KR20230029086A - Fuel Supply System and Method for Ships - Google Patents

Abstract

The present invention relates to a fuel supply system for a ship and a method thereof, which are able to prevent the generation volume of boil-off gas in a storage tank from increasing when maintaining the minimum flow rate of a fuel supply pump. According to the present invention, the fuel supply method for a ship comprises: a step of compressing boil-off gas or forced vaporized gas from liquefied gas and supplying the gas as fuel for an engine; and a step of reliquefying the gas fuel exceeding the required fuel volume of the engine and recollecting the reliquefied gas to a liquefied gas storage tank. The step of supplying the forced vaporized gas as fuel for the engine includes: a step of discharging liquefied gas from the liquefied gas storage tank; and a step of gasifying the discharged liquefied gas. When the engine requires gas fuel less than the operating range of the pump discharging the liquefied gas, the pump is not operated, and the reliquefied boil-off gas is vaporized and supplied to the engine.

Description

Fuel supply system and method for ships {Fuel Supply System and Method for Ships}

The present invention relates to a fuel supply system and method for a ship capable of preventing an increase in boil-off gas generation in a storage tank in order to maintain a minimum flow rate of a fuel supply pump.

BACKGROUND ART Consumption of liquefied gas such as liquefied natural gas (LNG) is rapidly increasing worldwide. Since liquefied gas obtained by liquefying gas at a low temperature has a very small volume compared to gas, it has the advantage of increasing storage and transfer efficiency. In addition, liquefied gas, including liquefied natural gas, can remove or reduce air pollutants during the liquefaction process, so it can be seen as an eco-friendly fuel with less air pollutant emissions during combustion.

Liquefied natural gas is a colorless and transparent liquid obtained by liquefying natural gas whose main component is methane by cooling it to about -163 ° C, and has a volume of about 1/600 compared to natural gas. Therefore, when the natural gas is liquefied and transported, it can be transported very efficiently.

However, since the liquefaction temperature of natural gas is a cryogenic temperature of -163 ° C., liquefied natural gas is sensitive to temperature changes and is easily evaporated. For this reason, although the storage tank for storing liquefied natural gas is insulated, external heat is continuously transmitted to the storage tank. ; Boil-Off Gas) occurs.

Evaporation gas is a kind of loss and is an important problem in transport efficiency. In addition, when boil-off gas is accumulated in the storage tank, the internal pressure of the tank may excessively rise, and in severe cases, there is a risk of damage to the tank. Therefore, various methods for treating the boil-off gas generated in the storage tank have been studied. Recently, for the treatment of boil-off gas, a method of using the boil-off gas as a fuel for a ship's engine, a method of re-liquefying the boil-off gas, and a storage tank A method of returning to , etc. is being used.

Among the engines used in ships, dual fuel engines that can use natural gas as fuel include ME-GI (MAN Electronic Gas Injection) engines and X-DF (eXtra long stroke Dual Fuel) engines. , DF engines (DFDE (Dual Fuel Diesel Electric), DFDG (Dual Fuel Diesel Generator)).

In order to effectively process boil-off gas in ships, the boil-off gas generated by natural vaporization of LNG in the LNG storage tank is compressed and supplied to the pressure required by the engine, and when the amount of boil-off gas is less than the amount required by the engine, LNG is supplied. is forcibly vaporized and supplied as fuel. The boil-off gas generated by natural vaporization of LNG is called NBOG (Natural Boil-off Gas), and the natural gas generated by forced vaporization of LNG is called forced vaporized gas or FBOG (Forced Boil-off Gas).

Referring to FIG. 1, in order to supply FBOG as fuel for the engine 400, a fuel supply pump 310 for discharging LNG for fuel from a cargo tank and pressurized transfer by a fuel supply pump 310 A vaporizer 320 for vaporizing the LNG is provided.

In the fuel supply pump 310, when the flow rate of the inlet falls below the minimum flow rate (pressure) of the fuel supply pump, there is a problem in that LNG is vaporized, causing a cavitation phenomenon, and accordingly, the fuel supply pump 310 Vibration and heat are generated in, and as a result, the fuel supply pump 310 may be damaged or damaged in severe cases, resulting in safety problems.

Therefore, the flow rate of the inlet of the fuel supply pump 310 should be maintained above the minimum flow rate. Conventionally, in order to satisfy the minimum flow rate of the fuel supply pump 310, a control valve (CV) and a bypass line (BL) were applied downstream of the fuel supply pump 310.

Specifically, when the flow rate of LNG fuel required by the engine 400 is less than the minimum flow rate of the fuel supply pump 310, the fuel supply pump 310 sucks and discharges LNG above the minimum flow rate, and then supplies the fuel. Of the LNG pressurized by the pump 310, the LNG fuel flow rate required by the engine 400 is transferred to the vaporizer 320 and the rest is returned to the storage tank through the bypass line BL, the control valve CV ) to control the opening degree.

While pressurized by the fuel supply pump 310, the pressure of the LNG increases as well as the temperature. As the temperature inside the tank rises, NBOG increases.

In addition, when the fuel supply pump 310 is provided inside the storage tank, natural vaporization of LNG is promoted by heat generated by the operation of the fuel supply pump 310, and for operating the fuel supply pump 310 There is a problem that power is excessively consumed. Even if the fuel supply pump 310 is not provided inside the storage tank, the same phenomenon occurs because a stripping pump installed inside the storage tank must be operated in order to supply LNG inside the storage tank to the fuel supply pump 310.

Therefore, the present invention is to solve the above problems, and the fuel supply system of the ship, which can solve the problem of the increase in the internal temperature of the storage tank and the increase in power consumption due to the heat inflow from the fuel supply pump, and We want to provide a way.

According to one aspect of the present invention for achieving the above object, a compressor for compressing the boil-off gas generated in the liquefied gas storage tank to a pressure required by the engine; a re-liquefaction unit for re-liquefying the compressed boil-off gas exceeding the amount of gas fuel required by the engine; a re-liquefaction line connecting the re-liquefaction unit and the liquefied gas storage tank so that the re-liquefied boil-off gas re-liquefied in the re-liquefaction unit is recovered to the liquefied gas storage tank; a fuel supply pump for discharging liquefied gas stored in a liquefied gas storage tank to supply fuel to the engine; a vaporizer that vaporizes the liquefied gas transported from the fuel supply pump and sends it to the compressor; a re-liquefaction fuel line branched from the re-liquefaction line and connected to the vaporizer so that the re-liquefaction boil-off gas from the re-liquefaction unit is transported to the vaporizer; a third valve provided in the re-liquefied fuel line; a controller for stopping operation of the fuel supply pump when the amount of gas fuel required by the engine is less than the minimum flow rate; and a flow controller configured to open the third valve to adjust the flow rate of the re-liquefied boil-off gas supplied to the carburetor when the amount of gas fuel required by the engine is less than the minimum flow rate of the fuel supply pump operating range. of fuel supply system is provided.

Preferably, the temperature of the liquefied gas discharged from the fuel supply pump is higher than the temperature of the liquefied gas sucked into the fuel supply pump and the temperature of the re-liquefied boil-off gas, and the liquefied gas discharged from the fuel supply pump is converted into a vaporizer. A first valve for controlling the opening and closing of the flow path to be supplied; a flow control line branching from a forced vaporization line connecting the fuel supply pump and the vaporizer so that the liquefied gas discharged by the fuel supply pump is returned to the liquefied gas storage tank; a second valve installed in the flow control line and having an opening rate controlled to control the flow rate of the liquefied gas supplied from the fuel supply pump to the carburetor; And by calculating the flow rate of the liquefied gas discharged from the fuel supply pump, the opening rate of the second valve is set so that an amount of liquefied gas exceeding the flow rate of liquefied gas required by the vaporizer is recovered to the liquefied gas storage tank. A flow controller for controlling; may further include.

Preferably, when the amount of gas fuel required by the engine is less than the minimum flow rate of the fuel supply pump operating range, the first valve is closed by the flow controller and the second valve is closed by the flow controller. can

Preferably, the re-liquefaction unit, a boosting compressor for further compressing the boil-off gas compressed by the compressor to a critical pressure or more; A heat exchanger that cools the compressed boil-off gas by exchanging heat between the boil-off gas compressed by the boosting compressor and the boil-off gas before compression supplied to the compressor from the liquefied gas storage tank; a pressure reducing valve for expanding the boil-off gas cooled by the heat exchanger; a gas-liquid separator for gas-liquid separation of the gas-liquid mixture generated by the pressure reducing valve; and a gas recovery line for joining the non-condensed evaporation gas in the gaseous state separated by the gas-liquid separator to the pre-compression evaporation gas flow supplied to the heat exchanger, including reliquefaction evaporation in the liquid state separated by the gas-liquid separator. Gas may flow along the re-liquefaction line or the re-liquefaction fuel line.

Preferably, a cooler for cooling the forced vaporized gas generated by vaporizing the liquefied gas in the vaporizer; a methane number regulator for gas-liquid separation of the gas-liquid mixture produced by the cooler; A condensate recovery line for discharging heavy hydrocarbons in a liquid state gas-liquid separated from the methane number regulator from the methane number regulator; and a forced vaporization line supplying gaseous light hydrocarbon gas-liquid separated in the methane number controller to the compressor.

According to another aspect of the present invention for achieving the above object, the boil-off gas or forced vaporization gas of liquefied gas is compressed and supplied as engine fuel, and the amount of gas fuel exceeding the amount of fuel required by the engine is Re-liquefying and recovering the liquefied gas to a liquefied gas storage tank, and supplying the forced vaporized gas as fuel for the engine includes discharging the liquefied gas from the liquefied gas storage tank and vaporizing the discharged liquefied gas, and In the case of requiring gas fuel less than the pump operating range for discharging the liquefied gas, there is provided a method for supplying fuel to a ship by vaporizing the re-liquefied boil-off gas and supplying it to the engine without operating the pump.

Preferably, the flow rate of the liquefied gas flowing from the pump to the vaporizer is measured, the flow rate of the liquefied gas discharged from the pump is calculated, and when the measured flow rate is greater than the flow rate required by the vaporizer, from the pump The opening rate of the valve may be adjusted so that an amount of liquefied gas exceeding a flow rate required by the vaporizer is returned to the liquefied gas storage tank among the discharged liquefied gas.

The fuel supply system and method of the ship according to the present invention can solve the problem of the increase in the internal temperature of the storage tank and the increase in power consumption due to the heat inflow accompanying the use of the fuel supply pump.

In addition, the methane number of the engine can be satisfied by vaporizing the re-liquefied boil-off gas and supplying the fuel to the engine.

1 is a block diagram schematically illustrating a fuel supply system of a general ship.
2 is a block diagram schematically illustrating a fuel supply system for a ship according to an embodiment of the present invention.

In order to fully understand the operational advantages of the present invention and the objects achieved by the embodiments of the present invention, reference should be made to the accompanying drawings illustrating preferred embodiments of the present invention and the contents described in the accompanying drawings.

Hereinafter, the configuration and operation of a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. In adding reference numerals to the components of each drawing, it should be noted that the same components are marked with the same numerals as much as possible, even if they are displayed on different drawings.

In embodiments of the present invention to be described later, the ship may be any type of ship provided with a storage tank for storing liquefied gas. Representatively, ships with self-propelled capabilities such as LNG carriers, liquid hydrogen carriers, and LNG RV (Regasification Vessel), as well as LNG FPSO (Floating Production Storage Offloading) and LNG FSRU (Floating Storage Regasification Unit) Offshore structures that do not have the capability but are floating on the sea may also be included.

In addition, in this embodiment, the liquefied gas is, for example, LNG (Liquefied Natural Gas), LEG (Liquefied Ethane Gas), LPG (Liquefied Petroleum Gas), liquefied ethylene gas (Liquefied Ethylene Gas), liquefied propylene gas (Liquefied Propylene Gas) It can be a low-temperature fluid stored and transported in a liquid state, such as ammonia or liquid hydrogen, that can be used as engine fuel. In embodiments to be described later, liquefied gas will be described by taking LNG as an example.

In addition, the ship according to the present embodiment may be a liquefied gas propulsion ship capable of being propelled by using a liquefied gas in a liquid state or a gas generated by forcibly evaporating a boil-off gas or liquefied gas generated by natural vaporization of a liquefied gas as fuel. there is.

For example, in the present embodiment, the engine may be a dual fuel engine capable of using natural gas and fuel oil selectively or in combination.

Among the engines used in ships, dual fuel engines that can use natural gas as fuel include the ME-GI (MAN Electronic Gas Injection) engine, the X-DF (eXtra long stroke Dual Fuel) engine, and the DF engine. (DFDE (Dual Fuel Diesel Electric), DFDG (Dual Fuel Diesel Generator)), etc.

ME-GI engines are mainly used for propulsion using a 2-stroke cycle. In addition, the ME-GI engine operates based on a diesel cycle in which high-pressure natural gas of about 300 bar is directly injected into a combustion chamber near the top dead center of a piston. The X-DF engine is mainly used for propulsion using a 2-stroke cycle, and like the ME-GI engine, a propeller is directly driven for propulsion of a ship. In addition, the X-DF engine uses medium-pressure natural gas of about 16 bar as fuel and operates based on an otto cycle. A DF engine is mainly used for power generation using a 4-stroke cycle. In addition, the DF engine operates based on the Otto cycle in which low-pressure natural gas of about 6.5 bar is injected into the combustion air inlet and compressed as the piston rises.

Since only air is compressed in a compression stroke in an engine operated based on a diesel cycle, a knocking phenomenon, which is a phenomenon in which premature ignition occurs before a piston reaches top dead center, does not fundamentally occur. However, since an engine operating based on an Otto cycle introduces a mixture of fuel and combustion air into a cylinder before an upstroke, premature ignition may occur before ignition by an ignition source, resulting in a knocking phenomenon.

In an embodiment of the present invention to be described later, an example in which an X-DF engine is applied as a propulsion engine and a DFDG engine is applied as a power generation engine will be described as an example.

Hereinafter, with reference to FIG. 2, a fuel supply system and method for a ship according to an embodiment of the present invention will be described. The ship fuel supply system according to an embodiment of the present invention shown in FIG. 2 is inside the storage tank to maintain the minimum flow rate of the fuel supply pump 310 generated in the general ship fuel supply system shown in FIG. An improved ship fuel supply system is provided to solve problems such as high temperature.

Referring to FIG. 2, in the fuel supply system for a ship according to an embodiment of the present invention, boil-off gas (NBOG) generated in an LNG storage tank (not shown) for storing LNG is transferred to a fuel demand place 400. A boil-off gas supply unit that supplies, and a forced vaporized gas supply unit that supplies forced vaporized gas (FBOG) obtained by forcibly vaporizing the LNG stored in the LNG storage tank to the fuel consumer 400, and exceeds the amount of gas fuel required by the fuel consumer 400. and a re-liquefaction unit for re-liquefying the boil-off gas or forced vapor gas in an amount to be recovered to the storage tank.

The boil-off gas supply unit includes a compressor 200 that compresses the boil-off gas transported through the boil-off gas supply line NL connected from the top of the storage tank and supplies it to the fuel consumer 400.

In this embodiment, the fuel consumer 400 generates thermal energy such as steam required by the onboard heat source consumer by burning gas fuel with the X-DF engine 410 as a propulsion engine and the DFDG 420 as a power generation engine. It may include an auxiliary boiler 430 and a gas combustion unit (GCU) 440 that burns and processes gas in an emergency.

The X-DF engine 410 requires about 10 to 18 bar, or about 12 to 16 bar gas fuel for combustion. The compressor 200 of this embodiment may compress the boil-off gas to a pressure required by the X-DF engine 410.

The boil-off gas compressed by the compressor 200 is transported to the fuel consumer 400 through a fuel supply line SL connecting the compressor 200 and the fuel consumer 400 .

On the other hand, a re-liquefaction line (RL) branched off from the fuel supply line (SL) connecting the compressor 200 and the fuel consumer 400 and connected to the re-liquefaction unit is further included, so that the amount of boil-off gas is reduced to the fuel consumer 400. If the amount is greater than the amount required by the fuel consumer 400, the BOG to be re-liquefied by an amount exceeding the amount required by the fuel consumer 400 is transported to the re-liquefaction unit through the re-liquefaction line RL, re-liquefied, and then stored in the storage tank. is returned as

The re-liquefaction unit of the present embodiment, the boosting compressor 510 for further compressing the surplus boil-off gas compressed in the compressor 200 to a threshold pressure or higher to increase the re-liquefaction efficiency, and the boosting compressor 510 to evaporate the boil-off gas compressed A heat exchanger 100 that cools the boil-off gas cooled by the cold heat of the boil-off gas before compression toward the compressor 100 through the gas supply line NL, and a low-temperature, low-pressure gas-liquid mixture while expanding the boil-off gas cooled by the heat exchanger 100 It includes a pressure reducing valve 520 to generate and a gas-liquid separator 530 for gas-liquid separation of the gas-liquid mixture generated by the pressure reducing valve 520.

The boosting compressor 510 of this embodiment may further compress the boil-off gas compressed in the compressor 300 to a critical pressure, for example, about 50 to 150 bar.

The pressure reducing valve 520 of the present embodiment may be a Joule-Thomson valve, and the temperature of the boil-off gas is lowered while the boil-off gas is isentropically expanded by the pressure-relief valve 520, and a gas-liquid mixture is generated in this process.

In this embodiment, the pressure-reducing valve 520 is described as an example of a Joule-Thomson valve, but the pressure-reducing valve 520 may be an expander, a compander that converts expansion work into compression work, or a power supply that converts expansion work into electric power. It could also be an expansion-generator that converts

The operating pressure of the gas-liquid separator 530 of this embodiment may be about 4.5 barg. That is, the pressure reducing valve 520 of this embodiment can reduce the boil-off gas to about 4.5 barg.

The reliquefied boil-off gas in liquid state separated in the gas-liquid separator 530 is returned to the storage tank through the re-liquefaction line RL connecting the gas-liquid separator 530 and the storage tank, and the gas separated in the gas-liquid separator 530 The uncondensed boil-off gas is evaporated introduced from the storage tank into the heat exchanger 100 through the gas recovery line GL connected from the gas-liquid separator 530 to the boil-off gas supply line NL upstream of the heat exchanger 100. can join the gas flow.

Meanwhile, when the amount of boil-off gas is less than the amount required by the fuel consumer 400, the forced vaporized gas supply unit may generate forced vaporized gas and supply it to the fuel consumer 400.

The forced vaporization gas supply unit of the present embodiment includes a fuel supply pump 310 for pressurizing and discharging LNG to be forcibly vaporized from a storage tank, and a vaporizer for vaporizing LNG transferred from the fuel supply pump 310 through the forced vaporization line FL. (320).

The fuel supply pump 310 may compress LNG to a pressure required by the vaporizer 320 . For example, the operating pressure of the vaporizer 320 of this embodiment is about 4 barg, and therefore, the fuel supply pump 310 of this embodiment pressurizes and transfers LNG so that the inlet pressure of the vaporizer 320 can be maintained at 4 barg. can do.

In addition, the forced vaporized gas supply unit of the present embodiment cools the forced vaporized gas vaporized in the vaporizer 320 to produce a gas-liquid mixture, and the gas-liquid mixture generated in the cooler 330 is separated into gas-liquid to produce light hydrocarbons And a methane number controller 340 for separating heavy hydrocarbons.

A cooling line (CL) branching from the forced vaporization line (FL) upstream of the vaporizer 320 may be connected to the cooler 430 of the present embodiment. In the cooler 430, a gas-liquid mixture is generated by mixing the forced vaporization gas generated in the vaporizer 320 and the LNG transported through the cooling line CL. In this process, the heavy hydrocarbon component with a high liquefaction point is condensed, and the light hydrocarbon component with a low liquefaction point, that is, methane, remains in a gaseous state.

The gas-liquid mixture generated in the cooler 430 is gas-liquid separated in the methane number controller 340, and the liquid separated in the methane number controller 340, that is, heavy hydrocarbons, is transferred to the storage tank through the condensate recovery line HL. Can be transferred. In addition, the gas separated from the methane number regulator 340, that is, the methane-rich gas, is supplied to the compressor 200 through a forced vaporization line FL connecting the methane number regulator 340 and the fuel supply line SL upstream of the compressor 200. ) can be transferred to

Meanwhile, the fuel supply pump 310 has a supportable flow rate range, that is, a minimum flow rate and a maximum flow rate, and in order to prevent damage to the fuel supply pump 310, the flow rate of the fuel supply pump 310 inlet is (310) must be maintained above the minimum flow rate supported. For example, if the flow rate range that the fuel supply pump 310 can support is 2 to 12 m ³ /hr, the flow rate at the inlet of the fuel supply pump 310 should be maintained at least 2 m ³ /hr or more.

When the flow rate of the forced vaporization line (FL) connecting the fuel supply pump 310 and the carburetor 320 maintains a preset value or more according to the supportable flow rate range of the fuel supply pump 310, the fuel supply pump 310 ) The flow rate of the inlet can be maintained above the minimum flow rate.

According to this embodiment, in order to control the flow rate of the fuel supply pump 310, the flow rate of the forced vaporization line FL connecting the fuel supply pump 310 and the vaporizer 320, that is, the inlet pressure of the vaporizer 320 ( A first valve (V1) installed on the forced vaporization line (FL) connecting the fuel supply pump 310 and the carburetor 320 as a control means for controlling the flow rate) to be maintained above a set value, and fuel supply It includes a flow control line (BL) branched from the forced vaporization line (FL) downstream of the pump 310 and connected to the storage tank again, and a second valve (V2) installed on the flow control line (BL).

In addition, the re-liquefaction fuel line (LL) connected from the gas-liquid separator 530 to the forced vaporization line (FL) connecting the fuel supply pump 310 and the vaporizer 320 and installed on the re-liquefaction fuel line (LL) It further includes a third valve (V3) to be.

In addition, a flow meter (FM) for measuring the flow rate of LNG transferred from the fuel supply pump 310 to the vaporizer 320, and an ammeter (CT) for measuring the current of the motor (M) for driving the fuel supply pump 310 more includes The flow rate of the fuel supply pump 310 may be calculated from the current measurement value of the ammeter CT.

In addition, the fuel supply calculated from the flow rate controller (FIC) controlling the opening and closing of the first valve (V1) and the third valve (V3) according to the flow rate measurement value of the flow meter (FM) and the current measurement value of the ammeter (CT) According to the flow rate of the pump 310, a flow controller (CIC) for controlling the opening and closing of the second valve (V2) is further included.

Conventionally, when the flow rate of LNG discharged from the fuel supply pump 310 exceeds the flow rate of LNG to be forcibly vaporized, that is, the inlet pressure of the vaporizer 320, the opening of the second valve V2 is adjusted, The high-temperature LNG discharged from the fuel supply pump 310 was returned to the storage tank through the flow control line BL.

In addition, in the past, even when the flow rate of LNG to be forcibly vaporized is less than the flow rate range that the fuel supply pump 310 can support, the fuel supply pump 310 sucks and discharges the LNG above the minimum flow rate from the storage tank. 2 By increasing the opening rate of the valve (V2), the amount of LNG exceeding the flow rate of LNG to be forcibly vaporized among the discharged LNG was recovered to the storage tank through the flow control line (BL).

However, according to this conventional method, there is a problem in that LNG whose temperature has been increased by compression is returned to the storage tank, and the internal temperature of the storage tank increases, thereby increasing the amount of boil-off gas.

According to this embodiment, the re-liquefaction fuel line (LL) is provided, and high-temperature LNG is recovered through the flow control line (BL), such as when the flow rate of LNG to be forcibly vaporized is less than the minimum flow rate of the fuel supply pump 310. In this case, instead of supplying LNG to be forcibly vaporized from the storage tank to the vaporizer 320, the vaporizer 320 receives the re-liquefied boil-off gas condensed in the gas-liquid separator 530 through the re-liquefied fuel line LL. ) can be supplied.

When the re-liquefied boil-off gas condensed in the gas-liquid separator 530 is supplied to the vaporizer 320, the flow controller FIC sends a signal to close the first valve V1, and the flow controller CIC sends a signal to the second valve ( V2) is sent to close the first valve (V1) and the second valve (V2) are closed, and the control unit (not shown) instructs the fuel supply pump 310 to be stopped. After that, the flow controller (FIC) adjusts the flow rate of LNG supplied from the gas-liquid separator 530 to the vaporizer 320 while adjusting the opening rate of the third valve (V3) according to the flow rate measurement value of the flow meter (FM). .

In this way, by supplying re-liquefied boil-off gas to the vaporizer 320 without operating the fuel supply pump 310, it is not necessary to recover pressurized LNG to maintain the minimum flow rate of the fuel supply pump 310, so conventional flow control lines ( By recovering the pressurized LNG through the BL), it is possible to prevent a problem in which the internal temperature of the storage tank rises.

In addition, it is possible to prevent the excessive increase in the generation of evaporation gas inside the storage tank.

In addition, since it is not necessary to operate the fuel supply pump 310, it is possible to prevent a problem in which the amount of boil-off gas generated in the storage tank increases due to the operation of the fuel supply pump 310, and to operate the fuel supply pump 310 It is possible to reduce the consumption of consumed power.

It is obvious to those skilled in the art that the present invention is not limited to the above embodiments and can be variously modified or modified without departing from the technical gist of the present invention. it did

100: heat exchanger
200: compressor
310: fuel supply pump
320: carburetor
330: cooler
340: methane number regulator
400: fuel demand place
510: boosting compressor
520: pressure reducing valve
530: gas-liquid separator
LL : Reliquefaction fuel line
V1: first valve
V2: 2nd valve
V3: 3rd valve
FIC: flow controller

Claims (7)

A compressor for compressing boil-off gas generated in the liquefied gas storage tank to a pressure required by the engine;
a re-liquefaction unit for re-liquefying the compressed boil-off gas exceeding the amount of gas fuel required by the engine;
a re-liquefaction line connecting the re-liquefaction unit and the liquefied gas storage tank so that the re-liquefied boil-off gas re-liquefied in the re-liquefaction unit is recovered to the liquefied gas storage tank;
a fuel supply pump for discharging liquefied gas stored in a liquefied gas storage tank to supply fuel to the engine;
a vaporizer that vaporizes the liquefied gas transported from the fuel supply pump and sends it to the compressor;
a re-liquefaction fuel line branched from the re-liquefaction line and connected to the vaporizer so that the re-liquefaction boil-off gas from the re-liquefaction unit is transported to the vaporizer;
a third valve provided in the re-liquefied fuel line;
a controller for stopping operation of the fuel supply pump when the amount of gas fuel required by the engine is less than the minimum flow rate; and
A flow rate controller that opens the third valve to adjust the flow rate of the re-liquefied boil-off gas supplied to the carburetor when the amount of gas fuel required by the engine is less than the minimum flow rate of the fuel supply pump operating range. fuel supply system. The method of claim 1,
The temperature of the liquefied gas discharged from the fuel supply pump is higher than the temperature of the liquefied gas sucked into the fuel supply pump and the temperature of the re-liquefied boil-off gas,
A first valve for controlling the opening and closing of the flow path so that the liquefied gas discharged from the fuel supply pump is supplied to the vaporizer;
a flow control line branching from a forced vaporization line connecting the fuel supply pump and the vaporizer so that the liquefied gas discharged by the fuel supply pump is returned to the liquefied gas storage tank;
a second valve installed in the flow control line and having an opening rate controlled to control the flow rate of the liquefied gas supplied from the fuel supply pump to the carburetor; and
By calculating the flow rate of liquefied gas discharged from the fuel supply pump, the opening rate of the second valve is controlled so that an amount of liquefied gas exceeding the flow rate of liquefied gas required by the vaporizer is returned to the liquefied gas storage tank. The fuel supply system of the vessel further comprising a; flow regulator to. The method of claim 2,
When the amount of gas fuel required by the engine is less than the minimum flow rate of the fuel supply pump operating range,
the first valve is closed by the flow controller;
Wherein the second valve is closed by the flow regulator. The method of claim 1,
The re-liquefaction unit,
a boosting compressor for further compressing the boil-off gas compressed by the compressor to a critical pressure or higher;
A heat exchanger that cools the compressed boil-off gas by exchanging heat between the boil-off gas compressed by the boosting compressor and the boil-off gas before compression supplied to the compressor from the liquefied gas storage tank;
a pressure reducing valve for expanding the boil-off gas cooled by the heat exchanger;
a gas-liquid separator for gas-liquid separation of the gas-liquid mixture generated by the pressure reducing valve; and
A gas recovery line for joining the non-condensed boil-off gas in the gaseous state separated by the gas-liquid separator to the pre-compression boil-off gas flow supplied to the heat exchanger;
The re-liquefied boil-off gas in a liquid state separated by the gas-liquid separator flows along the re-liquefaction line or the re-liquefaction fuel line. The method of claim 1,
a cooler for cooling the forced vaporized gas generated by vaporizing the liquefied gas in the vaporizer;
a methane number regulator for gas-liquid separation of the gas-liquid mixture produced by the cooler;
a condensate recovery line for discharging heavy hydrocarbons in a liquid state gas-liquid separated from the methane number regulator from the methane number regulator; and
A forced vaporization line for supplying gaseous light hydrocarbons gas-liquid separated in the methane number regulator to the compressor; further comprising a ship's fuel supply system. Compressing boil-off gas or forced vapor of liquefied gas and supplying it as fuel for the engine,
Gas fuel in an amount exceeding the amount of fuel required by the engine is re-liquefied and recovered to a liquefied gas storage tank,
Supplying the forced vaporization gas as fuel for the engine,
Discharging liquefied gas from the liquefied gas storage tank,
Including vaporizing the discharged liquefied gas,
When the engine requires gas fuel less than the pump operating range for discharging the liquefied gas, the pump is not operated, and the re-liquefied boil-off gas is vaporized and supplied to the engine. The method of claim 6,
Measuring the flow rate of liquefied gas flowing into the vaporizer from the pump,
Calculate the flow rate of the liquefied gas discharged from the pump,
When the measured flow rate is greater than the flow rate required by the vaporizer, the opening rate of the valve is set so that an amount of liquefied gas exceeding the flow rate required by the vaporizer is returned to the liquefied gas storage tank among the liquefied gas discharged from the pump. regulating, the method of supplying fuel to ships.

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