Industrial waste brine purification treatment and recovery system for caustic soda production

Abstract

The invention belongs to the technical field of caustic soda production, and particularly relates to an industrial waste brine purification treatment and recovery system for caustic soda production, which comprises a filter unit and a sodium chloride storage tank, and is additionally provided with a pretreatment unit and a deep purification unit, the deep purification unit is located between the filtrate output end of the filtering unit and the input end of the sodium chloride storage tank, and industrial waste brine is sequentially treated by the pretreatment unit, the filtering unit and the deep purification unit and then enters the sodium chloride storage tank to be stored. By additionally arranging the pretreatment unit and the deep purification unit, a coarse filtration, medium filtration and fine filtration stepped purification treatment system is formed, the blockage risk of the filter layer in the filter unit is greatly reduced, and the service life of the filter layer is prolonged.

Description

Technical Field

[0001] This invention belongs to the field of caustic soda production technology, specifically relating to an industrial waste brine purification and recovery system for caustic soda production. Background Technology

[0002] Caustic soda (sodium hydroxide), as a basic chemical raw material, is widely used in many industrial fields such as papermaking, textiles, printing and dyeing, petrochemicals, water treatment, food processing, and metallurgy, and its market demand is large. At present, the mainstream process for producing caustic soda in industry is the electrolysis method. The core principle of this process is to use an aqueous sodium chloride solution as an electrolytic raw material to generate caustic soda, chlorine gas, and hydrogen gas through electrode reactions.

[0003] In some chemical industries, large amounts of industrial waste brine containing sodium chloride are generated during production processes. This waste brine has recycling value as a raw material for caustic soda electrolysis. However, in addition to sodium chloride, industrial waste brine also contains other impurities such as heavy metals, organic matter, and precipitates. These impurities can easily clog the filter layer of filters.

[0004] In existing industrial wastewater treatment and recovery systems, when the filter layer becomes clogged, the entire system needs to be shut down for flushing or replacement, which severely impacts production continuity. Furthermore, because filters are replaced frequently and the connection components between traditional filters and mounting frames are complex, disassembly requires specialized tools, making the installation and disassembly steps cumbersome, time-consuming, and labor-intensive. This not only significantly increases the workload of maintenance personnel but also leads to low maintenance efficiency. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides an industrial waste brine purification and recovery system for caustic soda production. By adding a pretreatment unit and a deep purification unit, a stepped purification system of coarse filtration, medium filtration, and fine filtration is formed, which greatly reduces the risk of clogging of the filter layer in the filtration unit and extends the service life of the filter layer.

[0006] The specific technical solution adopted in this invention is as follows: An industrial waste brine purification and recovery system for caustic soda production includes a filtration unit and a sodium chloride storage tank. It also includes a pretreatment unit and a deep purification unit. The pretreatment unit is located at the waste liquid inlet of the filtration unit, and the deep purification unit is located between the filtrate outlet of the filtration unit and the inlet of the sodium chloride storage tank. The industrial waste brine is processed sequentially through the pretreatment unit, the filtration unit, and the deep purification unit before entering the sodium chloride storage tank for storage.

[0007] The pretreatment unit includes a filter grid and a pH adjustment tank. The output end of the pH adjustment tank is connected to the waste liquid input end of the filter unit. The pore size of the filter grid is 3-5 mm.

[0008] The filtration unit includes a first filter and a second filter. The input ends of the first filter and the second filter are connected in parallel with the main inlet pipe. The main inlet pipe serves as the waste liquid input end of the filtration unit and is connected to the pretreatment unit. The output ends of the first filter and the second filter are connected in parallel with the main outlet pipe. The main outlet pipe serves as the filtrate output end of the filtration unit and is connected to the deep purification unit.

[0009] The filtration unit also includes a backwash pump and a backwash main pipe. The output ends of the first filter and the second filter are also connected in parallel with the backwash main pipe. The backwash main pipe is connected to the output end of the backwash pump as the clean water input end of the filtration unit. The input end of the backwash pump is connected to the clean water supply end. The clean water flushes the filter element unit of the first filter or the second filter along the outlet main pipe and is discharged into the sewage tank along the sewage discharge main pipe.

[0010] The filtration unit further includes a control valve assembly, which includes a first inlet valve, a first outlet valve, a first backwash valve, a first drain valve, a second inlet valve, a second outlet valve, a second backwash valve, and a second drain valve. The first inlet valve is located at the input end of the first filter, the first outlet valve is located at the filtrate output end of the first filter, the first backwash valve is located at the clean water input end of the first filter, the first drain valve is located at the wastewater output end of the first filter, the second inlet valve is located at the input end of the second filter, the second outlet valve is located at the filtrate output end of the second filter, the second backwash valve is located at the clean water input end of the second filter, and the second drain valve is located at the wastewater output end of the second filter.

[0011] Both the first and second filters consist of multiple sets of filter element units connected in parallel. Each filter element unit includes a filter element housing and a mounting frame for fixing the filter element housing. The filter element housing is fixedly connected to the mounting frame via a connecting assembly, which includes a limiting ring. The limiting ring is fixedly connected to both the mounting frame and the filter element housing. The mounting frame is covered with a filter layer, forming an annular first filter cavity between the filter element housing and the filter layer. The mounting frame has channels for the filtrate to pass through, forming a second filter cavity within the mounting frame. The limiting ring has a first through hole and a second through hole. The first through hole communicates with the first filter chamber, and the second through hole communicates with the second filter chamber. The connecting assembly also includes a cap body. A limiting hook is provided on the side wall of the cap body. The limiting hook has the freedom to move back and forth along the axial direction of the filter element shell. The connecting end of the filter element shell abuts against the opening side of the cap body and forms a fixed connection by means of the hook and hook engagement of the limiting hook and the limiting ring. An inlet and an outlet are respectively provided on both sides of the outer wall of the cap body. Industrial waste brine enters the first filter chamber through the first through hole through the inlet of the cap body, permeates into the second filter chamber after passing through the filter layer, and is discharged through the outlet of the cap body through the second through hole.

[0012] The edge of the limiting ring is provided with a positioning notch for the limiting hook to pass through, and multiple sets of the positioning notches are arranged in a ring array with the center of the limiting ring as the center.

[0013] The outer wall of the connecting end of the cap body is provided with a concave sliding channel. The limiting hook includes a hook part and a driving part. The hook part and the driving part together form an L-shaped structure. The hook part is located in the sliding channel and has the freedom to engage with the hook of the limiting ring. The driving part protrudes from the side wall of the cap body along the side opening of the sliding channel. The outer wall of the cap body is also fitted with a rotating nut that engages with the thread of the cap body. The sliding channel forms a closed channel structure with the help of the rotating nut. The rotating nut abuts against the driving part of the limiting hook to form a pushing engagement and drive the hook part of the limiting hook to hold the limiting ring.

[0014] A raised water outlet pipe is provided at the center of the cap body. A sealing gasket is provided at the neck of the inlet end of the water outlet pipe. The inlet end of the water outlet pipe is sealed to the outlet end of the filter element shell by means of the sealing gasket. The outlet end of the water outlet pipe is connected to the water outlet on the side wall of the cap body.

[0015] The deep purification unit includes a resin adsorption column and an activated carbon filter. The input end of the resin adsorption column is connected to the filtrate output end of the filtration unit, the output end of the resin adsorption column is connected to the input end of the activated carbon filter, and the output end of the activated carbon filter is connected to the input end of the sodium chloride storage tank.

[0016] The beneficial effects of this invention are: 1. The industrial wastewater purification and recovery system of this invention adds a pretreatment unit and a deep purification unit. The industrial wastewater first enters the added pretreatment unit, which initially removes large particulate impurities and some suspended pollutants that easily cause filter clogging. The pretreated wastewater flows into the original filtration unit, where medium-sized impurities are further intercepted. The filtered liquid then enters the deep purification unit, where residual trace impurities are precisely removed. Finally, the refined brine, which meets the standards for raw materials in caustic soda electrolysis production, enters the sodium chloride storage tank as a raw material for caustic soda. This invention, through the two additional units of pretreatment and deep purification, forms a stepped purification system of coarse filtration, medium filtration, and fine filtration, significantly reducing the risk of clogging in the filter layer and extending the service life of the filter layer.

[0017] 2. In this invention, the connection between the filter element shell and the fixing frame is achieved by the hook and hook engagement between the limiting hook and the limiting ring. After the filter element shell and the cap body are in place, the limiting hook is moved horizontally by turning the nut until the limiting hook and the limiting ring form an abutment, thereby preventing the filter element shell from detaching from the cap body and achieving the fixing of the filter element shell and the fixing frame.

[0018] After the limiting ring abuts against the end of the cap body, it forms a closed annular groove. The first through hole is arranged in a circular pattern in the closed groove, thereby improving the uniformity of filtration, making the filter layer life uniform, and extending the service time. Attached Figure Description

[0019] Figure 1 A schematic diagram of the chemical process for an industrial waste brine purification and recovery system; Figure 2 This is a schematic diagram of the filter unit structure; Figure 3 This is a schematic diagram of the filter element unit. Figure 4 This is a schematic diagram of the filter element unit assembly. Figure 5 A schematic diagram of the filtrate output end of the filter layer; In the attached diagram, 1. Inlet main pipe, 2. Outlet main pipe, 3. Backwash main pipe, 4. Sewage main pipe, 5. First inlet valve, 6. First outlet valve, 7. First backwash valve, 8. First sewage valve, 9. Second inlet valve, 10. Second outlet valve, 11. Second backwash valve, 12. Second sewage valve, 13. Filter element unit, 1301. Filter element shell, 1302. Filter layer, 1303. First through hole, 1304. Second through hole, 14. Mounting bracket, 15. Cap body, 16. Limiting ring, 17. Limiting hook, 1701. Hook part, 1702. Drive part, 18. Inlet, 19. Outlet, 20. Positioning notch, 21. Rotating nut, 22. Outlet pipe, 23. Sealing gasket. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings and specific embodiments: Specific embodiments, such as Figure 1 As shown, the present invention provides an industrial waste brine purification and recovery system for caustic soda production, including a filtration unit and a sodium chloride storage tank, and further includes a pretreatment unit and a deep purification unit. The pretreatment unit is located at the waste liquid input end of the filtration unit, and the deep purification unit is located between the filtrate output end of the filtration unit and the input end of the sodium chloride storage tank. The industrial waste brine is processed sequentially through the pretreatment unit, the filtration unit, and the deep purification unit before entering the sodium chloride storage tank for storage.

[0021] In some chemical industries, large quantities of industrial waste brine containing sodium chloride are generated during production processes. This waste brine has recycling value as a raw material for caustic soda electrolysis. However, in addition to sodium chloride, industrial waste brine also contains other impurities such as heavy metals, organic matter, and precipitates. These impurities can easily clog the filter layer 1302 of the filter. In existing industrial waste brine treatment and recovery systems, when the filter layer 1302 becomes clogged, the entire system needs to be shut down for flushing or replacement, severely impacting production continuity.

[0022] Therefore, the industrial wastewater purification and recovery system of this invention adds a pretreatment unit and a deep purification unit. The industrial wastewater first enters the added pretreatment unit, where large particulate impurities and some suspended pollutants that easily cause clogging of the filter layer 1302 are initially removed. The pretreated wastewater flows into the original filtration unit, where medium-sized impurities are further intercepted. The filtered liquid then enters the deep purification unit, where residual trace impurities are precisely removed. Finally, the refined brine that meets the raw material standards for caustic soda electrolysis enters the sodium chloride storage tank as a raw material for caustic soda. This invention, through the two additional units of the pretreatment unit and the deep purification unit, forms a stepped purification system of coarse filtration, medium filtration, and fine filtration, which significantly reduces the risk of clogging of the filter layer 1302 in the filtration unit and extends the service life of the filter layer 1302.

[0023] like Figure 1 As shown, the pretreatment unit includes a filter grid and a pH adjustment tank. The output end of the pH adjustment tank is connected to the waste liquid input end of the filter unit. The pore size of the filter grid is 3-5 mm.

[0024] The 3-5mm mesh filter grid can intercept large particles and suspended solids in industrial wastewater, preventing these large impurities from entering subsequent units and scratching the filter layer 1302 or causing blockage of the pores of the filter layer 1302. The pH adjustment tank can adjust the acidity and alkalinity of the wastewater, so that some heavy metal ions and insoluble salts can form precipitates under suitable pH conditions and be separated with the pre-treated waste residue. At the same time, it can also prevent extremely acidic or alkaline liquids from corroding or damaging the performance of the filter layer 1302 and the adsorption materials of the deep purification unit.

[0025] like Figure 1 As shown, the filtration unit includes a first filter and a second filter. The input ends of the first filter and the second filter are connected in parallel with the main water inlet pipe 1. The main water inlet pipe 1 serves as the waste liquid input end of the filtration unit and is connected to the pretreatment unit. The output ends of the first filter and the second filter are connected in parallel with the main water outlet pipe 2. The main water outlet pipe 2 serves as the filtrate output end of the filtration unit and is connected to the deep purification unit.

[0026] The first and second filters in this system are connected in parallel and can work simultaneously or alternately as needed. When a filter needs maintenance due to blockage of the filter layer 1302, the inlet valve of that filter can be closed while the inlet valve of the other filter remains open. This allows the entire waste brine treatment system to be maintained without stopping the maintenance of a single filter, thus improving production continuity.

[0027] like Figure 1 As shown, the filtration unit also includes a backwash pump and a backwash main pipe 3. The output ends of the first filter and the second filter are also connected in parallel with the backwash main pipe 3. The backwash main pipe 3 serves as the clean water input end of the filtration unit and is connected to the output end of the backwash pump. The input end of the backwash pump is connected to the clean water supply end. The clean water flushes the filter element unit 13 of the first filter or the second filter along the outlet main pipe 2 and is discharged into the sewage tank along the sewage discharge main pipe 4.

[0028] The backwash pump can provide high-pressure clean water. The reverse water flow can impact the impurities attached to the surface of the filter layer 1302, and remove the fine impurities and suspended matter that are clogging the pores of the filter layer 1302. The removed impurities are discharged into the sewage tank along the sewage main pipe 4 with the water flow, thus cleaning the filter element unit 13.

[0029] like Figure 1-2 As shown, the filtration unit further includes a control valve group, which includes a first inlet valve 5, a first outlet valve 6, a first backwash valve 7, a first drain valve 8, a second inlet valve 9, a second outlet valve 10, a second backwash valve 11, and a second drain valve 12. The first inlet valve 5 is located at the input end of the first filter, the first outlet valve 6 is located at the filtrate output end of the first filter, the first backwash valve 7 is located at the clean water input end of the first filter, the first drain valve 8 is located at the wastewater output end of the first filter, the second inlet valve 9 is located at the input end of the second filter, the second outlet valve 10 is located at the filtrate output end of the second filter, the second backwash valve 11 is located at the clean water input end of the second filter, and the second drain valve 12 is located at the wastewater output end of the second filter.

[0030] During normal operation, the first inlet valve 5, the first outlet valve 6, the second inlet valve 9, and the second outlet valve 10 are open, and the remaining valve group is closed. At this time, the industrial waste brine flows through the first filter and the second filter for filtration. When the first filter needs to backwash the filter layer 1302, the first backwash valve 7, the first drain valve 8, the second inlet valve 9, and the second outlet valve 10 are opened, and the remaining valve group is closed. At this time, the industrial waste brine can only flow through the second filter for filtration. The backwash pump will then bring high-pressure clean water into the interior of the first filter through the first backwash valve 7 for rinsing, and discharge the wastewater carrying impurities through the first drain valve 8. When the first filter needs to replace the filter element 13, the second inlet valve 9 and the second outlet valve 10 are opened, and the remaining valve group is closed. At this time, no liquid passes through the first filter, and the industrial waste brine is filtered normally along the second filter.

[0031] The same applies when the second filter needs backwashing and when filter element 13 needs to be replaced.

[0032] By switching the valve groups described above, it is ensured that the operation of the two filters does not interfere with each other, avoiding the problem that the entire system needs to be shut down for maintenance when the filter layer 1302 of one filter is blocked. This allows for the independent maintenance of a single filter without affecting the normal operation of the other filter.

[0033] like Figure 2-5 As shown, both the first and second filters are composed of multiple sets of parallel filter element units 13. Each filter element unit 13 includes a filter element housing 1301 and a mounting frame 14 for fixing the filter element housing 1301. The filter element housing 1301 is fixedly connected to the mounting frame 14 via a connecting assembly. The connecting assembly includes a limiting ring 16, which is fixedly connected to both the mounting frame 14 and the filter element housing 1301. The mounting frame 14 is covered with a filter layer 1302, forming an annular first filter cavity between the filter element housing 1301 and the filter layer 1302. The mounting frame 14 has channels for the filtrate to pass through, forming a second filter cavity within it. The limiting ring 16 has a first through hole 1303 and a second through hole. 1304, the first through hole 1303 communicates with the first filter chamber, the second through hole 1304 communicates with the second filter chamber, the connecting assembly also includes a cap body 15, the side wall of the cap body 15 is provided with a limiting hook 17, the limiting hook 17 has the freedom to move back and forth along the axial direction of the filter element shell 1301, the connecting end of the filter element shell 1301 abuts against the opening side of the cap body 15 and forms a fixed connection by means of the hook and hook cooperation between the limiting hook 17 and the limiting ring 16, the outer walls of the cap body 15 are respectively provided with an inlet 18 and an outlet 19, the industrial waste brine enters the first filter chamber through the first through hole 1303 through the inlet 18 of the cap body 15, permeates into the second filter chamber after passing through the filter layer 1302, and enters the outlet 19 of the cap body 15 through the second through hole 1304 for discharge.

[0034] The connection components between the traditional filter element unit 13 and the mounting bracket have a complex structure. The disassembly process requires special tools, and the installation and disassembly steps are cumbersome, time-consuming, and labor-intensive. This not only significantly increases the labor intensity of maintenance personnel but also results in extremely low maintenance efficiency.

[0035] In this invention, the connection between the filter element shell 1301 and the fixing frame is achieved by the hook and hook engagement between the limiting hook 17 and the limiting ring 16. After the filter element 13 and the cap 15 are in place, the limiting hook 17 is moved horizontally by turning the rotating nut 21 until the limiting hook 17 and the limiting ring 16 are in contact, thereby preventing the filter element shell 1301 from detaching from the cap 15 and thus fixing the filter element shell 1301 to the fixing frame.

[0036] After the limiting ring 16 abuts against the connecting end of the cap body 15, an annular closed groove is formed. The first through hole 1303 is arranged in an annular shape in the closed groove, thereby improving the uniformity of filtration, making the filter layer 1302 have a uniform lifespan, and extending the service time.

[0037] like Figure 3-5 As shown, the edge of the limiting ring 16 is provided with a positioning notch 20 for the limiting hook 17 to pass through, and multiple sets of the positioning notches 20 are arranged in a ring array with the center of the limiting ring 16 as the center.

[0038] Traditional threaded connections can easily lead to metal shavings generated by friction at the threaded opening entering the filtrate. However, the hook part 1701 of this application pulls out the limiting ring 16 to form an abutment fit, avoiding repeated twisting, reducing the probability of shavings falling out, and improving the quality of the filtrate.

[0039] During installation, first pass the hook part 1701 of the limiting hook 17 through the positioning notch 20 through the limiting ring 16, and then rotate the filter element shell 1301 so that the positioning notch 20 is away from the limiting ring 16. At this time, the filter element shell 1301 will not fall off due to the support of the limiting hook 17. The operator can release the filter element shell 1301 and tighten the rotating nut 21 until the hook part 1701 of the limiting hook 17 abuts against the limiting ring 16 and the rotating nut 21 can no longer be tightened. During disassembly, slightly twist the rotating nut 21 in the opposite direction to give the filter housing 1301 a degree of rotational freedom. By rotating the filter housing 1301, align the positioning notch 20 of the limiting ring 16 with the hook part 1701 of the limiting hook 17. Then, pull out the filter housing 1301 and replace the filter layer 1302. The entire installation and disassembly process is simple, can be operated by one person, and does not require additional tools, which greatly improves the maintenance efficiency of the filter unit 13.

[0040] like Figure 3-5As shown, the outer side wall of the connecting end of the cap body 15 is provided with a concave sliding channel. The limiting hook 17 includes a hook part 1701 and a driving part 1702. The hook part 1701 and the driving part 1702 together form an L-shaped structure. The hook part 1701 is located in the sliding channel and has the freedom to hook and engage with the limiting ring 16. The driving part 1702 protrudes from the side wall of the cap body 15 along the side opening of the sliding channel. The outer side wall of the cap body 15 is also fitted with a rotating nut 21 that is threadedly engaged with the cap body 15. The sliding channel forms a closed channel structure with the help of the rotating nut 21. The rotating nut 21 abuts against the driving part 1702 of the limiting hook 17 to form a pushing engagement and drive the hook part 1701 of the limiting hook 17 to grip the limiting ring 16.

[0041] In this invention, the rotating nut 21, through its threaded engagement with the cap body 15, generates axial movement, which in turn pushes the drive part 1702 of the limiting hook 17, causing the hook part 1701 to move axially along the filter element shell 1301 within the sliding channel. When the rotating nut 21 rotates forward, it pushes the drive part 1702 to extend the hook part 1701 and tightly grip the limiting ring 16, thus firmly fixing the filter element shell 1301. When it rotates in the reverse direction, the nut retracts, the hook part 1701 resets, releasing the constraint on the limiting ring 16. At this time, the filter element shell 1301 has rotational freedom and can be removed. The sliding channel guides the limiting hook 17, ensuring precise movement of the hook part 1701 and preventing misalignment that could lead to hook failure.

[0042] like Figure 3-5 As shown, a protruding water outlet pipe 22 is provided at the center of the cap body 15. A sealing gasket 23 is provided at the neck of the inlet end of the water outlet pipe 22. The inlet end of the water outlet pipe 22 is sealed to the outlet end of the filter element shell 1301 by means of the sealing gasket 23. The outlet end of the water outlet pipe 22 is connected to the water outlet 19 on the side wall of the cap body 15.

[0043] When the second through hole 1304 of the filter element unit 13 is connected to the water outlet pipe 22, the sealing gasket 23 is squeezed to form a sealing surface, blocking the gap between the water outlet end of the filter element unit 13 and the inside of the cap body 15, thus preventing unfiltered waste salt water inside the cap body 15 from mixing into the filtered liquid through the gap.

[0044] like Figure 1 As shown, the deep purification unit includes a resin adsorption column and an activated carbon filter. The input end of the resin adsorption column is connected to the filtrate output end of the filtration unit, the output end of the resin adsorption column is connected to the input end of the activated carbon filter, and the output end of the activated carbon filter is connected to the input end of the sodium chloride storage tank.

[0045] The resin adsorption column and activated carbon filter can adsorb trace heavy metal ions and small molecule organic matter and other impurities remaining in the filtered brine, further purifying the water quality.

Claims

1. A system for purifying and recovering industrial waste brine for caustic soda production, comprising a filtration unit, and a sodium chloride storage tank, characterized in that, The pre-treatment unit is located at the waste liquid input end of the filtering unit, and the deep purification unit is located between the filtered liquid output end of the filtering unit and the input end of the sodium chloride storage tank.

2. The industrial waste brine purification treatment and recovery system for caustic soda production according to claim 1, characterized in that, The pre-treatment unit comprises a filter grid and a pH adjusting tank, and the output end of the pH adjusting tank is connected with the waste liquid input end of the filtering unit.

3. The industrial waste brine purification treatment and recovery system for caustic soda production according to claim 1, characterized in that, The filtering unit comprises a first filter and a second filter, and the input ends of the first filter and the second filter are arranged in parallel with the water inlet main pipe (1), the water inlet main pipe (1) being connected with the pre-treatment unit as the waste liquid input end of the filtering unit, and the output ends of the first filter and the second filter are arranged in parallel with the water outlet main pipe (2), the water outlet main pipe (2) being connected with the deep purification unit as the filtered liquid output end of the filtering unit.

4. The industrial waste brine purification treatment and recovery system for caustic soda production according to claim 3, characterized in that, The filtering unit further comprises a backwashing pump and a backwashing main pipe (3), and the output ends of the first filter and the second filter are further arranged in parallel with the backwashing main pipe (3), the backwashing main pipe (3) being connected with the output end of the backwashing pump as the clean water input end of the filtering unit, and the input end of the backwashing pump being connected with the clean water supply end, the clean water being used to flush the filter core unit (13) of the first filter or the second filter along the water outlet main pipe (2) and being discharged to the sewage tank along the sewage discharge main pipe (4).

5. The industrial waste brine purification treatment and recovery system for caustic soda production according to claim 4, characterized in that, The filtering unit further comprises a control valve group, the control valve group comprising a first water inlet valve (5), a first water outlet valve (6), a first backwashing valve (7), a first sewage discharge valve (8), a second water inlet valve (9), a second water outlet valve (10), a second backwashing valve (11) and a second sewage discharge valve (12), the first water inlet valve (5) being located at the input end of the first filter, the first water outlet valve (6) being located at the filtered liquid output end of the first filter, the first backwashing valve (7) being located at the clean water input end of the first filter, the first sewage discharge valve (8) being located at the sewage output end of the first filter, the second water inlet valve (9) being located at the input end of the second filter, the second water outlet valve (10) being located at the filtered liquid output end of the second filter, the second backwashing valve (11) being located at the clean water input end of the second filter, and the second sewage discharge valve (12) being located at the sewage output end of the second filter.

6. The industrial waste brine purification treatment and recovery system for caustic soda production according to claim 3, characterized in that, The first filter and the second filter are both composed of multiple groups of filter core units (13) in parallel, the filter core unit comprises a filter core shell (1301) and a mounting rack (14) for fixing the filter core shell (1301), the filter core shell (1301) is fixedly connected with the mounting rack (14) by means of a connecting assembly, the connecting assembly comprises a limiting ring (16), the limiting ring (16) is fixedly connected with the mounting rack (14) and the filter core shell (1301) respectively, a filter layer (1302) is coated on the mounting rack (14), a first filter cavity is formed between the filter core shell (1301) and the filter layer (1302), a hole is formed on the mounting rack (14) for the filtered liquid to pass through, a second filter cavity is formed in the mounting rack (14), a first through hole (1303) and a second through hole (1304) are respectively formed on the limiting ring (16), the first through hole (1303) is communicated with the first filter cavity, the second through hole (1304) is communicated with the second filter cavity, the connecting assembly further comprises a cap body (15), a limiting hook (17) is arranged on the sidewall of the cap body (15), the limiting hook (17) has the freedom of reciprocating along the axial direction of the filter core shell (1301), the connecting end of the filter core shell (1301) is abutted with the opening side of the cap body (15) and is fixedly connected by the hooking cooperation of the limiting hook (17) and the limiting ring (16), a water inlet (18) and a water outlet (19) are respectively arranged on the two sides of the outer wall of the cap body (15), industrial waste brine enters the first filter cavity through the first through hole (1303) from the water inlet (18) of the cap body (15), penetrates into the second filter cavity after passing through the filter layer (1302), and is discharged from the water outlet (19) of the cap body (15) through the second through hole (1304).

7. The industrial waste brine purification treatment and recovery system for caustic soda production according to claim 6, characterized in that, A positioning notch (20) is arranged on the edge of the limiting ring (16) for the limiting hook (17) to pass through, and the positioning notches (20) are arranged in multiple groups in a ring-like array with the center of the limiting ring (16) as the center.

8. The industrial waste brine purification treatment and recovery system for caustic soda production according to claim 6, characterized in that, The outer sidewall of the connecting end of the cap body (15) is provided with a concave sliding channel, the limiting hook (17) comprises a hooking part (1701) and a driving part (1702), the hooking part (1701) and the driving part (1702) jointly form an L-shaped structure, the hooking part (1701) is located in the sliding channel and has the freedom of hooking cooperation with the limiting ring (16), the driving part (1702) protrudes from the sidewall of the cap body (15) through the side opening of the sliding channel, and a rotating nut (21) threadedly matched with the cap body (15) is further sleeved on the outer sidewall of the cap body (15), the sliding channel forms a closed hole structure by means of the rotating nut (21), and the rotating nut (21) is abutted with the driving part (1702) of the limiting hook (17) to form a pushing cooperation and drive the hooking part (1701) of the limiting hook (17) to hold the limiting ring (16).

9. The industrial waste brine purification treatment and recovery system for caustic soda production according to claim 6, characterized in that, The center of the cap (15) is provided with a protruding water outlet pipe (22), the input end neck of the water outlet pipe (22) is provided with a sealing gasket (23), the input end of the water outlet pipe (22) is sealed and connected with the water outlet end of the filter core shell (1301) by the sealing gasket (23), and the output end of the water outlet pipe (22) communicates with the water outlet (19) of the side wall of the cap (15).

10. The industrial waste brine purification treatment and recovery system for caustic soda production according to claim 1, characterized in that, The depth purification unit comprises a resin adsorption column and an activated carbon filter, the input end of the resin adsorption column is connected with the filtered liquid output end of the filtering unit, the output end of the resin adsorption column is connected with the input end of the activated carbon filter, and the output end of the activated carbon filter is connected with the input end of the sodium chloride storage tank.

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