AU715939B2 - Method and device for storage and transport of liquefied natural gas - Google Patents

Method and device for storage and transport of liquefied natural gas Download PDF

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Publication number
AU715939B2
AU715939B2 AU67522/98A AU6752298A AU715939B2 AU 715939 B2 AU715939 B2 AU 715939B2 AU 67522/98 A AU67522/98 A AU 67522/98A AU 6752298 A AU6752298 A AU 6752298A AU 715939 B2 AU715939 B2 AU 715939B2
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Prior art keywords
decoction
methane
tank
condensed
lng
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AU67522/98A
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AU6752298A (en
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Carl Jorgen Rummelhoff
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Moss Maritime AS
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Kvaerner Maritime AS
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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—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
    • 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63J—AUXILIARIES ON VESSELS
    • B63J2/00—Arrangements of ventilation, heating, cooling, or air-conditioning
    • B63J2/12—Heating; Cooling
    • B63J2/14—Heating; Cooling of liquid-freight-carrying tanks
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C13/00—Details of vessels or of the filling or discharging of vessels
    • F17C13/02—Special adaptations of indicating, measuring, or monitoring equipment
    • 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
    • F25J1/0025—Boil-off gases "BOG" from storages
    • 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"
    • F25J1/0045—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration" by vaporising a liquid return stream
    • 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
    • F25J1/02—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
    • F25J1/0204—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 single flow SCR cycle
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
    • F25J1/0257—Construction and layout of liquefaction equipments, e.g. valves, machines
    • F25J1/0262—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
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2265/00—Effects achieved by gas storage or gas handling
    • F17C2265/03—Treating the boil-off
    • 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
    • F25J2210/00—Processes characterised by the type or other details of the feed stream
    • F25J2210/04—Mixing or blending of fluids with the feed stream
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2220/00—Processes or apparatus involving steps for the removal of impurities
    • F25J2220/60—Separating impurities from natural gas, e.g. mercury, cyclic hydrocarbons
    • F25J2220/62—Separating low boiling components, e.g. He, H2, N2, Air
    • 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
    • F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
    • F25J2230/08—Cold compressor, i.e. suction of the gas at cryogenic temperature and generally without afterstage-cooler
    • 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
    • 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
    • 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
    • F25J2235/00—Processes or apparatus involving steps for increasing the pressure or for conveying of liquid process streams
    • F25J2235/60—Processes or apparatus involving steps for increasing the pressure or for conveying of liquid process streams the fluid being (a mixture of) hydrocarbons
    • 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
    • F25J2280/00—Control of the process or apparatus
    • F25J2280/02—Control in general, load changes, different modes ("runs"), measurements
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2290/00—Other details not covered by groups F25J2200/00 - F25J2280/00
    • F25J2290/62—Details of storing a fluid in a tank
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T70/00—Maritime or waterways transport

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Combustion & Propulsion (AREA)
  • Ocean & Marine Engineering (AREA)
  • Filling Or Discharging Of Gas Storage Vessels (AREA)

Description

P:\WPDOCS\DYS\SPECIE\722220.SPE 7/12/99 -1- Method and device for storage and transport of liquefied natural gas The invention relates to a method for storage and transport of liquefied natural gas, hereinafter called LNG, containing nitrogen and other gases, principally methane and hereinafter called methane, in a tank wherein the LNG boils and LNG in a gaseous state is obtained, hereinafter called decoction, the decoction is taken from the tank, the pressure of the decoction is increased, and decoction with the increased pressure is cooled in a cooler, condensed and returned to the tank.
The invention further relates to a device for implementation of this method.
During storage and transport of LNG (Liquefied Natural Gas) at a pressure approximately corresponding to the pressure of the ambient atmosphere, a portion of this LNG will boil off and be converted to gas.
In ships which transport LNG, the decoction is used as fuel for propulsion of the ship, since a more economical alternative has not yet been found for this kind of transport. This, however, results in relatively expensive running of the ship, since the gas is used for production of steam and operation of steam turbines, whose efficiency is lower than, diesel motors for running ships.
From US-A-4 675 037 it is known a method which includes the steps indicated in the introduction, and wherein all decoction from the tank is condensed and returned to the tank.
This method, however, is very energy-demanding.
The object of the invention is to provide a method and a device of the abovementioned type for reduction of the costs of storage and transport of liquefied natural gas.
According to one aspect of the present invention there is provided a method for storage and S• transport of liquefied natural gas, hereinafter called LNG, containing nitrogen and other gases, 25 principally methane and hereinafter called methane, in a tank wherein the LNG boils and LNG in a gaseous state is obtained, hereinafter called decoction, the decoction is taken from the tank, the pressure of the decoction is increased, and decoction with the increased pressure is cooled in a cooler, condensed and returned to the tank, characterized in cooling the decoction to a temperature between the condensation temperature for the P:\WPDOCS\DYS\SPECIE\722220.SPE 7/12/99 -lacompressed methane and nitrogen, separating condensed methane from non condensed gaseous nitrogen, returning condensed methane to the tank, and releasing nitrogen which has not been condensed into the atmosphere.
According to another aspect of the present invention there is provided a device for implementation of the method as described above, for storage and transport of liquefied natural gas, hereinafter called LNG, containing nitrogen and other gases, hereinafter called methane, in a tank, wherein the LNG boils and LNG in a gaseous state is obtained, hereinafter called decoction, comprising a first compressor device for compression of decoction from the tank, and a condensation device with a cooler, whose inlet is connected to an outlet of the first compressor device, and which is arranged for cooling of the compressed decoction, characterised in that the cooler is arranged for cooling of the compressed decoction to a temperature between the condensation temperature for the compressed methane and nitrogen, and that the device has 15 a separator, which is arranged for separation of gaseous nitrogen from condensed methane, meh a first piping arrangement for returning condensed methane to the tank, and V- a second piping arrangement for venting of non condensed nitrogen to the atmosphere.
The invention will now be described in more detail with reference to the drawing whose single figure is a pipe diagram which schematically illustrates an embodiment of a system or plant for "storage or transport of LNG with a device according to the invention.
As illustrated in the figure, the system comprises a tank 2 containing LNG 4 whose surface is indicated by the reference numeral 6. The tank space over this surface 6 communicates via a pipeline 8 with the inlet of a first compressor device 10 comprising a first compressor 12 which is driven by a motor 14.
WO 98/43029 PCT/N098/00088 2 The outlet of the compressor device 10 communicates via a pipeline 16 with the inlet of a first passage 18 of a first cooler or heat exchanger 20, the outlet of this passage 18 communicating with an inlet of a liquid/gas separator 22.
In the cooler 20 there is provided a second passage 24, whose inlet is supplied with a cooled coolant from a standard per se cooling plant 26 via a pipeline 30, and whose outlet returns heated coolant to the cooling plant 26 via a pipe 28.
The outlet of the liquid/gas separator 22 from which separated liquid can flow, is connected via a pipeline 32 to an inlet of a pump 34. Separated gas can flow from the separator 22 to the ambient atmosphere via a pipeline 36.
An outlet of the pump 34 communicates via a pipeline 37 with the pipeline 16 at a lead-in point 38 thereof, a pipeline 40 with the tank space under the LNG surface in the tank 2, and a pipeline 42 with the space over the LNG surface in the tank 2.
The pipeline 42 may be terminated by a nozzle device 44 in the tank 2.
In the pipelines 40, 42 there may be provided respective shut-off valves 46 and 48.
Between the lead-in point 38 and the inlet of the first passage 18 of the cooler 20, there may be connected to the pipeline 16 a temperature sensor which may be connected via an electric cable 52 to an electrically operated shut-off valve 54.
The cooling plant 26 is of a known per se type and includes a second compressor device 56 comprising a second compressor 58 which is driven by a motor 60. On the downstream side of the second compressor 56 there is provided an intermediate cooler 62 on whose downstream side there is provided a third compressor 64.
The inlet of the second compressor 58 communicates with the outlet of a third passage 66 of a second cooler or heat exchanger 68 via a pipeline The outlet of the second compressor device 58 communicates with the inlet of a fourth passage 72 of the second heat exchanger 68 via a pipeline 73, and the outlet of the fourth passage 72 communicates with the inlet of an expansion turbine 74, whose outlet is connected to the inlet of the second WO 98/43029 PCT/N098/00088 3 passage 24 of the first heat exchanger 20 via the pipeline 30. The third compressor 64 is driven by the expansion turbine 74.
The device works as follows.
Decoction in the tank 2 flows via the pipeline 8 to the first compressor device 10, where it is compressed and thereby greatly overheated. From this compressor device 10 the decoction flows through the first passage 18 of the first heat exchanger 20 and is cooled to a temperature of between the condensation temperature for methane and the condensation temperature for nitrogen. A mixture of liquid and gas thereby flows to the separator 22 where the liquid methane is separated from the nitrogen gas which flows out into the atmosphere via the pipeline 36.
If the shut-off valve 46 is open, a first portion of the liquid methane is returned via the pipeline 40 to the tank 2 under the LNG surface level. If the shut-off valve 48 is open a second portion of the liquid methane is returned via the pipeline 42 to the tank 2 and sprayed into the decoction, i.e. over the LNG surface 6, via the nozzle device 44, thus cooling the decoction, with the result that a portion thereof may be condensed in the tank or the decoction is at least reduced.
When transporting LNG in full tanks in ships, the shut-off valve 48 will normally be closed and the shut-off valve 46 will be open. However, any combination of positions of the shut-off valves 46, 48 and 54 is possible.
If the temperature of the decoction in the pipe 16 between the first compressor device 10 and the first heat exchanger 20 exceeds a certain threshold value, a signal is transmitted from the temperature sensor 50 to the shut-off valve 54 for opening thereof. This may occur especially if there is not much LNG in the tank and thus very little decoction. In this case the operating condition of the first compressor device is not optimal, with the result that its efficiency is reduced and the temperature of the compressed decoction is relatively high. In this case a third portion of the liquid methane is supplied to the pipeline 16 via the lead-in point 38, thus enabling the temperature of the decoction flowing into the first heat exchanger 20 to be reduced to such an extent that this heat exchanger can thereby be capable of providing the remaining cooling of the decoction to the temperature required therefor.
P:\WPDOCS\DYS\SPECIE\722220.SPE 7/12/99 -4- When returning the third portion of the methane, the result may also be achieved of reducing the temperature of the decoction which is supplied to the first heat exchanger 20 to such an extent that the heat exchanger's components may be cheaply manufactured from aluminium in the normal manner.
With a complete condensation of all the decoction, an energy-recovery efficiency of approximately 20% can be achieved. With only partial condensation of the decoction, i.e. only condensation of the methane and release of nitrogen in a gaseous state to the atmosphere or air according to the invention, an efficiency of this kind of approximately 38% can be achieved.
A person skilled in the art will understand that if the first heat exchanger and the separator are arranged at a higher level than the tank, liquefied methane will be able to flow back to the tank due to gravity. On the other hand there is a need for a pump to return liquefied methane to the return point in front of the inlet of the first cooler S Furthermore, a person skilled in the art will understand that the compressor devices in the device according to the invention may include more compressors which are interconnected in series and between which intermediate coolers may be provided. It will also be understood that the device according to the invention may comprise further, known per se components of standard pipe arrangements, such as shut-offvalves, check valves etc. which can be connected between the above-mentioned components of the device to enable it to work in the abovementioned manner.
I S Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" or "comprising" will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

Claims (9)

1. A method for storage and transport of liquefied natural gas, hereinafter called LNG, containing nitrogen and other gases, principally methane and hereinafter called methane, in a tank wherein the LNG boils and LNG in a gaseous state is obtained, hereinafter called decoction, the decoction is taken from the tank, the pressure of the decoction is increased, and decoction with the increased pressure is cooled in a cooler, condensed and returned to the tank, characterized in cooling the decoction to a temperature between the condensation temperature for the compressed methane and nitrogen, separating condensed methane from non condensed gaseous nitrogen, returning condensed methane to the tank, and releasing nitrogen which has not been condensed into the atmosphere. 15
2. A method according to claim 1, "characterized in conveying a portion of the condensed methane into the decoction whose :pressure has been increased, but not yet cooled in the cooler.
A device for implementation of the method as defined in claim 1, for storage and transport of liquefied natural gas, hereinafter called LNG, containing nitrogen and other gases, hereinafter called methane, in a tank, wherein the LNG boils and LNG in a gaseous state is 0*t. obtained, hereinafter called decoction, comprising a first compressor device for compression of decoction from the tank, and a condensation device with a cooler, whose inlet is connected to an outlet of the first compressor device, and which is arranged for cooling of the compressed decoction, characterised in that the cooler is arranged for cooling of the compressed decoction to a temperature between the condensation temperature for the compressed methane and nitrogen, and that the device has a separator, which is arranged for separation of gaseous nitrogen from condensed methane, P:\WPDOCS\DYS\SPECIE\722220.SPE 7/12199 -6- a first piping arrangement for returning condensed methane to the tank, and a second piping arrangement for venting of non condensed nitrogen to the atmosphere.
4. A device according to claim 3, characterized in that it comprises a pump for pumping condensed methane from the separator to the first piping arrangement.
A device according to claim 3, characterized in that it comprises a pump for pumping condensed methane from the separator to a third piping arrangement for conveying condensed methane to a lead-in point on the upstream side of the cooler's inlet.
6. A device according to claim characterized in that the third piping arrangement comprises a temperature sensor which is arranged between the lead-in point and the cooler's inlet, a pipeline which connects the pump Soto the lead-in point, and a first shut-off valve, which is provided in the pipeline and controlled by the temperature sensor.
7. A device according to any one of the claims 3-6, characterised in that the first piping arrangement comprises a first pipeline which is terminated in the tank with a nozzle device which is provided in the upper part of the tank a S:
8. A device according to any one of the claims 3 7, characterized in that the first piping arrangement comprises a second pipeline which is S° 25 terminated in the tank at the bottom thereof.
9. A method for storage and transport of natural gas substantially as hereinbefore described with reference to the accompanying drawings. P:\WPDOCS\DYS\SPEC1E\722220.SPE 7/12/99 -7- A device substantially as hereinbefore described with reference to the accompanying drawings. Dated this 6th December, 1999 KVAERNER MARITIME A.S. By Its Patent Attorney DAVIES COLLISON CAVE
AU67522/98A 1997-03-21 1998-03-19 Method and device for storage and transport of liquefied natural gas Ceased AU715939B2 (en)

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Application Number Priority Date Filing Date Title
NO971364 1997-03-21
NO971364A NO305525B1 (en) 1997-03-21 1997-03-21 Method and apparatus for storing and transporting liquefied natural gas
PCT/NO1998/000088 WO1998043029A1 (en) 1997-03-21 1998-03-19 Method and device for storage and transport of liquefied natural gas

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AU6752298A AU6752298A (en) 1998-10-20
AU715939B2 true AU715939B2 (en) 2000-02-10

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AU (1) AU715939B2 (en)
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WO (1) WO1998043029A1 (en)

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JP2000503108A (en) 2000-03-14
NO305525B1 (en) 1999-06-14
FI114820B (en) 2004-12-31
AU6752298A (en) 1998-10-20
NO971364L (en) 1998-09-25
FI990552A0 (en) 1999-03-12
FI990552A (en) 1999-05-12
KR19990046828A (en) 1999-07-05
NO971364D0 (en) 1997-03-21
KR100356764B1 (en) 2002-10-18
JP3455765B2 (en) 2003-10-14
WO1998043029A1 (en) 1998-10-01

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