WO2021177588A1

WO2021177588A1 - Lng boil-off gas reliquefaction system for small- and medium-sized lng-powered ships and lng boil-off gas reliquefaction method using same

Info

Publication number: WO2021177588A1
Application number: PCT/KR2021/000246
Authority: WO
Inventors: 정제헌; 최금식
Original assignee: 선보공업주식회사; 선보유니텍주식회사
Priority date: 2020-03-02
Filing date: 2021-01-08
Publication date: 2021-09-10
Also published as: CN216113357U; KR20210111391A; JP3231536U; KR102388679B1

Abstract

The present invention relates to an LNG boil-off gas reliquefaction system for small- and medium-sized LNG-powered ships and an LNG boil-off gas reliquefaction method using same, wherein boil-off gas (BOG) generated from LNG fuel, which is emerging as a clean fuel, is reliquefied multiple times through a plurality of heat exchangers, so that the BOG, which would otherwise be discarded from small- and medium-sized ships not equipped with a separate reliquefaction system, is effectively recycled, and the operating costs and bunkering costs of such small- and medium-sized ships are reduced.

Description

LNG boil-off gas reliquefaction system for small and medium-sized LNG fueled propulsion ships and LNG boil-off gas reliquefaction method using the same

The present invention relates to an LNG boil-off gas reliquefaction system for small and medium-sized LNG fuel propulsion ships and a method for reliquefying LNG boil-off gas using the same. By reliquefying through a heat exchanger multiple times, it effectively recycles BOG discarded even in small and medium-sized vessels that are not equipped with a separate reliquefaction system, as well as reducing operating and bunkering costs of small and medium-sized vessels. It relates to a boil-off gas reliquefaction system and a method for reliquefying LNG boil-off gas using the same.

In general, LNG is emerging as a clean fuel that can reduce harmful substances such as SOx, NOx and carbon dioxide and greenhouse gases compared to conventional fossil fuels, and its application is very wide not only on land but also in the ocean, that is, in shipbuilding and ship fields. is the trend

LNG exists as a cryogenic liquid at -162°C under atmospheric pressure, and is supplied to individual consumers after being stored in a cryogenic tank. For reference, the pressure of the main pipeline supply chain for natural gas that is connected to the main demand varies from country to country, but is usually operated in the range of 70-120 bar.

The LNG stored inside the storage tank is suppressed from heat inflow through the use of insulating materials, but due to the temperature difference between the atmospheric temperature and the inside of the tank, heat flow is inevitable. It is known that 0.15% vol% of stored LNG is evaporated on a daily basis. The evaporated BOG is compressed by the BOG compressor, and the LNG stored in the tank is pressurized to the pressure of the main pipeline supply network through a low-pressure pump and a high-pressure pump, and then is vaporized and sent out.

BOG reliquefaction device is a device that cools/liquefies BOG with sub-cooled sensible heat of LNG by directly contacting the first boosted LNG with the low pressure pump and the pressurized BOG. Finally, BOG liquefied LNG is transferred to a high-pressure pump.

Such BOG reliquefaction apparatus is equipped with large LNG carriers, but in the case of small and medium-sized LNG fuel-powered ships, there is a problem in that proper facilities are not made due to the limitation of the scale.

Therefore, there is a need for a re-liquefaction facility for effectively cooling the BOG discarded even in small and medium-sized LNG fuel-propelled ships and reusing it as fuel.

The present invention is to solve the above-mentioned problems, and it is a small and medium-sized LNG fuel that effectively recycles BOG thrown away even in small and medium-sized vessels that are not equipped with a separate reliquefaction system, as well as reduces the operation and bunkering costs of small and medium-sized vessels. An object of the present invention is to provide an LNG BOG reliquefaction system for a propulsion ship and a method for reliquefying LNG BOG using the same.

The LNG boil-off gas reliquefaction system for a small and medium-sized LNG fuel propulsion ship according to an embodiment of the present invention is connected to an LNG fuel tank, and a boil-off gas compressor for compressing boil-off gas (BOG) in the LNG fuel tank, provided inside the LNG fuel tank An in-tank pump that pressurizes the LNG fuel and supplies it to the engine, connected to the in-tank pump, and pressurizing the LNG fuel supplied through the in-tank pump to the required pressure required by the engine A pressure pump for supplying to the engine by forming a pressure pump, which is provided between the in-tank pump and the pressurization pump, by exchanging heat between the LNG fuel supplied through the in-tank pump and the boil-off gas supplied through the boil-off gas compressor. A first heat exchanger for cooling the boil-off gas is provided between the pressurization pump and the boil-off gas compressor, and heat exchanges between the LNG fuel supplied through the pressurization pump and the boil-off gas supplied through the boil-off gas compressor to exchange the evaporated gas with each other. and a second heat exchanger for cooling the gas, wherein the BOG compressed through the BOG compressor is first cooled through the second heat exchanger, then is secondarily cooled through the first heat exchanger, and is then cooled through the pressurization pump It may be characterized in that it is supplied in the direction of the engine.

In one embodiment, the present invention provides a method for further cooling the BOG compressed by the BOG compressor by exchanging heat between the BOG supplied to the BOG compressor and the BOG compressed by the BOG compressor. 3 It may be characterized by further comprising a heat exchanger.

In one embodiment, the present invention may further include a boil-off gas additional compressor for recompressing the boil-off gas compressed through the boil-off gas compressor.

In one embodiment, the present invention may further include a booster pump provided between the in-tank pump and the first heat exchanger and further pressurizing the LNG fuel pressurized through the in-tank pump.

In an embodiment, a vaporizer for vaporizing the LNG fuel that has undergone heat exchange through the second heat exchanger may be provided between the second heat exchanger and the engine.

In one embodiment, the first heat exchanger supplies the cooled boil-off gas to a pipe connecting the in-tank pump and the first heat exchanger to mix with the LNG fuel supplied through the in-tank pump. can

In one embodiment, the first heat exchanger may be characterized in that the cooled boil-off gas is mixed with the LNG fuel supplied through the in-tank pump.

The LNG boil-off gas reliquefaction method using the LNG boil-off gas reliquefaction system for a small and medium-sized LNG fuel propulsion ship according to another embodiment of the present invention uses a boil-off gas compressor connected to the LNG fuel tank to reduce boil-off gas (BOG) in the LNG fuel tank. Compressing, after pressurizing the LNG fuel using an in-tank pump provided inside the LNG fuel tank, a pressure required by the engine is formed using a pressurization pump connected to the in-tank pump. supplying in the engine direction, by using a second heat exchanger provided between the BOG compressor and the pressurization pump to exchange heat between the LNG fuel supplied through the pressurization pump and the BOG supplied through the BOG compressor. First cooling the boil-off gas and using a first heat exchanger provided between the pressurized pump and the in-tank pump, the LNG fuel supplied through the in-tank pump and the second heat exchanger After secondary cooling of the boil-off gas by exchanging the boil-off gas with each other, the cooled boil-off gas may be supplied back to the engine direction through the pressurization pump.

According to one aspect of the present invention, by re-liquefying boil-off gas (BOG) multiple times through a plurality of heat exchangers, it has the advantage of effectively recycling the discarded BOG even in small and medium-sized ships that are not equipped with a separate re-liquefaction system. .

In addition, according to one aspect of the present invention, it is possible to re-liquefy BOG effectively and recycle it as a fuel, regardless of operating conditions, even in small and medium-sized LNG fuel-propelled ships that use naturally occurring BOG, and through this, the operating cost of the vessel and bunkering costs are reduced.

1 is a diagram showing the configuration of an LNG boil-off gas reliquefaction system 100 for a small and medium-sized LNG fuel propulsion ship according to an embodiment of the present invention.

FIG. 2 is a view showing another embodiment of the first heat exchanger 140 shown in FIG. 1 .

FIG. 3 is a view illustrating a method for reliquefying LNG boil-off gas using the LNG boil-off gas reliquefaction system for a small and medium-sized LNG fuel propulsion ship shown in FIG. 1 in a series sequence.

100: LNG boil-off gas reliquefaction system for small and medium-sized LNG fueled ships

110: boil-off gas compressor

120: in-tank pump

130: pressurized pump

140: first heat exchanger

150: second heat exchanger

160: third heat exchanger

170: boil-off gas additional compressor

180: booster pump

190: carburetor

Hereinafter, preferred examples are presented to help the understanding of the present invention. However, the following examples are only provided for easier understanding of the present invention, and the content of the present invention is not limited by the examples.

Referring to FIG. 1 , the LNG BOG reliquefaction system 100 for a small and medium-sized LNG fuel propulsion ship according to an embodiment of the present invention is largely a BOG compressor 110 , an in-tank pump 120 , a pressurization pump 130 , and a second It may be configured to include a first heat exchanger 140 and a second heat exchanger 150 .

In addition, in one embodiment, the third heat exchanger 160 , the boil-off gas additional compressor 170 , the booster pump 180 and the vaporizer 190 may be further included.

First, the boil-off gas compressor 110 is connected to the LNG fuel tank 10 , and serves to increase the temperature by pressurizing and compressing the boil-off gas (BOG) of low pressure generated in the LNG fuel tank 10 .

More specifically, the boil-off gas compressor 110 increases the temperature of the boil-off gas to a temperature of 100 to 150 degrees Celsius by compressing the boil-off gas of low pressure to a pressure corresponding to, for example, 30 barg to 100 barg, preferably 50 barg. . This boil-off gas is then liquefied while being cooled to a temperature of -130 degrees to -155 degrees below zero by heat-exchanging through the first and

second heat exchangers

140 and 150 .

The in-tank pump 120 serves to pressurize the LNG fuel while being provided inside the LNG fuel tank 10 and supply it to the pressurization pump 130 to be described later. At this time, the pressure value for pressurizing the LNG fuel in the in-tank pump 120 corresponds to the pressure value required by the pressurization pump 130 .

The pressurization pump 130 is connected to the in-tank pump 120, and by additionally pressurizing the pressurized LNG fuel supplied through the in-tank pump 120, forms the pressure required by the engine and supplies it to the engine. do.

The first heat exchanger 140 is located between the in-tank pump 120 and the pressurization pump 130 , and uses the cooling heat of the pressurized LNG fuel supplied through the in-tank pump 120 to the boil-off gas compressor 110 . ) serves to cool the boil-off gas by exchanging heat with each other.

In this case, the BOG supplied through the BOG compressor 110 corresponds to BOG that has been primarily cooled through the second heat exchanger 150 to be described later. That is, the first heat exchanger 140 secondaryly cools the BOG that has been primarily cooled through the second heat exchanger 150 to be described later so that the BOG becomes a liquefied LNG fuel.

The boil-off gas (liquefied state) that is secondarily cooled through the first heat exchanger 140 is again supplied to the engine direction through the pressure pump 130 .

At this time, the first heat exchanger 140 supplies the cooled boil-off gas toward the pipe connecting the in-tank pump 120 and the first heat exchanger 140 to each other, so that the pressure pump ( 120 ) through the in-tank pump ( 120 ). 130) and mixed with the LNG fuel supplied in the direction.

Accordingly, the BOG after secondary cooling can be directly used as fuel for the engine.

Meanwhile, the first heat exchanger 140 supplies the secondary cooled boil-off gas to a pipe connecting the in-tank pump 120 and the first heat exchanger 140 to each other, but Without going through the outside, the first heat exchanger 140 itself may be supplied in a direction toward the pressure pump 130 , which will be described with reference to FIG. 2 .

Referring to FIG. 2, the first heat exchanger 140 shown in FIG. 2 is different from the first heat exchanger 140 shown in FIG. It can be seen that the first heat exchanger 140 is supplied through a pipe connecting to each other, but the first heat exchanger 140 is supplied by itself from the inside rather than the outside.

That is, the first heat exchanger 140 shown in FIG. 1 mixes the additionally cooled BOG with the LNG fuel supplied from the in-tank pump 120 through a pipe connected to the outside of the first heat exchanger 140 . On the other hand, the first heat exchanger 140 shown in FIG. 2 mixes the additionally cooled BOG with the LNG fuel supplied from the in-tank pump 120 through a pipe connected to the inside of the first heat exchanger 140 . do.

In this case, as the temperature of the additionally cooled BOG is not increased by the external temperature of the first heat exchanger 140 , the efficiency may be maximized.

Returning to FIG. 1 again, the second heat exchanger 150 is located between the pressure pump 130 and the boil-off gas compressor 110 , and uses the cooling heat of the pressurized LNG fuel supplied through the pressure pump 130 . It serves to primarily cool the BOG by exchanging the BOG supplied through the BOG compressor 110 with each other. That is, after the second heat exchanger 150 preferentially cools the BOG, the first heat exchanger 140 further cools the BOG.

The cooling process of BOG through the first and

second heat exchangers

140 and 150 will be described in more detail with reference to FIG. 3 to be described later.

In the present invention, a third heat exchanger ( 160) is further included.

The third heat exchanger 160 is provided to span a line connecting the LNG fuel tank 110 and the BOG compressor 110 and a line connecting the BOG compressor 110 and the second heat exchanger 150 , respectively. do.

Accordingly, the BOG supplied to the second heat exchanger 150 through the BOG compressor 110 is cooled by the cooling heat of the BOG passing through the third heat exchanger 160 in the LNG fuel tank 10 .

In addition, in one embodiment, the present invention may include a boil-off gas additional compressor 170 for further compressing the boil-off gas compressed through the boil-off gas compressor 110 .

BOG additional compressor 170 is a consumer of compressed BOG and serves to recompress the remaining BOG remaining unused in a DF engine (DFGE) using natural gas as fuel and supply it back to the BOG compressor 110 . do In this case, the reliquefaction efficiency and the reliquefaction amount may be increased by further increasing the pressure of the reliquefied BOG.

For example, when the pressure of the BOG is in the vicinity of 150 bar to 170 bar, the reliquefaction amount shows the maximum value, and the BOG additional compressor 170 adjusts the pressure value of the BOG compressed through the BOG compressor 110 to 150 bar. It serves to further compress to 170 bar.

In addition, in one embodiment, in the present invention, a booster pump 180 for further pressurizing the LNG fuel pressurized through the in-tank pump 120 between the in-tank pump 120 and the first heat exchanger 140 may be included. can The booster pump 180 further pressurizes the LNG fuel pressurized through the in-tank pump 120 to supply the LNG fuel with a high pressure (eg, 300 barg) to the first heat exchanger 140 .

In addition, in one embodiment, the present invention includes a vaporizer 190 for vaporizing the LNG fuel that has undergone heat exchange between the second heat exchanger 150 and the engine of the ship through the second heat exchanger 150 . At this time, the vaporizer 190 serves to create the temperature required by the engine by vaporizing the LNG fuel pressurized by the pressure pump 130 and heat exchanged. In such a vaporizer, hot water or steam may be applied as a thermal medium.

Next, a process of re-liquefying LNG boil-off gas through FIG. 3 will be described in order.

First, the BOG discharged from the LNG fuel tank 10 is compressed using the BOG compressor 110 connected to the LNG fuel tank 10 (S301).

Next, after pressurizing the LNG fuel through the in-tank pump 120 provided inside the LNG fuel tank 10 , the pressure required by the engine is applied using the pressurization pump 130 connected to the in-tank pump 120 . formed and supplied to the engine (S302).

Next, through the second heat exchanger 150 provided in the BOG compressor 110 and the pressure pump 130 , the LNG fuel supplied through the pressure pump 130 and the BOG compressor 110 are supplied. By exchanging the BOG with each other, the BOG is primarily cooled (S303).

Next, through the first heat exchanger 140 provided between the pressure pump 130 and the in-tank pump 120 , the LNG fuel supplied through the in-tank pump 120 and the second heat exchanger 150 are mixed. After the BOG is secondarily cooled by exchanging heat with each other through the BOG that has been primarily cooled through the BOG, the cooled BOG is supplied back to the pressure pump 130 to be reused as engine fuel (3204).

As described above, according to the present invention, by using the first heat exchanger 140 and the second heat exchanger 150 to reliquefy the boil-off gas in the LNG fuel tank 10 to the primary and the secondary, a separate reliquefaction system This has the advantage of allowing the BOG to be effectively recycled even in small and medium-sized vessels that are not equipped.

Although the above has been described with reference to the preferred embodiments of the present invention, those skilled in the art can variously modify and change the present invention without departing from the spirit and scope of the present invention as set forth in the claims below. You will understand that you can.

According to the present invention, BOG thrown away can be effectively recycled even in small and medium-sized vessels that are not equipped with a separate reliquefaction system. The present invention is a technology that can be widely used in the LNG industry to realize its practical and economical value.

Claims

a boil-off gas compressor connected to the LNG fuel tank and compressing boil-off gas (BOG) in the LNG fuel tank;

an in-tank pump provided inside the LNG fuel tank and supplying the LNG fuel to the engine by pressurizing it;

a pressurization pump connected to the in-tank pump, pressurizing the LNG fuel supplied through the in-tank pump to form a required pressure required by the engine, and supplying it to the engine;

a first heat exchanger provided between the in-tank pump and the pressurization pump to cool the boil-off gas by exchanging heat between the LNG fuel supplied through the in-tank pump and the boil-off gas supplied through the boil-off gas compressor; and

a second heat exchanger provided between the pressurization pump and the boil-off gas compressor, the second heat exchanger cooling the boil-off gas by exchanging heat between the LNG fuel supplied through the pressurization pump and the boil-off gas supplied through the boil-off gas compressor and

After the BOG compressed through the BOG compressor is first cooled through the second heat exchanger, the BOG is secondarily cooled through the first heat exchanger, characterized in that it is supplied to the engine through the pressurization pump, LNG boil-off gas reliquefaction system for small and medium-sized LNG fueled ships.
According to claim 1,

By heat-exchanging the BOG supplied to the BOG compressor and BOG compressed by the BOG compressor with each other,

A third heat exchanger for further cooling the boil-off gas compressed by the boil-off gas compressor;
According to claim 1,

The LNG boil-off gas reliquefaction system for a small and medium-sized LNG fuel propulsion ship, characterized in that it further comprises; a boil-off gas additional compressor for recompressing the boil-off gas compressed through the boil-off gas compressor.
According to claim 1,

A booster pump provided between the in-tank pump and the first heat exchanger to additionally pressurize the LNG fuel pressurized through the in-tank pump; liquefaction system.
According to claim 1,

Between the second heat exchanger and the engine,

An LNG boil-off gas reliquefaction system for a small and medium-sized LNG fuel propulsion ship, characterized in that it is provided;
According to claim 1,

The first heat exchanger,

LNG boil-off gas material for small and medium-sized LNG fuel propulsion ships, characterized in that the cooled BOG is supplied to a pipe connecting the in-tank pump and the first heat exchanger to be mixed with the LNG fuel supplied through the in-tank pump. liquefaction system.
According to claim 1,

The first heat exchanger,

An LNG boil-off gas reliquefaction system for small and medium-sized LNG fuel propulsion ships, characterized in that the cooled boil-off gas is mixed with the LNG fuel supplied through the in-tank pump.
compressing the boil-off gas (BOG) in the LNG fuel tank using a boil-off gas compressor connected to the LNG fuel tank;

After pressurizing the LNG fuel using an in-tank pump provided inside the LNG fuel tank, a pressure required by the engine is formed using a pressurization pump connected to the in-tank pump and supplied in the engine direction. to do;

Using a second heat exchanger provided between the BOG compressor and the pressurization pump, the BOG is primarily cooled by exchanging heat between the LNG fuel supplied through the pressurization pump and the BOG supplied through the BOG compressor. making; and

By using a first heat exchanger provided between the pressurization pump and the in-tank pump, the LNG fuel supplied through the in-tank pump and the boil-off gas primarily cooled through the second heat exchanger are exchanged with each other to heat the boil-off gas. After secondary cooling, supplying the cooled BOG back to the engine direction through the pressure pump; liquefaction method.