Ammonia release system and method

Abstract

An ammonia release method and system comprising a space (1) for ammonia storage, transport or usage, a buffer tank (2) for receiving ammonia released from the space, a feed line (2A) for releasing ammonia from the space (1) to the buffer tank (2), a vent mast (3) for venting diluted ammonia to the environment; a vent line (3A) for venting ammonia from the buffer tank (2) to the vent mast (3), a fan (4) for drawing ambient air into the vent mast to dilute ammonia, and a bypass line (3B) for releasing ammonia from the space (1) directly to the vent mast (3).

Description

[0001] Ammonia release system and method

[0002] Technical Field

[0003]

[0001] The present disclosure concerns the field of release of ammonia. Specifically, the disclosure concerns an ammonia release system and an ammonia release method.

[0004] Background

[0005]

[0002] Ammonia (NH3), such as anhydrous ammonia, has recently gained increased interest as a carbon-free fuel in onshore and marine applications. Ammonia can either be used as a carrier for hydrogen, or as a zero-carbonemission fuel itself; during combustion ammonia does not emit CO2. Advantages of using ammonia as compared to hydrogen are that ammonia has both a higher energy-density and a higher liquefaction temperature. At atmospheric pressure ammonia boils at about -33 °C, whereas hydrogen is in the cryogenic domain, with a boiling temperature of -253 °C. Consequently, liquid ammonia requires significantly less cooling during storage, as compared to liquid hydrogen, which is especially favourable during long-term storage, such as during long sea journeys. An advantage of ammonia over other zero-carbon-emission fuels, such as methanol or e-methane, is a cheaper synthesis due to the lower amount of energy required. Furthermore, ammonia has a lower flammability compared to traditional carbonbased fuels.

[0006]

[0003] On the other hand, ammonia also has certain disadvantages, in that it is inherently toxic, implying a risk for human exposure through inhalation and I or skin contact. Ammonia can also have detrimental impacts on, e.g., aquatic life when vented in marine or on-shore environments. In order to mitigate these risks, systems must be provided at facilities utilizing ammonia, such as on ammonia- driven marine vessels, or ammonia production plants. Such systems, also known as ammonia release systems, or ammonia release mitigation systems (ARMS), should be able to release leaked or residual ammonia to the environment, whilst minimizing the risk for human operators of exposure to toxic ammonia concentrations, and for the environment itself.

[0007]

[0004] For instance, for marine applications limit concentrations of ammonia at vent mast outlets, measured on the inside of the vent mast, are currently set to 300 ppm by volume in several countries. Consequently, ammonia release systems will be required for all ammonia carrying vessels in these countries. For certain applications, such as marine bunkering of ammonia, it may furthermore be necessary to purge bunkering equipment with an inert gas after ammonia fuelling operations, to eliminate the risk of ammonia leakages when the bunkering equipment is not in use. For bunkering and other applications, it may therefore be desirable to significantly reduce the ammonia concentration in a short time span, such that the remaining ammonia can be vented directly to the environment.

[0008]

[0005] However, many current ammonia release systems are either expensive to implement, impractical and I or technically complex, thereby reducing attractiveness of ammonia as a fuel, or fuel-carrier. Examples of such known systems are combustion-based ammonia release systems, scrubber systems using water, or systems employing condensation-based separation techniques.

[0009] Furthermore, such systems known may require a large amount of space, which makes these systems less suitable for marine applications, where space is usually limited.

[0010]

[0006] In order to overcome the downsides of these known systems there is a need for an ammonia release system and an ammonia release method that are simple to implement, have a low cost, low space requirements, and do not require external reagents. Preferably, the system and method do not need water to operate in regular release mode. The system and method should further be able to handle aforementioned purging operations.

[0011] Summary of the Invention

[0012]

[0007] The present disclosure concerns an ammonia release system for a marine or on-shore structure, the system comprising a space for ammonia storage, transport or usage, a buffer tank for receiving ammonia released from the space, a feed line for releasing ammonia from the space to the buffer tank, a vent mast for venting diluted ammonia to the environment, a vent line for venting ammonia from the buffer tank to the vent mast, a fan for drawing ambient air into the vent mast to dilute ammonia, and a bypass line for releasing ammonia from the space directly to the vent mast.

[0008] According to a further embodiment of the system, the bypass line comprises a bypass valve, and wherein the bypass valve is configured to open when: the pressure in the buffer tank reaches a pressure limit, or the ammonia concentration in the space reaches a concentration limit.

[0013]

[0009] According to a further embodiment, the system further includes a control unit, at least one ammonia sensor, and a pressure sensor, and wherein the control unit is configured to open the bypass valve based on signals from the pressure sensor and I or at least one ammonia sensor.

[0014]

[0010] According to a further embodiment of the system, the vent line comprises a vent valve, configured to vent ammonia from the buffer tank to the vent mast.

[0015] [Oil] According to a further embodiment of the system, the volume Vs of the space and the volume VB of the buffer tank are related as 0,25*Vs =£ VB =£ 50*Vs.

[0016]

[0012] According to a further embodiment, the system further comprises a housing enclosing at least the buffer tank, wherein the housing comprises an inlet for ambient air.

[0017]

[0013] According to a further embodiment, the system further includes an inert gas source for purging the space.

[0018]

[0014] According to a further embodiment, a marine or on-shore facility is provided, comprising the ammonia release system of the present disclosure, wherein the marine or on-shore structure is a vessel, an offshore platform, an ammonia bunkering facility, an ammonia producing or processing plant, and I or an on-shore ammonia consumer.

[0019]

[0015] The present disclosure also concerns an ammonia release method for a marine or on-shore facility is provided, the method comprising providing a system according to the present disclosure, or a marine or on-shore facility according to the present disclosure, releasing ammonia from the space to the buffer tank, venting ammonia from the buffer tank to the vent mast, and diluting ammonia with air drawn through into the vent mast by the fan before venting diluted ammonia into the environment.

[0016] According to a further embodiment, the method further comprises purging the space with an inert gas, such as nitrogen.

[0020]

[0017] According to a further embodiment, the method further comprises opening the bypass valve and closing the feed valve to release ammonia from the space directly to the vent mast when the pressure in the buffer tank reaches a pressure limit, or the ammonia concentration in the space reaches a concentration limit.

[0021]

[0018] According to a further embodiment of the method, the pressure limit is based on the gas pressure in the space before release, the volume of the buffer tank, the volume of the space and I or the volume of an inert purging gas.

[0022]

[0019] According to a further embodiment of the method, the concentration limit is based on one or more of the capacity of the fan, an available time for purging of the space with an inert gas, and I or the volume of the buffer tank relative to the volume of the space.

[0023]

[0020] According to a further embodiment, the method further comprises monitoring the ammonia concentration in the space and I or in the vent mast.

[0024]

[0021] According to a further embodiment, the method further comprises drawing ambient air into a housing enclosing the buffer tank and drawing air from the housing into the vent mast by a housing fan.

[0025]

[0022] Advantageously, the system and method of the present disclosure do not require external liquids to function, and do not result in consumables and I or biproducts. Consequently, there is no need for additional waste management equipment, or designated hazardous areas, resulting in a small footprint. This is especially advantageous for applications where space requirements are strict, such as marine vessels or offshore platforms. Furthermore, no rotating parts are required, other than a regular fan. Advantageously, the system and method of the present disclosure can utilize existing ammonia vent masts, found on most ammonia handling facilities. Such systems normally include nitrogen-based purging systems, for purging ammonia from onboard or on-site equipment. Such systems may further include ventilation systems, for ventilating housings or enclosures on the facility or vessel. Brief Description of the Figures

[0026]

[0023] Figure 1 shows a schematic drawing of the ammonia release system of a first embodiment of the present disclosure.

[0027]

[0024] Figure 2 shows a schematic drawing of a second embodiment of the ammonia release system of the present disclosure.

[0028]

[0025] Figure 3 shows a schematic drawing of a third embodiment of the ammonia release system of the present disclosure, including a housing.

[0029]

[0026] Figure 4 show a schematic drawing of a fourth embodiment of the ammonia release system of the present disclosure, including a nitrogen source.

[0030]

[0027] Figure 5A shows a schematic drawing of a fifth embodiment of the ammonia release system of the present disclosure, including absorbing means.

[0031]

[0028] Figure 5B shows a schematic drawing of a variant of the fifth embodiment of the ammonia release system of the present disclosure.

[0032]

[0029] Figure 6 shows a schematic drawing of a sixth embodiment of the ammonia release system of the present disclosure, including suction means.

[0033] Detailed Description

[0034]

[0030] Referring to the first embodiment of figure 1, the present disclosure concerns an ammonia release system for a marine or on-shore facility. The system includes a space 1 for ammonia. The space 1 for ammonia may, for instance, be a space for ammonia storage, ammonia transport, and / or ammonia usage. The space has a volume Vs. Ammonia in the space 1 may preferably be anhydrous ammonia. Ammonia in the space 1 may be in gaseous form, in liquid form, or in a combination of both gaseous and liquid form. The space 1 may, for instance, comprise an ammonia transport pipe, such as an ammonia bunkering line, an ammonia process flow line, or an ammonia engine fuel line. Alternatively, the space may comprise an ammonia storage tank, such as an ammonia fuel tank, an ammonia process tank, or any other vessel for storing or handling of ammonia. Further alternatively, the space 1 may comprise an ammonia user, such as ammonia processing equipment, an ammonia-driven engine, or an ammonia fuel cell.

[0035]

[0031] The marine or on-shore facility may, for example, comprise a vessel, an offshore platform, or a floating structure. Alternatively, the marine or on-shore facility may comprise an ammonia bunkering facility, a process facility, an ammonia production plant, or an ammonia consuming facility or vehicle. Ammonia may be used as a fuel, driving an engine or a fuel cell. Alternatively, ammonia may be used as a hydrogen carrier.

[0036]

[0032] In operation, ammonia in the space 1 may have to be released therefrom. In one mode, ammonia release from the space 1 may be driven by pressure release. In this case, the ammonia gas pressure in the space is higher than the gas pressure in the buffer tank and I or in the vent mast, and release of ammonia from the space is driven by this pressure difference. In another mode, ammonia release from the space 1 may be driven by purging. In this case, ammonia is driven from the space by the introduction of a pressurized inert gas into the space 1. In yet another mode, ammonia release from the space 1 may be suction driven. In this case, means for sucking ammonia from the space 1 may be provided, as detailed below. In yet a further mode, ammonia release from the space 1 may be driven by a combination of two or more of the preceding modes, either simultaneously or sequentially. The different modes for ammonia release from the space are detailed with reference to the method described hereinbelow. In each case, released ammonia is in gaseous form, preferably in anhydrous gaseous form.

[0037]

[0033] At the onset of purging, the ammonia concentration C in the space may be 106ppm or lower. Here, and further hereinbelow, ammonia concentrations are indicated as ppm per volume. During an ongoing purging-driven release the ammonia concentration in the space may eventually fall to a concentration level Csafe that is safe for human operators and I or the environment. Upon reaching a safe concentration level, further release from the space may not be necessary. Alternatively, release of ammonia from the space may continue until reaching a negligible concentration, close to 0 ppm. Generally, an ammonia concentration of at most 300 ppm is considered safe. However, the safe level may also be higher, or lower, depending on the type of application, and I or regulations.

[0038]

[0034] Generally, ammonia release may be necessary before maintenance, when emptying ammonia bunkering lines at completed bunkering, or for other operational reasons. In each case, ammonia should be released from the space in a safe and controlled manner. For example, into the environment, at safe concentration levels to avoid harmful effects to human operators and the surrounding environment.

[0039]

[0035] Thereto, the system includes a buffer tank 2 for receiving ammonia, or a mixture of ammonia and inert gas, released from the space 1. Released ammonia preferably comprises ammonia gas, such as anhydrous ammonia gas. The buffer tank 2 is connected to the space 1 by a feed line 2A. Released ammonia, or a mixture of ammonia and inert gas, flows from the space 1 into the buffer tank 2, through the feed line 2A. The feed line 2A may further include a feed valve 2A'. The feed valve 2A' may preferably be a control valve. In the default position, the feed valve 2A' may be closed. The feed valve 2A' may be opened after receiving an automated signal. Alternatively, the feed valve 2A' may be opened by an operator, either manually or remotely. Further alternatively, the feed valve 2A' may be opened after pre-defined period of time has expired, such as after a pre-defined period upon completion of bunkering. A further buffer tank (not shown) may be included in the system. Such a further buffer tank may provide system redundancy, in case of equipment failure.

[0040]

[0036] The buffer tank 2 may be a single wall tank, or a double wall tank. The buffer tank 2 may be insulated. The buffer tank 2 may be configured to handle a maximum storage pressure Pmax of 10 - 18 bar (1 MPa - 1,8 MPa). The volume VB of the buffer tank may be at least a quarter of the volume Vs of the space, preferably at least half the volume of the space, more preferably at least equal to the volume of the space. A smaller volume VB may result in a higher buffer tank pressure during ongoing release and possibly in intermittent interruptions in ammonia release, to clear the buffer tank. Thereby, release from the space may proceed over a longer time, which may be advantageous to prevent system overloading when, for instance, ammonia dilution capacity (detailed below) is reduced. A smaller buffer tank also results in a smaller system footprint, which is especially advantageous when available space for equipment is limited, such as on marine vessels or offshore platforms. Furthermore, the volume VB of the buffer tank may preferably be at most fifty times the volume of the space Vs, preferably at most forty times the volume of the space, more preferably at most twenty times the volume of the space, most preferably at most ten times the volume of the space. In operation, it is thereby ensured that the bulk of ammonia in the space may quickly be released therefrom to the buffer tank, without exceeding the storage capacity of the buffer tank. Furthermore, the equalizing pressure is kept at a minimum due to the excess capacity of the buffer tank as compared to the space. The volume of the buffer tank VB and of the space Vs are thus related as:

[0041] 0,25*Vs < VB < 50*Vs.

[0042] Within these limits, the volume VB of the buffer tank 2 may further be adjusted based on operational criteria, as detailed below.

[0043]

[0037] The system also includes a vent mast 3 for releasing diluted ammonia to the environment. The vent mast 3 is connected to the buffer tank 2 by a vent line 3A. The vent line 3A may include a vent valve 3A'. The vent valve 3A' may preferably be a control valve, a pressure release valve, a bleed valve, or an automatic bleed valve. In the default position, the vent valve 3A' may be closed. Upon opening, the vent valve 3A' may be configured to vent ammonia, or a mixture of ammonia and inert gas, from the buffer tank 2 to the vent mast 3. Flow through the vent valve 3A' may preferably be at a lower rate than the flow through the feed valve 2A'. Preferably, the vent valve 3A' may be configured to vent ammonia, or a mixture of ammonia and inert gas, from the buffer tank 2 continuously. Further preferably, flow through the vent valve 3A’ may be regulated based on the pressure in the buffer tank 2 and I or the concentration of ammonia in the vent mast 3.

[0044]

[0038] The system further includes at least one fan 4, for drawing ambient air into the vent mast 3. Thereto, the fan 4 may include an inlet for ambient air. The fan 4 may, for instance, comprise an axial fan, or a centrifugal fan. The fan 4 is connected to the vent mast 3. Optionally, the fan 4 may be located within the vent mast 3. Alternatively, or additionally, the vent mast 3 may further include at least one inlet 3' for drawing ambient air into the vent mast 3. In operation, ambient air is drawn into the vent mast and mixed with ammonia, or a mixture of ammonia and inert gas, entering the vent mast by the action of the fan 4. Thereby ammonia, or a mixture of ammonia and inert gas, is diluted before venting from the vent mast. Advantageously, a low ammonia concentration is thereby achieved, allowing for a safe release into the environment. Operation of the fan 4 may be controlled by a control unit (detailed below). The rotational speed of the fan 4 may, for instance, be adjusted based on ammonia concentration levels in the vent mast 3, in the space 1, and I or in the buffer tank 2. A high concentration may require high fan speeds, and vice versa. In case the maximum fan speed is reached and the ammonia concentration in the vent mast 3 is above safe levels, the vent valve 3A' opening may preferably be restricted or closed.

[0045]

[0039] In operation, the system may allow a fast release of ammonia, or a mixture of ammonia and inert gas, from the space to the buffer tank and a subsequent slow release from the buffer tank to the vent mast and thereby, to the environment. A fast release from the space is beneficial for operational reasons, such as a rapid disconnection from bunkering lines upon completed bunkering, or a reduction of down-time during equipment maintenance. Further advantageously, a slow release to the environment allows ammonia to be mixed with ambient air and diluted, ensuring that the concentration of vented ammonia is non-toxic.

[0046]

[0040] With continued reference to figure 1, showing the first embodiment of the present disclosure, the system further includes a bypass line 3B for releasing ammonia, or a mixture of ammonia and inert gas, from the space 1 directly to the vent mast 3. Advantageously, further loading of the buffer tank can thereby be avoided. A smaller buffer tank may thereby be utilized, resulting in a small system footprint. The bypass line 3B may include a bypass valve 3B'. The bypass valve 3B' may preferably be a control valve. The bypass valve 3B' may be closed by default. The bypass valve 3B' may be configured to open based on operational criteria, as explained hereinbelow. Alternatively, the bypass valve 3B' may open based on operator input, or after a fixed, pre-defined time period has expired. The feed valve 2A' and I or the vent valve 3A' may be closed when the bypass valve 3B' is opened.

[0047]

[0041] The buffer tank 2, lines 2A, 3A, 3B, valves 2A, 3A', 3B', and vent mast 3, and any further equipment for ammonia in the present and following embodiments, preferably comprise steel, carbon steel, carbon-manganese teel, stainless steel, or any combinations thereof. Alternatively, or additionally, ammonia-resistant polymer materials, glass fiber reinforced materials, or composite materials may be utilized. Corrosive degrading due to the alkaline properties of ammonia can thereby be reduced, or preferably avoided.

[0048]

[0042] With reference to figure 2, showing a second embodiment, where same reference numerals denote the same features as for figure 1, the system may further include a control unit 5. The control unit 5 may comprise a CPU, a memory module, and an I / O bus. The control unit 5 may further comprise a screen, such as a touch screen, and I or an input module, such as keyboard, or similar. One or more of the fan 4, the feed valve 2A', the vent valve 3A', and / or the bypass valve 3B' may be connected to the control unit. The connection may be a wired or a wireless connection.

[0049]

[0043] The system may further include a first ammonia sensor 5A. The first ammonia sensor 5A may be located in, at, or near, the vent mast 3. Thereby, the ammonia concentration in the vent mast 3 before venting into the environment can be monitored. The system may further include a second ammonia sensor 5B. The second ammonia sensor 5B may be located in, or at, the space 1. Thereby, the ammonia concentration in the space 1 before and during release therefrom can be monitored. Optionally, the system may include a further ammonia sensor (not shown). The further ammonia sensor may be located in, or at, the buffer tank 2. The first, second and I or further ammonia sensors 5A, 5B may be coupled to the control unit 5. Additionally, or alternatively, the first, second and I or further ammonia sensors 5A, 5B may be coupled directly to the bypass valve 3B'. Optionally, the first, second and I or further ammonia sensors 5A, 5B may additionally be directly coupled to the feed valve 2A' and I or to the vent valve 3A'. The first, second and further ammonia sensors 5A, 5B may, for instance, comprise electrochemical gas sensors, gas chromatography sensors, optical sensors, or similar. Preferably, each ammonia sensor 5A, 5B measures ammonia concentration in ppm, such as ppm per volume. Alternatively, the control unit 5 may convert received sensor signals into ppm, such as ppm per volume. Thereby, a clear and easily understandable metric is conveyed to human system operators when considering operational safety.

[0050]

[0044] The system may further include at least one pressure sensor 5C. The pressure sensor may be located in the buffer tank 2. Thereby, the gas pressure in the buffer tank 2 can be monitored, especially during and after release of ammonia from the space 1. The pressure sensor 5C may be coupled to the control unit 5. Additionally, or alternatively, the pressure sensor 5C may be coupled directly to the bypass valve 3B'. Optionally, the pressure sensor 5C may be coupled directly to the feed valve 2A' and I or the vent valve 3A'. A further pressure sensor (not shown) may be located in the space 1. Optionally, one or more flow sensors (not shown) may be located in the feed line 2A, the vent line 3A, and I or the bypass line 3B. The flow sensors may be coupled to the control unit 5. Opening and closing of valves, as described hereinbelow, may be initiated by command signals sent by the control unit 5. The command signals from the control unit 5 may be based on signals received by the control unit 5 from the one or more sensors, described hereinabove. The feed valve 2A', vent valve 3A' and / or bypass valve 3B' may, for instance be controlled as a function of the output of the first ammonia sensor 5A. For a concentration above Csafe, the control unit 5 may restrict the feed valve 2A', vent valve 3A' and I or bypass valve 3B', or vice versa. The additional features of the second embodiment may be combined with the first embodiment.

[0051]

[0045] With further reference to figure 1 or 2, the bypass valve 3B' may be configured to open when the pressure in the buffer tank 2 reaches a pressure limit Piim . The feed valve 2A' may then be closed. The pressure limit is preferably lower than the maximum storage pressure of the buffer tank, Piim < ( Pmax - Psafe) , by at least an operational safety margin Psafe. Advantageously, a build- up of pressure beyond the operational safety of the buffer tank can thereby be prevented. The pressure limit Piim may be set based on the gas pressure in the space 1 before release and I or the expected pressure in the buffer tank 2 during or after release. The expected pressure in the buffer tank 2 may be determined based on the VB, VS and I or the volume of inert gas used for purging. The volume of inert gas VG used for purging may, for instance, range from 2* Vs to 50* Vs, or more. The volume VG of inert gas used for purging may be adjusted based on the speed of purging required and I or the desired value of Csafe after completed purging.

[0052] Advantageously, a higher VG may result in a better purging effect, releasing more ammonia from the space and resulting in a higher pressure in the buffer tank. On the other hand, a lower VG may result in a faster purging and a lower pressure in the buffer tank, which may be adequate when a non-negligible residual ammonia concentration in the space is acceptable. Alternatively, the expected pressure in the buffer tank 2 may be determined based on VB, VS, and a duration, such as the duration of purging, or the duration of pressure release. The duration of purging may, for instance, refer to a time period during which inert gas flows into the space. The duration of pressure release may, for instance, refer to a time period needed to achieve pressure equalization between the buffer tank and the space. Depending on the volume Vs of the space, the duration of purging and I or the duration of pressure release may, for instance, last from 5 s up to several minutes, or longer.

[0053]

[0046] Alternatively or additionally, the bypass valve 3B' may be configured to open when the ammonia concentration C in the space 1 falls to, or below, a concentration limit, C < C / / m. Preferably, Csafe < Cum. The feed valve may then be closed. As detailed hereinbelow, the concentration limit Cnmmay be chosen based on one or more of the capacity of the fan, an available time for purging, or the volume VB of the buffer tank relative to the volume Vs of the space. A higher value of Cum means that more ammonia flows through the bypass valve 3B', thereby requiring more time until the space is purged sufficiently to reach Csafe.

[0054]

[0047] The concentration limit Cum may be based on the capacity of the fan 4. The capacity to dilute ammonia is proportional to the volume of ambient air drawn into the vent mast 3. A high fan capacity therefore ensures a high capacity to dilute ammonia Alternatively, or additionally, the fan capacity may be adjustable by the control unit 5. In a further embodiment, one or more further fans (not shown) may be included in the system. The one or more further fans may be coupled to the control unit 5 and may, for instance, operate for a short period when a high dilution capacity is needed, such as during a fast purging of the space with inert gas via the bypass line 3B.

[0055]

[0048] Optionally, Cum may be inversely proportional to VB. For a high value of Cum, VB may be close or equal to 0,25*Vs. In this case, less ammonia may be released from the space 1 before reaching Cum. Therefore, less ammonia is stored in the buffer tank 2 and a small volume VB is required. Thereby, a system with a small footprint may be achieved. On the other hand, for a low value of Cum, VB may be close or equal to 50*Vs. In this case, more ammonia may be released from the space 1 before reaching Cum. Therefore, more ammonia may be stored in the buffer tank 2 and a large volume VB is required. A high inert gas pressure and / or a high inert gas volume may result in a fast purging of the space 1.

[0056]

[0049] A third embodiment is described with reference to figure 3, where same reference numerals denote the same features as for the first and second embodiment. In the third embodiment, the system may include a housing 6. The housing 6 may be accessible to human operators. The housing has an internal volume VH . The buffer tank 2 is placed within the housing 6. The housing 6 may further enclose at least a part of the feed line 2A, and I or the vent line 3A, and I or the bypass line 3B.

[0057]

[0050] The vent mast 3 may be coupled to an inlet 3', placed in the housing 6. The inlet 3' is preferably placed such that ambient air within the housing can be drawn into the vent mast 3. Thereto, the vent mast 3, or a pipe coupled to the vent mast 3, may extend into the housing 6. The inlet 3' may be provided in the portion of the vent mast 3, or of the pipe, extending into the housing 6. Preferably, the housing 6 further includes at least one inlet 6' for inflow of ambient air into the housing 6. At least one housing fan 6A may be located in the housing, for drawing air from the housing 6 into the inlet 3'. The housing fan 6A preferably has an Air Changes per Hour (ACH) of at least 10, preferably at least 20, more preferably at least 30. The ACH is a dimensionless number indicating fan capacity relative to the volume of the housing, per hour. The ACH is calculated by multiplying the fan capacity, in cubic meters I minute, by 60 minutes and dividing the resulting number by the volume of the housing in m3. If the housing, for example, has a volume of 12 m3and the housing fan 6A has capacity of 6 m3 / min, the ACH of the housing fan is 30.

[0058]

[0051] Advantageously, the housing 6 may comprise an engine room, or an ARMS room. Such rooms are, for instance, mandatory on commercial vessels or offshore platforms. The housing fan 6A may in this case comprise an engine room fan, or ARMS room fan, providing airflow for cooling, combustion, and I or maintaining over- or under-pressure. Regulatory requirements for housing ventilation may require that the housing fan 6A achieves at least 30 ACH. By using existing housing and housing fan, low implementation costs for the system and method can be achieved. The housing fan 6A may be coupled to the control unit 5. Thereby, the control unit 5 may monitor air flow in the housing and I or regulate housing fan 6A operation. The housing fan 6A may operate continuously, based on engine room, or ARMS room, safety regulations or other operational requirements. The air flow generated by the housing fan 6A may preferably contribute to ammonia dilution in the vent mast 3.

[0059]

[0052] With continued reference to figure 3, the system may further include a bleed line 3C. The bleed line may connect the buffer tank 2 with the vent mast 3. The bleed line 3C may include a bleed valve 3C'. The bleed valve 3C' may preferably be a control valve, a pressure release valve, an orifice, a bleed valve, or an automatic bleed valve. In the default position, the bleed valve 3C' may be open. The bleed valve 3C' may be configured to release ammonia, or a mixture of ammonia and inert gas, from the buffer tank 2 to the vent mast 3 continuously, or intermittently. The flowrate of ammonia through the bleed valve 3C' may preferably be defined by the capacity of the housing fan 6A. Preferably, the bleed valve 3C' may release ammonia, or a mixture of ammonia and inert gas, from the buffer tank 2 at a low rate. The flow through the bleed valve 3C' may be adjusted based on the pressure limit of the buffer tank (described hereinabove) or maximum ammonia concentration in the buffer tank 2, and I or the ammonia concentration at vent mast outlet. The flow rate of the bleed valve 3C' may preferably be less than the flow rate of the vent valve 3A'.

[0053] A fourth embodiment is described with reference to figure 4, where same reference numerals denote the same features as for the first to third embodiment. In the fourth embodiment an inert gas source 7 is provided. The inert gas source may comprise a tank or container comprising a pressurized inert gas, or a generator, or plant, for generating inert gas. The inert gas source 7 is connected to the space 1 by an inert gas line 7A. The inert gas line 7A may comprise an inert gas valve 7A'. The inert gas valve 7A' may be a control valve. The inert gas valve 7A' may be coupled to the control unit 5 (not shown). Preferably, the inert gas may comprise a nitrogen gas. The additional features of the fourth embodiment may be combined with any of the previous embodiments.

[0060]

[0054] A fifth embodiment is schematically shown in figure 5A, where same reference numerals denote the same features as for the first to fourth embodiment. Here, a secondary bypass line 3D is provided. The secondary bypass line 3D may connect the feed line 2A with the vent mast 3. The secondary bypass line 3D may include a secondary bypass valve 3D'. The secondary bypass valve 3D' may preferably be a control valve. In the default position, the secondary bypass valve 3D' may be closed. The secondary bypass line 3D is connected to an absorbing means 3E. The absorbing means 3E is placed between the secondary bypass valve 3D' and the vent mast 3. The absorbing means 3E may include means for absorbing ammonia in water, such as a water-based venturi scrubber, a water-based jet scrubber, a water-based packed-bed scrubber, or a water-based dissolution tank. The water in the absorbing means 3E may be seawater or fresh water.

[0061]

[0055] The secondary bypass valve 3D' may be configured to open when a sudden, fast ammonia release from the space 1 is required, such as during an emergency. Alternatively, or additionally, the secondary bypass valve 3D' may be configured to open when the pressure in the buffer tank 2 increases to a pressure limit (described hereinabove). The secondary bypass valve 3D' may, for instance, be opened upon receiving a signal from the control unit 5. The feed valve 2A' and the bypass valve 3C' may simultaneously be closed. Thereby, ammonia may be released through the secondary bypass line 3D only. From the absorbing means 3E, any remaining, non-absorbed ammonia flows to the vent mast 3, where the ammonia is diluted, as described hereinbefore. The additional features of the fifth embodiment may be combined with the first to fourth embodiment.

[0062]

[0056] In a variant of the fifth embodiment, schematically shown in figure 5B with a dash-dotted line, a scrub line 3F is provided. The scrub line 3F connects the vent line 3A with the secondary bypass line 3D. Preferably, the scrub line 3F is connected to the vent line 3A between the buffer tank 2 and the vent valve 3A'. Further preferably, the scrub line 3F is connected to the secondary bypass line 3D between the secondary bypass valve 3D' and the absorbing means 3E. That is, the scrub line 3F is connected downstream of the secondary bypass valve 3D' and upstream of the absorbing means 3E. Alternatively, the scrub line 3F is connected to the secondary bypass line 3D upstream of the secondary bypass valve 3D'. Further alternatively, the scrub line 3F is connected to the secondary bypass valve 3D'. In the latter case, the secondary bypass valve 3D' may be a three-way valve.

[0063]

[0057] The scrub line 3F is provided with a scrub line valve 3F'. The scrub line valve 3F' may preferably be a control valve. The scrub line valve 3F' may be connected to the control unit 5. In the default position, the scrub line valve 3F' may be closed. The scrub line valve 3F' may be configured to open when a fast ammonia release from the buffer tank 2, or a quick bleeding of ammonia from the buffer tank 2, is required. In this case the vent valve 3A' may be closed, or remain closed, and the scrub line valve 3F' may be opened. Ammonia may thereby flow from the buffer tank 2 to the absorbing means 3E. The scrub line valve 3F' may, for instance, be opened upon receiving a signal from the control unit 5. Thereby, ammonia may be released from the buffer tank 2, through the scrub line 3F and the absorbing means 3E, to the vent mast 3. In the absorbing means 3E ammonia is scrubbed, before being released into the environment through the vent mast 3, as described hereinbefore. The additional features of the present variant of the fifth embodiment may be combined with the first to fourth embodiment.

[0064]

[0058] A sixth embodiment is schematically shown in figure 6, where same reference numerals denote the same features as for the first to fifth embodiment. In the sixth embodiment, the system may include suction means 8 for sucking ammonia, or a mixture of ammonia and inert gas, from the space 1. The suction means 8 may include a vacuum pump, a compressor, a fan, a blower, or a similar apparatus. The vacuum pump may comprise a centrifugal pump, a gear pump, or similar. The suction means 8 may be connected to the feed line 2A. Preferably, the suction means 8 may be connected to the feed line 2A between the space 1 and the feed valve 2A'. Alternatively, the suction means 8 may be connected to the bypass line 3B, preferably between the space 1 and the bypass valve 3B'. The additional features of the sixth embodiment may, optionally, be combined with the first to fifth embodiment.

[0059] The present disclosure further concerns an ammonia release method for a marine or on-shore facility. The method may comprise providing a system according to the present disclosure, as described hereinabove. The method further comprises releasing ammonia, or a mixture of ammonia and inert gas, from the space 1 to the buffer tank 2. The method further comprises venting of ammonia, or a mixture of ammonia and inert gas, from the buffer tank 2 to the vent mast 3, and diluting ammonia with air drawn through into the vent mast 3 before venting diluted ammonia into the environment.

[0065]

[0060] Ammonia released from the space 1 is in gaseous form, preferably in anhydrous gaseous form. During purging-driven release, the ammonia concentration in the space may be reduced from 106ppm to C < Csafe (detailed hereinabove). Upon reaching Csafe, further release may be stopped, by closing the feed valve 2A' and I or the bypass valve 3B'. Alternatively, release may continue until reaching a negligible concentration, such as about 0 ppm. Presently, 300 ppm is considered to be an acceptable level for Csafe. Concentrations above 300 ppm are assumed to pose health risks for human operators and damage the environment. However, the acceptable value of Csafe may be raised or lowered, depending on the type of application, the ambient environment, or developing safety standards and regulations.

[0066]

[0061] The method of the present disclosure includes the following modes:

[0067]

[0062] According to a first mode, ammonia release from the space 1 is driven by pressure release. Initially, ammonia gas pressure in the space 1 is higher than the pressure in the buffer tank 2 and I or the bypass line 3B. The feed valve 2A' is opened to release ammonia from the space 1 to the buffer tank 2. Upon completing of initial pressure release, the feed valve 2A' may be closed and the bypass valve 3B' opened. The feed valve 2A' may, for instance, be closed when the pressure in the buffer tank 2 reaches Piim, or when the pressure in the space falls to a first desired level. Release through the bypass valve 3B' is limited by the capacity to reduce ammonia concentrations to a safe level at the outlet of the vent mast 3. Thereto, the bypass valve 3B' may be regulated by the control unit 5, based on signals from the first ammonia sensor 5A and I or the second ammonia sensor 5B. Further release of ammonia, through the bypass line 3B, may continue until reaching a second desired pressure in the space 1, such as ambient pressure, or a given operational pressure. Advantageously, overall duration of ammonia release from the space is thereby minimized, which is beneficial to operation of the space. Some ammonia may remain in the space to allow for a fast start-up of, for instance, an ammonia-driven engine, or ammonia processing equipment.

[0068]

[0063] Next, the bypass valve 3B' may be closed and the vent valve 3A' may be opened to vent ammonia from buffer tank 2. Alternatively, the vent valve 3A' may be opened simultaneously with the bypass valve 3B' and kept open when the bypass valve 3B' is reclosed. Venting from the buffer tank 2 is preferably at a lower rate than pressure release from the space 1 to the buffer tank 2. By venting from the buffer tank at a low rate, ammonia may be sufficiently diluted to achieve a safe concentration level. Release through the vent valve 3A' is limited by the capacity to reduce ammonia concentrations to a safe level at the outlet of the vent mast 3. Alternatively, or additionally, the capacity of the fan 4 may temporarily be reduced in proportion to the flow through the vent valve 3A'. The fan 4 capacity may be adjusted by the control unit 5, based on signals from the first ammonia sensor 5A and I or the pressure sensor 5C. Thereby a reduced energy consumption may be achieved. Release through the vent valve 3A' may proceed for a longer period than release through the bypass valve 3B', based on the volume of the buffer tank 2 as compared to the volume of ammonia remaining in the space 1 when the bypass valve 3B' is opened.

[0069]

[0064] Additionally, or alternatively, the vent valve 3A' and I or the bypass valve 3B' may be controlled as a function of the ammonia concentration in the vent mast 3, as measured by the first ammonia sensor 5A. For a concentration above Csafe, the control unit 5 may restrict the vent valve 3A' and I or the bypass valve 3B', and vice versa.

[0070]

[0065] According to a second mode, ammonia release from the space 1 is driven by purging. During purging, ammonia is driven from the space by a pressurized inert gas. Purging may be initiated by opening the inert gas valve 7A', such that pressurized inert gas flows from the inert gas source 7 into the space 1. The inert gas valve 7A' may, for instance, be opened upon a signal from the control unit 5. The feed valve 2A' may be opened simultaneously, or with a delay, to release the mixture of ammonia and inert gas from the space 1 to the buffer tank 2. The vent valve 3A' may preferably be opened after purging to the buffer tank 2 is completed. Alternatively, or additionally, the vent valve 3A' may be opened together with the feed valve 2A', during purging. Upon opening of the vent valve 3A', the mixture of ammonia and inert gas vents from the buffer tank 2 to the vent mast 3, as described hereinabove for the first mode. In the second mode, the feed valve 2A', and optionally the vent valve 3A', may be closed and the bypass valve 3B' opened when the ammonia concentration in the space falls to below Cam, as detailed hereinabove. Release through the bypass line 3B may then continue until reaching Csafe in the space 1. Next, the bypass valve 3B’ may be reclosed and the vent valve 3A’ may be opened, as described for the first mode. Alternatively, the vent valve 3A' may be opened simultaneously with the bypass valve 3B' and kept open when the bypass valve 3B' is reclosed, as described for the first mode. Upon completion of purging, the inert gas valve 7A' may be closed.

[0071]

[0066] According to a third mode, ammonia release from the space 1 may be driven by suction. Thereto suction means 8 for sucking ammonia, or a mixture of ammonia and inert gas, from the space 1 may be provided, as detailed hereinabove. The suction means 8 may be connected to the feed line 2A, preferably between the space 1 and the feed valve 2A'. Alternatively, the suction means 8 may be connected to the bypass line 3B, preferably between the space 1 and the bypass valve 3B'. Ammonia may be sucked from the space 1, into the buffer tank 2 and I or into the bypass line 3B by the suction means 8. The pressure in the space is thereby decreased from an initial pressure to a fraction of the initial pressure. Consequently, only a fraction of the original ammonia in the space 1 remains. Optionally, the inert gas valve 7A' may then be opened and an inert gas may be introduced into the space 1, to purge remaining ammonia from the space 1. A fast and efficient release of ammonia from the space is thereby achieved. Furthermore, utilizing suction may result in a small system footprint, allowing for system implementation in applications with strict space requirements, such as marine vessels and I or platforms.

[0072]

[0067] According to a fourth mode, ammonia release from the space 1 may initially be driven by pressure release, as described for the first mode, followed by purging with an inert gas, as described for the second mode. In the fourth mode, the feed valve 2A' is opened to release ammonia from the space 1 to the buffer tank 2. Upon reaching pressure equalization in the buffer tank 2 and the space 1, the inert gas valve 7 A' may be opened, initiating purging of remaining ammonia in the space 1 with an inert gas, as described hereinabove for the second mode. From the buffer tank 2 ammonia vents to the vent mast 3, as described for the first mode.

[0073]

[0068] According to a bypass mode, the secondary bypass valve 3D' may be opened when a sudden, fast ammonia release from the space 1 is required, such as during an emergency. Alternatively, or additionally, the secondary bypass valve 3D' may be opened when the pressure in the buffer tank 2 increases to a pressure limit (described hereinabove). Further alternatively, when the pressure in the buffer tank 2 increases to a pressure limit or when faster bleeding from the buffer tank 2 is required, the scrub line vent 3F' may be opened and the vent valve 3A' closed. Thereby, a fast release from the buffer tank 3 to the absorbing means 3E is achieved. In operation, the secondary bypass valve 3D' and I or the scrub line valve 3F' may be opened upon receiving a signal from the control unit 5. The feed valve 2A' , the vent valve 3A' and I or the bypass valve 3C' may simultaneously be closed. Thereby, ammonia may be released through the secondary bypass line 3D only, or through the scrub line 3F and the secondary bypass line 3D. From the absorbing means 3E, any remaining, non-absorbed ammonia flows to the vent mast 3, where the ammonia is diluted, as described hereinbefore.

[0074]

[0069] According to a fifth mode, ammonia release from the space 1 may initially be driven by pressure release, followed by purging with an inert gas, as for the fourth mode. For the fifth mode, ammonia release from the space 1 may be switched to the bypass line 3B, when the buffer tank pressure reaches Piim, or when the concentration in the space 1 falls below Cum, as detailed for the second mode. The feed valve 2A' is then closed and the bypass valve 3B' is opened. From the buffer tank 2 ammonia vents to the vent mast 3, as described for the first mode.

[0075]

[0070] Different aspects of the present disclosure have been defined herein in more detail. Each aspect may be combined with any other aspect or aspects, all falling within the scope of the appended claims. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous.

[0076] List of Reference Numbers

[0077] 1 space

[0078] 2 buffer tank

[0079] 2A feed line

[0080] 2A' feed valve

[0081] 3 vent mast

[0082] 3' inlet

[0083] 3A vent line A' vent valve B bypass line B' bypass valve C bleed line C' bleed valve D secondary bypass lineD' secondary bypass valveE absorbing means F scrub line F' scrub line valve fan control unit A first ammonia sensorB second ammonia sensorC pressure sensor housing ' housing inlet A housing fan inert gas source A inert gas line A' inert gas valve suction means

Claims

Claims1. An ammonia release system for a marine or on-shore structure, the system comprising:- a space (1) for ammonia storage, transport or usage;- a buffer tank (2) for receiving ammonia released from the space;- a feed line (2A) for releasing ammonia from the space to the buffer tank;- a vent mast (3) for venting diluted ammonia to the environment;- a vent line (3A) for venting ammonia from the buffer tank to the vent mast;- a fan (4) for drawing ambient air into the vent mast to dilute ammonia; and- a bypass line (3B) for releasing ammonia from the space directly to the vent mast.

2. The system of claim 1, wherein the bypass line (3B) comprises a bypass valve (3B'), and wherein the bypass valve (3B') is configured to open when:- the pressure in the buffer tank (2) reaches a pressure limit; or- the ammonia concentration in the space (1) reaches a concentration limit.

3. The system of claim 2, further including a control unit (5), at least one ammonia sensor (5A, 5B), and a pressure sensor (5C), and wherein the control unit (5) is configured to open the bypass valve (3B') based on signals from the pressure sensor (5C) and I or at least one ammonia sensor (5A, 5B).

4. The system of claim 1, wherein the vent line (3A) comprises a vent valve (3A'), configured to vent ammonia from the buffer tank (2) to the vent mast (3).

5. The system of clam 1, wherein the volume Vs of the space (1) and the volume VB of the buffer tank (2) are related as 0,25*Vs < VB < 50*Vs.

6. The system of any preceding claim, further comprising a housing (6) enclosing at least the buffer tank (2), wherein the housing comprises an inlet (6') for ambient air.

7. The system of any preceding claim, further including an inert gas source (7) for purging the space (1).

8. A marine or on-shore facility comprising the ammonia release system of any of claims 1 - 7, wherein the marine or on-shore structure is a vessel, an offshoreplatform, an ammonia bunkering facility, an ammonia producing or processing plant, and / or an onshore ammonia consumer.

9. An ammonia release method for a marine or on-shore facility, the method comprising:- providing a system according to any of claims 1 - 7, or a facility according to claim 8;- releasing ammonia from the space (1) to the buffer tank (2);- venting ammonia from the buffer tank (2) to the vent mast (3); and- diluting ammonia with air drawn through into the vent mast (3) by the fan (4) and venting the diluted ammonia into the environment.

10. The method of claim 9, further comprising purging the space (1) with an inert gas, such as nitrogen.

11. The method of claim 9 or 10, further comprising opening the bypass valve (3B') and closing the feed valve (2A') to release ammonia from the space (1) directly to the vent mast (3) when:- the pressure in the buffer tank (2) reaches a pressure limit; or- the ammonia concentration in the space (1) reaches a concentration limit.

12. The method of claim 11, wherein the pressure limit is based on the gas pressure in the space (1) before release, the volume of the buffer tank (2), the volume of the space (1) and I or the volume of an inert purging gas.

13. The method of claim 11, wherein the concentration limit is based on one or more of the capacity of the fan (4), an available time for purging of the space (1) with an inert gas, and I or the volume of the buffer tank (2) relative to the volume of the space (1).

14. The method of any one of claims 9 - 13, further comprising monitoring the ammonia concentration in the space (1) and I or in the vent mast (3).

15. The method of any of claims 9 - 14, further comprising drawing ambient air into a housing (6) enclosing the buffer tank (2), and drawing air from the housing (6) into the vent mast (3) by a housing fan (6A).

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