WO2022194346A1

WO2022194346A1 - A liquefied fuel discharge assembly in a storage tank

Info

Publication number: WO2022194346A1
Application number: PCT/EP2021/056591
Authority: WO
Inventors: Carl Jørgen RUMMELHOFF
Original assignee: Wärtsilä Gas Solutions Norway AS
Priority date: 2021-03-16
Filing date: 2021-03-16
Publication date: 2022-09-22

Abstract

Invention relates to a liquefied fuel discharge assembly (20) in a storage tank (10), the tank (10) comprising a storage space (12) having a bottom wall, where-in the fuel gas discharge assembly (20) comprising a fuel discharge pipe (30) which opens into the storage space (12) of the tank (10) and extends from the tank (10) through the bottom wall lead-through (22) in a sealed manner, a valve unit (26) arranged to the fuel discharge pipe (30) inside the storage tank (10), an enclosure (38) arranged inside the storage tank (10) enclosing the bottom wall lead-through (22) in a sealed manner, the valve unit (26) is arranged into the enclosure (38), which is enclosing the bot-tom wall lead-through (22), and the fuel discharge pipe (30) extends from the tank (10) space to the valve unit (26) in the enclosure (38) and further from the valve unit (26) inside the enclosure (38) to the lead-through (22) and out of the tank (10) in a sealed manner.

Description

A liquefied fuel discharge assembly in a storage tank

Technical field

[001] The present invention relates to a liquefied fuel discharge assembly in a storage tank according to the preamble of claim 1.

Background art

[002] Gas is becoming more and more attractive fuel for ships' and other marine vessels’ prime movers and auxiliary engines. Particularly, but not exclusively, natural gas (NG) is feasible due to its availability. Natural gas is a gaseous mixture in the ambient circumstances consisting primarily of methane and small amounts of ethane, propane, butane and nitrogen. It has high hydrogen content relative to coal, so when combusted it provides inter alia low amount of emissions, very clean burning process and it is basically free of contaminants. Usually gas is stored as liquefied gas (LG) at cryogenic temperature. The tanks must typically be pressure vessels, which usually are built in cylindrical form, and that the volume of the tanks could be at the magnitude of say 100 - 1500 m³.

[003] Generally, liquefied gas can be discharged from the tank at its upper part, or through its wall above the liquid level in the tank. An example of such arrangement is shown in the publication CN207316471 U.

[004] Publication WO2018202313A1 discloses a liquefied gas fuel supply system in which a fuel supply line is arranged to extend from the bottom of tank such the liquid phase gas is discharged from the tank. The fuel supply line comprises a liquid fuel pump pressurizing the gas in liquid phase, and a gas evaporator which is configured to evaporate the liquefied gas into gaseous form. The fuel supply line is also provided with a shut-off valve arranged between the tank and the pump.

[005] EP2705295B1 discloses a fuel tank and fuel supply system comprising a through-bottom fuel discharge system. The system comprises a safety vessel which is arranged to circumscribe the opening in the bottom inside the tank. The safety vessel is arranged so that its joint to the bottom wall of the tank may not allow the liquefied gas to flow through the joint. The safety vessel thus defines an inner space into which the first conduit section and at least one second conduit section of the fuel supply system are arranged to open.

[006] Although the solutions suggested in the prior art document may be ad- vantageous as such, there is a need to further improve the safety issues of handling of liquefied gas in a fuel supply system.

Disclosure of the Invention

[007] Objects of the invention can be met substantially as is disclosed in the independent claims and in the other claims describing more details of different embodiments of the invention.

[008] In this context liquefied fuel shall be understood as a liquid that is in a vapour state at standard atmospheric pressure and temperature (101.325 kPa and 15°C). Examples are Liquefied Natural Gas (LNG), Liquefied Ethane Gas (LEG) and Liquefied Petroleum Gas (LPG) and various pure components as e.g. ammonia.

[009] The invention presents a liquefied fuel discharge assembly in a storage tank, the tank comprising a storage space having a bottom wall, wherein the fuel discharge assembly comprising, a fuel discharge pipe which opens into the storage space of the tank and extends from the tank through the bottom wall lead-through in a sealed manner, a valve unit arranged to the fuel discharge pipe inside the storage tank, an enclosure arranged inside the storage tank being separated from the storage space in a sealed manner, the enclosure enclosing the bottom wall lead-through, wherein the valve unit is arranged into the enclosure, which is enclosing the bottom wall lead-through, and the fuel discharge pipe extends from the tank space to the valve unit in the enclosure and further from the valve unit inside the enclosure to the lead-through and out of the tank in a sealed manner. [0010] According to an embodiment of the invention the enclosure is a column comprising a lower section and an upper section, extending vertically from the bottom wall of the storage tank to the top wall and through the top wall of the tank, wherein the lower section of the column is at the bottom section of the tank and the upper section of the column reaches the top of the tank.

[0011] According to an embodiment of the invention column comprises a lower section and an upper section, the lower section having a first diameter and the upper section having a second diameter wherein the first diameter is greater than the second diameter. [0012] According to an embodiment of the invention column comprises a lower section and an upper section, the lower section having a first cross sectional area and the upper section having a second cross sectional are wherein the first cross sectional area is greater than the second cross sectional area.

[0013] According to an embodiment of the invention assembly comprising gas introduction means for feeding non-combustible gas into the enclosure and maintaining a predetermined pressure in the enclosure.

[0014] According to an embodiment of the invention assembly comprising gas removal means in the enclosure connected to a gas analyser system.

[0015] According to an embodiment of the invention the valve unit comprises a valve and a valve actuator.

[0016] According to an embodiment of the invention the valve unit comprises a valve, a valve actuator and a force transmission system between the valve and valve actuator, and the force transmission system is lead through a cover on top of the enclosure, and the valve actuator is arranged outside the tank. [0017] According to an embodiment of the invention the valve actuator is a pneumatic actuator, wherein line of pressurized air is arranged to extend from the upper section of the column to the lower section of the column.

[0018] According to an embodiment of the invention the valve actuator is a hydraulic actuator, wherein line of hydraulic fluid is arranged to extend from the upper section of the column to the lower section of the column. [0019] According to an embodiment of the invention the valve actuator is an electric actuator, wherein electric wire line is arranged to extend from the upper section of the column to the lower section of the column.

[0020] According to an embodiment of the invention a safety valve is arranged to the upper section of the column.

[0021] According to an embodiment of the invention the column is in flow communication with a source a pressurized non-combustible gas a pressure proof vessel.

[0022] According to an embodiment of the invention the source a pressurized non-combustible gas is a source of inert gas.

[0023] According to an embodiment of the invention the source of inert gas is a source of pressurized nitrogen.

[0024] According to an embodiment of the invention the bottom wall comprises a sump into which the fuel discharge pipe is arranged to open. [0025] According to an embodiment of the invention the assembly comprises the valve unit in the enclosure provided to the fuel discharge pipe and a shut-down valve provided to the fuel discharge pipe outside the tank.

[0026] According to an embodiment of the invention the valve unit in the enclosure is configured to close the fuel discharge pipe in case of an emergency. [0027] According to an embodiment of the invention the assembly comprises an emergency shut down system ESD which is configured to control the valve unit arranged to the fuel discharge pipe inside the storage tank.

[0028] According to an embodiment of the invention the assembly comprises an emergency shut down system ESD which is configured to detect leakage in the fuel discharge pipe and in case leakage is detected shut down the valve unit.

[0029] According to an embodiment of the invention a thermal relief valve is arranged in flow connection with the discharge pipe between the valve unit and the shut-down valve, inside the enclosure. [0030] According to an embodiment of the invention the assembly comprises at least two enclosures in the tank connected to the fuel discharge pipe each enclosure having the valve unit arranged into the enclosure, and the fuel discharge pipe extending from the tank space to the valve unit in both of the at least two enclosures, and further from the valve unit inside the enclosure to the lead- through and out of the tank in a sealed manner, increasing the redundancy of the assembly.

[0031] The arrangement provides a gas tight enclosure around the internal valve ensuring a safe internal secondary barrier against the liquid content in the tank. [0032] The enclosure is, according to an embodiment of the invention, filled with air or inert gas. Pressure in the enclosure may be allowed to be at the atmospheric pressure around the tank, in connection with both of the options of using air or inert gas. The enclosure may be advantageously pressurised to a pressure above the vapour pressure in the tank. [0033] The enclosure will typically be inerted, advantageously by using pressurized nitrogen.

[0034] If the pressure is kept higher than the said vapour pressure, it may be controlled to a dynamic pressure fluctuating with the vapour pressure or kept at a fixed higher pressure. [0035] Nitrogen removed from the enclosure may be routed to a gas detector checking for fuel gas leakages into the enclosure.

[0036] The emergency shut down system ESD configured to shut down the valve unit in case of detection of leakage provides a safe operation of the fuel supply system. [0037] The exemplary embodiments of the invention presented in this patent application are not to be interpreted to pose limitations to the applicability of the appended claims. The verb "to comprise" is used in this patent application as an open limitation that does not exclude the existence of also unrecited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims.

Brief Description of Drawings [0038] In the following, the invention will be described with reference to the accompanying exemplary, schematic drawings, in which

Figure 1 illustrates a storage tank provided with a liquefied fuel discharge assembly according to an embodiment of the invention,

Figure 2 illustrates a liquefied fuel discharge assembly according to another em- bodiment of the invention,

Figure 3 illustrates a liquefied fuel discharge assembly according to still another embodiment of the invention,

Figure 4 illustrates a liquefied fuel discharge assembly according to still another embodiment of the invention, Figure 5 illustrates a liquefied fuel discharge assembly according to still another embodiment of the invention, and

Figure 6 illustrates a liquefied fuel discharge assembly according to still another embodiment of the invention. Detailed Description of Drawings

[0039] Figure 1 depicts schematically a storage tank 10. The tank has a storage space 12 bordered by the walls of the tank 10. Here the tank has generally cylindrical wall 14 and dome-like ends 16. The tank’s storage space 12 has a region which is vertically lowest, when in installed for use, which is called here a bottom section 18 of the tank 10. There is a fuel discharge pipe 30 arranged at the bottom section 18 of the tank 10. Discharging the fuel from the bottom section facilitates the most effective emptying of the tank such that practically all fuel can be discharged via the discharge pipe 30. For safe and reliable discharge of liquid fuel from the storage tank 10 the tank comprises a liquefied fuel discharge assembly 20. The tank comprises a lead-through 22 in the wall 14 of the bottom section 18 the tank 10. The fuel discharge pipe 30 has an inlet opening 24 which opens into the storage space 12 of the tank 10. The fuel discharge pipe 30 extends from the tank through the bottom wall lead-through 22 in a sealed manner to outside of the tank 10. The fuel discharge pipe 30, which may also be referred to as a pipe, comprises a valve unit 26 next from the inlet opening 24 in the normal flow direction of the fuel when in use. The valve unit 26 comprises a valve 31 , its auxiliaries, and a valve actuator 32. The valve unit 26 is also inside the storage tank 10, but inside an enclosure 38 which encloses a space separate from the storage space 12. In other words, the liquefied fuel discharge assembly 20 comprises further an enclosure 38 arranged inside the storage tank 10 enclosing the bottom wall lead-through 22 and the valve unit 26 in a sealed manner. Thus, the valve unit 26 is arranged into the same enclosure which also surrounds and encloses the lead-through 22, in a gas tight manner.

[0040] As it becomes clear from the figure 1 the fuel discharge pipe 30 extends from the tank space 18 into the enclosure 38 and to the valve unit 26 in the enclosure, and further from the valve unit 26 inside the enclosure 38 to the lead- through 22, and therethrough out of the tank 10 in a sealed manner. The fuel discharge pipe is provided with an emergency shut-down valve 34. The arrangement provides a gas tight enclosure around the valve unit 26 and the lead- through ensuring a safe internal secondary barrier against the liquid content in the tank. The figure 1 does not show the precise construction of the enclosure 38 or the assembly, but it may be comprised of flanged sections for easy maintenance and/or repair or alternatively be fully welded structure requiring cutting off in case of repairs. The enclosure is a pressure proof vessel.

[0041] Advantageously the enclosure 38 is a column 28 comprising a lower section 28.1 and an upper section 28.2. The column 28 is a hollow, gas and liquid tight, elongated cylinder structure which provides an internal elongated channel or space. In its simplest form the column is a tubular. The column 28 is arranged to extend inside the tank 10 between the generally cylindrical wall 14, substantially perpendicularly to longitudinal direction of the tank 10. The column 28 extends vertically - when the tank 10 is assembled for use - from the bottom section 18 of the storage tank, more precisely from the wall 14 at the bottom section to the opposite wall 14 via the centre of the tank 10. The column may extend further through the top wall 14 of the tank 10 as is shown in the figure 1. Figures 2 to 5 disclose embodiments where the column 28 does not extend out from the tank 10, but only to the opposite wall 14 of the tank which has a suitable cover 15 on an access hole 29 arranged to the top of the column 28. Connection of the column 28 to the wall 14 is made gas tight so that internal space of the column is free and separated from the fuel in the tank. The lower section 28.1 of the column 28 is at the bottom section of the tank and the upper section 28.2 of the column is outside the tank 10. The column provides a gas tight and pressure proof enclosure around the valve unit 26 and the lead-through as well as the actuator 32 of the valve 31 , and any other auxiliary devices in the valve unit 26. The environment provided with the by the column provides reliable long-term op- eration of the valve unit 26 and means of reliable installation and maintenance of instrumentation lines 33 for the valve unit 26. Such instrumentation lines may comprise electric wires, data cables, pneumatic hoses by means of which the valve unit 26 can be operated and/or monitored. Advantageously data representing the position of the valve 31 is transmitted from the actuator to further pro- cessing for example in an electronic control unit ECU comprising a control computer.

[0042] Depending on the practical application, according to an embodiment of the invention the valve actuator 32 is a pneumatic actuator, wherein the instrumentation lines 33 comprise line of pressurized air, which is arranged to extend from the upper section of the column to the lower section of the column.

[0043] According to another embodiment of the invention the valve actuator is a hydraulic actuator, wherein the instrumentation lines 33 comprise a line of hydraulic fluid arranged to extend from the upper section of the column to the lower section of the column. [0044] According to still another embodiment of the invention the valve actuator

32 is an electric actuator, wherein the instrumentation lines 33 comprise electric wire line arranged to extend from the upper section of the column to the lower section of the column. [0045] Advantageously, a safety valve 50 is arranged to the upper section of the column.

[0046] In the embodiment of figure 1 there is also shown that the assembly 20 comprises a gas introduction means 36 for feeding non-combustible gas into the enclosure and maintaining a predetermined pressure in the enclosure 38. The tank 10 is provided with a pressure transmitter P the measurement signal of which is made available to the electronic control unit ECU comprising a control computer. Also the column 28, or the enclosure 38 is provided with a pressure transmitter P the measurement signal of which is also made available to the elec- tronic control unit ECU. Making use of the measured pressure in the tank and the column 28 the pressure in the column can be maintained at desired level with respect to the pressure in the tank 10.

[0047] There is a source of non-combustible gas 40 which is arranged in controllable flow communication with the inner space of the column 28. The control- lable flow communication may be realized by a conduit 42 provided with a control valve 44 and an inlet of the conduit in the column. The assembly is also provided with a gas removal means which comprises a gas purge conduit 46 provided with a valve 48 so as to remove or depressurize the space inside the column 28. The purge conduit may be provided with gas detector 47 for checking for fuel gas leakages into the enclosure. By introduction of non-combustible gas into the inner space of the column 28 the safety of operation of the valve unit 26 is increased. Advantageous the non-combustible gas is inert gas and the source of non-combustible gas 40 is a source of inert gas 40. It has been found that for example nitrogen is suitable inert gas. [0048] The column 28 provides a confined space, separated from the liquefied gas in the tank, where the valve unit 26 and the valve actuator 32 are located in suitable circumstances for reliable operation.

[0049] Fuel supply system to which the liquefied fuel discharge assembly and the storage tank are connected to is provided with an emergency shut down system ESD (figure 1). As is mentioned earlier the discharge pipe is provided with the shut-down valve 34 located at a distance from the tank 10. In practise, there is a considerable length of the pipe between the shut-down valve 34 and the tank which is not under control of the shut-down valve 34. Should there emerge a leak in the fuel system, or particularly in pipe between the tank and the shut-down valve 34, the leak can be stopped by the valve unit 26 according to the invention under control of the emergency shut down system ESD. [0050] Typically, but not exclusively, the valve unit 26 will be activated to close, initiated by detection of leakage in the fuel discharge pipe 30, particularly between the tank outlet and the externally located shut down valve 34. A leak detection system provides a signal to the ESD which will initiate alarm and/or emergency shut down action to close the internal valve 31 of the valve unit 26. The leak detection signal is made available to the ESD via its input 52, which is configured to control the valve unit 26 and the emergency shut down system ESD then controls the valve unit 26 to close its valve 31. Thus, the valve unit in the enclosure is configured to close the gas discharge pipe in case of an emergency. Simple temperature elements in spill collector underneath the outlet pipe can also function as leak detection. In case the fuel supply system, and particularly the pipe 30 and the lead-through, is intact, there is no need to close the valve unit 20 if the external valve 34 is operative. If the external valve 34 fails to close, in case of an emergency shut down, the valve unit 20 functions as an extra measure to close the fuel discharge pipe 30, which provides redundancy for closing the fuel discharge pipe 30.

[0051] The leak detection system can be of a type that detects a rapid temperature drop due to evaporation of the released liquefied gas. The leak detection system also can be for example a fiber optical system, in which temperature can affect fibers and locally change the characteristics of light transmission in the fiber. In short, distributed sensors offer the unique ability to measure temperature along their whole length. This capability allows the measurement of thousands of points using a single transducer. The most developed technology of distributed fiber optic sensors is based on Raman scattering. These systems make use of a nonlinear interaction between the light and the glass material of which the fiber is made. If light at a known wavelength is launched into a fiber, a very small amount of it is scattered back at every point along the fiber. Besides the original wavelength (called the Rayleigh component), the scattered light contains components at wavelengths that are different form the original signal (called the Raman and Brillouin components). These shifted components contain information on the local properties of the fiber, in particular the intensity of the Raman peak shows strong temperature dependence. Several other systems can also be combined to increase reliability and preventing false actions. Nonintrusive pres- sure measurements can be based on strain gauges, fiber optics or similar.

[0052] Figure 2 discloses a liquefied fuel discharge assembly 20 according to another embodiment of the invention, which is otherwise similar to that shown in the figure 1 but in which the column 28 comprises a lower section 28.1 having a first diameter D1 and an upper section 28.2 having a second diameter D2, wherein the first diameter D1 is greater than the second diameter D2. The first diameter is advantageously at least 2 times the second diameter. The second diameter is sufficiently large to accommodate necessary cabling and/or tubing. This way the column 28 occupies only a minimal space from the storage tank 10.

[0053] Even if tubular cross section is advantageous structure for the column 28, it may also be different, such as oval or polygonal or even rectangular. Also, in case the cross section deviates from tubular the column 28 comprises a lower section 28.1 and an upper section 28.2, the lower section having a first cross sectional area and the upper section having a second cross sectional area, the first cross sectional area may be greater than the second cross sectional area. [0054] Figure 3 discloses a liquefied fuel discharge assembly 20 according to another embodiment of the invention, which is otherwise similar to that shown in the figure 1 and 2 but in which the bottom section 18 of the tank comprises a sump 18’ into which the gas discharge pipe is arranged to open. The sump 18’ is an outwardly extending bulge in the bottom section 18 of the tank. The inlet 24 of the lead through 22 is below the tank bottom section 18 outside the sump 18’. By means of the sump only minimal amount of fuel is left in the tank when it is emptied.

[0055] Figure 4 discloses a liquefied fuel discharge assembly 20 according to another embodiment of the invention, which is otherwise similar to that shown in the figure 1 2 or 3 but in which a thermal relief valve 54 is arranged in flow connection with the discharge pipe 30 between the valve unit and the shut-down valve 34, inside the enclosure 38. Preferably the thermal relief valve 54 is installed at top of the tank 10, outside the column 28, but can also be installed inside the column. Purpose of the thermal relief valve 54 is to protect the pipe segment between the external shut down valve 34 and the internal valve unit 20 in the event that both valves are closed simultaneously. [0056] For redundancy two parallel fuel discharge assemblies can be provided in one storage tank 10 as is depicted in the Figure 5. There is shown an embodiment in which the bottom section 18 of the tank comprises a sump 18’ where both assemblies are arranged correspondingly to that shown in the figure 3. However, two or even more parallel assemblies can be arranged in the tank according to the embodiment of the figure 1 where the tank does not include the sump.

[0057] Figure 6 discloses a liquefied fuel discharge assembly 20 according to another embodiment of the invention, which is otherwise similar to that shown in other figures but in this embodiment the actuator 32 of the valve unit 26 is arranged outside the tank 10 and also outside the enclosure 38 , wherein a force transmission line 33’ is arranged to extend from the lower section of the column 28 to the upper section of the column and further outside the tank 10. Thus, it is conceivable to combine this feature with any other embodiment of the invention. The force transmission system is connected to the valve 31 , and on top of the column 28 led outside the tank 10, and the enclosure 38, through the cover 15 in a sealed manner, and connected to the actuator 32. The valve actuator 32 located outside the enclosure 38 is thereby coupled with the valve 31 by means of suitable force transmission system. This way the valve actuator is more easily accessible for maintenance work.

[0058] While the invention has been described herein by way of examples in connection with what are, at present, considered to be the most preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but is intended to cover various combinations or modifications of its features, and several other applications included within the scope of the invention, as defined in the appended claims. The details mentioned in connection with any embodiment above may be used in connection with another embodiment when such combination is technically feasible.

Claims

1. A liquefied fuel discharge assembly (20) in a storage tank (10), the tank (10) comprising a storage space (12) having a bottom wall, wherein the gas discharge assembly (20) comprises a fuel discharge pipe (30) which opens into the storage space (12) of the tank (10) and extends from the tank (10) through the bottom wall lead-through (22) in a sealed manner, a valve unit (26) arranged to the fuel discharge pipe (30) inside the storage tank

(10), an enclosure (38) arranged inside the storage tank (10) being separated from the storage space (12) in a sealed manner, the enclosure (38) enclosing the bottom wall lead-through (22), characterized in that the valve unit (26) is arranged into the enclosure (38), which is enclosing the bottom wall lead-through (22), and the fuel discharge pipe (30) extends from the tank (10) space to the valve unit (26) in the enclosure (38) and further from the valve unit (26) inside the enclosure (38) to the lead-through (22) and out of the tank (10) in a sealed manner.

2. A liquefied fuel discharge assembly (20) in a storage tank (10) according to claim 1 , characterized in that the enclosure (38) is a column (28) comprising a lower section (28.1) and an upper section (28.2), extending vertically from the bottom wall of the storage tank (10) to the top wall and through the top wall of the tank (10), wherein the lower section (28.1) of the column (28) is at the bottom section of the tank (10) and the upper section (28.2) of the column (28) reaches the top of the tank (10).

3. A liquefied fuel discharge assembly (20) in a storage tank (10) according to anyone of the preceding claims, characterized in that the assembly comprises an emergency shut down system (ESD) which is configured to control the valve unit (26).

4. A liquefied fuel discharge assembly (20) in a storage tank (10) according to claim 2, characterized in that the column (28) comprises a lower section and an upper section, the lower section having a first diameter (D1) and the upper section having a second diameter (D2) wherein the first diameter is greater than the second diameter.

5. A liquefied fuel discharge assembly (20) in a storage tank (10) according to anyone of the preceding claims 2 to 4, characterized in that the column (28) comprises a lower section and an upper section, the lower section having a first cross sectional area and the upper section having a second cross sectional area wherein the first cross sectional area is greater than the second cross sectional area.

6. A liquefied fuel discharge assembly (20) in a storage tank (10) according to anyone of the preceding claims, characterized in that the assembly (20) comprises gas introduction means for feeding non-combustible gas into the enclosure (38) and maintaining a predetermined pressure in the enclosure (38).

7. A liquefied fuel discharge assembly (20) in a storage tank (10) according to anyone of the preceding claims, characterized in that assembly (20) com- prises gas removal means in the enclosure (38) connected to a gas analyser system.

8. A liquefied fuel discharge assembly (20) in a storage tank (10) according to anyone of the preceding claims, characterized in that valve unit (26) comprises a valve (31) and a valve actuator (32).

9. A liquefied fuel discharge assembly (20) in a storage tank (10) according to claims 1 - 7, characterized in that the valve unit (26) comprises a valve (31), a valve actuator (32) and a force transmission system (33’) between the valve (31) and valve actuator (32), and the force transmission system (33’) is lead through a cover (15) on top of the enclosure (38), and the valve actuator (32) is arranged outside the tank (10).

10. A liquefied fuel discharge assembly (20) in a storage tank (10) according to claim 8, characterized in that the valve actuator is a pneumatic actuator, wherein line of pressurized air is arranged to extend from the upper section (28.2) of the column (28) to the lower section (28.1) of the column (28).

11. A liquefied fuel discharge assembly (20) in a storage tank (10) according to claim 8, characterized in that the valve actuator is a hydraulic actuator, wherein line of hydraulic fluid is arranged to extend from the upper section (28.2) of the column (28) to the lower section (28.1) of the column (28).

12. A liquefied fuel discharge assembly (20) in a storage tank (10) according to claim 8, characterized in that the valve actuator is an electric actuator, wherein electric wire line is arranged to extend from the upper section (28.2) of the column (28) to the lower section (28.1) of the column (28).

13. A liquefied fuel discharge assembly (20) in a storage tank (10) according to anyone of the preceding claims, characterized in that a safety valve is ar ranged to the upper section (28.2) of the column (28).

14. A liquefied fuel discharge assembly (20) in a storage tank (10) according to anyone of the preceding claims 2 to 13, characterized in that the column (28) is in flow communication with a source a pressurized non-combustible gas a pressure proof vessel.

15. A liquefied fuel discharge assembly (20) in a storage tank (10) according to claim 14, characterized in that the source a pressurized non-combustible gas is a source of inert gas.

16. A liquefied fuel discharge assembly (20) in a storage tank (10) according to claim 14, characterized in that the source of inert gas is a source of pressur ized nitrogen.

17. A liquefied fuel discharge assembly (20) in a storage tank (10) according to claim 1 , characterized in that the bottom wall comprises a sump into which the fuel discharge pipe (30) is arranged to open.

18. A liquefied fuel discharge assembly (20) in a storage tank (10) according to anyone of the preceding claims, characterized in that the valve unit (26) in the enclosure (38) is configured to close the fuel discharge pipe (30) in case of an emergency.

19. A liquefied fuel discharge assembly (20) in a storage tank (10) according to anyone of the preceding claims, characterized in that the assembly (20) comprises the valve unit (26) in the enclosure (38) provided to the gas discharge pipe (30) and a shut-down valve (34) provided to the fuel discharge pipe (30) outside the tank (10).

20. A liquefied gas fuel discharge assembly (20) in a storage tank (10) ac- cording to claim 3, characterized in that the assembly comprises an emergency shut down system (ESD) which is configured to detect leakage in the fuel discharge pipe (30) and in case leakage is detected shut down the valve unit (26).

21. A liquefied fuel discharge assembly (20) in a storage tank (10) according to anyone of the preceding claims, characterized in that a thermal relief valve (54) is arranged in flow connection with the discharge pipe (30) between the valve unit and the shut-down valve (34), inside the enclosure (38).

22. A liquefied fuel discharge assembly (20) in a storage tank (10) according to anyone of the preceding claims, characterized in that the assembly (20) comprises at least two enclosures (38) connected to the fuel discharge pipe (30 each enclosure having the valve unit (26) arranged into the enclosure (38), and the fuel discharge pipe (30) extending from the tank (10) space to the valve unit (26) in both of the at least two enclosures (38) and further from the valve unit (26) inside the enclosure (38) to the lead-through (22) and out of the tank (10) in a sealed manner.