Natural gas based solid oxide cell power generation and hydrogen production system and method

Abstract

A solid oxide battery power generation and hydrogen production system and method based on natural gas is disclosed. The power generation and hydrogen production system includes a fuel cell stack, a reformer, a fuel supply, an air supply, a deionized water supply, a thermal management module, a tail gas treatment and recycling module, and a bidirectional power supply. It can switch between two directions, using natural gas and steam to reform hydrogen-rich gas into the fuel cell stack. During the start-up and preheating phase, natural gas is supplied to the burner. During the power generation and operation phase, natural gas and protective gas are supplied, the total air volume of the air preheater and the flow rate of the high-temperature air branch are controlled, and deionized water is vaporized and delivered to the reformer or the fuel electrode of the fuel cell stack. The system achieves cascaded heat recovery and heat compensation during the mode switching transition phase. Its operation method includes power generation and hydrogen production modes and the switching between the two. It has advantages such as eliminating the thermal stress shock of the fuel cell stack and plate oxidation caused by the dual-mode switching window period, and having a generational advantage in fuel adaptability and operational stability.

Description

Technical Field

[0001] This invention relates to the field of new energy technology, and in particular to a solid oxide battery power generation and hydrogen production system and method based on natural gas. Background Technology

[0002] With the rapid development of renewable energy, the transformation of the energy structure has created an urgent need for large-scale, long-term energy storage technologies. Solid oxide cell (SOC) systems can convert fuel into electricity in SOFC (Solar-Oxide-Fuel-Cyclic) mode and convert electricity into hydrogen for storage in SOEC (Solar-Oxide-Electric) mode, offering advantages such as high efficiency and flexible operation. Especially when using natural gas as a feedstock, it can make full use of existing infrastructure, reduce fuel supply costs, and has promising engineering application prospects.

[0003] However, compared to systems using pure hydrogen fuel, natural gas-based SOC power generation and hydrogen production systems involve multiple physical processes such as reforming reactions, gas composition changes, and thermal coupling, significantly increasing system complexity. Existing technologies (such as Chinese patent document CN115101789A) are mostly designed for hydrogen-water vapor systems. When applied to switching between power generation and hydrogen production modes under natural gas fuel conditions, the lack of synergistic matching between the thermal effects of the reforming reaction and the thermal characteristics of the fuel cell stack still presents the following problems:

[0004] (1) Insufficient fuel adaptability: During the natural gas reforming process, the temperature distribution or gas-to-carbon ratio control is unstable, which can easily lead to incomplete reaction and carbon deposits, affecting the service life of the fuel cell stack.

[0005] (2) Thermal management and mode switching issues: During the switching process between power generation mode and hydrogen production mode, there is a lack of a refined thermal control mechanism, which can easily lead to stack temperature fluctuations and thermal stress concentration.

[0006] (3) Insufficient thermal integration of the system: Existing technologies mostly adopt simple heat exchange structures, and the thermal coupling efficiency between the air side and the fuel side is low, resulting in a decrease in the overall energy utilization efficiency under natural gas conditions.

[0007] Therefore, existing technologies still have shortcomings in terms of natural gas fuel adaptability, thermal management during mode switching, and system thermal integration optimization, and need further optimization.

[0008] To address the aforementioned issues, several individuals have publicly disclosed their findings: the inventor conducted a preliminary search using keywords such as "solid oxide battery (SOC), natural gas, dual-mode switching, thermal management, and exhaust gas recirculation."

[0009] Our research group found that existing technologies (such as CN115101789A) are designed for the "pure hydrogen-water vapor" system and can achieve the switching of shared components between power generation and electrolysis modes, but do not take into account the deep coupling of the direct application of natural gas and the thermal effects of reforming reaction with system thermal management.

[0010] Therefore, it is of great significance to develop a solid oxide battery power generation and hydrogen production system and method based on natural gas. Summary of the Invention

[0011] The objective of this invention is to overcome the shortcomings of existing technologies and provide a solid oxide battery power generation and hydrogen production system and method based on natural gas, which can achieve both [power generation and hydrogen production]. The core advantage of this invention lies in its innovative design of a "power load-based tail gas dynamic micro-circulation (10%~20%) architecture" and a "thermal-gas coordinated anti-impact switching control strategy" specifically for natural gas operating conditions. This not only completely solves the carbon deposition problem easily caused by direct natural gas input into the reactor, but also fundamentally eliminates the risks of reactor thermal stress shock and plate oxidation caused by the dual-mode switching window period, demonstrating a significant generational advantage over existing technologies in terms of fuel adaptability and operational stability.

[0012] The objective of this invention is achieved through the following technical solution:

[0013] A solid oxide battery power generation and hydrogen production system based on natural gas includes a fuel cell stack, a reformer, a fuel supply module, an air supply module, a deionized water supply module, a thermal management module, a tail gas treatment and recycling module, and a bidirectional power supply. The fuel cell stack enables bidirectional conversion of electrical energy to chemical energy between power generation and hydrogen production modes. The reformer's inlet is connected to the fuel supply module and the deionized water supply module, and its outlet is connected to the fuel electrode of the fuel cell stack. It is used to perform steam reforming of natural gas and steam to generate hydrogen-rich gas, which is then introduced into the fuel cell stack. The fuel supply module includes a first gas path and a second gas path. The first gas path is connected to a burner and supplies natural gas to the burner during the start-up preheating phase. The second gas path is connected to a steam generator and supplies natural gas during the power generation operation phase, and introduces protective gas during hydrogen production mode and mode switching phases. The air supply module includes a blower, an air flow meter, a main butterfly valve, and a sub-butterfly valve. The main butterfly valve controls the air entering for preheating. The total air volume of the reactor, the sub-butterfly valve is used to control the flow rate of the high-temperature air branch entering the reformer (6); the deionized water supply module includes a deionized water tank, a deionized water pump and the steam generator, which is used to vaporize the deionized water and deliver it to the reformer or the fuel electrode of the fuel cell stack; the thermal management module includes the air preheater, steam heat exchanger, steam electric heater, air electric heater and the burner, which is used to realize the cascade recovery of system heat and the heat compensation during the mode switching transition stage; the tail gas treatment and recycling module includes a condenser, a gas-water separator, a circulation solenoid valve, a circulation pump and an anode tail gas solenoid valve, the anode tail gas solenoid valve is used to control the flow rate of the dry tail gas to the burner, the circulation solenoid valve and the circulation pump are used to control the flow rate of the dry tail gas back to the front end of the system; the bidirectional power supply is electrically connected to the fuel cell stack, converting the DC power generated by the fuel cell stack into AC power output in the power generation mode, and converting external electrical energy into DC power input to the fuel cell stack in the hydrogen production mode.

[0014] A solid oxide battery power generation and hydrogen production system and method for natural gas, comprising a power generation mode step, a hydrogen production mode step, and a switching step between the power generation mode and the hydrogen production mode, wherein the switching step includes:

[0015] S1: Receive mode switching request signal;

[0016] S2: Determine the switching direction. When the switching direction is from power generation mode to hydrogen production mode, execute steps S3 to S9 in sequence; when the switching direction is from hydrogen production mode to power generation mode, execute steps S10 to S18 in sequence.

[0017] S3: Gradually reduce the output power of the power generation mode through the bidirectional power supply, and turn on the steam electric heater and the air electric heater for heat compensation;

[0018] S4: Gradually close the valves of the first gas circuit and the second gas circuit to cut off the natural gas supply;

[0019] S5: Low-concentration hydrogen is introduced through the second gas passage as a protective gas to purge the residual gas in the fuel electrode flow channel of the fuel cell stack, so that the fuel electrode of the fuel cell stack is in a reducing atmosphere.

[0020] S6: Determine whether the temperature of the fuel cell stack is stable within the set target operating temperature range. If not, return to step S5; otherwise, proceed to step S7.

[0021] S7: Open the solenoid valve of the deionized water circuit. The deionized water is heated by the steam generator, the steam heat exchanger, the reformer flow channel and the steam electric heater before entering the fuel electrode of the fuel cell stack.

[0022] S8: Switch the bidirectional power supply to DC electrolysis power supply mode;

[0023] S9: Entering stable operation in hydrogen production mode;

[0024] S10: Gradually reduce the electrolysis input power to standby state through the bidirectional power supply, reduce the power of the steam electric heater, and reduce the flow rate of deionized water entering the system;

[0025] S11: Maintain a low concentration of hydrogen gas flowing through the second gas path to keep the fuel cell stack in a hot standby and anti-oxidation state;

[0026] S12: The recirculated hydrogen or residual combustible gas in the system pipeline is introduced into the burner for ignition and combustion. The high-temperature exhaust gas generated is used by the air preheater and the steam generator to establish a reaction temperature field for the reformer, and the preheating rate is controlled by adjusting the sub-butterfly valve.

[0027] S13: Determine whether the reformer and the fuel cell stack have reached the set target operating temperature. If not, return to step S12; otherwise, proceed to step S14.

[0028] S14: Cut off the external hydrogen gas source at the front end of the second gas circuit and stop the supply of protective gas;

[0029] S15: Increase the deionized water inlet flow rate and introduce water vapor into the system;

[0030] S16: Adjust the valve of the second gas circuit to introduce natural gas and maintain the gas-to-carbon ratio of the reformer greater than the set value;

[0031] S17: After the open-circuit voltage of the fuel cell stack stabilizes, switch the bidirectional power supply to AC output mode and gradually increase the power generation capacity.

[0032] S18: Entering stable operation mode for power generation.

[0033] Compared with the prior art, the innovative points, advantages or effects of this invention are as follows:

[0034] (1) High system integration and flexible operation mode: The stack, reformer, bidirectional power supply and shared thermal management and fluid control module are integrated in a single device to realize the hardware reuse of SOFC and SOEC dual modes. Compared with the independently configured SOFC and SOEC systems, the equipment redundancy is significantly reduced. At the method level, the smooth switching between the two operation modes is realized through the timing coordination of the dual-mode switching control strategy, which can be applied to multiple scenarios such as grid peak shaving, distributed energy and energy storage.

[0035] (2) Good natural gas adaptability and long stack service life: By setting up a natural gas reforming-heat exchange unit consisting of a reformer, a steam generator and a steam heat exchanger, a dedicated structural basis is provided for the electrochemical utilization of natural gas fuel; at the method level, by using low-concentration hydrogen purging, maintaining an anti-oxidation atmosphere and a high steam-to-carbon ratio entry strategy, the tendency of natural gas to accumulate carbon at the cold end of the reformer or the inlet of the stack is fundamentally suppressed, and oxidation damage to high-temperature electrode materials is avoided, thereby improving the structural stability of the stack and the service life of the system.

[0036] (3) High level of thermal integration and excellent energy utilization efficiency: A multi-stage heat recovery path is formed by an air preheater, a steam heat exchanger, and a steam generator, and a circulating solenoid valve and a circulating pump are set to realize partial gas recycling; at the method level, through the seamless connection of reaction exothermic and electric heating, the use of circulating reflux hydrogen as a heat source, and the control strategy of controlling the preheating rate by a butterfly valve, high-efficiency thermal coupling between the air side and the fuel side is achieved. Under the preferred implementation method, the system power generation efficiency can reach about 55%~65%, and the hydrogen production efficiency can reach about 80%~90%, which is far superior to conventional low-temperature water electrolysis technology.

[0037] (4) Smooth switching process and low thermal stress risk: The system is equipped with thermal compensation and rate regulation components such as steam electric heater, air electric heater and sub-butterfly valve, which provide the hardware foundation for thermal field control during the mode switching process; at the method level, through full-process parameter boundary constraints and temperature target judgment and reflux control strategy, the problem of drastic temperature fluctuation and thermal stress concentration of the fuel cell stack during the mode switching process is fundamentally avoided, ensuring the reliability of dual-mode operation.

[0038] (5) Low system cost and good economic efficiency: Since the power generation and hydrogen production modes share the same key auxiliary subsystems (including air preheater, heat exchanger, fluid control valve group and bidirectional power supply, etc.), the number of equipment configurations can be greatly reduced and the system investment cost can be reduced. At the method level, the present invention adopts the time decoupling operation strategy of "natural gas peak period power generation + off-peak electricity hydrogen production for external supply", which can flexibly respond to grid load fluctuations, eliminate the dependence of traditional energy storage systems on large hydrogen storage containers, and improve overall economic efficiency and operational flexibility.

[0039] (6) Broad engineering application prospects: This system can be directly connected to existing natural gas infrastructure and power grid facilities without the need to build a new dedicated gas source; at the method level, the proposed dual-mode switching control strategy has standardized and modular features, which is suitable for multiple scenarios such as power grid peak shaving, industrial hydrogen production, hydrogen refueling stations and distributed energy, and has good potential for industrialization and promotion. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the structure of a natural gas-based solid oxide battery power generation and hydrogen production system in SOFC power generation mode, according to the present invention.

[0041] Figure 2 This is a schematic diagram of the structure of the solid oxide battery power generation and hydrogen production system based on natural gas in the hydrogen production SOEC mode of the present invention.

[0042] Figure 3 This is a schematic flowchart illustrating the method steps of the dual-mode switching control strategy for power generation and hydrogen production using a solid oxide battery based on natural gas, as described in this invention.

[0043] The symbols in the attached diagram represent:

[0044] 1. Air preheater 2. Air electric heater 3. Fuel cell stack 4. Burner 5. Steam electric heater 6. Reformer 7. Steam heat exchanger 8. Steam generator 9. Air filter 10. Blower 11. Air flow meter 12. Main butterfly valve 13. Sub-butterfly valve 14. Cooling water tank 15. Cooling water pump 16. Condenser 17. Air-cooled radiator 18. First gas circuit manual valve 19. First gas circuit solenoid valve 20. First gas circuit mass flow controller 21. First gas circuit check valve 22. Second gas circuit manual valve 23. Second gas circuit solenoid valve 24. Second gas circuit mass flow controller 25. Second gas circuit check valve 26. Deionized water circuit solenoid valve 27. Deionized water tank 28. Deionized water pump 29. Deionized water flow meter 30. Gas-liquid separator 31. Circulation circuit solenoid valve 32. Circulation pump 33. Anode tail gas solenoid valve 34. Bidirectional power supply

[0045] The present invention will now be described in further detail with reference to the accompanying drawings. Detailed Implementation

[0046] like Figures 1-3 As shown, the power generation and hydrogen production system includes a fuel cell stack 3, a reformer 6, a fuel supply module, an air supply module, a deionized water supply module, a thermal management module, a tail gas treatment and recycling module, and a bidirectional power supply 34. The fuel cell stack 3 is used to realize bidirectional conversion of electrical energy and chemical energy between power generation mode and hydrogen production mode. The inlet of the reformer 6 is connected to the fuel supply module and the deionized water supply module, and the outlet is connected to the fuel electrode of the fuel cell stack 3. It is used to perform steam reforming reaction of natural gas and steam to generate hydrogen-rich gas and introduce it into the fuel cell stack 3. The fuel supply module includes a first gas path and a second gas path. The first gas path is connected to the burner 4 and is used to supply natural gas to the burner 4 during the start-up preheating stage. The second gas path is connected to the steam generator 8 and is used to supply natural gas during the power generation operation stage and to introduce protective gas during the hydrogen production mode and mode switching stage. The air supply module includes a blower 10, an air flow meter 11, a main butterfly valve 12, and a sub-butterfly valve 13. The main butterfly valve 12 is used to control the total amount of air entering the air preheater 1, and the sub-butterfly valve 13... Valve 13 is used to control the flow rate of the high-temperature air branch entering the reformer 6; the deionized water supply module includes a deionized water tank 27, a deionized water pump 28, and the steam generator 8, used to vaporize the deionized water and deliver it to the reformer 6 or the fuel electrode of the fuel cell stack 3; the thermal management module includes the air preheater 1, the steam heat exchanger 7, the steam electric heater 5, the air electric heater 2, and the burner 4, used to realize the cascade recovery of system heat and heat compensation during the mode switching transition phase; the exhaust gas treatment and recycling... The module includes a condenser 16, a gas-liquid separator 30, a circulation solenoid valve 31, a circulation pump 32, and an anode tail gas solenoid valve 33. The anode tail gas solenoid valve 33 is used to control the flow rate of the dry tail gas to the burner 4. The circulation solenoid valve 31 and the circulation pump 32 are used to control the flow rate of the dry tail gas returning to the front end of the system. The bidirectional power supply 34 is electrically connected to the fuel cell stack 3. In the power generation mode, it converts the DC power generated by the fuel cell stack 3 into AC power output. In the hydrogen production mode, it converts external electrical energy into DC power input to the fuel cell stack 3.

[0047] The system can be further improved by:

[0048] The first gas circuit includes, in sequence, a first gas circuit manual valve 18, a first gas circuit solenoid valve 19, a first gas circuit mass flow controller 20, and a first gas circuit check valve 21; the second gas circuit includes, in sequence, a second gas circuit manual valve 22, a second gas circuit solenoid valve 23, a second gas circuit mass flow controller 24, and a second gas circuit check valve 25; the first gas circuit and the second gas circuit are set independently of each other.

[0049] The air supply module also includes an air filter 9. Air enters the air preheater 1 sequentially through the air filter 9, the blower 10, the air flow meter 11, and the main butterfly valve 12. The sub-butterfly valve 13 is located on the branch between the air preheater 1 and the reformer 6. The amount of high-temperature air entering the reformer 6 is adjusted by regulating the opening of the sub-butterfly valve 13, so as to control the reaction temperature of the reformer 6 and the preheating rate during the mode switching process.

[0050] The deionized water supply module also includes a deionized water circuit solenoid valve 26 and a deionized water flow meter 29; the steam generator 8 and the steam heat exchanger 7 form a series steam heating path, the steam generator 8 absorbs the waste heat of the tail gas to preheat the deionized water by vaporization, and the steam heat exchanger 7 further absorbs the waste heat of the high-temperature gas at the fuel electrode outlet of the fuel cell stack 3.

[0051] The thermal management module forms a multi-stage heat recovery path. The air preheater 1 is located downstream of the exhaust gas outlet of the burner 4 and is used for the first stage of preheating of the supplied air. The steam heat exchanger 7 is located downstream of the fuel electrode outlet of the fuel cell stack 3 and is used for the second stage of preheating of the mixture of steam and natural gas. The steam electric heater 5 and the air electric heater 2 are respectively set at the inlet ends of the fuel electrode and air electrode of the fuel cell stack 3 and are used for auxiliary heating during the mode switching transition stage and when the inlet gas temperature of the fuel cell stack is insufficient.

[0052] The exhaust gas treatment and recycling module also includes a cooling water tank 14, a cooling water pump 15, and an air-cooled radiator 17. The cooling water tank 14 supplies cooling water to the condenser 16 through the cooling water pump 15, and the air-cooled radiator 17 dissipates heat from the cooling water, forming a closed-loop cooling water circulation loop. The liquid water separated by the gas-water separator 30 flows back to the deionized water tank 27 for recycling.

[0053] The operation method of a natural gas-based solid oxide battery power generation and hydrogen production system includes a power generation mode step, a hydrogen production mode step, and a switching step between the power generation mode and the hydrogen production mode. The switching step includes:

[0054] S1: Receive mode switching request signal;

[0055] S2: Determine the switching direction. When the switching direction is from power generation mode to hydrogen production mode, execute steps S3 to S9 in sequence; when the switching direction is from hydrogen production mode to power generation mode, execute steps S10 to S18 in sequence.

[0056] S3: The output power of the power generation mode is gradually reduced by the bidirectional power supply 34, and the steam electric heater 5 and the air electric heater 2 are turned on for heat compensation.

[0057] S4: Gradually close the valves of the first gas circuit and the second gas circuit to cut off the natural gas supply;

[0058] S5: Low-concentration hydrogen is introduced through the second gas passage as a protective gas to purge the residual gas in the fuel electrode flow channel of the fuel cell stack 3, so that the fuel electrode of the fuel cell stack 3 is in a reducing atmosphere.

[0059] S6: Determine whether the temperature of the fuel cell stack 3 is stable within the set target operating temperature range. If not, return to step S5; otherwise, proceed to step S7.

[0060] S7: Open the solenoid valve 26 of the deionized water circuit. The deionized water is heated by the steam generator 8, the steam heat exchanger 7, the reformer 6 flow channel and the steam electric heater 5 and then enters the fuel electrode of the fuel cell stack 3.

[0061] S8: Switch the bidirectional power supply 34 to DC electrolysis power supply mode;

[0062] S9: Entering stable operation in hydrogen production mode;

[0063] S10: Gradually reduce the electrolysis input power to standby state through the bidirectional power supply 34, reduce the power of the steam electric heater 5, and reduce the flow rate of deionized water entering the system;

[0064] S11: Maintain a low concentration of hydrogen gas flowing through the second gas path to keep the fuel cell stack 3 in a hot standby and anti-oxidation state;

[0065] S12: The circulating hydrogen or residual combustible gas in the system pipeline is introduced into the burner 4 for ignition and combustion. The high-temperature exhaust gas generated is used by the air preheater 1 and the steam generator 8 to establish a reaction temperature field for the reformer 6, and the preheating rate is controlled by adjusting the sub-butterfly valve 13.

[0066] S13: Determine whether the reformer 6 and the fuel cell stack 3 have reached the set target operating temperature. If not, return to step S12; if yes, proceed to step S14.

[0067] S14: Cut off the external hydrogen gas source at the front end of the second gas circuit and stop the supply of protective gas;

[0068] S15: Increase the deionized water inlet flow rate and introduce water vapor into the system;

[0069] S16: Adjust the valve of the second gas circuit to introduce natural gas and maintain the gas-to-carbon ratio of the reformer 6 greater than the set value;

[0070] S17: After the open-circuit voltage of the fuel cell stack 3 stabilizes, the bidirectional power supply 34 is switched to AC output mode, and the power generation capacity is gradually increased.

[0071] S18: Entering stable operation mode for power generation.

[0072] The execution method can be further described as follows:

[0073] During the execution of the power generation mode step, hydrogen production mode step, and switching step, the allowable operating temperature range of the fuel cell stack 3 is controlled between 700℃ and 850℃, the inlet and outlet temperature difference of the fuel cell stack 3 is controlled to be no greater than 80℃, and the gas pressure difference on both sides of the fuel cell stack 3 is controlled to be no greater than 5kPa.

[0074] The exhaust gas treatment and recycling module in the power generation mode steps dynamically allocates the dry exhaust gas discharged from the fuel cell stack 3 based on the system power load: Under low power operation conditions, the circulation path solenoid valve 31 and the circulation pump 32 are closed, and all dry exhaust gas is introduced into the burner 4 through the anode exhaust gas solenoid valve 33; Under medium and high power operation conditions, the circulation path solenoid valve 31 and the circulation pump 32 are opened, and 10% to 20% of the dry exhaust gas is returned to the front end of the system and mixed with fresh natural gas and water vapor before re-entering the reformer 6, while the remaining dry exhaust gas is introduced into the burner 4 through the anode exhaust gas solenoid valve 33.

[0075] The volume concentration of low-concentration hydrogen in steps S5 and S11 is 5%~10%, and the flow rate is 0.5~1L / min. In the hydrogen production mode step, 5%~10% of the hydrogen after dehydration by the gas-liquid separator 30 is returned to the front end of the steam generator 8 through the circulation solenoid valve 31 and the circulation pump 32 to maintain the reducing atmosphere of the fuel electrode of the fuel cell stack 3.

[0076] The target operating temperature range in step S6 is 750℃±10℃; the steam-to-carbon ratio in step S16 is greater than the set value of a steam-to-carbon ratio S / C greater than 2.5.

[0077] In step S17, when gradually increasing the power generation, the current range is 10A~50A, and the fuel utilization rate is controlled at 65%; in step S8, under the DC electrolysis power supply mode, the water vapor utilization rate is controlled at 80%.

[0078] Example 1

[0079] System structure and methodology under SOFC (Single-State Power Generation) mode:

[0080] See Figure 1This embodiment describes the implementation of the SOFC power generation mode from two aspects: system hardware configuration and method operation flow. At the system level, the power generation mode involves a first gas circuit (including a first gas circuit manual valve 18, a first gas circuit solenoid valve 19, a first gas circuit mass flow controller 20, and a first gas circuit check valve 21), a second gas circuit (including a second gas circuit manual valve 22, a second gas circuit solenoid valve 23, a second gas circuit mass flow controller 24, and a second gas circuit check valve 25), an air circuit (including an air filter 9, a blower 10, an air flow meter 11, a main butterfly valve 12, and a sub-butterfly valve 13), and a deionized water circuit (including a deionized water circuit solenoid valve 26). The components include: a deionized water tank (27), a deionized water pump (28), a deionized water flow meter (29), a fuel cell stack (3), a reformer (6), a burner (4), an air preheater (1), a steam heat exchanger (7), a steam generator (8), a condensation and gas-liquid separation unit (including a condenser (16), a gas-liquid separator (30), a cooling water tank (14), a cooling water pump (15), an air-cooled radiator (17), a recycling module (including a circulation solenoid valve (31), a circulation pump (32), and an anode tail gas solenoid valve (33), and a bidirectional power supply (34). At the methodological level, the power generation mode's workflow sequentially includes four stages: start-up preheating, power generation operation, tail gas cascade heat exchange and condensation separation, and tail gas dynamic allocation and energy recovery based on power load, as detailed below:

[0081] (1) During the preheating stage, the first gas circuit manual valve 18 and the first gas circuit solenoid valve 19 are opened. Under the precise control of the first gas circuit mass flow controller 20, a certain amount of natural gas enters the burner 4 through the first gas circuit check valve 21. At the same time, the blower 10 in the air circuit is started. Cold air enters the blower 10 after being filtered by the air filter element 9, and the flow rate is measured and calibrated by the air flow meter 11. Then, it enters the air preheater 1, the air electric heater 2, and the cathode side of the fuel cell stack 3 through the main butterfly valve 12. In the burner 4, the introduced natural gas is mixed with the air and ignited. The high-temperature exhaust gas generated by the combustion enters the air preheater 1 (to preheat the cold air) and the fuel cell stack 3 (to raise the temperature of the fuel cell stack in a cold state) in sequence, and then enters the steam generator 8 (to provide the initial heat source for the subsequent vaporization of deionized water). After the heat of each component of the system is established, the exhaust gas is discharged from the system.

[0082] (2) During the power generation operation phase, when the temperature of the fuel cell stack 3 and the reformer 6 reaches the set operating temperature, the second gas circuit manual valve 22 and the second gas circuit solenoid valve 23 are opened. Under the control of the second gas circuit mass flow controller 24, the natural gas used as the power generation feedstock passes through the second gas circuit check valve 25 to the steam generator 8. At the same time, the deionized water circuit solenoid valve 26 is opened to introduce deionized water into the deionized water tank 27, and the deionized water pump 28 is started. Under the monitoring and adjustment of the deionized water flow meter 29, the system delivers deionized water to the steam generator 8 in a quantitative manner according to the set optimal steam-to-carbon ratio. After the deionized water is vaporized in the steam generator 8, it mixes with the natural gas to form a mixed gas, and then passes through the steam heat exchanger 7 to further absorb residual heat before entering the reformer 6. At this time, the amount of high-temperature air entering the reformer 6 is controlled by adjusting the air circuit butterfly valve 13 to maintain the temperature environment required for the reforming reaction. Natural gas undergoes steam reforming in reformer 6, and the resulting hydrogen-rich gas (containing H2, CO, and incompletely reformed CH4) enters the anode of fuel cell stack 3 to participate in electrochemical reactions. The direct current generated by the fuel cell stack is ultimately converted into alternating current for grid connection or output through bidirectional power supply 34.

[0083] (3) In the stage of tail gas cascade heat exchange and condensation separation, since the fuel utilization rate of the fuel cell stack is usually around 65%, the high-temperature tail gas discharged from the anode of the fuel cell stack contains a large amount of unreacted H2, CO and residual CH4 in addition to the H2O and CO2 generated by the reaction. The high-temperature anode tail gas first enters the steam heat exchanger 7 to exchange heat with the fresh natural gas / water vapor mixture that is about to enter the reformer, realizing the cascade recovery of high-grade heat energy; then the cooled tail gas enters the condenser 16, and under the action of the cooling water system (including cooling water tank 14, cooling water pump 15 and air-cooled radiator 17), the water vapor in the tail gas is condensed into liquid water. The gas-water mixture enters the gas-water separator 30, and the separated pure liquid water is directly returned to the deionized water tank 27 to realize the efficient closed-loop utilization of water resources.

[0084] (4) Dynamic distribution and energy recovery of exhaust gas based on power load: The dry anode exhaust gas after dehydration by gas-liquid separator 30 is mostly composed of carbon dioxide (CO2), with the remainder being high-calorific-value combustible gases (H2, CO, residual CH4). To balance the system's heat demand, fuel utilization rate, and ineffective heat load under different operating conditions, this example innovatively adopts a dynamic flow splitting control strategy based on system power load:

[0085] 1) Low-power operating conditions:

[0086] When the system is operating at low power or during the ramp-up phase after a cold start, the natural gas intake is small, and the overall heat generation of the system is limited. At this time, the primary control task is to maintain the high-temperature thermal balance of the fuel cell stack 3 and the reformer 6. Under this condition, the control system keeps the circulation circuit solenoid valve 31 closed, the circulation pump 32 shut down, and the exhaust gas circulation subsystem is not activated. All (100%) of the dried exhaust gas is introduced into the burner 4 through the anode exhaust gas solenoid valve 33, ensuring complete combustion of any remaining combustible gas in the exhaust gas. This maximizes the initial / maintenance heat source for the air preheater 1 and the steam generator 8, ensuring the system's temperature stability under low load.

[0087] 2) Medium-to-high power operating conditions:

[0088] When the system power increases to the set medium-high load threshold or rated operating condition, the natural gas intake volume increases significantly, the risk of carbon buildup at the inlet of reformer 6 increases sharply, and the internal reaction heat release is relatively abundant at this time. Under this condition, the control system automatically opens the circulation circuit solenoid valve 31 and starts the circulation pump 32 to accurately extract a small portion (preferably 10% to 20%) of the dry tail gas and return it to the front end of the system, where it mixes with fresh natural gas / water vapor and re-enters reformer 6.

[0089] This dynamic adjustment mechanism brings dual benefits: on the one hand, the small amount of H2 carried in the return gas effectively acts as a reducing protective gas, fundamentally suppressing the carbon deposition that is prone to occur in natural gas under medium and high load conditions; on the other hand, strictly controlling the circulation ratio at 10% to 20% perfectly avoids the ineffective heating energy consumption caused by pumping a large amount of non-calorific CO2 back to the front end (i.e., avoiding dragging down the thermodynamic efficiency of the system).

[0090] 3) Closed-loop combustion of exhaust gases and carbon emissions:

[0091] Under medium-to-high load cyclic conditions, the remaining majority, approximately 80-90% of the dry exhaust gas rich in CO2, is still introduced into the burner 4 for combustion through the anode exhaust gas solenoid valve 33, squeezing out the last bit of chemical energy (residual CH4, CO, and H2) to maintain the preheating of air and water vapor under medium-to-high load conditions. Regardless of the power level, all the carbon elements originally carried in the exhaust gas are ultimately safely discharged into the atmosphere as CO2 along with the combustion exhaust gas from the burner 4, achieving a closed-loop conservation of carbon matter under all operating conditions.

[0092] Example 2

[0093] System structure and process flow under SOEC (Solar-Optical Organic Hydrogen Production) mode:

[0094] See Figure 2This embodiment describes the implementation of SOEC hydrogen production mode from two aspects: system hardware configuration and method operation process. At the system level, the hydrogen production mode involves an air circuit (including air filter 9, blower 10, air flow meter 11, main butterfly valve 12), an air electric heater 2, a second gas circuit protection gas path (including second gas circuit hand valve 22, second gas circuit solenoid valve 23, second gas circuit mass flow controller 24, second gas circuit check valve 25), a deionized water circuit (including deionized water circuit solenoid valve 26, deionized water tank 27, deionized water pump 28, deionized water flow meter 29), a steam generator 8, a steam heat exchanger 7, a steam electric heater 5, an electric stack 3, a condensation and gas-liquid separation unit (including condenser 16, gas-liquid separator 30), a circulation circuit (including circulation circuit solenoid valve 31, circulation pump 32), and a bidirectional power supply 34. At the method level, the hydrogen production mode workflow includes four stages in sequence: system heating, electrode protection, electrolysis operation, and hydrogen reflux and output. In hydrogen production mode, this system acts as a cross-border energy conversion hub between the power grid and the gas grid. It primarily utilizes off-peak electricity or surplus renewable energy from the grid for efficient water electrolysis to produce hydrogen. The resulting high-purity hydrogen is directly supplied as a high-value-added energy commodity (e.g., for industrial use, hydrogen refueling station applications) or blended into the natural gas pipeline network, rather than being limited to internal power generation and reuse within the system. This time-decoupled operation strategy of "natural gas peak-hour power generation + off-peak electricity hydrogen production for external supply" effectively eliminates the dependence of traditional energy storage systems on large hydrogen storage containers, significantly improving the overall economic efficiency and operational flexibility of the system. Its specific workflow is as follows:

[0095] (1) During the system heating stage, the blower 10 is started to draw cold air into the system after it is filtered through the air filter element 9. The flow rate is measured and calibrated by the air flow meter 11, and the air enters the air preheater 1, the air electric heater 2, and the oxygen electrode side (anode) of the fuel cell stack 3 through the main butterfly valve 12. In the early stage of heating, due to the lack of reaction heat release, the system mainly heats the air entering the fuel cell stack by turning on the air electric heater 2, so that the fuel cell stack 3 gradually heats up. The hot air flowing through the fuel cell stack exchanges heat with the burner 4 (which is not ignited at this time, but only serves as a flow channel) and the air preheater 1, and then enters the steam generator 8 for subsequent water vaporization preheating, and finally exits the system.

[0096] (2) During the electrode protection stage, when the temperature of the fuel cell stack 3 rises to near the set threshold of the operating temperature, in order to prevent irreversible oxidation damage to the nickel-based material of the fuel electrode (cathode) under high temperature and high humidity conditions, the system introduces protective gas through the second gas circuit to establish a reducing atmosphere. The second gas circuit manual valve 22 and the second gas circuit solenoid valve 23 are opened, and under the precise control of the second gas circuit mass flow controller 24, low-concentration hydrogen gas with a volume concentration of 5% to 10% (with nitrogen as the balance gas, i.e., the industry standard safe nucleation gas) is introduced, and the flow rate is controlled within the safe range of 0.5 to 1 L / min. The protective gas passes sequentially through the second gas circuit check valve 25, steam generator 8, steam heat exchanger 7 and reformer 6 (at this time, there is no natural gas reaction inside the reformer) and then enters the steam electric heater 5. After auxiliary heating, it enters the fuel electrode side of the fuel cell stack 3, thus playing a crucial role in reducing and protecting the sensitive electrode material during the fuel cell stack temperature rise period. The protective gas flowing through the fuel cell stack is safely discharged from the system after heat exchange and condensation treatment.

[0097] (3) During the electrolysis operation phase, once the temperature of the fuel cell stack 3 reaches the set SOEC operating temperature, the system officially enters the electrolysis hydrogen production operation state. At this time, the deionized water circuit solenoid valve 26 is opened to introduce deionized water into the deionized water tank 27, and the deionized water pump 28 is started. Under the monitoring of the deionized water flow meter 29, the deionized water is quantitatively delivered to the steam generator 8. The deionized water absorbs the residual heat of the air-side tail gas in the steam generator 8 and vaporizes to form water vapor. It then passes through the steam heat exchanger 7 and the reformer 6 flow channel in sequence, and finally enters the fuel electrode side of the fuel cell stack 3 after end temperature compensation by the steam electric heater 5. Under the action of the bidirectional power supply 34 switching to DC power input (power supply), the fuel cell stack performs an efficient electrochemical cracking reaction on the high-temperature water vapor to generate high-purity hydrogen. The generated high-temperature hydrogen-rich gas (containing H2 and incompletely electrolyzed H2O) is discharged from the fuel cell stack, and enters the condenser 16 after waste heat recovery by the steam heat exchanger 7 (used to preheat the front-end cold water vapor). Under the action of the cooling water system, the water vapor in the mixed gas is condensed into liquid water, and then separated into gas and liquid by the gas-liquid separator 30. The separated pure water is returned to the deionized water tank 27 for recycling.

[0098] (4) Hydrogen reflux and output: The dried high-purity hydrogen gas, after being dehydrated by the gas-liquid separator 30, is divided into two streams and distributed as follows:

[0099] 1) Maintaining a reducing atmosphere through micro-circulation: Under system control, a small portion (preferably 5% to 10%) of pure hydrogen is extracted and returned to the front end of the steam generator 8 by opening the circulation circuit solenoid valve 31 and starting the circulation pump 32. After mixing with the newly introduced steam, it re-enters the fuel cell stack 3 to participate in the reaction. This return of hydrogen perfectly replaces the external protective gas in the aforementioned stage (2), continuously maintaining the reducing environment of the fuel electrode during pure steam electrolysis, greatly extending the service life of the fuel cell stack, and reducing dependence on external protective gas sources.

[0100] 2) Commercial output of high-purity hydrogen: The remaining vast majority (about 80% to 90%) of high-purity hydrogen is directly output to downstream hydrogen storage systems for high-pressure filling, or directly supplied to external hydrogen-using scenarios such as hydrogen refueling stations and chemical pipelines, thereby realizing the commercial value transformation of the system.

[0101] Example 3

[0102] System coordination and methodological steps for switching between power generation and hydrogen production modes:

[0103] The switching process between power generation and hydrogen production modes is explained from two aspects: system hardware configuration and methodological steps. At the system level, mode switching involves switching the power supply direction of the bidirectional power supply 34, timing control of the first and second gas circuit valves (18, 19, 22, 23), preheating rate adjustment of the sub-butterfly valve 13, heat compensation for the steam electric heater 5 and the air electric heater 2, and the delivery of return hydrogen through the circulation circuit (including the circulation circuit solenoid valve 31 and the circulation pump 32). At the methodological level, see [link to relevant documentation]. Figure 3 This embodiment proposes a dual-mode switching control strategy for a solid oxide battery (SOFC) power generation and hydrogen production method based on natural gas. Under system-wide parameter boundary constraints (step S0), the control subsystem receives the switching signal (step S1) and determines the switching direction (step S2). Then, it executes steps S3-S9 or S10-S18 along either the "SOFC→SOEC" or "SOEC→SOFC" path, ultimately entering the stable operating state of the corresponding mode. The switching process is based on real-time acquisition of stack temperature gradient, power load, and gas concentration signals. Through coordinated control of the timing and parameters of each step, it fundamentally solves common industry problems such as thermal stress cracking, instantaneous electrode oxidation, and reformer carbon buildup that are easily caused by dual-mode switching in traditional SOC systems. The specific switching process is as follows:

[0104] (1) Smooth switching from SOFC (Solar Power Generation) mode to SOEC (Solar Energy Production) mode: When the system receives a hydrogen production or energy storage demand signal, in order to avoid thermal shock caused by the sudden change from "exothermic reaction" to "endothermic reaction", the system implements the following transition strategy:

[0105] The first step involves power reduction and heat transfer: the bidirectional power supply 34 gradually reduces the SOFC output power, while simultaneously activating the steam electric heater 5 and the air electric heater 2 for heat compensation. During this process, the valves of the first and second gas circuits are gradually closed to achieve seamless heat transfer between the reaction exothermics and the electric heating.

[0106] The second step is gas replacement and anti-oxidation locking: After the natural gas is completely cut off, the system immediately opens the second gas circuit solenoid valve 23. Under the control of the second gas circuit mass flow controller 24, low-concentration hydrogen gas with a flow rate of 0.5 to 1 L / min and a concentration of 5% to 10% is introduced as a protective gas to purge the residual CO2 and CH4 in the fuel electrode flow channel and lock the electrode in a safe reducing atmosphere.

[0107] The third step is electrolysis loading: After the stack temperature stabilizes within the set operating range of 750℃±10℃ under protective gas, the deionized water circuit is opened to introduce water vapor, and the bidirectional power supply 34 is smoothly switched to DC power supply mode, and the system officially enters the hydrogen production operation state.

[0108] (2) Smooth transition from SOEC (hydrogen production mode) to SOFC (power generation mode): When the system receives a peak-shaving power generation demand signal, in order to avoid instantaneous carbon buildup in natural gas due to uneven temperature establishment, the system executes the following reverse transition strategy:

[0109] The first step is power unloading and heat source handover: the bidirectional power supply 34 is controlled to gradually reduce the electrolysis input power to standby mode; then the power of the steam electric heater 5 is reduced. At the same time, the flow rate of deionized water into the system is reduced to an extremely low level, and the low concentration of hydrogen gas introduced into the second gas circuit is maintained to ensure that the fuel cell stack is in a hot standby and anti-oxidation state.

[0110] The second step involves burner ignition and reformer preheating: a portion of the recirculated hydrogen or residual combustible gas from the system pipeline is introduced into burner 4, where it mixes with air and ignites. The resulting high-temperature exhaust gas passes through air preheater 1 and steam generator 8, rapidly establishing the temperature field required for the reforming reaction in reformer 6. Simultaneously, the preheating rate is controlled by adjusting sub-butterfly valve 13 to prevent thermal stress concentration.

[0111] The third step involves gas source switching and high vapor-to-carbon ratio prevention of carbon buildup: Once the reformer 6 and fuel cell stack 3 reach the set temperatures, the system executes a safe sequence for protective gas cutoff and natural gas inlet. First, the external hydrogen gas source at the front end of the second gas circuit is cut off (protective gas supply is stopped); then, the deionized water inlet flow is increased (high-flow steam is introduced first), and then the valves of the second gas circuit are slowly adjusted to introduce natural gas. In the initial stage of natural gas inlet, the control system deliberately maintains a high vapor-to-carbon ratio (e.g., S / C > 2.5) to completely eliminate the tendency for natural gas to accumulate carbon at the cold end of the reformer or the inlet of the fuel cell stack.

[0112] The fourth step is power generation loading: After the hydrogen-rich mixture generated by natural gas reforming completely fills the fuel cell stack flow channel and the open-circuit voltage of the fuel cell stack stabilizes, the bidirectional power supply 34 is smoothly switched to AC output mode and power is gradually loaded, so that the system smoothly transitions to a high-efficiency power generation state.

[0113] Example 4

[0114] System operating parameter boundary and method control constraints:

[0115] The operating parameter boundaries are described from two levels: system hardware configuration and method control constraints. At the system level, the control subsystem monitors the flow rates of each path in real time through air flow meter 11, deionized water flow meter 29, first gas path mass flow controller 20, and second gas path mass flow controller 24, and feeds back the electrical parameters of fuel cell stack 3 through bidirectional power supply 34. At the method level, the control subsystem performs the following parameter boundary controls during dual-mode switching and long-term operation to prevent damage to the fuel cell stack due to thermal stress or uneven gas distribution:

[0116] (1) Core temperature and pressure control: Whether it is SOFC for power generation or SOEC for hydrogen production, the core working temperature of the stack is strictly controlled within the range of 700 to 850℃; at the same time, the flow rate and heat tracing of each flow path are dynamically adjusted to ensure that the temperature difference between the inlet and outlet of the stack is ≤80℃ and the gas pressure difference on both sides is ≤5kPa.

[0117] (2) Reaction utilization rate and electrical parameters: In the power generation (SOFC) mode, the fuel utilization rate is preferably controlled at about 65%, and the current setting range is 10A to 50A; in the hydrogen production (SOE) mode, the steam utilization rate is preferably controlled at about 80% to achieve the optimal balance between hydrogen production efficiency and system parasitic power consumption.

[0118] As described above, the present invention can be well implemented. The above embodiments are only the best implementations of the present invention, but the implementation of the present invention is not limited to the above embodiments. Other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention should be considered equivalent substitutions and are all included within the protection scope of the present invention.

Claims

1. A solid oxide cell system for power and hydrogen production based on natural gas, characterized in that The system includes a fuel cell stack (3), a reformer (6), a fuel supply module, an air supply module, a deionized water supply module, a thermal management module, a tail gas treatment and recycling module, and a bidirectional power supply (34). The fuel cell stack (3) is used to achieve bidirectional conversion of electrical energy and chemical energy between power generation mode and hydrogen production mode. The inlet of the reformer (6) is connected to the fuel supply module and the deionized water supply module, and the outlet is connected to the fuel electrode of the fuel cell stack (3). It is used to perform steam reforming reaction between natural gas and steam to generate hydrogen-rich gas and introduce it into the fuel cell stack (3). The fuel supply module... The module includes a first gas path and a second gas path for supplying natural gas to the burner (4) during the start-up preheating stage. The second gas path is connected to the steam generator (8) for supplying natural gas during the power generation operation stage and for introducing protective gas during the hydrogen production mode and mode switching stage. The air supply module includes a blower (10), an air flow meter (11), a main butterfly valve (12), and a sub-butterfly valve (13). The main butterfly valve (12) is used to control the total amount of air entering the air preheater (1), and the sub-butterfly valve (13) is used to control the amount of high-temperature air entering the reformer (6). The gas branch flow rate; the deionized water supply module includes a deionized water tank (27), a deionized water pump (28) and the steam generator (8), used to vaporize the deionized water and deliver it to the reformer (6) or the fuel electrode of the stack (3); the thermal management module includes the air preheater (1), a steam heat exchanger (7), a steam electric heater (5), an air electric heater (2) and the burner (4), used to realize the cascade recovery of system heat and the heat compensation during the mode switching transition stage; the exhaust gas treatment and recycling module includes a condenser (16), a gas... The system includes a water separator (30), a circulation solenoid valve (31), a circulation pump (32), and an anode tail gas solenoid valve (33). The anode tail gas solenoid valve (33) is used to control the flow rate of the dry tail gas to the burner (4). The circulation solenoid valve (31) and the circulation pump (32) are used to control the flow rate of the dry tail gas back to the front end of the system. The bidirectional power supply (34) is electrically connected to the fuel cell stack (3). In the power generation mode, it converts the DC power generated by the fuel cell stack (3) into AC power output. In the hydrogen production mode, it converts external electrical energy into DC power input to the fuel cell stack (3).

2. The natural gas-based solid oxide cell system of claim 1, wherein The first gas circuit includes, in sequence, a first gas circuit manual valve (18), a first gas circuit solenoid valve (19), a first gas circuit mass flow controller (20), and a first gas circuit check valve (21); the second gas circuit includes, in sequence, a second gas circuit manual valve (22), a second gas circuit solenoid valve (23), a second gas circuit mass flow controller (24), and a second gas circuit check valve (25); the first gas circuit and the second gas circuit are set independently of each other.

3. The natural gas-based solid oxide cell system of claim 1, wherein The air supply module also includes an air filter (9), through which air enters the air preheater (1) via the air filter (9), the blower (10), the air flow meter (11), and the main butterfly valve (12). The sub-butterfly valve (13) is located on the branch between the air preheater (1) and the reformer (6). The amount of high-temperature air entering the reformer (6) is adjusted by regulating the opening of the sub-butterfly valve (13) to control the reaction temperature of the reformer (6) and the preheating rate during the mode switching process.

4. The natural gas-based solid oxide cell system of claim 1, wherein The deionized water supply module also includes a deionized water circuit solenoid valve (26) and a deionized water flow meter (29); the steam generator (8) and the steam heat exchanger (7) form a series steam heating path. The steam generator (8) absorbs the waste heat of the tail gas to preheat the deionized water by vaporization. The steam heat exchanger (7) further absorbs the waste heat of the high-temperature gas at the fuel electrode outlet of the fuel cell stack (3).

5. The natural gas-based solid oxide battery power and hydrogen generation system of claim 1, wherein, The thermal management module constitutes a multi-stage heat recovery path. The air preheater (1) is located downstream of the exhaust gas outlet of the burner (4) and is used to preheat the supplied air in the first stage. The steam heat exchanger (7) is located downstream of the fuel electrode outlet of the fuel cell stack (3) and is used to preheat the mixture of steam and natural gas in the second stage. The steam electric heater (5) and the air electric heater (2) are respectively set at the inlet end of the fuel electrode and air electrode of the fuel cell stack (3) and are used to provide auxiliary heating during the mode switching transition stage and when the inlet gas temperature of the fuel cell stack is insufficient.

6. The natural gas-based solid oxide cell system of claim 1, wherein The exhaust gas treatment and recycling module also includes a cooling water tank (14), a cooling water pump (15), and an air-cooled radiator (17). The cooling water tank (14) supplies cooling water to the condenser (16) through the cooling water pump (15), and the air-cooled radiator (17) dissipates heat from the cooling water, forming a closed-loop cooling water circulation loop. The liquid water separated by the gas-water separator (30) is returned to the deionized water tank (27) for recycling.

7. An operation method for a natural gas-based solid oxide battery power generation and hydrogen production system, characterized in that... This includes a power generation mode step, a hydrogen production mode step, and a switching step between the power generation mode and the hydrogen production mode. The switching step includes: S1: Receive mode switching request signal; S2: Determine the switching direction. When the switching direction is from power generation mode to hydrogen production mode, execute steps S3 to S9 in sequence; when the switching direction is from hydrogen production mode to power generation mode, execute steps S10 to S18 in sequence. S3: The output power of the power generation mode is gradually reduced by the bidirectional power supply (34), and the steam electric heater (5) and the air electric heater (2) are turned on for heat compensation; S4: Gradually close the valves of the first gas circuit and the second gas circuit to cut off the natural gas supply; S5: Low-concentration hydrogen is introduced through the second gas passage as a protective gas to purge the residual gas in the fuel electrode flow channel of the fuel cell stack (3) so that the fuel electrode of the fuel cell stack (3) is in a reducing atmosphere; S6: Determine whether the temperature of the fuel cell stack (3) is stable within the set target operating temperature range. If not, return to step S5; if yes, proceed to step S7. S7: Open the solenoid valve (26) of the deionized water circuit. The deionized water is heated by the steam generator (8), the steam heat exchanger (7), the reformer (6) flow channel and the steam electric heater (5) and then enters the fuel electrode of the fuel cell stack (3). S8: Switch the bidirectional power supply (34) to DC electrolysis power supply mode; S9: Entering stable operation in hydrogen production mode; S10: Gradually reduce the electrolysis input power to standby state through the bidirectional power supply (34), reduce the power of the steam electric heater (5), and reduce the flow rate of deionized water entering the system; S11: Maintain the second gas path to supply low concentration hydrogen gas, so that the fuel cell stack (3) is in a hot standby and anti-oxidation state; S12: The circulating hydrogen or residual combustible gas in the system pipeline is introduced into the burner (4) for ignition and combustion. The high-temperature exhaust gas generated is used by the air preheater (1) and the steam generator (8) to establish a reaction temperature field for the reformer (6), and the preheating rate is controlled by adjusting the sub-butterfly valve (13). S13: Determine whether the reformer (6) and the fuel cell stack (3) have reached the set target operating temperature. If not, return to step S12; if yes, proceed to step S14. S14: Cut off the external hydrogen gas source at the front end of the second gas circuit and stop the supply of protective gas; S15: Increase the deionized water inlet flow rate and introduce water vapor into the system; S16: Adjust the valve of the second gas circuit to introduce natural gas and maintain the gas-to-carbon ratio of the reformer (6) greater than the set value; S17: After the open-circuit voltage of the fuel cell stack (3) stabilizes, the bidirectional power supply (34) is switched to AC output mode and the power generation is gradually loaded. S18: Entering stable operation mode for power generation.

8. The operating method according to claim 7, characterized in that: During the execution of the power generation mode step, hydrogen production mode step and switching step, the allowable operating temperature range of the fuel cell stack (3) is controlled between 700℃ and 850℃, the inlet and outlet temperature difference of the fuel cell stack (3) is controlled to be no greater than 80℃, and the gas pressure difference on both sides of the fuel cell stack (3) is controlled to be no greater than 5kPa.

9. The operating method according to claim 7, characterized in that: The exhaust gas treatment and recycling module in the power generation mode steps dynamically allocates the dry exhaust gas discharged from the stack (3) based on the system power load: under low power operation conditions, the circulation path solenoid valve (31) and the circulation pump (32) are closed, and all dry exhaust gas is introduced into the burner (4) through the anode exhaust gas solenoid valve (33); under medium and high power operation conditions, the circulation path solenoid valve (31) and the circulation pump (32) are opened, and 10%~20% of the dry exhaust gas is returned to the front end of the system and mixed with fresh natural gas and water vapor before re-entering the reformer (6), and the remaining dry exhaust gas is introduced into the burner (4) through the anode exhaust gas solenoid valve (33).

10. The operating method according to claim 7, characterized in that: The volume concentration of low-concentration hydrogen in steps S5 and S11 is 5%~10%, and the flow rate is 0.5~1L / min. In the hydrogen production mode step, 5%~10% of the hydrogen after being dehydrated by the gas-water separator (30) is returned to the front end of the steam generator (8) through the circulation solenoid valve (31) and the circulation pump (32) to maintain the reducing atmosphere of the fuel electrode of the stack (3).

11. The operating method according to claim 7, characterized in that... The target operating temperature range in step S6 is 750℃±10℃; the steam-to-carbon ratio in step S16 is greater than the set value of the steam-to-carbon ratio S / C being greater than 2.

5.

12. The operating method according to claim 7, characterized in that: In step S17, when gradually increasing the power generation, the current range is 10A~50A, and the fuel utilization rate is controlled at 65%; in step S8, under the DC electrolysis power supply mode, the water vapor utilization rate is controlled at 80%.

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