Precooling mixed gas separation device of liquefied natural gas storage tank

Abstract

The utility model relates to a liquefied natural gas storage tank precooling mixed gas separation device in the technical field of gas separation. The liquefied natural gas storage tank precooling mixed gas separation device comprises a gas-liquid conveying system, a hydrate generation system, a cooling heat exchange system, a hydrate decomposition system, a separation and collection system and a data monitoring and collection system. The nano-bubble generator and the folded tubular reactor work cooperatively, nano-bubbles can be kept stable in a liquid carrier for a long time, high suction capacity and high generation efficiency can be guaranteed, natural gas and nitrogen mixed gas generated in the precooling process of the LNG storage tank is recycled at high efficiency and low cost, energy input is reduced, cost is reduced, and the production efficiency is improved. The resource waste is reduced, and the environmental pollution is reduced.

Description

Technical Field

[0001] This invention belongs to the field of gas separation technology, specifically relating to a liquefied natural gas (LNG) storage tank pre-cooling mixed gas separation device based on cold energy utilization. It is a technology for separating and recovering nitrogen-natural gas mixture generated during the pre-cooling process of LNG storage tanks, and can also be used for the recovery and utilization of pre-cooled mixed gas from other cryogenic storage tanks. Background Technology

[0002] The LNG industry chain mainly includes natural gas liquefaction, storage, transportation, receiving, and gasification. Among these, LNG storage is a very important link. For LNG liquefaction plants and LNG receiving terminals, LNG storage tanks are the key to the storage process.

[0003] Currently, LNG storage is primarily done in tanks. Before filling, LNG storage tanks need to be pre-cooled using liquid nitrogen. Liquefied nitrogen is injected into the LNG tank beforehand, and once the internal temperature drops to -162°C, LNG is injected to displace the nitrogen until the nitrogen content in the tank falls below 5%, at which point the displacement process stops. Typically, each tank is 16×10... 4 m 3 The cooling and replacement process of the atmospheric pressure LNG storage tank will consume approximately 2200 m³ of LNG. 3 This process generates a large amount of a mixture of natural gas and nitrogen, which is difficult to use in actual production and economic life. Therefore, all of this mixture must be vented, resulting in a lot of waste.

[0004] Currently, the most common treatment for these gas mixtures is combustion, where an ignition device is installed at the exhaust end to ignite the mixture. The natural gas burns to produce water and carbon dioxide, while nitrogen, which does not support combustion and does not participate in the reaction, is left untreated. However, this method wastes resources, exacerbates the greenhouse effect, contradicts the concept of green development, and may even pose safety hazards. Considering the physical properties of natural gas and the coldness carried by the gas mixture, natural gas hydrates can be generated to separate the natural gas from the mixture, thus achieving efficient resource utilization. Therefore, developing a feasible and efficient method and apparatus for separating gas mixtures using natural gas hydrates is of great significance. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a liquefied natural gas (LNG) storage tank pre-cooling mixed gas separation device based on cold energy utilization. This device achieves high-efficiency and low-cost recovery of the natural gas and nitrogen mixed gas generated during the pre-cooling of LNG storage tanks, saving resources and reducing environmental pollution.

[0006] This invention is achieved through the following technical solution:

[0007] This invention provides a pre-cooling mixed gas separation device for liquefied natural gas storage tanks, comprising a gas-liquid conveying system, a hydrate generation system, a cooling heat exchange system, a hydrate decomposition system, a separation and collection system, and a data monitoring and collection system;

[0008] The gas-liquid delivery system is used to deliver a mixture of nitrogen and natural gas;

[0009] The hydrate generation system is connected to the gas-liquid transport system and is used to generate nanobubbles from the mixed gas.

[0010] The cooling heat exchange system is connected to the hydrate generation system and is used to exchange heat between nanobubbles to generate hydrate slurry.

[0011] The hydrate decomposition system is connected to a cooling heat exchange system and is used to decompose the hydrate slurry into hydrates, remaining unreacted gases, and unreacted water.

[0012] The separation and collection system is connected to the hydrate decomposition system and is used to collect the hydrates decomposed by the hydrate decomposition system;

[0013] The data monitoring and collection system is connected to the hydrate generation system, the hydrate decomposition system, and the cooling heat exchange system, respectively, and is used to collect relevant data.

[0014] To facilitate the generation of a mixture of nitrogen and natural gas, the gas-liquid transport system includes a liquid nitrogen pipeline, an LNG pipeline, an LNG storage tank, a mixed gas discharge pipeline, and a heat exchanger. The liquid nitrogen pipeline and the LNG pipeline are respectively connected to the liquid inlet pipeline and the LNG storage tank. The LNG storage tank is connected to the mixed gas discharge pipeline, and the heat exchanger is connected to the mixed gas discharge pipeline.

[0015] To achieve the goal of energy-saving and efficient resource recycling, the hydrate generation system includes a low-temperature water tank, a low-temperature water bath, a dosing pipe, a gas compressor, a pressurized water pump, and a nanobubble generator. The low-temperature water bath is connected to the low-temperature water tank, and the low-temperature water tank is connected to a heat exchanger and a dosing pipe. The nanobubble generator is connected to the low-temperature water tank through the pressurized water pump and the gas compressor.

[0016] To ensure the quality of the nanobubbles, in a preferred embodiment of the present invention, the nanobubble generator includes a shell, a reaction chamber, a feeding section, and a discharging section. The reaction chamber is disposed inside the shell, and a cavity is formed between the reaction chamber and the inner wall of the shell. A gas pore channel communicating with the cavity is opened on the shell. The feeding section and the discharging section are respectively fixed at both ends of the shell and are respectively connected to the inner cavity of the reaction chamber. A plurality of gas pores communicating with the cavity are opened at one end of the reaction chamber near the feeding section.

[0017] To improve heat exchange efficiency, the cooling heat exchange system includes a folded tube reactor, which is connected to a low-temperature water bath and a nanobubble generator.

[0018] To further improve the heat exchange effect, in a preferred embodiment of the present invention, the folded tube reactor includes a box body and folded tubes, fins, spiral ribbons, a water collection chamber, a water distribution chamber, and baffles disposed within the box body. The two ends of the folded tubes are respectively connected to the water collection chamber and the water distribution chamber. The water distribution chamber is connected to a nanobubble generator. The fins are evenly distributed on the outer wall of the folded tubes. The spiral ribbons are disposed inside the folded tubes. The baffles are evenly distributed outside the folded tubes.

[0019] To improve decomposition efficiency, the hydrate decomposition system includes a hydrate separator and a hydrate decomposer. The hydrate separator is connected to the water collection chamber of the folded tubular reactor, and the hydrate decomposer is connected to both the hydrate separator and the low-temperature water tank.

[0020] To collect the decomposed nitrogen and natural gas, the separation and collection system includes a nitrogen storage tank and a natural gas storage tank. The nitrogen storage tank is connected to a hydrate separator, and the natural gas storage tank is connected to a hydrate decomposer.

[0021] In order to control the relevant temperature and pressure of each system and ensure the safety of the entire system, the data monitoring and collection system includes a PLC data acquisition processor and several temperature and pressure sensors. The temperature and pressure sensors are respectively installed in the low temperature water tank, low temperature water bath, folded tubular reactor, hydrate separator, and hydrate decomposer. The PLC data acquisition processor is connected to each temperature and pressure sensor.

[0022] The separation and recovery method of the above-mentioned liquefied natural gas storage tank precooling mixed gas separation device includes the following steps:

[0023] (1) First, liquid nitrogen is introduced into the LNG storage tank for heat exchange to cool down the LNG storage tank;

[0024] (2) When the temperature inside the LNG storage tank drops to a suitable temperature, inject LNG gas into the LNG storage tank to replace the nitrogen gas inside the LNG storage tank. This process produces a mixture of nitrogen and natural gas.

[0025] (3) After the mixed gas is heated by heat exchanger, it enters the low temperature water tank of the hydrate generation system. The temperature is kept stable by the heat exchange of water in the low temperature water tank, and a certain amount of cold energy is provided to the low temperature water tank.

[0026] (4) The hydrate in the low-temperature water tank is pressurized and sent into the nanobubble generator. The hydrate, adjusted to a suitable temperature and pressure, mixes in the nanobubble generator to generate a large number of nanobubbles.

[0027] (5) Nanobubbles enter the folded tube reactor of the cooling heat exchange system to fully stir and exchange heat, producing hydrate slurry;

[0028] (6) The hydrate slurry enters the hydrate separator of the hydrate decomposition system, where the hydrates, the remaining unreacted gas and the unreacted water generated are separated. The separated hydrates enter the hydrate decomposer, the remaining unreacted gas is pressurized and enters the nitrogen storage tank, and the unreacted water returns to the low temperature water tank.

[0029] (7) The separated hydrates are decomposed into water and natural gas in the hydrate decomposer. The natural gas is pressurized and enters the natural gas storage tank, while the water produced by decomposition returns to the low-temperature water tank.

[0030] In summary, the beneficial effects of this invention are:

[0031] ①This invention employs a nanobubble generator and a folded tubular reactor working together. The nanobubbles can remain stable in the liquid carrier for a long time, ensuring high gas intake and high generation efficiency, and realizing continuous and rapid separation of pre-cooled mixed gas using hydrates.

[0032] ②This invention makes full use of the low-temperature mixing of its own cold energy to produce gas hydrates, reducing energy input and lowering costs;

[0033] ③ The water in this system can be recycled within the system. Because the water produced after the decomposition of hydrates contains hydrate crystal nuclei, recycling this water within the system is conducive to the rapid generation of gas hydrates.

[0034] ④ The application of a cooling heat exchange system rapidly removes the heat of hydrate formation, ensuring efficient hydrate preparation;

[0035] ⑤ It achieves efficient and low-cost recovery of the natural gas and nitrogen mixture generated during the pre-cooling of LNG storage tanks, saving resources and reducing environmental pollution. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the pre-cooling mixed gas separation device for liquefied natural gas storage tanks according to the present invention;

[0037] Figure 2 This is a three-dimensional structural diagram of the nanobubble generator of the present invention;

[0038] Figure 3 This is a cross-sectional view of the nanobubble generator of the present invention;

[0039] Figure 4 This is a three-dimensional structural diagram of the folded tubular reactor of the present invention;

[0040] Figure 5This is a schematic diagram of the folded tube of the present invention. Detailed Implementation

[0041] The preferred embodiments of the present invention will now be described in detail with reference to 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 providing a clearer and more explicit definition of the scope of protection of the present invention.

[0042] like Figure 1 The device shown is a pre-cooling mixed gas separation device for liquefied natural gas storage tanks, comprising a gas-liquid conveying system, a hydrate generation system, a cooling heat exchange system, a hydrate decomposition system, a separation and collection system, and a data monitoring and collection system.

[0043] Specifically, the gas-liquid transport system is used to form and deliver a mixture of nitrogen and natural gas, including a liquid nitrogen pipeline 1, an LNG pipeline 2, an LNG storage tank 3, a mixed gas discharge pipeline 4, and a heat exchanger 5. The inlet ends of the liquid nitrogen pipeline 1 and the LNG pipeline 2 are connected to the liquid inlet pipeline, and the outlet ends of the liquid nitrogen pipeline 1 and the LNG pipeline 2 are connected to the LNG storage tank 3. The inlet end of the mixed gas discharge pipeline 4 is connected to the LNG storage tank 3, and the outlet end of the mixed gas discharge pipeline 4 is connected to the heat exchanger 5.

[0044] Specifically, the hydrate generation system is connected to the gas-liquid transport system and is used to generate nanobubbles from the mixed gas. It includes a low-temperature water tank 6, a low-temperature water bath 19, a dosing pipe 20, a gas compressor 9, a pressurized water pump 8, and a nanobubble generator 10. The low-temperature water bath 19 is connected to the low-temperature water tank 6. The low-temperature water tank 6 is connected to the heat exchanger 5 and the dosing pipe 20. The nanobubble generator 10 is connected to the low-temperature water tank 6 through the pressurized water pump 8 and the water supply pipe 7. At the same time, the nanobubble generator 10 is connected to the low-temperature water tank 6 through the gas compressor 9.

[0045] The specific structure of the nanobubble generator 10 is as follows: Figure 2 , Figure 3 As shown, the device includes a shell 28, a reaction chamber 32, a feeding section 31, and a discharging section 30. The reaction chamber 32 is coaxially disposed inside the shell 28, and there is a cavity 33 between the reaction chamber 32 and the inner wall of the shell 28. The shell 28 is provided with a vent channel 29 that communicates with the cavity 33. The feeding section 31 and the discharging section 30 are respectively fixed to both ends of the shell 28 and are respectively connected to the inner cavity of the reaction chamber 32. The reaction chamber 32 is provided with a plurality of vents 34 that communicate with the cavity 33 at one end near the feeding section 31.

[0046] Specifically, the cooling heat exchange system is connected to the hydrate generation system and is used to exchange heat between nanobubbles to generate hydrate slurry. The cooling heat exchange system includes a folded tubular reactor 11, which is connected to a low-temperature water bath 19 and a nanobubble generator 10.

[0047] The specific structure of the folded tubular reactor 11 is as follows: Figure 4 , Figure 5 As shown, the device includes a housing and folded tubes 21, fins 27, spiral ribbons 25, a water collection chamber 22, a water distribution chamber 24, and baffles 23 disposed within the housing. The two ends of the folded tube 21 are connected to the water collection chamber 22 and the water distribution chamber 24, respectively. The water distribution chamber 24 is connected to a nanobubble generator 10. The fins 27 are evenly distributed on the outer wall of the folded tube 21. The spiral ribbons 25 are disposed inside the folded tube 21. The baffles 23 are evenly distributed outside the folded tube 21. The folded tube 21 is fixed to the baffles 23 by flanges 26. Each baffle 23 divides the housing into continuous S-shaped channels.

[0048] Specifically, the hydrate decomposition system is connected to a cooling heat exchange system and is used to decompose the hydrate slurry into hydrates, remaining unreacted gas, and unreacted water. It includes a hydrate separator 12 and a hydrate decomposer 15. The hydrate separator 12 is connected to the water collection chamber 22 of the folded tubular reactor 11, and the hydrate decomposer 15 is connected to the hydrate separator 12 and the low-temperature water tank 6, respectively.

[0049] Specifically, the separation and collection system is connected to the hydrate decomposition system and is used to collect the hydrates decomposed by the hydrate decomposition system. It includes a nitrogen storage tank 14 and a natural gas storage tank 18. The nitrogen storage tank 14 is connected to the hydrate separator 12 through a gas compressor 13, and the natural gas storage tank 18 is connected to the hydrate decomposer 15 through a gas compressor 17.

[0050] Specifically, the data monitoring and collection system is connected to the hydrate generation system, the hydrate decomposition system, and the cooling heat exchange system, respectively, and is used to collect relevant data. It includes a PLC data acquisition processor and several temperature and pressure sensors 16. The temperature and pressure sensors 16 are respectively installed in the low-temperature water tank 6, the low-temperature water bath 19, the folded tubular reactor 11, the hydrate separator 12, and the hydrate decomposer 15. The PLC data acquisition processor is connected to each temperature and pressure sensor 16.

[0051] The separation and recovery method of the pre-cooled mixed gas separation unit for the liquefied natural gas storage tank is as follows:

[0052] Liquid nitrogen enters LNG storage tank 3 via liquid nitrogen pipeline 1 for pre-cooling. Once the temperature of LNG storage tank 3 drops below -162℃, the valve is opened to allow LNG to flow into LNG storage tank 3 via LNG pipeline 2. LNG replaces the nitrogen in the LNG storage tank. Replacement is stopped when the nitrogen content in the tank falls below 5%. The resulting mixed gas exits the storage tank via mixed gas discharge pipeline 4 and then passes through air heat exchanger 5, which raises the temperature of the mixed gas to -10 to 0℃. The gas then passes through cryogenic water tank 6, where heat exchange with the water maintains a stable temperature and provides some cooling energy to the tank. The mixed gas is then pressurized to approximately 5 MPa by the gas compressor 9 and enters the nanobubble generator 10. The low-temperature water tank 6 is connected to a low-temperature water bath 19 and a temperature and pressure sensor 16. When the water temperature in the low-temperature water tank 6 exceeds 7°C, the low-temperature water bath 19 is turned on for cooling, ensuring that the water temperature in the low-temperature water tank 6 is at a suitable temperature for hydrate formation. The water in the low-temperature water tank 6 is pressurized by the pressurized water pump 8 through the water supply pipe 7 and then enters the nanobubble generator 10. The mixed gas and low-temperature water, adjusted to a suitable temperature and pressure, mix in the nanobubble generator 10 to generate a large number of tiny nanobubbles, which then enter the folded tube type reverse... Reactor 11: A gas-liquid mixture containing nanobubbles enters the folded tubular reactor 11 and undergoes spiral flow. The nanobubbles are fully agitated and exchange heat, generating a hydrate slurry. The folded tubular reactor 11 is equipped with a cooling space. Cooling water at a temperature of 3°C is prepared by a low-temperature water bath 19 and connected to the cooling space of the folded tubular reactor 11 through a pipe for cooling heat exchange. Finally, the water returns to the low-temperature water bath 19 for the next cycle. The hydrate slurry further generates hydrates, residual unreacted gases, and unreacted water in the hydrate separator 12, which are then separated. The separated hydrates are then discharged as water. The mixture enters the hydrate decomposer 15 from the separator 12. The unreacted gas, i.e., nitrogen, is pressurized by the gas compressor 13 and enters the nitrogen storage tank 14. The separated liquid returns to the cryogenic water tank 6 through a pipeline, and then enters the pressurized water pump 8 together with the makeup water for the next cycle. The separated hydrate enters the hydrate decomposer 15 and is decomposed into water and natural gas. The natural gas is pressurized by the gas compressor 17 and enters the natural gas storage tank 18. The water produced by the decomposition returns to the cryogenic water tank 6 and enters the pressurized water pump 8 together with the makeup water for the next cycle. At this point, the decomposition of the mixed gas is completed.

[0053] Finally, it should be noted that the above embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit it. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the technical scope disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A pre-cooling mixed gas separation device for liquefied natural gas storage tanks, characterized in that: It includes a gas-liquid transport system, a hydrate generation system, a cooling heat exchange system, a hydrate decomposition system, a separation and collection system, and a data monitoring and collection system; The gas-liquid delivery system is used to deliver a mixture of nitrogen and natural gas; The hydrate generation system is connected to the gas-liquid transport system and is used to generate nanobubbles from the mixed gas. The cooling heat exchange system is connected to the hydrate generation system and is used to exchange heat between nanobubbles to generate hydrate slurry. The hydrate decomposition system is connected to a cooling heat exchange system and is used to decompose the hydrate slurry into hydrates, remaining unreacted gases, and unreacted water. The separation and collection system is connected to the hydrate decomposition system and is used to collect the hydrates decomposed by the hydrate decomposition system; The data monitoring and collection system is connected to the hydrate generation system, the hydrate decomposition system, and the cooling heat exchange system, respectively, and is used to collect relevant data.

2. The liquefied natural gas storage tank pre-cooling mixed gas separation device according to claim 1, characterized in that: The gas-liquid transport system includes a liquid nitrogen pipeline, an LNG pipeline, an LNG storage tank, a mixed gas discharge pipeline, and a heat exchanger. The liquid nitrogen pipeline and the LNG pipeline are respectively connected to the liquid inlet pipeline and the LNG storage tank. The LNG storage tank is connected to the mixed gas discharge pipeline, and the heat exchanger is connected to the mixed gas discharge pipeline.

3. The liquefied natural gas storage tank pre-cooling mixed gas separation device according to claim 2, characterized in that: The hydrate generation system includes a low-temperature water tank, a low-temperature water bath, a dosing pipe, a gas compressor, a pressurized water pump, and a nanobubble generator. The low-temperature water bath is connected to the low-temperature water tank, and the low-temperature water tank is connected to a heat exchanger and a dosing pipe. The nanobubble generator is connected to the low-temperature water tank via the pressurized water pump and the gas compressor.

4. The liquefied natural gas storage tank pre-cooling mixed gas separation device according to claim 3, characterized in that: The nanobubble generator includes a shell, a reaction chamber, a feeding section, and a discharging section. The reaction chamber is located inside the shell, and there is a cavity between the reaction chamber and the inner wall of the shell. The shell has air vents that communicate with the cavity. The feeding section and the discharging section are fixed at both ends of the shell and are connected to the inner cavity of the reaction chamber. The end of the reaction chamber near the feeding section has several air vents that communicate with the cavity.

5. The liquefied natural gas storage tank pre-cooling mixed gas separation device according to claim 4, characterized in that: The cooling heat exchange system includes a folded tubular reactor, which is connected to a low-temperature water bath and a nanobubble generator.

6. The liquefied natural gas storage tank pre-cooling mixed gas separation device according to claim 5, characterized in that: The folded tube reactor includes a box body and folded tubes, fins, spiral ribbons, a water collection chamber, a water distribution chamber, and baffles disposed within the box body. The two ends of the folded tubes are connected to the water collection chamber and the water distribution chamber, respectively. The water distribution chamber is connected to a nanobubble generator. The fins are evenly distributed on the outer wall of the folded tubes. The spiral ribbons are disposed inside the folded tubes. The baffles are evenly distributed on the outside of the folded tubes.

7. The liquefied natural gas storage tank pre-cooling mixed gas separation device according to claim 6, characterized in that: The hydrate decomposition system includes a hydrate separator and a hydrate decomposer. The hydrate separator is connected to the water collection chamber of the folded tubular reactor, and the hydrate decomposer is connected to both the hydrate separator and the low-temperature water tank.

8. The liquefied natural gas storage tank pre-cooling mixed gas separation device according to claim 7, characterized in that: The separation and collection system includes a nitrogen storage tank and a natural gas storage tank. The nitrogen storage tank is connected to a hydrate separator, and the natural gas storage tank is connected to a hydrate decomposer.

9. The liquefied natural gas storage tank pre-cooling mixed gas separation device according to claim 8, characterized in that: The data monitoring and collection system includes a PLC data acquisition processor and several temperature and pressure sensors. The temperature and pressure sensors are respectively installed in a low-temperature water tank, a low-temperature water bath, a folded tubular reactor, a hydrate separator, and a hydrate decomposer. The PLC data acquisition processor is connected to each temperature and pressure sensor.

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