CN115717680A

CN115717680A - Liquefied gas storage device

Info

Publication number: CN115717680A
Application number: CN202211260003.XA
Authority: CN
Inventors: A.布维尔; F.隆巴德
Original assignee: Gaztransport et Technigaz SA
Current assignee: Gaztransport et Technigaz SA
Priority date: 2018-05-30
Filing date: 2019-05-28
Publication date: 2023-02-28
Also published as: KR20220138421A; WO2019229097A1

Abstract

Liquefied gas storage device, in particular for liquefied gas vehicles or for land-based facilities, comprising: -at least one liquefied gas storage reservoir (12) having a reservoir bottom (14) and a reservoir ceiling (16) which together define a reservoir height (H), -means (20) for withdrawing gas in liquid and/or gaseous form in the at least one reservoir, and-means (10) for injecting gas in liquid form into the reservoir, characterized in that the gas injection means comprise at least one injector-mixer (10) which is located in an upper region of the reservoir which extends between 60 and 100% of the reservoir height, the reservoir height being measured from the reservoir bottom, and the injector-mixer being intended to be immersed in the liquefied gas contained in the reservoir.

Description

Liquefied gas storage device

The application is a divisional application of an invention patent application with the application number of 201980048776.1, the application date of 2019, 5 and 28 months and the invention name of "liquefied gas storage device".

Technical Field

The invention relates in particular to a liquefied gas storage device, in particular for liquefied gas vehicles or for land-based installations.

Background

In order to make it easier to transport a gas, for example natural gas, over long distances, the gas is usually liquefied (into liquefied natural gas-LNG) by cooling it to cryogenic temperatures, for example to 160 ℃ at atmospheric pressure. The liquefied gas is then loaded into vehicles, such as LNG carriers and filling vessels.

In order to limit the evaporation of the liquefied gas contained in the vessel's reservoir, it is known practice to store it under pressure in the reservoir so as to move on the evaporation curve of the liquefied gas in question, thereby increasing its evaporation temperature. Liquefied gas can therefore be stored at higher temperatures, which results in limited evaporation of the gas.

However, natural evaporation of Gas is unavoidable, and this phenomenon is called NBOG, which is an abbreviation for Natural Boil-Off Gas (Forced Boil-Off Gas), as opposed to FBOG or Forced Boil-Off Gas (Forced Boil-Off Gas). The naturally evaporated gas in the storage of the ship is typically used to power the energy generating means of the ship, which is intended to meet the energy requirements for the operation of the ship, in particular the propulsion of the ship and/or the power generation of the onboard equipment.

In the current state of the art, the improvement of the reservoir results in a lower and lower natural evaporation rate (BOR) of the liquefied gas and a higher and higher mechanical efficiency of the ship. As a result, there is a large difference between the amount of gas naturally produced by vaporization and the amount of gas required for the facilities of the ship. The excess gas is of particular interest when the consumption of the ship is low, that is to say, for example, when the ship is in an idle state, in a standby state or in a damaged state (for example, influencing the processing plant or the consumption is not zero).

Excess natural boil-off gas (NBOG) is then recondensed and re-injected into the reservoir. For this purpose, a re-liquefaction or re-condensation device is used, which converts the NBOG into a liquefied gas, which is then re-injected into the reservoir.

The generation of NBOG can also be reduced by lowering the temperature of a gas ceiling contained in the reservoir above the liquid-gas interface in the reservoir. To do this, the liquefied gas can be pumped out, cooled (or subcooled because it is already cold), and then re-injected into the reservoir via a spray bar of liquefied gas in the top gas.

This makes it possible to control the pressure in the reservoir (first target) by recondensing BOG in the gas ceiling. This also allows the temperature of the liquefied gas to be controlled in order to deliver "cold" LNG (second target). In fact, in the case of an LNG carrier or filling vessel, the maximum temperature of the LNG to be transferred may be required by the receiving terminal or vessel.

The first objective is primarily for LNG transfer operations between multiple storage facilities of the same facility and/or between multiple storage facilities of multiple facilities, in order to condense excess gas produced during LNG transfer operations, in order to achieve the transfer in a given time. The first target may also satisfy the demand for a loaded or nearly empty reservoir (if the target is control pressure).

A second objective is to respond to a demand for the filling vessel to receive relatively cold LNG in order to maintain a safety margin with respect to the safety valve. Thus, after a fuel loading operation, a tenant will want to keep its cargo as cold as possible, even cooling its cargo in order to comply with contracts with LNG-powered vessels. Therefore, it will use its own subcooling device to cool the LNG and prevent the pressure drop.

One of the objects of the present invention is to optimize the storage in a liquefied gas storage according to the desired needs, in particular for controlling the pressure or controlling the liquid temperature.

Disclosure of Invention

According to a first aspect, the invention proposes a liquefied gas storage device, in particular for a liquefied gas carrier or for a land-based facility, comprising:

at least one liquefied gas storage reservoir having a reservoir bottom and a reservoir top plate together defining a reservoir height,

-means for withdrawing gas in liquid and/or gaseous form from the reservoir, and

means for injecting gas in liquid form into said reservoir, preferably connected to gas extraction means,

characterized in that said gas injection means comprise at least one injector-mixer located in a lower region of said reservoir extending between 0 and 25% of the height of the reservoir, preferably between 0 and 15%, more preferably between 0 and 10%, said reservoir height being measured from the reservoir bottom, and said injector-mixer being intended to be immersed in said liquefied gas contained in the reservoir.

Preferably, said at least one injector-mixer is configured to inject a flow of liquid gas in a direction inclined upwards at an angle α with respect to the horizontal. The angle α may be 5 ° to 45 °, preferably 5 ° to 30 °, and more preferably 5 ° to 20 °. In a variant, the angle α may be 5 ° to 85 °, preferably 15 ° to 75 °, and more preferably 30 ° to 60 °.

According to a second aspect, the invention proposes a liquefied gas storage device, in particular for a liquefied gas carrier or for a land-based facility, comprising:

-at least one liquefied gas storage reservoir having a reservoir bottom and a reservoir ceiling together defining a reservoir height,

means for withdrawing liquid and/or gaseous gases from the at least one reservoir, and

means for injecting gas in liquid form into the reservoir, preferably connected to gas extraction means,

characterized in that said gas injection means comprise at least one injector-mixer located in an upper region of said reservoir extending between 60 and 100% of the height of the reservoir, or even between 75 and 100%, preferably between 60 and 98%, more preferably between 65 and 95%, or even more preferably between 65 and 80%, or 80 and 95%, said reservoir height being measured from the bottom of said reservoir, and said injector-mixer being intended to be immersed in said liquefied gas contained in the reservoir.

Preferably, at least one injector-mixer is configured to inject a flow of liquid gas in a direction inclined downwards at an angle β with respect to the horizontal plane. The angle β may be 5 ° to 45 °, preferably 5 ° to 30 °, and more preferably 5 ° to 20 °. In a variant, the angle β may be 5 ° to 85 °, preferably 15 ° to 75 °, and more preferably 30 ° to 60 °.

Advantageously, said at least one syringe-mixer is fixed to a wall of said reservoir. Preferably, the reservoir comprises vertical longitudinal side walls connected to the reservoir ceiling by inclined walls, the at least one injector-mixer being fixed to the area for connecting the vertical longitudinal walls to the inclined walls. The at least one injector-mixer may be fixed to the thickened metal plate and/or to the at least one wood block of the connection region. The plate may form part of the membrane of the reservoir and, therefore, like the membrane, the plate is in contact with the liquefied gas contained in the reservoir (when there is liquefied gas in the reservoir, or at least when there is no leakage). A block of wood may be located between the membrane and the hull of the vessel.

In each of the above aspects, the key principle sought is the ability to re-inject liquefied gas, which may or may not be pre-subcooled, into the liquid contained in the reservoir rather than into the headspace gas. In fact, re-injecting most of the cold power into the top gas will result in a significant pressure drop and cooling of the top gas, which will force the hot stream to re-enter the upper part of the reservoir. A large part of the liquefied gas re-injected into the top gas will be unnecessarily vaporized, which will limit the cold power to be supplied to the liquid. This is especially true because the latter will only distribute to the free surface of the liquid, which will result in slower diffusion kinetics. In contrast, the present invention proposes to inject cold power directly into the liquid below the free surface to reduce the effect on the temperature and pressure of the top gas. Furthermore, the injection of the liquefied gas below the free surface will make it possible to produce a mixing and stirring effect by adjusting the hydrodynamics at the outlet of the injector-mixer, its orientation, its height, etc. The invention also relates to the situation where the liquefied gas does not have to be subcooled before being injected into the reservoir. The main function of injecting the liquefied gas would then be to mix the liquefied gas contained in the reservoir. This is particularly useful for limiting the evaporation of liquefied gas, particularly when the subcooled liquefied gas is poured into the bottom of the reservoir, which is obtained by re-liquefaction of the evaporated gas. The nitrogen forced to evaporate from the reservoir is much higher (because nitrogen is more volatile than methane) than the naturally evaporating liquid. The evaporated gas is liquefied by the re-liquefying device and returned to the bottom of the reservoir. The condensate is therefore much heavier than the surrounding liquefied gas (because it is rich in nitrogen, but also colder). The nitrogen-enriched liquid collects at the bottom of the reservoir. As it naturally warms up, the nitrogen bubbles vaporize and rise to the surface, thereby enriching the top gas nitrogen. However, nitrogen is difficult to condense, which reduces the capacity of the liquefier and causes difficulties in controlling the pressure in the reservoir. This phenomenon is exacerbated when the reservoir is nearly empty, as the nitrogen bubbles do not have time to re-dissolve during the rise to the surface. This is why such devices never consider injection through a spray bar at the top of the reservoir due to the risk of nitrogen enrichment. This phenomenon can lead to degradation of the bottoming portion when using an almost empty reservoir, which limits the ability of the bottoming portion to cool the reservoir before the next loading.

The invention also relates to the situation where the liquefied gas is superheated before injection into the reservoir. The main function of the injected liquefied gas will then be to mix with the liquefied gas contained in the reservoir. This is particularly useful for limiting evaporation of the superheated liquefied gas, particularly when it is poured into the bottom of a reservoir. The superheated liquefied gas is hotter and therefore lighter than the surrounding liquefied gas (colder), which would evaporate without mixing means, even by injection at the bottom of the reservoir. In fact, it is lighter and will rise in colder and therefore heavier surrounding liquid until it evaporates when its static pressure becomes lower than its bubble point pressure. This is especially true in cases where the liquid level in the reservoir is low, because the static pressure at the bottom of the reservoir is lower compared to a higher liquid level. With a mixing device by venturi effect, suction, entrainment, etc. are particularly suitable for injecting the superheated liquefied gas, since it allows a dilution of at least 4 times. The superheated liquefied gas is obtained by recondensing (i.e., mixing) the pressurized boil-off gas with the liquefied gas from the reservoir. Superheated liquefied gas is typically vaporized for injection into a land-based gas network. If the land-based gas network requires the gasification unit to stop sending to the network, the superheated liquefied gas may be returned to the reservoir via the mixing device while limiting the natural evaporation of the gas stored in the reservoir. In the absence of mixing means, the evaporation produced by injecting the superheated liquefied gas into the reservoir produces additional evaporation which is added to the natural evaporation which must be recondensed in order to be re-injected into the reservoir. This results in an accelerated heating of the liquefied gas contained in the reservoir and therefore a faster pressure rise than with a mixing device.

Here, the injection of liquefied gas is performed by means of an injector-mixer configured to inject a flow of gas in liquid state and mix it with the liquid (which is injected into the liquid by means of venturi effect, suction, entrainment, etc.).

The device according to the invention may also have one or more of the following features, considered independently of each other or in combination with each other:

-the at least one injector-mixer is positioned as close as possible to the longitudinal side wall of the reservoir; in the present application, the term "closest" or "close" is understood to mean a distance of less than one meter, and preferably less than or equal to 0.5 meter, or even less,

the injection means comprise at least one horizontal row of injector(s) -mixer(s) configured to inject a flow of liquid gas in parallel or different directions,

the injection means comprise at least two horizontal rows of injector-mixers arranged on and/or along two longitudinal side walls of the reservoir, respectively,

-the gas injection means are connected to means for withdrawing gas of the or another reservoir through re-liquefaction means,

the reliquefaction means is configured to condense boil-off gas drawn from the reservoir or another reservoir and then pressurize by heat exchange with liquefied gas drawn from the reservoir or another reservoir,

-the gas injection means are connected to means for liquid gas drawn from the reservoir or another reservoir by supercooling means,

-the extraction means are configured to extract liquid gas from the lower zone,

the extraction means comprise at least one pump and a pipe, located in the reservoir or in another reservoir and intended to be at least partially immersed in the liquefied gas,

-the pump is configured to have a variable flow rate or rotor speed,

-the reservoir is of the "full-fill" type and is configured to be fillable to any level,

-the reservoir is of the "limited fill" type and is configured to be filled only to 10% and less, or 70% and more,

the extraction means and the injection means are located in the reservoir and are connected to each other by a conduit located entirely in the reservoir,

the conduit extends at least partially substantially parallel to and close to the bottom wall of the reservoir, and preferably to at least one side wall of the reservoir,

in case the extraction means are located at the center and at the bottom of the reservoir, the conduit may extend in opposite directions along the bottom wall of the reservoir up to the side wall of the reservoir,

the conduit may be configured to match the specific shape of the reservoir bottom, in particular the shape of any connection bevel between the bottom and the side wall of the reservoir.

The extraction means and the injection means are positioned perpendicular to the liquid dome of the reservoir and are preferably equipped with a pump tower accessible through the liquid dome,

-the at least one injector-mixer is connected to and supported by the liquid column of the pump tower,

-the injector-mixer comprises a primary duct for the passage of a primary jet of liquid and a secondary duct for the forced passage of a secondary jet of liquid by Venturi effect,

the injection means or even the extraction means are positioned relative to each other and are configured such that they create a back pressure and a suction effect in the reservoir, these effects creating a predetermined agitation cycle of the liquefied gas in the reservoir.

The invention also relates to a liquefied gas vehicle comprising at least one device as described above, which is free from supercooling and reliquefaction means between said extraction means and injection means, said reservoir being of the "full-fill" type and configured to be filled to any level.

The invention also relates to a liquefied gas vehicle comprising at least one device as described above, comprising means for supercooling and/or reliquefying between said extraction means and injection means, said reservoir being of the "full-fill" type or of the "limited-fill" type.

The invention also relates to a liquefied gas vehicle comprising at least one device as described above, which is free from supercooling and reliquefaction means between said extraction means and injection means, said reservoir being of the "limited filling" type and configured to be filled only up to 10% and less or up to 70% and more.

The invention also relates to a liquefied gas vehicle comprising at least one apparatus as described above, comprising means of supercooling and/or reliquefaction between said means of extraction and means of injection, said reservoir being of the "limited filling" type and configured to be filled only up to 10% and less or up to 70% and more.

In the case of filling in the lower part of the reservoir, the filling means are oriented upwards so as to create a back pressure and suction effect in the reservoir, and a stirring cycle, both for an almost empty reservoir ("ballasted") and for an almost full reservoir ("fully loaded"). In the case of an almost empty reservoir (liquid bottoming), this configuration makes it possible to stir the liquid over most of the length of the reservoir (a sufficiently small angle, i.e. close to horizontal), but without dispersing the liquid in an air gap, as this would cool the gas and thus increase the heat transfer.

Too large an angle (i.e. close to the vertical) will create accumulation of injected liquid close to the injector and extraction means and will resample the injected liquid towards the supercooling means, which risks freezing of the supercooled liquid (in combination with the supercooling means located between the extraction means and the injection means).

In the case of an almost full reservoir, this configuration makes it possible to stir the liquid over a large part of the height of the reservoir (a sufficiently large angle, i.e. close to the vertical), so that the temperature of the liquid is uniform over the entire height of the liquid. Too small an angle (i.e. close to the horizontal) will create an accumulation of injected liquid near the extraction means at the bottom of the reservoir and will resample the injected liquid towards the subcooling means, which risks the subcooled liquid freezing (in combination with the subcooling means located between the extraction means and the injection means). In the case of a homogeneous subcooled liquid that can accumulate at the bottom of the reservoir, there is also a risk of sudden depressurization of the reservoir, which may open if the pressure drops below atmospheric pressure.

The invention also relates to a method for injecting gas in liquid form into a reservoir of a ship as described above.

According to a first embodiment, the injection is performed when the "limited fill" reservoir is filled to 10% or less (in the lower region).

According to a variant embodiment, the injection is performed when the "full-filled" reservoir has any filling level, the injection angle (in the lower region) being independent of this level, while the injection rate is controlled according to this level. Preferably, the greater the volume of liquid in the reservoir, the greater the injection rate.

The invention also relates to a method of injecting gas in liquid form into a reservoir of a ship as described above, wherein the injection into the upper region is performed when the "limited-fill" reservoir is filled to 70% or more.

The invention also relates to a method of injecting gas in liquid form into a reservoir of a vessel as described above, wherein the injection into the reservoir is configured to prevent heated liquefied gas from rising along a longitudinal side wall of the reservoir.

The invention also relates to a method of injecting gas in liquid form into a reservoir of a vessel as described above, wherein the injected liquefied gas has a temperature which is lower than the temperature of the liquefied gas contained in the reservoir.

Advantageously, the injection means or even the extraction means are controlled such that they create a back pressure and a suction effect in the reservoir, these effects creating a predetermined agitation cycle of the liquefied gas in the reservoir. Advantageously, the agitation period is designed such that the liquefied gas circulates substantially parallel to and close to the liquid-gas interface in the reservoir. This makes it possible to limit the risk of forming a hot liquid layer at the interface and thus to limit the risk of evaporation of the liquefied gas.

In the context of the present application, it is,

"reservoir" means any reservoir with an internal liquefied gas storage of more than 100m3, preferably more than 1000m3, or even 10,000m3, or even 20,000m3; and/or any reservoir configured to store liquefied gas at a temperature of-163 ℃ or less,

a reservoir of the "fully filled" type refers to a reservoir configured to store any volume of liquefied gas, which may for example represent 50% of its total internal volume; vessels of the FSRU (floating storage regasification unit), ST (shore storage), GBS (gravity based structure), LBV (LNG refueling vessel), LFS (LNG fuelled vessel) type are usually equipped with such a storage,

"limited-fill" type of reservoir refers to a reservoir configured to store 10% by volume and less, 70% by volume or more of liquefied gas; thus, it cannot store moderate amounts of liquefied gas, for example 50% of its total internal volume, especially for safety reasons, which is the case for LNG ships that are susceptible to transport conditions during driving, which may cause fluctuations of the liquefied gas in the reservoir; LNGC type vessels (LNG carriers) are usually equipped with such reservoirs,

by "ship" is meant any unit for the marine transport of liquefied gases, such as LNG carriers, filling ships and the like,

"reliquefaction means" or "recondensing means" means configured to cause the condensation of a gas, typically BOG or NBOG, and thus the conversion of this gas into a liquefied gas; they may for example comprise means for compressing the gas under temperature and pressure conditions allowing it to condense,

"subcooling" means a device configured to further cool the liquefied gas, which is typically already at a temperature of-163 ℃ or less, such that, for example, the liquefied gas temperature can be reduced by about 10 °; the supercooling means includes, for example, means for evaporating or vaporizing the liquefied gas to generate cooling energy, and means for exchanging heat with the liquefied gas, so that the liquefied gas is supercooled by the energy,

the concept of "up" and "down" or "upper" and "lower" is evaluated relative to the normal position of the vessel when landing and floating on water, i.e. normal position when operating, and more generally relative to the centre of the earth (the top being further from the centre of the earth than the bottom).

Drawings

The invention will be better understood and other details, features and advantages thereof will appear more clearly on reading the following description, given by way of non-limiting example with reference to the accompanying drawings, in which:

figure 1 is a schematic longitudinal cross-sectional view of a first embodiment of a liquefied gas storage device according to the invention,

figure 2 is a schematic cross-sectional view of figure 1,

figure 3 is an enlarged view of figure 1,

figure 4 is a schematic longitudinal cross-sectional view of a second embodiment of a liquefied gas storage device according to the invention,

figure 5 is a schematic cross-sectional view of figure 4,

figure 6 is an enlarged view of figure 4,

figure 7 is a schematic perspective and sectional view of a liquefied gas storage device,

fig. 8 is a schematic perspective view of a connection region of a wall of a reservoir, such as the reservoir of fig. 7,

figures 9 and 10 are very schematic partial views of reservoirs having different geometries,

figures 11 and 12 are very schematic cross-sectional views of variant embodiments of the device according to the invention, figure 9 showing a cross-sectional view of the middle of the device, figure 10 showing a cross-sectional view of each longitudinal end of the device,

figure 13 is a very schematic top view of a variant embodiment of the device according to the invention,

figures 14 to 26 are very schematic cross-sectional views of variant embodiments of the device according to the invention,

figures 27 and 28 are respectively a schematic cross-sectional view and a schematic perspective view of an exemplary embodiment of the injector-mixer,

figure 29 is a block diagram illustrating various embodiments of a vessel and method according to the invention,

fig. 30 and 31 are views similar to fig. 4, showing the same reservoir in a "ballasted state" and thus filled with a liquid bottom (liquid heel), and in a "full state" and almost completely filled, respectively.

Detailed Description

As previously mentioned, the temperature and pressure in the liquefied gas (LNG) reservoir can be specifically controlled to control the production of NBOG in the reservoir.

Liquefied gas storage devices, in particular for liquefied gas vehicles, generally comprise:

-at least one reservoir for liquefied gas,

means for withdrawing liquid and/or gaseous gases in the reservoir, and

-means for injecting gas in liquid form into the reservoir, the means being connected to the gas extraction means.

As part of the first objective described above, the top gas is cooled using a super cooled LNG spray bar. LNG is withdrawn by the withdrawal means, subcooled by the subcooling means, and then injected by a rod (injection means) at the top of the reservoir. By maximizing the exchange surface between the droplets and the gas to condense it, the spray makes it possible to directly influence the temperature and pressure of the gas above.

In practice, there are usually two spray bars and they are identical: they are typically used simultaneously for initial cooling, while the single rod allows for normal cooling (while ballasted) prior to loading.

If the device is used for a full reservoir, the subcooled LNG is mainly sprayed at the liquid-gas interface, which is not very suitable if the aim is to influence the temperature of the liquid over the entire height of the reservoir and thus over the entire liquid volume.

If one or two rods are used in the case of a ballasted state (reservoir with liquid bottom), the temperature of the gas above (including the top plate) will be very cold (close to the equilibrium point = dew point temperature) and the heat flow from the outside through the insulation layer will thus increase.

Without using a rod to spray the sub-cooled gas, the overhead gas can be significantly stratified in temperature (hotter gas concentrated at the top and cooler gas concentrated at the bottom), which reduces evaporation and thus the cold power required to control the pressure and temperature in the reservoir. If subcooling means are used in the ballasted state when the overhead gas has warmed up, then in addition to increasing heat flow, the spray of subcooled liquid will also cause the reservoir pressure to increase as the dispersed LNG will vaporize upon cooling the thermal insulation of the heated reservoir.

In the case of the second objective, i.e. to control or even cool the stored LNG, it is desirable to re-inject the subcooled LNG into the reservoir. However, the subcooled LNG will be returned directly to the reservoir without mixing with the LNG already present in the reservoir. Furthermore, LNG that is subcooled by about 10 ° will be heavier than the LNG in the reservoir and will be difficult to mix with. In the event that subcooled LNG is re-injected at the bottom of the reservoir, it will collect in the bottom of the reservoir and can be withdrawn directly again through the withdrawal means described above, which can adversely affect the efficiency of the subcooling. In practice this would mean that LNG which has been subcooled is withdrawn which would overcool the LNG as the output temperature of the subcooling device is limited to avoid that the LNG freezes (mainly heavy compounds). Therefore, it is necessary to reduce the instantaneous power of the subcooling device. However, in order not to limit this power (and avoid recycling of the subcooled LNG) and to reduce the power consumption of the plant (avoid cooling the overhead gas), the invention proposes to inject the subcooled LNG below the liquid-gas interface and via at least one injector-mixer.

Figures 1 to 3 show one of the aspects of the invention in which the gas injection means comprises at least one injector-mixer 10 located in the upper region of the reservoir 12, extending between 60% and 100% of the height of the reservoir measured from the bottom 14 of the reservoir. The height of the reservoir 12 is measured between the reservoir bottom 14 and the reservoir ceiling 16. Reference numeral 18 indicates the liquid-gas interface or free surface of the liquefied gas in the reservoir, the liquid formed by the liquefied gas being heavier and therefore below the upper gas formed by the natural evaporation of the liquefied gas.

In addition to the reservoir 12 and the injector-mixer 10, the liquefied gas storage device also comprises means for withdrawing gas, here in liquid form. The extraction means here comprise a pump 20 which is immersed in the liquefied gas and is preferably located at the bottom of the reservoir. The liquefied gas may be withdrawn and injected into the same reservoir, or into another reservoir.

The pump 20 is connected to the injector-mixer 10 either directly or through a subcooling device 22. The subcooling means may be configured to reduce the temperature of the liquefied gas pumped by the pump by about 10 °.

The reservoir 12 may be of the "full fill" type or of the "limited fill" type. In both cases, when filled with liquefied gas (and not including the liquefied gas at the bottom of the reservoir, remaining at the bottom), it is filled to at least 70% of its volume. In practice, it is filled to 95% or more of the volume, preferably 98.5%.

The injector-mixer 10 is positioned and designed to inject liquefied gas that is drawn out (and possibly subcooled) below the interface 18 so that the liquefied gas flow mixes with the liquefied gas contained in the reservoir 12.

Advantageously, the injector-mixer 10 is configured to inject a flow of liquefied gas in a direction inclined downwards at an angle β with respect to the horizontal plane (fig. 3). The angle β is, for example, 5 ° to 85 °, preferably 15 ° to 75 °, and more preferably 30 ° to 60 °.

This makes it possible to promote the mixing of the liquefied gas in the reservoir over substantially the entire height of the liquefied gas and over the greatest possible distance, as is schematically indicated by the arrows in fig. 1.

In the case of injection of subcooled or superheated liquefied gas, that is to say from the subcooling device or recondensor injection described above, the injector-mixer(s) can advantageously be fixed to the pump tower.

The reservoir 12 has a generally parallelepiped and elongated shape, but may also have an angled corner, as shown in fig. 1 and 2. The reservoir 12 includes a rear longitudinal end 12a and a front longitudinal end 12b, the terms "rear" and "front" referring to the rear and front of the vehicle and its direction of travel. The reservoir also includes longitudinal side walls 12c.

In the example shown, the pump 20 and the syringe-mixer 10 are located at the rear end 12a of the reservoir 12.

The injector-mixer 10 is configured to inject a flow of liquefied gas forward to promote good mixing of the liquefied gas in the reservoir. In case the injected liquefied gas is to be subcooled, it will be cooler and therefore also heavier than the liquefied gas where it is injected, which proves to be reasonable to position slightly below the surface in the upper part of the reservoir and to orient slightly downwards at a small angle β to mix as much of the front of the reservoir as possible. This makes it possible to limit the recirculation of subcooled liquefied gas to the pump 20 and to limit the spray from the reservoir wall opposite the injector-mixer 10. Furthermore, since the subcooled liquefied gas has a density slightly greater than the liquefied gas in the reservoir and will therefore flow slowly downwards, injection at the top of the reservoir further facilitates mixing by diffusion due to gravity. Thus, when the reservoir is loaded, injection is sought just below the nominal liquid level, but sufficiently below the free surface, so as not to draw in gas from the top gas, in particular by the venturi effect.

The pump 20 and syringe-mixer 10 may be positioned substantially perpendicular to the "liquid dome" of the reservoir, which is schematically illustrated by the capital letter LD. In this case, the pump 20 and the injector-mixer 10 may be connected to the vertical pipe of a "pump tower". These conduits may then support the syringe 10.

Alternatively, the syringe-mixer 10 may be fixed to one side of the reservoir 12. Fig. 7 shows a more accurate example of the overall shape of a reservoir 12 for storing liquefied gas. The reservoir comprises longitudinal side walls 12c which are vertical and connected to a reservoir ceiling 16 and a reservoir bottom 14, respectively, by

inclined walls

12d, 12 e. The dimensions of the

walls

12c, 12d and 12e are variable, as schematically shown in fig. 9 and 10. In these figures, reference character H denotes the reservoir height described above, measured between the reservoir bottom 14 and the reservoir ceiling 16. H is, for example, greater than or equal to 15m, and may be, for example, 27m.

The reservoir 12 is generally of the membrane type, that is to say its

walls

12c, 12d and 12e and its bottom 14 are formed by a series of layers comprising, for example, a sheet metal film, an insulating layer and then the hull, from the inside towards the outside of the reservoir. In the connection regions of the

walls

12c, 12d and 12e, for example the regions indicated by the arrows in fig. 7, the reservoir is reinforced by a structure comprising a wooden block 30 and a metal reinforcement 32 made of a metal plate which is thickened compared to the metal plate used for the membrane.

The reinforcement 32 may form part of the membrane of the reservoir which is in contact with the liquefied gas contained in the reservoir. The reservoir may comprise a single membrane, the reinforcement 32 then forming part of this membrane, or the reservoir may comprise two membranes, respectively a primary membrane and a secondary membrane, between which a thermal insulation layer is placed, and the reinforcement 32 then forming part of this primary layer and thus intended to be in contact with the liquefied gas.

The wood block 30 may be located between the (primary) membrane of the reservoir and the hull of the vessel.

The syringe-mixer 10 of the device may be fixed to the reservoir 12 in such a connection region, for example in the connection region between the side wall 12c and the inclined wall 12d, as schematically shown in fig. 9 and 10.

As previously mentioned with respect to fig. 1 and 3, the injector-mixer 10 is positioned such that it can result in an optimal volume of mixture of liquefied gases in the reservoir. The power of the injector-mixer, that is to say the flow rate of the liquid flow which it can deliver, depends in particular on the power of the pump 20. Advantageously, the pump is a pump already fitted to the reservoir, in particular the above-mentioned pump tower, and therefore has a limited power, for example less than or equal to 100m3/h, for example less than or equal to 60m3/h.

The pump may be of the type having a variable speed and thus a variable flow rate. This in particular makes it possible for the power of the pump and thus the flow rate of the liquid flow injected by the injector-mixer to be matched to the volume of liquefied gas in the reservoir and thus to the filling level of the reservoir.

To remedy this and allow mixing of the total volume of liquefied gas in the reservoir, the reservoir may be equipped with a plurality of injector-mixers 10.

In all the concepts shown in fig. 9 to 20, that is to say in which the reservoir-mixer rod is located at the top of the reservoir, below the surface of the liquid, the injector-mixer is advantageously positioned close to the vertical wall of the reservoir, since one of the purposes is to prevent the rising of the LNG heated by the vertical wall. In practice, the LNG in the reservoir is heated near the vertical wall. As it becomes hotter than the surrounding LNG, it becomes lighter and therefore rises up the vertical wall. As shown in fig. 13, which is a top view of the reservoir, the annular space within the reservoir that is in contact with the vertical wall is where the heated LNG rises. Without the mixing device, the heated LNG reaches the surface and forms a warmer liquid layer at the surface, which preferably vaporizes, although the deep LNG is cooler than the surface LNG. This evaporation increases the pressure in the reservoir. Thus, positioning the injector(s) -mixer(s) rod in the liquid in the upper portion makes it possible to prevent the heated liquid from rising and to prevent a layer of hot liquid from forming on the surface.

Fig. 13 shows an exemplary reservoir 12 equipped with a plurality of injector-mixers 10, which are distributed in two horizontal rows on both longitudinal sides of the reservoir, respectively. Looking at the reservoir from above, reference LD denotes the liquid dome and reference GD denotes the gas dome of the reservoir. Line T1 represents the area of connection between the sloping wall 12d and the reservoir ceiling 16, while line T2 represents the area of connection between the sloping wall 12 and the side wall 12c. The injector-mixer 10 is evenly distributed over this area along the reservoir.

The syringe-mixers 10 of a reservoir or row may have similar or different orientations. In the embodiment of fig. 13, the two injector-mixers 10 located at the longitudinal ends of the reservoir on each row are oriented towards the bottom of the reservoir at an angle β min, for example, of 0 ° to 45 ° (fig. 12), preferably of 0 ° to 30 °, more preferably of 5 ° to 15 °. This angle makes it possible to mix as much liquefied gas as possible in the vicinity of the vertical transverse wall, since it is heated close to the liquefied gas and then rises towards the surface to form a vertical surface of the hot liquid layer, the formation of which should be avoided. The other injector-mixers located between the injector-mixers at the longitudinal end of the reservoir on each row are oriented towards the bottom of the reservoir at an angle β max which is greater than β min and is for example 45 ° to 90 °, preferably 70 ° to 90 °, more preferably 80 ° to 85 ° (fig. 11).

As can be seen in fig. 11 and 12, it is preferable to control the angle β so as to mix the least liquefied gas in the reservoir and the most liquefied gas in contact with the vertical wall. If the angle is too small and the injector-mixer injects the liquefied gas directly towards the center of the reservoir, the risk is to mix a large amount of central liquefied gas from the reservoir (schematically indicated by reference V). However, mixing large amounts of liquefied gas requires large pumping power, which can have the undesirable effect of reheating the liquefied gas and thus increasing the pressure in the reservoir more quickly.

In the case of fig. 11, the liquid surface layer is sucked up and discharged at a depth so that it mixes with the goods. The downward slope of the syringe-mixer 10 allows this liquid surface layer to be sucked up and mixed in small amounts. Injector-mixers located at the front and rear of the reservoir are oriented towards the center of the reservoir to prevent the rise of LNG heated by the vertical front and rear walls.

Fig. 14 illustrates a case where the syringe-mixer is oriented toward the top of the reservoir and does not allow a smaller amount of liquefied gas contained in the reservoir to be mixed. Due to the close proximity of the injector-mixer to the surface, the liquid layer is effectively destroyed, which advantageously reduces the power required to renew the surface layer of the liquid, but the low pumping power still risks heating the LNG remaining in the upper part of the reservoir. The position of the injector-mixer is advantageously possible thanks to the presence of the stiffening angle (the above-mentioned connection zone) between the vertical wall and the inclined upper wall. The injector-mixer is oriented towards the top of the reservoir at an angle β max greater than β min and for example, 0 ° to 60 °, preferably 0 ° to 30 °, more preferably 15 ° to 30 ° (fig. 14).

Fig. 15 and 16 show other cases where the first transverse row injector-mixer and the second transverse row injector-mixer located opposite the first row injector-mixer do not have the same orientation. In the case of fig. 15, the liquid layer is effectively destroyed due to the close proximity of the injector-mixer to the surface, which advantageously makes it possible to reduce the power required to renew the surface layer of this liquid, but the low pumping power still risks heating the LNG remaining in the upper part of the reservoir. The upwardly oriented first injector-mixer rod delivers liquefied gas toward a laterally opposite and horizontally oriented second injector-mixer rod that delivers it toward the first injector-mixer rod. The first injector-mixer is oriented towards the top of the reservoir at an angle β max that is greater than β min and is, for example, 0 ° to 60 °, preferably 15 ° to 60 °, more preferably 30 ° to 45 ° (fig. 15). The second injector-mixer is oriented towards the bottom of the reservoir at an angle β max greater than β min and for example between 0 ° and 30 °, and preferably between 0 ° and 15 ° (fig. 15). The volume of mixing appeared to be low. Working together the two rods helps to reduce the mixing power. In the case of fig. 16, the particularity compared to the case of fig. 15 consists in the orientation of the second injector-mixer rod, which is advantageously oriented downwards at an angle β, in order to discharge at a depth and mix the liquid surface layer with LNG coming from the colder bottom. β is comprised between β max, which is greater than β min and is for example 90 ° to 30 °, preferably 90 ° to 60 °, more preferably 85 ° to 75 ° (fig. 16). The volume of mixing appears to be low. The two rods working in cooperation contribute to a reduction of the mixing power and thus to a low pumping related heating.

However, injector-mixers 10 having different orientations may be associated with each other such that the entire volume of liquefied gas stored in the reservoir is effectively mixed and thus affected by the liquefied gas injected into the reservoir.

Figures 17 to 20 show a number of possible scenarios for supplying the injector-mixer. Fig. 17 shows a case where the rows on both sides are supplied in parallel. Fig. 18 shows a case where the rows on both sides are independently supplied. Fig. 19 shows the case where the reservoir includes one or more rows of supply tubes 34 through the reservoir wall, and fig. 20 shows the case where the reservoir includes one or more rows of supply tubes 34 that do not pass through the reservoir wall. The tubing 34 is then housed in a reservoir, together with the pump and syringe-mixer, to have a completely autonomous system. This is particularly interesting because in the case of a ship propelled with LNG, the regulations may require that the storage is isolated in case the ship or parts of the ship are damaged, whereas if the storage is isolated, the mixing system will not run anymore.

Fig. 4 to 6 show another aspect of the invention in which the gas injection means comprises at least one injector-mixer 10 located in the lower region of the reservoir 12, extending between 0% and 25% of the height of the reservoir measured from the bottom 14 of the reservoir.

In addition to the reservoir 12 and the injector-mixer 10, the liquefied gas storage device also comprises means for withdrawing gas, here in liquid form. The extraction means here comprise a pump 20 which is immersed in the liquefied gas and is preferably located at the bottom of the reservoir.

The liquefied gas may be withdrawn and injected into the same reservoir, or into another reservoir.

The pump 20 is connected to the injector-mixer 10 either directly or through a subcooling device 22. The supercooling means is, for example, of the type described above. The subcooling means may be configured to reduce the temperature of the liquefied gas pumped by the pump by about 10 ℃.

The reservoir 12 may be of the "full fill" type or of the "limited fill" type. In both cases, it may be left to fill with liquefied gas at the bottom of the reservoir, which represents at most 10% of the total internal volume of the reservoir. In the case of a fully filled reservoir, the reservoir may comprise any volume of liquefied gas.

The injection and mixing of the liquefied gas in the reservoir bottoming makes it possible to limit evaporation from the bottoming and to keep it at a low temperature for cooling before loading, without the need to cool the environment in the reservoir. Keeping the liquid bottom cold helps to reduce excess gas at the start of loading.

Injecting and mixing liquefied gas in a larger volume reservoir makes it possible to limit the risk of temperature stratification of the liquefied gas in the reservoir. Preferably, the mixing dynamics and the orientation of the liquid flow are ensured such that a sufficient mixing in the height direction of the reservoir can be ensured. In fact, the top gas naturally tends to stratify in temperature when there is less evaporation. That is, because it is light, hot gas accumulates at the top plate, which greatly reduces heat flow from the outside. Thus, cooling the environment in the reservoir (via return through the spray bar) increases the heat flow, and therefore a higher capacity of subcooling is required to compensate for the heat flow, which would represent a loss of energy and hence of liquefied gas. If the overhead gas temperature has stratified, even if the LNG is too cold, cooling the environment of the reservoir via return through the spray bars can cause the reservoir pressure to increase, as the dispersed LNG will vaporize upon cooling the insulation of the heated reservoir. Once the insulation has cooled, the injection of subcooled LNG will make it possible to control or even reduce the reservoir pressure. Thus, even in the case where the top gas has been warmed, injecting and mixing the liquefied gas in the remaining bottom of the reservoir makes it possible to immediately control/reduce the reservoir pressure.

Advantageously, the injector-mixer 10 is configured to inject a flow of liquefied gas in a direction inclined upwards at an angle α with respect to the horizontal plane (fig. 6). The angle α is, for example, 5 ° to 85 °, preferably 15 ° to 75 °, and more preferably 30 ° to 60 °.

As shown in fig. 4, 6, 21 to 24, 30 and 31 showing the reservoir, wherein the injection means is located at the bottom of the reservoir, it is preferred to control the angle alpha so that the mixing means is used in the ballasting condition (fig. 4, 23, 24 and 30) and the fully loaded condition (fig. 21, 22 and 30).

In the ballasting situation (the reservoir is almost empty), this configuration makes it possible to stir the liquid over most of the length of the reservoir (by a sufficiently small angle to achieve a greater distance, i.e. close to the horizontal). Too large an angle (i.e. close to the vertical) would cause liquid to be dispersed in the air gap, which would cool the gas and thus increase heat transfer. When using a supercooling means 22, too large an angle also causes a build-up of injected liquid in the vicinity of the injector and extraction means and the injected liquid is again extracted towards the supercooling means; there is a risk that the supercooled liquid is frozen.

In the fully loaded condition (the reservoir is almost full), a sufficiently large angle (i.e. close to the vertical) allows the liquid to be stirred over most of the height of the reservoir, so that the liquid temperature is uniform over the entire height of the liquid, thus making it possible to avoid a layer of hot liquid on the surface. Too small an angle (i.e. close to the horizontal) will not reach the surface of the liquid forming the hot liquid layer. When using a subcooling device, too small an angle would create an accumulation of injected liquid at the bottom of the reservoir and near the withdrawal device and allow the injected liquid to be withdrawn again towards the subcooling device; there is a risk that the supercooled liquid is frozen. In the case of a homogeneous subcooled liquid that can accumulate at the bottom of the reservoir, there is also a risk of sudden depressurization of the reservoir, which may open if the pressure drops below atmospheric pressure.

Still in the case of fig. 4, 6, 21 to 24, 30 and 31, the injected flow can advantageously be controlled according to the level of liquid in the reservoir. In an almost empty reservoir, the flow rate can be reduced to limit the power consumed by the extraction means, and the liquid is not dispersed in the air gap (which would cool the gas and thus increase the heat transfer). The flow rate may be increased in order to stir the liquid over a large part of the height of the reservoir in order to reach the surface and thus avoid forming a hot liquid layer on the surface. This flow rate control can be performed in various ways, for example by a variator of the extraction device or by a set of control valves.

This makes it possible to promote the mixing of the liquefied gas in the reservoir over substantially the entire height of the liquefied gas and over the greatest possible distance, as is schematically indicated by the arrows in fig. 4.

The reservoir 12 has a generally parallelepiped and elongated shape, and may also have beveled corners, as shown in fig. 4 and 5. The reservoir 12 includes a rear longitudinal end 12a and a front longitudinal end 12b.

In the example shown, the pump 20 and the syringe-mixer 10 are located at the rear end 12a of the reservoir 12. They may be positioned generally perpendicular to the liquid dome of the reservoir. In this case, the pump 20 and the injector-mixer 10 may be connected to the vertical pipe of a "pump tower". These conduits may then support the syringe 10.

As previously mentioned, the syringe-mixer 10 is positioned such that it can result in the most favorable in-reservoir conditionA mixture of a good volume of liquefied gas. The power of the injector-mixer, that is to say the flow rate of the liquid flow which it can deliver, depends in particular on the power of the pump 20. Advantageously, the pump is a pump already fitted to the reservoir, in particular a pump tower, and therefore has limited power, for example less than or equal to 100m ³ H, e.g. less than or equal to 60m ³ /h。

The pump may be of the type having a variable speed and therefore a variable flow rate. This in particular makes it possible for the power of the pump and thus the flow rate of the liquid flow injected by the injector-mixer to be matched to the volume of liquefied gas in the reservoir and thus to the filling level of the reservoir.

To remedy this and allow mixing of the total volume of liquefied gas in the reservoir, the reservoir may be equipped with a plurality of injector-mixers 10, as shown in fig. 13 and described previously.

As shown in fig. 21-24, which illustrate a fully filled or line-filled reservoir, the angle alpha is preferably controlled so as to mix the maximum amount of liquefied gas in the reservoir. If the angle alpha is too small and the injector-mixer injects the liquefied gas directly towards the bottom wall, there is a risk that not all of the liquefied gas in the reservoir can be mixed. The downward facing syringe-mixer may be combined with the upward facing syringe-mixer in the same reservoir (fig. 11-13 and 24).

Injector-mixers having different orientations may be associated with each other such that the entire volume of liquefied gas stored in the reservoir is effectively mixed and thus affected by the liquefied gas injected into the reservoir.

Thus, the orientation and number of injector-mixers 10 are therefore selected to promote good mixing of the liquefied gas in the reservoir, to limit recirculation of subcooled liquefied gas to the pump, and slightly upwards to limit the accumulation of heavier subcooled gas (temperature stratification of the liquid if the reservoir is full). Injection as close as possible to the bottom of the reservoir allows the injected liquefied gas to remain in the liquid at a lower filling level to limit as much as possible the cooling of the top gas (worst case injection would result in deformation of the free surface of the liquefied gas at the interface) and not to suck in gas, for example by venturi effect.

The apparatus of fig. 21 to 24 shows that the liquid withdrawal means (pump 20) can be connected to the syringe-mixer 10 by a conduit 34 and the assembly (including conduit 34) is located within the reservoir, which avoids having a wall penetration which can lead to tight sealing problems.

The conduit extends at least partially substantially parallel to and adjacent to the bottom wall of the reservoir and preferably to at least one side wall of the reservoir. In the case of the figures in which the pump is located at the centre and at the bottom of the reservoir, the conduit may extend in the opposite direction along the bottom wall of the reservoir up to the side wall of the reservoir. The conduit may be configured to match the specific shape of the bottom of the reservoir, in particular the shape of the connection bevel between the bottom and the side wall of the reservoir.

In the variant embodiment of fig. 25, the syringe(s) -mixer(s) rod in the upper part of the reservoir is combined with another rod in the lower part so that they can work together. That in the upper portion drains surface liquid to prevent a hot liquid layer from forming on the surface facing the injector located at the bottom of the reservoir. The liquid sucked in is the liquid in contact with the vertical wall so as to send it back to the first row of injectors. This forced circulation of liquid around the vertical walls and the surface makes it possible to prevent the formation of a liquid layer (since the liquid layer comprises LNG heated by the vertical walls).

In the variant embodiment of fig. 26, the syringe(s) -mixer(s) rod in the upper part of the reservoir is combined with another rod in the lower part so that they can work together. The one of the upper portions drains surface liquid toward the bottom to prevent a layer of hot liquid from forming on the surface facing the injector located at the bottom of the reservoir. This forced circulation of liquid around the vertical walls and the surface makes it possible to prevent the formation of a liquid layer (since the liquid layer comprises LNG heated by the vertical walls). In fact, the angle of the injectors makes it possible to effectively renew the liquid in contact with the vertical wall.

As previously mentioned, the two aspects of the invention may be combined together such that the same reservoir may be equipped with multiple injector-mixers, thus some oriented upwards and others downwards. In addition, the injector-mixer may be oriented more to the right or more to the left, that is to say more towards the front of the ship or more towards the back of the ship in the case of injector-mixers located on the longitudinal sides of the ship. Thus, a variety of positioning and orientation configurations of the injector-mixer of the reservoir are possible.

Fig. 1, 11-12 and 14 to 26 illustrate another advantage of the present invention.

The syringe-mixer 10 and possibly the pump 20 are positioned relative to each other and are configured to generate both a suction effect in the reservoir and a back pressure effect in the reservoir. These suction and backpressure effects result in a predetermined period of agitation of the liquefied gas in the reservoir, which is indicated by the arrows forming a closed loop.

The injector-mixer 10 itself can create a back pressure effect by injecting a liquefied gas and a suction effect due to the vacuum created in the injection zone. It should also be understood that the pump 20 may produce a pumping effect.

Advantageously, the agitation period is designed such that the liquefied gas circulates substantially parallel to and close to the liquid-gas interface in the reservoir. This makes it possible to limit the risk of forming a hot liquid layer at the interface and thus limit the risk of evaporation of the liquefied gas.

The natural convective motion of the liquefied gas completes the mixing cycle due to the temperature change of the liquefied gas in the reservoir. This is for example the case for very cold liquefied gases which are heavier than hot liquefied gases, which have a greater tendency to rise towards the liquid-gas interface in the reservoir. The liquefied gas may for example rise along the side walls of the reservoir, in particular when a brazing cycle takes place in the centre of the reservoir.

In fig. 11 and 12, injection downwards and at the side walls of the reservoir directly causes the discharge of liquefied gas downwards along these walls and indirectly (by induction) causes the suction of liquefied gas from the centre of the reservoir towards the centre of the reservoir and in particular towards the injector-mixer.

The observed effect is opposite to that of fig. 14. Injection upwards and at the side wall of the reservoir directly results in upward discharge of the liquefied gas and indirectly in suction of the liquefied gas from the centre of the reservoir towards the centre of the reservoir and in particular towards the injector-mixer.

In the case of fig. 15 and 16, the injector-mixer located on one side of the reservoir (on the left in the figure) is oriented upwards and delivers liquefied gas to the injector-mixer located on the opposite side, oriented downwards, and delivers liquefied gas to the other injector-mixer. The discharge of liquefied gas at the outlet of the injector-mixer creates a depression at the injector-mixer that attracts the liquefied gas discharged by the other injector-mixer, thus being a closed loop and therefore a concept of a stirring cycle.

As can be seen in fig. 21 to 26, the agitation cycle induced by the injector-mixer located on one side of the reservoir may be symmetrical or different from the agitation cycle induced by the injector-mixer located on the other side of the reservoir. In these figures, where the pump 20 is submerged, the pump 20 itself creates a pumping effect in the reservoir that actively participates in creating the agitation cycle. The pump can be located in the center of the reservoir and create a pumping effect which, in combination with the back pressure effect of the syringe-mixer located at the side of the reservoir, can cause a single agitation cycle in the reservoir (fig. 22 and 24, 26) or separate agitations on both sides of the reservoir (fig. 21 and 23).

Fig. 27 and 28 show a specific example of the injector-mixer 10. The injector-mixer 10 comprises a main duct 40 for the passage of a main jet 42 of liquid, and a secondary duct 44 coaxial to the main duct 40, the secondary duct 44 being intended to force a secondary jet 46 of liquid through by venturi effect at the outlet of the main duct 40. The

jets

42, 46 will then mix in the secondary duct 44 and these will be able to mix with the liquefied gas 48 at the outlet of the secondary duct 44, into which they are injected.

Examples of relationships between the flow rates of different jets are:

o main jet 42=1, for example 25m ³ /h，

o auxiliary jets 46=3 parts, e.g. 75m ³ /h，

o mixing

jets

42 and 46=4 parts, e.g. 100m ³ /h，

Liquefied gas drive flow rate 48=12 to 80 parts.

This example shows the efficiency of an injector-mixer with venturi effect, which allows a four-fold dilution of the flow rate of the supercooled liquid (without taking into account the induced flow). It further already allows mixing of the subcooled liquefied gas and limits the risk of accumulation (stratification) in the lower part of the reservoir, and the greater driving effect of the less dense, less viscous fluid compared to water.

As previously mentioned, the use of a variable flow pump or a more powerful pump will make it possible to increase the flow rate of the main jet and thus the unloading speed, and thus the range of the jet. However, increasing the flow too much may be counterproductive because more powerful pumps generate more heat, which may increase evaporation in the reservoir (e.g., the purpose of the subcooler is cooling). The pressure drop per bar between the main jet and the secondary jet may, for example, increase the range of the jet by about five meters.

FIG. 29 shows and summarizes various examples of applications of various aspects of the present invention.

The right part of the a-diagram illustrates the case without cooling and/or recondensing means between the extraction means (pump) and the injection means (injector-mixer):

a-1-when the reservoir is of limited fill type (LNGC type):

this concept is particularly relevant for storage of LNG carriers because the intermediate filling is unauthorized (10% to 70% unauthorized). Moreover, the phenomenon of forming a hot liquid layer with low filling (bottoming) is less feasible, and therefore the efficiency of the bottoming mixing system is lower.

Thus, the present invention includes one or more injector-mixer rods that are located in the liquid as close as possible to the liquid-gas interface.

The injector-mixer is located at the top of the reservoir in the liquid, near the interface, as the purpose is to refresh the layer of hot liquid at the interface. Thus, given a high reservoir height (up to 27m on LNG carriers), this positioning is most effective for reaching the water surface.

Considering the layer of hot liquid at the surface and the heat flow from the vertical walls, the distribution and orientation of the injector-mixer may make it possible not to mix the liquid core and thus to reduce the mixing power (since they do not participate in the formation of the layer of hot liquid), as described above.

Given this positioning of the injector-mixer (close to the surface), the pump can be of the variable flow type, in order to reduce the power and therefore the heat input generated by the mixing (and therefore increase the pressure rise time).

A-2-when the reservoir is of the full-fill type (LFS, FSRU, GBS, RT, LBV type):

the device includes a syringe-mixer located from the bottom thereof and oriented upward. The pump is ideally controlled so that the flow rate and supply pressure of the injector-mixer adapt as the surface approaches the mixer (i.e. the LNG level in the reservoir drops). This makes it possible to limit the cooling of the top gas and to avoid spraying the gas with an excessively large jet. Also, if the pump is variably controlled, the control will increase the pressure rise time and reduce the heat generation of the pump.

Especially for passenger ships, the device may be "self-contained", without any pipe protruding out of the reservoir. In fact, in case of damage (e.g. SOLAS SRTP = secure return port constraint and IGF code), then the reservoir must be automatically isolated (hence all valves at the intersection will automatically close). The time of the pressure rise should preferably be long enough to allow the ship and its passengers to return to the port without degassing the reservoir (SRTP constraint), or should be greater than 15 days (IGF-coding constraint).

B-left part of the figure illustrates the presence of cooling and/or recondensing means between the extraction means (pump) and the injection means (injector-mixer):

in each of the following concepts, the key principle sought is the ability to re-inject cold power (delivered by subcooled LNG) into the liquid rather than into the overhead gas.

In fact, re-injecting most of the cold power into the top gas will first cause a significant pressure drop due to the cooling of the top gas, and then the cooling of the insulated blocks of the reservoir will cause vaporization of the dispersed LNG, which will increase the pressure significantly during cooling. Finally, the cooling of the top gas will force a hot stream into the upper part of the reservoir and thus a large part of the LNG re-injected into the top gas will be unnecessarily vaporized, which will limit the cold power provided to the liquid. This is especially true because it will only distribute to the free surface of the liquid, which will result in slow diffusion kinetics.

In contrast, the present invention proposes to inject cold power directly into the liquid below the free surface to reduce the effect on the temperature and pressure of the top gas. Furthermore, injection below the free surface will produce a mixing and stirring effect by adjusting the hydrodynamics at the outlet of the return line, its orientation, its height, etc.

For these cases, it is not necessary to dispense the syringe-mixer into the reservoir in a uniform manner, since the aim is simply to dilute the injected liquid (and not reach the liquid-gas interface) with the liquid already present.

B-1-when the reservoir is full:

the reservoir is loaded (after loading and before unloading). The injection and mixing at the top of the reservoir promotes good mixing of the subcooled LNG with the stored LNG. In fact, the injected LNG is colder and heavier than the surrounding LNG, which proves to be reasonable to locate slightly below the surface in the upper part of the reservoir and to orient slightly downwards at a small angle a to mix as much of the front of the reservoir as possible. As a variant or additional feature, the injection of LNG can be carried out by means of a spray bar and can therefore be carried out in the top gas.

B-2-when the reservoir is empty or partially filled:

when the reservoir is empty (ballast stroke prior to loading) or at a medium level. Injection and mixing make it possible to cut off evaporation from the bottoms and to keep them cold for cooling before loading, without the need to cool the environment in the reservoir.

When the reservoir is partially loaded (after loading and before unloading), there is a risk of temperature stratification of the cold LNG. It is essential to ensure the mixing dynamics and orientation of the liquid streams such that sufficient mixing in the height direction of the reservoir can be ensured.

When there is less evaporation, the top gas naturally tends to stratify in temperature. That is, because of the lightness, hot gas accumulates at the reservoir ceiling, which greatly reduces heat flow from the outside. Thus, cooling the environment in the reservoir (via the spray bar) increases the heat flow and therefore requires the use of a higher capacity subcooling device to compensate for this flow, which will result in energy losses and hence loss of LNG. Simply dumping the LNG at the bottom of the reservoir without mixing would result in the risk of sucking in subcooled LNG, which would require stopping the subcooling device. Cooling the cold liquid bottoms helps to reduce excess gas at the start of loading.

When the reservoir is almost empty and incorporates the subcooling device 22, it is preferred for the reasons described above that the liquid at the bottom of the reservoir is injected directly into the retentate. However, with the angle α of the injector properly chosen, this injection system at the bottom of the reservoir can also be used when the reservoir is full (or nearly full). As shown in fig. 4, 6, 21 to 24, 30 and 31 showing the reservoir, wherein the injection means are located at the bottom of the reservoir, it is preferred to control the angle so that these injection means and thus the mixing means can be used in the ballasting condition (fig. 4, 23, 24 and 30) and in the fully loaded condition (fig. 21, 22 and 31).

In a ballasting situation (the reservoir is almost empty), this configuration makes it possible to stir the liquid over most of its length (by a sufficiently small angle to achieve a greater distance, i.e. close to the horizontal plane). Too large an angle (i.e. close to the vertical) can cause liquid to be dispersed in the air gap, which can cool the gas and thus increase heat transfer. When using a supercooling means 22, too large an angle also causes accumulation of injected liquid in the vicinity of the injector and the extraction means and extraction of the injected liquid again towards the supercooling means; there is a risk that the supercooled liquid is frozen.

In the fully loaded condition (the reservoir is almost full), a sufficiently large angle (i.e. close to the vertical) allows the liquid to be stirred over most of the height of the reservoir, so that the liquid temperature is uniform over the entire height of the liquid, thus making it possible to avoid a layer of hot liquid forming on the surface. Too small an angle (i.e. close to the horizontal) will not reach the surface of the liquid forming the hot liquid layer. When using a subcooling device, too small an angle would create an accumulation of injected liquid at the bottom of the reservoir and near the withdrawal device and allow the injected liquid to be withdrawn again towards the subcooling device; there is a risk that the supercooled liquid is frozen. In the case of a homogeneous subcooled liquid that can accumulate at the bottom of the reservoir, there is also a risk of sudden depressurization of the reservoir, which may open if the pressure drops below atmospheric pressure.

Claims

1. Liquefied gas storage device, in particular for liquefied gas vehicles or for land-based facilities, comprising:

-at least one liquefied gas storage reservoir (12) having a reservoir bottom (14) and a reservoir ceiling (16) together defining a reservoir height (H),

-means (20) for extracting gas in liquid and/or gaseous form from said at least one reservoir, and

-means (10) for injecting a gas in liquid form into the reservoir,

characterized in that said gas injection means comprise at least one injector-mixer (10) located in an upper region of said reservoir extending between 60 and 100% of the reservoir height, said reservoir height being measured from the reservoir bottom, and said injector-mixer being intended to be immersed in said liquefied gas contained in the reservoir.

2. The liquefied gas storage device according to claim 1, wherein the at least one injector-mixer (10) is configured to inject the liquid gas flow in a direction inclined downwards at an angle (β) with respect to the horizontal.

3. The liquefied gas storage device according to claim 2, wherein the angle (β) is 5 ° to 45 °, preferably 5 ° to 30 °, and more preferably 5 ° to 20 °.

4. The liquefied gas storage according to at least one of the preceding claims, wherein the at least one injector-mixer (10) is fixed to a wall of the reservoir (12).

5. The liquefied gas storage device according to at least one of the preceding claims, wherein the at least one injector-mixer (10) is positioned as close as possible to a longitudinal side wall (12 c) of the reservoir.

6. The liquefied gas storage device according to claim 5, wherein the reservoir comprises a vertical longitudinal side wall (12 c) connected to the reservoir ceiling (16) by an inclined wall (12 d), the at least one injector-mixer (10) being fixed to an area for connecting the vertical longitudinal wall to the inclined wall.

7. Liquefied gas storage device according to claim 6, wherein the at least one injector-mixer (10) is fixable to the thickened metal plate (32) and/or at least one wood block (30) of the connection area.

8. The liquefied gas storage device according to at least one of the preceding claims, wherein the injection means comprise at least one horizontal row of injector-mixers (10) configured to inject a flow of liquid gas in parallel or in different directions.

9. The liquefied gas storage device according to at least one of the preceding claims, wherein the injection means comprise at least two horizontal rows of injector-mixers (10) arranged on and/or along two longitudinal side walls (12 c) of the reservoir, respectively.

10. The liquefied gas storage device according to at least one of the preceding claims, wherein the gas injection means (10) is connected to means for withdrawing gas in the reservoir or another reservoir through re-liquefaction means (22).

11. The liquefied gas storage device according to claim 10, wherein the reliquefaction means (22) is configured to condense boil-off gas drawn from the or another reservoir and then pressurize by heat exchange with liquefied gas drawn from the or another reservoir.

12. The liquefied gas storage device according to at least one of claims 1 to 9, wherein the gas injection means (10) is connected to means (10) for liquid gas withdrawn from the reservoir or another reservoir by means of a subcooling means (22).

13. The liquefied gas storage device according to at least one of the preceding claims, wherein the extraction means (20) is configured to extract liquid gas from the lower region.

14. Liquefied gas storage device according to at least one of the preceding claims, the extraction means comprising at least one pump (20) located in the reservoir (12) or in another reservoir and intended to be submerged in the liquefied gas.

15. The liquefied gas storage device according to claim 14, wherein the pump (20) is configured to have a variable flow rate.

16. The liquefied gas storage device according to at least one of the preceding claims, wherein the reservoir (12) is of the "limited fill" type and is configured to be filled only to 10% and less, or 70% and more.

17. Liquefied gas storage device according to claim 16, wherein the injector-mixer (10) comprises a main conduit (40) for passing a main jet (42) of liquid and a secondary conduit (44) for forcing a secondary jet (46) of liquid through by venturi effect.

18. Liquefied gas storage according to claim 17, wherein the extraction means (20) and the injection means (10) are positioned perpendicular to a Liquid Dome (LD) of the reservoir (12), and are preferably equipped with a pump tower accessible through the liquid dome.

19. The liquefied gas storage device according to claim 18, wherein the at least one injector-mixer (10) is connected to and supported by a column of liquid of the pump tower.

20. Liquefied gas storage device according to at least one of the preceding claims, wherein the injector-mixer (10) comprises a main conduit (40) for passing a main jet (42) of liquid and a secondary conduit (44) for forcing a secondary jet (46) of liquid through the venturi effect.

21. The liquefied gas storage device according to at least one of the preceding claims, wherein the injection means (10) or even the extraction means (20) are positioned relative to each other and configured such that they create a back pressure and a suction effect in the reservoir, which effects create a predetermined stirring cycle of the liquefied gas in the reservoir.

22. Liquefied gas vehicle comprising at least one liquefied gas storage device according to at least one of the preceding claims, which is free of supercooling and reliquefaction means between the extraction means and injection means, the reservoir being of the "limited filling" type and being configured to be filled only to 10% and less or to 70% and more.

23. Liquefied gas vehicle comprising at least one liquefied gas storage device according to at least one of the preceding claims, comprising means of supercooling and/or reliquefaction between the extraction means and the injection means, the reservoir being of the "limited filling" type and being configured to be filled only to 10% and less or to 70% and more.

24. A method for injecting gas in liquid form into the reservoir of a vessel according to claim 22 or 23, wherein the injection into the upper region is performed when the "limited fill" reservoir is filled to 70% or more.

25. The method of claim 24, wherein the injection into the reservoir is configured to prevent heated liquefied gas from rising up a longitudinal sidewall of the reservoir.

26. The method of claim 24 or 25, wherein the injected liquefied gas has a temperature lower than the temperature of the liquefied gas contained in the reservoir.

27. Method according to one of claims 24 to 26, wherein the injection means (10) or even the extraction means (20) are controlled such that they create a back pressure and a suction effect in the reservoir, which effects create a predetermined stirring cycle of the liquefied gas in the reservoir.

28. A method according to claim 27, wherein the stirring period is designed such that the liquefied gas circulates substantially parallel to and close to a liquid-gas interface (18) in the reservoir.