Large turbocharged two-stroke uniflow crosshead type internal combustion engine

Abstract

A large turbocharged two-stroke uniflow crosshead type internal combustion engine is described having at least one operating mode in which the primary fuel is a low flash point fuel, e.g., ammonia, methanol, ethanol, DME, methane, ethane, or LPG, and the secondary fuel is a low flash point fuel, e.g., ammonia, methanol, ethanol, DME, methane, ethane, or LPG, such as ammonia, methanol, ethanol, DME, methane, ethane, or LPG, such as ammonia, methanol, ethanol, DME, methane, ethane, or LPG. The invention relates to an engine comprising: at least one cylinder having a cylinder liner (1), a reciprocating piston (10) in the cylinder and a cylinder head (22) covering the cylinder, a combustion chamber formed in the interior of the cylinder between the reciprocating piston (10) and the cylinder head (22); a low flash point fuel system (30) comprising a fuel supply line (36) and a fuel return line (38), and configured for supplying pressurized fuel to at least one fuel valve (50) arranged in the cylinder head (22) or in the cylinder liner (1); and a purge system for withdrawing low flash point fuel from the fuel supply line (36) and the fuel return line (38). The engine is unique in that the purge system comprises means (40, 75, 41) for conducting a liquid, such as water or diesel, through at least the fuel supply line (36) and the fuel return line (38) of the low flash point fuel system (30). Thus, low flash point fuel can be withdrawn from the fuel system in a safe and economical manner, where the low flash point fuel can be collected in a tank for reuse as fuel, and expensive and complex processing of nitrogen and fuel mixtures is avoided, as no inert gas such as nitrogen is used for purging.

Description

Technical Field

[0001] The present invention relates to a large turbocharged two-stroke single-flow crosshead internal combustion engine, which has at least one operating mode, in which the main fuel is a low-flashpoint fuel, for example, ammonia, methanol, ethanol, DME, methane, ethane or LPG, and the engine comprises: at least one cylinder having a cylinder liner, a reciprocating piston located in the cylinder and a cylinder head covering the cylinder, and a combustion chamber formed in the cylinder between the reciprocating piston and the cylinder head; a low-flashpoint fuel system, which comprises a fuel supply line and a fuel return line, and the low-flashpoint fuel system is configured to supply pressurized fuel to at least one fuel valve arranged in the cylinder head or in the cylinder liner; and a purge system, which is used to extract the low-flashpoint fuel from the fuel supply line and the fuel return line. Background Art

[0002] Large turbocharged two-stroke single-flow crosshead type internal combustion engines are typically used as prime movers for large ocean-going vessels (such as container ships) or power plants. These engines usually run on heavy fuel oil or fuel oil (such as diesel).

[0003] Recently, there has been a need for large two-stroke diesel engines that can handle alternative types of fuels, such as ammonia, methanol, ethanol, DME, methane, ethane or LPG and / or other similar fuels. Engines that can operate in both a fuel mode (in which the engine runs on fuel only) and an alternative fuel mode (in which the engine runs on an alternative fuel and a pilot fuel) are generally referred to as dual-fuel engines.

[0004] Dual fuel engines for low flash point fuels all have separate fuel systems for these highly volatile fuels. In all cases, there needs to be equipment for completely draining the fuel from the fuel system, i.e. fuel lines, valves, pumps, etc., to ensure safe engine shutdown, fuel conversion to fuel oil, or maintenance.

[0005] Known dual-fuel engines include a purge system for extracting low-flashpoint fuel from the fuel system. This purge system first ensures that the fuel system is depressurized and then purged with nitrogen. The disadvantage of purging with nitrogen is that the mixture of nitrogen and fuel gas needs to be handled and disposed of. In addition, the nitrogen needs to be produced on board, which increases costs in terms of OPEX and CAPEX.

[0006] EP3203053 B1 describes a gas turbine application, while US9732713 BB describes a dual fuel engine, in which gaseous fuel (e.g., low flash point fuel, as ammonia) is allowed to enter or be injected into the combustion zone during gas mode operation. In both documents, the fuel line is purged by a vacuum pump system. A vacuum pump for ammonia exists, but it is neither simple nor cheap for use with a large turbocharged two-stroke single-flow crosshead internal combustion engine. In addition, the liquid in the form of a small amount of NH3 remaining in the pipeline, which may have a small amount of water, must be boiled, so it is expected that the purging time may be extended. In addition, due to the circulation between the negative pressure during the purging that will bring pressure to all seals and the overpressure during the gas mode operation, the problem of keeping the pipeline system sealing of the low flash point fuel system may occur.

[0007] The invention also relates to a method for operating a large turbocharged two-stroke uniflow crosshead type internal combustion engine as described above and claimed in the appended claims. Summary of the invention

[0008] It is an object of the present invention to provide a large turbocharged two-stroke uniflow crosshead type internal combustion engine of the kind mentioned in the introduction in which the above-mentioned challenges associated with purging low flash point fuels from the fuel system are at least significantly reduced.

[0009] These and other objects are achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the drawings.

[0010] According to a first aspect, a large turbocharged two-stroke single-flow crosshead internal combustion engine is provided, the large turbocharged two-stroke single-flow crosshead internal combustion engine having at least one operating mode, in which the main fuel is a low-flashpoint fuel, for example, the low-flashpoint fuel is ammonia, methanol, ethanol, DME, methane, ethane or LPG, the engine comprising: at least one cylinder having a cylinder liner, a reciprocating piston located in the cylinder and a cylinder head covering the cylinder, a combustion chamber formed in the cylinder between the reciprocating piston and the cylinder head; a low-flashpoint fuel system comprising a fuel supply pipeline and a fuel a fuel return line, and the low-flashpoint fuel system is configured to supply pressurized fuel to at least one fuel valve arranged in the cylinder head or in the cylinder liner; and a purging system, the purging system is used to extract the low-flashpoint fuel from the fuel supply line and the fuel return line, and is characterized in that the purging system includes a device for guiding liquid through at least the fuel supply line and the fuel return line of the low-flashpoint fuel system, for example, the device for guiding liquid through at least the fuel supply line and the fuel return line of the low-flashpoint fuel system is a device for guiding water or diesel through at least the fuel supply line and the fuel return line of the low-flashpoint fuel system.

[0011] Thus, low-flash point fuels can be drawn from the fuel system in a safe and economical manner, wherein the low-flash point fuels can be collected in tanks for reuse as fuel, and expensive and complicated handling of mixtures of nitrogen and fuel is avoided, since no purging with an inert gas such as nitrogen is used. In the case where the low-flash point fuel is ammonia, not using an inert purging gas such as nitrogen is particularly advantageous, since subsequent scrubbing becomes much easier, since the scrubber does not have to be dimensioned for venting with nitrogen and can therefore be made smaller and cheaper.

[0012] Furthermore, some low flash point fuels such as ammonia, methanol, ethanol and dimethyl ether DME are soluble in water, while other low flash point fuels such as methane, ethane and others such as LPG are not soluble in water. Therefore, if the liquid used for the purge system is water, the water directed through the low flash point fuel system will either mix with the first mentioned low flash point fuel or simply push the last mentioned low flash point fuel to the front without carrying contaminants of the purge gas.

[0013] In the case of low flash point fuels that are not soluble in water, such as methane, ethane and LPG, the liquid used in the purge system may be diesel or a similar liquid.

[0014] The device for guiding liquid such as water or diesel through the fuel supply pipeline and the fuel return pipeline of the low flash point fuel system may include any suitable device, however, preferably, the device includes a liquid reservoir, a liquid pipeline line for connecting the liquid reservoir to the low flash point fuel system, and a valve for opening and closing the liquid pipeline line, for example, the valve is an on / off valve, a butterfly valve or the like.

[0015] In one embodiment of the invention, the liquid reservoir may be arranged at a height that provides sufficient potential energy for the liquid to direct the liquid through the low-flashpoint fuel system. In this embodiment, the device for directing the liquid through the low-flashpoint fuel system may also include a liquid pump arranged in the liquid pipeline line.

[0016] In alternative embodiments, the liquid reservoir may be arranged at any suitable height and the means for directing the liquid through the low flash point fuel may comprise a liquid pump arranged to connect to the liquid pipeline line.

[0017] In an embodiment of the present invention, it may be advantageous to drain some of the fuel from at least the fuel supply line and the fuel return line of the low-flashpoint fuel system and then direct the liquid through these lines, particularly when the fuel is in liquid form and / or is under a certain positive pressure. In such an embodiment, the purge system may include a device for decompressing and discharging the liquid fuel from the low-flashpoint fuel system to the tank. Such a device for decompressing and discharging the liquid fuel from the low-flashpoint fuel system to the tank may include any suitable device, however, preferably, the device includes a valve leading to the pipeline connecting the low-flashpoint fuel system to the tank, for example, the valve is an on / off valve, a butterfly valve or the like.

[0018] The purge system may include a first pipeline line and a second pipeline line, both of which are connected to the low-flash point fuel system, wherein the first pipeline line is used to guide the liquid low-flash point fuel to the tank, and the second pipeline line can be connected to the low-flash point fuel absorption system in the case where the gaseous low-flash point fuel is toxic (such as gaseous ammonia), or the second pipeline line can be connected to the vent in the case where the gaseous low-flash point fuel is non-toxic.

[0019] If the low flash point fuel is gaseous under atmospheric conditions, the extraction and discharge of the low flash point fuel from the fuel system can be performed in a two-step route, wherein the extraction in the first step is driven partly by gravity due to the inclination of the fuel line and / or partly by a partial pressure of the fuel above 1 bar absolute. Typically, the pressure in the low flash point fuel system is about 30 bar to 80 bar pressure when the engine is running on the fuel.

[0020] At the end of this depressurization and discharge step, the fuel system will typically be filled with a two-phase fuel mixture with wet inner tube surfaces and pockets of liquid fuel in places, which may not be drainable by gravity. Once part of the low-flash point fuel has been extracted from the fuel system by draining to a tank, the remainder will be forced out of the low-flash point fuel system in a second extraction step by directing a liquid (e.g., water or diesel) through the system and transferred to a tank. If the low-flash point fuel is a liquid at atmospheric pressure and normal ambient temperature, such as methanol or ethanol, it can simply be drained to a tank in a first step by gravity drive.

[0021] In order to completely empty the fuel system of low flash point fuel, the purge system may also include a venting system for forcing atmospheric air through the fuel line, the venting system comprising at least a valve for access to an air inlet or to a source of pressurized air or inert gas. Before atmospheric air is forced through the fuel line, it may be advantageous to drain as much water as possible to a drain tank by gravity.

[0022] In one embodiment, the purge system may include a separation tank configured to separate the liquid portion of the expanded low-flash point fuel from the gaseous portion. This embodiment is particularly suitable for low-flash point fuels, such as ammonia, LPG and DME. In this embodiment, the purge system may also include a device for directing the two low-flash point fuel portions to the same or separate tanks. In this embodiment, the device for directing the gaseous low-flash point fuel portion may include a liquefaction device in the form of a pressurizing device and / or a cooling device, for example.

[0023] However, in this embodiment including a separation tank, the purge system may include a device for conducting the gaseous low-flash point fuel portion to the low-flash point fuel absorption system, which is particularly important when the low-flash point fuel is ammonia. Therefore, in the case where the low-flash point fuel is ammonia, the low-flash point fuel absorption system may include at least one pressure vessel, which is at least partially filled with water during use for absorbing ammonia into water to form ammonia water. Ammonia water, also known as an aqueous solution of ammonia, is a solution of ammonia in water. The low-flash point fuel absorption system may also or alternatively include at least one absorption tank. If it includes more than one tank, they are preferably arranged in series to form a cascade. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The invention will be explained in more detail with reference to exemplary embodiments shown in the accompanying drawings, in which:

[0025] Figure 1 is an elevational front view of a large two-stroke diesel engine according to an exemplary embodiment.

[0026] Figure 2 yes Figure 1Elevation side view of a large two-stroke engine.

[0027] Figure 3 is based on Figure 1 Schematic diagram of a large two-stroke engine.

[0028] Figure 4 is a schematic diagram of an engine having a low-flash point fuel system and a low-flash point fuel purge system, wherein the low-flash point fuel is ammonia.

[0029] Figure 5 is a schematic diagram of an engine having a low-flash point fuel system and a low-flash point fuel purge system, wherein the low-flash point fuel is methanol or ethanol. DETAILED DESCRIPTION

[0030] In the following detailed description, the present invention will be described with respect to a large turbocharged two-stroke single-flow crosshead internal combustion engine, but it should be understood that the internal combustion engine may be of other types. Large turbocharged two-stroke single-flow crosshead internal combustion engines may be either high-pressure types, in which the fuel is injected at or near top dead center of the piston and compression ignited, usually by pilot ignition with an ignition fluid (e.g., fuel oil) to ensure reliable ignition, or low-pressure types, in which the fuel is admitted at a relatively low pressure as the piston moves toward top dead center. In reference to Figure 4 In the detailed description of the invention, the low flash point fuel is ammonia. Figure 5 In the detailed description of the invention, the low flash point fuel may be methanol or ethanol.

[0031] Figure 1 , Figure 2 and Figure 3 A large, low speed, turbocharged, two-stroke diesel engine is shown having a crankshaft 8 and a crosshead 9 . Figure 3 A schematic diagram of a large low-speed turbocharged two-stroke diesel engine with its intake and exhaust systems is shown. In this exemplary embodiment, the engine has six cylinders in line (in line, in series, in a linear arrangement). A large low-speed turbocharged two-stroke diesel engine typically has four to fourteen cylinders in line, which are carried by a cylinder frame 23, and the cylinder frame 23 is carried by an engine frame 11. The engine can be used, for example, as a main engine in an ocean-going vessel or as a fixed engine for operating a generator in a power station. The total output of the engine can be, for example, in the range of 1,000kW to 110,000kW.

[0032] In the present exemplary embodiment, the engine is a two-stroke single-flow dual-fuel compression ignition engine having a scavenging port 18 in the lower region of the cylinder liner 1 and a central discharge valve 4 at the top of each cylinder liner 1. The engine has at least one low-flash point fuel mode in which the engine operates with a low-flash point fuel such as ammonia, methanol, ethanol, DME, methane, ethane or LPG, and at least one conventional fuel mode in which the engine operates with a conventional fuel such as fuel oil (marine diesel) or heavy fuel oil.

[0033] The scavenging air is delivered from the scavenging air receiver 2 to the scavenging port 18 of each cylinder 1. The piston 10 reciprocating between the bottom dead center (BDC) and the top dead center (TDC) in the cylinder liner 1 compresses the scavenging air. In the illustrated embodiment, fuel in the form of a low flash point fuel, such as ammonia, methanol, ethanol, DME, methane, ethane or LPG, is injected into the combustion chamber at or near TDC in the cylinder liner 1 through a high pressure fuel valve 50 arranged in the cylinder head 22 in the low flash point fuel mode. In an alternative embodiment, the low flash point fuel can be allowed to enter somewhere between the scavenging port 18 and TDC through a fuel valve 50' arranged in the cylinder liner. Combustion then occurs and exhaust gas is generated. Each cylinder head 22 is provided with one or more fuel valves 50. The fuel valve 50 is configured to inject only one specific type of fuel (e.g., ammonia), and in this case, there will also be one or more fuel valves 50 for injecting conventional fuel into the combustion chamber. Therefore, the engine will have two or more fuel valves. In the case where the fuel valve 50 is suitable for injecting both low-flash point fuels (such as ammonia) and conventional fuels, there can be one or more fuel valves 50 per cylinder. The fuel valve 50 is arranged in the cylinder head 22 and surrounds the central discharge valve 4. In addition, in an embodiment, an additional, usually smaller fuel valve (not shown) is also provided in the cylinder head for injecting an ignition fluid to ensure reliable ignition of the low-flash point fuel. The ignition fuel is ordinary diesel fuel, but it can also be another form of ignition enhancer, such as dimethyl ether (DME) or hydrogen. Since the engine can be a dual-fuel engine, it can also be provided with a conventional fuel supply system (not shown) for supplying conventional fuel to the fuel valve 50. In another embodiment, the main fuel injection system can also be used to ensure the ignition of ammonia fuel.

[0034] When the exhaust valve 4 is open, the exhaust gas flows through the exhaust passage associated with the cylinder into the exhaust gas receiver 3 and then forwards to the turbine 6 of the turbocharger 5 through the first exhaust conduit 19 via the selective catalytic reduction (SCR) reactor 28, from which the exhaust gas flows away through the second exhaust conduit via the economizer 20 to the outlet 21 and into the atmosphere. The SCR reactor reduces emissions, in particular NOx emissions.

[0035] The turbine 6 drives a compressor 7 via a shaft, which is supplied with fresh air via an air inlet 12. The compressor 7 delivers pressurized scavenging air to a scavenging air duct 13 leading to a scavenging air receiver 2. The scavenging air in the scavenging air duct 13 passes through an intercooler 14 for cooling the scavenging air.

[0036] The cooled scavenging air passes through an auxiliary blower 16 driven by an electric motor 17, which pressurizes the scavenging air flow when the compressor 7 of the turbocharger 5 is unable to deliver sufficient pressure to the scavenging air receiver 2 (i.e., at low or part load conditions of the engine). At higher engine loads, the turbocharger compressor 7 delivers sufficient compressed scavenging air, and then the auxiliary blower 16 is bypassed via the non-return valve 15, and the electric motor 17 is deactivated.

[0037] Reference Figure 4 , the low flash point fuel is ammonia, so the engine is in a low flash point fuel mode running with ammonia as the main fuel, and ammonia is supplied to the ammonia valve 50 at a substantially stable pressure and temperature. Ammonia is supplied to the ammonia valve 50 in a liquid phase, and the ammonia can be an aqueous solution of ammonia (ammonia-water mixture).

[0038] Conventional fuel systems are well known and are not shown and described in further detail. The ammonia fuel system 30 supplies liquid ammonia to the fuel valve 50 at a medium supply pressure (e.g., 30 bar to 80 bar pressure). The engine is a compression ignition type, and the fuel valve 50 includes a supercharger that significantly increases the pressure of the ammonia fuel from the medium pressure to the high pressure to allow the ammonia fuel to be injected at a pressure far higher than the compression pressure of the engine. Typically, the injection pressure of the ignition compression engine is higher than 300 bar.

[0039] Figure 4 The ammonia fuel system 30 including the purge system is disclosed in more detail. Ammonia is stored in a pressurized storage tank 31 in liquid phase at about 17 bar. Ammonia can be stored in the ammonia storage tank 31 in liquid phase at a pressure above 8.6 bar and an ambient temperature of 20° C. Preferably, however, ammonia is stored at a pressure of about 17 bar or more in order to keep the ammonia in liquid phase when the ambient temperature rises.

[0040] The low-pressure ammonia supply line 32 connects the outlet of the ammonia storage tank 31 to the inlet of the medium-pressure supply pump 35. The low-pressure supply pump 33 forces liquid-phase ammonia from the tank 31 through the filter device 34 to the inlet of the medium-pressure supply pump 35. The medium-pressure supply pump 35 forces liquid ammonia to reach the fuel valve 50 through the medium-pressure ammonia supply line 36. A portion of the liquid ammonia supplied to the fuel valve 50 is injected into the combustion chamber of the engine, and another portion of the liquid ammonia supplied to the fuel valve 50 is returned to the ammonia return line 38, which connects the return port of the fuel valve 50 to the low-pressure supply line 32. Therefore, a portion of the liquid ammonia fuel is recycled to the inlet of the medium-pressure supply pump 35.

[0041] When operation on ammonia fuel is stopped, for example due to a malfunction of the ammonia fuel system 30, or when switching to conventional fuel for other reasons, the ammonia fuel system 30 is purged to remove ammonia from the system. To this end, a purge system is used as further explained below.

[0042] A first purge line 42 including a first purge valve 43 connects the medium pressure ammonia supply line 36 to a separation tank 46. Optionally, if a return line is installed in the system, such as Figure 4 As shown, the second purge line 44 including the second purge valve 45 connects the ammonia return line 38 to the separator 46. In the purge operation, the first purge valve 43 and the second purge valve 45 are opened, and the residual ammonia fuel is expanded from the ammonia fuel supply line 36 and the fuel return line 38 to the separator 46 by the excess pressure and gravity in the ammonia fuel supply system 30 in the first extraction step and then by guiding water from the water reservoir 40 through the ammonia fuel supply line 36 and the fuel return line 38 in the second extraction step. The separator 46 is configured to separate the liquid ammonia fuel from the gaseous ammonia. The liquid ammonia outlet is arranged in the lower region of the separator 46 and is connected to the recovery tank 57 via the pipeline 72 and the valve 59. The gaseous ammonia vent line 48 including the valve 49 connects the interior of the separator 46 to the surrounding environment to ventilate the gaseous ammonia from the recovery tank 57 back to the separator 46. The liquid ammonia in the recovery tank 57 is transported to the ammonia storage tank 31 in an embodiment not shown to be used as ammonia fuel. The gaseous ammonia outlet of the separation tank 46 is connected to the ammonia absorption system 60 via the third purge line 47 .

[0043] During a possible first extraction step, where the low flash point fuel (e.g. in the form of ammonia) is driven partly by gravity due to the inclination of the fuel line and partly by a partial pressure of the fuel above 1 bar absolute, the valve 74 in the third purge line 47 is opened. In this way, any gaseous ammonia in the knockout drum 46 can be driven to the ammonia absorption system 60 by the residual pressure.

[0044] After as much ammonia as possible (if any) is extracted from the ammonia fuel system by gravity and residual pressure, valve 41 is opened, and water is allowed to flow from the water reservoir 40 to the ammonia fuel system via the water line 75 and flow through the ammonia fuel system. In this way, the remaining ammonia fuel from the ammonia fuel system and the purge system (including ammonia fuel lines 36, 38, purge lines 42, 44) is directed to the separator 46. As shown, the water pump 73 can be arranged to be connected to the water line 75 to add additional energy to the water. Any gaseous ammonia in the separator 46 is conducted to the ammonia absorption system 60 via the purge line 47.

[0045] In order to completely purge the ammonia fuel system and force any remaining ammonia to the separator tank 46 and possible ammonia absorption system 60, the purge system may also include a ventilation system for forcing atmospheric air through the fuel lines 36, 38, the purge lines 42, 44, 47 and the separator tank 46, the ventilation system including at least a pressurized air source 81 and a valve 82 leading to the ammonia fuel system.

[0046] Before atmospheric air is forced through the fuel lines, it may be advantageous to drain as much water (dissolved residual low-flash point fuel) as possible by gravity to a drain tank 79. To this end, Figure 4 As shown, the purge system may include a water drain line 77 and valve 58 for draining water from the purge line 47 to a drain tank 79 , and a valve 78 for draining water from the fuel lines 36 , 38 and the purge line 42 to the drain tank 79 .

[0047] The ammonia absorption system 60 comprises in the embodiment shown a cascade of three absorption tanks 61 , 63 and 65 connected in series, which, during use, is at least partially filled with water for absorbing ammonia into the water to form aqueous ammonia.

[0048] Aqueous ammonia, also known as aqueous ammonia, is a solution of ammonia in water.

[0049] During the purge operation, gaseous ammonia is routed via the purge line 47 to a cascade of three absorbers in series, the cascade of three absorbers comprising a first absorber 61 , an intermediate absorber 63 , and a final absorber 65 .

[0050] The final absorption tank 65 is provided with a fourth vent 66, which connects the final absorption tank 65 to the surrounding environment. In an embodiment, there are more than three absorption tanks to make the ammonia concentration in the atmosphere above the water in the final absorption tank 10 lower, so that the ammonia concentration in the gas vented through the fourth vent 66 is lower.

[0051] The absorption efficiency of the cascade of absorption tanks is maintained by periodically replacing the water in the last absorption tank 65 from a pressurized (fresh) water source 71 and reusing slightly contaminated water from upstream tanks. Thus, the water in the last tank 65, which has absorbed some ammonia, replaced by water from the water source 71, is delivered to the intermediate absorption tank 63 via a first return water line 67 controlled by a first return water valve 68. Similarly, water from the intermediate absorption tank 63 is delivered to the first absorption tank 61 via a second return water line 69 controlled by a second return water valve 70. The system is configured to compensate for the evaporation of water in the absorption tanks 61, 63, 65 and the removal of 4% ammonia water from the first ammonia tank 61, i.e., the water levels in the absorption tanks 61, 63, 65 are maintained at Figure 4 The dashed line is between the minimum and maximum values.

[0052] Ammonia fume above the water in the first absorber 61 flows to the intermediate absorber 63 via the first ammonia vent line 62. Ammonia fume above the water in the intermediate absorber 63 flows to the final absorber 65 via the second ammonia vent line 64. This process is preferably driven by the pressure of the purge process.

[0053] The ammonia concentration in the fourth vent 66 is low enough to allow venting to the surrounding environment. However, if regulatory compliance is required, the ammonia emissions from the vent mast can be further reduced by introducing an additional absorption tower in which the absorption medium is an acid. In the process of forming ammonium hydroxide, the acid protonates the NH3 (aqueous solution), thereby reducing the ammonia vented to the atmosphere.

[0054] The resulting ammonia concentration in the water in the first absorption tank 61 is higher than the ammonia concentration in the water in the intermediate absorption tank 63 and the ammonia concentration in the water in the intermediate absorption tank 63 is higher than the ammonia concentration in the water in the final ammonia absorption tank 65 .

[0055] The ammonia water of the first absorption tank 61 is removed from the first absorption tank 61 through the first ammonia water return line 51 including the return pump 52. The second ammonia water return line 53 including the return pump 52' and the first return valve 54 connects the first ammonia water return line 51 to the low-pressure ammonia supply line 32. Therefore, when the first return valve 54 is opened, the ammonia water with a relatively high ammonia concentration from the first absorption tank 61 is mixed with the fuel from the ammonia storage tank 31, thereby reusing the ammonia absorbed by the ammonia absorption system 60 as fuel for the engine. The third ammonia water return line 55 including the second return valve 56 connects the first return line 51 to the reductant inlet associated with the SCR reactor 28. The reductant inlet may be part of the SCR reactor 28, or arranged in the exhaust gas flow path upstream of the SCR reactor 28. Therefore, when the second return valve 56 is opened, the ammonia absorbed by the ammonia absorption system 60 is used as a reductant in the SCR reactor 28.

[0056] The cascade system of water tanks 61, 63, 65 is completely passive, i.e. no pumps or other auxiliary systems are required when it is necessary to stop absorbing ammonia. Therefore, the system is inherently reliable and available when needed.

[0057] The low-pressure ammonia fuel line 32, the medium-pressure ammonia fuel line 36 and the ammonia return line 38 are in an embodiment completely or partially composed of double-walled pipes, wherein there is a space between the inner pipe and the outer pipe. Preferably, a detection system is provided to detect whether ammonia exists in the space between the inner pipe and the outer pipe. If ammonia is detected in the space, it allows the ammonia to be stopped, and then the ammonia fuel system is purged, and the residual ammonia is absorbed into the absorption and purge system 60.

[0058] The electronic control unit 100 is connected to the pumps and valves of the fuel system 30, the purge system and the ammonia absorption system 60 via signal lines or wirelessly. The electronic control unit 100 is configured to control these components, for example, by adjusting the speed of the pump and controlling the opening and closing of the corresponding valves to ensure the operation of the fuel system and the purge and absorption systems, as described above.

[0059] Reference Figure 5 , the low flash point fuel is methanol or ethanol, so the engine is in a low flash point fuel mode running with methanol or ethanol as the main fuel, which is supplied to the fuel valve 50 at a substantially stable pressure and temperature.

[0060] Figure 5 The methanol or ethanol fuel system 30 shown is combined with Figure 4 The depicted ammonia fuel system 30 includes a fuel storage tank 31, a supply line 32, a low-pressure supply pump 33, a filter device 34, and a medium-pressure supply pump 35 for forcibly sending the fuel to a fuel supply line 36.

[0061] When operation with methanol or ethanol fuel is stopped, the methanol or ethanol fuel system 30 is purged to remove methanol or ethanol from the fuel system. To this end, a purge system is used as further explained below.

[0062] The purge operation is performed in three steps. In the first purge step, the purge valves 92, 93 and 86 are opened, and the residual methanol or ethanol fuel is driven from the methanol or ethanol fuel supply line 36 and the fuel return line 38 to the first drain tank 87 by gravity and possibly the pressure feed pump 35 (if not bypassed). The purge valve 86 is then closed. In the second purge step, the vent valves 85 and 91 in the vent lines 84 and 90 are opened, respectively, and water is directed from the water reservoir 40 to the methanol or ethanol fuel supply line 36 and the fuel return line 38, possibly by means of the water pump 73 arranged in the water line 75, so that the methanol or ethanol fuel supply line 36 and the fuel return line 38 are completely filled with water. Subsequently, in the third purge step, the purge valve 88 is opened and the mixture of water and methanol or the mixture of water and ethanol is discharged from the methanol or ethanol fuel supply line 36 and the fuel return line 38 to the second drain tank 89 by gravity and possibly the pressure feed pump 35 (if not bypassed). After the fuel supply line 36 and the fuel return line 38 are completely discharged, the purge valve 88 is closed. The purge steps two and three can be repeated as needed to obtain the desired purge of the fuel supply line 36 and the fuel return line 38.

[0063] The first drain tank 87 will contain substantially clean methanol or ethanol fuel, while the second drain tank 89 will contain water with a low concentration of methanol or ethanol. The clean methanol or ethanol fuel in the first drain tank can be advantageously returned to the fuel storage tank 31 for use as fuel. The mixture of water and methanol or the mixture of water and ethanol in the second drain tank 89 can also be returned to the fuel storage tank 31. In one embodiment of the present invention, the system may include only one drain tank.

[0064] If the low flash point fuel is not soluble in water, such as methane, ethane and LPG, the liquid used in the purge system can be diesel or similar liquid, and the purge system can basically correspond to Figure 4 The system shown in , except that the tank 40 should instead contain diesel or similar liquid. In addition, the need for an absorption system is limited and can be omitted.

Claims

1. A large turbocharged two-stroke single-flow crosshead internal combustion engine, the large turbocharged two-stroke single-flow crosshead internal combustion engine having at least one operating mode, in which the main fuel is a low flash point fuel, for example, ammonia, methanol, ethanol, DME, methane, ethane or LPG, the engine comprising: At least one cylinder having a cylinder liner (1), a reciprocating piston (10) located in the cylinder and a cylinder head (22) covering the cylinder, and a combustion chamber formed in the interior of the cylinder between the reciprocating piston (10) and the cylinder head (22); a low-flashpoint fuel system (30), the low-flashpoint fuel system (30) comprising a fuel supply line (36) and a fuel return line (38), and the low-flashpoint fuel system (30) is configured to supply pressurized fuel to at least one fuel valve (50) arranged in the cylinder head (22) or the cylinder liner (1); and a purge system, the purge system being used to remove pressurized fuel from the fuel supply line (36) and the fuel return line (38). The low-flashpoint fuel is extracted from the fuel return line (38), characterized in that the purging system comprises a device (40, 75, 41) for guiding liquid through at least the fuel supply line (36) and the fuel return line (38) of the low-flashpoint fuel system (30), for example, the device (40, 75, 41) for guiding liquid through at least the fuel supply line (36) and the fuel return line (38) of the low-flashpoint fuel system (30) is a device (40, 75, 41) for guiding water or diesel through at least the fuel supply line (36) and the fuel return line (38) of the low-flashpoint fuel system (30).

2. The engine according to claim 1, characterized in that The device for guiding a liquid, such as water or diesel, through at least the fuel supply line (36) and the fuel return line (38) of the low-flashpoint fuel system (30) comprises: a liquid reservoir (40); a liquid pipeline (75) connecting the liquid reservoir with the low-flashpoint fuel system; and a valve (41) for opening and closing the liquid pipeline (75), for example, the valve (41) is an on / off valve, a butterfly valve or the like.

3. The engine according to claim 1, characterized in that The liquid reservoir (40) is arranged at a height that provides the liquid with sufficient potential energy to direct the liquid through the low flash point fuel system.

4. The engine according to claim 3, characterized in that The device for directing liquid through the low-flashpoint fuel system further comprises a liquid pump (73) arranged to be connected to the liquid pipeline (75).

5. The engine according to claim 4, characterized in that The water reservoir (40) is arranged at any suitable height, and the means for directing water through the low-flash point fuel comprises a water pump (73) arranged to be connected to the water pipeline (75).

6. The engine according to claim 1, characterized in that The purge system comprises means for depressurizing and discharging liquid fuel from the low-flashpoint fuel system to a tank (57), the means comprising valves (43, 45) leading to pipelines (42, 44) connecting the low-flashpoint fuel system to the tank (57), for example, the valves (43, 45) being on / off valves, butterfly valves or the like.

7. An engine according to any one of the preceding claims, characterised in that The purge system includes a separator tank (46) configured to separate a liquid portion from a gaseous portion of the expanded low-flash point fuel.

8. The engine according to claim 7, characterized in that The purge system comprises a device (47) for conducting a portion of the gaseous low-flashpoint fuel to an ammonia absorption system (60), for example, the purge system comprises a device (47) for conducting ammonia to an ammonia absorption system (60), and the ammonia absorption system (60) comprises at least one absorption tank (61, 63, 65).

9. An engine according to any one of the preceding claims, characterised in that The purge system also includes a ventilation system for forcing atmospheric air through the fuel lines 36, 38, the purge lines 42, 44, 47 and the knockout tank 46, the ventilation system including at least a pressurized air source (81) and a valve (82) leading to the ammonia fuel system.

10. An engine according to any one of the preceding claims, characterised in that The purge system includes a drain tank 79 , a water drain line 77 and a valve 58 for draining water from the purge line 47 to the drain tank 79 , and a valve 78 for draining water from the fuel lines 36 , 38 and the purge line 42 to the drain tank 79 .

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