WO2021256644A1

WO2021256644A1 - System and method for supplying fuel for liquefied gas carrier

Info

Publication number: WO2021256644A1
Application number: PCT/KR2020/018576
Authority: WO
Inventors: 김두혁; 최안철; 박성호; 태혁준; 이규성
Original assignee: 대우조선해양 주식회사
Priority date: 2020-06-18
Filing date: 2020-12-17
Publication date: 2021-12-23
Also published as: JP2023529204A; CN115697836A; JP7485796B2

Abstract

Disclosed are a system and a method for supplying fuel for a liquefied gas carrier. The system for supplying fuel for a liquefied gas carrier of the present invention comprises: a fuel supply line through which liquefied gas is supplied from a fuel supply tank provided on the deck of a vessel to an engine inside the vessel; a compression part which is provided in the fuel supply line and compresses the liquefied gas to be supplied to the engine inside the vessel to a pressure required for the engine; a return line which recirculates liquefied gas that has not been consumed by the engine from among the liquefied gas to an upstream of the engine; a separator which is provided in the return line and performs gas-liquid separation of the recirculated liquefied gas; and a decompression part which is provided in an upstream of the separator in the return line, wherein the liquefied gas recirculated through the return line is cooled under reduced pressure in the decompression part and introduced into the separator.

Description

[Amended by Rule 26 29.12.2020]　Liquefied gas carrier fuel supply system and method

The present invention relates to a fuel supply system and method for a liquefied gas carrier, and more particularly, to a fuel supply for a liquefied gas carrier that recovers and recirculates the remaining LPG from a ship using a liquefied gas such as LPG as a fuel to an engine in excess. It relates to systems and methods.

The consumption of liquefied gas such as LNG (Liquefied Natural Gas) or LPG (Liquefied Petroleum Gas) is rapidly increasing worldwide. Liquefied gas is transported in a gaseous state through a gas pipeline on land or offshore, or stored in a liquefied gas carrier in a liquefied state and transported to a remote consumer. Liquefied gas such as LNG or LPG is obtained by cooling natural gas or petroleum gas to cryogenic temperatures (approximately -163°C in the case of LNG).

The liquefaction temperature of petroleum gas is a low temperature of about -42°C under normal pressure, and can be stored in a liquid state up to a temperature of about 45°C at 18 bar and 20°C at 7 bar. Since LPG evaporates when the atmospheric pressure is higher than -42℃, the LPG storage tank of the ship is insulated. However, since external heat is continuously transferred to the LPG, the LPG is continuously vaporized in the LPG storage tank during the LPG transportation process, thereby generating boil-off gas in the LPG storage tank.

In LPG carriers, when BOG accumulates in the LPG storage tank, the pressure in the LPG storage tank rises excessively. do.

On the other hand, conventional LPG carriers employ a fuel supply system using heavy oil such as bunker C oil, which is relatively inexpensive as a propulsion fuel for ships. Due to the strengthening of regulations, a LSHFO tank with low sulfur content had to be installed separately, and the demand for an eco-friendly fuel supply system that meets international environmental regulations has grown.

Recently, the application of a fuel supply system that uses LPG or LNG and boil-off gas generated therefrom as a propulsion fuel is increasing in LPG or LNG carriers. The number of ships used as propulsion fuel is increasing.

In particular, LPG is easier to store than LNG, which is liquefied at cryogenic temperatures, and it does not significantly fall in SPECIFIC ENERGY and ENERGY DENSITY compared to conventional HFO, and has an excellent effect in reducing SOX, NOX, CO2, PM, etc. compared to conventional HFO.

An example of a fuel supply system from a ship using LPG as a fuel to a conventional engine is schematically shown in FIG. 1 .

As shown in FIG. 1, LPG to be supplied as fuel to the engine E is supplied from the fuel supply tank according to the fuel supply conditions of the engine through a fuel supply system including a compression pump and a heater. It is supplied to the engine of the ship via line L1.

LPG, an incompressible fluid, can be supplied in excess of the fuel required by the engine to respond immediately to changes in engine load. It is withdrawn from the engine upstream of the engine via line L2.

However, since LPG recovered through the recovery line is compressed and heated according to the fuel supply conditions of the engine and is in a high temperature and high pressure state, there is a problem in that the pressure and temperature in the tank increase when it is sent to the fuel supply tank, and the sealing oil introduced from the engine ), and there is a risk of crystallization when the temperature of the fuel supply tank falls below -10℃. On the other hand, there is a problem of wasting fuel if the recovered LPG is discharged and burned as it is.

An object of the present invention is to provide a system capable of efficiently supplying fuel while effectively processing LPG recovered from an engine by solving this problem.

According to one aspect of the present invention for solving the above-described problems, a fuel supply line through which liquefied gas is supplied from a fuel supply tank provided on the deck of a ship to an onboard engine;

a compression unit provided in the fuel supply line and compressing the liquefied gas to be supplied to the onboard engine to a pressure required for the engine;

a return line for recirculating the liquefied gas not consumed by the engine among the liquefied gas to an upstream of the engine;

a separator for gas-liquid separation of the recirculated liquefied gas provided in the return line; and

and a pressure reducing unit provided upstream of the separator in the return line;

The liquefied gas recirculated through the return line is cooled by the reduced pressure in the decompression unit, and there is provided a fuel supply system for a liquefied gas carrier, characterized in that it is introduced into the separator.

Preferably, the compression unit comprises: a first pump for pumping and transferring liquefied gas from the fuel supply tank; and a second pump for pumping the liquefied gas transferred from the first pump to increase the pressure to a required pressure in the engine, wherein the liquid liquefied gas separated from the separator is a fuel between the first pump and the second pump It can be supplied to the supply line and recycled.

Preferably, a vapor line for recovering the gas separated from the separator to the fuel supply tank; and a pressure control valve provided in the vapor line.

Preferably, the pressure of the rear end of the first pump is sensed, and the opening degree of the pressure control valve is adjusted according to the sensed pressure to maintain the pressure of the separator 0.5 to 2 bar higher than the pressure at the rear end of the first pump. have.

Preferably, a fuel heater provided at the rear end of the compression unit in the fuel supply line and heating the compressed liquefied gas to a temperature required by the engine; may further include.

Preferably, the return line includes: a first return line connected from the engine to the separator; and a second return line connected to the separator from a fuel supply line between the second pump and the fuel heater.

Preferably, the pressure reducing unit includes: a first pressure reducing device provided in the first return line; and a second pressure reducing device provided on the second return line.

Preferably, by sensing the rear end pressure of the second pump, when the sensed pressure is higher than the set value, the pump speed of the second pump is lowered first, and if it is still higher than the set value, the second pressure reducing device is opened to increase the pressure of the second pump. The back pressure can be lowered.

Preferably, the re-liquefaction unit for receiving the boil-off gas generated from the cargo tank for storing the liquefied gas to be transported provided on the ship and re-liquefied; and a cooling line connected from the reliquefaction unit to the cargo tank via the fuel supply tank, wherein the liquefied gas reliquefied in the reliquefaction unit cools the fuel supply tank along the cooling line and the cargo tank can be transferred to

Preferably, a fuel tank provided in the ship to store the liquefied gas to be supplied to the onboard engine: may further include, wherein the liquefied gas is transferred from the fuel tank to the fuel supply tank to cool the fuel supply tank .

Preferably, a discharge pipe provided at the bottom of the separator for separating and discharging the lubricating oil mixed in the liquefied gas returned to the separator; and a re-liquefaction unit for re-liquefying boil-off gas generated from a cargo tank for storing liquefied gas to be transported and provided on the ship, wherein the liquefied gas re-liquefied in the re-liquefaction unit passes through the fuel supply tank to the cargo tank By transport, it is possible to cool the fuel supply tank.

According to another aspect of the present invention, the liquefied gas is compressed in the compression unit along the fuel supply line from the fuel supply tank provided on the deck of the ship and supplied as fuel to the onboard engine,

A decompression unit is provided in a return line for recirculating liquefied gas not consumed by the engine among the liquefied gas compressed in the compression unit to an upstream side of the engine to reduce the pressure of the liquefied gas to be recirculated, and the recirculated liquefied gas cooled by the reduced pressure in the separator There is provided a fuel supply method for a liquefied gas carrier, characterized in that gas-liquid separation.

Preferably, the gas separated from the separator is recovered to the fuel supply tank, by detecting a rear end pressure of the first pump, and adjusting the amount of gas recovered to the fuel supply tank according to the sensed pressure, The pressure of the separator may be maintained 0.5 to 2 bar higher than the pressure at the rear end of the first pump.

Preferably, by sensing the pressure at the rear end of the second pump, if the detected pressure is higher than the set value, first lower the pump speed of the second pump, and if still higher than the set value, a part of the liquefied gas at the rear end of the second pump The pressure at the rear end of the second pump may be lowered by reducing the pressure and discharging it to the separator.

Preferably, the boil-off gas generated from the cargo tank for storing the liquefied gas to be transported provided in the ship is reliquefied in the reliquefaction unit, and the liquefied gas reliquefied in the reliquefaction unit passes through the fuel supply tank to the fuel supply tank It can be cooled and transferred to the cargo tank.

Preferably, the fuel supply tank can be cooled by transferring the liquefied gas to the fuel supply tank from a fuel tank that is provided in the ship to store the liquefied gas to be supplied to the onboard engine.

Preferably, a discharge pipe for separating and discharging the lubricant mixed in the liquefied gas returned to the separator may be provided at the bottom of the separator.

Preferably, the boil-off gas generated from the cargo tank for storing the liquefied gas to be transported provided in the ship is reliquefied in the reliquefaction unit, and the liquefied gas reliquefied in the reliquefaction unit is passed through the fuel supply tank to the cargo tank. It can be transferred to cool the fuel supply tank.

In the present invention, the liquefied gas not consumed in the engine is recirculated through the return line among the compressed liquefied gas for fuel supply to the engine, and the compressed liquefied gas is cooled in the return line at reduced pressure and separated from the gas-liquid through a separator to liquefy the liquid. Only gas is supplied to the fuel supply line to be recirculated. In this way, by recirculating the remaining liquefied gas that is oversupplied to the engine and consumed as fuel, it is possible to prevent lubricating oil from being mixed into the fuel, thereby preventing incomplete combustion of the engine and the generation of pollutants in the exhaust due to the incomplete combustion of the engine. It can prevent LPG contamination and crystallization of lubricating oil in the fuel supply tank.

In addition, by cooling the recirculated liquefied gas, separating the gas and liquid, and introducing it into the second pump together with the subcooled LPG supplied from the fuel supply tank through the first pump of the compression unit, the second pump suction of the compression unit It is possible to reduce the risk of vapor generation and prevent device failure of the compression unit without installing additional equipment to remove it.

The gas separated from the separator is transferred to the fuel supply tank, and the boil-off gas generated in the cargo tank is reliquefied and transferred to the cargo tank through the fuel supply tank through the cooling line. By cooling, the pressure and temperature of the tank can be safely maintained.

1 schematically shows a fuel supply system from a ship equipped with an engine using LPG as a fuel to a conventional engine.

2 schematically shows a fuel supply system for a liquefied gas carrier according to a first embodiment of the present invention.

3 schematically shows a fuel supply system for a liquefied gas carrier according to a second embodiment of the present invention.

4 schematically shows the configuration of a discharge unit for discharging lubricant oil from a separator in a fuel supply system of a liquefied gas carrier according to a second embodiment of the present invention.

In order to fully understand the operational advantages of the present invention and the objects achieved by the practice 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 the preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. Here, it should be noted that in adding reference signs to the elements of each drawing, the same elements are indicated with the same reference numerals as much as possible even though they are indicated on different drawings.

In an embodiment of the present invention to be described later, the vessel may be any type of vessel in which an engine capable of using liquefied petroleum gas as a fuel for a propulsion engine or a fuel for a power generation engine is installed. Typical examples include ships with self-propelled capabilities such as LPG carriers, LNG carriers, liquid hydrogen carriers, and LNG RVs (Regasification Vessels), LNG Floating Production Storage Offloading (FPSO), and LNG FSRU (Floating Storage Regasification Unit). It may also include offshore structures that do not have propulsion capabilities, but are floating in the sea.

In addition, this embodiment can be transported by being liquefied at a low temperature, and BOG is generated in a stored state and can be applied to a fuel supply system of all kinds of liquefied gas that can be supplied as fuel of an engine. Such liquefied gas is, for example, liquefied petrochemicals such as LNG (Liquefied Natural Gas), LEG (Liquefied Ethane Gas), LPG (Liquefied Petroleum Gas), Liquefied Ethylene Gas, Liquefied Propylene Gas, etc. gas and ammonia, and the like. However, in the embodiments to be described later, an example in which LPG, which is one of representative liquefied gases, is applied will be described.

As shown in FIG. 2, the fuel supply system of the first embodiment includes a fuel supply line (SL) through which liquefied gas is supplied from a fuel supply tank (DT) provided on the deck of the ship to the in-board engine (E), and a fuel supply

line Compression units

110 and 120 for compressing the liquefied gas to be supplied to the onboard engine to the pressure required for the engine, and a return line RL1 for recirculating the liquefied gas not consumed in the engine among the liquefied gas to the upstream of the engine. RL2), a separator 210 provided in the return line for gas-liquid separation of the recirculated liquefied gas, and

pressure reducing units

220 and 230 provided upstream of the separator in the return line.

In this embodiment, the liquefied gas recirculated through the return line is decompressed through the decompression unit, and the liquefied gas is cooled by the Joule-Thomson effect in the decompression process and introduced into the separator.

The compression unit includes a first pump 110 for pumping and transferring the liquefied gas from the fuel supply tank, and a second pump 120 for pumping the liquefied gas transferred from the first pump and boosting the pressure to the pressure required by the engine. It consists of two pumps.

The first pump 110 is a low-pressure pump for transporting liquefied gas and is a centrifugal pump, and the second pump 120 is a high-pressure pump that compresses the fuel supply pressure required by the engine, and is a diaphragm pump. ), and the liquefied gas passing through the first and second pumps is heated to a temperature required by the engine in the fuel heater 130 provided at the rear end of the compression unit in the fuel supply line and supplied to the engine.

In the fuel supply line, the compressed and heated liquefied gas through the compression unit and the fuel heater is supplied to the engine E through the filter 140 that filters out foreign substances in the fuel and the service valve unit SVT. In the service valve part, while supplying LPG to the engine, when LPG fuel supply is stopped due to engine fuel oil switching, LPG mode stop, trip, etc., each pipe is double-blocked through the valve to relieve pressure in the pipe.

An engine receiving such compressed and heated LPG as fuel may be, for example, a ME-LGIP engine of MAN Diesel & Turbo. In this case, LPG is supplied to the engine in a high-pressure liquid state of around 54 bar and 35° C. through the compression unit and the fuel heater, and the engine is operated by being hydraulically injected into the nozzle at a pressure of 600 to 700 bar.

That is, in the engine of this embodiment, compressed and heated fuel is supplied to the engine in a liquid state, and unlike the engine to which a compressible fluid having a large volume change according to a change in pressure, that is, gas fuel is supplied, the volume changes even when pressure is applied. When there is no or little incompressible fluid or liquid LPG as engine fuel, sufficient fuel is supplied to respond immediately to changes in engine load and excess LPG is supplied to the engine to prevent cavitation. Among the LPG supplied to the engine, the remaining LPG consumed as fuel is discharged from the engine through the return line and recirculated. ), and may pose a threat to tank and ship safety by increasing the pressure and temperature in the fuel supply tank.

In this embodiment, in order to solve this problem, the

decompression units

220 and 230 for decompressing the liquefied gas are provided in the return line, so that the liquefied gas discharged from the engine can be recirculated by decompressing the liquefied gas. The compressed liquefied gas is cooled by the Joule-Thomson effect while undergoing adiabatic or isentropic expansion during the decompression process.

The compressed liquefied gas recirculated from the engine E through the return line RL1 is reduced in pressure through the decompression unit 220 and cooled, introduced into the separator 210 for gas-liquid separation, and the liquid liquefied gas separated from the separator is It is supplied to the fuel supply line SL between the first pump 110 and the second pump 120 through the liquid line LL and recirculated, and the gas separated from the separator is supplied to the fuel supply tank through the vapor line VL. (DT) is recovered. The vapor line is provided with a pressure control valve 250 for controlling the gas transferred to the fuel supply tank (DT).

In this embodiment, the liquefied gas cooled through decompression is introduced into the separator, and the liquid liquefied gas after gas-liquid separation is supplied from the fuel supply tank through the first pump of the compression unit through the first pump of the compression unit and the second pump 120 together with the subcooled LPG. ), it is possible to reduce the risk of vapor generation in the suction part of the second pump and not configure a separate device for vapor removal.

In addition, when the temperature of the recirculated liquefied gas is high, the fuel heater must have a cooling function as well as a heating function in order to meet the fuel requirements of the engine. The gas in the decompressed recirculation liquefied gas is recovered to the fuel supply tank, and the mass flow of the high-temperature recirculated liquefied gas sucked into the second pump is reduced, so that fuel at an appropriate temperature can be supplied to the engine without additional cooling. Since the fuel heater only needs to have a heating function, the equipment cost can be reduced and operation is easy.

On the other hand, the return line includes a first return line RL1 connected from the engine E to the separator 210 and a separator ( and a second return line RL2 connected to 210 . In addition, the decompression unit may include a first decompression device 220 provided in the first return line and a second decompression device 230 provided in the second return line. The first and second pressure reducing devices may include an expander for cooling the compressed liquefied gas by adiabatic or isentropic expansion or an expansion valve such as a Joule-Thomson valve.

A return valve unit (RVT) and a filter 240 are provided upstream of the first pressure reducing device in the first return line, and the liquefied gas discharged from the engine is introduced into the first pressure reducing device through the return valve unit and the filter. The filter can filter lubricating oil mixed in the liquefied gas discharged from the engine.

The first return line and the first pressure reducing device depressurize the liquefied gas discharged from the engine, and the second return line and the second pressure reducing device decompress the compressed liquefied gas through the compression units of the first and second pumps from upstream of the fuel heater to form a separator. transfer to

Through this, the LPG remaining in the engine and fuel supply line can also be cooled under reduced pressure and transferred to the separator when the LPG fuel supply is interrupted, such as when the engine is stopped in LPG mode or when tripping. When the LPG fuel supply is stopped, it is not necessary to recirculate the LPG from the separator to the fuel supply line, so it can be sent to the fuel supply tank, and for this, a transfer line (not shown) from the separator to the fuel supply tank may be provided.

In the present embodiment system, a plurality of pressure sensing units are provided to control the operating pressure. A first pressure sensing unit PC1 that senses the pressure between the second pump and the fuel heater and sends a pressure signal, a second pressure sensing unit that senses the pressure between the filter and the first pressure reducing device in the first return line and sends a pressure signal A unit PC2, a third pressure sensing unit PC3 sensing the pressure of the rear end of the first pump, and a fourth pressure sensing unit PC4 sensing the pressure of the separator are provided, respectively.

The operating pressure in the system of the present embodiment may be controlled as follows, for example.

The operating pressure range of the fuel supply tank is 1 to 8 barg. Assuming that the operating pressure is 4 barg, the differential pressure of the first pump is about 2 bar, and the rear end pressure of the first pump is 6 barg. The operating pressure of the separator 210 is maintained at about 0.5 to 2 bar, more preferably 0.5 to 1 bar higher than the pressure at the rear end of the first pump, so that the liquid recirculation gas separated from the separator is smoothly transferred to the rear end of the first pump. can

To this end, the fourth pressure sensing unit PC4 receives the pressure signal from the third pressure sensing unit PC3, and the fourth pressure sensing unit PC4 sets the set value to the pressure control valve 250 of the vapor line VL. By sending a signal and adjusting the opening degree of the pressure control valve, the pressure of the separator is maintained at 6.5 to 7 barg.

The liquid separated from the separator is supplied to the front end of the second pump along the liquid line LL, and is pumped from the second pump and pressurized to 54 barg.

The first return line RL1 returning from the engine controls the first pressure reducing device 220 from the second pressure sensing unit to maintain the pressure upstream of the first pressure reducing device at 22 barg, and the pressure at the rear end of the first pressure reducing device is Maintain at 6.5 to 7 barg equal to the separator pressure.

When the rear end pressure of the second pump changes due to a change in fuel consumption due to a change in the load in the engine, the pressure is sensed by the first pressure sensing unit PC1 and is higher than the set value (54 barg) of the first pressure sensing unit. The pump speed is lowered by adjusting the VFD, and if the pressure is still increased from 54 barg or more to 55 barg, the second pressure reducing device 230 of the second return line is opened to lower the pressure.

The ship of this embodiment is provided with a cargo tank (not shown) for storing and transporting liquefied gas as a liquefied gas carrier, and the boil-off gas generated from the liquefied gas stored in the cargo tank is supplied to the re-liquefaction unit (RS) and re-liquefied. .

The temperature of the fuel supply tank may be increased by the gas separated from the separator and introduced. In this embodiment, the liquefied gas reliquefied from the reliquefaction unit RS passes through the fuel supply tank DT to the cargo tank (not shown). A cooling line CL is provided so as to be connected, so that the fuel supply tank can be cooled by using the cooling heat of the liquefied gas reliquefied in the reliquefaction unit.

Meanwhile, in the ship, fuel tanks FT1 and FT2 for supplying liquefied gas to be supplied as fuel of the onboard engine to the fuel supply tank DT disposed on the deck are additionally provided. It is also possible to supply liquefied gas from the fuel supply tank to the fuel supply tank to cool the fuel supply tank by the low-temperature liquefied gas.

As shown in FIG. 3, the fuel supply system of the second embodiment also includes a fuel supply line SL through which liquefied gas is supplied from the fuel supply tank DT provided on the deck of the ship to the in-board engine E, and the fuel supply A first pump 110 provided in the line and transferring liquefied gas to be supplied from the fuel supply tank to the engine, a second pump 120 provided in the fuel supply line and compressing the liquefied gas to the pressure required for the engine, among the liquefied gas Return lines RL1 and RL2 for recirculating the liquefied gas not consumed in the engine to the upstream of the engine, the separator 210 provided in the return line and receiving the recirculated liquefied gas to gas-liquid separation, the liquid liquefied gas separated from the separator It includes a liquid line LL for supplying to the rear end of the first pump of the fuel supply line, and a vapor line VL for recovering the gas separated from the separator to the fuel supply tank DT.

A pressure reducing unit for reducing the recirculated liquefied gas is provided upstream of the separator in the return line, and a pressure regulating valve 250 for controlling the gas transferred to the fuel supply tank DT is provided in the vapor line connected from the separator to the fuel supply tank. will be prepared

Amount of gas recovered from the separator to the fuel supply tank by sensing the pressure at the rear end of the first pump of the fuel supply line to which the liquefied gas separated from the separator and recirculated through the liquid line is supplied, and by controlling the pressure control valve according to the sensed pressure by adjusting the pressure of the separator to be maintained higher than the pressure sensed in the fuel supply line.

The process of supplying fuel to the engine in the system of the second embodiment is described in more detail as follows.

The fuel supply from the fuel supply tank to the engine includes a first pump 110 for pumping and transferring the liquefied gas, and a second pump 120 for pumping the transferred liquefied gas and boosting the pressure to the pressure required by the engine. It is made by two pumps.

The first pump 110 is a low-pressure pump for transporting liquefied gas, for example, a centrifugal pump, and the second pump 120 is a high-pressure pump that compresses the fuel supply pressure required by the engine. The diaphragm pump ( diaphragm pump), and the liquefied gas passing through the first pump and the second pump is heated to a temperature required by the engine in the fuel heater 130 provided at the rear end of the second pump and supplied to the engine.

In the fuel supply line, the compressed and heated liquefied gas through the second pump and the fuel heater is supplied to the engine E through the filter 140 that filters out foreign substances in the fuel and the service valve unit SVT. In the service valve part, while supplying LPG to the engine, when LPG fuel supply is stopped due to engine fuel oil switching, LPG mode stop, trip, etc., each pipe is double-blocked through the valve to relieve pressure in the pipe.

That is, in the engine of this embodiment, compressed and heated fuel is supplied to the engine in a liquid state, and unlike the engine to which a compressible fluid having a large volume change according to a change in pressure, that is, gas fuel is supplied, the volume changes even when pressure is applied. When there is no or little incompressible fluid or liquid LPG as engine fuel, sufficient fuel is supplied to respond immediately to changes in engine load and excess LPG is supplied to the engine to prevent cavitation. Among the LPG supplied to the engine, the remaining LPG consumed as fuel is discharged from the engine through the return line and recirculated. When the compressed and heated LPG is recirculated as it is or sent to the fuel supply tank, the vapor), and it may increase the pressure and temperature in the fuel supply tank, which may threaten the safety of the tank and ship.

In this embodiment, in order to solve this problem, the

decompression units

The compressed liquefied gas recirculated from the engine E through the return line RL1 is reduced in pressure through the decompression unit 220 and cooled, introduced into the separator 210 for gas-liquid separation, and the liquid liquefied gas separated from the separator is It is supplied to the fuel supply line SL between the first pump 110 and the second pump 120 through the liquid line LL and recirculated, and the gas separated from the separator is supplied to the fuel supply tank through the vapor line VL. (DT) is recovered.

In this embodiment, liquefied gas cooled through decompression is introduced into the separator, and after gas-liquid separation, the liquid liquefied gas is supplied from the fuel supply tank through the first pump to the second pump 120 together with subcooled LPG. Since it is introduced, it is possible to reduce the risk of vapor generation in the suction part of the second pump, and thus a separate device for removing vapor may not be configured.

The first return line and the first pressure reducing device depressurize the liquefied gas discharged from the engine, and the second return line and the second pressure reducing device reduce the liquefied gas compressed by the second pump to the fuel supply pressure of the engine from upstream of the fuel heater to form a separator. transfer to

The separator is provided with a level sensor (LC) that detects the liquid level of the separator, and controls the valve (V1) according to the liquid level of the separator detected by the level sensor to adjust the flow rate of the liquefied gas transferred to the fuel supply line. can

When the rear end pressure of the second pump changes due to a change in fuel consumption due to a change in the load in the engine, the first pressure sensing unit PC1 detects the pressure and, if it is higher than the set value (54 barg) of the first pressure sensing unit, first of the second pump The pump speed is lowered by adjusting the VFD, and if the pressure is still increased from 54 barg or more to 55 barg, the second pressure reducing device 230 of the second return line is opened to lower the pressure.

Meanwhile, a discharge pipe DL is provided at the bottom of the separator 210 . Lubricating oil separated from the separator is discharged to a discharge unit including a discharge pipe (DL). 4 schematically shows a configuration of a discharge unit for discharging lubricant oil from a separator in a fuel supply system of a liquefied gas carrier according to the second embodiment.

The liquefied gas recovered from the engine may contain, in addition to liquid LPG, gas such as boil-off gas generated through compression and heating for fuel supply and sealing oil introduced from the engine. If it is supplied as a fuel of Also, when lubricating oil flows into the fuel supply tank, there is a risk of crystallization in the tank. In the present embodiment, this can be prevented by separating and discharging the lubricant mixed in the liquefied gas from the separator through the discharge pipe DL provided at the bottom of the separator.

LPG is mainly composed of propane (C ₃ H ₈ ) and butane (C ₄ H ₁₀ ). Although there is a difference depending on the ratio of propane and butane, the specific gravity is about 0.5, and the specific gravity of the lubricant is about 0.9. Therefore, in the separator, the gas is separated to the upper part, and the lubricating oil heavier than LPG is layered at the bottom due to the difference in specific gravity. For smoother separation and discharge of lubricating oil, a floating buoyancy body capable of sinking in LNG and floating in lubricating oil may be provided in the separator.

If the pressure of the separator is maintained at 10 barg or less, the separation and discharge of the lubricant due to the difference in viscosity and specific gravity can be easily achieved.

The discharge part includes a discharge pipe (DL) connected from the bottom of the separator 210 and a lubricant discharge tank (SDT) where the discharged lubricant is collected, and a retention pot (retention pot, 300) between the separator and the lubricant discharge tank in the discharge pipe. ) is provided. A magnetic float level gauge 310 is provided in the retention pot to check the liquid level, and between the separator and the retention pot in the discharge pipe, as shown in FIG. 4 , a first discharge valve DV1 And a second discharge valve (DV2) is provided. A third discharge valve (DV3) is provided between the retention pod and the lubricant discharge tank to discharge the separated lubricant to the lubricant discharge tank. During normal discharge mode operation, the first and second discharge valves (DV1, DV2) are opened, the third discharge valve (DV3) is closed, and the retention time in the pipe is increased by the retention pot provided in the discharge pipe to separate the lubricant efficiency can be increased.

A fourth discharge valve that opens and closes the piping branched from the discharge pipe and connected to the lubricant discharge tank in order to relieve the pressure of the discharge pipe between the second discharge valve and the retention pod and to relieve the vacuum state when the lubricant is drained. (DV4) is provided. In addition, the level gauge 320 for measuring the liquid level is provided in the lubricant discharge tank SDT, and a fifth discharge valve DV5 is provided to discharge the lubricant from the lubricant discharge tank, and the discharged lubricant is in the engine room. It can be sent to the oil tank for reuse or disposal.

On the other hand, the ship of this embodiment is provided with a cargo tank (not shown) for storing and transporting liquefied gas as a liquefied gas carrier, and in this embodiment, boil off gas generated from the liquefied gas stored in the cargo tank (not shown) is liquid A cooling line CL is provided so that the liquefied gas re-liquefied by sending it to the re-liquefaction unit RS is connected to the cargo tank (not shown) through the fuel supply tank DT, and the re-liquefaction unit It was configured to cool the fuel supply tank by using the cooling heat of the liquefied gas re-liquefied in the

That is, the fuel supply tank supplies fuel to the onboard engine while storing LPG at a pressure of 8 barg or less. Since it is provided on the deck of the ship, the temperature in the tank increases due to external air or gas introduced from the separator. The pressure may rise, in this embodiment by configuring the cooling line CL to re-liquefy the boil-off gas generated from the liquefied gas cargo stored in the cargo tank and then to return to the cargo tank via the fuel supply tank DT, It is possible to cool the fuel supply tank by using the cooling heat of the reliquefied liquefied gas.

In this way, the temperature and pressure of the fuel supply tank can be adjusted by re-liquefying the boil-off gas generated from the cargo in the cargo tank and cooling the fuel supply tank with the cooling heat of the re-liquefied gas. By returning and storing, it is possible to prevent mixing of fuel and transported cargo.

The present invention is not limited to the above embodiments, and it is to those of ordinary skill in the art that various modifications or variations can be implemented without departing from the technical gist of the present invention. it is self-evident

Claims

a fuel supply line through which liquefied gas is supplied from the fuel supply tank provided on the deck of the ship to the onboard engine;

a compression unit provided in the fuel supply line and compressing the liquefied gas to be supplied to the onboard engine to a pressure required for the engine;

a return line for recirculating the liquefied gas not consumed by the engine among the liquefied gas to an upstream of the engine;

a separator for gas-liquid separation of the recirculated liquefied gas provided in the return line; and

and a pressure reducing unit provided upstream of the separator in the return line;

The liquefied gas recirculated through the return line is cooled under reduced pressure in the decompression unit and introduced into the separator.
According to claim 1, wherein the compression unit,

a first pump for pumping and transferring liquefied gas from the fuel supply tank; and

A second pump for pumping the liquefied gas transferred from the first pump to increase the pressure to the required pressure in the engine: Containing,

The liquid gas separated from the separator is supplied to a fuel supply line between the first pump and the second pump and recirculated.
3. The method of claim 2,

a vapor line for recovering the gas separated from the separator to the fuel supply tank; and

A fuel supply system for a liquefied gas carrier, characterized in that it further comprises; a pressure regulating valve provided in the vapor line.
4. The method of claim 3,

By sensing the pressure at the rear end of the first pump and adjusting the opening degree of the pressure control valve according to the sensed pressure, the pressure of the separator is maintained 0.5 to 2 bar higher than the pressure at the end of the first pump, characterized in that Fuel supply system for liquefied gas carriers.
4. The method of claim 3,

A fuel supply system for a liquefied gas carrier further comprising a; provided at the rear end of the compression unit in the fuel supply line and heating the compressed liquefied gas to a temperature required by the engine.
The method of claim 5, wherein the return line,

a first return line connected from the engine to the separator; and

A fuel supply system for a liquefied gas carrier including: a second return line connected to the separator from a fuel supply line between the second pump and the fuel heater.
The method of claim 6, wherein the pressure reducing unit,

a first pressure reducing device provided on the first return line; and

A fuel supply system for a liquefied gas carrier comprising: a second pressure reducing device provided in the second return line.
8. The method of claim 7,

By sensing the pressure at the rear end of the second pump, if the sensed pressure is higher than the set value, first lower the pump speed of the second pump,

If still higher than the set value, the fuel supply system of the liquefied gas carrier, characterized in that lowering the rear end pressure of the second pump by opening the second pressure reducing device.
9. The method according to any one of claims 1 to 8,

a re-liquefaction unit provided on the ship and receiving boil-off gas generated from a cargo tank storing liquefied gas to be transported and re-liquefied; and

Further comprising: a cooling line connected to the cargo tank from the reliquefaction unit through the fuel supply tank,

The liquefied gas reliquefied in the reliquefaction unit cools the fuel supply tank along the cooling line and is transferred to the cargo tank.
10. The method of claim 9,

Further comprising: a fuel tank for storing liquefied gas to be supplied to the onboard engine provided in the ship,

A fuel supply system for a liquefied gas carrier, characterized in that it can cool the fuel supply tank by transferring the liquefied gas from the fuel tank to the fuel supply tank.
9. The method according to any one of claims 1 to 8,

a discharge pipe provided at the bottom of the separator to separate and discharge the lubricating oil mixed in the liquefied gas returned to the separator; and

Further comprising: a re-liquefaction unit for re-liquefying boil-off gas generated from a cargo tank for storing liquefied gas to be transported provided in the ship;

A fuel supply system for a liquefied gas carrier, characterized in that by transferring the liquefied gas reliquefied in the reliquefaction unit to the cargo tank through the fuel supply tank, and cooling the fuel supply tank.
From the fuel supply tank provided on the deck of the ship, the liquefied gas is compressed in the compression unit along the fuel supply line and supplied as fuel to the onboard engine,

A decompression unit is provided in a return line for recirculating liquefied gas not consumed by the engine among the liquefied gas compressed in the compression unit to an upstream side of the engine to decompress the liquefied gas to be recirculated, and the recirculated liquefied gas cooled by reduced pressure in the separator A fuel supply method for a liquefied gas carrier, characterized in that gas-liquid separation.
13. The method of claim 12,

The compression unit may include: a first pump for pumping and transferring liquefied gas from the fuel supply tank; and a second pump for pumping the liquefied gas transferred from the first pump to increase the pressure to the required pressure in the engine:

The liquid gas separated from the separator is supplied to a fuel supply line between the first pump and the second pump and recirculated.
14. The method of claim 13,

The gas separated from the separator is recovered to the fuel supply tank,

By sensing the pressure at the rear end of the first pump and adjusting the amount of gas returned to the fuel supply tank according to the sensed pressure, the pressure of the separator is maintained 0.5 to 2 bar higher than the pressure at the end of the first pump A fuel supply method for a liquefied gas carrier, characterized in that.
15. The method of claim 14,

By sensing the pressure at the rear end of the second pump, if the sensed pressure is higher than the set value, first lower the pump speed of the second pump,

If it is still higher than the set value, a portion of the liquefied gas at the rear end of the second pump is decompressed and discharged to the separator to lower the rear end pressure of the second pump.
16. The method according to any one of claims 12 to 15,

Re-liquefying boil-off gas generated from a cargo tank for storing liquefied gas to be transported and provided on the ship in a re-liquefaction unit,

The liquefied gas re-liquefied in the re-liquefaction unit cools the fuel supply tank through the fuel supply tank, and the fuel supply method of a liquefied gas carrier, characterized in that it is transferred to the cargo tank.
17. The method of claim 16,

The fuel supply method of a liquefied gas carrier, characterized in that it is possible to cool the fuel supply tank by transferring the liquefied gas from a fuel tank for storing liquefied gas to be supplied to the onboard engine provided in the ship to the fuel supply tank.
16. The method according to any one of claims 12 to 15,

A fuel supply method for a liquefied gas carrier, characterized in that a discharge pipe for separating and discharging lubricating oil mixed in the liquefied gas returned to the separator is provided at the bottom of the separator.
19. The method of claim 18,

Re-liquefying boil-off gas generated from a cargo tank for storing liquefied gas to be transported and provided on the ship in a re-liquefaction unit,

The liquefied gas reliquefied in the reliquefaction unit is transferred to the cargo tank through the fuel supply tank to cool the fuel supply tank.