DK181454B1

DK181454B1 - A large two-stroke uniflow scavenged turbocharged internal combustion engine with a system for reducing nitrous oxide emissions and a method for reducing nitrous oxide emissions of such an engine

Info

Publication number: DK181454B1
Application number: DKPA202270087A
Authority: DK
Inventors: Kjemtrup Niels; Christensen Henrik
Original assignee: Man Energy Solutions Filial Af Man Energy Solutions Se Tyskland
Priority date: 2022-03-04
Filing date: 2022-03-04
Publication date: 2024-01-26
Also published as: CN116696520A; JP2023129320A; KR20230131441A; DK202270087A1

Abstract

A large two-stroke uniflow scavenged turbocharged internal combustion engine configured for removing nitrous oxide from exhaust gas using an electrogenerated mediator in a wet scrubber and a method for removing nitrous oxide from the exhaust gas of a large two-stroke uniflow scavenged turbocharged internal combustion engine by wet electroscrubbing.

Description

DK 181454 B1 1

A LARGE TWO-STROKE UNIFLOW SCAVENGED TURBOCHARGED INTERNAL

COMBUSTION ENGINE WITH A SYSTEM FOR REDUCING NITROUS OXIDE

EMISSIONS AND A METHOD FOR REDUCING NITROUS OXIDE EMISSIONS

OF SUCH AN ENGINE

TECHNICAL FIELD

This 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 with a system for reducing nitrous oxide emissions, and to a method for reducing nitrous oxide emissions of such 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 (CO2), as well as other greenhouse gases that contribute to atmospheric pollution and climate change. Unlike fossil fuel impurities that result in byproduct emissions, CO2 is an unavoidable result of hydrocarbon combustion. The energy density and CO2 footprint of a specific fuel depend on the

DK 181454 B1 2 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 and store. In order to reduce the C02 footprint, non-hydrocarbon fuels are being investigated.

Ammonia 1s 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 fueled engines tend to generate nitrous oxide (N20) as a side product of the combustion. Without countermeasures, exhaust gas containing this nitrous oxide will end up in the atmosphere. Nitrous oxide is known to have a substantial global warming potential, which is approximately 265 times that of CO2 according to FN climate report IPPC ARL. Hence, there is a need to reduce nitrous oxide emissions of large two-stroke uniflow scavenged turbocharged internal combustion engines that are fueled with ammonia.

Commercially available systems for removing nitrous oxide from exhaust gas use in catalytic decomposition and thermal destruction, these methods convert nitrous oxide into

DK 181454 B1 3 nitrogen and oxygen. Catalytic decomposition operates at about 500 °C and thermal destruction operates close to 1000 °C. The temperature of exhaust gas of large two-stroke uniflow scavenged turbocharged internal combustion engine is insufficient for use with these known methods, since the pre- turbine exhaust gas temperature is, depending on operating conditions, typically between 300-500 °C and the post-turbine exhaust gas temperature is, depending on operating conditions, typically between 150-250 °C. Hence, catalytic decomposition and thermal destruction are not suitable for removing nitrous oxide from the exhaust gas of ammonia fueled large two-stroke uniflow scavenged turbocharged internal combustion engines.

DK178072B1 discloses a large two-stroke uniflow scavenged turbocharged internal combustion engine, which operates with a first fuel that comprises the liquid fuel and a second fuel that comprises ammonia, and the engine comprises at least one cylinder with a cylinder liner and a reciprocating piston therein and a 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, a turbocharging system comprising at least one compressor for compressing scavenging air and at least one exhaust gas driven turbine. Scrubbers are provided for cleaning the recirculated exhaust gas before it reenters the combustion chambers.

Increasing the ratio of exhaust gas recirculation when operating on a lower caloric value fuel, such as ammonia ensures that NOx emissions are kept low.

DK 181454 B1 4

DK201900097U3 discloses a system for generating power on a ship. The system includes: an ammonia engine arranged to generate exhaust gas; and a turbocharger including a turbine and a compressor. The ammonia engine includes an exhaust gas outlet and an exhaust gas inlet connected to enable a first portion of the exhaust gas generated by the ammonia engine to be recycled back to the ammonia engine. The turbine is in communication with the ammonia engine and is arranged to rotate by a second portion of the exhaust gas generated by the ammonia engine. The compressor is arranged to be powered by turbine rotation to pressurize air, and the compressor is in communication with the ammonia engine to supply pressurized alr to the ammonia engine. The system further comprises a scrubber for washing and cooling the first portion of the exhaust gas with a scrubber fluid. The scrubber is in communication with the ammonia engine for receiving the first portion of exhaust gas from the ammonia engine. Further, a scrubber is in communication with the ammonia engine for supplying the first portion of the exhaust gas to the ammonia engine after cleaning and cooling the first portion.

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.

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.

DK 181454 B1

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: 5 - at least one cylinder with a cylinder liner and a reciprocating piston therein and a 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, - a turbocharging system comprising at least one compressor for compressing scavenging air and at least one exhaust gas driven turbine, and - a nitrous oxide scrubber downstream of said at least one exhaust gas driven turbine configured for transforming nitrous oxide in the exhaust gas flowing through the scrubber to ammonia and/or for reducing nitrous oxide in the exhaust gas flowing through the scrubber into nitrogen and oxygen or into nitrogen and hydroxide.

In a possible implementation form of the first aspect, the scrubber is an electroscrubber that couples wet-scrubbing with an electrogenerated mediator, preferably a NI based mediator, more preferably, a NiI[NiICN4]3- mediator, to transform nitrous oxide in a single process stage to ammonia and/or for reducing nitrous oxide in the exhaust gas flowing through the scrubber into nitrogen and oxygen or into nitrogen and hydroxide.

DK 181454 B1 6

In a possible implementation form of the first aspect, the engine comprises a circulation system circulating water containing a mediator through the scrubber, the mediator preferably being an electrogenerated mediator, and the circulation system preferably comprising an electrolytic tank coupled to an electric voltage source for electrogenerating the mediator, the electrolytic tank preferably comprising at least two electrodes coupled to the electric voltage source.

In a possible implementation form of the first aspect, the engine comprises means for separating the ammonia from the exhaust gas, the means for separating the ammonia from the exhaust gas being arranged downstream of the scrubber, and the means for separating the ammonia from the exhaust gas preferably comprising a scrubber tower.

In a possible implementation form of the first aspect, the engine comprises a condenser downstream of the turbine and upstream of the scrubber for removing a portion of the water in the exhaust gas, the condenser preferably being a controlled condenser, and the condenser preferably having an outlet for disposing of water removed from the exhaust gas, the condenser preferably having an inlet for receiving and cooling water an outlet for discharging cooling water.

In a possible implementation form of the first aspect, the engine comprises an ammonia feed pump with an outlet of the ammonia feed pump fluidically connected to the fuel valves as, the ammonia feed pump preferably has an inlet fluidically connected to an ammonia storage tank.

DK 181454 B1 7

In a possible implementation form of the first aspect, the engine comprises a controller, the controller being configured to control one or more of: - the activity of the condenser in response to a signal representative of the amount of water or fluid in the circulation system preferably to keep the amount of water in the circulation system constant, preferably by controlling the temperature of the cooling water passing through the condenser, - the amount of electric power provided by the voltage source to the electrolytic tank preferably in response to a signal representative of the concentration of the electrogenerated mediator in the recirculated water, - the amount and/or pressure of ammonia supplied by the ammonia fuel system to the engine, preferably by adjusting the speed of the ammonia feed pump.

In a possible implementation form of the first aspect, the reduction of nitrous oxide takes place at the mercury electrode in the presence of a small amount of a Nil! complex of [15 or 14]laneN4{[15 or 1l4JaneN4 = 1,4,8,12 (or 11)-tetra- azacyclopenta (or tetra)decane} in aqueous solution.

According to a second aspect, there is provided a method for removing nitrous oxide from the exhaust gas of a large two- stroke uniflow scavenged turbocharged internal combustion engine having a turbocharger, the method comprising: - operating the engine with ammonia as the main fuel, - wet-scrubbing the exhaust gas downstream of a turbine of the turbocharger using a Ni based mediator added to water, preferably a NiI[NiICN4]3- mediator added to

DK 181454 B1 8 water, thereby transforming nitrous oxide in the exhaust gas to ammonia in a single process stage, or using Nill complexes of macrocyclic polyamines added to water, thereby reducing said nitrous oxide into nitrogen and oxygen and/or into nitrogen and hydroxide.

In a possible implementation form of the second aspect, the method comprises electrogenerating the mediator, preferably in an electrolytic tank.

In a possible implementation form of the second aspect, the method comprises circulating water containing the mediator through a scrubber.

In a possible implementation form of the second aspect, the method comprises separating the ammonia from the exhaust gas subsequently to wet-scrubbing, preferably using a scrubber tower.

In a possible implementation form of the second aspect, the method comprises controlling the water content in the exhaust gas before wet scrubbing, preferably by removing water from the exhaust gas, preferably upstream of the turbine &6, preferably using a condenser.

In a possible implementation form of the second aspect, the method comprises recirculating water containing the NI based mediator in a circulation system comprising a wet scrubber.

In a possible implementation form of the second aspect, the method comprises controlling the amount of water in the

DK 181454 B1 9 circulation system by removing water from the exhaust gas before scrubbing, preferably by increasing the activity of the condenser when the amount of water in the circulation system is above an upper threshold and by decreasing the activity of the condenser when the amount of water in the circulation system is below a lower threshold.

In a possible implementation form of the second aspect, reducing N20 takes at a mercury electrode in the presence of a small amount of a Nil! complex of [15 or 14]aneN4{[1l5 or 14]aneN4 = 1,4,8,12 (or 11)-tetra-azacyclopental( or tetra)decane) in aqueous solution.

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

BRIEF DESCRIPTION OF THE DRAWINGS

In the following detailed portion of the present disclosure, the aspects, embodiments, and implementations will Lbe 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 an embodiment of the large two-stroke engine of Fig. 1 with an ammonia fuel system and a nitrous oxide abatement system,

DK 181454 B1 10

Fig. 4 is a diagrammatic representation of the engine of the embodiment of Fig 3 with the ammonia fuel system shown in greater detail, and

Fig. 5 is a diagrammatic representation of another embodiment of the large two-stroke engine of Fig. 1 with its ammonia fuel system and nitrous oxide abatement system.

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 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

DK 181454 B1 11 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 1s 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 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 fuel valves 50 that are arranged in the cylinder cover 22 into the combustion chamber either at high pressure when the piston is at or near TDC (Diesel principle) or at low pressure when the piston is on its way towards TDC (Otto principle). 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 (not shown in Fig. 3) injecting conventional fuel into

DK 181454 B1 12 the combustion chamber. 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 507 are arranged along the cylinder liner (shown by the interrupted lines) and admit the fuel into the cylinder 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, 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, which injects when the piston is at or near top dead center (TDC) and the pressure at which the fuel is injected needs to be significantly higher than the compression pressure. Thus, in an embodiment, the engine operates according to the Diesel principle (compression-ignition) and compresses on the scavenging gas, and in other embodiments, the engine operates according to the Otto cycle (timed ignition) and compresses a mixture of fuel and scavenging gas. The pressure at which the fuel supply system 30 needs to deliver fuel can be significantly lower when operating according to the Otto principle, and/or

DK 181454 B1 13 pressure boosters, that are often used in the fuel valves 50 for compression-ignition engines 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 an optional selective catalytic reactor 33 to a turbine 6 of the turbocharger 5, from which the exhaust gas flows away through a second exhaust conduit 28 via a condenser 20 towards an outlet 21 via a wet scrubber 40 and a scrubber tower 48 into the atmosphere. The wet scrubber 40 reduces nitrous oxide emissions NOx emissions, as will be described in further detail below.

Through a shaft, the turbine 6 of the turbocharger 5 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 air 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 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 turbocharging system may comprise more than one turbocharger 5.

DK 181454 B1 14

The engine is in the ammonia mode operated with ammonia as the main fuel which is supplied to the ammonia valves 50 by the ammonia fuel system 30 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.

In an embodiment, the engine is provided with an exhaust gas circulation system for reintroducing a portion of the exhaust gas to the combustion chambers, together with the scavenging alr, e.g. to reduce NOx generation

With reference to Fig. 4, the ammonia fuel system 30, is disclosed in greater detail. Ammonia is stored in the liquid

DK 181454 B1 15 phase in a pressurized storage tank 31 at approximately 17 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 50,50’. A portion of the liquid ammonia that is supplied to the fuel valves 50,50’ 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 the inlet of the medium pressure feed pump 35.

An electronic control unit 100 is connected via signal lines or wirelessly to the pumps and valves of the fuel system 30, to the controlled condenser 20, and to the nitrous oxide abatement system. 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

DK 181454 B1 16 the fuel system and the nitrous oxide abatement system as described in greater detail below.

Referring back to Fig. 3, the nitrous oxide abatement system comprises a nitrous oxide scrubber 40 downstream of the turbine 6 and downstream of the controlled condenser 20. The nitrous oxide scrubber 40 is configured for transforming nitrous oxide in the exhaust gas flowing through the scrubber 40 to ammonia in a single process stage. Thus, the exhaust gas leaving the scrubber 40 has a substantially reduced content of nitrous oxide compared to the exhaust gas entering the scrubber 40, and the exhaust gas leaving the scrubber 40 has an increased ammonia content compared to the exhaust gas entering the scrubber 40.

In an embodiment, the scrubber 40 comprises a packed column, which is packed with a material that ensures a high surface area at a low pressure loss. In another embodiment, the scrubber comprises a plate column. The nitrous oxide removal process will work regardless of the design of the column.

However, the efficiency and flow may be affected by the type and construction of the column.

The electroscrubber 40 couples wet-scrubbing with an electrogenerated mediator, preferably and N(I) based mediator, more preferably, an Ni (I) ([Ni(I) (CN)4]3-) mediator, to reduce nitrous oxide in a single process stage to ammonia.

The mediator is mixed with water that is circulated in a nitrous oxide removal system. Due to the high pH value of the recirculated water, the ammonia is not dissolved in the water and leaves the scrubber 40 with the exhaust gas.

DK 181454 B1 17

The circulation system circulates water using a circulation pump 45 in a circulation circuit 49. The water contains the mediator and is passed through the scrubber 40.

The presence of the electrogenerated electron mediator. e.g. [Ni (1) (CN) 4]3- (Ni (IT)) in e.g. 9 M KOH results in a consistent removal (typically 95% is removed) of nitrous oxide (N20) from the exhaust gas passing through the wet-scrubber 40 by converting the nitrous oxide to ammonia. The process does not require high temperatures and will work with temperatures as low as ambient temperatures. The exhaust gas entering the wet scrubber 40 will typically be in the range of 150-250 °C, depending on the engine operating conditions and the activity of the controlled condenser 20.

Nitrous oxide is removed from the exhaust gas at temperatures down to ambient by integrating a mediated electrocatalytic mediator Ni (I). The mediated electrocatalytic facilitates the transformation of N:0 to NH?, preferably in the presence of excess nitrogen. The transformation is enabled by a solution phase reaction. This has the benefit that NH? is generated, which can be used as fuel for the engine or as reductant in a selective catalytic reactor.

The mediator is an electrogenerated mediator and the circulation system comprises an electrolytic tank 44 coupled to an electric voltage source 46 for electrogenerating the mediator. The electrolytic tank 44 comprises at least two electrodes (anode/cathode) coupled to the electric voltage source 46. The circulation system also comprises a sensor

DK 181454 B1 18 (not shown) for sensing the amount of water in the circulation system.

The electric voltage source 46, the circulation pump 45, the sensor for sensing the amount of water in the circulation system, and the controllable condenser 20 are connected to the controller 100.

A scrubber tower 48 or other means for separating the ammonia from the exhaust gas is arranged downstream of the scrubber 40 with an outlet of the scrubber 40 being connected to an inlet of the scrubber tower 48. The exhaust gas leaving the scrubber tower 48 through the outlet 21 to the atmosphere contains no or very little ammonia. The ammonia that is separated from the exhaust gas in the scrubber tower 48 can be used as fuel for the engine or as a reductive in a selective catalytic reactor 33 that can be used to reduce NOx emissions.

The condenser 20 downstream of the turbine 6 and upstream of the scrubber 40 removes a portion of the water in the exhaust gas to avoid the amount of water in the circulation system increasing and thereby reducing the concentration of the mediator in the recirculated water. The condenser 20 preferably can be controlled by the controller 100 and has an outlet for disposing of water removed from the exhaust gas.

The condenser 20 1s provided with an inlet for receiving cooling water and an outlet for discharging cooling water. In an embodiment, the temperature and the lower rate of the cooling water through the condenser 20 is controlled by the controller 100.

DK 181454 B1 19

The controller 100 is configured to control one or more of: - the activity of the condenser 20 in response to a signal representative of the amount of water or fluid in the circulation system, e.g. from the above-mentioned sensor, preferably with the aim of keeping the amount of water in the circulation system constant or within limits, preferably by controlling the temperature and/or flow rate of the cooling water passing through the condenser 20 so that there is no or little evaporation and/or condensation in the scrubber 40, - the amount of electric power provided by the voltage source 46 to the electrolytic tank 44, preferably in response to a signal representative of the concentration of the electrogenerated mediator in the recirculated water preferably through a signal from a sensor arranged in the circulation system (not shown), - the amount and/or pressure of ammonia supplied by the ammonia fuel system to the engine, preferably by adjusting the speed of the ammonia feed pump 35.

In an embodiment, the method for removing nitrous oxide from the exhaust gas of the large two-stroke uniflow scavenged turbocharged internal combustion comprises: - operating the engine with ammonia as the main fuel, - wet-scrubbing the exhaust gas downstream of a turbine 6 of the turbocharger 5 using an N(I) based mediator added to water, preferably an Ni(I) ([Ni (I) (CN) 4]3-) mediator added to water, thereby reducing nitrous oxide in the exhaust gas to ammonia in a single process stage.

The method may further comprise electrogenerating the mediator, preferably in an electrolytic tank 44. The method

DK 181454 B1 20 may further comprise comprising circulating water containing the mediator through a scrubber 40, preferably using a circulation pump 45. The method may further comprise separating ammonia from the exhaust gas subsequently to wet- scrubbing, preferably using a scrubber tower 48. The method may further comprise controlling the water content in the exhaust gas before wet scrubbing, preferably by removing water from the exhaust gas, preferably upstream of the turbine 6, preferably using a condenser 20. The method may further comprise recirculating water containing an N(I) based mediator in the circulation system comprising the wet scrubber 40. The method may further comprise controlling the amount of water in the circulation system by removing water from the exhaust gas before scrubbing, preferably by increasing the activity of the condenser when the amount of water in the circulation system is above an upper threshold and by decreasing the activity of the condenser when the amount of water in the circulation system is below a lower threshold.

Fig. 5. illustrates another embodiment of the engine. In this embodiment, structures and features that are the same or similar to corresponding structures and features previously described or shown herein are denoted by the same reference numeral as previously used for simplicity. in this embodiment, the engine is provided with an electroscrubber 40 that is provided with electrodes connected to a source of DC current 46. Water is circulated through the electroscrubber 40 by a circulation pump 45. In an embodiment, the water that is recirculated through the electroscrubber 40 contains a catalyst. Nitrous oxide in the exhaust gas passing through the electrodes a 40 is decomposed using electrolysis into

DK 181454 B1 21 nitrogen and oxygen or into nitrogen and hydroxide. This process works with temperatures as low as ambient temperatures and will function well at the temperature range at which the exhaust gas will typically enter the electroscrubber 40 of 150-250 °C.

The electrodes comprise a mercury electrode. In an embodiment, the reduction of nitrogen oxide takes place at the mercury electrode to give only N2 in yields close to 100% in the presence of a small amount of a NiII complex of [15 or 14JaneN4 | [15 or 14]aneN4 = 1,4,8,12 (or 11)-tetra- azacyclopenta (or tetra)decane) in aqueous solution.

Alternatively, the reduction of nitrous oxide takes place at gas-diffusion electrodes modified by platinum and nickel electrocatalysts.

Since no ammonia is generated in the production process, there is no need in this embodiment for a scrubber tower 48 downstream of the electrospray roof 40 to remove ammonia.

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.

DK 181454 B1 22

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 181454 B1 23 PATENT CLAIM

1. Large, turbocharged, longitudinally scavenged two-stroke internal combustion engine having at least one mode of operation where the main fuel is ammonia, which engine comprises: - 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 formed inside the cylinder (1) between the reciprocating piston (10) and the cylinder cover (22), - an ammonia fuel system (30) configured to supply ammonia under pressure to fuel valves (50, 507) which are located 1 the cylinder cover (22) or in the cylinder liner (1), - a turbocharging system (5) comprising at least one compressor (7) for compressing scavenging air and at least one exhaust gas driven turbine ( 6), a wet scrubber downstream of the at least one gas-driven turbine, characterized in that the wet scrubber is a nitrous oxide scrubber (40) configured to convert nitrous oxide Å in the exhaust gas flowing through the scrubber (40) into ammonia, and/ or for the reduction of nitrous oxide Å in the exhaust gas, which flows through the scrubber (40), to nitrogen and oxygen or to nitrogen and hydroxide.

2. Engine according to claim 1, wherein the scrubber (44) is an electroscrubber that couples wet scrubbing with an electrogenerated mediator, preferably a Ni(I)-based mediator, more preferably a Ni (I) ([Ni(I) (CN) 4]3-) mediator,

DK 181454 B1 24 for the reduction of nitrous oxide in a single process step to ammonia.

3. Engine according to claim 1 or 2, and which comprises a circulation system for circulating water containing a mediator through the scrubber (40), where the mediator is preferably an electrogenerated mediator, and where the circulation system preferably comprises an electrolytic tank (44) coupled to an electric voltage source (46) for electrogeneration of the mediator, wherein the electrolytic tank (44) preferably comprises at least two electrodes coupled to the electrical voltage source (46).

An engine according to any preceding claim, comprising means (48) for separating the ammonia from the exhaust gas, wherein the means (48) for separating the ammonia from the exhaust gas is located downstream of the scrubber (40), and wherein the means (48) for separating the ammonia from the exhaust gas preferably comprises a scrubber tower.

An engine according to any one of the preceding claims, comprising a condenser (20) downstream of the turbine (6) and upstream of the scrubber (40) for removing part of the water in the exhaust gas, wherein the condenser (20) preferably is a controlled condenser, wherein the condenser preferably has an outlet for discharging water removed from the exhaust gas, and wherein the condenser preferably has an inlet for receiving and an outlet for discharging cooling water.

DK 181454 B1 25

An engine according to any one of the preceding claims, comprising an ammonia feed pump (35) having an outlet from the ammonia feed pump (35) in fluid communication with the fuel valves (such as 50, 507), wherein the ammonia feed pump (35) preferably has an inlet fluidly connected to an ammonia storage tank (31).

7. Motor according to any one of claims 3, 5 or 6, and comprising a control unit (100), which control unit (100) is configured to control one or more of: - the activity of the capacitor (20) in response to a signal representative of the amount of water or fluid in the circulation system preferably to keep the amount of water in the circulation system constant, preferably by controlling the temperature of the cooling water passing through the condenser (20), - the amount of electric current supplied by the voltage source (46) to the electrolytic tank (44), preferably in response to a signal representative of the concentration of the electrogenerated mediator 1 the recirculated water, - the ammonia quantity and/or pressure supplied by the ammonia fuel system to the engine, preferably by adjusting the speed of the ammonia supply pump (35).

8. An engine according to claim 1 and which comprises a Hg electrode and wherein the reduction of nitrous oxide occurs at the mercury electrode in the presence of a minor amount of a Nit' complex of [15 or 14]aneN4{[1l5 or 14]aneN4 = 1,4,8,12 (or 11)-tetra-azacyclopenta (or tetra)decane) in aqueous solution.

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9. Method for removing nitrous oxide from the exhaust gas of a large, turbocharged, two-stroke combustion engine with longitudinal scavenging and a turbocharger (5), which method comprises: - using the engine with ammonia as the main fuel, - wet scrubbing of the exhaust gas downstream of a turbine (6) 1 the turbocharger (5) characterized in that the wet scrubbing is carried out using a Ni(I)-based mediator added to water, preferably a Ni(I) ([Ni(I) (CN) 4]3-) mediator added to water, whereby the nitrous oxide 1 exhaust gas is converted to ammonia 1 in a single process step, or by means of Nill complexes of macrocyclic polyamines added to water, whereby the nitrous oxide is reduced to nitrogen and oxygen and/or to nitrogen and hydroxide.

10. Method according to claim 9, which comprises electrogenerating the mediator, preferably in an electrolytic tank (44).

11. Method according to claim 9 or 10, and which comprises circulating water containing the mediator through a scrubber (40).

12. Method according to any one of claims 9 to 11, and which comprises separating the ammonia from the exhaust gas after wet scrubbing, preferably by means of a scrubber tower (48).

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13. Method according to any one of claims 9 to 11, and which comprises controlling the water content before wet scrubbing, preferably by removing water from the exhaust gas, preferably upstream of the turbine (6), preferably by means of a condenser (20).

A method according to any one of claims 9 to 12, comprising recirculating water containing the N(I)-based mediator 1 in a circulation system comprising a wet scrubber (40).

15. Method according to any one of claims 9 to 14, and which comprises controlling the amount of water in the circulation system by removing water from the exhaust gas before scrubbing, preferably by increasing the activity of the condenser when the amount of water in the circulation system is above an upper threshold, and by lowering the activity of the condenser when the amount of water in the circulation system is below a lower threshold.

16. A process according to claim 9, which comprises reducing N 2 O at a mercury electrode in the presence of a small amount of a Nill complex of [15 or l14janeN4f[15 or 14]aneN4 = 1,4,8,12 (or 11) -tetra-azacyclopenta (or tetra)decane) in aqueous solution.