KR102462361B1 - Liquefied gas cooling method - Google Patents

Abstract

The present invention relates to a method for cooling a liquefied gas (8) stored in the interior space of a sealed and insulated vessel (2), wherein the liquefied gas (8) is brought into the container in a state of two-phase liquid-gas equilibrium. A lower liquid phase and an upper gas phase stored in the internal space of (2) and separated by an interface, the method comprising:
- introducing a stream stream of gaseous gas into an area of the gaseous phase in contact with the area of the interface; In the step of introducing the flow stream of the gaseous gas, the vaporization of the liquid phase is promoted in the region of the interface region, and the liquefied gas in contact with the region of the interface surface, the liquefied gas is the liquid-gas equilibrium of the liquefied gas at atmospheric pressure creating a sub-atmospheric pressure (P1) in the region of the gas phase to be in a two-phase liquid-gas equilibrium having a temperature lower than the temperature; and
- inducing the flow stream drawn into the gas phase into the circuit 13 for utilization of the gas phase gas
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Description

Liquefied gas cooling method

The present invention belongs to the field of cooling of gases stored in liquefied form, and in particular relates to the cooling of fuel gases such as liquefied natural gas (LNG).

Liquefied natural gas is stored cryogenically in sealed and insulated vessels. These vessels may be part of a land-based storage facility or installed on a floating structure such as an LNG carrier, for example.

The insulating barriers of a storage vessel of liquefied natural gas are inevitably the site of a thermal flux that tends to reheat the contents of the vessel. This reheating is converted to an increase in the enthalpy of the contents of the vessel, resulting in some or all of the cargo deviating from its equilibrium near atmospheric pressure. This increase in enthalpy thus tends to result in vaporization of liquefied natural gas and loss of stored natural gas in liquid form.

In order to limit the increase in enthalpy of liquefied natural gas, the insulation of the vessel is routinely improved. However, although the thermal insulation performance of the vessel tends to improve, the reheat rate of liquefied natural gas remains significant.

Of course, it is known in the prior art to utilize the gas resulting from natural gasification to supply energy to equipment using natural gas as a fuel. Thus, for example in an LNG carrier, the vaporized gas is used to energize a group of propulsion engines enabling the vessel to propel or an electric generator assembly that supplies the electricity necessary for the functioning of the on-board equipment. However, while this method may make the vaporized gas valuable in the vessel, it does not make it possible to control the vaporization rate of the liquefied gas, or to preserve the gas in a thermodynamic state that allows it to be stored in a durable manner. In addition, methods are known to utilize liquefaction systems for reliquefying excess vaporized gas, but such liquefaction systems are of low efficiency.

One idea on which the present invention is based is a method for cooling a liquefied gas and a method of cooling a liquefied gas that allows improved control of the natural vaporization of the liquefied gas while preserving most of the liquefied gas in a thermodynamic state that allows it to be stored in a durable manner. It is to propose a facility for storage and cooling.

According to one embodiment, the present invention provides a method for cooling a liquefied gas stored in the interior space of a sealed and insulated container; The liquefied gas is stored in the inner space of the container in a two-phase state of liquid-gas equilibrium and has a lower liquid phase and an upper gas phase separated by an interface, the method comprising:

- introducing a stream stream of gaseous gas into an area of the gaseous phase in contact with the area of the interface; In the step of introducing the flow stream of the gaseous gas, the vaporization of the liquid phase is promoted in the region of the interface region, and the liquefied gas in contact with the region of the interface surface, the liquefied gas is the liquid-gas equilibrium of the liquefied gas at atmospheric pressure creating a sub-atmospheric pressure (P1) in the region of the gas phase to be in a two-phase liquid-gas equilibrium having a temperature lower than the temperature; and

- Inducing the flow stream introduced into the gas phase into a circuit for utilization of the gas phase

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This method therefore makes it possible to take full advantage of the vaporization of the gas intended to supply energy to equipment consuming the gas in the gaseous phase to cool the liquefied gas stored in the container by removing the latent heat of vaporization from the liquefied gas.

In addition, by placing the interior space of the vessel at an absolute pressure lower than atmospheric pressure, the liquefied gas stored in the vessel can be cooled to a temperature lower than its equilibrium vaporization temperature at atmospheric pressure. Thus, the liquefied gas can be maintained in an undercooled thermodynamic state while maintaining a low or zero vaporization rate of the liquefied gas while allowing storage in or transfer to the vessel at atmospheric pressure. . Thus, this method enables better control of the vaporization of liquefied natural gas. Therefore, the loss of cargo is reduced and thus the financial value of the cargo is increased.

Also, thanks to this method, the vaporization of liquefied gas, which is intended to supply energy to equipment that consumes gas in the gaseous phase, differs from forced vaporization installations using seawater, intermediate liquid or heat exchange with combustion gases from engine systems or specific burners. It can be realized without the help of an external heat source. However, in some embodiments it is possible that such an external heat source is provided in a supplementary manner.

According to other advantageous embodiments, this cooling method may have one or more of the following characteristics:

- The pressure (P1) is absolutely higher than 120 mbar. It is in fact essential that the pressure inside the vessel is higher than the pressure corresponding to the triple point of the phase diagram of methane in order to prevent condensation of the natural gas inside the vessel.

- the pressure P1 can in particular be between 750 mbar and 980 mbar absolute.

- the inlet of the stream stream of gas in the gaseous phase is achieved by means of a vacuum pump;

- According to one embodiment, the vacuum pump is controlled as a function of the flow rate setpoint generated by the circuit for the use of gaseous gas.

- According to another embodiment, the pressure is measured in the region of the gas phase and the vacuum pump is controlled as a function of the pressure setpoint and the measured pressure.

- According to one embodiment, the vessel comprises a multi-layer structure mounted on a transport structure, said multi-layer structure comprising a sealing membrane in contact with the liquefied gas contained in the vessel and an insulating barrier disposed between the sealing membrane and the transport structure wherein the insulating barrier comprises insulating blocks and a vapor phase, the method comprising maintaining the vapor phase of the insulating barrier at a pressure P2 equal to or less than a pressure P1.

- according to one embodiment, said multilayer structure comprises, from the outside to the inside of the vessel, insulating blocks laid against the transport structure and a secondary insulating barrier comprising gas phase, a secondary sealing laid against insulating blocks of the secondary insulating barrier. A primary insulating barrier comprising a membrane, a gas phase and insulating elements laid against a secondary sealing membrane, and a primary sealing membrane designed to contact a liquefied gas contained in a vessel, the method comprising: and the gas phase of the secondary insulating barrier are maintained at a pressure P2 and a pressure P3, respectively, wherein the pressures P2 and P3 are equal to or less than the pressure P1.

- Advantageously, for the aforementioned embodiment, the pressure P3 is equal to or greater than the pressure P2. Therefore, in the case of gas leakage and gas penetration of the primary thermal insulation barrier, it is possible to avoid introducing gas from inside the secondary thermal insulation barrier. Thus, in relation to the primary insulating barrier, a slightly higher pressure of the secondary insulating barrier can be beneficial. In this case, the pressure difference between the pressures P2 and P3 is less than 100 mbar, preferably between 10 mbar and 50 mbar.

- The vessel is filled with a liquefied fuel gas selected from among liquefied natural gas, ethane and liquefied petroleum gas.

- circuits for the use of gaseous gases include energy production equipment;

- According to one embodiment, a vacuum container is installed in the container, which is placed in the inner space of the container and includes an upper part disposed in a gas phase and a lower part submerged in a liquid phase, and a gaseous region in which a stream of gas is drawn into the gas phase. formed by the upper part of the vacuum vessel.

- According to another embodiment, a pressure P1 is created in the upper part of the vessel containing the entire gas phase.

According to one embodiment, the present invention is a facility for storage and cooling of liquefied gas,

- a sealed and insulated container having an interior space designed to be filled with liquefied gas stored in a state of two-phase liquid-gas equilibrium such that the liquefied gas has a lower liquid phase and an upper gas phase separated by an interface; and

- As a circuit for the removal of gaseous gas,

- an inlet immersed into the interior space of the container above the maximum fill height of the container to empty the area of the gas phase in contact with the area of the interface when the container is full; and

- a two-phase liquid-gas equilibrium in which vaporization of the gas phase is promoted in the region of the interface region, and the liquefied gas in contact with the region of the interface has a temperature at which the liquefied gas has a temperature lower than the liquid-gas equilibrium temperature at atmospheric pressure of the liquefied gas pumped into the circuit for use of the gaseous gas, and introduced the flow stream of the gaseous gas present in the gaseous region through the inlet to maintain the gaseous region at a pressure lower than atmospheric pressure (P1) can vacuum pump

A circuit for the removal of gaseous gas comprising a

It provides a facility for storage and cooling of liquefied gas comprising a.

According to other advantageous embodiments, the installation may have one or more of the following characteristics.

- The facility is equipped with a sensor for measuring the flow rate to provide a signal representing the flow rate of the gas that is introduced through the inlet and pumped into the circuit for use, and a signal representing the flow rate of the gas and the circuit for the use of the gas. and a control device capable of controlling the vacuum pump as a function of the flow rate setpoint created by the

- the installation includes a pressure sensor capable of providing a signal representative of the pressure spread over the interior space of the vessel above the maximum fill height and a control unit capable of controlling the vacuum pump as a function of the pressure setpoint and the signal representative of the pressure includes

- The installation further comprises a circuit for the use of gaseous gas containing energy production equipment.

- the vessel comprises a multi-layer structure mounted on a carrier structure, said multi-layer structure comprising a sealing membrane in contact with the liquefied gas contained in the vessel, and an insulating barrier disposed between the sealing membrane and the carrier structure and comprising insulating blocks and gas phase wherein the installation further comprises a vacuum pump designed to maintain the gas phase of the insulating barrier at a pressure P2 equal to or less than the pressure P1.

- the multi-layer structure from the outside to the inside of the vessel, to the secondary insulating barrier comprising the gas phase and insulating blocks laid against the transport structure, the secondary sealing membrane laid against the insulating blocks of the secondary insulating barrier, the secondary sealing membrane A primary insulating barrier comprising a gas phase and insulating elements placed against each other, and a primary sealing membrane designed to be in contact with a liquefied gas contained in a vessel, the installation comprising: a first vacuum pump designed to maintain a pressure equal to or less than the pressure P2, and a second vacuum pump designed to maintain the gas phase of the secondary insulating barrier at a pressure P3 equal to or less than the pressure P1 do.

- the vessel includes an upper portion placed in the interior space of the vessel and designed to be placed in contact with the vapor phase of the liquefied gas stored in the interior space of the vessel and a lower portion designed to be immersed in the liquid phase of the liquefied gas stored in the interior space of the vessel A vacuum container is installed in which the inlet of the circuit for removing the gaseous gas empties the inside of the upper part of the vacuum container.

- The vacuum vessel is made of metal.

- The vacuum vessel comprises a horizontal cross section between 1/5 and 1/100 of the horizontal cross section of the vessel, for example on the order of 1/10.

- According to one embodiment, the vacuum vessel comprises hollow tubes passing through it from one side to the other.

- The installation includes a pressure sensor capable of providing a signal representative of the pressure spread over the upper part of the vacuum vessel.

According to one embodiment, the present invention relates to offshore liquefaction equipment, such as a vessel or liquefied barge, comprising facilities for the storage and cooling of the aforementioned liquefied gas.

According to one embodiment, the vessel comprises a shell, in which the sealed and insulated vessel of the installation is arranged.

According to one embodiment, the circuit for the use of gaseous gas is energy producing equipment, such as equipment for propulsion of a ship.

According to one embodiment, the present invention also provides a method of loading and unloading such a vessel, wherein the fluid is transferred via insulated conduits from a floating or ground-based storage facility to a vessel on the vessel, or from a vessel to a floating or above-ground vessel. transferred to the underlying storage facility.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will become better understood and other objects, details and advantages of which will become more apparent in the course of the following description of several specific embodiments of the invention, which are provided for illustrative purposes only and not limiting, with reference to the accompanying drawings. will be done
1 schematically shows a facility for storage and cooling of liquefied gas.
2 is a liquid-gas equilibrium diagram for methane.
3 is a schematic diagram of a facility for storage and cooling of liquefied gas;
4 is a schematic cross-sectional view of an LNG carrier equipped with a container and a terminal for loading/unloading the container.
5 schematically shows a facility for storing and cooling liquefied gas according to a second embodiment.

In the description and claims of the invention, the term 'gas' is a generic term in nature, and includes, without distinction, a gas composed of a single pure substance or a gas mixture composed of a plurality of components. Thus, liquefied gas refers to a chemical substance or mixture of chemicals that lies in a liquid phase at a low temperature and can exist in the gas phase under normal temperature and pressure conditions.

1 , an installation 1 for storage and cooling of liquefied gas according to a first embodiment is shown. Such installations 1 may be installed on a ground structure or on a floating structure such as a liquefaction barge or a regasification barge. In the case of above-ground structures, these facilities, whether attached to the storage unit or within the distribution network of gaseous gas supplied from the storage unit, include electrical generators, steam generators, burners or other elements consuming gaseous gas It may be designed as a storage unit associated with one or more consumers of phosphorus gas.

In the case of a floating structure, the facility may be designed as a vessel for transporting liquefied natural gas, such as an LNG carrier, but may be designed as any vessel whose engine propulsion assembly, electrical generator, steam generator or other consumer is supplied with gas. may be As an example, it may be a cargo transport vessel, a passenger transport vessel, a fishing boat, a floating electricity generation unit or other types.

The installation 1 comprises a sealed and insulated container 2 .

In the embodiment shown in FIG. 1 , the vessel 2 is a membrane type vessel. Such a membrane vessel comprises, from the outside to the inside of the vessel 2 , a secondary insulating barrier 3 comprising an insulating element lying against the transport structure 4 , a secondary sealing membrane lying against the secondary insulating barrier 3 . (5), a primary insulating barrier (6) comprising an insulating element placed against a secondary sealing membrane (5) and a primary sealing membrane (7) designed to be in contact with the liquefied gas (8) contained in the vessel; It may in particular include multi-layer structures. As an example, such membrane vessels 2 are disclosed in patent applications WO14057221, FR2691520 and FR2877638.

According to other alternative embodiments, the container 1 may be a container of type A, B or C. Such containers are self-supporting and may in particular have a parallelepiped, prismatic, spherical, cylindrical or multilobed shape. Type C vessels have the specificity of allowing the storage of liquefied natural gas at pressures significantly higher than atmospheric pressure.

The liquefied gas 8 is a fuel gas. In particular, the liquefied gas 8 is liquefied natural gas (LNG), ie mainly methane, as well as one or more other carbonized substances such as ethane, propane, n-butane, i-butane, n-pentane, i-pentane, neopentane. It may be a gas mixture comprising hydrogens and some nitrogen.

The fuel gas may be ethane or liquefied petroleum gas (LPG), ie a mixture of hydrocarbons derived from petroleum refining and comprising substantially propane and butane.

The liquefied gas 8 is stored in a two-phase liquid-gas equilibrium state in the interior space of the vessel. Thus, this gas is present in the gas phase in the upper portion of the vessel and in the liquid phase in the lower portion of the vessel. The equilibrium temperature of liquefied natural gas, which corresponds to a two-phase liquid-gas equilibrium state when stored at atmospheric pressure, is about -162°C.

The plant 1 comprises a circuit 9 for the removal of gaseous gases. The circuit 9 for removing this gaseous gas includes a conduit 10 penetrating the wall of the container 2 and forming a passage for discharging the gaseous phase from the inside of the container 2 to the outside. This conduit 10 comprises an inlet 11 which emerges into the interior of the interior space of the vessel 2 . This inlet 11 may in particular be exposed above the maximum filling limit of the container so as to be exposed to the gas phase.

The removal circuit 9 also comprises a vacuum pump 12 connected upstream to the conduit 10 and downstream to a circuit 13 for the use of gaseous gas. This vacuum pump 912 can thus draw a stream of gaseous gas present in the interior space of the vessel 92 through the conduit 10 and pump it into the circuit 13 for use of the gaseous gas. . In the illustrated embodiment, the removal circuit 9 is arranged upstream or downstream from the vacuum pump 12 and thus a check valve 19 preventing the backflow of a stream of gaseous gas into the interior space of the vessel 2 . or gates.

The vacuum pump 12 may generate a pressure P1 lower than atmospheric pressure in the gas phase located in the upper portion of the inner space of the vessel 2 . Accordingly, when the vacuum pump 12 is operating and draws a stream of gaseous gas from the inside of the interior space of the vessel 2 and pumps it into the circuit 13 for use of the gaseous gas, the vacuum pump 12 ) also creates a subatmospheric pressure P1 in the gas phase of the interior space of the vessel.

Thus, in the gas phase placed at a pressure P1 lower than atmospheric pressure, the vaporization of the liquefied gas present in the vessel 2 is promoted at the liquid/gas interface, while the liquefied gas 8 stored in the vessel 2 causes the liquefied gas to The liquefied gas is placed in a two-phase liquid-gas equilibrium state having a temperature lower than the liquid-gas equilibrium temperature at atmospheric pressure.

These phenomena are explained below with respect to Figure 3, which shows a liquid-gas equilibrium diagram of methane. The diagram shows the region marked L where methane is in the liquid phase and the region V where methane is in the gas phase as a function of temperature along the vertical axis and pressure along the horizontal axis.

Point P _t1 represents a two-phase equilibrium state corresponding to the state of methane stored in a vessel at atmospheric pressure, -162°C. When the storage pressure of methane in the vessel falls below atmospheric pressure, for example to an absolute pressure of about 500 mbar, the equilibrium of methane shifts to the left and shifts to the point P _t2 . Once equilibrium is reached, the methane so expanded undergoes a temperature decrease of about 7°C, while a portion of the liquid methane vaporizes, taking the heat necessary for its vaporization from the liquid methane stored in the vessel. Thus, by placing the liquefied gas at an absolute pressure less than atmospheric pressure, the liquefied gas is thermodynamically supercooled, such that the return to storage in the vessel at atmospheric pressure or further transfer to the vessel at atmospheric pressure can result in a low rate of vaporization of the liquefied gas, even This can be achieved by maintaining a vaporization rate of 0 (zero), thus preventing or reducing the flash vaporization phenomenon at the start of the transfer.

The vacuum pump 12 is a cryogenic pump, that is, a pump capable of withstanding a cryogenic temperature lower than -150°C. It must also be compatible with the ATEX standard. That is, it must be designed to avoid the risk of explosion.

3 shows that the removal circuit 9 and the vacuum pump 12 provide a refrigeration capacity P to the liquefied gas contained in the vessel 2 and a flow rate Q of the gaseous gas to the utilization circuit 13 The installation 1 is schematically shown to illustrate the fact that both are possible.

In some applications, the demand for the gaseous gas required by the utilization circuit 13 may be a key criterion for sizing and control of the vacuum pump 12 . In this example, the vacuum pump 12 is controlled as a function of the flow rate setpoint generated by the circuit 13 for use of the gaseous gas. To achieve this, the installation 1 has a flow rate measuring sensor capable of providing a signal representative of the flow rate of the gas pumped by the vacuum pump 12 , and a vacuum pump such that the value of the measured flow rate is dependent on the flow rate setpoint. A control device (18) capable of controlling (12) is provided. In this embodiment, the pressure spread within the vessel thus develops as a function of time and as a function of the flow rate setpoint generated by the use circuit 13 .

In addition, for these embodiments, the vacuum pump 12 is sized to produce a flow rate sufficient to supply the utilization circuit 13 . As an example, the average power of a main motor in ocean-going vessels is typically on the order of several MW to several tens of MW. If the flow rate Q of the gaseous gas pumped by the vacuum pump 12 does not produce a refrigeration capacity corresponding to the total demand in the storage vessel, the auxiliary refrigeration capacity P for the liquefied gas contained in the vessel 2 It is possible to provide an auxiliary cooling device, not shown, to supply _aux ).

In other applications, especially if the demand for the gaseous gas in the utilization circuit 8 is high and it is not desired to cool the liquid gas contained in the container in an excessive manner, the gas contained in the container is heated to its vaporization temperature at atmospheric pressure. The refrigeration capacity required to keep down may be a criterion for sizing and controlling the vacuum pump 12 . In this case, the vacuum pump is controlled as a function of the setpoint of the pressure spread over the interior space of the vessel. To achieve this, the installation 1 has a pressure sensor designed to measure the pressure in the inner space of the vessel and a control device 18 capable of controlling the vacuum pump 12 so that the value of the measured pressure is dependent on the pressure setpoint. ) is installed. In this embodiment, after a transition period of pressure drop in which the temperature and pressure of the liquefied natural gas decrease, a steady state corresponding to the target pair of pressure and temperature is obtained. The absolute setpoint pressure is greater than 120 mbar and lies between eg 750 mbar and 980 mbar.

For these embodiments, the vacuum pump 12 is sized to create a vacuum corresponding to a target pressure in the interior space of the vessel. In addition, if the steady state does not produce a flow rate of the gaseous gas corresponding to the total demand in the utilization circuit 13 , an auxiliary, not shown, to provide an auxiliary flow rate Q _aux of the gas phase to the utilization circuit 13 . It is possible to provide a vaporization device.

Accordingly, it will be understood from the above that the vacuum pump needs to have a flow rate/pressure characteristic adapted to the refrigeration capacity and the demand of the circuit 13 for the use of gaseous gas.

In the case of a ship-mounted installation 1 , the utilization circuit 13 may include, in particular, energy-producing equipment of an engine propulsion assembly, not shown, which enables the propulsion of the ship. Such energy production equipment is particularly chosen from among thermal engines, dusfy cells and gas turbines. If the energy production equipment is a heat engine, this engine may have a diesel/natural gas mixed feed. These engines can operate in either a diesel mode, in which the engine is fully supplied with diesel, or in a natural gas mode in which the engine's fuel consists primarily of natural gas while a small amount of pilot diesel is injected to initiate combustion.

In addition to this, according to an embodiment, the utilization circuit 13 further comprises a heat exchanger, not shown, which makes it possible to further heat the stream stream of gas in the gaseous phase to a temperature compatible with the operation of the gas consuming equipment. The additional heat exchanger is in particular between a stream of gas in the gaseous phase and sea water, or between a stream of a gas in a gaseous form and the combustion gases produced by the engine or directly by the energy production equipment, or between the stream of gas in the gaseous phase and the engine. It can ensure thermal contact between the air used as an oxidizer by the engine to boost efficiency. According to one embodiment, the utilization circuit 13 provides heating of the stream stream of gas in the gas phase and its reduction to a pressure compatible with the specifications of the energy production equipment to which the fuel gas is being supplied, for example from a pressure of 5 bar absolute to a pressure of the order of 6 bar. Compressors may be included to enable compression.

When the liquefied gas is a gas mixture composed of a plurality of components, the gaseous phase due to vaporization inside the container has a higher composition than that of the liquid phase in the most volatile component such as nitrogen. Accordingly, the stream of gas removed by circuit 9 for the removal of gaseous gases may have a significant amount of the most volatile components and thus may not be compatible with supply to energy production equipment. Therefore, according to an embodiment not shown, the apparatus 1 may include a forced vaporization device which removes a stream of liquid liquefied gas from the interior space of the vessel 2 and vaporizes it with the aid of a heat exchanger. . This stream of gas has substantially the same composition as that of the liquefied gas contained in the interior space of the vessel. The gaseous stream stream obtained in this way can thus be mixed with the stream stream of the removed gas through the removal circuit 9 to obtain an amount of the most volatile component compatible with the supply to the energy production equipment.

Returning to FIG. 1 , in the illustrated embodiment, the facility 1 moves into the interior space of the primary thermal insulation barrier 6 so as to be able to maintain the gas phase of the primary thermal insulation barrier 6 at a pressure P2 lower than atmospheric pressure. a vacuum pump 16 connected to an exposed pipeline 17 .

Similarly, the installation is connected to a pipeline 15 exposed to the interior space of the secondary insulating barrier 3 and thus a vacuum capable of maintaining the gas phase of the secondary insulating barrier 3 at an absolute pressure P3 lower than atmospheric pressure. It includes a pump (14).

It is particularly advantageous to keep the adiabatic barriers below subatmospheric pressures P2, P3. In fact, this on the one hand makes it possible to boost the thermal insulation performance of these thermal barriers. On the other hand, this also ensures that the pressure spread in the insulating barriers 3 , 6 is not much greater than the pressure spread in the interior space of the vessel 2 , which is the sealing membranes 7 , 5 , in particular 1 It tends to damage the car sealing membrane 7 and cause it to tear.

Also advantageously the vacuum pumps 14 , 16 provide a pressure P1 at which the pressure P2 of the primary insulating barrier 6 and the pressure P3 of the secondary insulating barrier 3 are spread over the interior space of the vessel. Controlled to be less than or equal to.

According to one particular embodiment, the pressure P3 may provide greater than or equal to the pressure P2, which prevents the entry of liquefied gas into the secondary thermal barrier in case the sealing membranes are insufficiently tight. make it possible Advantageously the pressure difference between the pressures P2 and P3 is less than 100 mbar, preferably between 10 mbar and 50 mbar.

Also, in an embodiment not shown, the installation 1 comprises a stirring device capable of creating a flow inside the interior space of the vessel 2 . Such a stirring device is intended to limit the thermal stratification inside the vessel 2 and thus to enable homogenization of the temperature of the liquefied gas and thus to optimize the efficiency of the process. The stirring device may in particular comprise a recirculation loop for the liquefied gas. To achieve this, the stirring device comprises one or more pumps, such as a drain pump for the vessel associated with the drain line, which may be arranged in communication with the vessel fill line to create a recirculation loop of the liquefied gas.

In the embodiment shown in FIG. 5 , the installation 1 further comprises a vacuum bell jar 20 placed in the interior space of the vessel 2 . The upper part of the vacuum container 20 is filled with the gas phase in contact with the gas phase of the gas stored in the container 2 , and the lower part thereof is immersed in the liquid phase of the gas stored in the container 2 on the upper side of the inner space of the container 2 . It is a hollow body arranged in a part. Here, the vacuum vessel 20 is cylindrical in shape with a circular cross-section. However, the vacuum vessel 20 may have other shapes, such as a parallelepiped with a square or rectangular cross-section.

The inlet 11 of the circuit 9 for the removal of gaseous gas is exposed as the upper part of the vacuum vessel 20 . Therefore, the vacuum pump 12 can promote vaporization of the liquefied gas in the vacuum container 20 by generating a pressure P1 lower than atmospheric pressure in the upper portion of the vacuum container.

It should be noted that, in this embodiment, when the vacuum pump 12 is controlled such that the measured pressure value is dependent on the pressure setpoint, the pressure sensor is advantageously arranged inside the upper part of the vacuum vessel 20 .

The use of such a vacuum vessel 20 reduces, in particular, the sizing restrictions of the vacuum pump 12 and in the case of membrane vessels of type A, B or C, to limit the stress on the primary sealing membrane 7 . It has the advantage of limiting the vacuum extending to the rest of the inner space of the vessel 2 for the purpose of this. In other words, the vacuum vessel 20 makes it possible to confine the evacuation to elements of a size smaller than the size of the vessel, and its design and sizing ensures that the target vacuum is achieved without the vessel as a whole being constrained by sizing thereby. can be optimized to have The sizing of the vessel can thus be optimized as a function of the internal operating pressure when the vacuum vessel is sized as a function of the target vacuum.

For sizing a vacuum vessel, the following may be considered.

- The strength at the target vacuum of the vacuum vessel shall be ensured by the use of the thickness of the material and optional reasonable reinforcement in terms of manufacturing cost.

- the ratio between the free surface inside the vacuum vessel 20, i.e. the surface of the boundary region between the liquid and gas phase in the vacuum vessel, and the free surface in the rest of the vessel, the application of the target vacuum inside the vacuum vessel 20 It is chosen to convert to an acceptable vacuum in vessel 2 .

The vacuum created inside the vessel can be estimated with the help of the relation

here:

S _{Bell jar} and S _Vessel are free surfaces of liquefied gas in the vacuum vessel and in the rest of the vessel;

ΔP _Vessel and ΔP _{Bell jar} are the relative negative pressures of the gas phase in the vessel and in the vacuum vessel.

Thus, if it is desired to limit the vacuum within the vessel to 1/10 of the vacuum within the vacuum vessel 20, the free surface inside the vacuum vessel must be at 1/10 the level of the free surface inside the vessel.

Also, with respect to Type C vessels designed to store liquefied gases at pressures significantly greater than atmospheric pressure, typically on the order of 3 bar to 9 bar, these are sized as a function of the maximum internal operating pressure they can withstand. It should be noted For the storage of liquefied natural gas, the maximum internal operating pressure is usually equal to or less than 10 bar. Further, when a vessel is subjected to an internal vacuum and a maximum internal working pressure, the following relationship can be established between the critical buckling pressure of such a vessel:

here:

P _Cr is the critical buckling pressure;

P _max is the maximum working pressure;

K is a factor of safety > 1;

E is the Young's modulus of the material of the sealing membrane of the container;

ν is the Poisson's ratio of the material;

σ is the elastic limit of the material.

The critical buckling pressure of the vessel is proportional to the cube of the vessel's maximum buckling pressure multiplied by this practically material-dependent constant and the designer's chosen safety factor. For most of the material candidates, this constant is less than 1 and often less than 0.1. Thus, when a vessel is subjected to a vacuum, the critical buckling pressure is often more than ten times greater than the maximum working pressure.

As an example, for a type C cylindrical vessel sized to withstand a maximum operating pressure of 10 bar and to have a target vacuum inside the vacuum vessel 20 at the level of 100 mbar, such that the vacuum spread over the remainder of the vessel is limited to 10 mbar. A ratio of the order of 10 may be selected as the ratio between the free surface inside the vacuum vessel 20 and the free surface of the rest of the vessel. In this case, the vacuum vessel 20 is thus able to reduce the vacuum that may spread over the rest of the gas phase of the vessel from 100 mbar to 10 mbar, which in particular enables a limiting of the thickness of the membrane of the vessel. As an example, for a cylindrical vessel of type C having a diameter of 10 m and whose membrane is made of stainless steel, the vacuum vessel 20 in the mentioned example can limit the thickness of the membrane to 25 mm, whereas the vacuum vessel 20 If there is no , it would have to be 29mm.

For most applications, the cross-section of the vacuum vessel is advantageously between 1/5 and 1/100 of the cross-section of the vessel.

For a cylindrical vessel in which the busbar is horizontal, the free surface of the liquefied gas inside the vessel develops as a function of the fill factor of the vessel. In fact, this free surface reaches a maximum when the container is filled to mid-height and decreases as it approaches the maximum of the filling factor of the container. Thus, the sizing of the vacuum vessel 20 will determine whether the criterion of sizing will be considered as the maximum free surface of the liquefied gas, i.e., corresponding to a vessel filled to mid-height or liquefied when the vessel approaches its maximum fill rate. It can be different depending on whether you want the free surface of the gas.

As an example, for a cylindrical vessel with a length of 20 meters and a radius of 4 meters, taking a pressure ratio of 10 between the vapor phase vacuum in the vessel and the vapor phase vacuum in the vacuum vessel, the radius of the cylindrical vacuum vessel is 2.25 meters It takes advantage of the maximum free surface of the liquefied gas. However, for vessels of liquefied natural gas transport vessels designed to fill near their maximum fill rate, a smaller vacuum vessel radius of the order of two is sufficient and it is possible to reduce the space occupied by the vacuum vessel 20 . Under these same conditions, a vacuum vessel of square cross section can have a side length of 4 meters.

According to one embodiment, the vacuum vessel is more complex such that the ratio between the free surface inside the vacuum vessel 20 and the free surface at the remainder of the vessel remains substantially constant throughout the height of the vacuum vessel 20 . It has a shape and its cross-section develops as a function of the height of the container.

The vacuum vessel 20 is made of, for example, metal to promote heat exchange between the gas existing inside and outside the vacuum vessel 20 .

The vacuum vessel 20 may be equipped with elements that reinforce the structure and allow it to withstand the target vacuum. These reinforcing elements may be of any type and in particular they may be hollow or solid reinforcing elements which pass transversely through the vacuum vessel or are disposed around the interior or exterior of the vacuum vessel 20 .

According to one embodiment, the vacuum vessel 20 extends in a substantially horizontal direction and may intersect the hollow tubes passing through the vacuum vessel from one side to the other. These hollow tubes allow the movement of the fluid and can promote heat exchange between the gases present inside and outside the vacuum vessel 20 . In addition to this, these hollow tubes may also contribute to the reinforcement of the vacuum vessel 20 .

When the vessel 20 is equipped with a loading and unloading tower not shown, the vacuum vessel 20 may be supported by the loading and unloading tower in particular to support its own weight and the force according to the movement of the liquefied gas. These loading and unloading towers extend substantially the entire height of the vessel and are suspended from the ceiling wall. The tower may consist of a triport type structure, that is, a structure including three vertical masts. The loading and unloading tower supports one or more unloading lines and one or more loading lines, each of which is associated with an unloading pump which is itself supported by the loading and unloading tower. However, the vacuum vessel 20 may be supported by other suitable means.

The vacuum vessel 20 is immersed quite deeply within the liquid so that its lower portion remains submerged in the liquid when the liquefied gas undergoes a 'sloshing' effect. To achieve this, the vacuum vessel 20 can in particular extend more than 1 meter below the height of the vessel corresponding to the maximum filling height.

Referring to FIG. 4 , a cross-sectional view of an LNG carrier 70 in which facilities for storage and cooling of liquefied natural gas are installed can be seen. 4 shows a generally prismatic sealed and insulated vessel 71 mounted on the double hull 72 of a ship. The wall of the vessel 71 comprises a primary sealing membrane designed to come into contact with the liquefied natural gas contained in the vessel, a secondary sealing membrane disposed between the one-dimensional sealing barrier and the double hull 72 of the vessel, and the primary sealing membrane and and two insulating barriers respectively disposed between the secondary sealing membrane and between the secondary sealing membrane and the double hull 72 .

In a manner known per se, the loading and unloading pipelines 73 arranged in the upper bridge of the vessel are connected by suitable connectors to the sea or port terminal to provide cargo of liquefied natural gas to or from vessel 71 . can be transported.

4 also shows an example of an offshore terminal comprising a loading and unloading station 75 , an underwater conduit 76 , and a ground facility 77 . The loading and unloading station 75 is a stationary offshore installation comprising a movable arm 74 and a tower 78 supporting the arm 74 . The movable arm 74 has a bundle of flexible insulated pipes 79 that can be connected with the loading and unloading pipelines 73 . The directional movable arm 74 is suitable for LNG carriers of all sizes. A connecting conduit, not shown, extends inside the tower 78 . The loading and unloading station 75 enables the loading and unloading of the LNG carrier 70 from or to the ground facility 77 . The latter comprises a container 80 for storage of liquefied gas and connecting conduits 81 joined by a submersible conduit 76 to a loading or unloading station 75 . The submersible conduit 76 enables the transfer of liquefied gas over large distances, such as 5 km, between the loading or unloading station 75 and the above-ground facility 77 , which allows the LNG carrier 70 to move ashore during loading and unloading operations. This allows it to be kept at a great distance from

In order to create the pressure necessary for the transport of the liquefied gas, pumps onboard the vessel 70 and/or pumps on the ground installation 77 and/or pumps onboard the loading and unloading station 75 are operated.

While the present invention has been described in connection with several specific embodiments, it is to be understood that it is not intended to be limited in any way thereto, and includes all technical equivalents of the described means, as well as combinations thereof, provided they fall within the scope of the invention. .

The verbs "accommodate," "comprise," "consist of," and their conjugations do not exclude the presence of other elements or steps other than those recited in a claim. The use of the indefinite article 'a' or 'an' (ie, any or one) for an element or step does not exclude the presence of a plural number of such element or step unless otherwise specified.

In the claims, reference signs placed between parentheses should not be construed as limitations on the claims.

Claims (23)

A method of cooling a liquefied gas (8) stored in the inner space of a sealed and insulated container (2), wherein the liquefied gas (8) is in a state of two-phase liquid-gas equilibrium inside the container (2). A lower liquid phase and an upper gas phase stored in space and separated by an interface, the method comprising:
- introducing by means of a vacuum pump a stream stream of gaseous gas into a region of the gaseous phase in contact with the region of the interface; In the step of introducing the flow stream of the gaseous gas, the vaporization of the liquid phase is promoted in the region of the interface region, and the liquefied gas in contact with the region of the interface surface, the liquefied gas is the liquid-gas equilibrium of the liquefied gas at atmospheric pressure creating a sub-atmospheric pressure (P1) in the region of the gas phase to be in a two-phase liquid-gas equilibrium having a temperature lower than the temperature; and
- inducing the flow stream drawn into the gas phase into the circuit 13 for utilization of the gas phase gas
A cooling method comprising a. The method according to claim 1, wherein the pressure (P1) is greater than 120 mbar absolute. 3. A gaseous gas according to claim 1 or 2, wherein the inlet of the flow stream of the gaseous gas is achieved by a vacuum pump (12), said vacuum pump (12) being produced by a circuit (13) for use of the gaseous gaseous gas. A controlled cooling method as a function of the set flow rate setpoint. 3. The vacuum pump (12) according to claim 1 or 2, wherein the inlet of the flow stream of gas in the gaseous phase is achieved by means of a vacuum pump (12), the pressure being measured in the region of the gas phase and the vacuum pump (12) being measured with the pressure setpoint. Controlled cooling method as a function of pressure. 3. A method according to claim 1 or 2, wherein the pressure (P1) is between 750 mbar and 980 mbar. 3. The container (20) according to claim 1 or 2, wherein the container (20) comprises a multi-layer structure mounted on a transport ship structure (4), said multi-layer structure comprising a sealing membrane (7) and a sealing membrane in contact with the liquefied gas contained in the container (4). an insulating barrier (6) disposed between (7) and the transport ship structure (4), said insulating barrier (6) comprising insulating blocks and gas phase, said method being equal to or less than pressure (P1) A method of cooling comprising maintaining the vapor phase of the insulating barrier (6) at a pressure (P2). 7. A secondary insulating barrier (3) according to claim 6, characterized in that the multilayer structure comprises gas phase and insulating blocks laid against the transport ship structure (4), from the outside to the inside of the vessel (2). ), a secondary sealing membrane (5) laid against the insulating blocks of comprising a primary sealing membrane (7) designed to , wherein the pressures (P2, P3) are equal to or less than the pressure (P1). 8. The method of claim 7, wherein the pressure (P3) is equal to or greater than the pressure (P2). 3. A method according to claim 1 or 2, wherein the vessel (2) is filled with a liquefied fuel gas (8) selected from among liquefied natural gas, ethane and liquefied petroleum gas. 3. The vessel (2) according to claim 1 or 2, wherein the vessel (2) is provided with a vacuum vessel (20) placed in the interior space of the vessel (2) and comprising an upper portion disposed in the gas phase and a lower portion submerged in the liquid phase, and the gas A cooling method in which the region of the gas phase into which the flow stem of is introduced into the gas phase is formed by the upper portion of the vacuum vessel (20). 3. A method according to claim 1 or 2, wherein a pressure (P1) is created in the upper part of the vessel containing the entire gas phase. A facility for storage and cooling of liquefied gas, comprising:
- a sealed and insulated vessel (2) having an interior space designed to be filled with liquefied gas (9) stored in a state of two-phase liquid-gas equilibrium such that the liquefied gas has a lower liquid phase and an upper gas phase separated by an interface ; and
- a circuit (9) for the removal of gaseous gases,
- an inlet 11 immersed into the interior space of the container 2 higher than the maximum filling height of the container to empty the area of the gas phase in contact with the area of the interface when the container is full; and
- a two-phase liquid-gas equilibrium in which vaporization of the gas phase is promoted in the region of the interface region, and the liquefied gas in contact with the region of the interface has a temperature at which the liquefied gas is lower than the liquid-gas equilibrium temperature at atmospheric pressure of the liquefied gas It is pumped to the circuit 13 for the use of the gaseous phase, to be put in the state of the gaseous phase, and the gaseous phase present in the gaseous phase through the inlet 11 to maintain the gaseous phase at a pressure P1 lower than atmospheric pressure. A vacuum pump (12) capable of drawing a stream of gas
A circuit for the removal of gaseous gas comprising a
Equipment for storage and cooling of liquefied gas comprising a. 13. The method of claim 12, further comprising: a sensor measuring the flow rate to provide a signal representative of the flow rate of the gas being drawn through the inlet and pumped into the circuit for use; A facility comprising a control device (18) configured to control the vacuum pump (12) as a function of the flow rate setpoint generated by the circuit (13) for 13. The vacuum pump (12) according to claim 12, wherein the pressure sensor is capable of providing a signal representative of the pressure spread in the interior space of the vessel above the maximum fill height, and the vacuum pump (12) as a function of the pressure setpoint and the signal representative of the pressure. A facility comprising a control device (18) capable of 15. Plant according to any one of claims 12 to 14, further comprising a circuit (13) for the use of gaseous gas comprising energy production equipment. 15. The vessel (2) according to any one of claims 12 to 14, wherein the vessel (2) comprises a multilayer structure mounted on a transport structure (4), said multilayer structure being in contact with a liquefied gas (8) contained in the vessel (2). a sealing membrane (7) that The installation further comprising a vacuum pump (16) designed to maintain the pressure (P2) equal to or less than the pressure (P1). 15. The multilayer structure according to any one of claims 12 to 14, wherein the multi-layer structure comprises, from the outside to the inside of the vessel (2), a secondary insulating barrier (3) comprising insulating blocks laid against the transport structure (4) and a gas phase; A secondary sealing membrane 5 laid against the insulating blocks of the secondary insulating barrier 3 , a primary insulating barrier 6 comprising a gas phase and insulating elements laid against the secondary sealing membrane 5 , and a container a primary sealing membrane (7) designed to be brought into contact with a liquefied gas (8) contained in (2), said installation providing the gas phase of the primary insulating barrier (6) at a pressure equal to or less than the pressure (P1) A first vacuum pump 16 designed to maintain at P2, and a second vacuum pump 14 designed to maintain the gas phase of the secondary insulating barrier 3 at a pressure P3 equal to or less than the pressure P1. ) further comprising a facility. 15 . The container according to claim 12 , wherein the container has an upper part designed to lie in the interior space of the container and to be placed in contact with the gas phase of liquefied gas stored in the interior space of the container and the interior space of the container. A vacuum container 20 including a lower part designed to be immersed in the liquid phase of the liquefied gas stored in the vacuum container 20, in which the inlet 11 of the circuit for removing the gaseous gas empties the inside of the upper part of the vacuum container 20 ) is installed. 19. An installation according to claim 18, comprising a pressure sensor capable of providing a signal representative of the pressure spread over the upper portion of the vacuum vessel (20). A vessel (70) comprising the installation (1) of any one of claims 12 to 14. 15. Offshore liquefaction equipment comprising the installation (1) of any one of claims 12 to 14. 21. The method of loading and unloading a vessel (70) of claim 20, wherein the fluid is transferred from a floating or ground-based storage facility (77) via insulated conduits (73, 79, 76, 81) to a vessel (70) of the vessel (70). 71), or from a container to a floating or ground-based storage facility. A system for transporting fluids, said system comprising insulated conduits (73) arranged to connect the vessel (70) of claim 20, a vessel (71) installed in the hull of the vessel (71) to a floating or ground-based storage facility (77). , 79, 76, 81), and a pump for driving fluid from a floating or ground-based storage facility to a vessel on a vessel or from a vessel on a vessel to a floating or ground-based storage facility through the insulated conduits. system.

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