A membrane method seawater desalination system for concentrated water stabilization resource

Abstract

The application relates to the technical field of seawater desalination, and discloses a membrane method seawater desalination system capable of stably recycling concentrated water. The system comprises a first-stage two-section seawater reverse osmosis device, a first-stage two-section fresh water reverse osmosis device, an industrial water tank and a concentrated water discharge port. Raw seawater enters the seawater reverse osmosis device, the water produced by the seawater reverse osmosis device is connected to the industrial water tank and the fresh water reverse osmosis device in two ways, and the concentrated water is discharged and returned to the water inlet of the seawater reverse osmosis device in two ways; the water produced by the fresh water reverse osmosis device is connected to the industrial water tank, and the concentrated water is returned to the water inlet of the seawater reverse osmosis device. The system can adapt to wide-range water TDS fluctuation, simultaneously produce high-quality industrial water and concentrated water with stable concentration, improve water resource utilization rate and reduce operation cost.

Description

Technical Field

[0001] This application relates to the field of seawater desalination technology, specifically to a membrane-based seawater desalination system for the stable resource utilization of concentrate. Background Technology

[0002] Membrane desalination is one of the most widely used seawater desalination technologies. With the continuous growth of industrial water demand, higher requirements are being placed on the operational stability, water resource utilization rate, and concentrate treatment capacity of seawater desalination systems. Existing membrane desalination systems are significantly affected by fluctuations in influent water quality during actual operation, making it difficult to maintain stable system operating parameters. Water resource recovery rates are low, and the generated concentrate cannot be directly utilized and must be discharged, resulting in water waste and environmental burden. Furthermore, the stability of the produced water quality is insufficient to meet the demands of high-quality industrial water. Summary of the Invention

[0003] To solve, or at least partially solve, the above-mentioned technical problems, this application provides a membrane-based seawater desalination system for the stable resource utilization of concentrate.

[0004] This application provides a membrane-based seawater desalination system for the stable resource utilization of concentrate. The system is designed to adapt to a wide range of feed water TDS fluctuations while producing high-quality industrial water and concentrate with stable concentration. The system includes a first-stage two-stage seawater reverse osmosis unit, a first-stage two-stage freshwater reverse osmosis unit, an industrial water tank, and a concentrate discharge outlet.

[0005] The raw seawater enters the first-stage two-stage seawater reverse osmosis device. The product water of the first-stage two-stage seawater reverse osmosis device is divided into first product water and second product water. The first product water is connected to the industrial water tank, and the second product water is connected to the inlet of the first-stage two-stage freshwater reverse osmosis device.

[0006] The concentrate of the first-stage two-stage seawater reverse osmosis device is divided into a first concentrate and a second concentrate. The first concentrate is discharged from the system through the concentrate outlet, and the second concentrate flows back to the inlet of the first-stage two-stage seawater reverse osmosis device.

[0007] The permeate from the first-stage two-stage freshwater reverse osmosis unit is connected to the industrial water tank, and the concentrate from the first-stage two-stage freshwater reverse osmosis unit is all returned to the inlet of the first-stage two-stage seawater reverse osmosis unit.

[0008] Optionally, the recirculation ratio of the second concentrate in the first-stage two-stage seawater reverse osmosis device is adjusted in real time according to the feed water TDS, so that the concentration of the first concentrate discharged from the concentrate outlet is kept above the first concentration threshold.

[0009] Optionally, the ratio of the first product water to the second product water in the first-stage two-stage seawater reverse osmosis device is adjusted in real time according to the influent TDS and temperature, so that the effluent TDS in the industrial water tank is kept below the second concentration threshold.

[0010] Optionally, the first-stage two-stage seawater reverse osmosis device includes a first-stage unit and a second-stage unit, wherein the second-stage unit can switch between a water production mode and a pure concentration mode;

[0011] When the TDS of the feed water is lower than the third concentration threshold, the second-stage unit switches to the pure concentration mode and does not produce water. All the produced water of the first-stage two-stage seawater reverse osmosis device comes from the first-stage unit. When in the water production mode, both the first-stage unit and the second-stage unit produce water.

[0012] Optionally, the concentrate of the first-stage two-stage freshwater reverse osmosis device is divided into a first reflux concentrate and a second reflux concentrate. The first reflux concentrate is refluxed to the middle inlet of the first stage unit of the first-stage two-stage seawater reverse osmosis device, and the second reflux concentrate is refluxed to the main inlet of the first-stage two-stage seawater reverse osmosis device.

[0013] Optionally, the system further includes a concentrate storage tank;

[0014] The first concentrated water of the first-stage two-stage seawater reverse osmosis device first enters the concentrated water storage tank, and is discharged in batches after the concentrated water concentration in the concentrated water storage tank reaches the fourth concentration threshold.

[0015] When the TDS of the feed water changes abruptly, the concentrate in the concentrate storage tank can be returned to the inlet of the first-stage two-stage seawater reverse osmosis unit.

[0016] Optionally, each membrane housing of the first-stage two-stage seawater reverse osmosis unit is equipped with a diversion valve at its permeate outlet, and the diversion valve switches the flow direction according to the TDS of the permeate from the corresponding membrane housing.

[0017] When the TDS of the permeate from the membrane housing is lower than the fifth concentration threshold, the permeate from the membrane housing is connected to the industrial water tank; when the TDS of the permeate from the membrane housing is higher than the fifth concentration threshold, the permeate from the membrane housing is connected to the inlet of the first-stage two-stage freshwater reverse osmosis unit.

[0018] Optionally, the system can also switch to an online cleaning mode;

[0019] When cleaning the membrane of the first-stage two-stage seawater reverse osmosis unit, all the permeate from the first-stage two-stage freshwater reverse osmosis unit is returned to the inlet of the first-stage two-stage seawater reverse osmosis unit, and the return ratio of the second concentrate from the first-stage two-stage seawater reverse osmosis unit is increased for flushing.

[0020] When cleaning the membrane of the first-stage two-stage freshwater reverse osmosis unit, the permeate from the first-stage two-stage seawater reverse osmosis unit can be used directly as flushing water, without the need to use the permeate from the first-stage two-stage freshwater reverse osmosis unit for flushing.

[0021] Optionally, the system also predicts future changes in influent water quality based on historical TDS data of the influent, and adjusts the reflux ratio of the second concentrate and the recovery rate of the second stage unit of the first-stage two-stage seawater reverse osmosis device in advance according to the prediction results, so as to keep the concentration of the first concentrate discharged from the concentrate outlet within the target concentration range.

[0022] Optionally, the system further includes an energy recovery device and a booster pump;

[0023] The first concentrate of the two-stage seawater reverse osmosis unit first passes through the energy recovery device to recover energy, and then is discharged from the system through the concentrate outlet.

[0024] The booster pump is connected to the energy recovery device and is used to supplement and boost the original seawater after it has been pressurized by the energy recovery device.

[0025] The system provided in this application has the following beneficial effects:

[0026] The system provided in this application enhances the basic treatment capacity and resistance to water quality fluctuations of a single-stage membrane system by combining a single-stage two-part seawater reverse osmosis unit and a single-stage two-part freshwater reverse osmosis unit. By separating the permeate from the seawater reverse osmosis unit and implementing concentrate recirculation and full concentrate recirculation in the freshwater reverse osmosis unit, the system's overall recovery rate is significantly improved, reducing the amount of raw seawater required. Simultaneously, the system can operate stably under a wide range of feed water TDS (Total Dissolved Solids) conditions, producing high-quality freshwater and stable-concentration concentrate that meets industrial requirements. The concentrate can be directly used for resource utilization such as salt production, avoiding resource waste and environmental impact caused by direct discharge of concentrate.

[0027] Furthermore, this application, by adjusting the concentrate recirculation ratio and permeate flow ratio of the seawater reverse osmosis unit in real time, can further stabilize the discharged concentrate concentration and the final permeate quality, rationally match the treatment load of the freshwater reverse osmosis unit, and reduce system operating energy consumption. By setting up a two-stage unit of the seawater reverse osmosis unit with switchable operating modes, the problem of low operating efficiency of the two-stage unit under low TDS feed water conditions is solved, extending the service life of the membrane elements. Through the settings of staged concentrate recirculation, concentrated concentrate temporary storage and batch discharge, and permeate flow for individual membrane housings, the system operating parameters are further optimized, concentrate concentration fluctuations are smoothed, and optimal permeate distribution is achieved. Through the settings of reagent-free online cleaning and concentrate concentration prediction and pre-control, membrane element cleaning can be completed without shutting down the system, eliminating the impact of control lag and improving system operational stability. By setting up an energy recovery device and a booster pump, the high-pressure energy carried by the concentrate can be fully recovered, further reducing the overall energy consumption of the system. Attached Figure Description

[0028] Figure 1 A schematic diagram illustrating the principle of a membrane-based seawater desalination system for stabilizing and utilizing concentrated water, provided in an embodiment of this application.

[0029] Figure 2 A schematic diagram illustrating the principle of another membrane-based seawater desalination system for the stable resource utilization of concentrated water provided in this application embodiment;

[0030] Figure 3 A schematic diagram illustrating the principle of another membrane-based seawater desalination system for the stable resource utilization of concentrated water provided in this application embodiment;

[0031] Figure 4 A schematic diagram illustrating the principle of another membrane-based seawater desalination system for the stable resource utilization of concentrated water provided in this application embodiment;

[0032] Figure 5 A schematic diagram illustrating the principle of another membrane-based seawater desalination system for the stable resource utilization of concentrated water provided in this application embodiment;

[0033] Figure 6 A schematic diagram illustrating the principle of another membrane-based seawater desalination system for the stable resource utilization of concentrated water provided in this application embodiment;

[0034] Figure 7 This is a schematic diagram illustrating the principle of another membrane-based seawater desalination system for the stable resource utilization of concentrate, provided in an embodiment of this application.

[0035] Figure reference numerals: 1. First-stage two-section seawater reverse osmosis unit; 2. First-stage two-section freshwater reverse osmosis unit; 3. Industrial water tank; 4. Concentrate discharge outlet; 5. Concentrate storage tank; 6. Diverter valve; 7. Energy recovery device; 8. Booster pump; 101. First-stage unit; 102. Second-stage unit; 201. Third-stage unit; 202. Fourth-stage unit. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this application clearer, specific embodiments of this application will be described in further detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely for explaining this application and not for limiting it. It should also be noted that, for ease of description, only the parts relevant to this application are shown in the drawings, not all of them. Before discussing exemplary embodiments in more detail, it should be mentioned that some exemplary embodiments are described as processes or methods depicted as flowcharts. Although the flowcharts describe operations (or steps) as sequential processes, many of these operations can be performed in parallel, concurrently, or simultaneously. Furthermore, the order of the operations can be rearranged. The process can be terminated when its operation is completed, but may also have additional steps not included in the drawings. The process can correspond to a method, function, procedure, subroutine, subprogram, etc.

[0037] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0038] See Figure 1 This application provides a membrane-based seawater desalination system for the stable resource utilization of concentrated water. The system is designed to adapt to a wide range of feed water TDS fluctuations while producing high-quality industrial water and concentrated water with stable concentration. The system includes a first-stage two-stage seawater reverse osmosis unit 1, a first-stage two-stage freshwater reverse osmosis unit 2, an industrial water tank 3, and a concentrated water discharge outlet 4.

[0039] The raw seawater enters the first-stage two-stage seawater reverse osmosis unit 1. The product water of the first-stage two-stage seawater reverse osmosis unit 1 is divided into first product water and second product water. The first product water is connected to the industrial water tank 3, and the second product water is connected to the inlet of the first-stage two-stage freshwater reverse osmosis unit 2.

[0040] The concentrate of the first-stage two-stage seawater reverse osmosis unit 1 is divided into a first concentrate and a second concentrate. The first concentrate is discharged from the system through the concentrate outlet 4, and the second concentrate is returned to the inlet of the first-stage two-stage seawater reverse osmosis unit 1.

[0041] The product water from the first-stage two-stage freshwater reverse osmosis unit 2 is connected to the industrial water tank 3, and all the concentrate from the first-stage two-stage freshwater reverse osmosis unit 2 is returned to the inlet of the first-stage two-stage seawater reverse osmosis unit 1.

[0042] Specifically, the system provided in this embodiment is used to adapt to a wide range of feed water TDS fluctuations, while simultaneously producing high-quality industrial water and concentrated concentrate with stable concentration. The system mainly includes a first-stage two-stage seawater reverse osmosis unit 1, a first-stage two-stage freshwater reverse osmosis unit 2, an industrial water tank 3, and a concentrate discharge outlet 4. Both the first-stage two-stage seawater reverse osmosis unit 1 and the first-stage two-stage freshwater reverse osmosis unit 2 use 7-core pressure vessels. The first stage of the first-stage two-stage seawater reverse osmosis unit 1 is equipped with 90 pressure vessels, and the second stage is equipped with 40 pressure vessels. The first stage of the first-stage two-stage freshwater reverse osmosis unit 2 is equipped with 32 pressure vessels in the first stage and 14 pressure vessels in the second stage. Figure 1 The first-stage two-stage seawater reverse osmosis unit 1 includes a first-stage unit 101 and a second-stage unit 102, and the first-stage two-stage freshwater reverse osmosis unit 2 includes a third-stage unit 201 and a fourth-stage unit 202.

[0043] The system operates as follows: After pretreatment, the raw seawater enters a single-stage two-stage seawater reverse osmosis unit 1 for desalination. The freshwater produced by unit 1 is divided into primary and secondary products. The primary product is directly connected to industrial water tank 3, while the secondary product is connected to the inlet of unit 2 for further desalination. The concentrate produced by unit 1 is divided into primary and secondary concentrates. The primary concentrate is discharged from the system via outlet 4, while the secondary concentrate is returned to the inlet of unit 1, mixed with the raw seawater, and desalinated again. The freshwater produced by unit 2 is connected to industrial water tank 3, mixed with the primary product, and then supplied as high-quality industrial water. All concentrate produced by unit 2 is returned to the inlet of unit 1, mixed with the raw seawater and secondary concentrate, and then treated again.

[0044] In actual operation, when the influent TDS is 8000 mg / L and the temperature is 1℃, the total system recovery rate can reach 90%, and the final permeate output is stable at 10050 m³ / d. When the influent TDS is 25000 mg / L and the temperature is 3℃, the total system recovery rate is 68%, and the final permeate output remains at 10050 m³ / d. When the influent TDS is 30000 mg / L and the temperature is 1℃, the total system recovery rate is 62%, and the final permeate output is also stable at 10050 m³ / d. When the system is shut down, the high-pressure pump and related valves are turned off first, and then the membrane modules are flushed with fresh water. After flushing, the system enters standby mode.

[0045] This system can adapt to a wide range of seawater TDS fluctuations and maintain a stable water production rate under different influent conditions. It produces high-quality freshwater that meets industrial requirements and concentrated water that can be directly used for resource utilization such as salt production. The system significantly improves the overall water resource recovery rate through concentrated water recirculation, reduces the amount of raw seawater used, and lowers the system's operating costs and environmental impact.

[0046] In some embodiments, the recirculation ratio of the second concentrate in the first-stage two-stage seawater reverse osmosis unit 1 is adjusted in real time according to the feed water TDS, so that the concentration of the first concentrate discharged from the concentrate outlet 4 is kept above the first concentration threshold.

[0047] If a fixed concentrate recirculation ratio is used, when the feed water TDS is low, the concentrate concentration produced by the first-stage two-stage seawater reverse osmosis unit 1 will decrease accordingly, failing to meet the requirements for subsequent resource utilization. When the feed water TDS is high, the fixed recirculation ratio will lead to excessive salt accumulation in the system, and the pressure difference across the membrane of the first-stage two-stage seawater reverse osmosis unit 1 will increase significantly. This will not only increase the system's operating energy consumption but also accelerate the damage to the membrane elements and shorten the service life of the equipment.

[0048] In this embodiment, the recirculation ratio of the second concentrate in the first-stage two-stage seawater reverse osmosis unit 1 can be adjusted in real time according to the feed water TDS to keep the concentration of the first concentrate discharged from the concentrate outlet 4 above the first concentration threshold. The first concentration threshold is 8% by mass, which is the minimum requirement for feed concentration in subsequent resource utilization processes such as salt production. The system is equipped with a TDS meter in the feed water pipeline of the first-stage two-stage seawater reverse osmosis unit 1 to collect feed water quality data in real time. Based on the collected feed water TDS value, the valve opening of the concentrate recirculation pipeline is automatically adjusted, thereby changing the recirculation ratio of the second concentrate.

[0049] When the influent TDS is 8000 mg / L and the temperature is 1℃, the system adjusts the second concentrate recirculation ratio to 76%, and the remaining 24% of the concentrate is discharged from concentrate outlet 4. At this time, the concentration of the discharged concentrate is 80042.27 mg / L, meeting the 8% mass fraction requirement. When the influent TDS is 25000 mg / L and the temperature is 3℃, the system automatically closes the valve of the concentrate recirculation pipeline, the second concentrate recirculation ratio is 0, and all concentrate is discharged from concentrate outlet 4. At this time, the concentration of the discharged concentrate is 80562.67 mg / L. When the influent TDS is 30000 mg / L and the temperature is 1℃, the system similarly closes the concentrate recirculation pipeline, and the concentration of the discharged concentrate is 80012.62 mg / L. Under all the above operating conditions, the final product water output of the system remains at 10050 m³ / d, and the product water quality is not affected by the adjustment of the concentrate recirculation ratio.

[0050] This method effectively offsets the impact of feedwater TDS fluctuations on concentrate concentration, ensuring that the discharged concentrate always meets the requirements for subsequent resource utilization such as salt production and bromine extraction, eliminating the need for an additional concentrate concentration device. Simultaneously, this method avoids excessive salt accumulation in the system when using high TDS feedwater, effectively reducing the pressure difference across the membrane in the first-stage two-stage seawater reverse osmosis unit 1, reducing system operating energy consumption, extending the service life of membrane elements, and lowering system operation and maintenance costs.

[0051] Based on the above implementation methods, the adjustment method of the concentrate recirculation ratio can be further optimized. For example, the system can use gradient pulse regulation instead of continuous proportional regulation, abandoning the constant recirculation ratio and adopting a periodic pulse mode that alternates between high and low recirculation ratios. The average concentration of discharged concentrate is controlled by adjusting the duty cycle of the pulses. When an average recirculation ratio of 50% is required, a cycle of 70% recirculation for 10 minutes and 30% recirculation for 10 minutes can be used. The periodic large fluctuations in the concentrate flow rate will create a shearing and scouring effect on the membrane surface of the first-stage two-stage seawater reverse osmosis unit, effectively removing loosely attached contaminants.

[0052] When the influent TDS changes slowly, the system can employ reverse pre-compensation adjustment. When the detected rate of change in influent TDS is less than 500 mg / L / h, a small adjustment is first made in the opposite direction to the normal adjustment. After the salinity in the system accumulates to the preset value, a large adjustment is then made. For example, when the influent TDS slowly increases from 20000 mg / L to 25000 mg / L, with a rate of change of 300 mg / L / h, the system first slightly increases the concentrate recirculation ratio from 0% to 10%, allowing the salinity in the system to accumulate slowly. Once the average salinity in the system reaches the preset value, the recirculation ratio is then significantly reduced to 0%, ensuring a smooth transition of the discharged concentrate concentration to the target value. This method can eliminate discharge concentration fluctuations caused by slow water quality changes, and significantly reduces the number of valve adjustments.

[0053] The system can also employ a two-stage priority diversion regulation for concentrate recirculation, splitting the second concentrate into two paths. One path recirculates back to the main inlet of the first-stage two-stage seawater reverse osmosis unit 1, while the other path recirculates back to the inlet of the second-stage unit 102. The diversion ratio is adjusted based on the inlet TDS. When the inlet TDS is 8000 mg / L, the total concentrate recirculation ratio remains at 55%, with 75% of the second concentrate recirculated back to the inlet of the second-stage unit 102 and 25% back to the main inlet. This directly increases the inlet osmotic pressure of the second-stage unit 102, naturally reducing the permeate output of the second-stage unit 102, and simultaneously reducing the inlet load of the first-stage two-stage freshwater reverse osmosis unit 2. This method is more energy-efficient than simply increasing the total recirculation ratio without changing the overall recirculation ratio.

[0054] In some embodiments, the ratio of the first and second product water in the first-stage two-stage seawater reverse osmosis unit 1 is adjusted in real time according to the influent TDS and temperature, so that the effluent TDS in the industrial water tank 3 is kept below the second concentration threshold.

[0055] If a fixed ratio of first and second product water is used, when the feed water TDS is low or the temperature is low, the overall product water quality of the first-stage two-stage seawater reverse osmosis unit 1 will improve. At this time, if too much water enters the first-stage two-stage freshwater reverse osmosis unit 2, the treatment capacity of the first-stage two-stage freshwater reverse osmosis unit 2 will be idle, increasing unnecessary operating energy consumption. When the feed water TDS is high or the temperature is high, the overall product water quality of the first-stage two-stage seawater reverse osmosis unit 1 will deteriorate. At this time, if the amount of water entering the first-stage two-stage freshwater reverse osmosis unit 2 is insufficient, the final product water quality after mixing will exceed the standard and fail to meet the requirements of high-quality industrial water.

[0056] In this embodiment, the ratio of the first and second product water in the first-stage two-stage seawater reverse osmosis unit 1 can be adjusted in real time according to the feed water TDS and temperature to keep the effluent TDS in the industrial water tank 3 below the second concentration threshold. The second concentration threshold is 10 mg / L, which is the salinity requirement for high-quality industrial water. The system simultaneously installs TDS and temperature sensors on the feed water pipeline of the first-stage two-stage seawater reverse osmosis unit 1 to collect feed water quality and temperature data in real time. Based on the collected values, the system automatically calculates and adjusts the valve openings of the first and second product water lines, changing the distribution ratio of the two product water lines. A TDS sensor is installed on the effluent pipeline of the industrial water tank 3. When the effluent TDS exceeds the second concentration threshold, the DCS panel automatically issues an alarm, reminding personnel to check the membrane element usage and the valve opening of the product water regulating valve.

[0057] When the influent TDS is 8000 mg / L and the temperature is 1℃, the system adjusts the proportion of the first-stage permeate to 28%, with the remaining 72% entering the first-stage two-stage desalination reverse osmosis unit 2. The final TDS of the mixed permeate is 4.60 mg / L. When the influent TDS is 25000 mg / L and the temperature is 3℃, the system adjusts the proportion of the first-stage permeate to 25%, with the remaining 75% entering the first-stage two-stage desalination reverse osmosis unit 2. The final TDS of the mixed permeate is 5.21 mg / L. When the influent TDS is 30000 mg / L and the temperature is 1℃, the system again adjusts the proportion of the first-stage permeate to 25%, with the final TDS of the mixed permeate being 4.85 mg / L. Under all the above operating conditions, the final permeate flow rate of the system remains at 10050 m³ / d.

[0058] This method enables precise control of the final product water quality, ensuring that the product water consistently meets the requirements for high-quality industrial water. Simultaneously, it allows for the rational matching of the treatment load of the first-stage two-stage desalination reverse osmosis unit 2 according to actual influent conditions, avoiding waste of equipment capacity, reducing the concentrate side pressure differential of the first-stage two-stage desalination reverse osmosis unit 2, lowering operating energy consumption, extending the service life of membrane elements, and reducing the long-term operation and maintenance costs of the system.

[0059] Based on the above implementation method, the ratio adjustment method of the first and second product water can be further optimized. The system can adjust the product water flow threshold according to the real-time operating load of the first-stage two-stage freshwater reverse osmosis unit 2, instead of using a fixed second concentration threshold. When the influent flow rate of the first-stage two-stage freshwater reverse osmosis unit 2 is less than 60% of the design value, the second concentration threshold is lowered from 10 mg / L to 8 mg / L, allowing more product water from the first-stage two-stage seawater reverse osmosis unit 1 to enter the first-stage two-stage freshwater reverse osmosis unit 2 for further treatment; when the influent flow rate of the first-stage two-stage freshwater reverse osmosis unit 2 is greater than 90% of the design value, the second concentration threshold is raised to 12 mg / L to reduce its influent load and avoid equipment overload. This method can fully utilize the idle processing capacity of the equipment and further improve the quality of the final product water without increasing energy consumption.

[0060] The system can also employ a time-sharing peak-shaving and diversion method, adjusting the production water diversion ratio according to the diurnal load changes of industrial water use. During the off-peak water use period at night, when the system produces excess water, the proportion of the first-stage production water is increased to 40% to 50%, significantly reducing the operating load of the first-stage two-stage desalination reverse osmosis unit 2, and even allowing it to shut down intermittently. During the peak water use period during the day, when the system's production water demand increases, the proportion of the first-stage production water is reduced to 20% to 25%, increasing the operating load of the first-stage two-stage desalination reverse osmosis unit 2 to ensure both the quality and quantity of produced water. This method reduces the system's energy consumption during nighttime operation.

[0061] The system can also employ membrane fouling gradient compensation adjustment, proactively adjusting the permeate flow ratio based on the membrane element's operating status. The system records the cumulative operating time of the membrane element and the change in pressure difference across the membrane. Every 100 hours of operation, the proportion of the first permeate is reduced by 0.5% to 1% to compensate for the decline in permeate quality caused by membrane fouling. When the membrane pressure difference of the first-stage two-stage seawater reverse osmosis unit 1 increases by 15%, the proportion of the first permeate is further reduced by 2% to 3%. Using this method, the fluctuation range of the final permeate quality can be controlled within an ideal range throughout the entire membrane element's lifespan.

[0062] In some embodiments, the first-stage two-stage seawater reverse osmosis unit 1 includes a first-stage unit 101 and a second-stage unit 102, the second-stage unit 102 being switchable between a water production mode and a pure concentration mode;

[0063] When the TDS of the feed water is lower than the third concentration threshold, the second-stage unit 102 switches to pure concentration mode and does not produce water. All the water produced by the first-stage two-stage seawater reverse osmosis unit 1 comes from the first-stage unit 101. When in water production mode, both the first-stage unit 101 and the second-stage unit 102 produce water.

[0064] exist Figure 1 During the corresponding system operation, the second-stage unit 102 of the first-stage two-stage seawater reverse osmosis unit 1 operates with low efficiency under low TDS feed water conditions. Due to insufficient feed water osmotic pressure, the permeate flux of the second-stage unit 102 is too high, making it easy for contaminants to deposit on the membrane surface and significantly accelerating membrane fouling. At the same time, the quality of the freshwater produced by the second-stage unit 102 is far worse than that of the first-stage unit 101. A large amount of low-quality freshwater entering the first-stage two-stage freshwater reverse osmosis unit 2 will significantly increase the treatment load of the first-stage two-stage freshwater reverse osmosis unit 2, offsetting some of the recovery rate benefits brought by concentrate recirculation. It will also lead to an increase in the pressure difference across the membrane of the first-stage two-stage freshwater reverse osmosis unit 2, shortening its service life.

[0065] In this embodiment, the first-stage two-stage seawater reverse osmosis unit 1 includes a first-stage unit 101 and a second-stage unit 102. The second-stage unit 102 can switch between a permeate mode and a pure concentration mode. The third concentration threshold is set to 15000 mg / L. When the influent TDS is lower than the third concentration threshold, the second-stage unit 102 switches to pure concentration mode, closes the permeate valve of the second-stage unit 102, and the second-stage unit 102 does not produce water. All permeate from the first-stage two-stage seawater reverse osmosis unit 1 comes from the first-stage unit 101. Figure 2 As shown; when the influent TDS is higher than or equal to the third concentration threshold, the second-stage unit 102 switches to water production mode, and both the first-stage unit 101 and the second-stage unit 102 produce water, which is then processed according to the basic system process.

[0066] When the influent TDS is 10000 mg / L and the temperature is 2℃, the system automatically switches the second-stage unit 102 to pure concentration mode. At this time, the influent flow rate of the first-stage two-stage freshwater reverse osmosis unit 2 is reduced by about 30% compared with the basic system, the concentrate recirculation ratio of the first-stage two-stage seawater reverse osmosis unit 1 is adjusted to 62%, the discharge concentrate concentration is 80125 mg / L, the final product water output is maintained at 10050 m³ / d, and the mixed product water TDS is 4.32 mg / L. When the influent TDS is 20000 mg / L and the temperature is 2℃, the system automatically switches the second-stage unit 102 to product water mode. The first-stage unit 101 and the second-stage unit 102 produce water simultaneously. The system operates normally according to the basic process, the discharge concentrate concentration is 80317 mg / L, and the final product water output and quality both meet the requirements.

[0067] This solution addresses the low operating efficiency of the second-stage unit 102 of the first-stage two-stage seawater reverse osmosis unit 1 under low TDS feed water conditions, significantly reducing the operating load of the first-stage two-stage freshwater reverse osmosis unit 2 and decreasing the deposition rate of contaminants on the membrane surface. Simultaneously, this approach effectively reduces the overall energy consumption of the system, extends the service life of the membrane elements in both the first-stage two-stage seawater reverse osmosis unit 1 and the first-stage two-stage freshwater reverse osmosis unit 2, and reduces equipment replacement and maintenance costs.

[0068] In some embodiments, the concentrate of the first-stage two-stage freshwater reverse osmosis device 2 is divided into a first reflux concentrate and a second reflux concentrate. The first reflux concentrate is refluxed to the middle section inlet of the first section unit 101 of the first-stage two-stage seawater reverse osmosis device 1, and the second reflux concentrate is refluxed to the main inlet of the first-stage two-stage seawater reverse osmosis device 1.

[0069] exist Figure 1 When the system is running, all the concentrate produced by the first-stage two-stage freshwater reverse osmosis unit 2 is returned to the total inlet of the first-stage two-stage seawater reverse osmosis unit 1. Under low TDS feed water conditions, the salt content of the total feed water will be continuously diluted, resulting in a persistently low feed water osmotic pressure of the first-stage two-stage seawater reverse osmosis unit 1. In order to maintain the concentration of the discharged concentrate up to standard, the concentrate return ratio can only be continuously increased, thus forming a cycle of continuous dilution of feed water and continuous increase in the concentrate return ratio. This causes the system operating pressure and energy consumption to increase simultaneously, affecting the overall operational stability.

[0070] like Figure 3 As shown in this embodiment, the concentrate of the first-stage two-stage freshwater reverse osmosis device 2 can be divided into a first reflux concentrate and a second reflux concentrate. The first reflux concentrate is returned to the middle section inlet of the first-stage unit 101 of the first-stage two-stage seawater reverse osmosis device 1, and the second reflux concentrate is returned to the total inlet of the first-stage two-stage seawater reverse osmosis device 1. In actual operation, the two reflux concentrates are distributed in a ratio of 60% to 70% and 30% to 40% to increase the salinity and osmotic pressure of the feed water in the second half of the first-stage unit 101, while reducing the dilution effect on the total feed water.

[0071] When the influent TDS is 8000 mg / L and the temperature is 1℃, the concentrate of the first-stage two-stage freshwater reverse osmosis unit 2 adopts a staged recirculation method, with the first recirculation concentrate accounting for 65% and the second recirculation concentrate accounting for 35%. At this time, the concentrate recirculation ratio of the first-stage two-stage seawater reverse osmosis unit 1 can be reduced from 76% to 55%, while the discharge concentrate concentration remains above 80000 mg / L, and the final product water output is maintained at 10050 m³ / d, with a mixed product water TDS of 4.52 mg / L. When the influent TDS is 12000 mg / L and the temperature is 2℃, the staged recirculation also maintains stable operation, the concentrate recirculation ratio decreases by about 20 percentage points, and the overall system pressure and energy consumption are at a low level.

[0072] This method can break the feed water dilution cycle caused by concentrate recirculation. Under the premise of ensuring that the concentration of discharged concentrate meets the standard, it can effectively reduce the concentrate recirculation ratio of the first-stage two-stage seawater reverse osmosis unit 1, reduce the system operating pressure and energy consumption, improve the product water quality of the second half of the first-stage unit 101, further optimize the overall product water structure, and extend the service life of membrane elements.

[0073] like Figure 4 As shown, in some embodiments, the system also includes a concentrate storage tank 5;

[0074] The first concentrated water of the first-stage two-stage seawater reverse osmosis unit 1 first enters the concentrated water storage tank 5. After the concentrated water concentration in the concentrated water storage tank 5 reaches the fourth concentration threshold, it is discharged in batches.

[0075] When the TDS of the feed water changes abruptly, the concentrate in the concentrate storage tank 5 can be returned to the inlet of the first-stage two-stage seawater reverse osmosis unit 1.

[0076] exist Figure 1 During system operation, the concentrate produced by the first-stage two-stage seawater reverse osmosis unit 1 is discharged directly in real time. When the TDS of the feed water suddenly increases or decreases, the concentration of the discharged concentrate may fluctuate dramatically. Subsequent resource utilization processes such as salt production require high stability of the feed concentration. Frequent fluctuations in the concentrate concentration will lead to unstable brine concentration in the salt production ponds, affecting the crystallization efficiency and product quality of the salt. In severe cases, it may even be necessary to suspend production for adjustments, reducing overall production efficiency.

[0077] In this embodiment, the system also includes a concentrate storage tank 5. The first concentrate from the first-stage two-stage seawater reverse osmosis unit 1 enters the concentrate storage tank 5. Once the concentrate concentration in the concentrate storage tank 5 reaches the fourth concentration threshold, it is discharged in batches. The fourth concentration threshold is set at 8% by mass, consistent with the minimum feed requirement of the resource utilization process. When the TDS of the feed water changes abruptly, the concentrate in the concentrate storage tank 5 can be returned to the inlet of the first-stage two-stage seawater reverse osmosis unit 1, mixed with the original seawater, and treated again to prevent the discharge of concentrate with unqualified concentrations.

[0078] The volume of the concentrate storage tank 5 is set at 500 m³, corresponding to the system's 8-hour concentrated wastewater discharge volume. The system performs a batch discharge every 8 hours. Using this method, the concentration fluctuation range of the discharged concentrate is reduced from ±500 mg / L in the basic system to ±100 mg / L. When the influent TDS suddenly drops from 25000 mg / L to 18000 mg / L, the system first discharges all the concentrate in the storage tank that meets the concentration standard. Then, it temporarily stores the newly generated low-concentration concentrate and returns it to the inlet. After the system stabilizes, normal storage and discharge resume. Throughout the entire process, no unqualified concentrate is discharged, and the final permeate output remains consistently 10050 m³ / d.

[0079] This method effectively smooths out instantaneous fluctuations in concentrate concentration, providing a stable feed for subsequent resource utilization units such as salt production and bromine extraction, ensuring the continuous and stable operation of the resource utilization process. Simultaneously, this method can cope with sudden changes in influent TDS, preventing the discharge of substandard concentrate, further improving the stability and reliability of system operation, and reducing the operating costs of subsequent resource utilization stages.

[0080] like Figure 5 As shown, in some embodiments, each membrane shell of the first-stage two-stage seawater reverse osmosis unit 1 is equipped with a diversion valve 6 at its permeate outlet. The diversion valve 6 switches the flow direction according to the TDS of the permeate from the corresponding membrane shell.

[0081] When the TDS of the permeate from the membrane housing is lower than the fifth concentration threshold, the permeate from the membrane housing is connected to the industrial water tank 3; when the TDS of the permeate from the membrane housing is higher than the fifth concentration threshold, the permeate from the membrane housing is connected to the inlet of the first-stage two-stage freshwater reverse osmosis unit 2.

[0082] Figure 1 In the corresponding system, the first-stage two-stage seawater reverse osmosis unit 1, with fixed positions at the front and rear ends of the membrane housings for permeate water flow, may not be able to adapt to the uneven fouling problem that occurs during membrane element operation. Due to differences in feed water distribution, water flow conditions, and pollutant deposition, the permeate water quality of individual membrane housings installed in the same batch will show significant differences after a period of operation. Some membrane housings located at the rear end may still maintain good permeate water quality, but are uniformly sent to the first-stage two-stage freshwater reverse osmosis unit 2 for treatment, resulting in a waste of high-quality permeate water; while some membrane housings located at the front end may have severely fouled permeate water with substandard quality, but are directly sent to the industrial water tank 3, affecting the final permeate water quality.

[0083] In this embodiment, each membrane housing in the first-stage two-stage seawater reverse osmosis unit 1 is equipped with a diversion valve 6 at its permeate inlet. The diversion valve 6 switches the flow direction according to the TDS of the permeate from the corresponding membrane housing. The fifth concentration threshold is set at 15 mg / L. When the TDS of the permeate from the membrane housing is lower than the fifth concentration threshold, the permeate from that membrane housing is connected to the industrial water tank 3; when the TDS of the permeate from the membrane housing is higher than the fifth concentration threshold, the permeate from that membrane housing is connected to the inlet of the first-stage two-stage freshwater reverse osmosis unit 2. The system collects the permeate TDS data of each membrane housing in real time and automatically controls the opening and closing status of the corresponding diversion valve 6.

[0084] After six months of continuous operation, in the first-stage two-stage seawater reverse osmosis unit 1, the TDS of permeate from 12 out of 90 membrane shells rose to 16-19 mg / L. The diversion valve 6 automatically switched this permeate to the inlet of the first-stage two-stage freshwater reverse osmosis unit 2. The TDS of the remaining 78 membrane shells remained between 12-14 mg / L, and the permeate was directly connected to the industrial water tank 3. When the inlet TDS was 25000 mg / L and the temperature was 3℃, using this diversion method reduced the inlet flow rate of the first-stage two-stage freshwater reverse osmosis unit 2 by approximately 8% compared to the basic system, while maintaining a final permeate flow rate of 10050 m³ / d. The mixed permeate TDS was 5.07 mg / L, indicating improved permeate quality.

[0085] This method can divert the permeate based on the actual permeate quality of each membrane element, achieving optimal permeate distribution and avoiding waste of high-quality permeate and mixing of substandard permeate. Furthermore, it can further reduce the processing load of the first-stage two-stage desalination reverse osmosis unit 2, reduce the pressure difference on the concentrate side, extend the service life of membrane elements, and improve the overall operating efficiency and permeate quality stability of the system.

[0086] In some implementations, the system can also switch to an online cleaning mode;

[0087] When cleaning the membrane of the first-stage two-stage seawater reverse osmosis unit 1, all the permeate from the first-stage two-stage freshwater reverse osmosis unit 2 is returned to the inlet of the first-stage two-stage seawater reverse osmosis unit 1, and the return ratio of the second concentrate of the first-stage two-stage seawater reverse osmosis unit 1 is increased for flushing.

[0088] When cleaning the membrane of the first-stage two-stage freshwater reverse osmosis unit 2, the concentrate from the first-stage two-stage seawater reverse osmosis unit 1 is reversed and fed into the membrane of the first-stage two-stage freshwater reverse osmosis unit 2 for salt washing.

[0089] After long-term operation, contaminants gradually accumulate on the membrane surface of conventional seawater desalination systems, leading to increased membrane pressure differential and decreased water production performance. Traditional treatment methods require shutdown and chemical cleaning, which not only interrupts production but also generates chemical cleaning wastewater, impacting the environment. Furthermore, frequent chemical cleaning shortens the overall lifespan of the membrane elements.

[0090] In this embodiment, the system can also switch to an online cleaning mode, allowing the membrane element cleaning operation to be completed without shutdown. When the membrane pressure differential of the first-stage two-stage seawater reverse osmosis unit 1 rises to a set value, the system switches to the corresponding cleaning state, returning all the permeate from the first-stage two-stage freshwater reverse osmosis unit 2 to the inlet of the first-stage two-stage seawater reverse osmosis unit 1. Simultaneously, the return ratio of the second concentrate from the first-stage two-stage seawater reverse osmosis unit 1 is increased. Low-salinity, high-velocity water is used to flush the membrane surface, carrying attached contaminants into the concentrate and discharging them out. Figure 6As shown. When the membrane pressure differential of the first-stage two-stage freshwater reverse osmosis unit 2 rises to the set value, the system directly introduces the permeate produced by the first-stage two-stage seawater reverse osmosis unit 1 into the membrane module of the first-stage two-stage freshwater reverse osmosis unit 2 for flushing. At this time, the first permeate of the first-stage two-stage seawater reverse osmosis unit 1 can be shut off, and the flushing water volume can be increased, such as... Figure 7 As shown.

[0091] In actual operation, the cleaning time of the first-stage two-stage seawater reverse osmosis unit 1 is controlled between 2 and 4 hours. During the cleaning period, the system's water production only decreases by 10% to 15%, and it can still maintain a partial water supply. The cleaning time of the first-stage two-stage freshwater reverse osmosis unit 2 is controlled between 1 and 2 hours, and no cleaning wastewater is discharged throughout the process. After adopting this online cleaning method, the chemical cleaning cycle of the membrane elements is significantly extended, and the operational stability of the membrane modules is effectively guaranteed.

[0092] This method enables online cleaning of membrane elements without shutting down the system or using chemical agents, avoiding losses caused by production interruptions, reducing the amount of chemical agents used and the generation of cleaning wastewater, while also reducing the damage of pollutants to the membrane elements, effectively extending the service life of the membrane elements, and reducing the overall operation and maintenance costs of the system.

[0093] In some implementations, the system also predicts future changes in the quality of the influent based on historical TDS data of the influent, and adjusts the reflux ratio of the second concentrate of the first-stage two-stage seawater reverse osmosis unit 1 and the recovery rate of the second-stage unit 102 in advance according to the prediction results, so as to keep the concentration of the first concentrate discharged from the concentrate outlet 4 within the target concentration range.

[0094] Specifically, Figure 1 The corresponding system controls the concentration of discharged concentrate by adjusting the concentrate recirculation ratio in real time. This is a passive response control method, which has a certain control lag effect. If the TDS of the influent changes rapidly and significantly, the system may not be able to adjust in time, resulting in a temporary exceedance or underestimation of the concentration of discharged concentrate. This can affect the stable operation of subsequent resource utilization processes such as salt production, and in severe cases, it may be necessary to suspend the feeding of the resource utilization unit, causing production losses.

[0095] In this embodiment, the system can also predict future changes in influent water quality based on historical TDS data, and adjust the recirculation ratio of the second concentrate and the recovery rate of the second-stage unit 102 of the first-stage two-stage seawater reverse osmosis unit 1 in advance according to the prediction results, so as to keep the concentration of the first concentrate discharged from the concentrate outlet 4 within the target concentration range. The system continuously collects and stores historical TDS data of the influent, establishes a water quality change prediction model, and can predict the trend of TDS change of the influent 1 to 2 hours in advance, adjust the system operating parameters in advance, and eliminate the impact of control lag.

[0096] When the system predicts that the influent TDS will decrease from 20,000 mg / L to 12,000 mg / L after 1.5 hours, the recirculation ratio of the second concentrate in the first-stage two-stage seawater reverse osmosis unit 1 can be gradually increased from 0% to 40% in advance, while the recovery rate of the second-stage unit 102 is reduced from 65% to 50%. When the influent TDS actually drops to 12,000 mg / L, the concentration of the discharged concentrate remains stable within the target concentration range of 80,000 mg / L to 82,000 mg / L. However, when using a passive adjustment method, under the same operating conditions, the concentration of the discharged concentrate will briefly drop to 72,000 mg / L, and it will take approximately 25 minutes to recover to the target concentration. Throughout the entire process, the final permeate flow rate remains at 10,050 m³ / d, and the permeate quality is unaffected.

[0097] This method effectively eliminates the lag in concentrate concentration control, achieving fluctuation-free control of the discharged concentrate concentration and completely avoiding concentration fluctuations caused by rapid changes in influent TDS. Simultaneously, it further optimizes system operating parameters, reduces energy consumption fluctuations, improves system stability and reliability, provides a continuous and stable feed for subsequent resource utilization processes, and ensures the continuous operation of the overall production process.

[0098] Continue reading Figure 1 In some embodiments, the system also includes an energy recovery device 7 and a booster pump 8;

[0099] The first concentrate of the two-stage seawater reverse osmosis unit 1 first passes through the energy recovery device 7 to recover energy, and then is discharged from the system through the concentrate outlet 4.

[0100] The booster pump 8 is connected to the energy recovery device 7 and is used to supplement and boost the original seawater after it has been pressurized by the energy recovery device 7.

[0101] exist Figure 1 During system operation, the first concentrate produced by the two-stage seawater reverse osmosis unit 1 has a high pressure, and direct discharge would result in a significant waste of high-pressure energy. The energy consumption of the seawater desalination system is mainly concentrated in the operation of the high-pressure pump. The energy carried by the concentrate accounts for more than 60% of the energy input to the high-pressure pump. If it is not recovered and utilized, it will significantly increase the operating cost of the system and reduce the overall economic efficiency.

[0102] In this embodiment, the system also includes an energy recovery device 7 and a booster pump 8. The first concentrate of the first-stage two-stage seawater reverse osmosis unit 1 first passes through the energy recovery device 7 to recover energy, and then is discharged from the system from the concentrate outlet 4. The booster pump 8 is connected to the energy recovery device 7. The raw seawater is divided into two paths. The first path first enters the energy recovery device 7, where it is initially pressurized using the residual pressure of the first concentrate. Then it enters the booster pump 8, which further pressurizes the raw seawater after it has been pressurized by the energy recovery device 7, so that the raw seawater reaches the working pressure required by the first-stage two-stage seawater reverse osmosis unit 1. The second path directly enters the first-stage two-stage seawater reverse osmosis unit 1.

[0103] In actual operation, the energy recovery efficiency of the energy recovery device 7 can reach over 90%. When the influent TDS is 25000 mg / L and the temperature is 3℃, the operating pressure of the first-stage two-stage seawater reverse osmosis unit 1 is 5.13 MPa. The energy recovery device 7 can utilize the residual pressure of the first concentrate to pressurize the original seawater to 4.6 MPa, and the booster pump 8 only needs to supplement 0.53 MPa of pressure to meet the system's operating requirements. After adopting this method, the input power of the system's high-pressure pump is reduced by approximately 32%, and the overall operating energy consumption is significantly reduced.

[0104] This method can fully recover and utilize the high-pressure energy carried by the concentrate in the first-stage two-stage seawater reverse osmosis unit, significantly reducing the overall energy consumption of the system and improving energy utilization efficiency. At the same time, it can reduce the workload of the high-pressure pump, extend its service life, lower the long-term operating costs of the system, and enhance the system's market competitiveness.

[0105] In some implementations, under low TDS feed water conditions, the treatment load of the first-stage two-stage desalination reverse osmosis unit 2 is significantly reduced, and the operating flux of its four-stage unit 202 is far below the design value. The treatment capacity of the membrane elements cannot be fully utilized, resulting in some equipment idleness. Simultaneously, to maintain a stable concentrate concentration, the system still needs to maintain a certain concentrate recirculation ratio, leaving room for further energy consumption reduction. Conventional solutions often involve reducing the operating pressure of the first-stage two-stage desalination reverse osmosis unit or shutting down some membrane modules, which cannot fundamentally solve the equipment idleness problem and is also insufficient to further reduce the overall system energy consumption.

[0106] exist Figure 1Based on the corresponding scheme, in this embodiment, the first-stage two-stage freshwater reverse osmosis device 2 includes a three-stage unit 201 and a four-stage unit 202. The four-stage unit 202 can switch between a product water mode and a concentrate pre-concentration mode. The sixth concentration threshold is set to 12000 mg / L. When the influent TDS is lower than the sixth concentration threshold, the four-stage unit 202 switches to the concentrate pre-concentration mode, closes the product water valve of the four-stage unit 202, and the concentrate produced by the three-stage unit 201 is first introduced into the four-stage unit 202 for pre-concentration. The pre-concentrated concentrate is then returned to the middle section inlet and the main inlet of the first-stage two-stage seawater reverse osmosis device 1 according to a preset ratio. When the influent TDS is higher than or equal to the sixth concentration threshold, the four-stage unit 202 switches to the product water mode, and both the three-stage unit 201 and the four-stage unit 202 produce water. The product water is then combined and connected to the industrial water tank 3.

[0107] When the influent TDS is 8000 mg / L and the temperature is 1℃, the system switches the fourth-stage unit 202 to concentrate pre-concentration mode. At this time, the concentrate concentration returned to the first-stage two-stage seawater reverse osmosis unit 1 is about 40% higher than that of the basic system. The concentrate return ratio of the first-stage two-stage seawater reverse osmosis unit 1 can be further reduced from 55% to 42%, while the discharge concentrate concentration remains above 80000 mg / L. The final product water output is maintained at 10050 m³ / d, and the mixed product water TDS is 4.48 mg / L.

[0108] This method fully utilizes the idle processing capacity of the four-stage unit 202 under low-load conditions, increasing the concentration of the return concentrate without adding any additional equipment, thereby further reducing the concentrate return ratio and system operating energy consumption of the first-stage two-stage seawater reverse osmosis unit 1. Simultaneously, this method can synergistically work with the aforementioned concentrated water staged return and two-stage unit 102 function switching schemes to further improve the system's operational economy and stability over a wide TDS feed water range.

[0109] The above description is merely a preferred embodiment and the technical principles employed in this application. This application is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions that can be made by those skilled in the art will not depart from the scope of protection of this application. Therefore, although this application has been described in detail through the above embodiments, this application is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of this application.

Claims

1. A membrane-based seawater desalination system for the stable utilization of concentrated water, characterized in that, The system is designed to adapt to a wide range of feed water TDS fluctuations while producing high-quality industrial water and concentrated concentrate with stable concentration. The system includes a first-stage two-stage seawater reverse osmosis unit (1), a first-stage two-stage freshwater reverse osmosis unit (2), an industrial water tank (3), and a concentrate discharge outlet (4). The raw seawater enters the first-stage two-stage seawater reverse osmosis device (1). The product water of the first-stage two-stage seawater reverse osmosis device (1) is divided into first product water and second product water. The first product water is connected to the industrial water tank (3), and the second product water is connected to the inlet of the first-stage two-stage freshwater reverse osmosis device (2). The concentrate of the first-stage two-stage seawater reverse osmosis device (1) is divided into a first concentrate and a second concentrate. The first concentrate is discharged from the system through the concentrate outlet (4), and the second concentrate flows back to the inlet of the first-stage two-stage seawater reverse osmosis device (1). The product water of the first-stage two-stage freshwater reverse osmosis device (2) is connected to the industrial water tank (3), and the concentrate of the first-stage two-stage freshwater reverse osmosis device (2) is all returned to the inlet of the first-stage two-stage seawater reverse osmosis device (1).

2. The system according to claim 1, characterized in that, The recirculation ratio of the second concentrate in the first-stage two-stage seawater reverse osmosis device (1) is adjusted in real time according to the influent TDS, so that the concentration of the first concentrate discharged from the concentrate outlet (4) is kept above the first concentration threshold.

3. The system according to claim 1, characterized in that, The ratio of the first-stage two-stage seawater reverse osmosis device (1) to the second-stage product water is adjusted in real time according to the influent TDS and temperature, so that the effluent TDS in the industrial water tank (3) is kept below the second concentration threshold.

4. The system according to claim 1, characterized in that, The first-stage two-stage seawater reverse osmosis device (1) includes a first-stage unit (101) and a second-stage unit (102), wherein the second-stage unit (102) can switch between a water production mode and a pure concentration mode; When the TDS of the feed water is lower than the third concentration threshold, the second-stage unit (102) switches to the pure concentration mode and does not produce water. All the water produced by the first-stage two-stage seawater reverse osmosis device (1) comes from the first-stage unit (101). When in the water production mode, both the first-stage unit (101) and the second-stage unit (102) produce water.

5. The system according to claim 4, characterized in that, The concentrate of the first-stage two-stage freshwater reverse osmosis device (2) is divided into a first reflux concentrate and a second reflux concentrate. The first reflux concentrate is refluxed to the middle section inlet of the first-stage two-stage seawater reverse osmosis device (1) and the second reflux concentrate is refluxed to the main inlet of the first-stage two-stage seawater reverse osmosis device (1).

6. The system according to claim 1, characterized in that, The system also includes a concentrate storage tank (5); The first concentrated water of the first-stage two-stage seawater reverse osmosis device (1) first enters the concentrated water storage tank (5), and is discharged in batches after the concentrated water concentration in the concentrated water storage tank (5) reaches the fourth concentration threshold. When the TDS of the feed water changes abruptly, the concentrate in the concentrate storage tank (5) can be returned to the inlet of the first-stage two-stage seawater reverse osmosis device (1).

7. The system according to claim 1, characterized in that, Each membrane shell of the first-stage two-stage seawater reverse osmosis device (1) is equipped with a diversion valve (6) at its permeate outlet. The diversion valve (6) switches the flow direction according to the permeate TDS of the corresponding membrane shell. When the TDS of the permeate from the membrane housing is lower than the fifth concentration threshold, the permeate from the membrane housing is connected to the industrial water tank (3); when the TDS of the permeate from the membrane housing is higher than the fifth concentration threshold, the permeate from the membrane housing is connected to the inlet of the first-stage two-stage freshwater reverse osmosis device (2).

8. The system according to claim 1, characterized in that, The system can also be switched to online cleaning mode; When cleaning the membrane of the first-stage two-stage seawater reverse osmosis device (1), all the permeate from the first-stage two-stage freshwater reverse osmosis device (2) is returned to the inlet of the first-stage two-stage seawater reverse osmosis device (1), and the return ratio of the second concentrate of the first-stage two-stage seawater reverse osmosis device (1) is increased for flushing. When cleaning the membrane of the first-stage two-stage freshwater reverse osmosis device (2), the inlet water of the first-stage two-stage freshwater reverse osmosis device (2) is used as the flushing water source, and the first product water is shut off.

9. The system according to claim 4, characterized in that, The system also predicts future changes in influent water quality based on historical TDS data of the influent, and adjusts the reflux ratio of the second concentrate of the first-stage two-stage seawater reverse osmosis device (1) and the recovery rate of the second-stage unit (102) in advance according to the prediction results, so that the concentration of the first concentrate discharged from the concentrate outlet (4) is kept within the target concentration range.

10. The system according to claim 1, characterized in that, The system also includes an energy recovery device (7) and a booster pump (8); The first concentrated water of the first-stage two-stage seawater reverse osmosis device (1) first passes through the energy recovery device (7) to recover energy, and then is discharged from the system from the concentrated water outlet (4); The booster pump (8) is connected to the energy recovery device (7) and is used to supplement the pressurization of the original seawater after it has been pressurized by the energy recovery device (7).

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