JP2022126753A - Gas fuel supply system and method for operating gas fuel supply system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a system for supplying pressurized gas fuel to a main engine of a vessel and a gas fuel consumption device of the vessel and a method for operating the gas fuel supply system.

SOLUTION: A gas fuel supply system includes: producing a pressurized gas fuel flow from a boil-off gas flow; supplying a first portion of the pressurized gas fuel flow to a consumption device; causing a second portion of the pressurized gas fuel flow to exchange heat with the boil-off gas flow and then, exchange heat with a high-pressure liquefied gas fuel flow; and at least partially liquefying the second portion that has undergone heat exchange through a throttle device 29, adding the liquefied portion to stored liquefied gas fuel and adding the gas portion to the boil-off gas flow.

SELECTED DRAWING: Figure 7

COPYRIGHT: (C)2022,JPO&INPIT

Description

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

background

A large two-stroke uniflow scavenging internal combustion engine of a crosshead type is used, for example, as a propulsion system for a large ship or as a prime mover of a power plant. The size of this large two-stroke engine is huge. Not only because of its enormous size, this large two-stroke engine has a different construction than other internal combustion engines.

Turbocharged large two-stroke uniflow scavenging internal combustion engines are increasingly using gas fuels such as liquefied natural gas (LNG) and liquefied petroleum gas (LPG) in place of conventional marine diesel fuel and heavy oil. there is The reason for replacing gas fuel is primarily to reduce emissions and to provide an environmentally friendly prime mover.

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

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

However, in order to inject gaseous fuel near TDC, the pressure of gaseous fuel supplied to the fuel valve that injects gaseous fuel into the combustion chamber must be much higher than the compression pressure of the combustion chamber. In practice, the gaseous fuel injected into the combustion chamber must have a pressure of at least 250 bar, preferably 300 bar. A pumping station pressurizes the liquefied gas fuel, for example to 300 bar, and the high pressure liquefied fuel is subsequently vaporized in a high pressure vaporization unit and delivered in the form of high pressure gas to the fuel injection valves of the main engine. This delivery system is more expensive than delivery systems for conventional liquid fuels.

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

For this reason, gas fuel supply systems for engines operating on gas fuel comprise an insulated tank for storing liquefied gas. The insulated tank keeps the liquid state for a long time. However, the ambient 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 creates a substantially steady flow of gaseous fuel. This must be removed from the tank and something must be done. For a 1800000 m3 LNG tanker, the amount of BOG that needs to be dealt with amounts to several tons per hour. Typically around 3000 kg/hour. On the other hand, the main engine gas requirement of this type of LNG tanker is approximately 4000 kg/hr, assuming that the main engine energy source 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. For this reason, 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 sets of such generators in addition to large turbocharged two-stroke internal combustion engines. Such generators are often 4-stroke internal combustion engines, much smaller than large turbocharged 2-stroke internal combustion engines, which drive the generators and alternators that produce the electrical power and heat used on board the ship.

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 simply burns.

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

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

A second type of engine is called a low pressure gas engine. Gas fuel is mixed with the scavenging air in this type of engine. A second type of engine compresses a mixture of gaseous fuel and scavenging air in a combustion chamber. In a second type of engine, gas fuel is injected from a fuel valve located midway through the cylinder liner. Fuel is injected midway through the compression stroke of the piston, well before the fuel valve closes. The piston compresses a mixture of gaseous fuel and scavenging air in the combustion chamber, and the compressed mixture is ignited near top dead center (TDC) by a timed ignition means (e.g., injection of pilot oil). be done. An advantage of this second type of engine is that it can be operated with gas fuel supplied at relatively low pressure (eg about 15 bar). This is because the pressure in the combustion chamber when the gaseous fuel is injected is relatively low. Therefore, the engine of the second type can be operated with the BOG pressure-increased by the pressure-increasing means. The gas supply system for the second type of engine is therefore cheaper than the gas supply system for the first type of engine. In the case of the first type of engine, the BOG flow coming from the tank must be processed and the boiler and generator sets can only use part of this BOG flow. For this reason, a relatively expensive reliquefaction system must be installed to operate with the gas supply system of the first type of engine.

However, because the second type of engine compresses the mixture in the combustion chamber, the effective compression ratio is considerably lower than that of the first type of engine. Typically, the effective compression ratio for engines of the first type is between about fifteen and about seventeen. In contrast, the effective compression ratio for the second type of engine is between about seven and about nine. It should be noted that the geometric compression ratio of the second type of engine is approximately 13.5. This very low, geometrically defined compression ratio makes the second type of engine significantly less fuel efficient than the first type of engine, and the same size of the first type of engine. This causes the second type of engine to have a low maximum continuous speed.

Moreover, the second type of engine usually requires a pre-chamber 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 very precisely controlled. This is to prevent pre-ignition due to (local) too low air factor and/or too high bulk temperature and to prevent misfire due to too high air factor and/or too low bulk temperature. Proper mixing resulting in a homogeneous mixture is very important for local conditions within the combustion chamber leading to pre-ignition and misfires. Controlling these conditions within the combustion chamber is particularly difficult during transient operation.

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 large two-stroke uniflow scavenging turbocharged internal combustion engine.

Thus, there is a need for eliminating or alleviating the above-described weaknesses of the first and second types of engines in large two-stroke uniflow scavenging internal combustion engines operating on gas fuel as the primary fuel. .

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

Summary

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

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

According to a first aspect, there is provided a system for supplying pressurized gaseous fuel to the main engine of a vessel and gaseous fuel consuming devices of the vessel. This system
a storage tank for storing the liquefied gas fuel in cryogenic conditions;
a high pressure cryopump unit having an inlet connected to said storage tank for receiving a supply of liquefied gas fuel;
a first supply pipe connected to the outlet of the high pressure cryopump unit;
a high pressure vaporizer;
Prepare.
The first supply line extends from an outlet of the high pressure cryopump unit to the high pressure vaporizer for conducting a 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 the boil-off gas outlet of said storage tank to the inlet of a compressor unit and conducting a flow of boil-off gas to said compressor unit;
a first heat exchanger;
Prepare.
said boil-off gas pipe passing through said first heat exchanger such that heat exchange of said boil-off gas stream takes place within said first heat exchanger;
The compressor unit increases the pressure of the boil-off gas stream to produce a pressurized gaseous fuel stream.
The system further includes:
a second supply line connected to an outlet of said compressor unit for delivering a first portion of said stream of pressurized gaseous fuel to one or more devices consuming pressurized gaseous fuel;
A second portion of the pressurized gaseous fuel stream is passed through the first heat exchanger and subsequently through the high pressure vaporizer for heat exchange with boil-off gas flowing through the first heat exchanger. a reliquefaction connected to an outlet of said compressor unit for passing said second portion of said pressurized gaseous fuel stream through said high pressure vaporizer for heat exchange with a high pressure liquefied fuel stream or vaporized gaseous fuel; a tube;
Prepare.

Chilling a portion of the pressurized gaseous fuel stream coming from the compressor with the boil-off gas in a heat exchanger and further chilling it with the high pressure gaseous fuel stream in the high pressure vaporizer, thereby using dedicated, complex and expensive reliquefaction equipment. A portion of the boil-off gas can be re-liquefied without the need for re-liquefaction, and thermal energy that would otherwise be wasted for re-liquefaction can be used for the re-liquefaction process.

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

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

In one example of implementation of the first aspect, the system comprises a reliquefied gas line 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.

There is also a gas recirculation line connecting the gas outlet of the separation vessel to the boil-off gas station.

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

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

According to a second aspect, a method of supplying a high pressure gaseous fuel stream to a main engine of a marine vessel and a method of supplying a pressurized gaseous fuel stream to pressurized gas consuming devices of the vessel are provided. This method
storing the liquefied gas fuel under cryogenic conditions;
pumping a liquefied gas fuel stream withdrawn from said stored liquefied gas fuel to a high pressure pump to produce a high pressure liquefied gas fuel stream;
vaporizing the high pressure liquefied gas fuel stream into a gas fuel stream;
supplying said high pressure gaseous fuel stream to said main engine;
directing a boil-off gas stream from said stored liquefied gas fuel to a compressor to produce a pressurized gas fuel stream;
supplying a first portion of the stream of pressurized gaseous fuel from the compressor to a device that consumes pressurized gaseous fuel;
directing a second portion of the pressurized gaseous fuel stream from the compressor to a reliquefaction conduit;
heat exchanging said second portion with said boil-off gas stream;
subsequently heat exchanging said second portion with said high pressure liquefied gas fuel stream;
including.

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

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

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

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

Various aspects, embodiments, and implementations are described in detail below 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. Figure 2 is a side view of the large two-stroke engine engine of Figure 1; 2 is a first schematic representation of the large two-stroke engine of FIG. 1; 2 is a cross-sectional view of the cylinder frame and cylinder liner of the engine of FIG. 1; FIG. Cylinder covers and exhaust valves are attached, and the pistons at TDC and BDC are also depicted. 4 is a graph depicting gas exchange and fuel injection cycles; 1 is a schematic representation of a gas fuel supply system, in accordance with certain embodiments; 4 is a schematic representation of a gas fuel supply system according to another embodiment; FIG. 5 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 two-stroke turbocharged internal combustion engine of the embodiment. 1-3 depict an example of a turbocharged large low speed two-stroke internal combustion engine. This engine has a crankshaft 8 and a crosshead 9 . 1 is a front view, and FIG. 2 is a side view. FIG. 3 is a schematic representation of the turbocharged large 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. Turbocharged large low speed two-stroke internal combustion engines typically have from 4 to 14 cylinders arranged in series. These cylinders are carried on the engine frame 11 . Such an engine can also be used, for example, as a main engine in ships or as a stationary engine for powering generators in power plants. The total power output of the engine can be, for example, 1,000 kW to 110,000 kW.

The engine combines the Diesel cycle and the Otto cycle in certain operating modes operating on gas fuel as the primary fuel. This is compression ignition because it compresses the air-fuel mixture. Note that this fuel is a first quantity of pressurized gaseous fuel introduced midway through the compression stroke of piston 10 . The compressed air-fuel mixture is ignited near TDC when the second quantity of high pressure gas fuel is injected.

In another operating mode, the engine can operate according to the diesel cycle, in which 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 operating mode, the engine can operate according to the Otto cycle. In this case, all gaseous fuel is mixed with the scavenging air and the air-fuel mixture is compressed during the compression stroke. Means are then provided for timed ignition near TDC.

The engine in this embodiment is a two-stroke uniflow scavenging engine, provided with a scavenging port 18 in the lower region of the cylinder liner 1 and an exhaust valve 4 centrally located at 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 which reciprocates in the cylinder liner between bottom dead center (BDC) and top dead center (TDC).

Scavenging air is directed from the scavenging receiver 2 to the scavenging ports 18 at the lower end of each cylinder 1 when the piston is below the scavenging ports 18 . 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 upstroke of the piston and before the piston passes the fuel valve (gas fuel inlet valve) 30 . The fuel valves are preferably evenly distributed around the circumference of the cylinder liner. Also preferably, it is arranged near the center in the longitudinal direction of the cylinder liner. The introduction of gaseous fuel therefore takes place when the compression pressure is relatively low. That is, 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. At or near TDC, high-pressure gas fuel is injected from the fuel injection valve 50 . Ignition is caused according to the Diesel principle by high temperatures caused by high pressures in the combustion chamber at or near TDC. Ignition may be assisted by a small amount of pilot oil (or suitable ignition fluid). In some cases, this pilot oil is injected from the fuel injection valve 50 together with the gas fuel, but in some cases it is configured to be supplied from a dedicated pilot oil valve 51 (not shown). be. In that case, the pilot oil valve 51 is preferably arranged on the cylinder cover 22 .

It should be noted that "TDC or its vicinity" and "TDC or its vicinity" mean that gas fuel is injected. point to the 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 gases are produced. Other forms of ignition systems may use prechambers, laser ignition, glow plugs (none shown), etc. 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 through the first exhaust pipe 19 to the turbine 6 of the turbocharger 5. . From there the exhaust gases flow through a second exhaust pipe 25 to the economizer 20 and out of an outlet 21 to the atmosphere. Turbine 6 drives compressor 7 via a shaft. Outside air is supplied to the compressor 9 through an air intake 12 . The compressor 7 sends the compressed scavenging air into the scavenging pipe 13 connected to the scavenging receiver 2 . The scavenging air in 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 cannot supply the scavenging air receiver 2 with the required pressure, ie when the engine is at low or partial 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 non-return valve 15 .

FIG. 3 illustrates a controller 60, such as an electronic control unit. The controller 60 is connected through signal lines or other communication channels to various sensors that communicate information to the controller 60 regarding the operating conditions of the engine. The controller 60 is also connected through signal lines or other communication channels to the various engine components controlled by the controller 60 . One such sensor is a crank angle sensor and is shown. This communicates the rotation angle of the crankshaft 8 to the controller 60 . A 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. Controller 60 operates fuel inlet valve 30 to introduce a first quantity of gaseous fuel from second source 40 of pressurized gaseous fuel into the combustion chamber during the stroke of piston 10 from BDC to TDC. Let The controller 60 also directs fuel to inject a second quantity 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. 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 sizes are diameters of 250 mm to 1000 mm and corresponding total lengths of 1000 mm to 4500 mm.

FIG. 4 depicts a state in which 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 therebetween.

In FIG. 4, the states of the piston 10 at its bottom dead center (BDC) and top dead center (TDC) are indicated by dashed lines. Of course, these two states do not occur simultaneously, but are separated by 180 degrees of rotation 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 lubrication oil as the piston 10 passes through the lubrication line 24 . Piston rings (not shown) then distribute the cylinder lubricating oil over the entire running surface of the cylinder liner.

A fuel valve 50 is mounted on the cylinder cover 22 . Typically, two or three fuel injectors 50 are distributed equally spaced around the exhaust valves in each cylinder. Fuel injector 50 is connected through first supply line 36 to first source 35 of high pressure gaseous fuel and through pilot line 28 to source 27 of pilot oil.

A third amount of ignition liquid is less than 5% of the caloric value of all fuel injected into the combustion chamber during a given engine cycle. Preferably less than 3%.

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 gas fuel.

The injection timing of the high pressure gas fuel and 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 signal lines indicated by dashed lines in FIG.

The cylinder liner 1 is equipped with a fuel introduction valve 30 . The fuel inlet valve 30 has a nozzle or inlet located substantially flush with the inner surface of the cylinder liner 1 . A 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 inlet valves 30 are provided in each cylinder liner 1 . These are equally spaced around the circumference of the cylinder liner 1 . In this embodiment, the fuel introduction valve 30 is arranged exactly in 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 inlet valve 30 through conceptually indicated signal lines.

The engine is configured to introduce a first quantity of pressurized gaseous fuel and inject a second quantity of high pressure gaseous fuel during one engine cycle. A first quantity of pressurized gaseous fuel is first introduced, followed by a second quantity of high pressure gaseous fuel injected at the opportunity when the piston approaches TDC (this is sometimes referred to as the first opportunity).

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 in the cylinder cover 22 through a first supply pipe 36 . A second source 40 of medium pressure gas fuel is also connected to the inlet of the gas fuel valve 30 through a fuel supply line 41 .

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

In the present example, the pressure P2 of the second source of medium pressure gaseous fuel 40 is approximately 1 to 3 MPa (10 to 30 bar). It is a medium pressure compared to P1. With this pressure, however, gaseous fuel can be introduced during the compression stroke.

FIG. 5 shows the valve opening ( 10 illustrates the valve opening period and the valve closing period. It can be seen from this graph that the window for introducing gas fuel is relatively short. Therefore, the time for the gaseous fuel to mix with the scavenging air in the combustion chamber is very short. Gas fuel is introduced during a very short window. High pressure gas fuel is injected during the window near TDC.

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

Thus, the ratio of the first amount and the second amount can be adjusted and adapted to the amount of fuel available from each source. For example, when relatively little high pressure fuel is available from the first source of high pressure gaseous fuel 35, the engine may operate at moderate pressure from the second source of pressurized gaseous fuel 40 introduced into the cylinder during the compression stroke. 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 will use more of the high pressure gas fuel injected at or near TDC. It can be operated with relatively little fuel introduced into the cylinder during the compression stroke from the two sources 40 .

FIG. 6 is a schematic representation of a gas supply system that may be used to supply gaseous fuel to a large two-stroke turbocharged internal combustion engine such as that depicted in FIGS. 1-4, for example. The gas supply system is an embodiment that can be installed on board a liquefied gas tanker, ie, a vessel that carries large quantities of liquefied gas fuels such as liquefied natural gas (LNG) and liquefied petroleum gas (LPG).

The gas supply system is configured to supply pressurized gaseous fuel to the main engine of the vessel and to the gaseous fuel consuming devices of the vessel. Gas fuel consumption devices include, for example, generator sets for generating heat and electricity for use in ships, boilers that operate on gas fuel, and the like. Such generators, typically four-stroke internal combustion engines, are significantly smaller than the ship's main engine and drive a generator and/or alternator. It is also used when the ship's main engine is stopped, especially when the ship is at a port for loading and unloading cargo.

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

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

The gas fuel supply system has 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 between slightly above zero and around 10 bar, eg about 5 bar, and a temperature of eg around 110K.

A first supply line 36 is connected to the outlet of the high pressure cryopump unit 37 to deliver a high pressure liquefied gas fuel stream from the high pressure pump 37 to the 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 main engine high pressure fuel injection system. Passing the high pressure gas fuel stream through the heater 39 is optional. This step may be necessary to ensure that the gaseous fuel delivered to the injection system of the main engine has a temperature that the injection system can handle. Such needs also depend on the materials and construction of the injection system. Many injection systems are not well suited to handle cryogenic temperatures, so it is often necessary to heat up the high pressure gaseous fuel stream.

The high pressure liquefied fuel stream exiting the high pressure cryopump unit 37 typically has a pressure of 150 to 450 bar. For example 350 bar. Also, the temperature is, for example, approximately 119K. The high pressure (vaporized) gaseous fuel stream leaving the high pressure vaporizer 38 typically has a pressure of 150 to 450 bar. For example 350 bar. Also, the temperature is, for example, approximately 154K. As the high pressure gaseous fuel passes through the heater 39, the pressure remains almost unchanged, but the temperature becomes, for example, 318K.

Thus, the high pressure liquefied gas fuel stream in certain embodiments has a pressure of 150 bar or more, and is converted from the high pressure liquefied gas fuel stream into a high pressure gas fuel stream for injection into the main engine, Pass through 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 stream to the compressor unit 48 . The boil-off gas line 42 is provided with a first heat exchanger 43 to increase the temperature of the boil-off gas stream delivered to the compressor unit 48 . In one embodiment, the pressure of the boil-off gas in the boil-off gas line 42 is approximately 1 bar. Also, the temperature is, for example, approximately 140K. When this passes through the first heat exchanger 43, it is heated to approximately 230K, for example.

A 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 multiple stages, each stage may be provided with a cooler 45 .

A second feed line 41 is connected to the outlet of the compressor unit 48 to deliver a first portion of the pressurized gaseous fuel stream to one or more devices that consume the pressurized fuel. This equipment includes, for example, a main engine that introduces pressurized gaseous fuel during the compression stroke. The apparatus may also include a generator set or boiler supplied with pressurized gaseous fuel through supply line 47 .

A reliquefaction pipe 46 is also connected to the outlet of the compressor unit 48 . It 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 vaporizer unit 38. Said second portion of the pressurized gaseous fuel stream is passed through a high pressure vaporization unit 38 for heat exchange with the flowing high pressure liquefied fuel stream or vaporized gaseous fuel. After passing through the heat exchanger 43, the temperature of the pressurized gaseous fuel stream is, for example, around 159 K, while the pressure remains almost unchanged, around 15 bar. 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 almost unchanged, around 15 bar. Most of the pressurized gaseous fuel stream in reliquefaction line 46 is then reliquefied.

Downstream of the high pressure vaporizer 38 , a reliquefaction line 46 is connected to the 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 line 33 connects between the liquid outlet of the separation vessel 32 and the inlet of the storage tank 26 and conducts the reliquefied gaseous fuel to the storage tank 26 . A gas recirculation line 34 also connects between the gas outlet of the separation vessel 32 and the boil-off gas line 42 to allow the remaining gaseous fuel to rejoin the liquefaction cycle.

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, structures and features that are the same as or correspond to structures and features already described or illustrated are labeled with the same reference numerals as previously used.

In this embodiment a throttling device 29 , for example an expansion valve, is provided in the reliquefaction line 46 . A throttling device 29 is disposed between the vaporizer 38 and the separation vessel 32 to subject the second portion of the pressurized gaseous fuel stream to a throttling process.

In one embodiment, throttle device 29 is an expansion valve. Throttle device 29 adds an additional cooling effect. This effect is known as the Joule-Thomson effect (or Joule-Kelvin effect, Kelvin-Joule effect). Describe the change in temperature when passing through a valve or porous plug in a situation where no pressure is applied. 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 passed through an orifice and subjected to a throttling operation. Throttle processes for cooling gases are widely used in refrigeration systems such as air conditioners, heat pumps and liquefiers.

Liquefaction of the boil-off gas in gas fueling 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 gaseous fuel. This is to give you what you need to run the Hampson-Linde cycle.
2) cooled in heat exchanger 43 by return gas from subsequent (and final) stages;
3) Cooling: done by exposing the gas to a chilled environment. Some of the heat (and thus energy) is lost in the high pressure vaporizer 38 .
4) Further cooling: done by passing the gas through a Joule-Thomson orifice. Heat is taken away, but energy is conserved. However, it is potential energy instead of kinetic energy.

These steps re-liquefy most of the gas fuel and the remaining gas fuel is the coldest in the current cycle. It is recycled and returned to the compressor unit 46 where it is used as coolant in the heat exchanger 43 to heat it and go back to the beginning to start 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 the boil-off gas produced from the storage tank. A high pressure vaporization system can supply 30-50% of the total fuel quantity required at maximum engine load.

This gas supply system is therefore inherently redundant. And so there is no need to provide a separate system for redundancy, which saves 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 structures and features already described or illustrated are labeled with the same reference numerals as previously used. The main difference of this embodiment compared to the embodiment of FIGS. In this embodiment, all of the fuel valves 30, 50 are arranged on the cylinder cover 22. As shown in FIG.

A number of aspects and implementations have been described with some examples. However, many variations in addition to those described exist in the practice of the claimed invention by one of ordinary skill in the art upon review of the specification, drawings, and claims of this application. understand and be able to implement it. The verbs "comprising," "having," and "including" in the claims do not exclude the presence of elements or steps not recited. The absence of an explicit plural number of an element in a claim does not exclude the presence of a plurality of such elements. The functions of several elements recited in the claims may be performed by a single processor, controller or other unit. The mere fact that certain items are recited in separate dependent claims does not preclude their joint practice, which may be practiced to advantage.

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

Claims (4)

1. A system for supplying pressurized gaseous fuel to a main engine of a ship and gaseous fuel consuming devices of the ship, said system comprising:
a storage tank for storing liquefied gas fuel under cryogenic conditions;
a high pressure cryopump unit having an inlet connected to said storage tank for receiving a supply of liquefied gas fuel;
a first supply pipe connected to the outlet of the high pressure cryopump unit;
a high pressure vaporizer;
and said first supply line extends from an outlet of said high pressure cryopump unit for conducting a high pressure liquefied gas fuel stream to said high pressure vaporizer for conversion into a high pressure gas fuel stream for said main engine. Through the high pressure vaporizer, the system further comprises:
a boil-off gas pipe connecting the boil-off gas outlet of said storage tank to the inlet of a compressor unit and conducting a boil-off gas stream to said compressor unit;
a first heat exchanger;
with
said boil-off gas pipe passing through said first heat exchanger such that heat exchange of said boil-off gas stream takes place within said first heat exchanger;
the compressor unit increases the pressure of the boil-off gas stream to produce a pressurized gaseous fuel stream;
The system further includes:
a second supply pipe connected to an outlet of said compressor unit for delivering a first portion of said stream of pressurized gaseous fuel to one or more devices consuming pressurized gaseous fuel;
A second portion of the pressurized gaseous fuel stream is passed through the first heat exchanger and subsequently through the high pressure vaporizer for heat exchange with boil-off gas flowing through the first heat exchanger. connected to an outlet of said compressor unit to pass said second portion of said pressurized gaseous fuel stream through said high pressure vaporizer for heat exchange with a high pressure liquefied gaseous fuel stream or a vaporized gaseous fuel stream; a reliquefaction tube;
with
The system further includes a throttling device in the reliquefaction line downstream of the high pressure vaporizer for applying a throttling process to the second portion of the pressurized gaseous fuel stream to liquefy it by the cooling effect of the throttling process. a separation vessel for collecting liquefied gas fuel produced by the cooling effect of said high pressure vaporizer and said throttling process and for separating excess gaseous fuel from re-liquefied gas fuel, said separation vessel downstream of said throttling device; , a separation vessel connected to said reliquefaction line. a reliquefied gas line connecting the liquid outlet of the separation vessel to the inlet of the storage tank and delivering reliquefied gas fuel to the storage tank;
a gas recirculation line connecting the gas outlet of the separation vessel to the boil-off gas pipe;
2. The system of claim 1, comprising: 3. A system according to claim 1 or 2, comprising a heater in said first supply line downstream of said high pressure carburetor to warm said high pressure gaseous fuel stream before supplying it to the main engine. 1. A method of supplying pressurized gas fuel to a main engine of a ship and supplying pressurized gas fuel streams to pressurized gas consuming devices of the ship, comprising:
storing the liquefied gas fuel in a storage tank under cryogenic conditions;
pumping a liquefied gas fuel stream withdrawn from said stored liquefied gas fuel to a high pressure pump to produce a high pressure liquefied gas fuel stream;
vaporizing the high pressure liquefied gas fuel stream into a high pressure gas fuel stream in a high pressure vaporizer;
supplying said high pressure gaseous fuel stream to said main engine;
directing a boil-off gas stream from said stored liquefied gas fuel to a compressor to produce a pressurized gas fuel stream;
cooling the boil-off gas stream with a cooler within the compressor;
supplying a first portion of the stream of pressurized gaseous fuel from the compressor to a device that consumes pressurized gaseous fuel;
directing a second portion of the pressurized gaseous fuel stream from the compressor to a reliquefaction line;
heat exchanging said second portion with said boil-off gas stream in a first heat exchanger; and subsequently heat exchanging said second portion with said high pressure liquefied gas fuel stream in a second heat exchanger. to exchange;
following heat exchange with said high pressure liquefied gaseous fuel stream, said second portion is passed through a throttling device to at least partially liquefy, followed by a liquefied portion and a gaseous portion of said second portion; through a separation vessel to separate the liquefied portion and the gaseous portion, adding the liquefied portion to the stored liquefied gas fuel and adding the gaseous portion to the boil-off gas stream;
A method, including

Images