Ammonia mitigation system and a method for operating the mitigation system

Abstract

The disclosure relates to an ammonia mitigation system (100) for receiving ammonia-containing streams generated by vent gases and / or vent streams during purging of an ammonia fuel supply system (10) and / or ammonia-fueled engine (20), the system being in fluid communication with a vent mast (160) leading the ammonia-containing streams with reduced ammonia content to the atmosphere, the system comprising a first ammonia mitigation arrangement (110) and a second ammonia mitigation arrangement (120), wherein the first and second arrangements are based on different technical solutions and are arranged to operate alternatingly or complementary to each other. The disclosure also relates to a method of operating the system.

Description

[0001] Ammonia mitigation system and a method for operating the mitigation system

[0002] Technical field

[0003] The present invention relates to an ammonia mitigation system for ammonia- containing streams generated by vent gases and / or vent streams during purging of an ammonia supply system and / or ammonia-fueled engine and to a method of operating the ammonia mitigation system as defined in the introductory parts of the independent claims.

[0004] Background art

[0005] Ammonia is one of the strategic fuels to achieve the International Maritime Organization’s ambitious decarbonization goals over the next decades. The marine shipping sector transporting people and goods worldwide plays a key role in the global economy. As per today, marine vessels are estimated to account for 2.9% of worldwide carbon dioxide emissions. The International Maritime Organization (IMO) has adopted a strategy to progressively reduce the marine industry’s greenhouse gas (GHG) emissions, in line with the Paris Agreement on climate change. The IMO strategy to progressively reduce the GHGs from shipping, adopted by the Marine Environment Protection Committee (MEPC) in 2018, includes inter alia the objectives of reducing CO2 emissions per transport work, as an average across international shipping by at least 40% by 2030, compared to the levels of 2008 and reducing total annual GHG emissions by at least 50% by 2050, compared to 2008.

[0006] Ammonia is traditionally made from fossil feedstocks via syngas (black ammonia). Renewable ammonia, instead, is produced from hydrogen produced from water by electrolysis via renewable electricity (green ammonia). When produced using renewable energy, ammonia can be considered as a carbon-neutral fuel in a well-to- wake perspective. When produced using hydrogen made from fossil energy sources with carbon capture and storage (>90% capture rate), ammonia is classified as “blue ammonia”. Both green and blue ammonia provide shipowners with a fuel option that could assist in meeting the International Maritime Organization’s (IMO) 2050 GHG emissions reduction targets.

[0007] Ammonia is, however, a toxic substance and potential releases to the atmosphere should be avoided or mitigated. A solution to reduce the concentration of ammonia in vent gases released into the atmosphere is therefore needed. EP4184052 A1 shows a ship comprising: a hull; an ammonia storage tank in which ammonia can be stored; an inert gas supply device that supplies an inert gas to an ammonia circulation path that communicates with the ammonia storage tank; a vent tube that guides the ammonia in the circulation path to the outside together with the inert gas supplied by the inert gas supply device; and a processing tank provided midway along the vent tube, water being stored inside the processing tank, and the inert gas and ammonia being introduced into the processing tank from the vent pipe below the surface of the water. However, such treatment may not provide sufficiently low ammonia content level in the treated gas, which is released into the atmosphere. Further, W02024008267 shows a method and system for inerting a fuel delivery system, in which the inerted fuel is directed via a buffer to a fuel processing vessel provided with a burner. The burner oxidizes the fuel. However, the burner needs to be activated before use. Therefore, further improvements and systems that are ready to use are needed.

[0008] Summary

[0009] The maritime industry has experience with ammonia as it is transported on gas carriers, and it is a well-known refrigerant used in the industry and onboard ships. However, the introduction of ammonia as fuel creates new safety challenges related to bunkering, onboard storage, supply and consumption. Ammonia is less flammable than other types of alternative fuels, e.g. liquefied natural gas (LNG), and is related with a lower, but not ignorable, explosion risk. The main safety issue given by ammonia is its toxicity, as mentioned above. Due to the toxicity, it is important to be able to control all leakage scenarios and ensure ammonia removal before releasing it to the atmosphere.

[0010] One objective with the present invention is to further develop and improve the technology for using ammonia onboard ships for propulsion and for auxiliary power generation, and especially technologies for preventing ammonia from escaping to the atmosphere in case of vent and / or purge of ammonia from ammonia supply systems and / or engine.

[0011] Generally, ammonia-containing vents can be generated in case of overpressure, purging procedures for emptying supply lines and equipment from ammonia, shutdown and e.g. leaks from vents, piping and equipment. In case of leaks and / or ammonia release into vents, it is important to also capture these and treat before releasing to atmosphere. Technology solutions are needed to remove ammonia from vents to comply with emission limits imposed by applicable rules.

[0012] Solutions for ammonia emission abatement from exhaust gases already exist in industrial sectors operating with ammonia. However, the solutions cannot be normally applied directly in the maritime sector because of the different applications, such as the limited safety distances available on vessels and a limited possibility of safe evacuation when at sea.

[0013] There are known solutions for ammonia mitigation systems based on ammonia absorption I neutralization. However, it has been noted that after a certain period of time the water and / or acid solutions will become saturated and will not be suitable for further absorption / neutralization. In some cases, it may take time to replace the saturated solutions with fresh ones.

[0014] Furthermore, ammonia mitigation systems, especially ones containing water tanks, may be space-requiring due to large amount of water to be used and stored when saturated. There is thus a need for more compact mitigation systems.

[0015] One further system for the mitigation of ammonia has been introduced in connection with boiler systems in which ammonia vent gases are combusted in burners of the boiler systems. Burners are generally referred to as “active systems”, since they need to be activated before burning of ammonia is possible. However, the burners require time to be activated, and they are thus not always ready and available to handle the ammonia-containing vents.

[0016] Consequently, there is a need for redundancy in ammonia mitigation systems. However, it needs to be taken into consideration that space onboard of marine vessels is limited.

[0017] It is therefore the objective of the present invention to mitigate, alleviate or eliminate one or more of the above-identified deficiencies and disadvantages in the prior art and solve at least the above-mentioned problems.

[0018] It is an objective of the present invention to provide a system and a method for handling ammonia-containing vent streams generated by a fuel supply system and an engine operating with ammonia, as well as a solution and a method for removing ammonia before discharging inert gas to atmosphere.

[0019] It is a further objective of the present invention to provide an ammonia mitigation system in which ammonia-containing vent gases are treated and that is suitable for use in maritime sector and onboard of marine vessels. Additionally, it is an objective to provide a mitigation system that is safe to use even when there are limited safety distances available and possibility of safe evacuation when at sea.

[0020] Additionally, it is an objective to provide redundancy in ammonia mitigation while taking into consideration that space onboard of a vessel is limited.

[0021] The present invention overcomes or alleviates at least some of the drawbacks of the prior art and the objectives are achieved with a system according to the appended claims.

[0022] According to a first aspect, there is provided an ammonia mitigation system for receiving ammonia-containing streams generated by vent gases and / or vent streams during purging of an ammonia fuel supply system and / or ammonia-fueled engine. The streams are fluidic streams that may comprise gas and / or liquid. The system is in fluid communication with a vent mast, i.e. exhaust piping, leading the ammonia-containing streams with reduced ammonia content to the atmosphere. The system comprises a first ammonia mitigation arrangement and a second ammonia mitigation arrangement, wherein the first and second arrangements are based on different technical solutions and are arranged to operate alternatingly or complementary to each other.

[0023] By arranging two technically different ammonia mitigation systems in cooperation with each other such that they can operate alternatingly or complementary to each other, redundancy to the ammonia mitigation systems is obtained. In this way it can be assured that at least one of the systems is able to reduce ammonia content of the ammonia-containing streams before releasing them to atmosphere.

[0024] The first and second ammonia mitigation arrangements may be fluidly connected via a valve arrangement to a first supply line for supplying ammonia- containing streams from the ammonia fuel supply system to the first and second ammonia mitigation arrangements, and a second supply line for supplying ammonia- containing streams from the ammonia-fueled engine to the first and second ammonia mitigation arrangements. Thus, by connecting the ammonia-containing streams via the valve arrangement, it can be assured that ammonia-containing streams from the fuel supply system, the engine, the interconnecting piping and any other source of release will be guided to mitigation arrangements. The valve arrangement may comprise one or more valves of different types and associated piping. The valve arrangement may be configured additionally via further piping to fluidly connect the first and second ammonia mitigation arrangements to further auxiliary arrangements, such as water regeneration or incineration of waste from the mitigation, such as water / acid solutions.

[0025] The valve arrangement is configured to supply the ammonia-containing streams to the first and second ammonia mitigation arrangements, respectively, preferably one at a time. At least one of the first and second ammonia mitigation arrangements is preferably always arranged operable, and thus available to handle the ammonia containing streams. In this way the streams will be sent to only that arrangement which is operable for mitigation. The valve arrangement may be configured such that in case of failure in the valve arrangement, the ammonia containing streams are supplied to the second ammonia mitigation arrangement, which is passive. In this way it can be ensured that the ammonia content in the streams will be mitigated before release to the atmosphere.

[0026] A buffer tank may be arranged upstream of the valve arrangement to receive the ammonia-containing streams from the fuel supply system, the engine, the interconnecting piping any other source of release. This provides a sort of hold up in case of high flow before supplying the streams to the mitigation arrangements.

[0027] Generally, the first and second ammonia mitigation arrangements are based on different functionality or technology. For example, the ammonia mitigation arrangements could comprise or be burners, such as burners connected to boilers used in marine vessels to provide steam. Absorption arrangements, such as water absorption tanks, neutralization arrangements, such as acid solution tanks, or combinations of absorption and neutralization arrangements, scrubbers, solid absorption arrangements, etc. can also be used as ammonia mitigation arrangements. Suitably, the second ammonia mitigation arrangement is a passive arrangement, such as water absorption and / or acid neutralization solution, which is immediately ready for use and needs no activation. Suitably, the first ammonia mitigation solution is an active arrangement, which may need to be activated, such as a burner. The first ammonia mitigation arrangement may comprise a burner. The burner may be comprised in and / or connected to a boiler system. The burner is fluidly connected via a first inlet line to the vent gases and / or vent streams from the ammonia fuel supply system and / or ammonia-fueled engine and is configured to bum the ammonia-containing vent gases and / or vent streams from the ammonia fuel supply system. The burner is normally an existing equipment in the marine vessel boiler systems, whereby the footprint of the ammonia mitigation system can be minimized. By the buffer tank it is possible to use the mitigation arrangements and especially the burner when the vented streams have high flow.

[0028] The second ammonia mitigation arrangement may comprise a first ammonia mitigation device and a second ammonia mitigation device. A valve device may be provided and be configured to fluidly connect the first and second supply lines and the first and second ammonia mitigation devices. The valve device may be configured to supply vent streams to the first ammonia mitigation device, or to bypass the first ammonia mitigation device and supply the streams directly to the second ammonia mitigation device via a bypass line. The valve device may be a multi-way valve or comprise several valves connected to each other so that it can be opened towards a supply line for the first ammonia mitigation device or a bypass line. The second ammonia mitigation arrangement is configured to absorb and / or neutralize the ammonia-containing vent gases and / or vent streams from the ammonia fuel supply system and / or the engine. By using absorption and / or neutralization, a mitigation technology which is passive and immediately available for use can be provided for ammonia mitigation, since no activation time is needed.

[0029] The first ammonia mitigation device may comprise at least one water tank storing water, and the second ammonia mitigation device may comprise at least one acid tank storing an acid solution. Alternatively, the first and second ammonia mitigation devices may be of the same kind and may comprise water tanks or acid tanks. The number of water and / or acid tanks may be more than 1 , for example 2, but even more than two could be considered. By using acid solution in acid tanks in both the first and the second ammonia mitigating devices, it has been noted that the ammonia mitigation arrangement can be made even more compact, because the volume of the acid in the acid tanks needs not to be as large as water in the water tanks. By using the acid solution in at least one tank, e.g. in the second ammonia mitigation device, the volume can be decreased compared to a system where only water tanks are used.

[0030] If the water and / or acid solutions are saturated, they can be automatically drained and replaced with fresh water and acid solutions.

[0031] The ammonia water used for absorption can be regenerated using a water regeneration system where ammonia is boiled off the solution and then transported to the burner for incineration. This can be performed for example by a method and system described in WO2025172142A1 . The water, with a lower ammonia content, can then be redirected back to the water tank. The water may be cooled, and the water can be redirected to the water tank after being cooled to a required level. Additionally, or alternatively, the liquid ammonia-containing water can be drained to either a tank or redirected for incineration in the burner or combustion system of a boiler, for example as described in EP25172156, and in which the waste liquid is fed to the combustion system via a conduit, which is separate from the fuel conduit. Similarly, the acid solution can be incinerated in the burner or the boiler when it has reached saturation.

[0032] However, since ammonia ends up in the absorption media, such as water, and in the neutralization media, such as acid solution, the solution after a certain period of time and depending on the amount of released ammonia and the volumes of water the water, will become saturated and will need to be discharged and replaced by fresh water. Therefore, it is advantageous in the two-technology system that the other ammonia mitigation arrangement, such as the burner in the boiler system, can operate, when the other ammonia mitigation arrangement cannot mitigate the ammonia content in a proper way.

[0033] The second ammonia mitigation arrangement may comprise ammonia and / or water or acid content monitoring devices in communication with the first ammonia mitigation arrangement. The supply of the ammonia-containing vent streams may be configured to be directed to the first ammonia mitigation arrangement when at least one of the ammonia content, water content or acid content is outside a pre-defined range for the ammonia and / or water or acid content, or when the water level and / or the acid level are / is outside a pre-defined level. Thus, it is possible to detect and predict when the second ammonia mitigation arrangement is not working satisfactorily and when the first ammonia mitigation arrangement should be used instead. On the other hand, the supply of the ammonia containing vent streams may be configured to be directed to the second ammonia mitigation arrangement, when the first ammonia mitigation arrangement is not activated to combust the ammonia- containing vent streams. This could be the situation for example in case of uncontrolled vent streams, like in case of release from safety valves releases. Such releases are not compatible with burner startup time, but on the other side, the water I acid base solution is always available.

[0034] By combining the two solutions, it is possible to send the ammonia contaminated vent streams to the burner every time that there is a purging, which is “activated” and there are compatible with burner activation time. This will help to reduce the amount of contaminated water I acid solution and extends the time period for the absorption / neutralization devices in the second mitigation arrangement between two freshwater fillings.

[0035] An ammonia gas detector may be arranged in fluid communication with the released gases in the exhaust piping and is configured to generate an alarm when the ammonia content is above a threshold. This will indicate that the ammonia mitigation system is not working properly.

[0036] The ammonia mitigation system may be fluidly connected to a catch tank inside the ammonia fuel supply system and / or a knockout drum upstream of the ammonia mitigation system. The catch tank is associated with the fuel supply system and can be suitably located close to the ammonia fuel supply system and can be located inside the ammonia fuel supply system. The catch tank may be used for example for engine pressure relief and to receive a certain amount of gas / l iquid ammonia. The catch tank may be used for I iquid / gas separation. In this way, the safety of the system can be improved. The ammonia mitigation system may additionally or alternatively comprise or be connected to a knock-out drum for the gas-liquid separation. The knock-out drum is a vessel designed to remove and accumulate condensed and / or entrained liquids from the vent / purge / relief gases. The system may comprise more than one knock-out drum. The knock-out drum may be arranged upstream of or included in the ammonia mitigation system.

[0037] The second ammonia mitigation arrangement may be mounted on a single skid. This way, it is possible to provide compact and easy transport and installation of the system. The present disclosure also relates to an ammonia mitigation arrangement, which can be used as a second ammonia mitigation arrangement described above, for reducing ammonia content in ammonia-containing streams generated by vent gases and / or vent streams during purging of an ammonia fuel supply system and / or ammonia-fueled engine. The arrangement may comprise a first ammonia mitigation device and a second ammonia mitigation device, and a valve device configured to fluidly connect a first supply line for supplying ammonia-containing streams from the ammonia fuel supply system to the ammonia mitigation arrangement. The arrangement further comprises a second supply line for supplying ammonia-containing streams from the ammonia-fueled engine to the ammonia mitigation arrangement. The ammonia mitigation arrangement is configured to neutralize the ammonia-containing vent gases and / or vent streams from the ammonia fuel supply system and / or engine. The first ammonia mitigation device comprises an acid tank storing acid solution, and the second ammonia mitigation device comprises an acid tank storing an acid solution. By using acid in both the first and the second ammonia mitigation devices, it is possible to provide a more compact mitigations system, which is a huge advantage in marine vessels, where the space is limited. The acid neutralization of ammonia requires less acid volume than water used for ammonia absorption.

[0038] The present invention also relates to a method of operating the ammonia mitigation system as defined above. The method comprises: supplying ammonia-containing streams generated by vent gases and / or vent streams during purging of the ammonia fuel supply system and / or ammonia- fueled engine or the interconnecting piping from any other source of release, to the first or second ammonia mitigation arrangement, and

[0039] • supplying the ammonia-containing vent streams to the second ammonia mitigation arrangement when the first ammonia mitigation arrangement is not activated, or

[0040] • supplying the ammonia-containing vent streams to the first ammonia mitigation arrangement based on pre-defined operating criteria and / or when at least one of the absorbed ammonia in water and / or acid solution is outside a pre-defined range for the ammonia and / or water or acid content, and releasing the mitigated ammonia stream to the atmosphere via the vent mast.

[0041] The method may further comprise:

[0042] • Supplying contaminated water from the second ammonia mitigation arrangement to a burner of the first ammonia mitigation arrangement, drain tank and / or water regeneration system, and / or

[0043] • Supplying the contaminated acid from the second ammonia mitigation arrangement to a drain tank and / or to the burner of the first ammonia mitigation arrangement.

[0044] The pre-defined operating criteria may be choice of the operation mode as the first ammonia mitigation arrangement. Alternatively, the choice can be made based on an upstream operation mode which can be, for example purging. This is an active operation mode in which a burner could be chosen as mitigation arrangement.

[0045] By the ammonia mitigation system described a solution for removing ammonia from ammonia-containing vent / purge exhaust I iquid / gas streams or safety valve reliefs before discharging is provided. These vent / purge exhaust streams do not contain engine exhaust gases from a combustion chamber of an engine, i.e. the exhaust gases resulting from the combustion of ammonia fuel during the operation of the internal combustion engine. The engine exhaust gases are normally denitrified in a selective catalytic reduction (SCR) device and / or equivalent method. The function of the present ammonia mitigation system is instead based on absorption and / or neutralizing of the ammonia vent / purge / relief exhaust gas and / or liquid streams before releasing to the atmosphere. The first and the second ammonia mitigation devices may comprise a liquid for absorbing and / or neutralizing the ammonia in the exhaust gases.

[0046] The components of the second ammonia mitigation arrangement may be frame- or skid-mounted, preferably on a single skid, in a compact manner. Further, the first and second ammonia mitigation devices may be mounted approximately on the same level, i.e. the devices do not need to be arranged in a cascade manner, where liquid falls from one device to another. Thus, a compact, modular and space-saving mitigation system can be provided. The first ammonia mitigation device may comprise a water tank storing water. Alternatively, the first ammonia mitigation device may comprise an acid tank storing an acid solution. The water acts as an absorbent from the ammonia. The acid neutralizes the ammonia. The first ammonia mitigation device may comprise more than one water or acid tank storing water or acid, respectively. The more than one water / acid tanks may be connected in parallel. Alternatively, the more than one water / acid tanks may be connected in series, whereby more than one absorption / neutralization stage can be added in the first ammonia mitigation device. The tank may have lower and higher water / acid threshold levels in the tank. Ammonia in the ammonia-containing streams can be at least partly absorbed in the water or neutralized by the acid, whereby the content of ammonia in the gas streams can be reduced. The ammonia-containing streams can be arranged to be supplied into the tank below the lower threshold level, whereby it can be assured that the ammonia-containing stream will come into contact with water or acid.

[0047] The first ammonia mitigation device may comprise at least one water level monitoring device arranged to monitor water level and alert when the water level is lower than the lower water threshold level or higher than the higher threshold level in the tank. In this way it is possible to adjust the water level when required. Similarly, the first ammonia mitigation device may comprise an acid solution level monitoring device arranged to monitor acid solution level and alert when the acid level is lower than the lower acid threshold level or higher than the higher threshold level in the tank. In this way it is possible to adjust the acid level when required.

[0048] The water or acid level monitoring device may be arranged in communication with a water or acid filling device and a drain device. Suitably the communication is arranged via a communication link, which may be wireless or via a physical cable, connecting the devices to a control unit. The water or acid filling device may be configured to start to fill water or acid to the first ammonia mitigation device, when the water or acid level, respectively, is lower than the lower water or acid threshold level. Alternatively, the drain device may be configured to open when the water or acid level is higher than the higher water or acid threshold level. In this way it can be ensured that the water or acid level in the tank is within the lower and higher threshold levels.

[0049] The first ammonia mitigation device may comprise an ammonia content monitoring device, which is arranged in communication with a drain configured to start draining and / or the regeneration system when the ammonia content in the water or acid tank is above an ammonia threshold value, and / or a water or acid filling device configured to start to fill water or acid when the ammonia content in the water or acid tank is above the ammonia threshold value and below the higher water or acid threshold level. In this way it can be ensured that the ammonia content can be diluted in a safe way.

[0050] The second ammonia mitigation device may comprise an acid tank storing an acid solution. The acid can neutralize the ammonia in the ammonia-containing stream entering the acid tank. In this way the content of ammonia can be effectively further reduced. The acid tank may have lower and higher acid threshold levels in the tank. The ammonia-containing streams may be arranged to be supplied into the tank below the lower threshold level. In this way it can be ensured that the streams will come into contact with the acid solution. According to a further alternative, the second ammonia mitigation device may alternatively or additionally comprise a water tank bringing a further absorption stage to the system.

[0051] The second ammonia mitigation device may comprise an acid level monitoring device arranged to monitor acid level and alert when the acid level is lower than the lower threshold level or higher than the higher threshold level in the tank. In this way it can be ensured that the acid solution level in the tank is within the lower and higher threshold levels.

[0052] The second ammonia mitigation device may comprise an acid content monitoring device in communication with an acid tank drain device and / or an acid refill device configured to fill acid when acid solution content or acidity in the second ammonia mitigation device is below a threshold.

[0053] The first and / or second ammonia mitigation device may comprise a temperature monitoring device configured to generate an alarm when the temperature in the first and / or second ammonia mitigation device is higher than a threshold temperature. This will improve the safety of the system, since overheating can be avoided, which may be possible due to the ammonia absorption and neutralization being exothermic processes, releasing heat to water and / or acid solutions.

[0054] The first and / or second ammonia mitigation device may comprise or be connected to a cooling device. The cooling device may be for example a submerged cooling coil or an external cooling system. The cooling device allows for a continuous or quicker cooling of the water and / or the acid solution in the respective first and / or second ammonia mitigation devices.

[0055] Suitably, the exhaust piping, which is herein also referred to as a vent mast, is fluidly connected to the second ammonia mitigation device. The second ammonia mitigation device is always used in the ammonia mitigation, while it is possible in some modes of operation to bypass the first ammonia mitigation device.

[0056] According to a variant, the second ammonia mitigation device may comprise a water tank.

[0057] The second ammonia mitigation arrangement may include a vacuum protection system comprising a vacuum breaker and / or an air inlet connection activated by a pressure transmitter detecting low pressure. Thereby, the ammonia mitigation system is protected from vacuum. The vacuum protection system may be located on the connecting pipe between the water tank and acid tank.

[0058] The upstream mode of operating the engine comprises shutting down the ammonia fuel supply system and performing emergency or engine liquid purging, and releasing engine pressure or supplying ammonia removed during purging of the engine to the catch tank, which is fluidly connected to the engine and the ammonia mitigation system. The stream may be first connected to the buffer tank and then to the first or second mitigation device via the valve device. The method of operating the second ammonia mitigation arrangement comprises:

[0059] - directing a gas / l iquid stream from venting of the catch tank via a connecting supply line, to the first ammonia mitigation device, or

[0060] - directing the venting stream to the second ammonia mitigation device, and

[0061] - directing the ammonia mitigated venting stream to the vent mast before releasing the stream to the atmosphere.

[0062] According to another variant, the mode of operating the second ammonia mitigation system is performed during engine gas purging generating ammonia-containing streams and comprising

[0063] - directing the ammonia-containing stream from the engine via the second supply line and the valve device to the second ammonia mitigation device via connecting via connecting supply lines, and directing the ammonia mitigated stream to the vent mast before releasing the stream to the atmosphere.

[0064] According to yet another variant, the mode of operating the ammonia mitigation system is performed during ammonia fuel supply system purging generating ammonia- containing vent streams. The stream may be first connected to the buffer tank and then to the first or second mitigation device via the valve device. The method may comprise:

[0065] - directing the ammonia-containing vent stream from the ammonia fuel supply system via connecting supply lines and the valve device and connecting supply line to the first ammonia mitigation device, or

[0066] - directing ammonia-containing stream from the first ammonia mitigation device to the second ammonia mitigation device via connecting supply lines, and

[0067] - directing the ammonia mitigated stream to the vent mast before releasing the stream to the atmosphere.

[0068] Effects and features of the second aspect is to a large extent analogous to those described above in connection with the first aspect. Embodiments mentioned in relation to the first aspect are largely compatible with the second aspect.

[0069] Additional objectives, advantages and novel features of the invention will be apparent to one skilled in the art from the following details, and through exercising the invention. While the invention is described below, it should be apparent that the invention may not be limited to the specifically described details. One skilled in the art, having access to the teachings herein, will recognize additional applications, modifications and incorporations in other areas, which are within the scope of the invention.

[0070] Brief description of the drawings

[0071] The above objects, as well as additional objects, features and advantages of the present disclosure, will be more fully appreciated by reference to the following illustrative and non-limiting detailed description of example embodiments of the present disclosure, when taken in conjunction with the accompanying drawings. Fig. 1 schematically illustrates an overview of an ammonia mitigation system according to an example;

[0072] Fig. 2 schematically illustrates components of a second ammonia mitigation arrangement according to an example;

[0073] Fig. 3 schematically illustrates components of a first ammonia mitigation arrangement according to an example.

[0074] Detailed description

[0075] The present disclosure will now be described with reference to the accompanying drawings, in which preferred example embodiments of the disclosure are shown. The disclosure may, however, be embodied in other forms and should not be construed as limited to the herein disclosed embodiments. The disclosed embodiments are provided to fully convey the scope of the disclosure defined in the appended claims to the skilled person.

[0076] Figure 1 schematically illustrates an overview of an ammonia mitigation system 100 of the present invention comprising an ammonia storage tank 210, a fuel supply system 10, a first ammonia mitigation arrangement 110, a second ammonia mitigation arrangement 120 and an engine 20 and the connections among each component. Ammonia is stored in the storage tank 210 which is arranged in fluid communication with the fuel supply system 10 via associated supply lines, pumps and valves. The ammonia consuming device in the illustrated example is an internal combustion engine 20 configured such that it can use ammonia as fuel. The engine 20 is in fluid communication with the fuel supply system 10 and receives ammonia as a fuel from the fuel supply system. The ammonia can be returned to the storage tank 2 from the fuel supply system 10. The ammonia mitigation system 100 can receive ammonia- contaminated vent / purging gas or liquid streams from the fuel supply system 10 and the engine 20 and reduces ammonia content in emissions to the atmosphere. The vent / purging gas or liquid streams from the fuel supply system 10 are supplied via a purge line 1a to an optional buffer and then directed to either the first or second ammonia mitigation arrangements 110 or 120, respectively, via a valve V and respective supply lines 2a and 2b. Similarly, the vent / purging gas or liquid streams from the tank 210 and the engine 20 are supplied via respective purge lines 1c and 1 b to an optional buffer and then directed to either the first or second ammonia mitigation arrangements 110 or 120, respectively, via a valve V and respective supply lines 2a and 2b. Boil-off gases (BOG) from the ammonia tank 210 can be directed to the burner M1 . Vents released from the tank that are other than the BOG, e.g. released from pressure safety valves can be directed to the buffer. The buffer may be a tank, which may be pressurized. The water regeneration system and the burner system are fluidly connected, and therefore, also the first ammonia mitigation arrangement M1 and the second ammonia mitigation system M2 are fluidly connected as shown schematically by line 3 in Fig. 1 .

[0077] According to an example embodiment of the invention, the first ammonia mitigation arrangement comprises a burner associated with a boiler system of a marine vessel and will be described more in detail in Fig. 3.

[0078] The objective of the present invention is to provide a technical configuration for a system for reducing ammonia content in the vent / purging streams generated from the ammonia fuel supply system and engine. The present invention additionally provides a method of operating the ammonia mitigation system with different modes.

[0079] Reference is made to Fig. 2 which generally shows components of the second ammonia mitigation arrangement 120. Both the first and the second ammonia mitigation arrangements are fluidly connected to and downstream of the engine 20 and the fuel supply system 10. An inert gas supply arrangement 122 is fluidly connected via a connecting supply line 121 and 123 to a fuel supply system 10 and via the connecting supply line 121 and 125 to the engine 20. The inert gas used for purging can be nitrogen but could be any other type of inert gas. The inert gas may be generated on board a marine vessel, or it can be held in an inert gas tank, for example. Generally, a purging circuit may be provided with one or more nitrogen inlets and may comprise one or more pressure indicators and transmitters. The purged ammonia can be collected and returned to a catch tank located inside the fuel supply system 10. The catch tank may receive discharge from relief devices in the fuel supply system.

[0080] The ammonia mitigation system 100 is thus aimed for ammonia-containing streams generated by vent gases and / or vent streams during purging of an ammonia supply system 10 and / or ammonia-fueled engine 20. The system 100 is arranged in fluid communication with an exhaust piping, or herein also referred to as a vent mast 160 leading the ammonia-containing streams with reduced ammonia content to the atmosphere. A chimney may be comprised in the exhaust piping 160. As shown in Fig. 2, the second ammonia mitigation arrangement 120 comprises a first ammonia mitigation device 130, which may be a “water tank”, and thus comprises a water tank filled with a liquid water. According to another variant, the first ammonia mitigation device 130 may comprise an acid tank containing an acid solution. When the first ammonia mitigation device contains water in the tank, the water absorbs ammonia and thereby reduces the ammonia content in the downstream gas stream. Alternatively, when acid is contained in the tank, the ammonia is neutralized by the acid, and thus the ammonia content is reduced in the downstream gas stream. The acid that is used could be for example citric acid or any other acid having similar properties. If the first ammonia mitigation device 130 comprises an acid tank, it may be smaller than the shown water tank 130 and may have the size of an acid tank 140 described more in detail below. In this way, the second ammonia mitigation arrangement 120 may be designed more compact than the second ammonia mitigation arrangement 120.

[0081] In case the first ammonia mitigation device comprises water stored in the tank, the water has lower and higher threshold levels in the tank, i.e. the level should be above the lower threshold level but should not be above the higher threshold level. The same applies for the levels if the first ammonia mitigation device comprises an acid solution. The respective threshold level can be determined according to the best practice in the technical field. The ammonia-containing streams are arranged to be supplied into the tank below the lower threshold level, so that it can be ensured that ammonia can be brought into contact with water or acid. The water or acid level can be monitored with a water level monitoring device 133, which is arranged to monitor water or acid level and alert when the water or acid level is lower than the lower water or acid threshold level or higher than the higher threshold level in the tank. The water or acid level monitoring device 133 may be arranged in communication with a water filling device 135 via a link 137, or an acid filling device in a similar manner, which in turn may be arranged in communication with a control system for the ammonia mitigation system. This in turn can be arranged in communication with a control system of the fuel supply system and / or the engine operation control system. The water filling device 135 may be configured to start to fill water to the first ammonia mitigation device 130, when the water level is lower than the higher water threshold level. That is, no water should be added if the water level is already at a maximum level, but water can be filled if the maximum level is not reached. The first ammonia mitigation device 130 also comprises a drain 131 , through which the tank of the device 130 may be emptied.

[0082] Thus, alternatively, water or acid drain 131 may be opened if the water level is higher than the higher water threshold level.

[0083] The first ammonia mitigation device 130 may further comprise an ammonia content monitoring device 134 in communication with the drain device 131. The drain device 131 may be configured to start draining the water or acid tank when the ammonia content in the tank is above an ammonia threshold value. In that case, the water in the tank may not be suitable for absorbing ammonia anymore, or in case of acid, to neutralize the ammonia anymore. Draining can be continued until the whole tank is drained, or until the lower threshold level is reached. Alternatively, or additionally clean fresh water can be filled by a water filling device 135, which may be configured to start to fill water when the ammonia content in the water tank is above the ammonia lower threshold value and below the higher water threshold level. Addition of acid can be performed in a similar manner.

[0084] The ammonia mitigation system 100 further comprises a second ammonia mitigation device 140. The second device 140 may comprise or consist of an acid tank 140 storing an acid solution. The second device may comprise alternatively or additionally a water tank or several tanks. The first and second ammonia mitigation devices 130, 140 are connected by a connecting pipe 116. The ammonia may be absorbed and neutralized by the acid solution. The acid tank may have lower and higher threshold levels, i.e. the physical level in the tank. The ammonia-containing streams from the fuel supply system or engine may be arranged to be supplied into the tank below the lower threshold level. In this way it can be ensured that the ammonia in the streams will contact the acid solution and can be thereby neutralized. The level of the acid solution may be monitored by means of a level monitoring device 143 and it may be arranged to monitor acid solution level and alert when the acid solution level is lower than the lower threshold level or higher than a higher threshold level in the tank.

[0085] The ammonia mitigation system 100 may include a vacuum protection system 170 comprising a vacuum breaker and / or an air inlet connection activated by a pressure transmitter detecting low pressure. Thereby, the ammonia mitigation system is protected from vacuum. The vacuum protection system 170 may be located on the connecting pipe 116 between the water tank 130 and acid tank 140. The second ammonia mitigation device and / or the first ammonia mitigation device when it contains acid, may comprise an acid content monitoring device 144. The acid monitoring device may monitor the acid content or the residual acidity of the acid solution, for example the pH. Thereby, information is obtained on whether the acid solution in the tank is still suitable for neutralizing ammonia that enters the tank. The second ammonia mitigation device comprises a drain device 141 for emptying the acid tank 140 of the liquid content in it. The acid monitoring device may be arranged in communication with an acid tank drain device 141 and / or an acid refill device configured to fill acid solution when the residual acidity in the second ammonia mitigation device is below a threshold. The acid refill device may comprise the acid tank 145 and an acid pump 146, which may be turned on when the acid solution needs to be filled to the acid tank 140. Valves and piping with automatic control arrangements may be associated with the acid refill device. The acid level monitoring device 143 and / or the acid content monitoring device 144 may be arranged in communication with the acid refill device and the drain device 141 via a link 147 to enable automatic control of the acid refill based on the acid level and / or content.

[0086] Ammonia absorption and neutralization are exothermic processes, releasing heat to water and / or acid solutions. For further control of the ammonia mitigation system, the first and / or second ammonia mitigation devices may each comprise a temperature monitoring device configured generate an alarm when the temperature in the first and / or second ammonia mitigation device is higher than a threshold temperature. In this way it is possible to take action to reduce the temperature, leading to a higher ammonia absorption efficiency. According to an embodiment, the first and / or second ammonia mitigation devices may comprise a respective cooling device, such submerged cooling coil 139, 149. The cooling coil may be of any known type and may e.g. be filled with cooling fluid and be connected to a cooling circuit. Alternatively, the cooling device may comprise an external cooling device connected to the first and / or second ammonia mitigation device.

[0087] The exhaust piping 160 may be fluidly connected to the second ammonia mitigation device. As explained more in detail below, during the use of the system, the ammonia streams will normally pass the acid tank 140. An ammonia gas detector 164 may be arranged in fluid communication with the released gases in the exhaust piping 160. The detector may be configured to generate an alarm when the ammonia content in the exhaust piping 160 is above a threshold. When the ammonia mitigation system is operated with the second ammonia mitigation arrangement 120, the ammonia-containing streams from the ammonia fuel supply system venting are supplied to a first supply line 111 (or 1 a, 2b in Fig. 1 ), which is in fluid communication with the ammonia supply system and the first and second ammonia mitigation devices, where venting is the operation done by opening vent valves and let liquid ammonia vaporizing as a result of depressurization. Ammonia- containing streams of purging gases from the fuel supply system and the engine are supplied further in the system via a second supply line 112 (or 1 b, 2b in Fig. 1 ), which is in fluid communication with the ammonia-fueled engine 20 and the first and second ammonia mitigation devices 130; 140, where purging is the operation of ammonia displacement by means of pressurized inert gas. A valve device 150 connecting the first and second ammonia supply lines and the first and second ammonia mitigation devices 130, 140.

[0088] As briefly discussed above, the ammonia streams may be in a first step supplied to the water tank for ammonia absorption followed by a second step of absorption into the acidic solution. The two-stage approach in series of the system and the method is based on the high hygroscopicity and on the caustic behavior of ammonia. Thanks to the two-stage approach, the proposed system and method can handle streams with a wide range of ammonia composition, from 100% ammonia to very low ammonia content in the inert gas.

[0089] Since the proposed system and method may comprise both water absorption and acid treatment, it can handle vent streams which are generated in an uncontrolled way, e.g. emergency vents, as well as vent streams generated during controlled operations, such as engine purging with inert gas followed by liquid ammonia recovery inside the fuel supply system. For this reason, the proposed solution can be classified as a “passive” solution, being always ready for receiving ammonia-containing streams, without any delay. The system is designed so that the received gas streams containing ammonia are treated differently depending on the upstream system’s operating mode and therefore on different expected ammonia content. The received stream can be directed to the water tank and in series to the acid tank, i.e. a two-steps process, or directly to the acid tank bypassing the water tank, i.e. a single step process, if the expected amount of ammonia is lower. The proposed method can automatically handle the refill of the liquids needed for absorption when needed, by continuously monitoring the progressive level of contamination. The proposed method can also keep the temperature of both fluids under control. The water tank is equipped with continuous level monitoring, activating automatic water refill when low level is detected and activating an alarm when low level is detected. Additionally, the acid tank is equipped with continuous level monitoring, activating an alert when low level is detected and activating an alarm when low level is detected.

[0090] The valve device 150 may be a three-way valve and is normally open to the first ammonia mitigation device 130, e.g. water tank. This is to ensure that a double stage ammonia removal can be performed even in case the valve is not activated or not working. Additionally, there is a free vapor connection between water tank and acid tank, and there is no obstruction in between.

[0091] As mentioned above, the system may involve water tank temperature monitoring and alarm by means of temperature transmitters. Also, the system may involve acid tank temperature monitoring and alarm by means of temperature transmitters. The exotherm icity of the water absorption can be kept under control by means of cooling water coil and the exotherm icity of the neutralization reaction can be kept under control by means of cooling water coil.

[0092] Further, the system may involve monitoring of water quality, for example by monitoring the dissolved ammonia content by measuring the pH and / or the conductivity in the water tank. This enables automatic discharge and refill in case of increased level of contamination of water, that is when the water is no longer suitable for ammonia absorption. In the same way the acidity solution quality is monitored, for example by measuring the pH and / or the conductivity of the solution. The monitoring results can then be used for automatic discharge and refill in case of decreased acidity and when the acid solution is no more suitable for ammonia neutralization.

[0093] According to another variant, instead of draining the ammonia water or acid, it can be incinerated in a burner, as described in EP25172156, and in which the waste liquid is fed to the combustion system via a conduit, which is separate from the fuel conduit. Similarly, the acid solution can be incinerated in the burner or the boiler when it has reached saturation.

[0094] In the system, the excess of gas can be vented through the exhaust gas piping to chimney. The exhaust gas piping can be equipped with a gas detector, which may continuously or at certain intervals monitor the level of ammonia in the gas stream, the gas detector may provide an alarm in case of exceeding threshold. All data in the system can be measured by the transmitters described above.

[0095] The measured data can be collected by a control unit of the ammonia mitigation system, which may be a part of the fuel supply system control unit. The data may be recorded and saved. It can be transferred to a cloud server. The cloud server may store and collect data, which may be stored periodically. Based on the data it is possible to provide operation information which can be used to detect need for maintenance or repair.

[0096] Reference is now made to Fig. 1 and 3. The first ammonia mitigation arrangement 110 is configured to combust ammonia-containing vent or purge streams originating from the fuel supply system and / or the engine, as described in Fig. 1 . As mentioned above, the purge gas may be generated when the ammonia fueled engine 20 switches fuel from ammonia to another fuel or when the ammonia fueled engine 20 shuts down, either in a controlled manner or as a result of an emergency situation. At this stage, the purge gas is toxic and should therefore not be vented directly to the atmosphere. The purge gas is typically a mixture of ammonia and an inert gas used to purge the ammonia from the ammonia fuel system 10. The ammonia may be liquid ammonia, gaseous ammonia, or a mixture thereof. The inert gas may be nitrogen. It should be noted that the inert gas may be any other inert gases as well.

[0097] Fig. 3 shows a schematic example of ta boiler system, which comprises a burner 104, a fuel inlet (not shown) to provide fuel to the burner for the combustion and a purge gas inlet PIL. The boiler may be an ammonia purge boiler as described for example in EP4060230B1 . The burner 104 may be configured to bum the purge streams comprising ammonia in gas and / or liquid phase originating from the ammonia fuel system 10. Put differently, the burner 104 is configured to combust the ammonia within the purge gas. The burner 104 may be a multi-fuel burner configured to bum two different fuels one at the time or simultaneously. The burner 104 may be of pressure atomizing type. The burner 104 may alternatively be of steam atomizing type. The burner may be of the type described in

[0098] The purge gas inlet PIL can be separated from the fuel inlet. The purge gas inlet is configured to intermittently receive the purge gas from the ammonia fuel system 10 and supply the purge gas to the burner 104, for example via a gas valve unit. The purge gas may be supplied from the ammonia fuel system 10 or the engine to the purge gas inlet PIL via a purge gas piping and a buffer, or from the second ammonia mitigation arrangement 120 to the PIL via connecting line 3, as shown in Fig. 1 . The return from the second ammonia mitigation arrangement may be via regeneration of the absorption water. The piping may be of double-walled type; especially for those parts of the piping where the purge is in gas phase.

[0099] Generally, the fuel inlet may be connected via a fuel supply line to a fuel source e.g. a fuel tank. The fuel source is configured to supply the fuel, via the fuel inlet to the burner 104. The fuel may be liquefied natural gas (LNG), distillate and residual fuels. This may e.g. include diesel, marine gas oil (MGO), very low Sulphur fuel oil (VLSFO), heavy fuel oil (HFO). The fuel may also be biofuel. However, it should be noted that the main fuel may be other fuels as well. The fuel may comprise one or more types of fuels. If the fuel comprises more than one type of fuel, the fuel inlet may be connected to more than one fuel sources. Thus, if the fuel comprises two types of fuel, one fuel type may be supplied from the fuel source and the other fuel type may be supplied from one other fuel source. Typically, the fuels are supplied to the burner 104 only one at a time.

[0100] The proposed scheme of the ammonia vent mitigation system can be modified if the vent piping connections are different than what has been described above, for example the number of connections, compositions of the system can be varied. The proposed scheme of the ammonia vent mitigation system can be modified according to different ammonia-fueled engine purging methods.

[0101] In the second arrangement, the type of acid can be varied. The system can be combined with a downstream dilution with air, if needed to achieve the maximum allowable ammonia concentration in the exhaust gas. Instead of using fluid cooled cooling coils, an external cooling system can be used instead. Additionally, an intermediate cooling water loop can be used in place of direct cooling with cooling water, to prevent water contamination in case of rupture. Further, the system can be provided with automatic acid refill from a dedicated additional tank.

[0102] The foregoing description of the embodiments has been furnished for illustrative and descriptive purposes. It is not intended to be exhaustive, or to limit the embodiments to the variations described. Many modifications and variations will obviously be apparent to one skilled in the art. The embodiments have been chosen and described in order to best explicate principles and practical applications, and to thereby enable one skilled in the art to understand the invention in terms of its various embodiments and with the various modifications that are applicable to its intended use. The components and features specified above may, within the framework of the disclosure, be combined between different embodiments specified.

Claims

25CLAIMS1 . An ammonia mitigation system (100) for receiving ammonia-containing streams generated by vent gases and / or vent streams during purging of an ammonia fuel supply system (10) and / or ammonia-fueled engine (20), the system being in fluid communication with a vent mast (160) leading the ammonia-containing streams with reduced ammonia content to the atmosphere, the system comprising a first ammonia mitigation arrangement (110) and a second ammonia mitigation arrangement (120), wherein the first and second arrangements are based on different technical solutions and are arranged to operate alternatingly or complementary to each other.

2. The ammonia mitigation system of claim 1 , wherein the first and second ammonia mitigation arrangements (110, M1 ; 120, M2) are fluidly connected via a valve arrangement (V) to- a first supply line (1a; 111) for supplying ammonia-containing streams from the ammonia fuel supply system (10) to the first and second ammonia mitigation arrangements, and- a second supply line (1 b, 112) for supplying ammonia-containing streams from the ammonia-fueled engine (20) to the first and second ammonia mitigation arrangements.

3. The ammonia mitigation system of claim 2, wherein the valve arrangement (V) is configured to supply the ammonia-containing streams to the first and second ammonia mitigation arrangements, respectively, preferably one at a time.

4. The ammonia mitigation system of claim 2 or 3, wherein a buffer tank is arranged upstream of the valve arrangement (V) to receive the ammonia-containing streams from the fuel supply system (10) and the engine (20).

5. The ammonia mitigation system of any one of the preceding claims, wherein the first ammonia mitigation arrangement (110, M1 ) comprises a burner (104), wherein the burner is fluidly connected via a first inlet line (2a, 121 ) to the vent gases and / or vent streams from the ammonia fuel supply system and / or ammonia-fueled engine,and configured to burn the ammonia-containing vent gases and / or vent streams from the ammonia fuel supply system (10).

6. The ammonia mitigation system of claim 5, wherein the burner (104) is comprised in a boiler system (102).

7. The ammonia mitigation system of any one of the preceding claims 1 -5, wherein the first ammonia mitigation arrangement comprises a scrubber.

8. The ammonia mitigation system of any one of the preceding claims, wherein the second ammonia mitigation (120, M2) arrangement comprises:- a first ammonia mitigation device (130);- a second ammonia mitigation device (140);- a valve device (150) configured to fluidly connect the first and second supply lines (1a, 1 b, 2b; 111 , 112) and the first and second ammonia mitigation devices (130; 140), wherein the second ammonia mitigation arrangement (M2; 120) is configured to absorb and / or neutralize the ammonia-containing vent gases and / or vent streams from the ammonia fuel supply system.

9. The ammonia mitigation system of claim 8, wherein the first ammonia mitigation device (130) comprises a water tank storing water, or an acid tank storing acid solution.

10. The ammonia mitigation system of claim 8 or 9, wherein the second ammonia mitigation device (140) comprises an acid tank storing an acid solution and / or a water tank storing water.11 . The ammonia mitigation system of any of claims 8 to 10, wherein the second ammonia mitigation arrangement (120) comprises ammonia and / or water or acid content monitoring devices in communication with the first ammonia mitigation arrangement, and wherein the supply of the ammonia-containing vent streams is configured to be directed to the first ammonia mitigation arrangement when at least one of the ammonia content, water content or acid content is outside a pre-definedrange for the ammonia and / or water or acid content, or when the water level and / or the acid level are / is outside a pre-defined level and / or when the first ammonia mitigation arrangement (110) is not operable.

12. The ammonia mitigation system of any one of the preceding claims, wherein the supply of the ammonia containing vent streams is configured to be directed to the second ammonia mitigation arrangement, when the first ammonia mitigation arrangement is not activated to combust the ammonia-containing vent streams.

13. The ammonia mitigation system of any one of the preceding claims, wherein an ammonia gas detector (164) is arranged in fluid communication with the released gases in the exhaust piping (160) and is configured to generate an alarm when the ammonia content is above a threshold.

14. The ammonia mitigation system according to any one of the preceding claims, wherein the ammonia mitigation system is fluidly connected to a catch tank (15) inside the ammonia fuel supply system and / or a knockout drum upstream of the ammonia mitigation system.

15. The ammonia mitigation system according to any one of the preceding claims, wherein the second ammonia mitigation arrangement is mounted on a single skid.

16. Ammonia mitigation arrangement (120) for reducing ammonia content in ammonia- containing streams generated by vent gases and / or vent streams during purging of an ammonia fuel supply system (10) and / or ammonia-fueled engine (20), the arrangement comprising:- a first ammonia mitigation device (130);- a second ammonia mitigation device (140);- a valve device (150) configured to fluidly connect a first supply line (1 a; 111 ) for supplying ammonia-containing streams from the ammonia fuel supply system (10) to the ammonia mitigation arrangement (120), and- a second supply line (1 b, 112) for supplying ammonia-containing streams from the ammonia-fueled engine (20) to the ammonia mitigation arrangement (120), wherein the ammonia mitigation arrangement (120) is28 configured to neutralize the ammonia-containing vent gases and / or vent streams from the ammonia fuel supply system and / or engine, and wherein the first ammonia mitigation device (130) comprises an acid tank storing acid solution, and the second ammonia mitigation device (140) comprises an acid tank storing an acid solution.

17. Method of operating the ammonia mitigation system (100) according to any one of the preceding claims, wherein the method comprises:- supplying ammonia-containing streams generated by vent gases and / or vent streams during purging of the ammonia fuel supply system (10) and / or ammonia-fueled engine (20) to the first or second ammonia mitigation arrangement, and• supplying the ammonia-containing vent streams to the second ammonia mitigation arrangement when the first ammonia mitigation arrangement is not activated, or• supplying the ammonia-containing vent streams to the first ammonia mitigation arrangement based on pre-defined operating criteria and / or when at least one of the ammonia and / or water or acid content is outside a pre-defined range for the ammonia and / or water or acid content, and• releasing the mitigated ammonia stream to the atmosphere via the vent mast (160).

18. The method according to claim 17, wherein the method comprises• Supplying contaminated water from the second ammonia mitigation arrangement (120) to a burner of the first ammonia mitigation arrangement, drain tank and / or water regeneration system, and / or• Supplying the contaminated acid from the second ammonia mitigation arrangement to a drain tank and / or to the burner of the first ammonia mitigation arrangement.

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