Method for handling liquefied gas cargo and storage device

Abstract

The present invention relates to a method for handling a liquefied gas cargo stored in a liquefied gas storage device (1), wherein the liquefied gas storage device (1) comprises: a fluid-tight and thermally insulated liquefied gas storage tank (2); a loading / unloading tower (3), which comprises at least two vertical columns (7, 8, 9); and at least one unloading pump (6); the method comprising: a step of cooling the vertical columns (7, 8, 9), during which the liquefied gas flow is selectively directed to each of the at least two vertical columns (7, 8, 9); and / or a step of cooling the unloading pump (6), during which the liquefied gas flow is selectively directed to the unloading pump (6).

Description

Technical Field

[0001] The present invention relates to the field of storage of liquefied gas cargoes such as liquefied natural gas (LNG).

[0002] In particular, the present invention relates to a method of handling a cargo of liquefied gas and storing it in a liquefied gas storage facility. Background Art

[0003] In the prior art, ships are known that are equipped with a device for storing liquefied gases such as LNG, comprising a fluid-tight and thermally insulated storage tank for the liquefied gas and a loading / unloading tower suspended from the tank's top wall. The tank's loading / unloading tower comprises a tripod-type structure, that is to say three vertical columns connected to one another by transverse beams, each defining a cargo unloading and / or unloading route and / or a spare well that can be lowered into a spare unloading pump and tank of the unloading route. The loading / unloading tower supports, at the level of its lower part, a pump for unloading cargo associated with the unloading route. Such a storage device is described in detail in document FR2785034.

[0004] It is known to carry out a step of cooling the tanks before loading the cargo into the tanks of the ship. This step aims to reduce the temperature in the tanks in order to effectively prevent excessive evaporation of the liquefied gas during the loading process and to limit the intensity of thermal stresses in certain equipment components. This cooling step is carried out by spraying and evaporating the liquefied gas supplied by the loading terminal in the upper part of the tank. The heat required for evaporating the liquefied gas is separated by the gas contained in the tank and by the tank walls. The gas produced is extracted from the tank and returned to the loading terminal in the form of steam. This operation is continued until the average temperature in the tank drops below a threshold temperature.

[0005] The duration of the above-mentioned cooling tank step is quite long, about 10 to 20 hours, which causes the ship to stop for a considerable time during its loading. Moreover, the amount of liquefied gas in the cooling tank is large. Summary of the invention

[0006] The present invention is based on the idea of ​​proposing a method for handling a cargo of liquefied gas which method allows to effectively improve the efficiency of the cooling step by reducing its duration and / or reducing the amount used for cooling said liquefied gas.

[0007] According to one embodiment, the present invention provides a method of processing a liquefied gas cargo stored in a liquefied gas storage facility, wherein the liquefied gas storage facility comprises:

[0008] - a fluid-tight and thermally insulated liquefied gas storage tank; and

[0009] - at least one unloading pump, located near the bottom wall of the tank-in-tank and connected to a route that passes through the tank wall and allows unloading the tank;

[0010] The method comprises:

[0011] - a step of cooling the unloading pump, during which the liquefied gas flow is selectively directed to the unloading pump and brought into contact with the unloading pump to cool the unloading pump by means of latent heat of evaporation and / or sensible heat of the liquefied gas.

[0012] According to an alternative or supplementary embodiment, the present invention provides a method of processing a liquefied gas cargo stored in a liquefied gas storage facility, comprising:

[0013] - Fluid-tight and thermally insulated liquefied gas storage tanks;

[0014] a loading / unloading tower suspended from the top wall of the tank, comprising a plurality of routes through the top wall of the tank and each allowing loading and / or unloading of the tank; the loading / unloading tower comprising at least two vertical columns fixed to each other and to the top wall of the tank by means of a crossbeam; the at least two vertical columns being hollow and each defining one of the routes; and

[0015] - at least one unloading pump, fixed to the bottom end of said loading / unloading tower and connected to one of said one routes;

[0016] The method comprises:

[0017] - A step of cooling the vertical columns, in which the liquefied gas stream is selectively directed to each vertical column and each liquefied gas stream contacts one of the vertical columns to cool the vertical column using latent heat of evaporation and / or sensible heat of the liquefied gas.

[0018] Thus, the method according to the above described embodiment allows localized cooling of the equipment most sensitive to thermal stresses, such as the unloading pumps and the vertical columns of the loading / unloading tower, without having to cool the air in all the tanks. Such a method thus reduces the duration of the cooling step and / or reduces the amount of liquefied gas required for the cooling step.

[0019] Therefore, after cooling the vertical column and the unloading pump, respectively, it is not necessary to cool the entire tank until the defined cooling criteria are reached. Instead, the predefined local cooling criteria can be met by the vertical column and the unloading pump, respectively, however, most of the tank hardware components, especially most of the tank wall or even 90% of its surface area, are maintained at a temperature much higher than the temperature obtained in the vertical column and the unloading pump, respectively. Therefore, by terminating the cooling operation by meeting the local cooling criteria, the duration and / or energy consumed of the cooling process can be greatly shortened and / or reduced.

[0020] For example, the duration of cooling the vertical column and the unloading pump separately may be less than 2 hours. The cooling energy provided to the unloading pump during the cooling period may be between 100 and 5000 MJ (inclusive), and the cooling energy provided to the vertical column may be between 500 and 15000 MJ (inclusive), so the cooling energy provided to the two selected cooling devices is between 100 and 20000 MJ (inclusive).

[0021] According to further advantageous embodiments, such a method may have one or more of the following features.

[0022] According to one embodiment, the step of cooling the unloading pump is performed until the temperature of the unloading pump reaches between -120°C and 140°C (inclusive).

[0023] According to one embodiment, the step of cooling the unloading pump is performed on an unloading pump having a temperature greater than -120°C, such as greater than -50°C, or even greater than -10°C, and such as less than 40°C.

[0024] According to one embodiment, a temperature variable of the unloading pump is measured, and when the temperature of the unloading pump reaches a threshold, the cooling operation of the unloading pump is terminated.

[0025] According to one embodiment, a temperature variable of the unloading pump is measured and when or as soon as the temperature of the unloading pump reaches a threshold value, for example -120°C, the step of loading the liquefied gas into the tank is triggered.

[0026] Therefore, before starting the loading step, the temperature of the pump does not rise above the threshold or above -120° C. Therefore, during the loading step, there is no risk of damage to the pump when the tank is filled with liquefied gas.

[0027] According to one embodiment, the temperature variable of the unloading pump is measured by arranging a temperature sensor in the unloading pump, for example in a stator of the pump or in contact with a surface of a pump housing.

[0028] According to one embodiment, the temperature variable of the unloading pump is measured by measuring the current I and the voltage U of the winding of the unloading pump.

[0029] According to one embodiment, the value representing the temperature T is related to the measurements of the current I and the voltage U by the following equation:

[0030]

[0031] R 20℃ Indicates the resistance of the winding at 20°C, B mat is a coefficient that is a function of the material used for the winding.

[0032] According to one embodiment, during the step of cooling the unloading pump, the average temperature in the tank, that is to say the average temperature of the entire gas phase stored in the tank, is maintained at greater than -120° C., such as greater than -50° C., or even greater than -10° C., and less than, for example, 40° C. According to one embodiment, during the step of cooling the unloading pump, the average temperature of the tank wall is maintained at greater than -120° C., such as greater than -50° C., or even greater than -10° C., and less than, for example, 40° C.

[0033] According to one embodiment, the liquefied gas flow is 0.05 to 10 m 3 / h (inclusive) for example 0.1 to 11m 3 / h, is selectively directed to the unloading pump.

[0034] The volume of the fluid-tight tank is, for example, between 1000 and 60000 m 3 (inclusive) between.

[0035] According to one embodiment, during the step of cooling the unloading pump, the flow of liquefied gas is sprayed towards the unloading pump.

[0036] According to one embodiment, the liquefied gas flow is sprayed towards the unloading pump through one or more nozzles.

[0037] According to one embodiment, the step of cooling the unloading pump is performed by a device for cooling the unloading pump, which is associated with the unloading pump and is suitable for guiding the liquefied gas flow to the unloading pump and making it contact with the unloading pump to cool the unloading pump by means of latent heat of evaporation and / or sensible heat of the liquefied gas.

[0038] According to one embodiment, before loading the tank with liquefied gas, a step of cooling the pump is performed, during which step the liquefied gas is guided from the loading terminal into the tank.

[0039] According to one embodiment, before each step of loading the liquefied gas into the tank, a cooling step is performed.

[0040] According to one embodiment, during the step of loading the tank with liquefied gas, said liquefied gas is guided into the tank from the unloading terminal via a route passing through the tank wall.

[0041] According to one embodiment, during the step of cooling the unloading pump, the liquefied gas flow directed to the unloading pump is previously sucked into the tank by a drainage pump arranged near the tank bottom wall.

[0042] According to one embodiment, during the step of cooling down said unloading pump, said flow of liquefied gas directed to said unloading pump is previously extracted from a loading terminal.

[0043] According to one embodiment, the device further comprises a loading / unloading tower, the tower being suspended from the top wall of the tank, the tower comprising a plurality of routes passing through the top wall of the tank, and each route allowing loading and / or unloading of the tank; the loading / unloading tower comprising at least two vertical columns, the columns being fixed to each other and to the top wall of the tank by a crossbeam; the at least two vertical columns being hollow and each column defining one of the routes; the unloading pump being fixed to the lower end of the loading / unloading tower, the method further comprising:

[0044] - A step of cooling the vertical columns, in which the liquefied gas stream is selectively directed to each vertical column and each liquefied gas stream is brought into contact with one of the two vertical columns to cool the vertical column using latent heat of evaporation and / or sensible heat of the liquefied gas.

[0045] According to one embodiment, the loading / unloading tower comprises three vertical columns.

[0046] According to one embodiment, the step of cooling the vertical column is performed until the final temperature of the vertical column reaches between -120°C and -140°C, inclusive.

[0047] According to one embodiment, the step of cooling the vertical column is performed at a final temperature of greater than -120°C, such as greater than -50°C, or even greater than -10°C, and such as less than 40°C.

[0048] According to one embodiment, during the step of cooling the vertical columns, the average temperature in the tank, that is to say the average temperature of the entire gas phase stored in the tank, is maintained at greater than -120° C. According to one embodiment, during the step of cooling the vertical columns, the average temperature of the tank wall is maintained at greater than -120° C., such as greater than -50° C., or even greater than -10° C., and less than, for example, 40° C.

[0049] According to one embodiment, the liquefied gas flow is 1 to 15 m 3 A relative flow rate of between 1000 Å and 2000 Å (inclusive) is selectively directed to each vertical column.

[0050] According to one embodiment, during the step of cooling the vertical columns, the average temperature in the tank is maintained at greater than -120°C.

[0051] According to one embodiment, during the step of cooling said vertical columns, said flow of liquefied gas is sprayed towards each vertical column.

[0052] According to one embodiment, the flow rate of the liquefied gas sprayed toward each vertical column is equal.

[0053] According to one embodiment, each of the liquefied gas streams is sprayed toward each of the vertical columns through one or more nozzles.

[0054] According to one embodiment, the step of cooling the vertical columns is performed by means of a device for cooling the vertical columns, which device is associated with the vertical columns and is suitable for directing a flow of liquefied gas to each vertical column and making it contact with each vertical column to cool the vertical columns by means of latent heat of evaporation and / or sensible heat of the liquefied gas.

[0055] According to one embodiment, before loading the tank with liquefied gas, a step of cooling the vertical columns is carried out, during which step the liquefied gas is guided from the loading terminal into the tank.

[0056] According to one embodiment, during the step of cooling said vertical columns, said flow of liquefied gas directed to said vertical columns is previously sucked into a tank by means of a drainage pump.

[0057] According to one embodiment, during the step of cooling said vertical columns, said flow of liquefied gas directed to said vertical columns is previously extracted from a loading terminal.

[0058] According to one embodiment, the method further comprises the step of cooling the unloading pump, during which the liquefied gas flow is selectively directed to the unloading pump and brought into contact with the unloading pump to cool the unloading pump by utilizing latent heat of evaporation and / or sensible heat of the liquefied gas.

[0059] According to one embodiment, the fluidizing gas is selected from the group consisting of: liquefied natural gas (LNG), liquefied petroleum gas (LPG) and ethane.

[0060] According to one embodiment, the present invention provides a liquefied gas storage device, comprising:

[0061] - Fluid-tight and thermally insulated liquefied gas storage tanks;

[0062] - at least one unloading pump arranged near the bottom wall of the tank and connected to a route passing through the tank wall, said route allowing unloading of the tank; and

[0063] - a device for cooling an unloading pump, the device being connected to the unloading pump and being adapted to direct the flow of liquefied gas to the unloading pump and into contact with the unloading pump so as to cool the unloading pump by means of latent heat of evaporation and / or sensible heat of the liquefied gas.

[0064] According to one embodiment, the present invention provides a liquefied gas storage device, comprising:

[0065] - Fluid-tight and thermally insulated liquefied gas storage tanks;

[0066] a loading / unloading tower suspended from the top wall of the tank, comprising a plurality of routes through the top wall of the tank and each allowing loading and / or unloading of the tank; the loading / unloading tower comprising at least two vertical columns fixed to each other and to the top wall of the tank by means of crossbeams; the at least two vertical columns being hollow and each defining one of the routes; and

[0067] - at least one unloading pump, fixed to the bottom end of said loading / unloading tower and connected to said one of the routes; and

[0068] - a device for cooling the vertical column, the device being connected to the vertical column and being capable of connecting the flow of the liquefied gas to the vertical column in order to cool the vertical column by means of latent heat of evaporation and / or sensible heat of the liquefied gas.

[0069] According to other advantageous embodiments, such a device may have one or more of the following features.

[0070] According to one embodiment, the device for cooling the unloading pump comprises a feed pipe for directing the flow of liquefied gas to one or more nozzles directed towards the unloading pump.

[0071] According to one embodiment, the / each nozzle of the device for cooling the unloading pump is located in alignment with the unloading pump.

[0072] According to one embodiment, the device for cooling the unloading pump said / each nozzle is arranged in the intersection area between the bottom wall close to the tank wall and the rear wall of the tank.

[0073] According to one embodiment, the / each nozzle of the device for cooling the unloading pump is located less than 5 meters from the unloading pump.

[0074] According to one embodiment, the feed pipe of the device for cooling the unloading pump is connected to the drain pump located in the tank and / or is suitable for connection to the loading terminal.

[0075] According to one embodiment, the device for cooling the vertical columns comprises a feed pipe for directing the flow of liquefied gas to one or more nozzles directed towards each vertical column.

[0076] According to one embodiment, the / each nozzle of the device for cooling the vertical column is located less than 5 meters from the vertical column.

[0077] According to one embodiment, the / each nozzle of the device for cooling the unloading pump is arranged in the region of the tank close to the rear wall of the tank.

[0078] According to one embodiment, the feed pipe of the device for cooling the vertical columns is connected to a drainage pump located in the tank or is suitable for connection to a loading terminal.

[0079] According to one embodiment, the device comprises a temperature sensor for measuring the temperature of the pump or of the fluid contained in the internal space of the tank, the height of the temperature sensor being between the lowest point of the pump and the highest point of the pump. Thanks to these characteristics, given the measurement of the temperature of the pump assembly or of the fluid environment in which the pump is immersed, in particular the gas temperature in which it is immersed, it is possible to obtain a relevant temperature for determining the real state of the pump.

[0080] The arrangement of a plurality of temperature sensors enables reliable temperature information to be obtained. A first possibility is to place the temperature sensor (i.e. at least the sensitive part of the sensor) in direct contact with a component of the pump, in particular to place the temperature sensor on or in a component of the pump. According to a plurality of embodiments, the temperature sensor may be arranged on an element selected from the group consisting of the outer housing of the pump, a portion of the discharge path adjacent to the outlet of the pump, a fixing flange connecting the discharge path and the outlet of the pump.

[0081] According to various embodiments, when the pump takes the form of a centrifugal pump or other rotating machine, the temperature sensor is arranged in the pump, preferably in the stator of the pump. During operation, such a temperature sensor is particularly suitable for measuring the temperature inside the channel of the pump for discharging fluid.

[0082] According to one embodiment, a temperature sensor is arranged on the loading / unloading tower to measure the temperature of the fluid contained in the inner space of the tank. According to one embodiment, the temperature sensor is arranged on a surface of the loading / unloading tower facing the unloading pump.

[0083] The temperature sensor can be manufactured by many technologies, in particular, it can be manufactured according to the temperature range required to be reached in use. In various embodiments suitable for LNG, the temperature sensor is a thermocouple or a platinum resistance thermometer.

[0084] According to one embodiment, the temperature sensor comprises means for measuring the current I and the voltage U of the winding of the motor of the unloading pump. For example, these measuring means may be a voltmeter, a strain gauge, a multimeter or any other measuring arrangement capable of determining the current and / or voltage of the winding.

[0085] According to one embodiment, the device comprises a calculation unit for calculating the temperature of the pump by means of measured values ​​of the current I and the voltage U of the winding which unloads the pump.

[0086] In one embodiment, the device further comprises an information system functionally connected to the temperature sensor to obtain a temperature measurement signal from the temperature sensor, and the information system further comprises a human-computer interface for communicating the temperature measurement value provided by the temperature sensor to a person responsible for operating the tank.

[0087] According to one embodiment, the device further comprises an information system adapted to control the device for cooling the unloading pump according to the unloading pump temperature measurement signal.

[0088] According to one embodiment, the present invention provides a ship for transporting fluids, the ship comprising the above-mentioned device.

[0089] According to one embodiment, the present invention provides a method of loading or unloading such a vessel, in which the fluid is transported to and from the tank via an insulated pipeline, either a floating or land-based loading / unloading terminal.

[0090] According to one embodiment, the present invention provides a fluid transfer system, which includes the above-mentioned ship, an insulated pipe and a pump, wherein the insulated pipe is used to connect the tank installed in the hull to a floating or land loading / unloading terminal, and the pump is used to drive the fluid from the floating or land loading / unloading terminal to the tank in the ship through the insulated pipe or to drive the fluid from the tank in the ship to the floating or land loading / unloading terminal. BRIEF DESCRIPTION OF THE DRAWINGS

[0091] The present invention will be better understood in conjunction with the accompanying drawings and a number of specific embodiments, and other objects, details, features and advantages thereof will become clearer and more explicit. It should be noted that the specific embodiments do not limit the present invention.

[0092] - Figure 1 It is a cross-sectional view of the liquefied gas storage device according to the first embodiment.

[0093] - Figure 2is a cross-sectional view of a liquefied gas storage device according to a second embodiment.

[0094] - Figure 3 It is a schematic cross-sectional view of a device according to another embodiment of the present invention.

[0095] - Figure 4 for Figure 3 Enlarged view of region IV.

[0096] - Figure 5 A cross-sectional view of a methane transport tanker including a liquefied gas storage facility and a loading / unloading terminal for the liquefied gas facility. DETAILED DESCRIPTION

[0097] Figure 1 A liquefied gas storage device 1 according to a first embodiment of the present invention is shown. The device 1 can be installed on land or on a floating structure. In the case of a floating structure, the device 1 can be used for liquefied natural gas carriers such as methane tankers, but can also be used for any ship that supplies gas to a propulsion device, an engine unit, a steam generator or any other consumer component.

[0098] The device 1 comprises a fluid-tight and thermally insulated liquefied gas storage tank 2. According to one embodiment, the tank 2 is a membrane tank capable of storing liquefied gas at atmospheric pressure. In particular, such a membrane tank comprises a multilayer structure, which comprises, from the outside to the inside of the tank 2, a secondary thermal insulation barrier, a secondary sealing membrane, a primary thermal insulation barrier, a primary sealing membrane, the secondary thermal insulation barrier comprising an insulating element resting against a supporting structure, the primary thermal insulation barrier comprising an insulating element resting against a secondary sealing member, the primary sealing membrane being used to contact the liquefied gas contained in the tank 2. For example, such membrane tanks are specifically described in patent applications WO14057221, FR2691520 and FR2877638.

[0099] The liquefied gas stored by the device 1 can be in particular liquefied natural gas (LNG), that is to say a gas mixture which mainly contains methane and one or more other hydrocarbons, such as ethane, propane, n-butane, isobutane, n-pentane, isopentane, neopentane and a small amount of nitrogen. Liquefied natural gas is stored at atmospheric pressure at a temperature of approximately -162° C. The liquefied gas can also be ethane or liquefied petroleum gas (LPG), that is to say a hydrocarbon mixture obtained by refining petroleum which mainly contains propane and butane.

[0100] The device 1 further comprises a loading / unloading tower 3, which is specifically capable of loading cargo into the tank 2 before transport and unloading cargo after transport. When the device 1 is on board a ship, such as a methane tanker, the loading / unloading tower 3 is, for example, installed near the rear wall 4 of the tank 2, because during unloading, the methane tanker is tilted to the rear, which can maximize the amount of LNG unloaded by the loading / unloading tower 3.

[0101] The loading / unloading tower 3 is suspended from the top wall of the tank 2 and extends substantially over the entire height of the tank 2. In an embodiment not shown, the loading / unloading tower 3 is suspended from the top wall of a region of the tank 2, termed the liquid dome. Such a liquid dome is described in detail in the application FR2991430FR.

[0102] The loading / unloading tower 3 supports one or more pumps 6 at its lower end, which are used to unload the cargo. The unloading pump 6 is arranged near the bottom wall of the tank. The purpose of arranging the unloading pump 6 near the bottom wall of the tank is to enable the pump to pump out most of the cargo stored in the tank, except for possible liquid losses of less than 10% of the tank capacity. The unloading pump 10 is a centrifugal pump that can suck out liquid fluid through an inlet located at the bottom of the unloading pump and discharge the liquid fluid into an unloading route, which is connected to an outlet located at the top of the unloading pump. The unloading pump 6 has a high nominal flow rate to ensure rapid processing of large quantities of cargo, such as 500m 3 / h.

[0103] Figure 1 Only one unloading pump 6 is shown. The loading tower 3 comprises a tripod structure, that is, it comprises three vertical columns 7, 8, 9, each of which is fixed to each other by a crossbeam 10. Each vertical column 7, 8, 9 is hollow and passes through the top wall 5 of the tank 2. Therefore, each vertical column 7, 8, 9 either defines a loading and / or unloading route, which can load or unload liquefied gas, or defines a spare well, which can lower a spare pump and an unloading route in the event of failure of other unloading pumps 6.

[0104] In a particular embodiment, two vertical columns 7, 8 define a tank unloading route, for which purpose they are connected to an unloading pump 6 fixed to the lower end of the loading / unloading tower 3, while a third vertical column 9 defines a reserve well. In such an embodiment, the loading / unloading tower 3 is equipped with one or more loading routes that do not constitute one of the vertical columns 7, 8, 9 of the tripod structure.

[0105] In addition, the device 1 comprises a device for cooling the vertical columns. Such a device for cooling the vertical columns 11 is arranged to direct the flow of liquefied gas towards each vertical column 7, 8, 9 in such a way that the liquefied gas flow evaporates in contact with the vertical column, so that the latent heat of evaporation of the liquefied gas flow cools the vertical columns 7, 8, 9. Such a device for cooling the vertical columns 11 makes it possible to homogeneously cool the vertical columns 7, 8, 9 before the liquefied gas is loaded into the tank 2. In fact, if the vertical columns 7, 8, 9 are not homogeneously cooled before the liquefied gas is loaded into the tank 2, the loading / unloading tower 3 tends to bend due to the temperature differences caused by the path of the liquefied gas in the loading route, and to exert high pressure on the top wall 5, with the possibility of damaging the top wall 5.

[0106] In the embodiment shown, the device for cooling the vertical column 11 comprises a supply pipe 12, which passes through the top wall 5, and a spray manifold 13, which is located inside the tank 2 and connected to the supply pipe 12. The spray manifold 13 is located in a straight line with the vertical columns 7, 8, 9 and comprises a plurality of nozzles 14, each nozzle 14 is directed toward each vertical column 7, 8, 9 and is arranged near the upper end of the vertical column 7, 8, 9, usually at a distance less than 5 meters, for example, in the range of about tens of centimeters to 1 meter.

[0107] According to one embodiment, the feed pipe 12 is connected to a drainage pump 15, which is arranged close to the bottom of the tank 2. In particular, the drainage pump 15 can be fixed to the lower end of the loading / unloading tower 3. The drainage pump 15 is able to pump the loss of liquefied gas remaining in the tank 2. Therefore, thanks to such a distribution, the vertical columns 7, 8, 9 can be cooled in seawater before the ship is moored at the loading terminal, which significantly shortens the operation duration. In an alternative or complementary way, the feed pipe 12 can be connected to the loading terminal so as to enable it to cool the vertical columns 7, 8, 9 by the flow of liquefied gas flowing out of the loading terminal.

[0108] In other embodiments not shown, the injection manifold 13 of the device for cooling the vertical columns 11 is replaced by other devices capable of utilizing the latent heat of evaporation of the liquefied gas stream to cool the vertical columns 7, 8, 9. Thus, for example, the device for cooling the vertical columns 11 may in particular comprise one or more heat exchangers comprising a cooling circuit integrated in the vertical columns 7, 8, 9, as a result of which the liquefied gas stream evaporates in the cooling circuit and thus cools the vertical columns 7, 8, 9.

[0109] Figure 2 FIG. 1 shows a liquefied gas storage device 1 according to a second embodiment of the present invention. The device 1 is different from Figure 1The device 1 concerned, since it does not comprise means for cooling the vertical column 11 but comprises means for cooling the unloading pump 6. It should be noted that, according to an advantageous embodiment, it is possible to combine Figure 1 and Figure 2 In the embodiment shown, the device 1 comprises means for cooling the vertical column 11 and means for cooling the unloading pump 16 .

[0110] The device for cooling the unloading pump 16 makes it possible to gradually reduce the temperature of the unloading pump 6 before loading the tank 2. In fact, the unloading pump 6 comprises components that are sensitive to thermal shocks, which would make it impossible to gradually cool the unloading pump 6 before loading the tank 2 with liquefied gas and risk damaging the unloading pump 6.

[0111] In the embodiment shown, the device for cooling the unloading pump 16 comprises a feed pipe 17, which passes through the top wall 5; and a spray manifold 18, which is located inside the tank 2. The spray manifold 18 is arranged near the bottom wall 4 of the tank 2 and is located on the same line as one or more unloading pumps 6. The spray manifold 18 includes one or more nozzles 19, each nozzle 19 is directly facing the unloading pump 6. Each nozzle 19 is arranged near the unloading pump 6, that is to say, a distance of usually less than 5 meters and, for example, in the range of about tens of centimeters to 1 meter.

[0112] In such Figure 1 In the embodiment shown, the feed pipe 17 is connected to a drain pump 15 which is arranged near the bottom of the tank 2 and / or which can be connected to a loading terminal.

[0113] Moreover, in other embodiments not shown, the injection manifold 18 of the device for cooling the unloading pump 16 is replaced by other devices capable of utilizing the evaporation latent heat of the liquefied gas stream to cool the vertical columns 7, 8, 9. Specifically, for example, the device for cooling the unloading pump 16 may include a heat converter, the heat converter including a cooling circuit connected to the pump body of the unloading pump, as a result of which the liquefied gas stream evaporates in the cooling circuit to cool the pump body of the unloading pump 6.

[0114] The following will describe the steps of cooling the unloading pump 6 and cooling the vertical columns 7, 8, 9 of the loading / unloading tower 3, both of which are performed before loading the tank 2 with the liquefied gas from the loading terminal through the supply path transported by the loading / unloading station 3.

[0115] Advantageously, in one embodiment, the step of cooling the vertical column and the step of cooling the unloading pump 6 are performed simultaneously.

[0116] Prior to this cooling, the average temperature of the vapour phase in tank 2 is typically greater than -120°C.

[0117] In order to cool the vertical columns 7, 8, 9, the liquefied gas flow remaining in the tank 2 can be sucked into the tank 2 by the drainage pump 15 at the liquefied gas loss level, or the liquefied gas flow can be drawn from the loading terminal and then sprayed to each vertical column 7, 8, 9. In order to ensure that the temperature between the vertical columns 7, 8, 9 is the same, the flow rate of the liquefied gas flow sprayed to each vertical column 7, 8, 9 is approximately the same. For example, the flow rate of the liquefied gas flow sprayed to each vertical column 7, 8, 9 is approximately several m / s. 3 / h or tens of m 3 / h, for example, between 1 and 15m 3 / h (inclusive).

[0118] The step of cooling the vertical columns 7, 8, 9 is performed until the final temperature of the upper ends of the vertical columns 7, 8, 9 is between -120 and -140° C. (inclusive), for example, about -130° C. Specifically, the duration of the cooling step can be estimated by measuring the initial temperature in the tank 2 and the flow rate of the liquefied gas flow once or more.

[0119] In order to cool the unloading pump 6, the residual liquefied gas flow can be sucked into the tank 2 at the level of liquefied gas loss through the drainage pump 15, or the liquefied gas flow can be extracted from the loading terminal and then sprayed to the unloading pump 6. In order to ensure the gradual cooling of the unloading pump 6, the flow rate of the liquefied gas sprayed to the unloading pump 6 is approximately several tenths of m 3 / h or several m 3 / h, for example, between 0.05 and 10 m 3 / h, preferably between 0.1 and 1 m 3 The step of cooling the unloading pump 6 is performed until the final temperature of the pump body of the unloading pump 6 is between -120°C and -140°C (inclusive), for example, about -130°C.

[0120] According to one embodiment, the duration of this step may be determined based on one or more measurements of the initial temperature in the tank and the flow rate of the liquefied gas flow.

[0121] In one embodiment, the temperature of the unloading pump 6 is measured, and when the temperature of the unloading pump reaches a threshold, the cooling step of the unloading pump 6 is terminated.

[0122] Figure 3 and Figure 4 An arrangement for measuring the temperature of an unloading pump is shown.

[0123] exist Figure 3In the figure, an unloading pump 110 is shown by way of example attached to a loading / unloading tower 107 close to the bottom wall 108, for example at a distance of approximately 1 m above the bottom wall 108. The unloading pump 110 is a centrifugal pump capable of sucking a liquid stream through an inlet 114 located at the bottom of the unloading pump 110 and discharging the liquid stream into an unloading line 111 connected to an outlet located at the top of the unloading pump 110, at the level of a fixed flange 112. The unloading line 111 raises the entire length of the loading / unloading tower 107 to the location of a liquid manifold circuit (not shown).

[0124] In order to measure the temperature of the unloading pump 110, a temperature sensor 120 is arranged in, on or in the immediate vicinity of the unloading pump 110. The temperature sensor 120 is functionally connected to an information system 121, for example by a cable or wireless connection 122, so that the temperature measurement results can be used by the staff responsible for operating the tank and / or by the automatic devices controlling the functions of the tank, in particular the automatic devices controlling the devices for cooling the unloading pump.

[0125] Figure 4 Multiple possible locations of the temperature sensor 200 are shown, namely a sensor 201 located inside the pump, a sensor 202 located on the outer surface of the pump casing, a sensor 203 located on the fixed flange 212, and a sensor 204 located on the loading / unloading tower 207 at the same height as the pump, i.e., located between the highest point of the pump 210 (here is the fixed flange 212) and the lowest point of the pump 210 (here is the inlet 214).

[0126] Because it is immersed in the same surrounding fluid as the housing of the pump 210 and is located in the vicinity of the pump 210, the sensor 204 located on the loading / unloading tower 207 can provide temperature measurements that reflect the actual state of the pump 210 in a relatively reliable manner. In particular, in the case where the surrounding fluid is a vapor phase with a stratified temperature field, the location of the sensor at substantially the same height as the pump 210 can ensure that reliable measurements are obtained.

[0127] As indicated by numeral 123 , according to known techniques, the information system 121 may also be connected to other sensors, in particular temperature sensors measuring the temperature at different heights, for example in the tank wall as indicated by numeral 124 .

[0128] In a ship, the information system 121 is part of a system for managing the tanks on board. The information system 121 includes a human-machine interface (not shown), such as a display screen, a dial, a printer, etc. located in a tank operation room or in a ship monitoring room to inform the operator supervising the tank about the status of the tank. The information system 121 formats the temperature data and transmits it to the human-machine interface.

[0129] The same temperature sensor can be used with other pumps of the tank, such as a dry pump or a circulation pump used to spray the liquid in the tank.

[0130] Thanks to the reliable temperature measurement provided by the sensor 120, the operator is able to make decisions on the control of the tank to ensure that the temperature state of the pump is consistent with the envisaged operation every time. Said decisions have an impact in particular on the step of stopping the cooling of the unloading pump. Thanks to the temperature sensor 120, the operator can distinguish whether the pump 110 has reached a predetermined temperature threshold, for example -130°C, to stop the cooling of the pump and trigger the filling of the tank. Said cooling of the unloading pump can also be stopped by programmed automatic means.

[0131] In contrast, in the absence of the temperature sensor 120 , the temperature state of the pump 110 should be estimated based on other measurement methods, such as temperature measurement of the wall, which is unsatisfactory in particular when cooling down during dedicated cooling of the unloaded pump.

[0132] In another embodiment, the temperature sensor is a winding of the motor of the pump and the temperature is obtained by measuring the evolution of the resistivity of the winding of the motor of the pump. The size of the winding is approximately the same as that of the pump itself, which makes it possible to obtain a general assessment of the cooling of the pump by calculating the temperature value of the pump by measuring the resistance of the winding. The principle in this embodiment is to avoid installing the sensor in the pump or in the vicinity of the pump and thus avoid pulling the cable of the sensor in the tank. For this purpose, only the already existing instruments and cables for the pump are used. The instruments already present on the pump are able to measure the voltage U and the current I of the motor winding of the pump. It is then possible to obtain the resistance R of the motor winding of the pump over time according to a simple ratio U / I. winding Then get the resistance R winding After that, the temperature T of the winding as a function of time can be calculated using the following formula:

[0133] R winding =R 20℃ *(1+C mat *(T-293.15))

[0134] R 20℃ Indicates the resistance of the winding at 20°C, C mat is a coefficient that is a function of the material used for the winding.

[0135] It is thus possible to relate the mean value of the temperature of the winding to the resistance of the winding and thus to obtain the mean value of the temperature of the unloading pump 6. The resistance threshold value is chosen to be the threshold value at which it can be determined that the cooling is sufficient.

[0136] refer to Figure 5, a cross-sectional view of a methane carrier 70 shows a fluid-tight insulated tank 71 having an overall prismatic shape installed in a double hull 72 of the ship. The wall of the tank 71 includes a primary fluid-tight barrier in contact with the LNG contained in the tank, a secondary fluid-tight barrier distributed between the primary fluid-tight barrier and the double hull 72 of the ship, and two thermal insulation barriers distributed between the primary fluid-tight barrier and the secondary fluid-tight barrier and between the secondary fluid-tight barrier and the double hull 72, respectively.

[0137] In a manner known per se, the loading / unloading pipeline 73 arranged on the top deck of the ship can be connected to an offshore or port loading or unloading terminal by suitable connections in order to transfer LNG cargo from or into the tank 71 .

[0138] Figure 5 An example of an offshore terminal is shown, which includes a loading and / or unloading station 75, an underwater pipeline 76 and a land installation 77. The loading and / or unloading station 75 is a fixed offshore installation, which includes a mobile arm 74 and a tower 78 supporting the mobile arm 74. The mobile arm 74 carries a bundle of insulated flexible pipes 79 that can be connected to the loading / unloading pipeline 73. The orientable mobile arm 74 is adapted to the loading capacity of all methane carriers. The connecting pipes, not shown, extend in the tower 78. The loading and / or unloading station 75 is capable of loading and unloading a methane carrier 70 from or to a land installation 77. The land installation 77 includes a liquefied gas storage tank 80 and a connecting pipeline 81, which is connected to the loading and / or unloading station 75 through an underground pipeline 76. The underground pipeline 76 allows the liquefied gas to be transferred between the loading or unloading station 75 and the land installation 77 over a long distance, for example 5 km, which allows the methane carrier 70 to be kept at a great distance from the coast during the loading and unloading operations.

[0139] In order to generate the pressure required for conveying the liquefied gas, pumps on board the ship 70 and / or pumps installed on the land installation 77 and / or pumps installed on the loading and unloading station 75 are used.

[0140] Although the present invention has been described in conjunction with a number of specific embodiments, it is apparent that the present invention is not limited to the above-described embodiments and covers all technical equivalents and combinations of the described means within the scope of the present invention.

[0141] Use of the verb "comprise" or "include" and its conjugations does not exclude the presence of elements or steps outside the scope of a claim.

[0142] In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim.

Claims

1. A method for handling a liquefied gas cargo stored in a liquefied gas storage device (1), characterized in that: The liquefied gas storage device includes: - Fluid-tight and thermally insulated liquefied gas storage tank (2); - a loading / unloading tower (3), the tower (3) being suspended from the bottom wall of the tank (2), the tower (3) comprising a plurality of routes passing through the top wall (5) of the tank (2), and each route allowing the tank (2) to be loaded and / or unloaded; the loading / unloading tower (3) comprising at least three vertical columns (7, 8, 9), the at least three vertical columns being fixed to each other and to the top wall (5) of the tank (2) by means of cross beams, the at least three vertical columns comprising a first vertical column, a second vertical column and a third vertical column; the first vertical column, the second vertical column and the third vertical column are hollow and each column defines one of the routes; - at least one unloading pump (6) fixed to the lower end of the loading / unloading tower (3) and connected to one of the routes; The method comprises: - a step of cooling the vertical columns (7, 8, 9), in which a first liquefied gas stream is selectively guided to the first vertical column, a second liquefied gas stream is selectively guided to the second vertical column, and a third liquefied gas stream is selectively guided to the third vertical column, and each of the first liquefied gas stream, the second liquefied gas stream and the third liquefied gas stream is in contact with one of the first vertical column, the second vertical column and the third vertical column to cool the first vertical column, the second vertical column and the third vertical column by utilizing latent heat of evaporation and / or sensible heat of liquefied gas, and the flow rates of the first liquefied gas stream, the second liquefied gas stream and the third liquefied gas stream guided to the first vertical column, the second vertical column and the third vertical column are substantially equal; Prior to loading liquefied gas into the tank (2), a step of cooling the vertical columns (7, 8, 9) is performed, during which the liquefied gas is guided from the loading terminal into the tank (2); Each of the first liquefied gas stream, the second liquefied gas stream, and the third liquefied gas stream is injected through one or more nozzles.

2. The method according to claim 1, characterized in that: The step of cooling the unloading pump (6) is performed until the final temperature of the first vertical column, the second vertical column and the third vertical column reaches between -120°C and -140°C.

3. The method according to claim 1 or 2, characterized in that: The first liquefied gas stream, the second liquefied gas stream and the third liquefied gas stream are selectively introduced into each of the first vertical column, the second vertical column and the third vertical column at a relative flow rate between 1 and 15 m3 / h, respectively.

4. The method according to claim 1 or 2, characterized in that: During the step of cooling the vertical columns (7, 8, 9), the first, second and third liquefied gas flows directed to the first, second and third vertical columns are previously sucked into the tank (2) by a drainage pump (15).

5. The method according to claim 1 or 2, characterized in that: The invention also comprises a step of cooling the unloading pump (6), during which a liquefied gas flow is selectively directed to the unloading pump (6) and brought into contact with the unloading pump (6) so as to cool the unloading pump (6) by utilizing latent heat of evaporation and / or sensible heat of the liquefied gas.

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