Water electrolysis hydrogen production waste heat green hydrogen preparation system and method

Abstract

The invention provides a water electrolysis hydrogen production waste heat green hydrogen preparation system and method, and belongs to the technical field of hydrogen production. The system comprises a water electrolysis hydrogen production module, a softened water treatment module, a waste heat recovery module, a metal cracking hydrogen production module and a hydrogen post-treatment module, the waste heat recovery module comprises a softened water alkali liquor heat exchanger and a heat storage tank; the water electrolysis hydrogen production module comprises a hydrogen production device, a circulating cooling water alkali liquor heat exchanger, an alkali liquor circulating pump and an electrolytic bath; the water electrolysis hydrogen production module is connected with the waste heat recovery module through the softened water alkali liquor heat exchanger; the softened water treatment module, the waste heat recovery module, the metal cracking hydrogen production module and the hydrogen aftertreatment module are connected in sequence. Compared with a conventional technology, the problem of waste of waste heat resources in a conventional water electrolysis hydrogen production system is essentially solved, the cold load requirement of circulating cooling water in the water electrolysis hydrogen production system is reduced, the energy utilization rate is increased, and the comprehensive preparation cost of green hydrogen is reduced.

Description

Technical Field

[0001] This invention belongs to the field of hydrogen production technology, specifically relating to a system and method for preparing green hydrogen from waste heat generated during water electrolysis. Background Technology

[0002] Hydrogen, as a green, efficient, abundant, and widely applicable clean energy source, is regarded as an important national energy strategy by countries around the world and will become a new way for humanity to solve increasingly serious energy and environmental problems in the future. Green hydrogen is hydrogen produced using renewable energy sources such as wind power, hydropower, solar power, and nuclear power. The utilization of hydrogen energy will be further improved in the future, and green hydrogen production is a key step in solving the demand for hydrogen energy.

[0003] Currently, water electrolysis is the primary method for producing green hydrogen. However, large-scale water electrolysis hydrogen production plants generate significant amounts of waste heat during production. Traditional water electrolysis hydrogen production systems often fail to effectively utilize this waste heat, resulting in substantial waste, inefficient energy use, and increased hydrogen production costs. Collecting and utilizing the waste heat generated during water electrolysis for green hydrogen production is an effective way to optimize system energy consumption, reduce the cost of water electrolysis hydrogen production, and is crucial for promoting the development and utilization of hydrogen energy.

[0004] Currently, no publicly published patents have been found regarding systems and methods for producing green hydrogen using waste heat from water electrolysis. Similar patents include: Utility model patent CN 216808138 U, which proposes a metal cracking water vapor hydrogen production system; and Utility invention patent CN 117466246 A, which proposes a cracking agent for hydrogen production and its preparation method. These two patents primarily focus on a single aspect: the setup of a metal cracking hydrogen production system and the preparation of the cracking agent. Utility model patent CN216107235 U, which proposes a waste heat recovery process system for a large-scale alkaline water electrolysis hydrogen production device, used in hot standby or cold start states; and Utility model patent CN 113137783 A, which proposes a system and method for recovering waste heat from water electrolysis hydrogen production using a heat pump, mainly for providing a heat source to external heating equipment. However, these two patents primarily focus on recovering waste heat from water electrolysis hydrogen production and applying it to equipment heating. Therefore, these patents are clearly not applicable to using waste heat from water electrolysis hydrogen production for green hydrogen production.

[0005] Considering the waste of waste heat during water electrolysis for hydrogen production and the economic value of green hydrogen production, and in order to comply with national energy conservation and emission reduction policies and maximize corporate profits, a waste heat green hydrogen production system and method for water electrolysis is proposed. This system and method can recover and utilize waste heat during the water electrolysis process, reducing waste heat energy waste, improving the comprehensive energy utilization rate, and helping to maintain the temperature of the alkaline solution when the water electrolysis hydrogen production unit is shut down, which is conducive to the rapid start-up of the water electrolysis hydrogen production unit. At the same time, by selecting appropriate equipment, the consumption of new energy power can be increased, thereby improving the overall project benefits. Summary of the Invention

[0006] To effectively utilize the waste heat generated by the water electrolysis hydrogen production unit, the following technical solution is proposed:

[0007] On one hand, the present invention provides a waste heat green hydrogen production system for water electrolysis, comprising: a water electrolysis hydrogen production device, a softened water treatment module, a waste heat recovery module, a metal cracking hydrogen production module, a hydrogen post-treatment module, a circulating cooling water alkali heat exchanger, an alkali circulation pump, and an electrolytic cell; the waste heat recovery module includes a softened water alkali heat exchanger and a heat storage tank; the softened water treatment module, waste heat recovery module, metal cracking hydrogen production module, and hydrogen post-treatment module are connected in sequence; the metal cracking hydrogen production module includes a steam flash tank, a boiler, a steam compressor, a packed tower, a spray tower, and a heat exchanger; the water electrolysis hydrogen production device is connected in sequence to the softened water alkali heat exchanger, the circulating cooling water alkali heat exchanger, the alkali circulation pump, and the electrolytic cell.

[0008] Furthermore, the softened water treatment module includes a softened water treatment device; the softened water treatment module is connected to the waste heat recovery module via a softened water alkaline solution heat exchanger, which is used for waste heat recovery from the hydrogen production unit and for providing raw materials for the metal cracking hydrogen production module; the softened water alkaline solution heat exchanger is also connected to a heat storage tank.

[0009] Furthermore, the steam flash tank, steam compressor, packed tower, spray tower, and heat exchanger are connected in sequence; one end of the boiler is connected to the heat storage tank of the waste heat recovery module, and the other end is connected to the packed tower; the metal cracking hydrogen production module is connected to the hydrogen post-processing module through the heat exchanger to efficiently utilize the recovered and stored waste heat as well as the waste heat in the production process of this system, and to prepare green hydrogen.

[0010] Furthermore, the waste heat recovery module is connected to the metal cracking hydrogen production module via a heat storage tank for the recovery and storage of waste heat from the water electrolysis hydrogen production unit; the heat storage tank is connected to the heat exchanger, packed tower and boiler in the metal cracking hydrogen production module respectively.

[0011] Furthermore, a metering pump is connected between the heat storage tank and the packed tower, and a first circulation pump is connected between the heat storage tank and the heat exchanger.

[0012] Furthermore, the hydrogen after-treatment module includes a cooler, a gas-liquid separator, a hydrogen compressor, a hydrogen buffer tank, and a hydrogen purification device, which are connected in sequence.

[0013] Furthermore, the connection in the waste heat green hydrogen production system for water electrolysis is via pipelines, including softened water pipelines, steam pipelines, and hydrogen pipelines.

[0014] Furthermore, the boiler is selected as a steam boiler or a thermal storage boiler.

[0015] Furthermore, the heat exchanger includes plate type, cast iron type, cylindrical type or steel type.

[0016] On the other hand, the present invention provides a method for preparing green hydrogen from waste heat in water electrolysis hydrogen production. This method is applied to the aforementioned water electrolysis hydrogen production waste heat green hydrogen preparation system and includes the following steps:

[0017] When the water electrolysis hydrogen production unit is working, the clean water treated by the softened water treatment module and the liquid water discharged from the steam flash tank are used together as a cold medium for waste heat recovery, and the flow rate of softened water flowing through the softened water alkaline heat exchanger is adjusted according to the real-time operating conditions.

[0018] The softened water in the heat storage tank is transported to the metal cracking hydrogen production module to perform secondary cooling and energy utilization on the generated high-temperature hydrogen.

[0019] The softened water, cooled by high-temperature hydrogen, is discharged from the spray tower outlet and transported to the steam flash tank to form steam.

[0020] Steam is transported to the packed tower where a metal cracking reaction occurs to produce hydrogen.

[0021] When the metal cracking hydrogen production reaction begins, if the amount of steam entering the packed tower is insufficient to meet the steam requirements of the reaction, softened water from the heat storage tank is transported to the packed tower to supplement the steam.

[0022] The high-temperature hydrogen produced by the metal cracking hydrogen production module is cooled twice, and then cooled by the hydrogen post-processing module for gas-liquid separation, compression, buffering and purification.

[0023] Furthermore, after the softened water in the heat storage tank is transported to the packed tower to supplement the steam volume, if the steam volume in the packed tower still does not meet the steam demand, the softened water in the heat storage tank is transported to the boiler, and the boiler generates steam as a supplementary steam source for the packed tower.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] Compared with conventional technologies, this invention is applicable to the process of waste heat recovery and green hydrogen production from water electrolysis hydrogen production systems. It recovers waste heat generated by the water electrolysis hydrogen production system by setting up a waste heat recovery module. Through the use of a softened water alkaline heat exchanger and a heat storage tank, the waste heat from water electrolysis hydrogen production is collected and stored via the softened water medium. Finally, green hydrogen is produced by a metal cracking hydrogen production unit. This fundamentally reduces the waste heat resource waste problem in conventional alkaline water electrolysis hydrogen production systems, reduces the cooling load requirement of circulating cooling water, improves energy utilization, realizes the recovery and utilization of waste heat resources, reduces the cost of metal cracking hydrogen production, and lowers the overall cost of green hydrogen production. When the water electrolysis unit operates intermittently, the reflux heat from the steam flash tank in the metal cracking hydrogen production module can be used to maintain the temperature of the alkaline solution, which is beneficial for the rapid start-up of the water electrolysis hydrogen production unit. Simultaneously, either a steam boiler or a thermal storage boiler can be used. Using a thermal storage boiler can increase the utilization rate of renewable energy curtailment and respond to off-peak electricity preferential policies, thereby improving the overall efficiency of the project.

[0026] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description and the drawings. Attached Figure Description

[0027] Figure 1 This invention provides a waste heat green hydrogen production system for water electrolysis. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the embodiments of this application will be described in detail below with reference to specific examples. Unless otherwise defined, the technical and scientific terms used in this invention have the meanings commonly understood by those skilled in the art. Without departing from the concept of this invention, those skilled in the art can make various improvements and changes to the specific embodiments described in this specification, and all such improvements and changes fall within the scope of protection of this invention.

[0029] This invention provides a waste heat-based green hydrogen production system for water electrolysis, comprising: an water electrolysis hydrogen production device, a softened water treatment module, a waste heat recovery module, a metal cracking hydrogen production module, a hydrogen post-treatment module, a circulating cooling water-alkali heat exchanger, an alkali circulation pump, and an electrolytic cell; the waste heat recovery module includes a softened water-alkali heat exchanger and a heat storage tank; the softened water treatment module, waste heat recovery module, metal cracking hydrogen production module, and hydrogen post-treatment module are connected in sequence; the water electrolysis hydrogen production device is connected in sequence to the softened water-alkali heat exchanger, the circulating cooling water-alkali heat exchanger, the alkali circulation pump, and the electrolytic cell.

[0030] The softened water treatment module includes a softened water treatment device; the softened water alkaline solution heat exchanger is also connected to a heat storage tank; the metal cracking hydrogen production module includes a steam flash tank, a boiler, a steam compressor, a packed tower, a spray tower, and a heat exchanger; the hydrogen post-treatment module includes a cooler, a gas-liquid separator, a hydrogen compressor, a hydrogen buffer tank, and a hydrogen purification device.

[0031] The softened water treatment module and the waste heat recovery module are connected through a softened water alkaline solution heat exchanger, which is used for waste heat recovery of the water electrolysis hydrogen production device and to provide raw materials for the metal cracking hydrogen production module.

[0032] The waste heat recovery module is connected to the softened water treatment module and the metal cracking hydrogen production module respectively, and is used for waste heat recovery and storage of the electrolytic water hydrogen production device system.

[0033] The metal cracking hydrogen production module is connected to the waste heat recovery module and the hydrogen post-processing module to efficiently utilize the recovered and stored waste heat as well as the waste heat generated during the production process of this system, and to prepare green hydrogen.

[0034] The hydrogen post-processing module is connected to the metal cracking hydrogen production module and is used for gas-liquid separation, buffering and purification of hydrogen.

[0035] Furthermore, the connection is made using pipes, including softened water pipes, steam pipes, and hydrogen pipes.

[0036] Furthermore, the boiler is selected as either a steam boiler or a thermal storage boiler. A thermal storage electric boiler is a new type of high-efficiency and energy-saving electric heating product, encouraged by the power sector to use electric heating during off-peak periods and enjoy preferential electricity prices. For users with limited space and relatively low hot water demand, a steam-type electric boiler is also a good choice.

[0037] The present invention will be further described below with reference to the embodiments:

[0038] like Figure 1As shown, the waste heat green hydrogen production system for water electrolysis includes: a softened water alkali heat exchanger 1, a heat storage tank 2, a steam flash tank 3, a steam compressor 4, a packed tower 5, a spray tower 6, a heat exchanger 7, a cooler 8, a gas-liquid separator 9, a hydrogen compressor 10, a hydrogen buffer tank 11, a boiler 12, a softened water treatment device 13, a first circulation pump 14, a second circulation pump 15, a metering pump 16, a circulating cooling water alkali heat exchanger 17, an alkali circulation pump 18, an electrolyzed water hydrogen production device 19, a hydrogen purification device 20, and an electrolyzer 21; pipelines A, B, C, F, H, I, J, and R are softened water pipelines, pipelines D, E, and G are steam pipelines, and pipelines K, L, M, N, O, P, and Q are hydrogen pipelines. All equipment is not limited to any particular type; as long as their functions are the same, they all fall within the scope of protection of this application.

[0039] In one specific embodiment of the present invention, the heat exchanger 7 is preferably a plate heat exchanger;

[0040] In one specific embodiment of the present invention, the boiler 12 is preferably a thermal storage boiler;

[0041] The electrolyte with a waste heat recovery temperature of 90±5℃ in this application reduces the cooling load requirement (i.e., the circulating cooling water requirement) of the circulating cooling water alkaline heat exchanger 17 on the one hand, and reduces the energy consumption of the boiler and steam compressor in the metal cracking hydrogen production module on the other hand.

[0042] Figure 1 The connection methods between devices are as follows:

[0043] The alkaline solution from the water electrolysis hydrogen production unit 19 enters the alkaline solution inlet of the softened water alkaline solution heat exchanger 1. The alkaline solution flowing out of the hot fluid outlet of the softened water alkaline solution heat exchanger 1 is connected in sequence to the circulating cooling water alkaline solution heat exchanger 17, the alkaline solution circulation pump 18 and the electrolytic cell 21 through pipelines. The cooled alkaline solution is then circulated back to the electrolytic cell.

[0044] The softened water alkali solution heat exchanger 1 uses hot alkali solution from the water electrolysis hydrogen production unit 19 as the heat medium and softened water as the cold medium. The cold medium inlet of the softened water alkali solution heat exchanger 1 is connected to the outlet of the softened water treatment unit 13, and the cold medium outlet of the softened water alkali solution heat exchanger 1 is connected to the inlet of the heat storage tank 2. The outlet of the heat storage tank 2 is connected to three devices: the cold fluid inlet of the heat exchanger 7, the outlet of the steam compressor 4 (i.e., the inlet of the packed tower 5), and the inlet of the boiler 12. The cold fluid outlet of the heat exchanger 7 is connected to the spray water inlet of the spray tower 6, the water outlet of the spray tower 6 is connected to the inlet of the steam flash tank 3, and the steam outlet of the steam flash tank 3 is connected to the inlet of the steam compressor 4. The outlet is connected to the inlet of packed tower 5, the outlet of packed tower 5 is connected to the inlet of spray tower 6, the outlet of spray tower 6 is connected to the hot fluid inlet of heat exchanger 7, the hot fluid outlet of heat exchanger 7 is connected to the inlet of cooler 8, the outlet of cooler 8 is connected to the inlet of gas-liquid separator 9, the gas outlet of gas-liquid separator 9 is connected to the inlet of hydrogen compressor 10, the outlet of hydrogen compressor 10 is connected to the inlet of hydrogen buffer tank 11, and the outlet of hydrogen buffer tank 11 is connected to the inlet of hydrogen purification device 20; the steam outlet of boiler 12 is connected to the inlet of packed tower 5; the liquid softened water outlet of steam flash tank 3 is connected to the cold medium inlet of softened water alkaline solution heat exchanger 1 and the inlet of heat storage tank 2, respectively.

[0045] Working process and principle:

[0046] The alkaline solution enters the softened water alkaline solution heat exchanger 1 from the water electrolysis hydrogen production unit 19. Under the action of the waste heat recovery module, the waste heat of the alkaline solution is recovered and stored. Then, the temperature of the alkaline solution is reduced to the optimal temperature required for the operation of the electrolyzer by the circulating cooling water alkaline solution heat exchanger 17. After being pressurized by the alkaline solution circulation pump 18, it is circulated to the electrolyzer 21.

[0047] Among them, after the clean water is treated by the water softening treatment device 13, the softened water is transported to the water softening alkaline heat exchanger 1 through the water softening pipeline J for heat exchange, and then enters the heat storage tank 2 through the water softening pipeline A for storage. These two processes are the waste heat recovery process of the water electrolysis hydrogen production device.

[0048] The liquid softened water flowing out of the steam flash tank 3 is pressurized by the second circulation pump 15 and then enters the heat storage tank 2 through the softened water pipelines H, I, and A in sequence. This process is the heat recovery process of the softened water.

[0049] The softened water in the heat storage tank 2 comes entirely from the softened water alkaline solution heat exchanger 1 and the steam flash tank 3. The softened water inside is pressurized by the first circulation pump 14 and transported to the heat exchanger 7 through the softened water pipeline B, and then transported to the spray tower 6 through the softened water pipeline R. This process cools down the high-temperature hydrogen gas produced by metal cracking and recovers the heat to achieve efficient energy utilization.

[0050] The liquid flowing out of the spray tower 6 is transported to the steam flash tank 3 via the softened water pipeline C to generate steam. The steam is then transported to the steam compressor 4 via the steam pipeline D for pressurization, and then transported to the packed tower 5 via the steam pipeline E to participate in the metal cracking reaction to produce hydrogen. This process aims to convert softened water into steam, and further produce green hydrogen through the metal cracking hydrogen production reaction.

[0051] The hydrogen produced by the packed tower 5 is transported to the spray tower 6 via the hydrogen pipeline K, then to the heat exchanger 7 via the hydrogen pipeline L for cooling, then to the cooler 8 via the hydrogen pipeline M for further cooling, and then to the gas-liquid separator 9 via the hydrogen pipeline N for gas-liquid separation. The separated hydrogen is compressed by the hydrogen compressor 10 and transported to the hydrogen buffer tank 11 for storage. Finally, it is sent to the hydrogen purification device 20 via the hydrogen pipeline Q for purification.

[0052] In addition, during intermittent operation of the water electrolysis hydrogen production unit, the liquid water flowing out of the steam flash tank 3 is pressurized by the second circulation pump 15 and then transported to the softened water alkali heat exchanger 1 through softened water pipelines H and J for heat exchange. It then enters the heat storage tank 2 for storage through the softened water pipeline A. This process is the temperature maintenance of the water electrolysis hydrogen production alkali by the high-temperature softened water. When the steam generated by the steam flash tank 3 cannot meet the needs of the packed tower 5, the softened water in the heat storage tank 2 is first transported to the packed tower 5 through the softened water pipeline F and the steam pipeline E equipped with the metering pump 16, provided that the process requirements for metal cracking hydrogen production are met. The steam generated in the tower is then used to carry out the metal cracking hydrogen production reaction. If enough steam still cannot be generated, the softened water in the heat storage tank 2 is transported to the boiler 12 through the softened water pipeline G to generate steam, and then transported to the packed tower 5 through the softened water pipeline E.

[0053] On the other hand, embodiments of the present invention provide a method for preparing green hydrogen from waste heat in water electrolysis hydrogen production. This method is applied to the aforementioned water electrolysis hydrogen production waste heat green hydrogen preparation system, and this method combines... Figure 1 An example includes the following steps:

[0054] Step 1: When the water electrolysis hydrogen production unit 19 operates intermittently or under varying loads, the treated water from the softened water treatment unit 13 and the liquid water discharged from the steam flash tank 3 are used together as a cooling medium for waste heat recovery. The flow rate of softened water flowing through the softened water alkaline heat exchanger 1 is adjusted according to the real-time operating conditions. (For example, when the water electrolysis hydrogen production unit is operating normally, the softened water flow rate is stable within the required dynamic range; when the water electrolysis hydrogen production unit is intermittent or under varying loads, causing shutdowns or insufficient load, the softened water flow rate will decrease. In this case, the softened water flow rate is increased to return it to the required dynamic range.)

[0055] Step 2: The first circulation pump 14 transports the preheated softened water in the heat storage tank 2 through pipelines to the heat exchanger 7 and the spray tower 6 in sequence, so as to perform secondary cooling and energy utilization on the high-temperature hydrogen produced by the metal cracking hydrogen production module.

[0056] Step 3: The softened water after cooling the high-temperature hydrogen gas is discharged through the outlet of spray tower 6 and transported to steam flash tank 3 to form steam;

[0057] Step 4: After being compressed by the steam compressor 4, the steam is transported to the packed tower 5 through the steam pipeline. Under the catalytic action of the cracking agent, the steam undergoes a cracking reaction in the packed tower 5, continuously generating hydrogen. (The selection of the cracking agent is not limited to the scope of this patent and can be selected according to conventional technology in this field.)

[0058] Step 5: After the metal cracking hydrogen production reaction begins, if the amount of steam entering the packed tower 5 is insufficient to meet the steam requirements of the reaction, while ensuring the normal progress of the metal cracking hydrogen production reaction in the packed tower 5, the softened water in the heat storage tank 2 is directly transported into the packed tower 5. Steam is generated using the high temperature inside the tower, and then the reaction is carried out under the catalysis of the cracking agent. (The selection of the metals involved in the metal cracking hydrogen production reaction is not limited to the scope of this patent and can be selected according to conventional techniques in the field.)

[0059] Step Six: If the amount of steam in the packed tower 5 still does not meet the steam demand after Step Five, the softened water in the heat storage tank 2 will be transported to the boiler 12, and the boiler 12 will generate steam as a supplementary steam source for the packed tower 5.

[0060] Step 7: The high-temperature hydrogen generated in the packed tower 5 is sequentially transported to the spray tower 6 and the heat exchanger 7 for two cooling processes, and finally cooled by the cooler 8 before entering the gas-liquid separator 9 for gas-liquid separation.

[0061] Step 8: After separation, the hydrogen is compressed by the hydrogen compressor 10 and then transported through a pipeline to the hydrogen buffer tank 11 to buffer the high-pressure hydrogen.

[0062] Step 9: The hydrogen stored in the hydrogen buffer tank 11 is transported through a pipeline to the hydrogen purification device 20 for purification.

[0063] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A waste heat green hydrogen production system for water electrolysis, characterized in that, include: Electrolytic water hydrogen production unit, softened water treatment module, waste heat recovery module, metal cracking hydrogen production module, hydrogen post-treatment module, circulating cooling water alkaline solution heat exchanger, alkaline solution circulating pump and electrolytic cell. The waste heat recovery module includes a softened water alkaline solution heat exchanger and a heat storage tank. The softened water treatment module, waste heat recovery module, metal cracking hydrogen production module, and hydrogen post-treatment module are connected in sequence. The metal cracking hydrogen production module includes a steam flash tank, a boiler, a steam compressor, a packed tower, a spray tower, and a heat exchanger; The water electrolysis hydrogen production device is connected in sequence to a softened water alkali heat exchanger, a circulating cooling water alkali heat exchanger, an alkali circulation pump, and an electrolysis cell.

2. The waste heat green hydrogen production system for water electrolysis according to claim 1, characterized in that, The softened water treatment module includes a softened water treatment device; The softened water treatment module and the waste heat recovery module are connected through a softened water alkaline solution heat exchanger, which is used for waste heat recovery of the water electrolysis hydrogen production device and to provide raw materials for the metal cracking hydrogen production module. The softened water alkaline solution heat exchanger is also connected to a heat storage tank.

3. The waste heat green hydrogen production system for water electrolysis according to claim 1, characterized in that, The steam flash tank, steam compressor, packed tower, spray tower and heat exchanger are connected in sequence; one end of the boiler is connected to the heat storage tank of the waste heat recovery module, and the other end is connected to the packed tower. The metal cracking hydrogen production module is connected to the hydrogen post-processing module via a heat exchanger, which efficiently utilizes the recovered and stored waste heat as well as the waste heat generated during the production process of this system, and produces green hydrogen.

4. The waste heat green hydrogen production system for water electrolysis according to claim 3, characterized in that, The waste heat recovery module is connected to the metal cracking hydrogen production module via a heat storage tank, and is used for the recovery and storage of waste heat from the water electrolysis hydrogen production unit. The heat storage tank is connected to the heat exchanger, packed tower and boiler in the metal cracking hydrogen production module.

5. The waste heat green hydrogen production system for water electrolysis according to claim 4, characterized in that, A metering pump is connected between the heat storage tank and the packed tower, and a first circulation pump is connected between the heat storage tank and the heat exchanger.

6. The waste heat green hydrogen production system for water electrolysis according to claim 1, characterized in that, The hydrogen post-processing module includes a cooler, a gas-liquid separator, a hydrogen compressor, a hydrogen buffer tank, and a hydrogen purification device, which are connected in sequence.

7. A waste heat green hydrogen production system for water electrolysis according to claims 1-6, characterized in that, The connection is made using pipes, including softened water pipes, steam pipes, and hydrogen pipes.

8. The waste heat green hydrogen production system for water electrolysis according to claim 3, characterized in that, The boiler is either a steam boiler or a thermal storage boiler.

9. A method for preparing green hydrogen from waste heat during water electrolysis, characterized in that, The green hydrogen preparation system using waste heat from water electrolysis as described in any one of claims 1-8 comprises the following steps: When the water electrolysis hydrogen production unit is working, the clean water treated by the softened water treatment module and the liquid water discharged from the steam flash tank are used together as a cold medium for waste heat recovery, and the flow rate of softened water flowing through the softened water alkaline heat exchanger is adjusted according to the real-time operating conditions. The softened water in the heat storage tank is transported to the metal cracking hydrogen production module to perform secondary cooling and energy utilization on the generated high-temperature hydrogen. The softened water, cooled by high-temperature hydrogen, is discharged from the spray tower outlet and transported to the steam flash tank to form steam. Steam is transported to the packed tower where a metal cracking reaction occurs to produce hydrogen. When the metal cracking hydrogen production reaction begins, if the amount of steam entering the packed tower is insufficient to meet the steam requirements of the reaction, softened water from the heat storage tank is transported to the packed tower to supplement the steam. The high-temperature hydrogen produced by the metal cracking hydrogen production module is cooled twice, and then cooled by the hydrogen post-processing module for gas-liquid separation, compression, buffering and purification.

10. A method for preparing green hydrogen from waste heat during water electrolysis according to claim 9, characterized in that, If, after the softened water in the heat storage tank is transported to the packed tower to supplement the steam volume, the steam volume in the packed tower still does not meet the steam demand, then the softened water in the heat storage tank is transported to the boiler, and the boiler generates steam as a supplementary steam source for the packed tower.

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