KR20200002561A - 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. The liquefied gas storage tank, which is stored liquefied gas therein and coexists with boil off gas in which the liquefied gas is vaporized, includes a stratification identification unit measuring or estimating temperature of a liquid surface which is a boundary surface of the liquefied gas and the boil off gas and determining the presence or absence of generation of a stratification phenomenon that temperature of the liquefied gas in a section from the liquid surface to a certain point downwards is increased toward the liquid surface so that the temperature of the liquefied gas in the liquid surface is higher than the temperature of the liquefied gas at an inner floor as the temperature of the liquefied gas and the boil off gas is differently heated by external heat penetration.

Description

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.

As environmental regulations have recently been tightened, the use of natural gas, which is close to an environmentally friendly fuel, is increasing among various fuels. Natural gas can be extracted in gaseous form from wells located in the inland or ocean strata. The extracted natural gas undergoes pretreatment such as mercury removal, drying, or NGL removal, followed by liquefaction for storage and transportation. Can be liquefied through.

Natural gas can be cooled to below the boiling point (for example, -162 ℃ under 1 atm) while being exchanged with a refrigerant, and can be converted into a liquid state. Transport efficiency can be increased.

The liquefied natural gas is made of a type such as a stand-alone, membrane type, pressurized type, and is stored in a liquid state in a storage tank having a heat insulating structure, and is transported by a gas carrier equipped with a storage tank.

However, since the thermal insulation structure provided in the storage tank can not completely block the external thermal penetration, as the external heat is transferred to the liquid natural gas, some natural gas is naturally vaporized and changed to the evaporation gas.

Therefore, liquid natural gas and gaseous vapor gas coexist in the storage tank. However, the heat capacity penetrated into the storage tank is not evenly distributed in the storage tank, and since the natural gas and the boil-off gas have different heat capacities (the range of temperature rise when heat is applied), natural by height based on the liquid level The temperature of the gas and the temperature of the boil-off gas are made different.

For example, while the temperature of the natural gas is relatively constant from the bottom of the inside of the storage tank to the liquid level, the temperature of the evaporated gas gradually increases from the liquid level to the top of the inside of the storage tank.

If this state continues for a certain time, the temperature rises as the liquefied gas from the liquid level down to a certain depth gets closer to the liquid level, and the occurrence of such an interval is called stratification. When the stratification phenomenon occurs, the temperature at the liquid level where the liquefied gas and the boil gas meets, the temperature rises, and the temperature rise at the liquid level promotes the generation of the boil-off gas, leading to an increase in the internal pressure of the storage tank.

Particularly, in the case of gas carriers, the storage tank is filled with about 98% of natural gas, which is a cargo, and is operated for a certain period of time. As a result, the internal pressure increases due to the generation of boiled gas may be a problem as the cargo volume is maintained during the operation.

Therefore, the conventional storage tank, in addition to the basic amount of boil-off gas generated by the external heat penetration during the operation of the gas carrier, should be constructed in consideration of the additional boil-off gas generated by the additional vaporization due to the stratification phenomenon, excessive design Cost has been caused.

The present invention was created to solve the problems of the prior art as described above, an object of the present invention, by lowering the temperature at the liquid level to suppress the stratification phenomenon, to ensure the transport stability of liquefied gas by delaying the internal pressure rise of the storage tank To provide liquefied gas storage tanks, gas fuel supply systems and ships.

The liquefied gas storage tank according to an aspect of the present invention is a liquefied gas storage tank in which liquefied gas is stored therein and evaporated gas in which liquefied gas has evaporated coexists, and measures a temperature of a liquid surface which is an interface between liquefied gas and evaporated gas Alternatively, as the temperature of the liquefied gas and the boil-off gas are differently heated due to external heat penetration, the temperature of the liquefied gas rises toward the liquid level in a section from the liquid level downward to a certain point, thereby liquefied gas temperature at the liquid level. It is characterized in that the stratification grasping unit is provided to determine whether the stratification phenomenon appearing higher than the liquefied gas temperature in the inner bottom.

Specifically, the stratified grasping portion, the lower temperature sensor for measuring the temperature of the lower end in the liquefied gas storage tank; And it may include a pressure sensor for measuring the internal pressure of the liquefied gas storage tank.

Specifically, the liquefied gas storage tank is a cargo tank mounted on a liquefied gas carrier, and the stratified grasping portion is installed adjacent to the liquid level when the liquefied gas storage tank is full in the liquefied gas storage tank. It may further include a liquid surface temperature sensor for measuring the temperature of the liquid surface.

In detail, the liquid level temperature sensor may be fixedly installed at the liquid level when the liquefied gas is filled in the liquefied gas storage tank at a predetermined ratio.

Specifically, the preset ratio may be 98% to 99%.

In detail, the stratification determining unit may determine that stratification occurs when the measured value of the liquid level temperature sensor is higher than a preset value compared to the measured value of the lower temperature sensor.

In detail, the liquefied gas storage tank is a fuel tank mounted on a liquefied gas propulsion vessel or a bunkering tank mounted on a bunkering vessel, and the stratification grasping unit has a temperature at the liquid level equal to the measured value of the lower temperature sensor. It is assumed that the internal pressure of the liquefied gas storage tank is estimated, and when the measured value of the pressure sensor is higher than the estimated preset pressure, the stratification may occur.

Specifically, the stratified grasping unit may estimate the internal pressure of the liquefied gas storage tank using table data in which internal pressure information of the liquefied gas storage tank corresponding to the temperature at the liquid level is stored.

Specifically, the table data may store internal pressure information of the liquefied gas storage tank according to the temperature at the liquid level and the amount of liquefied gas stored in the liquefied gas storage tank.

Specifically, the stratified grasping unit, the upper temperature sensor for measuring the temperature of the upper end in the liquefied gas storage tank further comprises, the measured value of the lower temperature sensor, the measured value of the upper temperature sensor, the liquefied gas storage The internal pressure of the liquefied gas storage tank may be calculated and estimated based on the amount of liquefied gas stored in the tank.

In detail, the stratification grasping unit may determine whether the stratification phenomenon occurs repeatedly at each preset time.

Specifically, the stratification determination unit may determine whether the stratification phenomenon occurs whenever the amount of liquefied gas stored in the liquefied gas storage tank changes to a predetermined value or more.

Specifically, stratification suppression that flows liquefied gas or evaporated gas stored in the liquefied gas storage tank to drop the liquefied gas temperature at the liquid level in a direction approaching the liquefied gas temperature at the inner bottom of the liquefied gas storage tank The stratification grasping unit may be configured to allow the liquefied gas or the evaporated gas to flow by the stratification suppressing unit when the occurrence of the stratification phenomenon is detected.

Gas fuel supply system according to an aspect of the present invention, characterized in that for supplying the liquefied gas stored in the liquefied gas storage tank to the demand destination.

Ship according to one aspect of the invention, characterized in that having the liquefied gas storage tank.

The liquefied gas storage tank, the gas fuel supply system and the ship according to the present invention utilize a variety of configurations to reduce the temperature of the interface between the liquefied gas and the boil-off gas, thereby delaying the period in which the internal pressure of the storage tank rises, thereby treating the evaporated gas. It is possible to minimize / omit the configuration and to enable stable operation of the vessel equipped with the storage tank.

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 stratification occurs in the liquefied gas storage tank.
FIG. 6 is a diagram illustrating an increase in internal pressure due to stratification in a liquefied gas storage tank. FIG.
7 is a view showing the temperature change at the liquid level due to the temperature difference between the liquefied gas and the evaporated gas.
8 is a conceptual diagram of a liquefied gas storage tank provided with stratification grasping portion 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 stratification suppression 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 stratification suppression according to the fifth embodiment of the present invention.
13 is a conceptual view 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 stratification suppression according to the sixth embodiment of the present invention.
15 is a conceptual view 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 stratification suppression according to the seventh embodiment of the present invention.
17 is a view showing the internal pressure rise delay due to the stratification suppression in the membrane type / independent type liquefied gas storage tank according to the present invention.
18 is a view showing a delay in internal pressure increase due to stratification suppression in a pressurized liquefied gas storage tank according to the present invention.
19 is a view showing the internal pressure change due to the stratification suppression in the pressurized liquefied gas storage tank according to the present invention.
20 is a view showing a temperature change with time in the pressurized liquefied gas storage tank according to the present invention.
21 is a view showing a pressure change with time in the 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 the preferred embodiments associated with the accompanying drawings. In the present specification, in adding reference numerals to the components of each drawing, it should be noted that the same components as possible, even if displayed on different drawings have the same number as possible. In addition, in describing the present invention, if it is determined that the detailed description of the related known technology may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Hereinafter, the gas may mean a material having a boiling point lower than room temperature as hydrocarbons such as LPG, LNG, and ethane, but for convenience, the present invention will be limited to the final production and storage of LNG (methane). In the present specification, the gas is not limited to the gas phase despite the term expression.

Hereinafter, high pressure (HP), low pressure (LP), high temperature, and low temperature are relative and do not represent an absolute value.

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

Referring to FIG. 1, the present invention may be a liquefied gas carrier that carries liquefied gas. The liquefied gas carrier is a ship 1 for transporting liquefied gas as a cargo, and a plurality of liquefied gas storage tanks 10 (cargo tanks) may be mounted in the vessel.

In the case of liquefied gas carriers, each liquefied gas storage tank 10 is operated in a state where 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 weight state). Can be operated by

Alternatively, the vessel 1 according to the present invention may be a vessel 1 other than a liquefied gas carrier that carries 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 vessel 1 may be a liquefied gas propulsion ship that loads liquefied gas as a fuel for propulsion.

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

Of course, in addition to the vessel (1) according to the present invention, it can be interpreted as meaning encompassing all of the offshore structures such as bunkering vessel (1), FSRU, FPSO, not the general merchant vessel.

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

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

The liquefied gas storage tank 10 stores liquefied gas therein. In this case, the liquefied gas stored in the liquefied gas storage tank 10 may be naturally vaporized due to external heat penetration, and the liquefied gas and the evaporated gas may exist together in the liquefied gas storage tank 10.

The liquefied gas storage tank 10 may be a membrane type or a standalone type when mounted as a cargo tank on a liquefied gas carrier, and may be a membrane type, a standalone type or a pressurized type when mounted as a fuel tank on a ship 1 outside the liquefied gas carrier. Yes is as described above.

The liquefied gas supply unit 20 supplies the liquefied gas stored in the liquefied gas storage tank 10 to the demand destination 50. In this case, the demand source 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 demand destination 50, and a low temperature. It may include a vaporizer 23 for heating the liquefied gas to the required temperature of the demand destination 50, the liquefied gas supply line (L20) may be provided from the liquefied gas storage tank 10 to the demand destination (50). .

In addition, the liquefied gas supply line (L20) is provided with a liquefied gas return line (L21) for returning the excess liquefied gas of the liquefied gas discharged from the transfer pump 21 to the liquefied gas storage tank 10, liquefied gas return line L21 branches from the outside of the liquefied gas storage tank 10 in the liquefied gas supply line L20 and extends into the liquefied gas storage tank 10. Of course, the liquefied gas return line (L21) may be branched from the liquefied gas supply line (L20) in the liquefied gas storage tank 10 and extend downward.

The boil-off gas supply unit 30 may supply the boil-off gas generated in the liquefied gas storage tank 10 to the demand destination 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 demand destination 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 required temperature of the demand destination 50. The cooler 32 may be included, and a heater may be provided in place of the cooler 32. In addition, the boil-off gas supply unit 30 has an boil-off gas supply line (L30) connected to the demand destination 50 in the liquefied gas storage tank (10).

However, the compressor 31 of the boil-off gas supply unit 30 is not a high-duty (HD) compressor that compresses the boil-off gas generated during bunkering to the liquefied gas storage tank 10 to a main oil source, but not a high-duty compressor. Means a low-duty (LD) compressor that compresses to supply the boil-off gas of (10) to the demand destination (50).

The boil-off gas liquefaction unit 40 liquefies the excess boil-off gas that cannot be consumed by the consumer 50 from the boil-off gas flowing through the boil-off gas supply line L30 and returns 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 by using a coolant, and the coolant circulation line in which the coolant pump 411 and the refrigerant expander 412 are disposed. L41 may be connected.

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

The gas-liquid separator 42 discharges the gas (flash gas, nitrogen as a main component) remaining in the gas state to the flash gas discharge line L42 even though the vaporized gas is heat-exchanged with the refrigerant in the liquefier 41. In 10), only liquid liquefied evaporated gas may be returned.

For reference, the configuration for processing liquefied gas / evaporative gas (liquefied gas supply unit 20, boil-off gas supply unit 30, boil-off gas liquefaction unit 40) in the present specification may be referred to as a gas fuel treatment unit, liquefied It is noted that the configuration (evaporation gas supply unit 30, boil-off gas liquefaction unit 40, etc.) for discharging and processing the boil-off gas from the gas storage tank 10 may be referred to as a boil-off gas treatment 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 boil-off gas treatment unit may omit the boil-off gas liquefaction unit 40. This is because the discharge of the boil-off gas does not generate excess boil-off gas, which will be described later, but is possible because the 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, the gas fuel supply system 2 according to the third embodiment of the present invention may also omit the boil-off gas supply unit 30 as 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 demand destination 50, and the boil-off gas may not be discharged from the liquefied gas storage tank 10 during operation. This configuration is possible as the stratification suppression is made 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 the boil-off gas as shown in FIGS. 3 and 4 will be described in detail.

5 is a view showing the stratification phenomenon occurs in the liquefied gas storage tank, Figure 6 is a view showing the internal pressure increase due to the stratification phenomenon in the liquefied gas storage tank. 7 is a view showing the temperature change at the liquid level due to the temperature difference between the liquefied gas and the evaporated gas.

In the liquefied gas storage tank 10 provided in the vessel 1 described with reference to FIG. 1, the liquefied gas may be stored therein and the liquefied gas may be co-evaporated. The boil-off gas inside 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 due to external thermal penetration.

In the liquefied gas storage tank 10 in which the liquefied gas and the boil-off gas coexist, the temperature graph as shown in the upper left of FIG.

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

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

Specifically, the boil-off gas stored in the liquefied gas storage tank 10 has a lower heat capacity than the liquefied gas (Lower heat capacity), and considering the installation position of the liquefied gas storage tank 10, heat penetration through the upper side is more active than the lower side. .

Therefore, the evaporation gas is heated more than the liquefied gas due to external heat penetration, and thus the temperature of the evaporated 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 evaporated gas. .

Furthermore, since the boil-off gas is heated more easily than the liquefied gas, the boil-off gas on the liquid surface may have a higher temperature than the liquefied gas on the liquid surface. In this case, for thermal equilibrium, the temperature of the liquefied gas at the liquid level is increased by the evaporated gas.

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

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

However, the assumption that the properties of the liquefied gas and the boil-off gas are the same (homogeneous model) and the case of the stratification phenomenon (thermal stratification model) show opposite trends in the pressure rise depending on the liquid level.

This stratification occurs because the heating of the liquefied gas and the boil-off gas is different from each other, and the condensation, vaporization, and pressure at the liquid level according to the heating temperature of the liquefied gas and the boil-off gas will be described with reference to FIG. 7. .

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

On the other hand, in FIG. 7B (evaporation gas temperature <liquefied gas temperature), the liquefied gas at the liquid surface naturally evaporates, thereby increasing the temperature and pressure of the liquefied gas, and the temperature and pressure of the liquefied gas decrease. Therefore, the temperature of the liquefied gas storage tank 10 is balanced to a uniform value.

However, since the heat capacity of the evaporated gas is smaller than the heat capacity of the liquefied gas, the case of FIG. 7B is unlikely to occur in reality, and only the case of FIG. 7A occurs.

That is, as long as the liquefied gas and the boil-off gas coexist in the liquefied gas storage tank 10, stratification is bound to occur. In this case, due to the rise of the temperature of the liquefied gas at the liquid level, the liquefied gas is promoted and the internal pressure rises quickly. .

Increasing the internal pressure of the liquefied gas storage tank 10 may be problematic because it requires operations such as discharge and treatment of fuel gas (fuel supply, reliquefaction, and combustion). Therefore, it is necessary to measure the occurrence of the stratification phenomenon, the following describes the stratification grasping unit 11 installed in the liquefied gas storage tank 10 of the present invention with reference to FIG.

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

Referring to FIG. 8, the stratified grasping unit 11 measures or estimates the temperature of the liquid surface, which is the interface between the liquefied gas and the boil-off gas, and from the liquid surface as the temperature of the liquefied gas and the boil-off gas is heated differently due to external heat penetration. The temperature of the liquefied gas rises toward the liquid level in a section up to a certain point downward to determine whether a stratification phenomenon occurs in which the liquefied gas temperature at the liquid level is higher than the liquefied gas temperature at the inner bottom.

To this end, the stratified grasping unit 11 includes a lower temperature sensor 111b for measuring the temperature of the lower end in the liquefied gas storage tank 10 and a pressure sensor for measuring the internal pressure of the liquefied gas storage tank 10 ( 112).

As shown in the left side of FIG. 8, when the liquefied gas storage tank 10 is a cargo tank mounted on the liquefied gas carrier, the stratified grasping 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 in a full or empty state, so that the liquid level in the liquefied gas storage tank 10 has a relatively fixed position. do.

Therefore, the stratified grasping unit 11 is inverted at the level of the liquid level when the liquefied gas storage tank 10 is fully loaded inside the liquefied gas storage tank 10 to directly measure the liquid surface temperature sensor 111c that directly measures the temperature of the liquid surface. It can be provided.

In this case, the liquid surface temperature sensor 111c may be fixedly installed at the liquid level when the liquefied gas is filled in the liquefied gas storage tank 10 at a predetermined ratio (98 to 99%, for example, 98.5%).

The stratification grasping unit 11 including the liquid level temperature sensor 111c indicates that stratification occurs when the measured value of the liquid level temperature sensor 111c is higher than or equal to a preset value compared to the measured value of the lower temperature sensor 111b. You can judge. In this case, the stratified grasping unit 11 may monitor the internal pressure increase of the liquefied gas storage tank 10 through the pressure sensor 112.

On the other hand, when the liquefied gas storage tank 10 is a fuel tank mounted on the liquefied gas propulsion ship or a bunkering tank mounted on the bunkering vessel 1, as shown in the right side of FIG. You can't.

Therefore, the stratification grasping unit 11 estimates the internal pressure of the liquefied gas storage tank 10 on the assumption 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 the pressure is higher than the preset internal pressure, it may be determined that stratification has occurred.

In connection with estimating 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 be.

At this time, the table data may be the internal pressure information 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, the amount of liquefied gas is generally in the liquefied gas storage tank 10 Can be measured and used through a level gauge (not shown) provided with.

In addition, the stratified grasping unit 11 further includes an upper temperature sensor 111a for measuring the temperature of the upper end in the liquefied gas storage tank 10, and a measured value of the lower temperature sensor 111b and an upper temperature sensor ( It is of course 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 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 wrong. Is higher than the measured value of the lower temperature sensor 111b, the stratification grasping unit 11 may determine that stratification has occurred.

The stratification grasping unit 11 may determine whether the stratification phenomenon occurs repeatedly at each preset time, and the stratification phenomenon may be determined whenever the amount of liquefied gas stored in the liquefied gas storage tank 10 is changed to a predetermined value or more. The occurrence can be determined.

According to the present invention, when stratification occurs in the liquefied gas storage tank 10 by the stratification grasping unit 11, the stratification suppression unit 60 may be used to suppress the stratification phenomenon and delay the internal pressure increase.

The stratification inhibiting unit 60 flows the liquefied gas or the evaporated gas stored in the liquefied gas storage tank 10 when the stratified phenomenon occurs and drops the liquefied gas temperature at the liquid level toward the liquefied gas temperature at the inner bottom. As a floating structure, it demonstrates in detail below with reference to FIG.

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

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

However, since the liquid level nozzle 61a will be fixedly installed in the liquefied gas supply line L20 or the like, 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. It may be the case that the liquid level is mounted on the carrier so that the liquid level is located at a relatively constant height.

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

Alternatively, the stratification suppression unit 60 may include an agitator 62 as shown in FIG. 9B. The stirrer 62 may rotate the impeller by using a power source such as a motor to mix the liquefied gas at the lower end with the liquefied gas inside the liquefied gas storage tank 10, and the shape of the stirrer 62 is arranged. , Number and the like are not particularly limited.

Alternatively, the stratification inhibiting unit 60 may include a lower nozzle 61b that sprays the liquefied gas transferred by the transfer pump 21 upward from the inner bottom toward the liquid surface as shown in FIG. 9C. .

As the stratification inhibiting unit 60 shown in FIGS. 9A, 9B, and 9C 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 under an initial (t0) condition. The temperature of the liquefied gas is constant regardless of up and down (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 surface temperature. Is determined (P = Psat (A0)).

After a certain time t as heat inflow is generated 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, the heat of the boil-off gas whose temperature is higher is transferred to the liquefied gas, and the temperature of the liquefied gas rises from the liquid level down to a certain section.

Therefore, according to the temperature gradient in the liquefied gas storage tank 10, the interior of the liquefied gas storage tank 10 is the liquefied gas section (section where the temperature of the liquefied gas is constant from the inner bottom to a certain point, B = C), stratification section (The section where the temperature of the liquefied gas gradually rises from a certain point to the liquid level, A> C), and the evaporation gas section (the section where the temperature of the boiled gas gradually rises from the liquid level to the inner top, D> A) The pressure of the gas storage tank 10 is determined by the saturation pressure at the liquid surface temperature (P = Psat (A)).

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

In this case, the temperature gradient is changed 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 surface temperature, and as the temperature of A1 is significantly lower than A, the pressure of the liquefied gas storage tank 10 Can also be lowered.

That is, the stratification inhibiting unit 60 of FIG. 9 is provided in the stratification section and the liquid level nozzle 61a for injecting the liquefied gas flowing in the liquefied gas supply line L20 into the stratification section, the liquefied gas section of the liquefied gas section, and the stratification section. As a stirrer 62 to mix the liquefied gas of the, and / or the lower nozzle 61b which is provided in the liquefied gas section and injects the liquefied gas flowing in the liquefied gas return line (L21) upward toward the stratification section The temperature of the liquefied gas at the liquid level can be drastically reduced from A to A1. As a result, the liquefied gas storage tank 10 may have a low pressure, thereby eliminating or reducing the need for boil-off gas discharge.

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

The upper nozzle 61c may be disposed in the boil-off gas section and spray downwardly the liquefied gas flowing in the stratification inhibiting line L60 toward the liquid surface in the boil-off gas section.

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

The stratification inhibiting unit 60 shown in FIGS. 11D and 11E transmits the liquefied gas in the liquefied gas section to the evaporated gas section, thereby reducing the temperature change width according to the height in the evaporated gas section and reducing the evaporated gas section. By lowering the temperature at, the temperature change range at least in the upper portion of the stratification section can be reduced, thereby lowering the liquefied gas temperature at the liquid level.

That is, by the stratification inhibiting unit 60 of FIG. 11, as shown in FIG. 12, the temperature gradient of B-C-A-D is changed to B-C-E-A2-D2 'through B-C-A-D2. Will change. Therefore, the present embodiment can suppress stratification by dropping the temperature of the liquid surface from A to A2 while inducing the temperature distribution in at least an upper portion of the boil-off gas section and the stratification section side by side.

FIG. 13 is a conceptual view of a liquefied gas storage tank provided with a stratification suppressing 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 evaporation gas, unlike the foregoing fourth and fifth embodiments using liquefied gas.

As shown in FIG. 13F, 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 bottom, and a lower nozzle 61b. have.

In this case, the lower nozzle 61b may be provided in the liquefied gas section and may spray the boil-off gas flowing in the stratification suppression line L60 toward the liquid level in the liquefied gas section.

Through this, the stratification inhibiting unit 60 transmits the boil-off gas in the boil-off gas section to the liquefied gas section, thereby reducing the temperature in the boil-off gas section and increasing the temperature in the liquefied gas section, while varying the temperature variation in the stratified section. By reducing the temperature of the liquefied gas at the liquid level.

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

15 is a conceptual view 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 diagram illustrating stratification suppression according to a seventh embodiment of the present invention.

Referring to FIG. 15G, the stratification inhibiting unit 60 according to the seventh embodiment of the present invention heats the liquefied gas in the liquefied gas section to a bubble unlike the previous (E) in FIG. 11. After making, it flows along the stratification inhibiting line (L60) extending to the inner bottom, and is delivered to the liquid level through the lower nozzle (61b) of the inner bottom.

In this case, 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.

Effects shown by operating the stratification inhibiting unit 60 as described above will be described below with reference to FIG. 17 and the like.

17 is a view showing a delay in the internal pressure rise due to the stratification suppression in the membrane type / independent liquefied gas storage tank according to the present invention, Figure 18 is a pressure increase due to the stratification suppression in the pressurized liquefied gas storage tank according to the present invention It is a figure which shows a delay.

Referring to FIG. 17, when the pressure requiring the discharge of the boil-off gas is about 0.6 barg, when the stratification suppressing unit 60 is not provided, the discharge of the boil-off gas occurs after about 14 days.

On the other hand, when the stratification suppression unit 60 is operated according to the stratification grasping unit 11, the discharge of the boil-off gas may be delayed after about 22 days. There may be a delay until approximately 29 days have elapsed.

Referring to FIG. 18, when the pressure requiring the discharge of the boil-off gas is about 5.5 barg, the stratification-inhibiting part 60 is compared with the case where the stratification suppressing part 60 is not provided (evaporation of the evaporation gas after 12 days). In the case of operating according to the stratification grasping unit 11 (evaporation of evaporated gas after 24 days) and in case of continuously operating the stratification inhibiting unit 60 (evaporation of evaporated gas after 26 days), the evaporation gas discharge may be considerably delayed. Can be.

That is, the present invention suppresses the stratification phenomenon by using the stratification inhibiting unit 60, so that the internal pressure of the liquefied gas storage tank 10 reaches a preset value (pressure required to discharge the boil-off gas from the liquefied gas storage tank 10). This can delay the period of time.

Therefore, the present invention can suppress the stratification phenomenon and delay the pressure rise of the liquefied gas storage tank 10, thereby shortening the period during which the boil-off gas must be discharged from the liquefied gas storage tank 10, and the stratification inhibiting part. In contrast to the case without the 60, the operation number, operating time, or load of the boil-off gas treatment unit during operation can be lowered.

In view of this, if the stratification inhibiting unit 60 is applied to the first embodiment described above, the load or the number of operations of the boil-off gas liquefaction unit 40 may be reduced, and the gas fuel supply in the second embodiment It is also possible to omit the boil-off gas liquefaction section 40, which is a device for re-liquefying boil-off gas like the system 2.

In this case, the boil-off gas treatment unit may include only the boil-off gas supply unit 30 among the boil-off gas liquefaction unit 40 and the boil-off gas supply unit 30, but operates the compressor 31 (HD compressor) during operation due to suppression of stratification. The start time may be delayed or the operation of the compressor 31 may be omitted during operation.

In addition, from the point of view of the gas fuel processing unit, the gas fuel processing unit may not supply liquefied gas as the main fuel of the demand destination 50 or supply boil-off gas to the demand destination 50 during operation, and re-enable the evaporated gas depending on the operation period. It is also possible to store in the liquefied gas storage tank 10 without liquefying.

If the period of the ship 1 is about 15 days to 20 days, the ship 1 according to the present invention is stored without any emissions of the evaporated gas during operation by using the stratification inhibiting unit 60. Even if, the internal pressure of the liquefied gas storage tank 10 can be maintained within a safe range.

Therefore, further from the second embodiment, the boil-off gas supply unit 30 can be omitted, as in the gas fuel supply system 2 in the third embodiment. That is, since the compressor 31 (LD compressor) for compressing the boil-off gas is omitted (the HD compressor for bunkering may be provided), the boil-off gas treatment unit may not supply the boil-off gas to the demand source 50 during operation, 50 can be operated by consuming only liquefied gas.

In contrast, the present invention, instead of having the boil-off gas liquefaction unit 40 which is a device for the boil-off gas treatment unit to re-liquefy the boil-off gas, it is also possible to omit the boil-off gas supply unit 30, wherein the boil-off gas liquefaction unit 40 Can liquefy the boil-off gas compressed by the HD compressor.

Hereinafter, with reference to FIGS. 19-22, the operation method of the stratification suppression part 60 is demonstrated about the case where the vessel 1 other than a liquefied gas carrier has the pressurized liquefied gas storage tank 10. FIG.

19 is a view showing the internal pressure change due to the stratification suppression in the pressurized liquefied gas storage tank according to the present invention, Figure 20 is a view showing the temperature change with time in the pressurized liquefied gas storage tank according to the present invention. 21 is a view showing a pressure change with time in the pressurized liquefied gas storage tank according to the present invention, Figure 22 is a view showing a temperature / pressure change with 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 of the liquid surface decreases due to the operation of the stratification inhibiting unit 60, the internal pressure falls within a short time. However, due to continuous external thermal penetration, stratification occurs again, causing an increase in internal pressure.

Accordingly, the present invention can implement the stratification inhibiting unit 60 periodically / continuously, however, in consideration of power, etc., the stratification suppressing unit 60 is repeatedly discontinuously operated so that the liquefied gas storage tank 10 can be operated. Pressure rise may be delayed.

That is, referring to FIG. 20, the stratification inhibiting unit 60 is repeatedly operated whenever the difference between the liquefied gas temperature at the liquid level and the liquefied gas temperature at the inner bottom becomes equal to or greater than the first preset value, thereby liquefied gas at the liquid level. The difference between the temperature and the liquefied gas temperature at the inner bottom may be equal to or less than the second preset value, wherein the second preset value may be less than or equal to the first preset value.

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

On the other hand, referring to Figure 21, it is possible to operate the stratification suppression unit 60 without changing the preset value. That is, the stratification restraining unit 60 may be formed in the internal bottom derived from the internal pressure of the liquefied gas storage tank 10 and the temperature of the liquefied gas at the inner bottom in consideration of the fact that the pressure change with time may occur in proportion. Whenever the difference between the saturation pressure is greater than or equal to the first preset value, it is repeatedly operated 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 smaller than the first preset value or zero.

Of course, whether the difference between the liquefied gas temperature at the liquid level and the liquefied gas temperature at the inner bottom is greater than or equal to the first predetermined value, or the inner bottom derived from the internal pressure of the liquefied gas storage tank 10 and the liquefied gas temperature at the inner bottom. Whether the difference between the saturation pressures at or equal to or greater than the first preset value can be checked continuously or periodically by the stratification grasping unit 11, and the stratification suppressing unit 60 is operated by the stratification grasping unit 11. This can be controlled.

FIG. 22 illustrates the temperature change of FIG. 20 and the pressure change of FIG. 21. When the stratification suppression unit 60 is operated as shown in FIG. 22, the temperature and the temperature change for a predetermined time during which the stratification suppression unit 60 operates. It can be seen that the pressures all fall. However, as the liquefied gas of the inner bottom flows by the stratification inhibiting unit 60, the liquefied gas temperature of the inner bottom may increase slightly.

As described above, the present embodiment solves the problem that the internal pressure rises rapidly as the stratification phenomenon occurs in the liquefied gas storage tank 10 in which the liquefied gas and the boiled gas coexist, thereby simplifying or omitting the evaporated gas treatment configuration. The overall efficiency of the system can be greatly improved.

The present invention is not limited to the above-described embodiments, and of course, a combination of the above embodiments or a combination of at least one of the above embodiments and known technologies may be included as another embodiment.

The present invention has been described above with reference to the embodiments of the present invention. However, the present invention is merely an example, and is not intended to limit the present invention. Those skilled in the art do not depart from the essential technical details of the present embodiment. It will be appreciated that various combinations or modifications and applications which are not exemplified in the embodiments are possible in the scope. Therefore, technical matters related to modifications and applications easily derivable 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: stratified grasping 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 part 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: demand source 60: stratification suppression unit
61a: liquid level nozzle 61b: lower nozzle
61c: upper nozzle 62: stirrer
63: cooler L60: stratification suppression line

Claims (15)

It is a liquefied gas storage tank that stores liquefied gas inside and co-exists with boiled gas evaporated liquefied gas,
By measuring or estimating the temperature of the liquid surface, which is the interface between the liquefied gas and the boil-off gas, the temperature of the liquefied gas is lowered from the liquid surface to a certain point as the temperature of the liquefied gas and the boiled gas is heated differently due to external heat penetration. Liquefied gas storage tank characterized in that the stratification grasping portion is provided to determine whether the stratification phenomenon occurs that rises toward the liquid level and the liquefied gas temperature at the liquid level is higher than the liquefied gas temperature at the inner bottom. The method of claim 1, wherein the stratification grasping unit,
A lower temperature sensor measuring a temperature of a lower end in the liquefied gas storage tank; And
Liquefied gas storage tank comprising a pressure sensor for measuring the internal pressure of the liquefied gas storage tank. The method of claim 2,
The liquefied gas storage tank is a cargo tank mounted on the liquefied gas carrier,
The stratified grasp unit further includes a liquid level temperature sensor installed adjacent to the liquid level when the liquefied gas storage tank is full in the liquefied gas storage tank and measuring a temperature of the liquid surface. Tank. The liquid level sensor of claim 3,
A liquefied gas storage tank, characterized in that the liquefied gas storage tank is fixed to the height of the liquid level when the liquefied gas is filled in a predetermined ratio. The method of claim 4, wherein the predetermined ratio is,
Liquefied gas storage tank, characterized in that 98% to 99%. The method of claim 4, wherein the stratification grasping unit,
When the measured value of the liquid level temperature sensor is higher than the predetermined value compared to the measured value of the lower temperature sensor, the liquefied gas storage tank, characterized in that it is determined that the stratification occurred. The method of claim 2,
The liquefied gas storage tank is a bunkering tank mounted on a fuel tank or bunkering ship mounted on a liquefied gas propulsion ship,
The stratification grasping unit estimates the internal pressure of the liquefied gas storage tank on the assumption that the temperature at the liquid level is the same as the measured value of the lower temperature sensor, and the measured value of the pressure sensor is equal to or greater than the estimated internal pressure. If high, the liquefied gas storage tank characterized in that it is determined that stratification has occurred. The method of claim 7, wherein the stratification grasping unit,
Liquefied gas storage tank, characterized in that for estimating the internal pressure of the liquefied gas storage tank using the table data stored the internal pressure information of the liquefied gas storage tank corresponding to the temperature at the liquid level. The method of claim 8, wherein the table data,
Liquefied gas storage tank, characterized in that the internal pressure information of the liquefied gas storage tank according to the temperature at the liquid level and the amount of liquefied gas stored in the liquefied gas storage tank. The method of claim 7, wherein the stratification grasping unit,
Further comprising a top temperature sensor for measuring the temperature of the upper end in the liquefied gas storage tank,
Liquefied gas storage tank, characterized in that to calculate and estimate the internal pressure of the liquefied gas storage tank based on the measured value of the lower temperature sensor, the measured value of the upper temperature sensor, the amount of liquefied gas stored in the liquefied gas storage tank. The method of claim 1, wherein the stratification grasping unit,
Liquefied gas storage tank, characterized in that for determining whether or not the stratification phenomenon occurs repeatedly every predetermined time. The method of claim 1, wherein the stratification grasping unit,
The liquefied gas storage tank, characterized in that it is determined whether the stratification phenomenon occurs whenever the amount of liquefied gas stored in the liquefied gas storage tank changes over a predetermined value. The method of claim 1,
The stratification restraining unit is provided to flow the liquefied gas or the boil-off gas stored in the liquefied gas storage tank to drop the liquefied gas temperature at the liquid level toward the liquefied gas temperature at the inner bottom of the liquefied gas storage tank. ,
The stratification grasping unit,
The liquefied gas storage tank, characterized in that liquefied gas or evaporated gas flows by the stratification inhibiting unit when the occurrence of stratification phenomenon is identified. The gas fuel supply system, characterized in that for supplying the liquefied gas stored in the liquefied gas storage tank of any one of claims 1 to 13. Ship having the liquefied gas storage tank of any one of claims 1 to 13.

Images