A solar thermoelectric hydrogen production system based on a solid oxide electrolysis cell

Abstract

The present invention discloses a solar thermoelectric combined hydrogen production system based on a solid oxide electrolyzer, belonging to the technical field of solar electrolytic water hydrogen production. It includes a water storage tank, a main water delivery pump, a medium-temperature solar collector, a starting hydrogen storage tank, a heat exchanger, an ejector, a high-temperature solar collector, a solid oxide electrolyzer, a high-temperature steam-hydrogen separator, a water-gas separator, a condensate water circulation pump, a vacuum pump, a compressor, and a hydrogen storage tank. The present invention uses two-stage solar collectors to generate high-temperature steam, and realizes the preliminary separation of water vapor and hydrogen in a high-temperature environment through a high-temperature hydrophobic hydrogen-permeable membrane; an ejector is used to reflux high-temperature electrolysis tail gas, improve the utilization rate of high-temperature water vapor, and provide a reducing atmosphere for the cathode of the electrolyzer; a vacuum pump is introduced into the normal-temperature pipeline, and the reliable regulation of the reflux flow of the ejector is realized by adjusting the pressure, meeting the fluctuating intake requirements of solar hydrogen production.

Description

Technical Field

[0001] The present invention relates to the technical field of solar electrolytic water hydrogen production, and particularly to a solar thermoelectric combined hydrogen production system based on a solid oxide electrolyzer. Background Art

[0002] Current electrolytic water hydrogen production technologies mainly include alkaline water electrolysis (AEC), proton exchange membrane electrolyzer (PEM), solid oxide electrolyzer (SOEC), etc. Alkaline water electrolysis has advantages in terms of structure and cost, but consumes too much electricity, is prone to corrosion and explosion. The efficiency of the proton exchange membrane electrolyzer is improved compared to that of alkaline electrolytic water, and its electrolysis process is relatively safe. However, the overall efficiency of the solar hydrogen production system still does not have an absolute advantage, and the price of the proton exchange membrane is relatively expensive. The fixed oxide electrolyzer has higher efficiency than the proton exchange membrane, and the electrolyzer material is functional ceramics, and the raw material price is relatively low.

[0003] The SOEC electrolyzer needs to maintain a high-temperature environment of 700°C - 800°C for electrolytic water hydrogen production, and liquid water needs to be converted into high-temperature steam at 700 - 800°C. The existing Chinese invention patent with the publication number CN114855188A discloses a solid oxide electrolyzer hydrogen production system, which uses traditional electric heating power supply to purify, compress and store the electrolyzed hydrogen. The existing Chinese invention patent with the publication number CN114024333A discloses a combined operation system of wind power, photovoltaic and solid oxide electrolytic hydrogen production, which supplies wind power and photovoltaic power to the electrolytic cell and the steam generation unit to make the system operate, and the steam generation unit uses a resistive electric boiler. Although the above two technical solutions can stably and continuously output steam and provide a high-temperature environment for the electrolytic cell, they still use the traditional electric heating method, resulting in low energy utilization rate of the system and losing the significance of using the SOEC high-temperature electrolytic water equipment.

[0004] The currently disclosed technical solutions for using solar energy to convert liquid water into high-temperature steam at 700°C - 800°C are to use trough or dish-shaped reflectors to concentrate sunlight on the central heat collection tube. The heat collection tube can use a vacuum structure of inner and outer tubes. The inner tube is made of stainless steel and coated with a solar selective absorption coating to directly prepare high-temperature steam. Existing Chinese invention patents such as the solar-driven solid oxide electrolyzer distributed polygeneration system and method with the publication number CN116121786A, the solar-driven RSOC distributed polygeneration system and its polygeneration method with the publication number CN116317175A, and a solar photovoltaic-thermal high-temperature electrolytic water hydrogen production system with the publication number CN111139493A disclose a scheme in which the heat collection tube uses high-temperature molten salt as a heat transfer medium to indirectly prepare high-temperature steam.

[0005] However, the above-mentioned patent does not take into account that the cathode catalyst of the solid oxide electrolyzer is mostly in a reduced state metal. Therefore, its working environment needs to maintain a reducing atmosphere (containing some hydrogen), otherwise the electrode catalyst will be oxidized and deactivated. The patent of the vaporizer and external steam for the solid oxide electrolyzer with the publication number of CN116417646A uses an external hydrogen storage tank to maintain the reducing atmosphere at the cathode of the electrolyzer, which increases the equipment cost to a certain extent. In fact, the electrolysis products of the SOEC contain high-temperature hydrogen and water vapor. Recycling the high-temperature tail gas to the intake end not only solves the problem of the reducing atmosphere of the electrolyzer, but also can further improve the overall efficiency of the SOEC electrolyzer system, because the heat exchange efficiency of the heat exchanger will be far lower than the energy efficiency of gas recycling. Making full use of the high-temperature electrolysis tail gas is the key to ensuring the efficiency of the SOEC electrolysis system. Realizing the preliminary separation of water vapor and hydrogen in the electrolysis tail gas at a high temperature will further improve the overall efficiency of the SOEC water electrolysis hydrogen production system.

[0006] Generally, the tail gas recycling methods include recycling by a circulation pump or an ejector. The circulation pump can control the recycling flow rate more precisely. However, due to the limitation of the working temperature of the circulation pump, the recycled gas needs to be cooled to a lower temperature, and the cooling process greatly reduces the overall energy efficiency of the SOEC water electrolysis hydrogen production system; the ejector can work at a higher temperature. However, due to the inherent limitation of the working principle of the Venturi tube, it is greatly affected by the intake flow rate and the exhaust pressure. When the operating power of the electrolysis system changes in real time with the solar illumination, relying solely on the ejector cannot achieve precise control of the recycling flow rate of the electrolysis tail gas. Summary of the Invention

[0007] In order to further improve the energy efficiency of the solar water electrolysis hydrogen production system and match the volatility characteristics of solar energy, the present invention provides a solar thermoelectric combined hydrogen production system based on the electrolytic gas partial recycling of a solid oxide electrolyzer.

[0008] The technical solution adopted by the present invention to solve its technical problems is: a solar thermoelectric combined hydrogen production system based on a solid oxide electrolyzer, including a cathode passage and an anode passage. The cathode passage includes a water storage tank, a main water pump, a medium-temperature solar collector, a starting hydrogen storage tank, an ejector, a high-temperature solar collector, a solid oxide electrolyzer, a high-temperature water vapor-hydrogen separator, and a water-gas separator; the water storage tank, the main water pump, the medium-temperature solar collector, the starting hydrogen storage tank, the ejector, the high-temperature solar collector, the solid oxide electrolyzer, and the high-temperature water vapor-hydrogen separator are sequentially connected through a cathode pipeline;

[0009] The water storage tank is used to store electrolysis water, and the main water pump transports the electrolysis water to the medium-temperature solar collector, and the medium-temperature solar collector heats the electrolysis water into medium-temperature high-pressure water vapor;

[0010] In the startup phase, the hydrogen storage tank starts to supplement additional hydrogen to the medium-temperature high-pressure water vapor to reduce the cathode catalyst of the solid oxide electrolyzer cell.

[0011] The medium-temperature high-pressure water vapor enters the main flow channel of the ejector. The ejector is used to reflux the mixed gas separated by the high-temperature water vapor-hydrogen separator and mix it evenly with the medium-temperature high-pressure water vapor before transporting it to the high-temperature solar collector.

[0012] After passing through the high-temperature solar collector, the mixed gas is heated to the set temperature. Then the mixed gas enters the cathode of the solid oxide electrolyzer cell. Under the electrolysis voltage provided by the solar cell, the water vapor undergoes an electrolysis reaction, generating hydrogen on the cathode side of the solid oxide electrolyzer cell and oxygen on the anode side.

[0013] The electrolytic gas generated by the solid oxide electrolyzer cell enters the high-temperature water vapor-hydrogen separator for preliminary separation. The high-temperature water vapor-hydrogen separator includes a tail gas reflux chamber and a hydrogen exhaust chamber. There is a reflux pipeline between the high-temperature water vapor-hydrogen separator and the ejector, and the tail gas reflux chamber is connected to the low-pressure area of the ejector through the reflux pipeline.

[0014] The hydrogen exhaust chamber is connected to the water-gas separator through an exhaust pipeline to further separate the water vapor. And the condensed water generated by the separation of the water-gas separator is pumped to the water storage tank by a circulation pump, and the hydrogen separated by the water-gas separator is input into a storage tank or a pipeline network.

[0015] Furthermore, the heating temperature of the medium-temperature solar collector is 400°C - 500°C; the heating temperature of the high-temperature solar collector is 750°C - 850°C.

[0016] Furthermore, the high-temperature water vapor-hydrogen separator adopts a high-temperature hydrophobic hydrogen-permeable membrane for the preliminary separation of water vapor and hydrogen at high temperatures; the high-temperature hydrophobic hydrogen-permeable membrane is a porous ceramic structure sintered from rare earth oxides.

[0017] Furthermore, the ratio of the number of hydrogen molecules to water vapor molecules passing through the high-temperature hydrophobic hydrogen-permeable membrane is not less than 10∶1.

[0018] Furthermore, the hydrogen exhaust pipeline is provided with a combined device of a vacuum pump and a compressor. The vacuum pump is connected to the hydrogen exhaust chamber of the high-temperature water vapor-hydrogen separator, used to adjust the pressure of the hydrogen exhaust chamber and control the flow rate passing through the high-temperature hydrophobic hydrogen-permeable membrane, so as to adjust the hydrogen production using the vacuum pump device.

[0019] Furthermore, the anode path is an open path, regulated by a throughput valve. The throughput valve passes air to the anode of the solid oxide electrolyzer cell, and the air flow takes the electrolytically generated oxygen out of the system.

[0020] The beneficial effects of the present invention:

[0021] 1. A solar thermoelectric hydrogen production system based on a solid oxide electrolyzer according to the present invention uses two-stage solar collectors to generate high-temperature steam, avoiding the use of high-temperature electric heaters. On the premise of ensuring the steam output and temperature, the energy efficiency of the solar thermoelectric hydrogen production system is effectively improved.

[0022] 2. A high-temperature hydrophobic hydrogen-permeable membrane is arranged in the high-temperature exhaust pipeline to achieve preliminary separation of water vapor and hydrogen at high temperature, reducing the cooling and heat exchange processes and improving the system efficiency.

[0023] 3. An ejector is added between the two-stage solar collectors to eject and recycle the mixed gas that has not passed through the high-temperature hydrophobic hydrogen-permeable membrane, improving the utilization rate of high-temperature water vapor; at the same time, the mixed gas contains hydrogen, which can maintain the reducing atmosphere at the cathode of the solid oxide electrolyzer.

[0024] 4. A vacuum pump is arranged in the low-temperature exhaust pipeline. The exhaust pressure and flow rate of the high-temperature hydrophobic hydrogen-permeable membrane are adjusted by the vacuum pump. By controlling the exhaust pressure and flow rate, the reliable regulation of the reflux flow rate of the ejector is indirectly achieved.

[0025] 5. A throttle valve is used to adjust the anode air flow rate, and natural convection is utilized to realize the flow of anode gas to discharge high-concentration oxygen, preventing the metal equipment of the solid oxide electrolyzer from being oxidized, thereby achieving the purpose of simplifying the structure and device and reducing energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is the principle structure diagram of a solar thermoelectric hydrogen production system based on a solid oxide electrolyzer according to the present invention.

[0027] In the figure: 1. Water storage tank; 2. Main water pump; 3. Medium-temperature solar collector; 4. Start-up hydrogen storage tank; 5. Cold fluid side of heat exchanger; 6. Ejector; 7. High-temperature solar collector; 8. Solid oxide electrolyzer; 9. Cathode of solid oxide electrolyzer; 10. Electrolyte of electrolyzer; 11. Anode of solid oxide electrolyzer; 12. Solar cell; 13. High-temperature water vapor-hydrogen separator; 14. High-temperature hydrophobic hydrogen-permeable membrane; 15. Hydrogen exhaust cavity; 16. Tail gas reflux cavity; 17. Hot fluid side of heat exchanger; 18. Water-gas separator; 19. Circulation pump; 20. Vacuum pump; 21. Compressor; 22. Hydrogen storage tank; 23. Throttle valve. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are all simplified schematic diagrams, only illustrating the basic structure of the present invention in a schematic manner, so they only show the components related to the present invention.

[0029] The present invention discloses a solar thermoelectric hydrogen production system based on a solid oxide electrolyzer.

[0030] Referring to Figure 1 , a solar thermoelectric hydrogen production system based on a solid oxide electrolyzer includes a cathode passage and an anode passage. The cathode passage includes a water storage tank 1, a main water pump 2, a medium-temperature solar collector 3, a starting hydrogen storage tank 4, a cold fluid side of a heat exchanger 5, an ejector 6, a high-temperature solar collector 7, a solid oxide electrolyzer 8, a high-temperature steam-hydrogen separator 13, a hot fluid side of a heat exchanger 17, a water-gas separator 18, a condensate water circulation pump 19, a vacuum pump 20, a compressor 21, and a hydrogen storage tank 22. Among them, the water storage tank 1, the main water pump 2, the medium-temperature solar collector 3, the starting hydrogen storage tank 4, the cold fluid side of the heat exchanger 5, the ejector 6, the high-temperature solar collector 7, the solid oxide electrolyzer 8, and the high-temperature steam-hydrogen separator 13 are sequentially connected as the main passages of the system.

[0031] The water storage tank 1 stores sufficient electrolysis water, which is pressurized by the main water pump 2 and transported to the medium-temperature solar collector 3; the electrolysis water is heated and vaporized in the medium-temperature solar collector 3 to generate medium-temperature high-pressure steam at 400°C - 500°C.

[0032] The starting hydrogen storage tank 4 stores high-pressure pure hydrogen gas. During the start-up stage of the system, the starting hydrogen storage tank 4 supplements hydrogen to the medium-temperature high-pressure steam to reduce the electrolytic cell cathode catalyst metal nickel. When the system is in normal operation, the starting hydrogen storage tank 4 is in a closed state.

[0033] The medium-temperature high-pressure steam passes through the cold fluid side of the heat exchanger 5 to absorb heat and further preheat the steam; the high-temperature high-pressure steam flows through the main flow channel of the ejector 6, and the potential energy is converted into kinetic energy at the nozzle of the ejector 6. According to Bernoulli's theory, the greater the flow velocity of the fluid in the pipeline, the smaller the pressure; thus, the mixed gas in the tail gas return cavity 16 of the high-temperature steam-hydrogen separator 13 can be refluxed to the ejector 6 under the pressure difference and mixed with the high-temperature low-pressure steam. Since the temperature of the mixed gas does not reach the operating temperature for electrolytic hydrogen production, it needs to be heated again. The high-temperature solar collector 7 reheats the mixed gas to 750°C - 850°C.

[0034] The preheated sufficient mixed gas enters the cathode 9 of the solid oxide electrolyzer. Under the electrolysis voltage provided by the solar cell 12, water vapor electrolyzes to produce hydrogen, and oxygen ions pass through the electrolyzer electrolyte 10 to generate oxygen at the anode 11 of the solid oxide electrolyzer.

[0035] Due to the concentration polarization phenomenon, water vapor cannot be completely electrolyzed, and there is still a certain amount of high-temperature water vapor in the electrolytic gas produced at the cathode 9 of the electrolytic cell and flowing out. Reusing this part of the remaining water vapor helps to further improve the overall efficiency. To improve the utilization rate of high-temperature water vapor, the electrolytic gas enters the high-temperature water vapor-hydrogen separator 13 for preliminary separation. The high-temperature water vapor-hydrogen separator 13 uses a high-temperature hydrophobic hydrogen-permeable membrane 14, which is a porous ceramic structure sintered from rare earth oxides. By reasonably designing the thickness, average pore diameter, permeability, and hydrophobicity of the hydrogen-permeable membrane, the selectivity ratio of hydrogen to water vapor passing through is not less than 10:1. Under the action of the high-temperature hydrophobic hydrogen-permeable membrane 14, high-concentration hydrogen permeates through the hydrogen-permeable membrane and enters the hydrogen exhaust cavity 15, and higher-concentration water vapor is retained in the tail gas reflux cavity 16.

[0036] The filtered residual gas in the tail gas reflux cavity 16 contains higher-concentration water vapor and a small amount of hydrogen. A reflux pipeline is provided between the high-temperature water vapor-hydrogen separator 13 and the ejector 6. The mixed gas in the tail gas reflux cavity 16 flows back to the low-pressure area of the ejector 6 along the reflux pipeline under the action of the pressure difference, and is mixed with the water vapor inlet generated by the medium-temperature solar collector 3 to achieve recirculation. This not only improves the utilization rate of high-temperature water vapor, but the hydrogen it contains also provides a reducing atmosphere for the cathode 9 of the solid oxide electrolytic cell, so that the system can operate without external hydrogen supplementation, reducing the complexity of the system equipment.

[0037] The high-concentration hydrogen in the hydrogen exhaust cavity 15 is connected to the hot fluid side 17 of the heat exchanger, the water-gas separator 18, the vacuum pump 20, and the compressor 21 in sequence through the low-temperature exhaust pipeline; the high-concentration hydrogen in the hydrogen exhaust cavity 15 passes through the hot fluid side 17 of the heat exchanger, releases heat to preheat the inlet gas, and then flows into the low-temperature water-gas separator 18 to further separate water vapor. The condensed water generated by the separation is pumped to the water storage tank 1 by the condensate circulation pump 19.

[0038] It should be noted that both the ejector 6 and the high-temperature water vapor-hydrogen separator 13 are passive devices and cannot reliably match the intermittent power generation and heat generation characteristics of solar energy. Therefore, in the present invention, a vacuum pump 20 is provided in the low-temperature exhaust pipeline. By controlling the rotation speed of the vacuum pump 20, the pressure in the low-temperature exhaust pipeline and the hydrogen exhaust cavity 15 is controlled, and the pressure difference between the hydrogen exhaust cavity 15 and the tail gas reflux cavity 16 is actively adjusted to control the gas flow rate passing through the high-temperature hydrophobic hydrogen-permeable membrane 14. Further, the gas pressure in the tail gas reflux cavity 16 affects the reflux flow rate of the ejector 6. The vacuum pump 20 indirectly controls the pressure in the tail gas reflux cavity by adjusting the hydrogen production, realizing the reliable regulation of the reflux flow rate of the ejector 6 by the vacuum pump 20, and finally realizing the matching of the entire steam supply subsystem to the intermittent power generation and heat generation characteristics of solar energy.

[0039] High-temperature and high-concentration oxygen is generated on the anode side of the solid oxide electrolyzer 8, which is extremely easy to oxidize the metal connectors and pipelines in the SOEC electrolyzed water system. An appropriate amount of air flow is required to carry the electrolyzed oxygen out of the system. In the present invention, the anode passage of the electrolyzer is an open channel: the air inlet is arranged at the bottom of the system and is connected to the external environment by a flow valve 23; the air outlet is arranged at the top of the system and is communicated with the external atmospheric environment. Under the action of thermal buoyancy, the electrolyzed oxygen will automatically float upward without external force, realizing the circulation of the anode air passage, and the flow rate of the air passage is controlled by the flow valve 23.

[0040] Based on the ideal embodiments of the present invention described above, through the above description, relevant workers can completely make various changes and modifications without departing from the technical idea of the present invention. The technical scope of the present invention is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A solar thermoelectric combined hydrogen production system based on a solid oxide electrolyzer cell, characterized in that: It includes a cathode path and an anode path. The cathode path includes a water storage tank (1), a main water pump (2), a medium-temperature solar collector (3), a start-up hydrogen storage tank (4), an ejector (6), a high-temperature solar collector (7), a solid oxide electrolyzer (8), a high-temperature steam-hydrogen separator (13), and a water-vapor separator (18); the water storage tank (1), the main water pump (2), the medium-temperature solar collector (3), the start-up hydrogen storage tank (4), the ejector (6), the high-temperature solar collector (7), the solid oxide electrolyzer (8), and the high-temperature steam-hydrogen separator (13) are sequentially connected through a cathode pipeline; The water storage tank (1) is used to store water for electrolysis. The main water pump (2) transports the water for electrolysis to the medium-temperature solar collector (3), and the medium-temperature solar collector (3) heats the water for electrolysis into medium-temperature high-pressure steam; In the start-up stage, the start-up hydrogen storage tank (4) supplements hydrogen to the medium-temperature high-pressure steam to reduce the cathode catalyst of the solid oxide electrolyzer (8); The medium-temperature high-pressure steam enters the main flow channel of the ejector (6). The ejector (6) is used to reflux the mixed gas separated by the high-temperature steam-hydrogen separator (13) and mix it evenly with the medium-temperature high-pressure steam and then transport it to the high-temperature solar collector (7); After passing through the high-temperature solar collector (7), the mixed gas is heated to a set temperature. Then the mixed gas enters the cathode (9) of the solid oxide electrolyzer. Under the electrolysis voltage provided by the solar cell (12), the steam undergoes an electrolysis reaction, generating hydrogen on the cathode side of the solid oxide electrolyzer (8) and generating oxygen on the anode side; The electrolytic gas generated by the solid oxide electrolyzer (8) enters the high-temperature steam-hydrogen separator (13) for preliminary separation. The high-temperature steam-hydrogen separator (13) includes a tail gas reflux chamber (16) and a hydrogen exhaust chamber (15). A reflux pipeline is provided between the high-temperature steam-hydrogen separator (13) and the ejector (6), and the tail gas reflux chamber (16) is connected to the low-pressure area of the ejector (6) through the reflux pipeline; The hydrogen exhaust chamber (15) is connected to the water-vapor separator (18) through an exhaust pipeline to further separate water vapor; and the condensed water generated by the separation of the water-vapor separator (18) is pumped to the water storage tank (1) by a circulation pump (19), and the hydrogen separated by the water-vapor separator (18) is input into a storage tank or a pipeline network; The hydrogen exhaust pipeline is provided with a combined device of a vacuum pump (20) and a compressor (21). The vacuum pump (20) is connected to the hydrogen exhaust chamber (15) of the high-temperature steam-hydrogen separator (13) and is used to adjust the pressure of the hydrogen exhaust chamber (15) and control the flow rate through the high-temperature hydrophobic hydrogen-permeable membrane (14) to realize the adjustment of hydrogen production using the vacuum pump (20) device; The high-temperature steam-hydrogen separator (13) adopts a high-temperature hydrophobic hydrogen-permeable membrane (14) for achieving preliminary separation of steam and hydrogen at high temperatures; the high-temperature hydrophobic hydrogen-permeable membrane (14) is a porous ceramic structure sintered from rare-earth oxides; the molecular number passing ratio of hydrogen and steam through the high-temperature hydrophobic hydrogen-permeable membrane (14) is not less than 10:

1.

2. The solar thermoelectric hydrogen production system based on a solid oxide electrolyzer according to claim 1, characterized in that: The heating temperature of the medium-temperature solar collector (3) is 400°C - 500°C; the heating temperature of the high-temperature solar collector (7) is 750°C - 850°C.

3. The solar thermoelectric hydrogen production system based on a solid oxide electrolyzer according to claim 1, characterized in that: The anode path is an open path, which is regulated by a flow valve (23). The flow valve (23) conducts air to the anode (11) of the solid oxide electrolytic cell, and the air flow takes the electrolytically generated oxygen out of the system.

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