JP7390257B2 - Gas fuel supply system and method of operating a gas fuel supply system - Google Patents

Description

TECHNICAL FIELD This specification relates to a gas fuel supply system for supplying high pressure gas fuel to a large crosshead two-stroke uniflow scavenged internal combustion engine, and a method of operating the gas fuel supply system.

background

A large crosshead two-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 generation plant. The size of this large two-stroke engine is enormous. Not only because of its huge size, but this large two-stroke engine also has a different structure than other internal combustion engines.

Large turbocharged two-stroke uniflow scavenged internal combustion engines are increasingly using gas fuels such as liquefied natural gas (LNG) and liquefied petroleum gas (LPG) instead of conventional marine diesel fuel and heavy oil. There is. The reason why it has replaced gas fuel is primarily to reduce emissions and to provide an environmentally friendly prime mover.

Technological developments towards the use of gas fuels have led to the development of two different types of large turbocharged two-stroke internal combustion engines that use gas fuels as their primary fuel.

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

However, in order to inject the gas fuel near 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 gaseous fuel injected into the combustion chamber must have a pressure of at least 250 bar, preferably 300 bar is desired. The pump station pressurizes the liquefied gas fuel to, for example, 300 bar, and the high-pressure liquefied fuel is then vaporized in a high-pressure vaporization unit and delivered in the form of a high-pressure gas to the fuel injection valves of the main engine. This supply system is more expensive than conventional supply systems for liquid fuels.

Gaseous fuels, such as natural gas, have a very low energy density compared to conventional fuels. To make it a useful energy source, its density must be increased. This is done by cooling the gaseous fuel to cryogenic temperatures. For example, in the case of natural gas, this is done by converting it into liquefied natural gas (LNG).

For this reason, gas fuel supply systems for engines operated on gas fuel include an insulated tank for storing liquefied gas. The insulated tank maintains the liquid state for a long time. However, the ambient heat flux increases the temperature inside the tank, leading to vaporization of the liquefied gas. The gas resulting from this process is called boil-off gas (BOG). The boil-off from the tank creates a virtually constant flow of gaseous fuel. This must be removed from the tank and some action must be taken. For a 1,800,000 m3 LNG tanker, the amount of BOG that needs to be dealt with is several tons per hour. Typically around 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 main engine's energy source is all natural gas.

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

BOG can also be pressurized to 10-20 bar using a compressor. It can then be used in gas-fueled generators operated at this pressure. Ships are often equipped with such generator sets in addition to large turbocharged two-stroke internal combustion engines. These generators are often four-stroke internal combustion engines, much smaller than the larger turbocharged two-stroke internal combustion engines, and drive generators and alternators that produce the electricity and heat used on ships.

BOG can also be reliquefied in a cryogenerator. However, reliquefaction requires expensive equipment and also consumes significantly more energy.

Also, in an emergency, the BOG can simply be burned.

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

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

The second type of engine is called a low pressure gas engine. In this type of engine, gaseous fuel is mixed with scavenging air. A second type of engine compresses a mixture of gaseous fuel and scavenge air in a combustion chamber. In the second type of engine, gaseous fuel is injected through a fuel valve located midway through the cylinder liner. Fuel is injected during the piston's compression stroke, well before the fuel valve closes. The piston compresses a mixture of gas fuel and scavenging air in the combustion chamber, and the compressed mixture is ignited near top dead center (TDC) by timed ignition means (for example, pilot oil injection). be done. The advantage of this second type of engine is that it can be operated on gaseous fuel supplied at relatively low pressure (eg about 15 bar). This is because the pressure within the combustion chamber when gaseous fuel is injected is relatively low. Therefore, the second type of engine can be operated with BOG whose pressure has been increased by the pressure increasing 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 stream originating from the tank has to be treated, and the boiler and generator set can only use a portion of this BOG stream. For this reason, a relatively expensive reliquefaction system must be installed and operated with the gas supply system of the first type of engine.

However, since the second type of engine compresses the air-fuel mixture in the combustion chamber, the effective compression ratio is considerably lower than that of the first type of engine. Typically, the first type of engine has an effective compression ratio between about 15 and about 17. In contrast, the effective compression ratio of the second type of engine is between about 7 and about 9. Note that the geometric compression ratio of the second type of engine is approximately 13.5. This very low, geometrically determined compression ratio makes the fuel efficiency of the second type engine significantly lower relative to the first type engine, and the fuel efficiency of the second type engine relative to the first type engine is significantly lower. This causes the maximum continuous rotation speed of the second type of engine to become low.

Additionally, the second type of engine typically requires a prechamber or synchronous ignition system to achieve reliable ignition.

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

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

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

Thus, there is a need for eliminating or mitigating the above-mentioned weaknesses of first and second type engines in large two-stroke uniflow scavenged internal combustion engines operated with gas fuel as the primary fuel. .

Further, in a gas supply system that supplies gas fuel to a large two-stroke uniflow scavenging internal combustion engine, the gas supply system provides high pressure gas fuel used for combustion in the large two-stroke uniflow scavenging internal combustion engine. A need exists for eliminating or mitigating the weaknesses of.

Abstract

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

The above-mentioned and other objects are achieved by the features set out in the independent claims. More specific implementation forms will become apparent from the dependent claims, the detailed description of the invention, and the drawings.

According to a first aspect, a system is provided for supplying pressurized gas fuel to a main engine of a ship or a gas fuel consumption device of the ship. This system is
a storage tank for storing liquefied gas fuel in cryogenic conditions;
a high-pressure cryopump unit having an inlet connected to the storage tank for receiving a supply of liquefied gas fuel;
a first supply pipe connected to the outlet of the high-pressure cryopump unit;
High pressure vaporizer;
Equipped with
The first supply pipe extends from the outlet of the high pressure cryopump unit to direct the high pressure liquefied gas fuel stream to the high pressure vaporizer for conversion into a high pressure gas fuel stream for the main engine. Pass through the vessel.
The system further includes:
a boil-off gas pipe connecting a boil-off gas outlet of the storage tank to an inlet of a compressor unit and directing a flow of boil-off gas to the compressor unit;
a first heat exchanger;
Equipped with
the boil-off gas pipe passes through the first heat exchanger such that heat exchange of the boil-off gas stream occurs within the first heat exchanger;
The compressor unit increases the pressure of the boil-off gas stream to create a pressurized gaseous fuel stream.
The system further includes:
a second supply pipe connected to an outlet of the compressor unit for delivering the first portion of the pressurized gas fuel stream to one or more devices that consume the pressurized gas fuel;
A second portion of the pressurized gaseous fuel stream is passed through the first heat exchanger for heat exchange with boil-off gas flowing through the first heat exchanger, and the second portion of the pressurized gaseous fuel stream is then passed through the high pressure vaporizer. A reliquefaction device connected to the outlet of the compressor unit for passing the second portion of the pressurized gaseous fuel stream to the high-pressure vaporizer for heat exchange with a high-pressure liquefied fuel stream or vaporized gaseous fuel. With tube;
Equipped with

Using specialized, complex and expensive reliquefaction equipment by cooling a portion of the pressurized gas fuel stream coming from the compressor with boil-off gas in a heat exchanger and further cooling with a high pressure gas fuel stream in the high pressure vaporizer. A part of the boil-off gas can be reliquefied without any waste, and thermal energy that would otherwise have to be thrown away can be used for the reliquefaction process.

In an example implementation of the first aspect, the system comprises a throttle device, such as an expansion valve, in the reliquefaction pipe downstream of the vaporization unit. This is to subject the second portion of the pressurized gas flow to a throttling process. Passing the pressurized gaseous fuel stream through the throttle device significantly reduces the temperature and pressure of the gaseous fuel. This increases the portion that is reliquefied.

In an example implementation of the first aspect, the system comprises a separation vessel connected to the reliquefaction pipe 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 to separate the excess gas fuel from the reliquefied gas fuel.

In an example implementation of the first aspect, the system includes a reliquefied gas pipe connecting a liquid outlet of the separation vessel to an inlet of the storage tank. This is to deliver the reliquefied gaseous fuel to the storage tank.

It also includes a gas recirculation path connecting the gas outlet of the separation vessel to the boil-off gas chamber.

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

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

According to a second aspect, there is provided a method of supplying a pressurized gas fuel stream to a main engine of a marine vessel and a method of supplying a pressurized gas fuel stream to a pressurized gas consumer of the marine vessel. This method is
storing liquefied gas fuel under cryogenic conditions;
directing a liquefied gas fuel stream removed from the stored liquefied gas fuel to a high pressure pump to create a high pressure liquefied gas fuel stream;
vaporizing the high pressure liquefied gas fuel stream into a gaseous fuel stream;
supplying the high pressure gaseous fuel stream to the main engine;
directing a boil-off gas stream from the stored liquefied gas fuel to a compressor to create a pressurized gas fuel stream;
supplying a first portion of the pressurized gas fuel stream from the compressor to a device that consumes the pressurized gas fuel;
directing a second portion of the pressurized gaseous fuel stream from the compressor to a reliquefaction tube;
heat exchanging the second portion with the boil-off gas stream;
subsequently heat exchanging the second portion with the high pressure liquefied gas fuel stream;
including.

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

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

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

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

These and other aspects will become more apparent from the examples described below.

Various aspects, embodiments, and implementations will now be described in detail with reference to exemplary embodiments illustrated in the drawings.
1 is a front view of a large two-stroke engine according to an exemplary embodiment; FIG. FIG. 2 is a side view of the large two-stroke engine of FIG. 1; 2 is a first schematic representation of the large two-stroke engine of FIG. 1; FIG. FIG. 2 is a cross-sectional view of the cylinder frame and cylinder liner of the engine of FIG. 1; The cylinder cover and exhaust valve are installed, and the pistons at TDC and BDC are also depicted. 1 is a graph depicting gas exchange and fuel injection cycles. 1 is a schematic representation of a gas fuel supply system according to an embodiment. 5 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 an exemplary crosshead large, low-speed, two-stroke, turbocharged internal combustion engine. 1-3 depict an embodiment of a large, low speed, two-stroke turbocharged 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 large turbocharged, low-speed, two-stroke diesel engine of FIGS. 1 and 2, together with its intake and exhaust systems. In this example, the engine has four cylinders in series. Large, low-speed, turbocharged, two-stroke internal combustion engines typically have four to fourteen cylinders arranged in series. These cylinders are carried by the engine frame 11. Such an engine can also be used, for example, as a main engine of a ship or as a stationary engine for driving a generator in a power plant. The total power of the engine may be, for example, from 1,000 kW to 110,000 kW.

The engine combines the diesel cycle and the Otto cycle in one mode of operation in which it operates with gas fuel as the primary fuel. This is because compression ignition compresses a mixture of air and fuel. Note that this fuel is a first amount of pressurized gaseous fuel that is introduced during the compression stroke of the piston 10. The compressed air-fuel mixture is ignited when a second amount of high pressure gaseous fuel is injected near TDC.

In another mode of operation, the engine can operate according to the diesel cycle, in which case no fuel is introduced during the compression stroke. In this mode, all fuel is injected near 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 the gaseous fuel is mixed with the scavenging air and the air-fuel mixture is compressed during the compression stroke. A means for timed ignition near TDC is then 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 at 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.

Scavenging air is directed from the scavenging air receiver 2 to the scavenging port 18 at the lower end of each cylinder 1 when the piston is below the scavenging port 18. Gas fuel is introduced from the gas fuel introduction valve 30 under the control of the electronic control unit 60 . This occurs during the upstroke of the piston and before it passes the fuel valve (gas fuel inlet valve) 30. The fuel valves are preferably evenly distributed around the circumference of the cylinder liner. Further, it is preferably arranged near the longitudinal center of the cylinder liner. Therefore, the introduction of gaseous fuel takes place when the compression pressure is relatively low. In other words, the compression is performed at a much lower compression pressure than when the piston 10 reaches TDC.

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

Note that "at or near TDC" and "at or near TDC" means that gas fuel is injected. Refers to a range. This range begins at the earliest when the piston is approximately 15 degrees before TDC and ends at the latest at approximately 40 degrees after TDC.

Combustion occurs and exhaust gas is produced. Other forms of ignition systems may use a prechamber, laser ignition, glow plugs (none of which are shown), or the like, to facilitate ignition, instead of or in addition to pilot oil.

When the exhaust valve 4 opens, the exhaust gas flows through the exhaust duct provided in the cylinder 1 to the exhaust gas receiver 3, and further passes through the first exhaust pipe 19 to the turbine 6 of the turbocharger 5. . From there, the exhaust gas flows through the second exhaust pipe 25 to the economizer 20 and is further discharged to the atmosphere through the outlet 21. Turbine 6 drives compressor 7 via a shaft. The compressor 9 is supplied with outside air through an air intake 12. The compressor 7 sends compressed scavenging air to the scavenging pipe 13 connected to the scavenging air receiver 2. The scavenging air in the tube 13 passes through an 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 air flow when the compressor 7 of the turbocharger 5 is unable to supply the required pressure to the scavenging air receiver 2, ie when the engine is at low or part load. At high engine loads, the turbocharger compressor 7 can supply sufficiently compressed scavenging air, so that the auxiliary blower 16 is bypassed by the check valve 15.

A controller 60, such as an electronic control unit, is illustrated in FIG. Controller 60 is connected through signal lines or other communication channels to various sensors that convey information to controller 60 regarding engine operating conditions. Controller 60 is also connected through signal lines or other communication channels to various engine components controlled by controller 60. One of the sensors mentioned above is a crank angle sensor and is shown. 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 to introduce a first amount of gaseous fuel from the second source of pressurized gaseous fuel 40 into the combustion chamber during the stroke of the piston 10 from BDC to TDC. let The controller 60 is also configured to inject a second amount of gaseous fuel from the first source 35 of pressurized gaseous 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 shows a cylinder liner 1 designed for a large crosshead two-stroke engine. Depending on the size of the engine, the cylinder liner 1 is made in various sizes. Typical dimensions are 250 mm to 1000 mm in diameter and a corresponding overall length of 1000 mm to 4500 mm.

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

In FIG. 4, the state of the piston 10 at its bottom dead center (BDC) and top dead center (TDC) is shown by broken lines. Of course, these two states do not occur at the same time, and 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 over the running surface of the cylinder liner.

The fuel valve 50 is mounted on the cylinder cover 22. Typically, in each cylinder, two or three fuel injection valves 50 are distributed at equal intervals around the exhaust valve. The fuel injector 50 is connected to a first source 35 of high pressure gaseous fuel through a first supply line 36 and to a source 27 of pilot oil through a pilot line 28 .

The third amount of ignition fluid is less than 5% of the caloric value of all fuel input to 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 along with a sufficient amount of high pressure gaseous fuel.

The injection timing of high pressure gas fuel and pilot oil by the fuel injection valve 50 is controlled by an electronic control unit 60. The electronic control unit 60 is connected to the fuel valve 50 through a signal line indicated 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 inlet located substantially in the same plane as the inner surface of the cylinder liner 1 . Further, the rear end of the fuel introduction valve 30 protrudes from the outer wall of the cylinder liner 1. Typically one or two, and at most three or four, fuel inlet valves 30 are provided in each cylinder liner 1. These are arranged at equal intervals around the circumference of the cylinder liner 1. In this embodiment, the fuel introduction valve 30 is arranged exactly at the center of the cylinder liner 1 in the longitudinal direction.

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

The engine is configured to introduce a first amount of pressurized gas fuel and inject a second amount of pressurized gas fuel during one engine cycle. A first amount of pressurized gaseous fuel is first introduced, followed by a second amount of high pressure gaseous fuel injected on an occasion when the piston approaches TDC (this may be referred to as a first occasion).

FIG. 4 is a conceptual and simplified depiction of the engine's gas fuel supply system. A first source 35 of high pressure gaseous fuel is connected to each fuel injector 50 of the cylinder cover 22 through a first supply pipe 36 . A second source 40 of medium pressure gaseous fuel is also connected to the inlet of the gaseous fuel valve 30 through a fuel supply pipe 41 .

In this example, the pressure P1 of the first source 35 of high pressure gaseous fuel is approximately 150 to 450 bar. This high pressure allows gaseous fuel to be injected against peak pressures near TDC.

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

FIG. 5 shows the valve opening ( This figure illustrates the valve opening (opening) period and the valve closing (closing) period. Looking at this graph, it can be seen that the window for introducing gas fuel is relatively short. Therefore, the time for mixing gaseous fuel with scavenging gas in the combustion chamber is extremely short. Gaseous fuel is introduced during a very short window. High pressure gaseous fuel is injected during the window near TDC.

The total amount of gas fuel introduced and injected during one revolution is influenced by the engine load. The total amount of gaseous fuel injected into the combustion chamber is the sum of the first amount of gaseous fuel introduced into the cylinder at pressure P2 and the high pressure gaseous fuel injected into the cylinder at pressure P2. In some embodiments, approximately 70% or 80% by caloric value of the gaseous fuel input to the cylinder is gaseous fuel introduced at pressure P2 from a second source 40 of pressurized gaseous fuel. In some embodiments, approximately 70% or 80% by caloric value of the gaseous fuel input to the cylinder is gaseous fuel injected at pressure P1 from the first source 35 of high pressure gaseous fuel.

In this way, the ratio of said first quantity and said second quantity can be adjusted and adapted to the quantity of fuel available from each source. For example, when there is relatively little high pressure fuel available from the first source of pressurized gaseous fuel 35, the engine may use medium pressure fuel introduced into the cylinder during the compression stroke from the second source of pressurized gaseous fuel 40. It can be operated with more gas fuel and relatively less high pressure gas fuel injected at or near TDC. On the other hand, if there is relatively little intermediate pressure gas fuel available from the second source of pressurized gas fuel 40, the engine will use more high pressure gas fuel injected at or near TDC and the second source of pressurized gas fuel It can be operated with relatively little fuel introduced into the cylinder during the compression stroke from the second source 40.

FIG. 6 is a schematic representation of a gas supply system that may be used to supply gaseous fuel to large two-stroke turbocharged internal combustion engines, such as those depicted in FIGS. 1-4. This gas supply system is an embodiment that can be installed on a liquefied gas tanker, that is, a ship that transports a large amount of liquefied gas fuel such as liquefied natural gas (LNG) or liquefied petroleum gas (LPG).

The gas supply system is configured to supply pressurized gas fuel to the main engine of the vessel and to the gas fuel consuming devices of the vessel. Note that gas fuel consumption devices include, for example, generator sets for generating heat and electricity used in ships, boilers that operate on gas fuel, and the like. These generators are typically four-stroke internal combustion engines, which are significantly smaller than the ship's main engine and drive generators and alternators. In particular, it is also used when the main engine of a ship is stopped, such as when the ship is at a port for loading and unloading cargo.

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

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

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

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 a high pressure vaporizer 38 . The (vaporized) high pressure liquefied gas fuel stream is passed 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 gaseous fuel stream through heater 39 is optional. This step may be necessary to ensure that the gaseous fuel delivered to the main engine's injection system has a temperature that can be handled by the injection system. Such a need also depends on the material and construction of the injection system. Many injection systems are not suitable for handling cryogenic temperatures, which often requires heating the high pressure gaseous 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, it is 350 bar. Further, the temperature is, for example, approximately 119K. The high pressure (vaporized) gaseous fuel stream exiting the high pressure vaporizer 38 typically has a pressure of 150 to 450 bar. For example, it is 350 bar. Further, the temperature is, for example, approximately 154K. When the high-pressure gas fuel passes through the heater 39, the pressure remains almost unchanged, but the temperature reaches, for example, 318K.

Thus, the high pressure liquefied gas fuel stream in some embodiments has a pressure of 150 bar or more, and in order to be converted from the high pressure liquefied gas fuel stream to a high pressure gas fuel stream for injection into the main engine. It passes through a high pressure vaporizer 38.

A boil-off gas pipe 42 connects the boil-off gas outlet of the storage tank 26 to the inlet of the compressor unit and directs 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 increase the temperature of the boil-off gas stream 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. Further, the temperature is, for example, approximately 140K. When this passes through the first heat exchanger 43, the temperature is raised to approximately 230K, for example.

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

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

A reliquefaction pipe 46 is also connected to the outlet of the compressor unit 48 . This passes a second portion of the pressurized gaseous fuel stream through the first heat exchanger 43 for heat exchange with the boil-off gas flowing through the first heat exchanger 43, followed by the high pressure vaporization unit 38. Said second portion of the pressurized gas fuel stream is passed through a 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 gaseous fuel stream is, for example, approximately 159 K, while the pressure remains approximately unchanged, approximately 15 bar. Upon passing through the high pressure vaporizer 38, the pressurized gaseous fuel stream is cooled by the vaporized high pressure gaseous fuel stream to a temperature of, for example, 122K. The pressure remains approximately unchanged, approximately 15 bar. Most of the pressurized gaseous fuel flow within reliquefaction tube 46 is then reliquefied.

Downstream of the high pressure vaporizer 38, a reliquefaction pipe 46 is connected to a separation vessel 32 to collect the liquefied gas fuel produced by the cooling action of the high pressure vaporizer 38. Separation vessel 32 separates the reliquefied gaseous fuel from the still gaseous fuel. A reliquefied gas pipe 33 connects the liquid outlet 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 connects the gas outlet of the separation vessel 32 and the boil-off gas pipe 42, so that the remaining gaseous fuel can be added to the liquefaction cycle again.

FIG. 7 depicts another embodiment of a gaseous 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, structures and features that are the same as or correspond to those already described or illustrated are given the same reference numerals as previously used.

In this embodiment, a throttle device 29, such as an expansion valve, is provided in the reliquefaction pipe 46. A throttle device 29 is disposed between the carburetor 38 and the separation vessel 32 and applies a throttling process to the second portion of the pressurized gaseous fuel stream.

In some embodiments, throttle device 29 is an expansion valve. Throttle device 29 adds further cooling effect. This effect is known as the Joule-Thomson effect (or Joule-Kelvin effect, Kelvin-Joule effect). Explain the temperature change when the fluid is passed through a valve or porous stopper in a situation where it is not possible to do so. This process is called the throttle process or Joule-Thomson process. When a gaseous fuel such as natural gas or petroleum gas is passed through an orifice and subjected to a throttling operation, it expands and cools according to the Joule-Thomson process. The throttling process that cools gases is widely used in cooling devices such as air conditioners, heat pumps, and liquefiers.

Liquefaction of boil-off gas in gas fuel supply systems 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 by compressing the gas in the compressor unit 48. That is, external energy is added to the pressurized gas fuel. This is to give the Hampson-Linde cycle what it needs to run.
2) Cooled in heat exchanger 43 by return gas from the subsequent (and last) stage.
3) Cooling: This is done by exposing the gas to a chilled environment. Within the high pressure vaporizer 38, some of the heat (and therefore energy) is lost.
4) Further cooling: done by passing gas through a Joule-Thompson orifice. Heat is lost, but energy is conserved. However, it is not kinetic energy, but potential energy.

These steps reliquefy most of the gaseous fuel and the remaining gaseous fuel is at its lowest temperature in the current cycle. This is recycled and returned to the compressor unit 46 where it is used as a coolant in the heat exchanger 43 to heat it and return to the initial stage to begin 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 accommodate all boil-off gas generated from the storage tank. High pressure vaporization systems can supply 30-50% of the total amount of fuel required at maximum load of the engine.

This gas supply system is therefore inherently redundant. Therefore, there is no need to provide a separate system for providing redundancy, which can save costs.

FIG. 8 depicts a further embodiment of a large two-stroke turbocharged internal combustion engine. The gas fuel supply system is essentially the same as the gas fuel supply system of the embodiment of FIGS. 1-4. In the embodiment of FIG. 8, structures and features that are the same as or correspond to those already described or illustrated are provided with the same reference numerals as previously used. The main difference of this embodiment compared to the embodiment of FIGS. 1-4 is that the cylinder cover 22 is equipped with a gas fuel inlet valve 30. In this embodiment, all of the fuel valves 30, 50 are arranged on the cylinder cover 22.

Many aspects and implementations have been described along with some examples. However, upon studying the specification, drawings, and claims of this application, those skilled in the art will realize that there are many variations in addition to the described embodiments in carrying out the invention described in the claims. You will be able to understand this and embody it. The use of the words "comprising," "having," and "including" in the claims does not exclude the presence of unstated elements or steps. Even if it is not explicitly stated that there is a plurality of elements recited in the claims, this does not exclude the existence of a plurality of the elements. The functions of several elements recited in the claims may be performed by a single processor, controller, or other unit. Even if several matters are recited in separate dependent claims, this does not preclude their implementation in combination, which can be implemented to advantage.

Any reference signs used in the claims shall not be construed as limiting the scope of the invention.

Claims (3)

A system for supplying pressurized gas fuel to a main engine of a ship and a gas fuel consumption device of the ship, the system comprising:
a storage tank for storing liquefied gas fuel under cryogenic conditions;
a high-pressure cryopump unit having an inlet for receiving a supply of liquefied gas fuel and connected to the storage tank;
a first supply pipe connected to the outlet of the high pressure cryopump unit;
a high-pressure vaporizer for converting a high-pressure liquefied gas fuel stream supplied from the high-pressure cryopump unit into a high-pressure gas fuel stream for the main engine;
the first supply pipe extends from the outlet of the high -pressure cryopump unit to the high-pressure vaporizer to guide the high-pressure liquefied gas fuel flow to the high-pressure vaporizer and convert it into the high-pressure gas fuel flow. , the system further comprises:
a boil-off gas pipe connecting the boil-off gas outlet of the storage tank to the inlet of a compressor unit and directing the boil-off gas flow to the compressor unit;
a first heat exchanger;
Equipped with
The compressor unit is a multi-stage compressor unit in which a cooler is provided after each stage,
the boil-off gas pipe passes through the first heat exchanger such that heat exchange of the boil-off gas stream occurs within the first heat exchanger;
the compressor unit increases the pressure of the boil-off gas stream to create a pressurized gaseous fuel stream;
The system further includes:
a second supply pipe connected to an outlet of the compressor unit for delivering the first portion of the pressurized gaseous fuel stream to one or more devices that consume the pressurized gaseous fuel;
a reliquefaction pipe connected to an outlet of the compressor unit, the reliquefaction pipe connecting a second portion of the pressurized gaseous fuel stream to the first heat exchanger for heat exchange with boil-off gas flowing through the first heat exchanger; The second portion of the pressurized gas fuel stream is passed to the high pressure a reliquefaction tube passing through the first heat exchanger and through the high pressure vaporizer to pass to a vaporizer ;
Equipped with
The system further includes a throttling device in the reliquefaction pipe downstream of the high pressure vaporizer for applying a throttling stroke to the second portion of the pressurized gaseous fuel stream to liquefy it by the cooling effect of the throttling stroke. and a separation vessel for collecting liquefied gas fuel produced by the cooling effect of the high-pressure vaporizer and the throttle process and separating excess gas fuel from the liquefied gas fuel , the separation vessel being downstream of the throttle device. and a separation vessel connected to the reliquefaction pipe. a reliquefied gas pipe connecting a liquid outlet of the separation vessel to an inlet of the storage tank and delivering reliquefied gaseous fuel to the storage tank;
a gas recirculation path connecting a gas outlet of the separation vessel to the boil-off gas pipe;
The system of claim 1, comprising: 3. The system of claim 1 or 2, comprising a heater in the first supply line downstream of the high pressure vaporizer to warm the high pressure gaseous fuel stream before supplying it to the main engine.

Images