JP2021011869A - Gas fuel supply system and method of operating gas fuel supply system - Google Patents

Abstract

To provide a device capable of supplying a boil-off gas as a fuel of an internal combustion engine.SOLUTION: A gas fuel supply system includes a boil-off gas pipe 42 for connecting a boil-off gas outlet of a storage tank 26 to an inlet of a compressor unit 48 and guiding flow of the boil-off gas to the compressor unit, and a first heat exchanger 43. The boil-off gas pipe is passed through the first heat exchanger so that heat of the boil-off gas flow is exchanged in the first heat exchanger, and the compressor unit creates a pressurized gas fuel flow by increasing a pressure of the boil-off gas flow. A re-liquefaction pipe 46 is connected to an outlet of the compressor unit so that a second part of the pressurized gas fuel flow is passed through the first heat exchanger for heat exchange with the boil-off gas flowing in the first heat exchanger, and continuously the second part of the pressurized gas fuel flow is passed through a high-pressure vaporizer for heat exchange with the high-pressure liquefied fuel flow flowing in a high-pressure vaporizer 38 or the vaporized gas fuel.SELECTED DRAWING: Figure 6

Description

The present specification relates to a gas fuel supply system for supplying high-pressure gas fuel to a cross-head type large two-stroke uniflow scavenging internal combustion engine, and a method for operating the gas fuel supply system.

background

The crosshead large 2-stroke uniflow scavenging internal combustion engine is used, for example, as a propulsion system for a large ship or as a prime mover for a power plant. The size of this large two-stroke engine is huge. This large two-stroke engine has a structure different from other internal combustion engines, not only because of its huge size.

Turbo supercharged large 2-stroke uniflow scavenging internal combustion engines often use gas fuels such as liquefied natural gas (LNG) and liquefied petroleum gas (LPG) instead of traditional marine diesel fuel and heavy oil. There is. The reason for replacing gas fuel is mainly to reduce emissions and to provide environmentally friendly prime movers.

Technological development towards the use of gas fuel has led to the development of two different types of turbocharged large two-stroke internal combustion engines that use gas fuel as the main fuel.

One of them is a direct injection type engine. In this type of engine, gas fuel is injected at high pressure near top dead center (TDC) and ignited by the high temperature generated by compression. That is, it ignites according to the diesel cycle. The gas fuel ignites the moment it is injected into the combustion chamber, and there is no concern about pre-ignition (premature ignition) due to the low excess air rate or misfire due to the high excess air rate. The efficient compression ratio for this first type turbocharged large two-stroke uniflow scavenging internal combustion engine operated on gas fuel is the conventional turbocharged large two stroke uniflow scavenging internal combustion engine using liquid fuel. As high as the efficient compression ratio of, and higher. Typically, the efficient compression ratio of this type of engine is from about 15 to about 17, while the geometric compression ratio is about 30. The advantage of the first type of engine described above is the very good fuel efficiency, which comes from the high compression ratio. Another advantage of the first type of engine described above is that it has a much lower risk of pre-ignition and misfire than the second type of engine described below.

However, in order to inject gas fuel near the TDC, the pressure of the gas fuel supplied to the fuel valve that injects the gas fuel into the combustion chamber must be much higher than the compression pressure of the combustion chamber. In fact, the gas fuel injected into the combustion chamber must have a pressure of at least 250 bar, preferably 300 bar. The pump station pressurizes the liquefied gas fuel to, for example, 300 bar, then vaporizes the high pressure liquefied fuel in the high pressure vaporization unit and delivers it to the fuel injection valve of the main engine in the form of high pressure gas. This supply system is more expensive than the conventional supply system for liquid fuels.

Gas fuels such as natural gas have a much lower energy density than conventional fuels. To be a useful energy source, the density must be increased. This is done by cooling the gas fuel to a very low temperature. For example, in the case of natural gas, it is made by using liquefied natural gas (LNG).

For this reason, gas fuel supply systems for engines operated on gas fuel include an adiabatic tank for storing liquefied gas. The adiabatic tank keeps the liquid state for a long time. However, the surrounding heat flux raises the temperature inside the tank, causing the liquefied gas to vaporize. The gas resulting from this process is called Boil-Off Gas (BOG). Boil-off from the tank forms a practical steady flow of gas fuel. It must be removed from the tank and some action must be taken. For an 18000000 m3 LNG tanker, the amount of BOG that needs to be dealt with can reach several tons per hour. Typically about 3000 kg / hour. On the other hand, the gas required by the main engine of this type of LNG tanker is approximately 4000 kg / hour, assuming that the energy source of the main engine is all natural gas.

However, it is technically very difficult to pressurize the boil-off gas with a compressor to an injection pressure of about 300 bar. Therefore, BOG cannot be used as fuel for the above-mentioned first type turbocharged large two-stroke internal combustion engine.

BOG can also be pressurized to 10 to 20 bar using a compressor. It can then be used in gas fuel generators operated at this pressure. Ships often include a set of such generators in addition to a turbocharged large two-stroke internal combustion engine. Such generators are often 4-stroke internal combustion engines, which are much smaller than turbocharged large 2-stroke internal combustion engines, and drive generators and alternators that generate electricity and heat used in ships.

The BOG can also be reliquefied in a cryogenerator. However, reliquefaction requires expensive equipment and consumes a considerable amount of energy.

Also, in an emergency, the BOG simply burns.

WO2016058611A1 discloses a first type large two-stroke uniflow scavenging turbocharged internal combustion engine.

DK201670361A1 also discloses a first type large two-stroke uniflow scavenging turbocharged internal combustion engine. The document also discloses a gas supply system for delivering high pressure gas fuel for high pressure injection into the combustion chamber.

The second type of engine is called a low pressure gas engine. In this type of engine, gas fuel is mixed with scavenging. The second type of engine compresses the mixture of gas fuel and scavenging in the combustion chamber. In the second type of engine, gas fuel is injected through a fuel valve provided in the middle of the cylinder liner. Fuel is injected during the compression stroke of the piston, well before the fuel valve closes. The piston compresses the gas fuel and scavenging air-fuel mixture in the combustion chamber, and the compressed air-fuel mixture is ignited near top dead center (TDC) by timely ignition means (for example, injection of pilot oil). Will be done. The advantage of this second type of engine is that it can be operated with gas fuel supplied at a relatively low pressure (eg about 15 bar). This is because the pressure in the combustion chamber when the gas fuel is injected is relatively low. Therefore, the second type engine can be operated by the BOG boosted by the pressure boosting means. Therefore, the gas supply system for the second type of engine is cheaper than the gas supply system for the first type of engine. In the case of the first type of engine, the BOG flow generated from the tank must be processed, and the set of boilers and generators can use only a part of this BOG flow. For this reason, a relatively expensive reliquefaction system must be introduced to operate in the gas supply system of the first type of engine.

However, since the second type engine compresses the air-fuel mixture in the combustion chamber, the effective compression ratio is considerably lower than that of the first type engine. Typically, the effective compression ratio of the first type engine is between about 15 and about 17. In contrast, the effective compression ratio of the second type engine is between about 7 and about 9. The geometric compression ratio of the second type engine is about 13.5. This very low, geometrically defined compression ratio significantly reduces the fuel efficiency of the second type engine relative to the first type engine, compared to the first type engine of the same size. This causes the maximum continuous rotation speed of the second type engine to decrease.

In addition, the second type of engine usually requires a prechamber or synchronous ignition system to achieve reliable ignition.

A further disadvantage of the second type of engine is that the excess air ratio and bulk temperature during the compression stroke of the piston must be controlled very accurately. This is to prevent pre-ignition due to (local) too low air excess and / or too high bulk temperature, and to prevent misfire due to too high air excess and / or too low bulk temperature. Proper mixing that results in a uniform mixture is very important for local conditions in the combustion chamber that result in pre-ignition and misfire. Controlling these conditions in the combustion chamber is particularly difficult in transient operation.

KR20130051539 discloses the engine according to the preamble of claim 1 of the present application and the method according to the preamble of the method according to claim 6 of the present application.

DK201770703 discloses a second type large two-stroke uniflow scavenging turbocharged internal combustion engine.

As described above, in a large two-stroke uniflow scavenging internal combustion engine operated by gas fuel as a main fuel, there is a need to eliminate or alleviate the above-mentioned weaknesses of the first type and second type engines. ..

Further, in a gas supply system for supplying gas fuel to a large two-stroke uniflow scavenging internal combustion engine and providing high-pressure gas fuel used for combustion of a large two-stroke uniflow scavenging internal combustion engine, the gas supply system described above. There is a need to eliminate or mitigate the weaknesses of.

Description

An object of the present invention is to provide an engine and gas fuel supply system, and a method that solves or at least alleviates the above-mentioned problems.

The above objectives and other objectives are achieved by the characteristics described in the independent claims. More specific implementations will become apparent from the dependent claims, detailed description of the invention, and drawings.

According to the first aspect, a system for supplying pressurized gas fuel to the main engine of a ship and the gas fuel consuming device of the ship is provided. This system
With a storage tank that stores liquefied gas fuel under cryogenic conditions;
With a high-pressure cryopump unit having an inlet connected to the storage tank for receiving a supply of liquefied gas fuel;
With the first supply pipe connected to the outlet of the high pressure cryopump unit;
With a high pressure vaporizer;
To be equipped.
The first supply pipe extends from the outlet of the high-pressure cryopump unit to guide the high-pressure liquefied gas fuel flow to the high-pressure vaporizer and change it into a high-pressure gas fuel flow for the main engine, and the high-pressure vaporization. Pass through the vessel.
The system further
With a boil-off gas pipe that connects the boil-off gas outlet of the storage tank to the inlet of the compressor unit and guides the flow of boil-off gas to the compressor unit;
With the first heat exchanger;
To be equipped.
The boil-off gas pipe passes through the first heat exchanger so that the heat exchange of the boil-off gas flow takes place in the first heat exchanger.
The compressor unit increases the pressure of the boil-off gas stream to create a pressurized gas fuel stream.
The system further
With a second supply pipe connected to the outlet of the compressor unit to deliver a first portion of the pressurized gas fuel stream to one or more devices consuming the pressurized gas fuel;
The second portion of the pressurized gas fuel stream is passed through the first heat exchanger and subsequently flows through the high pressure vaporizer for heat exchange with the boil-off gas flowing through the first heat exchanger. Reliquefaction connected to the outlet of the compressor unit to pass the second portion of the pressurized gas fuel stream through the high pressure vaporizer for heat exchange with the high pressure liquefied fuel stream or vaporized gas fuel. With a tube;
To be equipped.

A special complicated and expensive reliquefaction device is used by cooling a part of the pressurized gas fuel flow coming from the compressor with the boil-off gas in the heat exchanger and further cooling with the high pressure gas fuel flow in the high pressure vaporizer. A part of the boil-off gas can be reliquefied without the gas, and the heat energy that must be discarded unless it is used for the reliquefaction can be used for the reliquefaction treatment.

In one example of the implementation of the first aspect, the system comprises a throttle device, such as an expansion valve, in the reliquefaction tube downstream of the vaporization unit. This is to provide the second portion of the pressurized gas flow to the throttle process. By passing the pressurized gas fuel flow through the throttle device, the temperature and pressure of the gas fuel are significantly reduced. As a result, more parts are reliquefied.

In one example of the implementation of the first aspect, the system comprises a separation vessel connected to the reliquefaction tube downstream of the high pressure vaporizer or downstream of the throttle device. This is to collect the liquefied gas fuel produced by the cooling effect of the high pressure vaporizer and / or the throttle process and separate the excess gas fuel from the reliquefied gas fuel.

In one example of the implementation of the first aspect, the system comprises a reliquefied gas pipe that connects the liquid outlet of the separation container to the inlet of the storage tank. This is to deliver the reliquefied gas fuel to the storage tank.

Further, a gas recirculation path for connecting the gas discharge port of the separation container to the boil-off gas building is also provided.

In an example of the implementation of the first aspect, the system includes a heater in the first supply pipe downstream of the vaporization unit. This is to warm the high pressure gas fuel stream before supplying it to the main engine.

In an example of the implementation of the first aspect, the main engine is one of the devices that consumes pressurized gas fuel.

According to the second aspect, a method of supplying a high pressure gas fuel flow to the main engine of the ship and a method of supplying the pressurized gas fuel flow to the pressurized gas consuming device of the ship are provided. This method
Storing liquefied gas fuel under cryogenic conditions;
To create a high-pressure liquefied gas fuel flow by sending the liquefied gas fuel flow taken out from the stored liquefied gas fuel to a high-pressure pump;
To vaporize the high-pressure liquefied gas fuel stream into a gas fuel stream;
To supply the high pressure gas fuel flow to the main engine;
To guide the boil-off gas flow from the stored liquefied gas fuel to the compressor to create a pressurized gas fuel flow;
Supplying a first portion of the pressurized gas fuel stream from the compressor to a device consuming the pressurized gas fuel;
To guide the second part of the pressurized gas fuel stream from the compressor to the reliquefaction tube;
To exchange heat with the boil-off gas stream;
Subsequently, the second part is heat-exchanged with the high-pressure liquefied gas fuel stream;
including.

The advantages of the above method are the same as the advantages of the device of the first aspect.

In one example of the implementation of the second aspect, the method comprises reliquefying at least a third portion of the pressurized gas fuel stream and adding it to the stored liquefied gas fuel.

In an example of the implementation of the second aspect, the method comprises adding the residual gas of the second portion to the boil-off gas stream.

In one example of the implementation of the second aspect, the method comprises passing the second portion through a throttle device.

These and other aspects will be further clarified by the examples described below.

Hereinafter, various aspects, embodiments, and implementation examples will be described in detail with reference to the exemplary embodiments shown in the drawings.
FIG. 5 is a front view of a large two-stroke engine according to an exemplary embodiment. It is a side view of the large 2-stroke engine engine of FIG. It is the first schematic representation of the large two-stroke engine of FIG. It is sectional drawing of the cylinder frame and the cylinder liner of the engine of FIG. Cylinder covers and exhaust valves are attached and pistons at TDC and BDC are also depicted. It is a graph depicting a gas exchange and a fuel injection cycle. It is a schematic representation of a gas fuel supply system according to an embodiment. It is a schematic representation of a gas fuel supply system according to another embodiment. FIG. 3 is a cross-sectional view of a cylinder frame and cylinder liner according to another embodiment.

Detailed explanation

In the following detailed description, the internal combustion engine will be described with reference to the crosshead type large low-speed 2-stroke turbocharged internal combustion engine of the embodiment. 1 to 3 show an example of a turbocharged large low-speed 2-stroke internal combustion engine. This engine has a crankshaft 8 and a crosshead 9. FIG. 1 is a front view and FIG. 2 is a side view. FIG. 3 is a schematic representation of the turbocharged large low-speed 2-stroke diesel engine of FIGS. 1 and 2 together with its intake system and exhaust system. In this example, the engine has four cylinders in series. A turbocharged, large, low-speed, two-stroke internal combustion engine typically has 4 to 14 cylinders arranged in series. These cylinders are supported on the engine frame 11. Further, such an engine can be used, for example, as a main engine of a ship or a fixed engine for operating a generator in a power plant. The total output of the engine can be, for example, 1,000 kW to 110,000 kW.

The engine combines a diesel cycle and an Otto cycle in certain modes of operation in which it operates on gas fuel as the main fuel. This is a compression ignition because it compresses a mixture of air and fuel. This fuel is a first amount of pressurized gas fuel introduced in the middle of the compression stroke of the piston 10. The compressed air-fuel mixture is ignited when a second amount of high pressure gas fuel is injected near the TDC.

The engine can operate according to the diesel cycle in another mode of operation, in which case no fuel is introduced during the compression stroke. In this mode, all fuel is injected near the TDC. The main fuel in this mode can also be gas fuel. In yet another mode of operation, the engine can operate according to the Otto cycle. In this case, all gas fuels are mixed in the scavenging and the air-fuel mixture is compressed during the compression stroke. Then, in the vicinity of the TDC, a means for igniting at the right timing is provided.

The engine in this embodiment is a two-stroke uniflow scavenging engine, in which a scavenging port 18 is provided in the lower region of the cylinder liner 1, and an exhaust valve 4 is arranged in the center of the top of the cylinder liner 1. The combustion chamber is defined by a cylinder liner 1, a cylinder cover 22, and a piston 10 that reciprocates between bottom dead center (BDC) and top dead center (TDC) in the cylinder liner.

The scavenging is guided from the scavenging receiver 2 to the scavenging port 18 at the lower end of each cylinder 1 when the piston is below the scavenging port 18. The gas fuel is introduced from the gas fuel introduction valve 30 under the control of the electronic control unit 60. This is done during the ascending stroke of the piston and before the piston passes through the fuel valve (gas fuel introduction valve) 30. The fuel valves are preferably arranged so as to be evenly spaced over the circumference of the cylinder liner. Further, it is preferably arranged near the center in the longitudinal direction of the cylinder liner. Therefore, the introduction of gas fuel is performed when the compression pressure is relatively low. That is, it is performed when the compression pressure when the piston 10 reaches TDC is much lower than the compression pressure.

Within the cylinder liner 1, the piston 10 compresses a mixture of gas fuel and scavenging air. Then, high-pressure gas fuel is injected from the fuel injection valve 50 at or near the TDC. Ignition is triggered according to the principle of diesel by the high temperature caused by the high pressure in the combustion chamber at or near the TDC. Ignition may be assisted by a small amount of pilot oil (or suitable ignition liquid). In some cases, this pilot oil is injected from the fuel injection valve 50 together with the gas fuel, but in other cases, it is configured to be supplied from a dedicated pilot oil valve 51 (not shown). is there. In that case, the pilot oil valve 51 is preferably arranged on the cylinder cover 22.

Note that "TDC or its vicinity" and "TDC or its vicinity" mean that gas fuel is injected. Refers to a range. This range begins at about 15 degrees before TDC at the earliest and ends at about 40 degrees after TDC at the latest.

Combustion occurs and exhaust gas is produced. Other forms of ignition systems use prechambers, laser ignitions, glow plugs (neither shown), etc. in place of or in addition to pilot oils to facilitate ignition.

When the exhaust valve 4 is opened, the exhaust gas flows to the exhaust gas receiver 3 through the exhaust duct provided in the cylinder 1, and further proceeds to the turbine 6 of the turbocharger 5 through the first exhaust pipe 19. .. From there, the exhaust gas flows through the second exhaust pipe 25 to the economizer 20 and is further discharged into the atmosphere from the outlet 21. The turbine 6 drives the compressor 7 via a shaft. Outside air is supplied to the compressor 9 through the air intake port 12. The compressor 7 sends the compressed scavenging air to the scavenging pipe 13 connected to the scavenging receiver 2. The scavenging of the pipe 13 passes through the intercooler 14 for cooling the scavenging air.

The cooled scavenging air passes through an auxiliary blower 16 driven by an electric motor 17. The auxiliary blower 16 compresses the scavenging airflow when the compressor 7 of the turbocharger 5 is unable to supply the pressure required for the scavenging receiver 2, that is, when the engine is underloaded or partially loaded. When the engine load is high, the turbocharger compressor 7 can supply a fully compressed scavenger so that the auxiliary blower 16 is bypassed by the check valve 15.

FIG. 3 shows a controller 60 such as an electronic control unit. The controller 60 is connected to various sensors through signal lines or other communication channels, and these sensors convey information about the operating conditions of the engine to the controller 60. The controller 60 is also connected to various engine components controlled by the controller 60 through signal lines or other communication channels. One of the above sensors is a crank angle sensor, which is illustrated. This transmits the rotation angle of the crankshaft 8 to the controller 60. The controller 60 controls the fuel introduction valve 30, the fuel injection valve 50, and the exhaust valve 4.

The controller 60 is connected to the fuel introduction valve 30 and the fuel injection valve 50 and controls them. The controller 60 operates the fuel introduction valve 30 so that the piston 10 introduces the first amount of gas fuel from the second source 40 of the pressurized gas fuel into the combustion chamber in the middle of the stroke from the BDC to the TDC. Let me. The controller 60 also injects a second amount of gas fuel from the first source 35 of the pressurized gas fuel into at least one of the combustion chambers when the piston 10 is at or near top dead center. The injection valve 50 is operated.

FIG. 4 illustrates a cylinder liner 1 designed for a large crosshead two-stroke engine. Depending on the size of the engine, the cylinder liner 1 can be made in various sizes. Typical sizes are 250 mm to 1000 mm in diameter and the corresponding overall length is 1000 mm to 4500 mm.

In FIG. 4, the cylinder liner 1 is mounted on the cylinder frame 23, and the cylinder cover 22 is mounted on the cylinder liner 1. The cylinder liner 1 and the cylinder cover 22 are connected so that gas does not leak between them.

In FIG. 4, the state of the piston 10 at the bottom dead center (BDC) and the top dead center (TDC) is shown by a broken line. Of course, these two states do not occur at the same time, and these two states are separated by 180 degrees by the rotation angle of the crankshaft 8. The cylinder liner 1 is provided with a cylinder lubrication hole 25 and a cylinder lubrication line 24. These supply cylinder lubricating oil as the piston 10 passes through the lubrication line 24. A piston ring (not shown) then distributes the cylinder lubricant across the running surface of the cylinder liner.

The fuel valve 50 is mounted on the cylinder cover 22. Usually, in each cylinder, two or three fuel injection valves 50 are distributed around the exhaust valves at the same spacing. The fuel injection valve 50 is connected to the first source 35 of the high pressure gas fuel through the first supply pipe 36, and is connected to the pilot oil source 27 through the pilot line 28.

The third amount of igniting liquid is less than 5% of the caloric value of all fuels put into the combustion chamber during a given engine cycle. Preferably less than 3%.

The fuel valve 50 may be of the type disclosed in DK178519B1. This type of fuel valve has the ability to inject a small amount of pilot oil into the combustion chamber with a sufficient amount of high pressure gas fuel.

The injection timing of the high-pressure gas fuel and the pilot oil by the fuel injection valve 50 is controlled by the electronic control unit 60. The electronic control unit 60 is connected to the fuel valve 50 through a signal line shown by a broken line in FIG.

The cylinder liner 1 is equipped with a fuel introduction valve 30. The fuel introduction valve 30 has a nozzle or an introduction port located on substantially the same surface as the inner surface of the cylinder liner 1. The rear end of the fuel introduction valve 30 protrudes from the outer wall of the cylinder liner 1. Typically, one or two, at most three or four fuel introduction valves 30, are provided in each cylinder liner 1. These are arranged at equal intervals in the circumferential region of the cylinder liner 1. In this embodiment, the fuel introduction valve 30 is arranged at the center of the cylinder liner 1 in the longitudinal direction.

The injection timing of the pressurized gas fuel by the fuel injection valve 30 is controlled by the electronic control unit 60. In FIG. 3, the electronic control unit 60 is connected to the fuel introduction valve 30 through a conceptually shown signal line.

The engine is configured to introduce a first amount of pressurized gas fuel and inject a second amount of high pressure gas fuel during one engine cycle. First, a first amount of pressurized gas fuel is introduced, and then a second amount of high pressure gas fuel is injected at the opportunity for the piston to approach the TDC (this is sometimes referred to as the first opportunity).

FIG. 4 is a conceptual and simplified drawing of the engine gas fuel supply system. A first source 35 of high-pressure gas fuel is connected to each fuel injection valve 50 of the cylinder cover 22 through a first supply pipe 36. Further, a second source 40 of the medium pressure gas fuel is connected to the inlet of the gas fuel valve 30 through the fuel supply pipe 41.

In this embodiment, the pressure P1 of the first source 35 of the high pressure gas fuel is approximately 15 to 45 MPa (150 to 450 bar). This high pressure makes it possible to inject gas fuel against peak pressures near the TDC.

In this embodiment, the pressure P2 of the second source 40 of the medium pressure gas fuel is approximately 1 to 3 MPa (10 to 30 bar). The pressure is medium compared to P1. However, with this pressure, gas fuel can be introduced during the compression stroke.

FIG. 5 shows that the scavenging port 18, the exhaust valve 4, the fuel introduction valve (GA fuel valve) 30, and the fuel injection valve (Gi fuel valve) are opened as a function of the crank angle (the angle of the crankshaft 8). The opening) period and the valve closing (closing) period are illustrated. Looking at this graph, we can see that the window for introducing gas fuel is relatively short. Therefore, the time for mixing the gas fuel with scavenging in the combustion chamber is extremely short. Gas fuel is introduced in a very short window. High pressure gas fuel is injected between the windows near the TDC.

The total amount of gas fuel introduced and injected during one revolution is affected by the load on the engine. The total amount of gas fuel charged into the combustion chamber is the total amount of the first amount of gas fuel introduced into the cylinder at pressure P2 and the high-pressure gas fuel injected into the cylinder at pressure P2. In one embodiment, approximately 70% or 80% of the gas fuel charged into the cylinder in calorie value is the gas fuel introduced at pressure P2 from the second source 40 of the pressurized gas fuel. In one embodiment, approximately 70% or 80% of the gas fuel charged into the cylinder in calorie value is the gas fuel injected at pressure P1 from the first source 35 of the high pressure gas fuel.

In this way, the ratio of the first amount to the second amount can be adjusted and adapted to the amount of fuel available from each source. For example, if the high pressure fuel available from the first source 35 of the high pressure gas fuel is relatively low, the engine will have a medium pressure introduced into the cylinder during the compression stroke from the second source 40 of the high pressure gas fuel. It can be operated by using a large amount of gas fuel and using a relatively small amount of high-pressure gas fuel injected at or near the TDC. On the other hand, when the medium pressure gas fuel available from the second source 40 of the pressurized gas fuel is relatively small, the engine uses a large amount of the high pressure gas fuel injected at or near the TDC, and the pressure gas fuel is the first. The fuel introduced into the cylinder from the source 40 of No. 2 during the compression stroke is relatively small and can be operated.

FIG. 6 is a schematic representation of a gas supply system that can be used to supply gas fuel to a large two-stroke turbocharged internal combustion engine, for example as depicted in FIGS. This gas supply system is an embodiment that can be mounted on a liquefied gas tanker, that is, a ship that carries a large amount of liquefied gas fuel such as liquefied natural gas (LNG) and liquefied petroleum gas (LPG).

This gas supply system is configured to supply pressurized gas fuel to the main engine of the ship and the gas fuel consuming device of the ship. The gas fuel consuming device includes, for example, a set of generators for generating heat and electricity used in a ship, a boiler operated by gas fuel, and the like. The above generator is usually a 4-stroke internal combustion engine, which is significantly smaller than the main engine of a ship and drives a generator or alternator. In particular, it is also used when the main engine of the ship is stopped, such as when the ship is parked at a port for loading and unloading cargo.

The gas supply system is also configured to supply high pressure gas fuel for injecting gas fuel at or near the TDC.

This gas supply system can be the second source 40 of the pressurized gas fuel, that is, the source 40 that supplies the gas fuel at a pressure P2 (eg 10-30 bar), as indicated by reference numeral 40. The second source 40 of the pressurized gas fuel is shown by the dashed rectangle in FIG. The gas supply system can also be the first source 35 of the high pressure gas fuel, which has been indicated by reference numeral 35, i.e. the source 35 which supplies the gas fuel at a high pressure P1 (eg 150-450 bar). In FIG. 6, the first source 35 of the high pressure gas fuel is also indicated by a broken line rectangle.

The gas fuel supply system includes one or more storage tanks 26 for storing liquefied gas fuel under cryogenic conditions and a high pressure prio pump 37. The inlet of the high pressure cryopump unit 37 is connected to the storage tank 26 to receive the supply of liquefied gas fuel. The cryogenic liquefied gas fuel stream to the high pressure cryopump typically has a pressure between a pressure slightly above 0 and about 10 bar, such as about 5 bar, and also has a temperature of, for example, about 110 K.

A first supply pipe 36 is connected to the outlet of the high-pressure cryopump unit 37, and a high-pressure liquefied gas fuel flow is sent from the high-pressure pump 37 to the high-pressure vaporizer 38. The (vaporized) high-pressure liquefied gas fuel stream is sent from the high-pressure vaporizer 38 through the heater 39 to the high-pressure fuel injection system of the main engine. Passing the high pressure gas fuel stream through the heater 39 may be the case. This step may be necessary to ensure that the gas fuel delivered to the main engine injection system has a temperature sufficient for the injection system to handle. Such a need also depends on the material and configuration of the injection system. Many injection systems are not suitable for handling very low temperatures, which often requires raising the high pressure gas fuel stream.

The high pressure liquefied fuel stream discharged from the high pressure cryopump unit 37 typically has a pressure of 150 to 450 bar. For example, 350 bar. The temperature is, for example, about 119K. The high pressure (vaporization) gas fuel stream from the high pressure vaporizer 38 typically has a pressure of 150 to 450 bar. For example, 350 bar. The temperature is, for example, about 154K. When the high pressure gas fuel passes through the heater 39, the pressure is almost unchanged, but the temperature becomes, for example, 318K.

As described above, the high-pressure liquefied gas fuel flow in a certain embodiment has a pressure of 150 bar or more and is converted from the high-pressure liquefied gas fuel flow into a high-pressure gas fuel flow to be injected into the main engine. It passes through the high pressure vaporizer 38.

The boil-off gas pipe 42 connects the boil-off gas outlet of the storage tank 26 to the inlet of the compressor unit, and guides the boil-off gas flow to the compressor unit 48. A first heat exchanger 43 is provided in the boil-off gas pipe 42 to raise the temperature of the boil-off gas flow sent to the compressor unit 48. In one embodiment, the pressure of the boil-off gas in the boil-off gas pipe 42 is approximately 1 bar. The temperature is, for example, about 140K. When it passes through the first heat exchanger 43, it is heated to, for example, about 230K.

The compressor unit 48 increases the pressure of the boil-off gas stream to generate a pressurized gas fuel stream. The pressure of the pressurized gas fuel stream at the outlet of the compressor unit 48 is, for example, about 15 bar, and the temperature is, for example, about 318 K. Depending on the embodiment, the compressor unit 48 may be a single-stage compressor or a multi-stage compressor unit. In the case of multi-stage, a cooler 45 may be provided in each stage.

A second supply pipe 41 is connected to the outlet of the compressor unit 48 to send the first portion of the pressurized gas fuel stream to one or more devices consuming the pressurized fuel. The device includes, for example, a main engine that introduces pressurized gas fuel during the compression stroke. The device may also include a set of generators or a boiler to which pressurized gas fuel is supplied through the supply pipe 47.

A reliquefaction pipe 46 is also connected to the outlet of the compressor unit 48. This allows a second portion of the pressurized gas fuel stream to pass through the first heat exchanger 43 for heat exchange with the boil-off gas flowing through the first heat exchanger 43, followed by a high pressure vaporization unit 38. The second portion of the pressurized gas fuel stream is passed through the high pressure vaporization unit 38 for heat exchange with the flowing high pressure liquefied fuel stream or vaporized gas fuel. After passing through the heat exchanger 43, the temperature of the pressurized gas fuel stream becomes, for example, about 159K, but the pressure remains almost unchanged and remains at about 15 bar. After passing through the high pressure vaporizer 38, the pressurized gas fuel stream is cooled by the vaporized high pressure gas fuel stream, and the temperature becomes, for example, 122K. The pressure remains almost unchanged, remaining at about 15 bar. Then, most of the pressurized gas fuel flow in the reliquefaction pipe 46 is reliquefied.

Downstream of the high-pressure vaporizer 38, the reliquefaction pipe 46 is connected to the separation container 32, and the liquefied gas fuel produced by the cooling action of the high-pressure vaporizer 38 is collected. The separation container 32 separates the reliquefied gas fuel from the still gaseous fuel. A reliquefied gas pipe 33 is connected between the liquid discharge port of the separation container 32 and the inlet of the storage tank 26, and guides the reliquefied gas fuel to the storage tank 26. Further, a gas recirculation path 34 is connected between the gas discharge port of the separation container 32 and the boil-off gas pipe 42 so that the remaining gas fuel can be added to the liquefaction cycle again.

FIG. 7 depicts another embodiment of a gas fuel supply system. However, this embodiment is almost identical to the gas fuel supply system according to the embodiment of FIG. In the embodiment of FIG. 7, the same or corresponding configurations and features as the structures and features already described or illustrated are designated by the same reference numerals as those previously used.

In this embodiment, a throttle device 29, such as an expansion valve, is provided in the reliquefaction tube 46. The throttle device 29 is arranged between the vaporizer 38 and the separation vessel 32 and adds a throttle process to the second portion of the pressurized gas fuel stream.

In one embodiment, the throttle device 29 is an expansion valve. The throttle device 29 adds a further cooling effect. This effect is known as the Joule-Thomson effect (or Joule-Thomson effect, Kelvin-Jule effect). The Joule-Thomson effect is a heat exchange between a real gas or liquid (different from an ideal gas) and the external environment. The temperature change when passed through a valve or a porous plug in a situation where gas is not provided will be described. This process is called the throttle process or the Joule-Thomson process. Gas fuels such as natural gas and petroleum gas expand and cool according to the Joule-Thomson process when they are throttled through an orifice. The throttle process for cooling a gas is widely used in cooling devices such as air conditioners, heat pumps, and liquefiers.

The liquefaction of boil-off gas in the gas fuel supply system is similar to the Hampson-Linde cycle. (The Hampson-Linde cycle is widely used for gas liquefaction.) The Hampson-Linde cycle relies on the Joule-Thomson effect and has the following steps.
1) Heating: Heating is performed by compressing the gas in the compressor unit 48. That is, external energy is added to the pressurized gas fuel. This is to give you what you need to run the Hampson-Linde cycle.
2) In the heat exchanger 43, it is cooled by the return gas from the subsequent (and last) stage.
3) Cooling: This is done by exposing the gas to a chilled environment. In the high pressure vaporizer 38, some heat (and therefore energy) is lost.
4) Further cooling: This is done by passing gas through the Joule-Thomson orifice. Heat is taken away, but energy is preserved. However, it is potential energy, not kinetic energy.

By these steps, most of the gas fuel is reliquefied and the remaining gas fuel is the coldest in the current cycle. It is recycled and returned to the compressor unit 46 for use as coolant in the heat exchanger 43 for heating, returning to the first stage and initiating the next cycle. Then, it is heated again by the compressor unit 46.

The gas supply system is relatively simple, the compressor provides a pressure of approximately 10-20 bar and can handle all boil-off gas produced from the storage tank. The high pressure vaporization system can supply 30-50% of the total fuel required at maximum engine load.

Therefore, this gas supply system is inherently redundant. Therefore, it is not necessary to provide a separate system for providing redundancy, and the cost can be saved.

FIG. 8 depicts a further embodiment of a large two-stroke turbocharged internal combustion engine. The gas fuel supply system is basically the same as the gas fuel supply system of the embodiment shown in FIG. 1-4. In the embodiment of FIG. 8, the same or corresponding configurations and features as those already described or illustrated are designated by the same reference numerals as those previously used. The main difference of this embodiment as compared with the embodiment of FIG. 1-4 is that the gas fuel introduction valve 30 is mounted on the cylinder cover 22. In this embodiment, all of the fuel valves 30 and 50 are arranged on the cylinder cover 22.

Many aspects and implementations have been described with some examples. However, considering the specification, drawings, and claims of the present application, those skilled in the art have many variations in carrying out the inventions described in the claims in addition to the described examples. You will be able to understand and embody that. The terms "prepared", "have", and "include" described in the claims do not preclude the existence of elements or steps that are not described. Even if it is not explicitly stated that the number of elements described in the claims is plural, it does not exclude the existence of multiple elements. The functions of some of the elements described in the claims may be performed by a single processor, controller, or other unit. Even if some matters are described in separate dependent claims, it does not exclude the combination of these, and the combination can be profitable.

The codes used in the claims should not be construed as limiting the scope of the invention.

Claims (9)

A system for supplying pressurized gas fuel to the main engine of a ship and the gas fuel consuming device of the ship.
With a storage tank (26) that stores liquefied gas fuel under cryogenic conditions;
With a high-pressure cryopump unit (37) having an inlet for receiving the supply of liquefied gas fuel and having an inlet connected to the storage tank (26);
With the first supply pipe (36) connected to the outlet of the high pressure cryopump unit;
With high-pressure vaporizer (38);
The first supply pipe guides the high-pressure liquefied gas fuel flow to the high-pressure vaporizer (38) and changes the high-pressure gas fuel flow for the main engine into the high-pressure cryopump unit (37). Extending from the outlet of the high pressure vaporizer (38), the system further
With a boil-off gas pipe (42) that connects the boil-off gas outlet of the storage tank (26) to the inlet of the compressor unit (48) and guides the boil-off gas flow to the compressor unit (48);
With the first heat exchanger (43);
With
The boil-off gas pipe (42) passes through the first heat exchanger (43) so that the heat exchange of the boil-off gas flow takes place in the first heat exchanger (43).
The compressor unit (48) increases the pressure of the boil-off gas stream to create a pressurized gas fuel stream.
The system further
A second supply pipe (41) connected to the outlet of the compressor unit (48) to deliver a first portion of the pressurized gas fuel stream to one or more devices consuming the pressurized gas fuel. )When;
For heat exchange with the boil-off gas flowing through the first heat exchanger (43), a second portion of the pressurized gas fuel stream is passed through the first heat exchanger (43), followed by the said. The second portion of the pressurized gas fuel stream is passed through the high pressure vaporizer (38) for heat exchange with the high pressure liquefied gas fuel stream or the vaporized gas fuel stream flowing through the high pressure vaporizer (38). As described above, the reliquefaction pipe (46) connected to the outlet (48) of the compressor unit,
The system. In order to apply the throttle process to the second portion of the pressurized gas fuel stream, a throttle device (29) such as an expansion valve is attached to the reliquefaction pipe (46) downstream of the high pressure vaporizer (38). The system according to claim 1. The high pressure vaporizer (38) and / or the separation container (32) for collecting the liquefied gas fuel generated by the cooling effect of the throttle process and separating the excess gas fuel from the reliquefied gas fuel. The system according to claim 2, further comprising a separation container (32) connected to the reliquefaction pipe (46) downstream of the vaporizer (38) or downstream of the throttle device (29). With the reliquefied gas pipe (33), which connects the liquid discharge port of the separation container (32) to the inlet of the storage tank (26) and delivers the reliquefied gas fuel to the storage tank (26);
With the gas recirculation path (34) connecting the gas outlet of the separation container (32) to the boil-off gas pipe (42);
3. The system according to claim 3. One of claims 1 to 4, wherein the one supply pipe (36) downstream of the high pressure vaporizer (38) is provided with a heater (39) in order to warm the high pressure gas fuel flow before supplying it to the main engine. The system described. A method of supplying high-pressure gas fuel to the main engine of a ship and supplying a pressurized gas fuel stream to the pressurized gas consuming device of the ship.
Storing liquefied gas fuel under cryogenic conditions;
To create a high-pressure liquefied gas fuel flow by sending the liquefied gas fuel flow taken out from the stored liquefied gas fuel to a high-pressure pump (37);
To vaporize the high-pressure liquefied gas fuel stream into a gas fuel stream;
To supply the high pressure gas fuel flow to the main engine;
To guide the boil-off gas flow from the stored liquefied gas fuel to the compressor (48) to create a pressurized gas fuel flow;
Supplying the first portion of the pressurized gas fuel stream from the compressor (48) to a device consuming the pressurized gas fuel;
To guide the second portion of the pressurized gas fuel stream from the compressor (48) to the reliquefaction tube (46);
To exchange heat with the boil-off gas stream, and subsequently to exchange heat with the high-pressure liquefied gas fuel stream, the second portion;
Including methods. The method of claim 6, comprising reliquefying at least a portion of the second portion and adding the portion to the stored liquefied gas fuel. The method of claim 7, wherein the residual gas of the second portion is added to the boil-off gas stream. The method according to any one of claims 6 to 8, wherein the second portion is passed through a throttle device (29).