Seawater desalination and methanogenesis system based on high temperature electrolysis

Abstract

The application provides a seawater desalination and methane production system based on high-temperature electrolysis, comprising: a solar energy conversion unit for providing electric energy and heat energy; a seawater evaporation unit for generating water vapor, which exchanges heat with high-temperature gas generated by an electrolysis and methane synthesis unit and heat energy provided by the solar energy conversion unit, and then enters the electrolysis and methane synthesis unit to perform electrolysis reaction; a carbon dioxide supply unit for providing carbon dioxide required by the electrolysis and methane synthesis unit; the electrolysis and methane synthesis unit is used for co-electrolyzing carbon dioxide and water vapor, and synthesizing methane through Fischer-Tropsch process by using hydrogen and carbon monoxide generated by co-electrolysis; and a cooling and separation unit is used for cooling and separating products at the outlet of the electrolysis and methane synthesis unit to obtain methane and liquid water. The application improves the utilization rate of energy, generates a mixed gas mainly composed of methane, and can be further converted into chemical products with high added value, thereby having certain economic benefits.

Description

Technical Field

[0001] This invention relates to the field of clean energy technology, specifically to a seawater desalination and methane production system based on high-temperature electrolysis. Background Technology

[0002] Currently, power generation in coastal areas still relies primarily on coal-fired power, with a lack of further utilization of renewable energy sources such as solar, wind, and wave energy. While coastal areas are adjacent to the sea and possess abundant seawater resources, the process of converting seawater into freshwater is an energy-intensive and extremely energy-consuming process. Therefore, achieving green, low-carbon, and energy-efficient energy utilization, as well as optimizing seawater desalination, is one of the key factors for the development of coastal areas.

[0003] Electrolyzers are a technology that converts electrical energy into chemical energy. They can utilize intermittent energy sources such as wind and solar power and have advantages such as high efficiency, cleanliness, and low reactant costs. They are expected to play an important role in future applications such as renewable energy coupling and large-scale energy storage.

[0004] Compared to other electrolysis technologies, solid oxide electrolysis cells (SOECs) are more thermodynamically and kinetically favorable for most electrolysis reactions due to their higher operating temperatures. Furthermore, SOECs are more easily integrated with other chemical synthesis processes, such as the production of methanol and methane. Carbon-assisted solid oxide electrolysis cells (CA-SOECs) significantly lower the operating potential of the electrolysis cell and reduce energy consumption by adding carbon fuel to the anode, thereby reducing the energy barrier for oxygen ion transfer.

[0005] SOEC-based co-electrolysis technology can simultaneously electrolyze carbon dioxide and water vapor to produce carbon monoxide and hydrogen, and can further produce chemical products such as methane. It boasts high overall electrochemical energy efficiency and is a relatively advanced energy device. However, traditional SOEC and Fischer-Tropsch methane synthesis are carried out in two steps, resulting in a complex system and high power consumption, thus having certain limitations. Summary of the Invention

[0006] To address the above problems, this invention provides a seawater desalination and methane production system based on high-temperature electrolysis. It uses seawater as a source to produce steam and comprehensively utilizes the thermal and electrical energy converted from solar energy to achieve electrolysis and methane synthesis, thereby realizing seawater desalination and methane production while improving energy utilization efficiency.

[0007] This invention provides a seawater desalination and methane production system based on high-temperature electrolysis, comprising a seawater evaporation unit, a solar energy conversion unit, a carbon dioxide supply unit, an electrolysis and methane synthesis unit, and a cooling and separation unit, wherein...

[0008] The solar energy conversion unit provides the electrical energy required for electrolysis in the electrolysis and methane synthesis unit, as well as the thermal energy required for seawater evaporation in the seawater evaporation unit.

[0009] The seawater evaporation unit is used to generate water vapor. The water vapor exchanges heat with the high-temperature gas generated by the electrolysis and methane synthesis unit and the heat energy provided by the solar energy conversion unit before entering the electrolysis and methane synthesis unit for electrolysis reaction.

[0010] The carbon dioxide supply unit is used to provide the carbon dioxide required by the electrolysis and methane synthesis units;

[0011] The electrolysis and methane synthesis unit is used to co-electrolyze carbon dioxide and water vapor and use the hydrogen and carbon monoxide generated by co-electrolysis to synthesize methane via the Fischer-Tropsch process.

[0012] The cooling and separation unit is used to cool and separate the products from the electrolysis and methane synthesis unit to obtain methane and liquid water.

[0013] This invention utilizes seawater as a source of water vapor while simultaneously producing freshwater, making it more suitable for coastal areas lacking freshwater resources. It not only utilizes solar energy to provide the heat energy for water vapor generation and the electrical energy required for electrolysis in the electrolytic cell, but also fully leverages waste heat in the system, improving energy efficiency and making the entire system's energy utilization more green, low-carbon, and economical. The mixed gas, primarily composed of methane, produced through the electrolysis and methane synthesis units can be further converted into high-value-added chemical products, resulting in certain economic benefits.

[0014] In an optional technical solution of the present invention, the electrolysis and methane synthesis unit includes a cathode cavity, a cathode, an electrolyte, an anode, and an anode cavity arranged sequentially. The cathode cavity has a cathode cavity inlet and a cathode cavity outlet, and the cathode cavity is filled with nickel-based foam metal. The anode cavity includes a first cavity and a second cavity. The first cavity is sandwiched between the anode and the second cavity. The first cavity has an anode feed inlet and an anode discharge outlet and provides a carbon gasification site. The second cavity has an anode cavity inlet and an anode cavity outlet. The length of the anode is less than the length of the cathode, and the Fischer-Tropsch process occurs in the part of the cathode not covered by the anode.

[0015] According to this technical solution, the high-temperature electrolysis-based seawater desalination and methane production system has a compact structure, integrating the electrolysis reaction and Fischer-Tropsch synthesis reaction into the electrolysis and methane synthesis units, thus saving space. The use of nickel-based foam metal can improve conductivity, reduce gas diffusion resistance to enhance gas transport capacity, and improve battery performance. It also provides more reaction sites for the reverse methane reforming reaction, thereby increasing the yield of methane and fresh water.

[0016] In an optional technical solution of the present invention, the carbon dioxide supply unit includes a calcination chamber, a carbon chamber, and a mixer. The calcination chamber provides a calcination site for calcium carbonate and conveys the calcined solid product to the mixer. The heat of the calcination chamber comes from a high-temperature heat storage device. The carbon chamber provides carbon fuel to the anode chamber. The mixer mixes the carbon fuel and the solid product generated in the calcination chamber and provides it to the electrolysis and methane synthesis unit. The gaseous product from the outlet of the anode chamber of the electrolysis and methane synthesis unit is also input into the inlet of the cathode chamber through the calcination chamber to replenish the gas in the cathode chamber. The solid product from the outlet of the anode chamber is reused in the calcination chamber.

[0017] According to this technical solution, the heat in the calcination chamber comes from the solar energy converted from solar energy stored in the high-temperature thermal storage device, which saves energy and improves the utilization rate of solar energy. The carbon dioxide produced by the calcination of calcium carbonate can be used as the raw material gas for the cathode. The calcium oxide produced by calcination enters the anode cavity and can absorb the carbon dioxide in the anode cavity. The gas products discharged from the anode cavity can return to the cathode to participate in the electrochemical reaction, realizing the reuse of products. Adding carbon fuel to the anode cavity can improve battery performance and increase the electrochemical reaction rate by carbon-assisted water vapor gasification.

[0018] In an optional technical solution of the present invention, the operating voltage of the electrolysis and methane synthesis unit is 0.3 to 1.0 V.

[0019] According to this technical solution, the operating voltage of the electrolysis and methane synthesis unit does not exceed 1.0V, which reduces power consumption and helps save costs.

[0020] In the optional technical solution of the present invention, the operating temperature of the electrolysis section in the electrolysis and methane synthesis unit is 650-850°C, and the temperature of the Fischer-Tropsch synthesis section gradually decreases to 400-500°C.

[0021] According to the technical solution, the operating temperature of the SOEC section of the electrolysis and methane synthesis unit is 650-850℃, and then the temperature gradually decreases to 400-500℃ at the outlet in the Fischer-Tropsch synthesis section. This is beneficial to improve the reaction efficiency of electrolysis and Fischer-Tropsch synthesis, thereby improving the methane production efficiency. Moreover, this temperature range is suitable for the long-term stable operation of the electrolysis and methane synthesis unit. The gas at the outlet of the cathode cavity is a high-temperature gas, which is easy to achieve gas-liquid separation after cooling.

[0022] In the optional technical solution of the present invention, a steam pressurizing device and a carbon dioxide pressurizing device are also included. The steam pressurizing device is used to pressurize the high-temperature steam at the outlet of the seawater evaporation unit, and the carbon dioxide pressurizing device is used to pressurize the carbon dioxide supplied by the carbon dioxide supply unit. The working pressure of the electrolysis and methane synthesis unit is 2.5 to 3.5 bar.

[0023] According to this technical solution, carbon dioxide and water vapor are pressurized before entering the electrolysis and methane synthesis unit, so that the electrolysis and methane synthesis are carried out under high pressure, thereby improving the electrolysis efficiency and synthesis efficiency.

[0024] In the optional technical solution of the present invention, the flow rate of the gas introduced into the cathode and the anode is 20-100 mL / min.

[0025] According to this technical solution, at this flow rate, the reaction of the gaseous reactants can be more complete.

[0026] In an optional technical solution of the present invention, the seawater evaporation unit includes a seawater collection and purification device and an evaporation device.

[0027] According to this technical solution, seawater is collected, purified, and then evaporated, which improves the cleanliness of the water vapor and avoids the impact of impurities on electrolysis and methane synthesis.

[0028] In the optional technical solution of the present invention, the solar energy conversion unit includes a heat collection device, a high-temperature heat storage device, and a power generation device. The heat collection device is used to collect solar energy and convert it into heat energy. The high-temperature heat storage device is used to store the heat energy converted from solar energy. The high-temperature heat storage device is a thermochemical heat storage device, and the reaction temperature of the high-temperature heat storage device is 700-1100℃. The power generation device is a photovoltaic power generation device.

[0029] According to this technical solution, the reaction temperature of the high-temperature thermal storage device is matched with the operating temperature of the electrolysis and methane synthesis unit, which helps to ensure the smooth progress of electrolysis and methane synthesis and improve the system's working efficiency. The integrated use of the thermal collector and the power generation device can convert solar energy into thermal energy and electrical energy, thereby improving the energy utilization rate.

[0030] In an optional technical solution of the present invention, the heat exchange medium of the cooling separation unit is seawater.

[0031] According to this technical solution, the heat exchange medium is seawater, which is readily available and simplifies the cooling structure. Furthermore, the temperature of the seawater increases after heat exchange, making full use of thermal energy. The heated seawater can then evaporate further, saving the thermal energy required for evaporation and resulting in overall energy savings. Attached Figure Description

[0032] Figure 1This is a schematic diagram of the seawater desalination and methane production system based on high-temperature electrolysis in an embodiment of the present invention.

[0033] Figure 2 This is a schematic diagram of the electrolysis and methane synthesis unit in an embodiment of the present invention.

[0034] Figure label:

[0035] Seawater collection and purification device 1; seawater evaporation unit 2; steam pressurization device 3; carbon dioxide pressurization device 4; electrolysis and methane synthesis unit 5; cathode chamber 51; cathode 52; electrolyte 53; anode 54; anode chamber 55; first chamber 551; anode inlet 5511; anode outlet 5512; second chamber 552; anode chamber air inlet 5521; anode chamber air outlet 5522; calcination chamber 6; carbon chamber 7; mixer 8; water pump 9; methane storage tank 10; freshwater storage tank 11; first heat exchanger 12; heat collection device 13; high-temperature heat storage device 14; power generation device 15; second heat exchanger 16. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] Please see Figure 1 As shown, this invention provides a high-temperature electrolysis-based seawater desalination and methane production system, comprising a seawater collection and purification device 1; a seawater evaporation unit 2; a steam pressurization device 3; a carbon dioxide pressurization device 4; and an electrolysis and methane synthesis unit.

[0038] (CA-SOEC / FT unit) 5; calcination chamber 6; carbon chamber 7; mixer 8; cooling and separation unit (including feed water pump 9, methane storage tank 10, fresh water storage tank 11) first heat exchanger 12; solar energy conversion unit (including heat collection device 13, high temperature heat storage device 14, power generation device 15) and second heat exchanger 16.

[0039] The workflow is as follows: Seawater passes through collection and purification device 1 to remove insoluble substances. The purified seawater is heated to approximately 450°C by exchanging heat with the high-temperature gas at the outlet of electrolysis and methane synthesis unit 5 through the first heat exchanger 12. Then, it passes through the second heat exchanger 16 to exchange heat with the high-temperature air at the outlet of high-temperature heat storage device 14, heating the purified seawater to approximately 800°C. Subsequently, the high-temperature steam is pressurized to 3 bar and enters the cathode 52 and anode 54 of electrolysis and methane synthesis unit 5 for reaction. Simultaneously, the calcination chamber 6 exchanges heat with the high-temperature heat storage device 14 through the second heat exchanger 16, raising the temperature inside the calcination chamber 6 to 900–1000°C. Calcium carbonate is calcined in the calcination chamber 6 to produce CO2 and CaO (as shown in Equation 1), while unreacted C in the anode chamber 51 of the electrolysis and methane synthesis unit 5 continues to vaporize to produce CO and H2 (as shown in Equations 2 and 3). The gaseous products generated in this section are also pressurized to 3 bar and then enter the cathode 52 of the electrolysis and methane synthesis unit 5 for reaction. The remaining solid products (mainly CaO) in the calcination chamber 6 enter the mixer 8, mix with the carbon fuel from the carbon chamber 7, and then send them to the anode 54 of the electrolysis and methane synthesis unit 5. Subsequently, the anode products (CaCO3, Ca(OH)2) enter the calcination chamber 6 for reaction (as shown in Equations 1 and 4). The electrolysis and methane synthesis unit 5 is powered by a photovoltaic power generation device, which provides the electrical energy required for electrolysis. At the cathode 52, the introduced H2O / CO2 is converted into H2 / CO. In the subsequent Fischer-Tropsch process, H2 / CO is further converted into CH4 and water vapor. The pipeline containing the cathode product is placed in seawater for cooling, converting the gaseous water vapor into liquid fresh water. The gaseous product and liquid fresh water are then sent out by the feed water pump 9. The gaseous product, mainly methane, is sent to the methane storage tank 10, and the liquid fresh water is sent to the fresh water storage tank 11, thus achieving product collection.

[0040] CaCO3→CaO+CO2 (1)

[0041] C + H₂O → H₂ + CO (2)

[0042] C + CO₂ → 2CO (3)

[0043] Ca(OH)2→CaO+H2O (4)

[0044] In this embodiment of the invention, the seawater is heated in stages to generate high-temperature steam. The purified seawater is first heated to approximately 450°C by exchanging heat with the outlet gas of the electrolysis and methane synthesis unit 5. Then, the steam is heated to approximately 800°C by exchanging heat with the high-temperature heat storage device 14. Utilizing waste heat and solar energy absorbed by the high-temperature heat storage device 14 for steam heating helps improve the overall energy utilization efficiency of the system.

[0045] The seawater collection and purification device 1 is used to purify the collected seawater and remove insoluble substances. The seawater evaporation unit 2 is used to generate water vapor. The water vapor exchanges heat with the high-temperature gas generated by the electrolysis and methane synthesis unit 5 and the high-temperature heat storage device 14 of the solar energy conversion unit before entering the electrolysis and methane synthesis unit 5 for electrolysis reaction. The seawater is collected, purified, and then evaporated, which improves the cleanliness of the water vapor and avoids the influence of impurities on electrolysis and methane synthesis.

[0046] The solar energy conversion unit includes a heat collection device 13, a high-temperature heat storage device 14, and a power generation device 15. The power generation device 15 generates the electrical energy required for the co-electrolysis and methane synthesis unit 5. The heat collection device 13 converts solar energy into thermal energy, and the high-temperature heat storage device 14 stores the converted thermal energy and provides it to the seawater evaporation unit 2 and the calcination chamber 6. Preferably, the power generation device 15 uses a gallium arsenide solar cell device, and the heat collection device 13 uses a trough-type heat collector for heating. Using a gallium arsenide solar cell device is low-cost and its efficiency meets the operating conditions. Using a trough-type heat collector to heat water vapor has the advantages of convenient installation, simple structure, safety, and high reliability. The high-temperature heat storage device 14 is a thermochemical heat storage device with a reaction temperature of 700–1100°C. The reaction temperature of the high-temperature heat storage device 14 matches the operating temperature of the electrolysis and methane synthesis unit 5, which helps to ensure the smooth progress of electrolysis and methane synthesis, improve system efficiency, and enhance the long-term operational stability of the electrolysis and methane synthesis unit 5. Specifically, the high-temperature thermal storage device 14 uses a CuO / Cu2O system as the material, with a reaction temperature of 700–1100°C, which meets the temperature requirements for heating steam. Furthermore, this material has the advantages of completely reversible chemical reaction, good thermal stability, and high thermal storage density. It should be noted that although the above-described material is shown in this invention, those skilled in the art can select appropriate materials for the high-temperature thermal storage device 14 based on actual conditions.

[0047] The carbon dioxide supply unit is used to generate the carbon dioxide required by the electrolysis and methane synthesis unit 5. Specifically, the carbon dioxide supply unit includes a calcination chamber 6, a carbon chamber 7, and a mixer 8. The calcination chamber 6 provides a calcination site for calcium carbonate and transports the calcined solid product to the mixer 8. The heat of the calcination chamber 6 comes from the high-temperature heat storage device 14. The carbon chamber 7 provides carbon fuel to the anode chamber 55. The mixer 8 mixes the carbon fuel and the solid product generated in the calcination chamber 6 and supplies it to the electrolysis and methane synthesis unit 5. The gaseous product from the anode chamber outlet 5522 of the electrolysis and methane synthesis unit 5 is also input into the cathode chamber inlet 511 through the calcination chamber 6 to replenish the gas in the cathode chamber 51. The solid product from the anode chamber outlet enters the calcination chamber 6 for reuse.

[0048] The steam pressurizing device 3 is used to pressurize the high-temperature steam at the outlet of the seawater evaporation unit 2; the carbon dioxide pressurizing device 4 is used to pressurize the carbon dioxide supplied by the carbon dioxide supply unit. The pressure of the water vapor and carbon dioxide entering the electrolysis and methane synthesis unit 5 is 2.5 to 3.5 bar, preferably 3 bar.

[0049] In a preferred embodiment of the present invention, the electrolysis and methane synthesis unit 5 can simultaneously realize the electrolysis and synthesis of methane at a pressure of 3 bar, which has the following advantages: (1) it can save a lot of electrical energy; (2) the device operates at a higher pressure, the performance of the SOEC section can be improved, and the high pressure is conducive to the reverse methane reforming reaction.

[0050] Electrolysis and methane synthesis unit 5 is used for the co-electrolysis of carbon dioxide and water vapor, and the resulting hydrogen and carbon monoxide are used to synthesize methane via a Fischer-Tropsch process. Specifically, as shown... Figure 2 As shown, the electrolysis and methane synthesis unit 5 includes a cathode cavity 51, a cathode 52, an electrolyte 53, an anode 54, and an anode cavity 55 arranged sequentially. The cathode cavity 51 has a cathode cavity inlet 511 and a cathode cavity outlet 512. The anode cavity 55 has an anode cavity inlet 5521, an anode cavity outlet 5522, an anode feed inlet 5511, and an anode discharge outlet 5512. The length of the anode 54 is less than the length of the cathode 52. The Fischer-Tropsch process occurs in the part of the cathode 52 not covered by the anode 54. The cathode cavity 51 is filled with foam metal 513. Preferably, the foam metal 513 is nickel-based foam metal. The anode cavity 55 includes a first cavity 551 and a second cavity 552. The first cavity 551 provides a reaction site for carbon fuel and calcium oxide, and the second cavity 552 is a gas reaction site. The first cavity 551 is sandwiched between the anode 54 and the second cavity 552, and the first cavity 551 and the second cavity 552 are connected.

[0051] The high-temperature electrolysis-based seawater desalination and methane production system has a compact structure. The electrolysis reaction and the Fischer-Tropsch synthesis reaction occur together in the electrolysis and methane synthesis unit 5, saving space. Using nickel-based foam metal improves conductivity, reduces gas diffusion resistance to enhance gas transport capacity, and improves battery performance. It also provides more reaction sites for the reverse methane reforming reaction, thus increasing the yield of methane and fresh water.

[0052] In this embodiment, the working principle of the electrolysis and methane synthesis unit 5 is as follows:

[0053] Electrolysis reaction section: H2O / CO2 is introduced into the cathode cavity inlet 511. After the reactants diffuse to the three-phase interface of the cathode 52, a reduction reaction occurs to produce H2, CO and O. 2- (as shown in Equations 5 and 6), O 2-The electrolyte 53 is transferred to the anode 54. Simultaneously, water vapor (which can accelerate the carbon gasification reaction rate) is introduced into the anode chamber inlet 5521, and a mixture of carbon fuel and CaO from the mixer 8 is introduced into the anode chamber feed inlet 5511. Carbonate is added to the anode chamber 55 as a catalyst. The water vapor reacts with the carbon fuel in the first chamber 551 to produce H2 / CO (as shown in Equation 2), which then reacts with O2 at the three-phase interface of the anode 54. 2- The reaction occurs (as shown in Equations 7 and 8), and CO and water vapor also undergo a water vapor replacement reaction (as shown in Equation 9). CO2 in the anode chamber 55 reacts with CaO to produce CaCO3 (as shown in Equation 10). The remaining CO2 also reacts with carbon fuel to produce CO (as shown in Equation 3). The tail gas (H2, CO, H2O) generated by the anode 54 is discharged through the anode chamber outlet 552 and enters the calcination chamber 6. Then, it enters the cathode 52 through the calcination chamber 6 to participate in the cathode reaction, reducing carbon dioxide emissions and realizing the recycling of carbon dioxide and water vapor. The solid products (CaCO3, Ca(OH)2) discharged from the anode chamber outlet 5512 enter the calcination chamber 6 for calcination, realizing the reuse of CaCO3 raw material.

[0054] SOEC:

[0055] cathode H2O + 2e - →H2+O 2- (5)

[0056] CO2 + 2e - →CO+O 2- (6)

[0057] Anode H2+O 2- →H₂O + 2e - (7)

[0058] CO+O 2- →CO2 + 2e - (8)

[0059]

[0060] CaO + CO2 → CaCO3 (10)

[0061] The Fischer-Tropsch reaction section operates as follows: H2 / CO generated in the upper half of cathode 52 (the part corresponding to anode 54) enters the lower half of cathode 52 (the part not corresponding to anode 54 / the part not covering anode 54) and undergoes a reverse methane reforming reaction (as shown in Equation 11) to produce CH4 and water vapor. Simultaneously, a water vapor displacement reaction (as shown in Equation 9) also occurs.

[0062] FT:

[0063] 3H₂ + CO → CH₄ + H₂O (11)

[0064] Finally, in the anode cavity 55, the part not covered by the anode 54 will react with CaO due to the lower temperature, generating Ca(OH)2 (as shown in Formula 12).

[0065] CaO + H₂O → Ca(OH)₂ (12)

[0066] Further, in a preferred embodiment of the present invention, the cathode 52 is made of Ni / YSZ (ni-doped yttrium-stabilized zirconium), the electrolyte 53 is made of dense YSZ (yttrium-stabilized zirconium), and the anode 54 is made of LSM / YSZ (lanthanum-, strontium-, manganese-doped yttrium-stabilized zirconium). Using foam metal 513 improves conductivity because it shortens the electron transport path, allowing electrons to be transported vertically to the porous electrode, thus increasing conductivity. Simultaneously, the tortuous channels in the foam metal 513 significantly improve the uniformity of gas flow and reduce diffusion resistance. Furthermore, since nickel can act as a catalyst for the reverse methane steam reforming reaction, the foam metal 513 in the Fischer-Tropsch fraction also provides more reaction sites for the reverse methane steam reforming reaction, increasing the yield of methane and fresh water at the outlet. The cathode 52 and anode 54 materials are sufficiently porous for gas transport, while the electrolyte 53 material is sufficiently dense to facilitate O2 transport. 2- The carbon fuels used are inorganic carbon, including coal, biochar, and coke. The carbonate catalysts used include sodium carbonate, lithium carbonate, and potassium carbonate, which enhance the water gasification reaction. All materials are widely available, reducing the manufacturing cost of electrolysis and methane synthesis unit 5.

[0067] In a preferred embodiment of the present invention, the electrolysis and methane synthesis unit 5 is tubular, with a length of 18 cm, an inner diameter of 3.5 mm, and an outer diameter of 4.2 mm. The cathode 52 has a thickness of 308 μm, and the cathode cavity 51 is filled with nickel-based foam metal 513. The anode 54 has a thickness of 30 μm. The electrolyte 53 has a thickness of 12 μm, and the operating voltage is 0.3–1.0 V. The lower half of the cathode 52 has a length of 10 cm, and this part does not cover the anode 54. The maximum operating voltage of the electrolysis and methane synthesis unit 5 is no higher than 1.0 V, which is lower than the operating voltage (1.7 V) of existing similar solid oxide electrolyzers, thus reducing energy consumption. It should be noted that although the present invention shows the above-described dimensions of the electrolysis and methane synthesis unit 5, it does not constitute a limitation on the dimensions of the electrolysis and methane synthesis unit 5. Those skilled in the art can adjust the dimensions of the electrolysis and methane synthesis unit 5 according to actual needs.

[0068] In a preferred embodiment of the present invention, the flow rates of the gases introduced into the cathode 52 and the anode 54 are both 20–100 mL / min. At this flow rate, the reaction of the gaseous reactants can be more complete. It should be noted that although the present invention shows the above gas flow rates, those skilled in the art can adjust them according to actual conditions.

[0069] In a preferred embodiment of the present invention, the SOEC section of the electrolysis and methane synthesis unit 5 operates at a temperature of 650–850°C. The temperature of the gas generated by electrolysis gradually decreases as Fischer-Tropsch synthesis occurs in the cathode cavity 51, reaching a temperature of 400–500°C at the cathode cavity outlet 512. Operating at this temperature is beneficial for improving the reaction efficiency of electrolysis and Fischer-Tropsch synthesis, thereby increasing the methane production efficiency. Furthermore, this temperature range is suitable for the long-term stable operation of the electrolysis and methane synthesis unit 5. The gas at the cathode cavity outlet 512 is a high-temperature gas, which is easily separated into gas and liquid after cooling.

[0070] In a preferred embodiment of the present invention, the electrolysis and methane synthesis unit 5 may be one or more. When the number of electrolysis and methane synthesis units 5 is greater than 1, the electrolysis and methane synthesis units 5 may be connected in series or in parallel to increase the output of methane and fresh water.

[0071] In a preferred embodiment of the present invention, a cooling and separation unit is used to cool and separate the product from the outlet of the electrolysis and methane synthesis unit 5 to obtain methane and liquid water. Specifically, the cooling and separation unit uses seawater to exchange heat with the product from the outlet of the electrolysis and methane synthesis unit 5 for cooling. The heat exchange medium is seawater, which is readily available, simplifying the cooling structure. Furthermore, the temperature of the seawater increases after heat exchange, making full use of thermal energy. The heated seawater can further evaporate, saving the thermal energy required for evaporation, resulting in overall energy savings. In a preferred embodiment of the present invention, the cooling and separation unit includes a feedwater pump 9, a methane storage tank 10, and a freshwater storage tank 11. The outlet of the feedwater pump 9 is connected to the freshwater storage tank 11 and the methane storage tank 10 via a branch pipeline. Water vapor and methane from the outlet 512 of the cathode cavity of the electrolysis and methane synthesis unit 5 are cooled in seawater through a pipeline. The cooled liquid water is pumped to the freshwater storage tank 11 by the feedwater pump 9, and the cooled methane enters the methane storage tank 10.

[0072] This invention utilizes seawater as a source of water vapor while simultaneously producing freshwater, making it more suitable for coastal areas lacking freshwater resources. It not only leverages solar energy to provide the heat energy for water vapor generation and the electrical energy required for electrolysis in the electrolytic cell, but also fully utilizes waste heat in the system, improving energy efficiency and making the entire system's energy utilization more green, low-carbon, and economical. Through the electrolysis and methane synthesis unit, the resulting mixed gas, primarily composed of methane, can be further converted into high-value-added chemical products, resulting in certain economic benefits.

[0073] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A seawater desalination and methane production system based on high-temperature electrolysis, characterized in that, It includes a seawater evaporation unit, a solar energy conversion unit, a carbon dioxide supply unit, an electrolysis and methane synthesis unit, and a cooling and separation unit, among which, The solar energy conversion unit is used to provide the electrical energy required for electrolysis in the electrolysis and methane synthesis unit and the thermal energy required for evaporation of seawater in the seawater evaporation unit. The seawater evaporation unit is used to generate water vapor. The water vapor exchanges heat with the high-temperature gas generated by the electrolysis and methane synthesis unit and the heat energy provided by the solar energy conversion unit before entering the electrolysis and methane synthesis unit to carry out the electrolysis reaction. The carbon dioxide supply unit is used to provide the carbon dioxide required by the electrolysis and methane synthesis unit. The electrolysis and methane synthesis unit is used to co-electrolyze carbon dioxide and water vapor and use the hydrogen and carbon monoxide generated by co-electrolysis to synthesize methane through the Fischer-Tropsch process. The cooling and separation unit is used to cool and separate the products from the electrolysis and methane synthesis unit to obtain methane and liquid water. The electrolysis and methane synthesis unit includes a cathode cavity, a cathode, an electrolyte, an anode, and an anode cavity arranged sequentially. The cathode cavity has a cathode cavity inlet and a cathode cavity outlet, and is filled with nickel-based foam metal. The anode cavity includes a first cavity and a second cavity. The first cavity is sandwiched between the anode and the second cavity, and has an anode feed inlet and an anode discharge outlet. The first cavity provides a carbon gasification site. The second cavity has an anode cavity inlet and an anode cavity outlet. The length of the anode is less than the length of the cathode, and the Fischer-Tropsch process occurs in the portion of the cathode not covered by the anode.

2. The seawater desalination and methane production system based on high-temperature electrolysis according to claim 1, characterized in that, The carbon dioxide supply unit includes a calcination chamber, a carbon chamber, and a mixer. The calcination chamber provides a calcination site for calcium carbonate and conveys the calcined solid product to the mixer. The heat of the calcination chamber comes from a high-temperature heat storage device. The carbon chamber provides carbon fuel to the anode chamber. The mixer mixes the carbon fuel and the product from the calcination chamber and provides it to the electrolysis and methane synthesis unit. The gaseous product from the anode chamber outlet of the electrolysis and methane synthesis unit is also fed into the cathode chamber inlet through the calcination chamber to replenish the gas in the cathode chamber. The solid product from the anode outlet enters the calcination chamber for reuse.

3. The seawater desalination and methane production system based on high-temperature electrolysis according to claim 1, characterized in that, The operating voltage of the electrolysis and methane synthesis unit is 0.3~1.0V.

4. The seawater desalination and methane production system based on high-temperature electrolysis according to claim 3, characterized in that, The electrolysis section of the electrolysis and methane synthesis unit operates at a temperature of 650~850℃, while the temperature of the Fischer-Tropsch synthesis section gradually decreases to 400~500℃.

5. The seawater desalination and methane production system based on high-temperature electrolysis according to claim 4, characterized in that, It also includes a steam pressurization device and a carbon dioxide pressurization device. The steam pressurization device is used to pressurize the high-temperature steam at the outlet of the seawater evaporation unit, and the carbon dioxide pressurization device is used to pressurize the carbon dioxide supplied by the carbon dioxide supply unit. The working pressure of the electrolysis and methane synthesis unit is 2.5~3.5 bar.

6. The seawater desalination and methane production system based on high-temperature electrolysis according to claim 1, characterized in that, The flow rates of the gas introduced into the cathode and the anode are both 20-100 mL / min.

7. The seawater desalination and methane production system based on high-temperature electrolysis according to claim 1, characterized in that, The seawater evaporation unit includes a seawater collection and purification device and an evaporation device.

8. The seawater desalination and methane production system based on high-temperature electrolysis according to any one of claims 1 to 7, characterized in that, The solar energy conversion unit includes a solar collector, a high-temperature thermal storage device, and a power generation device. The solar collector is used to collect solar energy and convert it into thermal energy. The high-temperature thermal storage device is used to store the thermal energy converted from solar energy. The high-temperature thermal storage device is a thermochemical thermal storage device with a reaction temperature of 700~1100℃. The power generation device is a photovoltaic power generation device.

9. The seawater desalination and methane production system based on high-temperature electrolysis according to any one of claims 1 to 7, characterized in that, The heat exchange medium of the cooling separation unit is seawater.

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