A system for extracting sodium chloride crystals from wastewater

Abstract

This invention discloses a system for extracting sodium chloride crystals from wastewater, comprising a raw material tank, a thin-film evaporator, a thickener, and a mother liquor tank. The raw material tank stores wastewater, and its outlet is connected to the inlet of the thin-film evaporator. The bottom outlet of the thin-film evaporator is connected to the inlet of the thickener. The upper overflow port of the thickener is connected to the inlet of the mother liquor tank, and the outlet of the mother liquor tank is connected to the thin-film evaporator. The bottom of the thickener has an outlet for material discharge. Wastewater enters the thickener from the raw material tank and the thin-film evaporator. The clear liquid from the thickener flows out from the upper overflow port and returns to the thin-film evaporator via the mother liquor tank. The system also includes a heat exchanger located between the raw material tank and the thin-film evaporator. The wastewater flowing from the raw material tank is heated by the heat exchanger before entering the thin-film evaporator. This invention provides a system for extracting sodium chloride crystals from wastewater, reducing system operating energy consumption and production costs.

Description

Technical Field

[0001] This invention relates to the field of wastewater sodium chloride crystallization equipment technology, and more specifically, to a system for extracting sodium chloride crystals from wastewater. Background Technology

[0002] Industrial production processes generate large amounts of saline wastewater, which is rich in high concentrations of sodium chloride. Direct discharge of this wastewater not only causes severe soil salinization and water pollution but also results in a significant waste of salt resources, failing to meet the requirements for wastewater reduction, resource recovery, and harmless treatment. Currently, the industry commonly uses thin-film evaporation, gravity sedimentation, and centrifugal separation processes to recover sodium chloride from saline wastewater through crystallization. However, traditional evaporation and salt extraction systems have low waste heat utilization rates, with heating steam condensate being directly discharged, resulting in substantial waste heat loss, high system steam energy consumption, and high operating costs. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a system for extracting sodium chloride crystals from wastewater, thereby reducing system operating energy consumption and production costs.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: a system for extracting sodium chloride crystals from wastewater, comprising a raw material tank, a thin-film evaporator, a thickener, and a mother liquor tank. The raw material tank is used to store wastewater. The discharge end of the raw material tank is connected to the feed end of the thin-film evaporator. The bottom discharge end of the thin-film evaporator is connected to the feed end of the thickener. The upper overflow port of the thickener is connected to the feed port of the mother liquor tank. The discharge port of the mother liquor tank is connected to the thin-film evaporator. The bottom of the thickener is provided with a discharge port for material discharge. Wastewater enters the thickener from the raw material tank and the thin-film evaporator. The clear liquid from the thickener flows out from the upper overflow port of the thickener and returns to the thin-film evaporator via the mother liquor tank. The system also includes a heat exchanger located between the raw material tank and the thin-film evaporator. The wastewater flowing out of the raw material tank is heated by the heat exchanger before entering the thin-film evaporator.

[0005] Furthermore, it also includes a buffer tank, which is located between the thin-film evaporator and the thickener. Wastewater discharged from the bottom of the thin-film evaporator enters the thickener through the buffer tank.

[0006] Furthermore, the bottom of the buffer tank is equipped with a backflushing port. Wastewater discharged from the buffer tank is piped into the backflushing port to clean the bottom of the buffer tank.

[0007] Furthermore, it also includes an evaporative cooler, the gas phase inlet of which is connected to the gas phase outlet of the thin film evaporator. The gas flowing through the gas phase outlet is the steam generated by the heating and evaporation of wastewater. The outlet end of the evaporative cooler is connected to a condenser, and the liquid phase outlet of the condenser is reversed to the liquid inlet end of the evaporative cooler for cooling the evaporative cooler. The gas phase outlet of the condenser is connected to a vacuum pump.

[0008] Furthermore, it also includes a steam feed source, which is connected to the air inlet of the thin film evaporator. The high-temperature steam fed into the thin film evaporator is used to heat the wastewater in isolation. The steam used to heat the wastewater is cooled and discharged from the liquid phase outlet of the thin film evaporator.

[0009] Furthermore, the steam coolant discharged from the liquid phase outlet of the thin-film evaporator passes through a heat exchanger to isolate and heat the wastewater entering the heat exchanger.

[0010] Furthermore, the thickener includes a container body, an end cap is installed on the top of the container body, a shaft is rotatably connected to the end cap, the bottom of the shaft is inserted into the container body, and a tube is fixedly installed at the bottom of the shaft. The shaft can rotate along its own axis under external driving action, and the rotation of the shaft drives the tube to rotate synchronously. The tube includes a groove portion, and multiple groove portions are evenly distributed along the outer periphery of the tube.

[0011] Furthermore, the depth of the groove along the radial direction of the insert is 3%-5% of the insert radius.

[0012] Furthermore, the outer circumference of the insert is entirely curved.

[0013] In summary, the present invention has the following beneficial effects:

[0014] 1. The high-temperature steam condensate discharged from the thin-film evaporator is used to preheat the raw material saline wastewater, realizing waste heat recovery and utilization, effectively increasing the wastewater feed temperature, reducing the heating steam consumption of the thin-film evaporator, avoiding the problem of direct waste heat of steam condensate in traditional processes, and significantly reducing system operating energy consumption and production costs.

[0015] 2. This invention establishes a complete mother liquor circulation loop by setting up a mother liquor tank. The overflow clear liquid from the top of the thickener is returned to the thin film evaporator for further concentration via the mother liquor tank. The salt-containing mother liquor that has not precipitated crystals is repeatedly concentrated, which greatly reduces wastewater discharge and significantly improves the sodium chloride crystallization recovery rate, realizing the resource utilization of salt-containing wastewater.

[0016] 3. A closed vacuum system is constructed using a vacuum pump, evaporative cooler, and condenser to lower the boiling point of wastewater evaporation, achieving low-temperature evaporation and concentration. This avoids rapid salt crystal adhesion and scaling caused by high-temperature evaporation, effectively extending the cleaning cycle and service life of the thin-film evaporator. Simultaneously, the condensate is recycled in a closed loop as a cooling water source, eliminating the need for continuous replenishment of fresh cooling water and significantly reducing system water consumption. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the system in Embodiment 1;

[0018] Figure 2 This is a cross-sectional schematic diagram of Example 2;

[0019] Figure 3 for Figure 2 Enlarged view of point A in the middle;

[0020] Figure 4 This is a cross-sectional view of the insert in Example 2.

[0021] Reference numerals: 1. Raw material tank; 11. First pump body; 2. Heat exchanger; 3. Thin-film evaporator; 31. Steam feed source; 4. Buffer tank; 41. Second pump body; 42. First control valve; 43. Backflush port; 44. Second control valve; 5. Thickener; 51. Container body; 511. Bottom cylinder; 511. First channel; 5111. Second channel; 512. Detection probe; 513. End cap; 52. Fixing seat; 521. First bearing; 5211. Sleeve; 522. Second bearing; 5221. Guide... Pipe 5222, stirring shaft 53, bracket 54, motor 541, guide cylinder 55, feed inlet 551, insert 56, groove 561, shaft 57, first gear ring 571, second gear ring 572, connecting seat 5721, third bearing 57211, first plate 58, second plate 581, gear pair 59, mother liquor tank 6, third pump body 61, condenser 7, vacuum pump 71, fourth pump body 72, evaporator cooler 8, centrifuge 9. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1:

[0024] like Figure 1 As shown, this embodiment discloses a system for extracting sodium chloride crystals from wastewater, including a raw material tank 1, a thin-film evaporator 3, a thickener 5, and a mother liquor tank 6. The raw material tank 1 is used to store wastewater, which is pretreated high-salt industrial wastewater. The main solute in the wastewater is sodium chloride, with high salt content and trace impurities. After pretreatment to remove suspended solids, the wastewater is sent to the raw material tank 1 for storage. Raw material tank 1 has a volume of 10m³, is made of Q235B rubber-lined material, and is equipped with a magnetic level gauge with a measurement range of 0-3.0m. A pneumatic regulating valve 18 is installed on the discharge pipeline to realize closed-loop regulation of the liquid level.

[0025] The discharge end of the raw material tank 1 is connected to the heat exchanger 2 through a pipeline. A first pump body 11 is installed in the pipeline. The first pump body 11 is a CQB-F type fluoroplastic magnetic pump with a flow rate of 5 m³ / h and a head of 25 m. It is equipped with a 20-50 Hz frequency converter and is linked to the system feed flow parameters for adjustment.

[0026] The first pump 11 transports the wastewater from the raw material tank 1 to the heat exchanger 2. The heat exchanger 2 isolates and heats the wastewater, with high-temperature water as the heat source. The heat exchanger 2 is a shell-and-tube heat exchanger with a heat exchange area of ​​15 m². The tube side is made of 316L stainless steel, and the shell side is made of Q235B material. The tube side carries the saline wastewater raw material, while the shell side carries the steam condensate to achieve cascade utilization of waste heat.

[0027] The wastewater outlet of heat exchanger 2 is connected to the feed inlet of thin-film evaporator 3. The inlet of thin-film evaporator 3 is connected to a steam feed source 31. High-temperature steam from the steam feed source 31 is introduced into the thin-film evaporator 3 to isolate and heat the wastewater (i.e., the wastewater and high-temperature steam are separated by the pipe wall), causing the water in the wastewater to evaporate. Thin-film evaporator 3: Rotary hinge scraper type thin-film evaporator, equipment specifications φ1300×9900, heat transfer area 20m², 316L stainless steel material, equipped with an 18.5KW drive motor, reducer output speed 74r / min, design vacuum degree -0.07~-0.09MPa.

[0028] The steam used to heat the wastewater (introduced by steam feed source 31) is cooled (becomes liquid phase) and discharged from the liquid phase outlet of the thin film evaporator 3 and enters the heat exchanger 2. The steam, after being cooled and becoming liquid phase, also has a high temperature and enters the heat exchanger 2 to preheat the wastewater. The heating is also carried out by isolated heating.

[0029] The bottom discharge end of the thin film evaporator 3 is connected to a buffer tank 4 via a pipeline. The buffer tank 4 is a vertical tank with a conical section at the bottom, with specifications of Φ1000×5300, made of 316L stainless steel. The bottom of the conical section is equipped with a blind section, and it is equipped with a magnetic float level gauge and a closed-loop regulation module for level frequency conversion.

[0030] Buffer tank 4 is used to temporarily store the concentrate and eliminate flow fluctuations. The discharge end of buffer tank 4 is connected to the inlet end of thickener 5. A second pump body 41 is installed between the discharge end of buffer tank 4 and the inlet end of thickener 5. The second pump body 41 is used to transport the concentrate. Second pump body 41: fluoroplastic centrifugal pump, suction lift 5m, rated flow rate 5m³ / h, head 30m.

[0031] The outlet pipeline of the second pump body 41 includes two paths: one path leads to the thickener 5 through a valve, and the other path returns to the backflushing port 43 at the bottom of the buffer tank 4 through the first control valve 42. With the help of the high-pressure liquid in the outlet pipeline of the buffer tank 4, the liquid is injected from the backflushing port 43 into the conical bottom of the tank body, dispersing the accumulated salt mud and agglomerated salt crystals. The bottom outlet of the buffer tank 4 is controlled by the second control valve 44 to allow material to flow downwards.

[0032] Thickener 5: Specifications Φ1200×3400, adopts a vertical pressure-bearing structure combining an upper cylindrical straight settling chamber and a lower inverted conical thickening chamber, made of 316L stainless steel; a guide tube is arranged coaxially and vertically at the internal central axis, and a stirring drive mechanism is provided at the top.

[0033] The concentrated liquid is allowed to settle in thickener 5, where sodium chloride crystals sink and the clear liquid floats, achieving initial solid-liquid separation. The upper overflow port of thickener 5 is connected to the inlet of mother liquor tank 6, and the bottom of thickener 5 has an outlet for material discharge. After discharge, the material undergoes further solid-liquid separation in centrifuge 9. Centrifuge 9: PGZ800 type flatbed fully automatic centrifuge, separation factor 1000, material contact parts are made of 316L stainless steel, equipped with an 11KW drive motor, and a loading limit of 140kg.

[0034] Mother liquor tank 6: Vertical conical bottom tank, Φ1000×1800, made of 316L stainless steel, equipped with magnetic float level gauge section.

[0035] The outlet of the mother liquor tank 6 is connected to the thin film evaporator 3 through the third pump body 61. The bottom of the thickener 5 is provided with an outlet for material discharge. Wastewater enters the thickener 5 from the raw material tank 1 and the thin film evaporator 3. The clear liquid from the thickener 5 flows out from the overflow port at the top of the thickener 5 and returns to the thin film evaporator 3 through the mother liquor tank 6 for re-evaporation and recycling to improve the concentration rate.

[0036] It also includes evaporative cooler 8, which is a condenser LNZ650H with a rated air volume of 17,500 m³ / h, a matching fan power of 2×1.5kW, a fan rated current of 4.4A, a rated circulating water volume of 50 m³ / h, a heaviest component of the equipment weighing approximately 2,200 kg, and a total operating weight of 4,500 kg.

[0037] The gas phase inlet of the evaporative cooler 8 is connected to the gas phase outlet of the thin film evaporator 3. The gas flowing through the gas phase outlet is the steam generated by the heating and evaporation of wastewater. The evaporative cooler 8 cools the steam. The outlet end of the evaporative cooler 8 is connected to the condenser tank 7. The condenser tank 7 has a diameter of φ1200×2370 mm, a total volume of 2.08 m³, is made of 316L stainless steel, and is equipped with a magnetic level gauge.

[0038] The liquid outlet of the condenser 7 is connected to the inlet of the evaporator 8 via a pipeline for cooling the evaporator 8 (as a cooling source). The pipeline is equipped with a fourth pump body 72 for condensate delivery. The fourth pump body 72 is a fluoroplastic centrifugal pump with a rated flow rate of 10 m³ / h and a head of 25 m, equipped with a frequency conversion control module.

[0039] The vapor outlet of the condenser 7 is connected to a vacuum pump 71. The vacuum pump 71 discharges the gas, thereby reducing the gas pressure inside the thin-film evaporator 3, lowering the boiling point, and accelerating evaporation. Vacuum pump 71: a water ring vacuum pump with a rated pumping speed of 10 m³ / min and an ultimate vacuum of -0.098 MPa. It is equipped with a vacuum buffer tank to achieve stable control of the system vacuum.

[0040] The operating method of the system for extracting sodium chloride crystals from wastewater is as follows:

[0041] S1: Start-up Preparation: Perform compatibility and stability testing on the system, complete valve status calibration, and ensure valve opening and closing error is ≤±1%; complete accuracy calibration of the level sensor, pressure sensor, and current monitoring module, ensuring level measurement accuracy is ±5mm and pressure measurement accuracy is ±0.001MPa; set the level threshold, pressure control parameters, rated operating parameters of electrical equipment, and initial operating parameters of the frequency converter for each tank in the system. Add cooling water to the evaporator cooler 8 to the set initial level, and start the circulating water pump to establish cooling circulation; start the vacuum pump 71 according to the vacuum pump operating procedure, first open the inlet and outlet valves of the vacuum pump cooler circulating water, add water to 2 / 3 of the water tank sight glass, and start the vacuum pump after confirming that the oil level and instruments are normal. When the outlet pressure reaches -0.050MPa, open the vacuum pump inlet ball valve and adjust the system vacuum to stabilize at -0.075~-0.080MPa to meet the feeding requirements.

[0042] S2: Concentration Circulation: Start the corresponding pipeline valves and pumps. First, open the steam valve of the thin film evaporator 3. Control the steam feed source 31 to stabilize the inlet pressure at 0.3-0.4MPa through the steam regulating valve. Open the valves before and after the steam condensate drain valve to ensure smooth discharge of steam condensate. After the system vacuum stabilizes below -0.070MPa, start feeding. Control the feed flow rate at about 3.5m³ / h through the frequency converter of the first pump body 11. At the same time, start the scraper motor of the thin film evaporator 3. Monitor the equipment operating status in real time during operation to ensure no abnormal noise or leakage.

[0043] The saline wastewater raw material is fed into heat exchanger 2 via raw material tank 1 and feed pump. After exchanging heat with steam condensate and heating to 70-75℃, it is tangentially fed into thin film evaporator 3. Under the action of rotating scraper, it forms a uniform liquid film that adheres tightly to the inner wall of the evaporator. Under vacuum negative pressure, it is heated, evaporated and concentrated. The water vaporizes into steam and is discharged from the steam port. After being condensed by evaporator cooler 8, it flows into condenser tank 7. The uncondensed non-condensable gas is extracted by vacuum pump 71 and sent to the tail gas treatment system for discharge in compliance with standards. The concentrated material enters buffer tank 4 from the bottom outlet of thin film evaporator 3. The liquid level data is collected in real time by liquid level sensor. When the liquid level in buffer tank reaches 3000mm, the second pump body 41 is turned on to send the concentrated material to thickener 5.

[0044] When the liquid level in the mother liquor tank 6 reaches 300mm, the third pump body 61 is turned on to return the mother liquor in the mother liquor tank 6 to the circulating feed port of the thin film evaporator 3, thus establishing a concentration circulation loop. During operation, the material concentration is judged in real time by the change in the current of the stirring motor of the thickener 5. Simultaneously, the operating current, power, circulating water volume, and replenishment water volume of the fan and circulating water pump of the evaporator cooler 8 are monitored in real time to ensure the stability of the cooling circulation system and ensure that the system vacuum degree and evaporation efficiency meet the standards.

[0045] During operation, when the liquid level in condenser tank 7 reaches 1000 mm, the fourth pump body 72 is turned on to pump the condensate in condenser tank 7 into the water tank of evaporator cooler 8. At the same time, the circulating water supply valve is closed, and the condensate from the salt is used as the cooling water source for evaporator cooler. The heat is removed by high-flow circulation and replacement, ensuring the stable operation of evaporator cooler 8.

[0046] S3: Crystallization Separation: When the current of the stirring motor of the thickener 5 reaches the set threshold, and the material concentration reaches the set target value and the solid content of the crystal slurry is ≥30%, the bottom crystal slurry discharge valve of the thickener 5 is opened to send the bottom crystal slurry into the centrifuge 9. The equipment is started according to the operating procedure of the centrifuge 9, and the centrifuge speed is controlled at 1600r / min to separate the crystallization product from the mother liquor. The separation time is 10-15min. The separated sodium chloride crystal solids are discharged from the centrifuge hopper to the ton bag for packaging and external recycling. The mother liquor produced by the centrifuge separation is discharged to the ash water system to ensure the purity of the produced sodium chloride crystals.

[0047] During system operation, the crystal slurry in thickener 5 undergoes rapid sedimentation and thickening of crystal particles under the action of gravity sedimentation and shallow sedimentation of inclined plate separation components. The clear liquid overflows from the upper overflow port to the mother liquor tank 6 and flows back to the thin film evaporator 3 for circulation and concentration, thereby realizing the mother liquor circulation and concentration and significantly improving the sodium chloride crystallization recovery rate.

[0048] Example 2: The structure of the thickener 5 in Example 1 is as follows:

[0049] like Figures 2-4 As shown, the thickener 5 includes a container body 51, which includes a bottom cylinder 511 located at the bottom. The bottom cylinder 511 is conical and includes a first channel 5111 located at the bottom. The first channel 5111 is externally connected to a valve to discharge solid material from the container body 51.

[0050] An end cap 52 is installed on the top of the container body 51. A bracket 54 is located above the end cap 52, and a motor 541 is fixedly installed on the bracket 54. The output end of the motor 541 is connected to a stirring shaft 53. The stirring shaft 53 is connected to the bracket 54 via bearings. Driven by the motor 541, the stirring shaft 53 can rotate along its own axis. A guide cylinder 55 is installed at the lower end of the end cap 52. The stirring shaft 53 passes through the guide cylinder 55. The top of the guide cylinder 55 is provided with a feed inlet 551. The feed inlet 551 is connected to an external material source through a pipe. Specifically, the pipe extends from the container body 51 or the end cap 52 and connects to the external material source.

[0051] A shaft 57 is rotatably connected to the end cap 52, and multiple shafts 57 are evenly distributed along the circumference of the end cap 52. The bottom of the shaft 57 is inserted into the container body 51, and a tube 56 is fixedly installed at the bottom of the shaft 57. The shaft 57 can rotate along its own axis under the action of an external drive, and the rotation of the shaft 57 drives the tube 56 to rotate synchronously. A fixing seat 521 is fixedly installed on the end cap 52, and the shaft 57 passes through the fixing seat 521. The shaft 57 and the fixing seat 521 are connected by a first bearing 5211.

[0052] Specifically, the end cap 52 is rotatably connected to a connecting seat 5721 via a third bearing 57211. A second gear ring 572 is fixedly connected to the outer wall of the connecting seat 5721. The second gear ring 572 externally meshes with a gear pair 59 and is driven by a motor. The second gear ring 572 also externally meshes with a first gear ring 571. The gear pair 59 is located on top. The first gear ring 571 is fixedly connected to a shaft 57, which passes through the first gear ring 571. The shaft 57 and the first gear ring 571 are coaxially arranged. The rotation of the second gear ring 572 drives the first gear ring 571 to rotate, thereby causing the shaft 57 to rotate.

[0053] like Figure 4 As shown, the insert 56 includes a groove 561, and multiple grooves 561 are evenly distributed along the outer periphery of the insert 56. The depth of the groove 561 along the radial direction of the insert 56 is 3%-5% of the radius of the insert 56. The outer periphery of the insert 56 is a circular arc surface.

[0054] The container body 51 is equipped with a detection probe 513, which is used to detect the position of the upper surface of the solid deposit inside the container body 51.

[0055] The insertion depth of the plunger 56 into the upper surface of the solid sediment in the container 51 is 1 / 4 to 1 / 3 of the total depth of the solid sediment, meaning the plunger 56 is located at the top of the solid sediment. When the plunger 56 is stationary, the solid sediment fills the groove 561. When the plunger 56 rotates, it throws the solid sediment out of the groove 561. Due to the slow rebound of the solid sediment, it does not have enough time to rebound back into the groove 561, creating a cavity in the groove 561. At this time, the clear liquid in the solid sediment fills the groove 561. When the plunger 56 stops rotating, the solid sediment at the bottom rebounds into the groove 561 faster than the solid sediment at the top (the deeper the depth, the greater the pressure). This pushes the clear liquid in the groove 561 upward and collects it. This solves the problem that the pressure of the top solid sediment is lower than that of the bottom solid sediment, resulting in a slower upward separation speed of the clear liquid from the solid, thus improving efficiency.

[0056] When the depth of the groove 561 along the radial direction of the insert 56 exceeds 5% of the radius of the insert 56, the groove is too deep, forming a deep and narrow cavity structure. When fine salt mud and powdered salt crystals enter the groove, they are strongly bound by the groove wall. The centrifugal force generated by the rotation of the insert 56 can only eject large crystal particles; fine salt mud and powdered salt will get stuck in the dead corners of the deep groove and cannot be completely detached from the groove by centrifugal force. The embedded salt mud continuously compacts and solidifies, eventually causing the groove 561 to become blocked, losing its liquid storage and cavity replacement functions, ultimately leading to structural failure.

[0057] When the depth of the groove 561 along the radial direction of the insert 56 is less than 3% of the radius of the insert 56, the groove is too shallow and the effective volume is too small. Although it will not accumulate mud and become clogged, the volume of clear liquid it can hold is insufficient. After the insert 56 rotates and throws out the solid phase, the cavity formed is too small to enrich enough intercrystalline clear liquid; after stopping, the salt layer can fill the groove with a slight rebound, which cannot form a stable clear liquid enrichment and upward pushing effect.

[0058] A sleeve 522 is rotatably connected to shaft 57 via a second bearing 5221. The bottom surface of sleeve 522 is 2mm-5mm higher than the upper surface of the solid sediment in container 51 (the upper surface of the solid sediment is L2 in Figure 4, and the clear liquid level is L1). The position of the upper surface of the solid sediment is controlled by detection probe 513. After one feeding, container 51 is left to stand for solid-liquid separation. The clear liquid accumulates in the upper layer and is discharged through the second channel 512.

[0059] The sleeve 522 is equipped with a conduit 5222, which is connected to an external liquid pump to help extract the clear liquid in the groove 561 when the insert 56 rotates.

[0060] The inner wall of the container body 51 is equipped with a first plate 58, and the outer wall of the guide tube 55 is equipped with a second plate 581. Both the first plate 58 and the second plate 581 are inclined plates, which utilize the principle of shallow sedimentation to shorten the salt crystal sedimentation path. The suspended salt particles quickly settle on the plate surface and slide down the inclined plate to the bottom of the tank for enrichment. The clear liquid rises along the gap between the inclined plates to achieve efficient solid-liquid separation.

[0061] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A system for extracting sodium chloride crystals from wastewater, characterized in that, The system includes a raw material tank (1), a thin-film evaporator (3), a thickener (5), and a mother liquor tank (6). The raw material tank (1) is used to store wastewater. The discharge end of the raw material tank (1) is connected to the feed end of the thin-film evaporator (3). The bottom discharge end of the thin-film evaporator (3) is connected to the feed end of the thickener (5). The upper overflow port of the thickener (5) is connected to the feed port of the mother liquor tank (6). The discharge port of the mother liquor tank (6) is connected to the thin-film evaporator (3). The bottom of the thickener (5) is provided with a discharge port for material discharge. The wastewater enters the thickener (5) from the raw material tank (1) and the thin-film evaporator (3). The clear liquid of the thickener (5) flows out from the upper overflow port of the thickener (5) and returns to the thin-film evaporator (3) through the mother liquor tank (6). It also includes a heat exchanger (2), which is located between the raw material tank (1) and the thin film evaporator (3). The wastewater flowing out of the raw material tank (1) is heated by the heat exchanger (2) and then enters the thin film evaporator (3).

2. The system for extracting sodium chloride crystals from wastewater according to claim 1, characterized in that, It also includes a buffer tank (4), which is located between the thin film evaporator (3) and the thickener (5). Wastewater discharged from the bottom of the thin film evaporator (3) enters the thickener (5) through the buffer tank (4).

3. The system for extracting sodium chloride crystals from wastewater according to claim 2, characterized in that, The bottom of the buffer tank (4) is provided with a backflush port (43). Wastewater discharged from the buffer tank (4) is introduced into the backflush port (43) through a pipeline to clean the bottom of the buffer tank (4).

4. The system for extracting sodium chloride crystals from wastewater according to claim 1, characterized in that, It also includes an evaporative cooler (8), the gas phase inlet of which is connected to the gas phase outlet of the thin film evaporator (3), the gas flowing through the gas phase outlet is steam generated by the heating and evaporation of wastewater, the outlet end of the evaporative cooler (8) is connected to a condenser (7), the liquid phase outlet of the condenser (7) is reversed to the liquid inlet of the evaporative cooler (8) for cooling the evaporative cooler (8), and the gas phase outlet of the condenser (7) is connected to a vacuum pump (71).

5. The system for extracting sodium chloride crystals from wastewater according to claim 1, characterized in that, It also includes a steam feed source (31), which is connected to the air inlet of the thin film evaporator (3). The steam feed source (31) introduces high-temperature steam into the thin film evaporator (3) to isolate and heat the wastewater. The steam used to heat the wastewater is cooled and discharged from the liquid phase outlet of the thin film evaporator (3).

6. The system for extracting sodium chloride crystals from wastewater according to claim 5, characterized in that, The steam coolant discharged from the liquid phase outlet of the thin film evaporator (3) passes through the heat exchanger (2) to isolate and heat the wastewater entering the heat exchanger (2).

7. The system for extracting sodium chloride crystals from wastewater according to claim 1, characterized in that, The thickener (5) includes a container body (51), an end cap (52) is installed on the top of the container body (51), a shaft (57) is rotatably connected to the end cap (52), the bottom of the shaft (57) is inserted into the container body (51), and a tube (56) is fixedly installed at the bottom of the shaft (57). The shaft (57) can rotate along its own axis under the action of an external drive. The rotation of the shaft (57) drives the tube (56) to rotate synchronously. The tube (56) includes a groove (561), and multiple grooves (561) are evenly distributed along the outer periphery of the tube (56).

8. The system for extracting sodium chloride crystals from wastewater according to claim 7, characterized in that, The depth of the groove (561) along the radial direction of the insert (56) is 3%-5% of the radius of the insert (56).

9. The system for extracting sodium chloride crystals from wastewater according to claim 7, characterized in that, The outer periphery of the insert (56) is a circular arc surface.

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