Seawater electrolyzed water hydrogen production and energy cascade storage and utilization system

Abstract

The invention discloses a seawater electrolyzed water hydrogen production and energy cascade storage and utilization system which comprises an offshore steel frame platform. A seawater pump, a seawater purification device, a purified water storage tank, a water pump, an alkaline water electrolytic bath, a hydrogen purification and impurity removal device, a hydrogen storage tank, a hydrogen flow controller, a pyrolysis device, a gas purification and impurity removal device, a gaseous carbon dioxide storage tank, a carbon dioxide flow controller and a compressed carbon dioxide energy storage and heat exchange system are arranged on the offshore steel frame platform; the liquid carbon dioxide storage tank is arranged in the seabed below the offshore steel frame platform and connected with the compressed carbon dioxide energy storage and heat exchange system. Offshore wind power, photovoltaic energy and temperature difference energy are utilized for power generation, biomass is adopted for preparing seawater desalination wood and generating carbon dioxide, seawater is electrolyzed into hydrogen, the hydrogen and the carbon dioxide are synthesized and converted into green liquid fuel, and oxygen is used for supplying oxygen to an underwater system.

Description

Technical Field

[0001] The present invention relates to the technical field of comprehensive utilization of marine energy, and in particular to a system for producing hydrogen by electrolyzing seawater and storing and utilizing energy in stages. Background Art

[0002] In recent years, the comprehensive utilization of marine energy has become an important direction of the national marine strategy and an important energy layout. The scenarios for the production and utilization of energy such as offshore wind power and offshore photovoltaics are gradually increasing. However, due to the volatility, randomness and intermittency of offshore new energy, offshore wind power transmission and supply and demand have become problems that need to be solved. Offshore wind power, photovoltaics and other energy sources are coupled with water electrolysis to produce high-purity hydrogen, and then converted into ammonia, alcohol, oil and other fuels for cross-regional and time storage and transportation. It is a sustainable solution that meets national strategic needs.

[0003] Chinese patent CN117869186A discloses an offshore integrated energy system for compressed carbon dioxide energy storage and synthesis of dimethyl ether. Chinese patent CN117926277A discloses a system and method for producing water electrolysis electrodes using coastal garbage and producing methanol as a by-product. Both patents are typical ways of utilizing marine energy, but they do not involve the rational allocation of energy and the cascade utilization of energy. How to achieve offshore energy hydrogen production and storage and transportation, and improve the utilization rate of wind, light, and ocean energy, and realize the cascade utilization of energy, is an important means to solve the problems of offshore energy waste, storage and transportation, and cost. Therefore, it is necessary to provide a seawater electrolysis water hydrogen production and energy cascade storage and utilization system to solve the above problems. Summary of the invention

[0004] In order to solve the above technical problems, the present invention designs a seawater electrolysis water hydrogen production and energy cascade storage and utilization system, which uses offshore wind power, photovoltaic, and temperature difference energy to generate electricity, uses biomass to prepare seawater desalination wood and produce carbon dioxide, so that seawater is electrolyzed into hydrogen and synthesized with carbon dioxide to convert into green liquid fuel, and oxygen is used to supply oxygen to the underwater system.

[0005] The present invention adopts the following technical solution: A seawater electrolysis hydrogen production and energy cascade storage and utilization system, comprising an offshore steel frame platform, on which are arranged a seawater pump, a seawater purification device, a purified water storage tank, a water pump, an alkaline water electrolyzer, a hydrogen purification and impurity removal device, a hydrogen storage tank and a hydrogen flow controller, a pyrolysis device, a gas purification and impurity removal device, a gaseous carbon dioxide storage tank, a carbon dioxide flow controller, a compressed carbon dioxide energy storage and heat exchange system, a synthesis purification device, and a fuel storage tank; the seawater pump, the seawater purification device, the purified water storage tank, the water pump, the alkaline water electrolyzer, the hydrogen purification and impurity removal device, the hydrogen storage tank and the hydrogen flow controller are connected in sequence; the pyrolysis device, the gas purification and impurity removal device, the gaseous carbon dioxide storage tank, the carbon dioxide flow controller and the compressed carbon dioxide energy storage and heat exchange system are connected in sequence; the hydrogen flow controller and the carbon dioxide flow controller are connected to the synthesis purification device, the synthesis purification device is connected to the fuel storage tank, and the fuel in the fuel storage tank is transported by a transport ship and used for fuel supply of the transport ship; A liquid carbon dioxide storage tank is installed on the seabed under the offshore steel frame platform and is connected to the compressed carbon dioxide energy storage and heat exchange system.

[0006] Preferably, marine trees are planted in the seawater under the offshore steel frame platform for pyrolysis in the pyrolysis device. The pyrolysis device adopts a self-developed pyrolysis gasifier (CN117106489A) with a pyrolysis temperature of 800-850°C.

[0007] Preferably, the seawater electrolysis hydrogen production and energy cascade storage and utilization system also includes a wind generator and photovoltaic panels, a temperature difference energy power generation device, a DC converter, a receiving-end converter and a power grid. The wind generator and photovoltaic panels and the temperature difference energy power generation device are respectively connected to the DC converter, the DC converter is connected to the power grid through the receiving-end converter, and the full-platform power supply is connected to the DC converter.

[0008] Preferably, an oxygen storage tank, an oxygen flow controller and an underwater monitoring and viewing platform are also provided in the seawater under the offshore steel frame platform. The oxygen storage tank is connected to the alkaline water electrolyzer through a pipeline, and the oxygen flow controller is connected to the oxygen storage tank to control the supply of oxygen to the underwater monitoring and viewing platform and the marine trees. The underwater monitoring and viewing platform is the hub of the entire system, and the operation strategy of the entire system is adjusted according to the operation requirements, including the operation parameters of each module and the material input and output of each device. The marine trees are mainly planted offshore trees, including mangroves, white candle fruits and sea olives.

[0009] Preferably, the compressed carbon dioxide energy storage and heat exchange system includes an expander, a heat exchanger, a hot salt tank 1, a cold salt tank 1, a hot salt tank 2, a cold salt tank 2, a hot water tank, a cold water tank, a condenser, an evaporator and a compressor.

[0010] Preferably, the seawater purification device comprises a purification table base, a purification table fixture and a purification table support plate, a wedge-shaped flow channel is hung upside down on the purification table support plate, the bottom end of the wedge-shaped flow channel is connected to the purified water outlet channel, an evaporation storage tank is arranged on the purification table base, the evaporation storage tank is connected to the seawater inlet channel through a seawater primary filter, a seawater desalination wood is arranged above the evaporation storage tank, and the wedge-shaped flow channel corresponds to the top of the seawater desalination wood.

[0011] Preferably, the hydrogen purification and impurity removal device and the gas purification and impurity removal device respectively include molecular sieve physical adsorption and membrane separation subsequent processes.

[0012] Preferably, the alkaline electrolytic cell has an operating temperature of 55-95°C and a current density of 0.2-0.5 A / cm 2 , the stack energy consumption is 3.8~4.0 kWh / m 3 .

[0013] Preferably, in the compressed carbon dioxide energy storage and heat exchange system, the two molten salts in the hot salt tank one, the cold salt tank one and the hot salt tank two, the cold salt tank two are NaCl-Na2SO4-NaF and KNO3-NaNO2-NaNO3 respectively.

[0014] Preferably, a sea level stabilizing device and fixed piles are provided below the offshore steel frame platform.

[0015] Preferably, the liquid fuel is synthesized by a thermochemical method and impurities are removed. The molar ratio of hydrogen to carbon dioxide is 3:1. Under the control of the underwater monitoring and viewing platform, the synthesis ratio of the two products is reasonably allocated according to the purpose and demand. While transporting the fuel, the transport ship also uses it as a power source.

[0016] The beneficial effects of the present invention are as follows: the load regulation process of the present invention is smoother than the existing wind-solar hydrogen storage system; when the power load demand is higher than the power generation load, instructions are given through the underwater monitoring and viewing platform, the alkaline water electrolyzer and the liquid fuel synthesis and purification device operate at low load, and the compressed carbon dioxide energy storage and heat exchange system starts the energy release stage to supplement the insufficient load; and when the power load demand is lower than the power generation load, the compressed carbon dioxide energy storage and heat exchange system starts the energy storage stage to store excess electricity, synthesize liquid fuel and store and transport it.

[0017] The present invention adopts the mode of photovoltaic panel power generation and photothermal seawater purification, and couples the two light utilization modes of photovoltaic and photothermal, thereby improving the system density and enhancing the light energy utilization rate.

[0018] The hydrogen production process of the present invention adopts the independently designed nickel foam / Co3O4@NiFePc catalyst to reduce the reaction overpotential and improve the performance of the alkaline electrolyzer. The new catalyst is used to synthesize methanol and dimethyl ether, which improves the Faraday efficiency and enhances the stability. Under the control of the underwater monitoring and viewing platform, the synthesis ratio of the two liquid fuels is reasonably allocated according to the purpose and demand, and the fuel synthesis is carried out in two different synthesis devices respectively, ensuring the normal operation of the system while outputting liquid fuel to the outside, making the synthesis more accurate.

[0019] The desalination process of the present invention adopts the desalination method of wood for seawater desalination, which significantly reduces the residence time of seawater compared to the single membrane desalination method and does not require deep membrane purification. The photothermal method of wood for seawater desalination does not require additional input and improves the water quality entering the alkaline electrolyzer, thereby saving the cost of purification membranes and increasing the system life.

[0020] The present invention realizes the comprehensive utilization of wood biomass. The carbon dioxide after pyrolysis is used for subsequent energy storage and synthesis, and the coke of wood biomass is used as seawater desalination wood, thus realizing the comprehensive utilization of biomass.

[0021] The present invention realizes the comprehensive utilization of carbon dioxide and oxygen. A part of the carbon dioxide produced by pyrolysis is sent to the compressed carbon dioxide energy storage and heat exchange system to participate in the compressed carbon dioxide energy storage and heat exchange. Another part of the carbon dioxide participates in the synthesis of liquid fuel. The synthesized carbon dioxide comes from biomass and meets the certification standards of green methanol and green dimethyl ether. In addition, the oxygen produced by electrolysis of water is also effectively utilized. Under the control of the oxygen flow controller, oxygen is supplied to the underwater monitoring and viewing platform, and the excess oxygen can be used to supply oxygen to the planted marine tree system.

[0022] Compared with the existing wind and solar energy storage system, the present invention adds a temperature difference energy generation device, realizes the cascade utilization of energy, reduces the temperature difference between the various parts of the system, and reduces the risk of reducing the life of the device due to thermal stress. The heat source is partially derived from molten salt, which realizes the effective utilization of low-grade energy. At the same time, the heat of thermochemical synthesis is also partially derived from molten salt, which improves the heat utilization effect.

[0023] The present invention realizes the multi-level utilization of products. Dimethyl ether is a liquid fuel that is easy to transport. As a working fluid of the organic Rankine cycle, dimethyl ether does not need to be added as a circulating working fluid. While transporting green methanol and dimethyl ether in the fuel storage tank, the transport ship also uses it as a power source. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural schematic diagram of an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of a seawater purification device according to an embodiment of the present invention; Figure 3This is a schematic diagram of the structure of a compressed carbon dioxide energy storage and heat exchange system according to an embodiment of the present invention; In the figure: 1-seawater pump, 2-seawater purification device, 3-purified water storage tank, 4-water pump, 5-alkaline water electrolyzer, 6-hydrogen purification and impurity removal device, 7-hydrogen storage tank, 8-hydrogen flow controller, 9-oxygen storage tank, 10-oxygen flow controller, 11-underwater monitoring and viewing platform, 12-marine trees, 13-pyrolysis device, 14-gas purification and impurity removal device, 15-gaseous carbon dioxide storage tank, 16-carbon dioxide flow controller, 17-compressed carbon dioxide energy storage and heat exchange system, 18-liquid carbon dioxide storage tank, 19-synthetic purification device, 20-fuel storage tank, 21-transport ship, 22-offshore steel frame platform, 23-sea level stabilization device, 24-fixed piles, 25-wind turbine With photovoltaic panels, 26-temperature difference energy power generation device, 27-DC converter, 28-full platform power supply, 29-receiving end converter, 30-grid; 201-seawater inlet channel, 202-seawater primary filter, 203-evaporation storage tank, 204-seawater desalination wood, 205-wedge-shaped flow channel, 206-purified water outlet channel, 207-purification table base, 208-purification table fixture, 209-purification table support plate; 101-expander, 102-heat exchanger, 103-hot salt tank one, 104-cold salt tank one, 105-hot salt tank two, 106-cold salt tank two, 107-hot water tank, 108-cold water tank, 109-condenser, 110-evaporator, 111-compressor. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is further described in detail below through specific embodiments and in conjunction with the accompanying drawings: Example: Figure 1 As shown, a seawater electrolysis hydrogen production and energy cascade storage and utilization system includes an offshore steel frame platform 22, on which are arranged a seawater pump 1, a seawater purification device 2, a purified water storage tank 3, a water pump 4, an alkaline water electrolyzer 5, a hydrogen purification and impurity removal device 6, a hydrogen storage tank 7 and a hydrogen flow controller 8, a pyrolysis device 13, a gas purification and impurity removal device 14, a gaseous carbon dioxide storage tank 15, a carbon dioxide flow controller 16, a compressed carbon dioxide energy storage and heat exchange system 17, a synthesis purification device 19, and a fuel storage tank 20; the seawater pump, the seawater purification device, the purified water storage tank, the water pump, the alkaline water electrolyzer, the hydrogen purification and impurity removal device, the hydrogen storage tank and the hydrogen flow controller are connected in sequence; the pyrolysis device, the gas purification and impurity removal device, the gaseous carbon dioxide storage tank, the carbon dioxide flow controller and the compressed carbon dioxide energy storage and heat exchange system are connected in sequence; the hydrogen flow controller and the carbon dioxide flow controller are connected to the synthesis purification device, the synthesis purification device is connected to the fuel storage tank, and the fuel in the fuel storage tank is transported by a transport ship 21 and used for fuel supply of the transport ship; A liquid carbon dioxide storage tank is installed on the seabed under the offshore steel frame platform and is connected to the compressed carbon dioxide energy storage and heat exchange system.

[0026] Marine trees 12 are planted in the seawater under the offshore steel frame platform for pyrolysis in the pyrolysis device.

[0027] The seawater electrolysis hydrogen production and energy cascade storage and utilization system also includes a wind turbine and photovoltaic panel 25, a temperature difference energy power generation device 26, a DC converter 27, a receiving-end converter 29 and a power grid 30. The wind turbine and photovoltaic panel and the temperature difference energy power generation device are respectively connected to the DC converter, and the DC converter is connected to the power grid through the receiving-end converter. The full-platform power supply 28 is connected to the DC converter.

[0028] An oxygen storage tank 9, an oxygen flow controller 10 and an underwater monitoring and viewing platform 11 are also provided in the seawater under the offshore steel frame platform. The oxygen storage tank is connected to the alkaline water electrolyzer through a pipeline, and the oxygen flow controller is connected to the oxygen storage tank to control the supply of oxygen to the underwater monitoring and viewing platform and the marine trees. A sea level stabilizing device 23 and a fixed pile 24 are provided under the offshore steel frame platform.

[0029] like Figure 2 As shown, the seawater purification device includes a purification table base 207, a purification table fixture 208 and a purification table support plate 209, a wedge-shaped flow channel 205 is hung upside down on the purification table support plate, and the bottom end of the wedge-shaped flow channel is connected to the purified water outlet channel 206. An evaporation storage tank 203 is arranged on the purification table base, and the evaporation storage tank is connected to the seawater inlet channel 201 through a seawater primary filter 202. A seawater desalination wood 204 is arranged above the evaporation storage tank, and the wedge-shaped flow channel corresponds to the top of the seawater desalination wood.

[0030] like Figure 3 As shown, the compressed carbon dioxide energy storage and heat exchange system includes an expander 101, a heat exchanger 102, a hot salt tank 1 103, a cold salt tank 1 104, a hot salt tank 2 105, a cold salt tank 2 106, a hot water tank 107, a cold water tank 108, a condenser 109, an evaporator 110 and a compressor 111.

[0031] When the present invention is used, the seawater pump 1 on the steel frame platform extracts seawater under the dispatch of the underwater monitoring platform and sends it to the seawater purification device 2 for purification. The purified seawater is stored in the purified water storage tank 3 and sent to the alkaline water electrolyzer 5 through the water pump 4 under the dispatch of the underwater monitoring platform. Under the action of the system wind and solar power generation and temperature difference power generation, it is electrolyzed into hydrogen and oxygen. Hydrogen enters the hydrogen purification and impurity removal device 6, then enters the hydrogen storage tank 7, and then participates in further reactions under the control of the hydrogen flow controller 8. In addition, oxygen enters the oxygen storage tank 9, and then oxygen is supplied to the underwater monitoring and viewing platform 11 under the control of the oxygen flow controller 10. Excess oxygen is used for oxygen supply of the planted marine trees 12 system. The trees are sent to the pyrolysis device 13 after pretreatment. The coke after pyrolysis is used as seawater desalination wood 204. The gas (mainly carbon dioxide) generated after pyrolysis is sent to the gas purification and impurity removal device 14. The impurity-removed gas is sent to the gaseous carbon dioxide storage tank 15. Subsequently, under the action of the carbon dioxide flow controller 16, a portion of the carbon dioxide is sent to the compressed carbon dioxide energy storage and heat exchange system 17 to participate in the compressed carbon dioxide energy storage and heat exchange. The liquid carbon dioxide is stored in the liquid carbon dioxide storage tank 18. Another portion of the carbon dioxide and the hydrogen after the hydrogen flow controller 8 undergo a synthesis reaction in the liquid fuel synthesis purification device 19 to synthesize methanol and dimethyl ether fuel and remove impurities, and are sent to the fuel storage tank 20 respectively. After that, it is transported to the corresponding location on the shore by a transport ship 21. The power supply source of the system is a wind turbine, a photovoltaic panel 25, and a temperature difference energy power generation device 26. The new energy power generation is divided into two paths after passing through the DC converter 27. One of them is used as factory power 28. The other path is input into the power grid 30 after passing through the receiving end converter 29.

[0032] The overall structure of the seawater purification device includes a purification table base 207, a purification table fixture 208 and a purification table support plate 209. Seawater enters the seawater primary filter 202 through the seawater inlet channel 201. This filter is a reverse osmosis membrane filter with an inlet pressure of 0.1-0.3 Mpa and a flow rate of 0.4~0.5 tons / hour. After filtration, the seawater enters the evaporation storage tank 203. After evaporation by sunlight, the seawater is converted into steam through the seawater desalination wood 204 and condensed in the wedge-shaped flow channel 205, and is collected along the flow channel to the purified water outlet channel 206. The efficiency of condensation filtration is 80%~90%, and the flow rate through 206 is 0.32~0.4 tons / hour. The desalination wood is replaced every 7~10 days. The chloride after purification is less than 5 mg / L, the total hardness is less than 4 mg / L, and the dissolved solids are less than 10 mg / L.

[0033] The operating temperature of alkaline electrolytic cell 5 is 55~95℃, and the current density is 0.2~0.5 A / cm 2 , the stack energy consumption is 3.8~4.0kWh / m 3The maximum power is 5~10 MW, the hydrogen production rate is 200~400 Nm³ / h, the catalyst uses self-developed nickel foam / Co3O4@NiFePc catalyst, and the catalyst loading is 0.12~0.16 mg / cm 2 .

[0034] The hydrogen purification and impurity removal device 6 includes molecular sieve physical adsorption and membrane separation subsequent processes. The purity of hydrogen at the impurity removal outlet is higher than 99.9%. The oxygen storage tank 9 and the oxygen flow controller 10 are located in the seawater at a depth of 10 to 20 m and are fixed in the seawater with a steel structure.

[0035] The underwater monitoring and viewing platform 11 is the center of the entire system. It adjusts the operation strategy of the entire system according to the operation requirements, including the operation parameters of each module and the material input and output of each device. The control system and manual decision-making are used for joint regulation. Its power supply comes from the system's wind, solar and temperature difference power generation and adopts modular regulation, and uses cascaded power batteries as backup energy.

[0036] The marine trees 12 are mainly offshore trees planted, including mangroves, white candle fruit and sea almonds. The pre-processing process after harvesting is completed on the offshore steel frame platform 22.

[0037] The pyrolysis device 13 uses a self-developed pyrolysis gasifier (CN117106489A), and the pyrolysis temperature is 800-850° C. The generated impurity gas may contain carbon monoxide, hydrogen sulfide, methane, etc., which need to be further removed.

[0038] The gas purification and impurity removal device 14 includes molecular sieve physical adsorption and membrane separation subsequent processes. The purity of carbon dioxide at the impurity removal outlet is higher than 99.9%.

[0039] In the compressed carbon dioxide energy storage and heat exchange system, carbon dioxide comes from the pyrolysis device 13. In the gaseous carbon dioxide storage tank 15, the storage temperature of carbon dioxide is 22~26℃, and the storage pressure is 0.09~0.12 Mpa. The storage tank is located on the offshore steel frame platform 22. In the liquid carbon dioxide storage tank 18, the storage temperature of carbon dioxide is 4~14℃, and the storage pressure is 4.5~5.5Mpa. The storage tank is located on the seabed at 200~400 m. The medium used in the hot salt tank 103 and the cold salt tank 104 is molten salt NaCl-Na2SO4-NaF, and the medium used in the hot salt tank 105 and the cold salt tank 106 is molten salt KNO3-NaNO2-NaNO3. The volume of the hot salt tank 1 and the cold salt tank 1 is 350~370 m 3 The volume of hot salt tank 2 and cold salt tank 2 is 310~320 m 3 The volume of the hot water tank and the cold water tank is 210~230 m 3. During energy storage, the carbon dioxide in the gaseous carbon dioxide storage tank 15 is compressed to a high temperature and high pressure state by the compressor 111. Three-stage compression is adopted, and the single-stage compression ratio is 4-6. After that, the heat is released and cooled through the three-stage heat exchanger 102, and the compression heat is transferred to the molten salt from the cold salt tank 104 and the cold salt tank 2 106, and enters the hot salt tank 103 and the hot salt tank 2 105 respectively. Finally, the compression heat is transferred to the hot water storage from the cold water tank 108 and enters the hot water tank 107. The cooled carbon dioxide enters the condenser 109 and is condensed into liquid by the cooling water and stored in the liquid carbon dioxide storage tank 18. The hot salt in the hot salt tank 103 and the hot salt tank 2 105 can be partially used for system heating and to supplement the ocean temperature difference energy power generation heat source. The hot water in the hot water tank 107 can be partially used for underwater monitoring and visiting platform 11 to supply hot water. When releasing energy, liquid carbon dioxide is evaporated into gaseous state by a part of hot water storage from hot water tank 107 in evaporator 110, and then enters heat exchanger 102 to exchange heat with the remaining hot water storage in hot water tank. Medium-temperature and high-pressure carbon dioxide continues to exchange heat with hot salt in hot salt tank 2 105 and hot salt in hot salt tank 1 103 to increase temperature, enters expander 101 to generate power, and carbon dioxide at normal pressure is stored in gaseous carbon dioxide storage tank 15. Three-stage expansion is adopted, and the unipolar expansion ratio is 4-6. The water and molten salt after heat exchange are stored in cold water tank 108, cold salt tank 2 106 and cold salt tank 1 104.

[0040] Liquid fuel synthesis adopts thermochemical method and removes impurities. The conditions for synthesizing methanol are Cu 0.8 -Pd / CeO2 catalyst, temperature 200~210℃, pressure 2.8~3.0 Mpa, molar ratio of hydrogen to carbon dioxide 3:1, heat source is molten salt working fluid of compressed carbon dioxide energy storage and heat exchange system 17. Synthesis conditions of dimethyl ether are Cu 0.6 -Al / Mo2C catalyst, temperature 250~260℃, pressure 3.0~3.2 Mpa, hydrogen to carbon dioxide molar ratio 3:1, where the heat source is the molten salt working fluid of the compressed carbon dioxide energy storage and heat exchange system 17. Under the control of the underwater monitoring and viewing platform 11, the synthesis ratio of the two products is reasonably allocated according to the purpose and demand (hydrogen supply molar ratio 1:3~4:0), and fuel synthesis is carried out in two different synthesis devices respectively, ensuring the normal operation of the system while exporting liquid fuel to the outside.

[0041] The transport ship 21 transports the fuel from the fuel storage tank 20 and also uses it as a power source.

[0042] The temperature difference power generation device adopts an organic Rankine cycle, with a power generation capacity of 50~100 kW. Dimethyl ether synthesized from liquid fuel is used as a circulating working fluid, and no external circulating working fluid is required. The heat source is the compressed carbon dioxide energy storage and heat exchange system 17 and surface seawater. The cold source is the liquid carbon dioxide storage tank 18 at the bottom of the ocean and deep seawater.

[0043] Specific working method: When the power load demand is higher than the power generation load of the wind turbine, photovoltaic panel 25 and temperature difference energy power generation device 26, instructions are given through the underwater monitoring and viewing platform 11, the alkaline water electrolyzer 6 and the liquid fuel synthesis purification device 19 operate at low load, and the compressed carbon dioxide energy storage and heat exchange system 17 starts the energy release phase to supplement the insufficient load.

[0044] When the power load demand is lower than the power generation load of the wind turbine, photovoltaic panel 25 and temperature difference power generation device 26, the underwater monitoring and viewing platform 11 gives instructions, and the compressed carbon dioxide energy storage and heat exchange system 17 starts the energy storage phase to store excess electricity. After the energy storage is completed, the alkaline water electrolyzer 6 and the liquid fuel synthesis and purification device 19 are upgraded to operate, synthesize liquid fuel, and store and transport it.

[0045] The load regulation process of the present invention is more stable than that of the existing wind and solar hydrogen storage system. When the power load demand is higher than the power generation load, instructions are given through the underwater monitoring and viewing platform, the alkaline water electrolyzer and the liquid fuel synthesis and purification device are operated at low load, and the compressed carbon dioxide energy storage and heat exchange system starts the energy release stage to supplement the insufficient load. When the power load demand is lower than the power generation load, the compressed carbon dioxide energy storage and heat exchange system starts the energy storage stage to store excess electricity, synthesize liquid fuel, and store and transport it.

[0046] The present invention adopts the mode of photovoltaic panel power generation and photothermal seawater purification, and couples the two light utilization modes of photovoltaic and photothermal, thereby improving the system density and enhancing the light energy utilization rate.

[0047] The hydrogen production process of the present invention adopts a self-designed nickel foam / Co3O4@NiFePc catalyst to reduce the reaction overpotential and improve the performance of the alkaline electrolyzer. The new catalyst is used to synthesize methanol and dimethyl ether, which improves the Faraday efficiency and enhances stability. Under the control of the underwater monitoring and viewing platform 11, the synthesis ratio of the two liquid fuels is reasonably allocated according to the purpose and demand, and the fuel synthesis is carried out in two different synthesis devices respectively, ensuring the normal operation of the system while outputting liquid fuel to the outside, making the synthesis more accurate.

[0048] The desalination process of the present invention adopts the desalination method of wood for seawater desalination, which significantly reduces the residence time of seawater compared to the single membrane desalination method and does not require deep membrane purification. The photothermal method of wood for seawater desalination does not require additional energy input and improves the water quality entering the alkaline electrolyzer, thereby saving the cost of purification membranes and increasing the system life.

[0049] The present invention realizes the comprehensive utilization of wood biomass. The carbon dioxide after pyrolysis is used for subsequent energy storage and synthesis, and the coke of wood biomass is used as seawater desalination wood, thus realizing the comprehensive utilization of biomass.

[0050] The present invention realizes the comprehensive utilization of carbon dioxide and oxygen. A part of the carbon dioxide produced by pyrolysis is sent to the compressed carbon dioxide energy storage and heat exchange system to participate in the compressed carbon dioxide energy storage and heat exchange. Another part of the carbon dioxide participates in the synthesis of liquid fuel. The synthesized carbon dioxide comes from biomass and meets the certification standards of green methanol and green dimethyl ether. In addition, the oxygen produced by electrolysis of water is also effectively utilized. Under the control of the oxygen flow controller, oxygen is supplied to the underwater monitoring and viewing platform, and the excess oxygen can be used to supply oxygen to the planted marine tree system.

[0051] Compared with the existing wind and solar energy storage system, the present invention adds a temperature difference energy generation device, realizes the cascade utilization of energy, reduces the temperature difference between the various parts of the system, and reduces the risk of reducing the life of the device due to thermal stress. The heat source is partially derived from molten salt, which realizes the effective utilization of low-grade energy. At the same time, the heat of thermochemical synthesis is also partially derived from molten salt, which improves the heat utilization effect.

[0052] The present invention realizes the multi-level utilization of products. Dimethyl ether is a liquid fuel that is easy to transport. As a working fluid of the organic Rankine cycle, dimethyl ether does not need to be added as a circulating working fluid. While transporting green methanol and dimethyl ether in the fuel storage tank, the transport ship also uses it as a power source.

[0053] The above-described embodiment is only a preferred solution of the present invention and does not limit the present invention in any form. There are other variations and modifications without exceeding the technical solution described in the claims.

Claims

1. A system for producing hydrogen by electrolyzing seawater and storing and utilizing energy in stages, comprising an offshore steel frame platform, characterized in that: The offshore steel frame platform is provided with a seawater pump, a seawater purification device, a purified water storage tank, a water pump, an alkaline water electrolyzer, a hydrogen purification and impurity removal device, a hydrogen storage tank and a hydrogen flow controller, a pyrolysis device, a gas purification and impurity removal device, a gaseous carbon dioxide storage tank, a carbon dioxide flow controller, a compressed carbon dioxide energy storage and heat exchange system, a synthesis purification device, and a fuel storage tank; the seawater pump, the seawater purification device, the purified water storage tank, the water pump, the alkaline water electrolyzer, the hydrogen purification and impurity removal device, the hydrogen storage tank and the hydrogen flow controller are connected in sequence; the pyrolysis device, the gas purification and impurity removal device, the gaseous carbon dioxide storage tank, the carbon dioxide flow controller and the compressed carbon dioxide energy storage and heat exchange system are connected in sequence; the hydrogen flow controller and the carbon dioxide flow controller are connected to the synthesis purification device, the synthesis purification device is connected to the fuel storage tank, and the fuel in the fuel storage tank is transported by a transport ship and used for fuel supply of the transport ship; A liquid carbon dioxide storage tank is installed on the seabed under the offshore steel frame platform and is connected to the compressed carbon dioxide energy storage and heat exchange system.

2. A seawater electrolysis hydrogen production and energy cascade storage and utilization system according to claim 1, characterized in that: Marine trees are planted in the seawater under the offshore steel frame platform for pyrolysis in the pyrolysis device.

3. The system for producing hydrogen by electrolyzing seawater and storing and utilizing energy in stages according to claim 1 is characterized in that: It also includes wind turbines and photovoltaic panels, temperature difference energy power generation devices, DC converters, receiving-end converters and power grids. The wind turbines and photovoltaic panels and temperature difference energy power generation devices are respectively connected to the DC converters, and the DC converters are connected to the power grid through the receiving-end converters. The power supply of the entire platform is connected to the DC converter.

4. A seawater electrolysis hydrogen production and energy cascade storage and utilization system according to claim 2, characterized in that: An oxygen storage tank, an oxygen flow controller and an underwater monitoring and visiting platform are also provided in the seawater under the offshore steel frame platform. The oxygen storage tank is connected to the alkaline water electrolyzer through a pipeline, and the oxygen flow controller is connected to the oxygen storage tank to control the oxygen supply to the underwater monitoring and visiting platform and the marine trees.

5. The system for producing hydrogen by electrolyzing seawater and storing and utilizing energy in stages according to claim 1 is characterized in that: The compressed carbon dioxide energy storage and heat exchange system includes an expander, a heat exchanger, a hot salt tank 1, a cold salt tank 1, a hot salt tank 2, a cold salt tank 2, a hot water tank, a cold water tank, a condenser, an evaporator and a compressor.

6. The system for producing hydrogen by electrolyzing seawater and storing and utilizing energy in stages according to claim 1 is characterized in that: The seawater purification device includes a purification table base, a purification table fixture and a purification table support plate. A wedge-shaped flow channel is hung upside down on the purification table support plate. The bottom end of the wedge-shaped flow channel is connected to the purified water outlet channel. An evaporation storage tank is arranged on the purification table base. The evaporation storage tank is connected to the seawater inlet channel through a seawater primary filter. Seawater desalination wood is arranged above the evaporation storage tank, and the wedge-shaped flow channel corresponds to the seawater desalination wood.

7. The system for producing hydrogen by electrolyzing seawater and storing and utilizing energy in stages according to claim 1 is characterized in that: The hydrogen purification and impurity removal device and the gas purification and impurity removal device respectively include molecular sieve physical adsorption and membrane separation subsequent processes.

8. The system for producing hydrogen by electrolyzing seawater and storing and utilizing energy in stages according to claim 1 is characterized in that: The alkaline electrolytic cell has an operating temperature of 55-95°C and a current density of 0.2-0.5 A / cm 2 , the stack energy consumption is 3.8~4.0 kWh / m 3 .

9. The system for producing hydrogen by electrolyzing seawater and storing and utilizing energy in stages according to claim 1 is characterized in that: In the compressed carbon dioxide energy storage and heat exchange system, the two molten salts in the hot salt tank 1 and the cold salt tank 1 and in the hot salt tank 2 and the cold salt tank 2 are NaCl-Na2SO4-NaF and KNO3-NaNO2-NaNO3 respectively.

10. The system for producing hydrogen by electrolyzing seawater and storing and utilizing energy in stages according to claim 2 is characterized in that: A sea level stabilizing device and fixed piles are arranged below the offshore steel frame platform.

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