Fuel supply system and method for liquefied gas carriers

Abstract

This invention discloses a fuel supply system and method for a liquefied gas carrier. The fuel supply system for the liquefied gas carrier of this invention is characterized by comprising: a fuel supply pipeline for supplying liquefied gas from a fuel supply tank located on the deck of the ship to the engine inside the ship; a compression unit located in the fuel supply pipeline for compressing the liquefied gas to be supplied to the engine inside the ship at the pressure required by the engine; a return pipeline for recirculating the liquefied gas that has not been consumed by the engine back to upstream of the engine; a separator located in the return pipeline for gas-liquid separation of the recirculated liquefied gas; and a pressure reducing unit located upstream of the separator in the return pipeline, wherein the liquefied gas recirculated through the return pipeline is cooled by pressure reduction in the pressure reducing unit and then introduced into the separator.

Description

Technical Field

[0001] This invention relates to a fuel supply system and method for a liquefied gas carrier, and more specifically, to a fuel supply system and method for a liquefied gas carrier that recovers and recycles excess LPG that has been over-supplied to the engine in a ship using liquefied gas such as LPG as fuel. Background Technology

[0002] The consumption of liquefied gases such as LNG (liquefied natural gas) or LPG (liquefied petroleum gas) is rapidly increasing worldwide. Liquefied gases are transported in their gaseous state via land or sea pipelines, or stored in a liquefied state on LNG carriers and transported to distant points of consumption. LNG and LPG are obtained by cooling natural gas or petroleum gas to extremely low temperatures (approximately -163°C in the case of LNG), significantly reducing their volume compared to their gaseous state, making them ideal for long-distance maritime transport.

[0003] Liquefaction temperature of petroleum gas (LPG) is approximately -42°C at atmospheric pressure. It can be stored in a liquid state at approximately 45°C at 18 bar and at approximately 20°C at 7 bar. LPG evaporates at temperatures above -42°C at atmospheric pressure, therefore, LPG storage tanks on ships require insulation. However, due to continuous external heat transfer to the LPG, it is continuously vaporized within the storage tank during transport, resulting in boil-off gas.

[0004] In LPG carriers, if vaporized gas accumulates in the LPG storage tank, the pressure inside the LPG storage tank will rise excessively. Therefore, in addition to installing a pressure-resistant structure inside the LPG storage tank, a vaporized gas reliquefaction device is used to treat the vaporized gas generated inside the tank.

[0005] On the other hand, existing LPG carriers and other vessels use heavy oil, such as C-grade fuel oil, which is relatively inexpensive, as their propulsion fuel. However, due to the strengthening of international emission regulations on the use of heavy oil fuel, these systems require additional low-sulfur heavy oil fuel tanks (LSHFO tanks), increasing the demand for environmentally friendly fuel supply systems that meet international environmental regulations.

[0006] In recent years, the use of fuel supply systems that utilize LPG or LNG and the vapors generated therefrom as propulsion fuel in LPG or LNG carriers has been increasing. With the strengthening of international emissions regulations, in addition to LPG or LNG carriers, the use of LNG and other fuels as propulsion fuel in general ships is also gradually increasing.

[0007] In particular, compared to LNG, which is liquefied at extremely low temperatures, LPG is easier to store and does not significantly reduce specific energy or energy density compared to existing HFO. It also has the advantage of significantly reducing SOx, NOx, CO2, PM, etc. compared to existing HFO. Summary of the Invention

[0008] Technical problems to be solved

[0009] Figure 1 This diagram illustrates, in a simplified manner, an example of an existing fuel supply system for supplying fuel to the engine in a ship using LPG as fuel.

[0010] like Figure 1 As shown, LPG, which is to be supplied to the engine (E) as fuel, is supplied from the fuel supply tank to the ship's engine via the fuel supply system, which includes a compression pump, heater, etc., in a manner that meets the engine's fuel supply conditions through the supply pipeline L1.

[0011] As an incompressible fluid, LPG can be over-supplied compared to the fuel required by the engine to immediately respond to changes in engine load. The LPG that is over-supplied and remains after fuel consumption, or the LPG remaining due to changes in fuel consumption rate caused by changes in engine load, is recovered from the engine to the upstream of the engine through the recovery line L2.

[0012] However, because the LPG recovered through the recovery pipeline is compressed and heated to meet the engine's fuel supply conditions, resulting in a high-temperature and high-pressure state, sending it to the fuel supply tank raises concerns about increased pressure and temperature within the tank. There are also concerns about LPG contamination from sealing oil flowing from the engine, and the possibility of crystallization if the fuel supply tank temperature drops below -10°C. On the other hand, directly discharging and burning the recovered LPG results in fuel waste.

[0013] To address these problems, the present invention provides a system capable of efficiently processing LPG recovered from an engine while simultaneously supplying fuel efficiently.

[0014] Problem-solving methods

[0015] To solve the above-mentioned technical problems, according to one aspect of the present invention, a fuel supply system for a liquefied gas carrier is provided, characterized in that it comprises: a fuel supply line for supplying liquefied gas from a fuel supply tank disposed on the deck of the ship to an engine inside the ship; a compression unit disposed in the fuel supply line for compressing the liquefied gas to be supplied to the engine inside the ship at the pressure required by the engine; a return line for recirculating the liquefied gas that has not been consumed by the engine to upstream of the engine; a separator disposed in the return line for gas-liquid separation of the recirculated liquefied gas; and a pressure reducing unit disposed in the return line upstream of the separator, wherein the liquefied gas recirculated through the return line is cooled by pressure reduction in the pressure reducing unit and then introduced into the separator.

[0016] Preferably, the compression section may include: a first pump for pumping liquefied gas from the fuel supply tank for delivery; and a second pump for pumping the liquefied gas delivered from the first pump and pressurizing it at the pressure required by the engine, wherein the liquid liquefied gas separated in the separator is supplied to the fuel supply line between the first pump and the second pump for recycling.

[0017] Preferably, it may further include: a steam line for recovering the gas separated in the separator to the fuel supply tank; and a pressure regulating valve disposed on the steam line.

[0018] Preferably, the pressure at the rear end of the first pump can be sensed, and the opening of the pressure regulating valve can be adjusted according to the sensed pressure, thereby maintaining the pressure of the separator at 0.5 to 2 bar higher than the pressure at the rear end of the first pump.

[0019] Preferably, it may also include a fuel heater, which is disposed in the fuel supply line at the rear end of the compression section to heat the compressed liquefied gas at the temperature required by the engine.

[0020] Preferably, the return line may include: a first return line connected from the engine to the separator; and a second return line connected from the fuel supply line between the second pump and the fuel heater to the separator.

[0021] Preferably, the pressure reducing section may include: a first pressure reducing device disposed on the first return line; and a second pressure reducing device disposed on the second return line.

[0022] Preferably, the pressure at the rear end of the second pump can be sensed. When the sensed pressure is higher than a set value, the pump speed of the second pump is reduced first. When the sensed pressure is still higher than the set value, the second pressure reducing device is opened to reduce the pressure at the rear end of the second pump.

[0023] Preferably, it may further include: a reliquefaction unit that receives and reliquefies evaporated gas generated from a cargo hold, the cargo hold being located on the ship and storing the liquefied gas to be transported; and a cooling line connected from the reliquefaction unit to the cargo hold via the fuel supply tank, wherein the liquefied gas reliquefied in the reliquefaction unit cools the fuel supply tank along the cooling line and is delivered to the cargo hold.

[0024] Preferably, it may also include a fuel tank located on the vessel and storing liquefied gas to be supplied to the engine on board the vessel, and the liquefied gas being supplied from the fuel tank to the fuel supply tank, thereby enabling the fuel supply tank to be cooled.

[0025] Preferably, it may further include: a discharge pipe disposed at the bottom of the separator for separating and discharging lubricating oil mixed in with the liquefied gas recovered into the separator; and a reliquefaction unit for reliquefying the evaporated gas generated from the cargo hold, the cargo hold being disposed of on the ship and storing the liquefied gas to be transported, the liquefied gas reliquefied in the reliquefaction unit being transported to the cargo hold via the fuel supply tank, while cooling the fuel supply tank.

[0026] According to another aspect of the present invention, a fuel supply method for a liquefied gas carrier is provided, characterized by comprising the following steps: compressing liquefied gas from a fuel supply tank provided on the deck of the ship along a fuel supply pipeline in a compression section, and supplying it as fuel to the engine inside the ship; and providing a pressure reducing section in a return pipeline to reduce the pressure of the liquefied gas to be recirculated, wherein the recirculated liquefied gas cooled by pressure reduction is separated into gas and liquid in a separator, and the return pipeline recirculates the liquefied gas compressed in the compression section that was not consumed by the engine to the upstream of the engine.

[0027] Preferably, the compression section may include: a first pump for pumping liquefied gas from the fuel supply tank for delivery; and a second pump for pumping the liquefied gas delivered from the first pump and pressurizing it at the pressure required by the engine, wherein the liquid liquefied gas separated in the separator is supplied to the fuel supply line between the first pump and the second pump for recycling.

[0028] Preferably, the gas separated in the separator can be recovered to the fuel supply tank, the downstream pressure of the first pump is sensed, and the amount of gas recovered to the fuel supply tank is adjusted according to the sensed pressure, thereby maintaining the pressure of the separator at 0.5 to 2 bar higher than the downstream pressure of the first pump.

[0029] Preferably, the pressure at the rear end of the second pump can be sensed. When the sensed pressure is higher than a set value, the pump speed of the second pump is reduced first. When the sensed pressure is still higher than the set value, a portion of the liquefied gas is depressurized at the rear end of the second pump and discharged into the separator, thereby reducing the pressure at the rear end of the second pump.

[0030] Preferably, the evaporated gas generated from the cargo hold can be reliquefied in a reliquefaction unit, the cargo hold being located on the ship and storing the liquefied gas to be transported, and the liquefied gas reliquefied in the reliquefaction unit is cooled by the fuel supply tank and then delivered to the cargo hold.

[0031] Preferably, the liquefied gas can be supplied from the fuel tank to the fuel supply tank, thereby cooling the fuel supply tank, which is located on the ship and stores liquefied gas to be supplied to the ship's engines.

[0032] Preferably, a discharge pipe can be provided at the bottom of the separator, which separates and discharges the lubricating oil mixed in with the liquefied gas recovered into the separator.

[0033] Preferably, the evaporated gas generated from the cargo hold, which is located on the ship and stores the liquefied gas to be transported, can be reliquefied in a reliquefaction unit.

[0034] The liquefied gas reliquefied in the reliquefaction section is transported to the cargo hold via the fuel supply tank, while the fuel supply tank is cooled.

[0035] Invention Effects

[0036] In this invention, the liquefied gas that is compressed to supply fuel to the engine but not consumed by the engine is recirculated through a return line. The compressed liquefied gas is cooled by depressurization in the return line and undergoes gas-liquid separation by a separator, so that only the liquid liquefied gas is supplied to the fuel supply line for recirculation. As described above, by recirculating the liquefied gas remaining after being over-supplied to the engine and consumed as fuel, it is possible to prevent lubricating oil from mixing with the fuel, thereby preventing incomplete combustion of the engine and the resulting generation of pollutants in the exhaust, and preventing LPG contamination in the fuel supply tank and crystallization of lubricating oil caused by lubricating oil.

[0037] Furthermore, by cooling and separating the recirculated liquefied gas and introducing it into the second pump along with the subcooled LPG supplied from the fuel supply tank via the first pump of the compressor, the risk of vapor generation in the suction section of the second pump of the compressor can be reduced, and the compressor can be prevented from malfunctioning even without additional devices for removing the vapor.

[0038] The gas separated in the separator is delivered to the fuel supply tank. The evaporated gas generated from the cargo hold is reliquefied and then transported to the cargo hold via the fuel supply tank through cooling lines. This process cools the fuel supply tank with the reliquefied gas, thus safely maintaining the tank's pressure and temperature. Attached Figure Description

[0039] Figure 1 This diagram schematically illustrates an existing fuel supply system for supplying fuel to an engine in a ship equipped with an engine that uses LPG as fuel.

[0040] Figure 2 A fuel supply system for a liquefied gas carrier according to a first embodiment of the present invention is shown schematically.

[0041] Figure 3 A fuel supply system for a liquefied gas carrier according to a second embodiment of the present invention is shown schematically.

[0042] Figure 4 The structure of the discharge section for discharging lubricating oil from the separator in the fuel supply system of a liquefied gas carrier according to a second embodiment of the present invention is shown schematically. Detailed Implementation

[0043] To fully understand the advantages of the present invention and the objectives achieved through its implementation, reference should be made to the accompanying drawings illustrating preferred embodiments of the invention and the contents described therein.

[0044] Hereinafter, the structure and function of preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that when assigning reference numerals to structural elements in the drawings, the same reference numerals are used as much as possible for the same structural elements, even when shown in different drawings.

[0045] In the embodiments of the invention described later, the vessel can be any type of vessel equipped with an engine capable of using liquefied petroleum gas as fuel for a propulsion engine or a power generation engine. Representative examples include, in addition to vessels with their own propulsion capabilities such as LPG carriers, LNG carriers, liquid hydrogen carriers, and LNG RVs (regasification vessels), offshore structures that do not have propulsion capabilities but float on the sea, such as LNG FPSOs (floating production storage and offloading units) and LNG FSRUs (floating storage and regasification units).

[0046] Furthermore, this embodiment can be applied to fuel supply systems for all types of liquefied gases that can be liquefied at low temperatures for transportation and that generate vapors during storage, enabling them to be supplied as engine fuel. Such liquefied gases can be, for example, liquefied petroleum gases such as LNG (liquefied natural gas), LEG (liquefied ethane gas), LPG (liquefied petroleum gas), liquefied ethylene gas, liquefied propylene gas, and ammonia. However, in the embodiments described later, the application of LPG, as one of the representative liquefied gases, will be used as an example.

[0047] Figure 2 A fuel supply system for a liquefied gas carrier according to a first embodiment of the present invention is shown schematically.

[0048] like Figure 2 As shown, the fuel supply system of the first embodiment includes: a fuel supply line (SL) for supplying liquefied gas from a fuel supply tank (DT) located on the deck of the ship to an engine (E) inside the ship; a compression unit (110, 120) located in the fuel supply line for compressing the liquefied gas to be supplied to the engine inside the ship at the pressure required by the engine; a return line (RL1) (RL1, RL2) for recirculating the liquefied gas that has not been consumed by the engine back to the upstream of the engine; a separator (210) located in the return line for gas-liquid separation of the recirculated liquefied gas; and a pressure reducing unit (220) (220, 230) located in the return line upstream of the separator.

[0049] In this embodiment, the liquefied gas recirculated through the return pipeline is depressurized via a depressurization unit. During the depressurization process, the liquefied gas is cooled by the Joule-Thomson effect and introduced into the separator.

[0050] The compression section consists of two pumps, namely: a first pump (110) for pumping and delivering liquefied gas from the fuel supply tank; and a second pump (120) for pumping the liquefied gas delivered from the first pump and pressurizing it to the pressure required by the engine.

[0051] The first pump (110) is a low-pressure pump for conveying liquefied gas and can be a centrifugal pump. The second pump (120) is a high-pressure pump that compresses the liquefied gas at the fuel supply pressure required by the engine and can be a diaphragm pump. The liquefied gas from the first pump and the second pump is heated to the temperature required by the engine in the fuel heater (130) located at the rear end of the compression section in the fuel supply line and supplied to the engine.

[0052] The liquefied gas, compressed and heated in the fuel supply line through the compression section and fuel heater, is supplied to the engine (E) via a filter (140) that filters impurities from the fuel and a service valve section (SVT). When the engine is supplied with LPG, the fuel oil is switched, the LPG mode is stopped, or the LPG fuel supply is interrupted due to a trip, the service valve section double-closes each pipeline through valves and releases the pressure in the pipeline.

[0053] An example of an engine that receives compressed and heated LPG as fuel is the MANDiesel & Turbo ME-LGIP engine. In this case, LPG is supplied to the engine in a high-pressure liquid state of about 54 bar and 35°C via a compression section and a fuel heater, and is injected into the engine nozzle with a hydraulic pressure of 600 to 700 bar to drive the engine.

[0054] In this embodiment, the compressed and heated fuel is supplied to the engine in a liquid state. However, unlike engines that are supplied with compressible fluids, i.e., gaseous fuels, which change significantly in volume depending on pressure, engines that are supplied with incompressible fluids, i.e., liquid LPG, which does not change in volume or changes only slightly even when pressure is applied, can supply sufficient fuel to respond promptly even if the engine load changes, and supply excess LPG to the engine to prevent cavitation. The LPG supplied to the engine that is consumed as fuel and is subsequently recycled is discharged from the engine through a return line. If the compressed and heated LPG is directly recycled or sent to the fuel supply tank, there is a risk of vapor generation in the suction section of the compression unit, which could cause the pressure and temperature inside the fuel supply tank to rise, posing a threat to the safety of the tank and the ship.

[0055] In this embodiment, to address this problem, a pressure-reducing section (220) (220, 230) is provided in the return line to reduce the pressure of the liquefied gas, thereby enabling the liquefied gas discharged from the engine to be depressurized and recirculated. The compressed liquefied gas undergoes adiabatic or isentropic expansion during the pressure reduction process while being cooled by the Joule-Thomson effect.

[0056] Compressed liquefied gas recirculated from the engine (E) via the return line (RL1) is depressurized and cooled by the pressure reducing unit (220), and then introduced into the separator (210) for gas-liquid separation. The liquid liquefied gas separated in the separator (210) is supplied to the fuel supply line (SL) between the first pump (110) and the second pump (120) via the liquid line (LL) for recirculation. The gas separated in the separator is recovered to the fuel supply tank (DT) via the vapor line (VL). A pressure regulating valve (250) is provided on the vapor line to regulate the pressure of the gas supplied to the fuel supply tank (DT).

[0057] In this embodiment, the liquefied gas cooled by depressurization is introduced into the separator. The liquefied gas, which is in a liquid state after gas-liquid separation, is introduced into the second pump (120) together with the subcooled LPG supplied from the fuel supply tank via the first pump of the compression section. This reduces the risk of vapor generation in the suction section of the second pump, so that no additional device for removing vapor is required.

[0058] Furthermore, when the temperature of the recirculated liquefied gas is high, the fuel heater needs to have both heating and cooling functions in order to meet the fuel requirements of the engine. However, in this embodiment, the recirculated liquefied gas is cooled by a pressure reducing unit, and the gas in the recirculated liquefied gas that has been depressurized by the separator is recovered to the fuel supply tank. The mass flow of the high-temperature recirculated liquefied gas drawn into the second pump is reduced. Even without additional cooling, fuel at the appropriate temperature can be supplied to the engine. Thus, the fuel heater only needs to have a heating function, which reduces the cost of the equipment and makes it easy to operate.

[0059] On the other hand, the return lines include a first return line (RL1) and a second return line (RL2). The first return line (RL1) is connected from the engine (E) to the separator (210), and the second return line (RL2) is connected from the fuel supply line (SL) between the second pump (120) and the fuel heater (130) to the separator (210). Furthermore, the pressure reducing unit may be configured to include a first pressure reducing device (220) provided in the first return line and a second pressure reducing device (230) provided in the second return line. The first and second pressure reducing devices may be composed of an expander or an expansion valve such as a Joule-Thomson valve that cools the compressed liquefied gas by adiabatic or isentropic expansion.

[0060] A return valve section (RVT) and a filter (240) are installed upstream of the first pressure reducing device in the first return line. Liquefied gas discharged from the engine is introduced into the first pressure reducing device through the return valve section and the filter. Lubricating oil and other contaminants mixed in with the liquefied gas discharged from the engine can be filtered in the filter.

[0061] The first return line and the first pressure reducing device depressurize the liquefied gas emitted from the engine upstream of the fuel heater and deliver it to the separator. The second return line and the second pressure reducing device depressurize the liquefied gas compressed by the compression section of the first pump and the second pump upstream of the fuel heater and deliver it to the separator.

[0062] Therefore, when the engine's LPG mode stops or the LPG fuel supply is interrupted due to a trip, the remaining LPG in the engine and fuel supply lines can be cooled by depressurization and then delivered to the separator. When the LPG fuel supply is interrupted, there is no need to recirculate LPG from the separator to the fuel supply line, so LPG can be sent to the fuel supply tank. For this purpose, a delivery line (not shown) can be installed from the separator to the fuel supply tank.

[0063] In the system of this embodiment, multiple pressure sensing units are provided to control the operating pressure. These units are: 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 (PC2) that senses the pressure between the filter and the first pressure reducing device in the first return line and sends a pressure signal; a third pressure sensing unit (PC3) that senses the pressure at the rear end of the first pump; and a fourth pressure sensing unit (PC4) that senses the pressure of the separator.

[0064] In the system of this embodiment, as an example, the control can be performed as follows.

[0065] The operating pressure range of the fuel supply tank is 1 to 8 barg. Assuming an operating pressure of 4 barg, the differential pressure of the first pump is approximately 2 bar, and the pressure at the downstream end of the first pump is 6 barg. The operating pressure of the separator (210) is maintained at approximately 0.5 to 2 bar, more preferably 0.5 to 1 bar, higher than the pressure at the downstream end of the first pump, so that the liquid recirculated gas separated in the separator can be smoothly delivered to the downstream end of the first pump.

[0066] To this end, the fourth pressure sensing unit (PC4) receives the pressure signal from the third pressure sensing unit (PC3) and sends a set value signal from the fourth pressure sensing unit (PC4) to the pressure regulating valve (250) of the steam line (VL) to adjust the opening of the pressure regulating valve so that the pressure of the separator is maintained at 6.5 to 7 barg.

[0067] The liquid separated in the separator is supplied to the front end of the second pump along the liquid line (LL) and pumped from the second pump to be pressurized to 54 barg.

[0068] The first return line (RL1) returning from the engine controls the first pressure reducing device (220) via the second pressure sensing unit, thereby maintaining the upstream pressure of the first pressure reducing device at 22 barg and the downstream pressure of the first pressure reducing device at 6.5 to 7 barg, which is the same as the separator pressure.

[0069] When the fuel consumption changes due to changes in engine load, causing a change in the pressure at the back end of the second pump, the first pressure sensing unit (PC1) senses the pressure. If the pressure is above the set value (54 barg) of the first pressure sensing unit (PC1), the VFD of the second pump is adjusted to reduce the pump speed. If the pressure is still above 54 barg and rises to 55 barg, the second pressure reducing device (230) of the second return line is opened to reduce the pressure.

[0070] The ship in this embodiment is a liquefied gas carrier and has a cargo hold (not shown) for storing and transporting liquefied gas. The evaporated gas generated in the liquefied gas stored in the cargo hold is supplied to the reliquefaction unit (RS) and reliquefied.

[0071] The temperature of the fuel supply tank may rise due to the gas separated and introduced in the separator. However, in this embodiment, a cooling line (CL) is provided such that the liquefied gas reliquefied in the reliquefaction section (RS) is connected to the cargo hold (not shown) via the fuel supply tank (DT), so that the heat or cold of the liquefied gas reliquefied in the reliquefaction section can be used to cool the fuel supply tank.

[0072] On the other hand, fuel tanks (FT1, FT2) are also installed inside the ship. These fuel tanks (FT1, FT2) are used to supply liquefied gas, which is to be supplied as fuel for the ship's engines, to the fuel supply tanks (DT) located on the deck. However, when the reliquefaction unit is not in operation, liquefied gas can be supplied from the fuel tanks to the fuel supply tanks, thereby cooling the fuel supply tanks with the low-temperature liquefied gas.

[0073] Figure 3 A fuel supply system for a liquefied gas carrier according to a second embodiment of the present invention is shown schematically.

[0074] like Figure 3 As shown, the fuel supply system of the second embodiment of the present invention also includes: a fuel supply line (SL) for supplying liquefied gas from a fuel supply tank (DT) located on the deck of a ship to an engine (E) inside the ship; a first pump (110) located on the fuel supply line for conveying the liquefied gas to be supplied from the fuel supply tank to the engine; a second pump (120) located on the fuel supply line for compressing the liquefied gas at the pressure required by the engine; a return line (RL1) (RL1, RL2) for recirculating the liquefied gas that has not been consumed by the engine to the upstream of the engine; a separator (210) located on the return line for receiving the recirculated liquefied gas and performing gas-liquid separation; a liquid line (LL) for supplying the liquid liquefied gas separated in the separator to the downstream end of the first pump of the fuel supply line; and a vapor line (VL) for recovering the gas separated in the separator to the fuel supply tank (DT).

[0075] In the return line, a pressure reducing section is provided upstream of the separator to reduce the pressure of the recirculated liquefied gas, and a pressure regulating valve (250) is provided on the vapor line connecting the separator to the fuel supply tank to regulate the pressure of the gas supplied to the fuel supply tank (DT).

[0076] The invention is characterized by sensing the pressure at the rear end of the first pump of the fuel supply line, separating liquefied gas from the separator and supplying it to the fuel supply line through the liquid line, and controlling a pressure regulating valve based on the sensed pressure to adjust the amount of gas recovered from the separator to the fuel supply tank, thereby maintaining the pressure in the separator at a higher level than the pressure sensed in the fuel supply line.

[0077] In the system of the second embodiment of this invention, the process of supplying fuel to the engine is observed in more detail as follows.

[0078] The fuel supply from the fuel supply tank to the engine is achieved by two pumps, including: a first pump (110) for pumping and delivering liquefied gas; and a second pump (120) for pumping the delivered liquefied gas and pressurizing it to the pressure required by the engine.

[0079] The first pump (110) is a low-pressure pump for conveying liquefied gas, and for example, it can be a centrifugal pump. The second pump (120) is a high-pressure pump that compresses the liquefied gas at the fuel supply pressure required by the engine, and can be a diaphragm pump. The liquefied gas from the first pump and the second pump is heated to the temperature required by the engine in a fuel heater (130) provided at the rear end of the second pump and then supplied to the engine.

[0080] The liquefied gas, compressed and heated by the second pump and fuel heater in the fuel supply line, is supplied to the engine (E) through a filter (140) that filters impurities from the fuel and a service valve section (SVT). When the engine is supplied with LPG, the fuel oil is switched, the LPG mode is stopped, or the LPG fuel supply is interrupted due to a trip, the service valve section double-closes each pipeline through valves and releases the pressure in the pipeline.

[0081] An example of an engine that receives compressed and heated LPG as fuel is the MANDiesel & Turbo ME-LGIP engine. In this case, LPG is supplied to the engine in a high-pressure liquid state of about 54 bar and 35°C via a compression section and a fuel heater, and is injected into the engine nozzle with a hydraulic pressure of 600 to 700 bar to drive the engine.

[0082] In this embodiment, the compressed and heated fuel is supplied to the engine in a liquid state. However, unlike engines that are supplied with compressible fluids, i.e., gaseous fuels, which change significantly in volume depending on pressure, engines that are supplied with incompressible fluids, i.e., liquid LPG, which does not change in volume or changes only slightly even when pressure is applied, can supply sufficient fuel to respond promptly even if the engine load changes, and supply excess LPG to the engine to prevent cavitation. The LPG supplied to the engine that is consumed as fuel and is subsequently recycled is discharged from the engine through a return line. If the compressed and heated LPG is directly recycled or sent to the fuel supply tank, there is a risk of vapor generation at the suction section of the second pump, which could cause the pressure and temperature inside the fuel supply tank to rise, posing a threat to the safety of the tank and the ship.

[0083] In this embodiment, to address this problem, a pressure-reducing section (220) (220, 230) is provided in the return line to reduce the pressure of the liquefied gas, thereby enabling the liquefied gas discharged from the engine to be depressurized and recirculated. The compressed liquefied gas undergoes adiabatic or isentropic expansion during the pressure reduction process while being cooled by the Joule-Thomson effect.

[0084] The compressed liquefied gas recirculated from the engine (E) via the return line (RL1) is depressurized and cooled by the depressurization unit (220), and then introduced into the separator (210) for gas-liquid separation. The liquid liquefied gas separated in the separator (210) is supplied to the fuel supply line (SL) between the first pump (110) and the second pump (120) via the liquid line (LL) for recirculation. The gas separated in the separator is recovered to the fuel supply tank (DT) via the vapor line (VL).

[0085] In this embodiment, the liquefied gas cooled by depressurization is introduced into the separator. The liquefied gas, which is in a liquid state after gas-liquid separation, is introduced into the second pump (120) together with the subcooled LPG supplied from the fuel supply tank via the first pump. This reduces the risk of vapor generation in the suction section of the second pump, thus eliminating the need for additional devices for vapor removal.

[0086] Furthermore, when the temperature of the recirculated liquefied gas is high, the fuel heater needs to have both heating and cooling functions in order to meet the fuel requirements of the engine. However, in this embodiment, the recirculated liquefied gas is cooled by a pressure reducing unit, and the gas in the recirculated liquefied gas that has been depressurized by the separator is recovered to the fuel supply tank. The mass flow of the high-temperature recirculated liquefied gas drawn into the second pump is reduced. Even without additional cooling, fuel at the appropriate temperature can be supplied to the engine. Thus, the fuel heater only needs to have a heating function, which reduces the cost of the equipment and makes it easy to operate.

[0087] On the other hand, the return lines include a first return line (RL1) and a second return line (RL2). The first return line (RL1) is connected from the engine (E) to the separator (210), and the second return line (RL2) is connected from the fuel supply line (SL) between the second pump (120) and the fuel heater (130) to the separator (210). Furthermore, the pressure reducing unit may be configured to include a first pressure reducing device (220) provided in the first return line and a second pressure reducing device (230) provided in the second return line. The first and second pressure reducing devices may be composed of an expander or an expansion valve such as a Joule-Thomson valve that cools the compressed liquefied gas by adiabatic or isentropic expansion.

[0088] A return valve section (RVT) and a filter (240) are installed upstream of the first pressure reducing device in the first return line. Liquefied gas discharged from the engine is introduced into the first pressure reducing device through the return valve section and the filter. Lubricating oil and other contaminants mixed in with the liquefied gas discharged from the engine can be filtered in the filter.

[0089] The first return line and the first pressure reducing device depressurize the liquefied gas emitted from the engine upstream of the fuel heater and deliver it to the separator. The second return line and the second pressure reducing device depressurize the liquefied gas, which has been compressed to the engine's fuel supply pressure in the second pump, upstream of the fuel heater and deliver it to the separator.

[0090] Therefore, when the engine's LPG mode stops or the LPG fuel supply is interrupted due to a trip, the remaining LPG in the engine and fuel supply lines can be cooled by depressurization and then delivered to the separator. When the LPG fuel supply is interrupted, there is no need to recirculate LPG from the separator to the fuel supply line, so LPG can be sent to the fuel supply tank. For this purpose, a delivery line (not shown) can be installed from the separator to the fuel supply tank.

[0091] In the system of this embodiment, multiple pressure sensing units are provided to control the operating pressure. These units are: 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 (PC2) that senses the pressure between the filter and the first pressure reducing device in the first return line and sends a pressure signal; a third pressure sensing unit (PC3) that senses the pressure at the rear end of the first pump; and a fourth pressure sensing unit (PC4) that senses the pressure of the separator.

[0092] In the system of this embodiment, as an example, the control can be performed as follows.

[0093] The operating pressure range of the fuel supply tank is 1 to 8 barg. Assuming an operating pressure of 4 barg, the differential pressure of the first pump is approximately 2 bar, and the pressure at the downstream end of the first pump is 6 barg. The operating pressure of the separator (210) is maintained at approximately 0.5 to 2 bar, more preferably 0.5 to 1 bar, higher than the pressure at the downstream end of the first pump, so that the liquid recirculated gas separated in the separator can be smoothly delivered to the downstream end of the first pump.

[0094] To this end, the fourth pressure sensing unit (PC4) receives the pressure signal from the third pressure sensing unit (PC3) and sends a set value signal from the fourth pressure sensing unit (PC4) to the pressure regulating valve (250) of the steam line (VL) to adjust the opening of the pressure regulating valve so that the pressure of the separator is maintained at 6.5 to 7 barg.

[0095] The liquid separated in the separator is supplied to the front end of the second pump along the liquid line (LL) and pumped from the second pump to be pressurized to 54 barg.

[0096] A liquid level sensor (LC) is installed in the separator to sense the liquid level of the separator. The valve V1 is controlled based on the liquid level sensed by the liquid level sensor, thereby regulating the flow rate of liquefied gas delivered to the fuel supply line.

[0097] The first return line (RL1) returning from the engine controls the first pressure reducing device (220) via the second pressure sensing unit, thereby maintaining the upstream pressure of the first pressure reducing device at 22 barg and the downstream pressure of the first pressure reducing device at 6.5 to 7 barg, which is the same as the separator pressure.

[0098] When the fuel consumption changes due to changes in engine load, causing a change in the pressure at the back end of the second pump, the first pressure sensing unit (PC1) senses the pressure. If the pressure is above the set value (54 barg) of the first pressure sensing unit (PC1), the VFD of the second pump is adjusted to reduce the pump speed. If the pressure is still above 54 barg and rises to 55 barg, the second pressure reducing device (230) of the second return line is opened to reduce the pressure.

[0099] On the other hand, a discharge pipe (DL) is provided at the bottom of the separator (210). The lubricating oil separated in the separator is discharged to the discharge section including the discharge pipe (DL). Figure 4 The structure of the discharge section for discharging lubricating oil from the separator in the fuel supply system of a liquefied gas carrier according to a second embodiment of the present invention is shown schematically.

[0100] In addition to liquid LPG, the liquefied gas recovered from the engine may also contain sealed oil flowing from the engine, along with other gases such as vapors generated from the compression and heating of fuel. If this sealed oil is supplied as fuel to the engine, it may undergo incomplete combustion, potentially producing air pollutants in the exhaust and negatively impacting fuel efficiency. Furthermore, if the sealed oil flows into the fuel tank, there is a concern about crystallization within the tank. In this embodiment, this phenomenon is prevented by separating the sealed oil mixed in with the liquefied gas and discharging it through a drain pipe (DL) located at the bottom of the separator.

[0101] The main components of LPG are propane (C3H8) and butane (C4H8). 10The specific gravity of the gas (LPG) varies depending on the ratio of propane to butane, but is approximately 0.5, while that of the lubricating oil is approximately 0.9. Therefore, in the separator, the gas separates upwards, while the lubricating oil, which is heavier than LPG, separates to the bottom due to the difference in specific gravity. Thus, a discharge pipe can be installed at the bottom of the separator to discharge the separated lubricating oil. To facilitate smoother separation and discharge of the lubricating oil, a floating buoyancy body can be installed within the separator, which sinks in the LPG and floats in the lubricating oil.

[0102] If the pressure of the separator is kept below 10 barg, the separation and discharge of lubricating oil based on differences in viscosity and specific gravity can be easily achieved.

[0103] The discharge section includes a discharge pipe (DL) connected to the bottom of the separator (210) and a lubricating oil discharge tank (SDT) for collecting the discharged lubricating oil. A retention pot (300) is installed between the separator and the lubricating oil discharge tank in the discharge pipe. A magnetic float level gauge (310) is installed on the retention pot to confirm the liquid level, such as... Figure 4 As shown, a first discharge valve (DV1) and a second discharge valve (DV2) are installed between the separator and the retention pipe in the discharge pipeline. A third discharge valve (DV3) is installed between the retention pipe and the lubricating oil discharge tank to discharge the separated lubricating oil to the lubricating oil discharge tank. When the normal discharge mode is started, the first discharge valve (DV1) and the second discharge valve (DV2) are opened, the third discharge valve (DV3) is closed, and the retention pipe installed in the discharge pipeline increases the residence time in the pipe, thereby improving the separation efficiency of the lubricating oil.

[0104] To eliminate pressure in the discharge pipe between the second drain valve and the retention pipe and to remove the vacuum during lubricating oil drain, a pipe branching from the discharge pipe and connecting to the lubricating oil drain tank, and a fourth drain valve (DV4) for opening and closing the pipe, are provided. Additionally, a level gauge (320) for measuring the liquid level is installed in the lubricating oil drain tank (SDT), and a fifth drain valve (DV5) is installed to allow lubricating oil to be discharged from the drain tank. The discharged lubricating oil can be sent to the oil tank in the engine compartment for reuse or disposal.

[0105] On the other hand, the ship in this embodiment is a liquefied gas carrier and has a cargo hold (not shown) for storing and transporting liquefied gas. In this embodiment, the evaporated gas generated in the liquefied gas stored in the cargo hold (not shown) is sent to the reliquefaction unit (RS) for reliquefaction. A cooling line (CL) is provided so that the liquefied gas reliquefied in the reliquefaction unit (RS) is connected to the cargo hold (not shown) via a fuel supply tank (DT). This allows the fuel supply tank to be cooled by utilizing the heat and cold of the liquefied gas reliquefied in the reliquefaction unit.

[0106] That is, the fuel supply tank stores LPG at a pressure of less than 8 barg while supplying fuel to the ship's engines. Since it is located on the deck in the ship, the temperature and pressure inside the tank may rise due to external air or gas introduced from the separator. However, in this embodiment, a cooling line (CL) is constructed in which the evaporated gas generated by the liquefied gas cargo stored in the cargo hold is reliquefied and returned to the cargo hold via the fuel supply tank (DT). This allows the reliquefied gas to be cooled by the heat and cold of the reliquefied gas.

[0107] On the other hand, fuel tanks (FT1, FT2) are also installed inside the ship. These fuel tanks (FT1, FT2) are used to supply liquefied gas, which is to be supplied as fuel for the ship's engines, to the fuel supply tanks (DT) located on the deck. However, when the reliquefaction unit is not in operation, liquefied gas can be supplied from the fuel tanks to the fuel supply tanks, thereby cooling the fuel supply tanks with the low-temperature liquefied gas.

[0108] As described above, by reliquefying the vapors generated from the cargo in the cargo hold, and using the heat and cold of the reliquefied gas to cool the fuel supply tank, the temperature and pressure of the fuel supply tank can be regulated. The fuel is stored by using only the heat and cold of the reliquefied gas and returning it to the cargo hold, thereby preventing the fuel from mixing with the transported cargo.

[0109] This invention is not limited to the above embodiments. Various modifications or variations can be made without departing from the technical spirit of this invention, which will be obvious to those skilled in the art.

Claims

1. A fuel supply system for a liquefied gas carrier, characterized in that, include: Fuel supply pipelines supply liquefied gas from fuel supply tanks located on the ship's deck to the ship's engines. A compression unit is provided in the fuel supply pipeline to compress the liquefied gas to be supplied to the engine inside the ship at the pressure required by the engine. The return line recirculates the liquefied gas that was not consumed by the engine back to the upstream of the engine; A separator is installed in the return pipeline to perform gas-liquid separation on the recirculated liquefied gas; A pressure reducing unit is provided in the return line upstream of the separator; The reliquefaction unit receives and reliquefies the evaporated gas generated from the cargo hold, which is located on the ship and stores the liquefied gas to be transported. as well as Cooling lines connect from the reliquefaction unit to the cargo hold via the fuel supply tank. The liquefied gas, recirculated through the return line, is cooled by pressure reduction in the pressure reducing section and then introduced into the separator. The liquefied gas reliquefied in the reliquefaction section cools the fuel supply tank along the cooling pipeline and is then transported to the cargo hold.

2. The fuel supply system for a liquefied gas carrier according to claim 1, characterized in that, The compression section includes: A first pump delivers liquefied gas from the fuel supply tank; and The second pump pumps the liquefied gas supplied from the first pump and pressurizes it to the pressure required by the engine. The liquid liquefied gas separated in the separator is recycled by being supplied to the fuel supply line between the first pump and the second pump.

3. The fuel supply system for a liquefied gas carrier according to claim 2, characterized in that, Also includes: A steam line is used to recover the gas separated in the separator to the fuel supply tank; and A pressure regulating valve is installed on the steam pipeline.

4. The fuel supply system for a liquefied gas carrier according to claim 3, characterized in that, The pressure at the rear end of the first pump is sensed, and the opening of the pressure regulating valve is adjusted according to the sensed pressure, thereby maintaining the pressure of the separator at 0.5 to 2 bar higher than the pressure at the rear end of the first pump.

5. The fuel supply system for a liquefied gas carrier according to claim 3, characterized in that, It also includes a fuel heater, which is disposed in the fuel supply line at the rear end of the compression section to heat the compressed liquefied gas at the temperature required by the engine.

6. The fuel supply system for a liquefied gas carrier according to claim 5, characterized in that, The return line includes: A first return line connects from the engine to the separator; and The second return line is connected to the separator from the fuel supply line between the second pump and the fuel heater.

7. The fuel supply system for a liquefied gas carrier according to claim 6, characterized in that, The pressure relief unit includes: A first pressure reducing device is disposed on the first return pipeline; and The second pressure reducing device is installed in the second return pipeline.

8. The fuel supply system for a liquefied gas carrier according to claim 7, characterized in that, The system senses the pressure at the rear end of the second pump. When the sensed pressure exceeds a set value, it first reduces the pump speed of the second pump. When the sensed pressure is still higher than the set value, the second pressure reducing device is activated to reduce the pressure at the rear end of the second pump.

9. The fuel supply system for a liquefied gas carrier according to claim 1, characterized in that, It also includes fuel tanks, which are located on the vessel and store liquefied gas to be supplied to the ship's engines. The liquefied gas is supplied from the fuel tank to the fuel supply tank, thereby cooling the fuel supply tank.

10. The fuel supply system for a liquefied gas carrier according to any one of claims 1 to 8, characterized in that, Also includes: An exhaust pipe, located at the bottom of the separator, separates and discharges lubricating oil mixed in with the liquefied gas recovered into the separator.

11. A fuel supply method for a liquefied gas carrier, characterized in that, Includes the following steps: The liquefied gas is compressed in the compression section from fuel supply tanks located on the ship's deck, along fuel supply pipelines, and supplied as fuel to the ship's engines; and A pressure-reducing section is installed on the return line to reduce the pressure of the liquefied gas to be recirculated. The recirculated liquefied gas, cooled by pressure reduction, is separated into gas and liquid in a separator. The return line recirculates the liquefied gas that was compressed in the compression section but not consumed by the engine back to the upstream of the engine. The evaporated gas generated from the cargo hold, which is located on the ship and stores the liquefied gas to be transported, is reliquefied in the reliquefaction unit. The liquefied gas reliquefied in the reliquefaction section is supplied to the cargo hold via the fuel supply tank, while the fuel supply tank is cooled.

12. The fuel supply method for a liquefied gas carrier according to claim 11, characterized in that, The compression unit includes: a first pump for pumping liquefied gas from the fuel supply tank; and a second pump for pumping the liquefied gas from the first pump and pressurizing it at the pressure required by the engine. The liquid liquefied gas separated in the separator is recycled by being supplied to the fuel supply line between the first pump and the second pump.

13. The fuel supply method for a liquefied gas carrier according to claim 12, characterized in that, The gas separated in the separator is recovered to the fuel supply tank. The pressure at the rear end of the first pump is sensed, and the amount of gas recovered to the fuel supply tank is adjusted according to the sensed pressure, thereby maintaining the pressure of the separator at 0.5 to 2 bar higher than the pressure at the rear end of the first pump.

14. The fuel supply method for a liquefied gas carrier according to claim 13, characterized in that, The system senses the pressure at the rear end of the second pump. When the sensed pressure exceeds a set value, it first reduces the pump speed of the second pump. When the sensed pressure is still higher than the set value, a portion of the liquefied gas is depressurized at the rear end of the second pump and discharged into the separator, thereby reducing the pressure at the rear end of the second pump.

15. The fuel supply method for a liquefied gas carrier according to claim 11, characterized in that, The liquefied gas is supplied from the fuel tank to the fuel supply tank, thereby cooling the fuel supply tank, which is located on the ship and stores liquefied gas to be supplied to the ship's engines.

16. The fuel supply method for a liquefied gas carrier according to any one of claims 11 to 14, characterized in that, A discharge pipe is provided at the bottom of the separator, which separates and discharges the lubricating oil mixed in with the liquefied gas recovered into the separator.

Images