SOEC hydrogen production system and operation method thereof

Abstract

The SOEC hydrogen production system comprises an SOEC electric pile, a fan, an air preheater, an air reheater, a deionized water pump, a condenser, a steam generator, a steam superheater, an air electric heater, high-pressure bottled H2, high-pressure bottled air, high-pressure bottled protective gas, a direct-current power supply, an electromagnetic valve and a heat tracing band. According to the system, air reheating, steam overheating and high-temperature steam generation at an electric pile inlet are achieved through one electric heater, waste heat recovery is achieved through heat exchange between high-temperature air at an electric pile outlet and room-temperature air, the heat efficiency of the system is improved, and condensation dehydration and waste heat recovery of high-temperature hydrogen at the electric pile outlet are achieved in a condenser; the system is simple in process architecture, easy to regulate and control, low in manufacturing cost and low in comprehensive power consumption.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cell systems, and in particular to a SOEC hydrogen production system and an operation method thereof. Background Art

[0002] Solid Oxide Electrolysis Cell (SOEC) hydrogen production technology is an efficient green hydrogen production technology. Under external voltage and high temperature, water vapor is electrolyzed to produce high-purity hydrogen and oxygen, realizing the conversion of electrical energy and thermal energy into chemical energy.

[0003] Using renewable energy to electrolyze water to produce hydrogen has always been an important way to achieve green and sustainable development. However, in the selection of specific technical routes, the impact of renewable energy volatility on the electrolyzer must be considered. The volatility characteristics of renewable energy are mainly manifested in: real-time random fluctuations of wind power and periodic fluctuations of photovoltaic power generation during the day and night. When the input power fluctuates randomly or periodically, it is essentially the voltage and current of the electrolyzer that change randomly or periodically. Compared with the more common alkaline water electrolysis hydrogen production technology and proton exchange membrane electrolysis hydrogen production technology, SOEC electrolysis hydrogen production has the highest working efficiency and the largest current density. The most important thing is that SOEC has the strongest adaptability to periodic power sources and its service life is least affected by voltage fluctuations. In addition, SOEC is currently the most efficient water electrolysis technology. Therefore, SOEC water electrolysis hydrogen production has become one of the mainstream technical routes for the production of green hydrogen. It can produce hydrogen and oxygen by electrolyzing water under high temperature conditions, realizing the conversion of electrical energy and thermal energy into chemical energy. The high temperature and high heat generated by the production equipment in the chemical park can provide sufficient thermal energy for SOEC water electrolysis hydrogen production, and the product gas can be used as a raw material for the production equipment, thus forming a closed loop of the industrial chain.

[0004] The SOEC hydrogen production system mainly includes the supply and heating of air, the supply and heating of water vapor, the condensation and purification of product hydrogen, the waste heat recovery of the high-temperature air at the outlet of the fuel cell stack, the DC power supply and the electronic control system. Among them, the heating of the air usually adopts the method of air electric heater, the supply and heating of water vapor requires the cooperation of heat exchanger and air electric heater, and the condensation and purification of product hydrogen can be coupled with waste heat recovery. Conventional SOEC systems use two air electric heaters to heat the air and water vapor respectively, and use high-temperature circulation pumps or ejectors to realize the recycling of part of the product hydrogen at the outlet of the fuel cell stack to reduce the system's dependence on external hydrogen during the electrolysis process. However, this method places extremely high demands on equipment and system design, which is not conducive to the promotion and application of SOEC systems.

[0005] Therefore, developing a SOEC system with simple system architecture, easy control and high overall system efficiency will help expand the application scenarios of the SOFC system and play an important role in promoting the development of the SOEC system industry. Summary of the invention

[0006] Conventional SOEC systems use two sets of electric heating systems to heat the high-temperature air and high-temperature water vapor at the inlet of the stack respectively; a portion of the mixture of hydrogen and steam at the outlet of the SOEC stack is extracted and re-entered into the steam system and the SOEC stack for electrolysis. Although this method can save a part of the external hydrogen supply during the electrolysis process, the circulation of hydrogen requires a high-temperature circulation pump or ejector, and the system is relatively complex and difficult to control; the use of product hydrogen condensation circulation also adds an additional circulation system; in addition, the high-temperature air and high-temperature product hydrogen at the outlet of the high-temperature SOEC stack cannot effectively recover waste heat, which reduces the system efficiency. In view of the above problems, in order to reduce system cost and complexity and improve system efficiency, the present invention provides the following technical solutions:

[0007] The first object of the present invention is to provide a SOEC hydrogen production system, comprising a SOEC stack, a fan, an air preheater, an air reheater, a deionized water pump, a condenser, a steam generator, a steam superheater, an air electric heater, high-pressure bottled H2, high-pressure bottled air, high-pressure bottled protective gas, a solenoid valve, a heating belt, and a DC power supply for providing electrolysis electricity to the SOEC stack; the steam inlet of the SOEC stack is connected to the steam superheater, the steam generator, the condenser, and the deionized water pump in sequence, and the steam outlet of the SOEC stack is connected to the condenser; the high-pressure The bottled protective gas is connected to the hot side outlet pipeline of the steam generator through a solenoid valve; the high-pressure bottled H2 pipeline is connected in front of the cold side inlet of the steam superheater; the air inlet of the SOEC stack is connected to the air reheater, the air preheater and the fan in sequence, and the air outlet of the SOEC stack is connected to the air preheater; the cold side air inlet of the air preheater is connected to the high-pressure bottled air through a solenoid valve; a fan is provided in front of the electric air heater, and the electric air heater is connected to the steam superheater, the air reheater and the steam generator in sequence; the heating belt is located on the steam generator outlet pipeline.

[0008] The air used for system heating enters the air electric heater under the action of the fan and is heated to 900°C, then enters the steam superheater, air reheater, and hot side channel of the steam generator for heat exchange, and is finally cooled to below 150°C and discharged from the system.

[0009] The air used for heating the SOEC stack enters the cold side channel of the air preheater under the action of the fan, and exchanges heat with the high-temperature air from the air side outlet of the SOEC stack in the hot side channel; then enters the air reheater, and exchanges heat with the high-temperature air from the hot side outlet of the steam superheater in the hot side channel; then enters the air inlet of the SOEC stack, and after heat exchange with the SOEC stack, is discharged from the air outlet to the hot side channel of the air preheater, and finally discharged to the atmosphere.

[0010] High-pressure bottled H2 is used in the SOEC stack's heating, electrolysis, hot standby, cooling and other processes to provide the SOEC stack with a reducing atmosphere at high temperature and prevent the SOEC stack's electrode materials from being damaged by oxidation at high temperatures. The high-pressure bottled H2 pipeline is connected in front of the cold side inlet of the steam superheater.

[0011] Deionized water enters the cold side channel of the condenser under the action of the deionized water pump, and exchanges heat with the mixture of high-temperature product H2 and steam from the steam outlet of the SOEC stack on the hot side; then enters the cold side channel of the steam generator, and exchanges heat with the high-temperature air from the hot side outlet of the air reheater on the hot side; after being mixed with the high-pressure bottled H2, it then enters the cold side channel of the steam superheater, and exchanges heat with the high-temperature air from the outlet of the air electric heater on the hot side; then enters the SOEC stack for electrolysis reaction, and then flows to the condenser through the steam outlet to realize steam condensation, H2 separation and purification, and discharge system.

[0012] High-pressure bottled air is used to safely purge the system air pipeline when the system is suddenly stopped to ensure that the SOEC stack is cooled at a certain rate. The high-pressure bottled air outlet pipeline is connected in front of the air inlet on the cold side of the air preheater. A solenoid valve is installed on the high-pressure bottled air outlet pipeline, which automatically opens when the system is suddenly stopped.

[0013] The high-pressure bottled protective gas is composed of 5% H2 and 95% N2. It is used to safely purge the system's water vapor pipeline and hydrogen pipeline when the system is shut down suddenly, ensuring that the SOEC stack is cooled down at a certain rate and preventing the SOEC stack from being damaged by oxidation at high temperature. The high-pressure bottled protective gas outlet pipeline is connected to the hot side outlet pipeline of the steam generator and before the high-pressure bottled H2 access point. A solenoid valve is installed on the high-pressure bottled protective gas outlet pipeline, which automatically opens when the system is shut down suddenly.

[0014] The DC power supply provides electricity for electrolysis for the SOEC stack. The heating tape is located on the outlet pipeline of the steam generator. The maximum operating temperature of the heating tape should be above 400°C to ensure that the temperature of the laid pipeline can be stabilized at above 180°C.

[0015] The second object of the present invention is to provide an operation method of a SOEC hydrogen production system, comprising the following contents:

[0016] (1) Before cold starting the SOEC hydrogen production system, open the solenoid valves on the high-pressure bottled air and high-pressure bottled H2 outlet pipelines to purge the air pipeline and water vapor pipeline of the system respectively;

[0017] (2) During the initial warm-up phase of the cold start of the SOEC hydrogen production system, the solenoid valve on the outlet pipeline of the high-pressure bottled air is closed, the two fans are turned on and adjusted to an appropriate flow rate, the electric air heater is turned on, and a certain outlet air temperature rise rate is set. The air entering the SOEC stack is heated by the air preheater and the air reheater and then enters the SOEC stack for heating and temperature increase. In addition, the solenoid valve of the high-pressure bottled protective gas is opened, and the protective gas is heated by the steam superheater and then enters the steam inlet of the SOEC stack for heating and protection.

[0018] (3) As the temperature of the SOEC hydrogen production system continues to rise, the heating tape is turned on to heat the pipeline. When the temperature of all steam pipelines and steam superheaters between the cold side outlet of the steam generator and the steam inlet of the SOEC stack reaches above 180°C, the deionized water pump is turned on to supply deionized water to the system. After the deionized water is introduced, the solenoid valve of the high-pressure bottled protective gas is closed and the solenoid valve of the high-pressure bottled H2 is opened. The H2 is mixed with the water vapor at the outlet of the steam generator and heated by the steam superheater and enters the steam inlet of the SOEC stack for heating and protection.

[0019] (4) During the electrolysis hydrogen production process of the SOEC hydrogen production system; turn on the DC power supply and use the constant voltage mode for electrolysis. The voltage value of the electrolysis process is equal to the thermal neutralization voltage of the SOEC stack at that temperature. During the electrolysis process, the air flow rate entering the air inlet of the stack is controlled according to the temperature of the SOEC stack, and the outlet temperature of the air electric heater is adjusted to adjust the air temperature entering the SOEC stack and the temperature of the water vapor + H2 mixed gas; according to the electrolysis current, the amount of water vapor and the proportion of H2 entering the steam inlet of the SOEC stack are adjusted;

[0020] (5) During the cooling stage of the SOEC hydrogen production system, the cooling rate of the SOEC stack and the entire system is controlled by controlling the cooling rate of the air electric heater. At the beginning of the cooling stage, a mixture of water vapor and H2 is introduced into the steam inlet of the SOEC stack. When the temperature of all steam pipelines and steam superheaters between the cold side outlet of the steam generator and the steam inlet of the SOEC stack drops to 180°C, the deionized water pump and high-pressure bottled H2 are turned off and switched to protective gas. The heating belt is turned off when the temperature continues to drop to less than 120°C at the steam outlet of the SOEC stack. When the temperature drops below 80°C, the fan and air electric heater are turned off to complete the cooling process.

[0021] Compared with the prior art, the advantages of the present invention are: the system uses an electric heater to achieve air reheating at the inlet of the SOEC stack, steam superheating and high-temperature steam generation; the high-temperature air at the outlet of the SOEC stack is heat-exchanged with room-temperature air to achieve waste heat recovery and improve the thermal efficiency of the system; high-pressure bottled H2 is used to provide a reducing atmosphere on the fuel side for system heating and power generation, avoiding the use of complex equipment such as high-temperature circulating fans and ejectors, reducing the complexity of the system and facilitating regulation; the high-temperature hydrogen at the outlet of the SOEC stack is condensed and dehydrated and waste heat is recovered in the condenser; the system process architecture is simple, easy to regulate, the system manufacturing cost is low, and the overall power consumption is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 This is a process flow chart of a solid oxide fuel electrolysis cell hydrogen production system;

[0024] In the figure, 1. SOEC stack, 2. fan, 3. air preheater, 4. air reheater, 5. deionized water pump, 6. condenser, 7. steam generator, 8. steam superheater, 9. air electric heater, 10. high-pressure bottled H2, 11. high-pressure bottled air, 12. high-pressure bottled protective gas, 13. DC power supply, 14. solenoid valve. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0026] The specific implementation of the present invention will be described below in conjunction with the accompanying drawings:

[0027] like Figure 1As shown, a SOEC hydrogen production system includes a SOEC stack 1, a fan 2, an air preheater 3, an air reheater 4, a deionized water pump 5, a condenser 6, a steam generator 7, a steam superheater 8, an air electric heater 9, a high-pressure bottled H2 10, a high-pressure bottled air 11, a high-pressure bottled protective gas 12, a solenoid valve 14, a heating belt, and a DC power supply 13 for providing electrolysis electricity to the SOEC stack; the steam inlet of the SOEC stack 1 is connected to the steam superheater 8, the steam generator 7, the condenser 6, and the deionized water pump 5 in sequence, and the steam outlet of the SOEC stack 1 is connected to the condenser 6; the high-pressure bottled protective gas 12 is connected to the hot side outlet pipeline of the steam generator 7 through the solenoid valve 14; the high-pressure bottled H2 Pipeline 10 is connected in front of the cold side inlet of the steam superheater 8; the air inlet of the SOEC stack 1 is connected to the air reheater 4, the air preheater 3, and the fan 2 in sequence, and the air outlet of the SOEC stack 1 is connected to the air preheater 3; the cold side air inlet of the air preheater 3 is connected to the high-pressure bottled air 11 through the solenoid valve 14; the fan 2 is provided in front of the electric air heater 9, and the electric air heater is connected to the steam superheater 8, the air reheater 4, and the steam generator 7 in sequence; the heating belt is located on the outlet pipeline of the steam generator 7.

[0028] The air used for system heating enters the air electric heater 9 under the action of the fan 2 and is heated to 900°C, and then enters the hot side channel of the steam superheater 8, the air reheater 4, and the steam generator 7 for heat exchange, and is finally cooled to below 150°C and discharged from the system.

[0029] The air used to heat the SOEC stack 1 enters the cold side channel of the air preheater 3 under the action of the fan 2, and exchanges heat with the high-temperature air from the air side outlet of the SOEC stack 1 in the hot side channel; then enters the air reheater 4, and exchanges heat with the high-temperature air from the hot side outlet of the steam superheater 8 in the hot side channel; then enters the air inlet of the SOEC stack 1, and after heat exchange with the SOEC stack 1, is discharged from the air outlet to the hot side channel of the air preheater 3, and finally discharged to the atmosphere.

[0030] High-pressure bottled H2 10 is used in the processes of heating, electrolysis, hot standby, cooling, etc. of the SOEC stack 1, providing a reducing atmosphere at high temperature for the SOEC stack 1, and preventing the electrode materials of the SOEC stack 1 from being oxidized and damaged at high temperature; the high-pressure bottled H2 10 pipeline is connected before the cold side inlet of the steam superheater 8.

[0031] The deionized water enters the cold side channel of the condenser 6 under the action of the deionized water pump 5, and exchanges heat with the mixture of the high-temperature product H2 and steam from the steam outlet of the SOEC stack 1 on the hot side; then enters the cold side channel of the steam generator 7, and exchanges heat with the high-temperature air from the hot side outlet of the air reheater 4 on the hot side; after being mixed with the high-pressure bottled H2 10, it then enters the cold side channel of the steam superheater 8, and exchanges heat with the high-temperature air from the outlet of the air electric heater 9 on the hot side; then enters the SOEC stack 1 for electrolysis reaction, and then flows to the condenser 6 through the steam outlet to realize steam condensation, H2 separation and purification, and discharge system.

[0032] The high-pressure bottled air 11 is used to safely purge the system air pipeline when the system is suddenly stopped to ensure that the SOEC stack 1 is cooled at a certain rate. The outlet pipeline of the high-pressure bottled air 11 is connected in front of the air inlet on the cold side of the air preheater 3. A solenoid valve 14 is installed on the outlet pipeline of the high-pressure bottled air 11, which is automatically opened when the system is suddenly stopped.

[0033] The high-pressure bottled protective gas 12 is configured with 5% H2 and 95% N2, and is used to safely purge the system water vapor pipeline and hydrogen pipeline when the system is suddenly stopped, to ensure that the SOEC stack 1 is cooled at a certain rate and to prevent the SOEC stack 1 from being oxidized and damaged at high temperature; the outlet pipeline of the high-pressure bottled protective gas 12 is connected to the hot side outlet pipeline of the steam generator 7 and before the access point of the high-pressure bottled H2 10, and a solenoid valve 14 is installed on the outlet pipeline of the high-pressure bottled protective gas 12, which is automatically opened when the system is suddenly stopped.

[0034] The DC power supply 13 provides electricity for electrolysis for the SOEC stack 1. The heating tape is located on the outlet pipeline of the steam generator 7. The maximum operating temperature of the heating tape should be above 400°C to ensure that the temperature of the laid pipeline can be stabilized at above 180°C.

[0035] An operation method of a SOEC hydrogen production system includes the following contents:

[0036] (1) Before cold starting the SOEC hydrogen production system, open the solenoid valves 14 on the outlet pipelines of the high-pressure bottled air 11 and the high-pressure bottled H2 10 to purge the air pipeline and the water vapor pipeline of the system respectively;

[0037] (2) During the initial warm-up phase of the cold start of the SOEC hydrogen production system, the solenoid valve 14 on the outlet pipeline of the high-pressure bottled air 11 is closed, the two fans are turned on and adjusted to a suitable flow rate, the electric air heater 9 is turned on, and a certain outlet air temperature rise rate is set. The air entering the SOEC stack 1 is heated by the air preheater 3 and the air reheater 4 and then enters the SOEC stack 1 for heating and temperature rise; in addition, the solenoid valve 14 of the high-pressure bottled protective gas 12 is opened, and the protective gas is heated by the steam superheater 8 and then enters the steam inlet of the SOEC stack 1 for heating and protection;

[0038] (3) As the temperature of the SOEC hydrogen production system continues to rise, the heating tape is turned on to heat the pipeline. When the temperature of all steam pipelines and steam superheater 8 between the cold side outlet of the steam generator 7 and the steam inlet of the SOEC stack 1 reaches above 180°C, the deionized water pump 5 is turned on to supply deionized water to the system. After the deionized water is introduced, the solenoid valve 14 of the high-pressure bottled protective gas 12 is closed, and the solenoid valve 14 of the high-pressure bottled H2 10 is opened. The H2 is mixed with the water vapor at the outlet of the steam generator 7, heated by the steam superheater 8, and enters the steam inlet of the SOEC stack 1 to be heated and protected.

[0039] (4) During the electrolysis hydrogen production process of the SOEC hydrogen production system; turn on the DC power supply 13, and use the constant voltage mode for electrolysis. The voltage value of the electrolysis process is equal to the thermal neutralization voltage of the SOEC stack 1 at this temperature; during the electrolysis process, the air flow rate entering the air inlet of the stack is controlled according to the temperature of the SOEC stack 1, and the outlet temperature of the air electric heater 9 is adjusted to adjust the air temperature entering the SOEC stack 1 and the temperature of the water vapor + H2 mixed gas; according to the electrolysis current, the amount of water vapor and the proportion of H2 entering the steam inlet of the SOEC stack 1 are adjusted;

[0040] (5) During the cooling stage of the SOEC hydrogen production system, the cooling rate of the SOEC stack 1 and the entire system is controlled by controlling the cooling rate of the air electric heater 9. At the beginning of the cooling stage, a mixture of water vapor and H2 is introduced into the steam inlet of the SOEC stack 1. When the temperature of all steam pipelines and steam superheater 8 between the cold side outlet of the steam generator 7 and the steam inlet of the SOEC stack 1 drops to 180°C, the deionized water pump 5 and the high-pressure bottled H2 10 are turned off and switched to protective gas. The temperature continues to drop until the steam outlet temperature of the SOEC stack 1 is less than 120°C, and the heating belt is turned off. When the temperature drops below 80°C, the fan 2 and the air electric heater 9 are turned off to complete the cooling process.

[0041] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may still be modified, or some or all of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A SOEC hydrogen production system, characterized in that: The invention comprises a SOEC stack, a fan, an air preheater, an air reheater, a deionized water pump, a condenser, a steam generator, a steam superheater, an air electric heater, high-pressure bottled H2, high-pressure bottled air, high-pressure bottled protective gas, a solenoid valve, a heating belt, and a DC power supply for providing electrolysis electricity to the SOEC stack; the steam inlet of the SOEC stack is connected to the steam superheater, the steam generator, the condenser, and the deionized water pump in sequence, and the steam outlet of the SOEC stack is connected to the condenser; the high-pressure bottled protective gas is connected to the steam inlet of the SOEC stack through the solenoid valve. On the hot side outlet pipeline of the steam generator; the high-pressure bottled H2 pipeline is connected in front of the cold side inlet of the steam superheater; the air inlet of the SOEC stack is connected to the air reheater, air preheater and fan in sequence, and the air outlet of the SOEC stack is connected to the air preheater; the cold side air inlet of the air preheater is connected to the high-pressure bottled air through a solenoid valve; a fan is provided in front of the air electric heater, and the air electric heater is connected to the steam superheater, air reheater and steam generator in sequence; the heating belt is located on the steam generator outlet pipeline.

2. A SOEC hydrogen production system according to claim 1, characterized in that: The air used for system heating enters the air electric heater under the action of the fan and is heated to 900°C, then enters the steam superheater, air reheater, and hot side channel of the steam generator for heat exchange, and is finally cooled to below 150°C and discharged from the system.

3. A SOEC hydrogen production system according to claim 1, characterized in that: The air used for heating the SOEC stack enters the cold side channel of the air preheater under the action of the fan, and exchanges heat with the high-temperature air from the air side outlet of the SOEC stack in the hot side channel; Then it enters the air reheater and exchanges heat with the high-temperature air from the hot side outlet of the steam superheater in the hot side channel; then it enters the air inlet of the SOEC stack, exchanges heat with the SOEC stack, and is discharged from the air outlet to the hot side channel of the air preheater, and finally discharged to the atmosphere.

4. A SOEC hydrogen production system according to claim 1, characterized in that: The high-pressure bottled H2 is used in the heating, electrolysis, hot standby and cooling processes of the SOEC stack, providing a reducing atmosphere at high temperature for the SOEC stack to prevent the electrode materials of the SOEC stack from being oxidized and damaged at high temperature; the high-pressure bottled H2 pipeline is connected in front of the cold side inlet of the steam superheater.

5. A SOEC hydrogen production system according to claim 1, characterized in that: Deionized water enters the cold side channel of the condenser under the action of the deionized water pump, and exchanges heat with the mixture of high-temperature product H2 and steam from the steam outlet of the SOEC stack on the hot side; then enters the cold side channel of the steam generator, and exchanges heat with the high-temperature air from the hot side outlet of the air reheater on the hot side; after being mixed with the high-pressure bottled H2, it then enters the cold side channel of the steam superheater, and exchanges heat with the high-temperature air from the outlet of the air electric heater on the hot side; then enters the SOEC stack for electrolysis reaction, and then flows to the condenser through the steam outlet to realize steam condensation, H2 separation and purification, and discharge system.

6. A SOEC hydrogen production system according to claim 1, characterized in that: The high-pressure bottled air is used to safely purge the system air pipeline when the system is suddenly stopped to ensure that the SOEC stack is cooled at a certain rate. The high-pressure bottled air outlet pipeline is connected in front of the air inlet on the cold side of the air preheater. A solenoid valve is installed on the high-pressure bottled air outlet pipeline, which automatically opens when the system is suddenly stopped.

7. A SOEC hydrogen production system according to claim 1, characterized in that: The high-pressure bottled protective gas is composed of 5% H2 and 95% N2, and is used to safely purge the system's water vapor pipeline and hydrogen pipeline when the system is suddenly stopped, ensuring that the SOEC stack is cooled at a certain rate and preventing the SOEC stack from being oxidized and damaged at high temperature; the high-pressure bottled protective gas outlet pipeline is connected to the hot side outlet pipeline of the steam generator and before the high-pressure bottled H2 access point, and a solenoid valve is installed on the high-pressure bottled protective gas outlet pipeline, which is automatically opened when the system is suddenly stopped.

8. A SOEC hydrogen production system according to claim 1, characterized in that: The DC power supply provides electricity for electrolysis for the SOEC stack. The heating tape is located on the outlet pipeline of the steam generator. The maximum operating temperature of the heating tape should be above 400°C to ensure that the temperature of the laid pipeline can be stabilized at above 180°C.

9. The method for operating the SOEC hydrogen production system according to any one of claims 1 to 8, characterized in that: It includes the following: (1) Before cold starting the SOEC hydrogen production system, open the solenoid valves on the high-pressure bottled air and high-pressure bottled H2 outlet pipelines to purge the air pipeline and water vapor pipeline of the system respectively; (2) During the initial warm-up phase of the cold start of the SOEC hydrogen production system, the solenoid valve on the outlet pipeline of the high-pressure bottled air is closed, the two fans are turned on and adjusted to an appropriate flow rate, the electric air heater is turned on, and a certain outlet air temperature rise rate is set. The air entering the SOEC stack is heated by the air preheater and the air reheater and then enters the SOEC stack for heating and temperature increase. In addition, the solenoid valve of the high-pressure bottled protective gas is opened, and the protective gas is heated by the steam superheater and then enters the steam inlet of the SOEC stack for heating and protection. (3) As the temperature of the SOEC hydrogen production system continues to rise, the heating tape is turned on to heat the pipeline. When the temperature of all steam pipelines and steam superheaters between the cold side outlet of the steam generator and the steam inlet of the SOEC stack reaches above 180°C, the deionized water pump is turned on to supply deionized water to the system. After the deionized water is introduced, the solenoid valve of the high-pressure bottled protective gas is closed and the solenoid valve of the high-pressure bottled H2 is opened. The H2 is mixed with the water vapor at the outlet of the steam generator and heated by the steam superheater and enters the steam inlet of the SOEC stack for heating and protection. (4) During the electrolysis hydrogen production process of the SOEC hydrogen production system; turn on the DC power supply and use the constant voltage mode for electrolysis. The voltage value of the electrolysis process is equal to the thermal neutralization voltage of the SOEC stack at that temperature; During the electrolysis process, the air flow rate entering the air inlet of the SOEC stack is controlled according to the temperature of the SOEC stack, and the outlet temperature of the air electric heater is adjusted to adjust the air temperature entering the SOEC stack and the temperature of the water vapor + H2 mixed gas; the amount of water vapor and the proportion of H2 entering the steam inlet of the SOEC stack are adjusted according to the electrolysis current; (5) During the cooling stage of the SOEC hydrogen production system, the cooling rate of the SOEC stack and the entire system is controlled by controlling the cooling rate of the air electric heater. At the beginning of the cooling stage, a mixture of water vapor and H2 is introduced into the steam inlet of the SOEC stack. When the temperature of all steam pipelines and steam superheaters between the cold side outlet of the steam generator and the steam inlet of the SOEC stack drops to 180°C, the deionized water pump and high-pressure bottled H2 are turned off and switched to protective gas. The heating belt is turned off when the temperature continues to drop to less than 120°C at the steam outlet of the SOEC stack. When the temperature drops below 80°C, the fan and air electric heater are turned off to complete the cooling process.

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