On-line osmosis cleaning forward osmosis-nanofiltration integrated membrane method seawater desalination method and device

Abstract

The invention discloses an on-line osmotic cleaning forward osmosis-nanofiltration integrated membrane method seawater desalination method, which comprises: a, respectively feeding seawater and a draw solution into a raw material liquid side and a draw solution side of a forward osmosis system, feeding concentrated water into a raw material liquid tank, and feeding produced water into a draw solution tank; b, feeding the diluted draw solution into a nanofiltration system, feeding concentrated produced water on a concentrated water side into a concentrated water tank, and feeding produced water on a clear water side into a produced water tank; c, when the water production rate of the clear water side of the nanofiltration system is reduced to the set water production rate, closing the forward osmosis system and the nanofiltration system, and discharging the solution in the membrane component of the nanofiltration system; and d, feeding the concentrated water in the concentrated water tank as a cleaning solution into a permeation cleaning solution tank, feeding the cleaning solution in the permeation cleaning solution tank into the concentrated water side of the nanofiltration system, feeding the produced water in the produced water tank into the clear water side of the nanofiltration system, and carrying out online permeation cleaning on the nanofiltration membrane. According to the method disclosed by the invention, a mode of coupling a forward osmosis technology and a nanofiltration technology is adopted, so that low-energy-consumption seawater desalination is realized, and meanwhile, online cleaning of the nanofiltration membrane is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of water treatment, and specifically relates to an online osmotic cleaning forward osmosis-nanofiltration integrated membrane method for seawater desalination, and further relates to an online osmotic cleaning forward osmosis-nanofiltration integrated membrane method for seawater desalination. Background Art

[0002] The main seawater desalination technologies currently used are multi-effect evaporation, multi-stage flash evaporation, reverse osmosis, etc., but these technologies have disadvantages such as high energy consumption, high processing cost, serious membrane pollution or low water production rate, which restrict the development and utilization of seawater resources.

[0003] As a new membrane separation technology with low energy consumption, light membrane pollution, easy cleaning and high water production rate, forward osmosis technology has broad application prospects in seawater desalination, sewage and wastewater treatment and other fields.

[0004] Forward osmosis uses the osmotic pressure difference of the solutions on both sides of the membrane as the driving force, allowing water to spontaneously pass through the selective permeable membrane from the feed solution (with lower osmotic pressure) to the draw solution (with higher osmotic pressure). Forward osmosis uses special solutes to prepare the draw solution, which can be artificially controlled to prepare a high concentration of draw solution, thereby obtaining a higher osmotic driving pressure and achieving a higher water recovery rate.

[0005] However, the current forward osmosis desalination technology is complex and not conducive to reducing costs, and in-depth research on desalination technology is needed. Summary of the invention

[0006] The present invention is based on the inventor's discovery and understanding of the following facts and problems: forward osmosis faces two major problems in the process of seawater desalination. First, the forward osmosis liquid will be diluted after water permeates through it, and the osmotic pressure must be maintained by concentration recovery, and the recovery process must be combined with other treatment processes, such as evaporation, reverse osmosis, membrane distillation and other processes. Second, the nanofiltration membrane pollution problem used in the regeneration process of the liquid is that the cleaning and replacement of the membrane caused by membrane pollution in the seawater desalination process increases the overall cost. Therefore, it is urgent to develop a simple and low-cost seawater desalination method.

[0007] The present invention aims to solve at least one of the technical problems in the related art to a certain extent. To this end, the embodiment of the present invention proposes an online osmotic cleaning forward osmosis-nanofiltration integrated membrane seawater desalination method, which couples the nanofiltration and forward osmosis processes, not only realizing the recovery of the drawn liquid, but also realizing online osmotic cleaning of the contaminated nanofiltration membrane, thereby improving the water recovery rate, effectively alleviating the contamination of the nanofiltration membrane, and reducing the cost of using the membrane in the seawater desalination process.

[0008] The online osmosis cleaning forward osmosis-nanofiltration integrated membrane seawater desalination method according to the embodiment of the present invention comprises:

[0009] a. Send seawater and draw liquid to the raw liquid side and draw liquid side of the forward osmosis system respectively. After forward osmosis treatment, the concentrated water produced on the raw liquid side is sent to the raw liquid tank, and the produced water on the draw liquid side is sent to the draw liquid tank;

[0010] b. sending the drawn liquid diluted by the forward osmosis system in step a to the concentrated water side of the nanofiltration system; after being concentrated by nanofiltration, the produced water on the concentrated water side is sent to the concentrated water tank, and the produced water on the clean water side is sent to the produced water tank;

[0011] c. When the water production rate of the clean water side of the nanofiltration system drops to the set water production rate, the forward osmosis system and the nanofiltration system are closed, the pressure in the nanofiltration system pipeline is reduced to zero, and the solution in the nanofiltration system membrane assembly is discharged;

[0012] d. The concentrated water in the concentrated water tank after nanofiltration treatment in step b is sent to the osmotic cleaning liquid tank as cleaning liquid, and the cleaning liquid in the osmotic cleaning liquid tank is sent to the concentrated water side of the nanofiltration system. The produced water in the produced water tank in step b is sent to the clean water side of the nanofiltration system. The membrane component of the nanofiltration system performs an osmotic process in the opposite direction to the nanofiltration water production process, and the nanofiltration membrane is cleaned online by osmotic cleaning.

[0013] The advantages and technical effects brought by the online osmosis cleaning forward osmosis-nanofiltration integrated membrane seawater desalination method of the embodiment of the present invention are as follows: 1. In the embodiment of the present invention, forward osmosis technology is used to desalinate seawater, and nanofiltration technology is used to concentrate and regenerate the drawn liquid, thereby realizing low-energy seawater desalination and effectively reducing nanofiltration membrane pollution; 2. In the method of the embodiment of the present invention, forward osmosis and nanofiltration technology are integrated, and the diluted drawn liquid generated by the forward osmosis system is concentrated by nanofiltration. The concentrated water generated during the nanofiltration treatment process is used as a cleaning liquid for cleaning the nanofiltration membrane. The two membrane processes complement each other, reduce the use of external reagents, and realize online cleaning of the nanofiltration membrane; 3. In the method of the embodiment of the present invention, the cleaning of the nanofiltration membrane does not require disassembly of the membrane original and does not require external equipment, thereby realizing online cleaning of the membrane assembly, reducing damage to the membrane assembly, extending the service life of the membrane assembly, and reducing the operating cost of the process.

[0014] In some embodiments, in step a, the draw solution includes a sodium sulfate solution, and / or the concentration of the draw solution is 1.0 mol / L-1.7 mol / L.

[0015] In some embodiments, the forward osmosis treatment process in step a is continuously operated, and the nanofiltration treatment process in step b is intermittently operated. When the water production rate on the draw liquid side of the forward osmosis process drops by 20-30%, the nanofiltration treatment in step b is started, and the draw liquid is sent from the draw liquid tank to the concentrated water tank through a peristaltic pump. The draw liquid in the concentrated water tank is concentrated after nanofiltration treatment and returned to the concentrated water tank through a peristaltic pump, and then the concentrated draw liquid in the concentrated water tank is sent back to the draw liquid tank through a peristaltic pump.

[0016] In some embodiments, in step c, when the water production rate on the clean water side of the nanofiltration system decreases by 20-30% during the nanofiltration treatment in step b, the forward osmosis system and the nanofiltration system are turned off, the pressure in the nanofiltration system pipeline is reduced to zero, the solution in the nanofiltration system membrane assembly is discharged, and the nanofiltration membrane is subjected to the online osmosis cleaning of step d.

[0017] In some embodiments, in step d, the time for online osmotic cleaning of the nanofiltration membrane is 60-600 seconds, and the flow rate of the cleaning liquid during the cleaning process is 0.01-0.03 m / s.

[0018] The embodiment of the present invention also provides an online osmotic cleaning forward osmosis-nanofiltration integrated membrane seawater desalination device, including a forward osmosis system, a nanofiltration system, a raw material liquid tank, an extraction liquid tank, a concentrated water tank, a water production tank and an osmotic cleaning liquid tank, wherein

[0019] The forward osmosis system comprises a raw liquid side and an extraction liquid side, the water inlet of the raw liquid side is connected to the water outlet of the raw liquid tank, the water outlet of the raw liquid side is connected to the water inlet of the raw liquid tank, the water inlet of the extraction liquid side is connected to the water outlet of the extraction liquid tank, and the water outlet of the extraction liquid side is connected to the water inlet of the extraction liquid tank;

[0020] The nanofiltration system comprises a concentrated water side and a clean water side, the water inlet of the concentrated water side is connected to the water outlet of the concentrated water tank through a plunger pump, and the water inlet of the concentrated water side is connected to the water outlet of the osmotic cleaning liquid tank through a peristaltic pump, the water outlet of the concentrated water side is connected to the water inlets of the concentrated water tank and the osmotic cleaning liquid tank respectively, the water inlet of the clean water side is connected to the water outlet of the water production tank, and the water outlet of the clean water side is connected to the water inlet of the water production tank;

[0021] The water inlet of the drawn liquid tank is connected to the water outlet of the concentrated water tank, and the water outlet of the drawn liquid tank is connected to the water inlet of the concentrated water tank;

[0022] The water inlet of the permeate cleaning liquid tank is connected to the water outlet of the concentrated water tank.

[0023] The advantages and technical effects brought by the online osmosis cleaning forward osmosis-nanofiltration integrated membrane seawater desalination device of the embodiment of the present invention are as follows: 1. The device of the embodiment of the present invention combines the forward osmosis system with the nanofiltration system, and adopts the nanofiltration system to concentrate the diluted draw liquid generated by the forward osmosis system. The concentrated water generated by the nanofiltration system is used as the cleaning liquid for cleaning the nanofiltration membrane. The two membrane processes complement each other and reduce the use of external reagents. 2. The device of the embodiment of the present invention does not need to disassemble the nanofiltration membrane original when cleaning the membrane, and does not need external equipment, so the membrane assembly can be cleaned in an online manner, which reduces the damage to the membrane assembly, prolongs the service life of the membrane assembly, and reduces the operating cost of the process.

[0024] In some embodiments, the nanofiltration membrane of the nanofiltration system is NF90.

[0025] In some embodiments, the membrane module of the nanofiltration system is a spiral membrane or a plate membrane.

[0026] In some embodiments, an agitator and / or a temperature controller is provided in the raw material liquid tank, the extraction liquid tank, the concentrated water tank and / or the permeate cleaning liquid tank.

[0027] In some embodiments, a conductivity meter probe is provided in the draw liquid tank. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of an online osmotic cleaning forward osmosis-nanofiltration integrated membrane seawater desalination device according to an embodiment of the present invention;

[0029] Figure 2 It is a normalized flux curve diagram of the nanofiltration process of the online osmosis cleaning forward osmosis-nanofiltration integrated membrane seawater desalination device in long-term operation according to an embodiment of the present invention;

[0030] Figure 3 It is a curve diagram showing the change of the cleaning efficiency of the online osmosis cleaning forward osmosis-nanofiltration integrated membrane seawater desalination device according to an embodiment of the present invention as a function of the cleaning times. DETAILED DESCRIPTION

[0031] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0032] The embodiment of the present invention provides an online osmotic cleaning forward osmosis-nanofiltration integrated membrane method for seawater desalination, comprising:

[0033] a. Send seawater and draw liquid to the raw liquid side and draw liquid side of the forward osmosis system respectively. After forward osmosis treatment, the concentrated water produced on the raw liquid side is sent to the raw liquid tank, and the produced water on the draw liquid side is sent to the draw liquid tank;

[0034] b. sending the drawn liquid diluted by the forward osmosis system in step a to the concentrated water side of the nanofiltration system; after being concentrated by nanofiltration, the produced water on the concentrated water side is sent to the concentrated water tank, and the produced water on the clean water side is sent to the produced water tank;

[0035] c. When the water production rate of the clean water side of the nanofiltration system drops to the set water production rate, the forward osmosis system and the nanofiltration system are closed, the pressure in the nanofiltration system pipeline is reduced to zero, and the solution in the nanofiltration system membrane assembly is discharged;

[0036] d. The concentrated water in the concentrated water tank after nanofiltration treatment in step b is sent to the osmotic cleaning liquid tank as cleaning liquid, and the cleaning liquid in the osmotic cleaning liquid tank is sent to the concentrated water side of the nanofiltration system. The produced water in the produced water tank in step b is sent to the clean water side of the nanofiltration system. The membrane component of the nanofiltration system performs an osmotic process in the opposite direction to the nanofiltration water production process, and the nanofiltration membrane is cleaned online by osmotic cleaning.

[0037] The online osmotic cleaning forward osmosis-nanofiltration integrated membrane seawater desalination method of the embodiment of the present invention adopts forward osmosis technology to desalinate seawater, and adopts nanofiltration technology to concentrate and regenerate the drawn liquid, thereby realizing low-energy seawater desalination and effectively reducing nanofiltration membrane pollution. In the method of the embodiment of the present invention, forward osmosis and nanofiltration technologies are integrated, and the diluted drawn liquid generated by the forward osmosis system is concentrated by nanofiltration. The concentrated water generated during the nanofiltration treatment process is used as a cleaning liquid for cleaning the nanofiltration membrane. The two membrane processes complement each other, reduce the use of external reagents, and realize online cleaning of the nanofiltration membrane. In the method of the embodiment of the present invention, the cleaning of the nanofiltration membrane does not require disassembly of the membrane original and does not require external equipment, thereby realizing online cleaning of the membrane assembly, reducing damage to the membrane assembly, extending the service life of the membrane assembly, and reducing the operating cost of the process.

[0038] In some embodiments, in step a, the draw solution includes a sodium sulfate solution, and / or the concentration of the draw solution is 1.0 mol / L-1.7 mol / L.

[0039] In some embodiments, the forward osmosis treatment process in step a is continuously operated, and the nanofiltration treatment process in step b is intermittently operated. When the water production rate on the draw liquid side of the forward osmosis process drops by 20-30%, the nanofiltration treatment in step b is started, and the draw liquid is sent from the draw liquid tank to the concentrated water tank through a peristaltic pump. The draw liquid in the concentrated water tank is concentrated after nanofiltration treatment and returned to the concentrated water tank through a peristaltic pump, and then the concentrated draw liquid in the concentrated water tank is sent back to the draw liquid tank through a peristaltic pump.

[0040] In some embodiments, in step c, when the water production rate on the clean water side of the nanofiltration system decreases by 20-30% during the nanofiltration treatment in step b, the forward osmosis system and the nanofiltration system are turned off, the pressure in the nanofiltration system pipeline is reduced to zero, the solution in the nanofiltration system membrane assembly is discharged, and the nanofiltration membrane is subjected to the online osmosis cleaning of step d.

[0041] In some embodiments, in step d, the time for online osmotic cleaning of the nanofiltration membrane is 60-600 seconds, and the flow rate of the cleaning liquid during the cleaning process is 0.01-0.03 m / s.

[0042] like Figure 1 As shown, an embodiment of the present invention also provides an online osmotic cleaning forward osmosis-nanofiltration integrated membrane seawater desalination device, including a forward osmosis system 1, a nanofiltration system 2, a raw liquid tank 3, an extraction liquid tank 4, a concentrated water tank 5, a water production tank 6 and an osmotic cleaning liquid tank 7.

[0043] The forward osmosis system 1 includes a raw liquid side and an extraction liquid side, the water inlet of the raw liquid side is connected to the water outlet of the raw liquid tank 3, the water outlet of the raw liquid side is connected to the water inlet of the raw liquid tank 3, the water inlet of the extraction liquid side is connected to the water outlet of the extraction liquid tank 4, and the water outlet of the extraction liquid side is connected to the water inlet of the extraction liquid tank 4.

[0044] The nanofiltration system includes a concentrate side and a clean water side. The water inlet of the concentrate side is connected to the water outlet of the concentrate tank 5 through a plunger pump 8, and the water inlet of the concentrate side is connected to the water outlet of the osmotic cleaning liquid tank 7 through a peristaltic pump 9. The water outlet of the concentrate side is connected to the water inlets of the concentrate tank 5 and the osmotic cleaning liquid tank 7 respectively, the water inlet of the clean water side is connected to the water outlet of the water production tank 6, and the water outlet of the clean water side is connected to the water inlet of the water production tank 6.

[0045] The water inlet of the draw liquid tank 4 is connected to the water outlet of the concentrated water tank 5 , and the water outlet of the draw liquid tank 4 is connected to the water inlet of the concentrated water tank 5 . The water inlet of the permeate cleaning liquid tank 7 is connected to the water outlet of the concentrated water tank 5 .

[0046] In some embodiments, the nanofiltration membrane used in the nanofiltration system 2 is NF90.

[0047] In some embodiments, the membrane module of the nanofiltration system 2 is a spiral membrane or a plate membrane.

[0048] In some embodiments, a stirrer and a temperature controller (not shown in the figure) are provided in the raw material liquid tank 3 , the extraction liquid tank 4 , the concentrated water tank 5 , and the permeate cleaning liquid tank 7 .

[0049] In some embodiments, a conductivity meter probe is provided in the draw liquid tank 4. When the concentration of the draw liquid in the draw liquid tank is insufficient for the forward osmosis process, the forward osmosis seawater desalination process can be performed by additionally adding inorganic salts.

[0050] Example 1

[0051] use Figure 1 The device of the embodiment of the present invention shown performs seawater desalination processing.

[0052] The seawater is sent to the raw liquid side of the forward osmosis system 1 via the raw liquid tank 3, and a 1.2 mol / L sodium sulfate solution is used as the draw liquid and sent to the draw liquid side of the forward osmosis system 1 via the draw liquid tank 4. After the seawater is treated by the forward osmosis of the forward osmosis system 1, the concentrated water on the raw liquid side returns to the raw liquid tank 3, and the produced water on the draw liquid side returns to the draw liquid tank 4.

[0053] When the water production rate of the draw liquid side of the forward osmosis system 1 drops by 25%, the nanofiltration system 2 is started, and the nanofiltration membrane used in the membrane assembly of the nanofiltration system is the NF270 nanofiltration membrane. The draw liquid in the draw liquid tank 4 is pumped into the concentrated water tank 5, and enters the concentrated water side of the nanofiltration system 2 through the water outlet of the concentrated water tank 5 via the plunger pump 8. After the nanofiltration treatment, the concentrated draw liquid returns to the concentrated water tank 5, and the produced water on the clean water side of the nanofiltration system 2 enters the water production tank 6 to complete the seawater desalination treatment.

[0054] When the water production rate of the clean water side of the nanofiltration system 2 drops by 30%, close the inlet valve and outlet valve of the forward osmosis system 1, close the plunger pump 8, open the pressure regulating valve to make the pressure in the pipeline of the nanofiltration system 2 zero, discharge the solution in the membrane assembly of the nanofiltration system 2, and close the valve connecting the concentrated water side of the nanofiltration system 2 with the concentrated water tank 5. Pump the concentrated water in the concentrated water tank 5 into the permeation cleaning liquid tank 7 as the permeation cleaning liquid, send the cleaning liquid into the concentrated water side of the nanofiltration system 2 through the peristaltic pump 9, and pump the produced water in the water production tank 6 into the clean water side of the nanofiltration system 2. At this time, the membrane assembly of the nanofiltration system 2 is undergoing a permeation process in the opposite direction to the water production process of the nanofiltration treatment, and the nanofiltration membrane is cleaned online. The flow rate of the cleaning liquid is 0.0213m / s, and the cleaning time is 10min. During the permeation cleaning, the produced water on the concentrated water side of the nanofiltration system 2 is sent to the permeation cleaning liquid tank 7.

[0055] After cleaning in this embodiment, the cleaning efficiency of the nanofiltration membrane is 93.6%.

[0056] The cleaning efficiency is calculated as follows:

[0057] Cleaning efficiency = J1 / J0

[0058] Where J0 is the normalized flux of the nanofiltration membrane at the beginning of the nanofiltration process, L / (m 2 h);

[0059] J1——Normalized flux of nanofiltration membrane after nanofiltration process is completed and permeate cleaning, L / (m 2 h).

[0060] The quality of the produced water in the water production tank 6 after the seawater desalination treatment in this embodiment is shown in Table 1.

[0061] Table 1

[0062]

[0063] It can be seen from Table 1 that the concentrations of most ions meet the standards for drinking water. - The content is relatively high, which is mainly because some ions in the raw liquid pass through the forward osmosis membrane into the draw liquid during the forward osmosis process. The diluted draw liquid is concentrated in the nanofiltration desalination process due to the Donan effect on the divalent SO4 2- The interception effect of Cl - .

[0064] Comparative Example 1

[0065] The same seawater desalination method as in Example 1 is used, except that when the water production rate on the clean water side of the nanofiltration system 2 drops by 30%, the nanofiltration concentrated water in Example 1 is not used as the cleaning liquid for online osmosis cleaning. Instead, the forward osmosis system and the nanofiltration system are shut down, the nanofiltration membrane assembly is disassembled, and a 1.2 mol / L sodium sulfate solution is used as the cleaning liquid to clean the nanofiltration membrane.

[0066] After cleaning in this comparative example, the cleaning efficiency of the nanofiltration membrane is 84.3%.

[0067] Comparative Example 2

[0068] The method is the same as the seawater desalination method in Example 1, except that when the water production rate on the clean water side of the nanofiltration system 2 drops by 30%, the nanofiltration concentrated water in Example 1 is not used as the cleaning liquid for osmotic cleaning. Instead, the forward osmosis system and the nanofiltration system are shut down, the nanofiltration membrane assembly is disassembled, and clean water is used as the cleaning liquid to clean the nanofiltration membrane.

[0069] After cleaning in Comparative Example 2, the cleaning efficiency of the nanofiltration membrane was 81.6%.

[0070] The online osmotic cleaning method of Example 1 of the present invention combines the effects of physical flushing, osmotic backwashing and dissolution, greatly improving the cleaning efficiency, while the salt washing used in Comparative Example 1 can only achieve physical flushing and dissolution, and Comparative Example 2 can only achieve physical flushing, and the cleaning effect is significantly reduced.

[0071] The recovery of the flux of the nanofiltration membrane during long-term operation was investigated for the online osmotic cleaning forward osmosis-nanofiltration integrated membrane seawater desalination method of Example 1 and the method of Comparative Example 2.

[0072] Test conditions: the temperature is 25±1°C, and the transmembrane pressure difference during normal operation of the nanofiltration system is 0.7 MPa. During the nanofiltration membrane cleaning process, the concentration of the cleaning solution during the online osmotic cleaning process of Example 1 is 1.2 mol / L, the flow rate of the cleaning solution in Example 1 and Comparative Example 2 is 0.0213 m / s, and the cleaning time for each nanofiltration membrane is 10 min.

[0073] Figure 2 The normalized flux curve of the nanofiltration process in the online osmotic cleaning method of Example 1 and the hydraulic cleaning method of Comparative Example 2 in the long-term operation is shown in FIG. Figure 2 It can be seen that in the long-term operation, the normalized flux gradually decreases. After a total of 4 cleanings, the online osmotic cleaning method of Example 1 and the hydraulic cleaning method of Comparative Example 2 both increase the normalized flux, and then the normalized flux continues to decrease. However, as the number of cleanings increases, the online osmotic cleaning method of Example 1 is more conducive to the improvement of the normalized flux of the nanofiltration membrane after cleaning than the hydraulic cleaning method of Comparative Example 2. It can be seen that the osmotic cleaning method of Example 1 is significantly better than the hydraulic cleaning method of Comparative Example 1.

[0074] like Figure 3 As shown, with the increase of the number of cycles of the nanofiltration process, the cleaning efficiency of Example 1 and Comparative Example 2 both showed a decreasing trend to varying degrees. Using the online osmotic cleaning of Example 1, after four cleanings, the cleaning efficiency dropped from 93.6% to 86.7%, while using the hydraulic cleaning method of Comparative Example 2, after four cleanings, the cleaning efficiency dropped significantly from 81.6% to 73.3%. It can be seen that after multiple cleanings, the cleaning efficiency of the hydraulic cleaning of Comparative Example 2 dropped significantly faster than the osmotic cleaning of Example 1 of the present invention. The cleaning efficiency of the fourth cleaning in the cleaning method of Comparative Example 2 dropped by 8.3% compared with the first cleaning, while the online osmotic cleaning method of Example 1 of the present invention only dropped by 6.9%.

[0075] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", "some examples", etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples without contradiction.

[0076] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. An online osmotic cleaning forward osmosis-nanofiltration integrated membrane method for seawater desalination, characterized in that: include: a. Send seawater and draw liquid to the raw liquid side and draw liquid side of the forward osmosis system respectively. After forward osmosis treatment, the concentrated water produced on the raw liquid side is sent to the raw liquid tank, and the produced water on the draw liquid side is sent to the draw liquid tank; b. sending the drawn liquid diluted by the forward osmosis system in step a to the concentrated water side of the nanofiltration system; after being concentrated by nanofiltration, the produced water on the concentrated water side is sent to the concentrated water tank, and the produced water on the clean water side is sent to the produced water tank; c. When the water production rate of the clean water side of the nanofiltration system drops to the set water production rate, the forward osmosis system and the nanofiltration system are closed, the pressure in the nanofiltration system pipeline is reduced to zero, and the solution in the nanofiltration system membrane assembly is discharged; d. The concentrated water in the concentrated water tank after nanofiltration treatment in step b is sent to the osmotic cleaning liquid tank as cleaning liquid, and the cleaning liquid in the osmotic cleaning liquid tank is sent to the concentrated water side of the nanofiltration system. The produced water in the produced water tank in step b is sent to the clean water side of the nanofiltration system. The membrane component of the nanofiltration system performs an osmotic process in the opposite direction to the nanofiltration water production process, and the nanofiltration membrane is cleaned online by osmotic cleaning.

2. The method for seawater desalination by online osmosis cleaning forward osmosis-nanofiltration integrated membrane method according to claim 1, characterized in that: In the step a, the draw solution comprises a sodium sulfate solution, and / or the concentration of the draw solution is 1.0 mol / L-1.7 mol / L.

3. The method for desalination of seawater by online osmosis cleaning forward osmosis-nanofiltration integrated membrane method according to claim 1, characterized in that: The forward osmosis treatment process in step a is continuously operated, and the nanofiltration treatment process in step b is intermittently operated. When the water production rate on the draw liquid side of the forward osmosis process decreases by 20-30%, the nanofiltration treatment in step b is started, and the draw liquid is sent from the draw liquid tank to the concentrated water tank through a peristaltic pump. The draw liquid in the concentrated water tank is concentrated through nanofiltration treatment and then returned to the concentrated water tank, and then the concentrated draw liquid in the concentrated water tank is sent back to the draw liquid tank through a peristaltic pump.

4. The method for desalination of seawater by online osmosis cleaning forward osmosis-nanofiltration integrated membrane method according to claim 1, characterized in that: In the step c, when the water production rate on the clean water side of the nanofiltration system decreases by 20-30% during the nanofiltration treatment in the step b, the forward osmosis system and the nanofiltration system are turned off, the pressure in the nanofiltration system pipeline is reduced to zero, the solution in the nanofiltration system membrane assembly is discharged, and the nanofiltration membrane is subjected to the online osmotic cleaning of the step d.

5. The method for desalination of seawater by online osmosis cleaning forward osmosis-nanofiltration integrated membrane method according to claim 1, characterized in that: In the step d, the time for online osmotic cleaning of the nanofiltration membrane is 60-600 seconds, and the flow rate of the cleaning liquid during the cleaning process is 0.01-0.03 m / s.

6. An online osmotic cleaning forward osmosis-nanofiltration integrated membrane seawater desalination device, characterized in that: It includes forward osmosis system, nanofiltration system, raw material liquid tank, extraction liquid tank, concentrated water tank, water production tank and osmotic cleaning liquid tank. The forward osmosis system comprises a raw liquid side and an extraction liquid side, the water inlet of the raw liquid side is connected to the water outlet of the raw liquid tank, the water outlet of the raw liquid side is connected to the water inlet of the raw liquid tank, the water inlet of the extraction liquid side is connected to the water outlet of the extraction liquid tank, and the water outlet of the extraction liquid side is connected to the water inlet of the extraction liquid tank; The nanofiltration system comprises a concentrated water side and a clean water side, the water inlet of the concentrated water side is connected to the water outlet of the concentrated water tank through a plunger pump, and the water inlet of the concentrated water side is connected to the water outlet of the osmotic cleaning liquid tank through a peristaltic pump, the water outlet of the concentrated water side is connected to the water inlets of the concentrated water tank and the osmotic cleaning liquid tank respectively, the water inlet of the clean water side is connected to the water outlet of the water production tank, and the water outlet of the clean water side is connected to the water inlet of the water production tank; The water inlet of the drawn liquid tank is connected to the water outlet of the concentrated water tank, and the water outlet of the drawn liquid tank is connected to the water inlet of the concentrated water tank; The water inlet of the permeate cleaning liquid tank is connected to the water outlet of the concentrated water tank.

7. The online osmosis cleaning forward osmosis-nanofiltration integrated membrane seawater desalination device according to claim 6, characterized in that: The nanofiltration membrane of the nanofiltration system is NF90.

8. The online osmosis cleaning forward osmosis-nanofiltration integrated membrane seawater desalination device according to claim 6 or 7, characterized in that: The membrane component of the nanofiltration system is a roll membrane or a plate membrane.

9. The online osmosis cleaning forward osmosis-nanofiltration integrated membrane seawater desalination device according to claim 6, characterized in that: A stirrer and / or a temperature controller are arranged in the raw material liquid tank, the extraction liquid tank, the concentrated water tank and / or the permeation cleaning liquid tank.

10. The online osmosis cleaning forward osmosis-nanofiltration integrated membrane seawater desalination device according to claim 6, characterized in that: A conductivity meter probe is arranged in the draw liquid tank.

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