KR102237358B1 - liquefaction system of boil-off gas and ship having the same - Google Patents

Abstract

The present invention relates to a gas treatment system and a ship including the same, comprising: a liquefied gas storage tank; A boil-off gas compressor for compressing the boil-off gas of the liquefied gas storage tank in multiple stages and supplying it to the engine; A reliquefaction device for liquefying excess boil-off gas not consumed by the engine among boil-off gas compressed by the boil-off gas compressor as a refrigerant; And a gas-liquid separator for separating the re-liquefied boil-off gas by gas-liquid separation and transferring the liquid boil-off gas to the liquefied gas storage tank, wherein the gas-liquid separator includes a condensation return line for transferring the liquid boil-off gas to the liquefied gas storage tank. Is provided, and a purging valve is connected to the condensation return line to purify the inside of the condensation return line when the reliquefaction device is stopped.

Description

Liquefaction system of boil-off gas and ship having the same}

The present invention relates to a gas treatment system and a ship including the same.

According to recent technological developments, liquefied gases such as Liquefied Natural Gas and Liquefied Petroleum Gas have been widely used in place of gasoline or diesel.

Liquefied natural gas is liquefied by cooling methane obtained by refining natural gas collected from a gas field. It is a colorless and transparent liquid that contains little pollutants and has high calorific value, making it an excellent fuel. Liquefied petroleum gas, on the other hand, is a fuel made into a liquid by compressing gas containing propane (C3H8) and butane (C4H10) as main components from oil fields together with petroleum at room temperature. Liquefied petroleum gas, like liquefied natural gas, is colorless and odorless, and is widely used as fuel for home, business, industrial, and automobiles.

Such liquefied gas is stored in a liquefied gas storage tank installed on the ground or in a liquefied gas storage tank provided on a ship, which is a transportation means for sailing the ocean, and the liquefied natural gas is stored in a volume of 1/600 by liquefaction. The volume of liquefied petroleum gas is reduced to 1/260 of propane and 1/230 of butane by liquefaction, which has the advantage of high storage efficiency. The temperature and pressure required to drive the engine using the liquefied gas as fuel may be different from the state of the liquefied gas stored in the tank.

In addition, when LNG is stored in a liquid state, some LNG is vaporized as heat permeation occurs into the tank to generate boil off gas (BOG).These boil-off gases can cause problems in the boil-off gas reliquefaction system. To solve the problem, it was attempted to solve the problem by discharging the boil-off gas to the outside and burning it (previously, the boil-off gas was simply discharged to the outside to remove the risk of damage to the tank by lowering the tank pressure). It is causing the problem of waste.

The present invention was created to solve the problems of the prior art as described above, and an object of the present invention is to process boil-off gas, flash gas, vent gas, etc. while re-liquefying the boil-off gas generated in the liquefied gas storage tank into a refrigerant. It is intended to provide a gas treatment system and a ship including the same, in which the operation stability of the entire system is improved by efficiently improving the system.

A gas treatment system according to an aspect of the present invention includes a liquefied gas storage tank; A boil-off gas compressor for compressing the boil-off gas of the liquefied gas storage tank in multiple stages and supplying it to the engine; A reliquefaction device for liquefying excess boil-off gas not consumed by the engine among boil-off gas compressed by the boil-off gas compressor as a refrigerant; And a gas-liquid separator for separating the re-liquefied boil-off gas by gas-liquid separation and transferring the liquid boil-off gas to the liquefied gas storage tank, wherein the gas-liquid separator includes a condensation return line for transferring the liquid boil-off gas to the liquefied gas storage tank. Is provided, and a purging valve is connected to the condensation return line to purify the inside of the condensation return line when the reliquefaction device is stopped.

Specifically, the purging valve may inject a purging gas into the condensation return line to push the boil-off gas stagnant in the condensation return line to the liquefied gas storage tank.

Specifically, the purging gas may be nitrogen.

Specifically, the condensation return line may block a flow between a point where a purging gas is injected by the purging valve from the gas-liquid separator when the purging valve is opened.

Specifically, a high-pressure vent mast receiving and venting the high-pressure boil-off gas compressed by the boil-off gas compressor or the boil-off gas inside the gas-liquid separator may be further included.

Specifically, the gas-liquid separator may be provided with a flash gas discharge line for transferring the gas-liquid flash gas separated from the re-liquefied boil-off gas to the liquefied gas storage tank.

A ship according to an aspect of the present invention is characterized in that it has the gas treatment system.

The gas treatment system according to the present invention and a ship including the same, while using the liquefied gas or the boil-off gas of the liquefied gas storage tank as fuel for the propulsion engine, re-liquefy the excess boil-off gas as a refrigerant, but supplying or liquefied boil-off gas It is possible to improve liquefaction efficiency and reduce OPEX by improving the treatment of flash gas generated from boil-off gas.

1 is a conceptual diagram of a gas treatment system according to an embodiment of the present invention.
2 and 3 are partial conceptual diagrams of a gas treatment system according to an embodiment of the present invention.
4 is a partial plan view of a gas treatment system according to an 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 adding reference numerals to elements of each drawing in the present specification, it should be noted that, even though they are indicated on different drawings, only the same elements are to have the same number as possible. In addition, in describing the present invention, when 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. For reference, in the present specification, the liquefied gas may be LNG, but is not limited thereto, and the boiling point is lower than room temperature and is forcibly liquefied for storage, and all materials having a calorific value may be included.

In addition, in the present specification, it is noted that the liquefied gas/evaporated gas is classified based on the state inside the fuel tank, and is not necessarily limited to a liquid or gaseous phase due to the name.

The present invention includes a ship equipped with a gas processing system 1 described below, wherein the ship may be a gas carrier, FSRU, FLNG, a bunkering vessel, etc., which stores gas as cargo, but not gas (container, Minerals, etc.), merchant ships carrying people, and offshore plants.

1 is a conceptual diagram of a gas treatment system according to an embodiment of the present invention.

Referring to FIG. 1, a gas treatment system 1 according to an embodiment of the present invention includes a liquefied gas storage tank 10, a boil-off gas compressor 20, a reliquefaction device 30, a gas-liquid separator 40, It includes a forced vaporizer (50).

The liquefied gas storage tank 10 stores liquefied gas in a liquid state. The liquefied gas storage tank 10 of this embodiment may be a cargo tank such as a gas carrier, and may be a membrane type, a standalone SPB type, or a MOSS type, and of course, a standalone high pressure container type is also possible.

The liquid liquefied gas stored in the liquefied gas storage tank 10 naturally vaporizes due to external heat penetration and changes into evaporated gas, and the boil-off gas is discharged from the liquefied gas storage tank 10 to produce a propulsion engine (ME) or a power generation engine ( GE) can be used as fuel or returned to the liquefied gas storage tank 10 after reliquefaction.

The liquefied gas storage tank 10 is provided with lines passing through a dome, a boil-off gas discharge line (L1) for discharging the boil-off gas, and a liquefied gas discharge line (L3) for discharging the liquefied gas through the transfer pump (11). And, the liquefied gas return line L31 through which at least a portion of the liquefied gas is returned from the liquefied gas discharge line L3 may be provided to pass through the dome. In addition, a condensation return line L22 for returning the boil-off gas reliquefied by the reliquefaction device 30 to be described later to the liquefied gas storage tank 10 may also be provided to pass through the dome.

The liquefied gas storage tank 10 may be provided in plural, and the boil-off gas discharge lines L1 provided in at least two or more liquefied gas storage tanks 10 are integrated into one and then connected to the boil-off gas compressor 20. At this time, the part incorporating the boil-off gas discharge line L1 is referred to as a vapor main (VM).

In addition, after the liquefied gas discharge line (L3) provided in at least two liquefied gas storage tanks 10 is also integrated, it is connected to the forced vaporizer 50, and the part incorporating the liquefied gas discharge line (L3) is a liquid main (LM). It is called (liquid main).

Accordingly, liquefied gas or boil-off gas may be mixed from each liquefied gas storage tank 10 using vapor main (VM) and liquid main (LM), or may be distributed to each liquefied gas storage tank 10 in reverse.

The boil-off gas compressor 20 compresses the boil-off gas discharged from the liquefied gas storage tank 10 and supplies it to the engine. The boil-off gas compressor 20 may be provided in a structure that compresses the boil-off gas in multiple stages, and the pressure of the boil-off gas discharged by the boil-off gas compressor 20 is a propulsion engine (ME) (ME-GI, XDF, etc.) or a power generation engine. It can be set according to the pressure of (GE)(DFDE).

For example, in this embodiment, the propulsion engine (ME) may be XDF, and the boil-off gas compressor 20 may have a six-stage compression structure. The boil-off gas compressor 20 may be provided on the boil-off gas discharge line L1 connected from the liquefied gas storage tank 10 to the propulsion engine ME and the power generation engine GE. In the downstream, the boil-off gas discharge line (L1) is branched and connected to the propulsion engine (ME) and the power generation engine (GE), respectively.

Of course, in case there is a difference in the required pressure between the propulsion engine (ME) and the power generation engine (GE), the pressure is regulated between the branched point in the evaporation gas discharge line (L1) and the power generation engine (GE) or the propulsion engine (ME). A gas valve train (not shown) or a gas valve unit (not shown) may be provided as a valve.

In addition, the boil-off gas liquefaction line (L2) is branched from the boil-off gas discharge line (L1) downstream of the boil-off gas compressor (20). The boil-off gas liquefaction line L2 may be connected to a re-liquefaction device 30 and a gas-liquid separator 40 to be described later, and a condensation return line L22 provided between the gas-liquid separator 40 and the liquefied gas storage tank 10 is provided. The re-liquefied boil-off gas is returned to the liquefied gas storage tank (10).

The boil-off gas compressor 20 may distribute the compressed boil-off gas to the propulsion engine (ME) and the reliquefaction device (30). That is, the pressure of the boil-off gas flowing into the propulsion engine (ME), the power generation engine (GE), and the reliquefaction device 30 through the boil-off gas compressor 20 may be basically the same.

However, if the lubricating oil is mixed in the process of compressing the boil-off gas by the boil-off gas compressor 20, the liquefied gas is mixed with the boil-off gas that is re-liquefied from the re-liquefaction device 30 and returned to the liquefied gas storage tank 10. There is a problem that the quality of the liquefied gas in the storage tank 10 is deteriorated.

Accordingly, this embodiment uses a non-lubricating (oil-free) type compressor in which lubricating oil is not mixed in order to satisfy the requirement that lubricating oil is not mixed with the boil-off gas flowing into the reliquefaction device 30. At this time, the boil-off gas compressor 20 may be a centrifugal type.

The reliquefaction apparatus 30 liquefies excess boil-off gas not consumed by the engine among boil-off gas compressed by the boil-off gas compressor 20 into a refrigerant. In this case, the refrigerant may be an MR refrigerant in which a hydrocarbon-based material is mixed.

The reliquefaction device 30 will be described in detail with reference to FIGS. 2 and 3. Hereinafter, it is noted that the gaseous phase or liquid phase is classified based on the state of the refrigerant in the refrigerant separator 33, and may be vaporized or liquefied in a process such as heat exchange, and the state of the refrigerant is not limited due to the expression.

Referring first to FIG. 2, the reliquefaction device 30 includes a refrigerant compressor 31, a refrigerant cooler 32, a refrigerant separator 33, a liquefier 34, a pressure reducing valve 35, and a receiver 36. And, the refrigerant circulation line (L4) can connect the above components in series.

The refrigerant compressor 31 compresses a refrigerant. At this time, the refrigerant compressor 31 of the reliquefaction device 30 shown in FIG. 2 may be provided in a type of oil supply (oil-injected) into which lubricating oil is mixed when the refrigerant is compressed.

The refrigerant cooler 32 cools the compressed refrigerant. The MR refrigerant is a mixture of substances having different boiling points. Since the boiling point of some substances is increased by compression, a part of the MR refrigerant may be liquefied during cooling by the refrigerant cooler 32.

The refrigerant separator 33 separates the compressed and cooled refrigerant into gas-liquid. At this time, the separated gaseous refrigerant flows into the liquefier 34. In addition, the refrigerant may partially pass through the liquefier 34 after being cooled in the refrigerant cooler 32 and before flowing into the refrigerant separator 33. Through this, all of the lubricating oil remains in a liquid state, so that the lubricating oil in the gas phase refrigerant is Can be avoided.

Of course, the degree of cooling the refrigerant in the refrigerant cooler 32 and the degree of cooling through the liquefier 34 upstream of the refrigerant separator 33 may be set to a degree to prevent the lubricating oil from solidifying.

The liquid refrigerant separated by the refrigerant separator 33 may be joined in the middle of the characteristic stream of the liquefier 34, which will be described later.

The liquefier 34 heat-exchanges the refrigerant and the boil-off gas to liquefy the boil-off gas. The liquefier 34 may be a heat exchanger having a plurality of streams, and the structure is not limited as a fin & tube type, a PCHE type, or the like.

The liquefier 34 is the first stream delivered to the refrigerant separator 33 after the refrigerant cooled in the refrigerant cooler 32 partially flows, as viewed from the left to the right in the drawing, and separated by the refrigerant separator 33 A second stream through which the gaseous refrigerant flows, and a fourth stream through which the boil-off gas flows. In addition, the liquefier 34 has a third stream through which the liquid refrigerant introduced again through the pressure reducing valve 35 flows.

The pressure reducing valve 35 decompresses the gaseous refrigerant separated by the refrigerant separator 33 at the downstream of the liquefier 34 and re-inflows the gaseous refrigerant into the liquefier 34. The pressure reducing valve 35 may be a Joule-Thomson valve, and when the pressure is reduced, the refrigerant may be cooled and liquefied by the Joule-Thomson effect.

The receiver 36 temporarily stores the refrigerant passed through the liquefier 34 after depressurization and transfers the refrigerant to the refrigerant compressor 31. The receiver 36 may be in the form of a tank, and may serve as a buffer so that the liquid phase does not flow into the refrigerant compressor 31.

The liquid refrigerant existing in the receiver 36 may be stored in the receiver 36 instead of being delivered to the refrigerant compressor 31, and between the refrigerant separator 33 or the refrigerant separator 33 and the liquefier 34 It is also possible to deliver the refrigerant circulation line (L4).

In order to change the liquid phase in the receiver 36 into a gas phase, a refrigerant return line L42 returning the compressed refrigerant downstream of the refrigerant compressor 31 to the receiver 36 is provided between the refrigerant compressor 31 and the refrigerant cooler 32. It may be branched from the refrigerant circulation line L4 and connected to the receiver 36 upstream. When the high-pressure/high-temperature refrigerant compressed in the refrigerant compressor 31 returns to the receiver 36, the liquid refrigerant in the receiver 36 may be vaporized and transferred to the refrigerant compressor 31.

The refrigerant flow flowing along the refrigerant circulation line L4 will be described as follows. The refrigerant is cooled in the refrigerant cooler 32 and partially passes through the first stream of the liquefier 34 and then flows into the refrigerant separator 33. Thereafter, the gaseous refrigerant separated by the refrigerant separator 33 is discharged via the second stream of the liquefier 34.

The gaseous refrigerant that has escaped is introduced into a pressure reducing valve 35 to be described later, and is cooled (liquefied) by the Joule-Thomson effect during decompression. The refrigerant that has passed through the pressure reducing valve 35 flows back into the liquefier 34 and exchanges heat with the boil-off gas to liquefy the boil-off gas.

Of course, the boil-off gas in the liquefier 34 can be cooled while exchanging heat with other streams of refrigerant other than the refrigerant that has passed through the pressure reducing valve 35. You can also arrange to do it. In addition, heat exchange between refrigerants may be performed within the liquefier 34.

The liquid refrigerant separated by the refrigerant separator 33 may be in a state in which lubricating oil is mixed, and this refrigerant is a third stream from the liquefier 34 through the liquid refrigerant branch line L41 (refrigerant re-inflow after decompression). Stream).

That is, in the present embodiment, the refrigerant mixed with the lubricating oil is provided so that it does not freeze while exchanging heat with the boil-off gas at a low temperature so that the refrigerant mixed with the lubricating oil is joined at the intermediate point of the stream.

Of course, the reliquefaction device 30 in FIG. 2 includes a lubricant oil separator for separating the lubricant oil separately from the liquefier 34 upstream, a lubricant oil pump for circulating the separated lubricant oil to the refrigerant compressor 31, a lubricant cooler, etc. May be.

The reliquefaction device 30 of FIG. 2 may be referred to as a lube oil type in that it uses a refrigerant compressor 31 into which lubricating oil is mixed during compression, whereas the case of FIG. 3 described below may be referred to as a lube oil type. As a non-lubricating oil-free (oil-free) type refrigerant compressor 31 that does not contain lubricating oil, it may be referred to as a non-lube oil type.

Referring to FIG. 3, unlike FIG. 2, the reliquefaction device 30 is provided in a type in which the refrigerant compressor 31 is not mixed with lubricating oil, and thus a configuration for separating the lubricating oil may be omitted. However, the reliquefaction device 30 may include the configurations described above with reference to FIG. 2, provided that the refrigerant does not pass through the liquefier 34 between the refrigerant cooler 32 and the refrigerant separator 33, and the refrigerant is a refrigerant. It may be provided to pass through the cooler 32, the refrigerant separator 33, and the liquefier 34 in order.

In the reliquefaction device 30 of FIG. 3, the refrigerant separator 33 separates the gaseous refrigerant from the liquid refrigerant and transfers it to the liquefier 34 to increase heat exchange efficiency. The liquefier 34 is a first stream through which a gaseous refrigerant flows, a second stream through which the refrigerant is depressurized by the pressure reducing valve 35 and re-introduced into the liquefier 34 flows, and a third stream through which evaporation gas flows And the liquid refrigerant separated by the refrigerant separator 33 may be joined in the middle of the second stream.

In addition, the reliquefaction device 30 of FIG. 3 may not be provided with a configuration in which the lubricating oil is separately separated from the upstream of the refrigerant separator 33 and circulated to the refrigerant compressor 31.

In this reliquefaction device 30, a reliquefaction vent line L21 is separately provided. A vent function must be provided to prepare for an emergency situation on the flow of liquefied gas or boil-off gas, and different vent masts are used for vents depending on the pressure.

Specifically, the low-pressure liquefied gas or the boil-off gas in the upstream of the boil-off gas compressor 20 (between the liquefied gas storage tank 10 and the boil-off gas compressor 20, for example, a buffer tank 51 to be described later) is a low-pressure vent line ( L11) is delivered to the low-pressure vent mast (LV) and vented, and the high-pressure boil-off gas of the boil-off gas compressor 20 downstream (between the evaporation gas compressor 20 and the engine or a gas-liquid separator 40 to be described later) is high-pressure It is delivered to and vented to the high pressure vent mast HV through the vent line L12.

However, as described above, since the high-pressure boil-off gas compressed by the boil-off gas compressor 20 is distributed to the engine and the re-liquefaction device 30, the boil-off gas pressure in the re-liquefaction device 30 is the high-pressure vent line (L12). It corresponds to the pressure of the boil-off gas vented through. Therefore, the vent in the reliquefaction device 30 can also use a high-pressure vent mast (HV).

However, if the reliquefaction device 30 is vented with a high-pressure vent mast (HV), when the boil-off gas compressor 20 is tripped, it is vented with a high-pressure vent mast (HV) between the boil-off gas compressor 20 and the engine. When the refrigerant leaks from the reliquefaction device 30, it is not distinguishable from being vented to a high-pressure vent mast (HV). That is, there is a problem in that refrigerant leakage from the reliquefaction device 30 cannot be confirmed in a situation where the boil-off gas is vented due to trip of the boil-off gas compressor 20.

Accordingly, in this embodiment, in order to independently separate the vent of the reliquefaction apparatus 30 from the high pressure vent downstream of the boil-off gas compressor 20, a reliquefaction vent mast (RV) provided separately from the high pressure vent mast (HV) is provided. Can be equipped. At this time, a reliquefaction vent line L21 is connected between the reliquefaction device 30 and the reliquefaction vent mast RV, so that the refrigerant leaking from the reliquefaction device 30 is vented.

Therefore, the high-pressure vent mast (HV) receives and vents the high-pressure boil-off gas when the boil-off gas compressor 20 trips, and the reliquefaction vent mast (RV) is independent of the boil-off gas vented when the boil-off gas compressor 20 trips. As a result, the refrigerant may be received from the reliquefaction device 30 and vented.

To this end, the reliquefaction vent line L21 is provided independently from the high pressure vent line L12, and when the boil-off gas compressor 20 trips, the boil-off gas delivered to the high-pressure vent mast (HV) may not be introduced. A gas detector (not shown) may be installed in the liquefaction vent line L21 to detect a refrigerant leak from the reliquefaction device 30.

Accordingly, in this embodiment, even in a situation in which the boil-off gas is vented when the boil-off gas compressor 20 is tripped, leakage from the re-liquefaction device 30 can be clearly confirmed based on the detection of the refrigerant in the re-liquefaction vent line L21.

The gas-liquid separator 40 separates the boil-off gas re-liquefied in the re-liquefaction device 30 by gas-liquid separation and transfers the liquid boil-off gas to the liquefied gas storage tank 10. To this end, the gas-liquid separator 40 may be provided with a condensation return line L22 for transferring the liquid boil-off gas to the liquefied gas storage tank 10.

A purging valve 41 is connected to the condensation return line L22. When the reliquefaction device 30 is stopped, the liquid boil-off gas separated by the gas-liquid separator 40 may be stagnant in the condensation return line L22. Therefore, in this embodiment, in order to purify the inside of the condensation return line L22 when the reliquefaction device 30 is stopped, the purging line L23 and the purging valve 41 can be directly connected to the condensation return line L22. have.

At this time, the purging valve 41 injects purging gas (nitrogen, inert gas, etc.) delivered from the purging gas supply unit 42 to the condensation return line L22 to liquefy the stagnant boil-off gas in the condensation return line L22. It can be pushed out to the gas storage tank 10, and at this time, the gas-liquid separator 40 is arranged above the liquefied gas storage tank 10, so that the liquid boil-off gas is not stagnated by using the pressure of the purging gas in addition to gravity. It can be delivered to the liquefied gas storage tank (10).

However, the condensation return line (L22) blocks the flow between the point where the purging gas is injected by the purging valve 41 from the gas-liquid separator 40 when the purging valve 41 is opened, so that the purging gas is transferred to the gas-liquid separator 40 ), it is possible to smoothly push out the liquid boil-off gas in the condensation return line (L22) by the purging gas while suppressing the reverse flow.

In addition, the gaseous evaporation gas separated by the gas-liquid separator 40 is flash gas, and the temperature may be a material having a low temperature or a gaseous phase. In this case, the flash gas may be discharged from the gas-liquid separator 40 according to the internal pressure condition of the gas-liquid separator 40 in order to lower the internal pressure of the gas-liquid separator 40.

In this embodiment, the flash gas may be injected directly into the liquefied gas storage tank 10 instead of being circulated to the boil-off gas compressor 20. That is, the gas-liquid separator 40 transfers the gas-liquid flash gas separated from the re-liquefied boil-off gas to the liquefied gas storage tank 10 like the liquid boil-off gas.

To this end, the gas-liquid separator 40 may be provided with a flash gas discharge line L24 for delivering gaseous flash gas to the liquefied gas storage tank 10. In addition, the flash gas discharge line (L24) can deliver the flash gas at a position lower than the condensation return line (L22) in the liquefied gas storage tank (10), specifically, the flash gas discharge line (L24) is a gaseous flash gas. It can be delivered to the bottom of the liquefied gas storage tank (10).

Accordingly, the flash gas may be liquefied by the liquefied gas while flowing into the liquefied gas at the bottom of the liquefied gas storage tank 10 along the flash gas discharge line L24.

The flash gas discharge line (L24) is directly connected to the bottom of the liquefied gas storage tank 10 to inject the flash gas into the liquefied gas, or is connected to the liquid main (LM) through the liquefied gas return line (L31). The gaseous flash gas may be delivered to the liquefied gas storage tank 10.

Therefore, in this embodiment, the internal pressure of the gas-liquid separator 40 can be effectively lowered by returning the flash gas from the reliquefied boil-off gas to the inside of the liquefied gas storage tank 10, and the flash gas is reduced to the boil-off gas compressor 20. The load of the boil-off gas compressor 20 is reduced because it is not recirculated. In addition, since the flash gas does not return to the reliquefaction device 30 through the boil-off gas compressor 20, an improvement in the liquefaction efficiency in the reliquefaction device 30 can also be expected.

A high-pressure vent line (L12) may be connected to the gas-liquid separator 40, and when the overpressure of the gas-liquid separator 40 is not resolved by the flash gas discharge or when flash gas discharge is impossible, the inside of the gas-liquid separator 40 The boil-off gas may be delivered to and vented through the high-pressure vent line L12 to the high-pressure vent mast HV.

The forced vaporizer 50 forcibly vaporizes the liquefied gas in the liquefied gas storage tank 10 and delivers it to the boil-off gas upstream of the boil-off gas compressor 20. At this time, a buffer tank 51 (Mist separator) in which the forcibly vaporized liquefied gas is mixed with the boil-off gas discharged from the liquefied gas storage tank 10 is provided upstream of the boil-off gas compressor 20 in the boil-off gas discharge line L1. , It is possible to prevent the liquid phase from flowing into the boil-off gas compressor 20, and a low-pressure vent line (L11) is connected to the buffer tank 51 so that liquefied gas or boil-off gas from the buffer tank 51 is supplied to the low-pressure vent mast (LV). Can be delivered to and vented.

As described above, the boil-off gas compressor 20 of this embodiment is a centrifugal type that is non-lubricating (oil-free) so that lubricating oil is not mixed in the boil-off gas delivered to the reliquefaction device 30. ).

However, when the boil-off gas is insufficient, it is necessary to supply the liquefied gas together with the boil-off gas to the engine. When the boil-off gas compressor 20 is used and the liquefied gas is mixed downstream of the boil-off gas compressor 20, other Unlike the case of using the boil-off gas compressor 20 of the type (screw type, reciprocating type, etc.), there is a problem that it is difficult to immediately control the flow rate change according to the load of the engine. Furthermore, there is a concern that the mixed liquefied gas flows back to the boil-off gas compressor 20 to cause a trip.

Therefore, in this embodiment, while using a specific type of compressor so that the lubricant oil does not flow into the reliquefaction device 30, the forced vaporized liquefied gas is delivered to the boil-off gas upstream of the boil-off gas compressor 20 and mixed. In this embodiment, when the liquefied boil-off gas is returned to the liquefied gas storage tank 10, the quality of the liquefied gas is prevented from deteriorating, and the boil-off gas compressor 20 controls the discharge flow rate in response to changes in the engine load. Thus, by effectively controlling the amount of liquefied gas and boil-off gas supplied to the engine, it is possible to efficiently respond to engine load fluctuations and prevent compressor tripping.

4 is a partial plan view of a gas treatment system according to an embodiment of the present invention. For reference, each leakage scenario of FIG. 4 shows how the leaked refrigerant is diffused by ventilation when the refrigerant leaks from different locations of the reliquefaction skid 200.

Referring to FIG. 4, the gas treatment system 1 according to an embodiment of the present invention effectively detects a refrigerant leak in a compressor room 100 (CCR: Cargo Compressor Room) in which the boil-off gas compressor 20 is provided. can do. It will be described in detail below.

The compressor room 100 may be a space in which a boil-off gas compressor 20, a forced vaporizer 50, and the like are provided to change a state suitable for supplying liquefied gas or boil-off gas as fuel of an engine.

At this time, since the compressor room 100 is a space that handles explosive substances such as evaporation gas, periodic ventilation may be forcibly performed for safety (for example, 30 times per hour).

At this time, ventilation can be performed in various ways, in which external air is injected using a vent fan (not shown) that implements positive pressure, and the atmosphere inside the compressor room 100 is escaped using a duct (not shown). Or, conversely, by using a vent fan (not shown) that implements a negative pressure, external air may naturally flow into the compressor room 100 while extracting the atmosphere inside the compressor room 100 to the outside.

In the compressor room 100, a reliquefaction skid 200 in which the reliquefaction device 30 described above is mounted may be disposed. The reliquefaction skid 200 may be a support frame on which the detailed configuration of the reliquefaction device 30 mentioned in FIGS. 2 and 3 is mounted.

In this embodiment, gas detectors 201 and 202 for detecting refrigerant leaking in the compressor room 100 are provided, and the gas detectors 201 and 202 are disposed in the center of the facility at risk of leakage to detect refrigerant leakage. I can. Specifically, the gas detectors 201 and 202 are installed in the central portion A of the reliquefaction skid 200 to detect the refrigerant leaking from the reliquefaction device 30.

However, in the case of using only the gas detectors 201 and 202 of the central part A as described above, the gas detector 201 when the refrigerant leaking from the reliquefaction device 30 escapes to the outside due to the ventilation of the compressor room 100. , 202) is not detected because it is not close (leakage scenario 1 of FIG. 4).

Accordingly, in this embodiment, gas detectors 201 and 202 are additionally installed at the outlet portion B of the atmosphere to be ventilated in consideration of the spread of the leaking refrigerant due to the ventilation of the compressor room 100, thereby reliquefaction. The refrigerant leaking from the device 30 can be clearly detected. Here, the outlet portion of the atmosphere ventilated may be a position in the compressor room 100 that is biased toward the reliquefaction skid 200, and may be a position closer to the reliquefaction device 30 than the boil-off gas compressor 20.

At this time, the gas detectors 201 and 202 installed in the central part (A) of the reliquefaction skid 200 are referred to as the first gas detector 201, and are installed at the ventilation outlet part (B) in the compressor room 100 The gas detectors 201 and 202 may be referred to as a second gas detector 202, and the second gas detector 202 may be provided to detect the MR refrigerant leaking from the reliquefaction device 30.

Specifically, the second gas detector 202, when ventilating the compressor room 100 with a vent fan using negative pressure, may be installed around the vent fan (for example, the lower side in consideration of the density of the MR refrigerant compared to the atmosphere), Alternatively, if the outlet through which the atmosphere is exhausted is made of a duct, it may be installed around the duct. Of course, when both the vent fan and the duct are applied, the second gas detector 202 may be installed at an intermediate point between the vent fan and the duct.

Through this, the present embodiment, without installing the gas detectors 201 and 202 only in the central portion (A) of the reliquefaction skid 200, the ventilation outlet of the compressor room 100 accommodating the reliquefaction skid 200 By adding the gas detectors 201 and 202 to the portion B, it is possible to prevent the refrigerant leaking from the reliquefaction device 30 from being detected due to ventilation.

As described above, this embodiment can effectively respond to the engine load while preventing the lubricating oil from being mixed in the reliquefaction device 30, and applying a return to the liquefied gas storage tank 10 instead of the circulation of the flash gas, the boil-off gas compressor 20 ) Reduced load and increased reliquefaction efficiency.

In addition, this embodiment eliminates liquid stagnation by allowing the re-liquefied evaporative gas to be condensed and purged directly to the line returned to the liquefied gas storage tank 10, and implements an independent vent in the re-liquefier 30 and re-liquefy Gas detectors 201 and 202 may be installed in consideration of the ventilation of the compressor room 100 accommodating the skid 200 so that refrigerant leakage can be effectively identified.

In addition to the above-described embodiments, the present invention encompasses all embodiments generated by a combination of the above embodiments and known techniques.

Although the present invention has been described in detail through specific examples, this is for explaining the present invention in detail, and the present invention is not limited thereto, and within the technical scope of the present invention, by those of ordinary skill in the art. It would be clear that the transformation or improvement is possible.

All simple modifications to changes of the present invention belong to the scope of the present invention, and the specific scope of protection of the present invention will be made clear by the appended claims.

1: gas treatment system 10: liquefied gas storage tank
11: transfer pump 20: boil-off gas compressor
30: reliquefaction device 31: refrigerant compressor
32: refrigerant cooler 33: refrigerant separator
34: liquefier 35: pressure reducing valve
36: receiver 40: gas-liquid separator
41: purging valve 42: purging gas supply
50: forced vaporizer 51: buffer tank
100: compressor room 200: reliquefaction skid
201: first gas detector 202: second gas detector
ME: propulsion engine GE: power generation engine
LV: Low pressure vent mast HV: High pressure vent mast
RV: reliquefaction vent mast L1: boil-off gas discharge line
L11: low pressure vent line L12: high pressure vent line
L2: boil-off gas liquefaction line L21: re-liquefaction vent line
L22: condensation return line L23: purging line
L24: flash gas discharge line L3: liquefied gas discharge line
L31: liquefied gas return line L4: refrigerant circulation line
L41: liquid refrigerant branch line L42: refrigerant return line
LM: liquid main VM: vapor main

Claims (7)

Liquefied gas storage tank;
A boil-off gas compressor for compressing the boil-off gas of the liquefied gas storage tank in multiple stages and supplying the boil-off gas to the engine;
A reliquefaction device for liquefying excess boil-off gas not consumed by the engine among boil-off gas compressed by the boil-off gas compressor as a refrigerant; And
A gas-liquid separator for separating the reliquefied boil-off gas by gas-liquid separation and transferring the liquid boil-off gas to the liquefied gas storage tank,
The gas-liquid separator is provided with a condensation return line for transferring the liquid boil-off gas to the liquefied gas storage tank,
A purge valve is connected to the condensation return line to purify the inside of the condensation return line when the reliquefaction device is stopped,
The reliquefaction device,
A refrigerant compressor provided in an oil-injected type in which lubricating oil is mixed when refrigerant is compressed;
A refrigerant cooler that cools the accumulated refrigerant;
A refrigerant separator for gas-liquid separating the refrigerant;
A liquefier having a stream through which gaseous refrigerant separated by the refrigerant separator flows and a stream through which boil-off gas flows, and heat-exchanging the refrigerant and boil-off gas; And
And a pressure reducing valve for decompressing the gaseous refrigerant separated in the refrigerant separator at a downstream side of the liquefier and re-introducing the gaseous refrigerant into the liquefier,
The liquefier,
A stream through which the refrigerant cooled by the refrigerant cooler partially flows and then transferred to the refrigerant separator, a stream through which the gaseous refrigerant separated by the refrigerant separator flows, and a stream through which the refrigerant re-inflowed after depressurization by the pressure reducing valve flows And a stream through which boil-off gas flows,
A gas treatment system, characterized in that the liquid refrigerant mixed with lubricating oil and separated by the refrigerant separator is joined in the middle of a re-inflow refrigerant stream after depressurization. The method of claim 1, wherein the purging valve,
A gas treatment system, characterized in that by injecting a purging gas into the condensation return line to push the boil-off gas stagnated in the condensation return line to the liquefied gas storage tank. The method of claim 2, wherein the purging gas,
Gas treatment system, characterized in that nitrogen. The method of claim 2, wherein the condensation return line,
When the purging valve is opened, the flow between the gas-liquid separator and the point at which the purging gas is injected by the purging valve is blocked. The method of claim 1,
And a high-pressure vent mast receiving and venting the high-pressure boil-off gas compressed by the boil-off gas compressor or the boil-off gas inside the gas-liquid separator. The method of claim 1, wherein the gas-liquid separator,
A gas treatment system, characterized in that a flash gas discharge line is provided for transferring the gas-liquid gas-liquid flash gas separated from the re-liquefied boil-off gas to the liquefied gas storage tank. A ship comprising the gas treatment system according to any one of claims 1 to 6.

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