NZ626474B2 - Methods for storing cryogenic fluids in storage vessels - Google Patents

Methods for storing cryogenic fluids in storage vessels Download PDF

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Publication number
NZ626474B2
NZ626474B2 NZ626474A NZ62647412A NZ626474B2 NZ 626474 B2 NZ626474 B2 NZ 626474B2 NZ 626474 A NZ626474 A NZ 626474A NZ 62647412 A NZ62647412 A NZ 62647412A NZ 626474 B2 NZ626474 B2 NZ 626474B2
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NZ
New Zealand
Prior art keywords
cryogenic fluid
storage vessel
heat exchanger
liquid
fluid
Prior art date
Application number
NZ626474A
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NZ626474A (en
Inventor
Ron Lee
Original Assignee
Linde Aktiengesellschaft
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Publication date
Priority claimed from US13/344,824 external-priority patent/US20130174583A1/en
Application filed by Linde Aktiengesellschaft filed Critical Linde Aktiengesellschaft
Publication of NZ626474A publication Critical patent/NZ626474A/en
Publication of NZ626474B2 publication Critical patent/NZ626474B2/en

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Classifications

    • 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
    • F17C2201/00—Vessel construction, in particular geometry, arrangement or size
    • F17C2201/01—Shape
    • F17C2201/0104—Shape cylindrical
    • F17C2201/0109—Shape cylindrical with exteriorly curved end-piece
    • 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
    • F17C2201/00—Vessel construction, in particular geometry, arrangement or size
    • F17C2201/03—Orientation
    • F17C2201/032—Orientation with substantially vertical main axis
    • 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
    • F17C2201/00—Vessel construction, in particular geometry, arrangement or size
    • F17C2201/05—Size
    • F17C2201/054—Size medium (>1 m3)
    • 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
    • F17C2205/00—Vessel construction, in particular mounting arrangements, attachments or identifications means
    • F17C2205/01—Mounting arrangements
    • F17C2205/0153—Details of mounting arrangements
    • F17C2205/018—Supporting feet
    • 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
    • F17C2221/00—Handled fluid, in particular type of fluid
    • F17C2221/03—Mixtures
    • F17C2221/032—Hydrocarbons
    • F17C2221/033—Methane, e.g. natural gas, CNG, LNG, GNL, GNC, PLNG
    • 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
    • F17C2223/00—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel
    • F17C2223/01—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel characterised by the phase
    • F17C2223/0146—Two-phase
    • F17C2223/0153—Liquefied gas, e.g. LPG, GPL
    • F17C2223/0161—Liquefied gas, e.g. LPG, GPL cryogenic, e.g. LNG, GNL, PLNG
    • 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
    • F17C2223/00—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel
    • F17C2223/01—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel characterised by the phase
    • F17C2223/0146—Two-phase
    • F17C2223/0153—Liquefied gas, e.g. LPG, GPL
    • F17C2223/0169—Liquefied gas, e.g. LPG, GPL subcooled
    • 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
    • F17C2223/00—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel
    • F17C2223/03—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel characterised by the pressure level
    • F17C2223/033—Small pressure, e.g. for liquefied gas
    • 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
    • F17C2223/00—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel
    • F17C2223/04—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel characterised by other properties of handled fluid before transfer
    • F17C2223/042—Localisation of the removal point
    • F17C2223/046—Localisation of the removal point in the liquid
    • 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
    • F17C2225/00—Handled fluid after transfer, i.e. state of fluid after transfer from the vessel
    • F17C2225/04—Handled fluid after transfer, i.e. state of fluid after transfer from the vessel characterised by other properties of handled fluid after transfer
    • F17C2225/042—Localisation of the filling point
    • F17C2225/046—Localisation of the filling point in the liquid
    • 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
    • F17C2227/00—Transfer of fluids, i.e. method or means for transferring the fluid; Heat exchange with the fluid
    • F17C2227/03—Heat exchange with the fluid
    • F17C2227/0337—Heat exchange with the fluid by cooling
    • F17C2227/0341—Heat exchange with the fluid by cooling using another fluid
    • 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
    • F17C2250/00—Accessories; Control means; Indicating, measuring or monitoring of parameters
    • F17C2250/04—Indicating or measuring of parameters as input values
    • F17C2250/0404—Parameters indicated or measured
    • F17C2250/0439—Temperature
    • 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
    • F17C2270/00—Applications
    • F17C2270/01—Applications for fluid transport or storage
    • F17C2270/0134—Applications for fluid transport or storage placed above the ground
    • F17C2270/0139—Fuel stations
    • 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
    • F17C3/00—Vessels not under pressure
    • 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
    • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
    • F25D3/00—Devices using other cold materials; Devices using cold-storage bodies
    • 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
    • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
    • F25D3/00—Devices using other cold materials; Devices using cold-storage bodies
    • F25D3/005—Devices using other cold materials; Devices using cold-storage bodies combined with 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
    • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
    • F25D3/00—Devices using other cold materials; Devices using cold-storage bodies
    • F25D3/10—Devices using other cold materials; Devices using cold-storage bodies using liquefied gases, e.g. liquid 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
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/0002—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the fluid to be liquefied
    • F25J1/0022—Hydrocarbons, e.g. natural gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—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
    • F25J1/0221—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 the cold stored in an external cryogenic component in an open refrigeration loop
    • 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
    • F25J1/0258—Construction and layout of liquefaction equipments, e.g. valves, machines vertical layout of the equipments within in the cold box
    • 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
    • F25J2210/42—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
    • F25J2290/00—Other details not covered by groups F25J2200/00 - F25J2280/00
    • F25J2290/34—Details about subcooling of liquids
    • 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

Abstract

Disclosed is a method for maintaining a subcooled state of a cryogenic fluid such as liquefied natural gas (LNG) in a storage vessel (A) by the use of an external heat exchanger (B). The liquefied natural gas is removed from the bottom (line 1) of the storage vessel (A) and cooled in the external heat exchanger (B) by a cryogenic fluid such as liquid nitrogen (introduced into the heat exchanger via line 3 and vented out of line 4). The cooled liquefied natural gas is reintroduced back (line 2) into the storage vessel (A) at a higher position thereby maintaining a subcooled bottom layer or natural convection current in the storage vessel. at exchanger (B) by a cryogenic fluid such as liquid nitrogen (introduced into the heat exchanger via line 3 and vented out of line 4). The cooled liquefied natural gas is reintroduced back (line 2) into the storage vessel (A) at a higher position thereby maintaining a subcooled bottom layer or natural convection current in the storage vessel.

Description

/003107 METHODS FOR G CRYOGENIC FLUIDS IN STORAGE VESSELS BACKGROUND OF THE INVENTION The present ion provides for a method for maintaining a subcooled state of a cryogenic fluid such as liquefied natural gas (LNG) in a storage vessel. A portion of the cryogenic fluid is removed from the storage vessel, cooled and then reintroduced back into the e vessel.
Liquefied natural gas is composed primarily of methane, which comprises about 85 to 98% of the LNG on a molar basis. Lesser components that may be present include ethane. propane, carbon dioxide, oxygen and nitrogen. For the purposes of illustration, the properties of pure methane will be used to terize LNG.
Liquefied natural gas bulk storage vessels, ally those used in retuelling stations, are subject to both heat load and returned gas and/or two— phase associated with the fuelling ion. This causes a significant heat load to the storage vessel, which typically results in gas venting. This venting is both a loss of valuable product, as well as a cant environmental issue because natural gas is a ul greenhouse gas. Maintaining the contents of the bulk storage vessel in a subcooled state (temperature below the boiling point corresponding to the storage tank pressure) will prevent most or all of this venting. However, the amount of subcooling available depends on the temperature of the supplied liquid to the bulk storage vessel, and will be lost through warming after a period of time. Hence venting from LNG storage vessels is routine and a significant impediment to successful implementation of l gas as a vehicle fuel.
LNG vehicle fuel tanks typically have an optimum storage pressure of about 6~8 barg in order to deliver the fuel to the engine t the assistance of a pump or compressor. if the liquid supplied during refueling is at a temperature above the saturation temperature corresponding to the optimum storage pressure then the fuel tank must typically vent during refueling. It is therefore desirable for the temperature of the LNG supplied from the bulk storage tank be at or somewhat below the saturation temperature corresponding to the optimum onboard storage pressure. For example, at 6 barg the saturation temperature is about 431°C. This allows the refueling to occur with little or no venting, and the storage tank is filled at close to the optimum d storage pressure.
Further, in the case of an onboard fuel tank that is lly at an elevated pressure relative to the optimum pressure, it is generally advantageous to first introduce subcooled LNG in order to collapse the existing gas in the fuel tank.
] Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field. [0005b] It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to e a useful alternative.
SUMMARY OF THE INVENTION ing to a first aspect, the present invention provides a method for maintaining a subcooled state within a bottom layer of a cryogenic fluid in a storage vessel sing removing a portion of the cryogenic fluid, cooling the removed portion of cryogenic fluid in an external heat exchanger and reintroducing the removed portion of cryogenic fluid back into a liquid region of the storage vessel at a on higher than where the nic fluid was removed from the storage vessel wherein a thermosiphon effect is created to circulate the removed portion of cryogenic fluid. [0005d] According to a second , the present invention provides a method for maintaining a subcooled condition throughout a cryogenic fluid in a storage vessel comprising removing a portion of the cryogenic fluid, cooling the removed portion of cryogenic fluid in an external heat exchanger and reintroducing the removed portion of cryogenic fluid back into the e vessel at a position higher than where the cryogenic fluid was removed from the storage vessel wherein a thermosiphon effect is d to circulate the removed n of cryogenic fluid.
Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like are to be construed in an inclusive sense as opposed to an ive or exhaustive sense; that is to say, in the sense of “including, but not limited to”.
The invention provides for a method for maintaining a subcooied state within a cryogenic fluid such as liquefied natural gas in a storage vessel comprising removing a portion of the cryogenic fluid, cooling the removed portion of nic fluid and reintroducing the removed portion of cryogenic fluid back into the liquid region of the storage vessel.
Cryogenic fluids le for the present invention e liquefied natural gas, liquid nitrogen, liquid oxygen, liquid air, and liquid argon and es of these fluids. Other fluids and fluid mixtures, such as ethylene, while not typically classified as cryogenic are also le for the present invention. When these fluids or mixtures of fluids are stored in a vessel, it is natural for WO 02794 PCT/132012/003107 liquid and vapor fractions of the fluid to form and separate. Where mixtures of these fluids are contained as the sole contents of a storage vessel, then the molar ratio of the components will be different in the liquid and vapor phases according to equilibrium then'nodynamics..
The removed portion of cryogenic fluid is preferably removed from near the bottom of the storage vessel, and is preferably fed back into the storage vessel at a position higher than where the cryogenic fluid was removed. This will help establish a uniform bottom subcooled layer in the e . Typica‘ly a cryogenic fluid such as liquid nitrogen is used to cool the removed portion of cryogenic fluid; r other cryogenic fluids such as liquid air, oxygen, and argon and mixtures of these fluids can be employed or mechanical refrigeration means or a heat transfer fluid cooled by other means may be employed. The cooling provided by the cryogenic fluid such as liquid nitrogen is preferably performed in an al heat exchanger that is at an elevation higher than the position in the tank where the removed liquefied natural gas is returned. The cooling of the cryogenic fluid will increase its density and it will cause a natural circulation (thermosiphon) loop of removed liquefied natural gas and its return into the storage vessel, without the aid of a pump. While this is a preferred means, other methods of ation such as those aided by a pump may be employed. The removal of the cryogenic fluid can be performed continuously as needed or it can be performed ically in that cryogenic fluid is removed from the e vessel on an intermittent schedule- The cryogenic fluid such as liquid nitrogen is in a heat exchanger that is positioned al to the cryogenic fluid storage vessel. The amount of cryogenic fluid ed to the heat exchanger is adjusted to in the desired degree of subcooling of the cryogenic fluid present in the storage vessel. This cooling can also be provided by other cryogenic fluids, a heat transfer fluid PCT/182012/003107 cooled by other means, or mechanical refrigeration. The cryogenic fluid is vented from the heat exchanger after performing its heat exchange duties. lo another embodiment, there is disclosed a method for maintaining the naturai convection current of a nic fluid in a storage vessel comprising removing a portion of the cryogenic fluid, cooiing the removed portion of cryogenic fluid and reintroducing the removed portion of cryogenic fluid back into the storage vessel.
The storage vessel can be selected from any serviceable design, size or orientation. The piping connections into or out of the storage vessel may be suitably modified as well. The return flow of subcooled nic fluid into the storage vessel may be ether above or below the location where the cryogenic fluid is removed inside the bulk storage vessel. The piping used for the preferred mode of thermosiphon action for subcooling may be in addition to or the same as the piping used for thermosiphon cooling of an external cryogenic pump.
Additional piping into and/or out of the vessel is also possible. including for the return flow of gas and/or liquid into the bottom or top regions of the vessel. [0013} Additional l elements. as necessary, such as control valves, or temperature or pressure g s may also be used to control the degree and rate of external subcooling.
The cryogenic fluid such as en gas that is vented from the external heat exchanger may be used in other unit operations where the nic fluid storage vessel is located such as cooling ions, inerting, or as a pressurizing gas to operate valves.
PCT/IBZOIZ/ODS 107 The placement of the external heat exchanger can be modified to optimize the circulation due to thermosiphon behavior and the retum and supply lines can be mented with a cryogenic pump.
Additional methods for vessel pressure control and condensation of vapor are possible and may be used in conjunction with the invention. For example, during vessel filling a ation of top and bottom filling with subcooled liquid may be employed for maintaining storage vessel pressure.
Additionally, an external cryogenic pump maybe arranged to periodically ate a portion of the bottom subcooled liquid to the top of the nic vessel in order to directly condense vapor. {0017} While the detailed description of the invention below discusses liquefied natural gas as the cryogenic fluid that is present in the e , the methods of the invention would be applicable to other cryogenic fluids such as liquid nitrogen, liquid oxygen. liquid air. liquid argon, and ethylene and mixtures of these fluids BRIEF DESCRIPTION OF THE DRAWINGS The figure is a schematic of a cryogenic fluid storage vessel and secondary refrigeration source according to the invention.
DETAlLED DESCRlPTlON OF THE lNVENTlON Turning to the figure, a liquefied natural gas bulk storage vessel containing LNG at an elevated pressure is shown. ed natural gas is present in bulk storage vessel A which is in fluid communication with heat ger B. Liquid natural gas will be withdrawn from the bulk storage vessel A through line 1 where it will be directed to the heat exchanger B. The iiquefied natural gas in llne 1 will be cooled further by heat exchange with liquid nitrogen.
The further cooled liquefied natural gas is returned to the bulk storage vessel through line 2. The liquid en will be fed into heat exchanger B through line 3 which passes through heat exchanger B. The liquid nitrogen will be heated by the heat exchange process and be vented from the heat exchanger 8 through line 4 as en gas.
(AM, A liquefied natural gas (LNG) bulk e vessel contains LNG at an elevated pressure. The LNG in the bulk container is generally comprised of a top ted layer (liquid at the boiling point temperature corresponding to the storage pressure) and an underlying subcooled layer (liquid at a ature colder than the boiling point corresponding to the storage pressure). The ying subcooled layer may further have spatial temperature variation. The equitibrium condition of this two layer arrangement is for natural convection currents within the tank, caused by heat load from the vessel wall as well as gas which may be introduced into the bottom of the , to cause the top saturated layer to become ely thin. As heat or bottom gas is continued to be added to the vessei, oniy this thin top saturated layer will vaporize, while the bottom subcooled layer will warm without vaporization. During this period of time there will not typically be any significant venting because as liquid is withdrawn, the amount of vaporization of the thin saturated layer will be compensated by the volume of liquid withdrawn. Ultimately, however, the heat addition will destroy the subcooling throughout the bottom layer and the entire vessel will become ted. At that point, any further heat or gas addition will cause only LNG vaporization without warming. ln order to maintain the desired pressure within the vessel, it then becomes necessary to vent natural gas. [0021} The method the present invention is to inhibit the destruction of the bottom subcooled layer in a liquefied natural gas storage vessel. it is a r object of the present invention to maintain the bottom subcooled layer at a preferred temperature to facilitate optimum refueling of e fuel tank.
Accordingly the invention seeks to maintain a subcooled state within a bottom region of a cryogenic fluid in a storage vessel as well as in a subcooled state throughout the cryogenic fluid present in a storage vessel. By preventing the bottom subcooled layer‘s destruction over time, the bulk storage vessel will remain largely subcocled due to the natural convection currents previously described and the venting problem is significantly reduced or eliminated. This is accomplished by using a secondary refrigeration source (in this case, preferably a cryogenic fluid such as liquid nitrogen) to subcool a portion of the LNG in external heat exchanger. While a pump could be used to circulate this led LNG formed externally, a novel aspect of the invention and a red option is to rely on a thermosiphon effect for the circulation.
Turning to the figure, two lines are shown entering the bottom of the bulk storage vessel. preferably separated both ntally and vertically. The designation "h” refers to the elevation necessary for the external heat exchanger B to drive the thermosiphon effect as cooler liquefied natural gas is fed from a point higher in elevation than the point it is reintroduced into the bulk storage vessel. Liquefied natural gas is withdrawn from the storage vessel A through line 1 and directed to al heat exchanger B. Liquid nitrogen in line 3 is used to cool this side stream of LNG from Line 1 in the external heat exchanger B. As the external stream of LNG in the heat exchanger B is cooled sufficiently by the liquid nitrogen, which has a normal boiling point about 35°C lower than that of LNG, it naturally s denser and tends to drop. This highly subcooled side stream of LNG flows downward through line 2 and back into the bottom of the bulk LNG storage . As this highly subcooled LNG is returned to the bulk LNG storage vessel, it is naturally ed in the external heat exchanger B by W0 2013/]02794 PCT/132012/003107 return flow of warmer LNG from line 1. This l circulation or thermosiphon effect is continued as long as liquid nitrogen is provided to the external heat exchanger 8. [0023} The amount of liquid nitrogen ed is generally adjusted to maintain a red degree of bottom subcooling as indicated by the temperature T or other suitable temperature measurement of the LNG. A pump, not shown, is a possible addition to facilitate this circulation. However, one ment is the thermosiphon design described and illustrated as it provides a r, more reliable and lower cost solution. This thermosiphon design, in addition to piping arrangements, depends on a hydrostatic pressure head to drive the circulation. This distance, h, shown in the figure illustrates how the hydrostatic head is produced through suitable placement of the external heat exchanger relative to the internal pipe terminations inside the storage vessel. A typical value for h is between 1 to 3 .
It is noted that the thermosiphon arrangement as shown in the figure will only ly introduce ally subcooled LNG into the bottom region of the vessel. As earlier discussed, the natural convection ts that exist inside these vessels will ensure the majority of the vessel contents above this lower region will also be maintained in a subcooled state.
While this invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modifications of the invention will be obvious to those skilled in the art. The appended claims in this invention generally should be construed to cover all such obvious forms and modifications which are within the true spirit and scope of the invention.

Claims (22)

Claims:
1. A method for maintaining a led state within a bottom layer of a cryogenic fluid in a e vessel comprising removing a portion of the cryogenic fluid, cooling the removed portion of cryogenic fluid in an external heat exchanger and reintroducing the removed portion of cryogenic fluid back into a liquid region of the storage vessel at a position higher than where the cryogenic fluid was removed from the storage vessel wherein a siphon effect is created to circulate the removed portion of cryogenic fluid.
2. The method as d in claim 1 wherein a cryogenic fluid is used to cool the removed n of cryogenic fluid.
3. The method as claimed in claim 2 wherein the cryogenic fluid used to cool the removed portion of cryogenic fluid is in the heat exchanger.
4. The method as claimed in any one of claims 1 to 3 wherein the cooling is provided by a cryogenic fluid selected from the group consisting of liquefied en, liquid oxygen, liquid air, argon. ne and mixtures of these fluids.
5. The method as claimed in claim 1 wherein said cooling is provided by mechanical refrigeration.
6. The method as claimed in any one of claims 1 to 5 wherein a circulation is established in the removed n of cryogenic fluid.
7. The method as claimed in any one of claims 1 to 6 wherein said nic fluid in said storage vessel is selected from the group consisting of liquefied natural gas, liquid nitrogen, liquid oxygen, liquid air, liquid argon, and ethylene and mixtures of these fluids.
8. The method as claimed in any one of claims 1 to 7 wherein the cooling is based on the temperature of the removed portion of the cryogenic fluid.
9. The method as claimed in any one of claims 1 to 8 wherein the amount of cryogenic fluid supplied to the heat exchanger is adjusted to maintain the desired degree of subcooling of the cryogenic fluid.
10. The method as claimed in any one of claims 1 to 9 further comprising circulating the removed portion of cryogenic fluid back into the e vessel with a pump.
11. A method for maintaining a subcooled condition throughout a cryogenic fluid in a storage vessel comprising removing a portion of the cryogenic fluid, cooling the d portion of nic fluid in an external heat exchanger and reintroducing the removed portion of cryogenic fluid back into the storage vessel at a on higher than where the cryogenic fluid was removed from the storage vessel wherein a thermosiphon effect is created to circulate the removed n of nic fluid.
12. The method as claimed in claim 11 wherein a cryogenic fluid is used to cool the removed portion of cryogenic fluid.
13. The method as claimed in claim 12 wherein the cryogenic fluid used to cool the removed portion of cryogenic fluid is in the heat exchanger.
14. The method as claimed in any one of claims 11 to 13 wherein the cooling is ed by a cryogenic fluid selected from the group consisting of ied nitrogen, liquid oxygen. liquid air. argon, ethylene and mixtures of these fluids
15. The method as claimed in claim 11 wherein said cooling is provided by mechanical refrigeration.
16. The method as claimed in any one of claims 11 to 15 wherein a circulation is established in the cryogenic fluid.
17. The method as claimed in any one of claims 11 to 16 wherein said cryogenic fluid in said e vessei is selected from the group consisting of liquefied natural gas, liquid nitrogen, liquid oxygen, liquid air, iiquid argon, and ethylene and mixtures of these fluids.
18. The method as claimed in any one of claims 11 to 17 wherein the removal of a portion of the cryogenic fluid is continuous.
19. The method as claimed in any one of claims 11 to 18 wherein the amount of cryogenic fluid supplied to the heat exchanger is adjusted to maintain the desired degree of subcooling of the cryogenic fluid in said storage vessel.
20. The method as claimed in any one of claims 11 to 19 further comprising reintroducing the d n of cryogenic fluid back into the storage vessel with a pump.
21. A method for maintaining a subcooled state within a bottom layer of a cryogenic fluid in a storage vessel substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples, or part thereof.
22. A method for maintaining a subcooled condition throughout a cryogenic fluid in a storage vessel substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples, or part thereof.
NZ626474A 2012-01-06 2012-12-13 Methods for storing cryogenic fluids in storage vessels NZ626474B2 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US13/344,824 US20130174583A1 (en) 2012-01-06 2012-01-06 Methods for storing cryogenic fluids in storage vessels
US13/344,824 2012-01-06
PCT/IB2012/003107 WO2013102794A1 (en) 2012-01-06 2012-12-13 Methods for storing cryogenic fluids in storage vessels

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NZ626474A NZ626474A (en) 2016-02-26
NZ626474B2 true NZ626474B2 (en) 2016-05-27

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