KR20190054847A - Liquefied gas carrier having independent cargo containment system - Google Patents

Abstract

Provided is a competitive liquefied gas transportation vessel capable of having flexibility in driving modes by increasing the operational pressure of a liquefied gas cargo tank by raising the pressure in a hull cargo part of a liquefied gas transportation vessel including an IMO Type-A or IMO Type-B liquefied gas cargo tank. According to the present invention, since operational pressure of a liquefied gas cargo tank is increased, a liquefied gas transportation vessel, which can be safely driven in various driving environments, can be secured. In particular, in the case of FSRU, when LNG cargo has to be stored for a long time without the consumption of the LNG cargo, more LNG can be stored in an LNG cargo part, so a waste of LNG cargo can be minimized and safe driving can be facilitated, which leads to an increase in technological competitiveness of FSRU.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a liquefied gas carrier having an independent cargo tank,

The present invention relates to a liquefied gas carrier having a freestanding tank for storing liquefied gas as a cargo tank. More particularly, the present invention relates to a liquefied gas carrier which holds a liquefied gas cargo tank To a liquefied gas carrier capable of increasing the operating pressure of the liquefied gas cargo tank by lowering the maximum allowable pressure.

The use of natural gas is increasing in industrial fields such as power generation, and the demand for LNG carriers that transport LNG by ship is increasing. In order to transport natural gas onboard a vessel, it is made to have a density of 600 times higher than that of liquid, and is liquefied at about -163 ° C and transported in tank. LNG is vaporized by external heat invasion during operation, and there is a risk of evaporative gas generation and an increase in the pressure of the tank, which may damage the tank. LNG carriers are then transported out of the tank by the generated vapor, or the tank is built to have the strength to withstand the rising pressure during operation. However, in the case of large LNG carriers, there are technical limitations in increasing the design pressure of LNG cargo tanks and it is difficult to incur large costs. For Type-B tanks specified by the IMO, tanks other than Moss are designed to have a maximum design pressure of 0.7 barg, and Moss type valves up to 1.9 bar. However, safety valves are usually opened at about 0.25 barg for safety reasons. However, in the case of an LNG carrier storing a long-term LNG cargo such as FSRU, it is advantageous that the opening pressure of the safety valve is as high as possible so that the LNG carrier can be stored in the LNG cargo tank without wasting evaporation gas for a long time.

Therefore, it is necessary to increase the operating pressure of the liquefied gas cargo tank while securing the safety at a low cost and to enhance the competitiveness of the liquefied gas carrier, especially the FSRU, which requires various operating conditions.

The present invention increases the operating pressure of a liquefied gas cargo tank by increasing the pressure of a hull cargo hold of a liquefied gas carrier equipped with a stand-alone liquefied gas cargo tank such as IMO Type-A or IMO Type-B, To provide a liquefied gas carrier.

According to one aspect of the present invention, there is provided a liquefied gas cargo tank having IMO Type-A or Type-B for storing liquefied gas cargo, a cargo hold having a liquefied gas cargo tank and capable of being pressurized at a pressure higher than atmospheric pressure, A system for pressurizing and supplying nitrogen to the hull cargo window; a hull cargo window supply valve for controlling the amount of nitrogen supplied to the hull hold window in a system capable of pressurizing and supplying the nitrogen; A liquefied gas cargo tank pressure sensing unit for sensing the pressure inside the liquefied gas cargo tank; a hull cargo window discharge pipe branched from the hull cargo window and capable of discharging gas to the outside; A luggage cargo window discharge valve installed in the cargo window discharge pipe, a liquefied gas cargo tank safety valve installed in the liquefied gas cargo tank, And a first connecting pipe for connecting the liquefied gas cargo tank safety valve so that the pressure of the hull holding section acts in the closing direction of the liquefied gas cargo tank safety valve.

The pressure of the hull cargo hold and the liquefied gas cargo tank is sensed and the hull hold is pressurized to atmospheric pressure or more and the maximum working pressure of the liquefied gas cargo tank is subtracted from the operating pressure of the hull hold, It is possible to provide a liquefied gas carrier which is characterized in that the liquefied gas cargo tank is used as a design standard for the thickness, material and the like of the liquefied gas cargo tank.

The hull holds can be structurally reinforced to withstand the pressurized operating pressure.

The operating pressure of the hull holding part may be 0.3 barg or more.

And a blower having a pressure ratio of 1.5 or lower for discharging the evaporated gas generated from the liquefied gas cargo tank to the outside of the liquefied gas cargo tank.

And a liquefied gas cargo tank safety valve installed in the liquefied gas cargo tank. When the operating pressure of the liquefied gas cargo tank and the pressure difference in the hull hold section become the maximum permissible pressure, the liquefied gas cargo tank safety valve is mechanically opened, The gas can be discharged to the atmosphere.

Wherein the liquefied gas cargo tank safety valve includes a spring for exerting an elastic force to prevent the liquefied gas cargo tank safety valve from being opened to a maximum permissible pressure of the liquefied gas cargo tank, .

The evaporation gas discharge pipe for discharging the evaporation gas generated in the liquefied gas cargo tank to the atmosphere and the evaporation gas discharge valve disposed in the evaporation gas discharge pipe, The pressure signal measured by the tank pressure sensing unit is transmitted to the first control unit, and when the difference between the liquefied gas cargo tank pressure and the hull cargo window pressure is close to the maximum permissible pressure of the liquefied gas cargo tank, the evaporation gas discharge valve is opened, The gas can be discharged to the outside.

And a second hull cargo window safety valve for mechanically discharging the gas in the hull hold to the outside if the difference between the pressure of the hull hold and the operating pressure of the liquefied gas cargo tank becomes larger than a predetermined value.

And a spring for exerting an elastic force to prevent the second hull cargo window safety valve (46) from being opened when the pressure is below a certain pressure, wherein the pressure of the liquefied gas cargo tank is applied to the second hull cargo window safety valve And a second connection pipe for connecting the first connection pipe and the second connection pipe.

When the pressure difference between the hull cargo window and the liquefied gas cargo tank is greater than a predetermined value, the pressure signal measured by the hull cargo window pressure sensing unit and the liquefied gas cargo tank pressure sensing unit is transmitted to the second control unit. So that the gas in the hull holding portion can be discharged to the outside.

And a heat exchanger for lowering the temperature of nitrogen supplied to the hull holding section.

And a liquefied gas branch pipe branching from a liquefied gas supply line for supplying liquefied gas to a liquefied gas consuming place and transferring the liquefied gas to the heat exchanger. The nitrogen supplied to the hull cargo window passing through the heat exchanger can be cooled by the liquefied gas.

A plurality of hull cargo gates may be provided which include a plurality of liquefied gas cargo tanks and liquefied gas carrier lines operating at different pressures to the respective hull cargo gates.

According to the present invention, by increasing the operating pressure of the liquefied gas cargo tank, it is possible to secure a liquefied gas carrier which can operate safely in various operating environments. In particular, in the case of FSRU, it is necessary to store and store LNG cargoes for a long period without consuming LNG cargo. In this situation, by storing more LNG in the LNG cargo hold to minimize waste of LNG cargo and to enable safe operation, It can increase technological competitiveness.

1 is a view showing a liquefied gas carrier having a freestanding cargo tank of the present invention.
2 is a view for explaining a characteristic portion of the present invention.
3 is a view showing an example of a liquefied gas cargo tank safety valve according to the present invention.
4 is a view showing the mechanical liquefied gas cargo tank safety valve 30 according to the present invention together with the liquefied gas discharge valve 34 through automatic control.
5 is a view showing an example of a second hull cargo window safety valve according to the present invention.
6 is a view showing a mechanical hull cargo window safety valve 46 according to the present invention and a hull cargo window discharge valve 44 through automatic control.
FIG. 7 is a view showing a liquefied gas cargo tank system for supplying gas to the hull holding section according to the present invention and for cooling the gas supplied to the hull holding section through the liquefied gas.
8 is a view showing a liquefied gas carrier including a plurality of hull cargo windows and a plurality of liquefied gas cargo tanks.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention is capable of various modifications and various embodiments, and specific embodiments are illustrated in the drawings and described in detail in the detailed description. It should be understood, however, that the present invention is not intended to be limited to the specific embodiments, but includes modes, equivalents, and alternatives falling within the spirit and scope of the present invention. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a liquefied gas carrier having IMO Type-A or IMO Type-B tanks according to the present invention will be described in detail with reference to the accompanying drawings. In the following description, The same reference numerals are assigned to the same elements and a duplicate description thereof will be omitted.

The liquefied gas carrier according to the present invention includes all types of ships and marine plants storing LNG as freight as well as general LNG carrier, FSRU, FLNG and all kinds of liquefied gas such as ethane, ethylene, LPG, do. The technique of the present invention is applicable not only to maritime transportation means but also to a land fixed type liquefied gas storage facility.

In the present invention, the IMO Type-A tank and the Type-B tank can be defined in IGC code (International Code for the Construction and Equipment of Ships carrying Liquefied Gases in Bulk).

1 is a view showing a liquefied gas carrier having IMO Type-A or IMO Type-B tanks according to a first embodiment of the present invention.

Referring to FIG. 1, the liquefied gas carrier according to the present embodiment includes a liquefied gas cargo tank 10 of IMO Type-A or Type-B, a cargo hold for installing a liquefied gas cargo tank 10, (20) is maintained at a pressure higher than the atmospheric pressure and the pressure obtained by subtracting the operating pressure of the hull cargo hold section (20) from the maximum operating pressure of the liquefied gas cargo tank (10) And may be a design standard such as the thickness and material of the liquefied gas cargo tank 10.

The hull cargo window 20 may be structured so as to withstand the pressurized operating pressure. In the prior art, the hull cargo window 20 where a liquid gas cargo tank of Type-A or Type-B is installed is filled with a micro-pressure inert gas. However, in the present invention, since the hull cargo window 20 is pressurized to atmospheric pressure or higher Structural reinforcement is necessary if necessary.

The operating pressure of the hull cargo window 20 is preferably 0.3 barg or more. Conventional LNG carriers are being operated to open safety valves at about 0.25 barg to protect LNG cargo tanks. In this case, if there is no large compressor, it is difficult to transfer the evaporation gas to the land equipment near 0.25 barg and the liquefied gas pressure below 0.25 barg. Therefore, the compressor is included in the liquefied gas carrier and pressurized to about 2.0 barg. In the present invention, when the operating pressure of the hull cargo window 20 is operated at 0.3 barg or more, the differential pressure between the hull cargo window 20 and the liquefied gas cargo tank 10 can be increased to 0.55 barg It can be transported without compressors using this differential pressure through the conditions of the land equipment and piping design. It is advantageous in that the higher the operating pressure of the hull cargo hold section 20 is, the more easily the transfer can be performed. Preferably, the pressure of the hull cargo hold section 20 is adjusted to a value at which the pressure of the liquid cargo tank 10 is raised by the evaporation gas. The evaporation gas can be safely transported to the offshore facility without any additional equipment. That is, when the liquefied gas cargo is shipped or the evaporated gas generated in the liquefied gas cargo tank is returned to the land facility, the pressure in the liquefied gas cargo tank 10 is operated at 1.5 bara or more without the compressor, (10) and the land facility. At this time, the blower may have a pressure ratio of 1.5 or less in order to discharge the evaporated gas generated in the liquefied gas cargo tank 10 to the outside.

The liquefied gas cargo tanks 10 may be designed to be structurally safe when the operating pressure of the hull cargo window 20 is such that the liquefied gas cargo tanks 10 act as external pressure and the liquefied gas cargo tanks 10 are at atmospheric pressure . In this case, the problem of buckling due to the external pressure of the liquefied gas cargo tank 10 can be avoided, and if structural reinforcement is difficult in terms of technical and price, it should be avoided by operating other equipment such as air discharge.

The liquefied gas cargo tank is evaporated by the heat input from the outside and the pressure is raised. When the maximum allowable working pressure (MAWP) is reached for the protection of the tank, the safety valve is opened to discharge the liquefied gas Protect the tank. The maximum permissible pressure is a design criterion such as the material and thickness of the liquefied gas cargo tank. Accordingly, when the operating pressure of the liquefied gas reaches the maximum permissible pressure, the safety valve is opened and discharged to the atmosphere. Consequently, the maximum operating pressure of the liquefied gas is equal to the maximum permissible pressure of the tank, both of which are determined by the gauge pressure due to the difference from the atmosphere in which the liquefied gas is discharged.

One side of the present invention is further provided with a hull cargo window section 20 and the liquefied gas cargo tank 10 is installed in a hull cargo window section 20 maintained at a pressure higher than atmospheric pressure, To reduce the difference between the external pressure and the internal pressure affecting the structural stability of the tank. Therefore, the gauge pressure in the space where the liquefied gas cargo tank is installed is determined by the difference between the pressure inside the liquefied gas cargo tank 10 and the pressure in the hull cargo window 20, and the gauge pressure for obtaining the maximum allowable pressure is based on this external pressure Should be. Therefore, when the present invention is applied, it is possible to operate at a pressure higher than the maximum permissible pressure of the liquefied gas cargo tank.

The liquefied gas carrier according to the present embodiment includes a liquefied gas cargo tank discharge pipe 31 for discharging the gas of the liquefied gas cargo tank 10 to the outside and a liquefied gas cargo tank discharge pipe 31 for controlling the operating pressure of the liquefied gas cargo tank 10, And a liquefied gas cargo tank safety valve (30) mechanically discharging the gas of the liquefied gas cargo tank out of the tank through the liquefied gas cargo tank discharge pipe (31) when the pressure difference of the liquefied gas cargo tank have.

The liquefied gas cargo tank safety valve 30 includes a spring for exerting an elastic force to prevent the liquefied gas cargo tank 10 from being opened to a maximum permissible pressure, ) Of the liquefied gas cargo tank safety valve 30 so as to act in the closing direction of the liquefied gas cargo tank safety valve 30. Fig. 3 shows an example of such a safety valve. That is, when the elastic force of the spring is generated by a force corresponding to the maximum permissible pressure of the liquefied gas cargo tank 10 and the first connection pipe 35 is connected to transmit the pressure of the hull cargo window 20, The safety of the liquefied gas cargo tank 10 can be ensured irrespective of the operating pressure of the liquefied gas cargo tank 20. 3 shows an example of a safety valve for protecting the liquefied gas cargo tank 10 against pressure change of the hull cargo window 20 by being connected to the hull cargo window 20, , There is no limitation on the type and the method of the liquefied gas cargo tank safety valve 30 when the above object is satisfied.

In order to secure the safety of the liquefied gas cargo tank 10 according to the change in the pressure of the hull cargo window 20, the present invention can be achieved through electrical control other than mechanical safety valves. A hull cargo window pressure sensing part 42 for sensing the pressure of the hull cargo window 20, a liquefied gas cargo tank pressure sensing part 32 for sensing the pressure inside the liquefied gas cargo tank, a liquefied gas cargo tank 10 A liquefied gas cargo tank discharge pipe 31 branched from the liquefied gas cargo tank discharge pipe 31 and capable of discharging the gas to the outside and a liquefied gas discharge valve 34 provided in the liquefied gas cargo tank discharge pipe 31, The pressure signal measured by the sensing unit 42 and the liquefied gas cargo tank pressure sensing unit 32 is transmitted to the first control unit 33 so that the difference between the pressure of the liquefied gas cargo tank 10 and the pressure of the hull cargo window 20 When the liquefied gas storage tank is close to the maximum permissible pressure, the liquefied gas discharge valve 34 may be opened to discharge the gas of the liquefied gas cargo tank 10 to the outside. FIG. 4 also shows a configuration with a mechanical liquefied gas cargo tank safety valve 30 and automatic control.

One side of the present invention includes a hull cargo window discharge pipe 41 for discharging the gas of the hull cargo window 20 to the outside and a discharge port for discharging the difference between the pressure of the hull cargo window 20 and the operating pressure of the liquefied gas cargo tank 10 And a second hull cargo window safety valve 46 for mechanically discharging the gas of the hull cargo window portion 20 to the outside when the opening of the hull cargo window portion 20 becomes larger than a predetermined value. For safety, the hull cargo window safety valve 40, which is mechanically opened at the maximum allowable pressure of the hull cargo window 20, should be installed for protecting the hull cargo window 20 itself. The second hull cargo window safety valve 46 can be installed to protect the liquefied gas cargo tank 10. If the external pressure of the storage tank is greater than the internal pressure, the liquefied gas cargo tank should be designed to have sufficient strength to withstand such buckling since buckling may occur in the storage tank and may collapse. The strength against buckling is increased not only by the thickness but also by the length, the reinforcing material and the like. The buckling problem can be avoided by preventing the pressure of the hull cargo window portion 20 from becoming larger than a predetermined value or more than the pressure of the liquefied gas cargo tank 10 on the one hand. Since the pressure at which the buckling occurs varies depending on the type, material, thickness, size, stiffener, etc. of the tank, the numerical value can not be limited in the present invention. When the external pressure becomes larger than the constant pressure, the second hull cargo window safety valve 46 Can be opened to mechanically protect the liquefied gas cargo tank 10.

In order to equip such a mechanical safety valve, the second hull cargo window safety valve (46) is provided with a spring which exerts an elastic force to block the opening of the second hull cargo window safety valve (46) at a certain pressure or less, and the pressure of the liquefied gas cargo tank (10) And a second connection pipe 45 for connecting the cargo window safety valve 46 in a closing direction. 5 shows an example of a safety valve connected with the liquefied gas cargo tank 10 to mechanically lower the pressure of the hull cargo window 20 to avoid the problem of buckling of the liquefied gas cargo tank, Without being limited to this, the type and method of the second hull cargo hold safety valve 46 are not limited as long as this object is satisfied.

In order to ensure safety against buckling of the liquefied gas cargo tank 10, the present invention can be achieved through electrical control in addition to mechanical safety valves. A liquefied gas cargo tank pressure sensing part 32 for sensing the pressure inside the liquefied gas cargo tank 20, a hull cargo window part 20 for sensing the pressure inside the liquefied gas cargo tank 20, And a hull cargo window discharge valve (44) installed in the hull cargo window discharge pipe (41), and the hull cargo window pressure sensor (41) The pressure signal measured by the pressure sensor 42 and the pressure sensing unit 32 of the liquefied gas cargo tank is transmitted to the second control unit 43 so that the pressure difference between the hull cargo window 20 and the liquefied gas cargo tank 10 is equal to or greater than a predetermined value The hull cargo window discharge valve 40 may be opened to discharge the gas of the hull cargo window 20 to the outside. In FIG. 6, a mechanical hull cargo window safety valve 46 and automatic control are shown together.

One aspect of the present invention may be a form including a hull cargo window supply pipe 50 for supplying a gas to press the hull cargo window 20. And a hull cargo window supply valve 52 for controlling the flow rate supplied to the hull cargo window 20. The liquefied gas cargo tank pressure sensing unit 32 and the hull cargo window pressure sensing unit 42 And the third control unit 51 receives the measured pressure signal. When the pressure of the liquefied gas cargo tank 10 is higher than the pressure of the hull cargo window 20 and the pressure of the hull cargo window 20 is higher than the predetermined working pressure The hull cargo window supply valve 52 may be controlled to supply gas to the hull holding section. The operating pressure of the hull cargo window 20 can be adjusted automatically or manually through the hull cargo window supply valve or the hull cargo window discharge valve and the operating pressure of the hull cargo window 20 is higher than the operating pressure of the liquefied gas cargo tank It is desirable to operate with low pressure. This is because when the pressure of the hull cargo window 20 is higher when the liquefied gas cargo tank 10 is cracked, the liquefied gas does not leak out to the hull cargo window 20, but rather the gas of the hull cargo window 20 is liquefied You can enter the gas cargo tank. If the gas pressurized in the hull cargo window (20) is air, there is a possibility of potential fire hazard, water freezing, etc. if it leaks into a liquefied gas cargo tank. Even if the gas pressurized to the hull cargo window 20 is a safe gas such as nitrogen, mechanical damage of the liquefied gas cargo tank 10 may be difficult to detect early. When the pressure of the hull cargo window 20 is lower than that of the liquefied gas cargo tank 10, leakage occurs to the hull cargo window 20 when the liquefied gas cargo tanks are cracked, Or the problem of the liquefied gas cargo tank 10 can be detected early by the gas detector provided at the rear end of the hull cargo window discharge pipe 41. The gas detector includes all the monitoring methods that can detect the possibility of liquefied gas leakage by measuring the temperature or pressure, as well as the gas detectors that detect the components of the liquefied gas.

One aspect of the present invention includes a heat exchanger (60) installed in a hull cargo window supply pipe (50) for supplying gas to the hull cargo window (20) and lowering the temperature of the gas supplied to the hull cargo window Lt; / RTI > 7, the liquefied gas is branched from the liquefied gas supply pipe 61 connected to the liquefied gas cargo tank 10 to supply the liquefied gas to the liquefied gas consuming unit 63, and is supplied to the heat exchanger 60, And the liquefied gas branch piping 62 for passing the liquefied gas through the heat exchanger 60 is cooled by the liquefied gas. When it is necessary to pressurize the hull cargo window 20, the supplied gas is cooled by the liquefied gas so that the warm supply gas increases the temperature of the hull cargo window 20 and the heat penetration amount of the liquefied gas cargo tank 10 To avoid increasing.

One aspect of the present invention includes a plurality of hull cargo window portions 20 and a plurality of liquefied gas cargo tanks 10 and is operated independently of each other at different pressures applied to the respective hull cargo window portions 20 do. In particular, in the case of an LPG carrier, different types of cargo may be loaded in each tank, and thus the pressure of the LPG cargo tank may vary. Accordingly, in this case, by pressurizing the pressure of the hull cargo window 20 differently, different types of cargo can be loaded and the liquefied gas cargo tanks 10 having different pressures can be stably operated.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. will be.

10: liquefied gas cargo tank 20: hull cargo window
30: liquefied gas cargo tank safety valve 31: liquefied gas cargo tank discharge pipe
32: liquefied gas cargo tank pressure sensing unit 33: first control unit
34: liquefied gas discharge valve 35: first connection pipe
40: Hull cargo window safety valve 41: Hull cargo window discharge pipe
42: hull cargo window pressure sensing part 43: second control part
44: Hull cargo window outlet valve 45: Second connection pipe
46: Second hull cargo window safety valve 50: Hull cargo window supply piping
51: third control part 52: hull cargo window supply valve
60: heat exchanger 61: liquefied gas supply pipe
62: liquefied gas branch pipe 63: liquefied gas consumer
70: gas supply device 71: first hull cargo window supply pipe
72: second hull cargo window supply pipe 73: third hull cargo window supply pipe
81: first hull cargo window discharge pipe 82: second hull cargo window discharge pipe
83: Third Hull Cargo Window Discharge Pipe 100: Liquefied Gas Carrier

Claims (15)

IMO Type-A or Type-B liquefied gas cargo tanks (10) for storing liquefied gas cargo;
A cargo hold (20) installed inside the liquefied gas cargo tank (10) and capable of being pressurized to a pressure higher than atmospheric pressure;
A system 70 capable of pressurizing and supplying nitrogen to the hull cargo window 20;
A hull cargo window supply valve (52) for controlling the amount of nitrogen supplied to the hull cargo window (20) in a system (70) capable of pressurizing and supplying the nitrogen;
A hull cargo window pressure sensing part (42) for sensing the pressure of the hull cargo window part (20);
A liquefied gas cargo tank pressure sensing unit 32 for sensing a pressure inside the liquefied gas cargo tank 10;
A hull cargo window discharge pipe (41) branched from the hull cargo window (20) and capable of discharging gas to the outside;
A hull cargo window discharge valve (44) installed on the hull cargo window discharge pipe (41);
A liquefied gas cargo tank safety valve 30 installed in the liquefied gas cargo tank 10; And
And a first connection pipe (35) for connecting the liquefied gas storage tank safety valve (30) so that the pressure of the hull cargo window (20) acts in a closing direction of the liquefied gas cargo tank safety valve (30) . The method according to claim 1,
The pressure of the hull cargo window 20 and the liquefied gas cargo tank 10 is sensed to pressurize the hull cargo window 20 at atmospheric pressure or higher and the maximum operating pressure of the liquefied gas cargo tank 10 Characterized in that a pressure obtained by subtracting the operating pressure of the cargo window section (20) is set as a maximum permissible pressure so that the thickness and material design criteria of the liquefied gas cargo tank (10) are used. 3. The method of claim 2,
Characterized in that the hull cargo window (20) is structurally reinforced to withstand the pressurized operating pressure. The method according to claim 1,
Characterized in that the operating pressure of the hull cargo window (20) is at least 0.3 barg. The method according to claim 1,
In order to return the liquefied gas cargo or the vaporized gas generated from the liquefied gas cargo tank to the land facility, the pressure in the liquefied gas cargo tank 10 is operated at 1.5 bara or more and the liquefied gas cargo tank 10 and the land facility Wherein the liquefied gas carrier has a free-standing cargo tank. 6. The method of claim 5,
And a blower having a pressure ratio of 1.5 or less for discharging evaporated gas generated from the liquefied gas cargo tank (10) to the outside of the liquefied gas cargo tank (10). The method according to claim 1,
When the operating pressure of the liquefied gas cargo tank 10 and the pressure difference between the hull cargo window 20 reach the maximum permissible pressure, the liquefied gas cargo tank safety valve 30 is mechanically opened to discharge the evaporated gas into the atmosphere Liquefied gas carrier with independent cargo tanks. 8. The method of claim 7,
Said liquefied gas cargo tank safety valve (30) comprising a spring which exerts an elastic force to unblock it to said maximum permissible pressure of said liquefied gas cargo tank (10);
And the first connecting pipe (35) is connected to act in a direction of closing the liquefied gas cargo tank safety valve (30). The method according to claim 1,
A liquefied gas cargo tank discharge pipe 31 for discharging evaporated gas generated in the liquefied gas cargo tank 10 to the atmosphere;
And a liquefied gas discharge valve (34) attached to the liquefied gas cargo tank discharge pipe (31)
A pressure signal measured by the hull cargo window pressure sensing unit 42 and the liquefied gas cargo tank pressure sensing unit 32 is transmitted to the first control unit 33 so that the pressure of the liquefied gas cargo tank 10 and the hull cargo When the pressure difference of the window 20 is close to the maximum permissible pressure of the liquefied gas cargo tank 10, the liquefied gas discharge valve 34 is opened to discharge the gas of the liquefied gas cargo tank 10 to the outside Liquefied gas carrier with independent cargo tanks. The method according to claim 1,
When the difference between the pressure of the hull cargo window 20 and the operating pressure of the liquefied gas cargo tank 10 becomes greater than a predetermined value, the second hull cargo window 20, which mechanically discharges the gas of the hull cargo window 20, Characterized in that it comprises a safety valve (46). 11. The method of claim 10,
The second hull cargo window safety valve (46) includes a spring for exerting an elastic force to shut off the second hull cargo window safety valve (46) when the pressure is below a predetermined pressure;
And a second connection pipe (45) connecting the pressure of the liquefied gas cargo tank (10) so as to act in a direction of closing the second hull cargo window safety valve (46) Gas carrier. The method according to claim 1,
A pressure signal measured by the hull cargo window pressure sensing part 42 and the liquefied gas cargo tank pressure sensing part 32 is transmitted to the second control part 43 to be transmitted to the hull cargo window part 20 and the liquefied gas cargo tank 10) is greater than or equal to a preset value, the hull cargo window opening valve (40) is opened to discharge the gas of the hull cargo window section (20) to the outside, characterized in that the liquefied gas carrier . The method according to claim 1,
And a heat exchanger (60) for lowering the temperature of nitrogen supplied to the hull cargo window (20). 14. The method of claim 13,
And a liquefied gas branch pipe (62) branching at a liquefied gas supply line (61) for supplying liquefied gas to the liquefied gas consuming source (63) and delivering the liquefied gas to the heat exchanger (60)
And the nitrogen supplied to the hull cargo window (20) is cooled by the liquefied gas through the heat exchanger (60). The method according to claim 1,
One or more liquefied gas cargo tanks (10) are contained in the hull cargo window (20)
At least one hull cargo window (20) in which the at least one liquefied gas cargo tank (10) is contained is installed,
Characterized in that the pressure exerted on each of said liquefied gas cargo tanks (10) is independent.

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