Hydrate separation system, device and method for mixed gas pre-cooled by low-temperature storage tank

Abstract

The invention relates to a hydrate separation system, device and method for mixed gas obtained after precooling of a low-temperature storage tank. The hydrate separation system is composed of an LNG storage tank, a hydrate reaction collector, a nitrogen gas cylinder, a nitrogen storage tank, a methane storage tank, a data acquisition processor and the like. According to the invention, the hydrate method is innovatively utilized to efficiently separate the pre-cooled mixed gas, so that the separation efficiency of the mixed gas is improved; the hydrate reaction collector is composed of a twisted belt type spiral flow generator, a microbubble generator, a reaction accelerant bottle, a constant-temperature water bath device and the like, and high air suction capacity and high reaction efficiency can be ensured; a hydrate method is utilized to efficiently separate mixed gas pre-cooled by the low-temperature storage tank, so that the cold energy of the system is fully utilized, the energy consumption is reduced, and the cost is reduced; compared with a common mixed gas recycling method, an automatic control system is adopted, intelligent control over the steps of hydrate generation, decomposition, separated gas collection and the like is achieved, the labor cost is saved, and energy consumption is reduced; the investment and operation cost is low.

Description

Technical Field

[0001] The present invention belongs to the technical field of separation and recovery of mixed gases generated during the precooling process of cryogenic storage tanks, and in particular relates to a hydrate separation system, device and method for precooled mixed gases of liquid hydrogen storage tanks and LNG storage tanks. Background Art

[0002] As the global demand for clean energy continues to increase, how to effectively utilize LNG has become an important issue in the domestic natural gas field. Compared with other energy sources, LNG has the advantages of being clean and efficient, easy to transport and store, optimizing energy structure, excellent safety performance, and significant environmental benefits. The LNG industry chain mainly includes the liquefaction, storage, transportation, reception, and gasification of natural gas, among which the storage of LNG is a very important link. For LNG liquefaction plants and LNG receiving stations, LNG storage tanks are the key to the storage process.

[0003] LNG storage tanks need to be pre-cooled before filling. During the pre-cooling, liquefied nitrogen will be injected in advance. When the temperature in the tank drops to -162℃, LNG will be injected into the tank. During this process, a mixture of methane and nitrogen will be produced. In order to ensure the purity of LNG, the mixed gas must be discharged. The current treatment method is to directly ignite the discharged mixed gas. The methane in it will generate water and carbon dioxide after combustion, while nitrogen is not combustible and does not participate in the reaction, so it is not treated. However, this treatment method will not only lead to a large amount of resource waste, aggravate the greenhouse effect and environmental pollution, but the heat energy and open flames generated by the combustion will also bring safety hazards to the tank area. At the same time, the cold energy carried in the mixed gas is also wasted. Summary of the invention

[0004] Based on the above defects, the present invention proposes a hydrate separation system, device and method for mixed gas after pre-cooling in a low-temperature storage tank. Since the discharged mixed gas contains usable methane gas, considering energy saving and the characteristics of natural gas hydrates (natural gas hydrates are a non-stoichiometric ice-like clathrate generated by water and methane under low temperature and high pressure), the methane in the mixed gas can be separated by generating natural gas hydrates. This not only reduces safety hazards, but also utilizes the cold energy contained in the mixed gas to recover methane and nitrogen, thereby achieving the purpose of energy-saving and efficient resource recovery.

[0005] The present invention is achieved through the following technical solutions:

[0006] The present invention provides a hydrate separation system for mixed gas after precooling in a cryogenic storage tank, comprising a gas-liquid conveying system, a precooling system, a hydrate reaction system, a separated gas collection system, and a data detection and collection system;

[0007] The gas-liquid delivery system is used for liquid nitrogen and LNG;

[0008] The precooling system is connected to the gas-liquid delivery system and is used to precool the liquid nitrogen and replace the nitrogen with LNG;

[0009] The hydrate reaction system is connected to the precooling system to collect the nitrogen-methane mixed gas generated by the precooling system and separate the nitrogen, methane and water;

[0010] The separated gas collection system is connected to the hydrate reaction system and the precooling system respectively, and is used to receive the separated nitrogen, methane and water, and send the nitrogen to the precooling system;

[0011] The data detection and collection system is connected to the hydrate reaction system and the separated gas collection system respectively, and is used to detect the nitrogen and methane pressures in the hydrate reaction system and the separated gas collection system, determine the pressure difference between each container, and control the recovery and utilization of nitrogen, methane and water.

[0012] The present invention also provides a hydrate separation device for mixed gas after precooling in a cryogenic storage tank, which is used in the hydrate separation system for mixed gas after precooling in the cryogenic storage tank, comprising an LNG storage tank, a hydrate reaction collector, a nitrogen gas cylinder, a nitrogen storage tank, a methane storage tank and a data acquisition processor;

[0013] The LNG storage tank is connected to the liquid inlet pipeline, the hydrate reaction collector is connected to the LNG storage tank, the nitrogen cylinder, the nitrogen storage tank, and the methane storage tank are respectively connected to the hydrate reaction collector, and the nitrogen storage tank is connected to the LNG storage tank, and the data acquisition processor is respectively connected to the hydrate reaction collector, the nitrogen storage tank, and the methane storage tank through temperature and pressure sensors.

[0014] In order to achieve the purpose of energy-saving and efficient resource recovery, the hydrate reaction collector includes a microbubble generator, a twisted ribbon spiral flow generator, a hydrate separator and a hydrate decomposition tank;

[0015] The microbubble generator is connected to the LNG storage tank, the twisted ribbon spiral flow generator is connected to the microbubble generator, the hydrate separator is connected to the twisted ribbon spiral flow generator and the hydrate decomposition tank respectively, and the hydrate decomposition tank is connected to the methane storage tank and the microbubble generator respectively.

[0016] Among them, as the core part of the hydrate reaction collector of the present invention, the microbubble generator is composed of a metal microporous tube with a diameter of 20-40 mm, a length of 100-300 mm, a minimum pore size of 0.3 um, and an opening rate of 40-70%; the twisted ribbon spiral flow generator generates a spiral flow by a twisted ribbon, and the twist rate of the twisted ribbon ranges from 4.3 to 8.8.

[0017] In order to facilitate the control of feed, the liquid inlet pipeline is connected to the LNG storage tank through a plurality of connecting pipelines, and each connecting pipeline is respectively provided with a first one-way valve, a second one-way valve, and a third one-way valve.

[0018] In order to facilitate the control of the mixed gas entering the hydrate reaction collector, a fourth one-way valve is provided on the connecting pipeline between the LNG storage tank and the hydrate reaction collector. In order to facilitate the control of the recovered nitrogen entering the LNG storage tank, a fifth one-way valve is provided on the connecting pipeline between the LNG storage tank and the nitrogen storage tank.

[0019] In order to facilitate the control of the temperature in the hydrate reaction collector and the addition of the reaction accelerator, the hydrate reaction collector is connected to a constant temperature water bath and a reaction accelerator bottle.

[0020] In order to facilitate the nitrogen recovered in the hydrate reaction collector to enter the nitrogen storage tank, a sixth one-way valve, a first compressor and a seventh one-way valve are provided on the connecting pipeline between the hydrate reaction collector and the nitrogen storage tank.

[0021] In order to facilitate the addition of methane recovered in the hydrate reaction collector to the methane storage tank, an eighth one-way valve, a second compressor and a ninth one-way valve are provided on the connecting pipeline between the hydrate reaction collector and the methane storage tank.

[0022] The present invention also provides a method for separating hydrates of mixed gas after precooling in a cryogenic storage tank, based on the above-mentioned device for separating hydrates of mixed gas after precooling in a cryogenic storage tank, comprising the following steps:

[0023] (1) Liquid nitrogen enters the LNG storage tank through the liquid inlet pipeline for precooling;

[0024] (2) When the temperature of the storage tank drops to -162°C, LNG is introduced into the LNG storage tank through the liquid inlet pipeline, and nitrogen is replaced by LNG. When the amount of LNG introduced into the tank reaches a certain scale, LNG is continuously added into the tank through the liquid inlet pipeline, and replacement is stopped when the nitrogen concentration in the tank is lower than 5%;

[0025] (3) The nitrogen-methane mixed gas generated during the replacement process enters the hydrate reaction collector. The temperature in the hydrate reaction collector is adjusted to 3-7° C. by a constant temperature water bath. The pressure is controlled by a high-pressure nitrogen cylinder at a pressure of 3 MPa. When the temperature and pressure are appropriate, a reaction promoter, sodium dodecyl sulfate, is added from a reaction promoter bottle into the hydrate reaction collector.

[0026] (4) After the mixed gas enters the hydrate reaction collector, it enters the twisted ribbon spiral flow generator through the dosing port. Since the mixed gas has a certain amount of coldness, under the action of appropriate temperature, pressure and promoter, the methane and water in the mixed gas generate natural gas hydrate in the twisted ribbon spiral flow generator, and the nitrogen does not react. The temperature and pressure sensor detects the pressure change in the hydrate reaction collector. If the pressure gradually decreases and then tends to be stable, it means that the reaction is completed, and then the substances in the twisted ribbon spiral flow generator enter the hydrate separator, and the nitrogen enters the nitrogen storage tank through the pipeline;

[0027] (5) The temperature and pressure sensor connected to the nitrogen storage tank detects the pressure of the nitrogen storage tank, and the data acquisition processor determines the pressure difference between the two containers. If the pressure in the hydrate reaction collector is greater than the pressure in the nitrogen storage tank, the one-way valve is opened to allow nitrogen to automatically enter the nitrogen storage tank through the pipeline. If the pressures of the two containers are similar or the pressure in the nitrogen storage tank is greater than the pressure in the hydrate reaction collector, the compressor allows nitrogen to enter the nitrogen storage tank through the pipeline. The nitrogen in the nitrogen storage tank is cooled and returned to the pre-cooling pipeline in front of the LNG storage tank.

[0028] (6) The natural gas hydrate in the hydrate reaction collector is separated by the hydrate separator and then enters the hydrate decomposition tank to be decomposed into water and methane. The water returns to the inlet of the hydrate reaction collector for recycling, and the methane enters the methane storage tank for recovery. The temperature and pressure sensor connected to the methane storage tank detects the pressure of the methane storage tank, and the data acquisition processor determines the pressure difference between the methane storage tank and the hydrate reaction collector. If the pressure in the hydrate reaction collector is greater than the pressure in the methane storage tank, the one-way valve is opened to allow methane to automatically enter the methane storage tank through the pipeline. If the pressures of the two containers are similar or the pressure in the methane storage tank is greater than the pressure in the hydrate reaction collector, the compressor is used to allow methane to enter the methane storage tank through the pipeline. At this point, the separation of the mixed gas of methane and nitrogen is completed.

[0029] The beneficial effects of the present invention are:

[0030] ① The present invention innovatively utilizes the hydrate method to efficiently separate the pre-cooled mixed gas, thereby improving the separation efficiency of the mixed gas;

[0031] ②The hydrate reaction collector is composed of a twisted ribbon spiral flow generator, a microbubble generator, a reaction accelerator bottle, a constant temperature water bath, etc., which can ensure high air intake and high reaction efficiency;

[0032] ③ The hydrate method is used to efficiently separate the mixed gas after pre-cooling the cryogenic storage tank, making full use of the system's cold energy, reducing energy consumption and costs;

[0033] ④ Compared with the general mixed gas recovery and utilization method, the present invention adopts an automatic control system to realize intelligent control of hydrate generation, decomposition, separation gas collection and other steps, saving labor costs and energy consumption;

[0034] ⑤Low investment and operating costs;

[0035] ⑥ Select the appropriate type and concentration of kinetic promoter (tetrahydrofuran with a molar fraction of 5.56% + 100 mg kg -1 Sodium dodecyl sulfate solution system), using chemical and physical enhancement method to improve the hydrate formation efficiency and achieve maximum air intake. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a structural schematic diagram of the hydrate separation system of the mixed gas after precooling in the cryogenic storage tank of the present invention;

[0037] Figure 2 It is a schematic structural diagram of a hydrate separation device for mixed gas after precooling in a cryogenic storage tank according to the present invention;

[0038] Figure 3 It is a schematic structural diagram of a hydrate reaction collector of the present invention;

[0039] Figure 4 It is a schematic structural diagram of the microbubble generator of the present invention. DETAILED DESCRIPTION

[0040] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0041] Embodiment 1:

[0042] like Figure 1 A hydrate separation system for mixed gas after precooling in a cryogenic storage tank is shown, comprising a gas-liquid conveying system, a precooling system, a hydrate reaction system, a separated gas collection system, and a data detection and collection system;

[0043] The gas-liquid delivery system is used to deliver liquid nitrogen and LNG;

[0044] The precooling system is connected to the gas-liquid delivery system and is used to precool the liquid nitrogen and replace the nitrogen with LNG;

[0045] The hydrate reaction system is connected to the precooling system to collect the nitrogen-methane mixed gas generated by the precooling system and separate the nitrogen, methane and water;

[0046] The separated gas collection system is connected to the hydrate reaction system and the precooling system respectively, and is used to receive the separated nitrogen, methane and water, and send the nitrogen to the precooling system;

[0047] The data detection and collection system is connected to the hydrate reaction system and the separated gas collection system respectively, and is used to detect the nitrogen and methane pressures in the hydrate reaction system and the separated gas collection system, determine the pressure difference between each container, and control the recovery and utilization of nitrogen, methane and water.

[0048] The gas-liquid transportation system first sends liquid nitrogen into the precooling system for precooling, and then sends LNG into the precooling system to replace nitrogen. The mixed gas in the replacement process enters the hydrate reaction system, is separated by the hydrate reaction system, and is recovered by the separated gas collection system. The data detection and collection system detects the nitrogen and methane pressures in the hydrate reaction system and the separated gas collection system, determines the pressure difference between each container, and controls the reuse of nitrogen, methane and water, thereby realizing intelligent control of hydrate formation, decomposition, separated gas collection and other steps, saving labor costs and energy consumption.

[0049] Embodiment 2:

[0050] like Figure 2 The hydrate separation device for mixed gas after precooling in a cryogenic tank is shown, which is used in the hydrate separation system for mixed gas after precooling in the above-mentioned cryogenic tank, and includes an LNG storage tank 22, a hydrate reaction collector 21, a nitrogen cylinder 6, a nitrogen storage tank 23, a methane storage tank 17 and a data acquisition processor 9.

[0051] Specifically, the liquid inlet pipeline is connected to the LNG storage tank 22 through a plurality of connecting pipelines, and each connecting pipeline is respectively provided with a first one-way valve 1, a second one-way valve 2, and a third one-way valve 3. The hydrate reaction collector 21 is connected to the LNG storage tank 22, and a fourth one-way valve 4 is provided on the connecting pipeline. The nitrogen cylinder 6, the nitrogen storage tank 23, and the methane storage tank 14 are respectively connected to the hydrate reaction collector 21. The connecting pipeline between the hydrate reaction collector 21 and the nitrogen storage tank 23 is sequentially provided with a sixth one-way valve 11, a first compressor 12, and a seventh one-way valve 13. The connecting pipeline between the hydrate reaction collector 21 and the methane storage tank 17 is sequentially provided with an eighth one-way valve 14, a second compressor 15, and a ninth one-way valve 16. The connecting pipeline between the hydrate reaction collector 21 and the nitrogen cylinder 6 is A tenth one-way valve 7 is provided on the pipe connection, a fifth one-way valve 20 is provided on the connection pipe between the nitrogen storage tank 23 and the LNG storage tank 22, an eleventh one-way valve 19 is provided on the connection pipe between the nitrogen storage tank 23 and the inlet pipeline, the data acquisition processor 9 is connected to the hydrate reaction collector 21 through the first temperature and pressure sensor 8, connected to the nitrogen storage tank 23 through the second temperature and pressure sensor 10, and connected to the methane storage tank 17 through the third temperature and pressure sensor 18. In addition, the hydrate reaction collector 21 is connected to the constant temperature water bath 25 and the reaction accelerator bottle 24, and a twelfth one-way valve 5 is provided on the connection pipe between the hydrate reaction collector 21 and the reaction accelerator bottle 24, and the reaction accelerator bottle 24 is filled with 5.56% of tetrahydrofuran + 100mg kg -1 Sodium dodecyl sulfate solution system.

[0052] Combination Figure 3 , Figure 4 The hydrate reaction collector shown includes a micro bubble generator 28, a twisted ribbon spiral flow generator 29, a hydrate separator 31 and a hydrate decomposition tank 33;

[0053] The connection pipeline between the microbubble generator 28 and the LNG storage tank 22 is provided with a dosing port 26 and a thirteenth one-way valve 27. The microbubble generator 28 is composed of a metal microporous tube. The diameter of the metal microporous tube is 20-40 mm, the length is 100-300 mm, the minimum aperture of the micropore 36 is 0.3 um, the opening rate is 40-70%, and one end of the metal microporous tube has an air inlet 37. The twisted ribbon spiral flow generator 29 is connected to the microbubble generator 28. The hydrate separator 31 is connected to the hydrate separator 31. A fourteenth one-way valve 30 is provided on the connecting pipeline of the twisted ribbon spiral flow generator 29, the hydrate decomposition tank 33 is connected to the microbubble generator 28 and the methane storage tank 17 respectively, a fifteenth one-way valve 35 is provided on the connecting pipeline between the hydrate decomposition tank 33 and the microbubble generator 28, a sixteenth one-way valve 34 is provided on the connecting pipeline between the hydrate decomposition tank 33 and the methane storage tank 17, and a seventeenth one-way valve 32 is provided on the connecting pipeline between the hydrate separator 31 and the hydrate decomposition tank 33.

[0054] The separation method of the hydrate separation device of the mixed gas after precooling in the cryogenic storage tank comprises the following steps:

[0055] Liquid nitrogen enters the LNG storage tank 22 through the liquid inlet pipeline through the third one-way valve 3 for precooling. When the temperature of the LNG storage tank 22 drops to -162°C, open the first one-way valve 1 to allow LNG to enter the LNG storage tank 22 through the liquid inlet pipeline, and replace nitrogen with LNG. When the amount of LNG introduced into the tank reaches a certain scale, open the second one-way valve 2 to continue adding LNG into the tank through the liquid inlet pipeline. When the nitrogen concentration in the tank is lower than 5%, stop the replacement; the nitrogen-methane mixed gas generated during the replacement process passes through the fourth one-way valve 4 and enters the hydrate reaction collector 21 through the pipeline. The hydrate reaction collector 21 is connected to a temperature and pressure sensor 8. Open the constant temperature water bath 25 to adjust the temperature to 3-7°C. The pressure is controlled by the high-pressure nitrogen cylinder 6, and the pressure is 3MPa. When the temperature and pressure The twelfth one-way valve 5 is opened appropriately, and the reaction promoter sodium dodecyl sulfate is added into the hydrate reaction collector 21 through the reaction promoter bottle 24; after the mixed gas enters the hydrate reaction collector 21, it enters the microbubble generator 28 and the twisted ribbon spiral flow generator 29 through the dosing port 26. Since the mixed gas has a certain amount of coldness, under the action of appropriate temperature, pressure and promoter, the methane and water in the mixed gas generate natural gas hydrate in the twisted ribbon spiral flow generator 29, and the nitrogen does not react; the pressure change in the hydrate reaction collector 21 is detected by the temperature and pressure sensor 8. If the pressure tends to be stable after gradually decreasing, it means that the reaction is completed, and then the substances in the twisted ribbon spiral flow generator 29 enter the hydrate separator 31, and the nitrogen enters the nitrogen through the pipeline. The temperature and pressure sensor 10 connected to the nitrogen storage tank 23 detects the pressure of the nitrogen storage tank 23, and the data acquisition processor 9 determines the pressure difference between the two containers. If the pressure in the hydrate reaction collector 21 is greater than the pressure in the nitrogen storage tank 23, the seventh one-way valve 13 is opened to allow nitrogen to automatically enter the nitrogen storage tank 23 through the pipeline; if the pressures of the two containers are similar or the pressure in the nitrogen storage tank 23 is greater than the pressure in the hydrate reaction collector 21, the sixth one-way valve 11 and the seventh one-way valve 13 are opened, and the nitrogen is allowed to enter the nitrogen storage tank 23 through the pipeline through the first compressor 12. The nitrogen in the nitrogen storage tank 23 can be cooled and returned to the pre-cooling pipeline; the natural gas hydrate in the hydrate reaction collector 21 is separated by the hydrate separator 31 and then enters the hydrate decomposition The methane gas is decomposed into water and methane in the tank 33, and the water is returned to the inlet of the microbubble generator 28 for recycling, and the methane enters the methane storage tank 17 through the sixteenth one-way valve 34 for recovery; the temperature and pressure sensor 18 connected to the methane storage tank 17 detects the pressure of the methane storage tank 17, and the data acquisition processor 9 determines the pressure difference between the methane storage tank 17 and the hydrate reaction collector 21. If the pressure in the hydrate reaction collector 21 is greater than the pressure in the methane storage tank 17, the ninth one-way valve 16 is opened to allow methane to automatically enter the methane storage tank 17 through the pipeline; if the pressures of the two containers are similar or the pressure of the methane storage tank 17 is greater than the pressure in the hydrate reaction collector 21, the eighth one-way valve 14 and the ninth one-way valve 16 are opened, and the methane is allowed to enter the methane storage tank 17 through the pipeline through the second compressor 15;At this point, the separation of the mixed gas of methane and nitrogen is complete. ;

[0056] Finally, it should be noted that the above embodiments are only specific implementations of the present invention, which are used to illustrate the technical solutions of the present invention, rather than to limit them. The protection scope of the present invention is not limited thereto. Although the present invention is described in detail with reference to the above embodiments, ordinary technicians in the field should understand that any technician familiar with the technical field can still modify the technical solutions recorded in the above embodiments within the technical scope disclosed by the present invention, or can easily think of changes, or make equivalent replacements for some of the technical features therein; and these modifications, changes or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A hydrate separation system for mixed gas after precooling in a cryogenic storage tank, characterized in that: It includes gas-liquid transportation system, precooling system, hydrate reaction system, separation gas collection system, and data detection and collection system; The gas-liquid delivery system is used to deliver liquid nitrogen and LNG; The precooling system is connected to the gas-liquid delivery system and is used to precool the liquid nitrogen and replace the nitrogen with LNG; The hydrate reaction system is connected to the precooling system to collect the nitrogen-methane mixed gas generated by the precooling system and separate the nitrogen, methane and water; The separated gas collection system is connected to the hydrate reaction system and the precooling system respectively, and is used to receive the separated nitrogen, methane and water, and send the nitrogen to the precooling system; The data detection and collection system is connected to the hydrate reaction system and the separated gas collection system respectively, and is used to detect the nitrogen and methane pressures in the hydrate reaction system and the separated gas collection system, determine the pressure difference between each container, and control the recovery and utilization of nitrogen, methane and water.

2. A hydrate separation device for mixed gas after precooling in a cryogenic storage tank, used in the hydrate separation system for mixed gas after precooling in a cryogenic storage tank as claimed in claim 1, characterized in that: Including LNG storage tanks, hydrate reaction collectors, nitrogen cylinders, nitrogen storage tanks, methane storage tanks and data acquisition processors; The LNG storage tank is connected to the liquid inlet pipeline, the hydrate reaction collector is connected to the LNG storage tank, the nitrogen cylinder, the nitrogen storage tank, and the methane storage tank are respectively connected to the hydrate reaction collector, and the nitrogen storage tank is connected to the LNG storage tank, and the data acquisition processor is respectively connected to the hydrate reaction collector, the nitrogen storage tank, and the methane storage tank through temperature and pressure sensors.

3. The hydrate separation device for mixed gas after precooling in a cryogenic storage tank according to claim 2 is characterized in that: The hydrate reaction collector comprises a microbubble generator, a twisted ribbon spiral flow generator, a hydrate separator and a hydrate decomposition tank; The microbubble generator is connected to the LNG storage tank, the twisted ribbon spiral flow generator is connected to the microbubble generator, the hydrate separator is connected to the twisted ribbon spiral flow generator and the hydrate decomposition tank respectively, and the hydrate decomposition tank is connected to the methane storage tank and the microbubble generator respectively.

4. The hydrate separation device for mixed gas after precooling in a cryogenic storage tank according to claim 3 is characterized in that: The microbubble generator is composed of a metal microporous tube with a diameter of 20-40 mm, a length of 100-300 mm, a minimum pore size of 0.3 um, and an opening rate of 40-70%. The twisted ribbon spiral flow generator generates a spiral flow by a twisted ribbon with a twist rate ranging from 4.3 to 8.

8.

5. The hydrate separation device for mixed gas after precooling in a cryogenic storage tank according to claim 3 is characterized in that: The liquid inlet pipeline is connected to the LNG storage tank through a plurality of connecting pipelines, and a first one-way valve, a second one-way valve, and a third one-way valve are respectively arranged on each connecting pipeline.

6. The hydrate separation device for mixed gas after precooling in a cryogenic storage tank according to claim 5 is characterized in that: A fourth one-way valve is provided on the connecting pipeline between the LNG storage tank and the hydrate reaction collector, and a fifth one-way valve is provided on the connecting pipeline between the LNG storage tank and the nitrogen storage tank.

7. The hydrate separation device for mixed gas after precooling in a cryogenic storage tank according to claim 6, characterized in that: The hydrate reaction collector is connected to a constant temperature water bath and a reaction accelerator bottle.

8. The hydrate separation device for mixed gas after precooling in a cryogenic storage tank according to claim 7, characterized in that: The connecting pipeline between the hydrate reaction collector and the nitrogen storage tank is provided with a sixth one-way valve, a first compressor and a seventh one-way valve.

9. The hydrate separation device for mixed gas after precooling in a cryogenic storage tank according to claim 8, characterized in that: An eighth one-way valve, a second compressor and a ninth one-way valve are arranged on the connecting pipeline between the hydrate reaction collector and the methane storage tank.

10. A method for separating hydrates from mixed gas after precooling in a cryogenic storage tank, based on the hydrate separation device for separating hydrates from mixed gas after precooling in a cryogenic storage tank as claimed in any one of claims 2 to 9, characterized in that: The steps include: (1) Liquid nitrogen enters the LNG storage tank through the liquid inlet pipeline for precooling; (2) When the temperature of the storage tank drops to -162°C, LNG is introduced into the LNG storage tank through the liquid inlet pipeline, and nitrogen is replaced by LNG. When the amount of LNG introduced into the tank reaches a certain scale, LNG is continuously added into the tank through the liquid inlet pipeline, and replacement is stopped when the nitrogen concentration in the tank is lower than 5%; (3) The nitrogen-methane mixed gas generated during the replacement process enters the hydrate reaction collector. The temperature in the hydrate reaction collector is adjusted to 3-7° C. by a constant temperature water bath. The pressure is controlled by a high-pressure nitrogen cylinder at a pressure of 3 MPa. When the temperature and pressure are appropriate, a reaction promoter, sodium dodecyl sulfate, is added from a reaction promoter bottle into the hydrate reaction collector. (4) After the mixed gas enters the hydrate reaction collector, it enters the twisted ribbon spiral flow generator through the dosing port. Since the mixed gas has a certain amount of coldness, under the action of appropriate temperature, pressure and promoter, the methane and water in the mixed gas generate natural gas hydrate in the twisted ribbon spiral flow generator, and the nitrogen does not react. The temperature and pressure sensor detects the pressure change in the hydrate reaction collector. If the pressure gradually decreases and then tends to be stable, it means that the reaction is completed, and then the substances in the twisted ribbon spiral flow generator enter the hydrate separator, and the nitrogen enters the nitrogen storage tank through the pipeline; (5) The temperature and pressure sensor connected to the nitrogen storage tank detects the pressure of the nitrogen storage tank, and the data acquisition processor determines the pressure difference between the two containers. If the pressure in the hydrate reaction collector is greater than the pressure in the nitrogen storage tank, the one-way valve is opened to allow nitrogen to automatically enter the nitrogen storage tank through the pipeline. If the pressures of the two containers are similar or the pressure in the nitrogen storage tank is greater than the pressure in the hydrate reaction collector, the compressor allows nitrogen to enter the nitrogen storage tank through the pipeline. The nitrogen in the nitrogen storage tank is cooled and returned to the pre-cooling pipeline in front of the LNG storage tank. (6) The natural gas hydrate in the hydrate reaction collector is separated by the hydrate separator and then enters the hydrate decomposition tank to be decomposed into water and methane. The water returns to the inlet of the hydrate reaction collector for recycling, and the methane enters the methane storage tank for recovery. The temperature and pressure sensor connected to the methane storage tank detects the pressure of the methane storage tank, and the data acquisition processor determines the pressure difference between the methane storage tank and the hydrate reaction collector. If the pressure in the hydrate reaction collector is greater than the pressure in the methane storage tank, the one-way valve is opened to allow methane to automatically enter the methane storage tank through the pipeline. If the pressures of the two containers are similar or the pressure in the methane storage tank is greater than the pressure in the hydrate reaction collector, the compressor is used to allow methane to enter the methane storage tank through the pipeline. At this point, the separation of the mixed gas of methane and nitrogen is completed.

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