KR102011865B1 - 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 boil-off gas compressed by the first compressor or the second compressor is sent to the fuel demand (hereinafter, the boil-off gas to the fuel demand). Compressor for supplying the fuel is referred to as a 'fuel supply compressor'), the remaining evaporated gas of the boil-off gas compressed by the fuel supply compressor is sent to the first heat exchanger, The boil-off gas compressed by the remaining compressor other than the 'fuel supply compressor' among the first compressor and the second compressor is sent to the refrigerant cycle (hereinafter, the compressor for supplying the boil-off gas by the refrigerant cycle is referred to as a 'compressor cycle compressor'). The refrigerant cycle is a second pressure that depressurizes the fluid supplied to the refrigerant cycle after being compressed by the refrigerant cycle compressor. Pressure device; A fourth compressor for compressing the fluid used as the refrigerant in the second heat exchanger after the pressure is reduced by the second pressure reducing device; And a valve for adjusting a flow rate of the refrigerant circulating in the refrigerant cycle. When the vessel is in anchor, the opening degree of the valve is adjusted based on the pressure value of the refrigerant circulating in the refrigerant cycle. In operation, the opening degree of the valve is adjusted based on the temperature value of the refrigerant circulating in the refrigerant cycle.

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 a fuel such as an engine of a ship 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 boil-off gas compressed by the first compressor or the second compressor is sent to the fuel demand (hereinafter, the boil-off gas to the fuel demand). Compressor for supplying the fuel is referred to as a 'fuel supply compressor'), the remaining evaporated gas of the boil-off gas compressed by the fuel supply compressor is sent to the first heat exchanger, The boil-off gas compressed by the remaining compressor other than the 'fuel supply compressor' among the first compressor and the second compressor is sent to the refrigerant cycle (hereinafter, the compressor for supplying the boil-off gas by the refrigerant cycle is referred to as a 'compressor cycle compressor'). The refrigerant cycle is a second pressure that depressurizes the fluid supplied to the refrigerant cycle after being compressed by the refrigerant cycle compressor. Pressure device; A fourth compressor for compressing the fluid used as the refrigerant in the second heat exchanger after the pressure is reduced by the second pressure reducing device; And a valve for adjusting a flow rate of the refrigerant circulating in the refrigerant cycle. When the vessel is in anchor, the opening degree of the valve is adjusted based on the pressure value of the refrigerant circulating in the refrigerant cycle. When in operation, a boil-off boil-off liquefaction system is provided which adjusts the opening degree of the valve by using the temperature value of the refrigerant circulating in the refrigerant cycle as a factor.

The refrigerant cycle may form a closed loop connecting the 'refrigerant cycle compressor', the second decompression device, the second heat exchanger, the fourth compressor, and the 'refrigerant cycle compressor'.

The boil-off gas supplied to the refrigerant cycle after being compressed by the refrigerant cycle compressor is cooled by the second heat exchanger and further reduced in pressure by the second pressure reducing device to be cooled, and then back to the second heat exchanger. It can be supplied and used as a refrigerant.

The refrigerant cycle is closed to connect the 'refrigerant cycle compressor', the second heat exchanger, the second decompression device, the second heat exchanger, the fourth compressor, and the 'refrigerant cycle compressor' again. It can form a loop.

The valve may be installed in a line through which the fluid cooled by the second heat exchanger is sent to the second decompression device to adjust a flow rate of the fluid sent to the second decompression device.

The vessel boil-off liquefaction system may further include a pressure sensor installed in a line through which the fluid decompressed by the second decompression device is sent to the second heat exchanger to measure the pressure of the fluid. When berthing, the valve may be adjusted in accordance with the pressure value measured by the pressure sensor.

The vessel boil-off liquefaction system may further include a temperature sensor installed in a line through which a fluid used as a refrigerant in the second heat exchanger is sent to the fourth compressor, and measuring a temperature of the fluid. When the valve is in operation, the valve may be adjusted according to a temperature value measured by the temperature sensor.

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.

The third compressor may compress the boil-off gas to 150 to 300 bar.

The third compressor may compress the boil-off gas to 150 to 170 bar.

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

The boil-off gas separated by the gas-liquid separator may be combined with the boil-off gas before being used as the coolant in the first heat exchanger and used as the coolant in the first heat exchanger.

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) reducing the pressure in step 5-3) and using the refrigerant in the second heat exchanger; And 5-5) compressing by the fourth compressor after being used as the refrigerant of the second heat exchanger in step 5-4), and circulating the refrigerant cycle when the vessel is anchored. The flow rate of the boil-off gas circulating through the refrigerant cycle is adjusted by using the pressure value of the refrigerant as a factor, and when the vessel is in operation, the refrigerant cycle is circulated using the temperature value of the refrigerant circulating through the refrigerant cycle as a factor. There is provided a method for re-liquefying a boil-off boil-off gas for adjusting the flow rate of boil-off gas.

After cooling by the second heat exchanger by adjusting the flow rate of the fluid sent to the second pressure reducing device, it is possible to adjust the amount of the refrigerant circulating the refrigerant cycle.

During the anchoring of the vessel, the flow rate of the boil-off gas circulating through the refrigerant cycle may be adjusted by the pressure value of the fluid which is decompressed by the second pressure reducing device and then sent to the second heat exchanger.

When the pressure of the fluid sent to the second heat exchanger after the pressure is reduced by the second pressure reducing device is higher than the first set value, the flow rate of the boil-off gas circulating through the refrigerant cycle is increased, and the pressure is reduced by the second pressure reducing device. After the pressure of the fluid sent to the second heat exchanger is lower than the first set value, it is possible to reduce the flow rate of the boil-off gas circulating the refrigerant cycle.

During operation of the vessel, the flow rate of the boil-off gas circulating through the refrigerant cycle may be adjusted by a temperature value of the fluid which is used as the refrigerant in the second heat exchanger and then sent to the fourth compressor.

If the temperature of the fluid sent to the fourth compressor after being used as the refrigerant in the second heat exchanger is higher than the second set value, the flow rate of the boil-off gas circulating through the refrigerant cycle is increased, and the refrigerant is transferred from the second heat exchanger to the refrigerant. If the temperature of the fluid sent to the fourth compressor after use is lower than the second set value, it is possible to reduce the flow rate of the boil-off gas circulating through the refrigerant cycle.

According to another 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; A first decompression device for depressurizing the fluid cooled by the second heat exchanger; And a valve configured to adjust a flow rate of the refrigerant circulating through the refrigerant cycle, and when the temperature of the fluid used as the refrigerant in the second heat exchanger is higher than a second set value, increase the opening degree of the valve and the second heat exchange. When the temperature of the fluid used as the refrigerant in the air is lower than the second set value, the opening degree of the valve is lowered, but when the evaporative gas of maximum flow rate is supplied to the refrigerant cycle, the pressure of the refrigerant circulating in the refrigerant cycle A boil-off boil-off gas liquefaction system is provided which adjusts the opening degree of the valve by using a value as a factor.

Preferably, the system comprises a second pressure reducing device for reducing the evaporated gas supplied in the refrigerant cycle to supply the refrigerant to the second heat exchanger; And another compressor configured to compress the boil-off gas circulating through the refrigerant cycle by being driven by power generated by the second pressure reducing device to expand the fluid.

According to the present invention, when the vessel is moored, on the basis of the pressure value of the boil-off gas circulating through the refrigerant cycle (RC), the flow rate of the boil-off gas supplied to the refrigerant cycle (RC) is adjusted, the vessel is in operation Since the flow rate of the boil-off gas supplied to the coolant cycle RC is adjusted based on the temperature value of the boil-off gas circulating through the coolant cycle RC, the boil-off gas of an appropriate flow rate is efficiently supplied according to the operating conditions of the ship. It can supply to the cycle RC.

According to the present invention, the flow rate and reliquefaction process of the boil-off gas circulating through the refrigerant cycle RC is performed even when the ship is operated in which the amount of boil-off gas consumed at the fuel demand E increases or decreases according to the speed of the ship. Through the flow rate of the boil-off gas can be appropriately adjusted to efficiently liquefy the boil-off gas, it is possible to lower the probability of droplets.

1 is a schematic diagram of a boil-off gas reliquefaction system according to a preferred embodiment of the present invention.
2 is a graph schematically illustrating a phase change of methane according to temperature and pressure.
3 is a graph showing the temperature value of methane according to the heat flow amount under different pressure, respectively.
4 and 5 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 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, refrigerant cycle RC, and bypass line BL.

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.

2 is a graph schematically illustrating a phase change of methane according to temperature and pressure. Referring to FIG. 2, 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. 2) by the first decompression device 410, the temperature is lower than that in the case where the temperature is reduced in pressure (X → X 'in FIG. 2). It can be seen that when the pressure is reduced in the state (Y → Y ′ in FIG. 2), 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. 2). 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).

The refrigerant cycle RC through which the boil-off gas used as the refrigerant in the second heat exchanger 120 circulates includes a second pressure reducing device 420 and a fourth compressor 240.

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

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 cool the second pressure reducing device. After further depressurizing and cooling by 420, it is sent back to the second heat exchanger 120 to be used as a refrigerant.

The fourth compressor 240 compresses 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. The fourth compressor 240 forms the second pressure reducing device 420 and the compander C to be driven by the power generated by the second pressure reducing device 420 while inflating the fluid. Downstream), a fourth cooler 340 for cooling the boil-off gas compressed by the fourth compressor 240 may be installed.

According to the ship boil-off gas liquefaction system of the present embodiment, the boil-off gas compressed by the fourth compressor 240 may be sent upstream of the first compressor 210 and may be sent upstream of the second compressor 220. The refrigerant cycle RC may be configured to include the first compressor 210 and the refrigerant cycle may be configured to include the second compressor 220.

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 ( A closed loop refrigerant cycle RC is formed to connect 220, second pressure reducing device 420, second heat exchanger 120, fourth compressor 240, and second compressor 220. 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, A closed loop refrigerant cycle RC is formed to connect the second pressure reducing device 420, the second heat exchanger 120, the fourth compressor 240, and the second compressor 220.

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 ( A closed loop refrigerant cycle RC is connected to the 210, the second pressure reducing device 420, the second heat exchanger 120, the fourth compressor 240, and the first compressor 210. 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, A closed loop refrigerant cycle RC is formed to connect the second pressure reducing device 420, the second heat exchanger 120, the fourth compressor 240, and the first compressor 210 again.

According to this embodiment, 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 ) Or the refrigerant cycle RC can be circulated by the boil-off gas compressed by the other compressor that does not supply boil-off gas to the first heat exchanger 110, thereby operating the system freely.

In addition, according to the present embodiment, there is an advantage that the re-liquefaction efficiency and re-liquefaction amount 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.

The refrigerant cycle RC further includes a valve V for adjusting the flow rate of the refrigerant circulating through the refrigerant cycle RC. The valve V is installed in a line through which the fluid cooled by the second heat exchanger 120 is sent to the second pressure reducing device 420, and controls the flow rate of the fluid sent to the second pressure reducing device 420. It is preferable.

Looking at the control of the valve (V) when the ship is moored and the ship is operating as follows.

[When ship is moored]

When the ship is anchored and no fuel is supplied to the propulsion engines such as the ME-GI engine and the X-DF engine, there is almost no evaporated gas consumed in the fuel demand E, so the amount of the evaporated gas to be reliquefied becomes large. . In order to reliquefy a large amount of boil-off gas, the boil-off gas undergoing the re-liquefaction process is cooled not only by the first heat exchanger 110 but also by the second heat exchanger 120, and then, into the first pressure reducing device 410. And the evaporating gas at the maximum flow rate is supplied to the refrigerant cycle RC.

As described above, when the amount of boil-off gas to be reliquefied during ship anchoring is so high that the boil-off gas at the maximum flow rate is supplied to the refrigerant cycle RC, the pressure value of the refrigerant circulating in the refrigerant cycle RC is factored. To adjust the opening degree of the valve (V).

Specifically, during the anchoring of the ship, the opening degree of the valve V may be adjusted by the pressure value of the fluid which is decompressed by the second pressure reducing device 420 and then sent to the second heat exchanger 120. Since the refrigerant circulating through the refrigerant cycle RC has the lowest pressure and temperature after being decompressed by the second decompression device 420, during the berth of the ship, the decompression by the second decompression device 420 is followed by the second decompression. It is preferable to adjust the opening degree of the valve V by using the pressure value of the fluid sent to the heat exchanger 120 as a factor.

Pressure sensor between the second pressure reducing device 420 and the second heat exchanger 120 in order to measure the pressure value of the fluid sent to the second heat exchanger 120 after being decompressed by the second pressure reducing device 420. 610 may be installed. In addition, the pressure value measured by the pressure sensor 610 is transmitted to the control device 630, and the control device 630 uses the pressure value measured by the pressure sensor 610 as a factor to determine the opening degree of the valve V. I can regulate it.

When the pressure P 'measured by the pressure sensor 610 is higher than the first set value P (P'> P), the opening degree of the valve V is increased to increase the flow rate of the refrigerant circulating through the refrigerant cycle RC. If the pressure P 'measured by the pressure sensor 610 is lower than the first set value P (P' <P), the opening degree of the valve V is lowered to circulate the refrigerant cycle RC. Reduce the flow of

The fact that the pressure P 'measured by the pressure sensor 610 is higher than the first set value P (P'> P) indicates that the fluid having a sufficient flow rate is not supplied to the second decompression device 420 so that the second pressure decreases. Since the pressure reducing device 420 reduces the pressure less, the opening of the valve V is increased to increase the flow rate of the fluid flowing into the second pressure reducing device 420. When the flow rate of the fluid flowing into the second pressure reducing device 420 is increased so that the fluid having the flow rate required by the second pressure reducing device 420 is supplied to the second pressure reducing device 420, the second pressure reducing device 420 is set. The pressure allows the fluid to be depressurized.

In addition, the fact that the pressure P 'measured by the pressure sensor 610 is lower than the first set value P (P' <P) indicates that the fluid is excessively decompressed by the second pressure reducing device 420. In other words, when a fluid having a flow rate exceeding the flow rate required by the second pressure reducing device 420 is supplied to the second pressure reducing device 420, the second pressure reducing device 420 may reduce the fluid by exceeding the set pressure. have.

Therefore, when the pressure P 'measured by the pressure sensor 610 is lower than the first set value P (P' <P), the opening degree of the valve V is lowered to flow into the second pressure reducing device 420. To reduce the flow rate of the fluid. When the flow rate of the fluid flowing into the second decompression device 420 is reduced and the fluid having the flow rate required by the second decompression device 420 is supplied to the second decompression device 420, the second decompression device 420 is set. The pressure allows the fluid to be depressurized.

[Ship Operated  Occation]

The boil-off gas is used in the fuel demand (E), or sent to the first heat exchanger (110) for reliquefaction, or used as a refrigerant circulating the refrigerant cycle (RC), evaporation used in the fuel demand (E) If the amount of gas is increased, the amount of remaining boil-off gas that is subjected to reliquefaction or to the refrigerant cycle RC is reduced.

However, since the evaporation gas is sent to the refrigerant cycle RC to be used as a refrigerant for reliquefaction of the boil-off gas, even when the amount of the remaining boil-off gas sent to the refrigerant cycle or the refrigerant is reduced uniformly. When the same amount of evaporated gas is sent to the refrigerant cycle RC, the amount of the refrigerant circulating in the refrigerant cycle RC is too large and the amount of the evaporated gas to be reliquefied is inefficient compared to the evaporated gas to be reliquefied.

When the vessel starts to operate and the boil-off gas is supplied to the fuel demand (E) such as the propulsion engine, the amount of the remaining boil-off gas passed through the reliquefaction process or the refrigerant cycle (RC) is reduced, and the speed of the vessel As it increases, the amount of boil-off gas used in the propulsion engine also increases, so that the amount of the remaining boil-off gas passed through the reliquefaction process or sent to the refrigerant cycle RC is further reduced.

Accordingly, when the vessel starts to operate, it may be necessary to reduce the flow rate of the boil-off gas circulating in the refrigerant cycle RC. According to this embodiment, when the vessel is operated, the refrigerant circulating in the refrigerant cycle RC may be The flow rate of the boil-off gas sent to the refrigerant cycle RC is controlled by adjusting the opening degree of the valve V by using the temperature value as a factor.

Specifically, during operation of the ship, the opening degree of the valve V may be adjusted by the temperature value of the fluid which is used as the refrigerant in the second heat exchanger 120 and then sent to the fourth compressor 240. Knowing the temperature of the fluid used as the refrigerant in the second heat exchanger 120, it is possible to know whether the flow rate of the boil-off gas circulating through the refrigerant cycle RC is appropriate compared to the flow rate of the boil-off gas for reliquefaction. It is preferable to adjust the opening degree of the valve V by using the temperature value of the fluid which is used as the refrigerant in the second heat exchanger 120 and then sent to the fourth compressor 240 as a factor.

In order to measure the temperature value of the fluid which is used as the refrigerant in the second heat exchanger 120 and then sent to the fourth compressor 420, a temperature sensor between the second heat exchanger 120 and the fourth compressor 240 may be used. 620 may be installed. In addition, the pressure value measured by the temperature sensor 620 is transmitted to the control device 630, and the control device 630 uses the pressure value measured by the temperature sensor 620 as a factor to open the valve V. I can regulate it.

If the temperature T 'measured by the temperature sensor 620 is higher than the second set value T (T'> T), the opening degree of the valve V is increased to increase the flow rate of the refrigerant circulating through the refrigerant cycle RC. If the temperature T 'measured by the temperature sensor 620 is lower than the second set value T (T' <T), the opening degree of the valve V is lowered to circulate the refrigerant cycle RC. Reduce the flow of

When the temperature T 'measured by the temperature sensor 620 is higher than the second set value T (T'> T), the refrigerant circulating in the refrigerant cycle RC is transferred to the second heat exchanger 120. Since it means that a lot of cooling heat is taken away, it can be determined that the amount of the boil-off gas circulating in the refrigerant cycle RC is smaller than the flow rate of the boil-off gas to be reliquefied. Therefore, when the temperature T 'measured by the temperature sensor 620 is higher than the second set value T (T'> T), the opening degree of the valve V is increased to increase the opening of the refrigerant cycle RC. Increase the flow rate.

In addition, when the temperature T 'measured by the temperature sensor 620 is lower than the second set value T (T' <T), the refrigerant circulating in the refrigerant cycle RC is transferred to the second heat exchanger ( Since 120 means less cooling heat, it may be determined that the amount of boil-off gas circulating through the refrigerant cycle RC is greater than that of the boil-off gas to be reliquefied. Therefore, when the temperature T 'measured by the temperature sensor 620 is lower than the second set value T (T' <T), the refrigerant circulating the refrigerant cycle RC by lowering the opening degree of the valve V Reduce the flow of

According to this embodiment, even during operation of a vessel in which the amount of boil-off gas consumed in the fuel demand (E) increases or decreases according to the speed of the vessel, the flow rate of the boil-off gas circulating through the refrigerant cycle RC and the reliquefaction process are performed. By adjusting the flow rate of the boil-off gas appropriately, there is an advantage that the boil-off gas can be efficiently liquefied.

In addition, when the flow rate of the boil-off gas circulating through the refrigerant cycle RC is higher than the flow rate of the boil-off gas to be reliquefied, the average temperature of the boil-off gas circulating through the refrigerant cycle RC is lowered, so that the probability of droplets is increased. When the droplets flow into the second decompression device 420, fatal damage may occur. According to the present embodiment, even when the vessel is operated in which the amount of boil-off gas consumed by the fuel demand E increases or decreases according to the speed of the vessel. By appropriately adjusting the flow rate of the boil-off gas circulating through the refrigerant cycle RC and the flow rate of the boil-off gas undergoing the reliquefaction process, the average temperature of the boil-off gas circulating through the refrigerant cycle RC can be maintained within a predetermined temperature range. And, there is an advantage that it is possible to lower the probability of the droplets occur.

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.

3 is a graph showing the temperature values of methane according to the heat flow amount under different pressures, and referring to FIG. 3, the higher the pressure of the boil-off gas undergoing the reliquefaction process, the higher the efficiency of 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. 3 (a) 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. 3 (b) 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. 3, 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. 3A and 3B 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. 3 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. When the temperature after tc2 and the high temperature fluid pass through the heat exchanger is th1, and the temperature after the high temperature fluid passes through the heat exchanger is th2, and d1 = th2-tc1 and d2 = th1-tc2, (d2- d1) / ln (d2 / d1), the smaller the logarithmic mean temperature difference, the higher the efficiency of the heat exchanger.

On the graph, the logarithmic mean temperature difference LMTD is represented by the interval between the low temperature fluid (graph L of FIG. 3) used as the refrigerant and the high temperature fluid (graph K of FIG. 3) cooled by heat exchange with the refrigerant. It can be seen that (b) of FIG. 3 shows a narrower interval between the graph L and the graph K 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. 3B is higher than that of FIG. 3A.

That is, as a result of the simulation, in the case of FIG. 3A without 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 3 (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 logarithm 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. 3A, when the flow rate of the boil-off 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) used as the refrigerant. 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. 3B, 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 heat-exchanged with the refrigerant from the fluid (graph L) used as the refrigerant. 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.

4 and 5 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. 4 and 5 are graphs showing the reliquefaction amount according to the evaporation gas pressure in the PRS, and thus the reliquefaction amount is lower than that of the MRS which additionally reliquefies the evaporation gas by the evaporation gas circulating in the refrigerant cycle. . In the case of MRS, approximately 3300 kg of boil-off gas can be reliquefied per hour.

4 and 5, it can be seen that the amount of reliquefaction shows the maximum value when the pressure of the boil-off gas is around 150 to 170 bar, and there is little 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 an engine is large 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.

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
C: Compander E: Fuel demand
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 pressure reducing device 420: second pressure reducing device
500: gas-liquid separator 610: pressure sensor
620: temperature sensor 630: control device

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 a first decompression device for decompressing the fluid cooled by the second heat exchanger.
The boil-off gas compressed by the first compressor or the second compressor is sent 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').
The remaining boil-off gas not used in the fuel demand among the boil-off gas compressed by the fuel supply compressor is sent to the first heat exchanger.
The boil-off gas compressed by the remaining compressor other than the 'fuel supply compressor' among the first compressor and the second compressor is sent to the refrigerant cycle (hereinafter, the compressor for supplying the boil-off gas by the refrigerant cycle is referred to as a 'compressor for compressor cycle'). '),
The refrigerant cycle,
A second decompression device configured to depressurize the fluid supplied to the refrigerant cycle after being compressed by the refrigerant cycle compressor;
A fourth compressor for compressing the fluid used as the refrigerant in the second heat exchanger after the pressure is reduced by the second pressure reducing device; And
And a valve for adjusting a flow rate of the refrigerant circulating through the refrigerant cycle.
When the vessel is anchored, the opening degree of the valve is adjusted based on the pressure value of the refrigerant circulating in the refrigerant cycle,
If the vessel is in operation to adjust the opening degree of the valve by the temperature value of the refrigerant circulating the refrigerant cycle, the vessel boil-off liquefaction system. The method according to claim 1,
The refrigerant cycle, the vessel evaporation to form a closed loop connecting the 'refrigerant cycle compressor', the second decompression device, the second heat exchanger, the fourth compressor, and the 'refrigerant cycle compressor' again. Gas reliquefaction system. The method according to claim 1,
The boil-off gas supplied to the refrigerant cycle after being compressed by the refrigerant cycle compressor is cooled by the second heat exchanger and further reduced in pressure by the second pressure reducing device to be cooled, and then back to the second heat exchanger. Evaporative gas reliquefaction system for ships, which is supplied and used as a refrigerant. The method according to claim 3,
The refrigerant cycle is closed to connect the 'refrigerant cycle compressor', the second heat exchanger, the second decompression device, the second heat exchanger, the fourth compressor, and the 'refrigerant cycle compressor' again. Evaporative gas reliquefaction system for ships, forming a loop. The method according to claim 3,
And the valve is installed in a line through which the fluid cooled by the second heat exchanger is sent to the second decompression device, and regulates a flow rate of the fluid sent to the second decompression device. The method according to any one of claims 1 to 5,
And a pressure sensor installed in a line to which the fluid depressurized by the second decompression device is sent to the second heat exchanger to measure the pressure of the fluid,
When the vessel is anchored, the valve is a boil-off gas reliquefaction system for the opening degree is adjusted according to the pressure value measured by the pressure sensor. The method according to any one of claims 1 to 5,
The fluid used as the refrigerant in the second heat exchanger is installed in the line sent to the fourth compressor, further comprising a temperature sensor for measuring the temperature of the fluid,
When the vessel is in operation, the valve is a boil-off gas reliquefaction system for the opening degree is adjusted according to the temperature value measured by the temperature sensor. The method according to any one of claims 1 to 5,
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. The method according to claim 8,
The third compressor is a boil-off boil-off gas reliquefaction system for compressing the boil-off gas to 150 to 300 bar. The method according to claim 9,
The third compressor is a marine boil-off gas reliquefaction system for compressing the boil-off gas to 150 to 170 bar. The method according to any one of claims 1 to 5,
And a gas-liquid separator installed downstream of the first decompression device to separate the liquefied liquefied gas and the evaporated gas remaining in the gaseous state. The method according to claim 11,
The evaporated gas separated by the gas-liquid separator is combined with the evaporated gas before being used as the refrigerant in the first heat exchanger is used as the refrigerant in the first heat exchanger, marine vaporized gas reliquefaction 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) reducing the pressure in step 5-3) and using the refrigerant in the second heat exchanger; And
5-5) after being used as the refrigerant of the second heat exchanger in step 5-4) and compressed by a fourth compressor;
When the vessel is berthing, the flow rate of the boil-off gas circulating the refrigerant cycle is adjusted by using the pressure value of the refrigerant circulating the refrigerant cycle as a factor,
When the vessel is in operation to adjust the flow rate of the boil-off gas circulating through the refrigerant cycle by the temperature value of the refrigerant circulating the refrigerant cycle, the method for re-liquefying boil-off gas for ships. The method according to claim 13,
And adjusting the flow rate of the fluid which is cooled by the second heat exchanger and then sent to the second decompression device, thereby controlling the amount of refrigerant circulating in the refrigerant cycle. The method according to claim 13 or 14,
During berth of the vessel, the vessel evaporation gas reliquefaction method for regulating the flow rate of the boil-off gas circulating the refrigerant cycle by the pressure value of the fluid is decompressed by the second pressure reducing device and sent to the second heat exchanger. The method according to claim 15,
If the pressure of the fluid sent to the second heat exchanger after the pressure is reduced by the second pressure reducing device is higher than the first set value, the flow rate of the boil-off gas circulating the refrigerant cycle is increased,
And reducing the flow rate of the boil-off gas circulating through the refrigerant cycle if the pressure of the fluid sent to the second heat exchanger after being decompressed by the second pressure-reducing device is lower than the first set value. The method according to claim 13 or 14,
During the operation of the vessel, the vessel evaporation gas reliquefaction method for controlling the flow rate of the boil-off gas circulating through the refrigerant cycle by the temperature value of the fluid which is used as the refrigerant in the second heat exchanger and then sent to the fourth compressor. . The method according to claim 17,
If the temperature of the fluid sent to the fourth compressor after being used as the refrigerant in the second heat exchanger is higher than the second set value, increase the flow rate of the boil-off gas circulating the refrigerant cycle,
When the temperature of the fluid sent to the fourth compressor after being used as the refrigerant in the second heat exchanger is lower than the second set value, the flow rate of the boil-off gas for circulating the refrigerant cycle, reducing the vessel evaporation gas re-liquefaction method . 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;
A first decompression device for depressurizing the fluid cooled by the second heat exchanger; And
And a valve for adjusting a flow rate of the refrigerant circulating through the refrigerant cycle.
When the temperature of the fluid used as the refrigerant in the second heat exchanger is higher than the second set value, the opening degree of the valve is increased. When the temperature of the fluid used as the refrigerant in the second heat exchanger is lower than the second set value, the Lower the opening of the valve,
When the evaporation gas of the maximum flow rate is supplied to the refrigerant cycle, the opening degree of the valve is adjusted by the pressure value of the refrigerant circulating in the refrigerant cycle as a factor, the vessel boil-off gas liquefaction system. The method according to claim 19,
A second pressure reducing device for reducing the evaporation gas supplied through the refrigerant cycle and supplying the refrigerant to the second heat exchanger; And
And a second compressor configured to compress the boil-off gas circulating through the refrigerant cycle by driving the power generated by the second pressure-reducing device to expand the fluid.

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