A seawater desalination system and method based on density difference driving

Abstract

The application discloses a seawater desalination system and method based on density difference driving, which comprises a running liquid supplement pipeline (2), a seawater desalination pipeline (3), an external heat source (401), a fresh water collection pipeline (5) and a gas injection pipeline (6), the running liquid supplement pipeline (2) is in communication with the seawater desalination pipeline (3), the seawater desalination pipeline (3) comprises a heat exchanger (303), the external heat source (401) is in heat exchangeable communication with the heat exchanger (303), the seawater desalination pipeline (3) is in communication with the fresh water collection pipeline (5), and the gas injection pipeline (6) is in communication with the seawater desalination pipeline (3). The application forms siphon effect by setting high-low difference of the running liquid supplement pipeline and forms natural circulation flow by using fluid density difference, replaces traditional water pump driven forced circulation, significantly reduces dependence of the system on high-grade electric energy, and does not need external power input and is more stable in operation.

Description

Technical Field

[0001] This invention relates to the field of water resource utilization technology, specifically to a seawater desalination system and method driven by density difference. Background Technology

[0002] The current social development faces the problem of freshwater shortage, and seawater desalination technology is an important means to solve this problem. At present, the main seawater desalination methods include multi-stage flash evaporation, low-temperature multi-effect distillation, reverse osmosis, electrodialysis, membrane distillation, and 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 all been developed into mature technologies, their large-scale industrial application still faces bottlenecks such as high energy consumption, high cost, and low system efficiency. In terms of energy consumption, there is a significant contradiction between the energy grade and demand of mainstream technologies: although multi-stage flash evaporation and low-temperature multi-effect distillation rely on low-grade waste heat, and although high-temperature steam technology does not require thermal energy, high-pressure pumps consume a lot of electrical energy, and the flux decay of reverse osmosis membranes under high pressure further exacerbates energy waste; 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 reverse osmosis systems directly consume a lot of high-grade electrical energy; in terms of system consumption, the production of freshwater requires a lot of electrically driven water pumps for seawater transportation; in addition, the energy consumption of seawater transportation has long been neglected, and the continuous operation of electrically driven water pumps also requires a lot of energy, becoming a key bottleneck restricting overall energy efficiency.

[0003] Patent document CN1583581A discloses a method and apparatus for seawater desalination, including an evaporator and a condenser installed at a certain height above the ocean. Deep cold seawater enters the condenser via a deep-water pump using the siphon principle to act as a cooling medium, while surface warm seawater enters the evaporator via a shallow-water pump using the siphon principle. The vacuum generated in the evaporator at a certain height allows the surface warm seawater to vaporize at room temperature. The resulting water vapor is cooled in the condenser, ultimately forming fresh water. The deep cold seawater after heat exchange can also be used for mariculture. The pump power is mainly used to overcome pipeline resistance losses, and the energy mainly comes from the ocean's own temperature difference. However, it does not solve the problem that multi-stage flash evaporation and low-temperature multi-effect distillation technologies have high temperature requirements for thermal energy, and that the production of fresh water requires electrically driven water pumps for seawater transportation, consuming a large amount of energy.

[0004] Patent document CN1040261499B discloses a seawater desalination device and method based on natural circulation using seawater temperature difference energy. The device includes a natural circulation connecting pipe, a flash tank equipped with a vacuum pump, a condenser, a storage tank equipped with a water pump, a power supply device, and connecting pipes. The vacuum pump and water pump are powered by the power supply device. The upper part of the natural circulation connecting pipe is located inside the flash tank, and the lower part extends below the seawater surface. The bottom of the flash tank has an opening extending below the seawater surface. The depth of the natural circulation connecting pipe extending below the seawater surface is greater than the depth of the flash tank extending below the seawater surface. The device utilizes the buoyancy force generated by the density difference between surface warm seawater and deep cold seawater as a driving force, allowing seawater to enter from the bottom of the flash tank. However, this method does not solve the problems of high temperature requirements for thermal energy in multi-stage flash evaporation and low-temperature multi-effect distillation technologies, and the need for electrically driven water pumps to transport seawater during freshwater production, which consumes a large amount of energy.

[0005] In summary, neither of the two existing patents mentioned above has solved the problems of the high temperature requirements for thermal energy in multi-stage flash evaporation and low-temperature multi-effect distillation technologies, and the need for electrically driven water pumps to transport seawater during freshwater production, which consumes a large amount of energy. Summary of the Invention

[0006] Based on the above-mentioned technical problems, this invention proposes a seawater desalination system and method driven by density difference, which solves the problems that multi-stage flash distillation and low-temperature multi-effect distillation technologies have high temperature requirements for thermal energy and require electrically driven water pumps to transport seawater during freshwater production, consuming a large amount of energy.

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

[0008] A density difference-driven seawater desalination system includes an operating replenishment pipeline, a seawater desalination pipeline, an external heat source, a freshwater collection pipeline, and an air injection pipeline. The operating replenishment pipeline is connected to the seawater desalination pipeline. The seawater desalination pipeline includes a heat exchanger. The external heat source and the heat exchanger are heat-exchangeable. The seawater desalination pipeline is connected to the freshwater collection pipeline. The air injection pipeline is connected to the seawater desalination pipeline.

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

[0010] Furthermore, the seawater desalination pipeline includes a gas-liquid separation device, the freshwater 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 located in the pipeline between the gas-liquid separation device and the seawater mixing tank, and is configured to exchange heat 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 of the bottom surface.

[0013] Furthermore, a portion of the riser pipe is configured to exchange heat with the heat exchanger.

[0014] Furthermore, the seawater desalination pipeline includes a flash evaporation device, which is located on the riser pipeline between the heat exchanger and the gas-liquid separator.

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

[0016] Furthermore, the freshwater collection pipeline includes a preheater, which is connected to the replenishment pipeline of the operating replenishment pipeline and the steam transport pipeline of the seawater desalination pipeline, so that the replenishment pipeline and the steam transport pipeline are heat exchangeable.

[0017] Furthermore, the condenser is located downstream of the steam transport pipeline after the preheater.

[0018] Furthermore, the freshwater collection pipeline includes a non-condensable gas release chamber, which is located downstream of the condenser.

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

[0020] Furthermore, the freshwater collection pipeline includes a collection tank, which is connected to the non-condensable gas release chamber.

[0021] Furthermore, it includes an external cold source, wherein the external cold source and the condenser are configured to exchange heat.

[0022] Furthermore, the operating replenishment pipeline includes a first operating water tank and a second operating water tank, which are fluidly 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 such that the bottom surface of the first operating water tank is positioned higher than the liquid level inside the second operating water tank.

[0025] Furthermore, the start-up replenishment pipeline is connected to the operation replenishment pipeline, the seawater desalination pipeline, and the freshwater collection pipeline.

[0026] A density difference-driven seawater desalination method includes:

[0027] S2: Open the valve of the operating replenishment pipeline to replenish the seawater desalination pipeline, and start the external heat source and the heat exchanger to heat the seawater in the seawater desalination pipeline;

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

[0029] Furthermore, before step S2, the following steps are also included:

[0030] S1: Open the first, second, and third start-up replenishment valves of the start-up replenishment pipeline to allow fresh water in the start-up replenishment pipeline to flow into the operating replenishment pipeline and the seawater desalination pipeline to expel air. The vacuum pump is then used to pump out the gas-liquid separation device, thereby adjusting the interior of the seawater desalination pipeline to a negative pressure state.

[0031] Further, step S2 includes:

[0032] Open the drain control valve of the seawater desalination pipeline to discharge seawater from the seawater mixing tank at a fixed flow rate. Determine the replenishment flow rate by the sum of the flow rates of the steam valve of the freshwater collection pipeline and the drain control valve, and use this as the opening degree of the third replenishment valve of the operating replenishment pipeline for replenishment.

[0033] Further, step S2 includes:

[0034] Opening the air injection valve allows external air to be injected into the seawater desalination pipeline due to the pressure difference. The injected air flows upward, forcing the density of the rising pipeline to be less than that of the falling pipeline, thereby inducing a positive circulation flow.

[0035] Further, step S3 includes:

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

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

[0038] 1. This invention proposes a seawater desalination system and method based on density difference drive. By setting a height difference in the operating replenishment pipeline to create a siphon effect and utilizing the natural circulation flow formed by the fluid density difference, it replaces the traditional water pump-driven forced circulation. This significantly reduces the system's dependence on high-grade electrical energy, lowers energy consumption, requires no external power input, and operates more stably, reducing the risks caused by mechanical failures or unstable power supply. Furthermore, because the system in this invention adopts a passive design, it reduces dependence on electrical energy, lowers the electricity cost during operation, and reduces the demand for high-grade energy.

[0039] 2. This invention proposes a density difference-driven seawater desalination system and method. Through passive design and innovative system layout, it significantly improves the overall performance of the seawater desalination system. Specifically, utilizing density difference-driven natural circulation reduces reliance on mechanical components, thereby reducing mechanical wear and failure rates, extending system lifespan, and lowering maintenance costs. Simultaneously, the multi-stage series and parallel array design enables large-scale freshwater production, meeting freshwater demands of varying scales and demonstrating excellent economic scalability. Furthermore, the system's automatic adjustment capabilities and efficient gas-liquid separation device further enhance operational stability and desalination efficiency, reducing energy consumption per unit of freshwater production and increasing freshwater recovery rate. Overall, this invention achieves efficient, economical, and sustainable seawater desalination while reducing energy consumption, improving system stability, and extending lifespan, providing an innovative technical solution to the problem of freshwater resource scarcity.

[0040] 3. This invention proposes a density difference-driven seawater desalination system and method, which significantly alleviates the problem of freshwater shortage through efficient seawater desalination technology, and is particularly suitable for coastal and water-scarce areas. The system is environmentally friendly during operation, reducing dependence on traditional freshwater resources, while also reducing energy consumption and the demand for fossil fuels, thereby reducing carbon emissions and conforming to the global trend of energy conservation and emission reduction. In addition, this invention can effectively utilize renewable energy sources such as solar energy and industrial waste heat, as well as low-grade heat energy, further improving energy utilization efficiency, reducing energy waste, and achieving efficient and sustainable water and energy utilization, providing an innovative solution to solve water shortage and environmental protection. Attached Figure Description

[0041] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0042] Figure 1 A schematic diagram of a density difference-driven seawater desalination system according to one embodiment is shown.

[0043] The above figures include the following reference numerals:

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

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

[0046] 201. First operating replenishment valve; 202. First operating water tank; 203. Operating replenishment riser pipeline; 213. Replenishment transport pipeline; 214. Replenishment preheating heat exchange pipeline; 204. Operating replenishment faller pipeline; 205. Second operating replenishment valve; 206. Second operating water tank; 207. Third operating replenishment valve;

[0047] 301. Seawater mixing tank; 302. First one-way valve; 303. Heat exchanger; 304. Ascending pipeline; 314. Flash evaporator; 305. Gas-liquid separator; 306. Filter layer; 307. Second one-way valve; 308. Downsink pipeline; 309. Drainage 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 release chamber; 505. Vacuum pump; 506. Fresh water pipeline; 507. Fresh water valve; 508. Water collection tank;

[0050] 601. Air source; 602. Air injection valve. Detailed Implementation

[0051] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0052] The present invention will be further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed by the present invention. The term "comprising" indicates the presence of a feature, but does not exclude the presence or addition of one or more other features. The terms "lateral," "upper," "lower," "front," "rear," "left," "right," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the purpose of description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0053] In this description, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0054] Example

[0055] This invention proposes a seawater desalination system driven by density difference, such as... Figure 1 As shown, the system includes a liquid replenishment pipeline 2, a seawater desalination pipeline 3, an external heat source 401, a freshwater collection pipeline 5, and an air injection pipeline 6. The liquid 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 freshwater collection pipeline 5. The air injection pipeline 6 is connected to the seawater desalination pipeline 3.

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

[0057] Furthermore, in this 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 throughout the entire circulation process, usually liquid or gas, 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 water pumps to drive the circulation.

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

[0059] Furthermore, the first operating water tank 202 is connected to the operating replenishment riser pipeline 203 via the first operating replenishment valve 201, the outlet of the operating replenishment riser pipeline 203 is connected to the inlet of the replenishment preheating heat exchange pipeline 214, and the operating replenishment riser pipeline 203 is connected to the operating replenishment downcomer pipeline 204 via the replenishment transport pipeline 213.

[0060] Furthermore, the preheating heat exchange pipeline 214 forms the cold side of the preheater 502 of the freshwater collection pipeline 5. The outlet of the preheating heat exchange pipeline 214 is connected to the operating preheating downflow pipeline 204 and is connected to the second operating water tank 206 by the second operating preheating 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 a height of 65% through the third operating preheating valve 207.

[0061] Furthermore, the seawater 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 evaporator 314, a gas-liquid separator 305, a filter layer 306, a second one-way valve 307, a downcomer pipeline 308, and a drain control valve 309.

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

[0063] Furthermore, the inlet of the drain control valve 309 is connected to the bottom of the seawater mixing tank 301. The riser pipe 304 includes all the piping between the seawater mixing tank 301, the first one-way valve 302, the heat exchanger 303, and the gas-liquid separator 305. The flash evaporator 314 is installed inside the outlet section of the riser pipe 304. The seawater mixing tank 301 is connected to the inlet of the first one-way valve 302 via the riser pipe 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 separator 305. The filter layer 306 is placed inside the gas phase outlet side of the gas-liquid separator 305. The gas phase outlet of the gas-liquid separator 305 is connected to the freshwater collection pipe 5. The liquid phase outlet of the gas-liquid separator 305 is connected to the downcomer pipe 308 via the second one-way valve 307 and then 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 freshwater collection pipeline 5.

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

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

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

[0068] To achieve the above objectives, the present invention also proposes a seawater desalination method based on density difference, using a seawater desalination system based on density difference as described above, comprising the following steps:

[0069] A density difference-driven seawater desalination method includes:

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

[0071] Further, the first start-up replenishment valve 102, the second start-up replenishment valve 103, the third start-up replenishment valve 104, the first operating replenishment valve 201, the second operating replenishment valve 205, the first one-way valve 302, the second one-way valve 307, the steam valve 501, and the freshwater valve 507 of the start-up replenishment pipeline 1 are opened, but the equipment is not started. The remaining valves remain closed. Under the action of gravity, the freshwater in the start-up water tank 101 fills the freshwater pipeline 506 of the operating replenishment pipeline 2, the seawater desalination pipeline 3, and the freshwater collection pipeline 5. Among them, the gas originally in the operating replenishment pipeline 2 is discharged by the first operating replenishment valve 201 and the second operating replenishment valve 205. After the operating replenishment riser pipeline 203, the replenishment preheating heat exchange pipeline 214, and the operating replenishment faller pipeline 204 are filled with freshwater, the first start-up replenishment valve 102, the first operating replenishment valve 201, and the second operating replenishment valve 205 are closed and opened.

[0072] Furthermore, the gas originally present in the seawater desalination pipeline 3 is discharged through the steam valve 501 via the flow channel of the vacuum pump 505, and the gas in the freshwater pipeline 506 is discharged through the freshwater valve 507. When the seawater mixing tank 301, the cold side of the heat exchanger 303, the riser pipeline 304, the downcomer pipeline 308, and the freshwater pipeline 506 are filled with freshwater and the gas-liquid separator 305 still retains 1 / 3 of its volume of gas chamber, the second start-up liquid replenishment valve 103, the third start-up liquid replenishment valve 104, and the freshwater valve 507 are closed, and the vacuum pump 505 is turned on to evacuate the remaining small portion of space to a certain vacuum level before being shut off.

[0073] S2: Open the valve of the operating 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, by opening the first operating replenishment valve 201 and the second operating replenishment valve 205, a stable siphon flow is formed in the operating replenishment pipeline 2, causing the seawater in the first operating water tank 202 to flow into the second operating water tank 206 by itself through the operating replenishment rising pipeline 203, the replenishment preheating heat exchange pipeline 214 and the operating replenishment falling pipeline 204.

[0075] Furthermore, an external heat source 401 is connected to the heat exchanger 303 to heat the seawater in the riser pipe 304. When the cold-side outlet water temperature of the heat exchanger 303 is slightly lower than the operating temperature, the air injection valve 602 is opened. Since the local pressure in the riser pipe 304 at the connection is lower than atmospheric pressure at this time, the external air source 601 injects air into the seawater desalination pipe 3. The injected air flows upward, forcing the density in the riser pipe 304 to be less than that in the fallr pipe 308, thereby achieving positive circulation. The air is separated in the gas-liquid separator 305 and enters the freshwater. The collection pipe 5 is drawn out by the vacuum pump 505 to keep the volume of the gas chamber of the gas-liquid separator 305 constant. After continuously injecting gas for 1 to 3 minutes, the gas injection valve 602 and the steam valve 501 are closed. After observing that the circuit maintains a stable single-phase natural circulation, the power of the external heat source 401 is increased to 50 kW to 100 kW. In this embodiment, the power of the external heat source 401 is increased to 75 kW, which causes the seawater in the riser pipe 304 to undergo flash evaporation through the flash evaporator 314, and the system changes from single-phase natural circulation to two-phase natural circulation.

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

[0077] Furthermore, after startup, the drain control valve 309 is opened to discharge seawater from the seawater mixing tank 301 at a fixed flow rate. 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 degree of the third operating replenishment valve 207 to replenish the system. 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. 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, as can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0079] 1. This invention proposes a seawater desalination system and method based on density difference drive. By setting a height difference in the operating replenishment pipeline to form a siphon effect and utilizing the natural circulation flow formed by the fluid density difference, it replaces the traditional water pump-driven forced circulation. This significantly reduces the system's dependence on high-grade electrical energy, lowers energy consumption, requires no external power input, and operates more stably, reducing the risks caused by mechanical failures or unstable power supply. In addition, because the system in this invention adopts a passive design, it reduces dependence on electrical energy, lowers the electricity cost during operation, and reduces the demand for high-grade energy.

[0080] 2. This invention proposes a density difference-driven seawater desalination system and method. Through passive design and innovative system layout, it significantly improves the overall performance of the seawater desalination system. Specifically, utilizing density difference-driven natural circulation reduces reliance on mechanical components, thereby reducing mechanical wear and failure rates, extending system lifespan, and lowering maintenance costs. Simultaneously, the multi-stage series and parallel array design enables large-scale freshwater production, meeting freshwater demands of varying scales and demonstrating excellent economic scalability. Furthermore, the system's automatic adjustment capabilities and efficient gas-liquid separation device further enhance operational stability and desalination efficiency, reducing energy consumption per unit of freshwater production and increasing freshwater recovery rate. Overall, this invention achieves efficient, economical, and sustainable seawater desalination while reducing energy consumption, improving system stability, and extending lifespan, providing an innovative technical solution to the problem of freshwater resource scarcity.

[0081] 3. This invention proposes a density difference-driven seawater desalination system and method, which significantly alleviates the problem of freshwater shortage through efficient seawater desalination technology, and is particularly suitable for coastal and water-scarce areas. The system is environmentally friendly during operation, reducing dependence on traditional freshwater resources, while also reducing energy consumption and the demand for fossil fuels, thereby reducing carbon emissions and conforming to the global trend of energy conservation and emission reduction. In addition, this invention can effectively utilize renewable energy sources such as solar energy and industrial waste heat, as well as low-grade heat energy, further improving energy utilization efficiency, reducing energy waste, and achieving efficient and sustainable water and energy utilization, providing an innovative solution to solve water shortage and environmental protection.

[0082] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0083] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0084] It should be noted that, in the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

Claims

1. A seawater desalination system driven by density difference, characterized in that, The system includes a liquid replenishment pipeline (2), a seawater desalination pipeline (3), an external heat source (401), a freshwater collection pipeline (5), and an air injection pipeline (6). The liquid 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 freshwater collection pipeline (5). The air injection pipeline (6) is connected to the seawater desalination pipeline (3). The seawater desalination pipeline (3) includes a seawater mixing tank (301), which is connected to the operation replenishment pipeline (2). The seawater desalination pipeline (3) includes 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 close to 30% of the side height of the bottom surface. The air injection pipeline (6) includes an air injection valve (602) and an air source (601). The air injection valve (602) is connected to a portion of the riser pipeline (304) between the seawater mixing tank (301) and the heat exchanger (303). The air source (601) enters the riser pipeline (304) through the air injection valve (602).

2. The system according to claim 1, characterized in that, The seawater desalination pipeline (3) includes a gas-liquid separation device (305), and the freshwater collection pipeline (5) includes a vacuum pump (505). The gas-liquid separation device (305), the vacuum pump (505), and the seawater mixing tank (301) are connected by a pipeline.

3. The system according to claim 2, characterized in that, The heat exchanger (303) is located 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).

4. The system according to claim 3, characterized in that, A portion of the riser pipe (304) is heat-exchangeable with the heat exchanger (303).

5. The system according to claim 4, characterized in that, The seawater desalination pipeline (3) includes a flash evaporation device (314). The flash evaporation device (314) is located on the riser pipe (304), between the heat exchanger (303) and the gas-liquid separator (305).

6. The system according to claim 2, characterized in that, The freshwater collection pipeline (5) includes 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.

7. The system according to claim 6, characterized in that, The freshwater collection pipeline (5) includes a condenser (503). The condenser (503) is located downstream of the steam transport pipeline (511) after the preheater (502).

8. The system according to claim 7, characterized in that, The freshwater collection pipeline (5) includes a non-condensable gas release chamber (504). The non-condensable gas release chamber (504) is located downstream of the condenser (503).

9. The system according to claim 8, characterized in that, The vacuum pump (505) is connected to the noncondensable gas release chamber (504).

10. The system according to claim 8, characterized in that, The freshwater collection pipeline (5) includes a collection tank (508). The water collection tank (508) is connected to the non-condensable gas release chamber (504).

11. The system according to claim 8, characterized in that, Including external cold source (402). The external cold source (402) and the condenser (503) are configured to exchange heat.

12. The system according to claim 1, characterized in that, The operating replenishment pipeline (2) includes 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 fluidly connected through a pipe.

13. The system according to claim 12, characterized in that, The second operating water tank (206) is connected to the seawater desalination pipeline (3).

14. The system according to claim 13, characterized in that, The positional relationship between the first operating water tank (202) and the second operating water tank (206) is such that the bottom surface of the first operating water tank (202) is positioned higher than the liquid level inside the second operating water tank (206).

15. The system according to claim 1, characterized in that, It also includes starting the replenishment pipeline (1). The start-up replenishment pipeline (1) is connected to the operation replenishment pipeline (2), the seawater desalination pipeline (3), and the freshwater collection pipeline (5).

16. A desalination method based on the seawater desalination system according to any one of claims 1-15, characterized in that, include: S2: Open the valve of the operating 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); S3: Open the valve of the freshwater collection pipeline (5) to condense the steam generated in the seawater desalination pipeline (3) into freshwater and collect it.

17. The method according to claim 16, characterized in that, Before step S2, the method further includes: S1: Open the first start-up replenishment valve (102), the second start-up replenishment valve (103) and the third start-up replenishment valve (104) of the start-up replenishment pipeline (1) so that the fresh water in the start-up replenishment pipeline (1) flows into the running replenishment pipeline (2) and the seawater desalination pipeline (3) to expel the air, and use the vacuum pump (505) to pump out the gas-liquid separation device (305) so that the inside of the seawater desalination pipeline (3) is adjusted to a negative pressure state.

18. The method according to claim 16, characterized in that, Step S2 includes: Open the drain control valve (309) of the seawater desalination pipeline (3) to discharge seawater from the seawater mixing tank (301) at a fixed flow rate. Determine the replenishment flow rate by the sum of the flow rates of the steam valve (501) of the freshwater collection pipeline (5) and the drain control valve (309), and use this as the opening degree of the third operating replenishment valve (207) of the operating replenishment pipeline (2) for replenishment.

19. The method according to claim 16, characterized in that, Step S2 includes: Open the air injection valve (602) so that the external air source (601) is injected into the seawater desalination pipeline (3) due to the pressure difference. The injected air flows upward, forcing the density of the rising pipeline (304) to be less than that of the falling pipeline (308), thereby inducing a positive circulation flow.

20. The method according to claim 16, characterized in that, 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 tank (508).

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