KR101751859B1 - BOG Reliquefaction System and Method for Vessel - Google Patents

Abstract

Disclosed is a vaporizing gas re-liquefaction system for a ship, which re-liquefies a surplus evaporating gas used in an engine.
The ship evaporation gas re-liquefaction system comprises: a first compressor for compressing evaporative gas discharged from a storage tank; A second compressor for additionally compressing the evaporated gas compressed by the first compressor; A first heat exchanger for exchanging heat between the evaporated gas discharged from the storage tank and a portion of the evaporated gas compressed by the first compressor and the second compressor; A third compressor for compressing the other part of the evaporated gas compressed by the first compressor and the second compressor; A first bypass line for bypassing the third compressor and sending the remaining portion of the evaporated gas compressed by the first compressor and the second compressor to the rear end of the third compressor; A first decompression device for expanding the fluid cooled by the first heat exchanger after being compressed by the first compressor and the second compressor; A flow of the refrigerant expanded by the first decompression device into the refrigerant and a flow of the evaporated gas compressed by the third compressor and the evaporated gas sent to the rear end of the third compressor along the first bypass line are heat- A second heat exchanger; And a second decompression device for expanding the fluid cooled by the second heat exchanger, wherein the evaporated gas discharged from the storage tank passes through the first heat exchanger, 1 decompression device and the rest is sent to the first compressor and the evaporation gas sent to the downstream of the first decompression device along the second bypass line after passing through the first heat exchanger, And is used as a refrigerant in the second heat exchanger.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a system and method for re-

The present invention relates to a system and a method for re-liquefying residual surplus evaporative gas used in a marine engine.

In recent years, consumption of liquefied gas such as Liquefied Natural Gas (LNG) has been rapidly increasing worldwide. The liquefied gas obtained by liquefying the gas at a low temperature has an advantage of being able to increase the storage and transport efficiency because the volume becomes very small as compared with the gas. In addition, liquefied natural gas, including liquefied natural gas, can be removed as an eco-friendly fuel with less air pollutant emissions during combustion because air pollutants can be removed or reduced during the liquefaction process.

Liquefied natural gas is a colorless transparent liquid obtained by cooling methane-based natural gas to about -162 ° C and liquefying it, and it has a volume of about 1/600 of that of natural gas. Therefore, when the natural gas is liquefied and transported, it can be transported very efficiently.

However, since the liquefaction temperature of natural gas is a cryogenic temperature of -162 ° C at normal pressure, liquefied natural gas is sensitive to temperature changes and is easily evaporated. As a result, the storage tank storing the liquefied natural gas is subjected to heat insulation, but the external heat is continuously transferred to the storage tank. Therefore, in the transportation of liquefied natural gas, the liquefied natural gas is naturally vaporized continuously in the storage tank, -Off Gas, BOG) occurs. This also applies to other low temperature liquefied gases such as ethane.

Evaporation gas is a kind of loss and is an important issue in transport efficiency. Further, when the evaporation gas accumulates in the storage tank, the internal pressure of the tank may rise excessively, and there is a risk that the tank may be damaged. Accordingly, various methods for treating the evaporative gas generated in the storage tank have been studied. Recently, a method of re-liquefying the evaporated gas and returning it to the storage tank for treating the evaporated gas, a method of returning the evaporated gas to the storage tank And a method of using it as an energy source of a consuming place.

As a method for re-liquefying the evaporation gas, there is a method of re-liquefying the evaporation gas by heat exchange with the refrigerant by providing a refrigeration cycle using a separate refrigerant, and a method of re-liquefying the evaporation gas by using the evaporation gas itself as a refrigerant . Particularly, the system adopting the latter method is called a Partial Re-liquefaction System (PRS).

On the other hand, there are gas-fuel engines such as DFDE, ME-GI engine and X-DF engine which can be used as natural gas among the engines used in ships.

DFDE is used for power generation and consists of four strokes. (Otto Cycle), in which natural gas having a relatively low pressure of about 6.5 bar is injected into the combustion air inlet, and the piston is compressed as it ascends.

The ME-GI engine is used for propulsion and consists of two strokes. It adopts a diesel cycle in which high pressure natural gas near 300 bar is injected directly to the combustion chamber near the top dead center of the piston.

The X-DF engine is used for propulsion and consists of two strokes. It uses heavy-duty natural gas of about 16 bar as fuel and adopts autocycle.

The present invention seeks to provide a system and method for liquefying a ship's evaporative gas that can exhibit enhanced liquefaction performance of an evaporative gas compared to a conventional partial liquefaction system.

According to an aspect of the present invention, there is provided a system for re-liquefying a vapor of a ship, the system comprising: a first compressor for compressing an evaporated gas discharged from a storage tank; A second compressor for additionally compressing the evaporated gas compressed by the first compressor; A first heat exchanger for exchanging heat between the evaporated gas discharged from the storage tank and a portion of the evaporated gas compressed by the first compressor and the second compressor; A third compressor for compressing the other part of the evaporated gas compressed by the first compressor and the second compressor; A first bypass line for bypassing the third compressor and sending the remaining portion of the evaporated gas compressed by the first compressor and the second compressor to the rear end of the third compressor; A first decompression device for expanding the fluid cooled by the first heat exchanger after being compressed by the first compressor and the second compressor; A flow of the refrigerant expanded by the first decompression device into the refrigerant and a flow of the evaporated gas compressed by the third compressor and the evaporated gas sent to the rear end of the third compressor along the first bypass line are heat- A second heat exchanger; And a second decompression device for expanding the fluid cooled by the second heat exchanger, wherein the evaporated gas discharged from the storage tank passes through the first heat exchanger, 1 decompression device and the rest is sent to the first compressor and the evaporation gas sent to the downstream of the first decompression device along the second bypass line after passing through the first heat exchanger, And is used as a refrigerant in the second heat exchanger.

The first compressor and the first decompressor may form a compressing unit.

When the pressure generator fails, the second heat exchanger can use the evaporated gas supplied along the second bypass line as the refrigerant without using the fluid expanded by the first decompressor as the refrigerant.

The fluid used as the refrigerant in the second heat exchanger after being expanded by the first decompressor is combined with the evaporated gas used as the refrigerant in the first heat exchanger after being discharged from the storage tank, Can be sent.

The ship evaporating gas re-liquefaction system may further include a first valve installed on the first bypass line to regulate the flow rate and opening and closing of the evaporation gas, and the first valve is connected to the first bypass line in the second heat exchanger If it is necessary to increase the re-liquefaction efficiency, the flow rate of the fluid passing through the first bypass line is reduced, and if it is not necessary to increase the re-liquefaction efficiency in the second heat exchanger, the flow rate of the fluid passing through the first bypass line .

The ship evaporative gas re-liquefaction system may further include: a first cooler installed downstream of the first compressor for cooling the evaporated gas compressed by the first compressor; A second cooler installed downstream of the second compressor for cooling the evaporated gas compressed by the second compressor; And a third cooler installed downstream of the third compressor for cooling the evaporated gas compressed by the third compressor; And the first cooler, the second cooler, and the third cooler may be heat exchange coolers.

The ship evaporative gas re-liquefaction system includes a fourth cooler for cooling a part of the evaporated gas compressed by the first compressor and the second compressor, which is sent to the first heat exchanger; And a fifth cooler for cooling the evaporated gas compressed by the third compressor and sending the cooled evaporated gas to the second heat exchanger, wherein the fourth cooler and the fifth cooler may be air coolers.

The first bypass line may be branched at the downstream end of the second compressor and joined to the front end of the fifth condenser, and the fifth condenser is connected to the evaporator gas compressed by the third compressor and the first bypass line So that the combined flow of the evaporated gas sent to the end of the third compressor can be cooled.

The first bypass line may be branched at a downstream end of the second compressor and joined to a downstream end of the fifth condenser, and the evaporated gas compressed by the third compressor is cooled by the fifth condenser, 1 bypass line along with the evaporated gas sent to the downstream of the fifth cooler and may be sent to the second heat exchanger.

The marine evaporation gas re-liquefaction system may further include a gas-liquid separator provided at a downstream end of the second decompression device for separating the partially or fully re-liquefied fluid into liquefied natural gas and gaseous vaporized gas, The liquefied natural gas separated by the separator may be sent to the storage tank.

The evaporated gas separated by the gas-liquid separator may be combined with the evaporated gas discharged from the storage tank and sent to the first heat exchanger.

The evaporated gas separated by the gas-liquid separator can be directly sent to the first heat exchanger without merging with the evaporated gas discharged from the storage tank.

The remaining portion of the evaporated gas compressed by the first compressor and the second compressor, which is not sent to the first heat exchanger, may be sent to the engine.

The vessel may include a plurality of engines, and the plurality of engines may include an X-DF engine and a DFDE.

According to another aspect of the present invention, there is provided a method for liquefying a ship evaporative gas, which re-liquefies residual surplus evaporative gas used in an engine, comprising the steps of: 1) compressing evaporative gas discharged from a storage tank; 3) the part of the evaporated gas branched in the step 2) is cooled by heat exchange with the refrigerant discharged from the storage tank, and 4) The fluid cooled in the step 3) is expanded, and 5) another part of the evaporated gas branched in the step 2) is further compressed, and 6) the remaining part of the evaporated gas branched in the step 2) And 7) the flow merged in the step 6) is cooled by heat exchange with the refrigerant in the fluid expanded in the step 4), and 8) the refrigerant is cooled in the step 7) Cooled fluid The evaporated gas used as the refrigerant for the heat exchange in the step 3) after being expanded from the storage tank is partially used as the refrigerant for the heat exchange in the step 7) Is subjected to the compression process of the step (1).

The energy obtained by expanding the fluid in the step 4) may be used to compress the evaporation gas in the step 1).

The fluid used as the refrigerant of the heat exchange in the step 7) is combined with the fluid used as the refrigerant of the heat exchange in the step 3) after being discharged from the storage tank, and may be subjected to the compression process of the step 1).

In the step 3), the 'part of the evaporated gas branched in the step 2) may be cooled by exchanging the external air with the refrigerant and then being cooled by exchanging the evaporated gas discharged from the storage tank with the refrigerant.

The flow merged in the step 6) may be cooled after the outdoor air is cooled by heat exchange with the refrigerant, and then the heat expanded in the step 4) is heat-exchanged with the refrigerant.

The additional compressed evaporated gas in the step 5) may be joined with the remaining part of the evaporated gas branched in the step 2) in the step 6) after the external air is cooled by heat exchange with the refrigerant.

According to the present invention, the evaporation gas circulating through the refrigerant cycle in the open loop can be used as the refrigerant, and the liquefaction amount and the re-liquefaction efficiency can be increased as compared with the conventional case.

In particular, according to the present invention, since the evaporation gas subjected to the re-liquefaction process is further compressed and cooled while using a medium-pressure engine such as an X-DF engine as the propulsion engine, the re-liquefaction amount and re-liquefaction efficiency can be further increased.

According to the present invention, since the decompression device and the compressor are constituted by the compressing device, the energy obtained by expanding the fluid by the decompression device can be utilized, thereby saving energy.

Further, according to the present invention, since the heat-exchanging cooler and the air-cooling type cooler are used in combination, the system can be efficiently operated even in a ship environment of various ships.

According to the present invention, it is possible to use a low-temperature evaporation gas as an additional refrigerant since it is not subjected to the compression process after being discharged from the storage tank, thereby increasing the re-liquefaction efficiency and the amount of re-liquefaction, .

Lastly, according to the present invention, since the system can be operated flexibly in consideration of the re-liquefaction efficiency in the second heat exchanger, the energy consumed in the third compressor can be reduced.

1 is a schematic view of a vaporization gas re-liquefaction system for a ship according to a first preferred embodiment of the present invention.
2 is a schematic view of a vaporization gas re-liquefaction system for ships according to a second preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The system and method for liquefying the ship's evaporative gas according to the present invention can be applied to various applications such as a ship equipped with an engine using natural gas as fuel and a ship including a liquefied gas storage tank. In addition, the following examples can be modified in various forms, and the scope of the present invention is not limited to the following examples.

Systems for the treatment of the evaporative gas to be described below of the present invention include all types of ships and marine structures, such as liquefied natural gas carriers, liquefied ethane gas carriers, and the like, with storage tanks capable of storing low temperature liquid cargo or liquefied gas, It can be applied to marine structures such as LNG FPSO and LNG FSRU as well as ships such as LNG RV. However, in the following embodiments, liquefied natural gas, which is a typical low temperature liquid cargo, will be described as an example for convenience of explanation.

The fluid in each line of the present invention may be in any one of a liquid state, a gas-liquid mixed state, a gas state, and a supercritical fluid state, depending on operating conditions of the system.

1 is a schematic view of a vaporization gas re-liquefaction system for a ship according to a first preferred embodiment of the present invention.

1, the evaporative gas re-liquefaction system for a ship according to the present embodiment includes a first heat exchanger 110, a first compressor 210, a second compressor 220, a third compressor 230, a second heat exchanger (120), a first pressure reducing device (410), and a second pressure reducing device (420).

The storage tank T of this embodiment stores liquefied natural gas such as liquefied natural gas or liquefied ethane gas, and discharges the evaporated gas to the outside when the internal pressure exceeds a predetermined pressure. The evaporated gas discharged from the storage tank (T) is sent to the first heat exchanger (110).

The first heat exchanger 110 of this embodiment exchanges heat between the evaporated gas discharged from the storage tank T and the evaporated gas compressed by the first compressor 210 and the second compressor 220. That is, in the first heat exchanger 110 of the present embodiment, the evaporation gas discharged from the storage tank T is used as a refrigerant, and the evaporated gas compressed by the first compressor 210 and the second compressor 220 And cooled.

The first compressor 210 of this embodiment compresses the evaporated gas used as the refrigerant in the first heat exchanger 110 after being discharged from the storage tank T.

The evaporative gas re-liquefaction system for a ship according to the present embodiment includes a first cooler 310 installed at the downstream end of the first compressor 210, which is compressed by the first compressor 210 and cools the evaporated gas not only in pressure but also in temperature . The first cooler 310 of the present embodiment may be a heat exchange type cooler using fresh water or the like as a refrigerant.

The second compressor 220 of this embodiment further compresses the evaporated gas compressed by the first compressor 210 after being used as a refrigerant in the first heat exchanger 110.

The evaporative gas re-liquefaction system of the present embodiment includes a second cooler 320 installed downstream of the second compressor 220 for compressing the evaporated gas, which is compressed by the second compressor 220, . The second cooler 320 of the present embodiment may be a heat exchange type cooler using fresh water or the like as a refrigerant.

The third compressor 230 of this embodiment compresses the evaporated gas compressed by the first compressor 210 and the second compressor 220 once more.

The evaporating gas re-liquefaction system of this embodiment includes a third cooler 330 installed downstream of the third compressor 230, which is compressed by the third compressor 230 and cools the evaporated gas not only in pressure but also in temperature . The third cooler 330 of the present embodiment may be a heat exchange type cooler using fresh water or the like as a refrigerant.

The second heat exchanger 120 of the present embodiment is configured such that the fluid expanded by the first decompression device 410 and the flow of the evaporated gas sent to the rear end of the first decompressor 410 along the second bypass line L2 Exchanges the evaporated gas compressed by the first compressor 210, the second compressor 220, and the third compressor 230 with the refrigerant.

However, the second heat exchanger 120 of the present embodiment is not limited to the evaporation gas compressed by the first compressor 210, the second compressor 220, and the third compressor 230, And the evaporated gas that has been compressed by the second compressor 220 and then bypassed the third compressor 230 along the first bypass line L1. That is, the evaporated gas compressed by the first compressor 210, the second compressor 220, and the third compressor 230 and the evaporated gas compressed by the first compressor 210 and the second compressor 220 The evaporated gas bypassing the third compressor 230 along the bypass line L1 is merged at the subsequent stage of the third compressor 230 and cooled together by the second heat exchanger 120. [

The first decompression device 410 of the present embodiment expands the fluid cooled by the first heat exchanger 110 after being compressed by the first compressor 210 and the second compressor 220. The fluid inflated by the first decompressor 410 decreases not only the pressure but also the temperature, and the first decompressor 410 may be an inflator.

Further, the energy obtained by the first decompression device 410 while expanding the fluid can be used by the first compressor 210 to compress the evaporated gas. That is, the first compressor 210 and the first decompressor 410 may form a compressor 500.

The second decompression device 420 of the present embodiment expands the fluid cooled by the second heat exchanger 120. The second pressure reducing device 420 may be an expansion valve such as a line-Thomson valve.

The vessel evaporation gas re-liquefaction system of this embodiment may further include a gas-liquid separator 600. The gas-liquid separator 600 of the present embodiment is provided at the downstream end of the second decompression device 420 and performs a compression process by the first compressor 210, the second compressor 220 and the third compressor 230, The liquid that has been partially or totally re-liquefied through the cooling process by the first evaporator 120 and the expansion process by the second decompressor 420 is separated into liquefied natural gas and gaseous evaporated gas. The liquefied natural gas separated by the gas-liquid separator 600 can be sent to the storage tank T. The evaporated gas separated by the gas-liquid separator 600 is combined with the evaporated gas discharged from the storage tank T, And may be sent to the heat exchanger 110.

1, it is shown that the evaporated gas separated by the gas-liquid separator 600 is combined with the evaporated gas discharged from the storage tank T and sent to the first heat exchanger 110. However, according to the present embodiment, , The evaporated gas separated by the gas-liquid separator 600 may be sent to the first heat exchanger 110 without being merged with the evaporated gas discharged from the storage tank T and used as a refrigerant.

The flow of the fluid according to the first preferred embodiment of the present invention will now be described.

The evaporated gas discharged from the storage tank T is sent to the downstream of the first decompressor 410 along the second bypass line L2 after passing through the first heat exchanger 110, And is sent to the compressor 210. A second valve 820 may be provided on the second bypass line L2 of the present embodiment for controlling the flow rate and opening / closing of the fluid.

The evaporated gas sent to the downstream of the first decompressor 410 along the second bypass line L2 after passing through the first heat exchanger 110 is combined with the fluid expanded by the first decompressor 410, Evaporated gas that has been sent to the second heat exchanger 120 and passed through the first heat exchanger 110 and then sent to the first compressor 210 is compressed by the first compressor 210 and then supplied to the second compressor 220 And then branches to three flows.

The evaporated gas that has been compressed by the first compressor 210 and the second compressor 220 and then diverted into three flows is sent to the downstream of the third compressor 230 along the first bypass line L1, The other flow is compressed by the third compressor 230 and then sent to the second heat exchanger 120, and the remaining flow is again branched into two flows. On the first bypass line L1, a first valve 810 for controlling the flow rate and opening / closing of the evaporation gas may be provided.

In FIG. 1, among the evaporated gases compressed by the first compressor 210 and the second compressor 220, the evaporative gas sent to the third compressor 230 is branched first, and then the first bypass line L1 is branched However, the present invention is not limited to this, and the evaporative gas sent to the third compressor 230 may be branched after the first bypass line L1 is branched first.

The evaporated gas that is branched at the downstream end of the second compressor 220 and then sent to the downstream end of the third compressor 230 along the first bypass line L1 is combined with the evaporated gas compressed by the third compressor 230, And is sent to the heat exchanger 120.

The evaporated gas compressed by the third compressor 230 after branched at the downstream end of the second compressor 220 is combined with the evaporated gas supplied along the first bypass line L1 and then flows into the second heat exchanger 120, And is expanded by the second decompression device 420 to partially or totally re-liquefy.

When the vaporization gas re-liquefaction system for vessels of this embodiment includes the gas-liquid separator 600, among the vaporized gases expanded by the second pressure-reducing device 420 and partially or totally re-liquefied, Liquid separator 600 can be sent to the first heat exchanger 110 by being combined with the evaporated gas discharged from the storage tank T. The separated liquid natural gas can be sent to the storage tank T, have. The evaporated gas separated by the gas-liquid separator 600 may be sent to the first heat exchanger 110 without being merged with the evaporated gas discharged from the storage tank T and used as a refrigerant.

On the other hand, the evaporated gas branched from the rear end of the second compressor 220 and then branched into two flows without being sent to the third compressor 230 or the first bypass line L1 flows through the engines E1 and E2, And the other flow is sent to the first heat exchanger 110.

The ship to which the present embodiment is applied may include a plurality of engines, and each of the plurality of engines may require evaporative gas of different pressure as fuel. In FIG. 1, the evaporation gas sent to the engines E1 and E2 after branching from the downstream end of the second compressor 220 is diverted to two flows, and one flow is a first engine E1 and the remaining stream is sent to the second engine E2 which requires relatively low-pressure evaporative gas as fuel. Hereinafter, an engine that requires a relatively high-pressure evaporation gas as fuel is referred to as a high-pressure engine, and an engine that requires relatively low-pressure evaporation gas as fuel is referred to as a low-pressure engine.

A third decompression device 430 is installed at the front end of the second engine E2 to compress the evaporated gas compressed by the first compressor 210 and the second compressor 220 by the third decompressor 430, The pressure can be reduced to a pressure required by the engine E2 and supplied to the second engine E2. The first engine E1 of this embodiment may be an X-DF engine, and the second engine E2 may be a DFDE.

The evaporated gas that has been branched at the downstream end of the second compressor 220 and then branched to the two streams without being sent to the third compressor 230 or the first bypass line L1 is returned to the first heat exchanger 110 Is cooled by heat exchange with the refrigerant discharged from the storage tank (T) in the first heat exchanger (110).

The fluid that has been compressed by the first compressor 210 and the second compressor 220 and cooled by the first heat exchanger 110 is expanded by the first decompressor 410 so that the temperature is lowered, Is combined with the vaporized gas supplied along the line L2 and sent to the second heat exchanger 120. [

A part of the evaporated gas that has been discharged from the storage tank T and then has passed through the first heat exchanger 110 is discharged through the second bypass line L2 to the first decompressor The refrigerant can be used as additional refrigerant in the second heat exchanger 120 because the refrigerant is discharged to the rear end of the storage tank T and is not subjected to the compression process so that the low temperature evaporated gas can be used. It is possible to increase the amount. In addition, when the pressure generator 500 fails, the fluid supplied along the second bypass line (L2) can be used as the refrigerant in the second heat exchanger (120) instead of the fluid expanded by the first decompression device So that it is possible to cope with a case where the pressure device 500 fails.

The combined flow of the fluid expanded by the first decompression device 410 and the evaporation gas supplied along the second bypass line L2 is used as a refrigerant in the second heat exchanger 120 and then flows into the storage tank T The refrigerant is combined with the evaporated gas used as the refrigerant in the first heat exchanger 110 and sent to the first compressor 210.

The evaporation gas of this embodiment can be largely divided into an evaporation gas subjected to a re-liquefaction process and an evaporation gas used as a refrigerant. The evaporation gas subjected to the re-liquefaction process and the evaporation gas used as the refrigerant are completely separated from each other and operated However, after the liquefaction process, the remaining evaporation gas which is not re-liquefied is used again as the refrigerant, and some of the evaporation gas used as the refrigerant is subjected to the re-liquefaction process again. That is, the evaporation gas used as the refrigerant in this embodiment circulates in an open loop cycle. This will be described in detail with reference to FIG.

The evaporation gas that is discharged from the storage tank T and then compressed by the first compressor 210 and the second compressor 220 through the first heat exchanger 110 is supplied to the third compressor 230, And the first bypass line (L1) are subjected to a re-liquefaction process, and the evaporated gas sent to the first heat exchanger (110) is used as a refrigerant. The refrigerant is also used as evaporation gas that is discharged from the storage tank T and then sent to the downstream side of the first decompressor 410 along the second bypass line L2 via the first heat exchanger 110. [

The reason why the evaporated gas passing through the re-liquefaction process is further compressed by the third compressor 230 is to increase the amount of liquefaction and re-liquefaction efficiency.

The ship's evaporation gas re-liquefaction system of this embodiment is a system for re-liquefying remaining surplus evaporative gas used as fuel for the engines E1 and E2 or using it as a refrigerant and includes a system for supplying fuel to the engines E1 and E2 Or to a system for supplying fuel to the engines E1, E2.

That is, the marine evaporation gas re-liquefaction system of this embodiment utilizes the first compressor 210 and the second compressor 220, which are compressors for compressing the evaporation gas at the pressures demanded by the engines E1 and E2, The first compressor 210 and the second compressor 220 of the present embodiment compress the evaporation gas to a pressure required by the first engine E1 as the high pressure engine and the second engine E2 as the low pressure engine E2 may be used as the fuel as the evaporated gas which is compressed by the first compressor 210 and the second compressor 220 and then reduced by the third decompressor 430. [

In the case where the first engine E1 is an ME-GI engine requiring a high-pressure evaporation gas of about 300 bar as fuel, the first compressor 210 and the second compressor 220 require the ME- (Even if the ME-GI engine is used, additional compression may be required to increase the liquefaction efficiency). However, in the case where the first engine E1 is an X-DF engine requiring as the fuel a medium-pressure vapor of about 16 bar, if the compressed vaporized gas is directly remelted to the pressure required by the X-DF engine, The re-liquefaction efficiency may be lowered.

In designing the heat exchanger, the temperature and the heat flow rate of the fluid supplied to the heat exchanger are fixed and the logarithmic mean temperature difference (LMTD) is set to be lower than the temperature of the fluid used as the refrigerant So as to be as small as possible.

The logarithmic mean temperature difference (LMTD) is the temperature difference between the low-temperature fluid and the low-temperature fluid in the opposite direction and the opposite direction. In the case of countercurrent flow, the low-temperature fluid passes through the heat exchanger And the temperature after the high-temperature fluid has passed through the heat exchanger is th2 and d1 = th2-tc1, d2 = th1-tc2, d1) / ln (d2 / d1). As the logarithmic mean temperature difference is smaller, the efficiency of the heat exchanger increases.

A heat exchanger is designed to minimize the logarithmic mean temperature difference (LMTD) under defined initial conditions. If the pressure of the fluid supplied to the heat exchanger is increased, a smaller heat exchanger with a logarithmic mean temperature difference (LMTD) can be designed. That is, if the pressure of the evaporation gas passing through the re-liquefaction process is increased, a more efficient heat exchanger can be applied to the system, and as a result, the re-liquefaction amount and re-liquefaction efficiency of the entire system become high.

When the first engine E1 of the present embodiment is an X-DF engine, the evaporation gas compressed by the first compressor 210 and the second compressor 220 may be approximately 17 bar, and the first compressor 210, And the evaporated gas further compressed by the third compressor 230 after being compressed by the second compressor 220 may be approximately 150 bar.

On the other hand, even if all of the evaporated gas compressed by the first compressor 210 and the second compressor 220 is not compressed by the third compressor 230, the re-liquefaction efficiency in the second heat exchanger 120 is not so low The present embodiment includes the first bypass line L1 so that part of the evaporated gas compressed by the first compressor 210 and the second compressor 220 can be supplied to the third compressor 230 It is possible to carry out a re-liquefaction process without compressing the liquid.

Therefore, in the evaporative-gas re-liquefaction system for marine vessels according to the present embodiment, in consideration of the re-liquefaction efficiency in the second heat exchanger 120, the third compressor (230) Bypassing the third compressor 230 through the first bypass line L1, the energy consumed in the third compressor 230 can be reduced by operating the system in a resilient manner.

The first valve 810 of the present embodiment can reduce the flow rate of the fluid passing through the first bypass line L1 when the efficiency of re-liquefaction in the second heat exchanger 120 needs to be increased, ) Can be adjusted to increase the flow rate of the fluid passing through the first bypass line (L1) if it is not necessary to increase the re-liquefaction efficiency in the first bypass line (L1).

The reason for including two compressors 210 and 220 for compressing the evaporative gas supplied as fuel to the engines E1 and E2 is that the first compressor 210 and the second compressor 210, When the first decompression device 410 forms the compressing device 500, the evaporation gas is compressed to the pressure required by the engine E1 or E2 only by the energy generated by the first decompression device while expanding the fluid It is difficult to make. That is, according to the present embodiment, the evaporator gas is primarily compressed in the first compressor 210 using the energy supplied from the first decompressor 410, and the insufficient pressure is compressed in the second compressor 220 And satisfies the required pressures of the engines E1 and E2.

The present invention is not limited to the case of the present embodiment and the required pressure of the engines E1 and E2 can be adjusted only by the first compressor 210 forming the compression device 500, The second compressor 220 may be provided with a sufficient pressure by a plurality of compressors.

Meanwhile, in the present embodiment, the evaporated gas used as the refrigerant is compressed by the first compressor 210 and the second compressor 220 and then sent to the first heat exchanger 110 to be supplied to the first heat exchanger 110 Exchanged with the evaporation gas discharged from the storage tank T by the first decompression device 410 and cooled by the second decompression device 410 and then expanded by the first decompression device 410 and then cooled by the evaporation gas supplied along the second bypass line L2 And is used as a refrigerant in the second heat exchanger (120).

That is, in the present embodiment, the evaporation gas used as the refrigerant has the final object of cooling the evaporation gas passing through the re-liquefaction process in the second heat exchanger 120, and the first heat exchanger 110 and the first decompressor The second heat exchanger 410 serves to lower the temperature of the evaporation gas used as the refrigerant in the second heat exchanger 120 to increase the re-liquefaction efficiency and the amount of the re-liquefaction. According to this embodiment, the evaporated gas used as the refrigerant in the second heat exchanger 120 can be cooled to approximately -50 캜 or lower by the first heat exchanger 110.

2 is a schematic view of a vaporization gas re-liquefaction system for ships according to a second preferred embodiment of the present invention. The evaporative gas re-liquefaction system for ship according to the second embodiment shown in Fig. 2 is different from the system for evaporating liquefied gas for ship according to the first embodiment shown in Fig. 1 in that a fourth cooler 710 and a fifth cooler 720 There are differences in that they include, and the differences are mainly described below. The detailed description of the same members and features as those of the evaporative gas re-liquefaction system for marine vessel of the first embodiment will be omitted.

Referring to FIG. 2, the evaporative gas re-liquefaction system for a ship according to the present embodiment includes a first heat exchanger 110, a first compressor 210, a second compressor 220, a third compressor 230, a second heat exchanger 120, a first pressure reducing device 410, and a second pressure reducing device 420.

The storage tank T of this embodiment stores liquefied natural gas such as liquefied natural gas, liquefied ethane gas, or the like in its interior, as in the first embodiment, and discharges the evaporated gas to the outside when the internal pressure becomes a predetermined pressure or more. The evaporated gas discharged from the storage tank (T) is sent to the first heat exchanger (110).

The first heat exchanger 110 of the present embodiment is configured such that the first compressor 210 and the second compressor 220 use the evaporation gas discharged from the storage tank T as a refrigerant, The compressed evaporated gas is cooled by heat exchange.

The first compressor 210 of the present embodiment compresses the evaporation gas used as the refrigerant in the first heat exchanger 110 after being discharged from the storage tank T as in the first embodiment, The compressor 220 further compresses the evaporated gas compressed by the first compressor 210 after being used as a refrigerant in the first heat exchanger 110 as in the first embodiment, (230) compresses the evaporated gas compressed by the first compressor (210) and the second compressor (220) once more, as in the first embodiment.

The evaporating gas re-liquefaction system for marine vessels of the present embodiment includes a first cooler 310 installed at the downstream of the first compressor 210, like the first embodiment; A second cooler 320 installed at a rear end of the second compressor 220; And a third cooler (330) installed at a downstream end of the third compressor (230). The first cooler 310, the second cooler 320, and the third cooler 330 of the present embodiment may be heat-exchanging coolers using fresh water or the like as a coolant.

The second heat exchanger 120 of the present embodiment is configured such that the fluid expanded by the first pressure reducing device 410 and the fluid flowing along the second bypass line L2 to the rear stage of the first pressure reducing device 410 The refrigerant flows from which the sent evaporated gas is combined is cooled by heat exchange with the evaporated gas compressed by the first compressor (210), the second compressor (220), and the third compressor (230).

The second heat exchanger 120 of the present embodiment is similar to the first embodiment in that not only the evaporated gas compressed by the first compressor 210, the second compressor 220, and the third compressor 230 The first compressor 210, the second compressor 220, and then the evaporative gas bypassing the third compressor 230 along the first bypass line L1. That is, the evaporated gas compressed by the first compressor 210, the second compressor 220, and the third compressor 230 and the evaporated gas compressed by the first compressor 210 and the second compressor 220 The evaporated gas bypassing the third compressor 230 along the bypass line L1 is merged at the subsequent stage of the third compressor 230 and cooled together by the second heat exchanger 120. [

A first valve 810 may be provided on the first bypass line L1 of the present embodiment for controlling the flow rate and the opening and closing of the evaporation gas and the first valve 810 may be provided for the second heat exchange If it is not necessary to reduce the flow rate of the fluid passing through the first bypass line (L1) and to increase the efficiency of re-liquefaction in the second heat exchanger (120) when it is necessary to increase the re-liquefaction efficiency in the unit (120) Can be adjusted to increase the flow rate of the fluid passing through the line L1.

Also, as in the first embodiment, the evaporative gas sent to the third compressor 230 may be branched after the first bypass line L1 is first branched.

The first decompression device 410 of the present embodiment is configured to compress the fluid cooled by the first heat exchanger 110 after being compressed by the first compressor 210 and the second compressor 220, And the first decompression device 410 may be an expander.

Further, as in the first embodiment, the energy obtained by the first decompression device 410 while inflating the fluid can be used by the first compressor 210 to compress the evaporation gas. That is, the first compressor 210 and the first decompressor 410 may form a compressor 500.

The second decompression device 420 of the present embodiment expands the fluid cooled by the second heat exchanger 120 and the second decompression device 420 expands the expansion and contraction of the line- Valve.

The marine evaporation gas re-liquefaction system of this embodiment is provided at the downstream end of the second decompressor 420 to separate the fluid partially or totally re-liquefied into liquefied natural gas and gaseous evaporative gas Liquid separator 600 may be further included. The liquefied natural gas separated by the gas-liquid separator 600 can be sent to the storage tank T. The evaporated gas separated by the gas-liquid separator 600 is combined with the evaporated gas discharged from the storage tank T, And may be sent to the heat exchanger 110. The evaporated gas separated by the gas-liquid separator 600 of the present embodiment is sent to the first heat exchanger 110 without being merged with the evaporated gas discharged from the storage tank T as in the first embodiment, .

However, unlike the first embodiment, the evaporative gas re-liquefaction system for marine vessels of the present embodiment further includes a fourth cooler 710 and a fifth cooler 720.

The fourth cooler 710 of the present embodiment is installed in the downstream of the second compressor 220 and is disposed downstream of the first heat exchanger 110 among the evaporated gases compressed by the first compressor 210 and the second compressor 220. [ To cool the evaporated gas sent to the evaporator. The fourth cooler 710 may be an air-cooled cooler using outside air as a coolant.

The fifth cooler 720 of the present embodiment is disposed at the downstream end of the third compressor 230 and is connected to the evaporator gas compressed by the first compressor 210, the second compressor 220, and the third compressor 230 The refrigerant compressed by the first compressor 210 and the second compressor 220 and then flows along the first bypass line L1 to the rear end of the third compressor 230 is cooled.

1, the first bypass line L1 branched from the rear end of the second compressor 220 is joined to the front end of the fifth compressor 720. However, the present invention is not limited to this, The first bypass line L1 branched at the rear end may be joined to the rear end of the fifth condenser 720. [

When the first bypass line L1 is merged to the downstream end of the fifth cooler 720, the fifth cooler 720 is operated by the first compressor 210, the second compressor 220 and the third compressor 230 The fluid that has been compressed by the third compressor 230 and then cooled by the fifth cooler 720 is sent to the downstream of the fifth cooler 720 along the first bypass line L1 Is combined with the evaporated gas and sent to the second heat exchanger (120).

The fluid cooled by the fifth cooler 720 is sent to the second heat exchanger 120 and the fifth cooler 720 may be an air cooled cooler using the outside air as the coolant.

In the case where the fourth cooler 710 and the fifth cooler 720 of the present embodiment are air coolers, the fourth cooler 710 and the fifth cooler 720 cool the evaporated gas using the cold heat of the outside air, The liquefaction amount and the liquefaction efficiency of the evaporation gas re-liquefaction system for ships of this embodiment can be further increased.

Particularly, when a ship to which the present embodiment is applied is operated in the polar region or operated in a cold season so that the temperature of the outside air is low, the air-cooled cooler can cool the outside air at a lower temperature than the heat exchanging cooler using fresh water, When the fourth cooler 710 and the fifth cooler 720 of the present embodiment are air-cooled coolers, the system can be efficiently operated against various environments in which the ship is operated.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the invention. It is.

T: Storage tank E1, E2: Engine
110, 120: heat exchanger 210, 220, 230: compressor
310, 320, 330, 710, 720: cooler 410, 420, 430:
500: Compressor 600: Gas-liquid separator
810, 820: valve

Claims (20)

A system for re-liquefying a vaporizing gas for a ship, which re-liquefies a surplus evaporating gas used in an engine,
A first compressor for compressing the evaporated gas discharged from the storage tank;
A second compressor for additionally compressing the evaporated gas compressed by the first compressor;
A first heat exchanger for exchanging heat between the evaporated gas discharged from the storage tank and a portion of the evaporated gas compressed by the first compressor and the second compressor;
A third compressor for compressing the other part of the evaporated gas compressed by the first compressor and the second compressor;
A first bypass line for bypassing the third compressor and sending the remaining portion of the evaporated gas compressed by the first compressor and the second compressor to the rear end of the third compressor;
A first decompression device for expanding the fluid cooled by the first heat exchanger after being compressed by the first compressor and the second compressor;
A flow of the refrigerant expanded by the first decompression device into the refrigerant and a flow of the evaporated gas compressed by the third compressor and the evaporated gas sent to the rear end of the third compressor along the first bypass line are heat- A second heat exchanger; And
And a second decompression device for expanding the fluid cooled by the second heat exchanger,
The evaporated gas discharged from the storage tank passes through the first heat exchanger and a part of the evaporated gas is sent to the downstream of the first decompression device along the second bypass line and the rest is sent to the first compressor,
The evaporated gas sent through the first heat exchanger to the rear end of the first decompressor along the second bypass line is combined with the fluid expanded by the first decompressor and used as a refrigerant in the second heat exchanger , Evaporative gas re-liquefaction system for ships. The method according to claim 1,
Wherein the first compressor and the first decompressor form a compressing device. The method of claim 2,
Wherein the second heat exchanger does not use the fluid inflated by the first decompression device as a refrigerant and uses the evaporation gas supplied along the second bypass line as a refrigerant when the compressing device fails, Re-liquefaction system. The method according to any one of claims 1 to 3,
The fluid used as the refrigerant in the second heat exchanger after being expanded by the first decompressor is combined with the evaporated gas used as the refrigerant in the first heat exchanger after being discharged from the storage tank, The evaporating gas re-liquefaction system for ships. The method according to any one of claims 1 to 3,
Further comprising a first valve installed on the first bypass line for controlling the flow rate and opening and closing of the evaporation gas,
The first valve may reduce the flow rate of the fluid passing through the first bypass line if it is necessary to increase the re-liquefaction efficiency in the second heat exchanger, and if it is not necessary to increase the re-liquefaction efficiency in the second heat exchanger And is adjusted to increase the flow rate of the fluid passing through the first bypass line. The method according to any one of claims 1 to 3,
A first cooler installed downstream of the first compressor for cooling the evaporated gas compressed by the first compressor;
A second cooler installed downstream of the second compressor for cooling the evaporated gas compressed by the second compressor; And
A third cooler installed downstream of the third compressor for cooling the evaporated gas compressed by the third compressor; ≪ / RTI >
Wherein the first cooler, the second cooler, and the third cooler are heat exchanger coolers. The method according to any one of claims 1 to 3,
A fourth cooler for cooling a portion of the evaporated gas compressed by the first compressor and the second compressor to be sent to the first heat exchanger; And
And a fifth cooler for cooling the evaporated gas compressed by the third compressor and sending the cooled evaporated gas to the second heat exchanger,
Wherein the fourth cooler and the fifth cooler are air-cooled coolers. The method of claim 7,
The first bypass line is branched at the downstream end of the second compressor and joined to the front end of the fifth condenser,
Wherein the fifth cooler cools the flow of the evaporated gas compressed by the third compressor and the evaporated gas sent to the rear end of the third compressor along the first bypass line. The method of claim 7,
The first bypass line is branched at the rear end of the second compressor and joined to the rear end of the fifth cooler,
Wherein the evaporated gas compressed by the third compressor is cooled by the fifth cooler and then merged with the evaporated gas sent to the downstream of the fifth cooler along the first bypass line to be sent to the second heat exchanger, Evaporative gas re-liquefaction system. The method according to any one of claims 1 to 3,
Further comprising a gas-liquid separator provided at a downstream end of the second decompression device for separating the partially or fully re-liquefied fluid into liquefied natural gas and gaseous vaporized gas,
And the liquefied natural gas separated by the gas-liquid separator is sent to the storage tank. The method of claim 10,
Wherein the evaporated gas separated by the gas-liquid separator is combined with the evaporated gas discharged from the storage tank and sent to the first heat exchanger. The method of claim 10,
Wherein the evaporated gas separated by the gas-liquid separator is sent directly to the first heat exchanger without merging with the evaporated gas discharged from the storage tank. The method according to any one of claims 1 to 3,
The remaining evaporative gas not sent to the first heat exchanger is sent to the engine among the 'part of the evaporated gas compressed by the first compressor and the second compressor. 14. The method of claim 13,
Wherein the vessel comprises a plurality of engines, the plurality of engines including an X-DF engine and a DFDE. A method for liquefying a vaporized gas for a ship, which re-liquefies a surplus evaporated gas remaining in the engine,
1) compressing the evaporated gas discharged from the storage tank,
2) The evaporation gas compressed in the step 1) is branched into three streams,
3) A part of the evaporated gas branched in the step 2) is cooled by being heat-exchanged with the refrigerant discharged from the storage tank,
4) The fluid cooled in step 3) is expanded,
5) Another part of the evaporated gas which has branched off in the step 2) is further compressed,
6) The remaining part of the evaporated gas branched in the step 2) is further combined with the compressed evaporated gas in the step 5)
7) The flow merged in the step 6) is a step of cooling the expanded fluid in the step 4)
8) The fluid cooled in step 7) is expanded,
The evaporated gas used as the refrigerant for the heat exchange in the step 3) after being discharged from the storage tank is partially used as the refrigerant for the heat exchange in the step 7) ) Stage of compression of the evaporative gas for ship. 16. The method of claim 15,
Wherein the energy obtained by expanding the fluid in the step 4) is used for compressing the evaporation gas in the step 1). The method according to claim 15 or 16,
The fluid used as the refrigerant of the heat exchange in the step 7) is combined with the fluid used as the refrigerant of the heat exchange in the step 3) after being discharged from the storage tank, Re-liquefying method. The method according to claim 15 or 16,
In the step 3)
Wherein the part of the evaporated gas branched in the step 2) is cooled by heat exchange with the external air with the refrigerant, and then the evaporated gas discharged from the storage tank is cooled by heat exchange with the refrigerant. The method according to claim 15 or 16,
Wherein the flow merged in the step (6) is cooled by heat exchange with the outside air with the refrigerant, and thereafter the fluid expanded in the step (4) is cooled by heat exchange with the refrigerant. The method according to claim 15 or 16,
The evaporated gas further compressed in the step 5) is cooled by exchanging the external air with the refrigerant and then cooled. The evaporated gas for a ship, which is joined with the remaining part of the evaporated gas branched in the step 2) Liquefaction method.

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