KR102010881B1 - Boil-Off Gas Reliquefaction System and Method for Vessel - Google Patents

Abstract

A boil off gas reliquefaction system is disclosed.
The vessel boil-off gas liquefaction system, the first compressor for compressing the boil-off gas; A second compressor installed in parallel with the first compressor and compressing an evaporation gas of another flow which is not sent to the first compressor; A first heat exchanger configured to cool the boil-off gas compressed by the first compressor or the second compressor using a boil-off gas before being compressed by the first compressor or the second compressor as a refrigerant, and heat-cool by heat exchange; A second heat exchanger configured to further heat-exchange and cool the fluid cooled by the first heat exchanger by using an evaporated gas circulating in a refrigerant cycle as a refrigerant; And a first decompression device for depressurizing the fluid cooled by the second heat exchanger, wherein the refrigerant cycle comprises: a second decompression device for depressurizing the boil-off gas supplied to the refrigerant cycle; A third decompression device for further depressurizing the fluid decompressed by the second decompression device; And a fourth compressor and a fifth compressor for compressing the fluid used as the refrigerant in the second heat exchanger after the pressure is reduced by the third pressure reducing device.

Description

Boil-Off Gas Reliquefaction System and Method for Vessel

The present invention relates to a system and method for reliquefying boil-off gas (BOG) produced by natural vaporization of liquefied gas.

Recently, the consumption of liquefied gas such as liquefied natural gas (Liquefied Natural Gas, LNG) is increasing worldwide. Liquefied gas liquefied gas at low temperature has the advantage that the storage and transport efficiency can be improved because the volume is very small compared to the gas. In addition, liquefied gas, including liquefied natural gas can remove or reduce air pollutants during the liquefaction process, it can be seen as an environmentally friendly fuel with less emissions of air pollutants during combustion.

Liquefied natural gas is a colorless and transparent liquid obtained by liquefying natural gas containing methane as a main component at about -163 ℃ and having a volume of about 1/600 compared to natural gas. Therefore, when liquefied and transported natural gas can be transported very efficiently.

However, since the liquefaction temperature of natural gas is a cryogenic temperature of -163 ℃ at normal pressure, liquefied natural gas is sensitive to temperature changes and easily evaporated. As a result, the storage tank storing the liquefied natural gas is insulated. However, since the external heat is continuously transferred to the storage tank, the natural gas is continuously vaporized in the storage tank during the transport of the liquefied natural gas. -Off Gas, BOG) occurs.

Boil-off gas is a kind of loss and is an important problem in transportation efficiency. In addition, when boil-off gas is accumulated in the storage tank, the internal pressure of the tank may be excessively increased, and there is also a risk that the tank may be damaged. Accordingly, various methods for treating the boil-off gas generated in the storage tank have been studied. In recent years, for the treatment of the boil-off gas, a method of re-liquefying the boil-off gas to return to the storage tank, and returning the boil-off gas to the fuel of a ship engine The method used as an energy source of a consumer is used.

As a method for reliquefaction of the boil-off gas, a refrigeration cycle using a separate refrigerant is provided to re-liquefy the boil-off gas by exchanging it with the refrigerant, a method of re-liquefying the boil-off gas itself as a refrigerant without a separate refrigerant, and the like. There is this.

On the other hand, among the engines generally used in ships as a fuel that can use natural gas as a fuel gas engines such as DFDE, X-DF engine, ME-GI engine.

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

The X-DF engine consists of two strokes, uses about 16 bar of natural gas as fuel, and employs an auto cycle.

The ME-GI engine is composed of two strokes and employs a diesel cycle that directly injects high pressure natural gas near 300 bar into the combustion chamber near the top dead center of the piston.

Evaporative gas is reliquefied by using evaporation gas itself as a refrigerant without a separate refrigerant.The evaporated gas compressed by the compressor is cooled by heat-exchanging with the evaporated gas before being compressed by the compressor, and then expanded by a JT valve to evaporate. There is a method of reliquefaction of a part of the gas, and a system employing such a method is called a PRS (Partial Re-liquefaction System).

When there is a large amount of liquefied gas inside the storage tank and the amount of boil-off gas is generated, when the vessel is anchored or when the vessel is operated at a low speed and there is a small amount of boil-off gas used in the engine. However, the PRS alone may not meet the required amount of reliquefaction.

The PRS was improved to re-liquefy the boil-off gas to further cool the boil-off gas by the refrigerant cycle using the boil-off gas itself as a refrigerant. The system employing this method is called MRS (Methane Refrigeration). System).

The present invention is to improve the conventional MRS, to provide a ship boil-off gas reliquefaction system and method, configured to compensate for the problems caused by operating the existing MRS and to more efficiently liquefy the boil-off gas.

According to an aspect of the present invention for achieving the above object, a first compressor for compressing the boil-off gas; A second compressor installed in parallel with the first compressor and compressing an evaporation gas of another flow which is not sent to the first compressor; A first heat exchanger configured to cool the boil-off gas compressed by the first compressor or the second compressor using a boil-off gas before being compressed by the first compressor or the second compressor as a refrigerant, and heat-cool by heat exchange; A second heat exchanger configured to further heat-exchange and cool the fluid cooled by the first heat exchanger by using an evaporated gas circulating in a refrigerant cycle as a refrigerant; And a first decompression device for depressurizing the fluid cooled by the second heat exchanger, wherein the refrigerant cycle comprises: a second decompression device for depressurizing the boil-off gas supplied to the refrigerant cycle; A third decompression device for further depressurizing the fluid decompressed by the second decompression device; And a fourth compressor and a fifth compressor for compressing the fluid used as the refrigerant in the second heat exchanger after the pressure is reduced by the third pressure reducing device.

The fluid used as the refrigerant in the second heat exchanger may be branched into two flows, a part of which may be supplied to the fourth compressor, and the other of which may be supplied to the fifth compressor.

The boil-off gas compressed by the fourth compressor and the boil-off gas compressed by the fifth compressor may be combined to circulate the refrigerant cycle.

The vessel boil-off liquefaction system may further include one or more suction pipes installed in the refrigerant cycle to collect droplets included in the fluid in the lower portion by gravity.

The suction pipe may include a line through which the fluid decompressed by the second decompression device is sent to the third decompression device; And a line through which the fluid cooled by the second heat exchanger is sent to the second pressure reducing device. It can be installed in one or more of the.

The vessel boil-off liquefaction system may further include a water level sensor installed in the suction pipe, and when the water level of the droplet measured by the water level sensor is greater than or equal to a first set value, the liquid collected in the suction pipe may be discharged. have.

When the liquid level of the droplet measured by the water level sensor is equal to or greater than the first set value, an alarm may be notified to notify the time when the liquid droplets collected in the suction pipe are discharged.

The vessel boil-off liquefaction system may further include a first valve installed in a line through which the boil-off gas supplied to the refrigerant cycle is sent to the second decompression device, wherein the liquid level of the droplet measured by the water level sensor is When the value is equal to or greater than the second set value, the flow of the fluid may be blocked by closing the first valve, and the second set value may be greater than the first set value.

The ship boil-off gas reliquefaction system may further include a valve installed in a line through which the fluid decompressed by the second decompression device is sent to the third decompression device, and the level of the droplet measured by the water level sensor. When is greater than or equal to the second set value can close the valve can block the flow of the fluid.

The vessel boil-off liquefaction system, the bypass line for causing the fluid used as the refrigerant in the second heat exchanger bypass the fourth compressor and the fifth compressor; And a second valve installed at the bypass line. When the liquid level of the droplet measured by the water level sensor is equal to or greater than the second set value, the second valve is opened to the second heat exchanger. The fluid used as the refrigerant may bypass the fourth compressor and the fifth compressor along the bypass line.

The vessel boil-off liquefaction system may further include a non-return valve installed downstream of the fourth compressor and the fifth compressor to prevent a backflow of the fluid.

The non-return valve may be installed downstream of the point where the bypass line is joined.

Any one of the first compressor and the second compressor supplies the boil-off gas to the fuel demand (hereinafter, the compressor for supplying the boil-off gas to the fuel demand is referred to as a 'fuel supply compressor'), and the first compressor The remaining compressor which does not supply the boil-off gas to the fuel demand among the second compressors may supply the boil-off gas in the refrigerant cycle (hereinafter, the compressor for supplying the boil-off gas in the refrigerant cycle is referred to as a refrigerant cycle compressor).

The refrigerant cycle may include the 'refrigerant cycle compressor', the second decompression device, the third decompression device, the second heat exchanger, the fourth compressor or the fifth compressor, and the 'refrigerant cycle compressor'. It can form a closed loop connecting the.

The boil-off gas supplied to the refrigerant cycle may be sent to the second pressure reducing device after being cooled by the second heat exchanger.

The refrigerant cycle is the 'compressor cycle compressor', the second heat exchanger, the second pressure reducing device, the third pressure reducing device, the second heat exchanger, the fourth compressor or the fifth compressor, and again It is possible to form a closed loop connecting the 'refrigerant cycle compressor'.

The vessel boil-off liquefaction system is installed on a line for sending the boil-off 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. It may further include a third compressor for further compressing the boil-off gas.

According to another aspect of the present invention for achieving the above object, 1) using the boil-off gas as a refrigerant in the first heat exchanger; 2) branching the boil-off gas used as the refrigerant of the first heat exchanger into two streams in step 1); 3) out of the flow branched into two flows in step 2), one flow to the first compressor, the other flow to the second compressor; 4) sending the boil-off gas compressed by the first compressor or the second-compressor to the fuel demand (hereinafter, the compressor for supplying the boil-off gas to the fuel demand is called a 'fuel supply compressor'); 5) using the remaining evaporated gas which is not used in the fuel demand among the evaporated gas compressed by the fuel supply compressor, using the evaporated gas supplied to the first heat exchanger in step 1 as a refrigerant, Cooling by heat exchange with a heat exchanger; 6) sending the evaporated gas compressed by the remaining compressor other than the 'fuel supply compressor' among the first compressor and the second compressor to the refrigerant cycle (hereinafter, the compressor for supplying the boil-off gas by the refrigerant cycle Compressor '); 7) exchanging and cooling the fluid cooled by the first heat exchanger in step 5) using a boil-off gas circulating in the refrigerant cycle as a refrigerant and heat-exchanged by a second heat exchanger; And 8) reducing the fluid cooled by the second heat exchanger in step 7), wherein the boil-off gas circulating in the refrigerant cycle is compressed by the compressor for the refrigerant cycle. Becoming; 5-2) cooling by the second heat exchanger after being compressed in step 5-1); 5-3) a step of reducing the pressure by the second pressure reducing device after cooling in the step 5-2); 5-4) after the pressure reduction in the step 5-3) further reduced by the third pressure reducing device; 5-5) further reducing the pressure in step 5-4) and using the refrigerant in the second heat exchanger; And 5-6) branching into two flows after being used as the refrigerant of the second heat exchanger in step 5-5). 5-7) one of two flows branched in step 5-6) is sent to the fourth compressor, and the other flow is sent to the fifth compressor; And 5-8) condensing the boil-off gas compressed by the fourth compressor with the boil-off gas compressed by the fifth compressor.

A line through which the fluid decompressed by the second decompression device is sent to the third decompression device; And a line through which the fluid cooled by the second heat exchanger is sent to the second decompression device. The suction pipe may be installed at one or more of the liquid, and the liquid droplets included in the fluid may be collected under the suction pipe by gravity.

When the water level of the liquid droplets collected in the suction pipe is equal to or greater than the second set value, the flow of the fluid sent to the second pressure reducing device or the third pressure reducing device is blocked, and the fluid used as the refrigerant in the second heat exchanger is It is possible to bypass the fourth compressor and the fifth compressor.

According to the present invention, the boil-off gas supplied to the refrigerant cycle RC is further reduced in pressure by the third pressure reducing device 425 as well as the second pressure reducing device 420 to be used as the refrigerant of the second heat exchanger 120. Therefore, the reliquefaction efficiency and the amount of reliquefaction can be further increased.

According to one embodiment of the present invention, by calculating the boiling point according to the pressure of the refrigerant measured by the pressure sensor 615, the temperature of the refrigerant measured by the temperature sensor 610 is measured by the pressure sensor 615 Since the temperature does not fall below the boiling point according to the pressure, the temperature of the refrigerant circulating through the refrigerant cycle RC can be maintained in a range where no droplets are generated.

According to an embodiment of the present invention, since the suction pipe 620 is installed to collect the droplets in the suction pipe 620, it is possible to prevent the droplets from flowing into the second pressure reducing device 420 or the third pressure reducing device 425. have.

According to one embodiment of the present invention, if the level of the liquid droplets collected in the suction pipe 620 is too high to block the flow of the fluid flowing into the second pressure reducing device 420 or the third pressure reducing device 425, the second pressure reducing device It is possible to more thoroughly prevent the droplets from flowing into the 420 or the third pressure reducing device 425.

1 is a schematic diagram of a boil-off gas reliquefaction system according to a first preferred embodiment of the present invention.
2 is a schematic diagram of a boil-off gas reliquefaction system according to a second preferred embodiment of the present invention.
3 is a schematic view of a boil-off gas reliquefaction system according to a third preferred embodiment of the present invention.
4 is a graph schematically showing the phase change of methane with temperature and pressure.
Figure 5 is a graph showing the temperature value of methane according to the heat flow amount under different pressure, respectively.
6 and 7 are graphs showing the amount of reliquefaction according to the boil-off gas pressure in the PRS (Partial Re-liquefaction System).

Hereinafter, the configuration and operation of the preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. Evaporative gas reliquefaction system and method for ships of the present invention can be applied to a variety of applications, such as a ship equipped with an engine using a natural gas as a fuel, a vessel or a liquefied gas storage tank. In addition, the following examples may be modified in many different forms, and the scope of the present invention is not limited to the following examples.

In addition, 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 the operating conditions of the system.

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

Referring to FIG. 1, the ship boil-off gas reliquefaction system of the present embodiment includes a first heat exchanger 110, a first compressor 210, a second compressor 220, a second heat exchanger 120, and a first pressure reduction. Device 410, and a refrigerant cycle RC.

The first heat exchanger 110 uses the evaporated gas before being compressed by the first compressor 210 or the second compressor 220 as a refrigerant, and the first heat exchanger 110 uses the first compressor 210 or the second compressor 220. Cool the compressed boil-off gas.

The boil-off gas used as the refrigerant in the first heat exchanger 110 may be the boil-off gas discharged from the storage tank (T).

The boil-off gas used as the refrigerant in the first heat exchanger 110 is branched into two flows, one flow is sent to the first compressor 210 and the other flow is sent to the second compressor 220.

The first compressor 210 compresses one stream of the boil-off gas branched into two streams after being used as the refrigerant in the first heat exchanger 110. The first compressor 210 may be a multistage compressor, and a first cooler 310 may be installed downstream of the first compressor 210 to cool the boil-off gas compressed by the first compressor 210.

The second compressor 220 is installed in parallel with the first compressor 210 and sent to the first compressor 210 of the boil-off gas branched into two streams after being used as the refrigerant in the first heat exchanger 110. Compress the rest of the unflowed stream. The second compressor 220 may be a multi-stage compressor, and a second cooler 320 for cooling the boil-off gas compressed by the second compressor 220 may be installed downstream of the second compressor 220.

One of the first and second compressors 210 and 220 supplies the boil-off gas to the fuel demand E, and the other one supplies the boil-off gas to the refrigerant cycle RC. In addition, of the boil-off gas compressed by the compressor for supplying the boil-off gas to the fuel demand (E), surplus boil-off gas not used in the fuel demand (E) is sent to the first heat exchanger (110) to undergo a reliquefaction process. .

The fuel demand (E) is a ME-GI engine using approximately 300 bar of natural gas as fuel, an X-DF engine using approximately 16 bar of natural gas as fuel, and a DF using approximately 6.5 bar of natural gas as fuel. At least one of an engine DFGE, DFDE, and a gas combustion unit (GCU).

When the fuel demand E is an engine, the compressor for supplying fuel to the fuel demand E among the first compressor 210 and the second compressor 220 compresses the boil-off gas at the required pressure of the fuel demand E. Let's do it.

Compressors that supply fuel to the engine should have a redundancy design in case of emergency. Redundancy design is a replacement for another when one cannot be used due to failure, maintenance, etc. Designed to be used.

In the present embodiment, the first compressor 210 and the second compressor 220 may play a role of redundancy with each other. Conventionally, the first compressor 210 and the second compressor 220 are evaporated by one of the first compressor 210 and the second compressor 220. Compresses the gas and supplies it to the fuel demand (E), leaving the other unused in standby (Standby), and immediately when the compressor that supplied the boil-off gas to the fuel demand (E) becomes unavailable, It was operated to supply the boil-off gas to the fuel demand (E) by using the compressor of) state.

However, according to the conventional operation method, the use of the compressor supplying the boil-off gas to the fuel demand (E) is unlikely to occur even though it is unlikely to occur even if the duration is not long. In order to prepare, an extra compressor must be installed and the spare compressor must be kept in a standby state, which causes a problem in that a cost for the actual risks is wasted.

According to this embodiment, when both the first compressor 210 and the second compressor 220 can be used normally, one is used for supplying fuel to the fuel demand E, and the other is a refrigerant cycle. When the compressor used for supplying the evaporation gas to the RC and the compressor supplying the evaporation gas to the fuel demand E cannot be used, the evaporation gas is supplied to the refrigerant cycle RC to reliquefy the reliquefaction amount and the reliquefaction efficiency. To abandon the increase, the boil-off gas is supplied to the fuel demand (E) by a compressor that supplies the boil-off gas to the refrigerant cycle RC.

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

The first compressor 210 and the second compressor 220 are preferably compressors of the same performance so as to act as a redundancy with each other.

The second heat exchanger 120 is compressed by the first compressor 210 or the second compressor 220 using the evaporated gas circulating through the refrigerant cycle RC as the refrigerant, and then the first heat exchanger 110. The fluid cooled by the heat exchanger 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 boil-off gas is additionally cooled not only in the first heat exchanger 110 but also in the second heat exchanger 120, so that the boil-off gas cooled only by the first heat exchanger 110 is the first pressure reducing device ( Compared to the case where it is sent to 410, since the evaporated gas in a lower temperature is sent to the first decompression device 410, the reliquefaction efficiency and the amount of reliquefaction are increased. The following is a closer look at this.

4 is a graph schematically showing the phase change of methane with temperature and pressure. Referring to FIG. 4, the methane is in a supercritical fluid state at a temperature of about −80 ° C. or more and a pressure of about 55 bar or more. That is, in the case of methane, the critical point is about -80 ℃, 55bar state. The supercritical fluid state is a third state different from the liquid state or the gas state.

When the boil-off gas has a temperature lower than the critical point at a pressure above the critical point, it may be in a state similar to a dense supercritical fluid state different from the general liquid state. The state is hereinafter referred to as "high pressure liquid state".

The evaporated gas sent to the first heat exchanger 110 to undergo the reliquefaction process may be in a gaseous state or a supercritical fluid state depending on the degree of compression. When the boil-off gas sent to the first heat exchanger 110 is in a gaseous state, the boil-off gas in the gaseous state passes through the first heat exchanger 110 and the temperature is lowered to form a mixed state of liquid and gas. When the boil-off gas sent to the first heat exchanger 110 is in a supercritical fluid state, the fluid in the supercritical fluid state passes through the first heat exchanger 110 and the temperature is lowered to become a "high pressure liquid state."

The fluid cooled by the first heat exchanger 110 has a lower temperature while passing through the second heat exchanger 120. When the fluid passing through the first heat exchanger 110 is a mixture of liquid and gas, In this case, the fluid in the mixed state of the liquid and gas passes through the second heat exchanger 120 and the temperature is lowered so that the ratio of the liquid becomes a mixed state or becomes a 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 the temperature is lowered to become the "high pressure liquid state" in which the temperature is lower.

Also, even when the fluid passing through the second heat exchanger 120 is in the "high pressure liquid state", the fluid in the "high pressure liquid state" passing through the second heat exchanger 120 passes through the first pressure reducing device 410. As the pressure is lowered, the liquid becomes a liquid state or a mixture of liquid and gas.

Although the boil-off gas is lowered to the same degree (P in FIG. 4) by the first pressure reducing device 410, the temperature is lower than that in the case where the pressure is reduced in a higher state (X → X ′ in FIG. 4). It can be seen that when the pressure is reduced in the state (Y → Y ′ in FIG. 4), the ratio of the liquid becomes a higher mixed state. In addition, it can be seen that if the temperature can be further lowered, theoretically 100% of the evaporated gas can be reliquefied (Z → Z ′ in FIG. 4). 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 reliquefaction efficiency and the amount of reliquefaction are increased.

The first decompression device 410 decompresses 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. Let's do it. The first pressure reducing device 410 includes all means capable of reducing the evaporated gas to be cooled, 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. Expansion valves have the advantage of being inexpensive and less prone to failure than inflators.

The compression process by the first compressor 210 or the second compressor 220, the cooling process by the first heat exchanger 110 and the second heat exchanger 120, and the pressure reduction by the first pressure reducing device 410. Partially or all of the evaporated gas undergoes reliquefaction.

The vessel boil-off liquefaction system of this embodiment may further include a gas-liquid separator 500 installed downstream of the first decompression device 410 to separate the liquefied liquefied gas and the boil-off gas remaining in the gas state. .

The liquefied gas separated by the gas-liquid separator 500 may be sent to the storage tank T, and the boil-off gas separated by the gas-liquid separator 500 is an evaporated gas before being used as a refrigerant in the first heat exchanger 110. And may 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 the refrigerant, the evaporated gas separated by the gas-liquid separator 500 joins the evaporated gas discharged from the storage tank T. Can be sent to the first heat exchanger (110).

In addition, the boil-off gas separated by the gas-liquid separator 500 may be separately separated without joining the boil-off gas before being used as the coolant in the first heat exchanger 110 to be used as the coolant in the first heat exchanger 110. In this case, the first heat exchanger 110 may be composed of three flow paths.

When the ship boil-off gas liquefaction system of the present embodiment does not include the gas-liquid separator 500, some or all of the boil-off liquid liquefied boil-off gas may be sent directly from the first decompression device 410 to the storage tank (T).

In the refrigerant cycle RC through which the boil-off gas used as the refrigerant in the second heat exchanger 120 circulates, the second pressure reducing device 420, the third pressure reducing device 425, the fourth compressor 240, and the fifth Compressor 245 is included.

The boil-off gas, which is compressed by the first compressor 210 or the second compressor 220 and then supplied to the refrigerant cycle RC, is cooled by the second heat exchanger 120 and then sent to the second pressure reducing device 420. Lose.

The second pressure reducing device 420 lowers the temperature by reducing the boil-off gas supplied to the refrigerant cycle RC after being compressed by the first compressor 210 or the second compressor 220. The second pressure reducing device 420 includes all means capable of cooling the evaporated gas by reducing the pressure, 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 pressure reducing device 420 is an expander.

The third pressure reducing device 425 further lowers the temperature by further depressurizing the fluid decompressed by the second pressure reducing device 420. The third pressure reducing device 425 includes all means capable of reducing the evaporated gas to be cooled and may be an expansion valve such as a Joule-Thomson valve or an expander. In the present embodiment, it is preferable that the third pressure reducing device 425 is an expander.

The fluid sequentially depressurized by the second pressure reducing device 420 and the third pressure reducing device 425 is supplied to the second heat exchanger 120 to further supply the fluid cooled by the first heat exchanger 110. Used as a refrigerant to cool.

The boil-off gas supplied to the refrigerant cycle RC after being compressed by the first compressor 210 or the second compressor 220 is connected to the second heat exchanger 120 before being decompressed by the second pressure reducing device 420. Can pass. In this case, the boil-off gas compressed by the first compressor 210 or the second compressor 220 and then supplied to the refrigerant cycle RC is heat-exchanged by the second heat exchanger 120 to be cooled first. After the pressure is reduced by the second pressure reducing device 420 and cooled secondarily, the pressure is reduced by the third pressure reducing device 425 and thirdly cooled, and then sent to the second heat exchanger 120 to be used as a refrigerant.

The fourth compressor 240 and the fifth compressor 245 compress the fluid used as the refrigerant in the second heat exchanger 120 to maintain a constant pressure average of the boil-off gas circulating through the refrigerant cycle RC. Play a role.

Unlike the second decompression device 420 and the third decompression device 425 are connected in series to decompress the fluid sequentially, the fourth compressor 240 and the fifth compressor 245 are connected in parallel, and the second The fluid used as the refrigerant in the heat exchanger 120 is branched into two flows, one flow is sent to the fourth compressor 240 and the other flow is sent to the fifth compressor 245. The boil-off gas compressed by the fourth compressor 240 and the boil-off gas compressed by the fifth compressor 245 are combined to circulate the refrigerant cycle RC.

The fourth compressor 240 may be driven by the power generated by the second pressure reducing device 420 while expanding the fluid by forming the second pressure reducing device 420 and the first compander C1. 245 may be driven by power generated by the third pressure reducing device 425 to expand the fluid by forming the third pressure reducing device 425 and the second compander C2.

Further, downstream of the fourth compressor 240 and the fifth compressor 245, a fourth cooler 340 for cooling the boil-off gas compressed by the fourth compressor 240 or the fifth compressor 245 may be installed. have. When the present invention includes the fourth cooler 340, the boil-off gas compressed by the fourth compressor 240 and the boil-off gas compressed by the fifth compressor 245 are joined to the fourth cooler 340. Is sent.

In the ship boil-off gas liquefaction system of this embodiment, the flow which combined the boil-off gas compressed by the 4th compressor 240 and the boil-off gas compressed by the 5th compressor 245, the upstream of the 1st compressor 210 is carried out. The first compressor 210 may be configured to include a refrigerant cycle RC, and the second compressor 220 may be configured to include a refrigerant cycle. It was made.

When the boil-off gas compressed by the first compressor 210 is supplied to the fuel demand E and the boil-off gas compressed by the second compressor 220 is supplied to the refrigerant cycle RC, the second compressor ( 220, second pressure reducing device 420, third pressure reducing device 425, second heat exchanger 120, fourth compressor 240 or fifth compressor 245, and second compressor 220 again. A refrigerant cycle RC of a closed loop to be connected 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 pressure reducing device 420, the second compressor 220, the second heat exchanger 120, Connecting the second pressure reducing device 420, the third pressure reducing device 425, the second heat exchanger 120, the fourth compressor 240 or the fifth compressor 245, and the second compressor 220 again. A closed loop refrigerant cycle RC is formed.

When the boil-off gas compressed by the first compressor 210 is supplied to the refrigerant cycle RC and the boil-off gas compressed by the second compressor 220 is supplied to the fuel demand E, the first compressor ( 210, the second pressure reducing device 420, the third pressure reducing device 425, the second heat exchanger 120, the fourth compressor 240 or the fifth compressor 245, and again the first compressor 210. A refrigerant cycle RC of a closed loop to be connected 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 pressure reducing device 420, the first compressor 210, the second heat exchanger 120, Connecting the second pressure reducing device 420, the third pressure reducing device 425, the second heat exchanger 120, the fourth compressor 240 or the fifth compressor 245, and the first compressor 210 again. A closed loop refrigerant cycle RC is formed.

According to the present invention, one of the first compressor 210 and the second compressor 220 is selected to supply the boil-off gas to the fuel demand E or the first heat exchanger 110, and the fuel demand E B. Since the refrigerant cycle RC can be circulated with the boil-off gas compressed by another compressor that does not supply boil-off gas to the first heat exchanger 110, there is an advantage in that the operation of the system is free.

In addition, according to the present invention, there is an advantage that the re-liquefaction efficiency and the amount of re-liquefaction of the boil-off gas can be increased by utilizing a redundancy compressor that is not normally used even though it is conventionally installed in a ship.

In addition, according to the present invention, the boil-off gas supplied to the refrigerant cycle RC is further depressurized by the third pressure reducing device 425 as well as the second pressure reducing device 420 so that the second heat exchanger 120 Since it is used as a refrigerant, the reliquefaction efficiency and the amount of reliquefaction can be further increased.

According to the present embodiment, nitrogen may be injected into the refrigerant cycle RC so that the fluid in which the evaporation gas and nitrogen are mixed circulates through the refrigerant cycle RC and may be used as the refrigerant in the second heat exchanger 120.

The vessel boil-off liquefaction system of this embodiment is installed on the line which sends the boil-off gas compressed by the 1st compressor 210 or the 2nd compressor 220 to the 1st heat exchanger 110, and has the 1st compressor ( It may further include a third compressor 230 for further compressing the boil-off gas compressed by the 210 or the second compressor 220. In addition, a third cooler 330 may be installed downstream of the third compressor 230 to cool the boil-off gas compressed by the third compressor 230.

The reason for further compressing the boil-off gas sent to the first heat exchanger 110 after being compressed by the first compressor 210 or the second compressor 220 by the third compressor 230 may include a reliquefaction process. In order to increase the pressure of the boil-off gas to increase the amount of re-liquefaction and re-liquefaction, the details are as follows.

5 is a graph showing the temperature value of the methane according to the heat flow amount under different pressure, respectively, referring to Figure 5, the higher the pressure of the boil-off gas undergoing the reliquefaction process, it can be seen that the efficiency of the self-heat exchange. Self- of self-heat exchange means that the low-temperature evaporated gas itself is used as a refrigerant to heat the high-temperature evaporated gas to be cooled.

FIG. 5A shows the state of each fluid upstream and downstream of the second heat exchanger 120 when the ship boil-off gas reliquefaction system of the present embodiment does not include the third compressor 230. 5B shows the state of each fluid upstream and downstream of the second heat exchanger 120 when the marine boil-off gas reliquefaction system of the present embodiment includes the third compressor 230.

In FIG. 5, the boil-off 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, and the second pressure reducing device ( The case where the pressure is reduced by 420 and then supplied to the second heat exchanger 120 is illustrated.

The uppermost graph I of FIGS. 5A and 5B shows the fluid state at the point P1 of FIG. 1 supplied to the second heat exchanger 120, and the lowermost graph L is the second heat exchanger. After passing through the gas 120 and the second pressure reducing device 420 shows the fluid state of the point P2 of FIG. 1 which is supplied back to the second heat exchanger 120 to be used as a refrigerant, and the graph K and The graph J, which is overlaid, shows the fluid state at the point P3 of FIG. 1 supplied to the second heat exchanger 120 after passing through the first heat exchanger 110.

Since the fluid used as the refrigerant loses heat from the heat exchange process and gradually increases in temperature, the graph L proceeds from left to right with time, and the fluid heat-exchanged with the refrigerant cools the heat from the refrigerant during the heat exchange process. As the temperature is getting lower and lower, the graphs I and J progress from right to left over time.

The graph K of the middle part of (a) and (b) of FIG. 5 shows the graph I and the graph J combined. That is, the fluid used as the refrigerant in the second heat exchanger 120 is drawn as a graph L, and the fluid that is cooled by heat exchange with the refrigerant in the second heat exchanger 120 is drawn as a graph K.

When designing a heat exchanger, the temperature of the fluid supplied to the heat exchanger (that is, the fluid at points P1, P2, and P3 in FIG. 1) and the heat flow amount are fixed, and the temperature of the fluid at which the temperature of the fluid used as the refrigerant is cooled. Ensure that the Logarithmic Mean Temperature Difference (LMTD) is as small as possible, while not getting higher (i.e., intersecting graph L and graph K so that graph L does not appear above graph K).

Logical mean temperature difference (LMTD) is a heat exchange method in which the hot fluid and the low temperature fluid are injected in opposite directions and discharged from the opposite side, and the temperature before the low temperature fluid passes through the heat exchanger is tc1 and the low temperature fluid passes through the heat exchanger. After the temperature is tc2, the temperature before the high temperature fluid passes through the heat exchanger is called th1, and the temperature after the high temperature fluid passes through the heat exchanger is called th2, and d1 = th2-tc1, d2 = th1-tc2, and (d2- d1) / ln (d2 / d1), the smaller the logarithmic mean temperature difference, the higher the efficiency of the heat exchanger.

In the graph, the logarithmic mean temperature difference LMTD is represented by the interval between the low temperature fluid (graph L of FIG. 5) used as the refrigerant and the high temperature fluid (graph K of FIG. 5) cooled by heat exchange with the refrigerant. It can be seen that (b) of FIG. 5 shows that the interval between the graph L and the graph K is narrower than).

The difference is that the initial value of the graph J, the point indicated by the round circle, that is, the pressure of the fluid at the point P3 of FIG. 1 supplied to the second heat exchanger 120 after passing through the first heat exchanger 110 is determined. 5B is higher than that of FIG. 5A.

That is, in the case of FIG. 5A, which does not include the third compressor 230, the fluid at the point P3 of FIG. 1 may be approximately −111 ° C. and 20 bar, and the third compressor 230 may be used. In the case of Figure 5 (b) comprising a, the fluid at point P3 of Figure 1 may be approximately -90 ℃, 50 bar, under these initial conditions the heat exchanger so that the logarithmic mean temperature difference (LMTD) is the smallest In the design, the efficiency of the heat exchanger is higher in the case of FIG.

In the case of FIG. 5A, when the flow rate of the evaporated gas used as the refrigerant in the second heat exchanger 120 is approximately 6401 kg / h, the refrigerant is exchanged with the refrigerant from the fluid (graph L) used as the refrigerant and cooled. The total heat flow delivered to the fluid (graph K) is approximately 585.4 kW and the flow rate of the reliquefied boil-off gas is approximately 3441 kg / h.

In the case of FIG. 5B, when the flow rate of the boil-off gas used as the refrigerant in the second heat exchanger 120 is about 5368 kg / h, the refrigerant is exchanged with the refrigerant from the fluid (graph L) used as the refrigerant and cooled. The total heat flow delivered to the fluid (graph K) is approximately 545.2 kW, and the flow rate of the reliquefied boil-off gas is approximately 4325 kg / h.

That is, it can be seen that by increasing the pressure of the boil-off gas including the third compressor 230 undergoing the re-liquefaction process, it is possible to re-liquefy a larger amount of boil-off gas even with less refrigerant.

When the boil-off gas is further compressed by the third compressor 230 to increase the amount of re-liquefaction and re-liquefaction, the second heat exchanger 120 may re-liquefy the entire boil-off gas without further cooling the boil-off gas. And the time required to supply the boil-off gas to the refrigerant cycle RC eventually decreases, thereby fully securing the effect of the redundancy design in case the compressor supplying the boil-off gas to the fuel demand E fails. can do.

On the other hand, when the vessel boil-off liquefaction system of the present embodiment it is advantageous to further include a third compressor 230, and looks at the preferred pressure for the third compressor 230 to compress the boil-off gas as follows.

6 and 7 are graphs showing the amount of reliquefaction according to the boil-off gas pressure in the PRS (Partial Re-liquefaction System). The boil-off gas to be reliquefed means an boil-off gas that is cooled and re-liquefied and named to distinguish it from the boil-off gas used as a refrigerant.

However, FIGS. 6 and 7 are graphs showing the reliquefaction amount according to the boil-off pressure in the PRS, so that the reliquefaction amount is lower than that of the MRS which further reliquefies the boil-off gas by the boil-off gas circulating in the refrigerant cycle. . In the case of MRS, approximately 3300 kg of boil-off gas can be reliquefied per hour.

6 and 7, it can be seen that the reliquefaction amount shows the maximum value when the pressure of the boil-off gas is around 150 to 170 bar, and there is almost no change in the amount of liquefaction between 150 and 300 bar.

Evaporated gas compressed to the required pressure of the fuel demand (E) by one of the first compressor 210 and the second compressor 220 is sent to the fuel demand (E), and the evaporation gas to the fuel demand (E) Of the boil-off gas compressed by the supplying compressor, the excess boil-off gas not used in the fuel demand (E) is sent to the first heat exchanger 110 to undergo a reliquefaction process. When the third compressor 230 is not included, a part of the boil-off gas compressed at the required pressure of the fuel demand E is sent to the first heat exchanger 110 to undergo a reliquefaction process.

When the fuel demand (E) is an engine using natural gas of 150 bar or more, such as a ME-GI engine using approximately 300 bar of natural gas as fuel, the pressure required by the fuel demand (E) is required. There is no problem in that the excess evaporated gas which is not used in the fuel demand (E) is directly liquefied, but the fuel demand (E) uses approximately 16 bar of natural gas as fuel. In the case of an engine using less than 150 bar of natural gas as a fuel, such as a DF engine or a DF engine (DFGE, DFDE) that uses about 6.5 bar of natural gas as fuel, the third compressor 230 It is desirable to undergo further reliquefaction after further compression by.

In addition, the third compressor 230 preferably compresses the evaporated gas to about 150 to 300 bar, more preferably about 150 to 170 bar, so as to secure the maximum amount of reliquefaction. . In addition, since the amount of the third compressor 230 that compresses the boil-off gas decreases, the energy consumed by the third compressor 230 may be reduced. Thus, the third compressor 230 is more preferably approximately 150 bar. To compress the boil-off gas.

The third compressor 230 is generally sufficient to have approximately half the capacity of the first compressor 210 or the second compressor 220.

On the other hand, when the amount of liquefied gas stored in the storage tank (T) is small and the amount of evaporated gas discharged from the storage tank (T) is small, or when the evaporation gas used as fuel in the fuel demand (E) such as engine For example, when the amount of boil-off gas to be reliquefied is small, the boil-off gas undergoing the re-liquefaction process is cooled only by the first heat exchanger 110, and the second heat exchanger 120 bypasses the first heat exchanger. It may be sent to the decompression device 410 and operated in the same manner as the PRS.

When the evaporated gas undergoing the reliquefaction process is cooled only by the first heat exchanger 110 and the second heat exchanger 120 is bypassed, it is not necessary to supply the refrigerant to the second heat exchanger 120. The boil-off gas may not be supplied to the cycle RC.

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

The vessel boil-off liquefaction system of the second embodiment shown in FIG. 2 further includes a temperature sensor 610 and a pressure sensor 615 as compared to the vessel boil-off liquefaction system of the first embodiment shown in FIG. 1. Differences exist in this respect, and the following description will focus on the differences. Detailed descriptions of the same members as those of the ship boil-off gas liquefaction system of the first embodiment are omitted.

Referring to FIG. 2, the vessel boil-off liquefaction system of this embodiment, like the first embodiment, has a first heat exchanger 110, a first compressor 210, a second compressor 220, and a second heat exchanger. 120, a first pressure reducing device 410, and a refrigerant cycle RC.

The refrigerant cycle RC of the present embodiment, like the first embodiment, includes a second pressure reducing device 420, a third pressure reducing device 425, a fourth compressor 240, and a fifth compressor 245. .

The vessel boil-off liquefaction system of the present embodiment, like the first embodiment, may further include one or more of the third compressor 230 and the gas-liquid separator 500, when the amount of boil-off gas to be liquefied is small For example, the boil-off gas compressed by the first compressor 210 or the second compressor 220 is cooled only by the first heat exchanger 110, and the second heat exchanger 120 bypasses the first heat exchanger. It may be sent to the decompression device 410.

In addition, the second pressure reducing device 420 and the third pressure reducing device 425 of the present embodiment are expanders including a plurality of blades.

The refrigerant cycle RC of the present embodiment, unlike the first embodiment, may further include one or more suction pipes 620.

 The liquid decompressed by the second decompression device 420 and the temperature as well as the pressure is lowered may include droplets. When the fluid containing the droplets is sent to the third decompression device 425, a blade that rotates at a high speed. Drops may enter the blades and damage the blades.

Therefore, in the present embodiment, the suction pipe 620 is installed in a line through which the fluid decompressed by the second pressure reducing device 420 is sent to the third pressure reducing device 425, so that the droplets flow into the third pressure reducing device 425. Do not The fluid passes through the suction pipe 620, and droplets included in the fluid collect under the suction pipe 620 by gravity, and the gas component rises above the suction pipe 620.

In FIG. 2, although the suction pipe 620 is illustrated between the second pressure reducing device 420 and the third pressure reducing device 425, the evaporated gas supplied to the refrigerant cycle RC is transferred to the second heat exchanger 120. When the liquid is cooled and then sent to the second pressure reducing device 420, the liquid cooled by the second heat exchanger 120 may also contain droplets, so that the fluid cooled by the second heat exchanger 120 may be transferred to the second pressure reducing device 420. A suction pipe 620 may be installed in a line sent to the pressure reducing device 420. Of course, the line through which the fluid decompressed by the second decompression device 420 is sent to the third decompression device 425 and the fluid cooled by the second heat exchanger 120 are not sent to the second decompression device 420. Both suction lines 620 may be installed on the line.

A water level sensor 630 may be installed in the suction pipe 620, and when the liquid level of the droplet measured by the water level sensor 630 is greater than or equal to a predetermined height, the liquid droplets collected in the suction pipe 620 may be discharged.

The refrigerant cycle RC of the present embodiment, unlike the first embodiment, includes a temperature sensor 610 and a pressure sensor 615. The temperature sensor 610 measures the temperature of the refrigerant circulating through the refrigerant cycle RC, and the pressure sensor 615 measures the pressure of the refrigerant circulating through the refrigerant cycle RC.

According to the present embodiment, the boiling point (that is, the temperature at which the droplets are generated) according to the pressure of the refrigerant measured by the pressure sensor 615 is calculated, and the temperature of the refrigerant measured by the temperature sensor 610 is measured by the pressure sensor 615. Do not go below the boiling point according to the pressure measured by). That is, the temperature of the refrigerant circulating through the refrigerant cycle RC is maintained in a range where no droplets are generated.

In detail, the temperature measured by the temperature sensor 610 is a temperature higher than a boiling point according to the pressure measured by the pressure sensor 615 (hereinafter, the temperature higher than the boiling point by a predetermined value is referred to as 'third set value'). It can be kept above.

On the other hand, the refrigerant circulating through the refrigerant cycle RC is cooled by the second heat exchanger 120 and the fluid decompressed by the second pressure reducing device 420 after being cooled by the second heat exchanger 120. The fluid decompressed by the second decompression device 420 and then decompressed by the third decompression device 425 has the lowest temperature.

That is, droplets are more likely to occur in the fluid decompressed by the second decompression device 420 and the fluid decompressed by the third decompression device 425. Since it is sent to the heat exchanger 120, even if droplets are generated, it does not matter much. However, if droplets are generated in the fluid decompressed by the second decompression device 420, the droplets are introduced into the third decompression device 425 and the third The pressure reducing device 425 may be damaged.

Accordingly, the temperature sensor 610 and the pressure sensor 615 are installed downstream of the second pressure reducing device 420, and are cooled by the second heat exchanger 120 and then decompressed by the second pressure reducing device 420. It is desirable to measure the pressure and temperature of the fluid.

For the same reason, the suction pipe 620 is also preferably installed between the second pressure reducing device 420 and the third pressure reducing device 425, more preferably the suction pipe 620 is a temperature sensor 610 and pressure sensor 615. ) And upstream of the third pressure reducing device 425.

According to this embodiment, in order to maintain the temperature measured by the temperature sensor 610 above the third set value, when the temperature measured by the temperature sensor 610 is less than the third set value (the third pressure reducing device ( 425) can be reduced.

When the flow rate of the third pressure reducing device 425 is reduced, the flow rate of the refrigerant circulating in the refrigerant cycle RC is reduced, so that the average temperature of the refrigerant circulating in the refrigerant cycle RC is increased and the probability of droplet generation is lowered.

3 is a schematic view of a boil-off gas reliquefaction system according to a third preferred embodiment of the present invention.

The marine boil-off gas liquefaction system of the third embodiment shown in FIG. 3 further includes a suction pipe 620 and a bypass line BL as compared to the marine boil-off gas liquefaction system of the first embodiment shown in FIG. 1. Differences exist in the following, and the following description focuses on the differences. Detailed descriptions of the same members as those of the ship boil-off gas liquefaction system of the first embodiment are omitted.

Referring to FIG. 3, the vessel boil-off liquefaction system of this embodiment, like the first embodiment, has a first heat exchanger 110, a first compressor 210, a second compressor 220, and a second heat exchanger. 120, a first pressure reducing device 410, and a refrigerant cycle RC.

The refrigerant cycle RC of the present embodiment, like the first embodiment, includes a second pressure reducing device 420, a third pressure reducing device 425, a fourth compressor 240, and a fifth compressor 245. .

The vessel boil-off liquefaction system of the present embodiment, like the first embodiment, may further include one or more of the third compressor 230 and the gas-liquid separator 500, when the amount of boil-off gas to be liquefied is small For example, the boil-off gas compressed by the first compressor 210 or the second compressor 220 is cooled only by the first heat exchanger 110, and the second heat exchanger 120 bypasses the first heat exchanger. It may be sent to the decompression device 410.

In addition, the second pressure reducing device 420 and the third pressure reducing device 425 of the present embodiment are expanders including a plurality of blades.

The refrigerant cycle RC of the present embodiment, unlike the first embodiment, further includes one or more suction pipes 620.

 The liquid decompressed by the second decompression device 420 and the temperature as well as the pressure is lowered may include droplets. When the fluid containing the droplets is sent to the third decompression device 425, a blade that rotates at a high speed. Drops may enter the blades and damage the blades.

Therefore, in the present exemplary embodiment, the suction pipe 620 is installed in a line for sending the fluid decompressed by the second pressure reducing device 420 to the third pressure reducing device 425 so that the droplets do not flow into the third pressure reducing device 425. Do not The fluid passes through the suction pipe 620, and droplets included in the fluid collect under the suction pipe 620 by gravity, and the gas component rises above the suction pipe 620.

In FIG. 3, although the suction pipe 620 is illustrated between the second pressure reducing device 420 and the third pressure reducing device 425, the evaporated gas supplied to the refrigerant cycle RC is transferred to the second heat exchanger 120. When the liquid is cooled and then sent to the second pressure reducing device 420, the liquid cooled by the second heat exchanger 120 may include droplets, and thus, the fluid cooled by the second heat exchanger 120 may be transferred to the second pressure reducing device 420. The suction pipe 620 may be installed in a line to the decompression device 420. Of course, a line for sending the fluid decompressed by the second pressure reducing device 420 to the third pressure reducing device 425 and a line for sending the fluid cooled by the second heat exchanger 120 to the second pressure reducing device 420. Both suction pipes 620 may be installed.

A water level sensor 630 is installed in the suction pipe 620. When the level of the droplet measured by the water level sensor 630 is equal to or greater than the first set value, the liquid droplets collected in the suction pipe 620 may be discharged. In addition, when the level of the droplet measured by the water level sensor 630 is greater than or equal to the first set value, it may be designed to notify the time to discharge the droplets collected in the suction pipe 620 by the alarm.

Unlike the first embodiment, the refrigerant cycle RC of the present embodiment further includes a first valve V1 provided with a line through which the boil-off gas supplied to the refrigerant cycle RC is sent to the second decompression device 420. Include. When the boil-off gas supplied to the refrigerant cycle RC is cooled by the second heat exchanger 120 and then sent to the second pressure reducing device 420, the first valve V1 is the second heat exchanger 120. The fluid cooled by) is installed in the line sent to the second pressure reducing device 420.

The first valve V1 receives a signal from the water level sensor 630 so that the level of the liquid droplets measured by the water level sensor 630 is equal to or greater than the second set value, so that the droplets are reduced by the second pressure reducing device 420 or the third. If there is a possibility to flow into the decompression device 425 is closed to block the flow of the fluid, so that the fluid does not flow into the second decompression device (420). The second set value is greater than the first set value.

Unlike the first embodiment, the refrigerant cycle RC of the present embodiment further includes a bypass line BL and a second valve V2.

The bypass line BL allows the fluid used as the refrigerant in the second heat exchanger 120 after being decompressed by the third pressure reducing device 425 to bypass the fourth compressor 240 and the fifth compressor 245. , The second valve V2 is installed in the bypass line BL. When the fourth cooler 340 is installed downstream of the fourth compressor 240 and the fifth compressor 245, the bypass line BL is not only the fourth compressor 240 and the fifth compressor 245 but also the fourth cooler. Also bypass 340.

The second valve V2 receives a signal from the level sensor 630 and opens when the level of the droplet measured by the level sensor 630 becomes equal to or greater than the second set value. When the second valve V2 is opened, the fluid used as the refrigerant in the second heat exchanger 120 bypasses the fourth compressor 240 and the fifth compressor 245 along the bypass line BL.

That is, when the liquid level of the droplet measured by the water level sensor 630 becomes equal to or greater than the second set value and the droplet may flow into the second pressure reducing device 420 or the third pressure reducing device 425, the first valve ( V1) is closed to prevent the fluid from flowing into the second pressure reducing device 420, and the second valve V2 is opened to allow the fluid to bypass the fourth compressor 240 and the fifth compressor 245 so that the fourth compressor ( 240 and fifth compressor 245 are protected.

Although not shown in FIG. 3, a valve is further installed in a line through which the fluid decompressed by the second decompression device 420 is sent to the third decompression device 425, so that the liquid measured by the water level sensor 630 is provided. When the water level of the enemy is greater than or equal to the second set value, the valve provided between the second pressure reducing device 420 and the third pressure reducing device 425 may be closed so that the droplets do not flow into the third pressure reducing device 425.

In addition, a non-return valve V3 may be installed downstream of the fourth compressor 240 and the fifth compressor 245 to prevent the back flow of the fluid. The non-return valve V3 is installed downstream of the point where the bypass line BL joins, and when the fourth cooler 340 is installed downstream of the fourth compressor 240 and the fifth compressor 245, the non-return valve is prevented. The valve V3 is installed downstream of the fourth cooler 340.

The present invention is not limited to the above embodiments, and various modifications or changes may be made without departing from the technical spirit of the present invention, which will be apparent to those of ordinary skill in the art. It is.

T: Storage Tank RC: Refrigerant Cycle
V1: first valve V2: second valve
V3: check valve BL: bypass line
C1: first compander C2: second compander
E: fuel demand 110: first heat exchanger
120: second heat exchanger 210: first compressor
220: second compressor 230: third compressor
240: fourth compressor 245: fifth compressor
310: first cooler 320: second cooler
330: third cooler 340: fourth cooler
410: first pressure reducing device 420: second pressure reducing device
425: third pressure reducing device 500: gas-liquid separator
610: temperature sensor 615: pressure sensor
620: suction pipe 630: water level sensor

Claims (20)

A first compressor for compressing the boil-off gas;
A second compressor installed in parallel with the first compressor and compressing an evaporation gas of another flow which is not sent to the first compressor;
A first heat exchanger configured to cool the boil-off gas compressed by the first compressor or the second compressor using a boil-off gas before being compressed by the first compressor or the second compressor as a refrigerant, and heat-cool by heat exchange;
A second heat exchanger configured to further heat-exchange and cool the fluid cooled by the first heat exchanger by using an evaporated gas circulating in a refrigerant cycle as a refrigerant; And
And a first decompression device for depressurizing the fluid cooled by the second heat exchanger.
The refrigerant cycle, the second pressure reducing device for reducing the evaporated gas supplied to the refrigerant cycle; A third decompression device for further depressurizing the fluid decompressed by the second decompression device; And a fourth compressor and a fifth compressor for compressing the fluid used as the refrigerant in the second heat exchanger after the pressure is reduced by the third pressure reducing device.
The fluid used as the refrigerant in the second heat exchanger is divided into two flows, a part of which is supplied to the fourth compressor and the other of which is supplied to the fifth compressor. delete The method according to claim 1,
And a boil-off gas compressed by the fourth compressor and a boil-off gas compressed by the fifth compressor to circulate the refrigerant cycle. The method according to claim 1,
And at least one suction tube installed in the refrigerant cycle to collect droplets contained in the fluid in the lower portion by gravity. The method according to claim 4,
The suction pipe,
A line through which the fluid decompressed by the second decompression device is sent to the third decompression device; And
A line through which the fluid cooled by the second heat exchanger is sent to the second decompression device;
Evaporative gas reliquefaction system for ships, installed in one or more of the. The method according to claim 4,
Further comprising a water level sensor installed in the suction pipe,
When the liquid level of the droplets measured by the water level sensor is equal to or greater than the first set value, the liquid droplets collected in the suction pipe is discharged. The method according to claim 6,
And when the water level of the droplet measured by the water level sensor is equal to or greater than the first set value, an alarm sounds to indicate when to discharge the droplets collected in the suction pipe. The method according to claim 6,
And a first valve installed in a line through which the boil-off gas supplied to the refrigerant cycle is sent to the second decompression device.
When the liquid level of the droplet measured by the water level sensor is equal to or greater than a second set value, the first valve is closed to block the flow of fluid.
Wherein said second set point is a value greater than said first set point. The method according to claim 8,
And a valve installed in a line through which the fluid decompressed by the second pressure reducing device is sent to the third pressure reducing device.
When the liquid level of the droplet measured by the water level sensor is equal to or greater than the second set value, the valve is closed to shut off the flow of the fluid, marine evaporation gas reliquefaction system. The method according to claim 8,
A bypass line for causing the fluid used as the refrigerant in the second heat exchanger to bypass the fourth compressor and the fifth compressor; And
And a second valve installed at the bypass line.
When the liquid level of the droplet measured by the water level sensor is equal to or greater than the second set value, the second valve is opened so that the fluid used as the refrigerant in the second heat exchanger is along the bypass line. 5 Evaporative gas reliquefaction system for ships, bypassing the compressor. The method according to claim 10,
And a backflow check valve installed downstream of the fourth compressor and the fifth compressor to prevent a backflow of the fluid. The method according to claim 11,
The non-return valve is installed on the downstream of the point where the bypass line is joined, the vessel boil-off liquefaction system. The method according to any one of claims 1 and 3 to 12,
Any one of the first compressor and the second compressor supplies the boil-off gas to the fuel demand (hereinafter, the compressor for supplying the boil-off gas to the fuel demand is called a 'fuel supply compressor').
The remaining compressor which does not supply the boil-off gas to the fuel demand among the first compressor and the second compressor supplies the boil-off gas in the refrigerant cycle (hereinafter, referred to as a 'compressor for compressor cycle'). Evaporative gas reliquefaction system for ships. The method according to claim 13,
The refrigerant cycle may include the 'refrigerant cycle compressor', the second decompression device, the third decompression device, the second heat exchanger, the fourth compressor or the fifth compressor, and the 'refrigerant cycle compressor'. Forming a closed loop connecting the vessel, the boil-off gas reliquefaction system. The method according to claim 13,
The evaporated gas supplied to the refrigerant cycle is cooled by the second heat exchanger and then sent to the second decompression device, the ship boil-off gas reliquefaction system. The method according to claim 15,
The refrigerant cycle is the 'compressor cycle compressor', the second heat exchanger, the second pressure reducing device, the third pressure reducing device, the second heat exchanger, the fourth compressor or the fifth compressor, and again A boil-off gas reliquefaction system for forming a closed loop connecting the 'compressor cycle compressor'. The method according to any one of claims 1 and 3 to 12,
A third that is installed on a line for sending the boil-off gas compressed by the first compressor or the second compressor to the first heat exchanger and further compresses the boil-off gas compressed by the first compressor or the second compressor. Further comprising a compressor, marine gaseous liquefaction system. 1) using the boil-off gas as a refrigerant in the first heat exchanger;
2) branching the boil-off gas used as the refrigerant of the first heat exchanger into two streams in step 1);
3) out of the flow branched into two flows in step 2), one flow to the first compressor, the other flow to the second compressor;
4) sending the boil-off gas compressed by the first compressor or the second-compressor to the fuel demand (hereinafter, the compressor for supplying the boil-off gas to the fuel demand is called a 'fuel supply compressor');
5) using the remaining evaporated gas which is not used in the fuel demand among the evaporated gas compressed by the fuel supply compressor, using the evaporated gas supplied to the first heat exchanger in step 1 as a refrigerant, Cooling by heat exchange with a heat exchanger;
6) sending the evaporated gas compressed by the remaining compressor other than the 'fuel supply compressor' among the first compressor and the second compressor to the refrigerant cycle (hereinafter, the compressor for supplying the boil-off gas by the refrigerant cycle Compressor ');
7) exchanging and cooling the fluid cooled by the first heat exchanger in step 5) using a boil-off gas circulating in the refrigerant cycle as a refrigerant and heat-exchanged by a second heat exchanger; And
8) depressurizing the fluid cooled by the second heat exchanger in step 7);
Evaporating gas circulating through the refrigerant cycle,
5-1) compression by the 'refrigerant cycle compressor';
5-2) cooling by the second heat exchanger after being compressed in step 5-1);
5-3) a step of reducing the pressure by the second pressure reducing device after cooling in the step 5-2);
5-4) after the pressure reduction in the step 5-3) further reduced by the third pressure reducing device;
5-5) further reducing the pressure in step 5-4) and using the refrigerant in the second heat exchanger; And
5-6) branching into two flows after being used as a refrigerant of the second heat exchanger in step 5-5);
5-7) one of two flows branched in step 5-6) is sent to the fourth compressor, and the other flow is sent to the fifth compressor; And
5-8) joining the boil-off gas compressed by the fourth compressor and the boil-off gas compressed by the fifth compressor; the process comprising a; The method according to claim 18,
A line through which the fluid decompressed by the second decompression device is sent to the third decompression device; And
A suction pipe is installed in at least one of the lines through which the fluid cooled by the second heat exchanger is sent to the second decompression device,
Evaporative gas re-liquefaction method for ships, by collecting the liquid droplets contained in the fluid in the lower portion of the suction pipe by gravity. The method according to claim 19,
When the level of the liquid droplets collected in the suction pipe is equal to or greater than the second set value,
Block the flow of fluid to the second pressure reducing device or the third pressure reducing device;
And the fluid used as the refrigerant in the second heat exchanger bypasses the fourth compressor and the fifth compressor.

Images