KR102651898B1 - Fuel Supply System and Method for LNG Fueled Vessel - Google Patents

Abstract

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.
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 vaporizer that vaporizes liquefied natural gas stored in a storage tank; An expander that generates power using natural gas vaporized in the vaporizer and discharges depressurized natural gas; and a compressor that is connected to the expander by an axis and compresses the evaporation gas generated by natural vaporization in the storage tank. Including, the natural gas that has passed through the vaporizer and the expander and the evaporation gas compressed by the compressor are compressed into the Otto cycle engine. It is characterized by being able to be supplied as fuel.

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 by five compression units and five coolers.

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 vaporizer that vaporizes liquefied natural gas stored in a storage tank; An expander that generates power using natural gas vaporized in the vaporizer and discharges depressurized natural gas; and a compressor that is connected to the expander by an axis and compresses the evaporation gas generated by natural vaporization in the storage tank. Including, the natural gas that has passed through the vaporizer and the expander and the evaporation gas compressed by the compressor are compressed into the Otto cycle engine. A fuel supply system for a liquefied natural gas fuel ship that can be supplied as fuel is provided.

Preferably, the vaporized natural gas while passing through the expander forms a gas-liquid mixture, and further includes a gas-liquid separator that separates the gas-liquid mixture, and the liquid separated in the gas-liquid separator is recovered to the storage tank. , the gas separated in the gas-liquid separator can be supplied as fuel for the Otto cycle engine, thereby controlling the methane value of the natural gas fuel supplied to the Otto cycle engine.

Preferably, a fuel supply pump discharging liquefied natural gas from the storage tank; and a high-pressure pump that compresses the liquefied natural gas discharged by the fuel supply pump. It may further include supplying the natural gas compressed by the high-pressure pump to the vaporizer.

Preferably, a fuel gas heater that heats the gas separated in the gas-liquid separator to a temperature required by the Otto cycle engine; and an aftercooler that cools the evaporative gas compressed by the compressor to a temperature required by the Otto cycle engine.

Preferably, a liquefied natural gas fuel line providing a path for supplying liquefied natural gas from the storage tank to the engine; 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 joins the liquefied natural gas fuel line at a rear end of the fuel gas heater. It can be.

Preferably, the compressed liquefied natural gas supplied to the vaporizer and the liquid separated from the gas-liquid separator and returned to the storage tank can be heat exchanged to cool the re-liquefied natural gas returned to the storage tank.

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 for the ship.

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, one or more expanders are provided, and a generator is axially connected to any one of the one or more expanders and generates power using the power of the expander. Alternatively, it may further include a brake resistor that is axially connected to any one of the one or more expanders and consumes excess power of the expander.

According to another aspect of the present invention for achieving the above-described object, 1) discharging liquefied natural gas stored in a storage tank to the outside of the storage tank using a fuel supply pump and compressing it using a high-pressure pump; 2) vaporizing the compressed liquefied natural gas using a vaporizer; 3) supplying the vaporized natural gas to an expander to depressurize it and simultaneously produce power, and compressing the vaporized natural gas generated in the storage tank using a compressor connected to the expander; and 4) supplying the vaporized and decompressed natural gas and compressed boil-off gas as fuel for an Otto cycle engine that uses liquefied natural gas as fuel and operates according to the Otto cycle. A fuel supply method is provided.

Preferably, step 4) further includes supplying the vaporized natural gas in which the gas-liquid mixture is formed by the reduced pressure to a gas-liquid separator to separate the gas-liquid, wherein the gaseous natural gas separated in the gas-liquid separator is It is supplied as fuel for an Otto cycle engine, and the liquid re-liquefied natural gas separated in the gas-liquid separator can be recovered into the storage tank.

Preferably, step 4) includes heating the gaseous natural gas separated in the gas-liquid separator to the gas fuel temperature condition required by the Otto cycle engine; and cooling the compressed boil-off gas to a gas fuel temperature condition required by the Otto cycle engine, wherein the heated natural gas and the cooled boil-off gas have the same temperature and pressure and are then operated in the Otto cycle engine. can be supplied.

Preferably, the method may further include cooling the re-liquefied natural gas by heat-exchanging the compressed liquefied natural gas supplied to the vaporizer and the re-liquefied natural gas recovered to the storage tank.

Preferably, the Otto cycle engine includes two types of engines having different gas fuel pressure conditions, and natural gas and compressed boil-off gas supplied as fuel for the Otto cycle engine are supplied to one of the two types of engines. It may further include reducing the pressure to the gas fuel pressure condition required by the engine.

Preferably, when boil-off gas cannot be supplied to the compressor, power generated by the expander can be used to generate electricity, and only the heated natural gas can be supplied as fuel to the Otto cycle engine.

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 engine (ME, GE) the boil-off gas (BOG; Boil-Off Gas) generated by natural vaporization in the storage tank (10). (GL) is further included.

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.

In addition, in this embodiment, the engine that receives liquefied natural gas fuel along the liquefied natural gas fuel line (LL) and the boil-off gas fuel line (GL) is an Otto cycle engine (ME, GE) that applies the Otto cycle. ) can be.

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 the engine (ME, GE), stored at normal pressure or high pressure at cryogenic temperature in the storage tank 10, in this embodiment In the example, liquefied natural gas, which is stored in a liquid state at normal pressure at extremely low temperatures, must be heated and vaporized, compressed, and the methane value must be adjusted.

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 expander (EXP) that expands the natural gas vaporized in the vaporizer (30), and a gas-liquid that separates the gas-liquid mixture formed by expansion in the expander (EXP). A separator 50 is provided.

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 about 0 to 50°C, and the natural gas vaporized in the vaporizer 30 may be at, for example, about 300 bar and 0°C.

The temperature of the natural gas discharged from the vaporizer 30 can be controlled by a control unit (not shown) according to the flow rate of the compressed boil-off gas, which will be described later, and the amount of boil-off gas to be compressed by the compressor (COM), which will be described later, is primarily controlled. You can. That is, when the consumption of fuel gas is small, it is heated to a lower temperature, thereby reducing the power generated by the expander (EXP), and when the consumption of fuel gas is large, it is heated to a higher temperature, so that the expander (EXP) The power generated can be increased.

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 expander (EXP) of this embodiment generates power using high-pressure natural gas vaporized in the vaporizer 30 as a power source, and the temperature and pressure of the high-pressure natural gas that passes through the expander (EXP) are lowered.

The higher the high-pressure natural gas is heated to a higher temperature in the above-described vaporizer 30 and supplied to the expander (EXP), the more power can be obtained from the expander (EXP), and is discharged from the vaporizer 30 by a control unit (not shown). The temperature of high-pressure natural gas can be controlled. However, if the temperature of the high-pressure natural gas heated and discharged from the vaporizer 30 is too high, the temperature in the gas-liquid separator 50, which will be described later, increases and becomes an unsuitable temperature as fuel for the engine (ME, GE), or the gas-liquid separator 50 Since the gas-liquid performance may be poor, as described above, the high-pressure natural gas discharged from the vaporizer 30 may be controlled to be discharged at a temperature of about 0° C. and supplied to the expander (EXP).

In addition, natural gas discharged from the expander (EXP) at low pressure and temperature may be in a gas-liquid mixture state and is supplied to the gas-liquid separator 50.

In this embodiment, the gas-liquid mixture discharged from the expander (EXP) is controlled to expand to the pressure required by the Otto cycle engine (ME, GE) by a control unit (not shown), for example, the gas-liquid mixture discharged from the expander (EXP) The mixture can be controlled to be about 17 bar.

An expander (EXP), like a turbine, is a device that generates power using the energy of the fluid. High-temperature, high-pressure fluid rotates the impeller of the expander to generate power and is discharged as low-temperature, low-pressure fluid. . Since the expander can generate power in this way, by connecting a compressor, generator, or breaking resistor to the shaft of the expander, the expander (EXP) generates high-pressure natural gas as a power source. You can use the power you gave.

In this embodiment, as shown in FIG. 2, the compressor (COM) is connected to the axis of the expander (EXP) as an example, and it is shown that one expander (EXP) and one compressor (COM) are provided. , but is not limited to this, and if necessary, two or more sets may be provided, such as one expander and one compressor as one set, or one or more expanders, such as one set of expander and compressor and one set of expander and generator. is provided, and a compressor, generator, and braking resistor may be connected to each expander.

In this embodiment, the compressor (COM) is provided in the boil-off gas fuel line (GL) and uses the power generated by high-pressure natural gas in the expander (EXP) to naturally vaporize the boil-off gas (BOG) generated in the storage tank 10. ) can be compressed.

The evaporative gas fuel line (GL) is connected from the storage tank 10 to the rear end of the fuel gas heater 60, which will be described later, so that the evaporative gas generated in the storage tank 10 can be supplied as fuel for an Otto cycle engine (ME, GE). Connected to the liquefied natural gas fuel line (LL).

In addition, the evaporative gas fuel line (GL) cools the evaporative gas whose temperature has risen by compression in the compressor (COM) to the temperature required by the fuel gas conditions in the Otto cycle engine (ME, GE) at the rear end of the compressor (COM). An additional aftercooler (GHX) may be provided.

That is, according to this embodiment, the boil-off gas from the storage tank 10 is compressed as fuel for an Otto cycle engine (ME, GE), the natural gas vaporized in the carburetor 30 is compressed as a power source, and the compressed boil-off gas is used as an after-sale gas. By cooling in a cooler (GHX), the temperature and pressure can be adjusted to suit the fuel conditions of Otto cycle engines (ME, GE) and supplied as fuel.

In this embodiment, when two or more sets of an expander and a compressor are provided as one set, the boil-off gas can be compressed in two stages. In another embodiment, one set of an expander and a compressor, and one set of an expander and a generator are used. When a set is provided, the boil-off gas is compressed in one stage, and when there is no need to compress the boil-off gas or the boil-off gas is not supplied as fuel for the engine (ME, GE), the generator is driven by the surplus power generated from the expander. In another embodiment, if an additional set of an expander and a braking resistor is provided, the surplus power generated from the expander can be consumed as a braking resistor.

That is, the pressure of the boil-off gas compressed in the compressor (COM) and the temperature of the compressed boil-off gas cooled in the aftercooler (GHX) are the same pressure and temperature as the gaseous natural gas discharged from the gas-liquid separator 50, that is, the compressor (COM) must be operated so that the evaporative gas is compressed to about 17 bar, and the aftercooler (GHX) must be operated so that the evaporative gas is cooled to about -100 ~ -130℃.

In addition, in this embodiment, the compressor COM is preferably provided so that it can be driven by a motor in case the high pressure pump 20 cannot be used due to failure of the high pressure pump 20, etc. .

Alternatively, an expansion valve may be further provided in front of the gas-liquid separator 50 on the boil-off gas fuel line GL, and the compressed boil-off gas supplied to the gas-liquid separator 50 may be expanded to the same pressure as the gas-liquid mixture.

Likewise, an expansion valve 40 is further provided in the liquefied natural gas fuel line (LL) between the expander (EXP) and the gas-liquid separator 50, so that, if necessary, the pressure of the gas-liquid mixture supplied to the gas-liquid separator 50 can be adjusted to the engine ( It may be controlled to further expand to the pressure required by the ME, GE), preferably the X-DF engine (ME).

The expansion valve of this embodiment may be a Joule-Thomson valve that adiabatically expands the high-pressure natural gas that has passed through the vaporizer 30 or the boil-off gas compressed in the compressor (COM), and while passing through the expansion valve, Fluid can be cooled by expansion, and the temperature decrease of the fluid is greater as the difference between before and after passing through the expansion valve is greater.

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

The gas-liquid separator 50 of this embodiment separates the gas-liquid mixture formed while passing through the expander (EXP), and the separated liquid is connected to the liquefied natural gas recovery line ( It is recovered to the storage tank 10 through RL), 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. .

That is, in this embodiment, the gas-liquid separator 50 is a means for controlling the methane value of the fuel gas supplied to the engines (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 shows only the main components, and the fractions of normal butane (n-Butane), isopentane (i-Pentane), nitrogen (N ₂ ), and carbon dioxide (CO ₂ ) that may be included in very small amounts are It is omitted, and therefore 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 0.9876 0.6880 Ethane 0.0854 0.0119 0.2006 Propane 0.0311 0.0005 0.0792 i-Butane 0.0116 0.0000 0.0296

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 X-DF engine (ME) of the Otto cycle engine, or to the X-DF engine (ME) and power production engine ( When simultaneously supplying fuel gas to GE), the high pressure pump (20), carburetor (30), expander (EXP), etc. are controlled so that the pressure and temperature of the fuel gas satisfies the fuel conditions of the X-DF engine (ME). And, the pressure of the fuel gas supplied to the power generation engine (GE) can be controlled to match the fuel conditions of the power generation engine (GE) using the pressure reducing valve 70.

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, 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 at about 300 bar and -154°C compressed by the high pressure pump 20, and the liquid separated in the gas-liquid separator 50 and returned to the storage tank 10. As the components exchange heat, 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 (30) may be about 300 bar, -121°C, and is discharged after heat exchange in the liquefied natural gas cooler (31) to the storage tank (10). ) The liquid component recovered may be about -140 to -152°C.

The liquefied natural gas recovery line (RL) may further be provided with a pressure reducing valve (not shown) that reduces the pressure of the re-liquefied natural gas recovered to the storage tank 10 to a pressure similar to or the same as the liquefied natural gas stored in the storage tank 10. The re-liquefied natural gas passed through the liquefied natural gas cooler 31 and the pressure reducing valve and returned to the storage tank 10 may have a temperature of, for example, about 1.5 bar and -151.6°C.

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 , produces power using vaporized high-pressure natural gas, and uses an expander (EXP) that discharges low-pressure, low-temperature natural gas and a gas-liquid separator (50) that separates the gas-liquid mixture formed while passing through the expander (EXP). Fuel can be supplied by satisfying the fuel gas conditions required by the Otto cycle engine, and by using a high-pressure pump compared to the conventional method of using an evaporative gas compressor, operating costs and especially electric energy costs can be saved, and the installation area can be reduced. and installation equipment costs can be reduced.

In addition, by using a compressor (COM) connected to the expander (EXP), boil-off gas can also be used as fuel without requiring additional power, and the compressed boil-off gas compressed by the compressor (COM) is supplied to the carburetor (30). Liquefied natural gas can also be additionally heated.

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 vaporizer (30), and some of the vaporized gas is re-liquefied and recovered to 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
EXP: Expander
COM: Compressor
GHX: After Cooler
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
GL: Evaporative gas fuel line
31: Liquefied natural gas cooler

Claims (15)

An Otto cycle engine that uses medium- or low-pressure 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 to high pressure;
A vaporizer that vaporizes high-pressure liquefied natural gas compressed by the high-pressure pump;
An expander that generates power using high-pressure natural gas vaporized in the vaporizer and discharges the depressurized natural gas; and
Including a compressor that is axially connected to the expander and compresses the evaporation gas generated by natural vaporization in the storage tank,
A fuel supply system for a liquefied natural gas fuel ship that can supply natural gas that has passed through the vaporizer and expander and boil-off gas compressed in the compressor as fuel for the Otto cycle engine. In claim 1,
As it passes through the expander, the vaporized natural gas forms a gas-liquid mixture,
Further including a gas-liquid separator that separates the gas-liquid mixture,
The liquid separated in the gas-liquid separator is recovered in the storage tank, and the gas separated in the gas-liquid separator is supplied as fuel for the Otto cycle engine, and the methane value of the natural gas fuel supplied to the Otto cycle engine is adjusted. Liquefaction Fuel supply system for natural gas fueled ships. In claim 1,
Further including a fuel supply pump that discharges liquefied natural gas from the storage tank and supplies it to the high pressure pump,
A fuel supply system for a liquefied natural gas fuel ship that supplies natural gas compressed by the high pressure pump to the vaporizer. In claim 2,
a fuel gas heater that heats the gas separated in the gas-liquid separator to a temperature required by the Otto cycle engine; and
An aftercooler that cools the boil-off gas compressed in the compressor to a temperature required by the Otto cycle engine. The fuel supply system for a liquefied natural gas fuel ship further comprising a. In claim 4,
A liquefied natural gas fuel line that provides a path for supplying liquefied natural gas from the storage tank to the engine; 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,
The fuel supply system for a liquefied natural gas fuel ship, wherein the boil-off gas fuel line joins the liquefied natural gas fuel line at a rear end of the fuel gas heater. In claim 2,
A fuel supply system for a liquefied natural gas fuel ship, which cools the re-liquefied natural gas returned to the storage tank by heat exchanging the compressed liquefied natural gas supplied to the vaporizer and the liquid separated from the gas-liquid separator and recovered to the storage tank. In claim 4,
The Otto cycle engine,
An X-DF engine, a 2-stroke engine, as the propulsion engine of the ship; and
A fuel supply system for a liquefied natural gas fuel ship, including a DFDG (Dual Fuel Diesel Generator Engine), which is a 4-stroke engine as an engine for producing auxiliary power for the ship. In claim 7,
Further including a pressure reducing valve for depressurizing 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. The method of any one of claims 1 to 8,
At least one expander is provided,
A generator that is axially connected to one of the one or more expanders and generates power using the power of the expander; or
A fuel supply system for a liquefied natural gas fuel ship further comprising a brake resistor that is connected to one of the one or more expanders by an axis and consumes excess power of the expander. 1) Compressing the liquefied natural gas discharged from the storage tank to high pressure using a high pressure pump;
2) vaporizing the liquefied natural gas compressed at high pressure using a vaporizer;
3) supplying the natural gas vaporized at high pressure to an expander to depressurize it and simultaneously produce power, and compressing the boil-off gas generated in the storage tank using a compressor connected to the expander; and
4) supplying the vaporized and decompressed natural gas and compressed boil-off gas as fuel for an Otto cycle engine that uses medium- or low-pressure liquefied natural gas as fuel and operates according to the Otto cycle; liquefied natural gas, including; Fuel The method of supplying fuel to a ship. In claim 10,
In step 4),
Supplying the vaporized natural gas in which the gas-liquid mixture is formed by the reduced pressure to a gas-liquid separator to separate gas-liquid,
The gaseous natural gas separated in the gas-liquid separator is supplied as fuel for the Otto cycle engine,
A fuel supply method for a liquefied natural gas fuel ship, wherein the liquid re-liquefied natural gas separated in the gas-liquid separator is recovered to the storage tank. In claim 11,
In step 4),
Heating the gaseous natural gas separated in the gas-liquid separator to the gas fuel temperature condition required by the Otto cycle engine; and
Further including; cooling the compressed evaporative gas to the gas fuel temperature condition required by the Otto cycle engine,
A fuel supply method for a liquefied natural gas fuel ship, wherein the heated natural gas and the cooled boil-off gas are supplied to the Otto cycle engine at the same temperature and pressure. In claim 12,
A fuel supply method for a liquefied natural gas fuel ship further comprising: heat-exchanging the compressed liquefied natural gas supplied to the vaporizer and the re-liquefied natural gas recovered to the storage tank, thereby cooling the re-liquefied natural gas. The method of claim 12 or 13,
The Otto cycle engine,
Includes two types of engines with different gas fuel pressure conditions,
Depressurizing the natural gas and compressed boil-off gas supplied as fuel for the Otto cycle engine to the gas fuel pressure condition required by any one of the two types of engines; fuel for liquefied natural gas fuel ships, further comprising Supply method. In claim 14,
When boil-off gas cannot be supplied to the compressor,
Producing electric power using the power produced by the expander,
A fuel supply method for a liquefied natural gas fuel ship, wherein only the heated natural gas is supplied as fuel to the Otto cycle engine.

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