WO2022209850A1

WO2022209850A1 - Suppression device and suppression method

Info

Publication number: WO2022209850A1
Application number: PCT/JP2022/011594
Authority: WO
Inventors: 直子仲村; 篤志神谷
Original assignee: 株式会社前川製作所; 日揮グローバル株式会社
Priority date: 2021-03-29
Filing date: 2022-03-15
Publication date: 2022-10-06
Also published as: JP2022152490A; TW202240097A

Abstract

[Problem] To provide a suppression device and a suppression method with which BOG generation can be suppressed when a low-temperature liquefied gas is received. [Solution] This suppression device 1 has: a refrigerator 30 disposed in a path 10 which connects a cargo tank T1 and a storage tank T2; and a pump 40 which is provided inside the storage tank and can feed, toward the refrigerator, a liquid heel inside the storage tank.

Description

Suppression device and suppression method

The present invention relates to a suppressing device and suppressing method for suppressing the generation of BOG.

Low-temperature liquefied gas (hereinafter also referred to as liquefied gas) such as liquefied natural gas and liquid hydrogen is heated by heat input from the outside of the storage tank, and BOG (boil-off gas) is generated. Accompanying the generation of this BOG is an increase in pressure within the storage tank.

Also, when receiving liquefied gas from cargo tanks into storage tanks, the amount of BOG generated increases compared to when it is not received due to the vaporization of the received liquid due to the heat input in the cargo pump and receiving piping. The liquefied gas received from the cargo tank is called cargo liquid, and the liquefied gas stored in the storage tank is called heel liquid.

In relation to this, a treatment method for re-liquefying the generated BOG has been conventionally known (for example, Patent Document 1 below).

JP-A-10-19199

In general, a reliquefaction system for reliquefying BOG involves pressurizing with a compressor and then cooling with a heat exchanger to liquefy it, or injecting BOG into the liquefied gas to be sent out to liquefy it. , and then pumping with a pump is common. However, since this system is complicated, there are problems such as a reduction in reliability and an increase in the size of the device.

Furthermore, when re-liquefying the liquefied gas BOG with a refrigerator, a cryogenic cooling temperature is required, which reduces the thermal efficiency. Therefore, there is a problem that the power for operating the refrigerator increases. Moreover, when injecting BOG of the liquefied gas to be delivered, the flow rate of BOG that can be liquefied is limited by the flow rate of the liquefied gas to be delivered. There is a problem that the BOG cannot be reliquefied without the liquefied gas to be delivered.

From the above, it is required to suppress the generation of BOG rather than to reliquefy the generated BOG.

The present invention was invented to solve the above problems, and an object of the present invention is to provide a suppressing device and suppressing method capable of suppressing the generation of BOG.

A suppressing device according to the present invention that achieves the above object is a suppressing device that suppresses BOG that occurs when cargo liquid is received from a cargo tank to a storage tank. The suppression device includes a refrigerator arranged on a path connecting the cargo tank and the storage tank, and a suppressing device provided inside the storage tank, capable of feeding the heel liquid in the storage tank toward the refrigerator. a pump;

Further, a suppression method according to the present invention for achieving the above object includes: a refrigerator arranged between a path connecting a cargo tank and a storage tank; and a pump that feeds the heel liquid in the storage tank, and a suppressing device that suppresses BOG that occurs when cargo liquid is received from the cargo tank to the storage tank. The suppression method comprises the steps of cooling the cargo liquid to a subcooled state by the refrigerator when the cargo liquid is received in the storage tank, and transferring the cooled cargo liquid to the storage tank. have.

According to the suppression device and suppression method described above, when the cargo liquid is received from the cargo tank to the storage tank, the cargo liquid is cooled to a subcooled state by the refrigerator, and then the cargo liquid, the heel liquid, or both are transferred to the storage tank. Since the liquid is sent, it is possible to reduce the occurrence of BOG at the time of receiving.

It is a schematic diagram showing a restraining device concerning a 1st embodiment of the present invention. FIG. 4 is a state diagram for explaining a subcool state; FIG. It is a figure for demonstrating one suppression method of the suppression apparatus which concerns on 1st Embodiment. It is a figure for demonstrating the 2 suppression method of the suppression apparatus which concerns on 1st Embodiment. It is a figure for demonstrating the three suppression methods of the suppression apparatus which concerns on 1st Embodiment. FIG. 5 is a schematic diagram showing a restraining device according to a second embodiment of the invention; It is a figure for demonstrating the suppression method of the suppression apparatus which concerns on 2nd Embodiment. FIG. 3 is a schematic diagram showing a restraining device according to a third embodiment of the invention; It is a schematic diagram showing a modification of a restraining device concerning a 3rd embodiment.

<First embodiment>
A first embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. In the description of the drawings, the same elements are denoted by the same reference numerals, and overlapping descriptions are omitted. The dimensional ratios in the drawings are exaggerated for convenience of explanation and may differ from the actual ratios.

FIG. 1 is a schematic plan view showing a restraining device 1 according to the first embodiment of the invention. FIG. 2 is a state diagram for explaining the subcool state.

The suppression device 1 according to the first embodiment is a device that suppresses BOG generated when liquefied gas is received from the cargo tank T1 to the storage tank T2. Here, the liquefied gas is not particularly limited, but examples include LNG (liquefied natural gas), LPG (liquefied petroleum gas), liquid hydrogen, and liquefied nitrogen.

As shown in FIG. 1, the suppression device 1 includes a first route (corresponding to a route) 10 connecting a cargo tank T1 and a storage tank T2, and a bypass route 20 provided to branch off from the first route 10. , a refrigerator 30 arranged on a first path 10, a pump 40 provided in a storage tank T2, a second path 50 connecting the pump 40 and the first path 10, and a storage tank branched from the second path 50. A third path 60 for sending the liquefied gas in the tank T2 to the outside, a measuring unit 70 for measuring the temperature of the liquefied gas at three locations in the storage tank T2 in the height direction, and the operation of the refrigerator 30 are controlled. and a controller (not shown).

Cargo tank T1 is a cargo liquid cargo. Cargo tank T1 is, for example, the cargo of a ship. The storage tank T2 stores the residual heel liquid. The cargo liquid in the cargo tank T1 is sent to the storage tank T2 through the first path 10 at a predetermined timing.

A first valve 11 and a junction 12 are arranged in the first path 10, as shown in FIG. The first valve 11 is arranged on the cargo tank T1 side with respect to the junction 12 . The first valve 11 can control the amount of liquefied gas sent from the cargo tank T1 to the storage tank T2. The first route 10 is piping.

The confluence portion 12 is arranged in the refrigerator 30 of the first valve 11 . The confluence section 12 is arranged so that the liquefied gas from the cargo tank T1 and the liquefied gas from the storage tank T2 are mixed, and the mixed liquefied gas returns to the storage tank T2 via the refrigerator 30. .

In this embodiment, the end 10A of the first path 10 on the side of the storage tank T2 is desirably located near the center of the storage tank T2, as shown in FIG.

The bypass route 20 is provided so as to branch off from the first route 10 . A bypass valve 21 is arranged in the bypass path 20 as shown in FIG. The bypass valve 21 can adjust the amount of the liquefied gas that has flowed through the confluence section 12 and flows into the bypass route 20 . By providing the bypass route 20 in this way, the cargo liquid from the cargo tank T<b>1 can be passed through the bypass route 20 . Therefore, when the cargo liquid is sufficiently cooled to a subcooled state, it is not necessary to pass through the first path 10 cooled by the refrigerator 30 .

The refrigerator 30 subcools the cargo liquid received from the cargo tank T1 and/or the heel liquid sent by the pump 40 from the storage tank T2. The subcool state will be described below with reference to the state diagram of FIG.

Liquefied gas is normally in a saturated state at the boundary between the liquid phase and the gas phase indicated by the black circles in Figure 2. By cooling the liquefied gas in this saturated state with the refrigerator 30, it moves from the black circle to the white circle on the left, and enters a subcooled state. Since the liquefied gas in the subcooled state is in a completely liquid state, the generation of BOG can be suppressed.

The refrigerator 30 is not particularly limited as long as it can cool the liquefied gas to a subcooled state. For example, a reverse Brayton cycle or Stirling cycle refrigerator 30 can be used. The chiller 30 can be, for example, -165°C to -162°C by cooling the saturated liquefied gas at -160°C.

The pump 40 is provided near the bottom of the storage tank T2, as shown in FIG. The pump 40 is provided to send the heel liquid in the storage tank T2 to the outside through the third path 60. As shown in FIG. The pump 40 is also provided to return the liquefied gas in the storage tank T2 to the confluence section 12 via the second path 50 and mix it with the cargo liquid from the cargo tank T1. A known pump can be used as the pump 40 .

A second path 50 connects the pump 40 and the first path 10 . A second valve 51 is arranged in the second path 50 as shown in FIG. The second valve 51 can control the amount of the heel liquid sent from the storage tank T2 by the pump 40 to the confluence portion 12 side. The second path 50 is piping.

The third path 60 is a path for sending the heel liquid in the storage tank T2 to the outside. A third valve 61 is arranged in the third path 60, as shown in FIG. The third valve 61 can control the amount of the heel liquid sent from the storage tank T2 by the pump 40 to the outside. The third route 60 is piping.

As shown in FIG. 1, the measurement unit 70 measures the temperature at three points P1, P2, and P3 in the height direction inside the storage tank T2. Note that the number of measurement points in the height direction is not limited to three, and may be two or more. A known thermometer can be used as the measuring unit 70 . In addition to the temperature, the measurement unit 70 may be able to measure the height of the location where the temperature is measured.

The controller controls opening and closing of the first valve 11, the bypass valve 21, the second valve 51, and the third valve 61. The controller controls driving of the pump 40 . The control unit controls the operation of refrigerator 30 based on the temperature measured by measurement unit 70 . A control part is CPU, for example.

Next, a suppression method of the suppression device 1 according to the first embodiment will be described with reference to FIGS. 3 to 5. FIG. FIG. 3 is a diagram for explaining one suppression method of the suppression device 1 according to the first embodiment. FIG. 4 is a diagram for explaining two suppression methods of the suppression device 1 according to the first embodiment. FIG. 5 is a diagram for explaining three suppression methods of the suppression device 1 according to the first embodiment.

First, with reference to FIG. 3, one suppression method of the suppression device 1 according to the first embodiment will be described. One suppression method is a suppression method at the time of receiving liquefied gas, in which the heel liquid in the storage tank T2 and the cargo liquid from the cargo tank T1 are mixed, and the mixed liquefied gas is cooled by the refrigerator 30. It is characterized by being in a subcool state. In FIG. 3, the path through which the liquefied gas passes is indicated by a thick line.

First, the control section drives the pump 40 to feed the heel liquid in the storage tank T2 to the confluence section 12. On the other hand, the controller opens the first valve 11 so that the cargo liquid from the cargo tank T1 is sent to the confluence section 12 . At the confluence portion 12, the heel liquid in the storage tank T2 and the cargo liquid from the cargo tank T1 are mixed and sent to the refrigerator 30. The mixed liquefied gas is cooled to a subcooled state in the refrigerator 30 and sent into the storage tank T2. It should be noted that the third valve 61 may be in either open or closed state.

Here, for example, when the liquefied gas that has not been cooled by the refrigerator 30 is sent into the storage tank T2, the liquefied gas evaporates when received by the cargo pump or the receiving pipe due to the heat input, resulting in a large amount of BOG. occurs in

On the other hand, according to the first suppression method, the mixed liquefied gas is cooled to a subcooled state and sent into the storage tank T2, so the generation of BOG can be preferably suppressed.

Next, the second suppression method of the suppression device 1 according to the first embodiment will be described with reference to FIG. The second suppression method is a suppression method when receiving liquefied gas, and is characterized in that only the heel liquid from the cargo tank T1 is cooled by the refrigerator 30 to be in a subcooled state. In FIG. 4, the paths through which heel liquid and cargo liquid pass are indicated by thick lines.

First, the control unit opens the first valve 11 to send the cargo liquid from the cargo tank T1 to the refrigerator 30 via the junction section 12 . The cargo liquid from the cargo tank T1 is cooled to a subcooled state in the refrigerator 30 and sent into the storage tank T2. It should be noted that the third valve 61 may be in either open or closed state.

Thus, according to the second suppression method, the cargo liquid from the cargo tank T1 is cooled to a subcooled state and sent into the storage tank T2, so the generation of BOG can be preferably suppressed.

Next, with reference to FIG. 5, three suppression methods of the suppression device 1 according to the first embodiment will be described. The third suppressing method is a suppressing method in a steady state (when not receiving), and is characterized in that only the heel liquid in the storage tank T2 is cooled by the refrigerator 30 to be in a subcooled state. In FIG. 5, the paths through which heel liquid and cargo liquid pass are indicated by thick lines.

First, the control unit drives the pump 40 to feed the liquefied gas in the storage tank T2 to the confluence unit 12. Then, the heel liquid in the storage tank T2 is sent to the refrigerator 30, cooled to a subcooled state in the refrigerator 30, and sent to the storage tank T2. It should be noted that the third valve 61 may be in either open or closed state.

At this time, the measuring unit 70 measures the temperature of the liquefied gas at three points P1, P2, and P3 in the height direction in the storage tank T2 and the height of the place where the temperature is measured, and cools the liquefied gas to a subcooled state. Check if it is

When the temperature in the storage tank T2 is measured by the measurement unit 70, the control unit preferably turns off the operation of the refrigerator 30 when the heel liquid is surely cooled to a subcooled state. When the temperature in the storage tank T2 is measured by the measuring unit 70, and the temperature rises and the heel liquid approaches saturation, the control unit preferably turns on the operation of the refrigerator 30. . By controlling the operation of the refrigerator 30 by the control unit in this way, the refrigerator 30 does not need to be operated all the time, and the operation efficiency of the refrigerator 30 is improved.

Note that, unlike the above method of use, the operation of the refrigerator 30 may be controlled as follows. That is, the surplus power is used to turn on the refrigerator 30 to reliably cool the liquefied gas to a subcooled state. Then, when the electricity is insufficient, the refrigerator 30 is turned off. By using it in this way, variable renewable energy (solar power generation and wind power generation) can be effectively utilized.

Next, four suppression methods of the suppression device 1 according to the first embodiment will be described. In this case, the liquefied gas of interest is LNG. The fourth suppression method is a suppression method for suppressing the occurrence of stratification when cargo liquid having a density different from that of the heel liquid in the storage tank T2 is received.

First, the case where the cargo liquid from the cargo tank T1 is heavier than the heel liquid in the storage tank T2 will be described.

Before receiving the cargo liquid from the cargo tank T1, the control unit cools the heel liquid in the storage tank T2 with the refrigerator 30 to increase the degree of subcooling in the same manner as in the third control method described above.

Next, receive the cargo liquid from the cargo tank T1. At this time, the density of the heel liquid in the storage tank T2 is increased by increasing the degree of subcooling, and the density can be substantially the same as that of the cargo liquid from the cargo tank T1. Therefore, stratification of the liquefied gas in the storage tank T2 can be suitably suppressed.

Here, the substantially same density of the heel liquid in the storage tank T2 and the cargo liquid from the cargo tank T1 does not have to be completely the same, as long as the density difference is within a range that does not cause stratification in the storage tank T2. good.

Next, a case where the cargo liquid from the cargo tank T1 is lighter than the heel liquid in the storage tank T2 will be described.

Similarly to the second control method described above, the control unit cools the cargo liquid from the cargo tank T1 with the refrigerator 30 to increase the degree of subcooling and sends it into the storage tank T2. At this time, the density of the cargo liquid from the cargo tank T1 increases as the degree of subcooling increases, and the density can be made substantially the same as that of the heel liquid in the storage tank T2. Therefore, stratification of the liquefied gas can be suitably suppressed.

As described above, the suppression device 1 according to the first embodiment is a suppression device 1 that suppresses BOG that occurs when cargo liquid is received from the cargo tank T1 to the storage tank T2. The suppression device 1 includes a refrigerator 30 arranged on a first path 10 connecting a cargo tank T1 and a storage tank T2, and a heel liquid in the storage tank T2 provided inside the storage tank T2 toward the refrigerator 30. and a pump 40 capable of feeding the According to the suppression device 1 configured as described above, when the cargo liquid is received from the cargo tank T1 to the storage tank T2, the liquefied gas is cooled to a subcooled state by the refrigerator 30, and the cargo liquid, heel liquid, or its Since both are sent to the storage tank T2, it is possible to reduce the occurrence of BOG during reception.

In addition, the suppression device 1 further has a bypass route 20 that branches off from the first route 10 that connects the cargo tank T1 and the storage tank T2. According to the suppression device 1 configured in this manner, the liquefied gas from the cargo tank T1 can be passed through the bypass route 20 . Therefore, when the cargo liquid or the heel liquid or both of them are sufficiently cooled to a subcooled state, there is no need to pass through the first path 10 cooled by the refrigerator 30 .

In addition, the suppression device 1 further has a measurement unit 70 that measures temperatures at three points P1, P2, and P3 in the height direction inside the storage tank T2. According to the suppressing device 1 configured in this manner, the temperature in the storage tank T2 is measured by the measuring unit 70, and it can be confirmed whether the heel liquid is cooled to a subcooled state. Then, when the heel liquid is surely cooled to the subcooled state, the control unit turns off the operation of the refrigerator 30 . Then, when the heel liquid is close to being saturated, the control unit turns on the operation of the refrigerator 30 . Therefore, there is no need to keep the refrigerator 30 on all the time, and the operating efficiency of the refrigerator 30 is improved.

<Second embodiment>
Next, with reference to FIG. 6, the configuration of the suppression device 2 according to the second embodiment of the present invention will be described. In addition, the same code|symbol is attached|subjected about the structure similar to 1st Embodiment, and the description is abbreviate|omitted. FIG. 6 is a schematic diagram showing a restraining device 2 according to a second embodiment of the invention. The suppressing device 2 according to the second embodiment differs from the suppressing device 1 according to the first embodiment in the configuration of the first path 110 .

As shown in FIG. 6, the suppression device 2 according to the second embodiment includes a first path (corresponding to a path) 110 connecting the cargo tank T1 and the storage tank T2, and a refrigerator 30 arranged on the first path 110. a pump 40 provided in the storage tank T2; a second path 50 connecting the pump 40 and the first path 10; It has a third path 60 , a measurement unit (not shown) that measures the temperature of the heel liquid at three locations in the storage tank T<b>2 , and a control unit that controls the operation of the refrigerator 30 . In this case, the liquefied gas of interest is LNG.

As shown in FIG. 6, the first path 110 includes an upper path 111 that feeds the heel liquid cooled by the refrigerator 30 to the upper side of the storage tank T2, and a frozen liquid to the lower side of the storage tank T2. and a lower passageway 112 for conveying heel liquid cooled by machine 30 .

The upper path 111 and the lower path 112 are provided with regulating valves 113 and 114, respectively, for adjusting the amount of liquid sent to the storage tank T2.

Next, one suppression method of the suppression device 2 according to the second embodiment will be described with reference to FIG. The suppressing method of the suppressing device 2 according to the second embodiment is a suppressing method for suppressing the rollover phenomenon when the heel liquid is stratified in the storage tank T2. In FIG. 7, the paths through which heel liquid and cargo liquid pass are indicated by thick lines.

Here, the "rollover phenomenon" means that in the stratified storage tank T2, convection occurs inside each layer due to heat input from the outside, and mass transfer and heat transfer do not proceed through the boundary between the layers. The density difference gradually decreases, and after a certain period of time the densities of the upper and lower layers become equal, and when the boundary between the upper and lower layers disappears, the heat accumulated in the lower layer is released in a short time in the form of a large amount of BOG generation. Say.

First, the control unit drives the pump 40 to feed the liquefied gas in the storage tank T2 to the confluence unit 12. Then, the heel liquid in the storage tank T2 is sent to the refrigerator 30 and cooled in the refrigerator 30 to a subcooled state. The liquefied gas that has been cooled to a subcooled state by the refrigerator 30 has its flow rate adjusted by the regulating valves 113 and 114, and flows through the upper path 111 and the lower path 112 to the upper layer heel liquid and the lower layer heel liquid in the storage tank T2. returned to the liquid. It should be noted that the third valve 61 may be in either open or closed state.

Also, the upper path 111 may be replaced with a top feed pipe, which is an upper receiving pipe. Similarly, the lower passageway 112 may be replaced by a lower receiving piping, a bottom feed tube or a jet mixing nozzle.

As a result, it is possible to suppress the generation of BOG from the upper layer of the heel liquid and prevent the density from increasing. On the other hand, in the heel liquid of the lower layer, the decrease in density can be suppressed by suppressing the increase in the liquid temperature of the heel liquid due to heat input with the subcooled cargo liquid, the heel liquid, or both. Therefore, it is possible to suitably prevent the occurrence of rollover phenomenon caused by equal densities of the layered upper layer and the lower layer.

<Third Embodiment>
Next, with reference to FIG. 8, the configuration of the suppression device 3 according to the third embodiment of the present invention will be described. In addition, the same code|symbol is attached|subjected about the structure similar to 1st Embodiment, and the description is abbreviate|omitted. FIG. 8 is a schematic diagram showing a restraining device 3 according to a third embodiment of the invention. The suppressing device 3 according to the third embodiment differs from the suppressing device 1 according to the first embodiment in that a plurality of storage tanks T2 are provided.

In the suppression device 3 according to the third embodiment, three storage tanks T2 are provided as shown in FIG.

Of the three storage tanks T2, the heel liquid in one storage tank T21 is cooled by the refrigerator 30 to a subcooled state. Specifically, it is preferable to use the surplus electric power to turn on the refrigerator 30 to reliably cool the heel liquid in the one storage tank T21 to a subcooled state.

Then, the pump 40 sends the heel liquid in the subcooled one storage tank T21 to the cargo liquid receiving pipes of the other storage tanks T22 and T23, as illustrated in FIG. As a result, it is possible to suppress the occurrence of BOG during reception in the other storage tanks T22 and T23.

According to the suppression device 3 configured as described above, by storing the subcooled heel fluid in the one storage tank T21, it functions as an electric power storage system that stores renewable energy power as the subcooled heel fluid. can be made

It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims.

For example, in the first embodiment described above, the suppression device 1 has the bypass path 20 . However, the suppression device may not be provided with a bypass path.

In addition, in the above-described embodiments, the suppressing

devices

1 and 2 are provided with the measurement unit 70, and the measurement unit 70 measures the temperatures at three points P1, P2, and P3 in the storage tank T2 in the height direction. However, the measuring unit may be configured to continuously measure the temperature in the height direction inside the storage tank T2, the height at the location where the temperature is measured, and the density.

Also, in the second embodiment described above, the first route 110 has the upper route 111 and the lower route 112 . However, the first path may be only the upper path 111 or only the lower path 112 . In the case of this configuration, it is difficult to prevent the occurrence of the rollover phenomenon, but the time until the occurrence of the rollover phenomenon can be extended. By eliminating the stratification can be eliminated.

Also, in the above-described third embodiment, suppression of the generation of BOG during reception of cargo liquid from the cargo tank T1 has been described. However, it is not limited to this, and as shown in FIG. 9, it can also be applied to suppress the generation of BOG during a steady state (during non-reception).

This application is based on Japanese Patent Application No. 2021-055279 filed on March 29, 2021, the disclosure of which is incorporated by reference in its entirety.

1, 2 suppression device,
10, 110 first route,
20 bypass path,
30 refrigerator,
40 pumps,
50 second route,
60 third route,
70 measuring unit,
111 upper path,
112 lower path,
113 regulating valve,
114 regulating valve,
T1 cargo tank,
T2 storage tank.

Claims

A suppression device for suppressing BOG generated when cargo liquid is received from a cargo tank to a storage tank,
a refrigerator arranged on a path connecting the cargo tank and the storage tank;
and a pump provided inside the storage tank and capable of feeding the heel liquid in the storage tank toward the refrigerator.
The suppressing device according to claim 1, further comprising a bypass route that branches off from the route that connects the cargo tank and the storage tank.
The suppressing device according to claim 1 or 2, further comprising a measuring unit that measures temperatures at a plurality of points in the height direction inside the storage tank.
the path connecting the cargo tank and the storage tank,
an upper path for feeding the liquefied gas cooled by the refrigerator to the upper side of the storage tank;
a lower path for feeding the liquefied gas cooled by the refrigerator on the lower side of the storage tank,
The suppression device according to any one of claims 1 to 3, wherein said upper path and said lower path are provided with adjustment valves for adjusting the amount of liquid supplied to said storage tank.
A plurality of the storage tanks are provided,
The heel liquid in one storage tank is subcooled by the refrigerator,
The suppressing device according to any one of claims 1 to 4, wherein the heel liquid in the one storage tank subcooled by the pump is sent to another storage tank.
a refrigerator arranged between a path connecting a cargo tank and a storage tank; and a pump provided inside the storage tank for feeding the heel liquid in the storage tank toward the refrigerator. A suppression method for suppressing BOG generated when cargo liquid is received from the cargo tank to the storage tank by a suppression device,
cooling the cargo liquid to a subcooled state by the refrigerator when the cargo liquid is received in the storage tank;
and sending the cooled cargo liquid to the storage tank.
cooling the heel liquid in the storage tank to a subcooled state by sending the heel liquid in the storage tank to the refrigerator by the pump;
mixing the heel liquid that has been in the storage tank that has been cooled to a subcooled state with the cargo liquid from the cargo tank that has been cooled to a subcooled state;
7. The control method of claim 6, further comprising the step of feeding said mixed heel liquid and said cargo liquid to said storage tank.