KR102144182B1 - Boil-off gas cooling system and ship having the same - Google Patents

Abstract

The present invention relates to a boil-off gas cooling system and a ship, comprising: a compressor for compressing boil-off gas generated in a liquefied gas storage tank; And a heat exchanger for cooling the boil-off gas upstream of the compressor, wherein the heat exchanger cools the boil-off gas using the liquefied gas discharged from the liquefied gas storage tank and delivered to a customer.

Description

Boil-off gas cooling system and ship having the same}

The present invention relates to a boil-off gas cooling system and a ship.

Liquefied gas carriers that transport liquefied gases such as Liquefied Natural Gas and Liquefied Petroleum Gas among ships sailing the sea with various types of cargo loaded are gases with a boiling point lower than room temperature. It is provided with a storage tank that is forcibly liquefied and stored in a liquid state.

Liquefied natural gas is obtained by cooling and liquefying methane (CH4) obtained by refining natural gas collected from a gas field. It is a colorless and transparent liquid that contains almost no pollutants and has a high calorific value, making it an excellent fuel. Liquefied petroleum gas, on the other hand, is a liquid made of gas containing propane (C3H8) and butane (C4H10), which are produced with oil from oil fields as main components, and is widely used as fuel for home, business, industrial, and automobiles. Liquefied natural gas is reduced to 1/600 of volume by liquefaction, and liquefied petroleum gas is reduced to 1/260 of propane and 1/230 of butane by liquefaction, so storage efficiency is high.

However, although the storage tank for storing the liquefied gas has an insulation function, the vaporization of the liquefied gas cannot be completely blocked. Therefore, in the storage tank, a gaseous evaporated gas from which the liquefied gas is evaporated is generated, and the boil-off gas increases the internal pressure of the storage tank, so it must be discharged from the storage tank for safety.

In order to lower the internal pressure of the storage tank, the boil-off gas discharged from the storage tank is burned through a gas combustion unit and discarded. However, since the boil-off gas also corresponds to some of the cargo carried by the ship, the emission of the boil-off gas deteriorates the reliability of cargo transportation, which is a problem.

Therefore, in recent years, continuous research and development have been conducted on a method for effectively treating the boil-off gas generated in the storage tank without discarding it.

The present invention was created to solve the problems of the prior art as described above, and an object of the present invention is to improve compressor efficiency by pre-cooling the boil-off gas before compression, and to smoothly remove droplets generated during pre-cooling without compressed gas such as nitrogen. It is to provide a boil-off gas cooling system that can be returned to the tank and a ship including the same.

In addition, it is an object of the present invention to provide a boil-off gas cooling system capable of simplifying the system configuration by pre-cooling the boil-off gas with liquefied boil-off gas instead of liquefied boil-off gas, thereby minimizing the generation of droplets during pre-cooling, and a ship including the same. For.

In addition, an object of the present invention is to cool the boil-off gas using liquefied gas supplied to the engine, etc., and then compress it, so that the compressor can produce a higher pressure, thereby reducing the power consumption required for liquefaction. And it is to provide a ship including the same.

In addition, an object of the present invention is to implement a backup structure using three compressors having the same/similar head, while at least one compressor can lower the design pressure, thereby reducing the cost of installing the compressor and increasing the operating efficiency. And it is to provide a ship including the same.

Boil-off gas cooling system according to an aspect of the present invention, a compressor for compressing the boil-off gas generated in the liquefied gas storage tank; And a heat exchanger for cooling the boil-off gas upstream of the compressor, wherein the heat exchanger cools the boil-off gas using the liquefied gas discharged from the liquefied gas storage tank and delivered to a customer.

Specifically, a liquefier for liquefying the compressed boil-off gas; And a gas-liquid separator for gas-liquid separating the liquefied boil-off gas, wherein the heat exchanger may cool the boil-off gas using the liquefied gas delivered to the customer and the liquid boil-off gas separated by the gas-liquid separator.

Specifically, in the gas-liquid separator, the liquefied gas stored in the liquefied gas storage tank may be introduced.

Specifically, the gas-liquid separator may deliver vaporized gas in the gas phase to the compressor.

Specifically, it may further include a pre-cooler provided between the heat exchanger and the compressor to cool the boil-off gas by mixing the liquefied gas delivered to the customer.

Specifically, the liquefied gas storage tank further comprises a pump for pressurizing the liquefied gas via the gas-liquid separator, wherein the heat exchanger cools the boil-off gas using the liquefied gas downstream of the pump, and the precooler, The boil-off gas can be cooled by mixing the liquefied gas upstream of the pump.

A ship according to an aspect of the present invention is characterized in that it has the boil-off gas cooling system.

The boil-off gas cooling system according to the present invention and a ship including the same, while pre-cooling the boil-off gas before compression to further increase the pressure, and avoiding the need for a separate nitrogen supply in the process of returning the liquid generated during pre-cooling to the tank. Can be simplified.

In addition, the boil-off gas cooling system according to the present invention and a ship including the same, instead of the liquefied gas containing a large amount of heavy carbon, by using a liquefied boil-off gas mainly containing a component having a very low boiling point such as methane or nitrogen. By implementing pre-cooling, there is almost no occurrence of droplets during pre-cooling, so that the related configuration can be omitted.

In addition, the boil-off gas cooling system according to the present invention and a ship including the same cools the boil-off gas flowing into the compressor by using the liquefied gas supplied to the engine and the liquefied boil-off gas, so that even if a compressor of the same specifications is used, It is possible to improve the power consumption and re-liquefaction rate by increasing the pressure in.

In addition, the boil-off gas cooling system according to the present invention and the ship including the same can cover all of the boil-off gas generation amount, and can be backed up to each other by using three compressors having the same head, thereby reducing the installation cost of the compressor. .

1 is a conceptual diagram of a boil-off gas cooling system according to a first embodiment of the present invention.
2 is a conceptual diagram of a boil-off gas cooling system according to a second embodiment of the present invention.
3 is a conceptual diagram of a boil-off gas cooling system according to a third embodiment of the present invention.
4 is a conceptual diagram of a boil-off gas cooling system according to a fourth embodiment of the present invention.
5 is a conceptual diagram of a boil-off gas cooling system according to a fifth embodiment of the present invention.
6 is a conceptual diagram of a boil-off gas cooling system according to a sixth embodiment of the present invention.
7 is a conceptual diagram of a boil-off gas cooling system according to a seventh embodiment of the present invention.

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

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Hereinafter, in the present specification, gas may be used in the sense of encompassing all substances vaporized in a gaseous state at room temperature, such as LNG or LPG, ethylene, ethane, ammonia, etc., but hereinafter, liquefied gas in the present specification includes methane, propane, butane, etc. The explanation assumes that it is included LNG.

In addition, the liquefied gas refers to a gas that has been liquefied for storage, and the evaporated gas refers to a gas that has been naturally vaporized, and the states of the liquefied gas or the evaporated gas are not limited to liquid and gas, respectively. For reference, liquefied gas contains heavy carbon such as propane and butane, whereas natural evaporated evaporated gas does not (almost) contain heavy carbon and mainly contains methane.

In addition, hereinafter, liquefaction does not mean only when completely re-liquefied, and may be used to encompass cooling intended for at least part of liquefaction, and it is noted that high pressure and low pressure are not absolute values but relative meanings.

The present invention includes a ship having a boil-off gas cooling system described below, and the term "ship" includes all of the general commercial ships having no ship type limitation, such as a container ship or a bulk ship, in addition to a gas ship carrying liquefied gas. Furthermore, in the present specification, the ship may be used in the sense of encompassing a marine plant fixed or floating on the sea in addition to a general merchant ship.

1 is a conceptual diagram of a boil-off gas cooling system according to a first embodiment of the present invention.

Referring to Figure 1, the boil-off gas cooling system 1 according to the first embodiment of the present invention, a liquefied gas storage tank 10, a compressor 20, a pre-cooler 30, a separator 40, a liquefier (50), and a gas-liquid separator (60).

The liquefied gas storage tank 10 stores liquefied gas. The type of the liquefied gas storage tank 10 is not limited to a stand-alone type, a membrane type, a pressure vessel type, etc., and an installation location in the ship is not particularly limited.

For example, when the ship is a gas ship, the liquefied gas storage tank 10 may be a cargo tank provided in a plurality in the longitudinal direction on the ship, and in the case of another ship type such as a container ship other than a ship transporting liquefied gas, the deck It may be a pressure vessel placed on the fore or stern from above.

The liquefied gas storage tank 10 may implement heat insulation to store the liquefied gas in a liquid state, and/or may increase the storage pressure to prevent vaporization of the liquefied gas.

The boil-off gas generated in the liquefied gas storage tank 10 causes an increase in the internal pressure of the liquefied gas storage tank 10, so it can be discharged to the outside, and the boil-off gas discharged to the outside is a pre-cooler 30, which will be described later, liquefied. It may be cooled/liquefied by the device 50 and the like and returned to the liquefied gas storage tank 10, or may be consumed by the consumer 100.

For reference, in the present specification, the consumer 100 that consumes boil-off gas or liquefied gas may be a propulsion engine for propulsion of a ship or a power generation engine that generates power required within the ship, and/or a turbine, a boiler in addition to the engine , Gas combustion system (GCU), fuel cell, etc., the type is not limited.

The compressor 20 compresses the boil-off gas generated in the liquefied gas storage tank 10. The boil-off gas discharged from the liquefied gas storage tank 10 may be around 1 bar corresponding to the internal pressure of the liquefied gas storage tank 10, and the present specification describes the boil-off gas by using the compressor 20 to increase the boiling point of the boil-off gas. Can be compressed.

The compressor 20 is not limited to a centrifugal type, a reciprocating type, or the like, and may be provided in a single stage as shown in the drawing, or in a form in which two or more stages are arranged in series. Of course, a plurality of compressors 20 may be provided in parallel, and in this case, it may be possible to back up each other.

The boil-off gas liquefaction line L1 may be provided as a liquefier 50 to be described later through the compressor 20 in the liquefied gas storage tank 10, and the boil-off gas liquefaction line L1 is located downstream of the liquefier 50. It can be connected to the gas-liquid separator (60). In the boil-off gas liquefaction line (L1), the boil-off gas supply line (L6) may be branched to the customer 100, and the branch point of the boil-off gas supply line (L6) may be between the compressor (20) and the liquefier (50). However, it is not limited to this.

The precooler 30 cools the boil-off gas upstream of the compressor 20. The pre-cooler 30 can cool the boil-off gas using various substances such as boil-off gas, liquefied gas, air, sea water, and separate refrigerant, and cools the boil-off gas by heat exchange with the boil-off gas or mixing substances with the boil-off gas Can be implemented.

However, in the following description, the precooler 30 cools the boil-off gas by mixing a material with the boil-off gas, and the material is limited to the liquefied boil-off gas. Of course, the type of the precooler 30 or the material used in the precooler 30 may be various as described above.

The pre-cooler 30 does not mix the liquefied gas with the boil-off gas, but mixes the boil-off gas liquefied in the liquefier 50 with the boil-off gas discharged from the liquefied gas storage tank 10 to implement pre-cooling.

At this time, since the precooler 30 uses liquid boil-off gas with no or less heavy carbon ratio in place of the liquefied gas, there is (almost) no heavy carbon in the precooler 30. Therefore, despite precooling, most of the material to be introduced into the compressor 20 may be in a gaseous state, which will be described later with reference to FIG. 4.

The precooler 30 has a space for storing the boil-off gas supplied from the liquefied gas storage tank 10, and can mix the liquefied boil-off gas in the form of spraying the inside of the space, and is referred to as a mixer. Can be.

It is known in the art of the compressor 20 that when the temperature of the fluid flowing from the centrifugal compressor 20 of the same type is low, a higher pressure can be produced. In the present invention, in consideration of these characteristics of the compressor 20, by cooling the boil-off gas using the pre-cooler 30 and introducing it into the compressor 20, the discharge pressure of the compressor 20 can be further increased under the same specification conditions. .

When the discharge pressure of the compressor 20 increases, the boiling point of the boil-off gas increases, so that the liquefaction efficiency in the liquefier 50 can be increased. Therefore, the present invention can achieve the effect of increasing the liquefaction rate and reducing power consumption through precooling upstream of the compressor 20. However, at this time, the compressor 20 may be a cryogenic compressor 20.

The separator 40 separates the liquid between the precooler 30 and the compressor 20. Although it may vary depending on the type of the compressor 20, it is not desirable for droplets to flow into the compressor 20 in the operation of the compressor 20.

Accordingly, the separator 40 may separate the liquid contained in the boil-off gas at the front end of the compressor 20 and allow only the gas to flow into the compressor 20. In this case, the liquid separated by the separator 40 may be methane or heavy carbon such as propane and butane.

However, as described above, since the material mixed in the precooler 30 in the present invention may be a liquefied evaporation gas, the liquid separated from the separator 40 may be a small amount of methane, and the heavy carbon flows into the separator 40. May not be.

Since the liquid separated by the separator 40 is a material having energy, it needs to be collected for recycling. Accordingly, the liquid in the separator 40 may be returned to the liquefied gas storage tank 10 through the chamber 411 and the pressure vessel 412.

At this time, nitrogen can be injected for smooth return flow of liquid, but in this case, a pipe for injecting nitrogen is required, and if a pipe is added, heat penetration due to the pipe interferes with the system operation.

Accordingly, the present invention includes a liquid return part 41 so that the liquid separated from the separator 40 can be smoothly returned to the liquefied gas storage tank 10 without injection of a pressurized fluid such as nitrogen.

The liquid return part 41 returns the liquid separated by the separator 40 to the liquefied gas storage tank 10, and includes a chamber 411, a pressure vessel 412, and a valve part 413, and the separator ( A liquid discharge line L2 drained to the pressure vessel 412 via the chamber 411 at 40 is provided.

The chamber 411 receives the liquid from the separator 40. The chamber 411 may be installed at a lower position than the separator 40 so as to smoothly receive liquid from the separator 40. At this time, the liquid may be delivered by gravity.

The chamber 411 may be provided with a first pressure control line L30 connected to the separator 40, and the first pressure control line L30 may be provided separately from the liquid discharge line L2. Although described later, the first pressure control line L30 is for preventing a reverse flow of liquid from the chamber 411 to the separator 40.

The pressure vessel 412 is provided downstream of the chamber 411. The pressure vessel 412 may be installed at a lower position than the separator 40, particularly lower than the chamber 411, so that the liquid may be delivered from the chamber 411 by gravity.

The pressure vessel 412 is a configuration for increasing the pressure in the chamber 411. To this end, a second pressure control line L31 may be provided between the pressure vessel 412 and the chamber 411, and the second pressure control line L31 is a liquid discharge line similar to the first pressure control line L30. It is provided separately from (L2).

In addition to liquid, boil-off gas may be introduced into the pressure vessel 412, for example, boil-off gas compressed by the compressor 20 flows into the pressure vessel 412. Therefore, the pressure vessel 412 may have an internal pressure for boosting the pressure of the chamber 411.

Of course, since the pressure vessel 412 can maintain a state in which the pressure is increased as the liquid accumulates, the configuration in which the boil-off gas flows into the pressure vessel 412 in the present invention may be omitted.

A liquid return line (L4) may be connected to the pressure vessel 412 to the liquefied gas storage tank 10, and thus, the liquid separated from the separator 40 is stored in the liquefied gas through the chamber 411 and the pressure vessel 412 It is returned to the tank 10.

The valve unit 413 may adjust the pressure between the separator 40, the chamber 411, and the pressure vessel 412 so that the liquid can be smoothly returned without a separate pressurized fluid. To this end, the valve unit 413 includes a first discharge valve 413a and a second discharge valve 413b and a first pressure control line L30 provided respectively upstream and downstream of the chamber 411 in the liquid discharge line L2. ) And a first pressure control valve 413c and a second pressure control valve 413d respectively provided in the second pressure control line L31.

Of course, the valve unit 413 may include a combination of valves different from the above, as long as the liquid flow up and down the chamber 411 and the flows of the first and second pressure control lines L30 and L31 can be controlled.

When the liquid is separated from the separator 40, the valve part 413 allows the liquid to flow from the separator 40 to the chamber 411 in a state in which the flow from the chamber 411 to the pressure vessel 412 is blocked. To this end, the valve part 413 closes the second discharge valve 413b and the second pressure control valve 413d and opens the first discharge valve 413a and the first pressure control valve 413c.

However, when the first discharge valve 413a is opened, there is a possibility that the liquid present in the chamber 411 flows back to the separator 40, so that the first discharge valve 413a is after the opening of the first pressure control valve 413c. Can be done in

When the state of the valve unit 413 as described above is maintained, the liquid is transferred from the separator 40 to the chamber 411 by gravity. When the level of the liquid flowing into the chamber 411 exceeds a preset value, the valve unit 413 may open the flow from the chamber 411 to the pressure vessel 412.

Specifically, the valve unit 413 closes the first discharge valve 413a and the first pressure control valve 413c, and opens the second discharge valve 413b and the second pressure control valve 413d.

Due to the opening of the second pressure control valve 413d, the boil-off gas filled in the pressure vessel 412 is delivered to the chamber 411, thereby increasing the internal pressure of the chamber 411. Thereafter, when the atmospheric pressure of the chamber 411 is equal to the atmospheric pressure of the pressure vessel 412, the liquid may be transferred from the chamber 411 to the pressure vessel 412 through the second discharge valve 413b by gravity.

The pressure vessel 412 may basically have a higher internal pressure than the liquefied gas storage tank 10, and the liquid introduced into the pressure vessel 412 may be smoothly returned to the liquefied gas storage tank 10 without any problems. .

In this way, the valve part 413 controls the flow of the liquid discharge line L2 and the pressure control lines L30 and L31, so that the liquid separated from the separator 40 passes through the chamber 411 and the pressure vessel 412. While passing through, it is smoothly returned to the liquefied gas storage tank 10 without a separate pressurized fluid.

In other words, the valve unit 413 opens the liquid discharge line L2 upstream of the chamber 411 and the first pressure control line L30 between the separator 40 and the chamber 411, and the chamber 411 The downstream liquid discharge line L2 and the second pressure control line L31 between the chamber 411 and the pressure vessel 412 are closed to allow liquid to flow from the separator 40 to the chamber 411.

Thereafter, the valve unit 413, when the liquid level in the chamber 411 exceeds a preset value (or when the liquid delivery time to the chamber 411 passes a predetermined time), the liquid discharge line upstream of the chamber 411 ( L2) and the first pressure control line (L30) between the separator 40 and the chamber 411 is closed, and between the liquid discharge line (L2) downstream of the chamber 411 and the chamber 411 and the pressure vessel 412 By opening the second pressure control line (L31) of the liquid can be drained from the chamber 411 to the pressure vessel 412.

In particular, even when the air pressure of the pressure vessel 412 is higher than the pressure of the chamber 411, when the valve part 413 opens the liquid discharge line L2 and the second pressure control line L31 downstream of the chamber 411 , Boil-off gas may be introduced from the pressure vessel 412 to the chamber 411 according to the opened second pressure control line L31, through which the internal pressure of the chamber 411 increases, and the liquid from the chamber 411 It is drained into the pressure vessel 412.

Thereafter, when a predetermined amount of drain from the chamber 411 is achieved (for example, when the liquid level in the chamber 411 becomes less than the preset value or the drain has elapsed for a predetermined time), the second discharge valve 413b and the second pressure As the control valve 413d is closed, the liquid discharge line L2 downstream of the chamber 411 and the second pressure control line L31 between the chamber 411 and the pressure vessel 412 are closed.

In addition, while the first discharge valve 413a and the first pressure control valve 413c are open, the liquid discharge line L2 upstream of the chamber 411 and the first pressure control line L30 between the separator 40 and the chamber 411 are opened. ) Is open, and the pressure of the chamber 411 and the separator 40 can be equally adjusted.

Accordingly, the liquid flows from the separator 40 to the chamber 411 again. As described above, in this embodiment, the liquid separated from the separator 40 is returned to the liquefied gas storage tank 10 through the chamber 411 and the pressure vessel 412 without additional nitrogen supply, thereby adding unnecessary components. It can prevent and increase system operation efficiency.

The liquefier 50 liquefies the compressed boil-off gas. The liquefier 50 may cool the boil-off gas using various unrestricted refrigerants, and for example, the refrigerant may be nitrogen, liquefied gas, mixed refrigerant, or the like.

The boil-off gas liquefied by the liquefier 50 may be returned to the liquefied gas storage tank 10 in a liquid state. Therefore, even if boil-off gas is generated in the liquefied gas storage tank 10, the internal pressure of the liquefied gas storage tank 10 can be maintained at a stable level as the boil-off gas is discharged and returned after being liquefied.

However, the boil-off gas flowing into the liquefier 50 may be in a compressed state to increase the boiling point, and a valve for reducing the boil-off gas between the liquefier 50 and the liquefied gas storage tank 10 (not shown) ) Can be provided.

Of course, when considering the internal volume of the liquefied gas storage tank 10, even if the boil-off gas is returned without a separate decompression, the pressure reducing valve may not be provided because the pressure can be naturally reduced in the liquefied gas storage tank 10.

The gas-liquid separator 60 gas-liquid separates the liquefied boil-off gas. Even if the liquefier 50 liquefies the boil-off gas using nitrogen or the like, nitrogen or the like contained in the boil-off gas with a very low boiling point may remain in a gaseous state.

Accordingly, the gas-liquid separator 60 can filter out the material remaining in the gaseous state among the boil-off gas introduced through the liquefier 50, and the gaseous material is referred to as flash gas.

The flash gas contains nitrogen but still contains a component that has a calorific value, and is preferably recycled because it is in a low temperature state. Accordingly, the flash gas may be discharged from the gas-liquid separator 60 and introduced upstream of the compressor 20 or may be introduced into the precooler 30.

In the gas-liquid separator 60, a liquid return line L4 is provided as the liquefied gas storage tank 10. A liquid boil-off gas may flow into the liquefied gas storage tank 10 along the liquid return line L4.

The liquid delivery line L5 may be branched to the liquid return line L4, and the liquid delivery line L5 is connected to the precooler 30. Accordingly, the boil-off gas liquefied by the liquefier 50 and separated by gas-liquid may be used for cooling the boil-off gas in the pre-cooler 30.

As described above, in this embodiment, since the liquid separated from the separator 40 after precooling is smoothly returned to the liquefied gas storage tank 10 through the chamber 411 and the pressure vessel 412 without injection of nitrogen, the configuration is simplified. And prevent unnecessary heat penetration.

2 is a conceptual diagram of a boil-off gas cooling system according to a second embodiment of the present invention.

Hereinafter, the present embodiment will be mainly described in terms of differences from the previous embodiment, and parts omitted from description will be replaced with the previous content. Note that this is the same in other embodiments described below.

Referring to FIG. 2, in the boil-off gas cooling system 1 according to the second embodiment of the present invention, unlike the previous embodiment, the gas-liquid separator 60 is omitted and the pressure container 412 serves as the gas-liquid separator 60. Perform.

That is, in this embodiment, the pressure vessel 412 may receive the boil-off gas compressed by the compressor 20 and liquefied by the liquefier 50. However, since the pressure vessel 412 must perform a role of increasing the pressure of the chamber 411, the pressure vessel 412 may allow the internal pressure to slightly increase as the liquefied boil-off gas introduced therein is naturally evaporated. .

Accordingly, the pressure vessel 412 can use at least a portion of the liquefied boil-off gas to return the liquid separated from the separator 40, and the rest is returned to the liquefied gas storage tank 10 through the liquid return line (L4). can do.

A liquefied gas supply line L8 may be connected from the liquefied gas storage tank 10 to the pressure vessel 412, and a liquefied gas supply line L8 connected to the customer 100 may be branched to the liquid return line L4. I can.

At this time, the customer 100 may be the same as or different from the customer 100 to which the boil-off gas supply line L6 is connected. For example, the customer 100 to which the liquefied gas supply line L8 is connected is the main engine. In addition, the demand destination 100 to which the boil-off gas supply line L6 is connected may be a power generation engine or a GCU.

In this embodiment, in order to ensure the operation of the main engine, the customer 100, liquefied gas may be supplemented to the pressure container 412 in case the flow rate of the boil-off gas flowing into the pressure container 412 is insufficient. That is, the liquefied boil-off gas and the liquefied gas may be mixed in the pressure vessel 412 and delivered to the customer 100.

When all the boil-off gas generated in the liquefied gas storage tank 10 is mixed with the liquefied gas and supplied to the customer 100, the consumption of the liquefied gas decreases as the amount of boil-off gas is increased, so that energy consumption efficiency can be improved. have.

However, when the boil-off gas is used only as a fuel with the liquefied gas, there is a problem in that the energy consumption efficiency is deteriorated when the amount of boil-off gas is insufficient.

On the other hand, if all the boil-off gas generated in the liquefied gas storage tank 10 is re-liquefied and only the liquefied gas is supplied to the customer 100, the energy consumption efficiency has a relatively constant value regardless of the amount of boil-off gas generated.

However, in this case, there is a problem that some energy may be wasted because a refrigerant must be used to re-liquefy the evaporated gas at all times, and if the amount of evaporated gas is large, a large amount of refrigerant must be cooled. Efficiency becomes worse.

In this embodiment, in consideration of energy consumption efficiency in the case of using all of the boil-off gas as fuel and the case of re-liquefying all of the boil-off gas, it is possible to supply the re-liquefied boil-off gas as fuel while re-liquefying the boil-off gas. , Make it possible to mix liquefied gas with the boil-off gas supplied as fuel.

Through this, in the present embodiment, when the amount of boil-off gas is less (than the demanded amount), the boil-off gas is re-liquefied and the liquefied gas is mainly supplied as fuel (a mixture of liquefied gas and boil-off gas is supplied) to increase energy consumption efficiency, On the contrary, if the amount of boil-off gas is greater (than the demanded amount), it is possible to increase energy consumption efficiency by supplying the boil-off gas mainly as fuel (the supply of liquefied gas can be stopped).

At this time, the amount of boil-off gas generated may be measured by a pressure gauge provided in the liquefied gas storage tank 10 or a flow meter provided in the boil-off gas liquefaction line L1, and the required amount of the customer 100 is the ship speed set in the ship's operation control system, It is obvious that it can be confirmed through engine load, etc.

It is noted that the content of supplying liquefied gas to the customer 100 as described above can be equally applied to other embodiments in which the liquefied boil-off gas is introduced into the pressure vessel 412. However, in the case of the first embodiment, the liquefied gas supply line L8 may be connected from the liquefied gas storage tank 10 to the gas-liquid separator 60 or from the gas-liquid separator 60 to a customer.

3 is a conceptual diagram of a boil-off gas cooling system according to a third embodiment of the present invention.

Referring to FIG. 3, in the case of the boil-off gas cooling system 1 according to the third exemplary embodiment of the present invention, the position of the liquid discharge line L2 connected to the downstream of the chamber 411 may be different.

In the case of the embodiment described in FIG. 2 above, the liquid discharge line L2 is connected from the separator 40 to the pressure vessel 412 via the chamber 411, and the valve part 413 is the liquid level in the chamber 411. When this preset value is exceeded, the pressure in the chamber 411 and the pressure vessel 412 can be equally adjusted.

On the other hand, in the case of the present embodiment, the liquid discharge line L2 is connected to the liquid return line L4 from the separator 40 via the chamber 411 and bypassing the pressure vessel 412. Therefore, the valve unit 413 of this embodiment, instead of equally controlling the pressures of the chamber 411 and the pressure vessel 412, so that the liquid can be smoothly discharged from the chamber 411 to the liquid return line L4, It is possible to implement the delivery of the boil-off gas from the pressure vessel 412 to the chamber 411.

In this embodiment, the pressure vessel 412 may be replaced with a gas-liquid separator 60 in that it receives the liquefied boil-off gas and delivers it to the liquefied gas storage tank 10. That is, this embodiment can be interpreted as an invention in which the pressure vessel 412 is omitted and the gas-liquid separator 60 is used as the pressure vessel 412.

4 is a conceptual diagram of a boil-off gas cooling system according to a fourth embodiment of the present invention.

Referring to FIG. 4, in the boil-off gas cooling system 1 according to the fourth exemplary embodiment of the present invention, the liquid return part 41 may be omitted. As mentioned above, the pre-cooler 30 may cool the boil-off gas using the liquid boil-off gas separated by the gas-liquid separator 60.

In this case, the pre-cooler 30 cools the boil-off gas using a liquid boil-off gas having no or a small proportion of heavy carbon in place of the liquefied gas, so that the boil-off gas flowing into the separator 40 after pre-cooling is in a liquid state. May be (almost) free of heavy carbon.

Accordingly, in the present embodiment, the separator 40 may be provided to separate the liquid but store the liquid without discharging, and the chamber 411 or the pressure vessel 412 receiving the liquid from the separator 40 may be omitted.

In addition, in this embodiment, the separator 40 may also be omitted. This is because the boil-off gas discharged from the liquefied gas storage tank 10 does not already contain (almost) heavy carbon, a pre-cooler 30 that mixes the liquefied boil-off gas with the boil-off gas discharged from the liquefied gas storage tank 10. In ), too, the liquid heavy carbon may not be present, and the substances flowing into the compressor 20 may be only gaseous methane and nitrogen.

Accordingly, in the present embodiment, the configuration and process of separating the liquid from the boil-off gas flowing into the compressor 20 after precooling may be omitted.

5 is a conceptual diagram of a boil-off gas cooling system according to a fifth embodiment of the present invention.

5, the boil-off gas cooling system 1 according to the fifth embodiment of the present invention further includes a heat exchanger 70 and a pump 80.

For reference, in this embodiment, the boil-off gas is cooled in a heat exchanger 70 to be described later, compressed in a compressor 20, liquefied in a liquefier 50, and then passed through a gas-liquid separator 60 to a liquefied gas storage tank ( 10) can be returned.

The heat exchanger 70 cools the boil-off gas upstream of the compressor 20. The heat exchanger 70 may cool the boil-off gas flowing into the compressor 20 similar to the pre-cooler 30 in the previous embodiment, except that the heat exchanger 70 of this embodiment is a liquefied gas storage tank 10 ) It is possible to cool the boil-off gas using the liquefied gas that is discharged from and delivered to the customer 100.

In the gas-liquid separator 60 of this embodiment, not only the liquefied boil-off gas but also the liquefied gas discharged from the liquefied gas storage tank 10 may be introduced along the liquefied gas discharge line L7. At this time, part of the liquid is returned to the liquefied gas storage tank 10 through the liquid return line (L4), and a part of the liquid is branched from the liquid return line (L4) and connected to the customer 100 by a liquefied gas supply line (L8). It can be delivered to the customer 100 through.

That is, the liquid separated by the gas-liquid separator 60 may be returned to the liquefied gas storage tank 10 or supplied to the customer 100, and at this time, the liquid supplied to the customer 100 is a boil-off gas from the heat exchanger 70. Used for cooling of.

The liquid delivered to the heat exchanger 70 may be a liquefied gas discharged from the liquefied gas storage tank 10 and introduced into the gas-liquid separator 60, and also liquefied in the liquefier 50 and introduced into the gas-liquid separator 60. It may be an evaporated gas. Accordingly, the heat exchanger 70 may cool the boil-off gas using the liquefied gas delivered to the customer 100 and the liquid boil-off gas separated by the gas-liquid separator 60.

The boil-off gas from the liquefied gas storage tank 10 via the compressor 20 can be supplied to the customer 100 along the boil-off gas supply line (L6), and the gas separated by the gas-liquid separator 60 is As flash gas, it is mixed upstream of the compressor 20 in the boil-off gas supply line L6.

To this end, in the gas-liquid separator 60, a gas mixing line L9 may be provided as the boil-off gas supply line L6. In the case of initial behavior or when the temperature of the boil-off gas is high or the flow rate of the liquefied gas supplied to the customer 100 is low, etc., the pressure at the rear end of the compressor 20 is not sufficiently increased, so that the liquefaction cannot be partially performed, the gas-liquid separator 60 There is a two-phase state in which a liquid and a flash gas are mixed, and the temperature of the flash gas is the saturation temperature of the pressure of the gas-liquid separator 60.

Therefore, since the flash gas may be lower than the temperature introduced into the compressor 20, in this embodiment, the temperature of the boil-off gas flowing into the compressor 20 can be lowered further by joining the flash gas upstream of the compressor 20. The effect of increasing the pressure at the rear end of the compressor 20 and improving the liquefaction efficiency obtained by the compressor 20 is as described above.

However, in this embodiment, an auxiliary compressor (not shown) may be further provided between the point where the gas mixing line L9 is connected in the boil-off gas supply line L6 and the heat exchanger 70, and thus the boil-off gas is The gas may be cooled while being mixed, and may be first compressed in an auxiliary compressor, cooled in a heat exchanger 70, second compressed in a compressor 20, and then supplied to a customer 100 or liquefied in a liquefier 50.

The pump 80 pressurizes the liquefied gas via the gas-liquid separator 60 in the liquefied gas storage tank 10. The pump 80 may be a reciprocating pump 80 or the like, and liquefied gas (and liquefied gas) transferred from the gas-liquid separator 60 to the heat exchanger 70 along the liquid return line L4 and the liquefied gas supply line L8 The boil-off gas) can be pressurized to the required pressure of the customer 100.

Since the pump 80 can be provided upstream of the heat exchanger 70 in the liquefied gas supply line L8, the heat exchanger 70 can cool the boil-off gas using the liquefied gas downstream of the pump 80. . However, in this case, since the temperature of the liquefied gas pressurized by the pump 80 increases, precooling of the boil-off gas in the heat exchanger 70 may not be sufficiently performed.

In order to solve this problem, in the sixth embodiment below, a precooler 30 similar to that described above may be further included. It will be described later below.

6 is a conceptual diagram of a boil-off gas cooling system according to a sixth embodiment of the present invention.

Referring to FIG. 6, the boil-off gas cooling system 1 according to the sixth embodiment of the present invention further includes a precooler 30 and a separator 40 as compared to the fifth embodiment of FIG. 5.

The precooler 30 is similar to that described in the first embodiment, etc., except that the precooler 30 of this embodiment may utilize liquefied gas in addition to the liquefied boil-off gas. In this case, the pre-cooler 30 is provided between the heat exchanger 70 and the compressor 20 and may cool the boil-off gas by mixing the liquefied gas delivered to the customer 100. Specifically, the pre-cooler 30 is , The liquefied gas upstream of the pump 80 is mixed to cool the boil-off gas.

The separator 40 provided downstream of the precooler 30 may separate the liquid from the precooled boil-off gas. When the liquefied gas is mixed in the precooler 30, the heavy carbon may be separated into liquid in the separator 40, and thus the liquid return part 41 described above may be provided in the separator 40.

However, in this embodiment, the boil-off gas is first cooled by the heat exchanger 70, and as the liquefied gas is supplied to the customer 100, the flow rate of the liquefied gas delivered to the precooler 30 is compared with the first embodiment. Since it may be less, it is possible to reduce the capacity of the compressor 20 or the liquefier 50.

As described above, in this embodiment, by cooling the boil-off gas upstream of the compressor 20 using the liquefied gas and the liquefied boil-off gas supplied to the customer 100, the compression efficiency can be improved and the liquefaction performance can be improved.

7 is a conceptual diagram of a boil-off gas cooling system according to a seventh embodiment of the present invention.

Referring to FIG. 7, the boil-off gas cooling system 1 according to the seventh embodiment of the present invention includes a compressor 20, a precooler 30, and a liquefier 50.

The compressor 20 includes a first compressor 21 and a second compressor 22. The first compressor 21 compresses the boil-off gas generated in the liquefied gas storage tank 10, and the second compressor 22 is driven by a driving source different from the first compressor 21 and compressed in the first compressor 21. The resulting boil-off gas is further compressed. That is, the first compressor 21 and the second compressor 22 are arranged in series on the boil-off gas liquefaction line L1.

The first compressor 21 may have a design pressure less than or equal to a preset value, and the second compressor 22 may have a design pressure greater than or equal to the preset value. At this time, the preset value may be a value that distinguishes between the required pressure of the power generation engine (less than 10 bar) and the pressure suitable for reliquefaction (within 20 bar), or the required pressure of the main engine (within 20 bar) and the required pressure of the power generation engine. It may be a distinguishing value, and for example, it may be around 10 bar.

Therefore, the pressure of the boil-off gas compressed by the first compressor 21 may be a pressure suitable for the customer 100 such as a power generation engine or GCU, and the pressure of the boil-off gas compressed by the second compressor 22 is suitable for reliquefaction. It may be a pressure or a pressure suitable for the consumer 100 such as a main engine. A boil-off gas branch line L61 may be provided downstream of the first compressor 21 from the boil-off gas liquefaction line L1 to a consumer 100 such as a power generation engine.

That is, the second compressor 22 is manufactured to withstand the final pressure required by the liquefier 50 or the customer 100, whereas the first compressor 21 is designed to withstand only a lower pressure, and thus the compressor 20 ) You can reduce the overall cost.

In addition, in the present embodiment, both the first compressor 21 and the second compressor 22 having different design pressures can have a head (pressure head) less than or equal to a preset value. In this case, the head may be a meaning corresponding to the difference between the pressure difference between the front and rear of the compressor 20 and between the inlet pressure and the discharge pressure.

That is, in this embodiment, the head of the compressor 20 provided at the downstream is not larger than the head of the compressor 20 provided at the upstream, but the heads of both the first compressor 21 and the second compressor 22 provided in series are preset. It is provided below a value, and in this case, the preset value may be about 10 bar, and the heads of the first compressor 21 and the second compressor 22 may be the same or at least similar.

In this case, the pressure of the boil-off gas compressed by the first compressor 21 is about 10 bar, and the pressure of the boil-off gas compressed by the second compressor 22 is about 20 bar. Therefore, compression can be performed according to the effective pressure for reliquefaction or the pressure required by the main engine (for example, around 16bar when the main engine is XDF).

The second compressor 22 of the present embodiment is provided in plural and may be arranged in parallel with respect to the boil-off gas liquefaction line L1 connected from the liquefied gas storage tank 10 to the liquefier 50. For example, as shown in the drawing, the number of second compressors 22 may be two or more, and are provided to enable backup of each other.

In addition, in this embodiment, as the heads of both the first compressor 21 and the second compressor 22 are less than or equal to the preset value, the first compressor 21 is operated by at least one of the second compressors 22. Backup is possible.

However, for this purpose, in the boil-off gas liquefaction line L1 in which the first compressor 21 and the second compressor 22 are provided in series, one second compressor 22 is located downstream of one second compressor 22. A boil-off gas return line (L62) for transferring the boil-off gas to the upstream of) may be provided.

Therefore, when a problem occurs in the compression of the first compressor 21, the boil-off gas is compressed by one of the second compressors 22 by a head equal to or less than a preset value, and then the boil-off gas return line L62 One second compressor 22 may be further compressed by a head equal to or less than a preset value and compressed in a state corresponding to the final pressure.

In addition, so that the second compressor 22 can back up the first compressor 21, the boil-off gas return line L62 is provided upstream of the branch where the boil-off gas branch line L61 is branched, and the second compressor 22 The boil-off gas compressed in can be smoothly supplied to the power generation engine through the boil-off gas return line (L62).

In the above-described situation, the boil-off gas is bypassed to the first compressor 21 in the boil-off gas liquefaction line L1 to prevent the boil-off gas from flowing into the first compressor 21 having an operation problem. An evaporative gas bypass line L63 to be transmitted may be provided.

A boil-off gas distribution valve 23 is provided to distribute boil-off gas from the boil-off gas liquefaction line L1 to the second compressors 22 arranged in parallel, and the boil-off gas return valve ( 24) is provided, and the boil-off gas bypass valve 25 is provided in the boil-off gas bypass line L63.

For example, when a problem occurs in any one of the second compressors 22, the boil-off gas distribution valve 23 may deliver all of the boil-off gas to the second compressor 22 without a problem. Alternatively, when a problem occurs in the first compressor 21, the boil-off gas return valve 24 and the boil-off gas bypass valve 25 are opened, so that even if there is no compression by the first compressor 21, the second compressor 22 The final discharged boil-off gas may be compressed by twice or less (more than 1 time) of the preset head of each compressor 20.

In this way, the first compressor 21 and the second compressor 22 are both in the liquefied gas storage tank 10 so that the plurality of second compressors 22 can back up each other and also the first compressor 21. It may have a capacity capable of handling 100% of the evaporation gas generated.

The precooler 30 may be provided upstream of the liquefier 50 to pre-cool the boil-off gas before heat exchange with the refrigerant, thereby reducing the heat exchange burden of the refrigerant. In particular, the pre-cooler 30 is provided upstream of the second compressor 22 and reduces the volume of the boil-off gas flowing into the second compressor 22 to achieve a power saving effect in the second compressor 22.

The pre-cooler 30 may cool the boil-off gas using the liquid boil-off gas liquefied in the liquefier 50, similar to that described in the previous embodiments. At this time, the liquid boil-off gas heated in the precooler 30 may be further heated if necessary and then transferred to the customer 100 for consumption.

A portion of the boil-off gas liquefaction line L1 where the pre-cooler 30 is provided is provided in a parallel structure, and an auxiliary pre-cooler 31 for backing up the pre-cooler 30 may be provided. However, unlike the pre-cooler 30, the auxiliary pre-cooler 31 may lower the temperature of the boil-off gas by using a separate material such as fresh water or sea water instead of using an evaporative gas.

The pre-cooler 30 implements pre-cooling using the boil-off gas that is liquefied and then delivered to the customer 100, and the amount of the liquefied boil-off gas returned to the liquefied gas storage tank 10 and flows into the pre-cooler 30 When this decreases, sufficient precooling may not be performed in the precooler 30.

To solve this, an auxiliary precooler 31 may be provided that uses a material supplied regardless of the amount of boil-off gas generated or the operation of the customer 100, and of course, even if precooling is not performed, reliquefaction is not impossible. (31) can be omitted.

The liquefier 50 heat-exchanges the boil-off gas compressed by the second compressor 22 with a refrigerant to liquefy at least a portion. The cooling method used by the liquefier 50 is not particularly limited, and various types of refrigerants such as mixed refrigerants and the like may be used.

The boil-off gas liquefied in the liquefier 50 is delivered to the gas-liquid separator 60 along the boil-off gas liquefaction line L1, and the liquefied gas storage tank 10 in the gas-liquid separator 60 through the liquid return line L4. Can be returned to

Alternatively, the liquid boil-off gas delivered to the gas-liquid separator 60 may be supplied to and consumed by a consumer 100 such as a main engine along the boil-off gas supply line (L6), and at this time, flow to the boil-off gas supply line (L6). The liquid boil-off gas may pass through the pre-cooler 30.

However, since the final pressure required by the main engine may be higher than the appropriate pressure required for reliquefaction, a pump 80 is provided in the boil-off gas supply line (L6) to compress the liquid boil-off gas to the required pressure of the customer (100). Can be.

In this case, the design pressure of the second compressor 22 is a pressure suitable for reliquefaction, but may be a pressure that is less than the required pressure of the main engine.

As described above, in this embodiment, three compressors 20 having the same head head while being capable of processing 100% of the boil-off gas generated in the liquefied gas storage tank 10 are provided, so that even if a problem occurs in one compressor 20 While the other two compressors 20 can process all of the boil-off gas, the required pressure of the liquefier 50 or the main engine can be adjusted without problems.

In addition, in this embodiment, two compressors 20 having a head of 10 bar are continuously operated to produce a pressure higher than 10 bar, and one compressor 20 can reduce the design pressure, thereby reducing the overall cost of the compressor 20.

The present invention is not limited to the above-described embodiments, and a combination of at least two or more of the embodiments or a combination of at least one embodiment of the contents of the embodiments and a known technology may be included as other embodiments. Of course.

In the above, the present invention has been described based on the embodiments of the present invention, but this is merely an example and does not limit the present invention, and those skilled in the art to which the present invention pertains will not depart from the essential technical content of the present embodiment. It will be appreciated that various combinations or variations and applications not illustrated in the examples are possible in the scope. Accordingly, technical contents related to modifications and applications that can be easily derived from the embodiments of the present invention should be interpreted as being included in the present invention.

1: boil-off gas cooling system 10: liquefied gas storage tank
20: compressor 21: first compressor
22: second compressor 23: boil-off gas distribution valve
24: boil-off gas return valve 25: boil-off gas bypass valve
30: pre-cooler 31: auxiliary pre-cooler
40: separator 41: liquid return portion
411: chamber 412: pressure vessel
413: valve part 413a: first discharge valve
413b: second discharge valve 413c: first pressure regulating valve
413d: second pressure regulating valve 50: liquefier
60: gas-liquid separator 70: heat exchanger
80: pump 100: customer
L1: Boil-off gas liquefaction line L2: Liquid discharge line
L30: first pressure control line L31: second pressure control line
L4: liquid return line L5: liquid delivery line
L6: Boil-off gas supply line L61: Boil-off gas branch line
L62: boil-off gas return line L63: boil-off gas bypass line
L7: Liquefied gas discharge line L8: Liquefied gas supply line
L9: gas mixing line

Claims (7)

A compressor for compressing the boil-off gas generated in the liquefied gas storage tank; And
And a heat exchanger for cooling the boil-off gas upstream of the compressor,
The heat exchanger,
The boil-off gas is cooled using the liquefied gas discharged from the liquefied gas storage tank and delivered to the customer,
A liquefier for liquefying the compressed evaporated gas; And
Further comprising a gas-liquid separator for gas-liquid separation of the liquefied boil-off gas,
The heat exchanger is a boil-off gas cooling system, characterized in that the boil-off gas is cooled using the liquefied gas delivered to the customer and the liquid boil-off gas separated by the gas-liquid separator. The method of claim 1,
The boil-off gas cooling system further comprises an auxiliary compressor for compressing the boil-off gas between the liquefied gas storage tank and the heat exchanger. The method of claim 1, wherein the gas-liquid separator,
Boiled gas cooling system, characterized in that the liquefied gas stored in the liquefied gas storage tank is introduced. The method of claim 1, wherein the gas-liquid separator,
Boil-off gas cooling system, characterized in that delivering the vapor-phase boil-off gas to the compressor. The method of claim 1,
And a pre-cooler provided between the heat exchanger and the compressor to cool the boil-off gas by mixing the liquefied gas delivered to the customer. The method of claim 5,
Further comprising a pump for pressurizing the liquefied gas through the gas-liquid separator in the liquefied gas storage tank,
The heat exchanger cools the boil-off gas using the liquefied gas downstream of the pump,
The pre-cooler, the boil-off gas cooling system, characterized in that for cooling the boil-off gas by mixing the liquefied gas upstream of the pump. A ship comprising the boil-off gas cooling system according to any one of claims 1 to 6.

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