DK202170273A1

DK202170273A1 - A large two-stroke uniflow scavenged turbocharged internal combustion engine with ammonia absorption system

Info

Publication number: DK202170273A1
Application number: DKPA202170273A
Authority: DK
Inventors: Rene Hansen Kim; Munch Hansen Jesper; Christensen Henrik
Original assignee: Man Energy Solutions Filial Af Man Energy Solutions Se Tyskland
Priority date: 2021-05-26
Filing date: 2021-05-26
Publication date: 2022-09-26
Also published as: JP7410216B2; KR20220159900A; JP2023159287A; DK181016B1; CN115405442A; JP2022183044A

Abstract

A large two-stroke uniflow scavenged turbocharged internal combustion engine, which has at least one mode of operation in which the main fuel is ammonia. The engine comprises at least one cylinder with cylinder liner (1) and a reciprocating piston (10) therein and cylinder cover (22) covering the cylinder, a combustion chamber (15) formed inside the cylinder (10) between the reciprocating piston (10) and the cylinder cover (22), an ammonia fuel system (30) configured for supplying pressurized ammonia to fuel valves (50,50’) that are arranged in the cylinder cover (22) or in the cylinder liner (1), and an ammonia evacuation flow path (42,44,47) connecting an outlet of the ammonia fuel system (30) to an inlet an ammonia absorption system (60), the ammonia absorption system (60) containing water during use for absorbing ammonia supplied through the evacuation path into the water thereby forming ammonia water.

Description

DK 2021 70273 A1 1 A LARGE TWO-STROKE UNIFLOW SCAVENGED TURBOCHARGED INTERNAL

COMBUSTION ENGINE WITH AMMONIA ABSORPTION SYSTEM

TECHNICAL FIELD The disclosure relates to a large two-stroke uniflow scavenged turbocharged internal combustion engine, that is in at least one mode operated with ammonia as fuel for combustion in the engine.

BACKGROUND Large two-stroke uniflow scavenged turbocharged compression- ignited internal combustion crosshead engines are typically used in propulsion systems of large ships or as a prime mover in power plants. The sheer size, weight, and power output render them completely different from common combustion engines and place large two-stroke turbocharged compression- ignited internal combustion engines in a class for themselves. Internal combustion engines have in the past mainly been operated with hydrocarbon fuels, such as fuel oil, e.g. diesel oil, or fuel gas, e.g. natural gas or petroleum gas. The combustion of hydrocarbon fuels releases carbon dioxide (C02), as well as other greenhouse gases that contribute to atmospheric pollution and climate change. Unlike fossil fuel impurities that result in byproduct emissions, C02 is an unavoidable result of hydrocarbon combustion. The energy density and CO2 footprint of a fuel depend on the hydrocarbon chain length and the complexity of its hydrocarbon molecules. Hence, gaseous hydrocarbon fuels have a lower footprint than liquid hydrocarbon fuels, with the drawback that gaseous hydrocarbon fuels are more challenging and costly to handle

DK 2021 70273 A1 2 and store. In order to reduce the C02 footprint, non- hydrocarbon fuels are being investigated. Ammonia is a synthetic product obtained from fossil fuels, biomass, or renewable sources (wind, solar, hydro, or thermal), and when generated by renewable sources, ammonia will have virtually no carbon footprint or emit any C02, SOX, particulate matter, or unburned hydrocarbons when combusted.

Ammonia has been tested and used at a minor scale in small spark-ignition internal combustion engines but has not been used to power compression-ignition internal combustion engines.

Ammonia is hazardous and has a pungent smell. Therefore, it should be avoided that ammonia escapes from the engine. When operation on ammonia is discontinued and changed to e.g. operation on a conventional fuel, the ammonia in the fuel system needs to be purged and the purged ammonia cannot be simply vented to the atmosphere/surroundings. Other scenarios that require handling of excess ammonia could for example be caused by a leak or other malfunction of the engine. There is a need to provide a solution to the ending of ammonia in these and similar scenarios.

SUMMARY It is an object to provide a large two-stroke uniflow scavenged turbocharged internal combustion engine that overcomes or at least reduces the problems mentioned above.

DK 2021 70273 A1 3 The foregoing 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 figures.

According to a first aspect, there is provided a large two- stroke uniflow scavenged turbocharged internal combustion engine, which has at least one mode of operation in which the main fuel is ammonia, the engine comprising: - at least one cylinder with a cylinder liner a reciprocating piston therein and cylinder cover covering the cylinder, - a combustion chamber formed inside the cylinder between the reciprocating piston and the cylinder cover, - an ammonia fuel system configured for supplying pressurized ammonia to fuel valves that are arranged in the cylinder cover or in the cylinder liner, and - an ammonia evacuation flow path connecting an outlet of the ammonia fuel system to an inlet of an ammonia absorption system, the ammonia absorption system containing water during use for absorbing ammonia supplied through the evacuation path into the water thereby forming ammonia water. By providing a purging flow path and an ammonia absorption system, becomes possible to handle sudden events that require excess ammonia from the engine to be handled, such as a purging event necessary when ending operation on ammonia fuel or a leak event. By dissolving the ammonia in a water containing absorption system, it becomes possible to temporarily store a substantial amount of ammonia in water, thereby creating ammonia water. The ammonia water can be used

DK 2021 70273 A1 4 in the engine as fuel or as a reductant in an SCR reactor for cleaning exhaust gas. In a possible implementation form of the first aspect, the ammonia absorption system comprises at least one vessel, that is during use at least partially filled with water, the at least one vessel preferably comprising a water inlet for connection to a source of water, and preferably comprising an ammonia water outlet for evacuation of the ammonia water.

In a possible implementation form of the first aspect, the engine is a dual-fuel engine, preferably comprising a fuel system for supplying a conventional fuel to the cylinders of the engine.

In a possible implementation form of the first aspect, the ammonia water outlet is connected to the ammonia fuel system for combusting the ammonia water in the engine.

In a possible implementation form of the first aspect, the engine comprises an SCR reactor in an exhaust gas flow path of the engine, wherein the ammonia water outlet is connected to a reductant inlet associated with the SCR reactor.

In a possible implementation form of the first aspect, the ammonia absorption system comprises a pressure vessel that during use is at least partially filled with water, the pressure vessel preferably being provided with cooling system for reducing the temperature of pressure vessel, the pressure vessel preferably comprising a gas phase ammonia inlet for taking in gas phase ammonia and the pressure vessel preferably

DK 2021 70273 A1 being connected to a source of water and the pressure vessel preferably having an ammonia water outlet for evacuation of ammonia water.

5 In a possible implementation form of the first aspect, the ammonia absorption system comprises a packed absorption tower, the packed absorption tower preferably comprising a gas phase ammonia inlet for taking in gas phase ammonia, the packed absorption tower preferably being connected to a source of water and the packed absorption tower preferably having an ammonia water outlet for evacuation of ammonia water. In a possible implementation form of the first aspect, the ammonia absorption system comprises a cascade of water tanks that are during use at least partially filled with water, a first water tank preferably comprising a gas phase ammonia inlet and a gas phase ammonia outlet, a water inlet and an ammonia water outlet, a subsequent water tank preferably comprising a gas phase ammonia inlet connected to the gas phase ammonia outlet of the first water tank, and an ammonia water outlet connected to the water inlet of the first water tank and an ammonia gas phase outlet, the cascade of water tanks preferably being configured for a counterflow of a flow of water against a flow of gas phase ammonia, with the most upstream tank in the flow of gas phase ammonia during use having the highest concentration of ammonia in the water in the tank and being provided with an ammonia water outlet and the most downstream tank in the flow of gas phase ammonia during use having the lowest concentration of ammonia in the water in the tank, the most downstream tank in the flow of

DK 2021 70273 A1 6 gas phase ammonia preferably being provided with a vent for venting gaseous phase material from the tank.

In a possible implementation form of the first aspect, the ammonia fuel system comprises a purging system configured for evacuating ammonia from the fuel system to the ammonia absorption system, the purging system preferably comprising a source of pressurized nitrogen, the source of pressurized nitrogen preferably being connected to the fuel system via a purge valve, the purging system preferably using the ammonia evacuation flow path for purging ammonia from the ammonia fuel system to the ammonia absorption system.

In a possible implementation form of the first aspect, the ammonia fuel system comprises a medium pressure ammonia supply line and an ammonia return line, a first purge line connecting the medium pressure ammonia supply line to the ammonia absorption system, a second purge line connecting the ammonia return line to the ammonia absorption system, and preferably valving for selectively connecting the medium pressure ammonia supply valve and the ammonia return line to the ammonia absorption system.

In a possible implementation form of the first aspect, a knockout drum is arranged in the first and/or second purge line, the knockout drum being configured for separating liquid phase ammonia from gas phase ammonia, the knockout drum comprising a gas phase ammonia outlet and a liquid phase ammonia outlet, the gas phase ammonia outlet of the knockout drum being connected to the ammonia absorption system and the liquid phase ammonia outlet preferably being connected to a

DK 2021 70273 A1 7 recovery tank that in turn is connected to the ammonia fuel system.

In a possible implementation form of the first aspect, the ammonia fuel system comprises a supply line and a return line, wherein the piping forming the supply line and the return line comprises double-walled piping, and wherein a space between an inner pipe of the double-wall piping and an outer pipe of the double walled piping is fluidically connected to the ammonia absorption system by the ammonia evacuation path.

In a possible implementation form of the first aspect, the ammonia fuel system comprises a liquid phase ammonia fuel tank, a low-pressure ammonia supply line connecting the liquid phase ammonia fuel tank to an inlet of a medium pressure fuel pump by the action of a low-pressure pump, the fuel system preferably comprising a medium pressure fuel line connecting an outlet of the medium pressure pump to an inlet of the fuel valves, the fuel system preferably comprising a return line connecting an outlet of the fuel valves to the inlet of the medium pressure fuel pump.

In a possible implementation form of the first aspect, the at least one cylinder is provided with scavenging ports at a lower region of the cylinder.

In a possible implementation form of the first aspect, the cylinder cover is provided with a central exhaust valve, with two or more fuel valves surrounding the central exhaust valve.

DK 2021 70273 A1 8 According to a second aspect, there is provided a method of managing ammonia in a large two-stroke uniflow scavenged turbocharged internal combustion engine, which has at least one mode of operation in which the main fuel is ammonia, the engine comprising: - at least one cylinder with cylinder liner and a reciprocating piston therein and cylinder cover covering the cylinder, - a combustion chamber formed inside the cylinder between the reciprocating piston and the cylinder cover, - an ammonia fuel system configured for supplying pressurized ammonia to fuel valves that are arranged in the cylinder cover or in the cylinder liner, the method comprising: - conveying excess gas phase ammonia from the fuel system to an ammonia absorption system and absorbing the gas phase ammonia in water thereby forming ammonia water.

In a possible implementation form of the second aspect, the method comprises separating liquid phase ammonia and gas phase ammonia originating from the excess ammonia, preferably using a knock-out drum, conveying the gas phase ammonia to the ammonia absorbing system, and absorbing the ammonia in water thereby forming ammonia water.

In a possible implementation form of the second aspect, the method comprises using the ammonia water as fuel for the engine or as reductant for an SCR reactor of the engine.

These and other aspects will be apparent from and the embodiment (s) described below.

DK 2021 70273 A1 9

BRIEF DESCRIPTION OF THE DRAWINGS In the following detailed portion of the present disclosure, the aspects, embodiments, and implementations will be explained in more detail with reference to the example embodiments shown in the drawings, in which: Fig. 1 is an elevated front view of a large two-stroke diesel engine according to an example embodiment. Fig. 2 is an elevated side view of the large two-stroke engine of Fig. 1. Fig. 3 is a diagrammatic representation of the large two- stroke engine according to Fig. 1. Fig. 4 is a diagrammatic representation of the engine with ammonia fuel system, ammonia purging system, and ammonia absorption system according to a first embodiment, Fig. 5 is a diagrammatic representation of the engine with ammonia fuel system, ammonia purging system, and ammonia absorption system according to a second embodiment.

DETAILED DESCRIPTION In the following detailed description, an internal combustion engine will be described with reference to a large two-stroke low-speed uniflow scavenged turbocharged internal combustion engine with crossheads in the example embodiments, but it is understood that the internal combustion engine could be of another type. The large two-stroke low-speed > uniflow scavenged turbocharged internal combustion engine can be of the (high-pressure) type in which fuel is injected at or near top dead center of the pistons that is compression ignited or of the (low pressure) type in which fuel is mixed with the

DK 2021 70273 A1 10 scavenging air before or during compression that is spark ignited. In the latter case there will typically be a “pilot” ignition with an ignition fluid, e.g. fuel oil, for ensuring reliable ignition.

Figs. 1, 2, and 3 show a large low-speed turbocharged two- stroke diesel engine with a crankshaft 8 and crossheads 9. Fig. 3 shows a diagrammatic representation of a large low- speed turbocharged two-stroke diesel engine with its intake and exhaust systems. In this example embodiment, the engine has six cylinders in line. Large low-speed turbocharged two- stroke diesel engines have typically between four and fourteen cylinders in line, carried by a cylinder frame 23 that is carried by an engine frame 11. The engine may e.g. be used as the main engine in a marine vessel or as a stationary engine for operating a generator in a power station. The total output of the engine may, for example, range from 1,000 to 110, 000 kW.

The engine is in this example embodiment a dual-fuel compression-ignited engine of the two-stroke uniflow type with scavenging ports 18 in the lower region of the cylinder liners 1 and a central exhaust valve 4 at the top of each cylinder liner 1. The engine has at least one ammonia mode in which the engine is operated on ammonia fuel or an ammonia- based fuel and at least one conventional fuel mode in which the engine is operated on conventional fuel, e.g. fuel oil (marine diesel), or heavy fuel oil.

The scavenge air is passed from the scavenge air receiver 2 to the scavenge ports 18 of the individual cylinders 1. A

DK 2021 70273 A1 11 piston 10 that reciprocates in the cylinder liner 1 between the bottom dead center (BDC) and top dead center (TDC) compresses the scavenge air. Fuel (ammonia in the ammonia mode) is injected through (high-presure) fuel valves 50 that are arranged in the cylinder cover 22 into the combustion chamber in the cylinder liner 1 at or near TDC. Combustion follows, and exhaust gas is generated. Fach cylinder cover 22 is provided with two or more fuel valves 50. The fuel valves 50 are either configured to inject only one specific type of fuel, e.g. ammonia and in this case, there will also be two or more fuel valves 54 injecting conventional fuel into the combustion chamber. Hence, the engine will have four or more fuel valves. In case the fuel valves 50 are suitable for injecting both ammonia suitable for injecting conventional fuel there can be two or more fuel valves 50 for each cylinder. The fuel valves 50 are arranged in the cylinder cover 22 around the central exhaust valve 4. Further, additional, typically smaller fuel valves (not shown) are in an embodiment provided in the cylinder cover for injecting ignition fluid, for ensuring reliable ignition of the ammonia fuel. The ignition fuel is e.g. dimethyl ether (DME) or fuel oil, but can also be another form of ignition enhancer, such as 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 the conventional fuel to the fuel valves

50. In an embodiment, the fuel valves 50’ are arranged along the cylinder liner (shown by the interrupted lines) and admit the fuel into the cylinder liner before the piston 10 passes the fuel valves 50’ on its way from BDC to TDC. Thus, the piston 10 compresses a mixture of scavenging air and fuel. Timed ignition at or near TDC is triggered by spark, laser,

DK 2021 70273 A1 12 ignition fluid injection, or the like. In the embodiment with the fuel valves 50’ the pressure at which the fuel is admitted is substantially lower than the pressure at which the fuel is injected in the embodiment with the fuel valves 50 in the cylinder cover 22. Hence, the pressure at which the fuel supply system 30 needs to deliver fuel can be significantly lower, and/or pressure boosters, that are often used in the fuel valve 50 that are located in the cylinder cover can be avoided.

When an exhaust valve 4 is opened, the exhaust gas flows through an exhaust duct associated with the cylinders into the exhaust gas receiver 3 and onwards through a first exhaust conduit 19 via a Selective Catalytic Reduction (SCR) reactor 28 to a turbine 6 of the turbocharger 5, from which the exhaust gas flows away through a second exhaust conduit via an economizer 20 to an outlet 21 and into the atmosphere. The SCR reactor reduces emissions, in particular NOx emissions. Through a shaft, the turbine 6 drives a compressor 7 supplied with fresh air via an air inlet 12. The compressor 7 delivers pressurized scavenge air to a scavenge air conduit 13 leading to the scavenge air receiver 2. The scavenge air in the scavenge air conduit 13 passes an intercooler 14 for cooling the scavenge air. The cooled scavenge air passes via an auxiliary blower 16 driven by an electric motor 17 that pressurizes the scavenge alr flow when the compressor 7 of the turbocharger 5 does not deliver sufficient pressure for the scavenge air receiver 2, i.e. in low or partial load conditions of the engine. At

DK 2021 70273 A1 13 higher engine loads the turbocharger compressor 7 delivers sufficient compressed scavenge air and then the auxiliary blower 16 is bypassed via a non-return valve 15 and the electric motor 17 is deactivated.

The engine is in the ammonia mode operated with ammonia as the main fuel which is supplied to the ammonia valves 50 at a substantially stable pressure and temperature. The ammonia can be supplied to the ammonia valves 50 in the liquid phase or in the gaseous phase. The ammonia liquid phase can be aqueous ammonia (ammonia-water blend). The conventional fuel system is well known and not shown and described in further detail. The ammonia fuel system 30 supplies the fuel valves 50 with liquid phase ammonia at a medium supply pressure (e.g. 30 to 80 bar pressure). Alternatively, the ammonia fuel is supplied at a relatively low supply pressure (e.g. 30 to 80 bar pressure) to the ammonia valves 50 in the gaseous phase. If the engine of the compression-igniting type, the fuel valves 50 comprise a pressure booster that significantly raises the pressure of the ammonia fuel from the medium pressure to a high pressure to allow the ammonia fuel to be injected at a pressure well above the compression pressure of the engine. Typically, the injection pressure for an ignition-compressing engine is above 300 bar. With reference to Fig. 4, the ammonia fuel system 30, including a purging and ammonia absorption system 60 is disclosed in greater detail. Ammonia is stored in the liquid phase in a pressurized storage tank 31 at approximately 17

DK 2021 70273 A1 14 bar.

Ammonia can be stored in the liquid phase at a pressure above 8.6 bar and an ambient temperature of 20°C in an ammonia storage tank 31. However, ammonia is preferably stored at approximately 17 bar or higher to keep it in the liquid phase when the ambient temperature increases.

A low-pressure ammonia supply line 32 connects an outlet of the ammonia storage tank 31 to the inlet of a medium pressure feed pump 35. A low-pressure feed pump 33 forces the liquid phase ammonia from the tank 31, through a filter arrangement 34 to an inlet of the medium pressure feed pump 35. The medium pressure feed pump 35 forces the liquid ammonia through a medium pressure ammonia supply line 36 to the fuel valves 50. A portion of the liquid ammonia that is supplied to the fuel valves 50 is injected into the combustion chambers of the engine whilst another portion of the liquid ammonia that is supplied to the fuel valve 50 is returned to an ammonia return line 38 that connects a return port of the fuel valves 50 to the low-pressure supply line 32. Thus, a portion of the liquid ammonia fuel is recycled to inlet of the medium pressure feed pump 35. When operation on ammonia fuel is discontinued, for example due to a failure in the ammonia fuel system 30, or another reason for switching to conventional fuel, the ammonia fuel system 30 is purged to remove the ammonia from the system.

Hereto, a source of pressurized nitrogen 40, for example, a pressurized nitrogen vessel 40 is connected via a purge valve 41 to the medium pressure ammonia supply line 36, preferably just downstream of the medium pressure feed pump 35.

DK 2021 70273 A1 15 A first purge line 42 that includes a second purge valve 43 connects the medium pressure ammonia supply line 36 to a knockout drum 46. A second purge line 44 that includes a third purge valve 45 connects the ammonia return line 38 to the knockout drum 46. In a purging operation, the first, second, and third purging valves 41,43,45 are opened, and the pressurized nitrogen drives the residual ammonia fuel from the ammonia fuel supply and return lines 38,38 into the knockout drum 46. The knockout drum 46 is configured to separate the liquid phase ammonia fuel from gas phase ammonia.

A nitrogen vent line 48, which includes a nitrogen vent valve 49 connects the interior of the knockout drum 46 to the surroundings for venting nitrogen from the knockout drum 46. A liquid phase ammonia outlet is arranged in the lower area of the knockout drum 46 and connects to a recovery tank 57. The liquid ammonia in the recovery tank 57 is in an embodiment conveyed to the ammonia storage tank 31 for being used as ammonia fuel.

A gas phase ammonia outlet of the knockout drum 46 is connected via third purge line 47 to the ammonia absorption system 60. The ammonia absorption system 60 comprises at least one vessel that during use is at least partially filled with water for absorbing the ammonia into the water to form ammonia water.

Ammonia water, also referred to as aqueous ammonia, is a solution of ammonia in water.

The present embodiment comprises a pressure vessel 58 that is during use at least partially filled with water.

The pressure vessel 58 is preferably cooled (cooling means not shown) since heat is created when dissolving ammonia in water and the

DK 2021 70273 A1 16 ability of water to absorb ammonia decreases with increasing temperatures of the water.

Hence, the cooling means are configured to keep reduce the temperature of the water in the pressure vessel, for optimizing the capacity of the water in the pressure vessel 58 to absorb ammonia.

The pressure vessel 58 has a gaseous ammonia inlet for receiving gaseous ammonia via a pressure vessel ammonia supply conduit 59. The pressure vessel ammonia supply conduit 59 includes a nonreturn valve 73 to prevent the return of fluid from the pressure vessel 58 to the third purge line 47. The pressure vessel 58 has an inlet for (fresh) water that is connected via a conduit to a pressurized source of (fresh) water 71. In the present context, freshwater is water that does not have any substantial amount of ammonia dissolved therein and therefore has still been almost full potential to absorb ammonia.

The level of the water in the pressure vessel 58 is regulated between an upper and lower level.

The gaseous ammonia supplied to the pressure vessel 58 is absorbed in the water to form ammonia water.

The pressure in the pressure vessel is regulated and kept at a suitable high pressure since water can absorb a higher amount of gas phase ammonia at higher pressures.

The pressure vessel 58 is provided with an ammonia water outlet.

The amount of freshwater that is allowed into the pressure vessel 58 and the amount of ammonia water that is evacuated from the pressure vessel 58 is controlled, to ensure that there is sufficient capacity to absorb ammonia.

The ammonia water outlet connects to a third return line 55 via an ammonia water evacuation conduit 75. The ammonia water evacuation conduit 75 comprises a valve 76 for controlling the flow from the pressure vessel 58 to the third return line

DK 2021 70273 A1 17

55. From the third return line 5, the ammonia water is conveyed either to the SCR reactor 28 to be used as a reductant in that the SCR reactor 28, or to the low-pressure ammonia supply line 32 to be used as fuel in the engine, as described in greater detail further below. The third person 47 includes a pressure regulation valve 74, that opens when a predetermined pressure in the third purge line 47 has been exceeded. This printer pressure corresponds to the maximum pressure at which the pressure vessel 58 can operate that ensures that gas phase ammonia is instead routed to a cascade of three absorption tanks in series: a first absorption tank 61, a middle absorption tank 63, and a last absorption tank

65. In another embodiment, the control of the flow of gas phase ammonia from the third purge line 47 to either the pressure vessel 58 or to the cascade of water tank 61, 63, 65 is controlled by electronic control valves (not shown) instead of the shown pressure regulated system. The last absorption tank 65 is provided with a fourth vent 66 that connects the last absorption tank 65 to the surroundings. In an embodiment, there are be more than three absorption tanks to obtain a lower concentration of ammonia in the atmosphere above the water in the last absorption 10, and hence a lower concentration of ammonia in the gases vented through the fourth vent 66. The absorption efficiency of the cascade of absorption tanks is maintained by regular replacement of the water in the last absorption tank 65 from the pressurized source of (fresh) water 71 and reusing the slightly contaminated water in the upstream tanks. Hence, the water in the last tank 65 in which

DK 2021 70273 A1 18 some ammonia is absorbed that is replaced by water from the source of water 71 is transported to the middle absorption tank 63 through a first water return Lline 67 that is controlled by a first water return valve 68. Similarly, water from the middle absorption tank 63 is transported to the first absorption tank 61 through a second water return line 69 that is controlled by a second water return valve 70. The system is configured to compensate for the evaporation of water in the absorption tanks 61, 63, 65, and 4 ammonia water removed from the first ammonia tank 61, i.e. the water level in the absorption tanks 61, 63, 65 is kept between a minimum and maximum indicated by the dashed lines in Fig. 4. The ammonia fumes above the water in the first absorption tank 61 flow via a first ammonia vent line 62 to the middle absorption tank 63. The ammonia fumes above the water in the middle absorption tank 63 flow via a second ammonia vent line 64 to the last absorption tank 65. The process is preferably driven by the pressure of the purge process.

The ammonia concentration in the fourth vent 66 is sufficiently low to allow venting to the surroundings. However, if needed to comply with regulations the ammonia emissions from the vent mast can be further decreased by introducing an additional absorption column where the absorbing media is an acid. The acid protonates the NH3 (aq) under the formation of ammonium hydroxide and thus reduces the ammonia that is vented atmosphere.

The resulting ammonia concentration in the water in the first absorption tank 61 is higher than the ammonia concentration

DK 2021 70273 A1 19 in the water in the middle absorption tank 63 and the ammonia concentration in the water in the middle absorption tank 63 is higher than the ammonia concentration in the water in the last ammonia absorption tank 65.

The ammonia water of the first absorption tank 61 is removed from the first absorption tank 61 through a first ammonia water return line 51 that includes a return pump 52. A second ammonia water return line 53 that includes a first return valve 54 connects the first ammonia water return line 51 to the low-pressure ammonia supply line 32. Thus, when the first return valve 54 is opened the ammonia water with the relatively high ammonia concentration originating from the first absorption tank 61 is mixed with the fuel coming from the ammonia storage tank 31 and the ammonia that is absorbed by the ammonia absorption system 60 is thereby be reused as fuel for the engine. A third ammonia water return line 55 that includes a second return valve 56 connects the first return 51 to a reductant inlet associated with the SCR reactor

28. The reductant inlet can be part of the SCR reactor 28 or be arranged in the exhaust gas flow path upstream of the SCR reactor 28. Thus, when the second return valve 56 is open the ammonia that is absorbed by the ammonia absorption system 60 is used as a reductant in the SCR reactor 28.

Cascade of water tanks 61, 63, 65 system is fully passive, i.e. that no pumps or other axillary systems need to be available when a shutdown absorption of ammonia is required. Hence, the system will inherently be reliable and available when needed.

DK 2021 70273 A1 20 The low-pressure ammonia fuel line 32, the medium pressure ammonia fuel line 36, and the ammonia return line 38 are in embodiment completely or partially constructed of double- walled piping with a space between an inner pipe and an outer pipe. In this embodiment, the space between the inner and outer pipe is connected to the purging system, so that ammonia fuel that inadvertently leaks into the space between the inner and outer pipes is connected to the ammonia absorption system 60 for absorption. Thus, inadvertent admission of ammonia into the surroundings in case of a leak in any of the fuel lines can be avoided through absorption in the ammonia absorption system 60. Preferably, a detection system is provided that detects the presence of ammonia in the space between the inner and outer tubing, allowing for discontinuation of the operational ammonia if ammonia Ås detected in the space, followed by a subsequent purging of the ammonia fuel system and absorption of the residual ammonia into the absorption purging system 60.

An electronic control unit 100 is connected via signal lines or wirelessly to the pumps and valves of the fuel system 30, the purging system and the and the ammonia absorption 60. The electronic control unit 100 is configured to control these components, e.g. by regulating the speed of the pumps and by controlling the opening and closing of the respective valves, to ensure the operation of the fuel system and the purging and absorption system as described above.

Fig. 5 illustrates a second embodiment of the engine with its fuel, purging, and ammonia absorption system. In this embodiment, structures and features that are the same or

DK 2021 70273 A1 21 similar to corresponding structures and features previously described or shown herein are denoted by the same reference numeral as previously used for simplicity. The embodiment according to Fig. 5 is essentially identical to the embodiment according to Fig. 5, except that the cascade of water tanks is replaced by a packed absorption tower 78. The packed absorption tower 78 is used for gas absorption of ammonia and subsequent discharge of ammonia water. The gas-liquid (water) contact in the packed absorption tower 78 is continuous. The water flows down in the tower over a packing surface and the gas phase ammonia moves counter-currently, up the tower 78. A packed absorption tower 78 is a vessel that has a packed section. The tower is filled with one or more structured packing sections, which are stacked. The packed absorption tower 78 has an inlet for receiving ammonia gas that is connected to the third person 47 via the pressure regulation valve 74. The act absorption tower has an outlet for ammonia water that connects to the first ammonia water return line

51. The source of pressurized (fresh) water 71 connects to the packed absorption tower 78 and an inlet that is arranged above the structured packing sections. A vent 76 is provided for venting the space above the packed sections to the surroundings. The magnitude flow of water from the source of pressurized (fresh) for 71 is adapted to the magnitude of the flow of gas phase ammonia into the packed absorption tower

78. The amount of ammonia water that collects at the bottom of the pack absorption tower 78 is regulated and when needed transported to an intermediate ammonia water storage tank (not shown).

DK 2021 70273 A1 22 The various aspects and implementations have been described in conjunction with various embodiments herein.

However, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed subject-matter, from a study of the drawings, the disclosure, and the appended claims.

In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality.

A

The reference signs used in the claims shall not be construed as limiting the scope.

Unless otherwise indicated, the drawings are intended to be read (e.g., cross-hatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this disclosure.

Claims

DK 2021 70273 A1 23 CLAIMS

1. A large two-stroke uniflow scavenged turbocharged internal combustion engine, which has at least one mode of operation in which the main fuel is ammonia, said engine comprising: - at least one cylinder with a cylinder liner (1) and a reciprocating piston (10) therein and a cylinder cover (22) covering the cylinder, - a combustion chamber (15) formed inside the cylinder (10) between the reciprocating piston (10) and the cylinder cover (22), - an ammonia fuel system (30) configured for supplying pressurized ammonia to fuel valves (50,507) that are arranged in said cylinder cover (22) or in said cylinder liner (1), and - an ammonia evacuation flow path (42,44,47) connecting an outlet of said ammonia fuel system (30) to an inlet of an ammonia absorption system (60), sald ammonia absorption system (60) containing water during use for absorbing ammonia supplied through said evacuation path into said water thereby forming ammonia water.

2. The engine of claim 1, wherein said ammonia absorption system (60) comprises at least one vessel (58,61,63,65,78), that is during use at least partially filled with water, said at least one vessel (58,61,63,65, 78) preferably comprising a water inlet for connection to a source of water (71), and preferably comprising an ammonia water outlet for evacuation of said ammonia water.

DK 2021 70273 A1 24

3. The engine claim 2, wherein said ammonia water outlet is connected to said ammonia fuel system (30) for combusting sald ammonia water in said engine.

4. The engine according to claim 2 or 3, comprising an SCR reactor (28) in an exhaust gas flow path of the engine, wherein said ammonia water outlet is connected to a reductant inlet associated with said SCR reactor (28).

5. The engine according to any of the preceding claims, wherein said ammonia absorption system (60) comprises a pressure vessel (58) that during use is at least partially filled with water, said pressure vessel (58) preferably being provided with cooling system for reducing the temperature of pressure vessel (58), said pressure vessel (58) preferably comprising a gas phase ammonia inlet for taking in gas phase ammonia and said pressure vessel preferably being connected to a source of water (71) and said pressure vessel (58) preferably having an ammonia water outlet for evacuation of ammonia water.

6. The engine according to any of the preceding claims, wherein said ammonia absorption system (60) comprises a packed absorption tower (78), said packed absorption tower (78) preferably comprises a gas phase ammonia inlet for taking in gas phase ammonia, said ammonia absorption system (60) preferably being connected to a source of water (71) and said ammonia absorption system (60) preferably having an ammonia water outlet for evacuation of ammonia water.

DK 2021 70273 A1 25

7. The engine according to the preceding claims, wherein said ammonia absorption system (60) comprises a cascade of water tanks (61, 63, 65) that are during use at least partially filled with water, a first water tank (61) preferably comprising a gas phase ammonia inlet and a gas phase ammonia outlet, a water inlet and an ammonia water outlet, a subsequent water tank (62, 63) preferably comprising a gas phase ammonia inlet connected to the gas phase ammonia outlet of the first water tank (61), and an ammonia water outlet connected to the water inlet of the first water tank (61) and an ammonia gas phase outlet, said cascade of water tanks (61,62,65) preferably being configured for a counterflow of a flow of water against a flow of gas phase ammonia, with the most upstream tank (61) in the flow of gas phase ammonia during use having the highest concentration of ammonia in the water in the tank (61) and being provided with an ammonia water outlet and the most downstream tank (65) in the flow of gas phase ammonia during use having the lowest concentration of ammonia in the water in the tank (65), said most downstream tank (65) in the flow of gas phase ammonia preferably being provided with a vent for venting gaseous phase material from said tank (65).

8. The engine according to any one of the preceding claims, wherein said ammonia fuel system (30) comprises a purging system configured for evacuating ammonia from the fuel system (30) to the ammonia absorption system (60), said purging system preferably comprising a source of pressurized nitrogen (40), said source of pressurized nitrogen preferably being connected to said fuel system via a purge valve (41), said purging system preferably using said ammonia evacuation flow

DK 2021 70273 A1 26 path for purging ammonia from the ammonia fuel system (30) to the ammonia absorption system (60).

9. The engine according to claim 8, wherein said ammonia fuel system (30) comprises a medium pressure ammonia supply line (36) and an ammonia return line (38), a first purge line (42) connecting said medium pressure ammonia supply line (36) to sald ammonia absorption system (60), a second purge line (44) connecting said ammonia return line (38) to said ammonia absorption system (60), and preferably valving (43, 45) for selectively connecting said medium pressure ammonia supply valve (36) and said ammonia return line (38) to said ammonia absorption system (60).

10. The engine according to claim 9, comprising a knockout drum (46) in the first and/or second purge line (42, 44), said knockout drum (46) being configured for separating liquid phase ammonia from gas phase ammonia, said knockout drum (46) comprising a gas phase ammonia outlet and a liquid phase ammonia outlet, said gas phase ammonia outlet being connected to said ammonia absorption system (60) and said liquid phase ammonia outlet preferably being connected to a recovery tank (57) that in turn is connected to the ammonia fuel system (30).

11. The engine according to any one of the preceding claims, wherein said ammonia fuel system (30) comprises a supply line (32,36) and a return line (38), wherein the piping forming sald supply line (32,35) and said return line (38) comprises double-walled piping, and wherein a space between an inner pipe of said double-wall piping and an outer pipe of said

DK 2021 70273 A1 27 double-walled piping is fluidically connected to said ammonia absorption system (60) by said ammonia evacuation path.

12. The engine according to any one of the preceding claims, wherein said ammonia fuel system (30) comprises a liquid phase ammonia fuel tank (31), a low-pressure ammonia supply line (32) connecting said liquid phase ammonia fuel tank (31) to an inlet of a medium pressure fuel pump (35) by the action of a low-pressure pump (33), said fuel system (30) preferably comprises a medium pressure fuel line (36) connecting an outlet of said medium pressure pump (35) to an inlet of said fuel valves (50,507), said fuel system (30) preferably comprises a return line (38) connecting an outlet of said fuel valves (50,507) to the inlet of said medium pressure fuel pump (35).

13. A method of managing ammonia in a large two-stroke uniflow scavenged turbocharged internal combustion engine, which has at least one mode of operation in which the main fuel is ammonia, said engine comprising: - at least one cylinder with a cylinder liner (1) and a reciprocating piston (10) therein and a cylinder cover (22) covering the cylinder (1), - a combustion chamber (15) formed inside the cylinder (10) between the reciprocating piston (10) and the cylinder cover (22), - an ammonia fuel system (30) configured for supplying pressurized ammonia to fuel valves (50,507) that are arranged in said cylinder cover (22) or in the cylinder liner (1), said method comprising:

DK 2021 70273 A1 28 - conveying excess gas phase ammonia from said fuel system (30) to an ammonia absorption system (60) and absorbing said gas phase ammonia in water thereby forming ammonia water.

14. The method of claim 13, comprising separating liquid phase ammonia and gas phase ammonia originating from said excess ammonia, preferably using a knock-out drum (46), conveying sald gas phase ammonia to said ammonia absorbing system (60), and absorbing said ammonia in water thereby forming ammonia water.

15. The method of claim 13 or 14, comprising using said ammonia water as fuel for said engine or as a reductant for an SCR reactor (28) of said engine.