KR20200067717A - liquefaction system of boil-off gas and ship having the same - Google Patents

Abstract

The present invention relates to a reliquefying system for evaporation gas and a ship comprising the same. The reliquefying system for evaporation gas comprises: an evaporation gas compressor which compresses evaporation gas supplied from a liquefied gas storage tank; an evaporation gas heat exchanger which makes the evaporation gas compressed by the evaporation gas compressor exchange heat with the evaporation gas supplied from the liquefied gas storage tank; and a liquefying unit which liquefies the evaporation gas having exchanged heat by using a mixed refrigerant. The liquefying unit includes: a reliquefier which makes the evaporation gas exchange heat with the mixed refrigerant to liquefy the evaporation gas; a lubricant-free mixed refrigerant compressor which compresses the mixed refrigerant and prevents the lubricant from being introduced and mixed when compressing the mixed refrigerant; a mixed refrigerant cooler which cools the compressed mixed refrigerant to supply the mixed refrigerant to the reliquefier; and a mixed refrigerant pressure-reducing valve which reduces the pressure of the mixed refrigerant discharged from the reliquefier on a downstream of the reliquefier, and reintroduces the mixed refrigerant into the reliquefier. The reliquefier has a first mixed refrigerant flow, through which the mixed refrigerant supplied from the mixed refrigerant cooler flows, a second mixed refrigerant flow which is reintroduced by passing through the mixed refrigerant pressure-reducing valve, and an evaporation gas flow. The first mixed refrigerant flow and the second mixed refrigerant flow partially exchange heat with the evaporation gas. The reliquefying system for evaporation gas and the ship comprising the same can improve liquefying efficiency and prevent a lubricant from being mixed with a mixed refrigerant.

Description

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

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

According to recent technology development, liquefied gas such as Liquefied Natural Gas and Liquefied Petroleum Gas has been widely used to replace gasoline or diesel.

Liquefied natural gas is liquefied by cooling the methane obtained by refining natural gas collected from a gas field. It is a colorless and transparent liquid with little pollutants and high heat, making it an excellent fuel. On the other hand, liquefied petroleum gas is a fuel made of liquid by compressing gas mainly composed of propane (C3H8) and butane (C4H10), which come out with oil from the oil field at room temperature. Liquefied petroleum gas, like liquefied natural gas, is colorless and odorless, and is widely used as fuel for household, business, industrial, and automobile applications.

The liquefied gas is stored in a liquefied gas storage tank installed on the ground or in a liquefied gas storage tank provided in a ship that is a transportation means for navigating the ocean. The liquefied natural gas is liquefied to a volume of 1/600. It is reduced, and liquefied petroleum gas has the advantage of high storage efficiency because it is reduced to 1/260 of propane and 1/230 of butane by liquefaction. 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 to generate boil-off gas (BOG) as heat permeation into the tank occurs. In order to eliminate the risk of tank damage by lowering, the evaporated gas was simply discharged to the outside.) However, it tried to solve the problem by causing consumption, but this is causing environmental pollution and waste of resources.

The present invention was created to solve the problems of the prior art as described above, and the object of the present invention is to improve the liquefaction efficiency in the process of re-liquefying the evaporation gas using a mixed refrigerant, and using a mixed refrigerant compressor that does not use lubricant. It is to provide an evaporation gas reliquefaction system and a ship including the same, which can prevent the lubricating oil from being mixed with the mixed refrigerant.

An evaporation gas reliquefaction system according to an embodiment of the present invention, an evaporation gas compressor for compressing the evaporation gas supplied from the liquefied gas storage tank; An evaporation gas heat exchanger for exchanging the evaporation gas compressed from the evaporation gas compressor and the evaporation gas supplied from the liquefied gas storage tank; And a liquefaction unit for liquefying the evaporated gas heat-exchanged using a mixed refrigerant, and the liquefaction unit comprising: a re-liquefier for liquefying the evaporated gas by exchanging it with the mixed refrigerant; A lubricating oil-free type refrigerant mixture that compresses the mixed refrigerant and does not mix lubricant when the mixed refrigerant is compressed; A mixed refrigerant cooler that cools the compressed mixed refrigerant and supplies it to a re-liquefier; And a mixed refrigerant decompression valve for reducing the mixed refrigerant discharged from the re-liquefier downstream of the re-liquefier and re-injecting it into the re-liquefier, wherein the re-liquefier comprises: 1, the mixed refrigerant flow, the second mixed refrigerant flow and the evaporated gas flow re-introduced through the mixed refrigerant pressure reducing valve, and the first mixed refrigerant flow and the second mixed refrigerant flow partially exchange heat with the evaporated gas It is characterized by.

Specifically, the boil-off gas exchanged in the boil-off gas heat exchanger may be introduced into the re-liquefier spaced apart from one end of the re-liquefier through which the second mixed refrigerant stream is discharged.

Specifically, the liquefaction unit, a receiver for temporarily storing the mixed refrigerant to be supplied to the mixed refrigerant compressor; And a mixed refrigerant circulation line in which the receiver, the mixed refrigerant compressor, the mixed refrigerant cooler, the re-liquefier, and the mixed refrigerant pressure reducing valve are provided and the mixed refrigerant circulates.

Specifically, the boil-off gas re-liquefaction system, the boil-off gas supply line for supplying the boil-off gas compressed by the boil-off gas compressor to the customer; And it may further include a mixed refrigerant supplementation line for delivering the compressed boil-off gas from the boil-off gas compressor to the receiver.

Specifically, the evaporation gas re-liquefaction system further includes an evaporation gas liquefaction line that delivers the compressed evaporation gas from the evaporation gas compressor to the re-liquefaction, and supplements the point where the evaporation gas liquefaction line branches and the mixed refrigerant. The point at which the line branches off may be provided in series on the boil-off gas supply line.

Specifically, the liquefaction unit may further include a mixed refrigerant heat exchanger that is provided downstream of the mixed refrigerant compressor and cools the mixed refrigerant using the evaporated gas supplied from the liquefied gas storage tank.

Specifically, the mixed refrigerant heat exchanger may be provided between the mixed refrigerant cooler and the re-liquefier.

The ship according to an embodiment of the present invention is characterized by including the evaporation gas reliquefaction system.

The evaporation gas reliquefaction system and the ship according to the present invention re-liquefy the evaporation gas generated in the liquefied gas storage tank with a mixed refrigerant, and prevent re-liquefaction of lubricating oil into the mixed refrigerant.

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

The 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 addition, it should be noted that, in addition to reference numerals to the components of each drawing in the present specification, the same components have the same numbers as possible even though they are displayed on different drawings. In addition, in describing the present invention, when it is determined that detailed descriptions of related well-known technologies may unnecessarily obscure the subject matter of the present invention, detailed descriptions thereof will be omitted.

Hereinafter, liquefied gas may be used as a meaning to encompass all gas fuels generally stored in a liquid state, such as LNG or LPG, ethylene, ammonia, etc., and may be expressed as liquefied gas for convenience even when not in a liquid state by heating or pressurization. Can be. Evaporative gas can be applied as well. In addition, for convenience, LNG may be used to encompass not only NG (Natural Gas) in a liquid state, but also NG in a supercritical state, and evaporation gas may be used as a meaning including not only gaseous evaporation gas but also liquefied evaporation gas. have.

In addition, in the following, the decompression may be a state generated through expansion, and conversely, the decompression may be a state generated by expansion, so that the decompression and expansion may be used interchangeably.

Hereinafter, the evaporation gas reliquefaction system of the present invention will be described, and the present invention includes an evaporation gas reliquefaction system and a ship having the same. At this time, the ship may be a general merchant ship that loads cargo other than liquefied gas in addition to the liquefied gas carrier, and furthermore, it is noted that the marine vessels such as FSRU and FLNG, which are not merchant ships, are all expressions.

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

Hereinafter, the evaporation 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 an evaporation gas reliquefaction system according to a first embodiment of the present invention.

Referring to Figure 1, the boil-off gas re-liquefaction system 1 according to the first embodiment of the present invention, the liquefied gas storage tank 10, the boil-off gas compressor 20, the liquefaction section 30, the boil-off gas pressure reducing valve Include 40.

The liquefied gas storage tank 10 stores liquefied gas to be supplied to the consumer 100. Here, the demand source 100 may be a ship 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 demand source 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, a DFDE engine having a required pressure of about 10 bar or the like. Alternatively, the demand source 100 may be city gas or the like, and may be an engine (or turbine) for various purposes provided on the 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 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 stand-alone type, a membrane type, or the like, and the liquefied gas may be stored in a liquid state using various insulating structures, and the evaporation gas generated in the liquefied gas storage tank 10 will be described later. To be processed by the evaporative gas compressor 20 or the like.

Since the liquefied gas is stored in the liquefied gas storage tank 10, the liquefied gas storage tank 10 continuously generates an evaporated gas in which the liquefied gas naturally evaporates. At this time, since the internal pressure of the liquefied gas storage tank 10 may be excessive if the evaporated gas is not taken out, the present embodiment can return the liquefied gas stored in the liquefied gas storage tank 10 by liquefying (by reducing the volume). Therefore, the internal pressure of the liquefied gas storage tank 10 is maintained at an appropriate level.

The evaporation gas compressor 20 compresses the evaporation gas generated in the liquefied gas storage tank 10. The evaporative gas compressor 20 is provided in multiple stages, and may be, for example, 5 stages, and the demand source 100 is 5 stages downstream of the evaporation gas compressor 20 or 2 stages downstream of the evaporation gas compressor 20, depending on the required pressure. It can be connected to the back. In addition, an intermediate cooler (not shown) is provided downstream of each compression stage of the evaporation gas compressor 20 to cool the evaporation gas heated by the compression heat.

The liquefied gas storage tank 10 may be provided with an evaporation gas supply line L10 from the customer to the customer 100, and the evaporation gas compressed by the evaporation gas compressor 20 may flow in the evaporation gas supply line L10. have. At this time, the boil-off gas supply line (L10) is provided with a boil-off gas supply valve (21), it is possible to adjust the supply amount of boil-off gas supplied to the consumer (100).

However, in case the flow rate of the evaporation gas does not reach the desired flow rate at the demand source 100, the present invention provides a liquefied gas connection from the liquefied gas storage tank 10 to the demand destination 100 or the evaporation 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 of the liquefied gas storage tank 10, and may be a plurality according to the required pressure of the customer 100.

An liquefied gas liquefaction line L11 may be provided from the liquefied gas storage tank 10 to the liquefied portion 30 to be described later. The boil-off gas liquefaction line (L11) is branched from the boil-off gas supply line (L10), it is possible to connect the liquefaction unit 30 from the liquefied gas storage tank (10). At this time, the boil-off gas compressor 20 may be provided at a point where the boil-off gas liquefaction line L11 branches from the boil-off gas supply line L10, or upstream of the point.

In addition, an evaporation gas branch valve 22 may be provided downstream of the evaporation gas compressor 20 on the evaporation gas liquefaction line L11, and the reliquefaction unit 31 of the liquefaction unit 30 may be provided through the evaporation gas branch valve 22. ) Can control the flow rate of compressed boil-off gas.

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

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

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

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

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 evaporative gas compressor 20 (required pressure of the demander 100).

The mixed refrigerant compressor 32 is a type in which the lubricant is not mixed with the mixed refrigerant when compressing the mixed refrigerant, and for example, may be a lubricant-free oil type that does not use a lubricant for sealing and lubrication. That is, according to the present invention, by using the lubricating oil-free type mixed refrigerant compressor 32, even when compressing the mixed refrigerant, mixing of the lubricating oil into the mixed refrigerant can be prevented. Accordingly, the present invention does not need to be provided with a separate device for separating the lubricating oil mixed with the mixed refrigerant, unlike the case of using a mixed refrigerant compressor using lubricating oil, so that the reliquefaction system can be simplified.

In addition, according to the present invention, by using the lubricant-free type refrigerant mixture (32), when the refrigerant mixture mixed with the lubricant exchanges heat with the evaporation gas in the reliquefier 31, the lubricant is solidified due to the cold heat of the evaporation gas. It is possible to prevent the heat exchange efficiency of the reliquefaction 31 from being lowered or damage from occurring.

The mixed refrigerant cooler 33 is provided downstream of the mixed refrigerant compressor 32 and cools the compressed mixed refrigerant. Since the mixed refrigerant may be heated under compression heat during compression similarly to that described in the evaporative gas compressor 20, the present invention provides a mixed refrigerant cooler 33 between the mixed refrigerant compressor 32 and the re-liquefier 31. By providing, it is possible to lower the temperature of the mixed refrigerant.

The liquefaction unit 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 and separate the mixed refrigerant in the gas phase from the mixed refrigerant in the liquid phase. The gas-liquid separator 34 may be connected to the re-liquefier 31 through a gas phase mixed refrigerant discharge line L31 and a liquid mixed refrigerant discharge line L32.

At this time, the mixed refrigerant in the gas phase separated from the gas-liquid separator 34 is supplied to the re-liquefier 31 through the gas-phase mixed refrigerant discharge line L31, and the re-liquefier 31 includes a first mixed refrigerant containing a mixed refrigerant in the gas phase. The flow can flow. In addition, the mixed refrigerant of the liquid separated from 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 the liquid mixed refrigerant flowing into the second mixed refrigerant flow through the reliquefier 31 through the liquid mixed refrigerant discharge valve 341 may be provided. The flow rate of the mixed refrigerant can be controlled.

That is, according to the present invention, after the compressed and cooled mixed refrigerant is separated into a gas phase and a liquid phase, the liquefaction efficiency of the evaporated gas can be further improved by independently supplying it to the reliquefaction unit 31.

Meanwhile, the gas-liquid separator 34 in the liquefaction unit 30 may be omitted.

The mixed refrigerant decompression valve 35 can depressurize the first mixed refrigerant flow heat exchanged with the evaporation gas in the reliquefier 31. The mixed refrigerant pressure-reducing valve 35 may be a Joule-Thomson valve, and may reduce the temperature of the mixed refrigerant through reduced pressure.

The mixed refrigerant decompression valve 35 may depressurize the first mixed refrigerant flow and deliver it to the re-liquefier 31. The second mixed refrigerant stream including the mixed refrigerant in a liquid state under reduced pressure may flow in the reliquefaction unit 31.

The re-liquefier 31 has at least three flow paths through which the compressed evaporation gas, the first mixed refrigerant flow, and the second mixed refrigerant flow flow as described above, wherein both the first mixed refrigerant flow and the second mixed refrigerant flow are compressed. It can be used to cool the evaporated gas.

Alternatively, considering that the second mixed refrigerant flow is lower than the first mixed refrigerant flow, the second mixed refrigerant flow cools the compressed evaporation gas, and may be used to lower the temperature of the first mixed refrigerant flow.

At this time, the mixed refrigerant of the liquid separated from the gas-liquid separator 34 is joined to the second mixed refrigerant flow flowing in the re-liquefier 31, so that the evaporation gas can be cooled more effectively.

The receiver 36 may temporarily store the mixed refrigerant to be supplied to the mixed refrigerant compressor 32. At this time, the receiver 36 may separate the mixed refrigerant in the gas phase and supply it to the mixed refrigerant compressor 32. In addition, the receiver 36 may prevent pressure fluctuations of the mixed refrigerant to be supplied to the mixed refrigerant compressor 32, or may also serve to supplement the leaked mixed refrigerant.

The receiver 36 may temporarily store the second mixed refrigerant discharged from the re-liquefier 31 after receiving the flow, and then separate the mixed refrigerant in the gas phase and supply it to the mixed refrigerant compressor 32.

A mixed refrigerant replenishment line (L12) may be provided from the boil-off gas compressor (20) to the receiver (36). The mixed refrigerant replenishment line L12 may be branched downstream of the evaporative gas compressor 20 on the evaporated gas supply line L10.

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

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

The mixed refrigerant in the liquefaction unit 30 circulates in the mixed refrigerant circulation line (L30) to which the respective components are connected. Specifically, the mixed refrigerant is a re-liquefier (31) through a receiver (36), a mixed refrigerant compressor (32), a mixed refrigerant cooler (33), a gas-liquid separator (34), a re-liquefier (31), and a mixed refrigerant pressure reducing valve (35). ), and then recovered by the receiver 36.

At this time, the mixed refrigerant of the gas phase separated from the gas-liquid separator 34 is supplied to the re-liquefier 31 through the gas-phase mixed refrigerant discharge line (L31) to form a first mixed refrigerant flow, and the liquid phase separated from the gas-liquid separator 34 The mixed refrigerant may be joined to the second mixed refrigerant flow in the re-liquefier 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 re-liquefier (31) of the mixed refrigerant circulation line (L30), and can recover a portion of the compressed mixed refrigerant to the receiver (36). By recovering a portion of the compressed mixed refrigerant to the receiver 36, it is possible to suppress the residual of mixed liquid refrigerant in the receiver 36 to effectively supply the mixed refrigerant in the gas phase 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 the mixed refrigerant returned to the receiver (36) from the reliquefaction unit (31). It is possible to 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 mixed refrigerant before being cooled in the mixed refrigerant cooler 33 through the mixed refrigerant circulation line L30. By collecting to the receiver 36, it is possible to further suppress the accumulation of the mixed refrigerant in the liquid in the receiver 36. By suppressing the accumulation of the mixed refrigerant in the liquid in the receiver 36, it is possible to prevent the composition of the mixed refrigerant is changed 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 mixed refrigerant of the liquid remaining in the receiver 36, and the mixed refrigerant having a relatively high temperature relative to the receiver 36 is recovered in the receiver 36. It can be solved that the mixed refrigerant in the liquid phase can be changed into a mixed refrigerant in the gas phase, and the inflow amount of the mixed refrigerant supplied to the mixed refrigerant compressor 32 is reduced.

Through this, the evaporation gas reliquefaction system 1 can be stably operated to prevent the reliquefaction efficiency of the evaporation gas from falling.

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

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 re-liquefier 31. The liquid mixed refrigerant supply line L34 may join the liquid mixed refrigerant separated from the receiver 36 into the second mixed refrigerant flow in the reliquefier 31.

By separating the liquid mixed refrigerant from the receiver 36 and supplying it to the reliquefaction unit 31, the 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 determining the components of the mixed refrigerant circulating in the mixed refrigerant circulation line L30.

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

At this time, by using a gas sensor or the like to identify the components of the mixed refrigerant and when the composition of the mixed refrigerant is changed, the flow rate of supplying the mixed refrigerant of the liquid into the re-liquefier 31 is adjusted through the liquid mixed refrigerant supply line L34, 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 the flow rate of the mixed refrigerant of the liquid supplied to the reliquefier 31 may be controlled.

The mixed refrigerant of the liquid separated from the gas-liquid separator 34 may be supplied to the second mixed refrigerant flow in the re-liquefier 31 through the liquid mixed refrigerant discharge line L32, wherein 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 mixed refrigerant of the liquid separated from the gas-liquid separator 34 and the mixed refrigerant of the liquid separated from the receiver 36 may be combined to join the second mixed refrigerant flow in the re-liquefier 31.

By mixing the liquid mixed refrigerant separated from the receiver 36 in the flow into the second mixed refrigerant of the reliquefaction unit 31, the accumulation of liquid mixed refrigerant in the receiver 36 is suppressed, and the composition of the mixed refrigerant is formed. You can respond to change.

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

The evaporation gas decompression valve 40 depressurizes the evaporation gas downstream of the reliquefier 31. The boil-off gas decompression valve 40 may drop the temperature while decompressing 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 decompression valve 35 described above- It can be a Thompson valve.

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

The vaporized gas-liquid separator gas-separates the decompressed vaporized gas. The gas component separated from the vaporized gas-liquid separator may be flash gas, and may be discharged to the outside of the vaporized gas-liquid separator by a flash gas discharge line (not shown) connected to the vaporized gas-liquid separator. At this time, the flash gas discharged from the vapor-liquid gas-liquid separator may be delivered to a separate consumer or supplied to the interior of the liquefied gas storage tank 10.

The liquid component separated from the vaporized gas-liquid separator may be returned to the liquefied gas storage tank 10 as re-liquefied vaporized gas (LBOG), and the re-liquefied return line from the vaporized gas-liquid separator to the liquefied gas storage tank 10 ( May be connected). At this time, the re-liquefaction return line may spray the re-liquefied evaporation gas from the top of the inside of the liquefied gas storage tank 10, which is a heat exchange with the re-liquefied evaporation gas generated in the liquefied gas storage tank 10. This is to make it liquefy.

As described above, the present embodiment can prevent the mixing of the lubricating oil into the mixed refrigerant when the liquefied gas is re-liquefied using the lubricating oil-free type mixed refrigerant compressor 32, and improve the efficiency of re-liquefying the evaporated gas.

2 is a conceptual diagram of an evaporation gas reliquefaction system according to a second embodiment of the present invention.

Referring to Figure 2, the boil-off gas re-liquefaction system 1 according to the second embodiment of the present invention, the liquefied gas storage tank 10, the boil-off gas compressor 20, the liquefaction section 30, the boil-off gas pressure reducing valve Include 40.

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. It is noted that this also applies to the examples described below.

In the present embodiment, as in the previous embodiment, a mixed refrigerant replenishment line L12 from the evaporative gas compressor 20 to the receiver 36 may be provided. The mixed refrigerant replenishment line L12 may be branched downstream of the evaporative gas compressor 20 on the evaporated gas supply line L10.

However, in the present embodiment, unlike the previous embodiment, the mixed refrigerant supplementary line L12 is branched upstream from the point at which the liquefied gas liquefaction line L11 branches on the evaporated gas supply line L10, and mixed in the receiver 36 Refrigerant replenishment can be easily performed.

3 is a conceptual diagram of an evaporation gas reliquefaction system according to a third embodiment of the present invention.

Referring to FIG. 3, the evaporation gas reliquefaction system 1 according to the third embodiment of the present invention may include a mixed refrigerant heat exchanger 37 and an evaporation gas recovery line L40 in the liquefaction section 30. .

Liquefaction unit 30, re-liquefier 31, mixed refrigerant compressor 32, mixed refrigerant cooler 33, mixed refrigerant heat exchanger 37, gas-liquid separator 34, mixed refrigerant pressure reducing valve 35, receiver (36).

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 evaporated gas supplied from the liquefied gas storage tank (10) to the evaporated gas compressor (20) and mixed refrigerant. It is possible to exchange heat with the mixed refrigerant cooled in the cooler (33). By heat-exchanging the mixed refrigerant with the evaporated gas before compression, the mixed refrigerant is further cooled, so that the efficiency of liquefaction of the evaporated gas in the reliquefier 31 can be improved.

The mixed refrigerant heat exchanger 37 is provided on the evaporation gas recovery line L40, and the evaporation gas recovery line L40 is branched upstream of the evaporation gas compressor 20 of the evaporation gas supply line L10 and passed through a heat exchanger. After that, it returns to the evaporation gas supply line (L10).

The mixed refrigerant heat exchanger (37) has at least two flow paths through which mixed refrigerant cooled in the mixed refrigerant cooler (33) and evaporated gas recovered from the evaporated 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 evaporation gas delivered from.

In this embodiment, the mixed refrigerant contains methane and ethane as main components, and propane and butane may or may not be included in a small amount. When a mixed refrigerant containing methane and ethane as the main components is used for re-liquefaction of the evaporation gas, the boiling point of methane and ethane is low, making initial cooling of the mixed refrigerant difficult, which may cause problems during the initial operation of the re-liquefaction system. In an embodiment, this can be solved by cooling the mixed refrigerant using the cold heat of the evaporated gas in the mixed refrigerant heat exchanger (37).

In this way, the cooling of the mixed refrigerant is further cooled using the cold heat of the evaporated gas, whereby the reliquefaction efficiency of the evaporated gas can be improved.

4 is a conceptual diagram of an evaporation gas reliquefaction system according to a fourth embodiment of the present invention.

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

The boil-off gas heat exchanger 60 may cool the boil-off gas compressed in the boil-off gas compressor 20 by using the cold heat of the 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 it 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 heated by being compressed by the boil-off gas compressor 20 and heat-exchanged with a relatively high-temperature boil-off gas. The cryogenic compressor used as the compressor 20 can be replaced with a normal temperature compressor to reduce the equipment cost of the reliquefaction system.

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

The reliquefaction unit 31 may partially exchange heat between the first mixed refrigerant flow and the second mixed refrigerant flow with the evaporation gas. Specifically, the boil-off gas 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 through which the second mixed refrigerant stream is discharged.

That is, the re-liquefier 31, the first mixed refrigerant flow and the second mixed refrigerant flow heat exchange region with the evaporation gas, and only the first mixed refrigerant flow and the second mixed refrigerant flow to heat exchange without evaporation gas exchange It may include a region.

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

As the evaporation gas in the re-liquefier 31 partially exchanges heat with the first mixed refrigerant flow and the second mixed refrigerant flow, the load of the re-liquefier 31 is reduced and the amount of mixed refrigerant supplied to the re-liquefier 31 is reduced. Can be reduced. Through this, specifications and sizes of the receiver 36 passed through the mixed refrigerant, the mixed refrigerant compressor 32, the mixed refrigerant cooler 33, and the mixed refrigerant pressure reducing valve 35 are reduced to simplify the liquefaction unit 30. You can.

The present invention has been described in detail through specific examples, but this is for specifically describing the present invention, and the present invention is not limited to this, and by a person skilled in the art within the technical spirit of the present invention. It will be apparent that the modification or improvement is possible.

The present invention is not limited to the above-described embodiments, and it is needless to say that a combination of the above embodiments or a combination of at least one of the above embodiments and a known technology may be included as another embodiment.

All of the simple modifications and variations of the present invention belong to the scope of the present invention, and the specific protection scope of the present invention will become apparent by the appended claims.

1: Boil-off gas re-liquefaction system 10: Liquefied gas storage tank
20: evaporative gas compressor 30: liquefaction section
31: re-liquefier 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: evaporative gas pressure reducing valve
50: vaporizer 60: evaporative gas heat exchanger
100: Customer L10: Evaporation gas supply line
L11: Evaporation gas liquefaction line L12: Mixed refrigerant supplementation line
L13: Evaporation gas bypass line L20: Liquefied gas supply line
L30: Mixed refrigerant circulation line L31: Gas mixture refrigerant discharge line
L32: Liquid mixed refrigerant discharge line L33: Mixed refrigerant recovery line
L34: Liquid mixed refrigerant supply line L40: Evaporative gas recovery line

Claims (8)

A boil-off gas compressor that compresses boil-off gas supplied from a liquefied gas storage tank;
An evaporation gas heat exchanger for exchanging the evaporation gas compressed from the evaporation gas compressor and the evaporation gas supplied from the liquefied gas storage tank; And
It includes a liquefaction unit for liquefying the boil-off gas heat-exchanged using a mixed refrigerant,
The liquefaction unit,
A re-liquefaction unit that liquefies the evaporated gas by heat exchange with a mixed refrigerant;
A lubricating oil-free type refrigerant mixture that compresses the mixed refrigerant and does not mix lubricant when the mixed refrigerant is compressed;
A mixed refrigerant cooler that cools the compressed mixed refrigerant and supplies it to a re-liquefier; And
And a mixed refrigerant decompression valve for depressurizing the mixed refrigerant discharged from the re-liquefier downstream of the re-liquefier and re-injecting it into the re-liquefier,
The reliquefaction machine,
A first mixed refrigerant flow through which the mixed refrigerant supplied from the mixed refrigerant cooler flows, a second mixed refrigerant flow re-inflowed through the mixed refrigerant pressure reducing valve, and an evaporation gas flow is provided,
The first mixed refrigerant flow and the second mixed refrigerant flow is an evaporation gas re-liquefaction system, characterized in that to partially exchange heat with the evaporation gas. According to claim 1, The boil-off gas heat exchanged in the boil-off gas heat exchanger,
An evaporation gas reliquefaction system, characterized in that a second mixed refrigerant flow is introduced into the reliquefier spaced apart from one end of the reliquefier. According to claim 1, wherein the liquefaction unit,
A receiver for 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 re-liquefier, and the mixed refrigerant pressure reducing valve is provided and further comprising a mixed refrigerant circulation line to circulate the mixed refrigerant evaporated gas re-liquefaction system, characterized in that . The method of claim 3,
A boil-off gas supply line that supplies boil-off gas compressed by the boil-off gas compressor to a consumer; And
An evaporation gas reliquefaction system further comprising a mixed refrigerant replenishment line that delivers the compressed evaporation gas from the evaporation gas compressor to the receiver. The method of claim 4,
Further comprising a boil-off gas liquefaction line for transferring the boil-off gas compressed in the boil-off gas compressor to the re-liquefaction,
The point at which the liquefied gas liquefaction line is branched and the point at which the mixed refrigerant replenishment line is branched are provided in series on the liquefied gas supply line. According to claim 1, wherein the liquefaction unit,
An evaporation gas reliquefaction system further comprising a mixed refrigerant heat exchanger provided downstream of the mixed refrigerant compressor and cooling the mixed refrigerant using the evaporated gas supplied from the liquefied gas storage tank. The method of claim 6, wherein the mixed refrigerant heat exchanger,
Evaporation gas re-liquefaction system, characterized in that provided between the mixed refrigerant cooler and the re-liquefaction. A ship comprising the evaporative gas reliquefaction system of claim 1.

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