Methanol synthesis system capable of capturing carbon dioxide

Abstract

The invention relates to the technical field of methanol synthesis processes, in particular to a carbon dioxide capture methanol synthesis system, which comprises a hydrogen production subsystem, a carbon dioxide capture subsystem and a methanol synthesis subsystem, the air trapping subsystem comprises an air contactor, a precipitator, a crusher and firing equipment which are communicated in sequence; the methanol synthesis subsystem comprises a gas mixer, a methanol reactor, a gas-liquid separator and rectification equipment which are communicated in sequence, a carbon source pipeline is communicated between the gas phase output end of the firing equipment and the gas mixer, and a hydrogen source pipeline is communicated between the hydrogen separator and the gas mixer. During operation, methanol synthesis can be completed only by taking air and seawater as raw materials and electric energy as input, the device is suitable for being coupled with an ocean offshore wind power system, and the key technical bottlenecks of high carbon dioxide capture energy consumption and difficult realization of green methanol synthesis caused by lack of a stable external heat source of a deep and far sea isolated platform are solved.

Description

Technical Field

[0001] This invention relates to the field of methanol synthesis technology, and more specifically to a carbon dioxide capture methanol synthesis system. Background Technology

[0002] Offshore wind power, especially wind farms located in deep-sea areas, faces challenges such as high power transmission costs and difficulties in grid connection and absorption. Traditional submarine cable transmission methods suffer from significant losses and extremely high construction and maintenance costs over long distances, hindering the large-scale development of deep-sea wind power. Therefore, converting wind power into a chemical energy carrier that is easy to store and transport has become an effective way to improve wind power absorption capacity and reduce transmission costs. Among these methods, using offshore wind power to electrolyze water to produce hydrogen is a commonly used technology for utilizing offshore wind power.

[0003] Offshore wind power-to-hydrogen technology converts unstable wind power into green hydrogen through water electrolysis, solving the problem of wind power integration and obtaining zero-carbon emission hydrogen energy. However, hydrogen has low volumetric energy density, high liquefaction costs, and stringent requirements for storage and transportation safety, making long-distance offshore hydrogen transportation technically challenging. Methanol, as an important liquid energy carrier and chemical raw material, relies heavily on fossil fuels for its traditional production, resulting in significant carbon emissions. Further converting green hydrogen into high-energy-density, easily stored and transportable liquid hydrogen-based carriers such as green methanol is also an effective way to improve wind power integration capacity.

[0004] In existing technologies, the carbon source required for methanol synthesis can be directly captured from the atmosphere via air capture. However, the process of capturing carbon dioxide through air capture is energy-intensive, and its high-temperature calcination and regeneration stage requires a continuous and stable heat source. Reliable external energy supplies are difficult to obtain on isolated deep-sea platforms, making it difficult to realize the technical solution of using deep-sea wind power to produce hydrogen for further methanol synthesis in practical applications. Summary of the Invention

[0005] This invention provides a carbon dioxide capture methanol synthesis system to solve the problem of high energy consumption and difficulty in implementation in the existing process of synthesizing methanol from offshore wind power.

[0006] In a first aspect, the present invention provides a carbon dioxide capture and methanol synthesis system, comprising: A hydrogen production subsystem, comprising a seawater desalination unit and a water electrolysis hydrogen production unit connected in sequence, wherein an oxygen separator and a hydrogen separator are connected in sequence on the water electrolysis hydrogen production unit; An air capture subsystem includes an air contactor, a precipitator, a crusher, and a calcining device connected in sequence. An oxygen supply pipeline connects the oxygen separator to the calcining device, and a hydrogen supply pipeline connects the hydrogen separator to the calcining device. A methanol synthesis subsystem includes a gas mixer, a methanol reactor, a gas-liquid separator, and a distillation unit connected in sequence. A carbon source pipeline connects the gas phase output end of the calcination unit to the gas mixer, and a hydrogen source pipeline connects the hydrogen separator to the gas mixer.

[0007] In the methanol synthesis system using carbon dioxide capture, the process begins with seawater desalination and electrolysis to produce hydrogen via a hydrogen production subsystem, simultaneously separating oxygen and hydrogen. Simultaneously, an air capture subsystem captures air via an air contactor, then sends the captured air to a precipitator to absorb carbon dioxide and generate calcium carbonate precipitate. This carbonate precipitate is then transported to a combustion device. Oxygen and hydrogen generated by the hydrogen production subsystem participate in and promote the enrichment and conversion of carbon dioxide captured from the air in the combustion device, producing a gaseous product with carbon dioxide as the main component. Finally, the methanol synthesis subsystem mixes the carbon dioxide gaseous product with hydrogen generated by the hydrogen production subsystem in a gas mixer, then sends the mixture to a methanol reactor where it is synthesized under the catalysis of a catalyst. The methanol product is then obtained after separation and distillation. The entire system achieves a continuous production process from air capture of carbon dioxide to its conversion into methanol. The carbon dioxide capture methanol synthesis system requires only air and seawater as raw materials and electricity as input to synthesize methanol. It is suitable for coupling with offshore wind power systems and solves the key technical bottleneck of high energy consumption for carbon dioxide capture and difficulty in achieving green methanol synthesis due to the lack of stable external heat sources on isolated platforms in deep sea. This makes the engineering application of air capture technology in offshore wind power scenarios feasible, thereby realizing the on-site and efficient conversion of offshore wind power. It can avoid the huge losses of long-distance submarine cable transmission and reduce the transmission cost and consumption difficulty of deep sea wind power.

[0008] In one optional embodiment, the solid output end of the calcining equipment is connected to a digester, a water supply pipeline is connected between the seawater desalination equipment and the digester, and the solution output end of the digester is connected to the precipitator.

[0009] The solid output end of the calcination equipment transports the calcined solid material to the digester. The seawater desalination equipment supplies fresh water to the digester through a water supply pipeline. The solid material reacts with water in the digester to generate a solution, which is then returned to the precipitator for recycling through the digester's solution output end. The digester converts the solid product discharged from the calcination equipment back into recyclable alkaline solution, achieving adsorbent regeneration and recovery. This reduces the air capture subsystem's need for external alkaline replenishment, decreases chemical transportation and consumption costs, and improves the overall system's material self-sufficiency and economic efficiency.

[0010] In one optional embodiment, the air contactor is provided with a carbonate outlet and an alkali inlet, both of which are connected to the precipitator. The carbonate solution is adapted to be conveyed from the air contactor to the precipitator through the carbonate outlet, and the alkali solution is adapted to be conveyed from the precipitator to the air contactor through the alkali inlet.

[0011] The carbonate outlet on the air contactor transports the carbonate solution formed after absorbing carbon dioxide to the precipitator. The precipitator is connected to the alkali inlet of the air contactor. The alkali solution treated in the precipitator returns to the air contactor through the alkali inlet, forming a closed-loop cycle for the adsorbent. This allows the alkali absorbent to be reused, avoiding frequent replenishment of fresh alkali solution, reducing chemical consumption and waste discharge, and enhancing the system's ability to operate continuously in isolated deep-sea environments.

[0012] In one optional embodiment, the hydrogen production subsystem further includes an ultrapure water device, the inlet of which is connected to the freshwater outlet of the seawater desalination device, and the outlet of which is connected to the water electrolysis hydrogen production device.

[0013] Ultrapure water equipment can remove residual impurity ions from fresh water, providing qualified ultrapure water for water electrolysis hydrogen production equipment, extending the electrode life of water electrolysis hydrogen production equipment, reducing the risk of scaling and corrosion, and improving electrolysis efficiency and system stability.

[0014] In one optional embodiment, the oxygen separator is an oxygen-water separator, the outlet of the ultrapure water equipment is connected to the oxygen-water separator, and the liquid phase outlet of the oxygen-water separator is connected to the water electrolysis hydrogen production equipment.

[0015] The oxygen-water separator separates the gas generated at the anode of the water electrolysis hydrogen production equipment into gas and liquid phases. It condenses and recovers the water vapor carried during the oxygen electrolysis process and re-transports it to the water electrolysis hydrogen production equipment through the liquid phase outlet, realizing the internal circulation of process water, reducing the water production load of ultrapure water equipment and the additional energy consumption of seawater desalination equipment, and improving the efficiency of water resource utilization.

[0016] In one optional embodiment, the output end of the hydrogen separator is connected to a hydrogen storage device, and both the hydrogen supply pipeline and the hydrogen source pipeline are connected to the hydrogen storage device.

[0017] The hydrogen storage unit stores and buffers the hydrogen output from the hydrogen separator. Both the hydrogen supply pipeline and the hydrogen source pipeline draw hydrogen from the storage unit and deliver it to the combustion equipment and gas mixer, respectively. The hydrogen storage unit effectively balances the difference between the hydrogen production rate fluctuations caused by wind power fluctuations and the downstream hydrogen demand, avoiding frequent start-ups and shutdowns of the water electrolysis hydrogen production equipment, improving the continuity and reliability of system operation, and providing a stable gas supply for the methanol synthesis subsystem and the air capture subsystem.

[0018] In one optional embodiment, the liquid phase outlet of the gas-liquid separator is connected to the distillation apparatus, and a product heat exchanger is installed between the gas-liquid separator and the distillation apparatus.

[0019] The liquid phase outlet of the gas-liquid separator is connected to the distillation equipment. A product heat exchanger is installed between the gas-liquid separator and the distillation equipment. Before the crude methanol product is transported to the distillation equipment, it exchanges heat through the product heat exchanger to reduce the heating energy consumption of the distillation equipment.

[0020] In one alternative embodiment, a preheating heat exchanger is installed between the gas mixer and the methanol reactor.

[0021] The mixed gas output from the gas mixer is preheated by a preheating heat exchanger before entering the methanol reactor. This reduces the heating load on the methanol reactor, shortens the reaction start-up time, increases the reaction rate and conversion rate of the methanol reactor, and reduces system energy consumption.

[0022] In one optional embodiment, the hydrogen separator is also connected to a hydrogen venting pipeline. This prevents the system from operating under overpressure, ensuring the safety of equipment and personnel, while also avoiding a decrease in hydrogen production efficiency due to pressure fluctuations, and improving the system's safety redundancy under extreme operating conditions.

[0023] When the system pressure exceeds the set value or the hydrogen production is excessive, the hydrogen is safely discharged through the hydrogen venting pipeline.

[0024] In one alternative embodiment, the gas phase outlet of the gas-liquid separator is connected to the circulating gas inlet of the gas mixer.

[0025] Unreacted gas separated by the gas-liquid separator is returned to the circulating gas inlet of the gas mixer through the gas phase outlet, where it mixes with fresh feedstock and re-enters the methanol reactor. This recycling of unreacted gas significantly improves the overall conversion rate of hydrogen and carbon dioxide, reduces the consumption of fresh feedstock, and decreases waste gas emissions. Attached Figure Description

[0026] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the carbon dioxide capture and methanol synthesis system provided in an embodiment of the present invention.

[0028] Explanation of reference numerals in the attached figures: 1. Air blower; 2. Air contactor; 3. Sedimenter; 4. Crusher; 5. Conveyor; 6. Calcination equipment; 7. Carbon dioxide compressor; 8. Gas mixer; 9. Mixed gas compressor; 10. Preheating heat exchanger; 11. Methanol reactor; 12. Liquefaction heat exchanger; 13. Gas-liquid separator; 14. Centrifugal pump; 15. Product heat exchanger; 16. Distillation equipment; 17. Seawater booster pump; 18. Seawater desalination equipment; 19. Ultrapure water equipment; 20. Oxygen-water separator; 21. Hydrogen separator; 22. Electrolysis water hydrogen production equipment; 23. Hydrogen compressor; 24. Hydrogen storage unit; 25. Digester; 26. Oxygen compressor. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, 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.

[0030] The following is combined with Figure 1 The following describes embodiments of the present invention.

[0031] According to embodiments of the present invention, in one aspect, a carbon dioxide capture and methanol synthesis system is provided. This system aims to convert renewable energy sources such as offshore wind power into green methanol that is easy to store and transport, and is particularly suitable for deep-sea environments. Specifically, the system includes a hydrogen production subsystem, an air capture subsystem, and a methanol synthesis subsystem.

[0032] The hydrogen production subsystem includes a seawater desalination unit 18 and a water electrolysis hydrogen production unit 22. The freshwater outlet of the seawater desalination unit 18 and the inlet of the water electrolysis hydrogen production unit 22 are connected sequentially via pipelines. The seawater desalination unit 18 is used to desalinate seawater feedstock into freshwater that meets the requirements for electrolysis. The gas output end of the water electrolysis hydrogen production unit 22 is connected to an oxygen separator and a hydrogen separator 21. The oxygen separator separates the oxygen components generated during the electrolysis process, and the hydrogen separator 21 separates the hydrogen components generated during the electrolysis process. A seawater booster pump 17 is connected to the seawater inlet of the seawater desalination unit 18 to pump seawater into the desalination unit 18.

[0033] The air capture subsystem includes an air contactor 2, a precipitator 3, a crusher 4, and a calcining device 6. The gas outlet of the air contactor 2 is connected to the feed inlet of the precipitator 3, the solid outlet of the precipitator 3 is connected to the feed inlet of the crusher 4, and the discharge outlet of the crusher 4 is connected to the solid phase input end of the calcining device 6. These devices are connected in sequence to form a complete air capture and treatment process. An oxygen supply pipeline connects the oxygen separator and the calcining device 6, and an oxygen compressor 26 is installed on the oxygen supply pipeline to provide power for oxygen delivery. The oxygen supply pipeline delivers the oxygen separated by the oxygen separator to the calcining device 6 for use as an oxidant. A hydrogen supply pipeline connects the hydrogen separator 21 and the calcining device 6, and the hydrogen supply pipeline delivers the hydrogen separated by the hydrogen separator 21 to the calcining device 6 for use as fuel. At the same time, to facilitate the delivery of air to the air contactor 2, an air fan 1 is connected to the air inlet end of the air contactor 2, and the air fan 1 blows air into the air contactor 2.

[0034] The methanol synthesis subsystem includes a gas mixer 8, a methanol reactor 11, a gas-liquid separator 13, and a distillation unit 16. The outlet of the gas mixer 8 is connected to the inlet of the methanol reactor 11, the outlet of the methanol reactor 11 is connected to the inlet of the gas-liquid separator 13, and the liquid phase outlet of the gas-liquid separator 13 is connected to the inlet of the distillation unit 16. These devices are connected in sequence to form the methanol synthesis and purification process. A carbon source pipeline connects the gas phase output of the calcination unit 6 to the gas mixer 8, transporting the gas phase product, mainly composed of carbon dioxide, produced by the calcination unit 6 to the gas mixer 8 as a carbon source. A hydrogen source pipeline connects the hydrogen separator 21 to the gas mixer 8, transporting the hydrogen separated by the hydrogen separator 21 to the gas mixer 8 as a hydrogen source. A carbon dioxide compressor 7 is installed on the carbon source pipeline to provide power for the carbon dioxide transport.

[0035] When the carbon dioxide capture and methanol synthesis system is performing methanol synthesis, the entire process is carried out in an orderly manner according to the following steps: First, the hydrogen production subsystem starts operating. Seawater feedstock enters the seawater desalination unit 18, which desalinates the seawater, removing salt, impurities, and harmful ions to produce freshwater that meets the requirements for electrolytic water quality. The freshwater then enters the electrolytic water hydrogen production unit 22, which uses externally input electrical energy to electrolyze and decompose the freshwater, producing hydrogen at the cathode and oxygen at the anode. The mixed gas produced by electrolysis enters the oxygen separator and hydrogen separator 21, respectively. The oxygen separator separates the oxygen component from the mixed gas, and the hydrogen separator 21 separates the hydrogen component, achieving separate collection of hydrogen and oxygen.

[0036] Simultaneously, the air capture subsystem operates synchronously. Ambient air enters air contactor 2, which is filled with alkaline absorbent. The alkaline absorbent reacts chemically with carbon dioxide in the air, transferring the carbon dioxide from the gas phase to the liquid phase, forming a carbon dioxide-rich absorbent. This carbon dioxide-rich absorbent is then transported from air contactor 2 to precipitator 3. In precipitator 3, by adding a precipitant or adjusting the reaction conditions, the carbon dioxide dissolved in the absorbent is converted into solid carbonate precipitate. The resulting carbonate precipitate is discharged from precipitator 3 and enters crusher 4. Crusher 4 mechanically crushes the carbonate precipitate, breaking large carbonate particles into smaller ones to increase the specific surface area and improve subsequent calcination efficiency. To facilitate the entry of the carbonate precipitate from the crusher into the calcining equipment 6, a conveyor 5 is installed between the crusher and the calcining equipment 6. In this embodiment, the calcination equipment 6 is a gas-fired vertical kiln. The crushed carbonate particles are conveyed into the calcination equipment 6 via a belt conveyor 5. The hydrogen separated by the hydrogen separator 21 is transported into the calcination equipment 6 through a hydrogen supply pipeline as fuel for combustion. The oxygen separated by the oxygen separator is transported into the calcination equipment 6 through an oxygen supply pipeline as an oxidant to participate in the combustion reaction. The combustion of hydrogen and oxygen in the calcination equipment 6 releases a large amount of heat energy, providing a continuous and stable high-temperature environment for the calcination and decomposition of the carbonate particles. Under high-temperature calcination conditions, the carbonate particles decompose and regenerate, releasing high-purity carbon dioxide gas to form a gaseous product with carbon dioxide as the main component, while simultaneously generating a recyclable solid product.

[0037] Next, the methanol synthesis subsystem begins operation. The gaseous products generated by the calcination unit 6 are transported to the gas mixer 8 via a carbon source pipeline. Hydrogen separated by the hydrogen separator 21 is also transported to the gas mixer 8 via a hydrogen source pipeline. The gas mixer 8 thoroughly mixes carbon dioxide and hydrogen according to the stoichiometric ratio required for methanol synthesis, forming a homogeneous mixed reaction gas. This mixed reaction gas enters the methanol reactor 11 from the gas mixer 8. The methanol reactor 11 is filled with a methanol synthesis catalyst. Under the action of the catalyst, carbon dioxide and hydrogen undergo a methanol synthesis reaction, producing methanol and other byproducts. The reacted mixed gas then enters the gas-liquid separator 13 from the methanol reactor 11. The gas-liquid separator 13 separates the condensed liquid crude methanol from the unreacted gas through cooling condensation or distillation. The separated liquid crude methanol enters the distillation unit 16 from the liquid phase outlet of the gas-liquid separator 13. The distillation unit 16 performs distillation purification of the crude methanol, utilizing the difference in boiling points of the components to separate methanol from other impurities, ultimately obtaining a high-purity methanol product. The entire system achieves a continuous production process from capturing carbon dioxide from the air to converting it into methanol. A liquefaction heat exchanger 12 is installed between the methanol reactor 11 and the gas-liquid separator 13 to cool the product output from the methanol reactor 11 using a cooling medium such as seawater, thereby liquefying the methanol.

[0038] The carbon dioxide capture methanol synthesis system requires only air and seawater as raw materials and electricity as input to synthesize methanol, making it particularly suitable for coupled operation with offshore wind power systems. Through innovative process integration design, the system directly supplies oxygen and hydrogen, byproducts of the water electrolysis hydrogen production process, as fuel and oxidant to the combustion equipment 6. This provides a stable and reliable internal energy source for the calcination and regeneration of the adsorbent in the air capture subsystem, completely solving the key technical bottleneck of high energy consumption in carbon dioxide capture and the difficulty in achieving green methanol synthesis due to the lack of stable external heat sources on isolated platforms in deep-sea areas. This makes the engineering application of air capture technology in offshore wind power scenarios feasible.

[0039] The system enables efficient on-site conversion of offshore wind power, first converting unstable wind energy into chemical energy stored in hydrogen, and then further converting it into green methanol, which has a higher energy density and is easier to store and transport. This avoids the huge energy losses during long-distance submarine cable transmission and circumvents the technical obstacles and safety risks associated with direct hydrogen storage and transportation, significantly reducing the transmission costs and integration difficulties of deep-sea wind power. Simultaneously, the system converts renewable wind energy resources into zero-carbon emission liquid fuel methanol, providing a complete and feasible technical solution for the large-scale commercial development of deep-sea wind power while yielding high-value-added clean energy products, thus overcoming the economic and technical constraints of existing technologies in practical engineering applications.

[0040] In one embodiment, the solid output end of the calcining device 6 is connected to the feed inlet of the digester 25 via a pipe. The digester 25 is made of corrosion-resistant material and is equipped with a stirring device and a temperature control unit inside. One end of the water supply pipeline is connected to the freshwater outlet of the seawater desalination device 18, and the other end is connected to the water inlet of the digester 25, for transporting the freshwater produced by the seawater desalination device 18 to the digester 25 to participate in the reaction. A solution output end is provided on the top or side of the digester 25, and the solution output end is connected to the liquid inlet of the precipitator 3 via a return pipeline, forming a complete solid-liquid reaction and solution circulation loop.

[0041] The solid output end of the calcination device 6 continuously or intermittently delivers the calcined solid material, typically alkaline oxides or hydroxides such as calcium oxide or calcium hydroxide, to the digester 25. The seawater desalination device 18 supplies an appropriate amount of fresh water to the digester 25 via a water supply pipeline. The flow rate of the fresh water can be precisely controlled by valves and flow meters to ensure sufficient reaction of the solid material. The solid material undergoes an exothermic chemical reaction with water within the digester 25, generating a calcium hydroxide solution or suspension. During the reaction, a stirring device promotes mass and heat transfer, making the reaction more complete and uniform. The generated solution is pumped back to the precipitator 3 through the solution output end of the digester 25 for recycling. This solution continues to participate in the carbon dioxide capture process as an alkaline absorbent.

[0042] The digester 25 converts the solid products discharged from the calcination equipment 6 back into recyclable alkaline solution, achieving online regeneration and efficient recovery of the adsorbent and avoiding one-time consumption of the adsorbent. This reduces the air capture subsystem's need for external alkaline replenishment, decreasing chemical transportation and consumption costs, making it particularly suitable for applications on isolated platforms in deep-sea areas where chemical replenishment is difficult. Simultaneously, the coordinated operation of the digester 25 and the seawater desalination equipment 18 enables closed-loop material management, improving the overall system's material self-sufficiency, operational economy, and environmental friendliness.

[0043] The digester 25 can adopt a multi-stage series or parallel structure to improve digestion efficiency and system processing capacity. The stirring device can be of different forms, such as mechanical stirring, gas stirring, or jet stirring. The temperature control unit can include various temperature control methods, such as jacketed heat exchange, built-in coils, or external circulating cooling. A water quality adjustment device can be added to the water supply pipeline to adjust the pH or hardness of the freshwater produced by the seawater desalination equipment 18 to optimize the digestion reaction conditions.

[0044] In one embodiment, the air contactor 2 is provided with a carbonate outlet and an alkali inlet, both of which are connected to the precipitator 3. The carbonate solution is suitable for being conveyed from the air contactor 2 to the precipitator 3 through the carbonate outlet, and the alkali solution is suitable for being conveyed from the precipitator 3 to the air contactor 2 through the alkali inlet.

[0045] In this embodiment, the air contactor 2 has a carbonate outlet at its bottom or lower side, and an alkali inlet at its top or upper side. The carbonate outlet is connected to the middle or upper inlet of the precipitator 3 via a first conveying pipeline, and the alkali inlet is connected to the lower or bottom outlet of the precipitator 3 via a second conveying pipeline. A conveying pump, a flow control valve, and monitoring instruments are respectively installed on the first and second conveying pipelines to achieve directional conveying and control of the fluid.

[0046] The carbonate outlet on air contactor 2, after absorbing carbon dioxide, delivers a carbonate solution (e.g., sodium carbonate or potassium carbonate solution) to precipitator 3 via a first delivery pipeline. Precipitator 3 has crystallization or sedimentation zones inside, allowing the carbonate solution to react with the precipitant to form a solid carbonate precipitate. Precipitator 3 is connected to the alkali inlet of air contactor 2 via a second delivery pipeline. The supernatant after solid-liquid separation in precipitator 3 is the regenerated alkali solution, which returns to air contactor 2 through the alkali inlet, forming a closed-loop cycle for the alkali absorbent. The composition, concentration, and pH of the regenerated alkali solution can be monitored using an online analyzer, and the stability of the absorbent performance can be maintained by adding a small amount of fresh alkali solution or adjusting the flow rate.

[0047] The bidirectional connecting pipeline between the air contactor 2 and the precipitator 3, linking the carbonate outlet and the alkali inlet, allows for the reuse of the alkali absorbent, avoiding frequent replenishment of fresh alkali. This reduces chemical consumption and wastewater discharge, decreases the frequency of chemical transport vessels traveling to and from land, and lowers operating costs. Furthermore, the recycling of alkali enhances the system's continuous operation and autonomous maintenance capabilities in isolated deep-sea environments, improving system reliability and environmental adaptability.

[0048] The carbonate outlet and alkali inlet can be positioned at different heights on the air contactor 2 to optimize hydrodynamic performance. The delivery pipeline can employ a dual-pipeline backup design, allowing the other pipeline to continue operating while one is under maintenance. Multiple alkali spray layers can be installed inside the air contactor 2, with the alkali inlet connected to different spray layers for zoned control. The precipitator 3 can employ different solid-liquid separation structures, such as gravity settling, centrifugal separation, or filtration separation.

[0049] In one embodiment, the hydrogen production subsystem further includes an ultrapure water device 19, the inlet of which is connected to the fresh water outlet of the seawater desalination device 18, and the outlet of which is connected to the water electrolysis hydrogen production device 22.

[0050] In this embodiment, the ultrapure water equipment 19 can be an electro-deionization device, a mixed ion exchange resin device, or a combination of reverse osmosis and ion exchange. The inlet of the ultrapure water equipment 19 is connected to the freshwater outlet of the seawater desalination equipment 18 via a pipeline in a sealed manner, and the outlet of the ultrapure water equipment 19 is connected to the inlet of the electrolyzer of the water electrolysis hydrogen production equipment 22 via a high-pressure pipeline. Pressure gauges, flow meters, and online water quality monitoring instruments can be installed on the pipeline between the ultrapure water equipment 19 and the water electrolysis hydrogen production equipment 22 to monitor the ultrapure water supply status in real time.

[0051] The ultrapure water system 19 further removes residual trace impurity ions from the freshwater produced by the seawater desalination system 18, including sodium ions, chloride ions, calcium ions, magnesium ions, and other dissolved salts and organic matter, to meet the stringent requirements of the water electrolysis hydrogen production system 22 for influent conductivity. The ultrapure water system 19 purifies the freshwater to the ultrapure water quality required by the water electrolysis hydrogen production system 22 through deep purification processes such as ion exchange, electrodialysis, or reverse osmosis. This deep purification treatment effectively avoids the deposition and scaling of impurity ions on the electrode surface of the water electrolysis hydrogen production system 22, significantly extending the electrode's service life and reducing the risk of contamination of the electrolyzer membrane by impurities.

[0052] The ultrapure water system 19 provides high-purity feed water to the water electrolysis hydrogen production equipment 22, reducing the rate of scaling and corrosion, and decreasing the frequency and cost of maintenance. Extended electrode life and improved electrolysis efficiency directly enhance the long-term operational stability and overall economic benefits of the hydrogen production subsystem. In deep-sea wind power scenarios, equipment maintenance is difficult and costly; the ultrapure water system 19 effectively reduces maintenance requirements, enhances system reliability and durability, and ensures long-term continuous and stable operation.

[0053] In one embodiment, the oxygen separator is an oxygen-water separator 20. The outlet of the ultrapure water device 19 is connected to the oxygen-water separator 20, and the liquid phase outlet of the oxygen-water separator 20 is connected to the water electrolysis hydrogen production device 22. The oxygen-water separator 20 internally includes a cooling coil, a demister, and a gas-liquid separation chamber. The outlet of the ultrapure water device 19 is connected to the inlet of the oxygen-water separator 20 or a spray device via a branch pipe, providing ultrapure water for cooling and washing the oxygen-water separator 20. The gas phase inlet of the oxygen-water separator 20 is connected to the anode chamber of the water electrolysis hydrogen production device 22. An oxygen outlet is located at the top of the oxygen-water separator 20, and a liquid phase outlet is located at the bottom of the oxygen-water separator 20. This liquid phase outlet is connected to the water supply port of the electrolyzer in the water electrolysis hydrogen production device 22 via a return pipe.

[0054] The oxygen-water separator 20 separates the gas produced at the anode of the water electrolysis hydrogen production unit 22 into gas and liquid components. Since the high-temperature oxygen generated during electrolysis carries a large amount of water vapor, the oxygen-water separator 20 cools the mixed gas to below the dew point using internal cooling coils, causing the water vapor to condense into liquid water. Simultaneously, ultrapure water provided by the ultrapure water unit 19 can be used as a washing solution to further remove tiny droplets and impurities entrained in the oxygen. The condensed and recovered liquid water is collected through the liquid phase outlet at the bottom of the oxygen-water separator 20 and returned to the water electrolysis hydrogen production unit 22 via a reflux pipeline for reuse as process makeup water. This process achieves an internal closed-loop circulation of process water, significantly reducing the system's demand for fresh water.

[0055] The oxygen-water separator 20 enables effective water recovery and recycling, directly reducing the water production load of the ultrapure water equipment 19, thereby lowering its energy consumption and chemical regenerator consumption. Simultaneously, by reducing the additional water production requirements of the seawater desalination equipment 18, its operating time is shortened, resulting in a corresponding reduction in energy consumption. Overall, this design significantly improves water resource utilization efficiency and reduces overall system energy consumption, holding significant practical importance for deep-sea platforms where freshwater resources are scarce.

[0056] In one embodiment, the output end of the hydrogen separator 21 is connected to a hydrogen storage unit 24. Both the hydrogen supply pipeline and the hydrogen source pipeline are connected to the hydrogen storage unit 24. A hydrogen compressor 23 is installed on the pipeline between the hydrogen separator 21 and the hydrogen storage unit 24 to provide power for the hydrogen transportation and storage process. The hydrogen output end of the hydrogen separator 21 is connected to the inlet of the hydrogen storage unit 24 via a pipeline. The hydrogen storage unit 24 can be a high-pressure hydrogen storage tank, a low-pressure buffer tank, or a solid-state hydrogen storage device. The outlet of the hydrogen storage unit 24 is connected to both the hydrogen supply pipeline and the hydrogen source pipeline. The other end of the hydrogen supply pipeline is connected to the burner or reaction chamber of the firing equipment 6, and the other end of the hydrogen source pipeline is connected to the hydrogen inlet of the gas mixer 8. A pressure sensor, a temperature sensor, and a safety valve are installed on the hydrogen storage unit 24 to monitor the internal status of the storage unit in real time and ensure safe operation.

[0057] Hydrogen storage unit 24 stores and buffers the hydrogen output from hydrogen separator 21. Due to the intermittent and fluctuating nature of offshore wind power, the hydrogen production rate of water electrolysis hydrogen production equipment 22 fluctuates with changes in wind power output. Hydrogen storage unit 24, acting as a buffer container, can temporarily store excess hydrogen and release it when hydrogen production is insufficient, thereby balancing the difference between the hydrogen production rate fluctuations caused by wind power fluctuations and downstream hydrogen demand. Both the hydrogen supply pipeline and the hydrogen source pipeline draw hydrogen from the outlet of hydrogen storage unit 24. The hydrogen supply pipeline delivers hydrogen to combustion equipment 6 as fuel, while the hydrogen source pipeline delivers hydrogen to gas mixer 8 as a raw material for methanol synthesis.

[0058] The presence of hydrogen storage unit 24 effectively prevents frequent start-ups and shutdowns of the water electrolysis hydrogen production unit 22 due to unstable downstream hydrogen demand, reducing mechanical wear and electrical shocks and improving the continuity and reliability of system operation. Simultaneously, hydrogen storage unit 24 provides a stable gas supply for the methanol synthesis subsystem and the air capture subsystem, maintaining normal operation of both subsystems even during sudden drops in wind power, significantly improving the system's resilience and overall availability. On deep-sea platforms, this design reduces equipment failure rates and maintenance needs, demonstrating significant economic and safety value.

[0059] The hydrogen storage unit 24 can be constructed using multiple tanks connected in series or parallel to achieve tiered storage and flexible allocation. The hydrogen storage unit 24 can be equipped with a hydrogen purification device to further remove impurity gases. A pressure reducing valve and a flow controller can be installed at the storage unit outlet to control the hydrogen supply pressure.

[0060] In one embodiment, the liquid phase outlet of the gas-liquid separator 13 is connected to the distillation apparatus 16, and a product heat exchanger 15 is installed between the gas-liquid separator 13 and the distillation apparatus 16. A centrifugal pump 14 is installed between the product heat exchanger 15 and the liquid phase outlet of the gas-liquid separator 13 to provide power for transporting the liquid phase product separated in the gas-liquid separator 13.

[0061] The liquid phase outlet of the gas-liquid separator 13 is connected to the hot-side inlet of the product heat exchanger 15 via a pipeline, and the hot-side outlet of the product heat exchanger 15 is connected to the feed inlet of the distillation unit 16 via a pipeline. The product heat exchanger 15 can be a shell-and-tube heat exchanger, a plate heat exchanger, or a spiral plate heat exchanger. Cooling water, the feed gas to be heated, or other process media can be introduced to the cold side of the product heat exchanger 15 to achieve heat recovery and exchange. The product heat exchanger 15 is equipped with temperature monitoring points and flow regulation devices to optimize the heat exchange effect.

[0062] The liquid phase outlet of the gas-liquid separator 13 is connected to the distillation unit 16. After the reaction products from the methanol reactor 11 enter the gas-liquid separator 13, the unreacted gas is discharged from the gas phase outlet, and the condensed crude methanol liquid flows out from the liquid phase outlet. A product heat exchanger 15 is installed between the gas-liquid separator 13 and the distillation unit 16. Before being transported to the distillation unit 16, the crude methanol product undergoes heat exchange through the product heat exchanger 15. The residual heat of the crude methanol product can be used to preheat other cryogenic streams, or the crude methanol product can be precooled to a temperature suitable for distillation feed, thereby reducing the heating or cooling load of the distillation unit 16.

[0063] The product heat exchanger 15 fully utilizes the waste heat of the crude methanol product, achieving cascaded energy utilization and significantly reducing the heating energy consumption of the distillation unit 16, thereby improving the overall system's energy efficiency. On deep-sea platforms, where energy costs are high, any energy-saving measures are of paramount importance. The installation of the product heat exchanger 15 not only reduces operating costs but also decreases the heater size and power requirements of the distillation unit 16, optimizing the system configuration. Simultaneously, by preheating or precooling the crude methanol product, the product heat exchanger 15 helps the distillation unit 16 achieve more stable operating conditions and better separation results.

[0064] In one embodiment, a preheating heat exchanger 10 is installed between the gas mixer 8 and the methanol reactor 11. A mixed gas compressor 9 is installed between the preheating heat exchanger 10 and the gas mixer 8 to provide power for the delivery of the mixed gas.

[0065] The outlet of the mixed gas in the gas mixer 8 is connected to the cold-side inlet of the preheating heat exchanger 10 via a pipeline. The hot-side inlet of the preheating heat exchanger 10 can be supplied with a high-temperature heat source, such as heat transfer oil, steam, or high-temperature flue gas. The cold-side outlet of the preheating heat exchanger 10 is connected to the gas inlet of the methanol reactor 11 via a pipeline. The preheating heat exchanger 10 can be equipped with an electric heater, a steam heater, or a high-temperature gas heater. The preheating heat exchanger 10 is equipped with a temperature sensor, a pressure sensor, and an automatic control system for precisely controlling the preheating temperature of the mixed gas.

[0066] The mixed gas output from gas mixer 8 enters preheating heat exchanger 10 before entering methanol reactor 11. Preheating heat exchanger 10 heats the mixed gas from room temperature to the active temperature range required for the methanol synthesis reaction. The preheating process can be achieved through electric heating, steam heating, or heat exchange with other high-temperature process media. The preheated mixed gas enters methanol reactor 11 at a suitable temperature, and upon contact with the catalyst, the synthesis reaction is rapidly initiated.

[0067] The preheating heat exchanger 10 ensures that the mixed gas reaches the reaction temperature before entering the methanol reactor 11, reducing the heating load on the methanol reactor 11, shortening the reaction start-up time, and avoiding the risk of non-selective catalyst reaction and carbon buildup at low temperatures. The preheating heat exchanger 10 improves the reaction rate and single-pass conversion rate of the methanol reactor 11, reduces the recirculation ratio of the reactant gas, thereby lowering compression energy consumption and overall system energy consumption. In deep-sea wind power scenarios, the preheating heat exchanger 10 can also utilize surplus wind power for electric heating, achieving energy storage and conversion, and improving the system's flexibility and economy.

[0068] In one embodiment, the hydrogen separator 21 is also connected to a hydrogen venting line. When the system pressure exceeds a set value or the hydrogen production is excessive, the hydrogen is safely discharged through the hydrogen venting line.

[0069] In this embodiment, a hydrogen venting pipeline is provided on the top or side of the hydrogen separator 21, and the hydrogen venting pipeline is directly connected to the gas chamber of the hydrogen separator 21. A pressure sensor, an automatic shut-off valve, a safety valve, a flame arrester, and a discharge port are sequentially installed on the hydrogen venting pipeline. The automatic shut-off valve is interlocked with the system pressure signal; when the pressure sensor detects that the system pressure exceeds a preset safety value, the automatic shut-off valve opens. The safety valve, as a mechanical protection device, acts as a final safety barrier when the automatic shut-off valve fails. The flame arrester is installed upstream of the discharge port to prevent external fire sources from propagating back into the system. The discharge port points towards a safe area, away from personnel and equipment.

[0070] The hydrogen venting pipeline provides a pressure relief channel to prevent the system from operating under overpressure, ensuring the safety of equipment and personnel. Simultaneously, the hydrogen venting pipeline prevents a decrease in hydrogen production efficiency in the hydrogen separator 21 due to pressure fluctuations, enhancing the system's safety redundancy under extreme operating conditions. On deep-sea platforms, safety is the primary consideration. The hydrogen venting pipeline provides crucial safety protection, ensuring that the system can safely depressurize in abnormal situations such as sudden increases in wind power, downstream hydrogen supply interruptions, or equipment failures, preventing explosions or equipment damage.

[0071] Alternatively, the hydrogen venting line can be connected to a hydrogen flare system to combust the emitted hydrogen. The vent outlet can be equipped with a wind vane and warning signs to indicate the safe zone in real time. A silencer can be installed on the hydrogen venting line to reduce emission noise. The automatic shut-off valve can be pneumatically or electrically actuated and equipped with a manual emergency operation device. Furthermore, the hydrogen venting line can be connected to a hydrogen recovery system to temporarily store hydrogen instead of directly venting it when the pressure is too high, and reuse it after the system returns to normal, ensuring safety and avoiding hydrogen waste.

[0072] In one embodiment, the gas phase outlet of the gas-liquid separator 13 is connected to the circulating gas inlet of the gas mixer 8.

[0073] In this embodiment, the gas phase outlet of the gas-liquid separator 13 is connected to the circulating gas inlet of the gas mixer 8 via a circulating gas pipeline. A circulating compressor, a flow control valve, a gas analyzer, and a cooler are installed on the circulating gas pipeline (not shown in the diagram). The unreacted gas separated by the gas-liquid separator 13 mainly contains hydrogen, carbon dioxide, and small amounts of inert gases and byproducts. The circulating compressor pressurizes the unreacted gas to the same pressure level as the fresh feed gas, and the flow control valve adjusts the circulating gas flow rate according to the gas analysis results and reaction requirements. The cooler is used to cool the circulating gas to prevent excessively high temperatures from affecting the operation of the gas mixer 8.

[0074] Unreacted gas separated by gas-liquid separator 13 is discharged through the gas phase outlet and enters the recirculation gas pipeline. After being pressurized by the recirculation compressor and cooled by the cooler, it returns to the gas mixer 8 through the recirculation gas inlet. In the gas mixer 8, the recirculation gas is thoroughly mixed with fresh hydrogen from hydrogen separator 21 and fresh carbon dioxide from calcination equipment 6 to form a mixed reaction gas, which then re-enters the methanol reactor 11 for the synthesis reaction. In this way, unreacted gas is recycled, avoiding environmental pollution and raw material waste caused by direct emissions.

[0075] The recycling of unreacted gases significantly improves the overall conversion rate of hydrogen and carbon dioxide, enabling the methanol synthesis reaction, which previously had a low single-pass conversion rate, to achieve near-complete total conversion and significantly reducing the consumption of fresh feedstock. The utilization of recycled gas reduces waste gas emissions, making the system more environmentally friendly. Simultaneously, the presence of recycled gas dilutes the impurity concentration at the reactor inlet, improving the reaction efficiency and stability of the methanol synthesis subsystem and reducing the catalyst deactivation rate. On deep-sea platforms, where feedstock transportation costs are high, recycled gas technology significantly improves the system's economics and sustainability by maximizing the utilization of every unit of feedstock.

[0076] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A carbon dioxide capture and methanol synthesis system, characterized in that, include: A hydrogen production subsystem comprising a seawater desalination unit (18) and a water electrolysis hydrogen production unit (22) connected in sequence, wherein an oxygen separator and a hydrogen separator (21) are connected in sequence on the water electrolysis hydrogen production unit. An air capture subsystem includes an air contactor (2), a precipitator (3), a crusher (4), and a firing device (6) connected in sequence. An oxygen supply pipeline is connected between the oxygen separator and the firing device (6), and a hydrogen supply pipeline is connected between the hydrogen separator (21) and the firing device (6). The methanol synthesis subsystem includes a gas mixer (8), a methanol reactor (11), a gas-liquid separator (13), and a distillation unit (16) connected in sequence. A carbon source pipeline is connected between the gas phase output end of the calcination unit (6) and the gas mixer (8), and a hydrogen source pipeline is connected between the hydrogen separator (21) and the gas mixer (8).

2. The carbon dioxide capture and methanol synthesis system according to claim 1, characterized in that, The solid output end of the calcining device (6) is connected to the digester (25), the seawater desalination device (18) is connected to the digester (25) by a water supply pipeline, and the solution output end of the digester (25) is connected to the precipitator (3).

3. The carbon dioxide capture and methanol synthesis system according to claim 2, characterized in that, The air contactor (2) is provided with a carbonate outlet and an alkali inlet. Both the carbonate outlet and the alkali inlet are connected to the precipitator (3). The carbonate solution is suitable for being transported from the air contactor (2) to the precipitator (3) through the carbonate outlet, and the alkali solution is suitable for being transported from the precipitator (3) to the air contactor (2) through the alkali inlet.

4. The carbon dioxide capture and methanol synthesis system according to any one of claims 1 to 3, characterized in that, The hydrogen production subsystem also includes an ultrapure water device (19), the inlet of which is connected to the fresh water outlet of the seawater desalination device (18), and the outlet of which is connected to the electrolytic water hydrogen production device (22).

5. The carbon dioxide capture and methanol synthesis system according to claim 4, characterized in that, The oxygen separator is an oxygen-water separator (20). The outlet of the ultrapure water equipment (19) is connected to the oxygen-water separator (20), and the liquid phase outlet of the oxygen-water separator (20) is connected to the electrolytic water hydrogen production equipment (22).

6. The carbon dioxide capture and methanol synthesis system according to any one of claims 1 to 3, characterized in that, The output end of the hydrogen separator (21) is connected to a hydrogen storage device (24), and both the hydrogen supply pipeline and the hydrogen source pipeline are connected to the hydrogen storage device (24).

7. The carbon dioxide capture and methanol synthesis system according to any one of claims 1 to 3, characterized in that, The liquid phase outlet of the gas-liquid separator (13) is connected to the distillation equipment (16), and a product heat exchanger (15) is installed between the gas-liquid separator (13) and the distillation equipment (16).

8. The carbon dioxide capture and methanol synthesis system according to any one of claims 1 to 3, characterized in that, A preheating heat exchanger (10) is installed between the gas mixer (8) and the methanol reactor (11).

9. The carbon dioxide capture and methanol synthesis system according to any one of claims 1 to 3, characterized in that, The hydrogen separator (21) is also connected to a hydrogen venting pipeline.

10. The carbon dioxide capture and methanol synthesis system according to any one of claims 1 to 3, characterized in that, The gas phase outlet of the gas-liquid separator (13) is connected to the circulating gas inlet of the gas mixer (8).

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