KR102651092B1 - Fuel Supply System and Method for LNG Fueled Vessel - Google Patents

Abstract

The present invention is a liquefied natural gas fuel ship that allows fuel to be supplied according to the fuel supply conditions of the engine by using a pump and regasification equipment without using a compressor in a ship equipped with an engine fueled by liquefied natural gas. It relates to a fuel supply system and method.
The fuel supply system for a liquefied natural gas fuel ship according to the present invention includes an Otto cycle engine that uses liquefied natural gas as fuel and operates according to the Otto cycle; A fuel supply pump that discharges liquefied natural gas from a storage tank; A high-pressure pump that compresses the discharged liquefied natural gas; A vaporizer that vaporizes liquefied natural gas compressed by the high-pressure pump; An expansion valve that adiabatically expands the natural gas vaporized in the vaporizer; and a gas-liquid separator that separates the gas-liquid mixture formed by the expansion valve. Including, the liquid separated in the gas-liquid separator is recovered to the storage tank, and the gas separated in the gas-liquid separator is used as fuel for the Otto cycle engine. It is characterized by controlling the methane value of the natural gas fuel supplied to the Otto cycle engine.

Description

Fuel supply system and method for liquefied natural gas fuel vessels {Fuel Supply System and Method for LNG Fueled Vessel}

The present invention is a liquefied natural gas that allows ships equipped with engines using liquefied natural gas as fuel to supply liquefied natural gas fuel according to the fuel supply conditions of the engine by using a pump and regasification facility without using a compressor. Relates to a fuel supply system and method for gas-fueled ships.

In general, ships have propulsion power from engines that generate power through the combustion of fuel. Fuel oil such as diesel, heavy oil, and MDO (Marine Diesel Oil) used as ship fuel is a large amount of fuel generated during the combustion process. Harmful substances are causing environmental pollution. Recently, as international regulations to prevent air pollution have been strengthened, the fuel for ships is changing from fuel oil to natural gas. Natural gas has a low sulfur content and does not produce sulfur compounds or soot substances during combustion, making it relatively environmentally friendly. In response to this trend, a dual-fuel engine that can use natural gas along with fuel oil has been developed.

On the other hand, natural gas is in a gaseous state at room temperature and pressure and its volume is so large that space for storage is severely limited, so it is usually treated as an insulator using its property of maintaining a liquid state at a cryogenic temperature of about -163°C at normal pressure. Cryogenic LNG can be stored in a liquid state at normal pressure in a special storage tank.

In addition, as an eco-friendly ship (Green-ship), a ship (LFS; Liquefied Fueled Ship) that uses liquefied natural gas (LNG) as fuel has been developed and has received official certification (AIP; Approval In Principle) from each country's classification society. It has been approved and is meeting the demand for transition to clean energy due to environmental regulations. This LFS is being developed as a technology that can be applied not only to LNG carriers that transport LNG as cargo, but also to general merchant ships, including container ships and tankers.

Among engines generally used in ships, engines that can use natural gas as fuel include MEGI engines and DF (Dual Fuel) engines.

The ME-GI engine consists of two strokes and adopts the diesel cycle, which injects high-pressure natural gas around 300 bar directly into the combustion chamber near the top dead center of the piston.

The diesel cycle follows a constant pressure process where the pressure when combustion occurs near top dead center is constant, and only combustion air is sucked into the cylinder during the upward stroke, and the sucked combustion air is adiabatically compressed at a high compression ratio. At top dead center, the combustion air reaches a considerably high temperature due to adiabatic compression during the compression stroke, and when fuel is injected into the adiabatically compressed combustion air, spontaneous combustion occurs due to the high temperature.

In a diesel cycle, although the pressure of combustion air reaching top dead center is already high, the fuel injection pressure is appropriately adjusted to prevent the pressure from increasing further due to explosion due to fuel injection, so that the combustion pressure of the fuel at top dead center is maintained at a constant level. keep it that way

In diesel engines, combustion efficiency increases as the fuel compression ratio increases, but considering explosion pressure, the fuel is generally compressed at a compression ratio of about 15 to 22:1.

In addition, because only air is compressed in a diesel engine during the compression stroke, knocking, which is a phenomenon in which premature ignition occurs before the piston reaches top dead center, does not fundamentally occur.

The DF engine consists of a 4-stroke or 2-stroke engine and adopts the Otto Cycle, which injects natural gas with a relatively low pressure of about 6.5 bar or 18 bar into the combustion air inlet and compresses it as the piston rises. I'm doing it.

The Otto cycle follows a static process where the volume is constant when combustion occurs near top dead center, and the mixture of fuel and combustion air is introduced into the cylinder and compressed together before the upward stroke. The mixture flowing into the cylinder is adiabatically compressed and its temperature rises. If the mixture reaches a temperature that is too high, early ignition may occur. Therefore, the compression ratio of the Otto cycle is set lower than that of the diesel cycle.

Since the compression ratio of the Otto cycle is set relatively low, it is necessary to reach a high pressure when the fuel explodes from the ignition source at top dead center, and exploding the fuel in the shortest possible time helps increase engine efficiency.

In engines that follow the Otto cycle, the mixture of fuel and combustion air is introduced into the cylinder before the upward stroke, so early ignition may occur before ignition by the ignition source, and knocking may occur.

If knocking occurs, engine efficiency may decrease and engine damage may occur, so it is important to operate engines that follow the Otto cycle to prevent knocking.

Anti-knocking, the ability to prevent premature ignition of fuel used in engines following the Otto cycle, is determined by the octane number in the case of liquid fuel and the methane number in the case of gaseous fuel. , and in the case of DF engines, a methane number of 80 or higher is required.

In the case of the DF engine following the Otto cycle, the efficiency is lower compared to the ME-GI engine following the diesel cycle, but the combustion temperature of the fuel is not high and the amount of nitrogen oxides (NO _x ) generated due to high heat is small, so it is currently in effect. It has the advantage of satisfying IMO Tier III, the current nitrogen oxide regulation.

In this way, in order to supply the LNG stored in the storage tank according to the specifications required by the engine, various equipment and a fuel supply system need to be configured in consideration of the characteristics of the LNG and each engine.

Figure 1 is a schematic diagram illustrating the fuel supply system of a conventional LNG carrier.

Referring to FIG. 1, a conventional fuel supply system includes a evaporative gas supply system that supplies evaporative gas discharged from a storage tank (T) to the engines (E1, E2), and a evaporative gas supply system that uses the evaporative gas as fuel for the engines (E1, E2) and uses the remaining gas as fuel for the engines (E1, E2). It may include a re-liquefaction system for re-liquefying excess boil-off gas and a liquefied natural gas supply system for supplying the liquefied natural gas inside the storage tank (T) to the engines (E1 and E2).

The boil-off gas supply system includes a multi-stage compressor 200, and the liquefied natural gas supply system includes a first pump 610, a second pump 620, a vaporizer 700, a first heater 810, and a second It includes a pressure reducing device 420, and the reliquefaction system includes a first heat exchanger 110, a first pressure reducing device 410, and a gas-liquid separator 500.

The multi-stage compressor 200 compresses the boil-off gas discharged from the storage tank (T) in multiple stages, and includes a plurality of compression units (210, 220, 230, 240, 250) and a compression unit alternately installed at the rear end of the compression unit. It includes a plurality of coolers (310, 320, 330, 340, 350), and is generally used as a multi-stage compressor that compresses the boil-off gas in five stages with five compression units and five cooling units.

In addition, the multi-stage compressor 200 may include one or more branch lines, and the branch lines pass through the compression unit and re-supply the compressed boil-off gas back to the compression unit, thereby reducing the pressure of the boil-off gas passing through the multi-stage compressor 200. and adjust the flow rate. For example, as shown in FIG. 1, the branch line is a first branch line (L1) that branches off the boil-off gas at the rear end of the first compression unit 210 and supplies it to the front end of the first compression unit 210. 5 It may include a second branch line (L2) that branches off the boil-off gas at the rear end of the compression unit 250 and supplies it to the front end of the fourth compression unit 240.

The boil-off gas compressed through all stages of the multi-stage compressor 200 is sent to the first engine (E1), and the boil-off gas compressed through only some stages of the multi-stage compressor 200 is branched in the middle (L3 line) to the second engine (E1). It is sent to the engine (E2). The first engine (E1) may be a ME-GI engine, and the second engine (E2) may be a DF engine for power generation.

The first pump 610 is installed inside the storage tank (T) and discharges the liquefied natural gas stored in the storage tank (T), and the second pump 620 discharges the liquefied natural gas stored in the storage tank (T) by the first pump (610). The liquefied natural gas discharged from (T) is compressed to the required pressure of the first engine (E1).

The vaporizer 700 forcibly vaporizes the liquefied natural gas compressed by the second pump 620. A portion of the natural gas forcibly vaporized by the vaporizer 700 is supplied to the first engine E1, and the remainder is supplied to the first heater 810.

The first heater 810 heats the natural gas vaporized by the vaporizer 700 to the temperature required by the second engine E2, and the second pressure reducing device 420 heats the natural gas vaporized by the vaporizer 700 to the temperature required by the second engine E2. The heated natural gas is decompressed to the pressure required by the second engine (E2).

1 shows that the first heater 810 is installed at the rear of the vaporizer 700, and the second pressure reducing device 420 is installed at the rear of the first heater 810, but the first heater 810 and the second The decompression device 420 and its installation order may be changed, and the second decompression device 420 may be installed at the rear of the vaporizer 700, and the first heater 810 may be installed at the rear of the second decompression device 420. .

The first heat exchanger 110 cools the partially branched boil-off gas (L5 line) after being compressed through all stages of the multi-stage compressor 200 by heat-exchanging the boil-off gas discharged from the storage tank (T) with a refrigerant. . Among the evaporative gases discharged from the storage tank (T), the surplus evaporative gas that is not supplied to the first engine (E1) or the second engine (E2) is supplied to the first heat exchanger (110) and undergoes a re-liquefaction process. will be.

The first pressure reducing device 410 expands the fluid (L5 line) compressed by the multi-stage compressor 200 and then cooled by the first heat exchanger 110. The boil-off gas that has undergone a compression process by the multi-stage compressor 200, a cooling process by the first heat exchanger 110, and an expansion process by the first decompression device 410 is partially or entirely re-liquefied.

The gas-liquid separator 500 separates the liquefied natural gas that has been re-liquefied while passing through the multi-stage compressor 200, the first heat exchanger 110, and the first pressure reducing device 410, and the boil-off gas remaining in a gaseous state. . The liquefied natural gas separated by the gas-liquid separator 500 is returned to the storage tank (T), and the gaseous boil-off gas separated by the gas-liquid separator 500 joins the boil-off gas discharged from the storage tank (T). and is used as a refrigerant in the first heat exchanger (110).

If the second engine (E2) is an engine that follows the Otto cycle, such as a DF engine, the methane value of the natural gas supplied to the second engine (E2) must be adjusted to prevent knocking, which is forced by the liquefied natural gas supply system. In the case of vaporized natural gas, the methane number is lower than that of naturally vaporized boil-off gas supplied by the boil-off gas supply system.

According to the liquefied natural gas supply system, the liquefied natural gas at the bottom of the storage tank (T) is discharged and forcibly vaporized by the first pump 610 installed at the bottom of the storage tank (T), so the proportion of components with a relatively large specific gravity is high. Because.

Therefore, there is a need to control the methane value of natural gas that is forcibly vaporized by regasification equipment, such as a vaporizer of a liquefied natural gas supply system, and the present invention provides the methane value required by the Otto cycle engine, such as the methane value of natural gas supplied as fuel for the engine. The aim is to provide a fuel supply system and method for liquefied natural gas fuel ships that can satisfy the specifications of fuel gas.

According to one aspect of the present invention for achieving the above-described object, an Otto cycle engine that uses liquefied natural gas as fuel and operates according to the Otto cycle; A fuel supply pump that discharges liquefied natural gas from a storage tank; A high-pressure pump that compresses the discharged liquefied natural gas; A vaporizer that vaporizes liquefied natural gas compressed by the high-pressure pump; An expansion valve that adiabatically expands the natural gas vaporized in the vaporizer; and a gas-liquid separator that separates the gas-liquid mixture formed by the expansion valve. Including, the liquid separated in the gas-liquid separator is recovered to the storage tank, and the gas separated in the gas-liquid separator is used as fuel for the Otto cycle engine. A fuel supply system for a liquefied natural gas fuel ship is provided, which controls the methane value of the natural gas fuel supplied to the Otto cycle engine.

Preferably, it further includes a liquefied natural gas cooler that heat exchanges the liquefied natural gas compressed by the high-pressure pump and supplied to the vaporizer and the liquid separated from the gas-liquid separator and returned to the storage tank, and in the liquefied natural gas cooler The compressed liquefied natural gas supplied to the vaporizer can be heated and the liquid returned to the storage tank can be cooled.

Preferably, it further includes a fuel gas heater for heating the natural gas fuel separated from the gas-liquid separator and supplied as fuel for the Otto cycle engine, wherein the natural gas fuel passing through the expansion valve and the fuel gas heater is It can have the temperature required by the Otto cycle engine.

Preferably, the Otto cycle engine includes an X-DF engine, which is a 2-stroke engine as a propulsion engine for the ship; And a DFDG (Dual Fuel Diesel Generator Engine), which is a 4-stroke engine as an engine for producing auxiliary power of the ship, and the natural gas fuel passing through the fuel gas heater is used in the X-DF engine. can have the required pressure.

Preferably, it further includes a pressure reducing valve for reducing the pressure of the natural gas fuel to be supplied to the DFDG, so that the natural gas fuel passing through the fuel gas heater and the pressure reducing valve may have a pressure required by the DFDG.

Preferably, a liquefied natural gas fuel line providing a path for supplying liquefied natural gas from the storage tank to the engine through the high pressure pump and vaporizer; and an evaporative gas fuel line that provides a path so that evaporative gas generated in the storage tank is supplied as fuel for the engine, wherein the evaporative gas fuel line includes a compressor that compresses the evaporative gas; and an intermediate cooler that cools the boil-off gas heated by compression in the compressor.

Preferably, the boil-off gas cooler heat-exchanges the compressed and cooled boil-off gas with the compressed liquefied natural gas supplied to the vaporizer, wherein the compressed liquefied natural gas supplied to the vaporizer is heated in the boil-off gas cooler. , the evaporation gas can be cooled.

Preferably, it may further include an evaporation gas expansion valve that expands the compressed evaporation gas cooled in the evaporation gas cooler to the same pressure as the gas-liquid mixture supplied to the gas-liquid separator.

Preferably, it may further include a GCU (Gas Combustion Unit) that processes boil-off gas generated in the storage tank.

Preferably, it may further include a control unit that controls the temperature, pressure, and flow rate of the fluid supplied to or discharged from the high pressure pump, carburetor, expansion valve, and gas-liquid separator according to load changes of the Otto cycle engine.

According to another aspect of the present invention for achieving the above-mentioned object, 1) discharging liquefied natural gas stored in a storage tank to the outside using a fuel supply pump and compressing it using a high-pressure pump; 2) vaporizing the compressed liquefied natural gas using a vaporizer; 3) expanding the vaporized natural gas; 4) separating the gas-liquid mixture formed by the expansion; and 5) resupplying the gas-liquid separated liquid to the storage tank, and supplying the gas-liquid separated gas to an Otto cycle engine that uses liquefied natural gas as fuel and operates according to the Otto cycle. A fuel supply method for a liquefied natural gas fuel ship is provided, which can supply liquefied natural gas stored in a storage tank as fuel having the temperature, pressure, and methane number required by the Otto cycle engine.

Preferably, (1-1) before vaporizing the compressed liquefied natural gas in step 2), heat exchanging the compressed liquefied natural gas with the liquid re-supplied to the storage tank in step 5). Thus, the compressed liquefied natural gas can be vaporized after being heated by the liquid re-supplied to the storage tank, and the liquid re-supplied to the storage tank can be cooled by the compressed liquefied natural gas and then supplied to the storage tank.

Preferably, 5-1) heating the gaseous fuel separated from the gas-liquid in step 5) and supplied to the engine; and a control step of controlling the pressure, temperature, and flow rate of the fluid in one or more of the steps according to load changes of the Otto cycle engine. The fluid that has passed step 5-1) is It can have the pressure, temperature and methane number required by the cycle engine.

Preferably, it further includes the step of depressurizing the heated gaseous fuel, and the fluid that has passed step 5-2) may have the pressure, temperature, and methane value required by the Otto cycle engine. .

Preferably, the step of discharging the boil-off gas generated in the storage tank and compressing it in a compressor; and supplying the compressed boil-off gas as fuel for the Otto cycle engine, wherein the compressed boil-off gas may have a pressure and temperature required for the Otto cycle engine.

Preferably, the step of expanding the compressed boil-off gas may be further included, and the expanded boil-off gas may be supplied as fuel for the Otto cycle engine by joining the step 4).

Preferably, the step of cooling the compressed boil-off gas by heat exchanging the compressed boil-off gas and the compressed liquefied natural gas supplied to the vaporizer in step 2), further comprising converting the compressed and cooled boil-off gas to the Otto cycle engine. can be supplied as fuel.

According to the present invention, fuel that satisfies the fuel gas specifications required by the Otto cycle engine can be supplied, and in particular, operating costs can be reduced by using a high-pressure pump and regasification equipment compared to the conventional method of using a BOG compressor. High-pressure pumps and regasification facilities can reduce the installation area and cost of the installed equipment compared to applying a BOG compressor.

In addition, conventionally, even with the use of a high-pressure pump and regasification equipment, the methane number could not be adjusted to the required level in the case of an Otto cycle engine, but the methane number required by the engine can be secured.

In addition, since some of the gas is re-liquefied and re-supplied to the storage tank, the amount of naturally vaporized BOG can be minimized.

In addition, the load of the engine always changes during the operation of the ship, and according to the present invention, the required flow rate of fuel gas can be supplied while maintaining the temperature and pressure according to these changes. In particular, the flow rate control of the high pressure pump and the temperature of each equipment, Through pressure control, the required engine fuel temperature and pressure can be maintained constant by responding flexibly to the engine load.

Figure 1 is a schematic diagram illustrating the fuel supply system of a conventional LNG carrier.
Figure 2 is a schematic diagram illustrating a fuel supply system for a liquefied natural gas fuel ship according to an embodiment of the present invention.

In order to fully understand the operational advantages of the present invention and the objectives achieved by practicing 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 structure and operation of a preferred embodiment of the present invention will be described in detail with reference to the attached drawings. Here, in adding reference numerals to components in each drawing, it should be noted that identical components are indicated with the same reference numerals as much as possible, even if they are shown in different drawings.

In the following examples, the case of liquefied natural gas is explained as an example, but the present invention can be applied to various liquefied gases, and the following examples can be modified into various other forms, and the scope of the present invention is limited to the following examples. It doesn't work.

In the following examples, the fluid flowing through each flow path may be in a gaseous state, a gas-liquid mixture state, a liquid state, or a supercritical fluid state, depending on the operating conditions of the system.

Additionally, in the following examples, the ship may be a liquefied natural gas carrier (LNG Carrier) that transports liquefied natural gas as cargo, or it may be a general merchant ship equipped with a storage tank for storing liquefied natural gas. Therefore, this embodiment It can be applied to any ship that has an engine supplied with liquefied natural gas as fuel and has propulsion from the engine or can generate electricity by driving the engine.

Figure 2 is a schematic diagram illustrating a fuel supply system for a liquefied natural gas fuel ship according to an embodiment of the present invention. Hereinafter, a fuel supply system and method for a liquefied natural gas fuel ship according to an embodiment of the present invention will be described with reference to FIG. 2.

As shown in FIG. 2, the fuel supply system for a liquefied natural gas fuel ship according to an embodiment of the present invention supplies liquefied natural gas stored inside a storage tank 10 for storing liquefied natural gas to an engine (ME, GE). It includes a liquefied natural gas fuel line (LL) that supplies to.

The storage tank 10 for storing liquefied natural gas of this embodiment is a membrane tank designed and manufactured to store extremely low temperature liquefied natural gas at normal pressure or a membrane tank designed and manufactured to store extremely low temperature liquefied natural gas at relatively high pressure. It may be a Type C tank being manufactured, and can be selected depending on installation location, capacity, etc. However, the storage tank 10 of this embodiment is preferably a membrane tank.

The engine that receives liquefied natural gas fuel along the liquefied natural gas fuel line (LL) may be an Otto cycle engine (ME, GE) that applies the Otto cycle.

In this embodiment, the Otto cycle engine is a 2-stroke DFME (2-Stroke Dual Fuel Main Engine), which is a ship's main propulsion engine, an X-DF engine (ME) and a 4-stroke DFDG (4-Stroke Dual Fuel Diesel) Generator Engine) may include a ship's auxiliary power generation engine (GE), and the specifications of the natural gas supplied as fuel are different between the X-DF engine (ME) and the power generation engine (GE).

For example, in this embodiment, the ) requires natural gas fuel of approximately 5 barg, approximately 0 to 60°C, and a methane number of approximately 80 or more.

Therefore, in order to supply liquefied natural gas fuel to the engine (ME, GE) while satisfying the fuel gas requirements of such engines (ME, GE), in this embodiment, liquefied natural gas fuel stored in a liquid state at normal pressure at cryogenic temperature is used. The gas must be heated and vaporized, compressed, and the methane number controlled.

On the liquefied natural gas fuel line (LL) of this embodiment, the liquefied natural gas stored in the storage tank 10 is converted into fuel that satisfies the conditions such as pressure, temperature, and methane value of the fuel required by the Otto cycle engine (ME, GE). In order to supply gas, a fuel supply pump 11 for discharging liquefied natural gas from the storage tank 10, a high pressure pump 20 for compressing the liquefied natural gas discharged by the fuel supply pump 11, and a high pressure pump ( A vaporizer (30) that vaporizes the liquefied natural gas compressed by 20), an expansion valve (40) that adiabatically expands the natural gas vaporized in the vaporizer (30), and a gas-liquid mixture formed by expansion in the expansion valve (40). A gas-liquid separator 50 is provided for separation.

The fuel supply pump 11 of this embodiment may be provided inside the storage tank 10, and preferably may be installed at the bottom of the storage tank 10, near the bottom of the storage tank 10. That is, the fuel supply pump 11 pumps the liquefied natural gas stored at the bottom of the storage tank 10 and supplies it to the high pressure pump 20.

In addition, the fuel supply pump 11 transports the liquefied natural gas stored in the storage tank 10 from the inside of the storage tank 10 to the high pressure pump 20, and the size of the storage tank 10 and the fuel supply pump 11 The discharge pressure and flow rate can be determined depending on the pressure drop of the pipe connecting the high pressure pump 20, the amount of fuel gas to be supplied to the engine (ME, GE), etc.

The high pressure pump 20 of this embodiment is capable of compressing cryogenic liquefied natural gas discharged from the fuel supply pump 11 to high pressure. As the liquefied natural gas is compressed to high pressure by the high pressure pump 20, the temperature increases due to compression. Preferably, the liquefied natural gas maintains its liquid state even if the temperature rises.

For example, the high pressure pump 20 compresses liquefied natural gas at about 1.2 bar and -163°C discharged from the storage tank 10 to a pressure of about 300 bar, and the liquefied natural gas compressed by the high pressure pump 20 may be in a liquid state at about 300 bar and -154°C.

Additionally, the high pressure pump 20 of this embodiment may be of the piston type, and the flow rate may be adjusted by adjusting the rotation speed.

The vaporizer 30 of this embodiment is a type of heat exchanger that heats liquefied natural gas compressed to high pressure in the high pressure pump 20 using a heat source. In the vaporizer 30, the compressed liquefied natural gas obtains heat energy and is converted to at least part or all of it. It can be vaporized into a gaseous state.

For example, the vaporizer 30 heats compressed liquefied natural gas to a temperature of about -50°C, and the natural gas vaporized in the vaporizer 30 may be at about 300 bar and -50°C.

The heat source for heating the compressed liquefied natural gas in the vaporizer 30 may be steam or glycol water, and glycol water is heated by recovering seawater or waste heat from combustion devices in ships. However, the heat source of the vaporizer 30 is not limited to this.

The expansion valve 40 of this embodiment may be a Joule-Thomson valve that adiabatically expands the high-pressure natural gas that has passed through the vaporizer 30, and the high-pressure natural gas passes through the expansion valve 40. can be cooled by expansion, and the temperature decrease of the fluid decreases more significantly as the difference between before and after passing through the expansion valve 40 is larger.

In this embodiment, the expansion valve 40 may be capable of adiabatically expanding high-pressure natural gas to about 17 bar.

For example, when attempting to supply liquefied natural gas as fuel gas to an Otto cycle engine, especially an X-DF engine (ME), the high-pressure natural gas that has passed through the vaporizer 30 can be expanded to about 17 bar, and The natural gas that has passed through the valve 40 may be at a temperature of about 17 bar and -102.5°C, and is cooled by expansion to form a gas-liquid mixture.

In addition, when it is desired to supply liquefied natural gas as fuel gas to an Otto cycle engine, especially an electric power generation engine (GE), the high-pressure natural gas that has passed through the vaporizer 30 can be expanded to about 7 bar, and the expansion valve ( Natural gas that has passed through 40) may be in the state of a gas-liquid mixture at about 7 bar and -122.5°C.

The gas-liquid separator 50 of this embodiment separates the gas-liquid mixture formed in the expansion valve 40, and the separated liquid is connected to the liquefied natural gas recovery line (RL) connected from the lower part of the gas-liquid separator 50 to the inside of the storage tank 10. ), and the separated gas is supplied as fuel to the Otto cycle engine (ME, GE) along the liquefied natural gas fuel line (LL) connected to the upper part of the gas-liquid separator (50).

In this embodiment, the gas-liquid separator 50 is a means of controlling the methane value of the fuel gas supplied to the engine (ME, GE).

The methane number is a numerical representation of the resistance to knocking. The knocking phenomenon is when the mixture of fuel and combustion air is compressed during the upward stroke of the piston within the engine cylinder, and occurs at an abnormally early time. This refers to a phenomenon that explodes after reaching the spontaneous ignition temperature. It is accompanied by strong noise and shock, shortening the life of the engine and causing a decrease in engine output. Therefore, the fuel supplied to the engine must be adjusted to have the methane number required by the engine.

The methane number increases as the carbon number of the fuel decreases and the hydrogen/carbon ratio increases, and the higher the methane number, the greater the resistance to the knocking phenomenon.

In this embodiment, the gas component separated in the gas-liquid separator 50 and supplied as fuel to the engine (ME, GE) is mainly methane (CH ₄ ) and may include a small amount of heavy hydrocarbon components, and the gas-liquid separator 50 The liquid components separated from and recovered in the storage tank 10 are mainly heavy hydrocarbon components such as ethane, propane, and butane.

Accordingly, the gas-liquid separator 50 of this embodiment can supply fuel gas with a high methane number to the engine (ME, GE) because the component supplied as fuel is mainly methane with a low carbon number.

In this embodiment, the gas-liquid mixture supplied to the gas-liquid separator 50, the gas component separated in the gas-liquid separator 50 and discharged to the liquefied natural gas fuel line LL, and the gas component separated in the gas-liquid separator 50 to recover liquefied natural gas. The composition of the liquid component discharged to the line RL can be operated as shown in Table 1 below.

The composition of the fluid shown in Table 1 is based on HYSYS simulation, and is simulated assuming that it is liquefied natural gas at about 1.2 bar, -163°C, and 500 kg/hr supplied using the fuel supply pump 11. As shown in Table 1, the gas component separated and discharged from the gas-liquid separator 50 has a high methane concentration and a small heavy hydrocarbon fraction, and the liquid component has a high heavy hydrocarbon fraction.

In addition, the composition shown in Table 1 indicates only the main ingredients, and may contain additional small amounts of normal butane (n-Butane), isopentane (i-Pentane), nitrogen (N ₂ ), and carbon dioxide (CO _{2 ).} ), etc., were omitted, so the sum of the compositions shown in Table 1 may not necessarily be 1.0000.

Gas-liquid mixture (Inlet) Gas composition (Outlet) Liquid Ingredients (Outlet) Methane 0.8709 0.9943 0.6196 Ethane 0.0854 0.0056 0.2479 Propane 0.0311 0.0001 0.0944 i-Butane 0.0116 0.0000 0.0351

The methane value is determined by the composition of the supplied fuel gas. The main component of liquefied natural gas is methane, but it also contains small amounts of ethane, propane, butane, pentane, nitrogen, and carbon dioxide, so it is supplied depending on the characteristics of the fuel gas supply system. The composition of the fuel gas may vary, and the methane value may vary accordingly.

According to this embodiment, the liquefied natural gas stored at the bottom of the storage tank 10 is transported, vaporized, and supplied as fuel using the fuel supply pump 11, so that natural gas is relatively naturally vaporized in the storage tank 10. Since it has a higher methane value than boil-off gas, which has a high molar ratio of heavy hydrocarbons such as ethane and propane, a more suitable fuel can be supplied, and the liquid natural gas is vaporized using the high pressure pump (20) and vaporizer (30). , Even if it is supplied as fuel for an Otto cycle engine that requires medium- or low-pressure fuel rather than a diesel cycle engine that requires relatively high-pressure fuel, the methane value can be adjusted and supplied using the gas-liquid separator 50.

According to this embodiment, as shown in FIG. 2, the gas component separated in the gas-liquid separator 50 can be supplied to the engine (ME, GE) as fuel gas, and the liquefied natural gas at the rear of the gas-liquid separator 50 The fuel line LL may further include a fuel gas heater 60 that heats the fuel gas separated from the gas-liquid separator 50 and supplied to the engine (ME, GE) to the temperature required by the engine (ME, GE). there is.

In this embodiment, the fuel gas supplied to the engines (ME, GE) can be heated to about 45°C in the fuel gas heater 60.

In addition, as shown in FIG. 2, in this embodiment, the liquefied natural gas fuel line (LL) is connected from the storage tank 10 to the Otto cycle engine, but is connected to the X-DF engine (ME) and the power production engine (GE). ) can be branched and connected to each engine at the front end of the fuel gas heater 60 and the rear end of the fuel gas heater 60, and can supply fuel gas that meets the conditions required by each engine. However, the turning point is not necessarily limited to this.

In this embodiment, as shown in FIG. 2, the liquefied natural gas fuel line (LL) is connected from the storage tank 10 to the X-DF engine (ME), and the liquefied natural gas fuel line (LL) The fuel gas branch line (LB), which branches off from the front of the DF engine (ME), is further connected to supply liquefied natural gas fuel to the power generation engine (GE), and the fuel gas branch line (LB) can supply liquefied natural gas fuel to the power generation engine (GE). A pressure reducing valve 70 may be further provided to reduce the pressure of fuel gas flowing from the fuel line LL into the fuel gas branch line LB to match the fuel conditions of the power production engine GE.

That is, the liquefied natural gas stored in the storage tank 10 is compressed, vaporized, and expanded through the liquefied natural gas fuel line (LL) and supplied to the engine (ME, GE). The liquefied natural gas fuel line (LL) is connected to the storage tank. It is connected to the Otto cycle engine (ME, GE) from (10), and supplies liquefied natural gas fuel only to the When supplying gas simultaneously, the high pressure pump 20, carburetor 30, expansion valve 40, etc. are controlled to control the pressure and temperature of the fuel gas to satisfy the fuel conditions of the X-DF engine (ME), and depressurize. Using the valve 70, the pressure of fuel gas supplied to the power generation engine (GE) can be controlled to match the fuel conditions of the power generation engine (GE).

In this embodiment, the fuel gas supplied to the The fuel gas branched to (LB), passes through the pressure reducing valve 70, and is supplied to the power production engine (GE) may be about 6.5 bar and 45°C.

In addition, when liquefied natural gas is supplied as fuel to the power generation engine (GE) through the liquefied natural gas fuel line (LL), the compressed and vaporized natural gas can be expanded to about 7 bar in the expansion valve 40. there is .

In addition, according to this embodiment, as shown in FIG. 2, the liquefied natural gas compressed in the high pressure pump 20 is provided in the liquefied natural gas fuel supply line LL between the high pressure pump 20 and the vaporizer 30. It may further include a liquefied natural gas cooler 31 that heat exchanges the liquid component separated from the gas-liquid separator 50 and recovered to the storage tank 10 along the liquefied natural gas recovery line RL.

For example, in the liquefied natural gas cooler (31), compressed liquefied natural gas of about 300 bar and -154°C compressed by the high pressure pump (20) and about The liquid component at -122.5°C exchanges heat, so that the compressed liquefied natural gas is preheated before being supplied to the vaporizer (40), and the liquid component is cooled before being returned to the storage tank (10). Compressed liquefied natural gas discharged after heat exchange in the liquefied natural gas cooler (31) and supplied to the vaporizer (40) is heated to about 300 bar and -149.3°C, and the liquid component discharged after heat exchange and recovered to the storage tank (10) is about It may be -140 to -152°C.

Therefore, according to this embodiment, the liquid component separated from the gas-liquid separator 50 and re-supplied to the storage tank 10 can be cooled and recovered to the storage tank 10 at a lower temperature, so the storage tank 10 The amount of boil-off gas (BOG; Boil-Off Gas) generated within can be minimized.

In addition, the fuel supply system for a liquefied natural gas fuel ship according to an embodiment of the present invention is a liquefied natural gas that supplies liquefied natural gas to engines (ME, GE) using a high pressure pump 20 and a vaporizer 30. Along with the fuel line (LL), it may further include an evaporative gas fuel line (GL) that supplies evaporative gas generated by natural vaporization in the storage tank 10 as fuel for an Otto cycle engine (ME, GE).

In this embodiment, the boil-off gas fuel line (GL) may be connected from the storage tank 10 to the liquefied natural gas fuel line (LL) as shown in FIG. 2, and is preferably connected to the rear end of the fuel gas heater 60. You can join.

In addition, the boil-off gas fuel line (GL) may further include a boil-off gas branch line (GB1) branched from the boil-off gas fuel line (GL) and connected to the gas-liquid separator 50 of the liquefied natural gas fuel line (LL). , The evaporation gas branch line GB1 may be provided with an evaporation gas expansion valve 41 that adiabatically expands the fluid supplied to the gas-liquid separator 50.

The evaporative gas fuel line (GL) may be provided with a multi-stage compressor (MC) that compresses the evaporative gas discharged from the storage tank 10 and an evaporative gas cooler 32 that cools the evaporative gas compressed in the multi-stage compressor (MC). there is.

A multi-stage compressor (MC) includes multiple compressors that compress boil-off gas in multiple stages, and a plurality of inter-coolers provided at the rear of each compressor to cool the boil-off gas whose temperature has risen due to compression in each compressor. may include.

In this embodiment, the multi-stage compressor (MC) is a means for processing boil-off gas generated in the storage tank 10, and in case a problem such as failure of the high pressure pump 20 or vaporizer 30 occurs, It may be provided as a means for supplying the boil-off gas directly or through the gas-liquid separator 50 to the power generation engine (GE).

The multi-stage compressor (MC) of this embodiment is a two-stage compressor that includes two compressors and two intermediate coolers to compress the boil-off gas in two stages, or a two-stage compressor that includes one compressor and one intermediate cooler to compress the boil-off gas in one stage. It may be a single-stage compressor that compresses throughout.

The boil-off gas cooler 32 of this embodiment exchanges heat between the boil-off gas compressed in the multi-stage compressor (MC) and the liquefied natural gas compressed by the high-pressure pump 20 in the liquefied natural gas fuel line (LL) described above, and the high-pressure pump In (20), the cold heat of the compressed liquefied natural gas is used to cool the boil-off gas compressed in the multi-stage compressor (MC).

That is, in the boil-off gas cooler 32, the compressed liquefied natural gas compressed by the high-pressure pump 20 is heated and discharged, and the compressed boil-off gas compressed by the multi-stage compressor (MC) is cooled and discharged.

Preferably, the evaporation gas cooler 32 may be provided at the rear of the liquefied natural gas cooler 31 described above. That is, the compressed liquefied natural gas compressed in the high-pressure pump 20 exchanges heat with the re-liquefied natural gas separated from the gas-liquid separator 50 in the liquefied natural gas cooler 31 and returned to the storage tank 10, thereby performing primary heating. In the boil-off gas cooler 32, heat is exchanged with the compressed boil-off gas compressed in the multi-stage compressor (MC) to be secondarily heated and then supplied to the vaporizer 30.

In addition, in this embodiment, the compressed evaporation gas may further include a cooler bypass line (GB) that allows the compressed evaporation gas to bypass the evaporation gas cooler 32 and join the rear end of the evaporation gas cooler 32. Preferably, it may be stored. The evaporative gas generated by natural vaporization in the tank 10 is compressed in a multi-stage compressor (MC), then bypasses the evaporative gas cooler 32 along the cooler bypass line GB and joins the rear end of the fuel gas heater 60, The boil-off gas generated during the operation of the high-pressure pump (20) is compressed in the multi-stage compressor (MC), cooled in the boil-off gas cooler (32), and then expanded in the boil-off gas expansion valve (41) along the boil-off gas branch line (GB1). and can join the gas-liquid separator (50).

The boil-off gas expansion valve 41 must be able to expand to the same pressure as the expansion valve 40 of the liquefied natural gas fuel line (LL) described above, and the boil-off gas cooled in the boil-off gas cooler 32 is converted into liquefied natural gas. The temperature of the liquefied natural gas supplied to the gas-liquid separator 50 through the fuel line LL, that is, in this embodiment, must be cooled to about -50°C.

That is, the boil-off gas supplied to the gas-liquid separator 50 along the boil-off gas branch line GB1 and the liquefied natural gas supplied to the gas-liquid separator 50 along the liquefied natural gas fuel line LL are supplied at the same pressure and temperature. It must be done so as not to impair gas-liquid separation performance.

In addition, although not shown, the fuel supply system for a liquefied natural gas fuel ship according to the present invention uses GCU as a means of processing boil-off gas generated in the storage tank 10 without providing the boil-off gas fuel line (GL) described above. (Gas Combustion Unit) can also be prepared. In other words, the boil-off gas generated in the storage tank 10 can be treated by combustion rather than being used as fuel for an Otto cycle engine.

As described above, the fuel supply system and method for liquefied natural gas fuel ships of the present invention are LFS, especially ships equipped with Otto cycle engines such as low pressure two-stroke dual fuel oil engine (2SDFME) and dual fuel oil power generation engine (DFDG). It relates to a system and method for supplying fuel gas to the engine. According to the present invention, a high-pressure pump (20) that compresses liquefied natural gas from a liquid state to high pressure and a vaporizer (30) that vaporizes the compressed liquefied natural gas By using the expansion valve 40, which adiabatically expands the vaporized natural gas, and the gas-liquid separator 50, which separates the gas-liquid mixture formed by expansion, the fuel gas conditions required by the low-pressure Otto cycle engine are satisfied. can be supplied, and since a high-pressure pump is used compared to the conventional method of using an evaporative gas compressor, operating costs and especially electric energy costs can be saved, and installation area and installation equipment costs can be reduced.

In addition, the methane value can be adjusted even when fuel is supplied to a low-pressure Otto cycle engine using the high-pressure pump 20 and the vaporizer 30, and some of the vaporized gas is re-liquefied and returned to the storage tank 10, so that the storage tank 10 In (10), the amount of naturally evaporated gas can be minimized.

In addition, the load of the engine always changes during the operation of the ship. According to the present invention, the flow rate of the high pressure pump 20 is controlled by a control unit (not shown) and the temperature and pressure of various devices constituting the system are controlled to control the engine load. Fuel can be supplied while easily maintaining the temperature and pressure at the required flow rate of fuel gas in accordance with load changes.

The present invention is not limited to the above-mentioned embodiments, and it is obvious to those skilled in the art that the present invention can be implemented with various modifications or variations without departing from the technical gist of the present invention. It was done.

10: storage tank
11: Fuel supply pump
20: high pressure pump
30: carburetor
40: Expansion valve
50: Gas-liquid separator
60: Fuel gas heater
70: pressure reducing valve
ME: Low-pressure two-stroke dual fuel oil engine
GE: Dual fuel oil power generation engine
LL: Liquefied natural gas fuel line
RL: Liquefied natural gas recovery line
31: Liquefied natural gas cooler
32: Evaporative gas cooler

Claims (17)

Otto cycle engine, which uses liquefied natural gas as fuel and operates according to the Otto cycle;
A high-pressure pump that compresses liquefied natural gas discharged from a storage tank;
A liquefied natural gas cooler that heats the liquefied natural gas compressed by the high pressure pump;
An evaporation gas cooler that heats the fluid compressed by the high-pressure pump and then heated by the liquefied natural gas cooler;
a vaporizer that vaporizes the fluid heated by the evaporation gas cooler;
An expansion valve that expands the natural gas vaporized in the vaporizer; and
Including a gas-liquid separator that separates the gas-liquid mixture formed by the expansion valve.
The liquid separated in the gas-liquid separator is recovered to the storage tank, and the gas separated in the gas-liquid separator is supplied as fuel for the Otto cycle engine to adjust the methane value of the natural gas fuel supplied to the Otto cycle engine,
The liquefied natural gas cooler cools the liquid separated by the gas-liquid separator by heat exchange with the liquefied natural gas compressed by the high-pressure pump and then sends it to the storage tank,
The evaporative gas cooler cools the evaporative gas discharged from the storage tank by exchanging heat with the fluid heated by the liquefied natural gas cooler after being compressed by the high-pressure pump. delete In claim 1,
Further including a fuel gas heater that heats the natural gas fuel separated from the gas-liquid separator and supplied as fuel for the Otto cycle engine,
A fuel supply system for a liquefied natural gas fuel ship, wherein the natural gas fuel that has passed through the expansion valve and the fuel gas heater has a temperature required by the Otto cycle engine. In claim 3,
The Otto cycle engine,
An X-DF engine, a 2-stroke engine, as the propulsion engine of the ship; and
It includes a DFDG (Dual Fuel Diesel Generator Engine), which is a 4-stroke engine as an engine for producing auxiliary power for the ship,
A fuel supply system for a liquefied natural gas fuel ship, wherein the natural gas fuel that has passed through the fuel gas heater has the temperature and pressure required by the X-DF engine. In claim 4,
Further including a pressure reducing valve that depressurizes the natural gas fuel to be supplied to the DFDG,
A fuel supply system for a liquefied natural gas fuel ship, wherein the natural gas fuel that has passed through the fuel gas heater and the pressure reducing valve has the pressure required by the DFDG. According to any one of claims 1, 3, and 4,
A liquefied natural gas fuel line that provides a path to supply liquefied natural gas from the storage tank to the engine through the high pressure pump and vaporizer; and
It includes a evaporative gas fuel line that provides a path so that evaporative gas generated in the storage tank is supplied as fuel for the engine,
In the evaporation gas fuel line,
A compressor that compresses the boil-off gas; and
A fuel supply system for a liquefied natural gas fuel ship, including an intermediate cooler that cools the boil-off gas heated by compression in the compressor. delete In claim 1,
A fuel supply system for a liquefied natural gas fuel ship further comprising a evaporation gas expansion valve that expands the compressed evaporation gas cooled in the evaporation gas cooler to the same pressure as the gas-liquid mixture supplied to the gas-liquid separator. In claim 8,
Fuel for liquefied natural gas fuel ships, further comprising a control unit that controls the temperature, pressure, and flow rate of the fluid supplied to or discharged from the high pressure pump, carburetor, expansion valve, and gas-liquid separator according to load changes of the Otto cycle engine. supply system. According to any one of claims 1, 3, and 4,
A fuel supply system for a liquefied natural gas fuel ship, further comprising a GCU (Gas Combustion Unit) that processes boil-off gas generated in the storage tank. 1) Compressing the liquefied natural gas discharged from the storage tank using a high-pressure pump;
2) heating the liquefied natural gas compressed by the high pressure pump in step 1) using a liquefied natural gas cooler;
3) heating the fluid heated by the liquefied natural gas cooler in step 2) by an evaporation gas cooler;
4) vaporizing the fluid heated by the evaporation gas cooler in step 3) using a vaporizer;
5) expanding the natural gas vaporized by the vaporizer in step 4); and
6) separating the gas-liquid mixture formed by the expansion in step 5) using a gas-liquid separator;
7) The liquid separated from the gas-liquid in step 6) is sent to the storage tank, and the gas separated from the gas-liquid in step 6) is supplied to the Otto cycle engine to adjust the methane value of the natural gas fuel supplied to the Otto cycle engine. ,
The liquefied natural gas cooler cools the liquid separated by the gas-liquid separator by heat-exchanging it with the liquefied natural gas compressed by the high-pressure pump and then sends it to the storage tank,
The evaporation gas cooler cools the evaporation gas discharged from the storage tank by heat exchange with the fluid heated by the liquefied natural gas cooler after being compressed by the high-pressure pump. delete In claim 11,
6-1) A fuel supply method for a liquefied natural gas fuel ship, further comprising the step of heating the gas separated from the gas-liquid in step 6) and supplied to the Otto cycle engine. In claim 13,
6-2) A fuel supply method for a liquefied natural gas fuel ship, further comprising the step of depressurizing the gaseous fuel heated in step 6-1). In claim 14,
The evaporative gas discharged from the storage tank is compressed by a compressor and then sent to the evaporative gas cooler,
A fuel supply method for a liquefied natural gas fuel ship, wherein the fluid compressed by the compressor and then cooled by the evaporative gas cooler is supplied as fuel for the Otto cycle engine. In claim 15,
A fuel supply method for a liquefied natural gas fuel ship, in which part or all of the fluid compressed by the compressor and then cooled by the evaporation gas cooler is expanded by an evaporation gas expansion valve and then sent to the gas-liquid separator. delete

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