ENERGY STORAGE DEVICE FOR PRODUCING HYDROGEN BY WATER ELECTROLYSIS COUPLED WITH LOW TEMPERATURE AND ENERGY STORAGE METHOD

Abstract

The present invention relates to an energy storage device for producing hydrogen by low-temperature coupled water electrolysis and an energy storage method, which are used to solve the problem of contradiction between discontinuous photoelectric resources and continuous requirements of green hydrogen for production. The device comprises a liquid nitrogen pre-cooling hydrogen liquefaction system, a liquid hydrogen-liquid nitrogen heat exchange system, a cold energy storage system and a cold energy utilization system of an air separation device.According to the present invention, the systems are strongly coupled to each other, the photoelectric renewable energy can be maximized in the form of hydrogen storage, the energy consumption cost of preparing and using green hydrogen can be effectively reduced while the high-efficiency energy storage and peak regulation are realized, the energy-saving effect is achieved, and a good diffusion prospect appears.

Description

Title of the invention: Energy storage device for the production of hydrogen by electrolysis of water coupled with low temperature and energy storage method Technical field

[0001] The present invention relates to the fields of production of electrical energy from a solar renewable energy source, production of hydrogen by electrolysis of water from green electricity, storage of energy by liquefaction of hydrogen and hydrogen energy, in particular an energy storage device for the production of hydrogen by electrolysis of water coupled with a low temperature and an energy storage method. Prior art

[0002] Renewable energy, represented by solar energy, is greatly influenced by natural environmental factors (season and weather), and its energy input and power generation cannot achieve the precise control like energy in the process of electric power generation. Renewable energy has characteristics of large fluctuation, discontinuity, randomness, uncontrollability, etc., and it is difficult to directly access the power grid for use, resulting in the abandonment of large-scale lighting. Therefore, how to effectively inhibit the fluctuation of photoelectric energy and improve the photoelectric absorption capacity has become the main technical bottleneck that restricts the large-scale development of photoelectricity.As an energy buffer means, the energy storage system can effectively inhibit the fluctuation of photoelectric energy, reduce lighting abandonment and electricity abandonment, and play an increasingly important role in promoting the rational use of renewable energy.

[0003] Hydrogen energy is excellent in energy density, energy utilization efficiency, and cleanliness. Electric power, nuclear power, solar power, wind power, and hydropower can be converted into hydrogen energy for storage, transportation, or direct use. Hydrogen energy is considered the best carbon-neutral energy carrier and plays a key role in the "decarbonization" process. Hydrogen energy can be prepared by reforming natural gas or fossil fuels, purifying industrial by-product hydrogen, renewable electric electrolysis, and other large-scale methods. "Green hydrogen" produced by using renewable energy such as solar energy to generate Electricity and electrolysis is the "ultimate goal" of future energy sources, as the preparation process involves little or no carbon emissions. As a carrier of hydrogen energy, the use of hydrogen for concentrated processing of renewable resources has been popularized worldwide, which is conducive to the joint development of renewable resources and hydrogen energy and has broad market prospects. At present, hydrogen-related energy is mainly used in traditional industrial fields, such as oil refining, ammonia synthesis, methanol production, etc. However, the unstable flow rate of hydrogen as a raw material prepared by electric electrolysis using renewable energy such as solar energy will directly have a great impact on downstream processes.Therefore, how to prepare continuously supplied “green hydrogen” from renewable energy sources such as discontinuous and volatile solar energy is a hot and difficult point in current research.

[0004] In order to ensure the continuous supply of "green hydrogen", when the renewable energy source electric power generation system has sufficient electricity, i.e., sufficient sunlight, the green electricity generated at this stage can produce sufficient hydrogen by producing hydrogen through water electrolysis, which can be used as raw gas to be supplied to downstream factories and enterprises. At the same time, surplus hydrogen is also available. In order to fully utilize the surplus hydrogen, it can be stored as energy for additional energy supply in the event of an energy shortage stage. At present, hydrogen storage technologies mainly include high-pressure gaseous hydrogen storage, low-temperature liquid hydrogen storage, organic liquid hydrogen storage, and solid hydrogen storage.Due to its advantages in storage density and storage and transportation efficiency, liquid hydrogen energy storage has become a form of hydrogen energy storage more suitable for large-scale and long-distance storage and transportation needs. The surplus hydrogen from photoelectric green electrolysis hydrogen production is liquefied by the hydrogen liquefaction system and then sent to the liquid hydrogen storage tank for storage.When the renewable energy power generation system is short of electricity due to environmental changes, such as the solar power generation system cannot provide the electricity needed for green electrolysis hydrogen production at night, in order to continuously supply stable raw hydrogen to downstream plants, it is sufficient to vaporize the liquid hydrogen in the storage tank under . form of hydrogen and supply the hydrogen to the downstream processing pipe network. However, due to the extremely low boiling point (20°K) of hydrogen in the hydrogen liquefaction process, the energy consumption caused by liquefaction and refrigeration is high. How to reduce energy consumption in large-scale industrial hydrogen storage application becomes the key to hydrogen storage, which is also the key to "green hydrogen" to promote the rational use and development of renewable resources such as solar energy. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide an energy storage device for producing hydrogen by water electrolysis coupled with low temperature and an energy storage method, which are used to solve the problem of contradiction between discontinuous photoelectric resources and continuous hydrogen requirements for production. Photoelectric renewable energy can be maximized in the form of liquid hydrogen storage and the energy consumption cost of preparing and using green hydrogen can be effectively reduced, while high-efficiency energy storage and peak regulation are realized, to achieve an energy-saving effect. In order to achieve the above objective,The present invention uses the following technologies: an energy storage device for producing hydrogen by water electrolysis coupled at low temperature, wherein the device comprises a liquid nitrogen pre-cooling hydrogen liquefaction system, a liquid hydrogen-liquid nitrogen heat exchange system, a cold energy storage system and a cold energy utilization system of an air separation device; the liquid nitrogen pre-cooling hydrogen liquefaction system comprises a liquid nitrogen inlet system, a nitrogen outlet system, a liquid hydrogen outlet system and a hydrogen liquefaction system, all of which are connected by pipelines and are controlled by valves; the liquid hydrogen-liquid nitrogen heat exchange system comprises a liquid hydrogen storage tank, a liquid hydrogen pump,a liquid hydrogen-liquid nitrogen heat exchanger and a liquid nitrogen storage tank, all of which are connected by pipelines and are controlled by valves for vaporizing liquid hydrogen and liquefying nitrogen, wherein a liquid hydrogen inlet end of the liquid hydrogen storage tank is connected to a liquid hydrogen outlet system of the liquid nitrogen pre-cooling hydrogen liquefaction system, a liquid hydrogen inlet end of the liquid hydrogen pump is, connected to the liquid hydrogen outlet end of the liquid hydrogen storage tank, the liquid hydrogen inlet end of the liquid hydrogen-liquid nitrogen heat exchanger is connected to the liquid hydrogen outlet end of the liquid hydrogen pump, the nitrogen inlet end of the liquid hydrogen-liquid nitrogen heat exchanger is connected to a nitrogen outlet end of the product nitrogen outlet system of the air separation device of the cold energy utilization system of the air separation device, the liquid nitrogen outlet end of the liquid hydrogen-liquid nitrogen heat exchanger is connected to the liquid nitrogen inlet end of the liquid nitrogen storage tank, and the liquid nitrogen outlet end of the liquid nitrogen storage tank is connected to the inlet end of the liquid nitrogen inlet system of the liquid nitrogen precooling hydrogen liquefaction system.

[0006] Preferably, the cold energy storage system comprises a hydrogen-refrigerant heat exchanger, a refrigerant pump, a refrigerant-cold energy storage heat exchanger, a refrigerant storage tank and a cold energy storage tank, all of which are connected by pipelines and are controlled by valves to heat hydrogen and store cold energy, wherein the hydrogen inlet end of the hydrogen-refrigerant heat exchanger is connected to the hydrogen outlet end of the liquid hydrogen-liquid nitrogen heat exchanger, the refrigerant outlet end of the hydrogen-refrigerant heat exchanger is connected to the refrigerant inlet end of the refrigerant pump,the refrigerant outlet end of the refrigerant pump is connected to the inlet end of the refrigerant-cold energy storage heat exchanger, the refrigerant outlet end of the refrigerant-cold energy storage heat exchanger is connected to the inlet end of the hydrogen-refrigerant heat exchanger, the water outlet end of the refrigerant-cold energy storage heat exchanger is connected to the inlet end of the cold energy storage tank, and the refrigerant storage tank is connected to the refrigerant inlet end of the refrigerant pump by pipelines and valves.

[0007] Preferably, the cold energy utilization system of the air separation device comprises a circulating water system, a water cooling tower, a nitrogen outlet system of a product of the air separation device and a chilled water inlet system of an air separation device, all of which are connected by pipelines and are controlled by valves, the outlet end of the circulating water system is connected to the water inlet end of the refrigerant-cold energy storage heat exchanger, the outlet end of the tank cold energy storage system is connected to the upper inlet end of the water cooling tower, the outlet end of the nitrogen outlet system is connected to the lower inlet end of the water cooling tower, and the lower outlet end of the water cooling tower is connected to the inlet end of the chilled water inlet system of the air separation device.

[0008] Preferably, the liquid hydrogen-liquid nitrogen heat exchanger, the hydrogen-coolant heat exchanger and the coolant-cold energy storage heat exchanger are all coiled tube heat exchangers or plate heat exchangers.

[0009] Preferably, the water cooling tower is a packed tower.

[0010] An energy storage method applied to the energy storage device described above comprises the following steps: Step 1: When the production of hydrogen by photoelectric green water electrolysis is excessive, the excess hydrogen can be liquefied by a hydrogen liquefaction system, in which liquid nitrogen is used as a pre-cooling cold source for hydrogen liquefaction, the liquefied liquid hydrogen is sent to a liquid hydrogen storage tank for storage, the nitrogen which is vaporized and heated to a normal temperature enters the lower part of the water cooling tower through a pipeline from a nitrogen outlet system, and is then sprayed after the low-temperature water from the cold energy storage tank enters the upper part of the water cooling tower and the low-temperature water is further cooled,which is beneficial to the subsequent process of the air separation device and saves the energy consumption of the air separation device; ,

[0011] Step 2, when a renewable energy source electric power generation system such as photoelectricity lacks hydrogen production by green water electrolysis due to environmental changes, such as weakening of sunshine, the liquid hydrogen stored in the liquid hydrogen storage tank is pressurized through a liquid hydrogen pump, then enters a liquid hydrogen-liquid nitrogen heat exchanger to be vaporized and heated, and then enters a hydrogen-refrigerant heat exchanger to be heated to obtain hydrogen at normal temperature to supplement the lack of hydrogen production by green water electrolysis.At the same time, the normal temperature nitrogen from the produced nitrogen outlet system enters the liquid hydrogen-liquid nitrogen heat exchanger to provide a heat source for vaporization and reheating of liquid hydrogen and enters the liquid nitrogen storage tank after being liquefied and condensed into liquid nitrogen and is used as a partial supplement. to liquid nitrogen precooling during hydrogen liquefaction. At the same time, the refrigerant enters the hydrogen-refrigerant heat exchanger to provide a heat source for heating hydrogen and enters the refrigerant-cold energy storage heat exchanger after being pressurized through a refrigerant pump after being cooled, so as to cool the normal temperature water in the circulating water system, the normal temperature water leaves the refrigerant-cold energy storage heat exchanger and enters the cold energy storage tank after being cooled into low temperature water, the low temperature water in the cold energy storage tank enters the upper part of the water cooling tower through pipelines and valves to be sprayed to further reduce the water temperature.

[0012] Preferably, the refrigerant fluid is an inorganic or organic compound or the mixed solution or aqueous solution thereof. Furthermore, the refrigerant fluid is preferably an aqueous solution of an organic compound, such as an aqueous solution of ethylene glycol, an aqueous solution of propylene glycol, methanol, an aqueous solution of methanol or an aqueous solution of ethanol.

[0013] Preferably, the water cooling tower is filled with packing.

[0014] The present invention has the following beneficial effects.

[0015] The present invention utilizes photoelectric green water electrolysis hydrogen production and low temperature technology to couple energy storage. When photoelectric renewable energy is sufficient, the surplus hydrogen produced by green water electrolysis hydrogen production liquefies and stores hydrogen by means of the liquid nitrogen pre-cooling hydrogen liquefaction system. When photovoltaic renewable energy power generation is reduced due to environmental changes, resulting in insufficient green water electrolysis hydrogen production, the stored liquid hydrogen is vaporized and heated by the liquid hydrogen-liquid nitrogen heat exchange system and the cold energy storage system, and then supplied to the downstream processing pipe network.At the same time, the liquid nitrogen obtained by low-temperature heat exchange can provide a partial pre-cooling cold source for the hydrogen liquefaction system. The cold energy stored by the cold energy storage system can be utilized by the cold energy utilization system of the air separation device. The present invention solves the problem of contradiction between discontinuous photoelectric resources and continuous green hydrogen production requirements for production. Photoelectric renewable energy can be maximized in the form of hydrogen storage and the energy consumption cost of preparation. and the use of green hydrogen can be effectively reduced, while high-efficiency energy storage and peak regulation are realized, the energy-saving effect is achieved, and a good diffusion prospect appears. Brief description of the drawings

[0016] [Fig. 1] is a schematic diagram of the present invention.

[0017] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] In order to clarify the technical problems, technical schemes and beneficial effects to be solved by the present invention, the present invention will be explained in more detail with reference to the following drawings and specific embodiments. It should be emphasized that for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principle of the present invention and these improvements and modifications also fall within the scope of the claims of the present invention.

[0019] The present invention will be described in detail with reference to the accompanying drawings. As shown in [Fig.l], the present invention relates to an energy storage device for producing hydrogen by electrolysis of water coupled with low temperature. The device comprises a liquid nitrogen precooling hydrogen liquefaction system, a liquid hydrogen-liquid nitrogen heat exchange system, a cold energy storage system and a cold energy utilization system of an air separation device. The liquid nitrogen precooling hydrogen liquefaction system comprises a liquid nitrogen inlet system 11, a nitrogen outlet system 12, a liquid hydrogen outlet system 13 and a hydrogen liquefaction system 14, all connected by pipelines and controlled by valves.The liquid hydrogen-liquid nitrogen heat exchange system comprises a liquid hydrogen storage tank 21, a liquid hydrogen pump 22, a liquid hydrogen-liquid nitrogen heat exchanger 23 and a liquid nitrogen storage tank 24, all of which are connected by pipelines and are controlled by valves for vaporizing liquid hydrogen and liquefying nitrogen, wherein a liquid hydrogen inlet end of the liquid hydrogen storage tank 21 is connected to a liquid hydrogen outlet system 13 of the liquid nitrogen precooling hydrogen liquefaction system. A liquid hydrogen inlet end of the liquid hydrogen pump 22 is connected to the liquid hydrogen outlet end of the liquid hydrogen storage tank 21.The liquid hydrogen inlet end of the liquid hydrogen-liquid nitrogen heat exchanger 23 is connected to the liquid hydrogen outlet end of the liquid hydrogen pump 22. The nitrogen inlet end of the liquid hydrogen-liquid nitrogen heat exchanger 23 is connected to a . nitrogen outlet end of the nitrogen outlet system 43 of the product of the air separation device of the cold energy utilization system of the air separation device. The liquid nitrogen inlet end of the liquid hydrogen-liquid nitrogen heat exchanger 23 is connected to the liquid nitrogen outlet end of the liquid nitrogen storage tank 24. The liquid nitrogen outlet end of the liquid nitrogen storage tank 24 is connected to the inlet end of the liquid nitrogen inlet system 11 of the liquid nitrogen precooling hydrogen liquefaction system.The cold energy storage system comprises a hydrogen-refrigerant heat exchanger 31, a refrigerant pump 32, a refrigerant-cold energy storage heat exchanger 33, a refrigerant storage tank 34, and a cold energy storage tank 35, all of which are connected by pipelines and are controlled by valves to heat hydrogen and store cold energy, wherein the hydrogen inlet end of the hydrogen-refrigerant heat exchanger 31 is connected to the hydrogen outlet end of the liquid hydrogen-liquid nitrogen heat exchanger 23. The refrigerant inlet end of the hydrogen-refrigerant heat exchanger 31 is connected to the refrigerant outlet end of the refrigerant pump 32.The refrigerant outlet end of the refrigerant pump 32 is connected to the refrigerant inlet end of the refrigerant-cold energy storage heat exchanger 33. The refrigerant inlet end of the refrigerant-cold energy storage heat exchanger 33 is connected to the refrigerant outlet end of the hydrogen-refrigerant heat exchanger 31. The water outlet end of the refrigerant-cold energy storage heat exchanger 33 is connected to the inlet end of the cold energy storage tank 35. The refrigerant storage tank 34 is connected to the refrigerant inlet end of the refrigerant pump 32 by pipelines and valves.The cold energy utilization system of the air separation device comprises a circulating water system 41, a water cooling tower 42, a nitrogen outlet system 43 of a product of the air separation device and a chilled water inlet system 44 of an air separation device, all of which are connected by pipelines and are controlled by valves. The outlet end of the circulating water system 41 is connected to the water inlet end of the refrigerant-cold energy storage heat exchanger 33. The outlet end of the cold energy storage tank 35 is connected to the upper inlet end of the water cooling tower 42. The outlet end of the nitrogen outlet system 12 is connected to the lower inlet end of the water cooling tower 42. The lower outlet end of the water cooling tower 42 is connected to the inlet end of the . chilled water inlet system 44 of the air separation device. The liquid hydrogen-liquid nitrogen heat exchanger 23, the hydrogen-refrigerant heat exchanger 31 and the refrigerant-cold energy storage heat exchanger 33 are all coiled tube heat exchangers or plate heat exchangers. The water cooling tower 42 is a packed tower.

[0020] An energy storage method applied to the energy storage device described above comprises the following steps: Step 1: When the production of hydrogen by photoelectric green water electrolysis is excessive, the excess hydrogen can be liquefied by a hydrogen liquefaction system, in which liquid nitrogen is used as a pre-cooling cold source for hydrogen liquefaction. The liquefied liquid hydrogen is sent to a liquid hydrogen storage tank 21 for storage. Nitrogen which is vaporized and heated to a normal temperature enters the lower part of the water cooling tower 42 through a pipeline from a nitrogen outlet system 12, and is then sprayed after the low-temperature water from the cold energy storage tank 35 enters the upper part of the water cooling tower 42.The low temperature water is further cooled, which is beneficial to the subsequent process of the air separation device and saves the energy consumption of the air separation device.

[0021] Step 2, when a system for generating electric power from a renewable energy source such as photoelectricity lacks hydrogen production by green water electrolysis due to environmental changes, such as weakening of sunshine, the liquid hydrogen stored in the liquid hydrogen storage tank 21 is pressurized via a liquid hydrogen pump 22, then enters a liquid hydrogen-liquid nitrogen heat exchanger 23 to be vaporized and heated, and then enters a hydrogen-refrigerant heat exchanger 31 to be heated to obtain hydrogen at normal temperature to supplement the lack of hydrogen production by green water electrolysis.At the same time, the normal temperature nitrogen from the produced nitrogen outlet system 43 enters the liquid hydrogen-liquid nitrogen heat exchanger 23 to provide a heat source for vaporizing and reheating the liquid hydrogen and enters the liquid nitrogen storage tank 24 after being liquefied and condensed into liquid nitrogen and is used as a partial supplement to the liquid nitrogen precooling during the liquefaction of hydrogen and is used as a partial supplement to the liquid nitrogen precooling during the liquefaction of hydrogen. At the same time, the refrigerant enters the hydrogen-refrigerant heat exchanger 31 to provide a heat source for reheating the hydrogen and . enters the refrigerant-cold energy storage heat exchanger 33 after being pressurized via a refrigerant pump 32 after being cooled, so as to cool the normal temperature water from the circulating water system 41. The normal temperature water exits the refrigerant-cold energy storage heat exchanger 33 and enters the cold energy storage tank 35 after being cooled into low temperature water. The low temperature water from the cold energy storage tank 35 enters the upper part of the water cooling tower 42 through pipelines and valves to be sprayed to further reduce the water temperature.

[0022] The refrigerant fluid is an inorganic or organic compound or the mixed solution or aqueous solution thereof. Furthermore, the refrigerant fluid is preferably an aqueous solution of an organic compound, such as an aqueous solution of ethylene glycol, an aqueous solution of propylene glycol, methanol, an aqueous solution of methanol or an aqueous solution of ethanol. The water cooling tower 42 is filled with packing.

[0023] When the hydrogen production by photoelectric green water electrolysis is excessive, the excess hydrogen is liquefied by a hydrogen liquefaction system 14. The hydrogen liquefaction system 14 generally uses the liquid nitrogen precooling Claude hydrogen circulation hydrogen liquefaction system or the Brayton helium circulation hydrogen liquefaction system widely used in the market. Liquid nitrogen, which is a precooling cold source for hydrogen liquefaction, can be introduced into the hydrogen liquefaction system 14 from the liquid nitrogen storage tank 24 by means of the liquid nitrogen inlet system 11. The vaporized nitrogen enters the lower part of the water cooling tower 42 through the pipeline via the nitrogen outlet system 12.Nitrogen is sprayed after the low-temperature water from the cold energy storage tank 35 enters the upper part of the water cooling tower 42. The low-temperature water is further cooled. As is widely known of the air separation device, reducing the temperature of the low-temperature water in the water cooling tower of the pre-cooling system of the air separation device within a reasonable range is beneficial to saving the overall energy consumption of the air separation device and reducing the unit consumption of the product of the air separation device.

[0024] When a system for producing electrical energy from a renewable energy source such as photoelectricity lacks hydrogen production by electrolysis of green water due to environmental changes, such as weakening of sunshine, the liquid hydrogen stored in the tank of Liquid hydrogen storage tank 21 is pressurized to 1.6 MPa via a liquid hydrogen pump 22, and then enters a liquid hydrogen-liquid nitrogen heat exchanger 23. At the same time, nitrogen at a normal temperature of about 25°C from the nitrogen outlet system 43 of the air separation device enters the liquid hydrogen-liquid nitrogen heat exchanger 23 to provide a heat source for vaporizing and reheating liquid hydrogen and enters the liquid nitrogen storage tank 24 after being liquefied and condensed into liquid nitrogen and is used as a partial supplement to liquid nitrogen precooling during hydrogen liquefaction. The supplement rate can reach about 60%. The temperature of the vaporized and reheated hydrogen from the liquid hydrogen-liquid nitrogen heat exchanger 23 is still very low, generally around -100°C.The hydrogen must enter a hydrogen-refrigerant heat exchanger 31 to be reheated again to obtain hydrogen at normal temperature to supplement the lack of hydrogen production by electrolysis of green water. At the same time, the refrigerant, such as an aqueous solution of ethylene glycol, enters the hydrogen-refrigerant heat exchanger 31 to provide a heat source for heating hydrogen and enters the refrigerant-cold energy storage heat exchanger 33 after being brought under pressure to about 0.1 to 0.3 MPa via a refrigerant pump 32 after being cooled to about 0°C, so as to cool the normal temperature water with a temperature of 30°C from the circulating water system 4L. After being cooled to about 20°C, the normal temperature water becomes low temperature water.The low-temperature water exits the refrigerant-cold energy storage heat exchanger 33 and enters the cold energy storage tank 35 for storage. The low-temperature water from the cold energy storage tank 35 can continuously enter the upper part of the water cooling tower 42 through pipelines and valves to be sprayed to further reduce the temperature of the low-temperature water into chilled water.

Claims

1. Claims An energy storage device for producing hydrogen by water electrolysis coupled with low temperature, wherein the device comprises a liquid nitrogen precooling hydrogen liquefaction system, a liquid hydrogen-liquid nitrogen heat exchange system, a cold energy storage system and a cold energy utilization system of an air separation device; the liquid nitrogen precooling hydrogen liquefaction system comprises a liquid nitrogen inlet system, a nitrogen outlet system, a liquid hydrogen outlet system and a hydrogen liquefaction system, all of which are connected by pipelines and are controlled by valves; the liquid hydrogen-liquid nitrogen heat exchange system comprises a liquid hydrogen storage tank, a liquid hydrogen pump,a liquid hydrogen-liquid nitrogen heat exchanger and a liquid nitrogen storage tank, all of which are connected by pipelines and are controlled by valves for vaporizing liquid hydrogen and liquefying nitrogen, wherein a liquid hydrogen inlet end of the liquid hydrogen storage tank is connected to a liquid hydrogen outlet system of the liquid nitrogen pre-cooling hydrogen liquefaction system, a liquid hydrogen inlet end of the liquid hydrogen pump is connected to the liquid hydrogen outlet end of the liquid hydrogen storage tank, the liquid hydrogen inlet end of the liquid hydrogen-liquid nitrogen heat exchanger is connected to the liquid hydrogen outlet end of the liquid hydrogen pump,the nitrogen inlet end of the liquid hydrogen-liquid nitrogen heat exchanger is connected to a nitrogen outlet end of the product nitrogen outlet system of the air separation device of the cold energy utilization system of the air separation device, the liquid nitrogen outlet end of the liquid hydrogen-liquid nitrogen heat exchanger is connected to the liquid nitrogen inlet end of the liquid nitrogen storage tank, and the liquid nitrogen outlet end of the liquid nitrogen storage tank is connected to the system inlet end,

2.

3. liquid nitrogen inlet of the hydrogen liquefaction system by liquid nitrogen precooling. An energy storage device for producing hydrogen by low-temperature coupled water electrolysis according to claim 1, wherein the cold energy storage system comprises a hydrogen-refrigerant heat exchanger, a refrigerant pump, a refrigerant-cold energy storage heat exchanger, a refrigerant storage tank and a cold energy storage tank, all of which are connected by pipelines and are controlled by valves to heat hydrogen and store cold energy, wherein the hydrogen inlet end of the hydrogen-refrigerant heat exchanger is connected to the hydrogen outlet end of the liquid hydrogen-liquid nitrogen heat exchanger, the refrigerant outlet end of the hydrogen-refrigerant heat exchanger is connected to the refrigerant inlet end of the refrigerant pump,the refrigerant outlet end of the refrigerant pump is connected to the inlet end of the refrigerant-cold energy storage heat exchanger, the refrigerant outlet end of the refrigerant-cold energy storage heat exchanger is connected to the inlet end of the hydrogen-refrigerant heat exchanger, the water outlet end of the refrigerant-cold energy storage heat exchanger is connected to the inlet end of the cold energy storage tank, and the refrigerant storage tank is connected to the refrigerant inlet end of the refrigerant pump by pipelines and valves., An energy storage device for producing hydrogen by electrolysis of water coupled at a low temperature according to claim 2, wherein the cold energy utilization system of the air separation device comprises a circulating water system, a water cooling tower, a nitrogen outlet system of a product of the air separation device and a chilled water inlet system of an air separation device, all of which are connected by pipelines and are controlled by valves, the outlet end of the circulating water system is connected to the water inlet end of the heat exchanger refrigerant-cold energy storage, the outlet end of the cold energy storage tank is connected to the upper inlet end of the water cooling tower, the outlet end of the nitrogen outlet system is connected to the lower inlet end of the water cooling tower, and the lower outlet end of the water cooling tower is connected to the inlet end of the chilled water inlet system of the air separation device.

4. An energy storage device for producing hydrogen by electrolysis of water coupled at a low temperature according to claim 3, wherein the liquid hydrogen-liquid nitrogen heat exchanger, the hydrogen-coolant heat exchanger and the coolant-cold energy storage heat exchanger are all coiled tube heat exchangers or plate heat exchangers.

5. An energy storage device for producing hydrogen by electrolysis of water coupled to a low temperature according to claim 3, wherein the water cooling tower is a packed tower.

6. An energy storage method applied to the energy storage device according to any one of claims 1 to 5, comprising the following steps: - Step 1: when the production of hydrogen by electrolysis of photoelectric green water is excessive, the excess hydrogen is liquefied by a hydrogen liquefaction system, in which liquid nitrogen is used as a pre-cooling cold source for hydrogen liquefaction, the liquefied liquid hydrogen is sent to a liquid hydrogen storage tank for storage, the nitrogen which is vaporized and heated to a normal temperature enters the lower part of the water cooling tower through a pipeline from a nitrogen outlet system,and then is sprayed after the low-temperature water from the cold energy storage tank enters the upper part of the water cooling tower, and the low-temperature water is further cooled, which is beneficial to the subsequent process of the air separation device and saves the energy consumption of the air separation device;,

7. - Step 2, when a renewable energy source power generation system lacks hydrogen production by green water electrolysis due to environmental changes, such as weakening of sunshine, the liquid hydrogen stored in the liquid hydrogen storage tank is pressurized through a liquid hydrogen pump, then enters a liquid hydrogen-liquid nitrogen heat exchanger to be vaporized and heated, and then enters a hydrogen-refrigerant heat exchanger to be heated to obtain hydrogen at normal temperature to supplement the lack of hydrogen production by green water electrolysis; at the same time,the nitrogen at normal temperature from the produced nitrogen outlet system enters the liquid hydrogen-liquid nitrogen heat exchanger to provide a heat source for vaporizing and reheating liquid hydrogen and enters the liquid nitrogen storage tank after being liquefied and condensed into liquid nitrogen and is used as a partial supplement to liquid nitrogen precooling during hydrogen liquefaction and is used as a partial supplement to liquid nitrogen precooling during hydrogen liquefaction; at the same time, the refrigerant enters the refrigerant-hydrogen heat exchanger to provide a heat source for reheating hydrogen and enters the refrigerant-cold energy storage heat exchanger after being pressurized via a refrigerant pump after being cooled,so as to cool the normal temperature water of the circulating water system, the normal temperature water exits the refrigerant-cold energy storage heat exchanger and enters the cold energy storage tank after being cooled into low temperature water, the low temperature water of the cold energy storage tank enters the upper part of the water cooling tower through pipelines and valves to be sprayed to further reduce the water temperature. An energy storage method applied to the energy storage device according to claim 6, wherein the refrigerant is an inorganic or organic compound or the mixed solution or aqueous solution thereof.,

8. An energy storage method applied to the energy storage device according to claim 6, wherein the water cooling tower is filled with packing.

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