KR20190073931A - Boil-Off Gas Reliquefaction System and Method for Vessel - Google Patents

Abstract

Disclosed is a reliquefaction method for evaporation gas of a vessel. The reliquefaction method for evaporation gas of a vessel includes: a first step of using evaporation gas as a refrigerant in a first heat exchanger; a second step of enabling the evaporation gas used as the refrigerant in the first heat exchanger in the first step to diverge into two flows; a third step of enabling one flow to move into a first compressor and enabling the other flow to move into a second compressor among the flow diverging into the two flows in the second step; a fourth step of heat-exchanging the evaporation gas compressed by the first compressor or the second compressor by the first heat exchanger and cooling the same by using the evaporation gas supplied to the first heat exchanger as the refrigerant in the first step; a fifth step of heat-exchanging a fluid cooled by the first heat exchanger in the fourth step by a second heat exchanger and cooling the evaporation gas by using the evaporation gas circulating in a refrigerant cycle as the refrigerant; and a sixth step of decompressing the fluid cooled by the second heat exchanger in the fifth step. The evaporation gas circulating in the refrigerant cycle is processed by a step 5-1) of being compressed by the first compressor or the second compressor (the compressor compressing the evaporation gas supplied to the refrigerant cycle is called a compressor for a refrigerant cycle); a step 5-2) in which the density thereof is measured by a flowmeter; a step 5-3) of being cooled by the second heat exchanger; a step 5-4) of being decompressed; a step 5-5) of being used as the refrigerant in the second heat exchanger; a step 5-6) of being compressed; and a step 5-7) in which nitrogen is injected.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a boil-

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a system and a method for re-liquefying a boil-off gas (BOG) generated by natural gasification of liquefied gas.

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 which can be obtained by cooling methane-based natural gas to about -163 ° C and liquefying it, and has a volume of about 1/600 as compared with 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 -163 ° C at normal pressure, liquefied natural gas is susceptible to temperature change 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.

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 consumer.

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, a method of re-liquefying the evaporation gas itself as a refrigerant without any refrigerant .

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

The DFDE adopts the Otto Cycle, which consists of four strokes, and injects natural gas with a relatively low pressure of about 6.5 bar into the combustion air inlet, compressing the piston as it rises.

The X-DF engine is composed of two strokes, using natural gas of about 16 bar as fuel and adopting autocycle.

The ME-GI engine consists of two strokes and employs a diesel cycle in which high pressure natural gas at around 300 bar is injected directly into the combustion chamber at the top of the piston.

A method for re-liquefying an evaporation gas by using evaporation gas itself as a refrigerant without a separate refrigerant. The evaporation gas compressed by the compressor is cooled by heat exchange with the evaporation gas before being compressed by the compressor, expanded by a JT valve, There is a method of re-liquefying a part of the gas, and a system adopting such a method is called a PRS (Partial Re-liquefaction System).

When there is a large amount of liquefied gas in the storage tank, a large amount of evaporated gas is generated, or when there is a large amount of evaporative gas to be re-liquefied , The amount of liquefaction required only by PRS may not be satisfied.

The PRS was modified to further re-liquefy the evaporation gas, and the evaporation gas could be further cooled by the refrigerant cycle using the evaporation gas itself as the refrigerant. The system employing this method was called Mane Refrigeration System).

The present invention is to provide a system and a method for liquefying a vaporization gas for marine vessels, which is configured to improve the conventional MRS, complement the problems that have been caused by operating the MRS, and to re-liquefy the evaporation gas more efficiently.

According to one aspect of the present invention, there is provided a method of operating a refrigeration cycle comprising the steps of: 1) using a vaporized gas as a refrigerant in a first heat exchanger; 2) splitting the evaporation gas used as a refrigerant in the first heat exchanger into two flows in the step 1); 3) sending the first flow to the first compressor and the remaining flow to the second compressor among the flows branched to the two flows in the step 2); 4) cooling the evaporated gas compressed by the first compressor or the second compressor by heat exchange with the first heat exchanger using the evaporation gas supplied to the first heat exchanger as the refrigerant in step 1) ; 5) cooling the fluid cooled by the first heat exchanger in the step 4) by heat exchange with the second heat exchanger using the evaporation gas circulating the refrigerant cycle as the refrigerant; And 6) depressurizing the fluid cooled by the second heat exchanger in step 5), wherein the evaporated gas circulating in the refrigerant cycle is supplied to the first compressor or the second compressor (Hereinafter, the compressor for compressing the evaporation gas supplied to the refrigerant cycle is referred to as a compressor for refrigerant cycle); 5-2) the density is measured by the flow meter; 5-3) cooling by the second heat exchanger; 5-4) depressurizing; 5-5) being used as a refrigerant in the second heat exchanger; 5-6) compressing; And 5-7) injecting nitrogen into the vessel.

In step 5-7), the evaporated gas into which the nitrogen is injected may be sent to the compressor for the refrigerant cycle, and the refrigerant cycle may form a closed loop.

According to another aspect of the present invention, there is provided a refrigerant cycle system comprising: 1) an evaporation gas is used as a refrigerant in a first heat exchanger; 2) a refrigerant is used as a refrigerant in the first heat exchanger in step 1) Flow to the first compressor and the remaining flow to the second compressor, and 4) to the first compressor or the second compressor, (Hereinafter, referred to as a " fuel supply compressor " for supplying the evaporation gas to the fuel demanding place), and 5) an evaporation gas compressed by the 'fuel supply compressor' The remaining evaporation gas not used in the fuel consumer is cooled by heat exchange by the first heat exchanger using the evaporation gas supplied to the first heat exchanger as the refrigerant in step 1) (Hereinafter, referred to as " refrigerant cycle compressor ") for supplying the evaporated gas compressed by other compressors other than the 'fuel supply compressor' among the first compressor and the second compressor to the refrigerant cycle , 7) cooling the fluid cooled by the first heat exchanger in the step 5) by heat exchange by the second heat exchanger using the evaporation gas circulating the refrigerant cycle as the refrigerant, and 8) cooling in the step 7) There is provided a method of liquefying a ship evaporative gas for depressurizing a fluid cooled by the second heat exchanger and injecting nitrogen into the refrigerant cycle.

Nitrogen may be injected downstream of the second heat exchanger so that nitrogen may be mixed into the fluid used as the refrigerant in the second heat exchanger.

The fluid used as the refrigerant in the second heat exchanger can be compressed by the fourth compressor and nitrogen is injected downstream of the fourth compressor to be used as the refrigerant in the second heat exchanger, Nitrogen can be injected into the compressed evaporative gas.

The nitrogen-compressed fluid after being compressed by the fourth compressor may be sent to the compressor for the refrigerant cycle.

And the fluid depressurized by the second pressure reducing device can be used as the refrigerant in the second heat exchanger.

In the step 6), the evaporated gas compressed by the compressor for the refrigerant cycle and sent to the refrigerant cycle is cooled in the second heat exchanger and decompressed by the second decompressor, .

According to another aspect of the present invention, there is provided a compressor comprising: a first compressor for compressing an evaporative gas; A second compressor installed in parallel with the first compressor for compressing other flows of evaporative gas not sent to the first compressor; A first heat exchanger that cools the evaporated gas compressed by the first compressor or the second compressor by using heat as the refrigerant before the refrigerant is compressed by the first compressor or the second compressor; A second heat exchanger for further cooling the fluid cooled by the first heat exchanger by using the evaporation gas circulating the refrigerant cycle as a refrigerant for further heat exchange; And a first decompression device for decompressing the fluid cooled by the second heat exchanger, wherein nitrogen is injected into the refrigerant cycle.

The evaporated gas compressed by the first compressor or the second compressor can be sent to the fuel demanding place (hereinafter, the compressor supplying the evaporating gas to the fuel demanding place is referred to as a 'fuel supplying compressor'), The remaining evaporation gas that is not used in the fuel consumer can be sent to the first heat exchanger among the first compressor and the second compressor, The evaporated gas compressed by the compressor can be sent to the refrigerant cycle. (Hereinafter, the compressor for supplying the evaporative gas with the refrigerant cycle is referred to as a " compressor for refrigerant cycle ").

The refrigerant cycle includes a second decompression device that compresses the refrigerant cycle compressed by the compressor for refrigerant cycle and depressurizes the evaporated gas supplied to the refrigerant cycle; And a fourth compressor for compressing the fluid used as the refrigerant in the second heat exchanger after being reduced in pressure by the second pressure reducing device.

The evaporated gas supplied to the refrigerant cycle after being compressed by the compressor for the refrigerant cycle is cooled by the second heat exchanger and is further reduced in pressure by the second decompressor to be cooled and then returned to the second heat exchanger And can be used as a refrigerant.

Wherein the refrigerant cycle includes at least one of a refrigerant cycle compressor, a second heat exchanger, a second decompressor, a second heat exchanger, a fourth compressor, Loop can be formed.

Nitrogen may be injected downstream of the second heat exchanger so that nitrogen may be mixed into the fluid used as the refrigerant in the second heat exchanger.

The fluid used as the refrigerant in the second heat exchanger can be compressed by the fourth compressor and nitrogen is injected downstream of the fourth compressor to be used as the refrigerant in the second heat exchanger, Nitrogen can be injected into the compressed evaporative gas.

The ship evaporative gas re-liquefaction system is provided on a line that sends the evaporated gas compressed by the first compressor or the second compressor to the first heat exchanger, and is compressed by the first compressor or the second compressor And a third compressor for further compressing the evaporated gas.

The third compressor may compress the evaporation gas to 150 to 300 bar.

The third compressor may compress the evaporation gas to 150 to 170 bar.

The marine evaporation gas re-liquefaction system may further include a gas-liquid separator provided downstream of the first decompressor to separate the re-liquefied liquefied gas from the evaporated gas remaining in a gaseous state.

The evaporated gas separated by the gas-liquid separator may be combined with the evaporated gas before being used as a refrigerant in the first heat exchanger and used as a refrigerant in the first heat exchanger.

According to the present invention, it is possible to reduce the possibility that a droplet is introduced into the second decompression device 420 by injecting nitrogen into the refrigerant cycle RC.

According to an embodiment of the present invention, the mixing amount of the evaporation gas and nitrogen of the fluid circulating in the refrigerant cycle (RC) can be verified by the flow meter 600 to maintain the optimal mixing amount.

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.
3 is a graph schematically showing the phase change of methane with temperature and pressure.
4 is a graph showing the temperature values of methane according to the heat flow rate under different pressures, respectively.
5 and 6 are graphs showing the amount of resolidification according to the evaporation gas pressure in a PRS (Partial Re-liquefaction System).

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, a ship including a liquefied gas storage tank, or an offshore structure. 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.

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.

Referring to FIG. 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 second heat exchanger 120, Device 410, a refrigerant cycle (RC), and a bypass line (BL).

The first heat exchanger 110 is operated by the first compressor 210 or the second compressor 220 by using the evaporation gas before being compressed by the first compressor 210 or the second compressor 220 as a refrigerant. Cool the compressed evaporated gas.

The evaporating gas used as the refrigerant in the first heat exchanger 110 may be evaporated gas discharged from the storage tank T. [

The evaporated gas used as the refrigerant in the first heat exchanger 110 is diverted into two flows, one stream is sent to the first compressor 210 and the other stream is sent to the second compressor 220.

The first compressor 210 is used as a refrigerant in the first heat exchanger 110, and then compresses one of the evaporative gases branched into two flows. The first compressor 210 may be a multi-stage compressor, and a first cooler 310 may be installed downstream of the first compressor 210 to cool the evaporated gas compressed by the first compressor 210.

The second compressor 220 is installed in parallel with the first compressor 210 and is used as a refrigerant in the first heat exchanger 110 and then sent to the first compressor 210 among the evaporated gases branched into two flows Compress the remaining flow. The second compressor 220 may be a multi-stage compressor, and a second cooler 320 may be installed downstream of the second compressor 220 to cool the evaporated gas compressed by the second compressor 220.

Either one of the first compressor 210 and the second compressor 220 supplies the evaporative gas to the fuel consumer E and the other one supplies the evaporative gas to the refrigerant cycle RC. In addition, among the evaporated gas compressed by the compressor that supplies the evaporated gas to the fuel demand site E, the surplus evaporated gas not used in the fuel demand site E is sent to the first heat exchanger 110 and subjected to a liquefaction process .

The fuel demand (E) includes the ME-GI engine, which uses approximately 300 bar of natural gas as fuel, the X-DF engine, which uses approximately 16 bar of natural gas as fuel, and DF An engine (DFGE, DFDE), and a gas combustion unit (GCU).

The compressor that supplies the fuel to the fuel demand destination E among the first compressor 210 and the second compressor 220 when the fuel demanding entity E is an engine compresses the evaporation gas at the required pressure of the fuel demand site E .

The ship's regulations require that a compressor that supplies fuel to the engine be designed with redundancy in case of an emergency. Redundancy design means that when one of the compressors can not be used for reasons of failure, maintenance, etc., It means to design to be able to use.

In the present embodiment, the first compressor 210 and the second compressor 220 may serve as redundancies. Conventionally, one of the first compressor 210 and the second compressor 220 evaporates (E), and the other unused one is put in the standby state. If the compressor which supplied the evaporative gas to the fuel demand point (E) can not be used, ) State compressor to supply the evaporative gas to the fuel consumer (E).

However, according to the conventional operating method, although the probability that the compressor used as the evaporative gas can not be used at the fuel demand site E is low and the duration is not long even if it occurs, the emergency situation There is a problem in that a redundant compressor is installed and the extra compressor is kept in a stand-by state in order to prepare, so that the actual dangerous cost is wasted.

According to the present embodiment, when both the first compressor 210 and the second compressor 220 can be normally used, one is used for supplying the fuel to the fuel consumer E and the other is used for the refrigerant cycle When the compressor used for supplying the evaporative gas to the fuel demand site E can not be used, the evaporative gas is supplied to the refrigerant cycle RC to regain the re-liquefaction amount and the re-liquefaction efficiency And supplies the evaporated gas to the fuel consuming destination E by means of the compressor that supplied the evaporative gas to the refrigerant cycle RC.

Therefore, according to the present embodiment, there is an advantage that the re-liquefaction amount and the re-liquefaction efficiency can be improved by utilizing an extra compressor installed to prepare for an emergency situation while satisfying the ship regulations requiring redundancy design.

It is preferable that the first compressor 210 and the second compressor 220 are compressors having the same performance so that they can serve as redundancies.

The second heat exchanger 120 compresses the refrigerant in the first heat exchanger 110 or the second heat exchanger 110 after being compressed by the first compressor 210 or the second compressor 220 using the fluid circulating the refrigerant cycle RC as a refrigerant. The fluid cooled by the heat is further cooled by heat exchange. The fluid further cooled by the second heat exchanger (120) is sent to the first pressure reducing device (410).

According to the present embodiment, the evaporated gas is further cooled not only in the first heat exchanger 110 but also in the second heat exchanger 120 so that the evaporated gas cooled only by the first heat exchanger 110 flows into the first decompressor 410, the evaporated gas in a lowered temperature state is sent to the first pressure reducing device 410, so that the re-liquefaction efficiency and the liquefaction amount are increased. The following is a detailed description.

3 is a graph schematically showing the phase change of methane with temperature and pressure. Referring to FIG. 3, methane is in a supercritical fluid state at a temperature of approximately -80 占 폚 or higher and a pressure of approximately 55 bar or higher. That is, in the case of methane, the critical point is about -80 ° C, 55 bar. The supercritical fluid state is a third state different from the liquid state or gas state.

When the evaporation gas has a temperature lower than the critical point at a pressure equal to or higher than the critical point, it may be in a state similar to the supercritical fluid state having a higher density than the general liquid state. The evaporation gas having a pressure higher than the critical point and a temperature lower than the critical point State is hereinafter referred to as "high-pressure liquid state ".

The evaporation gas sent to the first heat exchanger 110 for the re-liquefaction process may be in a gaseous state or in a supercritical fluid state depending on the degree of compression. When the evaporated gas sent to the first heat exchanger 110 is in a gaseous state, the evaporated gas in the gaseous state passes through the first heat exchanger 110 and the temperature is lowered to become a mixed state of the liquid and the gas, 1 heat exchanger 110 is in the supercritical fluid state, the fluid in the supercritical fluid state passes through the first heat exchanger 110 and becomes low in temperature to be in the " high pressure liquid state ".

The temperature of the fluid cooled by the first heat exchanger 110 is lowered while passing through the second heat exchanger 120. When the fluid that has passed through the first heat exchanger 110 is in a mixed state of liquid and gas , The fluid in the liquid mixed state with the gas passes through the second heat exchanger 120 and becomes lower in temperature so that the ratio of the liquid becomes higher or becomes the liquid state and passes through the first heat exchanger 110 When the fluid is in the " high pressure liquid state ", the fluid in the "high pressure liquid state" passes through the second heat exchanger 120 and becomes the "high pressure liquid state "

In addition, even if the fluid that has passed through the second heat exchanger 120 is in the "high pressure liquid state ", the fluid of the" high pressure liquid state "through the second heat exchanger 120 passes through the first pressure reducing device 410 The pressure is lowered to become a liquid state or a mixture state of liquid and gas.

Even if the pressure of the evaporation gas is lowered to the same degree (P in FIG. 3) by the first pressure reducing device 410, the temperature is lower than that in the case where the pressure is reduced in the higher temperature state (X → X ' (Y - > Y 'in Fig. 3), the ratio of the liquid becomes higher. In addition, if the temperature can be further lowered, the evaporation gas can theoretically be 100% re-liquefied (Z → Z 'in FIG. 3). Therefore, when the fluid cooled by the first heat exchanger 110 is further cooled by the second heat exchanger 120 and then sent to the first pressure reducing device 410, the re-liquefaction efficiency and the liquefaction amount are increased.

The first decompression device 410 compresses the evaporated gas cooled by the first heat exchanger 110 and the second heat exchanger 120 after being compressed by the first compressor 210 or the second compressor 220, . The first decompression device 410 includes all the means capable of decompressing and cooling the evaporation gas, and may be an expansion valve such as a Joule-Thomson valve or an expander. In the present embodiment, it is preferable that the first pressure reducing device 410 is an expansion valve. The expansion valve has the advantage that the price is lower than the inflator and the risk of failure is less.

The compression process by the first compressor 210 or the second compressor 220 and the cooling process by the first heat exchanger 110 and the second heat exchanger 120 are performed by the first decompressor 410 or the second decompressor 410, Some or all of the evaporated gas that has undergone the process is re-liquefied.

The marine evaporation gas re-liquefaction system of this embodiment may further include a gas-liquid separator 500 disposed downstream of the first decompressor 410 for separating the re-liquefied liquefied gas from the remaining vaporized gas .

The liquefied gas separated by the gas-liquid separator 500 can be sent to the storage tank T and the evaporated gas separated by the gas-liquid separator 500 can be sent to the evaporator 200 before being used as a refrigerant in the first heat exchanger 110 And can be used as a refrigerant in the first heat exchanger 110. [

When the first heat exchanger 110 uses the evaporated gas discharged from the storage tank T as a refrigerant, the evaporated gas separated by the gas-liquid separator 500 is mixed with the evaporated gas discharged from the storage tank T And may be sent to the first heat exchanger 110.

The evaporated gas separated by the gas-liquid separator 500 may be separately used as a refrigerant in the first heat exchanger 110 without being merged with the evaporated gas before being used as a refrigerant in the first heat exchanger 110 In this case, the first heat exchanger 110 may be composed of three flow paths.

If the ship evaporative gas re-liquefaction system of this embodiment does not include the gas-liquid separator 500, the evaporated gas partially or fully re-liquefied may be sent directly to the storage tank T from the first decompressor 410.

The second decompressor 420 and the fourth compressor 240 may be included in the refrigerant cycle RC in which the fluid used as the refrigerant in the second heat exchanger 120 is circulated.

The second decompression device 420 reduces the temperature by reducing the pressure of the evaporation gas supplied to the refrigerant cycle RC after being compressed by the first compressor 210 or the second compressor 220. The second decompression device 420 includes all the means capable of decompressing and cooling the evaporation gas, and may be an expansion valve such as a Joule-Thomson valve or an expander. In the present embodiment, it is preferable that the second decompressor 420 is an expander.

The fluid depressurized by the second pressure reducing device 420 is supplied to the second heat exchanger 120 and is used as a refrigerant for further cooling the fluid cooled by the first heat exchanger 110.

The evaporated gas supplied to the refrigerant cycle (RC) after being compressed by the first compressor (210) or the second compressor (220) is supplied to the second heat exchanger (120) before being depressurized by the second decompressor It can pass. In this case, the evaporated gas supplied to the refrigerant cycle (RC) after being compressed by the first compressor (210) or the second compressor (220) is heat-exchanged by the second heat exchanger (120) The refrigerant is further decompressed and cooled by the second heat exchanger 420 and then sent again to the second heat exchanger 120 to be used as a refrigerant.

The fourth compressor 240 serves to compress the fluid used as the refrigerant in the second heat exchanger 120 and to keep the pressure average of the circulating fluid in the refrigerant cycle RC constant. The fourth compressor 240 may be driven by the second pressure reducing device 420 and the compander C so that the second pressure reducing device 420 may be driven by the power generated by expanding the fluid and the fourth compressor 240 A fourth cooler 340 for cooling the evaporated gas compressed by the fourth compressor 240 may be installed downstream.

According to the evaporative gas re-liquefaction system for ships of this embodiment, the evaporated gas compressed by the fourth compressor 240 can be sent upstream of the first compressor 210 or can be sent to the upstream of the second compressor 220, 1 compressor 210 to constitute a refrigerant cycle RC and may include a second compressor 220 to constitute a refrigerant cycle.

When the evaporated gas compressed by the first compressor 210 is supplied to the fuel consumer E and the evaporated gas compressed by the second compressor 220 is supplied to the refrigerant cycle RC, The refrigerant cycle RC of the closed loop connecting the second compressor 220, the second decompressor 420, the second heat exchanger 120, the fourth compressor 240, and the second compressor 220 is formed. When the evaporated gas supplied to the refrigerant cycle RC is cooled by the second heat exchanger 120 and then sent to the second decompressor 420, the second compressor 220, the second heat exchanger 120, A refrigerant cycle RC of a closed loop connecting the second decompression device 420, the second heat exchanger 120, the fourth compressor 240 and the second compressor 220 is formed.

When the evaporated gas compressed by the first compressor 210 is supplied to the refrigerant cycle RC and the evaporated gas compressed by the second compressor 220 is supplied to the fuel consumer E, A refrigerant cycle RC of a closed loop connecting the first compressor 210, the second decompressor 420, the second heat exchanger 120, the fourth compressor 240, and the first compressor 210 is formed. When the evaporated gas supplied to the refrigerant cycle RC is cooled by the second heat exchanger 120 and then sent to the second decompressor 420, the first compressor 210, the second heat exchanger 120, The refrigerant cycle RC of the closed loop connecting the second decompression device 420, the second heat exchanger 120, the fourth compressor 240, and the first compressor 210 again is formed.

According to the present embodiment, any one of the first compressor 210 and the second compressor 220 may be selected to supply the evaporative gas to the fuel demanding entity E or the first heat exchanger 110, And the refrigerant cycle (RC) can be circulated to the first heat exchanger (110) by the evaporated gas compressed by the other compressor that does not supply the evaporative gas, so that the operation of the system is advantageous.

According to the present embodiment, there is an advantage that the re-liquefaction efficiency and the liquefaction amount of the evaporation gas can be increased by utilizing the redundancy compressor which is conventionally installed on the ship but is not normally used.

On the other hand, when the amount of the liquefied gas stored in the storage tank T is small and the amount of the evaporated gas discharged from the storage tank T is small, or when there is a large amount of evaporated gas used as fuel in the fuel demand site E such as the engine The second heat exchanger 120 bypasses the first heat exchanger 120 and the second heat exchanger 120 directly bypasses the first heat exchanger 110. In this case, And may be sent to the decompression apparatus 410.

Since it is not necessary to supply the refrigerant to the second heat exchanger 120 when the evaporative gas passing through the re-liquefaction process is cooled only by the first heat exchanger 110 and the second heat exchanger 120 is bypassed, It may not supply the evaporation gas to the cycle RC.

The evaporative gas re-liquefaction system for a ship according to the present embodiment is installed on a line for sending the evaporated gas compressed by the first compressor 210 or the second compressor 220 to the first heat exchanger 110, 210) or a third compressor (230) for further compressing the evaporated gas compressed by the second compressor (220). A third cooler 330 for cooling the evaporated gas compressed by the third compressor 230 may be installed downstream of the third compressor 230.

The reason why the third compressor 230 further compresses the evaporated gas that is compressed by the first compressor 210 or the second compressor 220 and then sent to the first heat exchanger 110 is that the re- The pressure of the evaporation gas is increased to increase the liquefaction amount and the re-liquefaction efficiency.

FIG. 4 is a graph showing the temperature value of methane according to the heat flow rate under different pressures. Referring to FIG. 4, it can be seen that the higher the pressure of the evaporation gas through the re-liquefaction process, the higher the efficiency of the self-heat exchange. Self-heat self-exchange means that cold evaporation gas itself is used as refrigerant and heat is exchanged at high temperature evaporation gas.

4 (a) shows the state of each fluid in the upstream and downstream of the second heat exchanger 120 when the ship's evaporation gas re-liquefaction system according to the present embodiment does not include the third compressor 230 And FIG. 4 (b) shows the state of each fluid in the upstream and downstream of the second heat exchanger 120 when the ship evaporative gas re-liquefaction system of the present embodiment includes the third compressor 230.

4, the evaporated gas supplied to the refrigerant cycle (RC) after being compressed by the first compressor (210) or the second compressor (220) is cooled by the second heat exchanger (120) 420 and then supplied to the second heat exchanger 120 again.

The uppermost graph I in FIGS. 4 (a) and 4 (b) shows the fluid state at point P1 in FIG. 1 supplied to the second heat exchanger 120 and the lowermost graph L shows the second heat exchange 1, which is fed back to the second heat exchanger 120 to be used as a refrigerant after passing through the first and second decompression devices 120 and 420, The overlapped graph J shows the fluid state at the point P3 in FIG. 1, which is supplied to the second heat exchanger 120 after passing through the first heat exchanger 110. In FIG.

Since the fluid used as the refrigerant is deprived of the cold heat during the heat exchange process and the temperature gradually increases, the graph L advances from the left to the right according to the passage of time, and the fluid cooled by heat exchange with the refrigerant is cooled from the refrigerant in the heat exchange process Since the temperature is gradually decreased due to the supply, the graph I and the graph J proceed from right to left as time passes.

The graph K in the middle part of FIGS. 4 (a) and 4 (b) is a combination of the graph I and the graph J. That is, the fluid used as the refrigerant in the second heat exchanger 120 is drawn in a graph L, and the fluid cooled by heat exchange with the refrigerant in the second heat exchanger 120 is drawn in a graph K.

In designing the heat exchanger, the temperature and the heat flow of the fluid supplied to the heat exchanger (that is, the fluid at the points P1, P2, and P3 in FIG. 1) are fixed and the temperature of the fluid used as the refrigerant is controlled So that the logarithmic mean temperature difference (LMTD) can be minimized while preventing the graph L from crossing over the graph K so that the graph L does not appear above the graph K.

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.

The logarithmic mean temperature difference LMTD on the graph is represented by the interval between the low temperature fluid used as the coolant (graph L in FIG. 4) and the high temperature fluid cooled by heat exchange with the coolant (graph K in FIG. 4) (B) of FIG. 4 shows that the interval between the graph L and the graph K is narrower than the interval between the graph L and the graph K.

This difference is due to the fact that the initial value of the graph J, which is the point indicated by the round circle, that is, the pressure of the fluid at the point P3 in FIG. 1 fed to the second heat exchanger 120 after passing through the first heat exchanger 110 (B) of Fig. 4 is higher than that of Fig. 4 (a).

That is, as a result of the simulation, in the case of FIG. 4A in which the third compressor 230 is not included, the fluid at the point P3 in FIG. 1 may be approximately -111 DEG C and 20 bar, , The fluid at point P3 in FIG. 1 may be approximately -90 DEG C, 50 bar. Under these initial conditions, the heat exchanger may be used to minimize the logarithmic mean temperature difference (LMTD) In the case of FIG. 4 (b) in which the pressure of the evaporative gas passing through the re-liquefaction process is high, the efficiency of the heat exchanger becomes higher, and as a result, the total liquefaction amount and re-liquefaction efficiency of the entire system become high.

4A, when the flow rate of the evaporation gas used as the refrigerant in the second heat exchanger 120 is approximately 6401 kg / h, the refrigerant is heat-exchanged with the refrigerant from the fluid (graph L) (Graph K) is approximately 585.4 kW and the flow rate of the re-liquefied vapor is approximately 3441 kg / h.

4B, when the flow rate of the evaporative gas used as the refrigerant in the second heat exchanger 120 is approximately 5368 kg / h, the refrigerant is heat-exchanged with the refrigerant from the fluid (graph L) (Graph K) is approximately 545.2 kW, and the flow rate of the re-liquefied evaporation gas is approximately 4325 kg / h.

That is, if the pressure of the evaporative gas including the third compressor 230 is re-liquefied, a larger amount of the evaporated gas can be re-liquefied even if less refrigerant is used.

When the evaporator is further cooled by the third compressor 230 to increase the amount of re-liquefaction and re-liquefaction efficiency, the entire amount of evaporation gas can be re-liquefied without further cooling the evaporator by the second heat exchanger 120 The time required to supply the evaporative gas to the refrigerant cycle RC is reduced and thus the effect of the redundancy design that the compressor for supplying the evaporative gas to the fuel demand site E is prepared is sufficiently secured can do.

In the meantime, it will be appreciated that the evaporative gas re-liquefaction system of the present embodiment may advantageously include the third compressor 230 in some cases, and the preferred pressure for the third compressor 230 to compress the evaporative gas will be as follows.

5 and 6 are graphs showing the amount of resolidification according to the evaporation gas pressure in a PRS (Partial Re-liquefaction System). The evaporative gas to be re-liquefied refers to the evaporated gas which is cooled and re-liquefied, and is named to distinguish it from the evaporative gas used as the refrigerant.

5 and 6 are graphs showing the re-liquefaction amount according to the evaporation gas pressure in the PRS, so that the re-liquefaction amount is lower than that of the MRS in which the evaporation gas is additionally re-liquefied by the evaporation gas circulating in the refrigerant cycle . In the case of MRS, about 3300 kg of evaporative gas per hour can be re-liquefied.

Referring to FIGS. 5 and 6, it can be seen that the re-liquefaction amount shows a maximum value when the pressure of the evaporation gas is in the vicinity of 150 to 170 bar, and there is little change in the liquefaction amount in the range of 150 to 300 bar.

The evaporated gas compressed by the first compressor 210 and the second compressor 220 at the required pressure of the fuel consumer E is sent to the fuel consumer E and the evaporated gas is fed to the fuel consumer E A surplus evaporated gas not used in the fuel demand point E is sent to the first heat exchanger 110 among the evaporated gases compressed by the supplying compressor to be subjected to a liquefaction process so that the evaporation gas re- When the third compressor (230) is not included, a part of the evaporated gas compressed at the required pressure of the fuel consuming area (E) is sent to the first heat exchanger (110)

In the case of an engine using natural gas of 150 bar or more, such as ME-GI engine in which the demand for fuel (E) is natural gas of about 300 bar, the pressure required by the fuel demand point (E) However, when the fuel demand (E) is consumed at about 16 bar of the natural gas as the fuel, the X- In the case of a DF engine or a DF engine (DFGE, DFDE) using natural gas of about 6.5 bar as a fuel, in the case of an engine using natural gas less than 150 bar as fuel, the third compressor 230, And then subjected to a re-liquefaction process.

Further, it is preferable that the third compressor 230 compress the evaporation gas to approximately 150 to 300 bar, more preferably approximately 150 to 170 bar, so as to secure the maximum amount of resolidification . Further, since the energy consumed by the third compressor 230 can be reduced as the degree to which the third compressor 230 compresses the evaporation gas is reduced, the third compressor 230 further preferably has a capacity of about 150 bar So that the evaporation gas can be compressed.

It is generally sufficient that the third compressor 230 has approximately one half capacity of the first compressor 210 or the second compressor 220. [

According to the present embodiment, nitrogen is injected into the refrigerant cycle RC so that only the evaporated gas is circulated in the refrigerant cycle RC, and the refrigerant is circulated in the refrigerant cycle RC do.

As shown in FIG. 1, the position N where nitrogen is injected into the refrigerant cycle RC is determined by the position of the second heat exchanger 120 so that nitrogen is mixed with the fluid used as the refrigerant in the second heat exchanger 120. [ It is preferably downstream.

In the case where the refrigerant cycle RC includes the fourth compressor 240, it is preferable that the position N where nitrogen is injected into the refrigerant cycle RC is downstream of the fourth compressor 240, It is preferable that the position N where the nitrogen is injected into the refrigerant cycle RC is downstream of the fourth cooler 340. In the case where the fourth compressor 240 and the fourth cooler 340 are included,

The evaporated gas circulating in the refrigerant cycle (RC) is discharged from the refrigerant cycle (RC) because the amount of the evaporated gas to be re-liquefied is large in the case where the evaporated gas is not consumed or consumed in the fuel consuming destination The fluid cooled by the first heat exchanger 110 is further cooled by the second heat exchanger 120. However, when the amount of the evaporative gas generated in the storage tank T is small, The amount of the evaporative gas to be re-liquefied is small so that the fluid cooled by the first heat exchanger 110 can be supplied to the second heat exchanger 120 to the first decompressor 410 without being further cooled.

When the fluid cooled by the first heat exchanger 110 is not further cooled by the second heat exchanger 120, it is not necessary to circulate the refrigerant in the refrigerant cycle RC, so that the refrigerant cycle RC Purging is performed by nitrogen. In the present invention, nitrogen is injected into a refrigerant circulating in a refrigerant cycle (RC) by using equipment installed for purging the refrigerant cycle (RC) with nitrogen.

When the refrigerant cycle (RC) includes the second decompressor (420) and the fourth compressor (240), the flow of fluid at the start of the refrigerant cycle (RC) will be described as follows.

The evaporated gas compressed by the first compressor 210 or the second compressor 220 is supplied to the refrigerant cycle RC so that the compressor that supplies the evaporated gas to the refrigerant cycle RC is called a refrigerant cycle compressor, Is depressurized by the second decompression device 420 and then used as a refrigerant in the second heat exchanger 120 or cooled by the second heat exchanger 120 and is decompressed by the second decompressor 420 And is further used as a refrigerant in the second heat exchanger 120 after being depressurized.

The fluid used as the refrigerant in the second heat exchanger 120 after being decompressed by the second decompression device 420 is compressed by the fourth compressor 240 and is supplied to the evaporated gas compressed by the fourth compressor 240 Nitrogen is mixed (N), and the fluid mixed with the evaporation gas and nitrogen is supplied to the compressor for the refrigerant cycle again.

The above process is repeated until nitrogen is sufficiently supplied to the refrigerant cycle (RC) and the ratio of nitrogen contained in the fluid circulating in the refrigerant cycle (RC) becomes a constant value, and nitrogen is continuously supplied to the refrigerant cycle Supply.

When the ratio of the nitrogen contained in the fluid circulating in the refrigerant cycle (RC) becomes a certain value, the nitrogen injection is stopped and the fluid in which the nitrogen and the evaporation gas are mixed circulates in the refrigerant cycle (RC) It can be used as a refrigerant.

Droplets may occur in the fluid circulating in the refrigerant cycle (RC). If the liquid mixed with the droplets is sent to the second pressure reducing device 420, the second pressure reducing device 420 may be damaged, and the second pressure reducing device 420 may be burned.

Particularly, when the evaporated gas supplied to the refrigerant cycle (RC) is cooled by the second heat exchanger (120) and then sent to the second decompressor (420), the refrigerant is cooled by the second heat exchanger (120) The probability of droplet formation in the lowered evaporation gas is increased.

According to the present invention, nitrogen is injected into the refrigerant cycle (RC), and the fluid in which the evaporation gas and the nitrogen are mixed is circulated in the refrigerant cycle (RC), so that compared with the case where only the evaporation gas circulates in the refrigerant cycle Since the boiling point of the refrigerant circulating in the cycle RC can be lowered, the probability of occurrence of droplets can be lowered.

In addition, since the temperature is lower when the mixed fluid of the evaporation gas and the nitrogen is depressurized by the second decompressor 420, as compared with the case where only the evaporated gas is depressurized by the second decompressor 420, According to the present invention, the re-liquefaction efficiency can be further increased.

Nitrogen can be supplied by the nitrogen production equipment installed in the engine room of the ship.

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 second embodiment shown in FIG. 2 differs from the first embodiment shown in FIG. 1 in that the system includes a flow meter 600 as compared with the evaporation gas re-liquefaction system for a ship according to the first embodiment shown in FIG. 1, The difference is mainly explained. The detailed description of the same components as those of the evaporation gas re-liquefaction system for marine vessels of the first embodiment described above will be omitted.

The flow meter 600 is installed downstream of the 'refrigerant cycle compressor' of the refrigerant cycle RC and measures the flow rate of the fluid supplied to the refrigerant cycle RC after being compressed by the 'refrigerant cycle compressor'.

The refrigerant compressed by the compressor for the refrigerant cycle and supplied to the refrigerant cycle RC is then depressurized by the decompression device 420 after passing through the flow meter 600 so that the refrigerant of the second heat exchanger 120 Or may be cooled by the second heat exchanger 120 and reduced in pressure by the pressure reducing device 420 to be used as the refrigerant of the second heat exchanger 120.

However, when the evaporated gas supplied to the refrigerant cycle (RC) is cooled by the second heat exchanger (120) and then sent to the second decompressor (420), the droplet The present embodiment is particularly useful when the evaporated gas supplied to the refrigerant cycle RC is cooled by the second heat exchanger 120 and then sent to the second decompressor 420 .

Preferably, the flow meter 600 is a Coriolis flow meter, which is a mass flow meter that directly measures the mass flow rate of a fluid by vibrating the fluid-carrying tube, High. In addition, the Coriolis flowmeter is characterized in that it is possible to measure not only the flow rate of the fluid but also the density of the fluid.

According to this embodiment, when each device is connected in the same manner as the evaporative gas system for marine vessels of the present embodiment through the simulation device, in order to achieve the maximum liquefaction amount and re-liquefaction efficiency without generating droplets, Calculate how much the nitrogen content of the circulating fluid in the refrigerant cycle (RC) should be. In addition, the density of the mixed gas of the evaporated gas and the nitrogen is calculated when the mixed amount becomes the maximum liquefaction amount and the liquefaction efficiency without the droplet occurrence.

When the temperature of the fluid supplied to the second decompression device 420 becomes the lowest temperature in a range where no droplet is generated at the inlet of the second decompressing device 420, As shown in FIG.

In the next step, nitrogen is supplied to the refrigerant cycle (RC), the density of the fluid circulating through the refrigerant cycle (RC) is measured by the flow meter (600), and nitrogen is supplied until the optimum density It is injected into the refrigerant cycle (RC).

Also, even after the nitrogen injection process is completed, the density of the fluid circulating through the refrigerant cycle (RC) is continuously measured by the flow meter (600), and the fluid circulating in the refrigerant cycle (RC) Lt; / RTI > density.

If the density of the fluid circulating in the refrigerant cycle RC deviates from the optimum density calculated through the simulation apparatus by more than a certain range, the evaporation gas or nitrogen is additionally injected into the refrigerant cycle RC, So that the density of the circulating fluid is the optimum density calculated through the simulation apparatus.

Through this process, the nitrogen content of the circulating fluid in the actual refrigerant cycle (RC) can be made to be the optimum mixed content calculated through the simulation apparatus.

That is, since the vaporization gas re-liquefaction system for marine vessels of this embodiment is different in the density of the evaporation gas and the nitrogen, if the density of the fluid in which the evaporation gas and the nitrogen are mixed is known, , The flow meter installed to measure the flow rate of the fluid generally has a flow meter capable of measuring not only the flow rate of the fluid but also the density of the fluid. ), It is possible to determine the optimum mixing amount of the fluid circulating in the refrigerant cycle (RC).

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.

N: Location where nitrogen is injected into the refrigerant cycle
T: Storage tank RC: Refrigerant cycle
C: Compander E: Fuel Consumer
110: first heat exchanger 120: second heat exchanger
210: first compressor 220: second compressor
230: third compressor 240: fourth compressor
310: first cooler 320: second cooler
330: third cooler 340: fourth cooler
410: First decompression device 420: Second decompression device
500: gas-liquid separator 600: flow meter

Claims (20)

1) using evaporative gas as a refrigerant in a first heat exchanger;
2) splitting the evaporation gas used as a refrigerant in the first heat exchanger into two flows in the step 1);
3) sending the first flow to the first compressor and the remaining flow to the second compressor among the flows branched to the two flows in the step 2);
4) cooling the evaporated gas compressed by the first compressor or the second compressor by heat exchange with the first heat exchanger using the evaporation gas supplied to the first heat exchanger as the refrigerant in step 1) ;
5) cooling the fluid cooled by the first heat exchanger in the step 4) by heat exchange with the second heat exchanger using the evaporation gas circulating the refrigerant cycle as the refrigerant; And
6) depressurizing the fluid cooled by the second heat exchanger in step 5)
The evaporation gas circulating through the refrigerant cycle is supplied to the evaporator
5-1) The step of compressing by the first compressor or the second compressor (hereinafter, the compressor for compressing the evaporation gas supplied to the refrigerant cycle is referred to as a 'refrigerant cycle compressor');
5-2) the density is measured by the flow meter;
5-3) cooling by the second heat exchanger;
5-4) depressurizing;
5-5) being used as a refrigerant in the second heat exchanger;
5-6) compressing; And
5-7) injecting nitrogen;
Wherein the vaporized gas is passed through a process including a vaporizing step. The method according to claim 1,
In step 5-7), the evaporated gas into which the nitrogen is injected is sent to the compressor for the refrigerant cycle,
Wherein the refrigerant cycle forms a closed loop. 1) the evaporation gas is used as the refrigerant in the first heat exchanger,
2) In the step 1), the evaporation gas used as the refrigerant in the first heat exchanger is branched into two flows,
3) Among the flows branched to the two flows in the step 2), one flow is sent to the first compressor, the remaining flow is sent to the second compressor,
4) The evaporative gas compressed by the first compressor or the second compressor is sent to the fuel consumer (hereinafter, the compressor supplying the evaporative gas to the fuel consumer is referred to as a 'fuel feed compressor'),
5) The remaining evaporation gas not used in the fuel demanding place among the evaporation gases compressed by the 'fuel supply compressor' is used as the refrigerant in the evaporation gas supplied to the first heat exchanger in the step 1) 1 heat exchanger to cool it,
6) The first compressor and the second compressor send the evaporated gas compressed by the remaining compressors other than the 'fuel supply compressor' to the refrigerant cycle (hereinafter, the compressor that supplies the evaporated gas in the refrigerant cycle is referred to as'',
7) In the step 5), the fluid cooled by the first heat exchanger is cooled by heat exchange by the second heat exchanger using the evaporation gas circulating the refrigerant cycle as the refrigerant,
8) In step 7), the fluid cooled by the second heat exchanger is depressurized,
And injecting nitrogen into the refrigerant cycle. The method of claim 3,
Nitrogen is injected downstream of the second heat exchanger and nitrogen is mixed with the fluid used as the refrigerant in the second heat exchanger. The method of claim 4,
The fluid used as the refrigerant in the second heat exchanger is compressed by the fourth compressor,
Nitrogen is injected downstream of the fourth compressor, nitrogen is injected into the evaporated gas compressed by the fourth compressor after being used as a refrigerant in the second heat exchanger. The method of claim 5,
And the nitrogen-compressed fluid after being compressed by the fourth compressor is sent to the compressor for the refrigerant cycle. The method according to any one of claims 3 to 6,
And the fluid depressurized by the second pressure reducing device is used as a refrigerant in the second heat exchanger. The method of claim 7,
In the step 6), the evaporated gas compressed by the compressor for the refrigerant cycle and sent to the refrigerant cycle is cooled in the second heat exchanger and decompressed by the second decompressor, Wherein the vaporization gas is used as a vaporizer. A first compressor for compressing the evaporation gas;
A second compressor installed in parallel with the first compressor for compressing other flows of evaporative gas not sent to the first compressor;
A first heat exchanger that cools the evaporated gas compressed by the first compressor or the second compressor by using heat as the refrigerant before the refrigerant is compressed by the first compressor or the second compressor;
A second heat exchanger for further cooling the fluid cooled by the first heat exchanger by using the evaporation gas circulating the refrigerant cycle as a refrigerant for further heat exchange; And
And a first decompression device for decompressing the fluid cooled by the second heat exchanger,
And the nitrogen is injected into the refrigerant cycle. The method of claim 9,
The evaporated gas compressed by the first compressor or the second compressor is sent to a fuel demanding place (hereinafter, the compressor supplying the evaporating gas to the fuel demanding place is referred to as a 'fuel supplying compressor'),
The remaining evaporation gas that is not used in the fuel demanding place among the evaporation gases compressed by the 'fuel supply compressor' is sent to the first heat exchanger,
(Hereinafter, referred to as a " compressor for supplying a refrigerant cycle evaporated gas to a refrigerant cycle compressor ") is supplied to the refrigerant cycle in the first compressor and the second compressor, '), The evaporation gas re-liquefaction system for ships. The method of claim 10,
Wherein the refrigerant cycle includes:
A second decompression device for decompressing the evaporated gas supplied to the refrigerant cycle after being compressed by the 'compressor for refrigerant cycle'; And
A fourth compressor for compressing the fluid used as the refrigerant in the second heat exchanger after being depressurized by the second decompression device;
And an evaporative gas re-liquefaction system for the ship. The method of claim 11,
The evaporated gas supplied to the refrigerant cycle after being compressed by the compressor for the refrigerant cycle is cooled by the second heat exchanger and is further reduced in pressure by the second decompressor to be cooled and then returned to the second heat exchanger And is used as a refrigerant. The method of claim 12,
Wherein the refrigerant cycle includes at least one of a refrigerant cycle compressor, a second heat exchanger, a second decompressor, a second heat exchanger, a fourth compressor, A vapor liquefaction system for ships, forming a loop. The method according to any one of claims 9 to 13,
Nitrogen is injected downstream of the second heat exchanger and nitrogen is mixed with the fluid used as the refrigerant in the second heat exchanger. 15. The method of claim 14,
The fluid used as the refrigerant in the second heat exchanger is compressed by the fourth compressor,
Nitrogen is injected downstream of the fourth compressor and nitrogen is injected into the evaporated gas compressed by the fourth compressor after being used as a refrigerant in the second heat exchanger. The method according to any one of claims 9 to 13,
A third compressor for compressing the evaporated gas compressed by the first compressor or the second compressor and a third compressor for compressing the evaporated gas compressed by the first compressor or the second compressor, Further comprising a compressor. 18. The method of claim 16,
And the third compressor compresses the evaporation gas to 150 to 300 bar. 18. The method of claim 17,
And the third compressor compresses the evaporation gas to 150 to 170 bar. The method according to any one of claims 9 to 13,
Further comprising a gas-liquid separator provided downstream of the first decompression device for separating the re-liquefied liquefied gas and the vaporized gas remaining in a gaseous state. The method of claim 19,
Wherein the evaporated gas separated by the gas-liquid separator is combined with the evaporated gas before being used as a refrigerant in the first heat exchanger and is used as a refrigerant in the first heat exchanger.

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