Marine ammonia vapor reliquefaction treatment method and marine ammonia gas reliquefaction system

Abstract

The invention relates to the technical field of marine ammonia vapor reliquefaction treatment, and discloses a marine ammonia vapor reliquefaction treatment method and a marine ammonia gas reliquefaction system.The marine ammonia vapor reliquefaction treatment method comprises the following steps that liquid ammonia is extracted from a liquid ammonia storage tank, the liquid ammonia is conveyed to a cooler, the liquid ammonia exchanges heat with a refrigerant from a low-temperature refrigerating device in the cooler, and the refrigerant is cooled to the room temperature; the temperature of the liquid ammonia is reduced to be lower than the saturation temperature T1 of the liquid ammonia in the storage tank, supercooled liquid ammonia is obtained, the supercooled liquid ammonia is atomized and sprayed into a gas phase space of the liquid ammonia storage tank through a spraying device, supercooled liquid ammonia drops make contact with ammonia vapor in the gas phase space for heat exchange, and the ammonia vapor is condensed and liquefied. According to the method, through the closed-loop process of liquid ammonia extraction, supercooling strengthening and atomization heat exchange, condensation of ammonia vapor is achieved by directly utilizing cold energy of liquid ammonia without depending on a compressor, so that the system structure is simplified, the equipment cost and the operation energy consumption are reduced, and meanwhile stable control over the pressure in the liquid ammonia storage tank is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of marine ammonia vapor reliquefaction treatment, and in particular to a marine ammonia vapor reliquefaction treatment method and a marine ammonia reliquefaction system. Background Art

[0002] As a primary means of transport for international trade, controlling carbon emissions from ships has become a significant issue in the global environmental protection field. To reduce carbon emissions from ships, finding clean, efficient alternative fuels has become a key direction for industry development. Ammonia fuel, with its significant advantage of zero carbon emissions during combustion, is considered a highly promising alternative fuel for marine propulsion systems. Its application and promotion are crucial for the shipping industry to achieve its carbon neutrality goals.

[0003] In the operation of ammonia-fueled ships, the storage of liquid ammonia is one of the core links. Liquid ammonia usually needs to be stored in special storage tanks in a low-temperature environment. However, since the ambient temperature outside the tank is always higher than the storage temperature of liquid ammonia, external heat will continue to be transmitted into the tank through the tank wall. This process causes part of the liquid ammonia in the tank to vaporize due to heat, producing ammonia gas (evaporative gas), which gradually increases the pressure inside the tank. If these evaporated gases are not effectively treated in time, the tank pressure will continue to rise, and may eventually cause safety accidents such as overpressure rupture, seriously threatening the operational safety of the ship. Therefore, efficient treatment of the ammonia gas generated in the liquid ammonia storage tank and maintaining stable tank pressure are necessary guarantees for the safe operation of ammonia-fueled ships. Summary of the Invention

[0004] In view of this, the present invention provides a method for reliquefying marine ammonia vapor and a marine ammonia gas reliquefaction system to solve the problem of continuous increase in storage tank pressure caused by vaporization of liquid ammonia due to heat.

[0005] In a first aspect, the present invention provides a method for reliquefying marine ammonia vapor, comprising the following steps:

[0006] Extracting liquid ammonia from a liquid ammonia storage tank;

[0007] The liquid ammonia is transported to a cooler, where the liquid ammonia exchanges heat with a refrigerant from a low-temperature refrigeration device, so that the temperature of the liquid ammonia drops below the saturation temperature T1 of the liquid ammonia in the storage tank, thereby obtaining subcooled liquid ammonia;

[0008] Spraying the supercooled liquid ammonia into the gas phase space of the liquid ammonia storage tank through a spraying device;

[0009] The supercooled liquid ammonia droplets contact and exchange heat with the ammonia vapor in the gas phase space, causing the ammonia vapor to condense and liquefy.

[0010] The marine ammonia vapor reliquefaction treatment method realizes efficient condensation and recovery of ammonia vapor in the liquid ammonia storage tank through four orderly operations. Specifically:

[0011] Liquid ammonia is directly extracted from the liquid ammonia storage tank and used as the medium for cold energy transfer. This step utilizes the low temperature properties of liquid ammonia to provide a basic cold source for the subsequent heat exchange process, eliminating the need for additional refrigerant media, simplifying the process and reducing energy loss.

[0012] The extracted liquid ammonia is transported to the cooler for forced heat exchange with the refrigerant from the cryogenic refrigeration unit. Because the refrigerant temperature provided by the cryogenic refrigeration unit is lower than the saturation temperature T1 of the liquid ammonia in the liquid ammonia storage tank, the liquid ammonia is further cooled in the cooler, forming subcooled liquid ammonia. Its temperature is lower than the saturation temperature of the liquid ammonia in the storage tank, which has stronger heat absorption capacity and condensation potential.

[0013] Subcooled liquid ammonia is transported through pipelines to a spray device inside the liquid ammonia storage tank, where it is atomized into fine droplets and sprayed into the tank's vapor phase. This atomization process increases the contact area between the subcooled liquid ammonia and the ammonia vapor in the vapor phase, making the heat exchange process more complete and efficient.

[0014] After the ammonia vapor in the gas phase space comes into contact with the supercooled liquid ammonia droplets, the heat is absorbed by the droplets, the temperature drops below the condensation point, and it eventually liquefies into liquid ammonia and flows back to the bottom of the storage tank, completing the reliquefaction cycle of the ammonia vapor.

[0015] This method uses the closed-loop process of "liquid ammonia extraction-supercooling enhancement-atomization heat exchange" to directly utilize the cold energy of liquid ammonia itself to condense ammonia vapor without relying on a compressor, thereby simplifying the system structure, reducing equipment costs and operating energy consumption, and ensuring stable control of the pressure in the liquid ammonia storage tank, thereby improving the safety and economy of the marine ammonia fuel system.

[0016] In an optional embodiment, in the step of transporting the liquid ammonia to a cooler, the liquid ammonia exchanges heat with a refrigerant from a low-temperature refrigeration device in the cooler, so that the temperature of the liquid ammonia drops below the saturation temperature T1 of the liquid ammonia in the storage tank. In the step of obtaining supercooled liquid ammonia, the refrigerant temperature T2 must satisfy the following conditions:

[0017] T2 <T3<T1;

[0018] Wherein, T3 is the liquid ammonia temperature at the outlet of the cooler.

[0019] The refrigerant temperature T provided by the low-temperature refrigeration device must be lower than the liquid ammonia temperature T at the outlet of the cooler to ensure an effective temperature difference between the refrigerant and the liquid ammonia, enabling the refrigerant to continuously absorb the heat of the liquid ammonia. This temperature gradient is the driving force for heat transfer from the liquid ammonia to the refrigerant. Only when T < T can the liquid ammonia be continuously cooled in the cooler and finally reach a state lower than its saturation temperature T. The fact that the liquid ammonia temperature T at the cooler outlet needs to be lower than the saturation temperature T of the liquid ammonia in the storage tank is the key to forming "subcooled liquid ammonia". When the liquid ammonia temperature drops below the saturation temperature, its degree of subcooling increases. After entering the gas phase space of the storage tank, it can contact the ammonia vapor at a lower temperature, thus having a stronger heat absorption capacity and more efficiently promoting the condensation and liquefaction of the ammonia vapor, ensuring the stability and efficiency of the ammonia re-liquefaction process. Therefore, the temperature relationship of T2 < T3 < T1 is the prerequisite for the effective heat exchange between the refrigerant and the liquid ammonia and the formation of subcooled liquid ammonia, directly affecting the operation effect of the entire re-liquefaction system, ensuring that the subcooled liquid ammonia can fully absorb the heat of the ammonia vapor and achieving the efficient condensation and recovery of ammonia gas.

[0020] In an optional embodiment, T3 ≤ T1 - 5°C and T2 ≤ T3 - 5°C.

[0021] For T3 ≤ T1 - 5°C, this threshold requires the liquid ammonia temperature T3 at the cooler outlet to be at least 5°C lower than the saturation temperature T1 of the liquid ammonia in the storage tank. This is a quantitative guarantee for the "degree of subcooling" of the liquid ammonia. By setting a minimum temperature difference of 5°C, it can ensure that the liquid ammonia obtains sufficient subcooling degree. After entering the gas phase space of the storage tank, it can contact the ammonia vapor in a state significantly lower than the condensation temperature of the ammonia vapor, thereby enhancing the heat absorption capacity and avoiding the problem of low condensation efficiency of the ammonia vapor caused by insufficient subcooling degree, ensuring the rapid and full liquefaction of ammonia gas.

[0022] For T2 ≤ T3 - 5°C, this condition requires the refrigerant temperature T2 to be at least 5°C lower than the liquid ammonia temperature T3 at the cooler outlet. The purpose is to maintain sufficient heat exchange driving force between the refrigerant and the liquid ammonia. The minimum temperature difference of 5°C can ensure that the refrigerant continuously and efficiently absorbs the heat of the liquid ammonia, enabling the liquid ammonia to be stably cooled to the target subcooled temperature T3 in the cooler, avoiding insufficient heat exchange caused by too small temperature difference between the refrigerant and the liquid ammonia, and thus ensuring the reliability of the subsequent spray condensation process.

[0023] In an optional embodiment, in the step of spraying the subcooled liquid ammonia into the gas phase space of the liquid ammonia storage tank through a spraying device, the average droplet diameter ≤ 100 μm.

[0024] Smaller droplets can be more evenly dispersed in the gas phase space of the storage tank and form more sufficient contact with the ammonia vapor in the gas phase space. This large-area and highly dispersed contact method can accelerate the heat transfer rate between the subcooled droplets and the ammonia vapor. The heat of the ammonia vapor can be more quickly absorbed by the subcooled droplets, thus accelerating the process of the ammonia vapor cooling and condensing into liquid ammonia.

[0025] In an optional embodiment, the refrigerant is a liquid or gaseous medium provided by a low-temperature refrigeration device, and its evaporation temperature is lower than the condensation temperature of ammonia.

[0026] When the refrigerant is liquid, it absorbs the liquid ammonia's heat through its own evaporation during the heat exchange process, utilizing the latent heat of phase change to enhance the heat exchange effect. If it is gaseous, it can continuously absorb the liquid ammonia's heat through sensible heat exchange. Regardless of its physical state, as long as its evaporation temperature is lower than the condensation temperature of ammonia, it can ensure a sufficient temperature difference between the refrigerant and the liquid ammonia, driving heat transfer from the liquid ammonia to the refrigerant, reducing the liquid ammonia temperature to the target subcooling temperature T3, and providing subcooled liquid ammonia with sufficient cold energy for the subsequent spray condensation of ammonia vapor.

[0027] In an optional embodiment, the design pressure of the liquid ammonia storage tank is 0.7 bar-25 bar, the corresponding saturation temperature T1 is -23°C to 59°C, the refrigerant temperature T2 ≤ -33°C, and the liquid ammonia temperature at the cooler outlet T3 ≤ -28°C.

[0028] In an optional embodiment:

[0029] When the design pressure of the liquid ammonia storage tank is 0.7 bar, the corresponding saturation temperature T1 is -23°C, and T2 is controlled to be ≤-33°C and T3 ≤-28°C;

[0030] When the design pressure of the liquid ammonia storage tank is 10 bar, the corresponding saturation temperature T1 is 28°C, and T2 is controlled to be ≤18°C and T3 is ≤23°C;

[0031] When the design pressure of the liquid ammonia storage tank is 25 bar, the corresponding saturation temperature T1 is 59°C, and T2 is controlled to be ≤49°C and T3 ≤54°C.

[0032] In an optional embodiment, the liquid ammonia is transported to a cooler, and the liquid ammonia is heat-exchanged with a refrigerant from a low-temperature refrigeration device in the cooler to reduce the temperature of the liquid ammonia to below the saturation temperature T1 of the liquid ammonia in the storage tank. In the step of obtaining supercooled liquid ammonia, the supercooling degree of the liquid ammonia is ≥5°C.

[0033] Subcooling refers to the difference between the liquid ammonia temperature and its saturation temperature (i.e., the saturation temperature T1 of the liquid ammonia in the storage tank). Setting a liquid ammonia subcooling of 5°C or higher means that the cooled liquid ammonia has sufficient cold energy reserves. Upon entering the vapor phase of the liquid ammonia storage tank, it creates a significant temperature difference with the ammonia vapor. This temperature difference provides a strong driving force for heat transfer, prompting the ammonia vapor to quickly release heat and condense into a liquid state, effectively reducing the amount of ammonia vapor in the vapor phase and effectively controlling the pressure within the storage tank.

[0034] In an optional embodiment, the liquid ammonia is circulated and transported by a liquid ammonia pump, and the liquid ammonia pump is a ship fuel supply pump or a liquid cargo pump or a pump dedicated to the reliquefaction function.

[0035] A ship's fuel supply pump is originally used to transfer liquid ammonia from storage tanks to fuel-consuming equipment such as engines, while a liquid cargo pump is used for loading, unloading, or intertank transfer of liquid ammonia. Both pumps can extract and transfer liquid ammonia, and their compatibility with the liquid ammonia medium has been verified in daily ship operations. By directly using them as the liquid ammonia circulation device in this system, the need for a separate dedicated circulation pump is eliminated, significantly simplifying the system's equipment structure and reducing equipment procurement and installation costs.

[0036] In a second aspect, the present invention further provides a marine ammonia reliquefaction system, which adopts a marine ammonia vapor reliquefaction treatment method, comprising:

[0037] Liquid ammonia storage tanks;

[0038] a liquid ammonia pump, disposed on the bottom side of the liquid ammonia storage tank, and connected to a pipeline;

[0039] A cooler is placed outside the liquid ammonia storage tank and connected to the pipeline;

[0040] a low-temperature refrigeration device, placed outside the liquid ammonia storage tank, and transporting a refrigerant with a temperature lower than the condensation temperature of liquid ammonia into the cooler;

[0041] A spray device is placed on the top side of the liquid ammonia storage tank, and the spray device is connected to the cooler outlet pipe.

[0042] The system, through the synergistic effect of a liquid ammonia pump, chiller, cryogenic refrigeration unit, and spray device, directly utilizes the cold energy of supercooled liquid ammonia to condense the ammonia gas within the tank. This effectively reduces the ammonia concentration in the vapor phase and effectively controls the internal pressure of the liquid ammonia storage tank, avoiding safety risks caused by excessive pressure. Furthermore, the various components of the system are systematically connected by piping, resulting in a compact structure and strong synergy, enabling continuous and stable completion of the ammonia reliquefaction process and ensuring the safe operation of the liquid ammonia storage tank. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0044] Figure 1 The figure is a schematic structural diagram of a marine ammonia reliquefaction system according to an embodiment of the present invention.

[0045] Description of reference numerals:

[0046] 1. Liquid ammonia storage tank;

[0047] 2. Liquid ammonia pump;

[0048] 3. Cooler;

[0049] 4. Low temperature refrigeration device;

[0050] 5. Spray device. DETAILED DESCRIPTION

[0051] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative efforts shall fall within the scope of protection of the present invention.

[0052] As a primary means of transport for international trade, controlling carbon emissions from ships has become a significant issue in the global environmental protection field. To reduce carbon emissions from ships, finding clean, efficient alternative fuels has become a key direction for industry development. Ammonia fuel, with its significant advantage of zero carbon emissions during combustion, is considered a highly promising alternative fuel for marine propulsion systems. Its application and promotion are crucial for the shipping industry to achieve its carbon neutrality goals.

[0053] In the operation of ammonia-fueled ships, the storage of liquid ammonia is one of the core links. Liquid ammonia usually needs to be stored in special storage tanks in a low-temperature environment. However, since the ambient temperature outside the tank is always higher than the storage temperature of liquid ammonia, external heat will continue to be transmitted into the tank through the tank wall. This process causes part of the liquid ammonia in the tank to vaporize due to heat, producing ammonia gas (evaporative gas), which gradually increases the pressure inside the tank. If these evaporated gases are not effectively treated in time, the tank pressure will continue to rise, and may eventually cause safety accidents such as overpressure rupture, seriously threatening the operational safety of the ship. Therefore, efficient treatment of the ammonia gas generated in the liquid ammonia storage tank and maintaining stable tank pressure are necessary guarantees for the safe operation of ammonia-fueled ships.

[0054] In view of this, the present embodiment provides a method for reliquefying marine ammonia vapor and a marine ammonia gas reliquefaction system to solve the problem of continuous increase in storage tank pressure caused by vaporization of liquid ammonia due to heat.

[0055] The following combination Figure 1 , describing embodiments of the present invention.

[0056] According to an embodiment of the present invention, on the one hand, an ammonia reliquefaction system is provided, including a liquid ammonia storage tank 1, a liquid ammonia pump 2, a cooler 3, a low-temperature refrigeration device 4 and a spray device 5. The liquid ammonia pump 2 is placed on the bottom side of the liquid ammonia storage tank 1 or outside the liquid ammonia storage tank 1, and the liquid ammonia pump 2 is connected with a pipeline. The cooler 3 is placed on the outside of the liquid ammonia storage tank 1, and the cooler 3 is connected to the pipeline. The low-temperature refrigeration device 4 is placed on the outside of the liquid ammonia storage tank 1, and the low-temperature refrigeration device 4 transports a refrigerant with a temperature lower than the condensation temperature of liquid ammonia to the inside of the cooler 3; the spray device 5 is placed on the top side of the liquid ammonia storage tank 1, and the spray device 5 is connected to the outlet end pipeline of the cooler 3.

[0057] During the operation of this ammonia reliquefaction system, liquid ammonia storage tank 1, serving as a storage container for cryogenic liquid ammonia, experiences a temperature difference between its internal low-temperature environment and the external environment. This results in a continuous influx of heat, which vaporizes some of the liquid ammonia into ammonia gas, subsequently increasing the pressure within the tank. At this point, liquid ammonia pump 2, located at the bottom of tank 1, activates and pumps liquid ammonia from tank 1 through a connected pipeline, delivering it to cooler 3, located outside tank 1. Cooler 3, acting as a heat exchange component, receives liquid ammonia from pump 2 and exchanges heat with the refrigerant output from a cryogenic refrigeration unit 4, which simultaneously delivers it. Because the refrigerant provided by cryogenic refrigeration unit 4 is at a temperature lower than the condensation temperature of liquid ammonia, the liquid ammonia is rapidly cooled within cooler 3, significantly increasing its degree of subcooling and enhancing its heat absorption capacity. The subcooled liquid ammonia, after being treated by cooler 3, is then delivered via a pipeline to sprayer 5, located at the top of tank 1. Sprayer 5 atomizes the subcooled liquid ammonia into fine droplets, which are evenly sprayed into the vapor phase at the top of the tank. These supercooled droplets are in full contact with the ammonia in the gas phase and heat exchange occurs. The heat of the ammonia is absorbed by the supercooled droplets, the temperature drops, and it is eventually condensed into liquid ammonia and flows back into the liquid ammonia at the bottom of the storage tank, thereby achieving the reliquefaction of the ammonia.

[0058] When the liquid ammonia pump 2 is located outside the liquid ammonia storage tank 1 , the liquid ammonia pump 2 can be connected to the interior of the liquid ammonia storage tank 1 through a pipeline.

[0059] Through the coordinated action of the liquid ammonia pump 2, cooler 3, cryogenic refrigeration unit 4, and spray device 5, this system directly utilizes the cold energy of supercooled liquid ammonia to condense the ammonia gas within the tank. This effectively reduces the ammonia concentration in the vapor phase, effectively controls the internal pressure of liquid ammonia storage tank 1, and avoids safety risks caused by excessive pressure. Furthermore, the various components of the system are systematically connected through piping, resulting in a compact structure and strong synergy. This enables the continuous and stable completion of the ammonia reliquefaction process, ensuring the safe operation of liquid ammonia storage tank 1.

[0060] The cooler 3, low-temperature refrigeration device 4, and spray device 5 all utilize existing structures. For example, the cooler 3 may be a shell-and-tube cooler 3 or a plate cooler 3. The low-temperature refrigeration device 4 utilizes a vapor compression refrigeration unit or an absorption refrigeration unit. A vapor compression refrigeration unit consists of a compressor, condenser, expansion valve, and evaporator, generating low temperatures through a compression-condensation-expansion-evaporation cycle of a refrigerant (such as propane or R290). The spray device 5 may utilize a pressure-type atomizing nozzle, which pressurizes subcooled liquid ammonia and sprays it at high speed, utilizing the pressure energy of the liquid ammonia itself to form atomized droplets at the nozzle outlet.

[0061] According to another aspect of an embodiment of the present invention, a method for reliquefying marine ammonia vapor is provided, comprising the following steps:

[0062] Extracting liquid ammonia from liquid ammonia storage tank 1;

[0063] The liquid ammonia is transported to the cooler 3, where it exchanges heat with the refrigerant from the low-temperature refrigeration device 4, reducing the temperature of the liquid ammonia to below the saturation temperature T1 of the liquid ammonia in the storage tank, thereby obtaining subcooled liquid ammonia.

[0064] The supercooled liquid ammonia is sprayed into the gas phase space of the liquid ammonia storage tank 1 through the spray device 5;

[0065] The supercooled liquid ammonia droplets contact and exchange heat with the ammonia vapor in the gas phase space, causing the ammonia vapor to condense and liquefy.

[0066] The marine ammonia vapor reliquefaction treatment method realizes efficient condensation and recovery of ammonia vapor in the liquid ammonia storage tank 1 through four sequential operations. Specifically:

[0067] Liquid ammonia is directly extracted from the liquid ammonia storage tank 1 and used as the medium for cold energy transfer. This step utilizes the low temperature properties of liquid ammonia to provide a basic cold source for the subsequent heat exchange process, eliminating the need for additional refrigerant media, simplifying the process and reducing energy loss.

[0068] The extracted liquid ammonia is transported to cooler 3 for forced heat exchange with the refrigerant from cryogenic refrigeration unit 4. Because the temperature of the refrigerant provided by cryogenic refrigeration unit 4 is lower than the saturation temperature T1 of the liquid ammonia in the liquid ammonia storage tank 1, the liquid ammonia is further cooled in cooler 3, forming subcooled liquid ammonia. This temperature is lower than the saturation temperature of the liquid ammonia in the storage tank, and has stronger heat absorption capacity and condensation potential.

[0069] Subcooled liquid ammonia is transported via pipelines to spray device 5 inside liquid ammonia storage tank 1, where it is atomized into fine droplets and sprayed into the tank's vapor phase. This atomization process increases the contact area between the subcooled liquid ammonia and the ammonia vapor in the vapor phase, making the heat exchange process more complete and efficient.

[0070] After the ammonia vapor in the vapor space comes into contact with the subcooled liquid ammonia droplets, the heat is absorbed by the droplets, the temperature drops below the condensation point, and finally it liquefies into liquid ammonia and flows back to the bottom of the storage tank, completing the re-liquefaction cycle of the ammonia vapor.

[0071] This method uses a closed-loop process of liquid ammonia extraction - subcooling enhancement - atomization heat exchange, directly utilizes the cold energy of liquid ammonia itself to condense ammonia vapor, without relying on a compressor, thus simplifying the system structure, reducing equipment costs and operating energy consumption, while ensuring stable control of the pressure in the liquid ammonia storage tank 1, and enhancing the safety and economy of the marine ammonia fuel system.

[0072] In one embodiment, in the step of transporting liquid ammonia to the cooler 3, where the liquid ammonia exchanges heat with the refrigerant from the low-temperature refrigeration device 4 in the cooler 3 to lower the temperature of the liquid ammonia below the saturation temperature T1 of the liquid ammonia in the storage tank to obtain subcooled liquid ammonia, the refrigerant temperature T2 needs to satisfy:

[0073] T2 < T3 < T1;

[0074] Where, T3 is the temperature of the liquid ammonia at the outlet of the cooler 3.

[0075]

[0076] In the heat exchange process between the liquid ammonia and the refrigerant, in addition to satisfying the basic temperature relationship of T2 < T3 < T1, threshold conditions of T3 ≤ T1 - 5°C and T2 ≤ T3 - 5°C are further set.

[0077] ​For T3 ≤ T1-5°C, this threshold requires that the liquid ammonia temperature T3 at the outlet of cooler 3 be at least 5°C lower than the saturation temperature T1 of the liquid ammonia in the storage tank. This quantitatively guarantees the liquid ammonia's subcooling. By setting a minimum temperature difference of 5°C, the liquid ammonia is ensured to achieve sufficient subcooling. Upon entering the gas phase of the storage tank, it comes into contact with the ammonia vapor at a temperature significantly lower than the vapor condensation temperature. This enhances heat absorption, avoids inefficient ammonia vapor condensation due to insufficient subcooling, and ensures rapid and complete liquefaction of the ammonia.

[0078] For T2 ≤ T3 - 5°C, this condition requires the refrigerant temperature T2 to be at least 5°C lower than the liquid ammonia temperature T3 at the outlet of cooler 3. This is to maintain sufficient heat transfer driving force between the refrigerant and liquid ammonia. This minimum temperature difference of 5°C ensures that the refrigerant continuously and efficiently absorbs heat from the liquid ammonia, allowing the liquid ammonia to be stably cooled to the target subcooling temperature T3 within cooler 3. This avoids insufficient heat transfer caused by a small temperature difference between the refrigerant and liquid ammonia, thereby ensuring the reliability of the subsequent spray condensation process.

[0079] In one embodiment, in the step of atomizing and spraying the supercooled liquid ammonia into the gas phase space of the liquid ammonia storage tank 1 through the spraying device 5 , the average particle size of the droplets is ≤100 μm.

[0080] Smaller droplets are more evenly dispersed in the tank's gas phase, allowing for more complete contact with the ammonia vapor within. This large-area, highly dispersed contact accelerates heat transfer between the supercooled droplets and the ammonia vapor. Heat from the ammonia vapor is more quickly absorbed by the supercooled droplets, accelerating the cooling and condensation of the ammonia vapor into liquid ammonia.

[0081] In one embodiment, the refrigerant is a liquid or gaseous medium provided by the low-temperature refrigeration device 4 , and its evaporation temperature is lower than the condensation temperature of ammonia.

[0082] When the refrigerant is in liquid form, it absorbs the heat of the liquid ammonia through its own evaporation during the heat exchange process with liquid ammonia, utilizing the latent heat of phase change to enhance the heat exchange effect. If it is in gaseous form, it can continuously absorb the heat of the liquid ammonia through sensible heat exchange. Regardless of its physical state, as long as its evaporation temperature is lower than the condensation temperature of ammonia, it can ensure a sufficient temperature difference between the refrigerant and the liquid ammonia, driving heat transfer from the liquid ammonia to the refrigerant, reducing the liquid ammonia temperature to the target subcooling temperature T3 (lower than the saturation temperature of liquid ammonia in the storage tank T1), providing subcooled liquid ammonia with sufficient cold energy for the subsequent spray condensation of ammonia vapor.

[0083] In one embodiment, the design pressure of the liquid ammonia storage tank 1 is 0.7 bar-25 bar, the corresponding saturation temperature T1 is -23°C-59°C, the refrigerant temperature T2 ≤ -33°C, and the liquid ammonia temperature T3 at the outlet of the cooler 3 ≤ -28°C.

[0084] Table 1 Parameters

[0085]

[0086] As shown in Table 1, when the design pressure of liquid ammonia storage tank 1 is 0.7 bar, the corresponding saturation temperature T1 is -23°C, T1 = -23°C, and T2 is controlled to be ≤ -33°C and T3 ≤ -28°C. When the design pressure of liquid ammonia storage tank 1 is 10 bar, the corresponding saturation temperature T1 is 28°C, and T2 is controlled to be ≤ 18°C ​​and T3 ≤ 23°C. When the design pressure of liquid ammonia storage tank 1 is 25 bar, the corresponding saturation temperature T1 is 59°C, and T2 is controlled to be ≤ 49°C and T3 ≤ 54°C.

[0087] In one embodiment, liquid ammonia is transported to the cooler 3, where the liquid ammonia exchanges heat with the refrigerant from the low-temperature refrigeration device 4, so that the temperature of the liquid ammonia drops to below the saturation temperature T1 of the liquid ammonia in the storage tank. In the step of obtaining supercooled liquid ammonia, the supercooling degree of the liquid ammonia is ≥5°C.

[0088] Subcooling refers to the difference between the liquid ammonia temperature and its saturation temperature (i.e., the saturation temperature T1 of the liquid ammonia in the storage tank). Setting a liquid ammonia subcooling of 5°C or higher means that the cooled liquid ammonia has sufficient cold energy reserves. Upon entering the vapor phase of liquid ammonia storage tank 1, it creates a significant temperature difference with the ammonia vapor. This temperature difference provides a strong driving force for heat transfer, prompting the ammonia vapor to quickly release heat and condense into a liquid state, thereby effectively reducing the amount of ammonia vapor in the vapor phase and effectively controlling the pressure within the storage tank.

[0089] In one embodiment, liquid ammonia is circulated and transported by a liquid ammonia pump 2 , which is a ship fuel supply pump or a liquid cargo pump or a pump dedicated to reliquefaction function.

[0090] A ship's fuel supply pump is originally used to transfer liquid ammonia from storage tanks to fuel-consuming equipment such as engines, while a liquid cargo pump is used for loading, unloading, or intertank transfer of liquid ammonia. Both pumps can extract and transfer liquid ammonia, and their compatibility with the liquid ammonia medium has been verified in daily ship operations. By directly using them as the liquid ammonia circulation device in this system, the need for a separate dedicated circulation pump is eliminated, significantly simplifying the system's equipment structure and reducing equipment procurement and installation costs.

[0091] Although the embodiments of the present invention have been described with reference to the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention. Such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A method for reliquefying marine ammonia vapor, characterized in that: The steps include: extracting liquid ammonia from a liquid ammonia storage tank (1); The liquid ammonia is transported to a cooler (3), and the liquid ammonia is heat-exchanged with a refrigerant from a low-temperature refrigeration device (4) in the cooler (3), so that the temperature of the liquid ammonia is reduced to a temperature lower than the saturation temperature T1 of the liquid ammonia in the storage tank, thereby obtaining subcooled liquid ammonia; Spraying the supercooled liquid ammonia into the gas phase space of the liquid ammonia storage tank (1) through a spraying device (5); The supercooled liquid ammonia droplets contact and exchange heat with the ammonia vapor in the gas phase space, causing the ammonia vapor to condense and liquefy.

2. The method for reliquefying marine ammonia vapor according to claim 1, characterized in that: In the step of transporting the liquid ammonia to the cooler (3), the liquid ammonia exchanges heat with the refrigerant from the low-temperature refrigeration device (4) in the cooler (3), so that the temperature of the liquid ammonia drops to a temperature lower than the saturation temperature T1 of the liquid ammonia in the storage tank. In the step of obtaining supercooled liquid ammonia, the refrigerant temperature T2 must satisfy the following conditions: T2 <T3<T1; Wherein, T3 is the temperature of liquid ammonia at the outlet of the cooler (3).

3. The method for reliquefying marine ammonia vapor according to claim 2, wherein: T3≤T1-5℃ and T2≤T3-5℃.

4. The method for reliquefying marine ammonia vapor according to claim 1, wherein: In the step of atomizing and spraying the supercooled liquid ammonia into the gas phase space of the liquid ammonia storage tank (1) through the spraying device (5), the average particle size of the droplets is ≤100 μm.

5. The method for reliquefying marine ammonia vapor according to claim 1, wherein: The refrigerant is a liquid or gaseous medium provided by the low-temperature refrigeration device (4), and its evaporation temperature is lower than the condensation temperature of ammonia.

6. The method for reliquefying marine ammonia vapor according to any one of claims 1 to 5, characterized in that: The design pressure of the liquid ammonia storage tank (1) is 0.7 bar-25 bar, the corresponding saturation temperature T1 is -23°C to 59°C, the refrigerant temperature T2 is ≤-33°C, and the liquid ammonia temperature T3 at the outlet of the cooler (3) is ≤-28°C.

7. The method for reliquefying marine ammonia vapor according to claim 6, characterized in that: When the design pressure of the liquid ammonia storage tank (1) is 0.7 bar, the corresponding saturation temperature T1 is -23°C, and T2 is controlled to be ≤-33°C and T3 ≤-28°C; When the design pressure of the liquid ammonia storage tank (1) is 10 bar, the corresponding saturation temperature T1 is 28°C, and T2 is controlled to be ≤18°C and T3 ≤23°C; When the design pressure of the liquid ammonia storage tank (1) is 25 bar, the corresponding saturation temperature T1 is 59° C., and T2 is controlled to be ≤ 49° C. and T3 is controlled to be ≤ 54° C.

8. The method for reliquefying marine ammonia vapor according to claim 1, characterized in that: The liquid ammonia is transported to the cooler (3), and the liquid ammonia is heat-exchanged with the refrigerant from the low-temperature refrigeration device (4) in the cooler (3), so that the temperature of the liquid ammonia is reduced to below the saturation temperature T1 of the liquid ammonia in the storage tank. In the step of obtaining supercooled liquid ammonia, the supercooling degree of the liquid ammonia is ≥5°C.

9. The method for reliquefying marine ammonia vapor according to claim 1, characterized in that: The liquid ammonia is circulated and transported by a liquid ammonia pump (2), and the liquid ammonia pump (2) is a ship fuel supply pump or a liquid cargo pump or a pump dedicated to the reliquefaction function.

10. A marine ammonia reliquefaction system, using the marine ammonia vapor reliquefaction treatment method according to any one of claims 1 to 9, characterized in that: include: Liquid ammonia storage tank (1); a liquid ammonia pump (2), which is placed on the bottom side of the liquid ammonia storage tank (1) or outside the liquid ammonia storage tank (1), and is connected to a pipeline; A cooler (3) is placed outside the liquid ammonia storage tank (1), and the cooler (3) is connected to the pipeline; A low-temperature refrigeration device (4) is placed outside the liquid ammonia storage tank (1), and the low-temperature refrigeration device (4) transports a refrigerant with a temperature lower than the condensation temperature of liquid ammonia to the interior of the cooler (3); A spray device (5) is placed on the top side of the liquid ammonia storage tank (1), and the spray device (5) is connected to the outlet pipe of the cooler (3).

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