Sea water desalination system and method based on density difference driving

Abstract

The invention discloses a sea water desalination system and method based on density difference driving, the sea water desalination system comprises an operation liquid supplementing pipeline (2), a sea water desalination pipeline (3), an external heat source (401), a fresh water collection pipeline (5) and a gas injection pipeline (6), the operation liquid supplementing pipeline (2) is communicated with the sea water desalination pipeline (3), the sea water desalination pipeline (3) comprises a heat exchanger (303), and the external heat source (401) is communicated with the heat exchanger (303). The external heat source (401) and the heat exchanger (303) can exchange heat, the seawater desalination pipeline (3) is communicated with the fresh water collection pipeline (5), and the gas injection pipeline (6) is communicated with the seawater desalination pipeline (3); the siphon effect is formed by setting the height difference for the running liquid supplementing pipeline, natural circulation flow is formed by utilizing the fluid density difference, traditional water pump driving forced circulation is replaced, dependence of the system on high-grade electric energy is remarkably reduced, external power input is not needed, and running is more stable.

Description

Technical Field

[0001] The present invention relates to the technical field of water resource utilization, and in particular to a seawater desalination system and method based on density difference drive. Background Art

[0002] The current social development is facing the problem of shortage of fresh water resources, and seawater desalination technology is an important means to solve this problem. The main seawater desalination methods currently include multi-stage flash evaporation, low-temperature multi-effect distillation, reverse osmosis, electrodialysis, membrane distillation, humidification and dehumidification technologies. Among them, multi-stage flash evaporation, low-temperature multi-effect distillation and reverse osmosis are still the main technologies in large-scale production. Although they have developed into mature technologies, their large-scale industrial applications still face bottleneck problems such as high energy consumption, high cost and low system efficiency. In terms of energy consumption, there is a significant contradiction between the grade and demand of energy in mainstream technologies: although multi-stage flash evaporation and low-temperature multi-effect distillation rely on low-grade waste heat, and high-temperature steam technology does not require thermal energy, high-pressure pumps consume a lot of electrical energy, and the flux attenuation problem of reverse osmosis membranes under high pressure further aggravates the waste of energy; in terms of desalination energy consumption, multi-stage flash evaporation and low-temperature multi-effect distillation technologies have high temperature requirements for thermal energy, and the reverse osmosis system directly consumes a large amount of high-grade electrical energy; in terms of system consumption, a large number of electric-driven water pumps are required to transport seawater when producing fresh water; in addition, the energy consumption problem in the seawater transportation link has long been ignored, and the continuous operation of electric-driven water pumps also requires a lot of energy consumption, which has become a key shortcoming restricting overall energy efficiency.

[0003] Patent document CN1583581A discloses a method and device for desalination of seawater, including an evaporator and a condenser installed at a certain height above the ocean. Deep cold seawater enters the condenser as a cooling medium through a deep water pump using the siphon principle, and surface warm seawater enters the evaporator through a shallow water pump using the siphon principle. The surface warm seawater is vaporized at room temperature by the vacuum generated in the evaporator at a certain height, and the resulting water vapor is cooled in the condenser to finally form fresh water. The deep cold seawater after heat exchange can also be used for seawater aquaculture. The power of the pump is mainly used to overcome the loss of pipeline resistance, and the energy mainly comes from the temperature difference of the ocean itself. The multi-stage flash evaporation and low-temperature multi-effect distillation technology have not been solved. The temperature requirements for thermal energy are high, and the production of fresh water requires an electric-driven water pump to transport seawater, which consumes a lot of energy.

[0004] Patent document CN1040261499B discloses a seawater temperature difference energy natural circulation seawater desalination device and desalination method, comprising a natural circulation connecting pipe, a flash tank provided with a vacuum pump, a condenser, a liquid storage tank provided with a water pump, a power supply device and connecting pipelines, wherein the vacuum pump and the water pump are powered by the power supply device, the upper part of the natural circulation connecting pipe is located in the flash tank and the lower part leads to below the sea surface, the bottom of the flash tank has an opening leading to below the sea surface, the depth of the natural circulation connecting pipe leading to below the sea surface is greater than the depth of the flash tank leading to below the sea surface, the buoyancy formed by the density difference between the surface warm seawater and the deep cold seawater is used as the driving force, so that the seawater enters from the bottom of the flash tank, but the multi-stage flash evaporation and low-temperature multi-effect distillation technologies have high temperature requirements for thermal energy, and the problem that electric-driven water pumps are required to transport seawater when producing fresh water consumes a lot of energy is not solved.

[0005] In summary, the above two existing patents have not solved the problem that multi-stage flash evaporation and low-temperature multi-effect distillation technologies have high temperature requirements for thermal energy, and that electric-driven water pumps are needed to transport seawater when producing fresh water, which consumes a lot of energy. Summary of the invention

[0006] Based on the above technical problems, the present invention proposes a seawater desalination system and method based on density difference drive to solve the problem that multi-stage flash evaporation and low-temperature multi-effect distillation technologies have high temperature requirements for thermal energy, and that electric-driven water pumps are needed to transport seawater when producing fresh water, consuming a large amount of energy.

[0007] To achieve the above object, the present invention proposes a seawater desalination system driven by density difference.

[0008] A seawater desalination system driven by density difference comprises an operating fluid replenishment pipeline, a seawater desalination pipeline, an external heat source, a fresh water collection pipeline and an air injection pipeline, wherein the operating fluid replenishment pipeline is connected to the seawater desalination pipeline, the seawater desalination pipeline comprises a heat exchanger, the external heat source and the heat exchanger are heat-exchangeable, the seawater desalination pipeline is connected to the fresh water collection pipeline, and the air injection pipeline is connected to the seawater desalination pipeline.

[0009] Furthermore, the seawater desalination pipeline includes a seawater mixing tank, and the seawater mixing tank is connected to the operation replenishment pipeline.

[0010] Furthermore, the seawater desalination pipeline includes a gas-liquid separation device, the fresh water collection pipeline includes a vacuum pump, and the gas-liquid separation device, the vacuum pump and the seawater mixing tank are connected by a pipeline.

[0011] Furthermore, the heat exchanger is arranged in the pipeline between the gas-liquid separation device and the seawater mixing tank, and is heat-exchangeable with the external heat source.

[0012] Furthermore, the seawater desalination pipeline includes an ascending pipeline and a descending pipeline, the ascending pipeline is connected to the top of the seawater mixing tank, and the descending pipeline is connected to the bottom or side of the seawater mixing tank at a position within 30% of the side height close to the bottom surface.

[0013] Furthermore, a portion of the rising pipeline is heat exchangeably arranged with the heat exchanger.

[0014] Furthermore, the seawater desalination pipeline comprises a flash evaporation device, and the flash evaporation device is arranged on the rising pipeline, between the heat exchanger and the gas-liquid separation device.

[0015] Furthermore, the gas injection pipeline includes a gas injection valve and an air source, the gas injection valve is connected to the portion of the rising pipeline between the seawater mixing tank and the heat exchanger; the air source enters the rising pipeline through the gas injection valve.

[0016] Furthermore, the fresh water collection pipeline includes a preheater, and the preheater is connected to the replenishment transport pipeline of the operating replenishment pipeline and the steam transport pipeline of the seawater desalination pipeline, so that the replenishment transport pipeline and the steam transport pipeline are heat exchangeably arranged.

[0017] Furthermore, the condenser is arranged at a downstream position where the steam transport pipeline passes through the preheater.

[0018] Furthermore, the fresh water collection pipeline includes a non-condensable gas precipitation chamber, and the non-condensable gas precipitation chamber is arranged downstream of the condenser.

[0019] Furthermore, the vacuum pump is connected to the non-condensable gas precipitation chamber.

[0020] Furthermore, the fresh water collecting pipeline includes a collecting water tank, and the collecting water tank is connected to the non-condensable gas precipitation chamber.

[0021] Furthermore, it includes an external cold source, and the external cold source and the condenser are heat exchangeably arranged.

[0022] Furthermore, the operating fluid replenishing pipeline includes a first operating water tank and a second operating water tank, and the first operating water tank and the second operating water tank are fluidically connected through a pipeline.

[0023] Furthermore, the second operating water tank is connected to the seawater desalination pipeline.

[0024] Furthermore, the positional relationship between the first operating water tank and the second operating water tank is that the bottom surface of the first operating water tank is arranged at a position higher than the liquid level in the second operating water tank.

[0025] Furthermore, the startup fluid replenishment pipeline is connected to the operation fluid replenishment pipeline, the seawater desalination pipeline and the fresh water collection pipeline.

[0026] A seawater desalination method based on density difference driving, comprising:

[0027] S2: opening the valve of the running liquid replenishment pipeline to replenish the seawater desalination pipeline, and starting the external heat source and the heat exchanger to heat the seawater in the seawater desalination pipeline;

[0028] S3: Open the valve of the fresh water collection pipeline to condense the steam generated in the seawater desalination pipeline into fresh water and collect it.

[0029] Furthermore, before step S2, the method further includes:

[0030] S1: Open the first start-up fluid replenishment valve, the second start-up fluid replenishment valve and the third start-up fluid replenishment valve of the start-up fluid replenishment pipeline, so that the fresh water in the start-up fluid replenishment pipeline flows into the operating fluid replenishment pipeline and the seawater desalination pipeline to discharge the air, and the gas-liquid separation device is evacuated by the vacuum pump to adjust the inside of the seawater desalination pipeline to a negative pressure state.

[0031] Furthermore, the step S2 includes:

[0032] The discharge control valve of the seawater desalination pipeline is opened to discharge the seawater in the seawater mixing tank at a fixed flow rate, and the replenishment flow rate is determined by the sum of the flow rates of the steam valve and the discharge control valve of the fresh water collection pipeline, and this is used as the opening of the third operating replenishment valve of the operating replenishment pipeline for replenishment.

[0033] Furthermore, the step S2 includes:

[0034] The air injection valve is opened to allow the external air source to be injected into the seawater desalination pipeline due to the pressure difference. The injected air flows upward, forcing the density of the ascending pipeline to be less than that of the descending pipeline, thereby inducing a positive circulation flow.

[0035] Furthermore, the step S3 includes:

[0036] When the liquid level in the non-condensable gas precipitation chamber rises, the fresh water valve is opened to collect the fresh water into the collection water tank.

[0037] Based on the above technical solution, the present invention has at least the following beneficial effects:

[0038] 1. The present invention proposes a seawater desalination system and method based on density difference drive, which forms a siphon effect by setting a height difference in the running replenishment pipeline and utilizes the natural circulation flow formed by the fluid density difference, replacing the traditional water pump driven forced circulation, significantly reducing the system's dependence on high-grade electric energy, reducing energy consumption, and requiring no external power input, making the operation more stable, and reducing the risks caused by mechanical failure or unstable power supply; in addition, since the system in the present invention adopts a passive design, it reduces dependence on electric energy, reduces the electricity cost during operation and the demand for high-grade energy.

[0039] 2. The present invention proposes a seawater desalination system and method based on density difference drive, which significantly improves the overall performance of the seawater desalination system through passive design and innovative system layout. Specifically, the natural circulation driven by density difference reduces the dependence on mechanical components, thereby reducing mechanical wear and failure rate, extending the service life of the system and reducing maintenance costs; at the same time, the multi-stage series and parallel array design realizes large-scale freshwater production, meets the freshwater needs of different scales, and shows good economic scalability; in addition, the system further improves the operation stability and desalination efficiency through automatic adjustment capabilities and efficient gas-liquid separation devices, reduces the energy consumption per unit of freshwater production, and improves the freshwater recovery rate. In general, the present invention achieves efficient, economical and sustainable seawater desalination while reducing energy consumption, improving system stability and extending service life, and provides an innovative technical solution to solve the problem of freshwater resource shortage.

[0040] 3. The present invention proposes a seawater desalination system and method based on density difference drive. Through the efficient seawater desalination technology, the shortage of fresh water resources is significantly alleviated, and it is particularly suitable for coastal areas and water-scarce areas. The system is environmentally friendly during operation, reduces dependence on traditional fresh water resources, and at the same time reduces energy consumption and demand for fossil fuels, thereby reducing carbon emissions, which is in line with the global trend of energy conservation and emission reduction. In addition, the present invention can effectively utilize renewable energy such as solar energy, industrial waste heat, and low-grade thermal energy, further improve energy utilization efficiency, reduce energy waste, and achieve efficient and sustainable water resource utilization and energy utilization, providing an innovative solution to solve water resource shortages and environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0042] Figure 1 A schematic structural diagram of a seawater desalination system based on density difference drive according to an embodiment is shown.

[0043] The above-mentioned drawings include the following reference numerals:

[0044] 1. Start the fluid replenishment pipeline; 2. Run the fluid replenishment pipeline; 3. Seawater desalination pipeline; 5. Fresh water collection pipeline; 6. Gas injection pipeline;

[0045] 101. Start the storage water tank; 102. Start the first liquid replenishing valve; 103. Start the second liquid replenishing valve; 104. Start the third liquid replenishing valve;

[0046] 201, first operation liquid replenishment valve; 202, first operation water tank; 203, operation liquid replenishment ascending pipeline; 213, liquid replenishment transport pipeline; 214, liquid replenishment preheating heat exchange pipeline; 204, operation liquid replenishment descending pipeline; 205, second operation liquid replenishment valve; 206, second operation water tank; 207, third operation liquid replenishment valve;

[0047] 301, seawater mixing tank; 302, first one-way valve; 303, heat exchanger; 304, ascending pipeline; 314, flash evaporation device; 305, gas-liquid separation device; 306, filter layer; 307, second one-way valve; 308, descending pipeline; 309, discharge control valve;

[0048] 401, external heat source; 402, external cold source;

[0049] 501, steam valve; 511, steam transport pipeline; 502, preheater; 503, condenser; 504, non-condensable gas precipitation chamber; 505, vacuum pump; 506, fresh water pipeline; 507, fresh water valve; 508, collection water tank;

[0050] 601. Air source; 602. Air injection valve. DETAILED DESCRIPTION

[0051] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0052] The present invention is further described in detail below in conjunction with specific embodiments, and these embodiments cannot be understood as limiting the scope of protection claimed by the present invention. The term "including" when used indicates the existence of a feature, but does not exclude the existence or addition of one or more other features; the orientation or position relationship indicated by the terms "lateral", "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inside", "outside", etc. is based on the orientation or position relationship shown in the drawings, which is only for the convenience of description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention; in addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance.

[0053] In the description, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected, or indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances. In addition, in the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0054] Example

[0055] The present invention proposes a seawater desalination system based on density difference drive, such as Figure 1 As shown in, it includes an operating fluid replenishment pipeline 2, a seawater desalination pipeline 3, an external heat source 401, a fresh water collecting pipeline 5 and an air injection pipeline 6, the operating fluid replenishment pipeline 2 is connected to the seawater desalination pipeline 3, the seawater desalination pipeline 3 includes a heat exchanger 303, the external heat source 401 and the heat exchanger 303 are heat exchangeable, the seawater desalination pipeline 3 is connected to the fresh water collecting pipeline 5, and the air injection pipeline 6 is connected to the seawater desalination pipeline 3.

[0056] Furthermore, in the present invention, "connectivity" refers to connecting different containers or devices through pipes, pipelines, etc., so as to realize the transmission and distribution of fluids such as gases or liquids; in such a connected system, fluids such as gases or liquids can flow from one container to another or from one device to another under the action of pressure difference.

[0057] Furthermore, in the present invention, "single-phase natural circulation" and "two-phase natural circulation" refer to a fluid circulation system in which the fluid always maintains a single or two physical phases, usually liquid or gas, throughout the entire circulation process, and the circulation power of the fluid mainly comes from the density change caused by the temperature difference inside the fluid, without the need for external mechanical power such as a water pump to drive the circulation.

[0058] Furthermore, the operating fluid replenishment pipeline 2 includes a first operating water tank 202, a first operating fluid replenishment valve 201, an operating fluid replenishment ascending pipeline 203, a fluid replenishment transport pipeline 213, a fluid replenishment preheating heat exchange pipeline 214, an operating fluid replenishment descending pipeline 204, a second operating fluid replenishment valve 205, a second operating water tank 206 and a third operating fluid replenishment valve 207.

[0059] Furthermore, the first operation water tank 202 is connected to the operation liquid replenishment ascending pipeline 203 through the first operation liquid replenishment valve 201, the outlet of the operation liquid replenishment ascending pipeline 203 is connected to the inlet of the liquid replenishment preheating heat exchange pipeline 214, and the operation liquid replenishment ascending pipeline 203 is connected to the operation liquid replenishment descending pipeline 204 through the liquid replenishment transport pipeline 213.

[0060] Furthermore, the replenishment preheating heat exchange pipeline 214 constitutes the cold side of the preheater 502 of the fresh water collecting pipeline 5, and the outlet of the replenishment preheating heat exchange pipeline 214 is connected to the operating replenishment descending pipeline 204 and is connected to the second operating water tank 206 by the second operating replenishment valve 205. The second operating water tank 206 is connected to the side of the seawater mixing tank 301 of the seawater desalination pipeline 3 at 65% of the height through the third operating replenishment valve 207.

[0061] Furthermore, the desalination pipeline 3 includes a seawater mixing tank 301, a first one-way valve 302, a heat exchanger 303, an ascending pipeline 304, a flash evaporation device 314, a gas-liquid separation device 305, a filter layer 306, a second one-way valve 307, a descending pipeline 308 and a discharge control valve 309.

[0062] Furthermore, the inlet of the ascending pipe 304 is connected to the top of the seawater mixing tank 301, and the outlet of the descending pipe 308 can be connected to the bottom or side of the seawater mixing tank 301 close to the bottom surface at 30% of the side height. In other embodiments, it can also be set at 20% or 15% of the side height.

[0063] Furthermore, the inlet of the discharge control valve 309 is connected to the bottom of the seawater mixing tank 301, the ascending pipeline 304 includes all the pipelines between the seawater mixing tank 301, the first one-way valve 302, the heat exchanger 303 and the gas-liquid separation device 305, the flash device 314 is installed on the inner side of the outlet section of the ascending pipeline 304, the seawater mixing tank 301 is connected to the inlet of the first one-way valve 302 by the ascending pipeline 304, the outlet of the first one-way valve 302 is connected to the cold side inlet of the heat exchanger 303, the cold side outlet of the heat exchanger 303 is connected to the inlet of the gas-liquid separation device 305, the filter layer 306 is placed inside the gas phase outlet side of the gas-liquid separation device 305, the gas phase outlet of the gas-liquid separation device 305 is connected to the fresh water collection pipeline 5, and the liquid phase outlet of the gas-liquid separation device 305 is connected to the descending pipeline 308 through the second one-way valve 307 and connected to the seawater mixing tank 301.

[0064] Furthermore, the external heat source 401 is connected to the hot side of the heat exchanger 303 in the seawater desalination pipeline 3 , and the external cold source 402 is connected to the cold side of the condenser 503 in the fresh water collection pipeline 5 .

[0065] Furthermore, the fresh water collection pipeline 5 includes a steam valve 501 , a steam transport pipeline 511 , a preheater 502 , a condenser 503 , a non-condensable gas precipitation chamber 504 , a vacuum pump 505 , a fresh water pipeline 506 , a fresh water valve 507 and a collection water tank 508 .

[0066] Furthermore, the steam valve 501 connects the seawater desalination pipeline 3 to the fresh water collecting pipeline 5, the hot side outlet of the preheater 502 is connected to the hot side inlet of the condenser 503, the hot side outlet of the condenser 503 is connected to the inlet of the non-condensable gas precipitation chamber 504, the gas outlet of the non-condensable gas precipitation chamber 504 is connected to the outside through the vacuum pump 505, and the liquid outlet of the non-condensable gas precipitation chamber 504 is connected to the collecting water tank 508 through the fresh water pipeline 506 and the fresh water valve 507.

[0067] Furthermore, the gas injection pipeline 6 comprises an air source 601 and a gas injection valve 602 , and the air source 601 is connected to the rising pipeline 304 between the seawater mixing tank 301 and the first one-way valve 302 in the seawater desalination assembly through the gas injection valve 602 .

[0068] To achieve the above object, the present invention further proposes a seawater desalination method based on density difference drive, using the seawater desalination system based on density difference drive according to the above, comprising the following steps:

[0069] A seawater desalination method based on density difference driving, comprising:

[0070] S1: Open the first start-up fluid replenishment valve 102, the second start-up fluid replenishment valve 103 and the third start-up fluid replenishment valve 104 of the start-up fluid replenishment pipeline 1, so that the fresh water in the start-up fluid replenishment pipeline 1 flows into the operating fluid replenishment pipeline 2 and the seawater desalination pipeline 3 to discharge the air, and the gas-liquid separation device 305 is evacuated by the vacuum pump 505, so that the inside of the seawater desalination pipeline 3 is adjusted to a negative pressure state.

[0071] Further, the first start-up liquid replenishment valve 102, the second start-up liquid replenishment valve 103, the third start-up liquid replenishment valve 104, the first operation liquid replenishment valve 201, the second operation liquid replenishment valve 205, the first one-way valve 302, the second one-way valve 307, the steam valve 501, the fresh water valve 507 of the start-up liquid replenishment pipeline 1, open the flow channel of the vacuum pump 505 but do not start the equipment, and the other valves remain closed, and the fresh water in the start-up water tank 101 fills the operation liquid replenishment pipeline 2, the seawater desalination pipeline 3 and the fresh water pipeline 506 of the fresh water collection pipeline 5 under the action of gravity. Among them, the original gas in the operation liquid replenishment pipeline 2 is discharged by the first operation liquid replenishment valve 201 and the second operation liquid replenishment valve 205, and when the operation liquid replenishment ascending pipeline 203, the liquid replenishment preheating heat exchange pipeline 214 and the operation liquid replenishment descending pipeline 204 are filled with fresh water, the first start-up liquid replenishment valve 102, the first operation liquid replenishment valve 201 and the second operation liquid replenishment valve 205 are closed and opened.

[0072] Furthermore, the original gas in the seawater desalination pipeline 3 is discharged from the flow channel of the vacuum pump 505 through the steam valve 501, and the gas in the fresh water pipeline 506 is discharged through the fresh water valve 507. When the seawater mixing tank 301, the cold side of the heat exchanger 303, the ascending pipeline 304, the descending pipeline 308 and the fresh water pipeline 506 are full of fresh water and the gas-liquid separation device 305 still retains 1 / 3 of the volume of the air cavity, the second start-up liquid replenishment valve 103, the third start-up liquid replenishment valve 104 and the fresh water valve 507 are closed, and the vacuum pump 505 is turned on to pump the remaining small part of the space to a certain vacuum degree and then closed.

[0073] S2: Open the valve of the operating liquid replenishment pipeline 2 to replenish the seawater desalination pipeline 3, and start the external heat source 401 and the heat exchanger 303 to heat the seawater in the seawater desalination pipeline 3.

[0074] Furthermore, the first operating liquid replenishment valve 201 and the second operating liquid replenishment valve 205 are opened, and a stable siphon flow is formed in the operating liquid replenishment pipeline 2, so that the seawater in the first operating water tank 202 flows into the second operating water tank 206 in sequence through the operating liquid replenishment ascending pipeline 203, the liquid replenishment preheating heat exchange pipeline 214 and the operating liquid replenishment descending pipeline 204.

[0075] Furthermore, the external heat source 401 is connected to the heat exchanger 303 to heat the seawater in the ascending pipeline 304. When the water temperature at the cold side outlet of the heat exchanger 303 is slightly lower than the operating temperature, the air injection valve 602 is opened. Since the local pressure of the ascending pipeline 304 at the connection is lower than the atmospheric pressure, the external air source 601 is injected into the seawater desalination pipeline 3. The injected air flows upward, forcing the density of the ascending pipeline 304 to be less than that of the descending pipeline 308, thereby realizing a positive circulation flow. The air is separated in the gas-liquid separation device 305 and enters the desalination pipeline 308. The collecting pipeline 5 is extracted by the vacuum pump 505 to keep the air cavity volume of the gas-liquid separation device 305 unchanged; after continuous gas injection for 1 minute to 3 minutes, the gas injection valve 602 and the steam valve 501 are closed, and after observing that the single-phase natural circulation in the loop is stable, the power of the external heat source 401 is increased to 50kw-100kw. In this embodiment, the power 401 of the external heat source 4 is increased to 75kw, which causes the seawater in the rising pipeline 304 to flash through the flash evaporation device 314, and the system changes from a single-phase natural circulation to a two-phase natural circulation.

[0076] S3: Open the valve of the fresh water collection pipeline 5 to condense the steam generated in the seawater desalination pipeline 3 into fresh water and collect it.

[0077] Furthermore, after startup, the drain control valve 309 is opened to discharge the seawater in the seawater mixing tank 301 at a fixed flow rate, and the replenishment flow rate is determined by the sum of the flow rates of the steam valve 501 and the drain control valve 309, and this is used as the opening of the third operating replenishment valve 207 to open the valve to replenish the system, and when fresh water vapor is observed to be generated, the steam valve 501 is opened, and the fresh water vapor enters the fresh water collection pipeline 5, and when the liquid level in the non-condensable gas precipitation chamber 504 rises, the fresh water valve 507 is opened to collect the fresh water into the collection tank 508.

[0078] In summary, it can be seen from the above description that the above embodiments of the present invention achieve the following technical effects:

[0079] 1. The present invention proposes a seawater desalination system and method based on density difference drive, which forms a siphon effect by setting a height difference in the running replenishment pipeline and utilizes the natural circulation flow formed by the fluid density difference, replacing the traditional water pump driven forced circulation, significantly reducing the system's dependence on high-grade electric energy, reducing energy consumption, and requiring no external power input, making the operation more stable, and reducing the risks caused by mechanical failure or unstable power supply. In addition, since the system in the present invention adopts a passive design, it reduces dependence on electric energy, reduces the electricity cost during operation and the demand for high-grade energy.

[0080] 2. The present invention proposes a seawater desalination system and method based on density difference drive, which significantly improves the overall performance of the seawater desalination system through passive design and innovative system layout. Specifically, the natural circulation driven by density difference reduces the dependence on mechanical components, thereby reducing mechanical wear and failure rate, extending the service life of the system and reducing maintenance costs; at the same time, the multi-stage series and parallel array design realizes large-scale freshwater production, meets the freshwater needs of different scales, and shows good economic scalability; in addition, the system further improves the operation stability and desalination efficiency through automatic adjustment capabilities and efficient gas-liquid separation devices, reduces the energy consumption per unit of freshwater production, and improves the freshwater recovery rate. In general, the present invention achieves efficient, economical and sustainable seawater desalination while reducing energy consumption, improving system stability and extending service life, and provides an innovative technical solution to solve the problem of freshwater resource shortage.

[0081] 3. The present invention proposes a seawater desalination system and method based on density difference drive. Through the efficient seawater desalination technology, the shortage of fresh water resources is significantly alleviated, and it is particularly suitable for coastal areas and water-scarce areas. The system is environmentally friendly during operation, reduces dependence on traditional fresh water resources, and at the same time reduces energy consumption and demand for fossil fuels, thereby reducing carbon emissions, which is in line with the global trend of energy conservation and emission reduction. In addition, the present invention can effectively utilize renewable energy such as solar energy, industrial waste heat, and low-grade thermal energy, further improve energy utilization efficiency, reduce energy waste, and achieve efficient and sustainable water resource utilization and energy utilization, providing an innovative solution to solve water resource shortages and environmental protection.

[0082] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0083] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0084] It should be noted that, in the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

Claims

1. A seawater desalination system based on density difference drive, characterized in that: The invention comprises an operating fluid replenishment pipeline (2), a seawater desalination pipeline (3), an external heat source (401), a fresh water collection pipeline (5) and an air injection pipeline (6); the operating fluid replenishment pipeline (2) is connected to the seawater desalination pipeline (3); the seawater desalination pipeline (3) comprises a heat exchanger (303); the external heat source (401) and the heat exchanger (303) are heat exchangeable; the seawater desalination pipeline (3) is connected to the fresh water collection pipeline (5); and the air injection pipeline (6) is connected to the seawater desalination pipeline (3).

2. The system according to claim 1, characterized in that: The seawater desalination pipeline (3) comprises a seawater mixing tank (301), The seawater mixing tank (301) is connected to the operating liquid replenishment pipeline (2).

3. The system according to claim 2, characterized in that: The seawater desalination pipeline (3) comprises a gas-liquid separation device (305), and the fresh water collection pipeline (5) comprises a vacuum pump (505). The gas-liquid separation device (305), the vacuum pump (505) and the seawater mixing tank (301) are connected via a pipeline.

4. The system according to claim 3, characterized in that: The heat exchanger (303) is arranged in the pipeline between the gas-liquid separation device (305) and the seawater mixing tank (301), and is heat-exchangeable with the external heat source (401).

5. The system according to claim 4, characterized in that: The seawater desalination pipeline (3) comprises an ascending pipeline (304) and a descending pipeline (308). The ascending pipeline (304) is connected to the top of the seawater mixing tank (301), and the descending pipeline (308) is connected to the bottom or side of the seawater mixing tank (301) at a position within 30% of the side height close to the bottom surface.

6. The system according to claim 5, characterized in that: A portion of the ascending pipeline (304) and the heat exchanger (303) are configured to exchange heat.

7. The system according to claim 5, characterized in that: The seawater desalination pipeline (3) includes a flash evaporation device (314) The flash evaporation device (314) is disposed on the ascending pipeline (304) between the heat exchanger (303) and the gas-liquid separation device (305).

8. The system according to claim 5, characterized in that: The gas injection pipeline (6) comprises a gas injection valve (602) and an air source (601). The air injection valve (602) is connected to a portion of the ascending pipeline (304) between the seawater mixing tank (301) and the heat exchanger (303); the air source (601) enters the ascending pipeline (304) through the air injection valve (602).

9. The system according to claim 3, characterized in that: The fresh water collection pipeline (5) comprises a preheater (502), The preheater (502) is connected to the replenishment transport pipeline (213) of the operating replenishment pipeline (2) and the steam transport pipeline (511) of the seawater desalination pipeline (3), so that the replenishment transport pipeline (213) and the steam transport pipeline (511) are heat-exchangeable.

10. The system according to claim 9, characterized in that: The fresh water collecting pipeline (5) comprises a condenser (503), The condenser (503) is disposed at a downstream position of the steam transport pipeline (511) passing through the preheater (502).

11. The system according to claim 10, characterized in that: The fresh water collection pipeline (5) comprises a non-condensable gas separation chamber (504), The non-condensable gas precipitation chamber (504) is arranged downstream of the condenser (503).

12. The system according to claim 11, characterized in that: The vacuum pump (505) is connected to the non-condensable gas precipitation chamber (504).

13. The system according to claim 11, characterized in that: The fresh water collection pipeline (5) comprises a collection water tank (508), The collecting water tank (508) is connected to the non-condensable gas precipitation chamber (504).

14. The system according to claim 11, characterized in that: including an external cooling source (402), The external cold source (402) and the condenser (503) are heat exchangeable.

15. The system according to claim 1, characterized in that: The operating fluid replenishing pipeline (2) comprises a first operating water tank (202) and a second operating water tank (206), The first operating water tank (202) and the second operating water tank (206) are fluidically connected via a pipeline.

16. The system according to claim 15, characterized in that: The second operating water tank (206) is connected to the seawater desalination pipeline (3).

17. The system according to claim 16, characterized in that: The positional relationship between the first operating water tank (202) and the second operating water tank (206) is that the bottom surface of the first operating water tank (202) is arranged at a position higher than the liquid level in the second operating water tank (206).

18. The system according to claim 1, characterized in that: It also includes starting the fluid infusion line (1), The startup liquid replenishment pipeline (1) is connected to the operation liquid replenishment pipeline (2), the seawater desalination pipeline (3) and the fresh water collection pipeline (5).

19. A desalination method based on the seawater desalination system according to any one of claims 1 to 18, characterized in that: include: S2: opening the valve of the operating liquid replenishment pipeline (2) to replenish the seawater desalination pipeline (3), and starting the external heat source (401) and the heat exchanger (303) to heat the seawater in the seawater desalination pipeline (3); S3: Open the valve of the fresh water collection pipeline (5) to condense the steam generated in the seawater desalination pipeline (3) into fresh water and collect it.

20. The method according to claim 19, characterized in that: Before step S2, the method further includes: S1: opening the first start-up liquid replenishment valve (102), the second start-up liquid replenishment valve (103) and the third start-up liquid replenishment valve (104) of the start-up liquid replenishment pipeline (1), allowing the fresh water in the start-up liquid replenishment pipeline (1) to flow into the operating liquid replenishment pipeline (2) and the seawater desalination pipeline (3) to discharge the air, and pumping the gas-liquid separation device (305) through the vacuum pump (505) to adjust the inside of the seawater desalination pipeline (3) to a negative pressure state.

21. The method according to claim 19, characterized in that: The step S2 includes: The discharge control valve (309) of the seawater desalination pipeline (3) is opened to discharge the seawater in the seawater mixing tank (301) at a fixed flow rate, and the replenishment flow rate is determined by the sum of the flow rates of the steam valve (501) of the fresh water collection pipeline (5) and the discharge control valve (309), and this is used as the opening of the third operating replenishment valve (207) of the operating replenishment pipeline (2) for replenishment.

22. The method according to claim 19, characterized in that: The step S2 includes: The air injection valve (602) is opened to allow the external air source (601) to be injected into the seawater desalination pipeline (3) due to the pressure difference. The injected air flows upward, forcing the density of the ascending pipeline (304) to be less than that of the descending pipeline (308), thereby inducing a positive circulation flow.

23. The method according to claim 19, characterized in that: The step S3 includes: When the liquid level in the non-condensable gas precipitation chamber (504) rises, the fresh water valve (507) is opened to collect fresh water into the collection water tank (508).

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