exchanging heat with the high-pressure nitrogen introduced from the fourth heat exchanger 35 in the first condensing unit G1.
  • the expanded high-pressure nitrogen heated through the first subcooling section K1 and the first condensing section G1 provided in the high-pressure nitrogen heat exchanger 11 is guided to the high-pressure nitrogen booster 21.
  • the expanded high-pressure nitrogen guided to the high-pressure nitrogen booster 21 is boosted by the high-pressure nitrogen booster 21 to 3 MPa, 85 ° C., for example, and is guided to the fifth heat exchanger 36.
  • the pressurized high-pressure nitrogen led to the fifth heat exchanger 36 is heat-exchanged with the fresh water led from the fresh water system, and the temperature is lowered to 40 ° C., for example.
  • the high-pressure nitrogen whose temperature has been lowered through the fifth heat exchanger 36 is led to the high-pressure nitrogen compressor 13. As described above, high-pressure nitrogen is circulated in the high-pressure nitrogen loop 17.
  • the low-pressure nitrogen circulating in the low-pressure nitrogen loop 18 is compressed to, for example, 5 MPa by the low-pressure nitrogen compressor 14 driven by the low-pressure turbine-side speed reducer 23.
  • the compressed low-pressure nitrogen is led to the sixth heat exchanger 37.
  • the low-pressure nitrogen led to the sixth heat exchanger 37 exchanges heat with the feed water led from the feed water system, and the temperature is lowered to 85 ° C., for example.
  • the low-pressure nitrogen that has passed through the sixth heat exchanger 37 is further guided to the seventh heat exchanger 38.
  • the low-pressure nitrogen led to the seventh heat exchanger 38 exchanges heat with the feed water led from the feed water system, and the temperature is lowered to 40 ° C., for example.
  • the low-pressure nitrogen whose temperature has decreased after passing through the sixth heat exchanger 37 and the seventh heat exchanger 38 is guided to the low-pressure nitrogen heat exchanger 12.
  • the low-pressure nitrogen guided to the low-pressure nitrogen heat exchanger 12 is guided to the second condensing part G2 provided in the low-pressure nitrogen heat exchanger 12.
  • the low-pressure nitrogen led to the second condensing part G2 exchanges heat with the low-pressure nitrogen expanded through the second subcooling part K2.
  • the temperature of the low-pressure nitrogen that has passed through the second condensing part G2 is lowered to, for example, ⁇ 90 ° C.
  • the low-pressure nitrogen heat-exchanged in the second condensing part G2 is guided from the low-pressure nitrogen heat exchanger 12 to the low-pressure nitrogen expander 22.
  • the low-pressure nitrogen having a reduced temperature led to the low-pressure nitrogen expander 22 is expanded to, for example, 3 MPa and ⁇ 164 ° C.
  • the low-pressure nitrogen that has expanded and the temperature has further decreased is led to the third subcooling section K3 provided in the low-pressure nitrogen heat exchanger 12.
  • the expanded low-pressure nitrogen introduced to the third subcooling section K3 is heated to, for example, ⁇ 140 ° C. through heat exchange with the natural gas that has passed through the second subcooling section K2.
  • the expanded low-pressure nitrogen that has passed through the third subcooling section K3 further exchanges heat with the natural gas introduced from the Joule-Thompson expansion valve 16 to the low-pressure nitrogen heat exchanger 12 in the second subcooling section K2.
  • the low-pressure nitrogen expanded by exchanging heat with natural gas is heated to, for example, ⁇ 100 ° C.
  • the low-pressure nitrogen expanded through the second cooler K2 is further led to the second condensing part G2 provided in the low-pressure nitrogen heat exchanger 12.
  • the expanded low-pressure nitrogen led to the second condensing part G2 exchanges heat with the low-pressure nitrogen led from the seventh heat exchanger 38.
  • the expanded low-pressure nitrogen is, for example, 36 ° C. and is led out from the low-pressure nitrogen heat exchanger 12.
  • the low pressure nitrogen heated through the third subcooling section K3, the second subcooling section K2 and the second condensing section G2 provided in the low pressure nitrogen heat exchanger 12 is led to the low pressure nitrogen booster 24.
  • the expanded low-pressure nitrogen introduced to the low-pressure nitrogen booster 24 is boosted by the low-pressure nitrogen booster 24 to 1 MPa, 85 ° C., for example.
  • the increased low pressure nitrogen is led to the eighth heat exchanger 39.
  • the pressure-reduced low-pressure nitrogen led to the eighth heat exchanger 39 exchanges heat with the feed water led from the feed water system, and the temperature is lowered to 40 ° C., for example.
  • the low-pressure nitrogen whose temperature has been lowered after passing through the eighth heat exchanger 39 is guided to the low-pressure nitrogen compressor 14. As described above, the low pressure nitrogen circulates in the low pressure nitrogen loop 18.
  • Off-gas and boil-off gas that are led out from the second condensing part G2 provided in the low-pressure nitrogen heat exchanger 12 and heated to, for example, 30 ° C. are led to the boiler.
  • Off-gas and boil-off gas led to the boiler are burned as boiler fuel and generate high-temperature and high-pressure (for example, 555 ° C., 11 MPa) steam.
  • the steam generated in the boiler is guided to the high-pressure turbine 15 a of the compressor driving steam turbine 15.
  • the steam guided to the high-pressure turbine 15a converts the thermal energy into rotational energy of the high-pressure turbine 15a and rotationally drives the high-pressure turbine 15a.
  • the primary shaft 15e rotates.
  • the intermediate pressure turbine 15b and the high-pressure turbine-side speed reducer 20 provided on the primary shaft 15e are driven.
  • the steam that rotationally drives the high-pressure turbine 15a is, for example, 2 MPa and is derived from the high-pressure turbine 15a.
  • the steam led out from the high-pressure turbine 15a is guided to a reheater (not shown).
  • the steam guided to the reheater is changed to reheat steam at, for example, 555 ° C. by the reheater.
  • the reheated steam is guided to the intermediate pressure turbine 15 b of the compressor driving steam turbine 15.
  • the reheated steam guided to the intermediate pressure turbine 15b converts the thermal energy into rotational energy of the intermediate pressure turbine 15b and rotationally drives the intermediate pressure turbine 15b.
  • the primary shaft 15e As the intermediate pressure turbine 15b is driven to rotate, the primary shaft 15e further rotates.
  • the high-pressure turbine-side speed reducer 20 provided on the primary shaft 15e is further driven.
  • the intermediate pressure turbine 15b a part of the steam is extracted from the middle stage.
  • the extracted steam of, for example, 1 MPa is used for high-pressure miscellaneous steam used in the floating liquefied natural gas production facility 1 (see FIG. 1).
  • the steam that has passed through all the stages of the intermediate pressure turbine 15 b is, for example, 110 ° C., and is guided to the first low pressure turbine 15 c of the compressor driving steam turbine 15.
  • the steam guided to the first low-pressure turbine 15c converts the thermal energy into rotational energy of the first low-pressure turbine 15c, and rotationally drives the first low-pressure turbine 15c.
  • the secondary shaft 15f rotates.
  • the second low-pressure turbine 15d and the low-pressure turbine-side speed reducer 23 provided on the secondary shaft 15f are driven.
  • a part of the steam is extracted from the middle stage of the first low-pressure turbine 15c.
  • the extracted steam of, for example, 0.1 MPa is used for low-pressure miscellaneous steam used in the floating liquefied natural gas production facility 1 (see FIG. 1).
  • the steam that has passed through all the stages of the first low-pressure turbine 15c is guided to the second low-pressure turbine 15d provided on the secondary shaft 15f.
  • 0.6 MPa of assist steam is separately supplied to the second low-pressure turbine 15 d from an assist steam supply system (not shown).
  • the second low-pressure turbine 15d is rotationally driven by the supplied assist steam.
  • the second low-pressure turbine 15d is driven to rotate, it is possible to drive the low-pressure turbine-side speed reducer 23 connected to the secondary shaft 15f.
  • the steam that has passed through all stages of the first low-pressure turbine 15c and the assist steam that has driven the second low-pressure turbine 15d are led to a main condenser (not shown) to exchange heat with seawater to be condensed.
  • the compressor driving steam turbine 15 can independently control the high-pressure turbine-side speed reducer 20 and the low-pressure turbine-side speed reducer 23 with the primary shaft 15e and the secondary shaft 15f, and further assist steam.
  • the low-pressure turbine-side speed reducer 23 can be independently controlled by driving the second low-pressure turbine 15d.
  • FIG. 4 shows a TH diagram of the natural gas and nitrogen refrigerant of the present embodiment.
  • the vertical axis indicates the heat load (kW), and the horizontal axis indicates the temperature (° C.).
  • the solid line in FIG. 4 indicates natural gas whose pressure is increased to 15 MPa or 4 MPa, and the alternate long and short dash line indicates nitrogen that exchanges heat with natural gas when the pressure is increased to 4 MPa.
  • FIG. 5 is a TH diagram showing the relationship between natural gas and nitrogen at a plurality of pressures.
  • the vertical axis indicates the heat load (kW), and the horizontal axis indicates the temperature (° C.).
  • the solid line in FIG. 5 indicates natural gas whose pressure has been increased to 15 MPa
  • the dotted line indicates natural gas whose pressure has been increased to 4 MPa
  • the alternate long and short dash line indicates nitrogen having a small temperature difference with respect to the natural gas having a relatively low pressure of 4 MPa
  • a two-dot chain line indicates nitrogen having a small temperature difference with respect to a high-pressure natural gas of 15 MPa.
  • the 4 MPa natural gas (solid line) has a step shape in which the temperature hardly changes in the process of lowering the temperature by exchanging heat with nitrogen. Since the liquefaction efficiency of natural gas liquefaction is better when the temperature difference from nitrogen is smaller, the pinch point at which the temperature difference between nitrogen (dotted line) and natural gas becomes the smallest is stepped. Therefore, in the heat exchange process other than the step shape, the temperature difference between the natural gas and nitrogen is increased, and the liquefaction efficiency is lowered as a whole.
  • the step shape generated in the natural gas of 4 MPa disappears, and the temperature change of the natural gas becomes substantially linear. Therefore, the temperature difference between the natural gas of 15 MPa and nitrogen (two-dot chain line) becomes small and can be liquefied efficiently throughout.
  • the natural gas is pressurized to a high pressure (for example, 15 MPa) in the high temperature portion of the natural gas, and the natural gas is set to a relatively low pressure (for example, 4 MPa) in the low temperature portion of the natural gas.
  • a high pressure for example, 15 MPa
  • a relatively low pressure for example, 4 MPa
  • the high pressure natural gas is heat exchanged with the high pressure nitrogen of the high pressure nitrogen loop 17, and in the low temperature portion of the natural gas, the low pressure natural gas is heat exchanged with the low pressure nitrogen of the low pressure nitrogen loop 18.
  • a Joule Thompson expansion valve 16 is provided between the high-pressure nitrogen loop 17 and the low-pressure nitrogen loop 18 to expand the 15 MPa high-pressure natural gas to a 4 MPa low-pressure natural gas.
  • the natural gas that has passed through the high-pressure nitrogen heat exchanger 11 can be approximated to the temperature change of the low-pressure nitrogen by the Joule-Thomson expansion valve 16 and led to the low-pressure nitrogen heat exchanger 12. Therefore, the temperature difference due to heat exchange between natural gas and high-pressure nitrogen and the temperature difference due to heat exchange between natural gas and low-pressure nitrogen can be kept substantially constant in the heat exchange process. Therefore, natural gas can be liquefied efficiently using single component nitrogen (heat medium).
  • a high pressure nitrogen compressor (high temperature side heat medium compressor) 13 is connected to a primary shaft (high pressure turbine side shaft) 15e via a high pressure turbine side speed reducer 20, and a low pressure turbine side is connected to a secondary shaft (low pressure turbine side shaft) 15f.
  • the low-pressure nitrogen compressor (low temperature side heat medium compressor) 14 is connected via the speed reducer 23.
  • the high-pressure turbine 15a and the intermediate-pressure turbine which are connected to the primary shaft 15e
  • the high-pressure nitrogen compressor 13 and the low-pressure nitrogen compressor 14 are respectively controlled by controlling a first low-pressure turbine (low-pressure turbine) 15c and a second low-pressure turbine (low-pressure turbine) 15d connected to the secondary shaft 15f. And can be controlled independently. Therefore, the high-pressure nitrogen and the low-pressure nitrogen can be compressed independently of each other, and the refrigeration load of the high-pressure nitrogen circulating through the high-pressure nitrogen loop 17 and the low-pressure nitrogen circulating through the low-pressure nitrogen loop 18 can be controlled independently.
  • the high-pressure nitrogen heat exchanger 11 for exchanging heat between natural gas and high-pressure nitrogen a stainless plate diffusion type (plate type) was used. Therefore, the high-pressure nitrogen heat exchanger 11 can be reduced in size. Therefore, the cold box 5 in which the high-pressure nitrogen heat exchanger 11 constituting the liquefying apparatus 10 is stored can be made compact.
  • the pressure of the natural gas is lowered by passing through the Joule-Thompson expansion valve 16, and a plate fin type with aluminum brazing (plate type) is used for the low-pressure nitrogen heat exchanger 12. Therefore, the low-pressure nitrogen heat exchanger 12 can also be reduced in size. Therefore, the cold box 5 constituting the liquefying apparatus 10 can be made more compact.
  • the liquefying apparatus 10 constituted by the steam turbine 15 for driving the compressor driven by steam is used for the floating liquefied natural gas manufacturing facility (floating liquefied gas manufacturing facility) 1. Therefore, the cross-pound steam turbine used for the existing marine main engine can be applied to the compressor driving steam turbine 15. Therefore, it is not necessary to newly develop the compressor driving steam turbine 15 for driving the high-pressure nitrogen compressor 13 and the low-pressure nitrogen compressor 14, and the existing equipment can be used effectively.
  • a liquefier 10 comprising a high-pressure nitrogen compressor 13 and a low-pressure nitrogen compressor 14 using non-combustible nitrogen as a heat medium, a high-pressure nitrogen heat exchanger 11 and a low-pressure nitrogen heat exchanger 12 is used as a floating liquefied natural gas. It was decided to use it for manufacturing equipment 1. Further, the compressor driving steam turbine 15 is used to drive the high-pressure nitrogen compressor 13 and the low-pressure nitrogen compressor 14. Accordingly, it is possible to prevent the risk of explosion due to leakage of combustible gas such as a heat medium.
  • equipment such as the high pressure nitrogen compressor 13, the low pressure nitrogen compressor 14, and the compressor driving steam turbine 15 may be arranged in the liquefier power unit section 6 below the deck of the floating liquefied natural gas production facility 1. it can. Therefore, the arrangement space of the liquefying device 10 on the deck can be reduced.
  • liquefied natural gas LNG
  • LPG liquefied petroleum gas
  • the natural gas introduced from the booster compressor 31 to the high-pressure nitrogen heat exchanger 11 has been described as being precooled by the first heat exchanger 32 and the second heat exchanger 33, but the present invention is not limited thereto. It is not limited, It is good also as what does not pre-cool with chiller water, ie, does not provide the 2nd heat exchanger 33.
  • precooling from ⁇ 10 ° C. to about ⁇ 30 ° C. using chiller water, it is possible to increase the power reduction effect of compressing high-pressure nitrogen and low-pressure nitrogen led to the high-pressure nitrogen loop 17 and the low-pressure nitrogen loop 18. Precooling is not necessary.

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Abstract

A liquefaction method, a liquefaction device, and floating liquefied gas production equipment comprising the same which are capable of inhibiting reductions in liquefaction efficiency during liquefaction, are safe, and which make it possible to reduce the size of the equipment. The present invention is characterized in that the pressure of a gas that has undergone heat exchange with a single-component high-pressure heat carrier is reduced, and the reduced-pressure gas is liquefied by heat exchange with a low-temperature heat carrier that is of a similar type as the high-pressure heat carrier but has a lower temperature.

Description

液化方法、液化装置およびこれを備える浮体式液化ガス製造設備Liquefaction method, liquefaction apparatus, and floating liquefied gas production facility equipped with the same

　本発明は、液化方法、液化装置およびこれを備える浮体式液化ガス製造設備に関し、特に、天然ガスの液化に関する。 The present invention relates to a liquefaction method, a liquefaction apparatus, and a floating liquefied gas production facility including the same, and more particularly to liquefaction of natural gas.

　一般に、陸上の液化設備としては、被液化ガスをカスケード式冷凍サイクルや、数種類の冷媒の混合冷媒を用いた冷凍サイクルを用いて液化している（例えば特許文献１）。この液化設備の設置場所に、近年、洋上浮体が検討されている。洋上浮体に陸上と同様な液化設備を設置した場合には、対動揺性能や設置スペース、液化の容易性、安全性への考慮において舶用化の要件がある。そのため、ＬＮＧ船のボイルオフガスの再液化には用いられているが、液化設備としては液化効率に劣る窒素冷媒の窒素膨張サイクルでも適用される余地がある。 Generally, as an onshore liquefaction facility, liquefied gas is liquefied using a cascade refrigeration cycle or a refrigeration cycle using a mixed refrigerant of several types of refrigerants (for example, Patent Document 1). In recent years, offshore floating bodies have been studied at the place where this liquefaction facility is installed. When liquefaction equipment similar to that on land is installed on an offshore floating body, there are requirements for marine use in consideration of anti-sway performance, installation space, ease of liquefaction, and safety. Therefore, although it is used for reliquefaction of boil-off gas of an LNG ship, there is room for application as a liquefaction facility even in a nitrogen expansion cycle of nitrogen refrigerant inferior in liquefaction efficiency.

特表２００６－５０４９２８号公報JP-T-2006-504928 特表２００６－５０３２５２号公報Special table 2006-503252

　窒素冷凍サイクルにおける天然ガスおよび窒素の熱交換について図５を用いて説明する。図５において、縦軸は、温度（℃）を示し、横軸には、熱負荷（ｋＷ）を示す。また、図５中の実線は、４Ｍａに昇圧した天然ガスを示し、点線は、１５ＭＰａに昇圧した天然ガスを示す。さらに、図５中の一点鎖線は、４ＭＰａに昇圧した天然ガスと熱交換する場合の窒素を示し、二点鎖線は、１５ＭＰａに昇圧した天然ガスと熱交換する窒素を示す。 The heat exchange between natural gas and nitrogen in the nitrogen refrigeration cycle will be described with reference to FIG. In FIG. 5, the vertical axis represents temperature (° C.), and the horizontal axis represents heat load (kW). Moreover, the solid line in FIG. 5 shows the natural gas boosted to 4 Ma, and the dotted line shows the natural gas boosted to 15 MPa. Further, the alternate long and short dash line in FIG. 5 indicates nitrogen in the case where heat is exchanged with natural gas whose pressure is increased to 4 MPa, and the alternate long and two short dashes line indicates nitrogen which is heat exchanged with natural gas whose pressure is increased to 15 MPa.

　図５に示すように天然ガス（実線）を４ＭＰａに昇圧した場合には、温度が変化する過程において、熱負荷に対する天然ガスの温度変化が小さくなるステップ状を生じる。このステップ状は、冷媒である窒素が熱交換する過程において液相と気の間を相転移する間、温度が一定になるために生じる。そのため、４Ｍａに昇圧した天然ガスと窒素との温度差が最も小さくなるピンチポイントに合わせるように窒素（一点鎖線）を設定した場合には、ピンチポイント以外の熱交換過程では、天然ガスと窒素との温度差が大きくなり、一般的に温度差が小さい場合に比べ液化効率に劣る。 As shown in FIG. 5, when the natural gas (solid line) is boosted to 4 MPa, a step shape in which the temperature change of the natural gas with respect to the heat load is reduced in the process of changing the temperature. This step shape occurs because the temperature becomes constant during the phase transition between the liquid phase and the air in the process of heat exchange of nitrogen as a refrigerant. Therefore, when nitrogen (one-dot chain line) is set to match the pinch point where the temperature difference between natural gas and nitrogen increased to 4 Ma is the smallest, in the heat exchange process other than the pinch point, natural gas and nitrogen The temperature difference is generally large and the liquefaction efficiency is generally inferior to that when the temperature difference is small.

　熱媒体窒素の圧縮循環は、特許文献２に記載の発明のように、大きな所要動力の窒素圧縮機ゆえにガスタービンによって駆動される例が多いが、ガスタービンによって消費される燃料としては液化されるべき原料ガスの一部が想定されている。液化過程で生じるオフガスは、ガスタービンの燃料としては低圧であるので再加圧が必要となり用いられにくい。製品となる液化ガスを最大化するためにもプロセスオフガスの効率のよい燃料化の課題があった。 The compression circulation of heat medium nitrogen is often driven by a gas turbine because of the nitrogen compressor having a large required power, as in the invention described in Patent Document 2, but is liquefied as fuel consumed by the gas turbine. A part of the raw material gas is assumed. The off-gas generated in the liquefaction process is low in pressure as a fuel for the gas turbine, so that re-pressurization is required and is difficult to use. In order to maximize the liquefied gas used as a product, there was a problem of efficient process-off gas conversion.

　また、液化過程で生じるオフガスは、その圧力がほぼ大気圧であることや窒素成分が多く、窒素圧縮機を駆動するガスタービンの燃料に用いることが困難であるという問題があった。 Further, the off-gas generated in the liquefaction process has a problem that its pressure is almost atmospheric pressure, and there are many nitrogen components, so that it is difficult to use it as a fuel for a gas turbine that drives a nitrogen compressor.

　さらには、特許文献２に記載の発明のように、窒素圧縮機をガスタービンと蒸気タービン、または、蒸気タービンと電動機とのハイブリッドにして駆動している場合には、洋上浮体に適用させるため、船上保守が困難であること、予備品の必要性や電動化による冗長性の確保が問題となっていた。 Furthermore, in the case where the nitrogen compressor is driven as a hybrid of a gas turbine and a steam turbine or a steam turbine and an electric motor as in the invention described in Patent Document 2, in order to apply to a floating body on the ocean, Onboard maintenance is difficult, and the necessity of spare parts and securing of redundancy by electrification have been problems.

　一方、図５の点線で示すように、天然ガスを１５ＭＰａに昇圧した場合には、実線で示した４ＭＰａに昇圧した天然ガスに生じていたステップ状がなくなり略直線状になる。そのため、１５ＭＰａに昇圧した高圧の天然ガスと窒素（二点鎖線）との温度差を全体に渡って小さくして熱交換させることができるため効率的に液化することができる。しかし、高圧の天然ガスと窒素とを熱交換させるためには、シェルアンドチューブ式の熱交換器を用いる必要があるため熱交換器が大型し、液化装置の設置スペースを削減できないという問題があった。 On the other hand, as shown by the dotted line in FIG. 5, when the natural gas is boosted to 15 MPa, the step shape generated in the natural gas boosted to 4 MPa indicated by the solid line disappears and becomes substantially linear. Therefore, since the temperature difference between the high-pressure natural gas boosted to 15 MPa and nitrogen (two-dot chain line) can be reduced over the entire heat exchange, it can be liquefied efficiently. However, in order to exchange heat between high-pressure natural gas and nitrogen, it is necessary to use a shell-and-tube heat exchanger, so that the heat exchanger is large and the installation space for the liquefaction device cannot be reduced. It was.

　本発明は、このような事情に鑑みてなされたものであって、液化効率の低下を抑制しつつ、安全性にも優れ、かつ、設備のコンパクト化が可能な液化方法、液化装置およびこれを備える浮体式液化ガス製造設備を提供する。 The present invention has been made in view of such circumstances, and a liquefaction method, a liquefaction apparatus, and a liquefaction method that are excellent in safety and capable of downsizing equipment while suppressing a decrease in liquefaction efficiency. A floating liquefied gas production facility is provided.

　上記課題を解決するために、本発明の液化方法、液化装置およびこれを備える浮体式液化ガス製造設備は、以下の手段を採用する。
　本発明の第一の態様は、単一成分の高圧熱媒体と熱交換させた被液化ガスを所定圧に減圧した後に、減圧した前記被液化ガスを前記高圧熱媒体よりも低温かつ同種類の低温側熱媒体と熱交換させて液化することを特徴とする液化方法である。 In order to solve the above-described problems, the liquefaction method, the liquefaction apparatus, and the floating liquefied gas production facility including the same employ the following means.
In the first aspect of the present invention, the liquefied gas heat-exchanged with a single component high-pressure heat medium is depressurized to a predetermined pressure, and then the depressurized liquefied gas is lower in temperature and of the same type as the high-pressure heat medium. It is a liquefaction method characterized by heat-exchanging with a low temperature side heat carrier and liquefying.

　被液化ガスの液化は、熱媒体と熱交換させることによって行われている。被液化ガスの液化効率は、被液化ガスと熱媒体との温度差が熱交換過程に渡って均一に小さい方が望ましい。しかし、被液化ガスが高圧の場合には、熱媒体との温度差が熱交換過程に渡ってほぼ均一に小さいが、熱媒体と熱交換を行う熱交換器が大型化してしまう。また。被液化ガスが低圧の場合には、被液化ガスがその熱交換過程でステップ状になってしまう。そのため、被液化ガスと熱媒体との温度差が最も小さくなる箇所（ピンチポイント）に合わせて熱媒体の圧力を設定した場合には、ピンチポイント以外の過程では、被液化ガスと熱媒体の温度差が大きくなり、熱交換効率が劣ってしまう。 The liquefied gas is liquefied by exchanging heat with the heat medium. The liquefaction efficiency of the liquefied gas is desirably such that the temperature difference between the liquefied gas and the heat medium is uniformly small over the heat exchange process. However, when the liquefied gas is at a high pressure, the temperature difference with the heat medium is almost uniformly small over the heat exchange process, but the heat exchanger that exchanges heat with the heat medium is enlarged. Also. When the liquefied gas is at a low pressure, the liquefied gas is stepped during the heat exchange process. Therefore, when the pressure of the heat medium is set in accordance with the position (pinch point) where the temperature difference between the liquefied gas and the heat medium is the smallest, the temperature of the liquefied gas and the heat medium is changed in a process other than the pinch point. The difference becomes large and the heat exchange efficiency becomes poor.

　そこで、被液化ガスと熱媒体との温度差を小さくするために、炭化水素や窒素等の混合熱媒体もしくは複数の単一成分の熱媒体を複数の熱交換器により熱交換するカスケード方式が用いられている。しかし、カスケード方式の場合には、熱交換器等の機器が増加するという問題があった。また、混合熱媒体を用いる場合には、複数の成分からなるため被液化ガスの特性に合わせて複数の熱媒体が用いられるが、その一部に可燃性の熱媒体が用いられることから安全性に問題があった。 Therefore, in order to reduce the temperature difference between the liquefied gas and the heat medium, a cascade system is used in which heat is exchanged between a mixed heat medium such as hydrocarbon and nitrogen or a plurality of single-component heat medium using a plurality of heat exchangers. It has been. However, in the case of the cascade system, there is a problem that the number of devices such as a heat exchanger increases. In addition, when using a mixed heat medium, it consists of multiple components, so a plurality of heat mediums are used in accordance with the characteristics of the liquefied gas. There was a problem.

　そこで、本発明では、被液化ガスを単一成分の高温側熱媒体と熱交換させて、その後、所定圧に減圧する。さらに、減圧された被液化ガスを、高温側熱媒体と同種類であり、かつ、高温側熱媒体よりも低温の低温側熱媒体と熱交換させることとした。これにより、高温側熱媒体と熱交換した被液化ガスを低温側熱媒体の温度変化に近似させるように減圧してから、低温側熱媒体と熱交換させることができる。そのため、被液化ガスと高温側熱媒体および低温側熱媒体との温度差を略一定に保つことができる。したがって、単一成分の熱媒体を用いて、被液化ガスを効率的に液化することができる。
　なお、所定圧とは、熱媒体と熱交換する被液化ガスの臨界点に対応した圧力をいう。
　また、被液化ガスは、液化する前の原料ガスであり、天然ガス（ＬＮＧ）や液化石油ガス（ＬＰＧ）等が挙げられる。 Therefore, in the present invention, the liquefied gas is subjected to heat exchange with the single-component high-temperature side heat medium, and then reduced to a predetermined pressure. Furthermore, the reduced-pressure liquefied gas is of the same type as the high-temperature side heat medium and is subjected to heat exchange with the low-temperature side heat medium at a lower temperature than the high-temperature side heat medium. As a result, the liquefied gas heat-exchanged with the high-temperature side heat medium can be decompressed so as to approximate the temperature change of the low-temperature side heat medium, and then heat-exchanged with the low-temperature side heat medium. Therefore, the temperature difference between the liquefied gas, the high temperature side heat medium, and the low temperature side heat medium can be kept substantially constant. Therefore, the liquefied gas can be efficiently liquefied using a single component heat medium.
The predetermined pressure refers to a pressure corresponding to the critical point of the liquefied gas that exchanges heat with the heat medium.
The liquefied gas is a raw material gas before being liquefied, and examples thereof include natural gas (LNG) and liquefied petroleum gas (LPG).

　本発明の第二の態様は、被液化ガスと高温側熱媒体とが熱交換する高温側熱媒体用熱交換器と、該高温側熱媒体用熱交換器から導出された被液化ガスを減圧する減圧弁と、該減圧弁を通過した被液化ガスと、低温側熱媒体とが熱交換する低温側熱媒体用熱交換器と、を備え、前記高温側熱媒体および前記低温側熱媒体は、単一成分かつ同種類であって、前記減圧弁は、前記低温側熱媒体用熱交換器に導かれる被液化ガスを所定圧に減圧することを特徴とする液化装置である。 According to a second aspect of the present invention, a heat exchanger for a high temperature side heat medium that exchanges heat between the liquefied gas and the high temperature side heat medium, and the pressure of the liquefied gas derived from the heat exchanger for the high temperature side heat medium are reduced. A low-temperature side heat medium heat exchanger that exchanges heat between the liquefied gas that has passed through the pressure-reduction valve and the low-temperature side heat medium, and the high-temperature side heat medium and the low-temperature side heat medium include: The liquefaction apparatus is characterized in that it is a single component and of the same type, and the pressure reducing valve reduces the liquefied gas led to the low temperature side heat medium heat exchanger to a predetermined pressure.

　単一成分の高温側熱媒体を高温側熱媒体用熱交換器へ、高温側熱媒体と同種類の低温側熱媒体を低温側熱媒体用熱交換器へと導き、高温側熱媒体用熱交換器と低温側熱媒体用熱交換器との間には、被液化ガスを所定圧に減圧する減圧弁を設けることとした。これにより、高温側熱媒体用熱交換器を通過した被液化ガスを減圧弁により低温側熱媒体の温度変化に近似させて、低温側熱媒体用熱交換器へと導くことができる。そのため、被液化ガスと高温側熱媒体および低温側熱媒体との温度差を略一定に保つことができる。したがって、単一成分の熱媒体を用いて、被液化ガスを効率的に液化することができる。 The single component high-temperature side heat medium is led to the high-temperature side heat medium heat exchanger, and the same type of low-temperature side heat medium as the high-temperature side heat medium is led to the low-temperature side heat medium heat exchanger. A pressure reducing valve for reducing the liquefied gas to a predetermined pressure is provided between the exchanger and the heat exchanger for the low temperature side heat medium. Thereby, the liquefied gas that has passed through the heat exchanger for the high temperature side heat medium can be approximated to the temperature change of the low temperature side heat medium by the pressure reducing valve and led to the heat exchanger for the low temperature side heat medium. Therefore, the temperature difference between the liquefied gas, the high temperature side heat medium, and the low temperature side heat medium can be kept substantially constant. Therefore, the liquefied gas can be efficiently liquefied using a single component heat medium.

　本発明の第三の態様は、蒸気が導かれて駆動される高圧タービンと、該高圧タービンに接続される高圧タービン側軸と、前記高圧タービンから導出された蒸気が導かれて駆動される低圧タービンと、該低圧タービンに接続される低圧タービン側軸と、を有するクロスコンパウンドタービンと、前記高温側熱媒体用熱交換器に導かれる高温側熱媒体を圧縮する高温側熱媒体用圧縮機と、前記低温側熱媒体用熱交換器に導かれる低温側熱媒体を圧縮する低温側熱媒体用圧縮機と、前記高圧タービンに導かれる蒸気を発生する蒸気発生手段と、を備え、前記高温側熱媒体圧縮機を前記高圧タービン側軸に接続し、前記低温側熱媒体用圧縮機を前記低圧タービン側軸に接続することを特徴とする液化装置である。 A third aspect of the present invention is a high-pressure turbine that is guided and driven by steam, a high-pressure turbine side shaft that is connected to the high-pressure turbine, and a low-pressure that is guided and driven by steam derived from the high-pressure turbine. A cross-compound turbine having a turbine, a low-pressure turbine side shaft connected to the low-pressure turbine, and a high-temperature side heat medium compressor that compresses the high-temperature side heat medium guided to the high-temperature side heat medium heat exchanger; A low-temperature side heat medium compressor that compresses the low-temperature side heat medium guided to the low-temperature side heat medium heat exchanger, and a steam generation means that generates steam that is guided to the high-pressure turbine. The liquefying apparatus is characterized in that a heat medium compressor is connected to the high pressure turbine side shaft, and the low temperature side heat medium compressor is connected to the low pressure turbine side shaft.

　高圧タービン側軸に高温側熱媒体用圧縮機を接続し、低圧タービン側軸に低温側熱媒体用圧縮機を接続することとした。クロスコンパウンドタービンを構成している高圧タービン側軸と低圧タービン側軸とは、互いに分離しているため、高圧タービン側軸に接続されている高圧タービン、低圧タービン側軸に接続されている低圧タービンの各々を制御することによって、高温側熱媒体用圧縮機と低温側熱媒体用圧縮機とをそれぞれ独立に制御することができる。したがって、高温側熱媒体と低温側熱媒体とを互いに独立に圧縮することができ、高温側熱媒体と低温側熱媒体との冷凍負荷を独立に制御することができる。 The high-temperature side heat medium compressor was connected to the high-pressure turbine side shaft, and the low-temperature side heat medium compressor was connected to the low-pressure turbine side shaft. Since the high-pressure turbine side shaft and the low-pressure turbine side shaft constituting the cross-compound turbine are separated from each other, the high-pressure turbine connected to the high-pressure turbine side shaft and the low-pressure turbine connected to the low-pressure turbine side shaft By controlling each of these, the high temperature side heat medium compressor and the low temperature side heat medium compressor can be independently controlled. Therefore, the high temperature side heat medium and the low temperature side heat medium can be compressed independently of each other, and the refrigeration loads of the high temperature side heat medium and the low temperature side heat medium can be controlled independently.

　本発明に係る上述のいずれかの液化装置において、前記高温側熱媒体用熱交換器は、プレート式であってもよい。 In any of the above-described liquefaction apparatuses according to the present invention, the heat exchanger for the high temperature side heat medium may be a plate type.

　この構成によれば、被液化ガスと高温側熱媒体とが熱交換する高温側熱媒体用熱交換器には、プレート式を用いることとした。そのため、高温側熱媒体用熱交換器を小型化することができる。したがって、液化装置のコンパクト化を図ることができる。 According to this configuration, the plate type is used for the heat exchanger for the high temperature side heat medium in which the liquefied gas and the high temperature side heat medium exchange heat. Therefore, the heat exchanger for high temperature side heat medium can be reduced in size. Therefore, the liquefaction device can be made compact.

　本発明に係る上述のいずれかの液化装置において、前記蒸気発生手段は、液化ガス中のオフガスを燃料として蒸気を発生する構成であってもよい。 In any of the above-described liquefaction apparatuses according to the present invention, the steam generating means may be configured to generate steam using off-gas in the liquefied gas as fuel.

　この構成によれば、液化ガス中のオフガスを燃料として燃焼して蒸気を発生する蒸気発生手段を用いることとした。そのため、クロスコンパウンドタービンを駆動する蒸気を液化装置内で生じたほぼ大気圧状態のオフガスを用いて駆動することができる。したがって、液化装置から生じるオフガスを有効に利用することができる。 According to this configuration, steam generating means for generating steam by burning off gas in liquefied gas as fuel is used. Therefore, it is possible to drive the steam that drives the cross compound turbine using off-gas in an approximately atmospheric pressure state generated in the liquefaction apparatus. Therefore, the offgas generated from the liquefaction device can be used effectively.

　本発明の第四の態様は、上記のいずれかの液化装置を備えることを特徴とする浮体式液化ガス製造設備である。 A fourth aspect of the present invention is a floating-type liquefied gas production facility including any of the liquefying devices described above.

　蒸気によって駆動するクロスコンパウンドタービンによって構成される液化装置を浮体式液化ガス製造設備に用いることとした。そのため、クロスコンパウンドタービンとして、既存の舶用主機に用いられている蒸気タービンを適用することができる。したがって、高温側熱媒体用圧縮機および低温側熱媒体用圧縮機を駆動するためのクロスコンパウンドタービンの新たな開発が不要となり、既存の機器を有効利用することができる。 The liquefaction device composed of a cross compound turbine driven by steam was used for the floating liquefied gas production facility. Therefore, the steam turbine currently used for the existing marine main machine can be applied as a cross compound turbine. Therefore, it is not necessary to newly develop a cross-compound turbine for driving the high temperature side heat medium compressor and the low temperature side heat medium compressor, and the existing equipment can be used effectively.

　本発明に係る上述の浮体式液化ガス製造設備において、前記高温側熱媒体及び前記低温側熱媒体には、窒素を用いてもよい。 In the above-described floating liquefied gas production facility according to the present invention, nitrogen may be used for the high temperature side heat medium and the low temperature side heat medium.

　熱媒に不燃性の窒素を用いる高温側熱媒体用圧縮機および低温側熱媒体用圧縮機と、高温側熱媒体用熱交換器および低温側熱媒体用熱交換器とによって構成される液化装置を浮体式液化ガス製造設備に用いることとした。また、高温側熱媒体用圧縮機および低温側熱媒体用圧縮機の駆動には、蒸気タービンを用いることとした。これらにより、熱媒体等から可燃性ガスが漏洩することによる爆発の危険性を防止することができる。そのため、甲板下に、高温側熱媒体用圧縮機、低温側熱媒体用圧縮機や蒸気タービンなどの機器を配置することができる。したがって、甲板上の液化装置の配置スペースを削減することができる。 Liquefaction apparatus comprising a high-temperature side heat medium compressor and a low-temperature side heat medium compressor using non-combustible nitrogen as a heat medium, and a high-temperature side heat medium heat exchanger and a low-temperature side heat medium heat exchanger Was used in a floating liquefied gas production facility. In addition, a steam turbine is used to drive the high temperature side heat medium compressor and the low temperature side heat medium compressor. Accordingly, it is possible to prevent the risk of explosion due to leakage of combustible gas from the heat medium or the like. Therefore, devices such as a high-temperature side heat medium compressor, a low-temperature side heat medium compressor, and a steam turbine can be disposed under the deck. Therefore, the arrangement space of the liquefying device on the deck can be reduced.

　本発明によると、被液化ガスを単一成分の高温側熱媒体と熱交換させて、その後、所定圧に減圧する。さらに、減圧された被液化ガスを、高温側熱媒体と同種類であり、かつ、高温側熱媒体よりも低温の低温側熱媒体と熱交換させることとした。これにより、高温側熱媒体と熱交換した被液化ガスを低温側熱媒体の温度変化に近似させるように減圧してから、低温側熱媒体と熱交換させることができる。そのため、被液化ガスと高温側熱媒体および低温側熱媒体との温度差を略一定に保つことができる。したがって、単一成分の熱媒体を用いて、被液化ガスを効率的に液化することができる。 According to the present invention, the liquefied gas is heat-exchanged with a single component high-temperature side heat medium, and then depressurized to a predetermined pressure. Furthermore, the reduced-pressure liquefied gas is of the same type as the high-temperature side heat medium and is subjected to heat exchange with the low-temperature side heat medium at a lower temperature than the high-temperature side heat medium. As a result, the liquefied gas heat-exchanged with the high-temperature side heat medium can be decompressed so as to approximate the temperature change of the low-temperature side heat medium, and then heat-exchanged with the low-temperature side heat medium. Therefore, the temperature difference between the liquefied gas, the high temperature side heat medium, and the low temperature side heat medium can be kept substantially constant. Therefore, the liquefied gas can be efficiently liquefied using a single component heat medium.

本発明の一実施形態に係る液化装置を備えた浮体式液化ガス製造設備の概略構成図である。It is a schematic block diagram of the floating body type liquefied gas manufacturing equipment provided with the liquefying device concerning one embodiment of the present invention. 図１に示した液化装置の右側拡大構成図である。It is a right side expanded block diagram of the liquefying apparatus shown in FIG. 図１に示した液化装置の左側拡大構成図である。It is a left side expanded block diagram of the liquefying apparatus shown in FIG. 図２および図３に示した液化装置における天然ガスおよび窒素の関係を示したＴ－Ｈ線図である。FIG. 4 is a TH diagram showing the relationship between natural gas and nitrogen in the liquefaction apparatus shown in FIGS. 2 and 3. 複数の圧力における天然ガスおよび窒素の関係を示したＴ－Ｈ線図である。FIG. 4 is a TH diagram showing the relationship between natural gas and nitrogen at a plurality of pressures.

　本発明の一実施形態に係る液化装置を備えた浮体式液化ガス製造設備の概略構成図について図１に基づいて説明する。
　浮体式液化天然ガス製造設備（Ｆｌｏａｔｉｎｇ　ＬＮＧ：ＦＬＮＧ）１は、液化天然ガス（液化ガス）を貯蔵する複数の貨物タンク２と、前処理装置３と、液化装置（図示せず）と、浮体式液化天然ガス製造設備１内に電力を供給する電力供給装置（図示せず）とを備えている。
　浮体式液化天然ガス製造設備（浮体式液化ガス製造設備）１は、陸上や海底の地層下から高圧で噴出する原料ガスである天然ガス（被液化ガス）を精製液化して製品である液化天然ガス（Ｌｉｑｕｅｆｉｅｄ　ｎａｔｕｒａｌ　ｇａｓ：ＬＮＧ）にするものであり、洋上に設置されるものである。 The schematic block diagram of the floating body type liquefied gas manufacturing equipment provided with the liquefying apparatus which concerns on one Embodiment of this invention is demonstrated based on FIG.
A floating liquefied natural gas production facility (Floating LNG: FLNG) 1 includes a plurality of cargo tanks 2 for storing liquefied natural gas (liquefied gas), a pretreatment device 3, a liquefaction device (not shown), a floating type A power supply device (not shown) for supplying power to the liquefied natural gas production facility 1 is provided.
Floating liquefied natural gas manufacturing equipment (floating liquefied gas manufacturing equipment) 1 is a product of liquefied natural gas, which is a product obtained by refining and liquefying natural gas (liquefied gas), which is a raw material gas ejected at high pressure from the bottom of the earth or on the seabed Gas (Liquid Natural Gas: LNG) is installed on the ocean.

　貨物タンク（本図では、３つのみを示す。）２は、液化天然ガスを貯蔵するものである。貨物タンク２は、モス独立球形タンクである。
　前処理装置３は、原料ガスである天然ガス中に含まれている二酸化炭素、硫化水素、水分、重質分等の不純物を除去するものである。 The cargo tank (only three are shown in the figure) 2 stores liquefied natural gas. The cargo tank 2 is a moss independent spherical tank.
The pretreatment device 3 removes impurities such as carbon dioxide, hydrogen sulfide, moisture, and heavy components contained in natural gas that is a raw material gas.

　液化装置は、天然ガスを冷媒（冷却用熱媒体）と熱交換することによって液化するものである。液化装置は、後述する高圧窒素熱交換器（図示せず）や低圧窒素熱交換器（図示せず）が格納されているコールドボックス５と、船内に電力を供給する電力供給装置が設けられている船内動力設置区画４と、後述する高圧窒素圧縮機（図示せず）、低圧窒素圧縮機（図示せず）、圧縮機駆動用蒸気タービン（図示せず）などが格納されている液化装置用動力装置区画６と、後述するエンドフラッシュタンク（図示せず）などが設けられている貯蔵区画７とに分けられている。 The liquefaction device liquefies natural gas by heat exchange with a refrigerant (cooling heat medium). The liquefaction device is provided with a cold box 5 in which a high-pressure nitrogen heat exchanger (not shown) and a low-pressure nitrogen heat exchanger (not shown), which will be described later, are stored, and a power supply device that supplies power to the ship. For the liquefaction device in which the inboard power installation section 4 and a high-pressure nitrogen compressor (not shown), a low-pressure nitrogen compressor (not shown), a steam turbine for driving the compressor (not shown), etc., which will be described later, are stored. It is divided into a power unit section 6 and a storage section 7 provided with an end flash tank (not shown) described later.

　コールドボックス５は、甲板上に設けられている。コールドボックス５内には、液化装置の一部である高圧窒素熱交換器（高温側熱媒体用熱交換器）および低圧窒素熱交換器（低温側熱媒体用熱交換器）が設けられている。コールドボックス５は、外部との熱の出入りを防ぐために断熱措置が施してある。
　液化装置用動力装置区画６は、甲板下に設けられている。液化装置用動力装置区画６には、液化装置を構成している高圧窒素圧縮機（高温側熱媒体用圧縮機）や低圧窒素圧縮機（低温側熱媒体用圧縮機）、これらの圧縮機を駆動する圧縮機駆動用蒸気タービン（クロスコンパウンドタービン）が設けられている。 The cold box 5 is provided on the deck. The cold box 5 is provided with a high-pressure nitrogen heat exchanger (high-temperature side heat medium heat exchanger) and a low-pressure nitrogen heat exchanger (low-temperature side heat medium heat exchanger), which are part of the liquefaction apparatus. . The cold box 5 is heat-insulated to prevent heat from entering and exiting the outside.
The power unit section 6 for the liquefier is provided below the deck. In the power unit section 6 for the liquefier, a high-pressure nitrogen compressor (high-temperature side heat medium compressor), a low-pressure nitrogen compressor (low-temperature side heat medium compressor) constituting these liquefaction devices, and these compressors A compressor driving steam turbine (cross-compound turbine) is provided.

　貯蔵区画７は、甲板下に設けられており、エンドフラッシュタンクが設けられている。
　船内動力設置区画４は、甲板下に設けられおり、後述するボイラ（図示せず）と、ガス焚きディーゼル機関（図示せず）と、ガス焚きディーゼル機関駆動発電機（図示せず）とを備えている。浮体式液化天然ガス製造設備１内で必要な電力は、船内動力設置区画４に設けられているこれらの機器によって供給されることとなる。 The storage compartment 7 is provided under the deck and is provided with an end flash tank.
The inboard power installation section 4 is provided under the deck and includes a boiler (not shown), a gas-fired diesel engine (not shown), and a gas-fired diesel engine drive generator (not shown). ing. The electric power required in the floating liquefied natural gas production facility 1 is supplied by these devices provided in the inboard power installation section 4.

　次に、本実施形態の液化装置の構成について図２および図３を用いて説明する。
　図２には、図１に示した液化装置の右側拡大構成図が示されており、図３には、その左側拡大構成図が示されている。
　液化装置１０は、高圧窒素熱交換器１１と、低圧窒素熱交換器１２と、高圧窒素圧縮機１３と、低圧窒素圧縮機１４と、圧縮機駆動用蒸気タービン１５と、ジュールトムソン膨張弁（減圧弁）１６と、ボイラ（図示せず）と、エンドフラッシュタンク３０とを主に備えている。液化装置１０は、冷凍サイクルと、液化装置１０を駆動する駆動部とに分けられる。 Next, the structure of the liquefying apparatus of this embodiment is demonstrated using FIG. 2 and FIG.
FIG. 2 shows an enlarged configuration diagram on the right side of the liquefying apparatus shown in FIG. 1, and FIG. 3 shows an enlarged configuration diagram on the left side.
The liquefaction apparatus 10 includes a high-pressure nitrogen heat exchanger 11, a low-pressure nitrogen heat exchanger 12, a high-pressure nitrogen compressor 13, a low-pressure nitrogen compressor 14, a compressor driving steam turbine 15, and a Joule-Thomson expansion valve (reduced pressure). Valve) 16, a boiler (not shown), and an end flash tank 30 are mainly provided. The liquefaction apparatus 10 is divided into a refrigeration cycle and a drive unit that drives the liquefaction apparatus 10.

　冷凍サイクルは、高圧な天然ガス（例えば１５ＭＰａから２０ＭＰａ）と冷媒である窒素とが熱交換する高圧窒素ループ１７と、比較的低圧な天然ガス（例えば６ＭＰａ以下）と冷媒である窒素とが熱交換する低圧窒素ループ１８とを備えている。これら２つの冷凍サイクルは、互いに独立したループとなっている。
　駆動部は、圧縮機駆動用蒸気タービン１５を備えている。 In the refrigeration cycle, high-pressure natural gas (for example, 15 MPa to 20 MPa) and nitrogen as a refrigerant exchange heat with each other, and a relatively low-pressure natural gas (for example, 6 MPa or less) and nitrogen as a refrigerant exchange heat with each other. A low-pressure nitrogen loop 18. These two refrigeration cycles are independent loops.
The drive unit includes a compressor driving steam turbine 15.

　高圧窒素ループ１７は、主に、高圧窒素熱交換器１１と、高圧窒素圧縮機１３と、高圧窒素膨張機１９とを備えている。
　高圧窒素熱交換器１１は、高圧な天然ガスと、窒素（以下、「高圧窒素」）とが熱交換するものである。高圧窒素熱交換器１１には、例えば、Ｈｅａｔｒｉｃ社のプレート式のステンレスプレートディフュージョンタイプ（ｄｉｆｆｕｓｉｏｎ－ｂｏｎｄｅｄ　ｈｅａｔ　ｅｘｃｈａｎｇｅｒｓ）が好適に用いられる。 The high-pressure nitrogen loop 17 mainly includes a high-pressure nitrogen heat exchanger 11, a high-pressure nitrogen compressor 13, and a high-pressure nitrogen expander 19.
The high-pressure nitrogen heat exchanger 11 exchanges heat between high-pressure natural gas and nitrogen (hereinafter “high-pressure nitrogen”). As the high-pressure nitrogen heat exchanger 11, for example, a plate-type stainless steel plate diffusion type (diffusion-bonded heat exchangers) manufactured by Heatlic is preferably used.

　高圧窒素圧縮機１３は、高圧窒素（高温側熱媒体）を圧縮するものである。高圧窒素圧縮機１３には、後述する圧縮機駆動用蒸気タービン１５に接続している高圧タービン側減速機２０が接続されている。高圧窒素圧縮機１３は、高圧タービン側減速機２０が駆動されることによって高圧窒素を圧縮する。 The high-pressure nitrogen compressor 13 compresses high-pressure nitrogen (high-temperature side heat medium). The high-pressure nitrogen compressor 13 is connected to a high-pressure turbine-side speed reducer 20 connected to a compressor driving steam turbine 15 described later. The high-pressure nitrogen compressor 13 compresses high-pressure nitrogen by driving the high-pressure turbine-side speed reducer 20.

　高圧窒素膨張機１９は、高圧窒素を膨張させるものである。高圧窒素膨張機１９には、高圧窒素昇圧機２１が接続されている。高圧窒素昇圧機２１は、高圧窒素膨張機１９が高圧窒素を膨張して回転駆動することによって駆動される。高圧窒素昇圧機２１は、駆動されることによって高圧窒素を昇圧する。 The high-pressure nitrogen expander 19 expands high-pressure nitrogen. A high pressure nitrogen booster 21 is connected to the high pressure nitrogen expander 19. The high-pressure nitrogen booster 21 is driven by the high-pressure nitrogen expander 19 expanding and rotating the high-pressure nitrogen. The high-pressure nitrogen booster 21 boosts high-pressure nitrogen by being driven.

　低圧窒素ループ１８は、主に、低圧窒素熱交換器１２と、低圧窒素圧縮機１４と、低圧窒素膨張機２２とを備えている。
　低圧窒素熱交換器１２は、天然ガスと、窒素（以下、「低圧窒素」とう。）とが熱交換するものである。低圧窒素熱交換器１２には、アルミロウ付プレートフィンタイプの熱交換器が用いられる。 The low-pressure nitrogen loop 18 mainly includes a low-pressure nitrogen heat exchanger 12, a low-pressure nitrogen compressor 14, and a low-pressure nitrogen expander 22.
The low-pressure nitrogen heat exchanger 12 exchanges heat between natural gas and nitrogen (hereinafter referred to as “low-pressure nitrogen”). As the low-pressure nitrogen heat exchanger 12, a plate fin type heat exchanger with aluminum brazing is used.

　低圧窒素圧縮機１４は、低圧窒素（低温側熱媒体）を圧縮するものである。低圧窒素圧縮機１４には、後述する圧縮機駆動用蒸気タービン１５に接続されている低圧タービン側減速機２３が接続されている。低圧窒素圧縮機１４は、低圧タービン側減速機２３が駆動されることによって低圧窒素を圧縮する。 The low-pressure nitrogen compressor 14 compresses low-pressure nitrogen (low-temperature side heat medium). The low-pressure nitrogen compressor 14 is connected to a low-pressure turbine-side speed reducer 23 that is connected to a compressor driving steam turbine 15 described later. The low-pressure nitrogen compressor 14 compresses the low-pressure nitrogen when the low-pressure turbine-side speed reducer 23 is driven.

　低圧窒素膨張機２２は、低圧窒素を膨張させるものである。低圧窒素膨張機２２には、低圧窒素昇圧機２４が接続されている。低圧窒素昇圧機２４は、低圧窒素膨張機２２が低圧窒素を膨張して回転駆動することによって駆動される。低圧窒素昇圧機２４は、駆動されることによって低圧窒素を昇圧する。 The low-pressure nitrogen expander 22 expands low-pressure nitrogen. A low pressure nitrogen booster 24 is connected to the low pressure nitrogen expander 22. The low-pressure nitrogen booster 24 is driven by the low-pressure nitrogen expander 22 expanding and rotating the low-pressure nitrogen. The low pressure nitrogen booster 24 boosts the low pressure nitrogen by being driven.

　圧縮機駆動用蒸気タービン１５は、船舶の主機に用いられているクロスコンパウンド式の大型の蒸気タービンである。圧縮機駆動用蒸気タービン１５としては、三菱重工業製のＵＳＴ（Ｕｌｔｒａ　Ｓｔｅａｍ　Ｔｕｒｂｉｎｅ）が好的に用いられる。
　圧縮機駆動用蒸気タービン１５は、高圧タービン１５ａと、中圧タービン（高圧タービン）１５ｂと、第１低圧タービン１５ｃと、第２低圧タービン１５ｄとを備えている。高圧タービン１５ａと中圧タービン１５ｂとは、プライマリー軸１５ｅ（高圧タービン側軸）上に設けられている。第１低圧タービン（低圧タービン）１５ｃと第２低圧タービン（低圧タービン）１５ｄとは、セカンダリー軸（低圧タービン側軸）１５ｆ上に設けられている。 The compressor driving steam turbine 15 is a large cross-compound steam turbine used in a main engine of a ship. As the compressor driving steam turbine 15, UST (Ultra Steam Turbine) manufactured by Mitsubishi Heavy Industries is preferably used.
The compressor driving steam turbine 15 includes a high pressure turbine 15a, an intermediate pressure turbine (high pressure turbine) 15b, a first low pressure turbine 15c, and a second low pressure turbine 15d. The high-pressure turbine 15a and the intermediate-pressure turbine 15b are provided on the primary shaft 15e (high-pressure turbine side shaft). The first low pressure turbine (low pressure turbine) 15c and the second low pressure turbine (low pressure turbine) 15d are provided on a secondary shaft (low pressure turbine side shaft) 15f.

　プライマリー軸１５ｅの端部には、高圧タービン側減速機２０が接続されており、セカンダリー軸１５ｆの端部には、低圧タービン側減速機２３が接続されている。
　高圧タービン側減速機２０は、プライマリー軸１５ｅから伝達された出力を高圧窒素圧縮機１３へと伝達するものである。これにより、高圧窒素圧縮機１３は、高圧タービン１５ａまたは中圧タービン１５ｂが回転駆動されることによって駆動されることとなる。
　低圧タービン側減速機２３は、セカンダリー軸１５ｆから伝達された出力を低圧窒素圧縮機１４へと伝達するものである。これにより、低圧窒素圧縮機１４は、第１低圧タービン１５ｃまたは第２低圧タービン１５ｄが回転駆動されることによって駆動されることとなる。 A high-pressure turbine-side speed reducer 20 is connected to the end of the primary shaft 15e, and a low-pressure turbine-side speed reducer 23 is connected to the end of the secondary shaft 15f.
The high-pressure turbine-side speed reducer 20 transmits the output transmitted from the primary shaft 15 e to the high-pressure nitrogen compressor 13. Thereby, the high-pressure nitrogen compressor 13 is driven by the high-pressure turbine 15a or the intermediate-pressure turbine 15b being rotationally driven.
The low-pressure turbine-side speed reducer 23 transmits the output transmitted from the secondary shaft 15 f to the low-pressure nitrogen compressor 14. Thereby, the low-pressure nitrogen compressor 14 is driven by the first low-pressure turbine 15c or the second low-pressure turbine 15d being rotationally driven.

　ボイラ（蒸気発生手段）は、燃料として後述するオフガスやボイルオフガス等の液化天然ガスと重油とを燃料として用いる混焼ボイラである。
　エンドフラッシュタンク３０は、高圧窒素サイクル１７および低圧窒素サイクル１８を通過した液化天然ガスを膨張させて温度降下させるものである。エンドフラッシュタンク３０において、液化天然ガスは、含有されていた窒素成分が除去されることとなる。なお、エンドフラッシュタンク３０の代わりに減圧弁を用いても良い。 The boiler (steam generating means) is a co-fired boiler that uses liquefied natural gas such as off-gas and boil-off gas, which will be described later, and heavy oil as fuel.
The end flash tank 30 expands the liquefied natural gas that has passed through the high-pressure nitrogen cycle 17 and the low-pressure nitrogen cycle 18 to lower the temperature. In the end flash tank 30, the nitrogen component contained in the liquefied natural gas is removed. A pressure reducing valve may be used instead of the end flash tank 30.

　ジュールトムソン膨張弁１６は、高圧窒素ループ１７と、低圧窒素ループ１８との間に設けられている。ジュールトムソン膨張弁１６は、その絞り機構によって高圧窒素ループ１７を通過した天然ガスをジュールトムソン膨張させるものである。 The Joule-Thompson expansion valve 16 is provided between the high-pressure nitrogen loop 17 and the low-pressure nitrogen loop 18. The Joule-Thompson expansion valve 16 is for expanding Joule-Thompson natural gas that has passed through the high-pressure nitrogen loop 17 by its throttle mechanism.

　次に、天然ガスの液化方法について説明する。
　陸上や海底の地層下から噴出している原料ガスである天然ガスは、浮体式液化天然ガス製造設備１（図１参照）の甲板上に設けられている前処理装置３へと導かれる。天然ガスは、前処理装置３において、含有されている二酸化炭素、硫化水素、水分、重質分等が除去される。 Next, a method for liquefying natural gas will be described.
Natural gas, which is a raw material gas ejected from onshore or under the seabed, is led to a pretreatment device 3 provided on the deck of the floating liquefied natural gas production facility 1 (see FIG. 1). Natural gas contains carbon dioxide, hydrogen sulfide, moisture, heavy components and the like in the pretreatment device 3.

　前処理装置３によって精製された天然ガスは、コールドボックス５へと導かれる。コールドボックス５に導かれた天然ガスは、昇圧コンプレッサ３１（図２参照）等によって例えば１５ＭＰａ以上に昇圧される。なお、この昇圧は、１０ＭＰａ以上であることが望ましい。 The natural gas purified by the pretreatment device 3 is guided to the cold box 5. The natural gas guided to the cold box 5 is boosted to, for example, 15 MPa or more by a booster compressor 31 (see FIG. 2) or the like. Note that the pressure increase is desirably 10 MPa or more.

　昇圧コンプレッサ３１によって高圧にされた天然ガスは、第１熱交換器３２へと導かれる。第１熱交換器３２に導かれた天然ガスは、海水と熱交換して温度が例えば３０℃に下げられる。第１熱交換器３２によって温度が下げられた天然ガスは、さらに、第２熱交換器３３へと導かれる。第２熱交換器３３に導かれた天然ガスは、チラー水である清水と熱交換して温度が例えば－２０℃まで低下させられる。このようにチラー水と熱交換して予冷することによって、高圧窒素ループ１７における高圧窒素との熱交換効率を向上させることができる。 The natural gas that has been increased in pressure by the booster compressor 31 is guided to the first heat exchanger 32. The natural gas guided to the first heat exchanger 32 is heat-exchanged with seawater, and the temperature is lowered to, for example, 30 ° C. The natural gas whose temperature has been lowered by the first heat exchanger 32 is further guided to the second heat exchanger 33. The natural gas guided to the second heat exchanger 33 is subjected to heat exchange with fresh water which is chiller water, and the temperature is lowered to, for example, −20 ° C. Thus, the heat exchange efficiency with the high pressure nitrogen in the high pressure nitrogen loop 17 can be improved by heat-exchanging with chiller water and precooling.

　第２熱交換器３３によって予冷された天然ガスは、高圧窒素ループ１７へと導かれる。高圧窒素ループ１７に導かれた天然ガスは、高圧窒素ループ１７を構成している高圧窒素熱交換器１１へと導かれる。高圧窒素熱交換器１１に導かれた天然ガスは、高圧窒素熱交換器１１内に設けられている第１過冷却部Ｋ１において高圧窒素と熱交換する。第１過冷却部Ｋ１において高圧窒素と熱交換することによって、天然ガスは例えば－８０℃に低下する。 The natural gas precooled by the second heat exchanger 33 is guided to the high-pressure nitrogen loop 17. The natural gas guided to the high-pressure nitrogen loop 17 is guided to the high-pressure nitrogen heat exchanger 11 constituting the high-pressure nitrogen loop 17. The natural gas guided to the high-pressure nitrogen heat exchanger 11 exchanges heat with high-pressure nitrogen in the first subcooling section K1 provided in the high-pressure nitrogen heat exchanger 11. By exchanging heat with high-pressure nitrogen in the first subcooling section K1, the natural gas is lowered to, for example, −80 ° C.

　温度が低下した天然ガスは、ジュールトムソン膨張弁１６へと導かれる。ジュールトムソン弁１６に導かれた天然ガスは、ジュールトムソン膨張弁１６を通過することによって圧力が例えば１０ＭＰａに膨張（減圧）する。これにより、ジュールトムソン膨張弁１６を通過した天然ガスは、温度が例えば－９０℃まで低下させられることとなる。
　なお、ジュールトムソン膨張弁１６による膨張によって天然ガスは、１０ＭＰａ以下になることが望ましい。 The natural gas whose temperature has been lowered is guided to the Joule-Thomson expansion valve 16. The natural gas guided to the Joule-Thomson valve 16 expands (depressurizes) to a pressure of, for example, 10 MPa by passing through the Joule-Thomson expansion valve 16. As a result, the temperature of the natural gas that has passed through the Joule-Thompson expansion valve 16 is lowered to, for example, −90 ° C.
The natural gas is desirably 10 MPa or less due to expansion by the Joule-Thomson expansion valve 16.

　ジュールトムソン膨張弁１６を通過することによって膨張して温度の低下した天然ガスは、低圧窒素ループ１８へと導かれる。低圧窒素ループ１８に導かれた天然ガスは、低圧窒素ループ１８を構成している低圧窒素熱交換器１２へと導かれる。低圧窒素熱交換器１２に導かれた天然ガスは、低圧窒素と２段階に渡って熱交換する。すなわち、天然ガスは、低圧窒素熱交換器１２に設けられている第２過冷却部Ｋ２において例えば－１３５℃に温度が下げられ後、低圧窒素熱交換器１２に設けられている第３過冷却部Ｋ３において例えば－１６０℃にまで温度が下げられて液化される。 The natural gas which has been expanded by passing through the Joule-Thomson expansion valve 16 and whose temperature has been lowered is guided to the low-pressure nitrogen loop 18. The natural gas guided to the low pressure nitrogen loop 18 is guided to the low pressure nitrogen heat exchanger 12 constituting the low pressure nitrogen loop 18. The natural gas led to the low-pressure nitrogen heat exchanger 12 exchanges heat with the low-pressure nitrogen in two stages. That is, the temperature of the natural gas is lowered to, for example, −135 ° C. in the second subcooling section K2 provided in the low-pressure nitrogen heat exchanger 12, and then the third subcooling provided in the low-pressure nitrogen heat exchanger 12. In the part K3, the temperature is lowered to, for example, −160 ° C. to be liquefied.

　このようにして液化された液化天然ガスは、エンドフラッシュタンク３０へと導かれる。エンドフラッシュタンク３０に導かれた液化天然ガスは、エンドフラッシュタンク３０内で膨張することによってその温度が降下するとともに、液化天然ガス中の窒素分が放出される。温度がさらに低下して窒素分が放出された液化天然ガスは、図１に示した貨物タンク２へと導かれて貯蔵される。 The liquefied natural gas liquefied in this way is guided to the end flash tank 30. The temperature of the liquefied natural gas led to the end flash tank 30 is reduced by expanding in the end flash tank 30, and the nitrogen content in the liquefied natural gas is released. The liquefied natural gas from which the temperature has further decreased and the nitrogen content has been released is led to and stored in the cargo tank 2 shown in FIG.

　エンドフラッシュタンク３０に導かれた液化天然ガスの一部は、ガス化する。ガス化した液化天然ガス（以下、「オフガス」という。）の量は、エンドフラッシュタンク３０に導かれる液化天然ガスの温度を調節することによって、フラッシュ率が例えば１０％以下になるようにする。 A part of the liquefied natural gas led to the end flash tank 30 is gasified. The amount of gasified liquefied natural gas (hereinafter referred to as “off-gas”) is adjusted such that the flash rate becomes 10% or less by adjusting the temperature of the liquefied natural gas led to the end flash tank 30.

　オフガス（例えば－１４０℃）は、エンドフラッシュタンク３０から低圧窒素熱交換器１２へと導かれる。低圧窒素熱交換器１２に導かれたオフガスは、低圧窒素熱交換器１２に設けられている第２過冷却部Ｋ２において、前述した天然ガスと熱交換する。これにより、オフガスは、その温度が例えば－１００℃とされる。さらに、オフガスは、低圧窒素熱交換器１２に設けられている第２凝縮部Ｇ２へと導かれる。第２凝縮部Ｇ２に導かれたオフガスは、後述する低圧窒素と熱交換する。第２凝縮部Ｇ２において熱交換したオフガスは、その温度が例えば３０℃に加熱されて低圧窒素熱交換器１２から導出される。 Off gas (for example, −140 ° C.) is led from the end flash tank 30 to the low pressure nitrogen heat exchanger 12. The off gas guided to the low-pressure nitrogen heat exchanger 12 exchanges heat with the natural gas described above in the second subcooling section K2 provided in the low-pressure nitrogen heat exchanger 12. Thereby, the temperature of the off gas is set to, for example, −100 ° C. Further, the off gas is guided to the second condensing part G2 provided in the low-pressure nitrogen heat exchanger 12. The off gas guided to the second condensing part G2 exchanges heat with low-pressure nitrogen described later. The off-gas that has undergone heat exchange in the second condensing unit G2 is heated to, for example, 30 ° C. and is led out from the low-pressure nitrogen heat exchanger 12.

　また、貨物タンク２（図１参照）内において液化天然ガスの一部が気化したボイルオフガスも、オフガスと同様に低圧窒素熱交換器１２へと導かれる。低圧窒素熱交換器１２に導かれたボイルオフガスは、低圧窒素熱交換器１２に設けられている第２過冷却部Ｋ２および第２凝縮部Ｇ２において熱交換して、その温度が例えば３０℃に加熱されて低圧窒素熱交換器１２から導出される。 In addition, the boil-off gas in which a part of the liquefied natural gas is vaporized in the cargo tank 2 (see FIG. 1) is also led to the low-pressure nitrogen heat exchanger 12 in the same manner as the off-gas. The boil-off gas guided to the low-pressure nitrogen heat exchanger 12 is heat-exchanged in the second subcooling section K2 and the second condensing section G2 provided in the low-pressure nitrogen heat exchanger 12, and the temperature thereof becomes, for example, 30 ° C. It is heated and derived from the low pressure nitrogen heat exchanger 12.

　次に、高圧窒素の流れについて説明する。
　高圧窒素ループ１７内を循環している高圧窒素は、高圧タービン側減速機２０によって駆動される高圧窒素圧縮機１３によって例えば１２ＭＰａ、１２０℃に圧縮される。高圧とされた高圧窒素は、第３熱交換器３４へと導かれる。第３熱交換器３４に導かれた高圧窒素は、図示しない給水系統から導かれた給水と熱交換して温度が８５℃に下げられる。 Next, the flow of high pressure nitrogen will be described.
The high-pressure nitrogen circulating in the high-pressure nitrogen loop 17 is compressed to, for example, 12 MPa and 120 ° C. by the high-pressure nitrogen compressor 13 driven by the high-pressure turbine-side speed reducer 20. The high-pressure nitrogen having a high pressure is led to the third heat exchanger 34. The high-pressure nitrogen guided to the third heat exchanger 34 is heat-exchanged with water supplied from a water supply system (not shown), and the temperature is lowered to 85 ° C.

　第３熱交換器３４を通過した高圧窒素は、さらに第４熱交換器３５へと導かれる。第４熱交換器３５に導かれた高圧窒素は、図示しない清水系統から導かれた清水と熱交換して温度が４０℃に下げられる。４０℃まで温度が低下した高圧窒素は、高圧窒素熱交換器１１へと導かれる。高圧窒素熱交換器１１に導かれた高圧窒素は、高圧窒素熱交換器１１に設けられている第１凝縮部Ｇ１へと導かれる。 The high-pressure nitrogen that has passed through the third heat exchanger 34 is further guided to the fourth heat exchanger 35. The high-pressure nitrogen led to the fourth heat exchanger 35 is heat-exchanged with fresh water led from a not-shown fresh water system, and the temperature is lowered to 40 ° C. The high-pressure nitrogen whose temperature has decreased to 40 ° C. is led to the high-pressure nitrogen heat exchanger 11. The high-pressure nitrogen led to the high-pressure nitrogen heat exchanger 11 is led to the first condensing part G1 provided in the high-pressure nitrogen heat exchanger 11.

　第１凝縮部Ｇ１に導かれた高圧窒素は、第１過冷却部Ｋ１を通過して膨張した高圧窒素と熱交換する。これによって、第１凝縮部Ｇ１を通過した高圧窒素は、温度が例えば－２５℃に低下する。第１凝縮部Ｇ１において熱交換して温度が低下した高圧窒素は、高温窒素膨張機１９へと導かれる。高温窒素膨張機１９へと導かれた高圧窒素は、例えば２ＭＰａ、－８５℃に膨張される。膨張して温度の低下した高圧窒素は、高圧窒素熱交換器１１に設けられている第１過冷却部Ｋ１へと導かれる。 The high-pressure nitrogen guided to the first condensing unit G1 exchanges heat with the high-pressure nitrogen expanded through the first subcooling unit K1. As a result, the temperature of the high-pressure nitrogen that has passed through the first condensing part G1 falls to, for example, −25 ° C. The high-pressure nitrogen whose temperature has decreased due to heat exchange in the first condensing part G <b> 1 is guided to the high-temperature nitrogen expander 19. The high-pressure nitrogen introduced to the high-temperature nitrogen expander 19 is expanded to, for example, 2 MPa and −85 ° C. The high-pressure nitrogen that has expanded and the temperature has decreased is led to the first subcooling section K1 provided in the high-pressure nitrogen heat exchanger 11.

　第１過冷却部Ｋ１に導かれた膨張した高圧窒素は、前述した天然ガスと熱交換して例えば－３０℃に加熱される。第１過冷却部Ｋ１において加熱された高圧窒素は、第１凝縮部Ｇ１において第４熱交換器３５から導かれた高圧窒素と熱交換して例えば３５℃に加熱される。 The expanded high-pressure nitrogen introduced to the first subcooling section K1 is heated to, for example, −30 ° C. by exchanging heat with the natural gas described above. The high-pressure nitrogen heated in the first subcooling unit K1 is heated to, for example, 35 ° C. by exchanging heat with the high-pressure nitrogen introduced from the fourth heat exchanger 35 in the first condensing unit G1.

　高圧窒素熱交換器１１に設けられている第１過冷却部Ｋ１および第１凝縮部Ｇ１を通過して加熱された膨張した高圧窒素は、高圧窒素昇圧機２１へと導かれる。高圧窒素昇圧機２１に導かれた膨張した高圧窒素は、高圧窒素昇圧機２１によって昇圧されて例えば３ＭＰａ、８５℃とされて第５熱交換器３６へと導かれる。 The expanded high-pressure nitrogen heated through the first subcooling section K1 and the first condensing section G1 provided in the high-pressure nitrogen heat exchanger 11 is guided to the high-pressure nitrogen booster 21. The expanded high-pressure nitrogen guided to the high-pressure nitrogen booster 21 is boosted by the high-pressure nitrogen booster 21 to 3 MPa, 85 ° C., for example, and is guided to the fifth heat exchanger 36.

　第５熱交換器３６に導かれた昇圧された高圧窒素は、清水系統から導かれた清水と熱交換されて温度が例えば４０℃に下げられる。第５熱交換器３６を通過して温度の下げられた高圧窒素は、高圧窒素圧縮機１３へと導かれる。
　以上のように、高圧窒素は、高圧窒素ループ１７内を循環することとなる。 The pressurized high-pressure nitrogen led to the fifth heat exchanger 36 is heat-exchanged with the fresh water led from the fresh water system, and the temperature is lowered to 40 ° C., for example. The high-pressure nitrogen whose temperature has been lowered through the fifth heat exchanger 36 is led to the high-pressure nitrogen compressor 13.
As described above, high-pressure nitrogen is circulated in the high-pressure nitrogen loop 17.

　次に、低圧窒素の流れについて説明する。
　低圧窒素ループ１８内を循環している低圧窒素は、低圧タービン側減速機２３によって駆動される低圧窒素圧縮機１４によって例えば５ＭＰａに圧縮される。圧縮された低圧窒素は、第６熱交換器３７へと導かれる。第６熱交換器３７に導かれた低圧窒素は、給水系統から導かれた給水と熱交換して温度が例えば８５℃に下げられる。 Next, the flow of low-pressure nitrogen will be described.
The low-pressure nitrogen circulating in the low-pressure nitrogen loop 18 is compressed to, for example, 5 MPa by the low-pressure nitrogen compressor 14 driven by the low-pressure turbine-side speed reducer 23. The compressed low-pressure nitrogen is led to the sixth heat exchanger 37. The low-pressure nitrogen led to the sixth heat exchanger 37 exchanges heat with the feed water led from the feed water system, and the temperature is lowered to 85 ° C., for example.

　第６熱交換器３７を通過した低圧窒素は、さらに第７熱交換器３８へと導かれる。第７熱交換器３８に導かれた低圧窒素は、給水系統から導かれた給水と熱交換して温度が例えば４０℃に下げられる。第６熱交換器３７および第７熱交換器３８を通過して温度が低下した低圧窒素は、低圧窒素熱交換器１２へと導かれる。低圧窒素熱交換器１２に導かれた低圧窒素は、低圧窒素熱交換器１２に設けられている第２凝縮部Ｇ２へと導かれる。 The low-pressure nitrogen that has passed through the sixth heat exchanger 37 is further guided to the seventh heat exchanger 38. The low-pressure nitrogen led to the seventh heat exchanger 38 exchanges heat with the feed water led from the feed water system, and the temperature is lowered to 40 ° C., for example. The low-pressure nitrogen whose temperature has decreased after passing through the sixth heat exchanger 37 and the seventh heat exchanger 38 is guided to the low-pressure nitrogen heat exchanger 12. The low-pressure nitrogen guided to the low-pressure nitrogen heat exchanger 12 is guided to the second condensing part G2 provided in the low-pressure nitrogen heat exchanger 12.

　第２凝縮部Ｇ２に導かれた低圧窒素は、第２過冷却部Ｋ２を通過して膨張した低圧窒素と熱交換する。これによって、第２凝縮部Ｇ２を通過した低圧窒素は、温度が例えば－９０℃に下げられる。第２凝縮部Ｇ２において熱交換した低圧窒素は、低圧窒素熱交換器１２から低圧窒素膨張機２２へと導かれる。低圧窒素膨張機２２に導かれた温度の低下した低圧窒素は、膨張して例えば３ＭＰａ、－１６４℃にされる。膨張し温度がさらに低下した低圧窒素は、低圧窒素熱交換器１２に設けられている第３過冷却部Ｋ３へと導かれる。 The low-pressure nitrogen led to the second condensing part G2 exchanges heat with the low-pressure nitrogen expanded through the second subcooling part K2. As a result, the temperature of the low-pressure nitrogen that has passed through the second condensing part G2 is lowered to, for example, −90 ° C. The low-pressure nitrogen heat-exchanged in the second condensing part G2 is guided from the low-pressure nitrogen heat exchanger 12 to the low-pressure nitrogen expander 22. The low-pressure nitrogen having a reduced temperature led to the low-pressure nitrogen expander 22 is expanded to, for example, 3 MPa and −164 ° C. The low-pressure nitrogen that has expanded and the temperature has further decreased is led to the third subcooling section K3 provided in the low-pressure nitrogen heat exchanger 12.

　第３過冷却部Ｋ３に導かれた膨張した低圧窒素は、前述した第２過冷却部Ｋ２を通過した天然ガスと熱交換して例えば－１４０℃に加熱される。第３過冷却部Ｋ３を通過した膨張した低圧窒素は、さらに、第２過冷却部Ｋ２においてジュールトムソン膨張弁１６から低圧窒素熱交換器１２へと導かれた天然ガスと熱交換する。天然ガスと熱交換して膨張した低圧窒素は、例えば－１００℃まで加熱される。 The expanded low-pressure nitrogen introduced to the third subcooling section K3 is heated to, for example, −140 ° C. through heat exchange with the natural gas that has passed through the second subcooling section K2. The expanded low-pressure nitrogen that has passed through the third subcooling section K3 further exchanges heat with the natural gas introduced from the Joule-Thompson expansion valve 16 to the low-pressure nitrogen heat exchanger 12 in the second subcooling section K2. The low-pressure nitrogen expanded by exchanging heat with natural gas is heated to, for example, −100 ° C.

　第２冷却器Ｋ２を通過して膨張した低圧窒素は、さらに低圧窒素熱交換器１２に設けられている第２凝縮部Ｇ２へと導かれる。第２凝縮部Ｇ２に導かれた膨張した低圧窒素は、第７熱交換器３８から導かれた低圧窒素と熱交換する。これにより、膨張した低圧窒素は、例えば３６℃とされて低圧窒素熱交換器１２から導出される。 The low-pressure nitrogen expanded through the second cooler K2 is further led to the second condensing part G2 provided in the low-pressure nitrogen heat exchanger 12. The expanded low-pressure nitrogen led to the second condensing part G2 exchanges heat with the low-pressure nitrogen led from the seventh heat exchanger 38. Thereby, the expanded low-pressure nitrogen is, for example, 36 ° C. and is led out from the low-pressure nitrogen heat exchanger 12.

　低圧窒素熱交換器１２に設けられている第３過冷却部Ｋ３、第２過冷却部Ｋ２および第２凝縮部Ｇ２を通過して加熱された低圧窒素は、低圧窒素昇圧機２４へと導かれる。低圧窒素昇圧機２４に導かれた膨張した低圧窒素は、低圧窒素昇圧機２４によって昇圧されて例えば１ＭＰａ、８５℃とされる。昇圧された低圧窒素は、第８熱交換器３９へと導かれる。 The low pressure nitrogen heated through the third subcooling section K3, the second subcooling section K2 and the second condensing section G2 provided in the low pressure nitrogen heat exchanger 12 is led to the low pressure nitrogen booster 24. . The expanded low-pressure nitrogen introduced to the low-pressure nitrogen booster 24 is boosted by the low-pressure nitrogen booster 24 to 1 MPa, 85 ° C., for example. The increased low pressure nitrogen is led to the eighth heat exchanger 39.

　第８熱交換器３９に導かれた昇圧された低圧窒素は、給水系統から導かれた給水と熱交換して温度が例えば４０℃に下げられる。第８熱交換器３９を通過して温度が下げられた低圧窒素は、低圧窒素圧縮機１４へと導かれる。
　以上のように、低圧窒素は、低圧窒素ループ１８内を循環することとなる。 The pressure-reduced low-pressure nitrogen led to the eighth heat exchanger 39 exchanges heat with the feed water led from the feed water system, and the temperature is lowered to 40 ° C., for example. The low-pressure nitrogen whose temperature has been lowered after passing through the eighth heat exchanger 39 is guided to the low-pressure nitrogen compressor 14.
As described above, the low pressure nitrogen circulates in the low pressure nitrogen loop 18.

　次に、蒸気の流れについて説明する。
　低圧窒素熱交換器１２に設けられている第２凝縮部Ｇ２から導出されて例えば３０℃に加熱されたオフガスおよびボイルオフガスは、ボイラへと導かれる。ボイラに導かれたオフガスおよびボイルオフガスは、ボイラの燃料として燃焼されて高温高圧（例えば５５５℃、１１ＭＰａ）の蒸気を発生させる。ボイラで発生した蒸気は、圧縮機駆動用蒸気タービン１５の高圧タービン１５ａへと導かれる。高圧タービン１５ａに導かれた蒸気は、その熱エネルギーを高圧タービン１５ａの回転エネルギーへと変換して高圧タービン１５ａを回転駆動する。高圧タービン１５ａが回転駆動することによってプライマリー軸１５ｅが回転する。プライマリー軸１５ｅが回転することによって、プライマリー軸１５ｅに設けられている中圧タービン１５ｂおよび高圧タービン側減速機２０が駆動される。 Next, the flow of steam will be described.
Off-gas and boil-off gas that are led out from the second condensing part G2 provided in the low-pressure nitrogen heat exchanger 12 and heated to, for example, 30 ° C. are led to the boiler. Off-gas and boil-off gas led to the boiler are burned as boiler fuel and generate high-temperature and high-pressure (for example, 555 ° C., 11 MPa) steam. The steam generated in the boiler is guided to the high-pressure turbine 15 a of the compressor driving steam turbine 15. The steam guided to the high-pressure turbine 15a converts the thermal energy into rotational energy of the high-pressure turbine 15a and rotationally drives the high-pressure turbine 15a. When the high-pressure turbine 15a is driven to rotate, the primary shaft 15e rotates. As the primary shaft 15e rotates, the intermediate pressure turbine 15b and the high-pressure turbine-side speed reducer 20 provided on the primary shaft 15e are driven.

　一方、高圧タービン１５ａを回転駆動した蒸気は、例えば２ＭＰａとされて高圧タービン１５ａから導出される。高圧タービン１５ａから導出された蒸気は、図示しない再熱器へと導かれる。再熱器に導かれた蒸気は、再熱器によって例えば５５５℃の再熱蒸気とされる。この再熱蒸気は、圧縮機駆動用蒸気タービン１５の中圧タービン１５ｂへと導かれる。 On the other hand, the steam that rotationally drives the high-pressure turbine 15a is, for example, 2 MPa and is derived from the high-pressure turbine 15a. The steam led out from the high-pressure turbine 15a is guided to a reheater (not shown). The steam guided to the reheater is changed to reheat steam at, for example, 555 ° C. by the reheater. The reheated steam is guided to the intermediate pressure turbine 15 b of the compressor driving steam turbine 15.

　中圧タービン１５ｂに導かれた再熱蒸気は、その熱エネルギーを中圧タービン１５ｂの回転エネルギーへと変換して中圧タービン１５ｂを回転駆動する。中圧タービン１５ｂが回転駆動することによってさらにプライマリー軸１５ｅがさらに回転する。プライマリー軸１５ｅがさらに回転することによって、プライマリー軸１５ｅに設けられている高圧タービン側減速機２０がさらに駆動されることとなる。 The reheated steam guided to the intermediate pressure turbine 15b converts the thermal energy into rotational energy of the intermediate pressure turbine 15b and rotationally drives the intermediate pressure turbine 15b. As the intermediate pressure turbine 15b is driven to rotate, the primary shaft 15e further rotates. As the primary shaft 15e further rotates, the high-pressure turbine-side speed reducer 20 provided on the primary shaft 15e is further driven.

　中圧タービン１５ｂは、その途中段から蒸気の一部が抽気される。抽気された例えば１ＭＰａの蒸気は、浮体式液化天然ガス製造設備１（図１参照）内で用いる高圧雑用蒸気等に用いられる。
　中圧タービン１５ｂの全段を通過した蒸気は、例えば１１０℃とされて圧縮機駆動用蒸気タービン１５の第１低圧タービン１５ｃへと導かれる。 In the intermediate pressure turbine 15b, a part of the steam is extracted from the middle stage. The extracted steam of, for example, 1 MPa is used for high-pressure miscellaneous steam used in the floating liquefied natural gas production facility 1 (see FIG. 1).
The steam that has passed through all the stages of the intermediate pressure turbine 15 b is, for example, 110 ° C., and is guided to the first low pressure turbine 15 c of the compressor driving steam turbine 15.

　第１低圧タービン１５ｃに導かれた蒸気は、その熱エネルギーを第１低圧タービン１５ｃの回転エネルギーへと変換して第１低圧タービン１５ｃを回転駆動する。第１低圧タービン１５ｃが回転駆動することによってセカンダリー軸１５ｆが回転する。セカンダリー軸１５ｆが回転することによって、セカンダリー軸１５ｆに設けられている第２低圧タービン１５ｄおよび低圧タービン側減速機２３が駆動されることとなる。 The steam guided to the first low-pressure turbine 15c converts the thermal energy into rotational energy of the first low-pressure turbine 15c, and rotationally drives the first low-pressure turbine 15c. When the first low-pressure turbine 15c is driven to rotate, the secondary shaft 15f rotates. By rotating the secondary shaft 15f, the second low-pressure turbine 15d and the low-pressure turbine-side speed reducer 23 provided on the secondary shaft 15f are driven.

　第１低圧タービン１５ｃは、その途中段から蒸気の一部が抽気される。抽気された例えば０．１ＭＰａの蒸気は、浮体式液化天然ガス製造設備１（図１参照）内で用いる低圧雑用蒸気等に用いられる。
　第１低圧タービン１５ｃの全段を通過した蒸気は、セカンダリー軸１５ｆに設けられている第２低圧タービン１５ｄへと導かれる。 A part of the steam is extracted from the middle stage of the first low-pressure turbine 15c. The extracted steam of, for example, 0.1 MPa is used for low-pressure miscellaneous steam used in the floating liquefied natural gas production facility 1 (see FIG. 1).
The steam that has passed through all the stages of the first low-pressure turbine 15c is guided to the second low-pressure turbine 15d provided on the secondary shaft 15f.

　また、第２低圧タービン１５ｄには、別途、図示しないアシスト蒸気供給系統より例えば０．６ＭＰａのアシスト蒸気が供給される。供給されたアシスト蒸気により第２低圧タービン１５ｄは、回転駆動される。第２低圧タービン１５ｄが回転駆動ことによって、セカンダリー軸１５ｆに接続されている低圧タービン側減速機２３を駆動することが可能となっている。 Further, for example, 0.6 MPa of assist steam is separately supplied to the second low-pressure turbine 15 d from an assist steam supply system (not shown). The second low-pressure turbine 15d is rotationally driven by the supplied assist steam. When the second low-pressure turbine 15d is driven to rotate, it is possible to drive the low-pressure turbine-side speed reducer 23 connected to the secondary shaft 15f.

　第１低圧タービン１５ｃの全段を通過した蒸気および第２低圧タービン１５ｄを駆動したアシスト蒸気は、図示しない主復水器へと導かれて海水と熱交換して復水とされる。 The steam that has passed through all stages of the first low-pressure turbine 15c and the assist steam that has driven the second low-pressure turbine 15d are led to a main condenser (not shown) to exchange heat with seawater to be condensed.

　このように、圧縮機駆動用蒸気タービン１５は、プライマリー軸１５ｅとセカンダリー軸１５ｆとによって各々独立に高圧タービン側減速機２０と低圧タービン側減速機２３とを制御することができ、さらに、アシスト蒸気によって第２低圧タービン１５ｄを駆動することによっても低圧タービン側減速機２３を独立に制御することができるようになっている。 Thus, the compressor driving steam turbine 15 can independently control the high-pressure turbine-side speed reducer 20 and the low-pressure turbine-side speed reducer 23 with the primary shaft 15e and the secondary shaft 15f, and further assist steam. Thus, the low-pressure turbine-side speed reducer 23 can be independently controlled by driving the second low-pressure turbine 15d.

　ここで、本実施形態の天然ガスおよび窒素冷媒のＴ－Ｈ線図について図４および前述した図５を用いて説明する。
　図４には、本実施形態の天然ガスおよび窒素冷媒のＴ－Ｈ線図が示されている。
　図４では、縦軸に熱負荷（ｋＷ）を示し、横軸に温度（℃）を示す。図４の実線は、１５ＭＰａまたは４ＭＰａに昇圧した天然ガスを示し、一点鎖線は、４ＭＰａに昇圧した場合の天然ガスと熱交換する窒素を示す。 Here, the TH diagram of the natural gas and nitrogen refrigerant of the present embodiment will be described with reference to FIG. 4 and FIG. 5 described above.
FIG. 4 shows a TH diagram of the natural gas and nitrogen refrigerant of the present embodiment.
In FIG. 4, the vertical axis indicates the heat load (kW), and the horizontal axis indicates the temperature (° C.). The solid line in FIG. 4 indicates natural gas whose pressure is increased to 15 MPa or 4 MPa, and the alternate long and short dash line indicates nitrogen that exchanges heat with natural gas when the pressure is increased to 4 MPa.

　また、図５には、複数の圧力における天然ガスおよび窒素の関係を示したＴ－Ｈ線図が示されている。
　図５では、縦軸に熱負荷（ｋＷ）を示し、横軸に温度（℃）を示す。図５の実線は、１５ＭＰａに昇圧した天然ガスを示し、点線は、４ＭＰａに昇圧した天然ガスを示し、一点鎖線は、４ＭＰａの比較的低圧の天然ガスに対して温度差が小さな窒素を示し、二点鎖線は、１５ＭＰａの高圧の天然ガスに対して温度差が小さな窒素を示す。 FIG. 5 is a TH diagram showing the relationship between natural gas and nitrogen at a plurality of pressures.
In FIG. 5, the vertical axis indicates the heat load (kW), and the horizontal axis indicates the temperature (° C.). The solid line in FIG. 5 indicates natural gas whose pressure has been increased to 15 MPa, the dotted line indicates natural gas whose pressure has been increased to 4 MPa, the alternate long and short dash line indicates nitrogen having a small temperature difference with respect to the natural gas having a relatively low pressure of 4 MPa, A two-dot chain line indicates nitrogen having a small temperature difference with respect to a high-pressure natural gas of 15 MPa.

　図５に示すように、４ＭＰａの天然ガス（実線）は、窒素と熱交換して温度が低下する過程において温度変化がほとんど生じないステップ状が発生する。天然ガスの液化は、窒素との温度差が小さい方が液化効率がよいため、窒素（点線）と天然ガスとの温度差が最も小さくなるピンチポイントがステップ状になってしまう。そのため、ステップ状以外の熱交換過程では、天然ガスと窒素との温度差が大きくなり全体として液化効率が低下しまう。 As shown in FIG. 5, the 4 MPa natural gas (solid line) has a step shape in which the temperature hardly changes in the process of lowering the temperature by exchanging heat with nitrogen. Since the liquefaction efficiency of natural gas liquefaction is better when the temperature difference from nitrogen is smaller, the pinch point at which the temperature difference between nitrogen (dotted line) and natural gas becomes the smallest is stepped. Therefore, in the heat exchange process other than the step shape, the temperature difference between the natural gas and nitrogen is increased, and the liquefaction efficiency is lowered as a whole.

　天然ガスを例えば１５ＭＰａの高圧に昇圧した場合（点線）には、４ＭＰａの天然ガスにおいて生じていたステップ状がなくなり、天然ガスの温度変化が略直線状になる。そのため、１５ＭＰａの天然ガスと窒素（二点鎖線）との温度差が小さくなり全体に渡って効率的に液化することができる。 For example, when the natural gas is boosted to a high pressure of 15 MPa (dotted line), the step shape generated in the natural gas of 4 MPa disappears, and the temperature change of the natural gas becomes substantially linear. Therefore, the temperature difference between the natural gas of 15 MPa and nitrogen (two-dot chain line) becomes small and can be liquefied efficiently throughout.

　なお、図５に示すように、天然ガスの低温部においては、天然ガスの圧力が１５ＭＰａの場合であっても４ＭＰａの場合であっても、窒素との温度差は小さくなっている。 In addition, as shown in FIG. 5, in the low temperature part of natural gas, even if the pressure of natural gas is 15 MPa or 4 MPa, the temperature difference from nitrogen is small.

　本実施形態では、図４に示すように、天然ガスの高温部では、天然ガスを高圧（例えば１５ＭＰａ）に昇圧して、天然ガスの低温部では、天然ガスを比較的低圧（例えば４ＭＰａ）に昇圧して窒素と熱交換させることによって熱交換過程の全域に渡って略均一の温度差にすることとした。 In the present embodiment, as shown in FIG. 4, the natural gas is pressurized to a high pressure (for example, 15 MPa) in the high temperature portion of the natural gas, and the natural gas is set to a relatively low pressure (for example, 4 MPa) in the low temperature portion of the natural gas. By increasing the pressure and exchanging heat with nitrogen, the temperature difference was made substantially uniform throughout the entire heat exchanging process.

　すなわち、天然ガスの高温部では、高圧の天然ガスを高圧窒素ループ１７の高圧窒素と熱交換させ、天然ガスの低温部では、低圧の天然ガスを低圧窒素ループ１８の低圧窒素と熱交換させる。
　また、高圧窒素ループ１７と低圧窒素ループ１８との間には、ジュールトムソン膨張弁１６を設けて１５ＭＰａの高圧の天然ガスを４ＭＰａの低圧の天然ガスに膨張させることにした。これにより、図４に示すように、天然ガスの高圧部における温度と、４ＭＰａの低圧の天然ガスの温度との差を小さくして、天然ガスの全領域にわたる温度変化を略直線状になるようにすることができる。 That is, in the high temperature portion of the natural gas, the high pressure natural gas is heat exchanged with the high pressure nitrogen of the high pressure nitrogen loop 17, and in the low temperature portion of the natural gas, the low pressure natural gas is heat exchanged with the low pressure nitrogen of the low pressure nitrogen loop 18.
Further, a Joule Thompson expansion valve 16 is provided between the high-pressure nitrogen loop 17 and the low-pressure nitrogen loop 18 to expand the 15 MPa high-pressure natural gas to a 4 MPa low-pressure natural gas. As a result, as shown in FIG. 4, the difference between the temperature of the natural gas at the high pressure portion and the temperature of the low pressure natural gas of 4 MPa is reduced so that the temperature change over the entire region of the natural gas becomes substantially linear. Can be.

　以上の通り、本実施形態に係る液化装置１０およびこれを備えている浮体式液化天然ガス製造設備１によれば、以下の作用効果を奏する。
　単一成分の高圧窒素（高温側熱媒体）を高圧窒素熱交換器（高温側熱媒体用熱交換器）１１へ、高圧窒素と同種類の低圧窒素（低温側熱媒体）を低圧窒素熱交換器（低温側熱媒体用熱交換器）１２へと導き、高圧窒素熱交換器１１と低圧窒素熱交換器１２との間には、天然ガス（被液化ガス）を所定圧に減圧するジュールトムソン膨張弁（減圧弁）１６を設けることとした。これにより、高圧窒素熱交換器１１を通過した天然ガスをジュールトムソン膨張弁１６により低圧窒素の温度変化に近似させて低圧窒素熱交換器１２へと導くことができる。そのため、天然ガスと高圧窒素との熱交換による温度差と、天然ガスと低圧窒素との熱交換による温度差とをそれぞれ熱交換過程において略一定に保つことができる。したがって、単一成分の窒素（熱媒体）を用いて、天然ガスを効率的に液化することができる。 As described above, according to the liquefying apparatus 10 according to the present embodiment and the floating liquefied natural gas production facility 1 including the liquefying apparatus 10, the following operational effects are obtained.
Single component high pressure nitrogen (high temperature side heat medium) to high pressure nitrogen heat exchanger (high temperature side heat medium heat exchanger) 11 and low pressure nitrogen (low temperature side heat medium) of the same type as high pressure nitrogen to low pressure nitrogen heat exchange Joule Thompson that leads to a low pressure side heat exchanger (heat exchanger for low temperature side heat medium) 12 and reduces natural gas (liquefied gas) to a predetermined pressure between the high pressure nitrogen heat exchanger 11 and the low pressure nitrogen heat exchanger 12 An expansion valve (pressure reducing valve) 16 was provided. As a result, the natural gas that has passed through the high-pressure nitrogen heat exchanger 11 can be approximated to the temperature change of the low-pressure nitrogen by the Joule-Thomson expansion valve 16 and led to the low-pressure nitrogen heat exchanger 12. Therefore, the temperature difference due to heat exchange between natural gas and high-pressure nitrogen and the temperature difference due to heat exchange between natural gas and low-pressure nitrogen can be kept substantially constant in the heat exchange process. Therefore, natural gas can be liquefied efficiently using single component nitrogen (heat medium).

　プライマリー軸（高圧タービン側軸）１５ｅに高圧タービン側減速機２０を介して高圧窒素圧縮機（高温側熱媒体用圧縮機）１３を接続し、セカンダリー軸（低圧タービン側軸）１５ｆに低圧タービン側減速機２３を介して低圧窒素圧縮機（低温側熱媒体用圧縮機）１４を接続することとした。圧縮機駆動用蒸気タービン（クロスコンパウンドタービン）１５を構成しているプライマリー軸１５ｅとセカンダリー軸１５ｆとは、互いに分離しているため、プライマリー軸１５ｅに接続されている高圧タービン１５ａおよび中圧タービン（高圧タービン）１５ｂ、セカンダリー軸１５ｆに接続されている第１低圧タービン（低圧タービン）１５ｃおよび第２低圧タービン（低圧タービン）１５ｄとを各々制御することによって高圧窒素圧縮機１３と低圧窒素圧縮機１４とをそれぞれ独立に制御することができる。したがって、高圧窒素と低圧窒素とを互いに独立に圧縮することができ、高圧窒素ループ１７を循環する高圧窒素と低圧窒素ループ１８を循環する低圧窒素との冷凍負荷を独立に制御することができる。 A high pressure nitrogen compressor (high temperature side heat medium compressor) 13 is connected to a primary shaft (high pressure turbine side shaft) 15e via a high pressure turbine side speed reducer 20, and a low pressure turbine side is connected to a secondary shaft (low pressure turbine side shaft) 15f. The low-pressure nitrogen compressor (low temperature side heat medium compressor) 14 is connected via the speed reducer 23. Since the primary shaft 15e and the secondary shaft 15f constituting the compressor driving steam turbine (cross compound turbine) 15 are separated from each other, the high-pressure turbine 15a and the intermediate-pressure turbine (which are connected to the primary shaft 15e) The high-pressure nitrogen compressor 13 and the low-pressure nitrogen compressor 14 are respectively controlled by controlling a first low-pressure turbine (low-pressure turbine) 15c and a second low-pressure turbine (low-pressure turbine) 15d connected to the secondary shaft 15f. And can be controlled independently. Therefore, the high-pressure nitrogen and the low-pressure nitrogen can be compressed independently of each other, and the refrigeration load of the high-pressure nitrogen circulating through the high-pressure nitrogen loop 17 and the low-pressure nitrogen circulating through the low-pressure nitrogen loop 18 can be controlled independently.

　天然ガスと高圧窒素とが熱交換する高圧窒素熱交換器１１には、ステンレスプレートディフュージョンタイプ（プレート式）を用いることとした。そのため、高圧窒素熱交換器１１を小型化することができる。したがって、液化装置１０を構成している高圧窒素熱交換器１１が格納されているコールドボックス５のコンパクト化を図ることができる。 As the high-pressure nitrogen heat exchanger 11 for exchanging heat between natural gas and high-pressure nitrogen, a stainless plate diffusion type (plate type) was used. Therefore, the high-pressure nitrogen heat exchanger 11 can be reduced in size. Therefore, the cold box 5 in which the high-pressure nitrogen heat exchanger 11 constituting the liquefying apparatus 10 is stored can be made compact.

　また、ジュールトムソン膨張弁１６を通過することによって天然ガスの圧力を低下させて低圧窒素熱交換器１２にアルミロウ付プレートフィンタイプ（プレート式）を用いることとした。そのため、低圧窒素熱交換器１２も小型化することができる。したがって、液化装置１０を構成しているコールドボックス５を更にコンパクトにすることができる。 Further, the pressure of the natural gas is lowered by passing through the Joule-Thompson expansion valve 16, and a plate fin type with aluminum brazing (plate type) is used for the low-pressure nitrogen heat exchanger 12. Therefore, the low-pressure nitrogen heat exchanger 12 can also be reduced in size. Therefore, the cold box 5 constituting the liquefying apparatus 10 can be made more compact.

　液化天然ガス中のオフガスおよびボイルオフガスを燃料として燃焼して蒸気を発生するボイラ（蒸気発生手段）を用いることとした。そのため、圧縮機駆動用蒸気タービン１５を駆動する蒸気を液化ガス装置１０において生じたオフガスやボイルオフガスを用いて駆動することができる。したがって、液化装置１０から生じるオフガスやボイルオフガスを有効に利用することができる。 It was decided to use a boiler (steam generating means) that generates steam by burning off gas and boil off gas in liquefied natural gas as fuel. Therefore, the steam for driving the compressor driving steam turbine 15 can be driven by using the off-gas and boil-off gas generated in the liquefied gas device 10. Therefore, the off gas and boil off gas generated from the liquefying apparatus 10 can be used effectively.

　蒸気によって駆動する圧縮機駆動用蒸気タービン１５によって構成されている液化装置１０を浮体式液化天然ガス製造設備（浮体式液化ガス製造設備）１に用いることとした。そのため、圧縮機駆動用蒸気タービン１５には、既存の舶用主機に用いられているクロスパウンド式の蒸気タービンを適用することができる。したがって、高圧窒素圧縮機１３および低圧窒素圧縮機１４を駆動するために圧縮機駆動用蒸気タービン１５の新たな開発が不要となり、既存の機器を有効利用することができる。 The liquefying apparatus 10 constituted by the steam turbine 15 for driving the compressor driven by steam is used for the floating liquefied natural gas manufacturing facility (floating liquefied gas manufacturing facility) 1. Therefore, the cross-pound steam turbine used for the existing marine main engine can be applied to the compressor driving steam turbine 15. Therefore, it is not necessary to newly develop the compressor driving steam turbine 15 for driving the high-pressure nitrogen compressor 13 and the low-pressure nitrogen compressor 14, and the existing equipment can be used effectively.

　熱媒体に不燃性の窒素を用いる高圧窒素圧縮機１３および低圧窒素圧縮機１４と、高圧窒素熱交換器１１および低圧窒素熱交換器１２とによって構成されている液化装置１０を浮体式液化天然ガス製造設備１に用いることとした。また、高圧窒素圧縮機１３および低圧窒素圧縮機１４の駆動には、圧縮機駆動用蒸気タービン１５を用いることとした。これらにより、熱媒体等の可燃性ガスが漏洩することによる爆発の危険性を防止することができる。そのため、浮体式液化天然ガス製造設備１の甲板下の液化装置用動力装置区画６に、高圧窒素圧縮機１３、低圧窒素圧縮機１４や圧縮機駆動用蒸気タービン１５などの機器を配置することができる。したがって、甲板上の液化装置１０の配置スペースを削減することができる。 A liquefier 10 comprising a high-pressure nitrogen compressor 13 and a low-pressure nitrogen compressor 14 using non-combustible nitrogen as a heat medium, a high-pressure nitrogen heat exchanger 11 and a low-pressure nitrogen heat exchanger 12 is used as a floating liquefied natural gas. It was decided to use it for manufacturing equipment 1. Further, the compressor driving steam turbine 15 is used to drive the high-pressure nitrogen compressor 13 and the low-pressure nitrogen compressor 14. Accordingly, it is possible to prevent the risk of explosion due to leakage of combustible gas such as a heat medium. Therefore, equipment such as the high pressure nitrogen compressor 13, the low pressure nitrogen compressor 14, and the compressor driving steam turbine 15 may be arranged in the liquefier power unit section 6 below the deck of the floating liquefied natural gas production facility 1. it can. Therefore, the arrangement space of the liquefying device 10 on the deck can be reduced.

　また、本実施形態では、液化装置１０に用いられる熱媒体として、窒素を用いて説明したが不燃性の熱媒体であればよい。
　また、本実施形態では、被液化ガスとして液化天然ガス（ＬＮＧ）を用いて説明したが、液化石油ガス（Ｌｉｑｕｅｆｉｅｄ　ｐｅｔｒｏｌｅｕｍ　ｇａｓ：ＬＰＧ）等であっても良い。 Moreover, in this embodiment, although demonstrated using nitrogen as a heat medium used for the liquefying apparatus 10, what is necessary is just a nonflammable heat medium.
In the present embodiment, liquefied natural gas (LNG) is used as the liquefied gas. However, liquefied petroleum gas (LPG) or the like may be used.

　また、本実施形態では、昇圧コンプレッサ３１から高圧窒素熱交換器１１へと導かれる天然ガスを第１熱交換器３２および第２熱交換器３３によって予冷するとして説明したが、本発明はこれに限定されるものではなく、チラー水によって予冷しない、すなわち第２熱交換器３３を設けないものとしても良い。チラー水を用いて－１０℃から－３０℃程度まで予冷することによって、高圧窒素ループ１７および低圧窒素ループ１８に導かれる高圧窒素および低圧窒素を圧縮する動力の削減効果を高めることができるが、予冷を行わなくても良い。 In the present embodiment, the natural gas introduced from the booster compressor 31 to the high-pressure nitrogen heat exchanger 11 has been described as being precooled by the first heat exchanger 32 and the second heat exchanger 33, but the present invention is not limited thereto. It is not limited, It is good also as what does not pre-cool with chiller water, ie, does not provide the 2nd heat exchanger 33. By precooling from −10 ° C. to about −30 ° C. using chiller water, it is possible to increase the power reduction effect of compressing high-pressure nitrogen and low-pressure nitrogen led to the high-pressure nitrogen loop 17 and the low-pressure nitrogen loop 18. Precooling is not necessary.

　また、船内動力設置区画４に設けられているガス焚きディーゼル機関から排出される高温の排気ガスを排熱回収ボイラ等の排熱回収装置（図示せず）へと導いて蒸気を発生させ、排熱回収ボイラによって発生した蒸気を圧縮機駆動用蒸気タービン１５へと導いて圧縮機駆動用蒸気タービン１５の起動等に利用しても良い。これにより、ガス焚きディーゼル機関からの排熱を有効に利用することができる。 In addition, high-temperature exhaust gas discharged from the gas-fired diesel engine provided in the inboard power installation section 4 is led to an exhaust heat recovery device (not shown) such as an exhaust heat recovery boiler to generate steam, and exhaust The steam generated by the heat recovery boiler may be guided to the compressor driving steam turbine 15 and used for starting the compressor driving steam turbine 15 or the like. Thereby, the exhaust heat from a gas-fired diesel engine can be used effectively.

１　浮体式液化天然ガス製造設備（浮体式液化ガス製造設備）
１０　液化設備
１１　高圧窒素熱交換器（高温側熱媒体用熱交換器）
１２　低圧窒素熱交換器（低温側熱媒体用熱交換器）
１６　ジュールトムソン膨張弁（減圧弁） 1 Floating liquefied natural gas production facility (floating liquefied gas production facility)
10 Liquefaction equipment 11 High-pressure nitrogen heat exchanger (heat exchanger for high-temperature side heat medium)
12 Low pressure nitrogen heat exchanger (heat exchanger for low temperature side heat medium)
16 Joule Thomson expansion valve (pressure reducing valve)

Claims (7)

　単一成分の高圧熱媒体と熱交換させた被液化ガスを減圧した後に、減圧した前記被液化ガスを前記高圧熱媒体よりも低温かつ同種類の低温側熱媒体と熱交換させて液化する液化方法。 The liquefied gas is liquefied by depressurizing the liquefied gas heat-exchanged with a single-component high-pressure heat medium and then exchanging heat with the low-temperature side heat medium of the same type and at a lower temperature than the high-pressure heat medium. Method. 　被液化ガスと高温側熱媒体とが熱交換する高温側熱媒体用熱交換器と、
　該高温側熱媒体用熱交換器から導出された被液化ガスを減圧する減圧弁と、
　該減圧弁を通過した被液化ガスと、低温側熱媒体とが熱交換する低圧熱媒用熱交換器と、を備え、
　前記高温側熱媒体および前記低温側熱媒体は、単一成分かつ同種類であって、
　前記減圧弁は、前記低温側熱媒体用熱交換器に導かれる被液化ガスを所定圧に減圧する液化装置。 A heat exchanger for the high temperature side heat medium in which the liquefied gas and the high temperature side heat medium exchange heat;
A pressure reducing valve for depressurizing the liquefied gas derived from the heat exchanger for the high temperature side heat medium;
A liquefied gas that has passed through the pressure reducing valve, and a heat exchanger for a low-pressure heat medium that exchanges heat between the low-temperature side heat medium,
The high temperature side heat medium and the low temperature side heat medium are a single component and the same kind,
The pressure reducing valve is a liquefying device that reduces the liquefied gas led to the low temperature side heat medium heat exchanger to a predetermined pressure. 　蒸気が導かれて駆動される高圧タービンと、
　該高圧タービンに接続される高圧タービン側軸と、
　前記高圧タービンから導出された蒸気が導かれて駆動される低圧タービンと、
　該低圧タービンに接続される低圧タービン側軸と、を有するクロスコンパウンドタービンと、
　前記高温側熱媒体用熱交換器に導かれる高温側熱媒体を圧縮する高温側熱媒体用圧縮機と、
　前記低温側熱媒体用熱交換器に導かれる低温側熱媒体を圧縮する低温側熱媒体用圧縮機と、
　前記高圧タービンに導かれる蒸気を発生する蒸気発生手段と、を備え、
　前記高温側熱媒体用圧縮機を前記高圧タービン側軸に接続し、前記低温側熱媒体用圧縮機を前記低圧タービン側軸に接続する請求項２に記載の液化装置。 A high-pressure turbine in which steam is guided and driven;
A high pressure turbine side shaft connected to the high pressure turbine;
A low-pressure turbine driven by the steam derived from the high-pressure turbine;
A cross-compound turbine having a low-pressure turbine side shaft connected to the low-pressure turbine;
A high temperature side heat medium compressor that compresses the high temperature side heat medium guided to the high temperature side heat medium heat exchanger;
A low-temperature side heat medium compressor that compresses the low-temperature side heat medium guided to the low-temperature side heat medium heat exchanger;
Steam generating means for generating steam guided to the high-pressure turbine,
The liquefaction apparatus according to claim 2, wherein the high temperature side heat medium compressor is connected to the high pressure turbine side shaft, and the low temperature side heat medium compressor is connected to the low pressure turbine side shaft. 　前記高温側熱媒体用熱交換器は、プレート式である請求項２または請求項３に記載の液化装置。 The liquefying apparatus according to claim 2 or 3, wherein the heat exchanger for the high temperature side heat medium is a plate type. 　前記蒸気発生手段は、液化ガス中のオフガスを燃料として蒸気を発生する請求項２から請求項４のいずれかに記載の液化装置。 The liquefying apparatus according to any one of claims 2 to 4, wherein the steam generating means generates steam using off-gas in the liquefied gas as fuel. 　請求項２から請求項５のいずれかに記載の液化装置を備える浮体式液化ガス製造設備。 A floating liquefied gas production facility comprising the liquefying device according to any one of claims 2 to 5. 　前記高温側熱媒体及び前記低温側熱媒体には、窒素を用いる請求項６に記載の浮体式液化ガス製造設備。 The floating liquefied gas production facility according to claim 6, wherein nitrogen is used for the high temperature side heat medium and the low temperature side heat medium.
PCT/JP2011/073255 2010-10-13 2011-10-07 Liquefaction method, liquefaction device, and floating liquefied gas production equipment comprising same Ceased WO2012050068A1 (en)

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