KR102673082B1 - System for reliquefying lng boil-off gas using hydrogen boil-off gas - Google Patents

Abstract

One embodiment of the present invention is an LNG fuel tank storing LNG (Liquefied Natural Gas), a liquefied hydrogen bunkering tank storing liquefied hydrogen (LH ₂ ), and hydrogen BOG (Boil Off Gas) generated from the liquefied hydrogen bunkering tank. ), a sub-cooler that re-liquefies the NG BOG (Natural Gas Boil Off Gas) generated in the LNG fuel tank by cooling, and a re-liquefaction tank that receives and stores the LNG re-liquefied by the sub-cooler. Provides an LNG BOG re-liquefaction system using the BOG of a liquefied hydrogen tank.

Description

LNG BOG reliquefaction system using the BOG of the liquefied hydrogen tank {SYSTEM FOR RELIQUEFYING LNG BOIL-OFF GAS USING HYDROGEN BOIL-OFF GAS}

The present invention relates to an LNG BOG reliquefaction system, and more specifically, to an LNG BOG reliquefaction system using the BOG of a liquefied hydrogen tank.

Consumption of liquefied gases such as LNG (Liquefied Natural Gas) and LPG (Liquefied Petroleum Gas) is rapidly increasing worldwide.

Liquefied gas, which is made by liquefying gas at low temperature, has a much smaller volume than gas, so it has the advantage of increasing storage and transportation efficiency. Liquefied gas, including LNG, can remove or reduce air pollutants during the liquefaction process, so it can be burned. It is an eco-friendly fuel that emits little air pollutants.

In connection with this, the construction of LNG transport ships, bunkering ships, and ships propelled by LNG as fuel is increasing to reduce marine environmental pollution.

The main ingredient of liquefied gas is methane. It is colorless, odorless, lighter than air, and has the characteristic of being liquefied at a very low temperature. It is cooled to -162℃ and used in a volume reduced to about 1/600 of that of gas. do.

This liquefied gas is stored in a liquid state in an insulated storage tank, but as external heat is continuously transferred to the storage tank, the liquefied gas is continuously naturally vaporized within the storage tank, producing boil-off gas (BOG). Occurs.

Such evaporation gas is a type of loss, and if evaporation gas accumulates in the storage tank, a problem may occur in which the pressure inside the tank increases excessively.

Therefore, various methods are being studied to treat BOG generated within storage tanks. Recently, a method of reliquefying BOG and returning it to the storage tank for BOG treatment and a method of using BOG as an energy source for fuel consumers such as ship engines are being studied. Re-liquefaction and recovery techniques, such as the method used, have been proposed.

Conventionally, BOG generated from LNG tanks was re-liquefied through a re-liquefaction device or disposed of through combustion (incineration). However, this method requires a separate installation of a device for re-liquefaction, which takes up a lot of space and reduces operating costs and energy. There is a limit to how much consumption there is.

Republic of Korea Patent Publication No. 10-2019-0034877 (announced on April 3, 2019)

The technical problem to be achieved by the present invention is to re-liquefy NG BOG generated in an LNG fuel tank using hydrogen (H ₂ ) BOG generated in a liquefied hydrogen tank, thereby reducing the space occupied by eliminating the need to install a separate device for re-liquefaction. The aim is to provide an LNG BOG reliquefaction system that can not only reduce , but also minimize additional operating costs and energy consumption.

The technical problem to be achieved by the present invention is not limited to the technical problem mentioned above, and other technical problems not mentioned can be clearly understood by those skilled in the art from the description below. There will be.

In order to achieve the above technical problem, an embodiment of the present invention includes an LNG fuel tank storing LNG (Liquefied Natural Gas), a liquefied hydrogen bunkering tank storing liquefied hydrogen (LH ₂ ), and the liquefied hydrogen bunkering tank. A sub-cooler that re-liquefies the NG BOG (Natural Gas Boil Off Gas) generated in the LNG fuel tank using the generated hydrogen BOG (Boil Off Gas), and the LNG re-liquefied by the sub-cooler. We provide an LNG BOG reliquefaction system that utilizes the BOG of a liquefied hydrogen tank, including a reliquefaction tank for delivery and storage.

In an embodiment of the present invention, the sub-cooler measures the temperature of the NG BOG flowing in and discharged from the LNG fuel tank, and cools the hydrogen BOG flowing in from the liquefied hydrogen bunkering tank according to the measured temperature of the NG BOG. Flow rate can be adjusted.

In an embodiment of the present invention, the sub-cooler, when the temperature of the NG BOG discharged and introduced from the LNG fuel tank is higher than -152.46 ℃, the flow rate of the hydrogen BOG discharged and introduced into the liquefied hydrogen bunkering tank is adjusted. The temperature can be lowered by increasing it.

In an embodiment of the present invention, a first valve unit connected to the reliquefaction tank and the sub-cooler and formed on a line through which the reliquefied LNG flows into the reliquefaction tank, the reliquefaction tank, and the A second valve unit is connected to the LNG fuel tank and formed on a line through which the LNG stored in the reliquefaction tank flows out to the LNG fuel tank, and is connected to the reliquefaction tank and the hydrogen gas mixer to reliquefy the reliquefaction tank. It may further include a third valve unit formed on a line through which the gas inside the tank is discharged to the hydrogen gas mixer.

In an embodiment of the present invention, when the reliquefied LNG is charged in the reliquefaction tank, the second valve unit blocks to prevent NG BOG from flowing in from the LNG fuel tank, and the third valve unit blocks the NG BOG from flowing into the LNG fuel tank. The valve unit may open when the internal pressure of the reliquefaction tank is higher than the first critical pressure to control the internal pressure of the reliquefaction tank.

In an embodiment of the present invention, when the reliquefied LNG is charged into the reliquefaction tank and reaches a preset reference level, the first valve unit and the second valve are used to increase the pressure inside the reliquefaction tank. Both the unit and the third valve unit can be blocked.

In an embodiment of the present invention, the second valve unit opens when the pressure inside the reliquefaction tank becomes higher than the preset second critical pressure after the reliquefaction tank is filled with the reliquefied LNG. Reliquefied LNG can be injected into the LNG fuel tank.

According to an embodiment of the present invention, the NG BOG generated in the LNG fuel tank is re-liquefied by using the hydrogen (H ₂ ) BOG generated in the liquefied hydrogen tank, so there is no need to install a separate device for re-liquefaction, so the space occupied is reduced. Not only can it be reduced, but additional operating costs and energy consumption can be minimized.

The effects of the present invention are not limited to the effects described above, and should be understood to include all effects that can be inferred from the configuration of the invention described in the description or claims of the present invention.

Figure 1 is a diagram schematically showing the configuration of an LNG BOG reliquefaction system using the BOG of a liquefied hydrogen tank according to an embodiment of the present invention.
Figure 2 is a diagram illustrating in a more simplified manner the configuration of an LNG BOG re-liquefaction system using the BOG of a liquefied hydrogen tank according to another embodiment of the present invention.
Figure 3 is a reference diagram illustrating the first operation of the reliquefaction tank according to the LNG BOG reliquefaction system according to an embodiment of the present invention.
Figure 4 is a reference diagram illustrating the second operation of the reliquefaction tank according to the LNG BOG reliquefaction system according to an embodiment of the present invention.
Figure 5 is a reference diagram illustrating the third operation of the reliquefaction tank according to the LNG BOG reliquefaction system according to an embodiment of the present invention.

Hereinafter, the present invention will be described with reference to the attached drawings. However, the present invention may be implemented in various different forms and, therefore, is not limited to the embodiments described herein. In order to clearly explain the present invention in the drawings, parts unrelated to the description are omitted, and similar parts are given similar reference numerals throughout the specification.

Throughout the specification, when a part is said to be "connected (connected, contacted, combined)" with another part, this means not only "directly connected" but also "indirectly connected" with another member in between. "Includes cases where it is. Additionally, when a part is said to “include” a certain component, this does not mean that other components are excluded, but that other components can be added, unless specifically stated to the contrary.

The terms used in this specification are merely used to describe specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, terms such as “comprise” or “have” are intended to designate the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, but are not intended to indicate the presence of one or more other features. It should be understood that this does not exclude in advance the possibility of the existence or addition of elements, numbers, steps, operations, components, parts, or combinations thereof.

Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings.

Figure 1 is a diagram schematically showing the configuration of an LNG BOG reliquefaction system using the BOG of a liquefied hydrogen tank according to an embodiment of the present invention.

Referring to Figure 1, the LNG BOG reliquefaction system according to an embodiment of the present invention includes an LNG fuel tank 100, a sub-cooler 200, a liquefied hydrogen bunkering tank 300, a reliquefaction tank 400, and a mixer ( 500), and as shown in FIG. 1, it further includes an LNG vaporizer, a buffer tank, a heater module, a pump module, a BOG re-condensor, and a BOG processing system. It could be.

Figure 2 is a diagram illustrating in a more simplified manner the configuration of an LNG BOG re-liquefaction system using the BOG of a liquefied hydrogen tank according to another embodiment of the present invention.

The LNG fuel tank 100 of the present invention is a tank in which LNG (Liquefied Natural Gas) is stored. In the process of using the LNG stored in the LNG fuel tank 100 as fuel, external heat is continuously transferred to the LNG fuel tank, and liquefied gas (LNG) is continuously naturally vaporized within the LNG fuel tank. NG BOG, boil-off gas (BOG), is generated.

The LNG fuel tank 100 uses LNG as fuel and transfers the remaining surplus NG BOG to the sub-cooler 200. At this time, the operating pressure of the LNG BOG in the LNG fuel tank of the present invention may be 2.0 barg, and the temperature of the NG BOG may be -164°C to -120°C.

The liquefied hydrogen bunkering tank 300 of the present invention is a tank that stores liquefied hydrogen (LH ₂ ). In the liquefied hydrogen bunkering tank 300, hydrogen BOG is generated as the liquefied hydrogen is vaporized.

The liquefied hydrogen bunkering tank 300 transfers hydrogen (H ₂ ) BOG generated internally to the sub-cooler 200. At this time, the operating pressure of hydrogen BOG in the liquefied hydrogen bunkering tank 300 of the present invention may be 2.0 barg, and the temperature of hydrogen BOG may be -253°C to -200°C.

The sub-cooler 200 can re-liquefy the NG BOG by using the hydrogen BOG generated in the liquefied hydrogen bunkering tank 300 to cool the NG BOG generated in the LNG fuel tank 100.

The main ingredient of LNG is methane, the critical temperature of methane is -82.3℃, and the critical pressure is 46barg. In other words, considering the phase balance of methane, when the operating pressure of NG BOG is 2.0 barg, if the temperature is lower than -152.46℃, NG BOG, which is an boil-off gas, can change phase into a liquid phase.

The sub-cooler 200 according to this embodiment measures the temperature of the NG BOG discharged and introduced from the LNG fuel tank 100, and according to the measured temperature of the NG BOG, the temperature of the NG BOG discharged and introduced from the liquefied hydrogen bunkering tank 300 The flow rate of hydrogen BOG can be adjusted.

More specifically, if the temperature of the NG BOG discharged and introduced from the LNG fuel tank 100 is higher than the critical temperature, the sub cooler 200 cools the hydrogen discharged and introduced from the liquefied hydrogen bunkering tank 300 through valve control. The flow rate of BOG can be increased.

For example, the critical temperature may be -152.46°C, and if the temperature of the incoming NG BOG is higher than -152.46°C, the sub-cooler 200 controls the opening and closing of the valve so that the inflow amount of relatively low-temperature hydrogen BOG increases. As the inflow of hydrogen BOG increases, the temperature of NG BOG decreases again and the NG BOG can be re-liquefied as the phase changes to the liquid phase.

The reliquefaction tank 400 receives the LNG reliquefied by the subcooler 200 and stores it internally. The operating pressure of the reliquefaction tank 400 of the present invention may be 2.0 barg.

Figure 3 is a reference diagram illustrating the first operation of the reliquefaction tank according to the LNG BOG reliquefaction system according to an embodiment of the present invention.

Referring to Figure 3, the LNG BOG reliquefaction system according to an embodiment of the present invention includes a first valve unit 610 and a second valve unit (610) formed in each of a plurality of lines connected to the reliquefaction tank 400. 620), and may further include a third valve unit 630.

The first valve unit 610 is formed on a line connecting the reliquefaction tank 400 and the sub-cooler 200, and the second valve unit 620 is formed on the reliquefaction tank 400 and the LNG fuel tank 100. ), and is formed on the line through which LNG, which is the reliquefied NG BOG stored in the reliquefaction tank 400, flows out to the LNG fuel tank 100. And the third valve unit 630 is a valve connected to the reliquefaction tank 400 and the mixer 500 and formed on a line through which the gas inside the reliquefaction tank 400 is discharged to the mixer 500.

Referring to FIG. 3, in the process of filling the reliquefaction tank 400 with LNG reliquefied by the sub-cooler 200, the second valve unit 620 reliquefies the NG BOG from the LNG fuel tank 100. Close to prevent it from flowing into the tank 400.

Meanwhile, the third valve unit 630 is opened when the internal pressure of the reliquefaction tank 400 is higher than a predetermined first critical pressure, thereby controlling the internal pressure of the reliquefaction tank 400.

Figure 4 is a reference diagram illustrating the second operation of the reliquefaction tank according to the LNG BOG reliquefaction system according to an embodiment of the present invention.

Referring to Figure 4, as the LNG reliquefied by the sub-cooler 200 is transferred to the reliquefaction tank 400 and charged, when the stored amount of the charged LNG reaches a preset reference level, the first valve unit 610 ), the second valve unit 620, and the third valve unit 630 can all be operated to increase the internal pressure of the reliquefaction tank 400 by closing the opening and closing.

Figure 5 is a reference diagram illustrating the third operation of the reliquefaction tank according to the LNG BOG reliquefaction system according to an embodiment of the present invention.

Referring to FIG. 5, after the LNG reliquefied by the sub-cooler 200 is charged into the reliquefaction tank 400, the second valve unit 620 adjusts the internal pressure of the reliquefaction tank 400 to a preset value. 2 When the pressure becomes higher than the critical pressure, it can be opened and driven to inject the reliquefied LNG into the LNG fuel tank 100.

For example, when the pressure of the reliquefaction tank 400 rises to 3.5 to 4.0 barg, which is the second critical pressure, the second valve unit 620 opens to release the reliquefied LNG stored in the reliquefaction tank 400. is injected into the LNG fuel tank 100.

Meanwhile, the reliquefaction tank 400 according to this embodiment can set the design pressure to 6.0 barg or more to prevent accidents.

According to an embodiment of the present invention shown in Figure 5, gas (Vapor) generated in the reliquefaction tank 400 can be transferred to the mixer 500.

The mixer 500 according to an embodiment of the present invention may be a mixer that mixes NG and hydrogen (H ₂ ).

The description of the present invention described above is for illustrative purposes, and those skilled in the art will understand that the present invention can be easily modified into other specific forms without changing the technical idea or essential features of the present invention. will be. Therefore, the embodiments described above should be understood in all respects as illustrative and not restrictive. For example, each component described as single may be implemented in a distributed manner, and similarly, components described as distributed may also be implemented in a combined form.

The scope of the present invention is indicated by the claims described below, and all changes or modified forms derived from the meaning and scope of the claims and their equivalent concepts should be construed as being included in the scope of the present invention.

100: LNG fuel tank
200: Sub cooler
300: Liquefied hydrogen bunkering tank
400: Reliquefaction tank
500: mixer
610: first valve unit
620: second valve unit
630: Third valve unit

Claims (7)

An LNG fuel tank in which LNG (Liquefied Natural Gas) is stored,
A liquefied hydrogen bunkering tank that stores liquefied hydrogen (LH2),
A sub-cooler that re-liquefies NG BOG (Natural Gas Boil Off Gas) generated in the LNG fuel tank by using hydrogen BOG (Boil Off Gas) generated in the liquefied hydrogen bunkering tank;
A reliquefaction tank for receiving and storing LNG reliquefied by the sub-cooler,
A hydrogen gas mixer that receives gas (vapor) generated from the reliquefaction tank,
A first valve unit connected to the reliquefaction tank and the sub-cooler and formed on a line through which the reliquefied LNG flows into the reliquefaction tank;
a second valve unit connected to the reliquefaction tank and the LNG fuel tank and formed on a line through which LNG stored in the reliquefaction tank flows out into the LNG fuel tank;
A third valve unit connected to the reliquefaction tank and the hydrogen gas mixer and formed on a line through which the gas inside the reliquefaction tank is discharged to the hydrogen gas mixer,
The sub-cooler measures the temperature of the NG BOG flowing in and discharged from the LNG fuel tank, and adjusts the flow rate of the hydrogen BOG flowing in from the liquefied hydrogen bunkering tank according to the measured temperature of the NG BOG,
The third valve unit opens when the reliquefaction tank is filled with the reliquefied LNG and the internal pressure of the reliquefaction tank is higher than the first critical pressure to adjust the internal pressure of the reliquefaction tank,
After the reliquefied LNG is charged in the reliquefaction tank, the second valve unit opens when the internal pressure of the reliquefaction tank is higher than a preset second critical pressure to use the reliquefied LNG as the LNG fuel. LNG BOG reliquefaction system using the BOG of a liquefied hydrogen tank, which is characterized by injection into the tank.
delete According to paragraph 1,
The sub cooler is,
When the temperature of the NG BOG discharged and introduced from the LNG fuel tank is higher than -152.46 ℃, the flow rate of the hydrogen BOG discharged and introduced into the liquefied hydrogen bunkering tank is increased, using the BOG of the liquefied hydrogen tank. LNG BOG reliquefaction system.
delete According to paragraph 1,
When the reliquefied LNG is charged into the reliquefaction tank,
The second valve unit is a LNG BOG reliquefaction system using the BOG of a liquefied hydrogen tank, characterized in that it blocks to prevent NG BOG from flowing in from the LNG fuel tank.
According to paragraph 1,
When the reliquefied LNG reaches a preset reference level as it is charged into the reliquefaction tank,
An LNG BOG reliquefaction system using the BOG of a liquefied hydrogen tank, characterized in that the first valve unit, the second valve unit, and the third valve unit are all blocked to increase the pressure inside the reliquefaction tank.
delete

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