Offshore energy system based on carbon dioxide air capture

Abstract

According to the offshore energy system based on carbon dioxide air trapping, in the system, a PEM electrolytic hydrogen production subsystem electrolyzes water through electric power to generate hydrogen; the carbon dioxide air trapping subsystem is used for directly trapping carbon dioxide from air; the hydrogen-methanol synthesis subsystem is connected with the PEM electrolytic hydrogen production subsystem and the carbon dioxide air trapping subsystem so as to react hydrogen with carbon dioxide to synthesize methanol; the heat pump subsystem is connected with the PEM electrolytic hydrogen production subsystem, the carbon dioxide air trapping subsystem and the hydrogen methanol synthesis subsystem, recovers waste heat, improves quality, and supplies the waste heat to the carbon dioxide air trapping subsystem and the low-temperature multi-effect evaporation seawater desalination subsystem respectively; and the low-temperature multi-effect evaporation seawater desalination subsystem is connected with the heat pump subsystem and utilizes the waste heat energy as a driving heat source to evaporate and desalinate the seawater to generate fresh water.

Description

Technical Field

[0001] This invention relates to the field of comprehensive utilization of renewable energy and seawater desalination, and in particular to a marine energy system based on carbon dioxide air capture, which is a marine energy system that couples PEM electrolysis for hydrogen production, carbon dioxide air capture, methanol synthesis and seawater desalination. Background Technology

[0002] Carbon dioxide (CO2) utilization, through the active capture and conversion of atmospheric CO2, can directly reduce the content of greenhouse gases in the atmosphere and alleviate the environmental pressure caused by global warming. However, this method of offshore renewable energy utilization faces several constraints: First, the PEM (Polymerized Emission Management) hydrogen production process consumes a large amount of high-purity freshwater, while freshwater resources in the marine environment are extremely scarce. Relying on external transportation for freshwater replenishment is not only costly but also subject to weather and shipping conditions, making it difficult to guarantee a stable supply. Second, waste heat is generated in the cooling of the captured mixture and the compression of CO2, as well as the waste heat from the electrochemical reaction in the PEM hydrogen production system and the system waste heat from the hydrogen-methanol synthesis reaction. These are not effectively utilized and are directly emitted into the environment, resulting in serious energy waste. Among offshore freshwater acquisition technologies, low-temperature multi-effect evaporation seawater desalination technology has become the mainstream choice due to its low equipment corrosion risk and high operational stability. Its core advantage lies in its ability to utilize low-grade waste heat as a driving heat source, eliminating the need to consume large amounts of high-grade electrical energy.

[0003] In summary, existing technologies suffer from four major pain points: First, the transportation cost of offshore renewable energy is high, and its utilization is difficult; second, the "electricity-hydrogen-methanol" conversion relies on freshwater, which is scarce and expensive to replenish at sea; third, the carbon dioxide required for methanol synthesis is difficult to replenish externally at sea, resulting in high costs; and fourth, the waste heat from hydrogen production, methanol synthesis, and carbon dioxide capture processes is not recovered, leading to low energy utilization efficiency. Therefore, there is an urgent need to design an integrated system that can collaboratively address these issues, achieving efficient utilization of offshore renewable energy, cascaded energy utilization, self-sufficient freshwater supply and recycling, and stable in-situ utilization and utilization of carbon dioxide, thereby promoting the large-scale and green development of comprehensive utilization of offshore new energy.

[0004] The information disclosed in the background section is only intended to enhance the understanding of the background of the present invention, and therefore may contain information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] In view of the above problems, the purpose of this invention is to overcome the defects of the prior art and provide a marine energy system that couples PEM electrolysis for hydrogen production, carbon dioxide air capture, methanol synthesis and seawater desalination, so as to achieve efficient absorption of marine renewable energy, cascade utilization of energy, self-sufficiency and recycling of freshwater, and in-situ stable absorption and utilization of carbon dioxide, while taking into account both energy and ecological benefits.

[0006] A marine energy system coupling PEM electrolysis for hydrogen production, carbon dioxide air capture, methanol synthesis, and seawater desalination includes,

[0007] The PEM electrolysis hydrogen production subsystem uses electricity to electrolyze water to generate hydrogen.

[0008] The carbon dioxide air capture subsystem directly captures carbon dioxide from the air;

[0009] A hydrogen-methanol synthesis subsystem, which connects the PEM electrolysis hydrogen production subsystem and the carbon dioxide air capture subsystem to react the hydrogen with carbon dioxide to synthesize methanol;

[0010] A heat pump subsystem connects the PEM electrolysis hydrogen production subsystem, the carbon dioxide air capture subsystem, and the hydrogen methanol synthesis subsystem, recovers waste heat and upgrades the quality, and supplies heat to the carbon dioxide air capture subsystem and the low-temperature multi-effect evaporation seawater desalination subsystem respectively.

[0011] The low-temperature multi-effect evaporation seawater desalination subsystem is connected to a heat pump subsystem and uses waste heat energy as a driving heat source to evaporate and desalinate seawater to produce fresh water. At least part of the fresh water produced by the seawater desalination subsystem is transported to the PEM electrolysis hydrogen production subsystem and the carbon dioxide air capture subsystem to form a water resource closed loop. The heat pump subsystem constitutes an energy coupling hub to realize the cascade utilization of waste heat from hydrogen production and synthesis processes to seawater desalination.

[0012] Preferably, the PEM electrolysis hydrogen production subsystem includes:

[0013] Freshwater storage tank (104) stores freshwater from the seawater desalination subsystem;

[0014] An electrolysis feed pump (105) is connected to a freshwater storage tank (104) to deliver the freshwater;

[0015] The first mixer (106) mixes the fresh water with the cooled electrolytic circulating heat dissipation water and sends it into the electrolytic cell (107).

[0016] An electrolytic cell (107) electrolyzes water to produce hydrogen at the cathode and oxygen at the anode;

[0017] Oxygen-water separator (108) and hydrogen-water separator (109) are connected to the electrolytic cell (107) to separate the electrolytic cell circulating cooling water entrained in oxygen and the electrolytic cell circulating cooling water entrained in hydrogen, respectively.

[0018] A second mixer (110) is connected to the oxygen-water separator (108) and the hydrogen-water separator (109) to collect the separated electrolytic cell circulating cooling water.

[0019] Electrolyte cooling water pump (112) pumps electrolyte cooling water to the first heat exchanger (111) to cool the electrolyte circulating heat dissipation water from the second mixer (110);

[0020] The product cooling water pump (101) pumps the product cooling water to the hydrogen heat exchanger (102) and the oxygen heat exchanger (103) to absorb the residual heat from the hydrogen and oxygen, respectively.

[0021] The third mixer (113) is used to combine the endothermic electrolytic cell cooling water and the product cooling water and send them into the heat pump subsystem.

[0022] Preferably, fresh water from the fresh water storage tank (104) and the cooled electrolytic cell circulating heat dissipation water are pumped to the electrolytic cell (107); the electrolytic cell (107) generates hydrogen at the cathode and enters the hydrogen-water separator (109), and generates oxygen at the anode and enters the oxygen-water separator (108); the hydrogen and oxygen separated by the separator are cooled by the hydrogen heat exchanger (102) and the oxygen heat exchanger (103), wherein the hydrogen is sent to the hydrogen storage tank; the product cooling water is sent to the heat pump system after absorbing the heat of the product, and the electrolytic cell cooling water is sent to the heat pump system after absorbing the heat of the electrolytic circulating heat dissipation water.

[0023] Preferably, the hydrogen methanol synthesis subsystem includes,

[0024] Hydrogen storage tank (201) temporarily stores hydrogen from the PEM electrolysis hydrogen production subsystem;

[0025] A raw material mixer (202) is connected to a hydrogen storage tank (201), a carbon dioxide air capture subsystem, and a recycle gas compressor to mix hydrogen, carbon dioxide, and reaction recycle gas materials to form raw materials;

[0026] The second heat exchanger (203) preheats the raw material;

[0027] The reactor (204) is connected to the raw material mixer (202), and the preheated raw material reacts hydrogen and carbon dioxide under the action of a catalyst to produce crude methanol.

[0028] The third heat exchanger (211) preheats the crude methanol;

[0029] The fourth heat exchanger (205) uses waste heat recovery cooling water to cool the crude methanol from the third heat exchanger (211);

[0030] The first flash evaporator (206) performs preliminary gas-liquid separation on the cooled crude methanol.

[0031] The first diverter (207) is connected to the first flash tank (206) to divert part of the reaction cycle gas material;

[0032] The first compressor (208), which is connected to the first distributor (207), compresses the remaining reaction cycle gas material to the reaction pressure and sends it into the raw material mixer (202).

[0033] A first pressure reducing valve (209) is connected to the first flash tank (206) to reduce the pressure of the crude methanol at its bottom to the pressure required for distillation.

[0034] A second flash tank (210) is connected to the first flash tank (206) to remove gaseous impurities from the crude methanol;

[0035] The distillation column (212) distills the crude methanol that has been preheated by the third heat exchanger (211). The methanol vapor enters the distillation condenser (213), and the waste is discharged from the bottom.

[0036] Waste heat recovery cooling water pump (214) pumps waste heat recovery cooling water for cascade waste heat recovery; distillation condenser (213) transfers the heat of methanol vapor to the waste heat recovery cooling water; and fourth heat exchanger (205) recovers the remaining waste heat of crude methanol to the waste heat recovery cooling water.

[0037] The fifth heat exchanger (215) recovers heat from the cooling water of the reactor (204) into the waste heat recovery cooling water, and finally sends the waste heat recovery cooling water into the heat pump subsystem.

[0038] Preferably, hydrogen and carbon dioxide from the hydrogen storage tank (201), along with the reaction cycle gas material, are preheated and then fed into the reactor (204). The crude methanol produced by the reaction is used to preheat the reaction feed and distillation feed, then cooled and enters the first flash tank (206) to separate the reaction cycle gas material from the crude methanol. The reaction cycle gas material is compressed to the reaction pressure and then fed back into the reactor (204) for reaction. The crude methanol is first throttled to the distillation pressure and then enters the second flash tank (210) to remove gaseous impurities. After preheating, it enters the distillation column (212) for distillation. The gaseous methanol produced at the top of the distillation column (212) is cooled to obtain refined methanol. The waste heat recovery cooling water first recovers the heat of condensation of the lower-temperature methanol, then recovers the remaining heat of the crude methanol, and finally recovers the heat of the waste heat cooling water before sending it to the heat pump system.

[0039] Preferably, the heat pump subsystem includes:

[0040] The multi-stream heat exchange evaporator (301) transfers low-grade heat from the waste heat recovery cooling water of the PEM electrolysis hydrogen production subsystem, carbon dioxide air capture subsystem and hydrogen methanol synthesis subsystem to the refrigerant. At the same time, as a heat pump evaporator, the refrigerant absorbs heat and vaporizes.

[0041] The second compressor (302) compresses the fully vaporized refrigerant to the condensing pressure;

[0042] The heat pump condenser (303) transfers the high-grade heat released by the condensation of the refrigerant to the power steam of seawater desalination.

[0043] The second pressure reducing valve (304) throttles the pressure of the condensed refrigerant to the evaporation pressure before it enters the next cycle.

[0044] Preferably, in the multi-stream heat exchange evaporator (301), the refrigerant first exchanges heat countercurrently with the waste heat recovery cooling water of the PEM electrolysis hydrogen production subsystem at a lower temperature, and then exchanges heat countercurrently with the waste heat recovery cooling water of the hydrogen methanol synthesis subsystem at a higher temperature, so as to realize the stepwise recovery of waste heat of different grades. The heat pump subsystem adopts a vapor compression heat pump cycle, and the operating temperature range is: average temperature on the evaporator side 20~40℃, and output temperature on the condenser side 65~80℃; the refrigerant is water or carbon dioxide.

[0045] Preferably, the low-temperature multi-effect evaporation seawater desalination subsystem includes,

[0046] Seawater pump (401), used for pumping feed seawater;

[0047] The four-effect evaporator is heated by the power steam provided by the heat pump in the first effect evaporator. The subsequent evaporators use the secondary steam generated by the previous effect as the heat source. The secondary steam of the last effect evaporator preheats the feed seawater in the sixth heat exchanger (402). The condensate of the four-effect evaporator is collected into the fresh water storage tank (104) via the fourth mixer (408). The concentrated brine is discharged from the system.

[0048] The second distributor (403) is used to distribute the feed flow rate to each effect evaporator.

[0049] Preferably, after the seawater is evenly diverted, it enters each effect of the four-effect evaporator. The secondary steam generated by the seawater evaporation in the first three effects enters the next effect to release heat, and the secondary steam in the last effect is used to preheat the feed seawater. The secondary steam in each effect is condensed and collected as fresh water and enters the fresh water storage tank. The concentrated brine generated by each effect is discharged. The power steam enters the first effect evaporator to release heat and then enters the heat pump to absorb heat.

[0050] Preferably, the carbon dioxide air capture subsystem includes:

[0051] The third splitter (501) divides the fresh water required for steam generation into two streams, one of which absorbs heat from the heat pump system and the other is electrically heated.

[0052] The first flow control valve (502) controls the flow rate of water entering the heat pump system to absorb heat.

[0053] The second flow control valve (503) controls the flow rate of water heated by electricity;

[0054] An electric heater (504) heats fresh water to produce high-temperature steam;

[0055] The fifth mixer (505) mixes electrically heated steam with high-temperature steam generated from heat absorption from a heat pump;

[0056] The first blower (506) blows the mixed high-temperature steam into the air contactor;

[0057] The second fan (507) blows air into the air contactor;

[0058] An air contactor (508) is used to absorb carbon dioxide from the air during the adsorption stage and release carbon dioxide into high-temperature steam during the desorption stage.

[0059] The seventh heat exchanger (509) is used to cool high-temperature steam containing carbon dioxide;

[0060] The third flash tank (510) is used to separate cooled carbon dioxide from condensate;

[0061] The third compressor (511) is used to compress carbon dioxide to the storage pressure;

[0062] The eighth heat exchanger (512) is used to cool compressed carbon dioxide;

[0063] Carbon dioxide storage tank (513), which is used to store carbon dioxide;

[0064] A vacuum pump (514) is used to remove the remaining gas in the air contactor (508) during the desorption phase;

[0065] The first cooling water pump (515) is used to pump cooling water for high-temperature steam.

[0066] The second cooling water pump (516) is used to pump cooling water for high-pressure carbon dioxide.

[0067] The sixth mixer (517) is used to mix the cooling water of high-temperature steam with the cooling water of high-pressure carbon dioxide and send it into the heat pump subsystem.

[0068] Compared with the prior art, the present invention has the following advantages:

[0069] (1) Efficiently absorb renewable energy: convert unstable offshore wind and solar power into stable chemical energy (hydrogen and methanol), solving the problems of renewable energy storage and transportation.

[0070] (2) Cascaded energy utilization with high efficiency: The low-grade waste heat generated in the hydrogen production and synthesis process is upgraded by heat pump technology and converted into a high-grade heat source that can be used for seawater desalination, which greatly improves the overall energy utilization efficiency of the system.

[0071] (3) Achieve self-sufficiency in freshwater: The system produces freshwater internally and reuses it in the electrolysis process, reducing dependence on external freshwater resources, which is particularly suitable for water-scarce offshore platforms and coastal areas.

[0072] (4) Green and low-carbon: The whole process uses green electricity as the source to capture carbon dioxide in the air and use it as raw material to produce methanol, realizing the recycling of carbon. It is a typical "negative carbon" technology path.

[0073] (5) Integration and modularization: The system has a compact structure, which is suitable for modular design and offshore deployment.

[0074] Although existing technologies include independent PEM electrolysis for hydrogen production, carbon dioxide air capture, methanol synthesis, and seawater desalination systems, simply combining these systems cannot solve the core problem of comprehensive offshore energy utilization. Data shows that 15%–25% of the input electrical energy is lost as heat during PEM electrolysis, and 40%–60% of the input energy is lost as heat during methanol synthesis and distillation. Even with independent waste heat recovery from the PEM electrolysis and methanol synthesis subsystems in existing technologies, the overall waste heat recovery rate is typically below 30% due to the low grade of the waste heat, making direct utilization difficult. Furthermore, hydrogen production through water electrolysis requires high-purity freshwater, methanol synthesis requires a stable source of carbon dioxide, and the operation of the seawater desalination and carbon dioxide air capture modules requires a significant amount of additional energy, greatly reducing system energy efficiency. Therefore, simply coupling existing subsystems based on material requirements results in low system efficiency and high costs, making it impossible to achieve efficient operation of a comprehensive energy system in highly integrated offshore platforms.

[0075] Compared with existing technologies, this invention achieves the tiered recovery and upgrading of waste heat from hydrogen production and methanol synthesis processes through a heat pump, and utilizes high-grade heat energy for seawater desalination and carbon dioxide air capture, forming a closed-loop coupling of energy-carbon dioxide-water-chemical energy storage. By recovering heat from the electrolyzer, waste heat from electrolysis products, heat energy from the methanol synthesis feed compression and cooling, heat energy from the methanol reactor, heat energy from the methanol crude product cooling, heat energy from the methanol distillation condenser, heat energy from the distillation product cooling, waste heat from the carbon dioxide capture contact steam, and waste heat from the carbon dioxide product compression and cooling according to temperature grade levels, this low-grade waste heat is then upgraded in a heat pump via a multi-stream heat exchanger. Finally, through multi-stream heat exchange, the slightly lower-temperature portion of this heat is used for seawater desalination, and the slightly higher-temperature portion is used for carbon dioxide air capture, achieving a closed-loop operation for waste heat utilization.

[0076] The above description is merely an overview of the technical solution of the present invention. In order to make the technical means of the present invention clearer and more understandable, so that those skilled in the art can implement it according to the contents of the specification, and in order to make the above and other objects, features and advantages of the present invention more obvious and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0077] Various other advantages and benefits of the present invention will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. Furthermore, the same reference numerals denote the same parts throughout the drawings.

[0078] In the attached diagram:

[0079] Figure 1 A schematic diagram of a marine energy integrated utilization system coupling PEM electrolysis for hydrogen production, carbon dioxide air capture, methanol synthesis, and seawater desalination, according to one embodiment of the present invention, wherein:

[0080] PEM electrolysis hydrogen production subsystem: 101-Product cooling water pump; 102-Hydrogen heat exchanger; 103-Oxygen heat exchanger; 104-Fresh water storage tank; 105-Electrolysis feed water pump; 106-First mixer; 107-Electrolyzer; 108-Oxygen-water separator; 109-Hydrogen-water separator; 110-Second mixer; 111-First heat exchanger; 112-Electrolyzer cooling water pump; 113-Third mixer;

[0081] The hydrogen-methanol synthesis subsystem comprises: 201-hydrogen storage tank; 202-raw material mixer; 203-second heat exchanger; 204-reactor; 205-fourth heat exchanger; 206-first flash tank; 207-first distributor; 208-first compressor; 209-first pressure reducing valve; 210-second flash tank; 211-third heat exchanger; 212-distillation column; 213-distillation condenser; 214-waste heat recovery cooling water pump; 215-fifth heat exchanger.

[0082] The heat pump subsystem includes: 301-multi-stream heat exchange evaporator; 302-second compressor; 303-heat pump condenser; 304-second pressure reducing valve;

[0083] The low-temperature multi-effect evaporation seawater desalination subsystem includes: 401-seawater pump; 402-sixth heat exchanger; 403-second distributor; 404-first effect evaporator; 405-second effect evaporator; 406-third effect evaporator; 407-fourth effect evaporator; and 408-fourth mixer.

[0084] The carbon dioxide air capture subsystem comprises: 501-Third distributor; 502-First flow control valve; 503-Second flow control valve; 504-Electric heater; 505-Fifth mixer; 506-First fan; 507-Second fan; 508-Air contactor; 509-Seventh heat exchanger; 510-Third flash tank; 511-Third compressor; 512-Eighth heat exchanger; 513-Carbon dioxide storage tank; 514-Vacuum pump; 515-First cooling water pump; 516-Second cooling water pump; 517-Sixth mixer.

[0085] Figure 2 In another embodiment, a comparison chart of the energy efficiency of the present invention system and the energy efficiency of a system without waste heat recovery is provided.

[0086] Figure 3 In another embodiment, a comparison chart of the freshwater production of the present invention system and the freshwater production of a traditional material coupling system is shown.

[0087] The present invention will be further explained below with reference to the accompanying drawings and embodiments. Detailed Implementation

[0088] Specific embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While specific embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art.

[0089] It should be noted that certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that different terms may be used to refer to the same component. This specification and claims do not distinguish components based on differences in terminology, but rather on differences in function. The terms "comprising" or "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising but not limited to." The following descriptions are preferred embodiments for carrying out the invention; however, these descriptions are for the purpose of understanding the general principles of the specification and are not intended to limit the scope of the invention. The scope of protection of this invention is determined by the appended claims.

[0090] To facilitate understanding of the embodiments of the present invention, the following will be described in conjunction with the accompanying drawings. Figures 1 to 3 The following explanation is based on specific embodiments, and the accompanying drawings do not constitute a limitation on the embodiments of the present invention.

[0091] To better understand, such as Figure 1 The illustrated marine energy system, which couples PEM electrolysis for hydrogen production, carbon dioxide air capture, methanol synthesis, and seawater desalination, includes:

[0092] The PEM electrolysis hydrogen production subsystem uses electricity to electrolyze water to generate hydrogen.

[0093] The carbon dioxide air capture subsystem directly captures carbon dioxide from the air;

[0094] A hydrogen-methanol synthesis subsystem, which connects the PEM electrolysis hydrogen production subsystem and the carbon dioxide air capture subsystem to react the hydrogen with carbon dioxide to synthesize methanol;

[0095] A heat pump subsystem connects the PEM electrolysis hydrogen production subsystem, the carbon dioxide air capture subsystem, and the hydrogen methanol synthesis subsystem, recovers waste heat and upgrades the quality, and supplies heat to the carbon dioxide air capture subsystem and the low-temperature multi-effect evaporation seawater desalination subsystem respectively.

[0096] The low-temperature multi-effect evaporation seawater desalination subsystem is connected to a heat pump subsystem and uses waste heat energy as a driving heat source to evaporate and desalinate seawater to produce fresh water. At least part of the fresh water produced by the seawater desalination subsystem is transported to the PEM electrolysis hydrogen production subsystem and the carbon dioxide air capture subsystem to form a water resource closed loop. The heat pump subsystem constitutes an energy coupling hub to realize the cascade utilization of waste heat from hydrogen production and synthesis processes to seawater desalination.

[0097] In a preferred embodiment of the marine energy system coupling PEM electrolysis for hydrogen production, carbon dioxide air capture, methanol synthesis, and seawater desalination, the PEM electrolysis for hydrogen production subsystem includes:

[0098] Freshwater storage tank 104 stores freshwater from the seawater desalination subsystem;

[0099] An electrolysis feed pump 105 is connected to a freshwater storage tank 104 to deliver the freshwater.

[0100] The first mixer 106 mixes the fresh water with the cooled electrolytic circulating heat dissipation water and then sends it into the electrolytic cell 107.

[0101] Electrolyzer 107, which electrolyzes water to produce hydrogen at the cathode and oxygen at the anode;

[0102] Oxygen-water separator 108 and hydrogen-water separator 109 are connected to the electrolytic cell 107 to separate the electrolytic cell circulating cooling water entrained in oxygen and the electrolytic cell circulating cooling water entrained in hydrogen, respectively.

[0103] The second mixer 110 is connected to the oxygen-water separator 108 and the hydrogen-water separator 109 to collect the separated electrolytic cell circulating cooling water.

[0104] Electrolyte cooling water pump 112 pumps electrolyte cooling water to the first heat exchanger 111 to cool the electrolyte circulating heat dissipation water from the second mixer 110;

[0105] The product cooling water pump 101 pumps the product cooling water to the hydrogen heat exchanger 102 and the oxygen heat exchanger 103 to absorb the waste heat from the hydrogen and oxygen, respectively.

[0106] The third mixer 113 is used to combine the endothermic electrolytic cell cooling water and the product cooling water and send them into the heat pump subsystem.

[0107] In a preferred embodiment of the marine energy system that couples PEM electrolysis for hydrogen production, carbon dioxide air capture, methanol synthesis, and seawater desalination, fresh water from freshwater storage tank 104 and cooled circulating heat dissipation water from the electrolyzer are pumped to electrolyzer 107. Hydrogen is generated at the cathode of electrolyzer 107 and enters hydrogen-water separator 109, while oxygen is generated at the anode and enters oxygen-water separator 108. The hydrogen and oxygen separated by the separators are cooled by hydrogen heat exchanger 102 and oxygen heat exchanger 103, with the hydrogen being sent to a hydrogen storage tank. Product cooling water is sent to a heat pump system after absorbing heat from the product, and electrolyzer cooling water is sent to a heat pump system after absorbing heat from the circulating heat dissipation water from the electrolysis system.

[0108] In a preferred embodiment of the marine energy system that couples PEM electrolysis for hydrogen production, carbon dioxide air capture, methanol synthesis, and seawater desalination, the hydrogen-methanol synthesis subsystem includes,

[0109] Hydrogen storage tank 201, which temporarily stores hydrogen from the PEM electrolysis hydrogen production subsystem;

[0110] The raw material mixer 202 is connected to the hydrogen storage tank 201, the carbon dioxide air capture subsystem and the circulating gas compressor to mix hydrogen, carbon dioxide and reaction circulating gas materials to form raw materials;

[0111] The second heat exchanger 203 preheats the raw material;

[0112] Reactor 204, which is connected to the raw material mixer 202, wherein the preheated raw material reacts hydrogen and carbon dioxide under the action of a catalyst to produce crude methanol;

[0113] The third heat exchanger 211 preheats the crude methanol;

[0114] The fourth heat exchanger 205 uses waste heat recovery cooling water to cool the crude methanol from the third heat exchanger 211.

[0115] The first flash evaporator 206 performs preliminary gas-liquid separation on the cooled crude methanol.

[0116] The first diverter 207 is connected to the first flash tank 206 to divert part of the reaction cycle gas material;

[0117] The first compressor 208, which is connected to the first distributor 207, compresses the remaining reaction circulating gas material to the reaction pressure and sends it into the raw material mixer 202.

[0118] First pressure reducing valve 209; it is connected to the first flash tank 206 to reduce the pressure of the crude methanol at the bottom of the tank to the pressure required for distillation;

[0119] The second flash tank 210 is connected to the first flash tank 206 to remove gaseous impurities from the crude methanol.

[0120] Distillation column 212 distills crude methanol that has been preheated by the third heat exchanger 211. Methanol vapor enters distillation condenser 213 and waste is discharged from the bottom.

[0121] Waste heat recovery cooling water pump 214 pumps waste heat recovery cooling water for cascade waste heat recovery. Distillation condenser 213 transfers the heat of methanol vapor to the waste heat recovery cooling water. Fourth heat exchanger 205 recovers the remaining waste heat from crude methanol to the waste heat recovery cooling water.

[0122] The fifth heat exchanger 215 recovers heat from the cooling water in the reactor 204 into the waste heat recovery cooling water, and finally sends the waste heat recovery cooling water into the heat pump subsystem.

[0123] In a preferred embodiment of the marine energy system that couples PEM electrolysis for hydrogen production, carbon dioxide air capture, methanol synthesis, and seawater desalination, hydrogen and carbon dioxide from hydrogen storage tank 201, along with the reaction cycle gas, are preheated and then fed into reactor 204. The crude methanol produced by the reaction is used to preheat the reaction feed, and after being cooled by distillation, it enters the first flash tank 206 to separate the reaction cycle gas and crude methanol. The reaction cycle gas is compressed to the reaction pressure and then fed back into reactor 204 for further reaction. The crude methanol is first throttled to the distillation pressure and then enters the second flash tank 210 to remove gaseous impurities. After preheating, it enters the distillation column 212 for distillation. The gaseous methanol produced at the top of the distillation column 212 is cooled to obtain refined methanol. The waste heat recovery cooling water first recovers the heat of condensation of the lower-temperature methanol, then recovers the remaining heat of the crude methanol, and finally recovers the heat of the waste heat cooling water before sending it to the heat pump system.

[0124] In a preferred embodiment of the marine energy system that couples PEM electrolysis for hydrogen production, carbon dioxide air capture, methanol synthesis, and seawater desalination, the heat pump subsystem includes:

[0125] The multi-stream heat exchange evaporator 301 transfers low-grade heat from the waste heat recovery cooling water of the PEM electrolysis hydrogen production subsystem, carbon dioxide air capture subsystem and hydrogen methanol synthesis subsystem to the refrigerant. At the same time, it acts as a heat pump evaporator, where the refrigerant absorbs heat and vaporizes.

[0126] The second compressor 302 compresses the completely vaporized refrigerant to the condensing pressure;

[0127] The heat pump condenser 303 transfers the high-grade heat released by the condensation of the refrigerant to the power steam of seawater desalination.

[0128] The second pressure reducing valve 304 throttles the pressure of the condensed refrigerant to the evaporation pressure before it enters the next cycle.

[0129] In a preferred embodiment of the marine energy system that couples PEM electrolysis for hydrogen production, carbon dioxide air capture, methanol synthesis, and seawater desalination, the refrigerant in the multi-stream heat exchange evaporator 301 first exchanges heat counter-currently with the waste heat recovery cooling water of the lower-temperature PEM electrolysis for hydrogen production subsystem, and then exchanges heat counter-currently with the waste heat recovery cooling water of the higher-temperature hydrogen-methanol synthesis subsystem, thereby achieving cascaded recovery of waste heat of different grades. The heat pump subsystem adopts a vapor compression heat pump cycle, with an operating temperature range of: an average temperature of 20~40℃ on the evaporator side and an output temperature of 65~80℃ on the condenser side; the refrigerant is water or carbon dioxide.

[0130] In a preferred embodiment of the marine energy system that couples PEM electrolysis for hydrogen production, carbon dioxide air capture, methanol synthesis, and seawater desalination, the low-temperature multi-effect evaporation seawater desalination subsystem includes,

[0131] Seawater pump 401 is used to pump feed seawater.

[0132] The four-effect evaporator is heated by the power steam provided by the heat pump in the first effect evaporator. The subsequent evaporators use the secondary steam generated by the previous effect as a heat source. The secondary steam of the last effect evaporator preheats the feed seawater in the sixth heat exchanger 402. The condensate of the four-effect evaporator is collected into the fresh water storage tank 104 via the fourth mixer 408. The concentrated brine is discharged from the system.

[0133] The second distributor 403 is used to distribute the feed flow rate to each effect evaporator.

[0134] In a preferred embodiment of the marine energy system that couples PEM electrolysis for hydrogen production, carbon dioxide air capture, methanol synthesis, and seawater desalination, seawater is evenly diverted into each of the four-effect evaporators. The secondary steam generated by the seawater evaporation in the first three effect evaporators enters the next effect to release heat, and the secondary steam in the last effect evaporator is used to preheat the feed seawater. The secondary steam from each effect is condensed and collected as freshwater in a freshwater storage tank. The concentrated brine generated by each effect evaporator is discharged. The motive steam enters the first effect evaporator to release heat and then enters the heat pump to absorb heat.

[0135] In a preferred embodiment of the marine energy system that couples PEM electrolysis for hydrogen production, carbon dioxide air capture, methanol synthesis, and seawater desalination, the carbon dioxide air capture subsystem includes:

[0136] The third splitter 501 divides the fresh water required for steam generation into two streams: one stream absorbs heat from the heat pump system, and the other stream is electrically heated.

[0137] The first flow control valve 502 controls the flow rate of water entering the heat pump system to absorb heat.

[0138] The second flow control valve 503 controls the flow rate of water heated by electricity;

[0139] Electric heater 504 heats fresh water to produce high-temperature steam;

[0140] The fifth mixer 505 mixes electrically heated steam with high-temperature steam generated from heat absorption from a heat pump;

[0141] The first fan, 506, blows the mixed high-temperature steam into the air contactor;

[0142] The second fan 507 blows air into the air contactor;

[0143] Air contactor 508 is used to absorb carbon dioxide from the air during the adsorption stage and release carbon dioxide into high-temperature steam during the desorption stage.

[0144] The seventh heat exchanger 509 is used to cool high-temperature steam containing carbon dioxide;

[0145] The third flash tank 510 is used to separate cooled carbon dioxide from condensate.

[0146] The third compressor 511 is used to compress carbon dioxide to the storage pressure;

[0147] The eighth heat exchanger 512 is used to cool compressed carbon dioxide;

[0148] Carbon dioxide storage tank 513 is used to store carbon dioxide;

[0149] Vacuum pump 514 is used to remove the remaining gas in air contactor 508 during the desorption phase;

[0150] The first cooling water pump 515 is used to pump cooling water for high-temperature steam.

[0151] The second cooling water pump 516 is used to pump cooling water for high-pressure carbon dioxide.

[0152] The sixth mixer 517 is used to mix the cooling water of high-temperature steam with the cooling water of high-pressure carbon dioxide and send it into the heat pump subsystem.

[0153] In one embodiment, a marine energy integrated utilization system coupling PEM electrolysis for hydrogen production, carbon dioxide capture, methanol synthesis, and seawater desalination includes: a PEM electrolysis for hydrogen production subsystem, a carbon dioxide air capture subsystem, a methanol synthesis subsystem, a heat pump subsystem, and a low-temperature multi-effect evaporation seawater desalination subsystem; the PEM electrolysis for hydrogen production subsystem is used to produce hydrogen by electrolyzing water using electricity; the carbon dioxide air capture subsystem is used to directly capture carbon dioxide from the air; the hydrogen-methanol synthesis subsystem is used to synthesize methanol by reacting hydrogen with carbon dioxide; the heat pump subsystem is used to recover and upgrade the waste heat from the PEM electrolysis for hydrogen production subsystem, the carbon dioxide air capture subsystem, and the hydrogen-methanol synthesis subsystem, and supply it to the carbon dioxide air capture subsystem and the low-temperature multi-effect evaporation seawater desalination subsystem, respectively; the low-temperature multi-effect evaporation seawater desalination subsystem uses the heat source provided by the heat pump subsystem to produce fresh water, and supplies a portion of the fresh water to the PEM electrolysis for hydrogen production subsystem and the carbon dioxide air capture subsystem.

[0154] The PEM electrolysis hydrogen production subsystem includes: a freshwater storage tank 104 for storing freshwater from a seawater desalination subsystem; an electrolysis feed pump 105 for pumping freshwater from the freshwater storage tank 104 into the electrolyzer; a first mixer 106 for mixing the freshwater from the electrolysis feed pump 105 with electrolysis circulating heat dissipation water cooled by a first heat exchanger 111; an electrolyzer 107 that utilizes the freshwater supplied by the first mixer 106 (such as an electrolysis mixer) to primarily generate oxygen at the anode and the circulating water flows to an oxygen-water separator 108, while generating hydrogen at the cathode and flowing to a hydrogen-water separator 109; and an oxygen-water separator 108 that separates oxygen from water. The system includes a hydrogen-water separator 109, which separates hydrogen from water; a second mixer 110, which mixes the water produced by the oxygen-water separator 108 with the water produced by the hydrogen-water separator 109 to form circulating cooling water for the electrolyzer; an electrolyzer cooling water pump 112, which pumps the electrolyzer cooling water to the first heat exchanger 111 to cool the circulating cooling water from the second mixer 110; a product cooling water pump 101, which pumps the product cooling water to the hydrogen heat exchanger 102 and the oxygen heat exchanger 103 to absorb the residual heat from the hydrogen and oxygen, respectively; and a third mixer 113, which mixes the heat-absorbing electrolyzer cooling water and the product cooling water before they enter the heat pump subsystem.

[0155] The methanol synthesis subsystem includes: a hydrogen storage tank 201, which stores hydrogen produced by the PEM electrolysis hydrogen production subsystem; a raw material mixer 202, which mixes hydrogen from the hydrogen storage tank 201, carbon dioxide from the carbon dioxide air capture subsystem, and reaction cycle gas materials, and sends them to a second heat exchanger 203 for preheating; a reactor 204, in which the preheated raw materials undergo partial reaction to generate crude products, which first enter the second heat exchanger 203 to preheat the reaction raw materials, and then enter the third heat exchanger 211 to preheat the crude methanol; a fourth heat exchanger 205, which uses waste heat recovery cooling water to cool the crude products from the third heat exchanger 211; a first flash tank 206, which performs preliminary gas-liquid separation on the cooled crude products; a first distributor 207, which diverts a small portion of the reaction cycle gas materials from the first flash tank 206 to prevent the accumulation of by-products; and a first compressor 208, which... The remaining gaseous material from the reaction cycle in the first distributor 207 is compressed to the reaction pressure and remixed with the raw materials before being fed into the reactor 204 for reaction. A first pressure reducing valve 209 reduces the pressure of the crude methanol at the bottom of the first flash tank 206 to the pressure required for distillation. A second flash tank 210 further discharges gaseous impurities from the crude methanol. A distillation column 212 distills the crude methanol preheated by the third heat exchanger 211; the methanol vapor enters the distillation condenser 213, and the waste is discharged from the bottom. A waste heat recovery cooling water pump 214 pumps waste heat recovery cooling water for cascaded waste heat recovery. The distillation condenser 213 transfers the heat from the methanol vapor to the waste heat recovery cooling water. A fourth heat exchanger 205 recovers the remaining waste heat from the crude product to the waste heat recovery cooling water. A fifth heat exchanger 215 recovers the heat from the reactor cooling water to the waste heat recovery cooling water, which is then finally sent to the heat pump subsystem.

[0156] The heat pump subsystem includes: a multi-stream heat exchange evaporator 301, which transfers low-grade heat from the waste heat recovery cooling water of the PEM electrolysis hydrogen production subsystem, carbon dioxide air capture subsystem, and methanol synthesis subsystem to the heat pump refrigerant, and simultaneously acts as a heat pump evaporator, where the refrigerant absorbs heat and vaporizes; a second compressor 302, which compresses the completely vaporized refrigerant to the condensing pressure; a heat pump condenser 303, which sequentially transfers the high-grade heat released by the refrigerant condensation to the high-temperature steam from carbon dioxide capture and the power steam from seawater desalination, and simultaneously acts as a heat pump condenser, cooling the refrigerant to a saturated liquid state; and a second pressure reducing valve 304, which throttles the pressure of the condensed refrigerant to the evaporation pressure for the next cycle.

[0157] The low-temperature multi-effect evaporation seawater desalination subsystem includes: a four-effect evaporator, wherein the heat source of the first-effect evaporator comes from the motive steam absorbed by the heat pump, the motive steam is circulated back to the heat pump to absorb heat after releasing heat, and the generated secondary steam enters the second-effect evaporator as a heat source for condensation and heat release, and so on until the last effect, the steam generated in the last effect is used in the sixth heat exchanger 402 to preheat the feed seawater; a seawater pump 401, which is used to pump the feed seawater; a second distributor 403, which is used to distribute the feed flow rate to each evaporator; and a fourth mixer 408, which collects the freshwater condensed from each effect into a freshwater storage tank.

[0158] The carbon dioxide air capture subsystem includes: a third splitter 501, which divides the fresh water required for steam generation into two streams, one of which absorbs heat from a heat pump and the other is electrically heated; a first flow control valve 502, which controls the flow rate of water entering the heat pump for heat absorption; a second flow control valve 503, which controls the flow rate of water for electric heating; an electric heater 504, which heats the fresh water to generate high-temperature steam; a fifth mixer 505, which mixes the electrically heated steam with the high-temperature steam generated from heat absorption by the heat pump; a first fan 506, which blows the mixed high-temperature steam into an air contactor; a second fan 507, which blows air into the air contactor; and an air contactor 508, which absorbs carbon dioxide from the air during the adsorption stage and releases carbon dioxide into the high-temperature steam during the desorption stage. The system comprises: a seventh heat exchanger 509 for cooling high-temperature steam containing carbon dioxide; a third flash tank 510 for separating cooled carbon dioxide from condensate; a third compressor 511 for compressing carbon dioxide to storage pressure; an eighth heat exchanger 512 for cooling compressed carbon dioxide; a carbon dioxide storage tank 513 for storing carbon dioxide; a vacuum pump 514 for removing remaining gas from the air contactor 508 during the desorption phase; a first cooling water pump 515 for pumping cooling water for high-temperature steam; a second cooling water pump 516 for pumping cooling water for high-pressure carbon dioxide; and a sixth mixer 517 for mixing the cooling water for high-temperature steam with the cooling water for high-pressure carbon dioxide and sending it into the heat pump subsystem.

[0159] The system is preferably powered by renewable energy sources such as wind and solar power. This system can be applied to both offshore platforms and coastal production.

[0160] The electrolysis pressure in the PEM electrolysis hydrogen production subsystem is the same as the reactor pressure in the methanol synthesis subsystem. Hydrogen storage tanks with the same pressure are used to cope with fluctuating operating conditions, and the energy consumption of the compression process is saved through direct connection.

[0161] The carbon dioxide air capture subsystem uses a solid adsorbent for carbon dioxide adsorption. The heat required for the desorption stage is provided by high-temperature steam, which is generated by a heat pump and an electric heater. By adjusting the water flow rate of these two components, the heat energy provided by the heat pump is prioritized to meet the heat demand of the low-temperature multi-effect seawater desalination system. If the heat required for the desorption process is insufficient, it is provided by the electric heater. The subsystem can be horizontally expanded according to scale requirements, increasing the number of units. When the number of units is large, the stable and continuous carbon dioxide production of the system can be adjusted by controlling the time difference between the adsorption and desorption processes of different units.

[0162] In the methanol synthesis subsystem, the main source of waste heat is the heat carried by the crude product, which is first used to preheat the raw materials and preheat the internal heat demand of the distillation feed. The remaining heat is then recovered and upgraded.

[0163] In the methanol synthesis subsystem, the waste heat recovery process involves sequentially recovering waste heat from distillation condensation heat recovery, crude product heat recovery, and reactor heat recovery.

[0164] In the heat pump subsystem, the heat pump evaporator undergoes zoned heat exchange via a multi-stream heat exchanger. The low-temperature refrigerant first exchanges heat counter-currently with the waste heat recovery cooling water from the PEM electrolysis hydrogen production subsystem, which has a lower temperature, and then exchanges heat counter-currently with the waste heat recovery cooling water from the methanol synthesis subsystem and the carbon dioxide capture subsystem, which have relatively higher temperatures. This allows for the cascaded utilization of waste heat of different grades, maximizing the total amount of waste heat recovered and reducing system losses. In the heat pump condenser, the heat-carrying refrigerant first exchanges heat with the carbon dioxide desorption steam, which requires a higher temperature, and then exchanges heat with the seawater desalination power steam, which requires a relatively lower temperature. This ensures sufficient freshwater production while utilizing the system's waste heat to provide the necessary heat energy for the carbon dioxide desorption process, further improving the overall energy utilization rate of the system.

[0165] In the heat pump subsystem, a vapor compression power cycle is used. With the evaporator operating at approximately 20 degrees Celsius and the condenser operating at approximately 70-100 degrees Celsius, carbon dioxide is preferred as the refrigerant. The carbon dioxide capture system has a stable source of carbon dioxide and requires no additional cost. Using corresponding organic refrigerants would result in relatively high transportation costs for offshore platforms, and therefore is not the preferred option.

[0166] Material flow direction of the system:

[0167] In PEM electrolysis for hydrogen production, fresh water from the storage tank and cooled circulating water from the electrolyzer are pumped to the electrolyzer. Hydrogen is generated at the cathode and enters the hydrogen-water separator, while oxygen is generated at the anode and enters the oxygen-water separator. The hydrogen and oxygen separated by the separator are cooled, with the hydrogen being sent to a hydrogen storage tank. The water separated by the separator is cooled and then recycled back to the electrolyzer. The cooling water in the electrolyzer absorbs heat from the circulating water and is then sent to a heat pump system. The cooling water for the product absorbs heat from the product and is then sent to a heat pump system.

[0168] In methanol synthesis, hydrogen from the hydrogen storage tank and carbon dioxide from the carbon dioxide storage tank, along with the circulating gas, are preheated before being fed into the reactor. The crude product generated from the reaction is used to preheat the reaction feed and distillation feed, then cooled before entering the first flash tank to separate the circulating gas from the crude methanol. The circulating gas is compressed to the reaction pressure and then fed back into the reactor for further reaction. The crude methanol is first throttled to the distillation pressure and then enters the second flash tank to remove gaseous impurities. After preheating, it enters the distillation column for distillation. The gaseous methanol produced at the top of the distillation column is cooled to obtain refined methanol. The waste heat recovery cooling water first recovers the heat of condensation of the lower-temperature methanol, then recovers the residual heat of the crude product, and finally recovers the heat of the reactor cooling water before being sent to the heat pump system.

[0169] In the heat pump system, the refrigerant absorbs heat from the PEM electrolysis hydrogen production cooling water, carbon dioxide capture cooling water, and methanol synthesis cooling water in the multi-stream heat exchanger. It enters the second compressor at a superheated state of 5°C and is compressed to the condensing pressure. Then, it enters the condenser to release heat and become a saturated liquid. After being depressurized by the second pressure reducing valve, it re-enters the evaporator to absorb heat and circulate. Fresh water absorbs heat and evaporates in the condenser before entering the carbon dioxide capture system. Seawater desalination power steam absorbs heat in the condenser and then enters the low-temperature multi-effect evaporation seawater desalination system.

[0170] In a low-temperature multi-effect evaporation seawater desalination system, seawater is evenly distributed and enters each effect evaporator. The secondary steam generated by the seawater evaporation in the first three effects enters the next effect to release heat, and the secondary steam in the last effect is used to preheat the feed seawater. The secondary steam in each effect is condensed and collected as fresh water and enters the fresh water storage tank. The concentrated brine generated by each effect evaporator is discharged. The motive steam enters the first effect evaporator to release heat and then enters the heat pump to absorb heat.

[0171] In the carbon dioxide air capture subsystem, adsorption and desorption processes alternate sequentially. During adsorption, air is blown into the air contactor, where carbon dioxide is absorbed by the solid adsorbent, and the remaining gas is discharged. During desorption, a vacuum pump first removes the remaining gas from the air generator, then pressurizes it. High-temperature steam (around 100°C) generated by heat pump heating and electric heating enters the air contactor for heating, achieving carbon dioxide desorption. The high-temperature steam carrying carbon dioxide is discharged, and the air contactor cools to ambient temperature before entering the next cycle. The discharged mixed gas is first cooled to ambient temperature and then mixed with carbon dioxide and condensate in a third flash tank. The carbon dioxide is compressed and cooled before entering the storage tank. The cooling water absorbs heat from the mixed gas and the compressed carbon dioxide, and then enters the heat pump system for upgrading.

[0172] The energy flow direction of the system is as follows:

[0173] First, the system's input electrical energy flows to the electrolyzer and various auxiliary equipment (water pumps, compressors, distillation reboilers, and carbon dioxide capture electric heaters). Of the energy input to each auxiliary equipment, a portion is converted into the internal energy of the material flow, and another portion is dissipated as heat. The electrical energy input to the electrolyzer is converted into the chemical and thermal energy contained in the hydrogen gas; the thermal energy flows in three directions: heat flowing out with the circulating water, heat flowing out with the products, and heat dissipated into the environment. Second, through the reaction of hydrogen and carbon dioxide, the chemical energy contained in the hydrogen gas is converted into the chemical and thermal energy contained in the methanol; the thermal energy flows in three directions: heat carried by the reactor cooling water, heat flowing out with the products, and heat dissipated into the environment. The chemical energy contained in the methanol serves as the final product of electrical energy storage. The heat carried out by the electrolysis circulating water and the product, the heat carried by the cooling water of the methanol synthesis reactor and the product, and the heat carried by the carbon dioxide capture mixture and high-pressure carbon dioxide are recovered and fed into the heat pump for upgrading, and then supplied to the low-temperature multi-effect evaporation seawater desalination system and the carbon dioxide air capture subsystem. In the low-temperature multi-effect evaporation seawater desalination system, part of the heat is used for the latent heat of seawater evaporation, part is used for preheating the feed seawater, and the remaining low-temperature heat is lost to the environment. In the carbon dioxide air capture subsystem, the heat from the heat pump and the electric heater is mainly used for carbon dioxide desorption, and part of the remaining heat is recovered by the heat pump for upgrading, while the rest is lost to the environment.

[0174] In another embodiment, see Figure 2 The diagram shows a comparison of the energy efficiency of the system of the present invention and the energy efficiency of the system without waste heat recovery; wherein,

[0175] The system recovers some waste heat from the electrolytic hydrogen production, hydrogen-to-methanol production, and carbon dioxide air capture processes. This waste heat is then upgraded using a heat pump and reused in seawater desalination and carbon dioxide capture. The resulting freshwater is used for water electrolysis to produce hydrogen, and the generated carbon dioxide is used for methanol synthesis. The system's energy efficiency is equal to the ratio of the chemical energy of the methanol produced to the total energy input to the system. Compared to direct material coupling systems involving electrolytic hydrogen production, hydrogen-to-methanol production, carbon dioxide air capture, and seawater desalination, the figure compares the system energy efficiency at different scales (1MW, 5MW, 10MW, 20MW, and 50MW), showing a significant improvement in the energy efficiency of this system.

[0176] See further Figure 3 The diagram shows a comparison of the freshwater production of the system of the present invention with that of a traditional material coupling system; wherein,

[0177] The figure compares and calculates the freshwater production of different system scales: 1MW, 5MW, 10MW, 20MW, and 50MW. Existing research shows that, with other conditions remaining constant, the freshwater production of low-temperature multi-effect evaporation seawater desalination increases with increasing heat supply. For traditional material-coupled systems, the freshwater production of seawater desalination needs to meet the water consumption requirements of electrolysis and the steam requirements of carbon dioxide capture and desorption while allowing for a certain margin. Increasing the freshwater production would lead to an increase in the energy consumption of the seawater desalination system. However, the system described above utilizes waste heat for seawater desalination, requiring no additional heat supply. After deducting some waste heat supplied to the carbon dioxide capture system, the remaining waste heat can produce more freshwater than the system's water consumption requirements. It can be observed that the freshwater production of this system is significantly better than that of traditional material-coupled systems.

[0178] Although embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments and application fields described above. The specific embodiments described above are merely illustrative and guiding, and not restrictive. Those skilled in the art can make many other modifications based on the guidance of this specification and without departing from the scope of the claims of the present invention, and all of these modifications are within the scope of protection of the present invention.

Claims

1. An offshore energy system based on carbon dioxide air capture, characterized in that, It comprises, a PEM electrolysis hydrogen production subsystem which utilizes electricity to electrolyze water to produce hydrogen gas; a carbon dioxide air capture subsystem which directly captures carbon dioxide from air; a hydrogen methanol synthesis subsystem which connects the PEM electrolysis hydrogen production subsystem and the carbon dioxide air capture subsystem to react the hydrogen gas with carbon dioxide to synthesize methanol; a heat pump subsystem which connects the PEM electrolysis hydrogen production subsystem, the carbon dioxide air capture subsystem and the hydrogen methanol synthesis subsystem to recover waste heat and upgrade, and supplies the carbon dioxide air capture subsystem and a low-temperature multi-effect evaporation seawater desalination subsystem respectively; a low-temperature multi-effect evaporation seawater desalination subsystem which connects the heat pump subsystem and utilizes waste heat energy as a driving heat source to evaporate and desalinate seawater to produce fresh water; the fresh water produced by the seawater desalination subsystem is at least partially transported to the PEM electrolysis hydrogen production subsystem and the carbon dioxide air capture subsystem to form a water resource closed loop, and the heat pump subsystem forms an energy coupling hub to realize step-by-step utilization of waste heat from the hydrogen production and synthesis processes to seawater desalination.

2. The offshore energy system of coupling PEM electrolysis of hydrogen production, carbon dioxide air capture, methanol synthesis and seawater desalination of claim 1, wherein, Preferably, the PEM electrolysis hydrogen production subsystem comprises: a fresh water storage tank (104) which stores fresh water from the seawater desalination subsystem; an electrolysis feed water pump (105) which connects the fresh water storage tank (104) to transport the fresh water; a first mixer (106) which mixes the fresh water with cooled electrolysis cycle heat removal water and sends it into an electrolysis cell (107); the electrolysis cell (107) which electrolyzes water to produce hydrogen gas at the cathode and oxygen gas at the anode; an oxygen water separator (108) and a hydrogen water separator (109) which connect the electrolysis cell (107) to separate electrolysis cell cycle heat removal water entrained in the oxygen gas and electrolysis cell cycle heat removal water entrained in the hydrogen gas respectively; a second mixer (110) which connects the oxygen water separator (108) and the hydrogen water separator (109) to collect the separated electrolysis cell cycle heat removal water, an electrolysis cell cooling water pump (112) which pumps electrolysis cell cooling water to a first heat exchanger (111) to cool the electrolysis cell cycle heat removal water from the second mixer (110); a product cooling water pump (101) which pumps product cooling water to a hydrogen gas heat exchanger (102) and an oxygen gas heat exchanger (103) to absorb waste heat in the hydrogen gas and the oxygen gas respectively, a third mixer (113) which is used to mix the cooled electrolysis cell cooling water and the product cooling water and send them into the heat pump subsystem.

3. The offshore energy system of coupling PEM electrolysis of hydrogen production, carbon dioxide air capture, methanol synthesis and seawater desalination of claim 2, wherein, The fresh water from the fresh water storage tank (104) and the cooled electrolysis cell cycle heat removal water are pumped into the electrolysis cell (107); the electrolysis cell (107) produces hydrogen gas at the cathode into the hydrogen water separator (109) and produces oxygen gas at the anode into the oxygen water separator (108); the separated hydrogen gas and oxygen gas are cooled by the hydrogen gas heat exchanger (102) and the oxygen gas heat exchanger (103), wherein the hydrogen gas is sent into a hydrogen gas storage tank; the product cooling water is sent into the heat pump system after absorbing product heat, and the electrolysis cell cooling water is sent into the heat pump system after absorbing electrolysis cycle heat removal water heat.

4. The offshore energy system of coupling PEM electrolysis of hydrogen production, carbon dioxide air capture, methanol synthesis and seawater desalination of claim 2, wherein, The hydrogen methanol synthesis subsystem comprises, a hydrogen gas storage tank (201) which temporarily stores hydrogen gas from the PEM electrolysis hydrogen production subsystem; A raw material mixer (202); A second heat exchanger (203) preheats the raw material; A reactor (204) connected to the raw material mixer (202), in which the preheated raw material reacts with hydrogen and carbon dioxide under the action of a catalyst to produce crude methanol; A third heat exchanger (211) preheats the crude methanol; A fourth heat exchanger (205) cools the crude methanol from the third heat exchanger (211) using waste heat recovery cooling water; A first flash tank (206) preliminarily separates the cooled crude methanol into gas and liquid; A first splitter (207) connected to the first flash tank (206) to split part of the reaction cycle gas material; A second flash tank (210) connected to the first flash tank (206) to discharge gas impurities in the crude methanol; A rectification column (212).

5. The offshore energy system of coupling PEM electrolysis of hydrogen production, carbon dioxide air capture, methanol synthesis and seawater desalination of claim 4, wherein, Hydrogen from a hydrogen storage tank (201) and carbon dioxide, preheated reaction cycle gas material are fed into the reactor (204); the crude methanol produced by the reaction is used to preheat the reaction feed and the rectification feed, and then cooled and fed into the first flash tank (206) to separate the reaction cycle gas material from the crude methanol; the reaction cycle gas material is compressed to the reaction pressure and then re-fed into the reactor (204) for reaction; the crude methanol is first throttled to the rectification pressure, then fed into the second flash tank (210) to remove gas impurities, preheated and fed into the rectification column (212) for rectification; gaseous methanol produced at the top of the rectification column (212) is cooled to obtain refined methanol; the waste heat recovery cooling water first recovers the condensation heat of the methanol at a lower temperature, then recovers the remaining heat of the crude methanol, and finally recovers the heat of the waste heat cooling water before being fed into the heat pump system.

6. The offshore energy system of coupling PEM electrolysis of water for hydrogen production, CO2 air capture, methanol synthesis and seawater desalination as claimed in claim 1, wherein, The heat pump subsystem includes: A multi-stream heat exchanger evaporator (301) that transfers the low-grade heat of the waste heat recovery cooling water from the PEM electrolytic hydrogen production subsystem, the carbon dioxide air capture subsystem and the hydrogen methanol synthesis subsystem to the refrigerant, while serving as a heat pump evaporator, and the refrigerant absorbs heat and vaporizes.

7. The offshore energy system of coupling PEM electrolysis of hydrogen production, carbon dioxide air capture, methanol synthesis and seawater desalination of claim 6, wherein, The refrigerant in the multi-stream heat exchanger evaporator (301) first counter-currently exchanges heat with the PEM electrolytic hydrogen production subsystem waste heat recovery cooling water at a lower temperature, and then counter-currently exchanges heat with the hydrogen methanol synthesis subsystem waste heat recovery cooling water at a higher temperature, thereby achieving step-by-step recovery of waste heat of different grades; the heat pump subsystem adopts a vapor compression heat pump cycle, and the operating temperature range is: the average temperature at the evaporator side is 20-40°C, and the output temperature at the condenser side is 65-80°C; the refrigerant is water or carbon dioxide.

8. The offshore energy system of coupling PEM electrolysis of hydrogen production, carbon dioxide air capture, methanol synthesis and seawater desalination of claim 1, wherein, The low-temperature multi-effect evaporation seawater desalination subsystem includes, A seawater pump (401) for pumping feed seawater; A four-effect evaporator, in which the first effect evaporator is heated by power steam provided by the heat pump, and each subsequent effect evaporator uses the secondary steam generated by the previous effect as a heat source; the secondary steam of the last effect evaporator preheats the feed seawater in the sixth heat exchanger (402); the condensate water of the four-effect evaporator is collected into a fresh water storage tank (104) through a fourth mixer (408), and concentrated brine is discharged from the system.

9. The offshore energy system of coupling PEM electrolysis of hydrogen production, carbon dioxide air capture, methanol synthesis and seawater desalination of claim 8, wherein, The seawater is evenly split and then fed into each effect evaporator of the four-effect evaporator.

10. The offshore energy system of coupling PEM electrolysis of water for hydrogen production, carbon dioxide air capture, methanol synthesis and seawater desalination as claimed in claim 1, wherein, The carbon dioxide air capture subsystem includes: A third flow divider (501) divides the water required for steam generation into two streams, one stream absorbs heat from the heat pump system, and the other stream is heated by electricity; A first flow control valve (502) controls the flow of water into the heat pump system to absorb heat; A second flow control valve (503) controls the flow of water heated by electricity.

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