A multi-stage gradient cooling system for liquid ammonia fuel

Abstract

This invention proposes a multi-stage gradient cooling system for liquid ammonia fuel, relating to the field of liquid ammonia fuel cooling technology. It includes a liquid ammonia feed pipeline for conveying liquid ammonia to be cooled; a liquid ammonia discharge pipeline for conveying cooled liquid ammonia; a primary cooling unit, a secondary cooling unit, and a tertiary cooling unit sequentially arranged between the liquid ammonia feed pipeline and the liquid ammonia discharge pipeline; and a refrigerant delivery module for providing cooling media of different states to the tertiary and secondary cooling units. The primary cooling unit performs the first cooling of the liquid ammonia, the secondary cooling unit performs the second cooling, and the tertiary cooling unit performs the third cooling or heats up excessively low-temperature liquid ammonia. This invention employs a three-stage gradient cooling mode, replacing the traditional one-time large-amplitude direct cooling process. The cooling logic is reasonable, the heat exchange temperature difference is gradual, and it can effectively improve the problem of sudden temperature changes during the liquid ammonia cooling process.

Description

Technical Field

[0001] This invention belongs to the field of liquid ammonia fuel cooling technology, and particularly relates to a multi-stage gradient cooling system for liquid ammonia fuel. Background Technology

[0002] Liquid ammonia, as a clean and low-carbon alternative fuel for ships, boasts advantages such as high energy density, low carbon emissions, and mature storage and transportation technologies, making it one of the important fuels for the shipping industry to achieve green and low-carbon navigation at present. During the refueling operation of liquid ammonia-fueled ships, the temperature of liquid ammonia at room temperature is usually maintained at around 25°C. However, shipboard liquid ammonia fuel storage tanks have stringent low-temperature storage requirements for the fed liquid ammonia. Liquid ammonia at room temperature cannot directly meet the safe storage and refueling transportation conditions of shipboard storage tanks. It must be cooled to a low temperature of -30°C to -40°C to complete compliant transportation and storage.

[0003] Currently, the industry's cooling technology for liquid ammonia fueled ships is relatively simple. Conventional cooling methods mostly use a single refrigeration unit for direct cooling, which suffers from problems such as large temperature gradient differences, high cooling energy consumption, low refrigeration efficiency, and poor temperature control stability. Meanwhile, in existing liquid ammonia transportation processes, the cryogenic liquid ammonia is highly susceptible to vaporization during cryogenic liquid ammonia refueling and transportation due to the influence of ambient temperature and pipeline pressure drop, generating large amounts of ammonia gas. Current technology lacks a structure for recovering and reusing vaporized ammonia gas. Direct emission of vaporized ammonia gas not only wastes fuel resources but also increases pollutant emissions. Furthermore, ammonia gas is toxic and corrosive, and direct emission can easily pollute the surrounding environment, posing safety hazards.

[0004] Therefore, there is an urgent need to propose a multi-stage cooling, recyclable vaporized ammonia gas, and lower energy consumption liquid ammonia cryogenic transportation and processing solution to solve the problems existing in the above-mentioned technologies. Summary of the Invention

[0005] In response to the problems raised in the background art, the present invention proposes a multi-stage gradient cooling system for liquid ammonia fuel.

[0006] To achieve this objective, the present invention adopts the following technical solution: A multi-stage gradient cooling system for liquid ammonia fuel includes: The liquid ammonia feed line is used to transport liquid ammonia to be cooled. The liquid ammonia discharge pipeline is used to transport cooled liquid ammonia. The cooling module includes a primary cooling unit, a secondary cooling unit, and a tertiary cooling unit sequentially disposed between the liquid ammonia inlet pipeline and the liquid ammonia outlet pipeline. A refrigerant delivery module is used to provide the tertiary cooling unit with heat exchanger in a first material state and / or in a second material state, and to provide the secondary cooling unit with heat exchanger in a second material state. The recovery module is used to recover the ammonia gas vaporized during the transportation of cooled liquid ammonia in the liquid ammonia discharge pipeline to the secondary cooling unit; The primary cooling unit is used for the initial cooling of liquid ammonia; The secondary cooling unit uses a heat exchanger in the first material state to perform a second cooling of liquid ammonia or to cool the recovered ammonia gas. The three-stage cooling unit uses a heat exchanger in the first material state to cool the liquid ammonia for the third time, and uses a heat exchanger in the second material state to heat the liquid ammonia.

[0007] Preferably, the primary cooling unit includes a throttling valve, which is used to throttle and depressurize the liquid ammonia to be cooled for the first cooling, and to transport the throttled and depressurized liquid ammonia along the liquid ammonia feed pipeline to the secondary cooling unit.

[0008] Preferably, the secondary cooling unit includes a heat exchanger, the feed end of which is used to receive liquid ammonia after being throttled and depressurized by the throttling valve and ammonia gas recovered by the recovery module; The refrigerant delivery module supplies heat exchanger in a second material state to the heat exchanger through the refrigerant discharge pipeline; The heat exchanger uses a heat exchanger in a second material state to perform a second cooling of the throttled and depressurized liquid ammonia, as well as to cool the ammonia gas delivered by the recovery module.

[0009] Preferably, the three-stage cooling unit is equipped with at least two condensers, each condenser is independently equipped with a single condensing pipe, multiple condensers are used in series and are equipped with a series condensing pipe, and multiple condensers are used in parallel and are equipped with a parallel condensing pipe. The three-stage cooling unit is used to receive liquid ammonia and ammonia gas cooled by the heat exchanger, and through the condenser where the single condenser pipe, series condenser pipe, or parallel condenser pipe is located, the refrigerant delivery module provides heat exchanger in the first material state to liquefy ammonia gas into liquid ammonia and cool the liquid ammonia to the target temperature. When the three-stage cooling unit cools the liquid nitrogen to below the target temperature, the refrigerant delivery module provides a heat exchanger in a second material state to raise the temperature of the liquid ammonia below the target temperature to meet the target temperature.

[0010] Preferably, the three-stage cooling unit delivers liquid ammonia cooled to the target temperature to the liquid ammonia discharge pipeline, and the liquid ammonia discharge pipeline delivers the liquid ammonia to the liquid ammonia fuel ship via a magnetic pump.

[0011] Preferably, the inlet end of the single condensation pipeline is connected to the liquid ammonia inlet pipeline through a single inlet gate valve, and the outlet end of the single condensation pipeline is connected to the liquid ammonia outlet pipeline through a single outlet gate valve. Each of the aforementioned single condenser lines has an independent condenser installed between its inlet and outlet ends; When the system selects a single condensation pipeline to cool liquid ammonia, only the single inlet gate valve and the single outlet gate valve of the selected single condensation pipeline are in the open state, so that the single condensation pipeline is connected to the liquid ammonia inlet pipeline and the liquid ammonia outlet pipeline. Multiple single condensing pipes are connected in series via branch pipes to form the series condensing pipe, and each condenser in the series condensing pipe is connected in series. The feed end of the series condenser pipeline is equipped with a switching gate valve, and the branch pipeline is equipped with a branch gate valve; When the system uses the series condenser pipes to cool liquid ammonia, only the switching gate valve, each of the branch gate valves, the single feed gate valve of the first single condenser pipe through which the liquid ammonia flows, and the single discharge gate valve of the last single condenser pipe through which the liquid ammonia flows are in the open state, so that the first single condenser pipe through which the liquid ammonia flows is connected to the liquid ammonia feed pipe, and the last single condenser pipe through which the liquid ammonia flows is connected to the liquid ammonia discharge pipe; Multiple single condensing pipes are connected in parallel to form the parallel condensing pipe, and each condenser in the parallel condensing pipe is connected in parallel with each other; When the system uses the parallel condenser pipes to cool liquid ammonia, only the switching gate valve, the single feed gate valve and the single discharge gate valve of each single condenser pipe are in the open state, so that each single condenser pipe is connected to the liquid ammonia feed pipe and the liquid ammonia discharge pipe.

[0012] Preferably, the refrigerant delivery module includes a refrigerant delivery pipeline, which includes a refrigerant inlet pipeline, multiple refrigerant branch pipes, and a refrigerant outlet pipeline; The inlet end of each refrigerant branch pipe is connected to the refrigerant inlet pipeline through a refrigerant inlet gate valve, and the outlet end is connected to the refrigerant outlet pipeline through a refrigerant outlet gate valve. Each of the refrigerant branch pipes is connected to a condenser, and the refrigerant branch pipes are used to supply heat exchanger in the first material state to the condenser; A connecting pipe is provided between each pair of refrigerant branch pipes, and a connecting gate valve is installed on the connecting pipe.

[0013] Preferably, the refrigerant delivery module further includes a refrigerant temperature control pipeline, which includes a temperature control feed pipeline, heating equipment, and multiple temperature control branch pipes; The feed end of each of the temperature-regulating branch pipes is connected to the temperature-regulating feed pipeline through a temperature-regulating feed gate valve, and the discharge end of each of the temperature-regulating branch pipes is connected to a refrigerant branch pipe; the temperature-regulating feed pipeline is equipped with the heating device and the heating gate valve, and the heating device is arranged between the heating gate valve and the temperature-regulating feed gate valve. The heating device is used to heat the heat exchanger in the refrigerant temperature control pipeline from a first material state to a second material state. The temperature-regulating branch pipe is used to supply the heat exchanger in the second material state to the condenser.

[0014] Preferably, the recovery module includes a recovery pipeline, the inlet end of which is connected to the liquid ammonia fuel ship, and the outlet end of which is connected to the heat exchanger. The recovery pipeline is sequentially equipped with the heating device and the compressor.

[0015] Preferably, the heat exchanger in the first material state is liquid nitrogen; The heat exchanger in the second material state is nitrogen.

[0016] The advantages of this invention over the prior art are: 1. This invention employs a three-stage gradient cooling mode, replacing the traditional one-time large-scale direct cooling process. The cooling logic is reasonable, and the heat exchange temperature difference is gradual, effectively improving the problem of sudden temperature changes during liquid ammonia cooling. First, adiabatic throttling and pressure reduction cooling is achieved through a throttling valve, utilizing the pressure drop of liquid ammonia itself for initial self-cooling without additional refrigerant consumption. This pre-lowers the base temperature of liquid ammonia, reducing subsequent cooling load. Second, a secondary heat exchange cooling is achieved using nitrogen in a heat exchanger, realizing the exchange of waste heat and cooling capacity within the system. Finally, deep cryogenic cooling is achieved through a liquid nitrogen condenser, precisely bringing the liquid ammonia to the ship refueling temperature range of -30℃ to -40℃. This multi-stage gradient cooling method avoids the heat exchange stress impact caused by single large-temperature-difference cooling, reducing the risk of pipe frosting, cold shrinkage deformation, and low-temperature vibration, and extending the service life of cooling pipes and equipment. 2. This invention utilizes the combined operation of liquid nitrogen cryogenic cooling and cryogenic nitrogen temperature regulation to achieve precise bidirectional control of liquid ammonia temperature. Cryogenic liquid nitrogen provides high-intensity, high-efficiency cooling, while cryogenic nitrogen compensates for slight warming after supercooling. This cooling and heating mechanism forms a closed-loop temperature control logic, stably confining liquid ammonia within the optimal filling temperature range of -30℃ to -40℃, effectively avoiding various drawbacks caused by supercooled liquid ammonia. On the one hand, it prevents increased load on pipelines and pumps, as well as the risk of cryogenic brittle cracking caused by supercooled liquid ammonia, reducing equipment wear and safety hazards and improving the operational safety of the filling system. On the other hand, it avoids pressure fluctuations and uneven vaporization within the storage tank caused by abnormal liquid ammonia temperature, ensuring stable operating conditions in the ship's fuel storage tanks. 3. In this invention, the vaporized ammonia is pressurized and transported back to the heat exchanger through a compression device, so that it participates in the heat exchange process. On the one hand, the vaporized ammonia is recovered and reused, reducing fuel loss and improving the overall utilization rate of liquid ammonia. On the other hand, the high-temperature vaporized ammonia can participate in heat exchange in the heat exchanger, assisting in the regulation of the heat exchange medium temperature and further improving the system's energy utilization rate. Attached Figure Description

[0017] Figure 1 This is a schematic block diagram of the liquid ammonia fuel cooling system of the present invention; Figure 2 This is a schematic diagram of the liquid ammonia cooling route of the first single condenser pipe in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the liquid ammonia cooling route of the second single condenser pipe in Embodiment 2 of the present invention; Figure 4 This is a schematic diagram of the liquid ammonia cooling route of the series condenser pipe in Embodiment 3 of the present invention; Figure 5 This is a schematic diagram of the liquid ammonia cooling route of the series condenser pipe in Embodiment 4 of the present invention; Figure 6 This is a schematic diagram of the liquid ammonia cooling route of the parallel condenser pipe in Embodiment 5 of the present invention; Figure 7 This is a schematic diagram of the refrigerant delivery pipeline supplying liquid nitrogen to the first condenser in Embodiment Six of the present invention; Figure 8 This is a schematic diagram of the refrigerant delivery pipeline supplying liquid nitrogen to the second condenser in Embodiment 7 of the present invention; Figure 9 This is a schematic diagram of the refrigerant delivery pipeline supplying liquid nitrogen to the first condenser and the second condenser according to Embodiment 8 of the present invention; Figure 10 This is a schematic diagram of the refrigerant temperature control pipeline supplying nitrogen to the first condenser and the second condenser in Embodiment 9 of the present invention. Figure 11 This is a schematic diagram of the delivery route of liquid nitrogen from the refrigerant temperature control pipeline to the refrigerant feed pipeline in Embodiment 10 of the present invention; Figure 12 This is an overall schematic diagram of the liquid ammonia fuel cooling system of the present invention.

[0018] The system includes: a primary cooling unit 1, a secondary cooling unit 2, a tertiary cooling unit 3, a refrigerant delivery module 4, a recovery module 5, a residual liquid collection tank 6, a throttling valve 7, a heat exchanger 8, a compressor 9, a magnetic pump 10, a liquid ammonia feed line 11, a liquid ammonia discharge line 22, a refrigerant feed line 33, a refrigerant discharge line 44, a temperature-regulating feed line 55, a feed switching line 66, a recovery line 77, a first condenser A, a first single condenser line a, a first single feed gate valve A1, a first single discharge gate valve A2, a second condenser B, a second single condenser line b, a second single feed gate valve B1, and a... Two single discharge gate valves B2, first switching gate valve C, second switching gate valve D, first branch pipeline E, branch gate valve E1, second branch pipeline F, first refrigerant branch pipe M, first refrigerant inlet gate valve M1, first refrigerant discharge gate valve M2, second refrigerant branch pipe N, second refrigerant inlet gate valve N1, second refrigerant discharge gate valve N2, connecting pipeline P, connecting gate valve P1, feed switching gate valve G, heating gate valve H, heating equipment I, first temperature regulating branch pipe J, first temperature regulating inlet gate valve J1, second temperature regulating branch pipe K, second temperature regulating inlet gate valve K1, second liquid nitrogen inlet R1, second liquid nitrogen inlet R2. Detailed Implementation

[0019] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0020] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] The terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this invention are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, apparatus, product, or end that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or ends.

[0022] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0023] Currently, the industry's cooling technology for liquid ammonia fuel tankers is relatively simple. Conventional cooling methods mostly use a single refrigeration unit for direct cooling, which suffers from problems such as large temperature gradient differences, high cooling energy consumption, low refrigeration efficiency, and poor temperature control stability. Furthermore, in existing liquid ammonia transportation processes, the cryogenic liquid ammonia is highly susceptible to vaporization during cryogenic liquid ammonia refueling and transportation due to the influence of ambient temperature and pipeline pressure drop, generating large amounts of ammonia gas. Existing technologies lack a structure for recovering and reusing vaporized ammonia gas; direct emission of vaporized ammonia gas not only wastes fuel resources but also increases pollutant emissions. Moreover, ammonia gas is toxic and corrosive, and direct emission can easily pollute the surrounding environment, posing safety hazards. In addition, traditional cooling processes have fixed refrigeration modes and do not incorporate multi-stage gradient cooling principles, failing to rationally utilize waste heat and cryogenic media to achieve staged cooling. The cooling capacity utilization rate is low, energy loss is severe, and the pressure stability of the cooled liquid ammonia is insufficient, making it difficult to meet the continuous, stable, and safe refueling and transportation requirements of ship fuel tankers. To address the above problems, this application proposes a multi-stage gradient cooling system for liquid ammonia fuel, including: Liquid ammonia feed line 11 is used to transport liquid ammonia to be cooled; Liquid ammonia discharge pipeline 22 is used to transport cooled liquid ammonia; The cooling module includes a primary cooling unit 1, a secondary cooling unit 2 and a tertiary cooling unit 3, which are sequentially arranged between the liquid ammonia inlet pipe 11 and the liquid ammonia outlet pipe 22. The refrigerant delivery module 4 is used to provide the heat exchanger in the first material state and / or the heat exchanger in the second material state to the three-stage cooling unit 3, and to provide the heat exchanger in the second material state to the two-stage cooling unit 2. The recovery module 5 is used to recover the ammonia gas vaporized during the transportation of cooled liquid ammonia in the liquid ammonia discharge pipeline 22 to the secondary cooling unit 2; The primary cooling unit 1 is used for the first cooling of liquid ammonia; The secondary cooling unit 2 uses a heat exchanger in the first material state to perform a second cooling of liquid ammonia or to cool the recovered ammonia gas. The three-stage cooling unit 3 uses a heat exchanger in the first material state to perform a third cooling of liquid ammonia, and uses a heat exchanger in the second material state to heat up the liquid ammonia.

[0024] The heat exchanger in the first material state is liquid nitrogen; The heat exchanger in the second material state is nitrogen.

[0025] In this scheme, the inlet end of the liquid ammonia feed pipeline 11 is connected to a storage device containing liquid ammonia fuel to be cooled, such as a normal temperature liquid ammonia storage tank truck, etc. The storage temperature of normal temperature liquid ammonia is approximately 25°C or higher. The outlet end of the liquid ammonia fuel feed pipeline is sequentially equipped with a primary cooling unit 1, a secondary cooling unit 2, and a tertiary cooling unit 3. The refrigerant delivery module 4 provides nitrogen to the secondary cooling unit 2 and liquid nitrogen and cryogenic nitrogen to the tertiary cooling unit 3. In this embodiment, the temperature of liquid nitrogen itself is very low, approximately -196°C, which is far lower than the freezing point of liquid ammonia -77.7°C. Therefore, the liquid nitrogen cools the tertiary cooling unit 3, and then the tertiary cooling unit 3 is used to achieve indirect heat exchange with the liquid ammonia to be cooled. When using nitrogen to cool liquid ammonia, cryogenic nitrogen is required for effective heat transfer, and the nitrogen is pre-cooled to a temperature lower than that of liquid ammonia. Liquid ammonia fuel at room temperature is fed into the liquid ammonia feed pipe 11. After the first cooling by the primary cooling unit 1, it enters the secondary cooling unit 2, where cryogenic nitrogen is used to cool the liquid ammonia a second time. Then it enters the tertiary cooling unit 3, where liquid ammonia is cooled a third time using indirect heat exchange with liquid nitrogen. This stabilizes the temperature of the liquid ammonia after the third cooling to -30°C to -40°C. The fuel is then transported along the liquid ammonia discharge pipe 22 to the liquid ammonia fuel ship for refueling. During the cooling process in the tertiary cooling unit 3, the temperature of the liquid ammonia may drop below -40°C. In this case, cryogenic nitrogen is used to replace the liquid ammonia in the tertiary cooling unit 3, raising the temperature of the liquid ammonia below the target temperature to -30°C to -40°C. Furthermore, during the process of refueling the liquid ammonia fuel into the liquid ammonia fuel ship after cooling, some of the liquid ammonia will vaporize and form low-temperature ammonia gas. This solution is equipped with a recovery module 5, which is used to recover the low-temperature ammonia gas to the secondary cooling unit 2, and then cool it down through the secondary cooling unit 2 and the tertiary cooling unit 3 before being transported back to the liquid ammonia fuel ship.

[0026] This solution employs a three-stage gradient cooling mode, replacing the traditional one-time large-amplitude direct cooling process. The cooling logic is rational, and the heat exchange temperature difference is gradual, effectively mitigating the problem of sudden temperature changes during liquid ammonia cooling. The multi-stage gradient cooling method avoids the heat exchange stress impact caused by single large-temperature-difference cooling, reducing the risks of pipe frosting, cold shrinkage deformation, and low-temperature vibration, thus extending the service life of cooling pipes and equipment. Simultaneously, the secondary cooling unit 2 and the tertiary cooling unit 3 use the same cooling medium in different states, significantly reducing overall refrigeration power consumption and cost. Furthermore, a vaporized ammonia recovery and reflux structure is added to achieve the resource reuse of waste ammonia, further improving the system's energy utilization rate.

[0027] Preferred, such as Figure 1 and Figure 12 As shown, the primary cooling unit 1 includes a throttle valve 7, which is used to throttle and depressurize the liquid ammonia to be cooled for the first cooling, and to transport the throttled and depressurized liquid ammonia along the liquid ammonia feed pipeline 11 to the secondary cooling unit 2.

[0028] In this embodiment, the primary cooling unit 1 is configured as a throttling valve 7. Room-temperature liquid ammonia fuel first enters the throttling valve 7 along the liquid ammonia feed pipe 11. The throttling valve 7 adiabatically throttles and reduces the pressure of the room-temperature liquid ammonia fuel, achieving initial self-cooling by utilizing the liquid ammonia's own pressure reduction and throttling. No additional refrigerant is required, which can pre-lower the base temperature of the liquid ammonia and reduce subsequent cooling load. In practical applications, the throttling and pressure reduction of the throttling valve 7 can remove 8%-10% of the heat from the room-temperature liquid ammonia fuel.

[0029] Preferred, such as Figure 1 and Figure 12 As shown, the secondary cooling unit 2 includes a heat exchanger 8, the feed end of which is used to receive liquid ammonia after being throttled and depressurized by the throttling valve 7 and ammonia gas recovered by the recovery module 5; The refrigerant delivery module 4 supplies heat exchanger in a second material state to the heat exchanger 8 through the refrigerant discharge pipeline 44; The heat exchanger 8 uses a heat exchanger in a second material state to perform a second cooling of the throttled and depressurized liquid ammonia, as well as to cool the ammonia gas delivered by the recovery module 5.

[0030] In this embodiment, the liquid ammonia fuel, after being throttled and depressurized by the throttle valve 7, flows into the heat exchanger 8 along the liquid ammonia feed pipeline 11. The heat exchanger 8 uses the low-temperature nitrogen provided by the refrigerant delivery module 4 to perform a second cooling of the liquid ammonia fuel, thereby realizing the exchange of waste heat and cooling capacity within the system.

[0031] Meanwhile, in addition to providing a second cooling for the liquid ammonia fuel, the heat exchanger 8 is also used to cool the ammonia gas delivered by the recovery module 5.

[0032] Specifically, such as Figure 1 and Figure 12 As shown, the recycling module 5 includes a recycling pipeline 77, the inlet end of which is connected to the liquid ammonia fuel ship, and the outlet end of which is connected to the heat exchanger 8. The recycling pipeline 77 is sequentially equipped with the heating device I and the compressor 9.

[0033] In this embodiment, during the process of transporting the finally cooled liquid ammonia to the liquid ammonia fuel ship via the liquid ammonia discharge pipeline 22, the cryogenic liquid ammonia is prone to generating a large amount of vaporized ammonia gas due to pipeline pressure drop and ambient heat radiation during the refueling and transportation process. Traditional processes often directly vent this gas, which not only wastes liquid ammonia fuel but also causes environmental pollution and safety hazards due to the toxicity and corrosiveness of ammonia gas. This solution recovers the vaporized ammonia gas through the recovery pipeline 77. During the recovery process, because the pressure of the liquid ammonia fuel ship is in a slightly positive pressure state, it is impossible to directly recover the vaporized ammonia gas. Therefore, a compressor 9 is configured in the recovery pipeline 77 to compress and pressurize the vaporized ammonia gas for recovery. At the same time, the vaporized liquid ammonia is still in a cryogenic state during the refueling process of the liquid ammonia fuel ship. In order to protect the compressor 9, a heating device I is set before the compressor 9 to heat the cryogenic ammonia gas to room temperature. Finally, the heated ammonia gas is input into the secondary cooling unit 2 for recooling through the discharge end of the recovery pipeline 77.

[0034] The secondary cooling unit 2 cools the recovered room-temperature ammonia gas, turning it into low-temperature ammonia gas. The low-temperature ammonia gas is then transported to the tertiary cooling unit 3 along with the liquid ammonia gas from the second cooling process. The tertiary cooling unit 3 cools the low-temperature ammonia gas, liquefying it into liquid ammonia gas, and continuously cools it until its temperature meets the target temperature.

[0035] This scheme uses a compression device to pressurize and transport the vaporized ammonia back to heat exchanger 8, allowing it to participate in the heat exchange process. On the one hand, this achieves the recovery and reuse of vaporized ammonia, reducing fuel consumption and improving the overall utilization rate of liquid ammonia. On the other hand, the vaporized ammonia can participate in heat exchange within heat exchanger 8, assisting in the regulation of the heat exchange medium temperature and further improving the system's energy utilization rate.

[0036] Furthermore, the ammonia reflux compression structure of the recovery module 5 can stabilize the system pipeline pressure and improve the safety of refueling. Since the vaporization of cryogenic liquid ammonia can easily cause a sudden increase in local pipeline pressure, creating a potential pressure hazard, this solution promptly extracts the vaporized cryogenic ammonia, heats it, and compresses it back into the pipeline. This reduces the degree of gas phase enrichment inside the pipeline, avoids adverse conditions such as high pressure, gas resistance, and liquid hammer, and stabilizes the delivery pressure.

[0037] Preferably, the three-stage cooling unit 3 is equipped with at least two condensers, each condenser is independently equipped with a single condensing pipe, multiple condensers are used in series and are equipped with a series condensing pipe, and multiple condensers are used in parallel and are equipped with a parallel condensing pipe. The three-stage cooling unit 3 is used to receive the liquid ammonia and ammonia gas cooled by the heat exchanger 8, and through the condenser where the single condenser pipe, series condenser pipe, or parallel condenser pipe is located, the refrigerant delivery module 4 provides the heat exchanger in the first material state to liquefy the ammonia gas into liquid ammonia and cool the liquid ammonia to the target temperature. When the three-stage cooling unit 3 cools the liquid nitrogen to below the target temperature, the refrigerant delivery module 4 uses a heat exchanger in a second material state to raise the temperature of the liquid ammonia below the target temperature to meet the target temperature.

[0038] Preferably, the inlet end of the single condensation pipeline is connected to the liquid ammonia inlet pipeline 11 through a single inlet gate valve, and the outlet end of the single condensation pipeline is connected to the liquid ammonia outlet pipeline 22 through a single outlet gate valve. Each of the aforementioned single condenser lines has an independent condenser installed between its inlet and outlet ends; When the system selects a single condensation pipeline to cool liquid ammonia, only the single inlet gate valve and the single outlet gate valve of the selected single condensation pipeline are in the open state, so that the single condensation pipeline is connected to the liquid ammonia inlet pipeline 11 and the liquid ammonia outlet pipeline 22. For a single condenser piping system, this solution provides two embodiments for explanation. Embodiment 1 includes a first condenser A and a second condenser B, as follows: Figure 2 As shown, the inlet end of the first single condensing pipe a, where the first condenser A is located, is equipped with a first single inlet gate valve A1. The first single condensing pipe a is connected to the liquid ammonia inlet pipe 11 through the first single inlet gate valve A1. The outlet end of the first single condensing pipe a is equipped with a single inlet gate valve A2. The first single condensing pipe a is connected to the liquid ammonia outlet pipe 22 through the single inlet gate valve A2. When the first single condensing pipe a of the first condenser A is activated to cool the liquid ammonia fuel, the liquid ammonia fuel delivery route is as follows: Figure 2 As shown by the red line, after the liquid ammonia fuel and the recovered low-temperature ammonia gas flow through the liquid ammonia feed pipeline 11, the first single feed gate valve A1 opens, allowing the room temperature liquid ammonia fuel to flow into the first condenser A. The first condenser A cools the liquid ammonia fuel and the recovered low-temperature ammonia gas after the two cooling cycles by liquid nitrogen supplied by the refrigerant delivery pipeline, reducing their temperature to the target temperature. Then, the first single discharge gate valve A2 opens, and the liquid ammonia fuel after the third cooling flows into the liquid ammonia discharge pipeline 22, from which it is transported to the liquid ammonia fuel ship.

[0039] Example 2 includes a first condenser A and a second condenser B, as follows: Figure 3As shown, the inlet end of the second single condensing pipe b, where the second condenser B is located, is equipped with a second single inlet gate valve B1. The second single condensing pipe b is connected to the liquid ammonia inlet pipe 11 through the second single inlet gate valve B1 and the first switching gate valve C. The outlet end of the second single condensing pipe b is equipped with a second single outlet gate valve B2. The second single condensing pipe b is connected to the liquid ammonia outlet pipe 22 through the second single outlet gate valve B2. When the second single condensing pipe b of the second condenser B is activated to cool the liquid ammonia fuel, the liquid ammonia fuel delivery route is as follows: Figure 3 As shown by the red line, after the liquid ammonia fuel and the recovered low-temperature ammonia gas flow through the liquid ammonia feed pipeline 11, the first switching gate valve C and the second single feed gate valve B1 are opened, allowing the room temperature liquid ammonia fuel to flow into the second condenser B. The second condenser B cools the liquid ammonia fuel and the recovered low-temperature ammonia gas after the two cooling cycles by liquid nitrogen supplied by the refrigerant delivery pipeline, reducing their temperature to the target temperature. The second single discharge gate valve B2 is then opened, and the liquid ammonia fuel after the third cooling flows into the liquid ammonia discharge pipeline 22, from where it is discharged and transported to the liquid ammonia fuel ship.

[0040] It should be noted that Embodiments 1 and 2 described above represent the first operating mode of this application. In this first operating mode, the liquid ammonia fuel cooling system selects one single condenser pipe to cool the liquid ammonia fuel and recovered low-temperature ammonia gas after two cooling cycles. In this first operating mode, when one single condenser pipe is activated, the other single condenser pipes are closed. This achieves independent operation of a single condenser under low-flow refueling conditions, using only one condenser to complete the deep cooling of liquid ammonia. This avoids refrigerant waste and equipment idling losses caused by simultaneous operation of two units, effectively reducing equipment energy consumption and operating costs, and improving the refrigeration economy under low-flow conditions.

[0041] Preferably, multiple single condensing pipes are connected in series via branch pipes to form the series condensing pipe, wherein each condenser in the series condensing pipe is connected in series. The feed end of the series condenser pipeline is equipped with a switching gate valve, and the branch pipeline is equipped with a branch gate valve; When the system uses the series condenser pipes to cool liquid ammonia, only the switching gate valve, each of the branch gate valves, the single feed gate valve of the first single condenser pipe through which the liquid ammonia flows, and the single discharge gate valve of the last single condenser pipe through which the liquid ammonia flows are in the open state, so that the first single condenser pipe through which the liquid ammonia flows is connected to the liquid ammonia feed pipe 11, and the last single condenser pipe through which the liquid ammonia flows is connected to the liquid ammonia discharge pipe 22; Regarding the aforementioned series condenser piping, this solution provides two embodiments for explanation. Embodiment three, as follows: Figure 4As shown, when the first condenser A is connected in series with the second condenser B, the liquid ammonia fuel delivery route is as follows: Figure 4 As shown by the red line, the liquid ammonia fuel, after two cooling cycles, and the recovered cryogenic ammonia gas flow sequentially from the liquid ammonia feed pipe 11 through the first switching gate valve C and the second single feed gate valve B1, then along the second single condenser pipe b into the second condenser B. After being cooled by the second condenser B, it enters the first branch pipe E, flows through the branch gate valve E1 into the first condenser A, and after being cooled again by the first condenser A, it flows through the first single discharge gate valve A2 into the liquid ammonia discharge pipe 22, from where it is discharged and transported to the liquid ammonia fuel ship. In this transport route, the second single discharge gate valve B2 and the first single feed gate valve A1 are in the closed state.

[0042] Example 4, as Figure 5 As shown, when the first condenser A is connected in series with the second condenser B, the liquid ammonia fuel delivery route is as follows: Figure 5 As shown by the red line, the liquid ammonia fuel, after two cooling cycles, and the recovered cryogenic ammonia gas flow sequentially from the liquid ammonia feed pipe 11 through the first single feed gate valve A1, along the first single condenser pipe a into the first condenser A, and after being cooled down by the first condenser A, through the second switching gate valve D into the second branch pipe F. From the second branch pipe F, it flows along the second single condenser pipe b through the second single feed gate valve B1 into the second condenser B, and after being cooled down again by the second condenser B, it flows through the second single discharge gate valve B2 into the liquid ammonia discharge pipe 22, from where it is discharged and transported to the liquid ammonia fuel ship. In this transport route, the first switching gate valve C and the first single discharge valve A2 are in the closed state.

[0043] It should be noted that Embodiments 3 and 4 described above are the second operating mode of this application. In the second operating mode, the system connects multiple single condenser pipes in series to form the series condenser pipes to cool the liquid ammonia fuel and the recovered low-temperature ammonia gas after two cooling cycles. In the second operating mode, under the refueling conditions with ultra-high flow rate and high cooling accuracy requirements, a dual-condenser series cooling mode is adopted. The liquid ammonia flows through the two condensers in sequence to exchange heat and cool down step by step, increasing the heat exchange temperature drop of the liquid ammonia, enhancing the deep cooling effect, and ensuring that the high-flow-rate liquid ammonia can still stably reach the low-temperature refueling standard of -30℃ to -40℃, avoiding problems such as insufficient cooling and excessive temperature fluctuations.

[0044] Preferably, multiple single condensing pipes are connected in parallel to form the parallel condensing pipe, and each condenser in the parallel condensing pipe is connected in parallel with each other; When the system uses the parallel condenser pipes to cool liquid ammonia, only the switching gate valve, the single feed gate valve and the single discharge gate valve of each single condenser pipe are in the open state, so that each single condenser pipe is connected to the liquid ammonia feed pipe 11 and the liquid ammonia discharge pipe 22.

[0045] Regarding the parallel condenser piping, this solution provides Example 5 for explanation. Example 5, as follows... Figure 6 As shown, when the first condenser A is connected in parallel with the second condenser B, the liquid ammonia fuel delivery route is as follows: Figure 6 As shown by the red line, after two cooling cycles, the liquid ammonia fuel and recovered cryogenic ammonia gas flow from the liquid ammonia feed line 11 through the first switching gate valve C, splitting into two paths. One path passes sequentially through the first switching gate valve C and the second single feed gate valve B1, then enters the second condenser B via the second single condenser line b. After being cooled by the second condenser B, it flows through the second single discharge gate valve B2 and merges into the liquid ammonia discharge line 22. The other path passes through the first single feed gate valve A1 and enters the first condenser A. After being cooled by the first condenser A, it flows through the first single discharge valve A2 and merges into the liquid ammonia discharge line 22. This ensures that the liquid ammonia fuel, after being split from the liquid ammonia feed line 11, is cooled by the first condenser A and the second condenser B respectively, before merging into the liquid ammonia discharge line 22 and being transported to the liquid ammonia fuel ship. In this transport route, the second switching gate valve D and the branch gate valve E1 are in the closed state.

[0046] It should be noted that the above-described fifth embodiment is the third operating mode of this application. In the third operating mode, the system connects multiple single condenser pipes in parallel to form a parallel condenser pipe to cool the liquid ammonia fuel and the recovered low-temperature ammonia gas after two cooling cycles. In the third operating mode, under the condition of medium to high flow rate and requiring balanced temperature control during refueling, a dual-condenser parallel cooling mode is adopted. The liquid ammonia is diverted to two condensers for independent cooling and then converged to the main pipe. This increases the overall heat exchange area, reduces the processing load of a single condenser, makes the liquid ammonia cooling more uniform, reduces the phenomenon of local vaporization of liquid ammonia inside the pipeline, reduces the pressure of vaporized ammonia reflux treatment, and improves the operational stability and safety of the entire cooling and conveying system.

[0047] Preferably, the refrigerant delivery module 4 includes a refrigerant delivery pipeline, which includes a refrigerant inlet pipeline 33, multiple refrigerant branch pipes, and a refrigerant outlet pipeline 44; The inlet end of each refrigerant branch pipe is connected to the refrigerant inlet pipe 33 through a refrigerant inlet gate valve, and the outlet end is connected to the refrigerant outlet pipe 44 through a refrigerant outlet gate valve. Each of the refrigerant branch pipes is connected to a condenser, and the refrigerant branch pipes are used to supply heat exchanger in the first material state to the condenser; A connecting pipe is provided between each pair of refrigerant branch pipes, and a connecting gate valve is installed on the connecting pipe.

[0048] This solution provides each condenser with a separate refrigerant branch pipe, enabling independent refrigerant charging for each condenser. At the same time, a connecting pipe P is set between each pair of refrigerant branch pipes, allowing multiple refrigerant branch pipes to be used in series.

[0049] Preferably, the refrigerant delivery module 4 further includes a refrigerant temperature control pipeline, which includes a temperature control feed pipeline 55, a heating device I, and multiple temperature control branch pipes; The feed end of each of the temperature-regulating branch pipes is connected to the temperature-regulating feed pipeline 55 through a temperature-regulating feed gate valve, and the discharge end of each of the temperature-regulating branch pipes is connected to a refrigerant branch pipe; the temperature-regulating feed pipeline 55 is equipped with the heating device I and the heating gate valve, and the heating device I is arranged between the heating gate valve and the temperature-regulating feed gate valve. The heating device I is used to heat the heat exchanger in the refrigerant temperature control pipeline from a first material state to a second material state. The temperature-regulating branch pipe is used to supply the heat exchanger in the second material state to the condenser.

[0050] In this scheme, the refrigerant temperature control pipeline is equipped with a temperature control feed pipeline 55, a heating device I, and multiple temperature control branch pipes. When the liquid ammonia fuel in the condenser pipeline cools excessively, causing the temperature to drop too low, liquid nitrogen enters from the feed end of the temperature control feed pipeline 55 and is heated into nitrogen gas by the heating device I. The nitrogen gas is then distributed to each temperature control branch pipe, and each branch pipe delivers the nitrogen gas to its corresponding refrigerant branch pipe. The refrigerant branch pipe then delivers the nitrogen gas to its corresponding condenser, where the condenser uses the nitrogen gas to exchange heat and raise the temperature of the excessively cold liquid ammonia fuel. It should be noted that during this process, the refrigerant feed pipeline 33 must not supply liquid nitrogen to the refrigerant branch pipes to avoid conflict between the liquid nitrogen and the low-temperature nitrogen gas.

[0051] Preferably, the feed end of the temperature-controlled feed pipeline 55 is equipped with a feed switching gate valve G; A feed switching pipeline 66 is provided between the temperature regulating feed pipeline 55 and the refrigerant feed pipeline 33, and the feed end of the feed switching pipeline 66 is located between the feed switching gate valve G and the heating gate valve H. The temperature-controlled feed line 55 delivers heat exchanger in its first material state to the refrigerant feed line 33 through the feed switching line 66.

[0052] Furthermore, a feed switching pipeline 66 is provided between the feed end of the temperature-controlled feed pipeline 55 and the refrigerant feed pipeline 33. This means that when the liquid nitrogen supply in the refrigerant feed pipeline 33 is insufficient, the temperature-controlled feed pipeline 55 can also transport liquid nitrogen to the refrigerant feed pipeline 33 through the feed switching pipeline 66, thereby adjusting the liquid nitrogen supply through the two pipelines.

[0053] Preferably, when a single condenser pipe is selected to cool liquid ammonia fuel, the refrigerant branch pipe connected to the condenser corresponding to that single condenser pipe is activated, and the activated refrigerant branch pipe provides the condenser with heat exchanger in a first material state or a heat exchanger in a second material state.

[0054] In Example 6, as Figure 7 As shown, when only the single condenser line containing the first condenser A is used, the liquid nitrogen delivery line is as follows: Figure 7 As shown in the red line, liquid nitrogen flows from the first liquid nitrogen inlet R1 along the refrigerant feed pipeline 33, through the first refrigerant feed gate valve M1, along the first refrigerant branch pipe M to the first condenser A, and then through the first refrigerant discharge gate valve M2 into the refrigerant discharge pipeline 44. In Example 7, as Figure 8 As shown, when only the single condenser line containing the second condenser B is used, the liquid nitrogen delivery line is as follows: Figure 8 As shown by the red line, liquid nitrogen flows from the first liquid nitrogen inlet R1 along the refrigerant feed pipe 33, through the second refrigerant feed gate valve N1, and is transported to the second condenser B along the second refrigerant branch pipe N. Then, it enters the refrigerant discharge pipe 44 through the second refrigerant discharge gate valve N2.

[0055] Preferably, when using the series condenser pipes or the parallel condenser pipes to cool liquid ammonia, the refrigerant branch pipe connected to the condenser corresponding to the series condenser pipes or the parallel condenser pipes is activated, and the activated refrigerant branch pipe independently provides heat exchanger in a first material state or a second material state to its respective condenser.

[0056] In this embodiment, when the series condenser pipeline or the parallel condenser pipeline is used to cool the liquid ammonia fuel, that is, when the first condenser A and the second condenser B are simultaneously activated, the conveying lines containing the first condenser A and the second condenser B can be activated simultaneously, meaning that liquid nitrogen is simultaneously transported along the pipeline. Figure 7 and Figure 8 The red route is used for transportation.

[0057] Preferably, when using the series condenser pipes or the parallel condenser pipes to cool liquid ammonia, the refrigerant branch pipes connected to the condensers corresponding to the series condenser pipes or the parallel condenser pipes are activated, and the connecting gate valve P1 between the activated refrigerant branch pipes is opened so that the activated refrigerant branch pipes are connected in series in sequence, providing heat exchanger in a first material state or a heat exchanger in a second material state to their respective condensers.

[0058] In Example 8, as Figure 9 As shown, when the series condenser circuit or the parallel condenser circuit is used to cool liquid ammonia fuel, that is, the first condenser A and the second condenser B are simultaneously activated. The liquid nitrogen delivery line is as follows: Figure 9 As shown by the red line, liquid nitrogen flows from the first liquid nitrogen inlet R1 along the refrigerant feed pipe 33, through the first refrigerant feed gate valve M1, and along the first refrigerant branch pipe M to the first condenser A. Then, it passes through the connecting pipe P and the connecting gate valve P1, and along the second refrigerant branch pipe N to the second condenser B. Finally, it passes through the second refrigerant discharge gate valve N2 and enters the refrigerant discharge pipe 44.

[0059] It should be noted that in Examples 6 to 8, as Figure 12 As shown, the liquid nitrogen vaporizes into cryogenic nitrogen gas after heat exchange with the first condenser A and the second condenser B. The cryogenic nitrogen gas enters the refrigerant discharge pipeline 44 through the first refrigerant discharge gate valve M2 or the second refrigerant discharge gate valve N2. The refrigerant discharge pipeline 44 delivers the cryogenic nitrogen gas to the heat exchanger 8, which is used by the heat exchanger 8 to perform a second cooling of the liquid ammonia fuel after the first cooling, as well as to cool the recovered room temperature ammonia gas. This significantly reduces the consumption of expensive liquid nitrogen, realizes the cascade utilization of cold energy, effectively reduces the operating energy consumption and refueling cost of cryogenic liquid ammonia treatment, and has significant energy-saving and economic benefits. It is more suitable for large-scale and continuous refueling operations on ships.

[0060] Furthermore, the low-temperature nitrogen gas passing through heat exchanger 8 needs to be heated by heating device I to ensure that the temperature is above 8 degrees Celsius before it can be discharged, in order to avoid creating an asphyxiating environment and affecting personnel safety. Therefore, this solution installs the heating device I at the end of the refrigerant discharge pipe 44 to heat the low-temperature nitrogen gas.

[0061] Furthermore, the process of supplying nitrogen to the condenser using a refrigerant temperature control pipeline is as shown in Example 9. In Example 9, as... Figure 10As shown, firstly, the refrigerant feed line 33 is closed to ensure that the refrigerant branch pipe does not transport liquid nitrogen to the first condenser A and the second condenser B. Then, liquid nitrogen enters from the second liquid nitrogen inlet R2 along the feed end of the temperature-regulating feed line 55. After passing through the feed switching gate valve G and the heating gate valve H, it is heated by the heating device I, causing the liquid nitrogen to be heated into low-temperature nitrogen gas. The first temperature-regulating feed gate valve J1 of the first temperature-regulating branch pipe J is opened, and the second temperature-regulating feed gate valve K1 of the second temperature-regulating branch pipe K is opened. The low-temperature nitrogen gas is diverted into the first temperature-regulating branch pipe J and the second temperature-regulating branch pipe K. Temperature-regulating branch pipe K and the first temperature-regulating branch pipe J deliver low-temperature nitrogen to the first refrigerant branch pipe M. The second temperature-regulating branch pipe K delivers low-temperature nitrogen to the second refrigerant branch pipe N. The first refrigerant branch pipe M delivers low-temperature nitrogen to the first condenser A, and then enters the refrigerant discharge pipeline 44 through the first refrigerant discharge gate valve M2. The second refrigerant branch pipe N delivers low-temperature nitrogen to the second condenser B, and then enters the refrigerant discharge pipeline 44 through the second refrigerant discharge gate valve N2. The refrigerant discharge pipeline 44 then supplies low-temperature nitrogen to the heat exchanger 8.

[0062] It should be noted that the first temperature regulating branch pipe J or the second temperature regulating branch pipe K should be activated according to the usage of the first condenser A or the second condenser B.

[0063] Furthermore, in Example 10, as Figure 11 As shown, when the feed switching gate valve G is open and the heating gate valve H is closed, liquid nitrogen can enter the feed switching pipeline 66 from the second liquid nitrogen inlet R2 along the temperature-regulating feed pipeline 55, and then be transported to the refrigerant feed pipeline 33.

[0064] Preferred, such as Figure 12 As shown, the three-stage cooling unit 3 delivers liquid ammonia cooled to the target temperature to the liquid ammonia discharge pipeline 22, and the liquid ammonia discharge pipeline 22 delivers the liquid ammonia to the liquid ammonia fuel ship via the magnetic pump 10.

[0065] In this scheme, the liquid ammonia discharge pipeline 22 will pressurize and extract the cooled liquid ammonia fuel through the magnetic suction pump 10, so as to avoid the liquid ammonia fuel being unable to be transported and refueled to the liquid ammonia fuel ship under slight positive pressure in the low temperature and low pressure pipeline.

[0066] Furthermore, this application provides residual liquid collection tanks 6 in the condenser of the third-stage cooling unit 3, the heat exchanger 8 of the second-stage cooling unit 2, and the refueling system of the liquid ammonia fuel ship. The residual liquid collection tanks 6 are used to collect residual liquid ammonia. The residual liquid collection tanks 6 are filled with water, and the residual liquid ammonia is collected and treated by utilizing the property that ammonia is soluble in water.

[0067] The technical principles of the present invention have been described above with reference to specific embodiments. These descriptions are merely for explaining the principles of the invention and should not be construed as limiting the scope of protection of the invention in any way. Based on this explanation, those skilled in the art can readily conceive of other specific embodiments of the invention without inventive effort, and these embodiments will all fall within the scope of protection of the present invention.

Claims

1. A multi-stage gradient cooling system for liquid ammonia fuel, characterized in that, include: The liquid ammonia feed line is used to transport liquid ammonia to be cooled. The liquid ammonia discharge pipeline is used to transport cooled liquid ammonia. The cooling module includes a primary cooling unit, a secondary cooling unit, and a tertiary cooling unit sequentially disposed between the liquid ammonia inlet pipeline and the liquid ammonia outlet pipeline. A refrigerant delivery module is used to provide the tertiary cooling unit with heat exchanger in a first material state and / or in a second material state, and to provide the secondary cooling unit with heat exchanger in a second material state. The recovery module is used to recover the ammonia gas vaporized during the transportation of cooled liquid ammonia in the liquid ammonia discharge pipeline to the secondary cooling unit; The primary cooling unit is used for the initial cooling of liquid ammonia; The secondary cooling unit uses a heat exchanger in the first material state to perform a second cooling of liquid ammonia or to cool the recovered ammonia gas. The three-stage cooling unit uses a heat exchanger in the first material state to cool the liquid ammonia for the third time, and uses a heat exchanger in the second material state to heat the liquid ammonia.

2. The multi-stage gradient cooling system for liquid ammonia fuel according to claim 1, characterized in that: The primary cooling unit includes a throttling valve, which is used to throttle and depressurize the liquid ammonia to be cooled for the first time, and to transport the throttled and depressurized liquid ammonia along the liquid ammonia feed pipeline to the secondary cooling unit.

3. The multi-stage gradient cooling system for liquid ammonia fuel according to claim 2, characterized in that: The secondary cooling unit includes a heat exchanger, the feed end of which is used to receive liquid ammonia after being throttled and depressurized by the throttling valve and ammonia gas recovered by the recovery module; The refrigerant delivery module supplies heat exchanger in a second material state to the heat exchanger through the refrigerant discharge pipeline; The heat exchanger uses a heat exchanger in a second material state to perform a second cooling of the throttled and depressurized liquid ammonia, as well as to cool the ammonia gas delivered by the recovery module.

4. The multi-stage gradient cooling system for liquid ammonia fuel according to claim 3, characterized in that: The three-stage cooling unit is equipped with at least two condensers, each condenser is independently equipped with a single condensing pipe, multiple condensers are used in series and are equipped with a series condensing pipe, and multiple condensers are used in parallel and are equipped with a parallel condensing pipe. The three-stage cooling unit is used to receive liquid ammonia and ammonia gas cooled by the heat exchanger, and through the condenser where the single condenser pipe, series condenser pipe, or parallel condenser pipe is located, the refrigerant delivery module provides heat exchanger in the first material state to liquefy ammonia gas into liquid ammonia and cool the liquid ammonia to the target temperature. When the three-stage cooling unit cools the liquid nitrogen to below the target temperature, the refrigerant delivery module provides a heat exchanger in a second material state to raise the temperature of the liquid ammonia below the target temperature to meet the target temperature.

5. The multi-stage gradient cooling system for liquid ammonia fuel according to claim 4, characterized in that: The three-stage cooling unit delivers liquid ammonia cooled to the target temperature to the liquid ammonia discharge pipeline, which then uses a magnetic pump to deliver and refuel the liquid ammonia fuel ship.

6. The multi-stage gradient cooling system for liquid ammonia fuel according to claim 4, characterized in that: The feed end of the single condenser pipeline is connected to the liquid ammonia feed pipeline through a single feed gate valve, and the discharge end of the single condenser pipeline is connected to the liquid ammonia discharge pipeline through a single discharge gate valve. Each of the aforementioned single condenser lines has an independent condenser installed between its inlet and outlet ends; When the system selects a single condensation pipeline to cool liquid ammonia, only the single inlet gate valve and the single outlet gate valve of the selected single condensation pipeline are in the open state, so that the single condensation pipeline is connected to the liquid ammonia inlet pipeline and the liquid ammonia outlet pipeline. Multiple single condensing pipes are connected in series via branch pipes to form the series condensing pipe, and each condenser in the series condensing pipe is connected in series. The feed end of the series condenser pipeline is equipped with a switching gate valve, and the branch pipeline is equipped with a branch gate valve; When the system uses the series condenser pipes to cool liquid ammonia, only the switching gate valve, each of the branch gate valves, the single feed gate valve of the first single condenser pipe through which the liquid ammonia flows, and the single discharge gate valve of the last single condenser pipe through which the liquid ammonia flows are in the open state, so that the first single condenser pipe through which the liquid ammonia flows is connected to the liquid ammonia feed pipe, and the last single condenser pipe through which the liquid ammonia flows is connected to the liquid ammonia discharge pipe; Multiple single condensing pipes are connected in parallel to form the parallel condensing pipe, and each condenser in the parallel condensing pipe is connected in parallel with each other; When the system uses the parallel condenser pipes to cool liquid ammonia, only the switching gate valve, the single feed gate valve and the single discharge gate valve of each single condenser pipe are in the open state, so that each single condenser pipe is connected to the liquid ammonia feed pipe and the liquid ammonia discharge pipe.

7. The multi-stage gradient cooling system for liquid ammonia fuel according to claim 4, characterized in that: The refrigerant delivery module includes a refrigerant delivery pipeline, which includes a refrigerant inlet pipeline, multiple refrigerant branch pipes, and a refrigerant outlet pipeline. The inlet end of each refrigerant branch pipe is connected to the refrigerant inlet pipeline through a refrigerant inlet gate valve, and the outlet end is connected to the refrigerant outlet pipeline through a refrigerant outlet gate valve. Each of the refrigerant branch pipes is connected to a condenser, and the refrigerant branch pipes are used to supply heat exchanger in the first material state to the condenser; A connecting pipe is provided between each pair of refrigerant branch pipes, and a connecting gate valve is installed on the connecting pipe.

8. The multi-stage gradient cooling system for liquid ammonia fuel according to claim 5, characterized in that: The refrigerant delivery module also includes a refrigerant temperature control pipeline, which includes a temperature control feed pipeline, heating equipment, and multiple temperature control branch pipes; The feed end of each of the temperature-regulating branch pipes is connected to the temperature-regulating feed pipeline through a temperature-regulating feed gate valve, and the discharge end of each of the temperature-regulating branch pipes is connected to a refrigerant branch pipe; the temperature-regulating feed pipeline is equipped with the heating device and the heating gate valve, and the heating device is arranged between the heating gate valve and the temperature-regulating feed gate valve. The heating device is used to heat the heat exchanger in the refrigerant temperature control pipeline from a first material state to a second material state. The temperature-regulating branch pipe is used to supply the heat exchanger in the second material state to the condenser.

9. The multi-stage gradient cooling system for liquid ammonia fuel according to claim 8, characterized in that: The recovery module includes a recovery pipeline, the inlet end of which is connected to the liquid ammonia fuel ship, and the outlet end of which is connected to the heat exchanger. The recovery pipeline is sequentially equipped with the heating equipment and the compressor.

10. The multi-stage gradient cooling system for liquid ammonia fuel according to claim 1, characterized in that: The heat exchanger in the first material state is liquid nitrogen; The heat exchanger in the second material state is nitrogen.

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