KR102189080B1 - liquefaction system of boil-off gas and ship having the same - Google Patents

Abstract

The present invention relates to a boil-off gas re-liquefaction system and a ship including the same, wherein the boil-off gas re-liquefaction system includes a liquefied part for liquefying the boil-off gas using a mixed refrigerant, and the liquefaction part heat-exchanges the boil-off gas with the mixed refrigerant. A reliquefier to liquefy; A lubricant-free type mixed refrigerant compressor that compresses the mixed refrigerant and does not contain lubricant when the mixed refrigerant is compressed; A mixed refrigerant cooler for cooling the compressed mixed refrigerant and supplying it to the reliquefier; A mixed refrigerant pressure reducing valve for decompressing the mixed refrigerant discharged from the re-liquefier at a downstream side of the re-liquefier and re-introducing the mixed refrigerant into the re-liquefier; And a receiver temporarily storing the mixed refrigerant to be supplied to the mixed refrigerant compressor, wherein the reliquefier comprises a first mixed refrigerant flow through which the mixed refrigerant supplied from the mixed refrigerant cooler flows, and re-inflow through the mixed refrigerant pressure reducing valve A second mixed refrigerant flow and a boil-off gas flow are provided, and the liquid mixed refrigerant separated from the receiver joins the second mixed refrigerant flow in the reliquefier.

Description

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

The present invention relates to a boil-off gas reliquefaction 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 almost no pollutants and has a high calorific value. 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 oil 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.The liquefied natural gas is liquefied in a volume of 1/600. 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 differ from the state of the liquefied gas stored in the tank.

In addition, when LNG is stored in a liquid state, some LNG is evaporated as heat permeation occurs into the tank to generate boil off gas (BOG).In the past, a method of discharging boil-off gas to the outside and burning it (in the past, the tank pressure is To eliminate the risk of damage to the tank by lowering it, the boil-off gas was simply discharged to the outside.) To solve the problem, it was attempted to solve the problem, but this is causing problems of environmental pollution and resource 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 improve the liquefaction efficiency in the process of reliquefaction of boil-off gas using a mixed refrigerant, and by using a mixed refrigerant compressor that does not use lubricating oil. It is to provide a boil-off gas reliquefaction system capable of preventing mixing of lubricating oil in a mixed refrigerant, and a ship including the same.

The boil-off gas re-liquefaction system according to an embodiment of the present invention includes a liquefaction unit for liquefying boil-off gas using a mixed refrigerant, and the liquefaction unit includes: a re-liquefier for liquefying the boil-off gas by heat exchange with the mixed refrigerant; A lubricant-free type mixed refrigerant compressor that compresses the mixed refrigerant and does not contain lubricant when the mixed refrigerant is compressed; A mixed refrigerant cooler for cooling the compressed mixed refrigerant and supplying it to the reliquefier; A mixed refrigerant pressure reducing valve for decompressing the mixed refrigerant discharged from the re-liquefier at a downstream side of the re-liquefier and re-introducing the mixed refrigerant into the re-liquefier; And a receiver temporarily storing the mixed refrigerant to be supplied to the mixed refrigerant compressor, wherein the reliquefier comprises a first mixed refrigerant flow through which the mixed refrigerant supplied from the mixed refrigerant cooler flows, and re-inflow through the mixed refrigerant pressure reducing valve A second mixed refrigerant flow and a boil-off gas flow are provided, and the liquid mixed refrigerant separated from the receiver joins the second mixed refrigerant flow in the reliquefier.

Specifically, the liquefaction unit may further include a mixed refrigerant circulation line provided with the receiver, the mixed refrigerant compressor, the mixed refrigerant cooler, the reliquefier, and the mixed refrigerant pressure reducing valve and circulate the mixed refrigerant. .

Specifically, the boil-off gas reliquefaction system includes: an boil-off gas compressor for compressing the boil-off gas supplied from a liquefied gas storage tank and supplying the boil-off gas to the re-liquefier; A boil-off gas supply line for supplying boil-off gas compressed by the boil-off gas compressor to a customer; And it may further include a mixed refrigerant supplement line for delivering the boil-off gas compressed by the boil-off gas compressor to the receiver.

Specifically, the boil-off gas re-liquefaction system further includes an boil-off gas liquefaction line for transferring the boil-off gas compressed by the boil-off gas compressor to the re-liquefier, and a branch point of the boil-off gas liquefaction line and the mixed refrigerant supplement The branching point of the line may be provided in series on the boil-off gas supply line.

Specifically, the liquefied part may further include a mixed refrigerant heat exchanger provided downstream of the mixed refrigerant compressor and cooling the mixed refrigerant using boil-off gas supplied from the liquefied gas storage tank.

Specifically, the mixed refrigerant heat exchanger may be provided between the mixed refrigerant cooler and the reliquefier.

A ship according to an embodiment of the present invention is characterized in that it includes the boil-off gas reliquefaction system.

In the boil-off gas re-liquefaction system and ship according to the present invention, the boil-off gas generated in the liquefied gas storage tank is re-liquefied into a mixed refrigerant, but when re-liquefied, the lubricating oil can be prevented from being mixed into the mixed refrigerant.

1 is a conceptual diagram of a boil-off gas reliquefaction system according to a first embodiment of the present invention.
2 is a conceptual diagram of a boil-off gas reliquefaction system according to a second embodiment of the present invention.
3 is a conceptual diagram of a boil-off gas reliquefaction system according to a third embodiment of the present invention.
4 is a conceptual diagram of a boil-off gas reliquefaction system according to a fourth 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.

In the following, liquefied gas may be used in the sense of encompassing all gaseous fuels generally stored in a liquid state, such as LNG or LPG, ethylene, ammonia, etc., and when not in a liquid state by heating or pressurization, it is also expressed as liquefied gas for convenience. I can. This can be applied to boil-off gas as well. In addition, for convenience, LNG can be used to mean not only NG (Natural Gas) in liquid state, but also NG in supercritical state, etc., and evaporation gas can be used to mean not only gaseous evaporation gas but also liquefied evaporation gas. have.

In addition, hereinafter, the decompression may be in a state generated through expansion, and conversely, since the decompression may be in a state generated by expansion, decompression and expansion may be used interchangeably.

Hereinafter, the boil-off gas re-liquefaction system of the present invention will be described, and the present invention includes a boil-off gas re-liquefaction system and a ship having the same. In this case, it should be noted that the ship may be a general merchant ship that loads cargo other than liquefied gas in addition to a liquefied gas carrier, and furthermore, it is an expression that encompasses all offshore structures such as FSRU and FLNG, which are not commercial ships.

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

Hereinafter, the boil-off gas reliquefaction system of the present invention will be described in detail with reference to FIGS. 1 to 4.

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

1, the boil-off gas reliquefaction system 1 according to the first embodiment of the present invention includes a liquefied gas storage tank 10, a boil-off gas compressor 20, a liquefaction unit 30, and a boil-off gas pressure reducing valve. It includes (40).

The liquefied gas storage tank 10 stores liquefied gas to be supplied to the customer 100. Here, the customer 100 may be a marine propulsion engine (or turbine) or a power generation engine, and does not limit high pressure, medium pressure, low pressure, and the like. For example, the customer 100 may be a ME-GI engine having a required pressure of 200 to 400 bar, an XDF engine having a required pressure of 15 to 50 bar, or a DFDE engine having a required pressure of about 10 bar. Alternatively, the consumer 100 may be a city gas or the like, and may be an engine (or turbine) for various purposes provided on land.

The liquefied gas storage tank 10 should store the liquefied gas in a liquid state. At this time, the liquefied gas storage tank 10 may store the liquefied gas at a pressure of 1 bar to 10 bar (for example, 1.03 bar).

The liquefied gas storage tank 10 may be a standalone type, a membrane type, etc., and various insulating structures may be used to store the liquefied gas in a liquid state, and the boil-off gas generated in the liquefied gas storage tank 10 will be described later. It can be processed by the boil-off gas compressor 20 or the like.

Since the liquefied gas is stored in the liquefied gas storage tank 10, the boil-off gas from which the liquefied gas is naturally evaporated is continuously generated in the liquefied gas storage tank 10. At this time, if the boil-off gas is not taken out, the internal pressure of the liquefied gas storage tank 10 may be excessive, so in this embodiment, the boil-off gas generated in the liquefied gas storage tank 10 can be liquefied (reduced in volume) and returned. Therefore, the internal pressure of the liquefied gas storage tank 10 is maintained at an appropriate level.

The boil-off gas compressor 20 compresses boil-off gas generated in the liquefied gas storage tank 10. The boil-off gas compressor 20 is provided in multiple stages and may be, for example, a 5-stage, and the customer 100 is a 5-stage downstream of the boil-off gas compressor 20 or a 2-stage downstream of the boil-off gas compressor 20 according to the required pressure. Can be connected to the back. In addition, an intermediate cooler (not shown) is provided downstream of each compression stage of the boil-off gas compressor 20 to cool boil-off gas heated by compression heat.

A boil-off gas supply line L10 may be provided from the liquefied gas storage tank 10 to the customer 100, and the boil-off gas compressed by the boil-off gas compressor 20 may flow through the boil-off gas supply line L10. have. At this time, the boil-off gas supply valve 21 is provided in the boil-off gas supply line L10, and the supply amount of the boil-off gas supplied to the customer 100 can be adjusted.

However, in case the flow rate of the boil-off gas does not reach the desired flow rate in the consumer 100, the present invention supplies liquefied gas connected from the liquefied gas storage tank 10 to the consumer 100 or the boil-off gas supply line L10. A line L20 may be further included, and a liquefied gas pump 11 and a vaporizer 50 may be provided in the liquefied gas supply line L20. At this time, the liquefied gas pump 11 may be provided inside and/or outside the liquefied gas storage tank 10, and may be plural according to the pressure required by the customer 100.

A boil-off gas liquefaction line L11 may be provided from the liquefied gas storage tank 10 to the liquefied part 30 to be described later. The boil-off gas liquefaction line L11 may be branched from the boil-off gas supply line L10 to connect the liquefied part 30 from the liquefied gas storage tank 10. At this time, the boil-off gas compressor 20 may be provided at a point at which the boil-off gas liquefaction line L11 is branched from the boil-off gas supply line L10 or upstream of the point.

In addition, a boil-off gas branch valve 22 may be provided downstream of the boil-off gas compressor 20 on the boil-off gas liquefaction line L11, and the re-liquefier 31 of the liquefaction unit 30 through the boil-off gas branch valve 22 The flow rate of the compressed boil-off gas supplied to) can be adjusted.

The liquefaction unit 30 liquefies the boil-off gas. The liquefaction unit 30 may liquefy the boil-off gas compressed by the boil-off gas compressor 20 into a mixed refrigerant. At this time, the mixed refrigerant means MR (Mixed Refrigerant), a refrigerant in which methane, ethane, propane, butane, nitrogen, etc. are mixed, and may be a material already known in the field of reliquefaction, and the mixing ratio is the customer 100 It may vary depending on the required pressure and the type and size of the liquefied gas storage tank 10 and is not limited in the present invention.

The liquefaction unit 30 serves as a reliquefier 31, a mixed refrigerant compressor 32, a mixed refrigerant cooler 33, a mixed refrigerant pressure reducing valve 35, and a receiver 36.

The reliquefier 31 may be provided downstream of the boil-off gas compressor 20 on the boil-off gas liquefaction line L11. The reliquefier 31 is provided in a structure having three or more streams, and is compressed by a flow path through which compressed evaporative gas flows, a mixed refrigerant compressor 32, and cooled by a mixed refrigerant cooler 33, thereby reliquefaction 31 ), the flow path through which the flow of the first mixed refrigerant flows, and the flow of the first mixed refrigerant heat-exchanged with the evaporation gas is depressurized by the mixed refrigerant pressure reducing valve 35 and re-introduced into the reliquefier 31 This flowing flow path may be included.

In this case, in the reliquefier 31, a flow path through which the first mixed refrigerant flow flows and a flow channel through which the second mixed refrigerant flow flows may be independently provided. In addition, the first mixed refrigerant flow in the reliquefier 31 may include a gaseous mixed refrigerant, and the second mixed refrigerant flow may include a liquid mixed refrigerant. The boil-off gas compressed in the reliquefier 31 may be effectively liquefied by exchanging heat with at least the second mixed refrigerant flow among the first mixed refrigerant flow and the second mixed refrigerant flow.

The mixed refrigerant compressor 32 compresses the mixed refrigerant. At this time, the pressure of the mixed refrigerant compressed by the mixed refrigerant compressor 32 may correspond to the pressure of the boil-off gas compressed by the boil-off gas compressor 20 (required pressure of the customer 100).

The mixed refrigerant compressor 32 is a type in which lubricating oil is not mixed with the mixed refrigerant during compression of the mixed refrigerant, and may be, for example, a lubricating oil-free type that does not use lubricating oil for sealing and lubrication. That is, in the present invention, by using the mixed refrigerant compressor 32 of an oil-free type, even when the mixed refrigerant is compressed, the lubricating oil can be prevented from being mixed into the mixed refrigerant. Therefore, in the present invention, unlike the case of using a mixed refrigerant compressor using lubricating oil, there is no need to provide a separate device for separating the lubricating oil mixed in the mixed refrigerant, so that the reliquefaction system can be more simplified.

In addition, the present invention uses the lubricating oil-free type mixed refrigerant compressor 32, so that when the mixed refrigerant mixed with the lubricating oil exchanges heat with the boil-off gas in the reliquefier 31, the lubricating oil is solidified due to the cooling heat of the boil-off gas. The heat exchange efficiency of the reliquefier 31 may be lowered or damage may be prevented in advance.

The mixed refrigerant cooler 33 is provided downstream of the mixed refrigerant compressor 32 and cools the compressed mixed refrigerant. Since the mixed refrigerant can be heated by receiving compression heat during compression similar to the aforementioned description of the boil-off gas compressor 20, the present invention provides the mixed refrigerant cooler 33 between the mixed refrigerant compressor 32 and the reliquefier 31. By providing, it is possible to lower the temperature of the mixed refrigerant.

The liquefied part 30 may include a gas-liquid separator 34. The gas-liquid separator 34 may receive the mixed refrigerant cooled by the mixed refrigerant cooler 33 to separate the gas-phase mixed refrigerant and the liquid mixed refrigerant. The gas-liquid separator 34 may be connected to the reliquefier 31 through a gaseous mixed refrigerant discharge line L31 and a liquid mixed refrigerant discharge line L32.

At this time, the gas-phase mixed refrigerant separated by the gas-liquid separator 34 is supplied to the reliquefier 31 through the gas-phase mixed refrigerant discharge line L31, and the first mixed refrigerant including the gas-phase mixed refrigerant in the reliquefier 31 The flow can flow. In addition, the liquid mixed refrigerant separated by the gas-liquid separator 34 may be joined to the second mixed refrigerant flow through the liquid mixed refrigerant discharge line L32. A liquid mixed refrigerant discharge valve 341 may be provided in the liquid mixed refrigerant discharge line L32, and a liquid mixed refrigerant flowing through the liquid mixed refrigerant discharge valve 341 The flow rate of the mixed refrigerant can be controlled.

That is, in the present invention, the compressed and cooled mixed refrigerant is separated into a gas phase and a liquid phase and then independently supplied to the reliquefier 31, thereby further improving the liquefaction efficiency of the boil-off gas.

Meanwhile, the gas-liquid separator 34 may be omitted from the liquefied part 30.

The mixed refrigerant pressure reducing valve 35 may reduce the pressure of the first mixed refrigerant flow exchanged with the boil-off gas in the reliquefier 31. The mixed refrigerant pressure reducing valve 35 may be a Joule-Thomson valve, and the temperature of the mixed refrigerant may be lowered through depressurization.

The mixed refrigerant pressure reducing valve 35 may reduce the pressure of the first mixed refrigerant flow and transfer it to the reliquefier 31. The pressure is reduced so that the second mixed refrigerant flow including the liquid mixed refrigerant may flow in the reliquefier 31.

The reliquefier 31 has at least three flow paths through which the compressed boil-off gas, the first mixed refrigerant flow, and the second mixed refrigerant flow flow as described above, and at this time, both the first mixed refrigerant flow and the second mixed refrigerant flow are compressed. It can be used for cooling the evaporated gas.

Alternatively, when considering that the second mixed refrigerant flow is lower than that of the first mixed refrigerant flow, the second mixed refrigerant flow cools the compressed boil-off gas, and may be utilized to lower the temperature of the first mixed refrigerant flow.

At this time, the liquid mixed refrigerant separated by the gas-liquid separator 34 joins the flow of the second mixed refrigerant flowing in the reliquefier 31, thereby more effectively cooling the boil-off gas.

The receiver 36 may temporarily store a mixed refrigerant to be supplied to the mixed refrigerant compressor 32. At this time, the receiver 36 may separate the gaseous mixed refrigerant and supply it to the mixed refrigerant compressor 32. In addition, the receiver 36 may prevent a pressure fluctuation of the mixed refrigerant to be supplied to the mixed refrigerant compressor 32, or may perform a role of supplementing the leaked mixed refrigerant.

The receiver 36 may receive a flow of the second mixed refrigerant discharged from the reliquefier 31 and temporarily store the second mixed refrigerant, and then separate the gaseous mixed refrigerant and supply it to the mixed refrigerant compressor 32.

A mixed refrigerant supplement line L12 may be provided from the boil-off gas compressor 20 to the receiver 36. The mixed refrigerant supplement line L12 may be branched from the boil-off gas compressor 20 downstream of the boil-off gas supply line L10.

The boil-off gas liquefaction line (L11) and the mixed refrigerant supplement line (L12) are branched from the boil-off gas supply line (L10), and at this time, the point where the boil-off gas liquefaction line (L11) is branched and the mixed refrigerant supplement line (L12) is branched. The points may be provided in series on the boil-off gas supply line L10. Specifically, the mixed refrigerant supplement line L12 may be branched downstream from a point at which the boil-off gas liquefaction line L11 is branched from the boil-off gas supply line L10.

The compressed boil-off gas may be supplied to the receiver 36 through the mixed refrigerant supplement line L12, and the boil-off gas supplied to the receiver 36 may be used to supplement the mixed refrigerant. The mixed refrigerant replenishment line L12 may be provided with a mixed refrigerant replenishment valve 23, and when replenishment of the mixed refrigerant is required, the mixed refrigerant replenishment valve 23 may be opened to supply compressed boil-off gas to the receiver 36. . That is, the mixed refrigerant can be replenished by receiving the boil-off gas from the liquefied gas storage tank 10, and thus the system can replenish the mixed refrigerant from the inside.

The mixed refrigerant in the liquefied part 30 circulates in the mixed refrigerant circulation line L30 to which the components are connected. Specifically, the mixed refrigerant is reliquefied through the receiver 36, the mixed refrigerant compressor 32, the mixed refrigerant cooler 33, the gas-liquid separator 34, the reliquefier 31, and the mixed refrigerant pressure reducing valve 35. After flowing back to ), it may be recovered to the receiver 36.

At this time, the gaseous mixed refrigerant separated by the gas-liquid separator 34 is supplied to the reliquefier 31 through the gaseous mixed refrigerant discharge line L31 to form a first mixed refrigerant flow, and the liquid phase separated by the gas-liquid separator 34 The mixed refrigerant may be joined to the flow of the second mixed refrigerant in the reliquefier 31 through the liquid mixed refrigerant discharge line L32.

The liquefaction unit 30 may include a mixed refrigerant recovery line L33. The mixed refrigerant recovery line L33 is branched between the mixed refrigerant compressor 32 and the reliquefier 31 of the mixed refrigerant circulation line L30 to recover a part of the compressed mixed refrigerant to the receiver 36. By recovering a part of the compressed mixed refrigerant to the receiver 36, the liquid mixed refrigerant is suppressed from remaining in the receiver 36, and the gas-phase mixed refrigerant can be effectively supplied to the mixed refrigerant compressor 32.

The mixed refrigerant recovery line (L33) is branched between the mixed refrigerant compressor (32) and the mixed refrigerant cooler (33) of the mixed refrigerant circulation line (L30), and is returned from the reliquefier (31) to the receiver (36). It may join the circulation line L30.

The mixed refrigerant compressed in the mixed refrigerant compressor 32 is relatively high pressure and high temperature than the mixed refrigerant temporarily stored in the receiver 36, and the mixed refrigerant before being cooled in the mixed refrigerant cooler 33 through the mixed refrigerant circulation line L30 The accumulation of the liquid mixed refrigerant in the receiver 36 can be further suppressed by recovering it by the receiver 36. By suppressing the accumulation of the liquid mixed refrigerant in the receiver 36, it is possible to prevent the composition of the mixed refrigerant from changing and stabilize the mixed refrigerant circulation line L30.

The mixed refrigerant recovered through the mixed refrigerant circulation line (L30) has a higher temperature than the liquid mixed refrigerant remaining in the receiver 36, and the relatively high temperature mixed refrigerant is recovered in the receiver 36. The liquid mixed refrigerant may be changed into a gaseous mixed refrigerant, and the inflow amount of the mixed refrigerant supplied to the mixed refrigerant compressor 32 may be reduced.

Through this, it is possible to stably operate the boil-off gas re-liquefaction system 1 to prevent the reduction in the re-liquefaction efficiency of the boil-off gas.

Meanwhile, the mixed refrigerant recovery line L33 in the liquefaction unit 30 may be omitted.

The liquefaction unit 30 may include a liquid mixed refrigerant supply line L34. A liquid mixed refrigerant supply line L34 may be provided from the receiver 36 to the reliquefier 31. The liquid mixed refrigerant supply line L34 may join the liquid mixed refrigerant separated in the receiver 36 to the flow of the second mixed refrigerant in the reliquefier 31.

By separating the liquid mixed refrigerant from the receiver 36 and supplying it to the reliquefier 31, accumulation of the liquid mixed refrigerant in the receiver 36 can be suppressed.

A gas sensor (not shown) may be provided on the mixed refrigerant circulation line L30, and the gas sensor may be a component analyzer capable of grasping a component of the mixed refrigerant circulating in the mixed refrigerant circulation line L30.

The liquefied part 30 basically has a mixed refrigerant circulation line L30 in the form of a closed loop, but the mixed refrigerant circulating in the mixed refrigerant circulation line L30 such as leakage of a small amount of mixed refrigerant while the liquefied part 30 is driven. A phenomenon in which the composition is changed may occur.

At this time, the component of the mixed refrigerant is identified using a gas sensor, etc., and when the composition of the mixed refrigerant is changed, the flow rate of supplying the liquid mixed refrigerant into the reliquefier 31 through the liquid mixed refrigerant supply line (L34) is adjusted, The composition of the mixed refrigerant can be kept constant. A liquid mixed refrigerant supply valve 361 may be provided in the liquid mixed refrigerant supply line L34, and a flow rate of the liquid mixed refrigerant supplied to the reliquefier 31 may be controlled.

The liquid mixed refrigerant separated in the gas-liquid separator 34 may be supplied to the second mixed refrigerant flow in the reliquefier 31 through the liquid mixed refrigerant discharge line L32, and at this time, the liquid mixed refrigerant connected to the receiver 36 The supply line L34 may be connected to the liquid mixed refrigerant discharge line L32. That is, the liquid mixed refrigerant separated in the gas-liquid separator 34 and the liquid mixed refrigerant separated in the receiver 36 may be combined to join the second mixed refrigerant flow in the reliquefier 31.

As described above, the liquid mixed refrigerant separated from the receiver 36 is joined to the flow to the second mixed refrigerant of the reliquefaction unit 31, thereby suppressing accumulation of the liquid mixed refrigerant in the receiver 36, and the composition of the mixed refrigerant. Can respond to change.

Meanwhile, the liquid mixed refrigerant supply line L34 in the liquefaction unit 30 may be omitted.

The boil-off gas pressure reducing valve 40 depressurizes the boil-off gas downstream of the reliquefier 31. The boil-off gas reducing valve 40 can reduce the temperature while reducing the high-pressure boil-off gas compressed by the boil-off gas compressor 20 to a low pressure, and the same/similar to the mixed refrigerant pressure reducing valve 35 described above- It could be a Thompson valve.

At least a portion of the boil-off gas may be liquefied by the re-liquefier 31 of the liquefaction unit 30, and in addition to this, it may be further liquefied while being reduced by the boil-off gas pressure reducing valve 40. At this time, the liquefied boil-off gas may be delivered to the boil-off gas gas-liquid separator (not shown) along the boil-off gas liquefaction line L11.

The boil-off gas gas-liquid separator separates the reduced-pressure boil-off gas by gas-liquid separation. The gas component separated in the boil-off gas-liquid separator may be flash gas, and may be discharged to the outside of the boil-off gas gas-liquid separator by a flash gas discharge line (not shown) connected to the boil-off gas-liquid separator. At this time, the flash gas discharged from the boil-off gas-liquid separator may be delivered to a separate consumer or may be supplied to the inside of the liquefied gas storage tank 10.

The liquid component separated from the boil-off gas-liquid separator can be returned to the liquefied gas storage tank 10 as reliquefied boil-off gas (LBOG), and the re-liquefied return line from the boil-off gas-liquid separator to the liquefied gas storage tank 10 ( Not shown) can be connected. At this time, the re-liquefied return line can spray re-liquefied boil-off gas from the top of the inside of the liquefied gas storage tank 10 in a spray method, which heat exchange with the re-liquefied boil-off gas generated in the liquefied gas storage tank 10 It is to liquefy while doing.

As described above, in this embodiment, when the boil-off gas is re-liquefied using the lubricating oil-free type mixed refrigerant compressor 32, the lubricating oil is prevented from being mixed into the mixed refrigerant, and the re-liquefaction efficiency of the boil-off gas can be improved.

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

2, the boil-off gas reliquefaction system 1 according to the second embodiment of the present invention includes a liquefied gas storage tank 10, a boil-off gas compressor 20, a liquefaction unit 30, and a boil-off gas pressure reducing valve. It includes (40).

Hereinafter, the description will be made mainly on points that the present embodiment is different from the previous embodiment, and portions omitted from the description will be replaced with the previous contents. It should be noted that this is the same for the embodiments described below.

In this embodiment, as in the previous embodiment, a mixed refrigerant supplement line L12 may be provided from the boil-off gas compressor 20 to the receiver 36. The mixed refrigerant supplement line L12 may be branched from the boil-off gas compressor 20 downstream of the boil-off gas supply line L10.

However, in this embodiment, unlike the previous embodiment, the mixed refrigerant supplement line (L12) is branched upstream from the point where the boil-off gas liquefaction line (L11) is branched on the boil-off gas supply line (L10), and is mixed in the receiver (36). Refrigerant replenishment can be easily performed.

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

3, the boil-off gas reliquefaction system 1 according to the third embodiment of the present invention may include a mixed refrigerant heat exchanger 37 and an boil-off gas recovery line L40 in the liquefaction unit 30 .

The liquefaction unit 30 includes a reliquefier 31, a mixed refrigerant compressor 32, a mixed refrigerant cooler 33, a mixed refrigerant heat exchanger 37, a gas-liquid separator 34, a mixed refrigerant pressure reducing valve 35, and a receiver. (36) may be included.

The mixed refrigerant heat exchanger 37 is provided between the mixed refrigerant cooler 33 and the gas-liquid separator 34, and recovers part of the boil-off gas supplied to the boil-off gas compressor 20 from the liquefied gas storage tank 10 Heat exchange with the mixed refrigerant cooled in the cooler 33 may be performed. The boil-off gas liquefaction efficiency in the reliquefier 31 can be improved by further cooling the mixed refrigerant by exchanging the boil-off gas and the mixed refrigerant before being compressed.

The mixed refrigerant heat exchanger 37 is provided on the boil-off gas recovery line L40, and the boil-off gas recovery line L40 is branched upstream of the boil-off gas compressor 20 of the boil-off gas supply line L10 to pass through the heat exchanger. Later, it returns to the boil-off gas supply line (L10).

The mixed refrigerant heat exchanger 37 has at least two flow paths through which the mixed refrigerant cooled by the mixed refrigerant cooler 33 and the boil-off gas recovered from the boil-off gas supply line L10 flow, and the liquefied gas storage tank 10 The mixed refrigerant may be further cooled by using the cold heat of the boil-off gas delivered from.

In this embodiment, the mixed refrigerant includes methane and ethane as main components, and propane and butane may or may not be included in small amounts. When a mixed refrigerant containing methane and ethane is used for reliquefaction of the evaporation gas, the initial cooling of the mixed refrigerant is difficult due to the low boiling point of methane and ethane, which may cause problems during the initial operation of the reliquefaction system. In the embodiment, this may be solved by cooling the mixed refrigerant using the cold heat of the boil-off gas in the mixed refrigerant heat exchanger 37.

In this way, by further cooling the mixed refrigerant using the cooling heat of the boil-off gas, the efficiency of re-liquefaction of the boil-off gas can be improved.

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

4, the boil-off gas reliquefaction system 1 according to the fourth embodiment of the present invention includes a liquefied gas storage tank 10, a boil-off gas compressor 20, a boil-off gas heat exchanger 60, and a liquefaction unit. (30), and a boil-off gas pressure reducing valve (40).

The boil-off gas heat exchanger 60 may cool the boil-off gas compressed by the boil-off gas compressor 20 by using cold heat of boil-off gas supplied from the liquefied gas storage tank 10. The boil-off gas cooled in the boil-off gas heat exchanger 60 may be supplied to the re-liquefier 31. By cooling the compressed boil-off gas in the boil-off gas heat exchanger 60 and transferring the compressed boil-off gas to the re-liquefier 31, the load of the re-liquefier 31 can be reduced as described later.

In addition, the boil-off gas supplied from the liquefied gas storage tank 10 through the boil-off gas heat exchanger 60 can be compressed by the boil-off gas compressor 20 and heated by heat exchange with the relatively high-temperature boil-off gas. By replacing the cryogenic compressor used as the compressor 20 with a room temperature compressor, it is possible to reduce the equipment cost of the reliquefaction system.

The liquefaction unit 30 may include a reliquefier 31, a mixed refrigerant compressor 32, a mixed refrigerant cooler 33, a mixed refrigerant pressure reducing valve 35, and a receiver 36.

The reliquefier 31 may partially heat-exchange the flow of the first mixed refrigerant and the flow of the second mixed refrigerant with the boil-off gas. Specifically, the boil-off gas heat-exchanged in the boil-off gas heat exchanger 60 may be introduced into the re-liquefier 31 spaced apart from one end of the re-liquefier 31 from which the second mixed refrigerant flow is discharged.

That is, the reliquefier 31 is a region in which the first mixed refrigerant flow and the second mixed refrigerant flow exchange heat with the boil-off gas, and only the first mixed refrigerant flow and the second mixed refrigerant flow exchange heat without heat exchange with the boil-off gas. It can include areas.

Since the compressed boil-off gas is cooled through the boil-off gas heat exchanger 60 before being supplied to the reliquefier 31, the boil-off gas in the re-liquefier 31 partially flows with the first mixed refrigerant flow and the second mixed refrigerant flow. Even in the case of heat exchange, re-liquefaction of the boil-off gas can be effectively performed.

As the boil-off gas is partially heat-exchanged with the first mixed refrigerant flow and the second mixed refrigerant flow in the reliquefier 31, the load of the re-liquefier 31 is reduced and the amount of mixed refrigerant supplied to the re-liquefier 31 Can be reduced. Through this, the specifications and sizes of the receiver 36, the mixed refrigerant compressor 32, the mixed refrigerant cooler 33, and the mixed refrigerant pressure reducing valve 35 are reduced, thereby simplifying the liquefaction unit 30. I can.

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, those of ordinary skill in the art It would be clear that the transformation or improvement is possible.

It goes without saying that the present invention is not limited to the above-described embodiments, and may include a combination of the above embodiments or a combination of at least one of the above embodiments and a known technology as another embodiment.

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: boil-off gas reliquefaction system 10: liquefied gas storage tank
20: boil-off gas compressor 30: liquefaction unit
31: reliquefier 32: mixed refrigerant compressor
33: mixed refrigerant cooler 34: gas-liquid separator
35: mixed refrigerant pressure reducing valve 36: receiver
37: mixed refrigerant heat exchanger 40: boil-off gas pressure reducing valve
50: vaporizer 60: boil-off gas heat exchanger
100: customer L10: boil-off gas supply line
L11: boil-off gas liquefaction line L12: mixed refrigerant supplement line
L13: boil-off gas bypass line L20: liquefied gas supply line
L30: mixed refrigerant circulation line L31: gaseous mixed refrigerant discharge line
L32: liquid mixed refrigerant discharge line L33: mixed refrigerant recovery line
L34: liquid mixed refrigerant supply line L40: boil-off gas recovery line

Claims (7)

It includes a liquefied part for liquefying the boil-off gas using a mixed refrigerant,
The liquefied part,
A reliquefier for liquefying the boil-off gas by heat exchange with the mixed refrigerant;
A lubricant-free type mixed refrigerant compressor that compresses the mixed refrigerant and does not contain lubricant when the mixed refrigerant is compressed;
A mixed refrigerant cooler for cooling the compressed mixed refrigerant;
A gas-liquid separator for gas-liquid separating the cooled mixed refrigerant and supplying the gas-phase mixed refrigerant to the reliquefier;
A mixed refrigerant pressure reducing valve for decompressing the gaseous mixed refrigerant separated in the gas-liquid separator at a downstream side of the reliquefier to re-introduce it into the reliquefier;
A receiver temporarily storing the mixed refrigerant to be supplied to the mixed refrigerant compressor; And
The receiver, the mixed refrigerant compressor, the mixed refrigerant cooler, the gas-liquid separator, the reliquefier, and the mixed refrigerant pressure reducing valve are provided, and a mixed refrigerant circulation line for circulating the mixed refrigerant,
The reliquefier includes a first mixed refrigerant flow through which the mixed refrigerant supplied from the mixed refrigerant cooler flows, a second mixed refrigerant flow re-introduced through the mixed refrigerant pressure reducing valve, and a boil-off gas flow,
The liquefied part,
A liquid mixed refrigerant discharge line for allowing the liquid mixed refrigerant separated in the gas-liquid separator to merge onto the second mixed refrigerant flow of the reliquefier; And
In order to suppress the accumulation of liquid mixed refrigerant in the receiver, liquid mixed refrigerant connected to the liquid mixed refrigerant discharge line from the receiver and separated from the receiver into a second mixed refrigerant flow of the reliquefier Boil-off gas reliquefaction system, characterized in that it further comprises a refrigerant supply line. delete The method of claim 1,
A boil-off gas compressor for compressing the boil-off gas supplied from the liquefied gas storage tank and supplying it to the re-liquefier;
A boil-off gas supply line for supplying boil-off gas compressed by the boil-off gas compressor to a customer; And
The boil-off gas reliquefaction system further comprising a mixed refrigerant supplement line for transferring the boil-off gas compressed by the boil-off gas compressor to the receiver. The method of claim 3,
Further comprising a boil-off gas liquefaction line for transferring the boil-off gas compressed by the boil-off gas compressor to the re-liquefier,
The boil-off gas reliquefaction system, characterized in that the branching point of the boil-off gas liquefaction line and the branching point of the mixed refrigerant supplement line are provided in series on the boil-off gas supply line. The method of claim 1, wherein the liquefied part,
And a mixed refrigerant heat exchanger provided downstream of the mixed refrigerant compressor and cooling the mixed refrigerant using boil-off gas supplied from the liquefied gas storage tank. The method of claim 5, wherein the mixed refrigerant heat exchanger,
Boiled gas reliquefaction system, characterized in that provided between the mixed refrigerant cooler and the reliquefier. A vessel comprising the boil-off gas reliquefaction system of any one of claims 1, 3 to 6.

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