Deep and far sea self-sufficient carbon dioxide-to-methanol heat coupling system and peak shaving process

Abstract

The invention relates to the technical field of green methanol and wind power generation peak regulation, in particular to a deep and far sea self-sufficient carbon dioxide to methanol heat coupling system and a peak regulation process. The process comprises the following steps: hydrogen production by water electrolysis, hydrogen storage, capture of carbon dioxide in air, carbon dioxide pressurization, combined compression, methanol synthesis, peak regulation of crude methanol, methanol rectification, methanol boiler and the like. According to the thermal coupling system disclosed by the invention, through split production and control of methanol synthesis and methanol rectification, high coupling of heat, large-interval heat balance and small-interval methanol boiler steam supply are realized. According to the peak shaving process, flexible production of the methanol device is achieved through peak shaving of the crude methanol, specifically, in the peak of wind power supply, the crude methanol is produced with the maximum load, the maximum wind power is consumed through peak shaving of the crude methanol, and electricity is not abandoned; in a wind power supply valley, methanol synthesis fluctuates with electricity, crude alcohol is supplied through peak regulation of the crude alcohol, and methanol rectification stable load production is maintained.

Description

Technical Field

[0001] The invention relates to the technical field of green methanol and wind power generation peak regulation, and specifically to a deep-sea self-sufficient carbon dioxide-to-methanol heat coupling system and a peak regulation process. Background Art

[0002] 1. Green Methanol

[0003] There is no unified international standard for the definition of green methanol. The International Renewable Energy Agency (IRENA) recommends that methanol be classified into green, blue, gray and brown according to the source of raw materials. When the raw materials hydrogen and carbon dioxide are both renewable, the synthesized methanol can be labeled as green methanol. According to the research report of the Global Methanol Association, renewable hydrogen refers to hydrogen produced using renewable energy, and renewable carbon dioxide refers to carbon dioxide from biomass or direct air capture.

[0004] Against the backdrop of green methanol, China has been planning a number of wind power-to-green methanol projects.

[0005] (II) Deep and deep offshore wind power

[0006] Deep sea generally refers to the sea area 50km offshore and deeper than 50m. Due to the huge cost of transmitting deep sea wind power and the high cost of electricity, it is estimated that the transmission cost of each kilometer of deep sea cable is about 100 million yuan, and the loss rate of submarine cables is high, about 1-5%. Submarine cables also need to consider insulation, protective layer, materials and other complex factors. Local consumption of deep sea wind power is an urgent problem to be solved. A lot of research has been carried out in China, among which local consumption and conversion into methanol for easy transportation is a promising application approach.

[0007] Deep sea wind power has a large volatility, fluctuating within different ranges every hour, day and month. Figure 3 and Figure 4 This is a graph showing the output variation of a wind turbine in a certain wind farm in one day and one month. It can be clearly seen from the graph that wind power not only fluctuates frequently, but also varies over a wide range.

[0008] There are several contradictions that need to be resolved for the deep-sea green methanol synthesis process. The first contradiction is that the by-product heat of methanol synthesis does not match the heat required for methanol distillation. The heat gap is about 63%, and steam needs to be supplied from outside. The offshore platform produces steam for every ton of methanol, and the cost of methanol increases by 1,000 to 2,000 yuan for every ton of steam supplied from outside, which significantly reduces the economic efficiency of methanol. The second contradiction is that wind power fluctuates greatly. If the wind power is not peak-shifted, either the power will be abandoned, which is uneconomical; or it will be started and stopped every day, which is labor-intensive and has high safety risks. The third contradiction is that methanol synthesis and methanol distillation are typical chemical plants and need to be as stable as possible, especially distillation. Each load fluctuation takes about 4 hours to stabilize. How to achieve stable operation of methanol synthesis, especially distillation, when wind power fluctuates frequently is a difficult point.

[0009] To solve this kind of problem, the conventional method on land is to load-bearing electricity to the grid. The following table shows the patents that have been applied for so far for load-bearing similar to fluctuating electricity such as wind power.

[0010]

[0011]

[0012] In view of the wind peak regulation and heat coupling in the deep sea, ZL202410339647.0 proposed to regulate the peak by coupling marine ranches with offshore wind power. Specifically, according to the breeding cycle, the output of the offshore wind farm is provided by the distribution equipment based on the power dispatch model at the seasonal time scale, the daytime and night time scale, and the short-term time scale. Different power distribution strategies are used to supply the required energy to each device, and various resources are organically combined to meet the energy consumption requirements of the marine ranch breeding process, reduce the carbon emissions of the marine ranch throughout the production cycle, and reduce the peak regulation cost of the power grid through the energy synergy of marine ranches and offshore wind power. It can regulate the peak to a certain extent, but it is constrained by the characteristics of the organisms themselves and cannot adapt to large-scale wind fluctuations. ZL202311590984.9 proposes a renewable energy flexible hydrogen production and ammonia synthesis system for offshore platforms. It generates electricity through liquid ammonia to meet the power trough, and stores hydrogen to meet the wind power peak. It can achieve fluctuation and peak regulation of wind power within a certain range, but the peak utilization rate of wind power in the deep sea is not high, and the hydrogen storage capacity cannot be achieved on a large scale due to the problem of hydrogen compression ratio. Summary of the invention

[0013] The purpose of the present invention is to provide a deep-sea self-sufficient carbon dioxide to methanol thermal coupling system and peak-shaving process. The thermal coupling system of the present invention realizes a high degree of thermal coupling through the split production and control of methanol synthesis and methanol distillation, with thermal balance in large intervals and steam supply from methanol boilers in small intervals. Specifically, when the methanol synthesis load is greater than 138% of the methanol distillation load, the heat is balanced and steam is supplied externally; when the methanol synthesis load is lower than 138% of the methanol distillation load, a small amount of steam is supplemented by a self-produced methanol boiler. The peak-shaving process of the present invention realizes flexible production of the methanol device through crude alcohol peak-shaving, specifically, when the wind power supply peaks, crude methanol is produced at maximum load, and the maximum wind power is consumed by crude alcohol peak-shaving without abandoning electricity; when the wind power supply is low, methanol synthesis fluctuates with electricity, and crude alcohol is supplied through crude alcohol peak-shaving to maintain stable load production of methanol distillation.

[0014] In order to achieve the above invention object, the specific technical solution of the present invention is:

[0015] A deep-sea self-sufficient carbon dioxide to methanol thermal coupling peak-shaving process is specifically implemented by the following steps:

[0016] 1) Combined compression: hydrogen and carbon dioxide are mixed, and the circulating gas from methanol synthesis is also compressed;

[0017] 2) Methanol synthesis: The compressed gas is converted into methanol in a methanol synthesis tower to obtain crude alcohol;

[0018] 3) Crude alcohol peak shaving: crude alcohol can be cached by setting up crude alcohol storage tanks of different specifications; a large amount of crude alcohol can be stored when methanol synthesis is in maximum load production; crude alcohol reserves can be released when methanol synthesis is in lower load production to ensure long-term stable load production of methanol distillation;

[0019] 4) Methanol distillation: Use three-tower distillation to purify the synthesized crude alcohol to obtain methanol of the required purity, i.e. refined methanol;

[0020] 5) Methanol boiler: A small amount of refined methanol is used to provide fuel and produce steam, which supplements the insufficient steam from methanol distillation;

[0021] 6) Refined methanol: Store the produced methanol to complete the terminal storage of carbon fixation, and at the same time provide raw materials for methanol boilers when wind power is at low levels.

[0022] As a better implementation mode in the present application, in step 1) of the deep-sea self-sufficient carbon dioxide to methanol thermal coupling peak-shaving process, the hydrogen is produced by electrolysis of water, that is, hydrogen prepared by electrolysis of water by green electricity; the carbon dioxide gas is carbon dioxide captured from the air, and the purity of the carbon dioxide is above 99%.

[0023] As a better implementation method in the present application, in step 1) of the deep-sea self-sufficient carbon dioxide to methanol thermal coupling peak-shaving process, part of the prepared hydrogen is stored; to ensure system stability, the storage pressure is 1.5 to 2.5 MPa.

[0024] As a better implementation in the present application, in step 1) of the deep-sea self-sufficient carbon dioxide to methanol thermal coupling peak-shaving process, the gas is jointly compressed to 5-10 MPa.

[0025] As a better implementation in the present application, in step 2) of the deep-sea self-sufficient carbon dioxide to methanol thermal coupling peak-shaving process, the pressure of methanol synthesis is 5-10 MPa and the temperature is 210-280°C.

[0026] A deep-sea self-contained carbon dioxide to methanol heat coupling system, the system comprising a gas heat exchanger, a methanol synthesis tower, a cooler, a pre-rectification tower reboiler, a pre-rectification tower, a pressurized distillation tower waste heat reboiler, a pressurized distillation tower steam reboiler, a pressurized distillation tower, an atmospheric distillation tower reboiler and an atmospheric distillation tower;

[0027] Among them, the raw gas is connected to the methanol synthesis tower pipe after passing through the gas-to-gas heat exchanger. The outlet gas of the methanol synthesis tower pipe is heated by the gas-to-gas heat exchanger and then connected to the pressure distillation tower waste heat reboiler, pre-distillation tower reboiler, and cooler in sequence. Then it enters the pre-distillation tower, pressure distillation tower, atmospheric distillation tower reboiler, and atmospheric distillation tower in sequence for methanol purification. At the same time, when the methanol synthesis is at low load, part of the refined methanol is sent to the methanol synthesis tower by-product steam network through the methanol boiler to supply the pressure distillation tower steam reboiler.

[0028] Furthermore, when the methanol synthesis load is not less than 138% of the methanol distillation load, steam is supplied externally after internal heat balance; when the methanol synthesis load is lower than 138% of the methanol distillation load, a small amount of steam is produced by sending self-produced methanol to the methanol boiler to supplement the insufficient heat.

[0029] In a deep-sea self-sufficient CO2-to-methanol peak-shaving process, methanol synthesis and methanol distillation are produced and controlled separately through crude alcohol peak-shaving. The methanol synthesis scale is set according to the maximum value of the wind power curve; the methanol distillation scale is set according to the average value of the wind power curve, and the maximum wind power is consumed through crude alcohol peak-shaving, with no or less power abandonment.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1) High utilization rate of wind power; the design load of the device is the maximum power supply capacity of wind power. During the peak power supply period, methanol is produced at full load without power abandonment.

[0032] 2) High thermal coupling degree; when the methanol synthesis load is greater than 138% of the methanol distillation load, the heat is balanced and steam is supplied externally; when the methanol synthesis load is lower than 138% of the methanol distillation load, a small amount of steam is supplemented through the self-produced methanol boiler.

[0033] 3) The methanol distillation operation is stable; through the peak regulation of crude alcohol, the load of the distillation tower remains unchanged all year round, and only the methanol synthesis fluctuates with the electricity, and the stability is greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The present invention is a flowchart of a deep-sea self-sufficient carbon dioxide to methanol peak-shaving process.

[0035] Figure 2 This is a schematic structural diagram of a deep-sea self-sufficient carbon dioxide to methanol heat coupling system according to the present invention.

[0036] Attached Figure 2 mark:

[0037] Gas-gas heat exchanger (1); methanol synthesis tower (2); cooler (3)

[0038] Pre-distillation tower reboiler (4); Pre-distillation tower (5);

[0039] A pressurized distillation tower waste heat reboiler (6); a pressurized distillation tower steam reboiler (7); a pressurized distillation tower (8);

[0040] Atmospheric distillation tower reboiler (9); Atmospheric distillation tower (10);

[0041] Figure 3 This is a diagram showing the output variation of a wind turbine unit in a certain wind power plant in the background technology during one day;

[0042] Figure 4 The figure is a graph showing the output variation of a wind turbine unit in a certain wind power plant in the background technology in one month. DETAILED DESCRIPTION

[0043] A deep-sea self-contained carbon dioxide to methanol heat coupling system and peak-shaving process, comprising the following steps:

[0044] 1) Hydrogen production by water electrolysis: Hydrogen is produced by electrolyzing water using green electricity such as wind power.

[0045] 2) Hydrogen storage: Store part of the hydrogen to ensure system stability, with a storage pressure of 1.5 to 2.5 MPa.

[0046] 3) Air capture of carbon dioxide: Capture carbon dioxide from the air as a carbon source for methanol synthesis, with a carbon dioxide purity of more than 99%.

[0047] 4) Combined compression: The hydrogen and carbon dioxide mixed gas is compressed to 5-10 MPa, and the circulating gas from methanol synthesis is also compressed to 5-10 MPa.

[0048] 5) Methanol synthesis: Under the conditions of pressure 5-10 MPa and temperature 210-280°C, carbon dioxide and hydrogen are converted into methanol in a methanol synthesis tower.

[0049] 6) Crude alcohol peak shaving: Crude alcohol storage tanks of different specifications are set up to buffer crude alcohol. When methanol synthesis is produced at the maximum load, a large amount of crude alcohol can be stored; when methanol synthesis is produced at a lower load, the crude alcohol reserves can be released to ensure the long-term stable load production of methanol distillation.

[0050] 7) Methanol distillation: Three-tower distillation is used to purify the synthesized crude alcohol to obtain methanol of the required purity.

[0051] 8) Methanol boiler: A small amount of refined methanol is produced to provide fuel and produce steam to supplement the insufficient steam from distillation.

[0052] 9) Refined methanol: Store the produced methanol to complete the terminal storage of carbon fixation, and at the same time provide raw materials for methanol boilers when wind power is low.

[0053] A deep-sea self-contained carbon dioxide to methanol thermal coupling system, wherein the raw gas is connected to the methanol synthesis tower pipe after passing through the gas-to-gas heat exchanger, and the outlet gas of the methanol synthesis tower pipe is heated by the gas-to-gas heat exchanger and connected to the pressure distillation tower waste heat reboiler, the pre-distillation tower reboiler, and the cooler in sequence, and then enters the pre-distillation tower, the pressure distillation tower, and the atmospheric distillation tower in sequence for methanol purification. At the same time, when the methanol synthesis is at low load, part of the refined methanol is sent to the methanol synthesis tower by-product steam network through the methanol boiler to supply the pressure distillation tower steam reboiler.

[0054] When the methanol synthesis load is not less than 138% of the methanol distillation load, steam is supplied externally after internal heat balance; when the methanol synthesis load is lower than 138% of the methanol distillation load, a small amount of steam is produced by sending self-produced methanol to the methanol boiler to supplement the insufficient heat.

[0055] In the deep sea self-sufficient carbon dioxide to methanol peak shaving process, methanol synthesis and methanol distillation are produced and controlled separately through crude alcohol peak shaving. The methanol synthesis scale is designed according to the maximum output of wind power; the methanol distillation scale is designed according to the average output of wind power, and the maximum wind power is consumed through crude alcohol peak shaving without abandoning electricity.

[0056] All features disclosed in this specification, or steps in all methods or processes disclosed, except mutually exclusive features and / or steps, can be combined in any manner.

[0057] Any feature disclosed in this specification (including claims and abstract), unless otherwise stated, may be replaced by other equivalent or alternative features having similar purposes. That is, unless otherwise stated, each feature is only an example of a series of equivalent or similar features.

[0058] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0059] In the present invention, some conventional operating equipment, devices and components are omitted or only briefly described, and this part is the prior art.

[0060] Embodiment 1:

[0061] A deep-sea self-sufficient carbon dioxide to methanol heat coupling system and peak-shaving process: A wind turbine has a maximum output of 135MW, an average output of 85MW, and fluctuates between 0 and 135MW in other time periods. Figure 1 Process shown.

[0062] 1) Hydrogen production by water electrolysis: 27 sets of 1000Nm 3 / h electrolyzer, meeting the maximum output of 135MW.

[0063] 2) To store part of the hydrogen, three groups of hydrogen gas tanks are set up with a volume of 2,000 cubic meters and a storage pressure of 1.5 MPa.

[0064] 3) Air capture of carbon dioxide: Capture carbon dioxide from the air and produce 9000Nm of carbon dioxide 3 / h, purity over 99%.

[0065] 4) Combined compression: The hydrogen and carbon dioxide mixed gas is compressed to 8MPa, and the circulating gas from methanol synthesis is also compressed to 8MPa.

[0066] 5) Methanol synthesis: At a pressure of 8 MPa and a temperature of 230°C, carbon dioxide and hydrogen are converted into methanol in a methanol synthesis tower. The maximum processing design of 135MW is 100,000 tons / year of methanol, and the synthesis fluctuates within the range of 10-100%.

[0067] 6) Crude alcohol peak shaving: Based on the deviation between the production capacity of synthetic crude alcohol and the production capacity of distilled refined alcohol, four 2,000-cubic-meter crude alcohol storage tanks are installed to store a large amount of crude alcohol for peak shaving wind power.

[0068] 7) Methanol distillation: Based on the average output of 85MW, the methanol distillation load is determined to be 63,000 tons / year of methanol, and the distillation is operated according to this load all year round.

[0069] 8) Methanol boiler: When the methanol synthesis load is above 87% of the design load, the heat is balanced and the methanol boiler does not need to be turned on; when the methanol synthesis load is below 87% of the design load, the methanol boiler is turned on to supply steam.

[0070] 9) Refined methanol: Two 2,000-cubic-meter refined methanol storage tanks are installed to meet the storage needs of refined methanol for ~8 days.

[0071] Embodiment 2:

[0072] The maximum output of a wind turbine is 135MW, the average output is 85MW, and the output fluctuates between 0 and 135MW in other time periods. The process is the same as in Example 1. Figure 2 The heat is coupled.

[0073] When methanol synthesis is at 100% load, the by-product steam is 5.63t / h. When the outlet temperature of the pre-distillation tower reboiler is 90℃, the low-level waste heat that can be utilized is 15GJ / h. When methanol distillation is at 100% load, the pre-distillation tower requires 0.945GJ / h of heat and the pressurized distillation tower requires 25.83GJ / h of heat.

[0074] When the methanol synthesis load fluctuates between 87% and 100%, 0 to 1.424 t / h of 2.5 MPa saturated steam can be produced as a by-product; when the methanol synthesis load fluctuates between 10% and 87%, a methanol boiler is required to supply 0 to 8.46 t / h of steam.

[0075] Embodiment 3:

[0076] The maximum output of a wind turbine is 135MW, the average output is 85MW, and the output fluctuates between 0 and 135MW in other time periods. The process is the same as in Example 1, and the heat coupling is the same as in Example 2. When the methanol synthesis is 100% loaded, the following operating parameters are used:

[0077] The methanol synthesis tower 2 reacts at 8.0MPa and 230℃. The temperature of the outlet gas from the methanol synthesis tower 2 pipe side drops to 129℃ after passing through the gas-to-gas heat exchanger 1, drops to 96.8℃ after passing through the waste heat reboiler 6 of the pressurized distillation tower, and drops to 90.5℃ after passing through the reboiler 4 of the pre-distillation tower. In addition to its own use, the by-product steam is supplied to the outside at 1.424t / h.

[0078] Embodiment 4:

[0079] The maximum output of a wind turbine is 1.63GW, the average output is 0.46GW, and the output fluctuates between 0 and 1.63GW in other time periods. Figure 1 Process shown.

[0080] 1) Hydrogen production by water electrolysis: 326 sets of 1000Nm3 / h electrolyzers are configured to meet the maximum output of 1.63GW.

[0081] 2) To store part of the hydrogen, 11 sets of hydrogen gas tanks are installed, with a volume of 2,000 cubic meters and a storage pressure of 1.5 MPa.

[0082] 3) Air capture of carbon dioxide: Capture carbon dioxide from the air and produce 108666Nm3 / h of carbon dioxide with a purity of more than 99%.

[0083] 4) Combined compression: The hydrogen and carbon dioxide mixed gas is compressed to 8.5MPa, and the circulating gas from methanol synthesis is also compressed to 8.5MPa.

[0084] 5) Methanol synthesis: At a pressure of 8 MPa and a temperature of 245°C, carbon dioxide and hydrogen are converted into methanol in a methanol synthesis tower. According to the 1.63GW maximum processing design, the methanol synthesis load is 1.2 million tons / year of methanol, and the synthesis fluctuates within the range of 10-100%.

[0085] 6) Crude alcohol peak shaving: Based on the deviation between the production capacity of synthetic crude alcohol and the production capacity of distilled refined alcohol, 8 5,000 cubic meter crude alcohol storage tanks are installed to store a large amount of crude alcohol for peak shaving wind power.

[0086] 7) Methanol distillation: Based on the average output of 0.46GW, the methanol distillation load is determined to be 340,000 tons / year of methanol, and the distillation is operated at this load all year round.

[0087] 8) Methanol boiler: When the methanol synthesis load is above 39% of the design load, the heat is balanced and the methanol boiler does not need to be turned on; when the methanol synthesis load is below 39% of the design load, the methanol boiler is turned on to supply steam.

[0088] 9) Refined methanol: 4 5,000 cubic meter refined methanol storage tanks are installed to meet the storage needs of refined methanol for ~5 days.

[0089] The above-mentioned embodiments only express the specific implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the protection scope of the present application. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the technical solution concept of the present application, and these all belong to the protection scope of the present application.

[0090] This background section is provided to generally present the context of the invention, and the work of the presently named inventors, the work to the extent described in this background section, and aspects of this section that did not constitute prior art at the time of application are neither explicitly nor implicitly admitted to be prior art to the present invention.

Claims

1. A deep sea self-sufficient carbon dioxide to methanol heat coupling peak regulation process, characterized in that The following steps are involved: 1) Combined compression: hydrogen and carbon dioxide are mixed, and the circulating gas from methanol synthesis is also compressed; 2) Methanol synthesis: The compressed gas is converted into methanol in a methanol synthesis tower to obtain crude alcohol; 3) Crude alcohol peak shaving: crude alcohol can be cached by setting up crude alcohol storage tanks of different specifications; a large amount of crude alcohol can be stored when methanol synthesis is in maximum load production; crude alcohol reserves can be released when methanol synthesis is in lower load production to ensure long-term stable load production of methanol distillation; 4) Methanol distillation: Use three-tower distillation to purify the synthesized crude alcohol to obtain methanol of required purity, i.e. refined methanol; 5) Methanol boiler: A small amount of refined methanol is used to provide fuel and produce steam, which supplements the insufficient steam from methanol distillation; 6) Refined methanol: Store the produced methanol to complete the terminal storage of carbon fixation, and at the same time provide raw materials for methanol boilers when wind power is at low levels.

2. The deep-sea self-sufficient carbon dioxide to methanol thermal coupling peak-shaving process according to claim 1, characterized in that: In step 1), the hydrogen is produced by electrolysis of water, that is, hydrogen produced by electrolysis of water using green electricity; the carbon dioxide is carbon dioxide captured from the air, and the purity of the carbon dioxide is above 99%.

3. The deep-sea self-sufficient carbon dioxide to methanol thermal coupling peak-shaving process according to claim 2 is characterized by: Part of the prepared hydrogen is stored; to ensure system stability, the storage pressure is 1.5-2.5 MPa.

4. The deep-sea self-sufficient carbon dioxide to methanol thermal coupling peak-shaving process according to claim 1, characterized in that: In step 1), the gases are jointly compressed to 5-10 MPa.

5. The deep-sea self-sufficient carbon dioxide to methanol heat coupling peak-shaving process according to claim 1 is characterized in that The pressure of methanol synthesis in step 2) is 5-10 MPa and the temperature is 210-280°C.

6. A deep sea self-contained carbon dioxide to methanol peak shaving process according to any one of claims 1 to 5, characterized in that: Through crude alcohol peak regulation, methanol synthesis and methanol distillation are produced and controlled separately.

7. A deep sea self-contained carbon dioxide to methanol peak shaving process according to any one of claims 1 to 5, characterized in that: The scale of methanol synthesis is designed according to the maximum output of wind power.

8. A deep sea self-contained carbon dioxide to methanol peak shaving process according to any one of claims 1 to 5, characterized in that: The scale of methanol distillation is designed according to the average output of wind power, and the maximum wind power is absorbed through peak regulation of crude alcohol without wasting electricity.

9. A deep sea self-contained carbon dioxide to methanol thermal coupling system, characterized in that It comprises a gas heat exchanger (1), a methanol synthesis tower (2), a cooler (3), a pre-distillation tower reboiler (4), a pre-distillation tower (5), a pressure distillation tower waste heat reboiler (6), a pressure distillation tower steam reboiler (7), a pressure distillation tower (8), an atmospheric distillation tower reboiler (9) and an atmospheric distillation tower (10); The raw gas is connected to the pipe side of the methanol synthesis tower (2) after passing through the gas-to-gas heat exchanger (1); the outlet gas of the pipe side of the methanol synthesis tower (2) is heated by the gas-to-gas heat exchanger (1) and then connected to the waste heat reboiler (6) of the pressure distillation tower, the reboiler (4) of the pre-distillation tower, and the cooler (3) in sequence; then, it enters the pre-distillation tower (5), the pressure distillation tower (8), the reboiler (9) of the atmospheric distillation tower, and the atmospheric distillation tower (10) in sequence for methanol purification; at the same time, when the methanol synthesis is at a low load, part of the refined methanol is sent to the by-product steam network of the methanol synthesis tower (2) through the steam produced by the methanol boiler, and supplied to the steam reboiler (7) of the pressure distillation tower.

10. The deep sea self-contained carbon dioxide to methanol thermal coupling system according to claim 9, characterized in that: When the methanol synthesis load is not less than 138% of the methanol distillation load, steam is supplied externally after internal heat balance; when the methanol synthesis load is lower than 138% of the methanol distillation load, a small amount of steam is produced by sending self-produced methanol to the methanol boiler to supplement the insufficient heat.

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