Filtering device

Abstract

A filtering device comprises a nanofiltration device, a preservation filter externally connected with a raw water treatment pipeline is arranged at the front end of the nanofiltration device, a corresponding water storage device is arranged at the rear end of the nanofiltration device, all the device parts are communicated through corresponding pipelines, and a corresponding power device and a corresponding monitoring device are arranged on the corresponding pipelines. Corresponding control valves are arranged at the front and rear ends of the nanofiltration device and the water storage device. According to the utility model, the sulfate radical rejection rate is higher, the nanofiltration salt separation effect is better, and the economic values of crystallized salt and filtered water are improved.

Description

Technical Field

[0001] The utility model belongs to the technical field of filtration, and in particular relates to a salt separation and filtration device using a secondary nanofiltration technology. Background Art

[0002] Nanofiltration technology is a membrane separation technology between ultrafiltration and reverse osmosis. Its molecular weight cutoff is in the range of 80-1000 and its pore size is a few nanometers, so it is called nanofiltration. Nanofiltration is a pressure-driven membrane separation process between reverse osmosis and ultrafiltration. It is mainly used for purification of drinking water and industrial water, purification of wastewater, and concentration of valuable components in process fluids.

[0003] When nanofiltration technology is used in salt separation filtration in water treatment, the existing salt separation nanofiltration device is a one-stage three-stage structure. The pressure in the third stage of this structure is often insufficient during operation, which can easily cause fouling of the membrane elements and a decrease in the overall sulfate retention rate. This has a great impact on the subsequent evaporation and crystallization operation, resulting in low salt separation efficiency and poor results. The purity of the crystallized salt is also low, and the crystallized salt from evaporation and crystallization is mixed salt, which has a low economic value. Utility Model Content

[0004] The utility model aims to provide a two-stage nanofiltration device with better salt separation effect and higher efficiency, so as to solve the technical problems of insufficient pressure in the third stage, poor filtering and salt separation effect and low efficiency in the existing one-stage three-stage salt separation nanofiltration device.

[0005] To achieve the above purpose, the specific technical solution of the utility model is as follows:

[0006] A filtering device includes a nanofiltration device, wherein a preservation filter connected to an external raw water treatment pipeline is provided at the front end of the nanofiltration device, and a corresponding water storage device is provided at the rear end of the nanofiltration device. The components of the devices are connected through corresponding pipelines, and corresponding power devices and monitoring devices are provided on the corresponding pipelines. Corresponding control valves are provided at both the front and rear ends of the nanofiltration device and the water storage device. The nanofiltration device includes a primary nanofiltration and a secondary nanofiltration, which are connected through an intermediate pipeline, and the primary nanofiltration includes a first nanofiltration stage and a second nanofiltration stage.

[0007] Furthermore, the nanofiltration device includes a primary nanofiltration and a secondary nanofiltration, wherein the primary nanofiltration includes a first nanofiltration stage and a second nanofiltration stage connected in series through a second connecting pipe, the power device includes a raw water pump, a first booster pump and a second booster pump, the water inlet end of the preservation filter is connected to an inlet pipe of an external raw water pretreatment pipeline, the raw water pump is arranged on the inlet pipe, the preservation filter and the nanofiltration device are connected through a first connecting pipe, the first booster pump is arranged on the first connecting pipe, and a second booster pump is arranged on the intermediate pipeline.

[0008] Furthermore, the nanofiltration stage 1 and the nanofiltration stage 2 are connected in series through a second connecting pipe. The structures of the nanofiltration stage 1, the nanofiltration stage 2 and the secondary nanofiltration are the same, including a tubular shell with a hollow interior and openings at both ends. The two ends of the shell are respectively provided with corresponding upper end covers and lower end covers. The inner cavity of the shell is provided with a partition layer that divides it into a brine chamber and a post-filtration chamber. The partition layer is provided with a water passage that connects the brine chamber and the post-filtration chamber. The water passage is provided with a corresponding nanofiltration membrane assembly. The upper end cover is provided with a water inlet connected to the brine chamber, and the lower end cover is provided with a water outlet connected to the post-filtration chamber. The bottom of the side wall of the brine chamber is provided with a brine inlet connected to the outside. The nanofiltration device is connected to the preservation filter through the nanofiltration stage 1. The two ends of the first connecting pipe are respectively connected to the water outlet end of the preservation filter and the water inlet of the nanofiltration stage 1, the two ends of the second connecting pipe are respectively connected to the water outlet of the nanofiltration stage 1 and the water inlet of the nanofiltration stage 2, and the two ends of the intermediate pipeline are respectively connected to the water outlet of the nanofiltration stage 2 and the water inlet of the secondary nanofiltration.

[0009] Furthermore, the multiple water outlets are evenly distributed on the separation layer in a matrix manner, and each water outlet is provided with a corresponding nanofiltration membrane assembly. The nanofiltration membrane assembly is arranged in the brine chamber, and includes a tubular nanofiltration membrane, a top cover is provided at the upper end, and a fixed seat is provided at the lower end thereof and is installed corresponding to the separation layer. The inner and outer layers of the nanofiltration membrane are provided with corresponding support nets, and the two ends of the support nets are respectively connected to the top cover and the fixed seat, and the fixed seat is provided with a drain corresponding to the water outlet, and a corresponding sealing gasket is provided between the fixed seat and the separation layer.

[0010] Furthermore, the water storage device includes a first concentrated water tank, a second concentrated water tank, a clean water tank and an intermediate water tank, wherein the first concentrated water tank is connected to the brine inlet of the first-level nanofiltration through a first outlet pipe, the second concentrated water tank is connected to the brine inlet of the second-level nanofiltration through a second outlet pipe, the inlet of the clean water tank is connected to the outlet of the second-level nanofiltration through a third outlet pipe, and an intermediate water tank is provided on the intermediate pipeline between the first-level nanofiltration and the second booster pump. The intermediate water tank divides the intermediate pipeline into two sections, a middle-upper pipeline and a middle-lower pipeline. The inlet of the intermediate water tank is connected to the outlet of the second section of the nanofiltration through the middle-upper pipeline, and the outlet of the intermediate water tank is connected to the water inlet of the second-level nanofiltration through the middle-lower pipeline.

[0011] Furthermore, the first water outlet pipe includes a section a pipeline and a section b pipeline connected in parallel, and the outlet ends of the two are connected in parallel to the inlet of the first concentrated water tank, wherein the inlet of section a pipeline is connected to the brine inlet of the first nanofiltration stage, and the inlet of section b pipeline is connected to the brine inlet of the second nanofiltration stage.

[0012] Furthermore, the monitoring device includes a first pressure gauge provided on a first connecting pipe between the first booster pump and the nanofiltration device and a second pressure gauge provided on an intermediate pipeline between the second booster pump and the secondary nanofiltration device.

[0013] Furthermore, the water outlets of the primary nanofiltration and the secondary nanofiltration are both provided with corresponding sampling ports.

[0014] Furthermore, a return water pipeline is connected to the outlet of the clean water tank, and the clean water tank is connected to the inlet of the middle and lower pipelines through the return water pipeline. The outlet of the return water pipeline and the outlet of the middle water tank are connected in parallel to the inlet of the middle and lower pipelines.

[0015] The filtering device of the utility model transforms the first-stage three-stage salt separation nanofiltration into a second-stage nanofiltration, thereby improving the water pressure of the second-stage nanofiltration, making the sulfate retention rate of the filtering device higher, the nanofiltration salt separation effect better, the purity of the filtered water and the subsequent crystallized salt higher, making the usable range of the filtered water wider, improving the economic value of the crystallized salt and the filtered water, and making the economic benefits of the two better. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the structure of the utility model;

[0017] Figure 2 This is a schematic diagram of the internal half-section structure of a nanofiltration stage of the utility model;

[0018] Figure 3 For this utility model Figure 2 Structural diagram in AA direction;

[0019] Figure 4 For this utility model Figure 2 A schematic diagram of the local enlarged structure at point B;

[0020] Explanation of the markings in the figure: 1. Primary nanofiltration; 11. First stage of nanofiltration; 12. Second stage of nanofiltration; 13. Second stage of nanofiltration; 2. Shell; 21. Upper end cover; 22. Lower end cover; 23. Separation layer; 24. Brine chamber; 25. Post-filtration chamber; 26. Water inlet; 27. Water inlet; 28. Water outlet; 29. ​​Brine inlet; 3. Nanofiltration membrane assembly; 31. Nanofiltration membrane; 32. Top cover; 33. Fixed seat; 34. Support net; 35. Water outlet; 36. Sealing gasket; 37. Fixed net; 38. Support ring; 4. Security filter; 5. Water inlet pipe; 51. First connecting pipe; 52. Second connecting pipe; 53. Intermediate pipeline; 531. Middle-upper pipeline; 532. Middle-lower pipeline; 54. First water outlet pipe; 541. Section a pipeline; 542. Section b pipeline; 55. Second water outlet pipe; 56. Third water outlet pipe; 57. Sampling port; 58. Return water pipeline; 6. Raw water pump; 61. First booster pump; 62. Second booster pump; 7. First concentrated water tank; 71. Second concentrated water tank; 72. Clean water tank; 73. Intermediate water tank; 8. First pressure gauge; 81. Second pressure gauge; 9. Control valve. DETAILED DESCRIPTION

[0021] In order to better understand the purpose, structure and function of the utility model, a filtering device of the utility model is further described in detail below in conjunction with the accompanying drawings.

[0022] like Figure 1-4 As shown, the filtering device of the utility model includes a nanofiltration device, a preservation filter 4 and a water storage device, wherein the preservation filter 4 is arranged at the front end of the nanofiltration device, the filtering device is externally connected to the raw water pretreatment pipeline through the water inlet end of the preservation filter 4, the water outlet end of the preservation filter 4 is connected to the water inlet end of the nanofiltration device, and the water outlet end of the nanofiltration device is provided with a corresponding water storage device, the above device components are connected through corresponding pipelines, and corresponding power devices and monitoring devices are provided on the corresponding pipelines. The power device provides power for the water in the pipeline, and the pretreated raw water is transported to the preservation filter 4 under its action. The particulate impurities in the raw water that have been leaked during the pretreatment are intercepted by the preservation filter 4 to prevent them from causing pollution or damage to the membrane elements in the subsequent nanofiltration device, and the salt water filtered by the preservation filter 4 is transported to the nanofiltration device, and after the salt separation treatment by the nanofiltration device, it is finally transported to the corresponding water storage device by the corresponding pipeline for storage, and waits for the processing of the subsequent process. In this process, the monitoring device monitors the water pressure in the pipeline in real time to avoid danger caused by excessive pressure or affect the filtration quality due to inappropriate pressure.

[0023] The nanofiltration device includes a primary nanofiltration 1 and a secondary nanofiltration 13, wherein the primary nanofiltration 1 includes a first nanofiltration stage 11 and a second nanofiltration stage 12 connected in series, and the structures of the first nanofiltration stage 11, the second nanofiltration stage 12 and the secondary nanofiltration 13 are the same, and include a shell 2, which is a tubular body with a hollow interior and openings at both ends, and an upper end of the shell 2 is provided with a corresponding upper end cover 21, and a lower end of the shell 2 is provided with a corresponding lower end cover 22. After the upper end cover 21 and the lower end cover 22 are correspondingly installed, the inner cavity of the shell 2 becomes a sealed chamber, and a partition layer 23 is provided in the inner cavity of the shell 2, and the partition layer 23 divides the inner cavity of the shell 2 into a salt water cavity 24 and a post-filtration cavity 25. In this embodiment, the partition layer 23 is arranged The lower part of the inner cavity of the shell 2 has an upper chamber as a salt water chamber 24 and a lower chamber as a post-filtration chamber 25. The partition layer 23 is provided with a water inlet 26 connecting the salt water chamber 24 and the post-filtration chamber 25. A plurality of water inlets 26 are evenly distributed on the partition layer 23 in a matrix. Each water inlet 26 is provided with a nanofiltration membrane assembly 3 for performing nanofiltration and salt separation on the water flowing through the water inlet 26. The nanofiltration membrane assembly 3 is arranged in the salt water chamber 24. The upper end cover 21 is provided with a water inlet 27 connected to the salt water chamber 24. The lower end cover 22 is provided with a water outlet 28 connected to the post-filtration chamber 25. The bottom of the side wall of the salt water chamber 24 is provided with a salt water inlet 29 connected to the outside. The water to be filtered enters the salt water chamber 24 through the water inlet 27. The clean water treated by the nanofiltration membrane assembly 3 flows into the post-filtration chamber 25 through the water inlet 26, and is then discharged through the water outlet 28. The concentrated water retained by the nanofiltration membrane assembly 3 after the clean water in the brine chamber 24 is filtered is discharged through the brine inlet 29, thereby completing the nanofiltration and salt separation of the brine. In order to achieve a better salt separation effect, the nanofiltration device is provided with a primary nanofiltration 1 and a secondary nanofiltration 13. The nanofiltration device is connected to the water outlet end of the preservation filter 4 through the water inlet 27 of the nanofiltration stage 11. The pipeline connecting the two is a first connecting pipe 51. The two ends of the first connecting pipe 51 are respectively connected to the water outlet end of the preservation filter 4 and the water inlet 27 of the nanofiltration stage 11. The nanofiltration stage 11 and the nanofiltration stage 2 12 are connected through the second The connecting pipes 52 are interconnected, and the two ends of the second connecting pipe 52 are respectively connected to the water outlet 28 of the first nanofiltration stage 11 and the water inlet 27 of the second nanofiltration stage 12. The first nanofiltration stage 1 and the second nanofiltration stage 13 are interconnected through an intermediate pipeline 53, and the two ends of the intermediate pipeline 53 are respectively connected to the water outlet 28 of the second nanofiltration stage 12 and the water inlet 27 of the second nanofiltration stage 13. The filtered water treated by the first nanofiltration stage 1 flows out through the water outlet 28 of the second nanofiltration stage 12, and is then transported to the second nanofiltration stage 13 through the intermediate pipeline 53 for further nanofiltration and salt separation treatment. The clean water and concentrated water after the salt separation treatment by the nanofiltration device are respectively transported to different water storage devices through corresponding pipelines for storage, waiting for the next step of processing.

[0024] The nanofiltration membrane assembly 3 includes a tubular nanofiltration membrane 31, a top cover 32 is provided at the upper end thereof, and a fixed seat 33 is provided at the lower end thereof and is installed corresponding to the separation layer 23. The inner and outer layers of the nanofiltration membrane 31 are provided with corresponding support nets 34, and the two ends of the support net 34 are respectively connected to the top cover 32 and the fixed seat 33 to provide support for the nanofiltration membrane 31. The fixed seat 33 is provided with a water outlet 35 corresponding to the water outlet 26. The filtered water in the inner cavity of the nanofiltration membrane 31 flows into the post-filtration cavity 25 through the water outlet 35. A corresponding sealing gasket 36 is provided between the fixed seat 33 and the separation layer 23 to prevent the unfiltered water in the brine cavity 24 from flowing into the post-filtration cavity 25 through the gap between the two, thereby affecting the filtering effect. The nanofiltration membrane assembly 3 arranged in multiple matrices increases the area of ​​the nanofiltration membrane 31 and the water base, so that the nanofiltration effect is better.

[0025] A fixed net 37 is provided at the upper part of the inner cavity of the nanofiltration device shell 2, and the outer circle of the fixed net 37 is connected to the inner wall of the inner cavity of the shell 2. The fixed net 37 is provided with a plurality of support rings 38 corresponding to the nanofiltration membrane assembly 3. The support rings 38 are slidably connected to the nanofiltration membrane assembly 3. The upper surface of the fixed net 37 is lower than the height of the top surface of the nanofiltration membrane assembly 3. The fixed net 37 provides support assistance for the nanofiltration membrane assembly 3 to prevent it from tilting under the action of water pressure, thereby affecting the nanofiltration effect.

[0026] The power device includes a raw water pump 6, a first booster pump 61 and a second booster pump 62. A connected water inlet pipe 5 is provided at the water inlet end of the preservation filter 4, which is connected to the raw water pretreatment pipeline through the water inlet pipe 5. The raw water pump 6 is arranged on the water inlet pipe 5 at the front end of the preservation filter 4 to provide power for the pretreated raw water, so that the pretreated raw water has a certain pressure before entering the preservation filter 4, thereby improving the filtration rate of the raw water in the preservation filter 4. The first booster pump 61 is arranged on the first connecting pipe 51 between the preservation filter 4 and the nanofiltration device. The first booster pump 61 is for entering a The water of the first-stage nanofiltration 1 provides power. The water treated by the preservation filter 4 has a certain pressure under the action of the first booster pump 61, which improves its efficiency and effect in the first-stage nanofiltration 1. A second booster pump 62 is provided on the intermediate pipeline 53 between the first-stage nanofiltration 1 and the second-stage nanofiltration 13. The second booster pump 62 re-pressurizes the filtered water treated by the first-stage nanofiltration 1, thereby increasing the pressure of the water entering the second-stage nanofiltration 13, preventing the water entering the second-stage nanofiltration 13 from damaging the membrane elements of the second-stage nanofiltration 13 due to too low pressure, and at the same time improving the overall sulfate retention rate of the second-stage nanofiltration 13.

[0027] The water storage device includes a first concentrated water tank 7, a second concentrated water tank 71, a clean water tank 72 and an intermediate water tank 73, wherein the first concentrated water tank 7 is connected to the brine port 29 of the primary nanofiltration 1 through a first outlet pipe 54, and the first outlet pipe 54 includes a section a pipeline 541 and a section b pipeline 542 connected in parallel, and the outlet ends of the two are connected in parallel to the inlet of the first concentrated water tank 7, wherein the inlet of the section a pipeline 541 is connected to the brine port 29 of the first nanofiltration stage 11, and the inlet of the section b pipeline 542 is connected to the brine port 29 of the first nanofiltration stage 11. The salt water inlet 29 of the second nanofiltration stage 12 is connected, the first concentrated water intercepted by the first nanofiltration stage 1 is collected in the first concentrated water tank 7 through the first outlet pipe 54, the second concentrated water tank 71 is connected to the salt water inlet 29 of the second nanofiltration stage 13 through the second outlet pipe 55, the second concentrated water intercepted by the second nanofiltration stage 13 is collected in the second concentrated water tank 71 through the second outlet pipe 55, the inlet of the clean water tank 72 is connected to the outlet 28 of the second nanofiltration stage 13 through the third outlet pipe 56, and the clean water after the secondary nanofiltration treatment is passed through the second concentrated water tank 71. The water is concentrated in the clean water tank 72 through the third water outlet pipe 56. The intermediate water tank 73 is arranged on the intermediate pipeline 53 between the primary nanofiltration 1 and the second booster pump 62, and serves as a buffer for the connection between the two. The intermediate water tank 73 divides the intermediate pipeline 53 into two sections, the middle upper pipeline 531 and the middle lower pipeline 532. The inlet of the intermediate water tank 73 is connected to the water outlet 28 of the second nanofiltration section 12 through the middle upper pipeline 531, and the outlet of the intermediate water tank 73 is connected to the water inlet 27 of the secondary nanofiltration 13 through the middle lower pipeline 532. The filtered water treated by the primary nanofiltration 1 first enters the intermediate water tank 73, and after accumulating to a certain level, it is transported to the secondary nanofiltration 13 through the second booster pump 62 for secondary nanofiltration salt separation. The setting of the intermediate water tank 73 can prevent the second booster pump 62 from idling due to less filtered water in the pipeline, thereby affecting subsequent devices, and can also prevent the pipeline from being damaged due to more filtered water in the pipeline, so that the overall device can run better and more smoothly.

[0028] The monitoring device includes a first pressure gauge 8 and a second pressure gauge 81. The first pressure gauge 8 is arranged on the first connecting pipe 51 between the first boosting pump 61 and the nanofiltration device. It monitors and controls the water pressure after the first boosting pump 61 is pressurized in real time to avoid affecting the subsequent first-level nanofiltration 1 due to water pressure problems. The second pressure gauge 81 is arranged on the middle and lower pipeline 532 between the second boosting pump 62 and the secondary nanofiltration 13. It monitors and controls the water pressure after the second boosting pump 62 is pressurized in real time to avoid affecting the subsequent secondary nanofiltration 13 due to water pressure problems. The setting of the monitoring device is not only a control insurance for the nanofiltration effect, but also a protection for the overall device.

[0029] Corresponding sampling ports 57 are provided at the water outlets 28 of the primary nanofiltration 1 and the secondary nanofiltration 13, through which the water treated by the two can be sampled, so that the staff can better control the filtering effects of the two and have a better understanding of the water treatment situation, so as to better control the subsequent processes.

[0030] The outlet of the clean water tank 72 is connected to a return water pipeline 58, and the clean water tank 72 is connected to the middle and lower pipeline 532 through the return water pipeline 58. The outlet of the return water pipeline 58 is connected to the inlet of the middle and lower pipeline 532. The outlet of the return water pipeline 58 and the outlet of the intermediate water tank 73 are connected in parallel, and both are connected to the inlet of the middle and lower pipeline 532 at the same time. If necessary, the water in the clean water tank 72 can enter the secondary nanofiltration 13 again through the return water pipeline 58 and the middle and lower pipeline 532 under the action of the second booster pump 62, and be filtered for salt separation again. This design can further increase the retention of salt in the water and obtain cleaner water.

[0031] Corresponding control valves 9 are provided at the front and rear ends of each component of the nanofiltration device and the water storage device. The flow direction of water in the filtration device can be better controlled by the control valves 9, thereby achieving a better nanofiltration effect.

[0032] During operation, the pretreated raw water enters the preservation filter 4 through the water inlet pipe 5 under the action of the first booster pump 61. After the residual particulate impurities are filtered out in the preservation filter, the raw water enters the primary nanofiltration 1 through the first connecting pipe 51 under the action of the first booster pump 61. The raw water passes through the first nanofiltration stage 11 and the second nanofiltration stage 12 in the primary nanofiltration 1 in sequence to undergo the first nanofiltration salt separation treatment. The concentrated water after the first nanofiltration is concentrated into the first concentrated water tank 7 through the first water outlet pipe 54. The filtered water after the first nanofiltration is accumulated in the intermediate water tank 73 through the middle-upper pipeline 531. After the water in the intermediate water tank 73 accumulates to an appropriate amount, it is transported to the secondary nanofiltration 13 through the middle-lower pipeline 532 under the action of the second booster pump 62 for the second The concentrated water after the secondary nanofiltration 13 treatment is concentrated into the second concentrated water tank 71 through the second outlet pipe 55, and the clean water after the secondary nanofiltration 13 treatment is concentrated into the clean water tank 72 through the third outlet pipe 56. The water in each water storage device is concentrated and waits for subsequent treatment. The concentrated water in the first concentrated water tank 7 is added with the corresponding precipitant, and the corresponding divalent salt can be obtained after precipitation treatment. The concentrated water in the second concentrated water tank 71 can obtain the corresponding monovalent salt after crystallization treatment. If the water in the clean water tank 72 does not meet the requirements after detection, it can enter the secondary nanofiltration 13 through the return pipe 58 and the middle and lower pipes 532 under the action of the second booster pump 62 for further treatment until it is qualified. The qualified clean water is concentrated for subsequent use.

[0033] The filtering device of the utility model adds a second booster pump 62 at the front end of the secondary nanofiltration 13, so that the first-stage three-stage salt separation nanofiltration is transformed into the secondary nanofiltration 13. The second booster pump 62 provides water inlet pressure for water entering the secondary nanofiltration 13, thereby improving the sulfate retention rate of the nanofiltration device, making the salt separation effect of the nanofiltration device better, thereby improving the purity of subsequent salt crystallization, making it more economical, and at the same time, the water filtering effect is better, the purity of the filtered water is higher, and its scope of use is also wider.

[0034] It is understood that the present invention is described by some embodiments, and those skilled in the art are aware that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the scope of protection of the present invention.

Claims

1. A filtering device, characterized in that: The invention comprises a nanofiltration device, wherein a safety filter (4) connected to an external raw water treatment pipeline is provided at the front end of the nanofiltration device, and a corresponding water storage device is provided at the rear end of the nanofiltration device. The components of the devices are connected through corresponding pipelines, and corresponding power devices and monitoring devices are provided on the corresponding pipelines. The power device comprises a raw water pump (6), a first booster pump (61) and a second booster pump (62). The water inlet end of the safety filter (4) is connected to a water inlet pipe (5) connected to an external raw water pretreatment pipeline. The raw water pump (6) is provided on the water inlet pipe (61). 5), the security filter (4) and the nanofiltration device are connected via a first connecting pipe (51), a first booster pump (61) is arranged on the first connecting pipe (51), and corresponding control valves (9) are arranged at both the front and rear ends of the nanofiltration device and the water storage device. The nanofiltration device comprises a primary nanofiltration (1) and a secondary nanofiltration (13), which are connected via an intermediate pipeline (53), a second booster pump (62) is arranged on the intermediate pipeline (53), and the primary nanofiltration (1) comprises a first nanofiltration stage (11) and a second nanofiltration stage (12).

2. The filtering device according to claim 1, characterized in that: The first nanofiltration stage (11) and the second nanofiltration stage (12) are connected in series via a second connecting pipe (52). The first nanofiltration stage (11), the second nanofiltration stage (12) and the secondary nanofiltration stage (13) have the same structure, comprising a tubular shell (2) which is hollow inside and open at both ends. The two ends of the shell (2) are respectively provided with a corresponding upper end cover (21) and a lower end cover (22). The inner cavity of the shell (2) is provided with a partition layer (23) which divides it into a salt water cavity (24) and a post-filtration cavity (25). The partition layer (23) is provided with a water outlet (26) which connects the salt water cavity (24) and the post-filtration cavity (25). The water outlet (26) is provided with a corresponding nanofiltration membrane assembly (3). The upper end cover (21) is provided with a The water inlet (27) of the safety filter (4) is provided, the lower end cover (22) is provided with a water outlet (28) connected to the post-filtration chamber (25), the bottom of the side wall of the salt water chamber (24) is provided with a salt water inlet (29) connected to the outside, the nanofiltration device is connected to the security filter (4) through the first nanofiltration stage (11), the two ends of the first connecting pipe (51) are respectively connected to the water outlet end of the security filter (4) and the water inlet (27) of the first nanofiltration stage (11), the two ends of the second connecting pipe (52) are respectively connected to the water outlet (28) of the first nanofiltration stage (11) and the water inlet (27) of the second nanofiltration stage (12), and the two ends of the intermediate pipeline (53) are respectively connected to the water outlet (28) of the second nanofiltration stage (12) and the water inlet (27) of the secondary nanofiltration (13).

3. The filtering device according to claim 2, characterized in that: The plurality of water passages (26) are evenly distributed on the separation layer (23) in a matrix manner, each water passage (26) is provided with a corresponding nanofiltration membrane assembly (3), the nanofiltration membrane assembly (3) is arranged in the brine chamber (24), and comprises a tubular nanofiltration membrane (31), the upper end of which is provided with a top cover (32), and the lower end of which is provided with a fixed seat (33) installed corresponding to the separation layer (23), the inner and outer layers of the nanofiltration membrane (31) are provided with corresponding support nets (34), the two ends of the support net (34) are respectively connected to the top cover (32) and the fixed seat (33), the fixed seat (33) is provided with a lower water outlet (35) corresponding to the water passage (26), and a corresponding sealing gasket (36) is provided between the fixed seat (33) and the separation layer (23).

4. The filtering device according to claim 3, characterized in that: The water storage device comprises a first concentrated water tank (7), a second concentrated water tank (71), a clean water tank (72) and an intermediate water tank (73), wherein the first concentrated water tank (7) is connected to the brine inlet (29) of the primary nanofiltration (1) through a first water outlet pipe (54), the second concentrated water tank (71) is connected to the brine inlet (29) of the secondary nanofiltration (13) through a second water outlet pipe (55), and the inlet of the clean water tank (72) is connected to the water outlet (28) of the secondary nanofiltration (13) through a third water outlet pipe (56). An intermediate water tank (73) is provided on the intermediate pipeline (53) between the first nanofiltration stage (1) and the second booster pump (62). The intermediate water tank (73) divides the intermediate pipeline (53) into two sections, namely, an upper middle pipeline (531) and a lower middle pipeline (532). The inlet of the intermediate water tank (73) is connected to the water outlet (28) of the second nanofiltration stage (12) through the upper middle pipeline (531), and the outlet of the intermediate water tank (73) is connected to the water inlet (27) of the second nanofiltration stage (13) through the lower middle pipeline (532).

5. The filtering device according to claim 4, characterized in that: The first water outlet pipe (54) comprises a section a pipeline (541) and a section b pipeline (542) connected in parallel, and the outlet ends of the two are connected in parallel and connected to the inlet of the first concentrated water tank (7), wherein the inlet of the section a pipeline (541) is connected to the brine inlet (29) of the first nanofiltration stage (11), and the inlet of the section b pipeline (542) is connected to the brine inlet (29) of the second nanofiltration stage (12).

6. The filtering device according to claim 1, characterized in that: The monitoring device comprises a first pressure gauge (8) provided on a first connecting pipe (51) between a first booster pump (61) and a nanofiltration device, and a second pressure gauge (81) provided on an intermediate pipeline (53) between a second booster pump (62) and a secondary nanofiltration device (13).

7. The filtering device according to claim 2, characterized in that: The water outlets (28) of the primary nanofiltration (1) and the secondary nanofiltration (13) are both provided with corresponding sampling ports (57).

8. The filtering device according to claim 4, characterized in that: The outlet of the clean water tank (72) is connected to a return water pipeline (58), the clean water tank (72) is connected to the inlet of the middle and lower pipeline (532) through the return water pipeline (58), and the outlet of the return water pipeline (58) and the outlet of the middle water tank (73) are connected in parallel to the inlet of the middle and lower pipeline (532).

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