A system for hydrogen production based on energy island multi-energy collaborative hydrogen production coupled with green ammonia production

Abstract

This invention discloses a multi-energy synergistic hydrogen production and green ammonia production system based on an energy island. Integrated into an offshore energy island platform, it leverages wind, solar, and wave energy synergy to provide green electricity. The system employs reverse osmosis seawater desalination, proton exchange membrane electrolysis of water to produce hydrogen, and air liquefaction separation to produce nitrogen. Hydrogen and nitrogen gases are compressed in multiple stages and mixed with circulating gas. The mixture is preheated to the reaction temperature by high-temperature reaction products and then enters the ammonia synthesis reactor to catalytically generate ammonia. Energy is recovered and cooled through a three-stage heat exchange network, followed by purification via an ammonia separator and low-pressure flash evaporation to obtain a green ammonia product with a mass fraction of 99.5%. Unreacted hydrogen and nitrogen mixtures are compressed and refluxed by a circulating compressor, achieving efficient recycling of raw materials. This invention addresses the limitations of space and fluctuating energy supply on offshore energy islands by introducing seawater as a cooling medium to recover waste heat, solving the problems of high energy consumption and unsuitability for traditional ammonia synthesis processes, and achieving efficient conversion and comprehensive utilization of multiple renewable energy sources at sea.

Description

Technical Field

[0001] This application relates to the fields of green energy and chemical synthesis technology, and in particular to a green ammonia production system based on multi-energy synergistic hydrogen production coupled with energy island. Background Technology

[0002] Against the backdrop of escalating global climate change, achieving carbon peaking and carbon neutrality has become a core strategy for accelerating my country's low-carbon energy transition. A profound adjustment of the energy structure is key to achieving this goal, and building a new power system based on new energy sources is an inevitable trend. Deep-sea areas possess abundant renewable energy resources, boasting more stable and higher-quality wind, solar, and wave energy resources than nearshore and onshore areas. Offshore energy islands are comprehensive energy platforms integrating energy collection, conversion, storage, and transmission, serving as crucial carriers for efficient utilization of deep-sea energy and ensuring offshore energy supply. According to the latest data from the National Energy Administration, as of the end of September 2025, the cumulative installed capacity of wind power generation nationwide reached 580 million kilowatts, a year-on-year increase of 21.3%, of which the cumulative grid-connected capacity of offshore wind power reached 44.61 million kilowatts. Offshore wind power is developing from nearshore to deep-sea and from small-scale to large-scale operations. While offshore wind energy resources are abundant and have enormous development potential, with increasing distance from shore, traditional submarine cable transmission faces challenges such as high energy loss and high transmission costs. By utilizing the wind-solar-wave multi-energy complementary power generation technology of offshore energy islands, the fluctuating renewable energy can be converted into electricity, providing stable power support for the electrolysis of water to produce green hydrogen. This can effectively solve the problems of difficulty in grid connection and consumption of offshore power and high cost of long-distance power transmission, and realize the "on-site conversion and on-site consumption" of marine energy.

[0003] However, as a high-energy-density secondary energy source, hydrogen's inherent physical properties present significant limitations for its storage and transportation in the deep-sea energy island environment. Hydrogen has an extremely low volumetric energy density, making large-scale storage difficult at ambient temperature and pressure. Traditional high-pressure hydrogen storage methods face challenges such as stringent sealing requirements, poor safety, and high storage and transportation costs. To address this issue, further converting the produced green hydrogen into green ammonia with nitrogen obtained from an air separation unit presents an ideal method for offshore energy storage and utilization. Ammonia, as an excellent energy carrier, boasts a high hydrogen content (up to 17.8%) and can be liquefied and stored at ambient temperature and pressure. Its mild storage and transportation conditions, mature safety technology, and zero carbon dioxide emissions allow for a zero-carbon process, making it an ideal carrier for renewable energy storage and utilization on energy islands.

[0004] Currently, although renewable energy-to-green ammonia technology has entered the stage of industrial demonstration at the 10,000-ton level, existing green ammonia production processes still have significant shortcomings under the specific circumstances of energy islands: On the one hand, offshore new energy exhibits more significant volatility, randomness, and intermittency than on land. Changes in offshore wind speed, alternation of sunlight intensity, and fluctuations in wave energy cause frequent fluctuations in the hydrogen flow rate produced by the electrolysis hydrogen production system. Traditional ammonia synthesis systems are mostly designed based on constant loads, which places higher demands on the dynamic response capability and continuous stable operation of offshore ammonia synthesis processes; on the other hand, due to the extremely special and harsh construction environment of offshore energy islands, the space on the energy island platform is limited, which requires the system to achieve a high degree of integration of "wind, solar, and wave energy harvesting—seawater desalination—water electrolysis for hydrogen production—air separation for nitrogen production—ammonia synthesis—storage and transportation". Existing technologies are mostly decentralized unit designs, resulting in large equipment size, complex piping connections, and numerous auxiliary systems, which cannot meet the requirements of compact ammonia production units for deep-sea energy islands. On the other hand, although existing processes are developing towards lower temperatures and pressures to reduce energy consumption, they generally rely on using circulating cooling water to recover high-grade waste heat, which is then fed into the boiler system as by-product steam. This approach is not only incompatible with the isolated and compact nature of the units on energy islands, but also fails to fully utilize the temperature differences within the system streams to achieve cascaded heat utilization, requiring a significant amount of additional electricity to drive the condensing unit, leading to low overall system energy efficiency.

[0005] Based on the above problems, given the limited space resources of deep-sea energy islands and the strong random fluctuations in power supply, there is an urgent need to develop a compact green ammonia synthesis system that can break away from the dependence on traditional large-scale circulating water and boiler systems and achieve deep thermal integration throughout the entire process. Summary of the Invention

[0006] This application provides a green ammonia production system based on multi-energy synergistic hydrogen production coupled with energy island. Its technical purpose is to achieve efficient synthesis of green ammonia in the energy island scenario, adapt to the working conditions of compact energy island space and limited cooling medium, improve the system's energy utilization efficiency, and obtain high-purity liquid ammonia products.

[0007] The above-mentioned technical objectives of this application are achieved through the following technical solutions: A multi-energy synergistic hydrogen production coupled with green ammonia production system based on an energy island includes: Offshore energy generation systems: This system is used to convert fluctuating marine energy into stable electrical energy. The marine energy power generation system obtains renewable energy through the synergistic effect of offshore wind power, offshore photovoltaic power, and wave energy generation. The green electricity generated by the marine energy power generation system can directly power core equipment such as compressors and heaters in seawater desalination plants, proton exchange membrane electrolyzers, air liquefaction separation plants, and green ammonia production systems. It can also be used for energy storage in liquid compressed air, supplemented by a certain capacity of electrochemical energy storage, to meet the system's emergency power and black start needs, increase the rotational inertia of the power system, and achieve combined supply of cold, heat, and electricity, while simultaneously meeting air separation requirements.

[0008] Hydrogen and nitrogen feedstock preparation system: This system receives stable green electricity from offshore power generation systems and produces hydrogen and nitrogen through seawater desalination, electrolysis, and air separation, providing high-purity hydrogen and nitrogen feedstocks for subsequent ammonia synthesis. The green hydrogen and nitrogen produced by the hydrogen and nitrogen feedstock preparation system can be directly mixed at a molar ratio of 3:1 to form fresh feedstock gas and transported to the ammonia synthesis system, or they can be temporarily stored separately in hydrogen and nitrogen storage tanks.

[0009] Cascade heat exchange system: This system is used for preheating the feed gas, cooling the reaction products, and utilizing waste heat from the hydrogen and nitrogen feedstock preparation system. The cascade heat exchange system constructs a three-stage cascade heat exchange network: "reaction products-feed gas, reaction products-seawater, and reaction products-circulating gas." This achieves efficient waste heat recovery and cascaded energy utilization within the system, reducing energy consumption for heating the feed gas and minimizing external cold source consumption for cooling the reaction products. Furthermore, by utilizing seawater as a cooling medium, it adapts to the marine resource characteristics of the energy island, effectively improving the system's overall energy utilization efficiency.

[0010] Ammonia synthesis and separation system: This product is used for the catalytic synthesis and purification of ammonia. In the ammonia synthesis and separation system, green hydrogen produced by a PEM electrolyzer and nitrogen from an air separation unit are introduced into the reaction tower at a molar ratio of 3:1. Ammonia is synthesized by catalytic reaction using an iron-based catalyst under reaction conditions of 15 MPa and 400℃. The ammonia is then condensed, separated, and purified through a stepped heat exchange system to obtain high-purity liquid ammonia. The liquid ammonia product can be directly supplied to offshore energy island maintenance vessels as fuel, or transported overseas via liquid ammonia transport ships.

[0011] Recirculating gas treatment system: It is used to preheat and compress unreacted hydrogen-nitrogen mixtures and reflux them into the ammonia synthesis system, thereby improving raw material utilization and system energy efficiency.

[0012] Furthermore, the offshore energy power generation system includes wind power generation modules, photovoltaic power generation modules, and wave energy generation modules: The wind power generation module, photovoltaic power generation module, and wave energy generation module are used to convert wind energy, solar energy, and wave energy into electrical energy.

[0013] Furthermore, the hydrogen and nitrogen feedstock preparation system includes a seawater desalination module, a water electrolysis hydrogen production module, and a nitrogen production module: The seawater desalination module includes a reverse osmosis seawater desalination unit, which uses a high-pressure pump to drive seawater through a semi-permeable membrane to separate salt, providing raw materials for electrolytic hydrogen production. In the electrolytic hydrogen production module, stable green electricity output from the offshore energy power generation system is connected to a proton exchange membrane water electrolysis unit to electrolyze the desalinated water into high-purity hydrogen and oxygen. In the air separation nitrogen production module, nitrogen is captured from the sea air through an air liquefaction separation unit, and after compression, purification, and cryogenic liquefaction distillation, high-purity nitrogen with a purity of not less than 99.99% is obtained. The green hydrogen and nitrogen produced by this hydrogen and nitrogen raw material preparation system can be directly mixed at a molar ratio of 3:1 to form fresh feed gas and transported to the ammonia synthesis system.

[0014] The water electrolysis hydrogen production module includes a proton exchange membrane water electrolysis hydrogen production device, which connects the stable green electricity output from the marine energy power generation system to the proton exchange membrane water electrolysis device to electrolyze the desalinated seawater into high-purity hydrogen and oxygen, and then transports the hydrogen to the ammonia synthesis and separation system. The nitrogen generation module includes an air liquefaction and separation device for separating high-purity nitrogen and oxygen from the air, wherein the nitrogen is supplied to the ammonia synthesis and separation system.

[0015] Furthermore, the cascade heat exchange system includes three stages of heat exchange devices, a heating device, and a condensing device: The first-stage heat exchanger device uses high-temperature reaction products to directly preheat the mixed gas, achieving high-grade waste heat recovery. The heating device uses a heater powered by green electricity provided by an offshore energy power generation system to heat the raw material gas to the temperature required for the reaction. The second-stage heat exchanger device introduces seawater from the vicinity of the energy island as a cooling medium to further exchange heat with the cooled reaction products, while simultaneously recovering waste heat from the seawater. The third-stage heat exchanger device uses the low-temperature waste heat of the reaction products to preheat the circulating gas. The condensation device condenses the reaction products through a condenser, preparing for ammonia separation.

[0016] Furthermore, the ammonia synthesis and separation system includes an ammonia synthesis module and an ammonia separation module: The ammonia synthesis module includes a multi-stage compressor, a mixer, and an ammonia synthesis reaction tower. It is used to pressurize the premixed feed gas to the process requirement pressure, and after pressurization, it is mixed with the circulating gas in the mixer. The mixer is then introduced into the ammonia synthesis reaction tower to catalyze the reaction to generate ammonia-containing reaction products. The ammonia separation module includes an ammonia separation device and a flash evaporation device, which are used to separate and purify the condensed reaction products into gas and liquid, to obtain a high-purity liquid ammonia product with a mass fraction of 99.5%. The liquid ammonia product can be directly supplied to the offshore energy island maintenance vessel as a power fuel, and can also be transported outwards by liquid ammonia transport ships.

[0017] Furthermore, the recirculating gas treatment system includes a purge gas discharge device and a recirculating compression device: The purge gas discharge device is used to discharge part of the purge gas from the gaseous products of the ammonia separator to avoid the accumulation of inert gas in the system. A circulating compression device is used to compress and increase the pressure of the circulating gas to match the pressure of the raw material gas.

[0018] The beneficial effects of this application are as follows: This invention adopts a multi-energy synergistic hydrogen production coupled with green ammonia production system based on an energy island. It relies on renewable energy sources such as wind, solar, and solar power to provide green electricity. It produces hydrogen through proton exchange membrane electrolysis of water and nitrogen through air liquefaction separation, providing high-purity hydrogen and nitrogen raw materials for ammonia synthesis, thus achieving zero-carbon energy supply for the entire green ammonia preparation process. The system architecture is based on an offshore energy island platform, which is adapted to the characteristics of compact space and fluctuating energy supply on offshore platforms. It constructs a three-stage heat exchange network using seawater as a cooling medium to achieve efficient recovery of waste heat from reaction products, reduce cooling energy consumption in the ammonia synthesis process, and solve the problems of unsuitability and high energy consumption in traditional ammonia synthesis processes. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the green ammonia synthesis system described in this invention.

[0020] In the diagram: 100. Power generation unit, 101. Seawater desalination unit, 102. Air liquefaction and separation unit, 103. Proton exchange membrane electrolyzer, 104. Hydrogen storage tank, 105. Multistage compressor, 106. Mixer, 107. First-stage heat exchanger, 108. Heater, 109. Ammonia synthesis reaction tower, 110. Second-stage heat exchanger, 111. Third-stage heat exchanger, 112. Ammonia condenser, 113. Ammonia separator, 114. Flash tank, 115. Stream separator, 116. Circulating compressor, 117. Seawater, 118. Liquid ammonia transport ship, 119. Maintenance vessel. Detailed Implementation

[0021] The technical solution of this application will now be described in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0022] In one embodiment of the present invention, a multi-energy synergistic hydrogen production coupled with green ammonia production system based on an energy island is provided. This system is used on an offshore energy island platform to obtain high-purity green ammonia by relying on wind, solar and wave green electricity through electrolysis to produce hydrogen, air separation to produce nitrogen, followed by compression, mixing, heat exchange, catalytic synthesis, separation and purification and recycling, so as to achieve efficient conversion and transmission of offshore renewable energy.

[0023] As shown in Figure 1, the system in this embodiment includes an offshore energy power generation system, a hydrogen and nitrogen feedstock preparation system, a cascade heat exchange system, an ammonia synthesis and separation system, and a circulating gas treatment system.

[0024] The marine energy power generation system is a power generation device 100 that includes wind power generation, photovoltaic power generation and wave power generation. The green electricity generated by the power generation device 100 directly supplies power to the seawater desalination device 101, the air liquefaction separation device 102, the proton exchange membrane electrolyzer 103, the multi-stage compressor 105 and the heater 108. When there is excess electricity, it can store energy through liquid compressed air, supplemented by a certain capacity of electrochemical energy storage, to meet the needs of emergency power supply and black start of the system, increase the rotational inertia of the power system, and realize the combined supply of cold, heat and electricity, while meeting the requirements of air separation. The hydrogen and nitrogen feedstock preparation system includes a seawater desalination module, an electrolytic hydrogen production module, and an air separation nitrogen production module. It is used to receive stable green electricity output from the offshore energy power generation system and provide high-purity hydrogen and nitrogen feedstocks for subsequent ammonia synthesis. Specifically, in the nitrogen feedstock preparation system, The seawater desalination module includes a high-pressure pump and a reverse osmosis seawater desalination device 101. The high-pressure pump drives seawater through a semi-permeable membrane to separate salts, providing standard-compliant water resources for the water electrolysis hydrogen production module. The electrolytic hydrogen production module includes a proton exchange membrane electrolyzer 103 and a hydrogen storage tank 104. The stable green electricity output from the marine energy power generation system is connected to the proton exchange membrane water electrolysis device 103 to electrolyze the desalinated seawater into high-purity hydrogen and oxygen. The hydrogen produced at the cathode undergoes separation, deoxygenation, and compression processes to produce green hydrogen with a purity of not less than 99.99%, which is stored in the hydrogen storage tank 104 for subsequent power generation or for ammonia and alcohol production. The oxygen produced at the anode is dried and purified and can be collected for comprehensive utilization. The air separation nitrogen generation module includes an air liquefaction separation device 102, which captures nitrogen from the sea air, and after compression, purification, and low-temperature liquefaction distillation, obtains high-purity nitrogen with a purity of not less than 99.99%. The produced green hydrogen and nitrogen are directly mixed at a molar ratio of 3:1 as fresh raw material gas and transported to the ammonia synthesis and separation system.

[0025] The cascade heat exchange includes a first-stage heat exchanger 107, a second-stage heat exchanger 110, a third-stage heat exchanger 111, a heater 108, and an ammonia condenser 112, forming a three-stage cascade heat exchange network of "reaction product-raw material gas, reaction product-seawater, and reaction product-circulating gas".

[0026] Specifically, in the aforementioned cascade heat exchange system, The first stage heat exchanger 107 receives the raw material gas output from the mixer 106 and passes it through the tube side. The 400°C high-temperature reaction product from the ammonia synthesis reaction tower 109 is passed through the shell side of the first stage heat exchanger 107. The high-temperature reaction product and the raw material gas exchange heat in a countercurrent manner, preheating the raw material gas to 356°C and cooling the reaction product to 97°C. The heater 108 is driven by green electricity provided by the power generation device 100, which further heats the raw gas, which has been preheated by the first-stage heat exchanger 107, to the temperature required for the ammonia synthesis reaction, 400°C. The second-stage heat exchanger 110 uses seawater 117 as the cooling medium. The reaction products after heat exchange in the first-stage heat exchanger 107 are introduced into the tube side of the second-stage heat exchanger 110, and seawater 117 is introduced into the shell side. Through heat exchange, the reaction products are further cooled to 40°C, and the seawater is heated to 45°C. The heated seawater is then transported through pipelines to the pretreatment unit of the seawater desalination device 101 or the island's domestic heating system to realize the secondary utilization of waste heat. The third-stage heat exchanger 111 is used to realize the heat exchange between the reaction products and the circulating gas. The shell side of the third-stage heat exchanger 111 is fed with the reaction products cooled by the second-stage heat exchanger 110, and the tube side is fed with the circulating gas discharged from the ammonia separator 113. Through heat exchange, the temperature of the reaction products is reduced to 34°C and the temperature of the circulating gas is increased to 35°C. This can reduce the energy consumption of subsequent compression and preheating of the circulating gas, and at the same time further reduce the temperature of the reaction products, creating conditions for subsequent condensation and separation. The reaction products are condensed to 10°C in an ammonia condenser 112 after passing through a three-stage heat exchanger, in preparation for ammonia separation and purification.

[0027] The ammonia synthesis and separation system includes a multi-stage compressor 105, a mixer 106, an ammonia synthesis reaction tower 109, an ammonia separation tank 113, and a flash tank 114, and is used for the catalytic synthesis and separation purification of ammonia.

[0028] Specifically, in the ammonia synthesis and separation system, The multi-stage compressor 105 and mixer 106 are mainly used to pressurize and heat the fresh hydrogen and nitrogen feed gas and mix it with the circulating gas. The green hydrogen produced by the proton exchange membrane electrolyzer 103 and the nitrogen provided by the air liquefaction separation device 102 are fed into the multi-stage compressor 105 at a molar ratio of 3:1 and compressed to 15 MPa through two stages. The pressurized fresh gas is then transported to the mixer 106 through pipelines and fully mixed with the circulating gas returned from the circulating gas treatment module. Then it is directly transported to the first stage heat exchanger 107 of the stepped heat exchange network for preheating. The ammonia synthesis reaction tower 109 uses an iron-based catalyst, with the reaction pressure controlled at 15 MPa and the reaction temperature maintained at 400℃. The mixed feed gas, heated by heater 108, is introduced into the ammonia synthesis reaction tower 109 and flows downward along the catalyst bed. The hydrogen-nitrogen mixture undergoes a synthesis reaction under the action of the catalyst. ; The ammonia separator 113 and flash tank 114 are used to separate and purify ammonia. The gas-liquid mixture after being condensed by the ammonia condenser 112 is introduced into the middle of the ammonia separator 113. A baffle assembly is installed inside the pipe to prolong the gas-liquid contact time. The liquefied ammonia component settles to the bottom of the tank under gravity, while the unliquefied hydrogen-nitrogen mixture is discharged from the top. The liquid ammonia discharged from the bottom of the ammonia separator 113 is introduced into the flash tank 114 for purification. The ammonia is separated from trace impurities by a sudden pressure drop. The impurity gas escapes from the top of the flash tank 114 and is combined with the purge gas for treatment. The liquid ammonia product is discharged from the bottom and sent to the green ammonia storage tank on the energy island by the product transfer pump. The obtained liquid ammonia product can be directly supplied to the offshore energy island maintenance vessel 119 as power fuel, and can also be transported out via the liquid ammonia transport vessel 118.

[0029] The circulating gas treatment system includes a stream distributor 115 and a circulating compressor 116, which are used to improve the utilization rate of raw materials and the energy efficiency of the system.

[0030] Specifically, in the recirculated gas treatment system, The stream separator 115 is installed on the gas phase outlet pipeline at the top of the ammonia separation unit 113. Part of the unliquefied hydrogen-nitrogen mixture is discharged as purge gas to remove inert impurities accumulated in the system, and part of it is transported as circulating gas to the third-stage heat exchanger 111 for preheating treatment. The circulating compressor 116 compresses the circulating gas, which has been preheated by the third-stage heat exchanger 111, to 15 MPa, matching the pressure of the fresh gas after it has been pressurized. The gas is then sent to the mixer 106 to mix with the fresh gas, thereby realizing the recycling of unreacted raw material gas.

[0031] The technical means disclosed in this invention are not limited to those disclosed in the above embodiments, but also include technical solutions composed of any combination of the above technical features. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention.

Claims

1. A multi-energy synergistic hydrogen production coupled with green ammonia production system based on an energy island, characterized in that, This includes offshore energy power generation systems, hydrogen and nitrogen feedstock preparation systems, cascade heat exchange systems, ammonia synthesis and separation systems, and recirculating gas treatment systems; The offshore energy power generation system is a power generation device that includes wind power generation, photovoltaic power generation and wave power generation. The green electricity generated by the power generation device directly supplies power to the seawater desalination device, air liquefaction separation device, proton exchange membrane electrolyzer, multi-stage compressor and heater. When there is excess electricity, it can store energy through liquid compressed air, supplemented by a certain capacity of electrochemical energy storage, to meet the system's emergency power supply and black start requirements, increase the rotational inertia of the power system, and realize the combined supply of cold, heat and electricity, while meeting the air separation requirements. The hydrogen and nitrogen feedstock preparation system includes a seawater desalination module, an electrolytic hydrogen production module, and an air separation nitrogen production module. It is used to receive stable green electricity output from the offshore energy power generation system and provide high-purity hydrogen and nitrogen feedstocks for subsequent ammonia synthesis. The cascade heat exchange includes a first-stage heat exchanger, a second-stage heat exchanger, a third-stage heat exchanger, a heater, and an ammonia condenser, constructing a three-stage cascade heat exchange network of "reaction products-raw material gas, reaction products-seawater, and reaction products-circulating gas". The ammonia synthesis and separation system includes a multi-stage compressor, a mixer, an ammonia synthesis reaction tower, an ammonia separation tank, and a flash tank, and is used for the catalytic synthesis and separation and purification of ammonia. The circulating gas treatment system includes a stream distributor and a circulating compressor, which are used to improve raw material utilization and system energy efficiency.

2. The green ammonia production system based on multi-energy synergistic hydrogen production coupled with energy island as described in claim 1, characterized in that, In the nitrogen raw material preparation system The seawater desalination module includes a high-pressure pump and a reverse osmosis seawater desalination device. The high-pressure pump drives seawater through a semi-permeable membrane to separate salts, providing standard-compliant water resources for the water electrolysis hydrogen production module. The electrolytic hydrogen production module includes a proton exchange membrane electrolyzer and a hydrogen storage tank. Stable green electricity output from the marine energy power generation system is connected to the proton exchange membrane water electrolysis device to electrolyze desalinated seawater into high-purity hydrogen and oxygen. The hydrogen produced at the cathode undergoes separation, deoxygenation, and compression processes to produce green hydrogen with a purity of not less than 99.99%, which is stored in the hydrogen storage tank for subsequent power generation or for ammonia and alcohol production. The oxygen produced at the anode is dried and purified, and can be collected for comprehensive utilization. The air separation nitrogen generation module includes an air liquefaction separation device, which captures nitrogen from the sea air, and after compression, purification, and low-temperature liquefaction distillation, obtains high-purity nitrogen with a purity of not less than 99.99%. The produced green hydrogen and nitrogen are directly mixed at a molar ratio of 3:1 as fresh raw material gas and transported to the ammonia synthesis and separation system.

3. The green ammonia production system based on multi-energy synergistic hydrogen production coupled with energy island as described in claim 1, characterized in that, In the cascade heat exchange system In the first-stage heat exchanger, the raw material gas output from the mixer is fed into the tube side of the first-stage heat exchanger, and the 400°C high-temperature reaction product from the ammonia synthesis reaction tower is fed into the shell side of the first-stage heat exchanger. The high-temperature reaction product and the raw material gas exchange heat countercurrently, preheating the raw material gas to 356°C and cooling the reaction product to 97°C. The heater is driven by green electricity provided by the power generation unit, which further heats the raw gas, which has been preheated by the first-stage heat exchanger, to the temperature required for the ammonia synthesis reaction, 400°C. The second-stage heat exchanger uses seawater as the cooling medium. The reaction products after heat exchange in the first-stage heat exchanger are introduced into the tube side of the second-stage heat exchanger, and seawater is introduced into the shell side. Through heat exchange, the reaction products are further cooled to 40°C, and the seawater is heated to 45°C. The heated seawater is then transported through pipelines to the pretreatment unit of the seawater desalination device or the island's domestic heating system to realize the secondary utilization of waste heat. The third-stage heat exchanger is used to realize the heat exchange between the reaction products and the circulating gas. The shell side of the third-stage heat exchanger is fed with the reaction products cooled by the second-stage heat exchanger, and the tube side is fed with the circulating gas discharged from the ammonia separator. Through heat exchange, the temperature of the reaction products is reduced to 34°C and the temperature of the circulating gas is increased to 35°C. This can reduce the energy consumption of subsequent compression and preheating of the circulating gas, and at the same time further reduce the temperature of the reaction products, creating conditions for subsequent condensation and separation. The reaction products are condensed to 10°C through a three-stage heat exchanger and then through an ammonia condenser to prepare for ammonia separation and purification.

4. The green ammonia production system based on multi-energy synergistic hydrogen production coupled with energy island as described in claim 1, characterized in that, In the ammonia synthesis and separation system The multi-stage compressor and mixer are mainly used to increase the pressure and temperature of fresh hydrogen and nitrogen feed gas and mix it with the circulating gas. The green hydrogen produced by the proton exchange membrane electrolyzer and the nitrogen provided by the air liquefaction separation device are fed into the multi-stage compressor at a molar ratio of 3:1 and compressed to 15 MPa through two stages. The pressurized fresh gas is then transported to the mixer through pipelines and fully mixed with the circulating gas returned from the circulating gas treatment module. It is then directly transported to the first stage heat exchanger of the stepped heat exchange network for preheating. The ammonia synthesis reaction tower uses an iron-based catalyst, with the reaction pressure controlled at 15 MPa and the reaction temperature maintained at 400℃. The mixed feed gas, heated by a heater, is introduced into the ammonia synthesis reaction tower and flows downwards along the catalyst bed. The hydrogen-nitrogen mixture undergoes a synthesis reaction under the action of the catalyst. ; The ammonia separator and flash tank are used to separate and purify ammonia. The gas-liquid mixture after being condensed by the ammonia condenser is introduced from the middle of the ammonia separator. A baffle assembly is installed inside the tube to prolong the gas-liquid contact time. The liquefied ammonia component settles to the bottom of the tank under the action of gravity, and the unliquefied hydrogen-nitrogen mixture is discharged from the top. Liquid ammonia discharged from the bottom of the ammonia separator is fed into a flash tank for purification. The ammonia is separated from trace impurities by a sudden pressure drop. The impurity gas escapes from the top of the flash tank and is combined with the purge gas for further treatment. The liquid ammonia product is discharged from the bottom and pumped to the green ammonia storage tank on the energy island for storage.

5. The green ammonia production system based on multi-energy synergistic hydrogen production coupled with energy island as described in claim 1, characterized in that, In the recirculating gas treatment system The stream separator is installed on the gas phase outlet pipeline at the top of the ammonia separation unit. It discharges part of the unliquefied hydrogen-nitrogen mixture as purge gas to remove inert impurities accumulated in the system, and sends part of it as circulating gas to the third-stage heat exchanger for preheating. The circulating compressor compresses the circulating gas, which has been preheated by the third-stage heat exchanger, to 15 MPa, matching the pressure of the fresh gas after it has been pressurized. The gas is then sent to the mixer to mix with the fresh gas, thus realizing the recycling of unreacted raw material gas.

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