Concentration system and method for brackish water with low salt content

Abstract

The invention provides a low-salt-content brackish water concentration system and a low-salt-content brackish water concentration method. The low-salt-content brackish water concentration system comprises a fresh water tank, a concentrated water tank, a first water treatment device, a second water treatment device, an energy recovery device and a return pipeline, wherein an inlet of the second water treatment device is connected with a concentrated water outlet of the first water treatment device through a second pipeline; the pressure of concentrated water discharged from the concentrated water outlet of the second water treatment device is greater than that of concentrated water discharged from the concentrated water outlet of the first water treatment device; a high-pressure water outlet of the energy recovery device is connected with an inlet of the first water treatment device, and a high-pressure water inlet of the energy recovery device is connected with a concentrated water outlet of the second water treatment device through a fifth pipeline; an inlet of the return pipeline is communicated with a concentrated water outlet of the second water treatment device, and an outlet of the return pipeline is communicated with the fourth pipeline. Therefore, the low-salt-content brackish water concentration system disclosed by the invention is low in energy consumption and high in fresh water recovery rate.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, specifically to a low-salinity brackish water concentration system and method. Background Technology

[0002] Brackish water is an important water resource between freshwater and seawater. Utilizing reverse osmosis technology for its efficient desalination and concentration is of great significance in alleviating water shortages in arid inland areas. However, related technologies often face the following technical bottlenecks when treating this low-salinity brackish water and pursuing high recovery rates: 1. The contradiction between energy consumption and recovery rate: Increasing the recovery rate requires increasing the operating pressure or the number of membranes. For low-salinity water, the system operating pressure is already low, and the energy recovery from the residual pressure of the concentrate is often neglected or inefficient, resulting in insufficient overall energy consumption optimization. 2. Membrane stack efficiency limitations: When multiple membrane elements are connected in series to improve the single-stage recovery rate, the narrow permeate flow channel of the standard membrane element leads to a significant increase in internal pressure drop (freshwater side), resulting in insufficient driving force at the end of the membrane stack, which in turn limits the improvement of the recovery rate and may cause membrane compaction. 3. The challenge of controlling scaling risks: Under high recovery rate conditions, concentrate recirculation will drastically increase the concentration of scaling ions on the feed side. Traditional chemical scale inhibition methods have problems with reagent costs, environmental risks, and membrane fouling. Summary of the Invention

[0003] This invention aims to at least partially address one of the technical problems in related technologies. To this end, embodiments of this invention propose a low-salinity brackish water concentration system and method.

[0004] The low-salinity brackish water concentration system of this invention includes: A freshwater tank, the freshwater tank being used to contain freshwater; A concentrate tank, used to contain concentrate; A first water treatment device is used to recycle fresh water, and the fresh water outlet of the first water treatment device is connected to the fresh water tank through a first pipeline. The second water treatment device is used to recycle fresh water. The inlet of the second water treatment device is connected to the concentrated water outlet of the first water treatment device through a second pipeline. The fresh water outlet of the second water treatment device is connected to the fresh water tank. The concentrated water pressure discharged from the concentrated water outlet of the second water treatment device is greater than the concentrated water pressure discharged from the concentrated water outlet of the first water treatment device. An energy recovery device is provided, wherein the low-pressure inlet of the energy recovery device is connected to the outlet of the third pipeline, the inlet of the third pipeline is used to introduce brackish water, the high-pressure outlet of the energy recovery device is connected to the inlet of the first water treatment device through the fourth pipeline, the high-pressure inlet of the energy recovery device is connected to the concentrated water outlet of the second water treatment device through the fifth pipeline, and the low-pressure outlet of the energy recovery device is connected to the concentrated water tank. The return pipeline has its inlet connected to the concentrate outlet of the second water treatment device, and its outlet connected to the fourth pipeline.

[0005] Therefore, the low-salinity brackish water concentration system according to embodiments of the present invention consumes less energy and has a high freshwater recovery rate.

[0006] In some embodiments, the pressure of the slightly saline water at the outlet of the fourth pipeline is greater than or equal to 0.8 MPa and less than or equal to 2 MPa, and the operating pressure of the first water treatment device is greater than or equal to 0.8 MPa and less than or equal to 2 MPa. The pressure of the concentrated water discharged from the concentrated water outlet of the second water treatment device is greater than or equal to 4 MPa and less than or equal to 6 MPa.

[0007] In some embodiments, a high-pressure pump is provided on the second pipeline, and the concentrated water in the second pipeline is pressurized by the high-pressure pump and then introduced into the second water treatment device. A water pump is installed on the third pipeline.

[0008] In some embodiments, the first water treatment device is a water treatment membrane stack including reverse osmosis membrane elements; The reverse osmosis membrane element includes a housing, a permeate core tube, and a reverse osmosis membrane. The reverse osmosis membrane is wound around the outside of the permeate core tube and disposed inside the housing along with the permeate core tube. The reverse osmosis membrane comprises a screen, a membrane body, and a diaphragm screen stacked sequentially, wherein the thickness of the screen is greater than or equal to 1.2 mm and less than or equal to 1.8 mm.

[0009] In some embodiments, the membrane comprises a polyamide layer, an ultrafiltration membrane layer, and a nonwoven fabric layer stacked sequentially, wherein the thickness of the polyamide layer is greater than or equal to 5 μm.

[0010] In some embodiments, the salinity of the slightly saline water is greater than or equal to 1000 mg / L and less than or equal to 3000 mg / L; The salt content of the concentrated water discharged from the concentrated water outlet of the first water treatment device is greater than or equal to 20,000 mg / L and less than or equal to 30,000 mg / L; The salt content of the concentrated water discharged from the concentrated water outlet of the second water treatment device is greater than or equal to 60,000 mg / L and less than or equal to 70,000 mg / L.

[0011] In some embodiments, a scale inhibition device is provided on the return pipeline; The ratio of the concentrated water flow rate in the return pipeline to the concentrated water flow rate discharged from the concentrated water outlet of the second water treatment device is greater than or equal to 15% and less than or equal to 30%.

[0012] In some embodiments, the scale inhibition device is a pulse scale inhibition device capable of generating a high-frequency electromagnetic field or a preset frequency pulse signal. The energy recovery device is a pressure exchanger or a booster pump type energy recovery device; and / or The second water treatment device is a fouling-resistant desalination membrane device; and / or The return pipeline is equipped with a flow regulating valve.

[0013] The present invention also proposes a method for concentrating low-salinity brackish water using the above-mentioned low-salinity brackish water system, comprising the following steps: S1: Slightly saline water with a salt content greater than or equal to 1000 mg / L and less than or equal to 3000 mg / L is sent to the energy recovery device through the third pipeline for pressurization, and then transported to the first water treatment device through the fourth pipeline. The fresh water separated by the first water treatment device is transported to the fresh water tank through the first pipeline. S2: The concentrated water separated by the first water treatment device is pressurized and then fed into the second water treatment device, and the fresh water separated by the second water treatment device is fed into the fresh water tank. S3: The first part of the concentrated water separated by the second water treatment device is introduced into the fourth pipe through the return pipe and then into the first water treatment device. The second part of the concentrated water separated by the second water treatment device is introduced into the energy recovery device through the fifth pipe to release pressure in order to increase the water pressure of the brackish water, and then into the concentrated water tank.

[0014] In some embodiments, in step S1, the pressure at the inlet of the first water treatment device is greater than or equal to 0.8 MPa and less than or equal to 2 MPa. In step S2, the pressure at the inlet of the second water treatment device is greater than or equal to 4 MPa and less than or equal to 6 MPa. The return pipeline is equipped with a scale inhibitor. In step S3, the ratio of the concentrate flow rate in the return pipeline to the concentrate discharge flow rate from the outlet of the second water treatment device is greater than or equal to 15% and less than or equal to 30%. After the concentrate in the return pipeline is inhibited by the scale inhibitor, it is introduced into the fourth pipeline. The ratio of the concentrate flow rate in the fifth pipeline to the concentrate discharge flow rate from the outlet of the second water treatment device is greater than or equal to 70% and less than or equal to 85%. The salt content of the concentrated water discharged from the concentrated water outlet of the first water treatment device is greater than or equal to 20,000 mg / L and less than or equal to 30,000 mg / L; The salt content of the concentrated water discharged from the concentrated water outlet of the second water treatment device is greater than or equal to 60,000 mg / L and less than or equal to 70,000 mg / L. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of a low-salinity brackish water concentration system according to an embodiment of the present invention.

[0016] Figure 2 This is a schematic diagram of a reverse osmosis membrane element according to an embodiment of the present invention.

[0017] Figure label: 1. Freshwater pool; 2. Concentrate pool; 3. First water treatment device; 31. Shell; 32. Permeate core tube; 33. Reverse osmosis membrane; 34. Screen; 35. Membrane body; 36. Diaphragm screen. 4. Second water treatment unit; 5. Energy recovery device; 6. Scale inhibition device; 71. High-pressure pump; 72. Water supply pump; 73. Scale inhibition device; 81. First pipeline, 82. Second pipeline, 83. Third pipeline, 84. Fourth pipeline, 85. Fifth pipeline, 86. Return pipeline, 87. Sixth pipeline, 88. Seventh pipeline. Detailed Implementation

[0018] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0019] The low-salinity brackish water concentration system of the present invention is described below with reference to the accompanying drawings. Figure 1 and Figure 2As shown, the low salinity brackish water concentration system according to an embodiment of the present invention includes a freshwater tank 1, a concentrated water tank 2, a first water treatment device 3, a second water treatment device 4, an energy recovery device 5, and a return pipeline 86.

[0020] Freshwater tank 1 is used to hold freshwater, and concentrated water tank 2 is used to hold concentrated water. A first water treatment device 3 is used to recover freshwater, and its freshwater outlet is connected to freshwater tank 1 via a first pipe 81. A second water treatment device 4 is also used to recover freshwater. Its inlet is connected to the concentrated water outlet of the first water treatment device 3 via a second pipe 82, and its freshwater outlet is connected to freshwater tank 1. The pressure of the concentrated water discharged from the concentrated water outlet of the second water treatment device 4 is greater than that of the concentrated water discharged from the concentrated water outlet of the first water treatment device 3. Specifically, the freshwater separated from the slightly saline water by the first water treatment device 3 flows into freshwater tank 1, and the primary concentrated water separated by the first device flows into the second water treatment device 4. The freshwater separated again by the second device flows into freshwater tank 1. The pressure of the secondary concentrated water discharged from the concentrated water outlet of the second water treatment device 4 is greater than that of the primary concentrated water. For example, the freshwater outlet of the second water treatment device 4 is connected to the first pipe 81 via a sixth pipe 87. For example, the first water treatment device 3 has a freshwater recovery rate of greater than or equal to 80%.

[0021] The low-pressure inlet of the energy recovery device 5 is connected to the outlet of the third pipe 83, and the inlet of the third pipe 83 is used to introduce brackish water. The high-pressure outlet of the energy recovery device 5 is connected to the inlet of the first water treatment device 3 through the fourth pipe 84. The high-pressure inlet of the energy recovery device 5 is connected to the concentrate outlet of the second water treatment device 4 through the fifth pipe 85, and the low-pressure outlet of the energy recovery device 5 is connected to the concentrate tank 2. The inlet of the return pipe 86 is connected to the concentrate outlet of the second water treatment device 4, and the outlet of the return pipe 86 is connected to the fourth pipe 84.

[0022] Specifically, a portion of the secondary concentrate discharged from the concentrate outlet of the second water treatment device 4 is fed into the return pipe 86, and the other portion is fed into the energy recovery device 5. The secondary concentrate is fed into the high-pressure inlet of the energy recovery device 5, and then into the energy recovery device 5 to release pressure and form a low-pressure concentrate, which is then discharged from the low-pressure outlet of the energy recovery device 5 and fed into the concentrate pool 2.

[0023] After the brackish water enters the energy recovery device 5 through the third pipe 83, the secondary concentrate can increase the water pressure of the brackish water through the energy recovery device 5. The pressurized brackish water then enters the fourth pipe 84 and mixes with the secondary concentrate in the return pipe 86 before entering the first water treatment device 3. The energy recovery device 5 and the secondary concentrate in the return pipe 86 ensure that the water pressure entering the first water treatment device 3 meets its operating pressure requirements, thus enabling energy recovery and reducing energy consumption. Furthermore, the brackish water can undergo secondary treatment through the first water treatment device 3 and the second water treatment device 4. A portion of the resulting secondary concentrate, mixed with the brackish water, can be reintroduced into the first water treatment device 3 to separate fresh water, thereby improving the fresh water recovery rate. For example, the concentrate outlet of the second water treatment device 4 is connected to the return pipe 96 and the fifth pipe 85 through the seventh pipe 88.

[0024] Therefore, the low-salinity brackish water concentration system according to embodiments of the present invention consumes less energy and has a high freshwater recovery rate.

[0025] like Figure 1 As shown, in some embodiments, a water pump 72 is provided on the third pipeline 83, which can provide power to the slightly saline water in the third pipeline 83 so that it can enter the energy recovery device 5. For example, the energy recovery device 5 is a pressure exchanger or a booster pump type energy recovery device.

[0026] In some embodiments, a scale inhibition device 6 is provided on the return line 86. Specifically, the scale inhibition device 6 is a pulse scale inhibition device 6 capable of generating a high-frequency electromagnetic field or a preset (specific) frequency pulse signal. The scale inhibition device 6 uses a high-frequency electromagnetic field or a preset (specific) pulse to inhibit scale-forming ions (such as Ca²⁺) in the concentrated water. + CO3² - SO4² - The water undergoes physical modification to inhibit crystallization. This pretreated concentrate is then safely returned to the inlet side of the first water treatment unit 3 for further concentration. This loop increases the overall system recovery rate to over 85% without significantly increasing the risk of scaling in the primary inlet water.

[0027] In some embodiments, the ratio of the concentrate flow rate in the return line 86 to the concentrate discharge flow rate from the concentrate outlet of the second water treatment device 4 is greater than or equal to 15% and less than or equal to 30%. Specifically, a flow regulating valve is provided on the return line 86 to regulate the concentrate flow rate of the secondary concentrate in the return line 86. This allows the concentrate flow rate of the secondary concentrate in the return line 86 to account for 15% to 30% of the total secondary concentrate flow rate, and the concentrate flow rate of the secondary concentrate in the fifth line 85 to account for 70% to 85% of the total secondary concentrate flow rate.

[0028] like Figure 2As shown, in some embodiments, the first water treatment device 3 is a water treatment membrane stack including reverse osmosis membrane elements.

[0029] The reverse osmosis membrane element includes a housing 31, a permeate core tube 32, and a reverse osmosis membrane 33. The reverse osmosis membrane 33 is wound around the outside of the permeate core tube 32 and disposed inside the housing 31. The reverse osmosis membrane 33 includes a screen 34, a membrane body 35, and a diaphragm screen 36 stacked sequentially. Specifically, the housing 31 is tubular, with one end being the inlet and the other end being the concentrate outlet. The permeate core tube 32 is located at the central axis of the housing 31, and multiple freshwater inlet holes are formed on the tube wall. The reverse osmosis membrane 33 is wound around the outside of the permeate core tube 32 to form a multi-layered filtration annular structure. Slightly saline freshwater passes through the multi-layered reverse osmosis membrane 33 and enters the permeate core tube 32 through the freshwater inlet holes, so that the separated freshwater can be discharged from the permeate core tube 32, and the primary concentrate separated from the freshwater can be discharged from the concentrate outlet of the housing 31.

[0030] The thickness of screen 34 is greater than or equal to 1.2 mm and less than or equal to 1.8 mm. The relatively large thickness of screen 34 allows for increased feed water flow rate for slightly saline water. Membrane 35 comprises a polyamide layer, an ultrafiltration membrane layer, and a nonwoven fabric layer stacked sequentially, with the polyamide layer having a thickness greater than or equal to 5 μm. Specifically, the first water treatment device 3 employs a thickened reverse osmosis membrane element (the permeate flow channel is 1.2-1.8 times the standard thickness, and the polyamide layer thickness is greater than 5 μm), which significantly reduces the flow resistance (pressure drop) of the permeate within the membrane stack. Therefore, under relatively low feed water pressure, the effective driving force of each section of the membrane stack remains uniform, enabling stable primary recovery exceeding 85%.

[0031] In some embodiments, the pressure of the brackish water at the outlet of the fourth pipeline 84 is greater than or equal to 0.8 MPa and less than or equal to 2 MPa, and the operating pressure of the first water treatment device 3 is greater than or equal to 0.8 MPa and less than or equal to 2 MPa. The lower operating pressure of the first water treatment device 3 can reduce system energy consumption and keep the effective driving force of each section of the membrane stack uniform.

[0032] like Figure 1 As shown, in some embodiments, a high-pressure pump 71 is installed on the second pipeline 82. The concentrated water in the second pipeline 82 is pressurized by the high-pressure pump 71 and then introduced into the second water treatment device 4. Specifically, the increased secondary concentrated water is introduced into the second water treatment device 4 to meet the operating pressure of the second water treatment device 4. The pressure of the concentrated water discharged from the concentrated water outlet of the second water treatment device 4 is greater than or equal to 4 MPa and less than or equal to 6 MPa. For example, the second water treatment device 4 is a fouling-resistant desalination membrane device.

[0033] In some embodiments, the salinity of the brackish water is greater than or equal to 1000 mg / L and less than or equal to 3000 mg / L. The salinity of the concentrated water discharged from the concentrated water outlet of the first water treatment device 3 is greater than or equal to 20000 mg / L and less than or equal to 30000 mg / L. The salinity of the concentrated water discharged from the concentrated water outlet of the second water treatment device 4 is greater than or equal to 60000 mg / L and less than or equal to 70000 mg / L.

[0034] Specifically, the pretreated low-salinity brackish water (TDS 1000 mg / L-3000 mg / L) is first powered by the feed water pump 72, and then enters the most critical active energy recovery device 5 (pump / pressure exchanger) of the system. Here, the low-pressure raw water undergoes direct or indirect pressure exchange with the high-pressure concentrated wastewater (secondary concentrate) discharged from the second water treatment unit 4, thereby being pre-pressurized to 0.8 MPa-2.0 MPa. The pre-pressurized raw water enters the first water treatment unit 3. The first water treatment unit 3 produces high-quality fresh water (TDS < 300 mg / L) which enters the freshwater tank 1, while simultaneously generating pre-concentrated primary concentrate (TDS approximately 20000 mg / L-30000 mg / L).

[0035] The primary concentrate is pressurized a second time by high-pressure pump 71 to the desalination stage pressure (4.0-6.0 MPa), and then enters the second water treatment unit 4 for deep desalination and extreme concentration. The freshwater produced by this system is incorporated into the freshwater tank 1, and a secondary concentrate with extremely high concentration (TDS up to 60,000 mg / L-70,000 mg / L) is generated. The secondary concentrate, which accounts for approximately 70%-85% of the total secondary concentrate in the fifth pipeline 85, carries the high-pressure energy obtained from high-pressure pump 71 and enters the high-pressure side of the active energy recovery device 5, where it serves as the driving fluid to transfer its pressure energy to the incoming raw water. After the energy transfer is completed, the final concentrate, with pressure reduced to near atmospheric pressure, is discharged into the concentrate tank 2.

[0036] The present invention also proposes a method for concentrating low-salinity brackish water using a system according to embodiments of the present invention. The low-salinity brackish water concentration method includes the following steps: S1: Slightly saline water with a salt content greater than or equal to 1000 mg / L and less than or equal to 3000 mg / L is sent to the energy recovery device 5 through the third pipeline 83 for pressurization, and then transported to the first water treatment device 3 through the fourth pipeline 84. The fresh water separated by the first water treatment device 3 is transported to the freshwater tank 1 through the first pipeline 81. Specifically, the pressure at the inlet of the first water treatment device 3 is greater than or equal to 0.8 MPa and less than or equal to 2 MPa. S2: The concentrated water separated by the first water treatment device 3 is pressurized and then fed into the second water treatment device 4. The fresh water separated by the second water treatment device 4 is fed into the freshwater tank 1. Specifically, the primary concentrated water from the second pipeline 52 is pressurized by the high-pressure pump 41 and then fed into the second water treatment device 4. The pressure at the inlet of the second water treatment device 4 is greater than or equal to 4 MPa and less than or equal to 6 MPa. The salt content of the concentrated water discharged from the concentrated water outlet of the first water treatment device 3 is greater than or equal to 20,000 mg / L and less than or equal to 30,000 mg / L.

[0037] S3: The first portion of the concentrated water separated from the second water treatment device 4 is fed into the fourth pipe 84 through the return pipe 86 and then into the first water treatment device 3. The second portion of the concentrated water separated from the second water treatment device 4 is fed into the energy recovery device 5 through the fifth pipe 85 to release pressure and increase the water pressure of the slightly saline water, and then into the concentrated water tank 2. In step S3, the ratio of the concentrated water flow rate in the return pipe 86 to the concentrated water flow rate discharged from the concentrated water outlet of the second water treatment device 4 is greater than or equal to 15% and less than or equal to 30%. The concentrated water in the return pipe 86 is fed into the fourth pipe 84 after being inhibited by the scale inhibitor 6. The ratio of the concentrated water flow rate in the fifth pipe 85 to the concentrated water flow rate discharged from the concentrated water outlet of the second water treatment device 4 is greater than or equal to 70% and less than or equal to 85%. The salinity of the concentrated water discharged from the concentrated water outlet of the second water treatment device 4 is greater than or equal to 60,000 mg / L and less than or equal to 70,000 mg / L.

[0038] The first water treatment device 3 of the low-salinity brackish water concentration system according to an embodiment of the present invention employs a dedicated membrane element with a thickened product water flow channel and a modified reverse osmosis membrane layer. The polyamide layer thickness is greater than 5 μm, which significantly reduces the internal pressure drop under high flow rates. This allows the membrane stack to stably achieve a recovery rate of over 85% at a relatively low pressure of only 0.8-2.0 MPa, breaking through the efficiency bottleneck of traditional membrane stacks. The energy of the high-pressure concentrate (4.0-6.0 MPa) discharged from the second water treatment device 4 is directly utilized to pressurize the low-pressure raw water, forming the maximum usable pressure difference and achieving the theoretically optimal energy recovery efficiency, significantly reducing the overall energy consumption of the system. By physically modifying a portion of the high-concentration secondary concentrate through the pulse scale inhibitor 6 and then recirculating it to the first-stage feed water, the overall system recovery rate is increased to over 85%. Simultaneously, the formation and deposition of scale crystals are inhibited in a green and chemical-free manner, resolving the fundamental contradiction between high recovery rate and scaling risk, and ensuring the long-term operational stability of the system. The two-stage membrane system (a high-recovery membrane stack optimized for low salinity and a fouling-resistant desalination membrane system for deep concentration) works in a coordinated manner, combining intelligent reflux and efficient energy recovery. The system has a compact structure and high processing efficiency, and is particularly suitable for low-salinity and brackish water scenarios with a concentration of 1000mg / LTDS-3000mg / LTDS. It has excellent economic and environmental benefits.

[0039] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0040] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0041] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0042] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0043] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the 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.

[0044] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A low-salinity brackish water concentration system, characterized by, The system comprises: a fresh water pool for containing fresh water; a concentrated water pool for containing concentrated water; a first water treatment device for recovering fresh water, a fresh water outlet of the first water treatment device being communicated with the fresh water pool through a first pipeline; a second water treatment device for recovering fresh water, an inlet of the second water treatment device being connected with a concentrated water outlet of the first water treatment device through a second pipeline, a fresh water outlet of the second water treatment device being communicated with the fresh water pool, and a concentrated water outlet of the second water treatment device discharging concentrated water with a pressure greater than that of the concentrated water outlet of the first water treatment device; an energy recovery device, a low pressure water inlet of the energy recovery device being connected with an outlet of a third pipeline, an inlet of the third pipeline being used for passing brackish water, a high pressure water outlet of the energy recovery device being connected with an inlet of the first water treatment device through a fourth pipeline, and a high pressure water inlet of the energy recovery device being connected with the concentrated water outlet of the second water treatment device through a fifth pipeline, and a low pressure water outlet of the energy recovery device being communicated with the concentrated water pool; a reflux pipeline, an inlet of the reflux pipeline being communicated with the concentrated water outlet of the second water treatment device, and an outlet of the reflux pipeline being communicated with the fourth pipeline.

2. The low-salt-content brackish water concentration system according to claim 1, wherein a pressure of the brackish water at the outlet of the fourth pipeline is greater than or equal to 0.8 MPa and less than or equal to 2 MPa, and an operating pressure of the first water treatment device is greater than or equal to 0.8 MPa and less than or equal to 2 MPa; and a pressure of the concentrated water discharged from the concentrated water outlet of the second water treatment device is greater than or equal to 4 MPa and less than or equal to 6 MPa.

3. The low-salt-content brackish water concentration system according to claim 2, wherein a high pressure pump is arranged on the second pipeline, and the concentrated water in the second pipeline is pressurized by the high pressure pump and then passed into the second water treatment device; and a feed water pump is arranged on the third pipeline.

4. The low-salt-content brackish water concentration system according to claim 1, wherein the first water treatment device is a water treatment membrane stack comprising a reverse osmosis membrane element; the reverse osmosis membrane element comprises a shell, a permeate core pipe and a reverse osmosis membrane, the reverse osmosis membrane being wound outside the permeate core pipe and arranged in the shell together with the permeate core pipe; the reverse osmosis membrane comprises a screen, a membrane body and a diaphragm screen which are stacked in sequence, and a thickness of the screen is greater than or equal to 1.2 mm and less than or equal to 1.8 mm; and the membrane body comprises a polyamide layer, an ultrafiltration membrane layer and a non-woven fabric layer which are stacked in sequence, and a thickness of the polyamide layer is greater than or equal to 5 μm.

6. The low-salt-content brackish water concentration system according to any one of claims 1-5, wherein a salt content of the brackish water is greater than or equal to 1000 mg / L and less than or equal to 3000 mg / L; and a salt content of the concentrated water discharged from the concentrated water outlet of the first water treatment device is greater than or equal to 20000 mg / L and less than or equal to 30000 mg / L. ​ ​ ​ ​ ​ ​ 5. The low-salinity brackish water concentration system of claim 4, wherein, ​ ​ ​ ​ The salt content of the concentrated water discharged from the concentrated water outlet of the second water treatment device is greater than or equal to 60000 mg / L and less than or equal to 70000 mg / L.

7. The low-salt-content brackish water concentration system according to claim 6, wherein, A scale inhibition device is arranged on the reflux pipeline; The ratio of the concentrated water flow in the reflux pipeline to the concentrated water flow discharged from the concentrated water outlet of the second water treatment device is greater than or equal to 15% and less than or equal to 30%.

8. The low-salt-content brackish water concentration system according to claim 7, wherein, The scale inhibition device is a pulse scale inhibition device capable of generating a high-frequency electromagnetic field or a preset frequency pulse signal; The energy recovery device is a pressure exchanger or a booster pump type energy recovery device; and / or The second water treatment device is an anti-pollution seawater desalination membrane device; and / or A flow regulating valve is arranged on the reflux pipeline.

9. A method of utilizing the low-salt-content brackish water concentration system according to claims 1-8, characterized in that, The method comprises the following steps: S1: The brackish water with a salt content greater than or equal to 1000 mg / L and less than or equal to 3000 mg / L is sent into the energy recovery device through the third pipeline to increase the pressure, and then is transported into the first water treatment device through the fourth pipeline, and the fresh water separated by the first water treatment device is transported into the fresh water pool through the first pipeline; S2: The concentrated water separated by the first water treatment device is pressurized and then is introduced into the second water treatment device, and the fresh water separated by the second water treatment device is introduced into the fresh water pool; S3: A first part of the concentrated water separated by the second water treatment device is introduced into the first water treatment device through the reflux pipeline and then is introduced into the fourth pipeline, and a second part of the concentrated water separated by the second water treatment device is introduced into the energy recovery device through the fifth pipeline to release the pressure so as to increase the water pressure of the brackish water, and then is introduced into the concentrated water pool.

10. The low-salt-content brackish water concentration method according to claim 9, wherein, In the step S1, the pressure at the inlet of the first water treatment device is greater than or equal to 0.8 Mpa and less than or equal to 2 Mpa; In the step S2, the pressure at the inlet of the second water treatment device is greater than or equal to 4 Mpa and less than or equal to 6 Mpa; A scale inhibition device is arranged on the reflux pipeline, and in the step S3, the ratio of the concentrated water flow in the reflux pipeline to the concentrated water flow discharged from the concentrated water outlet of the second water treatment device is greater than or equal to 15% and less than or equal to 30%, the concentrated water in the reflux pipeline is introduced into the fourth pipeline after scale inhibition by the scale inhibition device, and the ratio of the concentrated water flow in the fifth pipeline to the concentrated water flow discharged from the concentrated water outlet of the second water treatment device is greater than or equal to 70% and less than or equal to 85%; The salt content of the concentrated water discharged from the concentrated water outlet of the first water treatment device is greater than or equal to 20000 mg / L and less than or equal to 30000 mg / L; The salt content of the concentrated water discharged from the concentrated water outlet of the second water treatment device is greater than or equal to 60000 mg / L and less than or equal to 70000 mg / L.

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