KR102460504B1 - liquefied gas tank, fuel gas supply system, and ship having the same - Google Patents

Abstract

The present invention relates to a liquefied gas storage tank, a gas fuel supply system and a ship, and as a gas fuel supply system provided in a liquefied gas carrier that transports liquefied gas as cargo, stores liquefied gas therein and evaporates the liquefied gas a plurality of liquefied gas storage tanks in which gas coexists; By flowing the liquefied gas or boil-off gas stored in the liquefied gas storage tank, the temperature of the liquefied gas at the liquid level, which is the interface between the liquefied gas and the boil-off gas, approaches the temperature of the liquefied gas at the inner bottom of the liquefied gas storage tank. Dropping stratification inhibitor; a liquefied gas supply unit for supplying the liquefied gas of the liquefied gas storage tank to a consumer; and a boil-off gas processing unit for receiving and processing boil-off gas of the liquefied gas storage tank, wherein the boil-off gas processing unit suppresses the stratification phenomenon by the stratification suppressing unit to delay the pressure rise of the liquefied gas storage tank, It is characterized in that the boil-off gas is not supplied to the consumers during operation.

Description

Liquefied gas storage tank, gas fuel supply system, and ship {liquefied gas tank, fuel gas supply system, and ship having the same}

The present invention relates to a liquefied gas storage tank, a gas fuel supply system and a ship.

Recently, as environmental regulations are strengthened, the use of natural gas, which is close to an eco-friendly fuel, among various fuels is increasing. Natural gas can be extracted in a gaseous state from a gas well located inland or offshore, and the extracted natural gas undergoes pretreatment such as mercury removal, drying, and NGL removal, and then undergoes a liquefaction process for storage and transportation. can be liquefied through

Natural gas can be changed to a liquid state by cooling below its boiling point (for example, -162°C under 1 atm) while exchanging heat with a refrigerant. Transport efficiency can be increased.

The liquefied natural gas is made of stand-alone, membrane, pressurized, and the like, and is stored as a liquid in a storage tank having a thermal insulation structure, and is transported by a gas carrier equipped with a storage tank.

However, since the insulation structure provided in the storage tank cannot completely block external heat penetration, as external heat is transferred to the liquid natural gas, some of the natural gas is naturally vaporized and changed into boil-off gas.

Therefore, liquid natural gas and gaseous boil-off gas coexist in the storage tank. However, the heat capacity that penetrates into the storage tank is not evenly distributed inside the storage tank, and since natural gas and boil-off gas have different heat capacities (the width of temperature rise is different when heat is applied), The temperature of the gas and the temperature of the boil-off gas are different.

For example, in natural gas, the temperature from the bottom inside the storage tank to the liquid level appears relatively constant, whereas in the boil-off gas, the temperature from the liquid level to the top inside the storage tank gradually rises.

If this state continues for a certain period of time, the liquefied gas from the liquid level down to a certain depth forms a section in which the temperature rises as it approaches the liquid level, and the occurrence of this section is called stratification. When the stratification phenomenon occurs, the temperature at the liquid level where the liquefied gas and the boil-off gas meet rises.

In particular, in the case of a gas carrier, since the storage tank is filled with natural gas, which is cargo, to about 98% and operated for a certain period of time, the internal pressure rises continuously due to the generation of boil-off gas as the cargo volume is maintained during operation, which may cause a problem.

Therefore, in the conventional storage tank, in addition to the basic amount of BOG generated due to external heat penetration during the operation period of the gas carrier, an insulation structure must be constructed in consideration of the amount of BOG that will be additionally vaporized by the stratification phenomenon. This has resulted in costly waste.

The present invention was created to solve the problems of the prior art as described above, and an object of the present invention is to suppress the stratification phenomenon by lowering the temperature at the liquid level, thereby delaying the rise of the internal pressure of the storage tank to ensure the transportation stability of the liquefied gas It is to provide a liquefied gas storage tank, a gas fuel supply system, and a ship that can

A gas fuel supply system according to an aspect of the present invention is a gas fuel supply system provided in a liquefied gas carrier that transports liquefied gas as cargo, and stores liquefied gas therein, and a plurality of boil-off gas from which liquefied gas has evaporated coexist. liquefied gas storage tanks; By flowing the liquefied gas or boil-off gas stored in the liquefied gas storage tank, the temperature of the liquefied gas at the liquid level, which is the interface between the liquefied gas and the boil-off gas, approaches the temperature of the liquefied gas at the inner bottom of the liquefied gas storage tank. Dropping stratification inhibitor; a liquefied gas supply unit for supplying the liquefied gas of the liquefied gas storage tank to a consumer; and a boil-off gas processing unit for receiving and processing boil-off gas of the liquefied gas storage tank, wherein the boil-off gas processing unit suppresses the stratification phenomenon by the stratification suppressing unit to delay the pressure rise of the liquefied gas storage tank, It is characterized in that the boil-off gas is not supplied to the consumers during operation.

Specifically, the stratification suppression unit delays the period in which the internal pressure of the liquefied gas storage tank reaches a preset value by suppressing the stratification phenomenon, and the preset value is, the liquefied gas storage tank requires the discharge of BOG It can be pressure.

Specifically, the consumer may operate by consuming only the liquefied gas of the liquefied gas storage tank.

Specifically, the boil-off gas processing unit may omit a compressor for supplying the boil-off gas of the liquefied gas storage tank to the consumer.

Specifically, the boil-off gas processing unit includes a high-duty (HD) compressor that compresses the boil-off gas generated during bunkering to the liquefied gas storage tank to return to the gas source, and the boil-off gas of the liquefied gas storage tank to the demand destination. Among the LD (Low-Duty) compressors that are compressed for supply, only the HD compressor may be provided.

Specifically, the boil-off gas processing unit may omit a device for re-liquefying the boil-off gas of the liquefied gas storage tank.

Liquefied gas carrier according to an aspect of the present invention, characterized in that it has the gas fuel supply system.

The liquefied gas storage tank, gas fuel supply system and ship according to the present invention reduce the temperature of the interface between liquefied gas and boil-off gas by using various configurations to delay the period during which the internal pressure of the storage tank rises, thereby treating boil-off gas It is possible to minimize/omit the configuration and enable stable operation of ships equipped with storage tanks.

1 is a side view of a ship according to the present invention;
2 is a conceptual diagram of a gas fuel supply system according to a first embodiment of the present invention.
3 is a conceptual diagram of a gas fuel supply system according to a second embodiment of the present invention.
4 is a conceptual diagram of a gas fuel supply system according to a third embodiment of the present invention.
5 is a view showing that the stratification phenomenon occurs in the liquefied gas storage tank.
6 is a view showing an increase in internal pressure due to a stratification phenomenon in a liquefied gas storage tank.
7 is a diagram illustrating a temperature change at the liquid level due to a temperature difference between liquefied gas and boil-off gas.
8 is a conceptual diagram of a liquefied gas storage tank provided with a stratification detection unit according to the present invention.
9 is a conceptual diagram of a liquefied gas storage tank provided with a stratification suppression unit according to a fourth embodiment of the present invention.
10 is a view showing the suppression of stratification according to the fourth embodiment of the present invention.
11 is a conceptual diagram of a liquefied gas storage tank provided with a stratification suppression unit according to a fifth embodiment of the present invention.
12 is a view showing the suppression of stratification according to the fifth embodiment of the present invention.
13 is a conceptual diagram of a liquefied gas storage tank provided with a stratification suppression unit according to a sixth embodiment of the present invention.
14 is a view showing the suppression of stratification according to the sixth embodiment of the present invention.
15 is a conceptual diagram of a liquefied gas storage tank provided with a stratification suppression unit according to a seventh embodiment of the present invention.
16 is a view showing the suppression of stratification according to the seventh embodiment of the present invention.
17 is a view showing a delay in internal pressure rise due to suppression of stratification in a membrane type/independent type liquefied gas storage tank according to the present invention.
18 is a view showing the internal pressure increase delay due to the suppression of stratification in the pressurized liquefied gas storage tank according to the present invention.
19 is a view showing a change in internal pressure due to suppression of stratification in a pressurized liquefied gas storage tank according to the present invention.
20 is a view showing a change in temperature over time in a pressurized liquefied gas storage tank according to the present invention.
21 is a view showing a change in pressure over time in a pressurized liquefied gas storage tank according to the present invention.
22 is a view showing the temperature/pressure change with time in the liquefied gas storage tank according to the present invention.

The objects, specific advantages and novel features of the present invention will become more apparent from the following detailed description and preferred embodiments taken in conjunction with the accompanying drawings. In the present specification, in adding reference numbers to the components of each drawing, it should be noted that only the same components are given the same number as possible even though they are indicated on different drawings. In addition, in describing the present invention, if it is determined that a detailed description of a related known technology may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Hereinafter, the gas may mean a substance with a boiling point lower than room temperature as hydrocarbons such as LPG, LNG, ethane, etc. However, for convenience, the present invention is limited to the final production and storage of LNG (methane). In addition, in this specification, gas is not limited to a gaseous state, despite the terminology.

Hereinafter, it should be noted that high pressure (HP: High pressure), low pressure (LP: low pressure), high temperature, and low temperature are relative and do not represent absolute values.

1 is a side view of a ship according to the present invention;

Referring to Figure 1, the present invention may be a liquefied gas carrier for transporting liquefied gas. A liquefied gas carrier is a ship 1 that transports liquefied gas as cargo, and at this time, a plurality of membrane or independent liquefied gas storage tanks 10 (cargo tanks) may be mounted in the ship.

In the case of a liquefied gas carrier, each liquefied gas storage tank 10 is operated in a state in which the maximum amount of liquefied gas is filled (full state, for example, 98.5% filling), or the liquefied gas storage tank 10 is empty (light state) can fly with

Alternatively, the vessel 1 according to the present invention may be a vessel 1 other than a liquefied gas carrier for transporting cargo other than liquefied gas, and for example, the vessel 1 may be a container ship, a bulk carrier, or the like. In this case, the ship 1 may be a liquefied gas propulsion ship loaded with liquefied gas as a fuel for propulsion.

In the case of a ship (1) other than a liquefied gas carrier, a membrane type, independent type or pressurized type liquefied gas storage tank 10 (fuel tank) may be mounted onboard/offboard to load liquefied gas as fuel, and liquefied gas The storage tank 10 may be installed in various positions that do not interfere with the cargo loading space.

Of course, in addition, the ship 1 according to the present invention can be interpreted to encompass all marine structures such as the bunkering ship 1, the FSRU, and the FPSO, which are not general commercial ships.

2 is a conceptual diagram of a gas fuel supply system according to a first embodiment of the present invention.

Referring to FIG. 2 , the gas fuel supply system 2 according to the first embodiment of the present invention is installed on the ship 1 described above, and includes a liquefied gas storage tank 10 , a liquefied gas supply unit 20 , and evaporation. It includes a gas supply unit 30 and a boil-off gas liquefaction unit 40 .

The liquefied gas storage tank 10 stores liquefied gas therein. At this time, the liquefied gas stored in the liquefied gas storage tank 10 may be naturally vaporized due to external heat penetration, and liquefied gas and boil-off gas may exist together in the liquefied gas storage tank 10 .

The liquefied gas storage tank 10 may be of a membranous type or an independent type when mounted as a cargo tank on a liquefied gas carrier, and a membrane type, independent type or pressurized type when mounted as a fuel tank on a vessel 1 other than a liquefied gas carrier. is as described above.

The liquefied gas supply unit 20 supplies the liquefied gas stored in the liquefied gas storage tank 10 to the consumer 50 . At this time, the consumer 50 may be a propulsion engine for propelling the vessel 1, but is not limited thereto, and may be a generator, a land consumer, or the like.

The liquefied gas supply unit 20 includes a transfer pump 21 for transferring the liquefied gas stored in the liquefied gas storage tank 10 to the outside, a high-pressure pump 22 for pressurizing the liquefied gas to the required pressure of the customer 50, and a low temperature may include a vaporizer 23 and the like for heating the liquefied gas of the customer 50 to the required temperature, and a liquefied gas supply line L20 may be provided from the liquefied gas storage tank 10 to the demand 50. .

In addition, the liquefied gas return line L21 for returning an excess of liquefied gas among the liquefied gas discharged from the transfer pump 21 to the liquefied gas storage tank 10 is provided in the liquefied gas supply line L20, and the liquefied gas return line (L21) is branched from the outside of the liquefied gas storage tank (10) in the liquefied gas supply line (L20) extends to the inside of the liquefied gas storage tank (10). Of course, it is also possible that the liquefied gas return line (L21) is branched from the liquefied gas supply line (L20) in the liquefied gas storage tank 10 and extends downward.

The boil-off gas supply unit 30 may supply the boil-off gas generated in the liquefied gas storage tank 10 to the consumer 50 . However, the boil-off gas supply unit 30 may deliver the boil-off gas to a gas combustion device (not shown) in addition to the consumer 50 .

The boil-off gas supply unit 30 adjusts the boil-off gas compressor 31 for compressing the boil-off gas discharged from the liquefied gas storage tank 10 and the temperature of the boil-off gas heated by the compression to the temperature required by the consumer 50 . It may include a cooler 32 that is, of course, a heater may be provided instead of the cooler 32 . In addition, the boil-off gas supply unit 30 includes a boil-off gas supply line L30 connected from the liquefied gas storage tank 10 to the consumer 50 .

However, the compressor 31 of the boil-off gas supply unit 30 is not an HD (High-Duty) compressor that compresses the boil-off gas generated during bunkering to the liquefied gas storage tank 10 to return to the fueling source, but a liquefied gas storage tank. It means an LD (Low-Duty) compressor that compresses the boil-off gas of (10) in order to supply it to the consumer (50).

The boil-off gas liquefaction unit 40 liquefies excess boil-off gas that cannot be consumed by the consumer 50 among the boil-off gas flowing through the boil-off gas supply line L30 and returns it to the liquefied gas storage tank 10 .

The boil-off gas liquefaction unit 40 may include a liquefier 41 for cooling and liquefying the boil-off gas using a refrigerant, and a refrigerant circulation line in which a refrigerant pump 411 and a refrigerant expander 412 are disposed in the liquefaction unit. (L41) may be connected.

The BOG liquefaction unit 40 may be provided with a BOG liquefaction line L40 branched from the BOG supply line L30 and connected to the liquefied gas storage tank 10, and the BOG liquefaction line L40 is liquefied. A gas-liquid separator 42 is provided downstream of the group 41 .

The gas-liquid separator 42 discharges the gas (flash gas, nitrogen as the main component) remaining in a gaseous state even though the boil-off gas is heat-exchanged with the refrigerant in the liquefier 41 to the flash gas discharge line L42, and the liquefied gas storage tank ( In 10), only liquid liquefied BOG can be returned.

For reference, in the present specification, components for processing liquefied gas/evaporated gas (liquefied gas supply unit 20, boil-off gas supply unit 30, boil-off gas liquefaction unit 40) may be collectively referred to as a gas fuel processing unit, and liquefied It should be noted that the configuration for discharging and processing boil-off gas from the gas storage tank 10 (such as the boil-off gas supply unit 30, the boil-off gas liquefaction unit 40, etc.) may be collectively referred to as a boil-off gas processing unit.

3 is a conceptual diagram of a gas fuel supply system according to a second embodiment of the present invention.

Referring to FIG. 3 , in the gas fuel supply system 2 according to the second embodiment of the present invention, the BOG processing unit may omit the BOG liquefaction unit 40 . This is because the discharge of BOG is not to generate excess BOG, which will be described later, but this is possible because stratification in the liquefied gas storage tank 10 is suppressed.

4 is a conceptual diagram of a gas fuel supply system according to a third embodiment of the present invention.

Referring to FIG. 4 , in the gas fuel supply system 2 according to the third embodiment of the present invention, the boil-off gas supply unit 30 may also be omitted when compared with the second embodiment in FIG. 3 .

That is, in this embodiment, the gas fuel processing unit supplies only the liquefied gas of the liquefied gas storage tank 10 to the consumer 50 , and BOG may not be discharged from the liquefied gas storage tank 10 during operation. This configuration is possible according to the suppression of stratification in the liquefied gas storage tank 10 as in the second embodiment.

Hereinafter, the reason why the gas fuel supply system 2 of the present invention can reduce/omit the processing configuration of BOG as shown in FIGS. 3 and 4 will be described in detail.

FIG. 5 is a view showing that the stratification phenomenon occurs in the liquefied gas storage tank, and FIG. 6 is a view showing the increase in internal pressure due to the stratification phenomenon in the liquefied gas storage tank. In addition, FIG. 7 is a view showing the temperature change at the liquid level due to the temperature difference between the liquefied gas and the boil-off gas.

The liquefied gas storage tank 10 provided in the ship 1 described with reference to FIG. 1 stores liquefied gas therein, and boil-off gas from which the liquefied gas has evaporated may coexist. BOG in the liquefied gas storage tank 10 may be generated when the liquefied gas is loaded into the liquefied gas storage tank 10 or may be generated by natural evaporation of the liquefied gas due to external heat penetration.

In the liquefied gas storage tank 10 in which the liquefied gas and the boil-off gas coexist, in the initial condition in which the temperatures of the liquefied gas and the boil-off gas are the same, a temperature graph such as the upper left of FIG.

However, since the liquefied gas storage tank 10 is continuously heat penetrated from the outside, the temperature of the liquefied gas and the boil-off gas can be uniformly increased as shown in the upper right of FIG. 5 .

The above case is possible only when the properties of the liquefied gas and the boil-off gas are the same (homogeneous model). In fact, since the heat capacity of the liquefied gas and the boil-off gas are different, the temperature graph inside the liquefied gas storage tank 10 is shown in FIG. Unlike the upper side, it appears as shown in the lower side of FIG. 5 .

Specifically, the boil-off gas stored in the liquefied gas storage tank 10 has a lower heat capacity than that of the liquefied gas, and heat penetration is active through the upper side rather than the lower side when the installation location of the liquefied gas storage tank 10 is considered. .

Therefore, the boil-off gas is heated more than the liquefied gas due to external heat penetration, so the temperature of the boil-off gas increases toward the inner upper end of the liquefied gas storage tank 10 based on the liquid level, which is the interface between the liquefied gas and the boil-off gas. .

Furthermore, since the boil-off gas is heated more easily compared to the liquefied gas, the boil-off gas at the liquid level may have a higher temperature than the liquefied gas at the liquid level. In this case, for thermal equilibrium, the temperature of the liquefied gas at the liquid level is affected by the boil-off gas and rises.

As a result, in the section from the liquid level downward to a certain point, the temperature of the liquefied gas rises toward the liquid level so that the temperature of the liquefied gas at the liquid level is higher than the temperature of the liquefied gas at the inner bottom of the liquefied gas storage tank 10 . This phenomenon is called stratification, and the section in which the temperature of the liquefied gas gradually increases is called the stratification section.

When the stratification phenomenon occurs, the vaporization of the liquefied gas is accelerated, the generation of boil-off gas is increased, and the internal pressure of the liquefied gas storage tank 10 is increased. As shown in FIG. 6 , in the liquefied gas storage tank 10 having the same liquid level, when the stratification phenomenon occurs, it can be seen that the internal pressure rises faster as time passes compared to the case where the stratification phenomenon does not occur. .

However, the case where it is assumed that the properties of liquefied gas and boil-off gas are the same (homogeneous model) and the case where stratification occurs (thermal stratification model) show the opposite tendency in pressure increase according to the liquid level.

This stratification phenomenon occurs because the heating of the liquefied gas and the boil-off gas is different from each other. .

In the case of (A) of FIG. 7 (evaporation gas temperature > liquefied gas temperature), the boil-off gas adjacent to the liquid level may be condensed by the low-temperature liquefied gas, and the temperature and pressure of the boil-off gas are decreased. In this case, the temperature of the liquefied gas at the liquid level rises, but the temperature of the entire liquefied gas does not rise when considering the heat transfer and diffusion rate, and a gradual rise in the temperature of the liquefied gas appears in a certain section. Therefore, in Fig. 7(A), stratification occurs and a local equilibrium is reached at the liquid level.

On the other hand, in the case of (B) of FIG. 7 (evaporation gas temperature < liquefied gas temperature), the liquefied gas at the liquid level naturally evaporates, so that the temperature and pressure of the boil-off gas rise, and the temperature and pressure of the liquefied gas fall. Therefore, the temperature of the entire liquefied gas storage tank 10 is balanced to a uniform value.

However, since the heat capacity of the boil-off gas is small compared to the heat capacity of the liquefied gas, there is no realistic possibility of occurrence in the case of FIG. 7B, and only the case of FIG.

That is, as long as liquefied gas and boil-off gas coexist in the liquefied gas storage tank 10, a stratification phenomenon inevitably occurs. .

An increase in the internal pressure of the liquefied gas storage tank 10 may be a problem because it requires work such as discharge and treatment of boil-off gas (fuel supply, re-liquefaction, combustion). Therefore, it is necessary to measure the occurrence of the stratification phenomenon. Hereinafter, the stratification detection unit 11 installed in the liquefied gas storage tank 10 of the present invention will be described with reference to FIG. 8 .

8 is a conceptual diagram of a liquefied gas storage tank provided with a stratification detection unit according to the present invention.

Referring to FIG. 8 , the stratification grasping unit 11 measures or estimates the temperature of the liquid level, which is the interface between the liquefied gas and the BOG. In the section up to a certain point in the downward direction, the temperature of the liquefied gas rises toward the liquid level to determine whether a stratification phenomenon occurs in which the temperature of the liquefied gas at the liquid level is higher than the temperature of the liquefied gas at the bottom of the interior.

To this end, the stratification detection unit 11 includes a lower temperature sensor 111b for measuring the temperature of the lower end inside the liquefied gas storage tank 10, and a pressure sensor for measuring the internal pressure of the liquefied gas storage tank 10 ( 112) may be included.

As shown on the left side of FIG. 8 , when the liquefied gas storage tank 10 is a cargo tank mounted on a liquefied gas carrier, the stratification detection unit 11 further includes a liquid level temperature sensor 111c. If the liquefied gas storage tank 10 is a cargo tank, as described above, the liquefied gas storage tank 10 is placed in a full or empty state, so the liquid level in the liquefied gas storage tank 10 is a relatively fixed position. do.

Therefore, the stratification detection unit 11 is installed in the inverter at the liquid level when the liquefied gas storage tank 10 is full inside the liquefied gas storage tank 10 and directly measures the liquid level temperature sensor 111c. can be provided

At this time, the liquid level temperature sensor 111c may be fixedly installed at the liquid level when the liquefied gas storage tank 10 is filled with liquefied gas at a preset ratio (98 to 99%, for example, 98.5%).

The stratification detection unit 11 having the liquid level temperature sensor 111c is determined that the stratification phenomenon has occurred when the measured value of the liquid level temperature sensor 111c is higher than the preset value compared to the measured value of the lower temperature sensor 111b. can judge In this case, the stratification detection unit 11 may monitor an increase in the internal pressure of the liquefied gas storage tank 10 through the pressure sensor 112 .

On the other hand, as shown on the right side of FIG. 8 , when the liquefied gas storage tank 10 is a fuel tank mounted on a liquefied gas propulsion ship or a bunkering tank mounted on a bunkering vessel 1, unlike in a liquefied gas carrier, the liquid level is constant. may not

Therefore, the stratification determination unit 11 estimates the internal pressure of the liquefied gas storage tank 10 assuming that the temperature at the liquid level is the same as the measured value of the lower temperature sensor 111b, and the measured value of the pressure sensor 112 is When it is higher than the preset value compared to the estimated withstand pressure, it may be determined that the stratification phenomenon has occurred.

In relation to the estimation of the internal pressure, the stratification grasping unit 11 estimates the internal pressure of the liquefied gas storage tank 10 using table data in which internal pressure information of the liquefied gas storage tank 10 corresponding to the temperature at the liquid level is stored. can

At this time, the table data may be stored information on the internal pressure of the liquefied gas storage tank 10 according to the temperature at the liquid level and the amount of liquefied gas stored in the liquefied gas storage tank 10, and the amount of liquefied gas is generally in the liquefied gas storage tank 10 It can be measured and used through a level gauge (not shown) provided with the .

In addition, the stratification detection unit 11 further includes an upper temperature sensor 111a for measuring the temperature of the upper end inside the liquefied gas storage tank 10, the measured value of the lower temperature sensor 111b, the upper temperature sensor ( It is of course also possible to calculate and estimate the internal pressure of the liquefied gas storage tank 10 based on the measured value of 111a) and the amount of liquefied gas stored in the liquefied gas storage tank 10 .

If the estimated internal pressure is higher by a large difference than the measured value by the pressure sensor 112, it means that the assumption that the temperature at the liquid level is the same as the measured value of the lower temperature sensor 111b is incorrect, and the temperature at the liquid level is incorrect. Since is higher than the measured value of the lower temperature sensor 111b, the stratification detection unit 11 may determine that stratification has occurred.

The stratification detection unit 11 can determine whether or not the stratification phenomenon occurs repeatedly at every preset time, and whenever the amount of liquefied gas stored in the liquefied gas storage tank 10 changes to more than a preset value, the stratification phenomenon occurrence can be determined.

In the present invention, when the occurrence of stratification in the liquefied gas storage tank 10 is detected by the stratification detection unit 11, the stratification suppression unit 60 to be described later is used to suppress the stratification phenomenon, thereby delaying the internal pressure increase.

The stratification suppression unit 60 flows the liquefied gas or boil-off gas stored in the liquefied gas storage tank 10 when the stratification phenomenon occurs to lower the liquefied gas temperature at the liquid level in a direction closer to the liquefied gas temperature at the inner bottom. As a configuration to drop, it will be described in detail below with reference to FIG. 9 and the like.

9 is a conceptual diagram of a liquefied gas storage tank provided with a stratification suppression unit according to a fourth embodiment of the present invention, and FIG. 10 is a view showing stratification suppression according to a fourth embodiment of the present invention.

Referring to FIG. 9 , the stratification suppression unit 60 according to the fourth embodiment of the present invention is a liquefied gas supply line provided in the vertical direction inside the liquefied gas storage tank 10 as shown in FIG. 9A . It may include a liquid level nozzle 61a provided in at least one of the (L20) and the liquefied gas return line (L21).

However, since the liquid level nozzle 61a will be fixedly installed on the liquefied gas supply line L20, etc., when the liquid level nozzle 61a is provided, the liquefied gas storage tank 10 in which the stratification suppression unit 60 is provided is liquefied gas Since it is mounted on a carrier, it may be a case where the liquid level is located at a relatively constant height.

The liquid level nozzle 61a directly supplies the liquefied gas at the inner lower end of the liquefied gas storage tank 10 delivered by the transfer pump 21 to the liquid level. In this case, the temperature of the liquefied gas at the liquid level is lowered while the low-temperature liquefied gas at the bottom of the inside is mixed.

Alternatively, the stratification suppression unit 60 may include a stirrer 62 as shown in FIG. 9B . The agitator 62 rotates the impeller using a power source such as a motor, so that the liquefied gas at the inner bottom of the liquefied gas storage tank 10 and the liquefied gas at the liquid level are mixed, and the shape of the agitator 62 is arranged , the number, etc. are not particularly limited.

Alternatively, the stratification suppression unit 60 may include a lower nozzle 61b for spraying the liquefied gas transferred by the transfer pump 21 upwardly from the bottom to the liquid level as in FIG. 9C . .

As the stratification suppression unit 60 shown in (A), (B) and (C) of FIG. 9 is operated, the temperature distribution of the liquefied gas storage tank 10 may be changed as shown in FIG. 10 .

Referring to FIG. 10 , a temperature gradient connecting B0 - A0 - D0 is formed in the initial (t0) condition. The temperature of the liquefied gas is constant regardless of the top and bottom (B0 = A0), but the temperature of the boil-off gas increases as it goes up (D0 > A0), and the pressure of the liquefied gas storage tank 10 is the saturation pressure at the liquid level. is determined (P = Psat(A0)).

After a certain period of time (t) as heat is introduced from the outside, a temperature gradient connecting B - C - A - D is formed. Due to the difference in heat capacity, the temperature of the boil-off gas rises faster than the temperature of the liquefied gas, and the heat of the boil-off gas with the increased temperature is transferred to the liquefied gas, and the temperature of the liquefied gas rises from the liquid level downward to a certain section.

Therefore, according to the temperature gradient in the liquefied gas storage tank 10, the inside of the liquefied gas storage tank 10 is a liquefied gas section (a section in which the temperature of the liquefied gas from the inner bottom to a certain point is constant, B = C), a stratified section It can be divided into (section where the temperature of liquefied gas gradually rises from a certain point to the liquid level, A > C), and boil-off gas section (section where the temperature of boil-off gas gradually rises from the liquid level to the top of the inside, D > A), The pressure of the gas storage tank 10 is determined by the saturation pressure at the liquid level (P = Psat(A)).

In this stratification state, the stratification suppression unit 60 of FIG. 9 delivers the liquefied gas in the liquefied gas section to the stratification section, and induces the temperature distribution in the stratification section to be parallel to the temperature distribution in the liquefied gas section Thus, the temperature of the liquefied gas at the liquid level can be lowered. However, since the delivery of the liquefied gas does not affect the boil-off gas at the upper end of the interior, the stratification suppressor 60 increases the range of temperature change according to the height in the boil-off gas section.

In this case, the temperature gradient changes to B - C - A1 - D. At this time, the pressure of the liquefied gas storage tank 10 is determined by the saturation pressure (P = Psat(A1)) at the liquid level. As the temperature of A1 is significantly lower than that of A, the pressure of the liquefied gas storage tank 10 It can also be lowered.

That is, the stratification suppression unit 60 of FIG. 9 is provided in the stratification section and sprays the liquefied gas flowing from the liquefied gas supply line L20, etc. into the stratification section, the liquid level nozzle 61a, and the liquefied gas and stratification section of the liquefied gas section The agitator 62 for mixing the liquefied gas of , the liquefied gas temperature at the liquid level can be drastically reduced from A to A1. As a result, the pressure of the liquefied gas storage tank 10 is lowered, so that the necessity of discharging BOG can be eliminated or reduced.

11 is a conceptual diagram of a liquefied gas storage tank provided with a stratification suppression unit according to a fifth embodiment of the present invention, and FIG. 12 is a view showing stratification suppression according to a fifth embodiment of the present invention.

Referring to FIG. 11 , the stratification suppression unit 60 according to the fifth embodiment of the present invention branches from the liquefied gas supply line L20 or the liquefied gas return line L21 as shown in FIG. 11D . It has a stratification suppression line L60, and an upper nozzle 61c is provided on the stratification suppression line L60.

The upper nozzle 61c is provided in the boil-off gas section and can spray the liquefied gas flowing in the stratification suppression line L60 downward toward the liquid level in the boil-off gas section.

Alternatively, as shown in (E) of FIG. 11, the stratification suppression unit 60 is branched from the liquefied gas supply line L20 and is connected to the upper nozzle 61c via the cooler 63. The stratification suppression line L60. may be provided.

The stratification suppression unit 60 shown in (D) and (E) of FIG. 11 transmits the liquefied gas of the liquefied gas section to the boil-off gas section, reduces the temperature change according to the height in the boil-off gas section, and reduces the temperature change in the boil-off gas section. While lowering the temperature in the stratification section, the temperature change width in at least an upper part of the stratified section can be reduced, thereby lowering the temperature of the liquefied gas at the liquid level.

That is, by the stratification suppression unit 60 of FIG. 11, as shown in FIG. 12, the temperature gradient of B-C-A-D goes through B-C-A-D2 to B-C-E-A2-D2'. will change Therefore, in the present embodiment, it is possible to suppress stratification by dropping the temperature of the liquid level from A to A2 while guiding the temperature distribution in at least an upper part of the boil-off gas section and the stratification section in parallel.

13 is a conceptual diagram of a liquefied gas storage tank provided with a stratification suppression unit according to a sixth embodiment of the present invention, and FIG. 14 is a view showing stratification suppression according to a sixth embodiment of the present invention.

Referring to FIG. 13 , the stratification suppression unit 60 according to the sixth embodiment of the present invention may utilize boil-off gas, unlike the previous fourth and fifth embodiments in which liquefied gas is used.

As shown in (F) of FIG. 13 , the stratification suppression unit 60 may include a stratification suppression line L60 branched from the boil-off gas supply line L30 and extending to the inner floor, and a lower nozzle 61b. have.

At this time, the lower nozzle 61b may be provided in the liquefied gas section, and may upwardly inject the boil-off gas flowing in the stratification suppression line L60 toward the liquid level within the liquefied gas section.

Through this, the stratification suppression unit 60 delivers the BOG in the BOG section to the liquefied gas section, thereby lowering the temperature in the BOG section and increasing the temperature in the liquefied gas section, while increasing the temperature change in the stratification section. By reducing it, it is possible to lower the temperature of the liquefied gas at the liquid level.

That is, as the temperature gradient of B - C - A - D changes to B3 - C3 - A3 - D3 as shown in FIG. 14 , and the liquid level drops from A to A3, stratification can be suppressed.

15 is a conceptual diagram of a liquefied gas storage tank provided with a stratification suppression unit according to a seventh embodiment of the present invention, and FIG. 16 is a view showing stratification suppression according to a seventh embodiment of the present invention.

Referring to (G) of Figure 15, the stratification suppression unit 60 according to the seventh embodiment of the present invention, different from (E) in Figure 11 above, by heating the liquefied gas in the liquefied gas section into bubbles After making, it flows along the stratification suppression line L60 extending to the inner floor, and transfers to the liquid level through the lower nozzle 61b of the inner floor.

At this time, as shown in FIG. 16 , the temperature gradient is changed from B-C-A-D to B4-C4-A4-D, and the temperature at the liquid level is lowered from A to A4, so that stratification can be suppressed.

The effect of operating the stratification suppression unit 60 will be described below with reference to FIG. 17 and the like.

17 is a view showing a delay in internal pressure rise due to stratification suppression in a membrane type/independent type liquefied gas storage tank according to the present invention, and FIG. It is a diagram showing the delay.

Referring to FIG. 17 , when the pressure required to discharge BOG is about 0.6 barg, when the stratification suppressor 60 is not provided, BOG discharge occurs when about 14 days have elapsed.

On the other hand, when the stratification suppression unit 60 is operated according to the stratification detection unit 11, the emission of BOG may be delayed to about 22 days elapse, and when the stratification suppression unit 60 is continuously operated, the emission of BOG is It may be delayed until about 29 days have elapsed.

Also, referring to FIG. 18 , when the pressure required to discharge the BOG is about 5.5 barg, the stratification suppression unit 60 is provided in comparison with the case where the stratification suppression unit 60 is not provided (BOG emission when 12 days have elapsed). In the case of operating according to the stratification detection unit 11 (BOG emission after 24 days) and in the case of continuously operating the stratification suppression unit 60 (BOG emission after 26 days), the emission of BOG will be significantly delayed. can

That is, the present invention suppresses the stratification phenomenon by using the stratification suppression unit 60, and the internal pressure of the liquefied gas storage tank 10 reaches a preset value (the pressure required to discharge the boil-off gas from the liquefied gas storage tank 10). period may be delayed.

Therefore, in the present invention, as the pressure rise of the liquefied gas storage tank 10 is delayed by suppressing the stratification phenomenon, the period during which the boil-off gas must be discharged from the liquefied gas storage tank 10 can be shortened, and the stratification suppression unit In contrast to the case without (60), the number of operation, operation time, or load of the boil-off gas processing unit during operation can be reduced.

In consideration of this, if the stratification suppression unit 60 is applied to the first embodiment described above, the load or the number of operation of the boil-off gas liquefaction unit 40 may be reduced, and gas fuel supply in the second embodiment It is also possible to omit the boil-off gas liquefaction unit 40, which is a device for re-liquefying boil-off gas, such as the system (2).

In this case, the BOG processing unit may include only the BOG supply unit 30 among the BOG liquefaction unit 40 and the BOG supply unit 30, but the compressor 31 (HD compressor) is operated during operation due to stratification suppression. The start time may be delayed or the operation of the compressor 31 may be omitted during operation.

Also, from the perspective of the gas fuel processing unit, the gas fuel processing unit may not supply liquefied gas as the main fuel of the customer 50 or may not supply BOG to the customer 50 during operation, and may regenerate the BOG depending on the operation period. It is also possible to store it in the liquefied gas storage tank 10 without being liquefied.

If the period during which the vessel 1 operates one time is about 15 to 20 days, the vessel 1 according to the present invention uses the stratification suppressor 60, so that the BOG is stored without any emission during operation. Even so, the internal pressure of the liquefied gas storage tank 10 can be maintained within a safe range.

Therefore, further in the second embodiment, like the gas fuel supply system 2 in the third embodiment, the boil-off gas supply unit 30 may be omitted. That is, the BOG processing unit may not supply BOG to the consumer 50 during operation as the compressor 31 (LD compressor) for compressing BOG is omitted (an HD compressor for bunkering may be provided), and the BOG may not be supplied to the consumer ( 50) can be operated by consuming only liquefied gas.

Alternatively, in the present invention, the BOG processing unit may omit the BOG supply unit 30 instead of the BOG liquefaction unit 40, which is a device for re-liquefying BOG, and in this case, the BOG liquefaction unit 40 can liquefy the boil-off gas compressed by the HD compressor.

Hereinafter, in the case of having a pressurized liquefied gas storage tank 10 as a vessel 1 other than a liquefied gas carrier with reference to FIGS. 19 to 22 , the operation method of the stratification suppression unit 60 will be described.

19 is a view showing a change in internal pressure due to stratification suppression in a pressurized liquefied gas storage tank according to the present invention, and FIG. 20 is a view showing a change in temperature over time in a pressurized liquefied gas storage tank according to the present invention. , Figure 21 is a view showing the pressure change over time in the pressurized liquefied gas storage tank according to the present invention, Figure 22 is a view showing the temperature / pressure change over time in the liquefied gas storage tank according to the present invention.

Referring to FIG. 19 , when the stratification phenomenon occurs, the internal pressure gradually increases, but when the liquefied gas temperature at the liquid level is lowered by the operation of the stratification suppression unit 60, the internal pressure decreases within a short time. However, due to the continuous external heat penetration, stratification occurs again and the internal pressure rises.

Therefore, in the present invention, the operation of the stratification suppression unit 60 can be implemented periodically/continuously, but when considering power, etc., the stratification suppression unit 60 is discontinuously and repeatedly operated to prevent the liquefied gas storage tank 10 from being operated. It can delay the pressure rise.

That is, referring to FIG. 20 , the stratification suppression unit 60 is repeatedly operated whenever the difference between the temperature of the liquefied gas at the liquid level and the temperature of the liquefied gas at the inner bottom becomes greater than or equal to the first preset value, and the liquefied gas at the liquid level The difference between the temperature and the temperature of the liquefied gas in the inner floor may be set to be less than or equal to a second preset value, in which case the second preset value may be a value smaller than the first preset value or zero.

However, since the change in temperature over time may not occur proportionally, the first preset value may be a value that decreases as the temperature of the liquefied gas at the inner floor increases during operation.

On the other hand, referring to FIG. 21 , it is possible to operate the stratification suppression unit 60 without changing the preset value. That is, the stratification suppression unit 60 considers that the change in pressure over time may occur proportionally, and in It is repeatedly operated whenever the difference between the saturation pressures is equal to or greater than the first preset value, so that the difference between the internal pressure of the liquefied gas storage tank 10 and the saturation pressure at the inner bottom is less than or equal to the second preset value, In this case, the second preset value may be a value smaller than the first preset value or 0.

Of course, whether the difference between the temperature of the liquefied gas at the liquid level and the temperature of the liquefied gas at the inner floor is equal to or greater than the first preset value, or the inner floor derived from the internal pressure of the liquefied gas storage tank 10 and the temperature of the liquefied gas at the inner floor Whether or not the difference between the saturation pressures in the . This can be controlled.

22 is a view showing the temperature change of FIG. 20 and the pressure change of FIG. 21 together. As shown in FIG. 22, when the stratification inhibitor 60 is operated, the temperature and It can be seen that all the pressures drop. However, as the liquefied gas of the inner floor flows by the stratification suppression unit 60, the temperature of the liquefied gas of the inner floor may slightly increase.

As such, in this embodiment, in the liquefied gas storage tank 10 in which liquefied gas and boil-off gas coexist, the internal pressure rapidly rises as the stratification phenomenon occurs, thereby simplifying or omitting the boil-off gas treatment configuration. The overall efficiency of the system can be greatly improved.

It goes without saying that the present invention is not limited to the above-described embodiments, and a combination of the embodiments or a combination of at least one of the embodiments and a known technology may be included as another embodiment.

In the above, the present invention has been described focusing on the embodiments of the present invention, but this is only an example and does not limit the present invention. It will be appreciated that various combinations or modifications and applications not illustrated in the embodiments are possible within the scope. Accordingly, descriptions related to variations and applications that can be easily derived from the embodiments of the present invention should be interpreted as being included in the present invention.

1: Ship 2: Gas fuel supply system
10: liquefied gas storage tank 11: stratification identification unit
111a: upper temperature sensor 111b: lower temperature sensor
111c: liquid level temperature sensor 112: pressure sensor
20: liquefied gas supply unit 21: transfer pump
22: high pressure pump 23: carburetor
L20: Liquefied gas supply line L21: Liquefied gas return line
30: boil-off gas supply unit 31: compressor
32: cooler L30: boil-off gas supply line
40: boil-off gas liquefaction unit 41: liquefier
411: refrigerant pump 412: refrigerant expander
42: gas-liquid separator L40: boil-off gas liquefaction line
L41: Refrigerant circulation line L42: Flash gas discharge line
50: consumer 60: stratification suppression unit
61a: liquid level nozzle 61b: lower nozzle
61c: upper nozzle 62: agitator
63: cooler L60: stratification suppression line

Claims (7)

As a gas fuel supply system provided in a liquefied gas carrier that transports liquefied gas as cargo,
a plurality of liquefied gas storage tanks in which liquefied gas is stored and the boil-off gas from which the liquefied gas is evaporated coexists;
By flowing the liquefied gas or boil-off gas stored in the liquefied gas storage tank, the temperature of the liquefied gas at the liquid level, which is the interface between the liquefied gas and the boil-off gas, approaches the temperature of the liquefied gas at the inner bottom of the liquefied gas storage tank. Dropping stratification inhibitor;
a liquefied gas supply unit for supplying the liquefied gas of the liquefied gas storage tank to a consumer; and
and a boil-off gas processing unit for receiving and processing the boil-off gas of the liquefied gas storage tank,
The BOG processing unit, as the stratification suppression unit suppresses the stratification phenomenon and delays the pressure rise of the liquefied gas storage tank, does not supply BOG to the consumer during operation,
The stratification suppression unit,
Each time the difference between the internal pressure of the liquefied gas storage tank and the saturation pressure in the internal bottom derived from the liquefied gas temperature in the internal bottom becomes more than a first preset value, the internal pressure of the liquefied gas storage tank is repeatedly operated Gas fuel supply system, characterized in that the difference between the saturation pressure at the bottom and the second preset value or less. According to claim 1, wherein the stratification suppression unit,
By suppressing the stratification phenomenon, the period for which the internal pressure of the liquefied gas storage tank reaches a preset value is delayed,
The preset value is a gas fuel supply system, characterized in that the pressure required to discharge the boil-off gas from the liquefied gas storage tank. According to claim 1, wherein the demand,
Gas fuel supply system, characterized in that it consumes only the liquefied gas of the liquefied gas storage tank and operates. According to claim 1, wherein the boil-off gas processing unit,
Gas fuel supply system, characterized in that the compressor for supplying the boil-off gas of the liquefied gas storage tank to the customer is omitted. According to claim 4, wherein the boil-off gas processing unit,
A high-duty (HD) compressor that compresses the boil-off gas generated during bunkering to the liquefied gas storage tank to return it to the gas source, and a low-duty (LD) compressor that compresses the boil-off gas of the liquefied gas storage tank to supply the boil-off gas to the customer. Duty) of the compressors, the gas fuel supply system, characterized in that only the HD compressor is provided. According to claim 1, wherein the boil-off gas processing unit,
Gas fuel supply system, characterized in that the device for re-liquefying the boil-off gas of the liquefied gas storage tank is omitted. A liquefied gas carrier having the gas fuel supply system according to any one of claims 1 to 6.

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