FR3081967A1 - LIQUEFIED GAS STORAGE DEVICE - Google Patents

Abstract

Liquefied gas storage device, in particular for a liquefied gas maritime transport vessel or for a land installation, comprising: - at least one liquefied gas storage tank (12), which comprises a tank bottom and a ceiling tank which define between them a tank height, - means (20) for sampling gas, in liquid and / or gaseous form, in said tank, and - means (10) for injecting gas in liquid form in said tank tank, which are connected to said gas sampling means, characterized in that said gas injection means comprise at least one injector-mixer (10) which is located in a lower zone of said tank extending between 0 and 25 % of the tank height measured from said tank bottom, or in an upper zone of said tank extending between 75 and 100% of the tank height measured from said tank bottom, and which is intended to be immersed in said tank liquefied gas contained in s the tank.

Description

LIQUEFIED GAS STORAGE DEVICE

TECHNICAL AREA

The invention relates in particular to a device for storing liquefied gas, in particular for a liquefied gas maritime transport vessel or for a land installation.

STATE OF THE ART

In order to more easily transport gas, such as natural gas, over long distances, the gas is generally liquefied (to become liquefied natural gas - LNG) by cooling it to cryogenic temperatures, for example -160 ° C at atmospheric pressure. The liquefied gas is then loaded into maritime transport vessels, such as LNG carriers and bunkering vessels.

In order to limit the evaporation of the liquefied gas contained in a tank of a ship, it is known to store it under pressure in this tank so as to move on the liquid-vapor equilibrium curve of the liquefied gas considered, thus increasing its vaporization temperature. The liquefied gas can thus be stored at higher temperatures, which has the effect of limiting the evaporation of the gas.

Natural evaporation of the gas is however inevitable, this phenomenon being called NBOG which is the acronym of the English Natural Boil-Off Gas (as opposed to the forced evaporation of gas or FBOG, acronym of the English Forced Boil- Off Gas). The gas which evaporates naturally in the tank of a ship is generally used to supply an installation for the production of energy of the ship, which is intended to supply the energy needs of the operation of the ship, in particular for the propulsion of the ship and / or the production of electricity for on-board equipment.

In the current technique, the improvements in the tanks are such that the natural evaporation rates (BOR - acronym for the Boil-Off Rate) of the liquefied gases are increasingly low, while the machines of a ship are increasingly more efficient. This has the consequence that the difference is very large between the quantity of gas naturally produced by evaporation and that required by the installation of a ship. The excess gas is particularly important when the consumption of the ship is low, that is to say for example when the slowed down ship, is in the waiting phase, or in a damaged situation such as processing or consumption equipment. gas is no longer available.

The excess naturally produced evaporation gas (NBOG) is then recondensed and reinjected into the tank. For this, re-liquefaction or re-condensation means are used, which transform the NBOG into liquefied gas which is then reinjected into the tank.

It is also possible to decrease the production of NBOG by lowering the temperature of the gaseous overhead contained in the tank above the liquid-gas interface in the tank. For this, it is possible to take liquefied gas, to cool it (or to sub-cool it because it is already very cold), then to reinject it into the tank by means of spraying liquefied gas in the gaseous sky.

This allows the pressure in the tank to be controlled by re-condensing BOG in the gaseous air (first objective). This also makes it possible to control the temperature of the liquefied gas in order to deliver cold LNG (second objective). Indeed, within the framework of an LNG carrier or a bunkering vessel, a maximum temperature of LNG to be delivered may be required by the terminal or receiving vessel.

The first objective responds mainly to the LNG transfer operation between several storage facilities of the same installation and / or between several storage facilities of several installations, in order to condense the excess gas generated during the LNG transfer operation, and this in order to complete the transfer within a given time. The first objective can also meet the need for a loaded or almost empty tank (if the goal is to control the pressure).

The second objective responds to the request of the supported vessel to receive relatively cold LNG in order to maintain a safety margin compared to the safety valves. After the bunker loading operation, the charterer will therefore wish to keep its cargo as cold as possible, or even cool its cargo in order to respect its contract with the LNG-powered vessel. He will therefore use his sub-cooling equipment to cool the LNG and not to drop the pressure.

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

STATEMENT OF THE INVENTION

According to a first aspect, the invention proposes a device for storing liquefied gas, in particular for a vessel for the maritime transport of liquefied gas or for a land installation, comprising:

- at least one liquefied gas storage tank, which comprises a tank bottom and a tank ceiling which define between them a tank height,

means for taking gas, in liquid and / or gaseous form, from said tank, and

- means for injecting gas in liquid form into said tank, which are connected to said means for withdrawing gas, characterized in that said means for injecting gas comprise at least one injector-mixer which is located in a lower zone of said tank extending between 0 and 25%, preferably between 0 and 15%, and more preferably between 0 and 10%, of the tank height measured from said tank bottom, and which is intended to be immersed in said liquefied gas contained in the tank.

Preferably, said at least one injector-mixer is configured to inject a flow of liquid gas in a direction which is inclined upwards by an angle oc relative to a horizontal plane. Said angle oc can be between 5 ° and 45 °, preferably between 5 and 30 °, and more preferably between 5 and 20 °.

According to a second aspect, the invention proposes a device for storing liquefied gas, in particular for a vessel for the maritime transport of liquefied gas or for a land installation, comprising:

- at least one liquefied gas storage tank, which comprises a tank bottom and a tank ceiling which define between them a tank height,

means for withdrawing gas, in liquid and / or gaseous form, from said at least one tank, and

- means for injecting gas in liquid form into said tank, characterized in that said gas injection means comprise at least one injector-mixer which is located in an upper zone of said tank extending between 60 and 100 % or even between 75 and 100%, preferably between 60 and 98%, and more preferably between 65 and 95%, or even more preferably between 65 and 80% or between 80 and 95%, of the tank height measured from said bottom tank, and which is intended to be immersed in said liquefied gas contained in the tank.

Preferably, at least one injector-mixer is configured to inject a flow of liquid gas in a direction which is inclined downward by an angle β relative to a horizontal plane. Said angle β can be between 5 ° and 45 °, preferably 5 and 30 °, and more preferably between 5 and 20 °.

Advantageously, said at least one injector-mixer is fixed to a wall of said tank. Preferably, said tank has a vertical lateral longitudinal wall connected by a bias wall to said tank ceiling, said at least one injector-mixer being fixed to a connection zone of said vertical longitudinal wall to said bias wall. Said at least one injector-mixer can be fixed to a thickened sheet and / or to at least one wooden block of said connection zone. This sheet can be part of a membrane of the tank and therefore be, as is the case with the membrane, in contact with the liquefied gas contained in the tank (in the presence of liquefied gas in the tank, or at least in l 'no leak). The block of wood can be located between this membrane and the hull of the ship.

In each of the above aspects, the key principle sought is to be able to re-inject liquefied gas, which is pre-cooled or not, in the liquid and not in the gaseous overhead contained in the tank. In fact reinjecting the majority of the cold power into the gaseous head will have the effect of a significant drop in pressure, and the cooling of the gaseous head which will force the flow of heat entering the upper part of the tank. A significant part of the liquefied gas reinjected into the gaseous air would then be unnecessarily vaporized, which would limit the cold power supplied to the liquid. Especially since this will be distributed only to the free surface of the liquid, which would cause the kinetics of diffusion to be slow. On the contrary, the invention proposes to reinject the cold power directly into the liquid under the free surface in order to reduce the influence on the temperature and the pressure of the gaseous sky. In addition, injecting liquefied gas under the free surface makes it possible to create a mixing and stirring effect by varying the kinetics of the liquid at the outlet of the injector-mixer, its orientation, its elevation, etc.

The invention also relates to the case where the liquefied gas is not necessarily sub-cooled before its injection into the tank. The essential function of injecting liquefied gas would then be to mix the liquefied gas contained in the tank. This is particularly useful for limiting the evaporation of the liquefied gas, in particular when sub-cooled liquefied gas is poured into the bottom of the tank, this sub-cooled liquefied gas being obtained by reliquefaction of evaporation gas. Forced evaporations from the tank are much richer in nitrogen compared to the naturally evaporating liquid (due to the volatility of nitrogen compared to methane). The evaporated gas is liquefied by means of reliquefaction and returned to the bottom of the tank. The condensate is therefore much heavier than the surrounding liquefied gas (because it is richer in nitrogen, but also colder). The liquid rich in nitrogen accumulates at the bottom of the tank. As it warms up naturally, nitrogen bubbles vaporize and rise to the surface, which enriches the gaseous sky with nitrogen. Nitrogen is difficult to condense, which reduces the capacity of the liquefier and causes difficulties in controlling the pressure of the tanks. The phenomenon is amplified when the tank is almost empty because the nitrogen bubbles do not have time to re-dissolve during the ascent to the surface. It is for this reason that injection by the spray bars at the top of the tank is never considered with this type of equipment, due to the risk of nitrogen enrichment. In almost empty tank use, this phenomenon generates heel aging which limits the ability of the heel to cool the tanks before the next load.

The invention also relates to the case where the liquefied gas is overheated before being injected into the tank. The injection of liquefied gas would then have the essential function of being mixed with the liquefied gas contained in the tank. This is particularly useful for limiting the evaporation of said superheated liquefied gas, in particular when it is poured into the bottom of the tank. Said superheated liquefied gas being hotter therefore lighter than the surrounding liquefied gas (colder), this liquefied gas would evaporate without a mixing device, even when injected at the bottom of the tank. Indeed, being lighter, it would rise in the surrounding liquid colder therefore heavier, until evaporating when its static pressure would become lower than its bubble pressure. This is particularly true in the case where the liquid level is low in the tank because the static pressure at the bottom of the tank is lower compared to a higher liquid level. The use of a mixing device by venturi effect, suction, entrainment, etc., is particularly suitable for the injection of said superheated liquefied gas because it allows a dilution of at least 4 times. This superheated liquefied gas is obtained by recondensation (i.e. mixing) of pressurized evaporating gas with liquefied gas from a tank. The superheated liquefied gas is normally vaporized for injection into the terrestrial gas network. If the terrestrial gas network requests the vaporization unit to stop sending on the network, the superheated liquefied gas can then be returned to the tank via the mixing device while limiting the natural evaporation of the gas stored in tank. Without a mixing device, the evaporations generated by the injection into the tank of said superheated liquefied gas generate additional evaporations which are added to the natural evaporations which must then be recondensed to be reinjected into the tank. This results in accelerated heating of the liquefied gas contained in the tanks and therefore a faster rise in pressure compared to the use of a mixing device.

The injection of liquefied gas is carried out here by means of an injector-mixer which is configured to inject a flow of liquid gas and cause it to mix with the liquid in which it is injected by venturi effect, suction, entrainment, etc.

The device according to the invention may include one or more of the following characteristics, taken in isolation from one another or in combination with each other:

- Said at least one injector-mixer is located as close as possible to a longitudinal side wall of said tank; in the present application, the term "nearest" or "near" means a distance less than one meter, and preferably less than or equal to 0.5 meters, or even less,

said injection means comprise at least one horizontal row of injector (s) -mixer (s) which are configured to inject flows of liquid gas in parallel or different directions,

said injection means comprise at least two horizontal rows of injector-mixers disposed respectively on and / or along two longitudinal side walls of said tank,

- said gas injection means are connected by means of reliquefaction to means for withdrawing boiling gas from said tank or from another tank,

- said reliquefaction means are configured to recondense evaporation gas taken from said tank or from another tank and then pressurized, by heat exchange with liquefied gas taken from said tank or from another tank,

- said gas injection means are connected by means of sub-cooling to means for withdrawing liquid gas from said tank or from another liquefied gas storage tank,

said sampling means are configured to take liquid gas from said lower zone,

said sampling means comprise at least one pump and pipes situated in said tank or in another tank and intended to be at least partly immersed in said liquefied gas,

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

- said tank is of the "all filling" type and is configured to be filled at any level,

- said tank is of the “restricted filling” type and is configured to be filled only to 10% and less, or to 70% and more,

- said sampling means and said injection means are located in said tank and connected to each other by pipes located entirely in the tank,

- the pipes extend at least partly substantially parallel and close to a bottom wall of the tank, and preferably up to at least one side wall of this tank,

- in the case where the sampling means are located in the center and at the bottom of the tank, pipes can extend in opposite directions along the bottom wall and up to the side walls of the tank,

- the pipes can be configured to match the specific shape of the tank bottom and in particular of possible connecting chamfers between the bottom and side walls of the tank.

- said sampling means and said injection means are located in line with a liquid dome of said tank, and preferably equip a pumping tower accessible by this liquid dome,

said at least one injector-mixer is connected to a column of liquid from said pumping tower, and supported by this column,

said injector-mixer comprises a main pipe for the passage of a main jet of liquid, and a secondary pipe for forced passage of a secondary jet of liquid by the venturi effect,

- Said injection means, or even also said withdrawal means, are positioned with respect to each other and configured so that they generate discharge and suction effects in the tank, these effects generating a cycle of predetermined mixing of the liquefied gas in the tank.

The present invention also relates to a liquefied gas maritime transport vessel, comprising at least one device as described above, this device being devoid of sub-cooling and reliquefaction means between said withdrawal and injection means, said tank being of the "all filling" type and being configured to be filled at any level.

The present invention further relates to a liquefied gas maritime transport vessel, comprising at least one device as described above, this device comprising sub-cooling and / or reliquefaction means between said sampling and injection means. , said tank being of the “all filling” or “limited filling” type.

The present invention also relates to a liquefied gas maritime transport vessel, comprising at least one device as described above, this device being devoid of sub-cooling and reliquefaction means between said withdrawal and injection means, said tank being of the “restricted filling” type and being configured to be filled only to 10% and less, or to 70% and more.

The present invention further relates to a liquefied gas maritime transport vessel, comprising at least one device as described above, this device comprising sub-cooling and / or reliquefaction means between said sampling and injection means. , said tank being of the “restricted filling” type and being configured to be filled only to 10% and less, or to 70% and more.

The present invention also relates to a method for injecting gas in liquid form into a tank of a ship as described above, in which the injection into the lower zone takes place when the tank "with limited filling" is 10% full or less.

The present invention also relates to a method for injecting gas in liquid form into a tank of a ship as described above, in which the injection into the upper zone takes place when the tank "with limited filling" is 70% or more filled.

The present invention also relates to a method for injecting gas in liquid form into a tank of a ship as described above, in which the injection into the tank is configured to prevent the rise of heated liquefied gas along longitudinal side walls of this tank.

The present invention also relates to a method for injecting gas in liquid form into a tank of a ship as described above, in which the injected liquefied gas has a temperature lower than that of the liquefied gas contained in said tank.

Advantageously, said injection means, or even also said withdrawal means, are controlled so that they generate discharge and suction effects in the tank, these effects generating a predetermined mixing cycle of the liquefied gas in the tank. The brewing cycle is advantageously designed so that liquefied gas circulates substantially parallel to the liquid-gas interface in the tank, and near this interface. This limits the risk of formation of a hot liquid layer at the interface, and therefore of evaporation of the liquefied gas.

In the present application, the following definitions mean:

- "tank", any tank having an internal liquefied gas storage volume greater than 100m ³ , and preferably greater than 1000m ³ , see 10 000m ³ , see 20 000m ³ ; and / or any tank configured to store liquefied gas at a temperature of -163 ° C or less,

- tank of the "all filling" type, a tank which is configured to store any volume of liquefied gas, which can for example represent 50% of its total internal volume; a vessel of the FSRU (Floating Storage Regasification Unit), ST (Shore Tank), GBS (Gravity Base Structure), LBV (LNG Bunker Vessel), LFS (LNG Fueled Ship) type is generally equipped with such a vessel,

- tank of the “restricted filling” type, a tank which is configured to store a volume of 10% and less, and 70% and more, of liquefied gas; it is thus not designed to store an intermediate volume of liquefied gas, representing for example 50% of its total internal volume, in particular for safety reasons, which is the case of an LNG tanker which is capable of be subject to transport conditions during a journey which may cause wave movements of the liquefied gas in the tank; an LNGC type vessel (LNG carrier) is generally equipped with such a tank,

- a "vessel", any liquefied gas marine transport unit, such as an LNG carrier, a bunkering vessel, etc.,

- "reliquefaction means" or "recondensation means", means configured to cause the condensation of gas and therefore the transformation of this gas into liquefied gas, the gas generally being BOG or NBOG; they may for example include means for compressing gas at temperature and pressure conditions allowing its condensation,

- "sub-cooling" means, means configured to cool the liquefied gas further, which is generally already at a temperature of -163 ° C. or even less, the sub-cooling making it possible for example to reduce the temperature of the liquefied gas d 'about 10 °; sub-cooling means for example comprise means for evaporating or vaporizing liquefied gas to generate refrigerating energy, and means for exchanging heat with liquefied gas so that the latter is sub-cooled by this energy,

- the concepts of "top" and "bottom" or "upper" and "lower" are assessed in relation to the conventional position, that is to say the operation of a ship when it is set down and floats on the water, and more generally in relation to the center of the earth (the top being further away from the bottom of the center of the earth).

BRIEF DESCRIPTION OF THE FIGURES

The invention will be better understood and other details, characteristics and advantages of the present invention will appear more clearly on reading the description which follows, given by way of nonlimiting example and with reference to the appended drawings, in which:

FIG. 1 is a schematic view in longitudinal section of a first embodiment of a device for storing liquefied gas according to the invention,

FIG. 2 is a schematic view in cross section of the device in FIG. 1,

- Figure 3 is an enlarged view of part of Figure 1,

FIG. 4 is a schematic view in longitudinal section of a second embodiment of a device for storing liquefied gas according to the invention,

FIG. 5 is a schematic cross-sectional view of the device in FIG. 4,

FIG. 6 is a view on a larger scale of part of FIG. 4,

FIG. 7 is a schematic perspective view in section of a liquefied gas storage tank,

FIG. 8 is a schematic perspective view of a zone for connecting the walls of a tank, such as that of FIG. 7,

FIGS. 9 and 10 are very schematic partial views of tanks having different geometries,

- Figures 11 and 12 are very schematic sectional views of alternative embodiments of the device according to the invention, Figure 9 showing a sectional view of the middle of this device, and Figure 10 showing a sectional view of each end longitudinal of this device,

FIG. 13 is a very schematic top view of an alternative embodiment of the device according to the invention,

- Figures 14 to 26 are very schematic sectional views of alternative embodiments of the device according to the invention,

FIGS. 27 and 28 are schematic views, respectively in section and in perspective, of an exemplary embodiment of an injector-mixer, and

- Figure 29 is a block diagram illustrating several embodiments of a ship and a method according to the invention.

DETAILED DESCRIPTION

As mentioned in the above, the temperature and pressure in a liquefied gas (LNG) storage tank can be controlled to control in particular the production of NBOG in the tank.

A liquefied gas storage device, in particular for a liquefied gas maritime transport vessel, generally comprises:

- at least one liquefied gas storage tank,

means for taking gas, in liquid and / or gaseous form, from the tank, and

- means for injecting gas in liquid form into the tank, which are connected to the means for withdrawing gas.

As part of the first objective mentioned above, the gaseous sky is cooled by sub-cooled LNG spraying booms. LNG is withdrawn by the withdrawal means, is sub-cooled by sub-cooling means, then is injected by the ramps (injection means) at the top of the tank. Spraying directly impacts the temperature and pressure of the gaseous sky by maximizing the exchange surface between the droplets and the gas in order to condense it.

In practice, two spraying booms are conventionally available and identical: they are generally used simultaneously to carry out the initial cooling, while a single boom makes it possible to carry out the normal cooling (ballast) before loading.

If this device is used for a full tank, the sub-cooled LNG is sprayed mainly on the liquid-gas interface, which is unsuitable if one wishes to impact the temperature of the liquid over the entire height of the tank and therefore all the volume of liquid.

If one or two ramps are used in the event of ballast (tank with liquid heel), the temperature of the gaseous sky (including the ceiling) is therefore very cold (close to equilibrium = Dew temperature) and the heat flow through the insulation from the outside is therefore increased. Without spraying of sub-cooled gas by means of the ramps, the gaseous sky stratifies significantly in temperature (hotter gas is concentrated at the top and colder gas is concentrated at the bottom), which reduces evaporation, and therefore the cold power necessary to control the pressure and the temperature in the tank.

As part of the second objective, which is to control or even cool the stored LNG, the ideal would be to re-inject sub-cooled LNG into the tank. However, the sub-cooled LNG would be returned directly to the tank without being mixed with the LNG already present in the tank. In addition, the LNG sub-cooled by around 10 ° would be heavier than the LNG in the tank and would have difficulty mixing with the latter. In the event that the sub-cooled LNG is reinjected at the bottom of the tank, it would concentrate at the bottom of the tank and it could be directly re-sampled by the abovementioned sampling means, which would adversely affect the efficiency of the sub-cooling. Indeed, this would amount to taking LNG already sub-cooled and whose sub-cooling would tend to over-cool the LNG because the outlet temperature of the sub-cooling means is limited in order to avoid freezing of the LNG (mainly heavy compounds). Therefore, it would be necessary to reduce the instantaneous power of the sub-cooling means. However, in order not to limit this power (and to avoid the recirculation of sub-cooled LNG) and to reduce the electrical consumption of the equipment (avoid cooling the gaseous sky), the invention proposes to inject the sub-cooled LNG cooled under the liquid-gas interface and via at least one injector-mixer.

Figures 1 to 3 illustrate one aspect of the invention in which the gas injection means comprise at least one injector-mixer 10 which is located in an upper zone of the tank 12 extending between 60 and 100% of the tank height measured from the tank bottom 14. The tank height 12 is measured between the tank bottom 14 and the tank ceiling 16. The reference 18 designates the liquid-gas interface or the free surface of the liquefied gas in the tank, the liquid formed by the liquefied gas being heavier and therefore under the gaseous sky which is formed by natural evaporation of the liquefied gas.

In addition to the tank 12 and the injector-mixer 10, the liquefied gas storage device comprises means for withdrawing gas, here in liquid form. The sampling means here comprise a pump 20 immersed in the liquefied gas and preferably located at the bottom of the tank. The liquefied gas can be taken and injected into the same tank, or into a different tank.

The pump 20 is connected to the injector-mixer 10, directly or by means of sub-cooling means 22. The sub-cooling means can be configured to decrease the temperature of the liquefied gas withdrawn by the pump, about 10 °.

The tank 12 can be of the “all filling” type or of the “restricted filling” type. In both cases, when it is filled with liquefied gas (and does not include only a heel of liquefied gas at the bottom of the tank), it is filled to at least 70% of its volume. In practice, it is filled to a volume of 95% or more, and preferably 98.5%.

The injector-mixer 10 is positioned and designed to inject liquefied gas withdrawn (and possibly sub-cooled) under the interface 18, so that the flow of liquefied gas mixes the liquefied gas contained in the tank 12.

Advantageously, the injector-mixer 10 is configured to inject a flow of liquefied gas in a direction which is inclined downward by an angle β relative to a horizontal plane (Figure 3). The angle β is for example between 0 ° and 45 °, preferably between 0 ° and 30 °, and more preferably between 5 ° and 30 °.

This makes it easier to mix the liquefied gas in the tank, over substantially the entire height of the liquefied gas and over the greatest possible distance, as is schematically represented by the arrows in FIG. 1.

In the case of an injection of sub-cooled or superheated liquefied gas, that is to say coming from a sub-cooling equipment or a recondensor presented above, the injector (s) - mixer (s) can advantageously be fixed on the pumping tower.

The tank 12 has a generally parallelepiped and elongated shape, but can also be chamfered, as shown in FIGS. 1 and 2. The tank 12 comprises a rear longitudinal end 12a and a front longitudinal end 12b, the terms rear and front referring to aft and forward of the transport vessel and its direction of travel. The tank further comprises longitudinal side walls 12c.

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

The injector-mixer 10 is configured to inject a flow of liquefied gas towards the front so as to promote good mixing of the liquefied gas in the tank. In the case where the injected liquefied gas is sub-cooled, it would be colder and therefore heavier than that in which it is injected, which justifies the positioning in the upper part of the tank, slightly below the surface and slightly oriented downwards. and a relatively small angle β for maximum mixing of the front of the tank. This makes it possible to limit the recirculation of sub-cooled liquefied gas towards the pump 20, and the watering of the tank wall opposite to the injector-mixer 10. Furthermore, the injection at the top of the tank promotes even more the mixing by gravity diffusion the fact that the sub-cooled liquefied gas has a density slightly higher than that in the tank and therefore it will flow slowly downwards. An injection just below the nominal liquid level when the tank is loaded will therefore be sought, but sufficiently below the free surface so as not to suck gas from the gas overhead, in particular by venturi effect.

The pump 20 and the injector-mixer 10 can be located substantially in line with a "liquid dome" of the tank, schematically represented by the capital letters LD (acronym for Liquid Dome). In this case, the pump 20 and the injector-mixer 10 can be connected to vertical pipes of a "pumping tower", known under the English name "pump tower". These lines can then support the injector 10.

Alternatively, the injector-mixer 10 can be attached to one side of the tank

12. Figure 7 shows a more specific example of the general shape of a liquefied gas storage tank 12. This tank comprises a longitudinal side wall 12c which is vertical, and which is connected by walls 12d, 12e at an angle, respectively to the tank ceiling 16 at the bottom of the tank 14. The dimensions of the walls 12c, 12d and 12e are variable, as shown diagrammatically in FIGS. 9 and 10. In these drawings, the reference H designates the tank height mentioned above, and measured between the tank bottom 14 and the tank ceiling 16. H is for example greater than or equal to 15m, and can be 27m for example.

The tank 12 is generally of the membrane type, that is to say that its walls 12c, 12d and 12e as well as its bottom 14 are formed by a succession of layers comprising for example, from the inside of the tank towards the exterior, a sheet metal membrane, an insulator, a sheet metal membrane, an insulator and then the ship's hull. In the connection zones of the walls 12c, 12d and 12e, such as the zone identified by the arrow in FIG. 7, the tank is reinforced by structures comprising wooden blocks 30 and metal reinforcements 32 made of sheet metal which is thickened by compared to the sheet used for the membranes.

The reinforcements 32 can be part of the membrane of the tank which is in contact with the liquefied gas contained in the tank. The tank may comprise a single membrane and the reinforcements 32 then form part of this membrane, or else the tank comprises two membranes, respectively primary and secondary, between which an insulating layer is disposed, and the reinforcements 32 then form part of the primary layer and are therefore intended to be in contact with the liquefied gas.

The block of wood 30 can be located between the membrane (primary) of the tank and the hull of the ship.

The injector-mixer 10 of the device can be fixed to the tank 12 in such a connection zone, such as that between the side wall 12c and the bias wall 12d, as is schematically represented in FIGS. 9 and 10.

As mentioned in the foregoing in relation to FIGS. 1 to 3, the injector-mixer 10 is positioned so that it can cause an optimal volume of liquefied gas to be mixed in the tank. The power of the injector-mixer, that is to say the liquid flow rate that it can deliver, depends in particular on the power of the pump 20. Advantageously, this pump is the one already fitted to the tank and in particular the aforementioned pumping tower and therefore has a limited power, for example less than or equal to 100 m ³ / h, and for example less than or equal to 60 m ³ / h.

The pump could be of the speed and therefore variable flow type. This makes it possible in particular to adapt the power of the pump and therefore the flow rate of the liquid flow injected by the injector-mixer to the volume of liquefied gas in the tank and therefore to the filling level of the tank.

To remedy this and allow mixing of the total volume of liquefied gas in the tank, it is possible to equip the tank with several injector-mixers 10.

In all the concepts illustrated in FIGS. 9 to 20, that is to say in which the injector - mixer ramps are located at the top of the tank, under the liquid surface, the injector - mixers are advantageously positioned close to the walls vertical of the tank, because one of the objectives is to prevent the LNG heated by the vertical walls from rising. In fact, the LNG in the tank is heated near the vertical walls. Then becoming hotter than the surrounding LNG, it becomes lighter and therefore rises along the vertical walls. As shown in Figure 13 which is a top view of a tank, the annular space inside the tank, in contact with the vertical walls is the location of the heated LNG. Without a mixing device, the heated LNG reaches the surface and forms a warmer liquid layer on the surface, which evaporates preferentially, despite the fact that deep LNG is cooler than surface LNG. This evaporation increases the pressure in the tank. The positioning of the injector (mixer) ramps in the liquid in the upper part therefore makes it possible to prevent the rising of the heated liquid and the formation of the hot liquid stratum on the surface.

FIG. 13 shows an example of a tank 12 equipped with several injector-mixers 10 which are distributed in two horizontal rows respectively on the two longitudinal sides of the tank. This tank is seen from above, the reference LD designating the liquid dome and the reference GD designating the gas dome of the tank. The line T1 represents the connection zone between the bias wall 12d and the tank ceiling 16, and the line T2 represents the connection zone between this bias wall 12 and the side wall 12c. Injector-mixers 10 are regularly distributed over this zone, along the tank.

The injector-mixers 10 of a tank or a row can have similar or different orientations. In the embodiment of Figure 13, the two injector-mixers 10 located at the longitudinal ends of the tank on each row, are oriented towards the bottom of the tank, at an angle βιτιίη, for example between 0 and 45 ° (Figure 12), preferably between 0 ° and 30 °, and more preferably between 5 ° and 15 °. This angle makes it possible to mix the most liquefied gas close to the vertical transverse wall because it is near the vertical surfaces that the liquefied gas heats up then rises towards the surface to form the hot liquid stratum which it is desired to avoid the formation. The other injector-mixers located between those located at the longitudinal ends of the tank of each row, are oriented towards the tank bottom, at an angle βιτίΒχ, which is greater than βιτιίη, and for example between 45 and 90 °, preferably between 70 ° and 90 °, and more preferably between 80 ° and 85 ° (Figure 11).

As seen in Figures 11 and 12, it is preferable to control the angle β so as to mix the minimum of liquefied gas in the tank, and the maximum of liquefied gas in contact with the vertical walls. If the angle is too small and the injector-mixers inject liquefied gas directly towards the center of the tank, the risk is to mix a large central volume of liquefied gas from the tank, schematically designated by the reference V. Or, mixing a large volume of liquefied gas requires significant pumping power, which would have the unintended effect of heating the liquefied gas and therefore increasing the pressure of the tank more quickly.

In the case of Figure 11, the liquid surface layer is sucked up and pushed back in depth in order to mix it with the cargo. The inclination of the injector-mixers 10 downwards makes it possible to aspirate this surface liquid stratum and to mix a small volume. The injector-mixers located at the front and at the rear of the tank are oriented towards the center of the tank in order to prevent the rising of LNG heated by the front and rear vertical walls.

FIG. 14 illustrates a case where the injector-mixers are oriented towards the top of the tank and do not allow a lower volume of liquefied gas contained in the tank to be mixed. The liquid layer is effectively broken due to the proximity of the injector-mixers with the surface, which advantageously makes it possible to reduce the power necessary for the renewal of this surface liquid layer, but the low pumping power still risks heating the LNG which remains in the upper part of the tank. The position of the injector-mixers is advantageously made possible due to the presence of the reinforced angle (connection zone described above) between the vertical wall and the upper oblique wall. The injector mixers are oriented towards the top of the tank, at an angle pmax, which is greater than βιτιίη, and for example between 0 and 60 °, preferably 0 ° and 30 °, and more preferably 15 ° and 30 ° (figure 14).

FIGS. 15 and 16 illustrate other cases where the injector-mixer of a first lateral row, and the injector-mixer of the second lateral row and located opposite the injector-mixer of the first row, n don't have the same orientations. In the case of FIG. 15, the liquid layer is effectively broken due to the proximity of the injector-mixers with the surface, which advantageously makes it possible to reduce the power necessary for the renewal of this surface liquid layer but the low pumping power risks all the same to reheat the LNG which remains in the upper part of the tank. A first ramp of injector-mixers oriented upwards discharges liquefied gas towards the second ramp of injector-mixers opposite laterally and oriented horizontally which discharges it towards the first ramp of injector-mixers. The first injector mixers are oriented towards the top of the tank, at an angle pmax, which is greater than βιτιίη, and for example between 0 and 60 °, preferably between 15 ° and 60 °, and more preferably between 30 ° and 45 ° (figure 15). The second injector-mixers are oriented towards the bottom of the tank, at an angle βιτίΒχ, which is greater than βιτιίη, and for example between 0 and 30 °, and preferably between 0 ° and 15 ° (Figure 15). The mixed volume seems low. The two ramps operating in concert promotes lower mixing power. In the case of FIG. 16, the peculiarity with respect to the case of FIG. 15 is the orientation of the second ramp of injector-mixers, which is advantageously oriented towards the bottom by an angle β in order to push back in depth and to mix the liquid surface layer with the LNG from the cooler bottom, β is between βιτίΒχ, which is greater than βιτιίη, and is for example between 90 and 30 °, preferably between 90 ° and 60 °, and more preferably between 85 ° and 75 ° (Figure 16). The mixed volume seems small. The two ramps operating in concert promotes lower mixing power and therefore low heating due to pumping.

However, injector-mixers 10 having different orientations can be associated with each other so that the entire volume of liquefied gas stored in a tank is effectively mixed and therefore impacted by the liquefied gas injected into the tank.

Figures 17 to 20 illustrate several possibilities for supplying injector-mixers. Figure 17 illustrates the case where the rows on both sides are fed in parallel. Figure 18 illustrates the case where the rows on both sides are supplied independently. FIG. 19 illustrates the case where the tank comprises one or more rows of which the supply lines 34 pass through a wall of the tank, and FIG. 20 illustrates the case where the tank comprises one or more rows of which the supply lines 34 do not pass through the wall of the tank. The lines 34 are then housed, with the pump and the injector-mixers, in the tank, so as to have a completely autonomous system. This is particularly interesting because, in the case of ships powered by LNG, the code may require isolating the tank in the event of damage to the ship or part of the ship and the mixing system would then no longer be operational if the tank was insulated.

FIGS. 4 to 6 illustrate another aspect of the invention in which the gas injection means comprise at least one injector-mixer 10 which is located in a lower zone of the tank 12 extending between 0 and 25% of the tank height measured from the tank bottom 14.

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

The liquefied gas can be taken and injected into the same tank, or into a different tank.

The pump 20 is connected to the injector-mixer 10, directly or by means of sub-cooling means 22. The sub-cooling means are for example of the aforementioned type. The sub-cooling means can be configured to reduce the temperature of the liquefied gas taken off by the pump, by about 10 ° C.

The tank 12 can be of the “all filling” type or of the “restricted filling” type. In both cases, it can be filled with a heel of liquefied gas at the bottom of the tank, representing at most 10% of the total internal volume of the tank. In the case of a full filling tank, this tank may include any volume of liquefied gas.

The injector-mixer 10 is positioned and designed to inject liquefied gas withdrawn (and possibly sub-cooled) under the interface 18, so that the flow of liquefied gas mixes the liquefied gas contained in the tank 12.

By injecting and mixing liquefied gas into the heel of a tank, it is possible to limit evaporation from the heel and keep it cold for cooling before loading, without cooling the atmosphere of the tank. Keeping a liquid liquid heel reduces excess gas when loading begins.

By injecting and mixing liquefied gas into a larger volume of a tank, the risk of temperature stratification of the liquefied gas in the tank is limited. It is preferable to ensure that the mixing kinetics and the orientation of the liquid flow make it possible to ensure sufficient mixing in the height direction of the tank. Indeed, the gaseous sky naturally tends to stratify in temperature when there is less evaporation. That is, the hot gas collects at the ceiling because it is lighter, which greatly reduces the heat flow from the outside. Cooling the atmosphere of the tank (via a return by spraying booms) would therefore increase the heat flow and would therefore require using the higher capacity sub-cooling to compensate for the heat flow, which would represent a loss of energy and therefore of liquefied gas.

Advantageously, the injector-mixer 10 is configured to inject a flow of liquefied gas in a direction which is inclined upward by an angle oc relative to a horizontal plane (FIG. 6). The angle oc is for example between 5 ° and 45 °, preferably between 5 and 30 °, and more preferably between 5 and 20 °.

This makes it easier to mix the liquefied gas in the tank, over substantially the entire height of the liquefied gas and over the greatest possible distance, as is schematically represented by the arrows in FIG. 4.

The tank 12 has a generally parallelepipedic and elongated shape, and can be chamfered as can be seen in FIGS. 4 and 5. The tank 12 comprises a rear longitudinal end 12a and a front longitudinal end 12b.

In the example shown, the pump 20 and the injector-mixer 10 are located at the rear end 12a of the tank 12. They can be located substantially in line with the liquid dome of the tank. In this case, the pump 20 and the injector-mixer 10 can be connected to vertical pipes of the pumping tower. These lines can then support the injector 10.

As mentioned in the above, the injector-mixer 10 is positioned so that it can cause an optimal volume of liquefied gas to be mixed in the tank. The power of the injector-mixer, that is to say the liquid flow rate that it can deliver, depends in particular on the power of the pump 20. Advantageously, this pump is the one already fitted to the tank and in particular the pumping tower and therefore has a limited power, for example less than or equal to 100 m ³ / h, and for example less than or equal to 60 m ³ / h.

The pump could be of the speed and therefore variable flow type. This makes it possible in particular to adapt the power of the pump and therefore the flow rate of the liquid flow injected by the injector-mixer to the volume of liquefied gas in the tank and therefore to the filling level of the tank.

To remedy this and allow mixing of the total volume of liquefied gas in the tank, it is possible to equip the tank with several injector-mixers 10, as illustrated in FIG. 13 and described in the foregoing.

As seen in Figures 21 to 24 which illustrate full tanks, it is preferable to control the angle oc so as to mix the maximum amount of liquefied gas in the tank. If the angle oc is too large and the injector-mixers inject liquefied gas directly towards the bottom wall, the risk is of not mixing all the liquefied gas from the tank. Downward-facing injector-mixers can be combined in the same tank with upward-facing injector-mixers (Figures 11-13 and 24).

Injector-mixers with different orientations can thus be associated with each other so that the entire volume of liquefied gas stored in a tank is effectively mixed and therefore impacted by the liquefied gas injected into the tank.

The orientations and the number of injector-mixers 10 are therefore chosen to promote good mixing of the liquefied gas in the tank, limit the recirculation of sub-cooled liquefied gas towards the pump, and slightly upwards to limit the accumulation of gas. sub-cooled which is heavier (stratification in liquid temperature if the tank is filled). The injection as close as possible to the bottom of the tank allows the injected liquefied gas to remain in the liquid with low filling, to limit as much as possible the cooling of the gaseous sky (at worst, the injection will cause a deformation of the free surface of the gas liquefied at the interface), and not to suck gas by venturi effect for example.

The devices in FIGS. 21 to 24 show that the means for withdrawing liquid (pump 20) can be connected to the injector mixers 10 by lines 34, and the assembly (including the lines 34) is located inside the tank. , which avoids having wall crossings liable to generate sealing problems.

The pipes extend at least in part substantially parallel and close to the bottom wall of the tank, and preferably up to at least one side wall of this tank. In the case illustrated in the drawings where the pump is located in the center and at the bottom of the tank, the pipes can extend in opposite directions along the bottom wall and up to the side walls of the tank. The pipes can be configured to match the specific shape of the tank bottom and in particular that of the connecting chamfers between the bottom and side walls of the tank.

In the alternative embodiment of FIG. 25, a ramp of injector (s) mixer (s) in the upper part of the tank is combined with another ramp in the lower part so that they can operate in concert. The upper part discharges the surface liquid in order to prevent the formation of a hot liquid layer on the surface towards the injectors positioned at the bottom of the tank. The liquid sucked is the liquid in contact with the vertical wall to return it to the first injector rail. This forced circulation of the liquid around the vertical walls and the surface makes it possible to prevent the formation of a liquid layer (because the surface liquid layer consists of LNG heated through the vertical walls).

In the alternative embodiment of FIG. 26, a ramp of injector (s) mixer (s) in the upper part of the tank is combined with another ramp in the lower part so that they can operate in concert. The upper part pushes the surface liquid towards the bottom in order to prevent the formation of a hot liquid layer on the surface towards the injectors positioned at the bottom of the tank. This forced circulation of the liquid around the vertical walls and the surface makes it possible to prevent the formation of a liquid layer (because the surface liquid layer consists of LNG heated through the vertical walls). Indeed, the angle of the ejectors makes it possible to efficiently renew the liquid in contact with the vertical walls.

As mentioned in the foregoing, the two aspects of the invention can be combined so that the same tank can be equipped with several injector-mixers, therefore some are oriented upwards and others are directed downwards. The injector-mixers can also be oriented more to the right or more to the left. Several configurations of positions and orientations of the injector-mixers of a tank are thus possible.

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

The injector-mixers 10, and possibly the pumps 20, are positioned in relation to each other and configured so as to generate both suction effects in the tank and discharge effects in the tank. These suction and discharge effects cause a predetermined mixing cycle of the liquefied gas in the tank, which is illustrated by the arrows forming closed loops.

The injector-mixers 10 can alone generate a discharge effect by injection of liquefied gas and a suction effect due to the vacuum created in the injection zone. It will also be understood that the pumps 20 can generate a suction effect.

The brewing cycle is advantageously designed so that liquefied gas circulates substantially parallel to the liquid-gas interface in the tank, and near this interface. This limits the risk of formation of a hot liquid layer at the interface, and therefore of evaporation of the liquefied gas.

The natural convective movements of liquefied gas, due to temperature variations of the liquefied gas in the tank, complete this brewing cycle. This is for example the case of very cold liquefied gas which is heavier than hotter liquefied gas, the latter tending to rise towards the liquid-gas interface in the tank. This liquefied gas can rise, for example, along the side walls of the tank, in particular when a brazing cycle takes place in the center of the tank.

In FIGS. 11 and 12, the injection downwards and at the level of the side walls of the tank directly cause the backflow of liquefied gas down these walls, and indirectly (by induced effect) the suction of gas liquefied from the center of the tank to the walls and in particular to the injector-mixers.

The effects observed are opposite in FIG. 14. The injection upwards and at the level of the side walls of the tank directly causes the backflow of liquefied gas upwards, and indirectly the suction of liquefied gas from the center of the tank towards the walls and in particular towards the injector-mixers.

In the case of FIGS. 15 and 16, the injector-mixers located on one side of the tank, on the left in the drawings, are oriented upwards and discharge liquefied gas towards the injector-mixers located on the opposite side, which are they face downwards and deliver liquefied gas to the other injector-mixers. The discharge of liquefied gas at the outlet of the injector mixers creates depressions at the level of the injector-mixers which attract the liquefied gas discharged by the other injector-mixers, hence the concept of closed loop and therefore of brewing cycle.

As can be seen in Figures 21 to 26, the brewing cycles induced by the injector-mixers located on one side of the tank can be symmetrical or different from those generated by the injector-mixers located on the other side of the tank . In these figures where the pump 20 is submerged, it itself generates a suction effect in the tank which actively participates in the creation of the brewing cycle. The pump can be located in the center of the tank and generate a suction effect which, combined with the discharge effects of the injector-mixers located on the sides of the tank, can induce a single brewing cycle in the tank (Figures 22 and 24-26) or separate brewing cycles on both sides of the tank (Figures 21 and 23).

FIGS. 27 and 28 show a particular example of a injector-mixer 10. This injector-mixer 10 comprises a main pipe 40 for passing a main jet 42 of liquid, and a secondary pipe 44 coaxial with the main pipe 40 for the forced passage a secondary jet 46 of liquid by venturi effect at the outlet of the main pipe 40. The jets 42, 46 then mix in the secondary pipe 44 and these jets will then mix with the liquefied gas 48 into which they are injected, at the outlet of the secondary pipe 44.

An example of a relationship between the flow rates of the different jets is: o main jet 42 = 1 part, for example 25m ³ / h, o secondary jet 46 = 3 parts, for example 75m ³ / h, o mixture of jets 42 and 46 = 4 parts, for example 100m ³ / h, o liquefied gas entrainment rate 48 = 12 to 80 parts.

This example shows the efficiency of a venturi injector-mixer, which allows a four-fold dilution of the sub-cooled liquid flow (without considering the induced flow). It also already allows a mixture of the sub-cooled liquefied gas and limits the risk of accumulation (stratification) in the lower part of the tank, and the more significant knock-on effect with a less dense and less viscous fluid than the water.

The use of a variable flow pump or a more powerful pump, as mentioned above, would increase the flow of the main jet but also the speed of unloading and therefore the range of the jet. However, it would be counterproductive to excessively increase this flow because a more powerful pump would generate more heat (or the purpose of the subcooler is to cool). Each pressure drop bar between the main jet and the secondary jet can for example increase the range of the jet by about five meters.

FIG. 29 illustrates and summarizes several examples of application of the various aspects of the invention.

A- The right part of the drawing illustrates the cases for which there are no cooling and / or recondensation means between the withdrawal means (pump) and the injection means (injector-mixer):

A-1- When the tank is of the limited filling type (LNGC type):

This concept is particularly relevant for LNG tanker storage because intermediate filling is not authorized (10% to 70% not authorized). What is more, the phenomenon of formation of the hot liquid stratum with low filling (heel) is unlikely, therefore a mixing system on heel is less effective.

The invention therefore consists of one or more injector-mixer ramps located in the liquid as close as possible to the liquid-gas interface.

The injector-mixers are at the top of the tank, in the liquid, close to the interface because the objective is to renew the hot liquid layer at the interface. This positioning is therefore the most effective for reaching the surface given a large tank height (up to 27m on LNG carriers).

Considering the hot liquid stratum on the surface and the heat fluxes coming from the vertical walls, a distribution and an orientation of the injector-mixers can make it possible not to mix the core of the liquid and therefore reduce the mixing power (because not participating in the formation of the hot liquid stratum), as in the above.

Given this positioning of the injector-mixers (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 mixture (and therefore increase the rise time in pressure).

A-2- When the tank is of the full filling type (LFS, FSRU, GBS, RT, LBV type):

The device includes injector-mixers positioned at the bottom of the tank and oriented upwards. The pump is ideally controlled so that the flow rate and supply pressure of the injector-mixers are adapted as the surface approaches the mixers (i.e. the LNG level drops in the tank). This limits the cooling of the gaseous head and avoids watering the gas due to an overly powerful jet. What is more, if the pump is variably controlled, this control increases the pressure build-up time and reduces the heating of the pump.

Particularly for passenger ships, the device can be "autonomous" without any outlet of pipes outside the tank. Indeed, in case of damage (example of the SOLAS SRTP constraint = Safe Return To Port), the tank must be automatically isolated (all the valves at the bushings are therefore automatically closed). The pressure build-up time should preferably be long enough to allow the ship and its passengers to return to port without degassing the tank.

B- The left part in the drawing illustrates the cases for which there are cooling and / or recondensation means between the withdrawal means (pump) and the injection means (injector-mixer):

In each of the concepts below, the key principle sought is to be able to reinject the cold power (transported by sub-cooled LNG) into the liquid and not into the gaseous sky.

In fact, reinjecting the majority of the cold power into the gaseous head will first have a significant drop in pressure, the cooling of the gaseous head which will force the flow of heat entering the upper part of the tank. A significant part of the LNG reinjected into the gaseous sky will then be unnecessarily vaporized, which would limit the cold power supplied to the liquid. Especially since this will be distributed only to the free surface of the liquid, which would cause the kinetics of diffusion to be slow.

On the contrary, the invention proposes to reinject the cold power directly into the liquid under the free surface in order to reduce the influence on temperature and the pressure of the gaseous sky. In addition, injecting under the free surface will create a mixing and stirring effect by playing on the kinetics of the liquid at the outlet of the return line, its orientation, its elevation etc.

For these cases, it is not necessarily necessary to distribute the injector-mixers homogeneously in the tank because we are simply trying to dilute the injected liquid with the liquid already present (and not to reach the liquid-gas interface).

B-1- When the tank is filled:

The tank is loaded (after loading and before unloading). The injection and mixing at the top of the tank promotes good mixing of the sub-cooled LNG with the stored LNG. Indeed, the injected LNG is colder therefore heavier than the surrounding one, which justifies the positioning in the upper part of the tank slightly below the surface and slightly oriented downwards with an angle a relatively small to mix the front as much as possible. of the tank. As a variant or additional characteristic, the injection of LNG could take place via the spray bars, therefore in the gaseous sky.

B-2- When the tank is empty or partially filled:

When the tank is empty (ballast trip before loading) or at an intermediate filling level. The injection and the mixture allow to cut the evaporations of the heel, to keep it cold for the cooling before loading without cooling the atmosphere of the tank.

When the tank is partially loaded (after loading and before unloading), there is a risk of temperature stratification of cold LNG. It will be necessary to ensure that the mixing kinetics and the orientation of the liquid flow allow sufficient mixing in the height direction of the tank.

The gaseous sky naturally tends to stratify in temperature the less there is evaporation. That is to say that the hot gas accumulates at the level of the tank ceiling because it is lighter, which greatly reduces the heat flux coming from the outside. Cooling the atmosphere in the tank (via the spray bars) would therefore increase the heat flow and would therefore require the use of higher capacity sub-cooling means to compensate for the flow, which would generate energy losses and therefore LNG. The simple pouring of LNG at the bottom of the tank, without mixing, risks causing suction of the sub-cooled LNG, which would require stopping the sub-cooling means. Cooling the cold liquid heel reduces excess gas at the start of loading.

Claims (28)

1. Liquefied gas storage device, in particular for a liquefied gas maritime transport vessel or for a land installation, comprising: - at least one tank (12) for liquefied gas storage, which comprises a tank bottom (14) and a tank ceiling (16) which define between them a tank height (H), means (20) for withdrawing gas, in liquid and / or gaseous form, from said at least one tank, and - means (10) for injecting gas in liquid form into said tank, characterized in that said gas injection means comprise at least one injector-mixer (10) which is located in an upper zone of said tank s 'extending between 60 and 100% of the tank height measured from said tank bottom, and which is intended to be immersed in said liquefied gas contained in the tank. 2. Device according to the preceding claim, wherein said at least one injector-mixer (10) is configured to inject a flow of liquid gas in a direction which is inclined downward by an angle β relative to a horizontal plane. 3. Device according to the preceding claim, wherein said angle β is between 5 ° and 45 °, preferably between 5 and 30 °, and more preferably between 5 and 20 °. 4. Device according to one of the preceding claims, wherein said at least one injector-mixer (10) is fixed to a wall of said tank (12). 5. Device according to one of the preceding claims, wherein said at least one injector-mixer (10) is located closest to a longitudinal side wall (12c) of said tank. 6. Device according to the preceding claim, wherein said tank has a vertical longitudinal side wall (12c) connected by a bias wall (12d) to said tank ceiling, said at least one injector-mixer (10) being fixed to a zone connecting said longitudinal side wall to said bias wall. 7. Device according to the preceding claim, wherein said at least one injector-mixer (10) is fixed to a thickened sheet (32) and / or to at least one wooden block (30) of said connecting zone. 8. Device according to one of the preceding claims, in which said injection means comprise at least one horizontal row of injector mixers (10) which are configured to inject flows of liquid gas in parallel or different directions. 9. Device according to one of the preceding claims, wherein said injection means comprise at least two horizontal rows of injector-mixers (10) disposed respectively on and / or along two longitudinal side walls (12c) of said tank . 10. Device according to one of the preceding claims, in which said means (10) for injecting gas are connected by means of reliquefaction (22) to means for withdrawing boiling gas from said tank or from another tank. 11. Device according to the preceding claim, wherein said reliquefaction means (22) are configured to recondense evaporation gas taken from said tank or from another tank and then pressurized, by heat exchange with liquefied gas taken from said tank. or in another tank. 12. Device according to one of claims 1 to 9, in which said means (10) for injecting gas are connected by means of subcooling (22) to means (20) for withdrawing liquid gas from said tank or in another liquefied gas storage tank. 13. Device according to one of the preceding claims, in which said withdrawal means (20) are configured to withdraw liquid gas from said lower zone. 14. Device according to one of the preceding claims, in which said sampling means comprise at least one pump (20) located in said tank (12) or in another tank and intended to be immersed in said liquefied gas. 15. Device according to the preceding claim, wherein said pump (20) is configured to have a variable flow. 16. Device according to one of the preceding claims, in which said tank (12) is of the “restricted filling” type and is configured to be filled only with a volume of 10% and less, or with a volume of 70% and more. 17. Device according to the preceding claim, wherein said withdrawal means (20) and said injection means (10) are located in said tank (12) and connected to each other by conduits (34) located entirely in the tank. 18. Device according to the preceding claim, wherein said sampling means (20) and said injection means (10) are located in line with a liquid dome (LD) of said tank, and preferably equip a pumping tower accessible through this liquid dome. 19. Device according to the preceding claim, wherein said at least one injector-mixer (10) is connected to a column of liquid from said pumping tower, and is supported by this column. 20. Device according to one of the preceding claims, in which said injector-mixer (10) comprises a main pipe (40) for passing a main jet of liquid (42), and a secondary pipe (44) for forced passage a secondary jet (46) of liquid by venturi effect. 21. Device according to one of the preceding claims, in which said injection means (10), or also also said withdrawal means (20), are positioned with respect to each other and configured so that they generate discharge and suction effects in the tank, these effects generating a predetermined stirring cycle of the liquefied gas in the tank. 22. Liquefied gas maritime transport vessel, comprising at least one device according to one of the preceding claims, this device being devoid of sub-cooling and / or reliquefaction means between said withdrawal and injection means, said tank. being of the "restricted filling" type and being configured to be filled only to a volume of 10% or less, or to a volume of 70% and more. 23. Liquefied gas maritime transport vessel, comprising at least one device according to one of claims 1 to 21, this device comprising means for sub-cooling and / or reliquefaction between said means of sampling and injection, said tank being of the “restricted filling” type and being configured to be filled only to a volume of 10% and less, or to a volume of 70% and more. 24. A method of injecting gas in liquid form into a tank of a ship according to claim 22 or 23, wherein the injection in the upper zone takes place when the tank, preferably "limited filling", is filled at a volume of 70% and more. 25. Method according to the preceding claim, wherein the injection into the tank is configured to prevent the rise of heated liquefied gas along the longitudinal side walls of this tank. 26. The method of claim 24 or 25, wherein the injected liquefied gas has a temperature lower than that of the liquefied gas contained in said tank. 27. Method according to one of claims 24 to 26, in which said injection means (10), or also also said withdrawal means (20), are controlled so that they generate backflow effects and suction in the tank, these effects generating a predetermined stirring cycle of the liquefied gas in the tank. 28. Method according to the preceding claim, wherein the stirring cycle is designed so that liquefied gas circulates substantially parallel to the liquid-gas interface (18) in the tank, and near this interface.