A leachate concentrate re-concentration system and control method

Abstract

The application discloses a landfill leachate concentrate reconcentration system and a control method, and belongs to the technical field of wastewater treatment. The system comprises a circulating water tank, a first circulating pump, an ice crystal generator, a three-phase separator, an original water pool, a centrifuge, an ice melting barrel, a heat exchanger and a controller. The circulating water tank, the first circulating pump, the ice crystal generator and the three-phase separator are sequentially connected to form a closed loop circulating loop. The outlet of the first circulating pump is also connected to a concentrate discharge port through a fourth pipeline, and serves as a concentrate discharge power source. The outlet of the ice melting barrel is connected to a third circulating pump. The outlet of the third circulating pump is divided into two paths. One path is connected to the heat exchanger through a sixth electromagnetic valve, and the other path is connected to a standard water discharge port through a seventh electromagnetic valve. The control method comprises five steps of circulation, refrigeration crystallization, water replenishment, concentrate discharge and ice melting water discharge. The controller adjusts the rotating speed of an ice cutter through a PID algorithm to maintain the stability of ice slurry concentration, and judges the concentrate end point through triple continuous sampling. The application realizes concentrate reduction treatment and clean water standard discharge through low-temperature freezing concentration, and has the advantages of low energy consumption, difficulty in fouling and high automation degree.

Description

Technical Field

[0001] This application belongs to the field of wastewater treatment technology, specifically relating to a landfill leachate concentrate reconcentration system, which is particularly suitable for the deep reduction treatment of high-concentration concentrate produced after landfill leachate has undergone membrane treatment (such as RO reverse osmosis), so as to achieve clean water discharge in compliance with standards. Background Technology

[0002] After biological treatment and membrane separation (nanofiltration, reverse osmosis), landfill leachate produces a concentrate that accounts for approximately 20% to 30% of the original volume. This concentrate typically has a COD concentration of 3000–5000 mg / L, a conductivity of 30000–80000 μS / cm, a BOD5 / COD ratio of less than 0.1, poor biodegradability, high salinity, and complex composition, making it a typical difficult-to-treat wastewater.

[0003] Currently, there is no mature and economical treatment process for landfill leachate concentrate. In practical engineering, evaporation, incineration, or reinjection are the main methods used.

[0004] Evaporation crystallization involves heating water to vaporize it, condensing it to obtain fresh water, and disposing of the remaining solid residue as hazardous waste. This process has the following problems: (1) The latent heat of vaporization of water is about 2260 kJ / kg, resulting in extremely high energy consumption; (2) Calcium and magnesium ions and organic matter in the concentrate deposit and form scale on the heat exchange surface under heating conditions, forming a hard scale layer that requires frequent shutdowns for cleaning, which can lead to the scrapping of the equipment in severe cases; (3) Chloride ions accelerate the corrosion rate of metal equipment at high temperatures, shortening the service life of the equipment; (4) The system equipment is complex, the material requirements are high, and the initial investment is large.

[0005] The incineration method involves injecting the concentrated liquid into the incinerator or mixing it with the waste for incineration. The drawbacks of this process are: (1) the concentrated liquid has a high water content, and the vaporization of water consumes a large amount of heat energy, requiring additional auxiliary fuel; (2) alkali metal salts melt at high temperatures, forming adhesive ash and coking in the furnace and heat exchange surfaces, affecting the safe and stable operation of the incinerator; (3) the hydrogen chloride, sulfur oxides and dioxins produced by incineration require a complex flue gas purification system, further increasing investment and operating costs.

[0006] Refilling landfills is simple and low-cost, but it does not remove or reduce pollutants. Long-term refilling leads to the continuous accumulation of salt and organic matter in the landfill, affecting the normal operation of the leachate treatment system. This method has been restricted by environmental regulations.

[0007] Therefore, this application provides a landfill leachate concentrate reconcentration system, which applies cryogenic concentration technology to landfill leachate concentrate treatment through structural design and automated control, thereby achieving concentrate volume reduction and clean water discharge that meets standards. Summary of the Invention

[0008] The purpose of this application is to provide a landfill leachate concentrate reconcentration system and control method, which aims to achieve deep volume reduction of the concentrate at low temperature through freeze concentration, so as to achieve clean water discharge that meets standards with low energy consumption, anti-caking and corrosion resistance.

[0009] To achieve the above objectives, this application provides the following technical solution: A landfill leachate concentrate reconcentration system includes: Circulating water tank; First circulating pump; The ice crystal generator has its inlet connected to the outlet of the first circulating pump via a first pipeline, and its outlet connected to the inlet of the three-phase separator. The three-phase separator is equipped with an ice crystal outlet and a bottom drain outlet; The outlet of the circulating water tank is connected to the inlet of the first circulating pump via a second pipeline; The bottom drain port of the three-phase separator is connected to the second pipeline via a third pipeline; The outlet of the first circulation pump is also connected to the concentrate discharge port via a fourth pipeline; The circulating water tank, the first circulating pump, the ice crystal generator, and the three-phase separator are connected in sequence through pipelines to form a closed-loop circulation circuit.

[0010] Furthermore, a first solenoid valve is provided on the first pipeline, a second solenoid valve is provided on the second pipeline, a third solenoid valve is provided on the third pipeline, and a fourth solenoid valve is provided on the fourth pipeline.

[0011] Furthermore, it also includes a raw water tank, a water supply pipeline, a centrifuge, an ice-melting tank, and a heat exchanger; The raw water tank is connected to the water inlet of the circulating water tank via a water supply pipeline, and the water supply pipeline is equipped with a fifth solenoid valve and a water supply pump. The ice crystal outlet of the three-phase separator is connected in sequence to the centrifuge and the ice-melting tank via pipelines; The heat exchanger is provided with a first flow channel and a second flow channel that are isolated from each other. The first flow channel is connected in series to the water supply pipe, and the second flow channel is connected in series to the ice-melting circulation pipe of the ice-melting tank.

[0012] Furthermore, it also includes a controller, which is electrically connected to a liquid level sensor located in the circulating water tank, a temperature sensor located on the ice crystal generator, a conductivity sensor located in the circulating water tank or the third pipeline, and the first solenoid valve, the second solenoid valve, the third solenoid valve, and the fourth solenoid valve.

[0013] Furthermore, the controller controls the start and stop of the fifth solenoid valve and the water replenishment pump based on the signal from the liquid level sensor; controls the start and stop of the refrigeration unit based on the signal from the temperature sensor; determines the concentration endpoint based on the signal from the conductivity sensor through a triple continuous sampling judgment logic, and controls the first solenoid valve to close, the second and third solenoid valves to remain open, and the fourth solenoid valve to open.

[0014] Furthermore, an ice slurry concentration sensor is installed on the pipeline between the slurry outlet of the ice crystal generator and the feed inlet of the three-phase separator. The controller adjusts the speed of the ice blade reduction motor on the ice crystal generator according to the signal of the ice slurry concentration sensor through a PID algorithm, so that the ice slurry concentration is maintained within the set target range.

[0015] Furthermore, the controller is also connected to a pressure sensor located on the outlet pipeline of the first circulating pump, which outputs an emergency stop signal when the pipeline pressure is higher than a set value.

[0016] Furthermore, the liquid outlet of the centrifuge is connected to the circulating water tank via a return liquid pipeline, and a second circulating pump is provided on the return liquid pipeline; the outlet of the ice-melting bucket is connected to a third circulating pump, and the outlet of the third circulating pump is divided into two paths, one path is connected to the second flow channel of the heat exchanger via a sixth solenoid valve, and the other path is connected to the qualified water discharge port via a seventh solenoid valve, and both the sixth and seventh solenoid valves are electrically connected to the controller.

[0017] Furthermore, the ice-melting bucket is equipped with a second temperature sensor, a second liquid level sensor, and a second conductivity sensor, which are electrically connected to the controller.

[0018] A control method for a landfill leachate concentrate reconcentration system includes the following steps: Circulation steps: Open the first solenoid valve, the second solenoid valve and the third solenoid valve, close the fourth solenoid valve, start the first circulation pump, so that the liquid in the circulating water tank flows back to the circulating water tank through the ice crystal generator and the three-phase separator, forming a closed loop circulation; Refrigeration and crystallization steps: Start the refrigeration unit, cool down the ice crystal generator to below the freezing point, generate ice crystals and scrape them off. The ice crystals and the concentrate form ice slurry which enters the three-phase separator. The ice crystals float to the top, and the concentrate sinks and flows back to the circulating water tank through the bottom drain. Water replenishment step: When the liquid level in the circulating water tank is lower than the set lower limit, the fifth solenoid valve and the water replenishment pump are opened to replenish the liquid to be treated. When the liquid level reaches the set upper limit, the fifth solenoid valve and the water replenishment pump are closed. Concentrate removal procedure: Real-time monitoring of the conductivity of the concentrate. When the conductivity reaches the set upper limit of discharge, close the first solenoid valve, keep the second and third solenoid valves open, open the fourth solenoid valve, and discharge the concentrate. After the concentrate removal is completed, close the fourth solenoid valve, open the first solenoid valve, and continue the cycle. De-icing and drainage steps: After ice crystals enter the de-icing tank, start the third circulation pump, open the sixth solenoid valve and close the seventh solenoid valve to allow the water in the de-icing tank to circulate and exchange heat through the heat exchanger to melt the ice crystals; when the liquid level in the de-icing tank reaches the set upper limit value, close the sixth solenoid valve and open the seventh solenoid valve to drain the clean water; when the liquid level reaches the set lower limit value, stop draining and close the seventh solenoid valve.

[0019] Furthermore, in the concentration removal step, the determination that the conductivity reaches the set emission limit value adopts a triple continuous sampling judgment logic: when the conductivity value of three consecutive samples with a 60-second interval between each sample is ≥ the set emission limit value, it is determined that the concentration endpoint has been reached.

[0020] Furthermore, in the refrigeration crystallization step, the start and stop of the refrigeration unit are controlled according to the temperature inside the ice crystal generator: the refrigeration unit is started when the temperature is higher than the sum of the solution freezing point temperature and 2°C, and the refrigeration unit is stopped when the temperature is lower than the difference between the solution freezing point temperature and 3°C.

[0021] Furthermore, in the water replenishment step, when the liquid level is lower than the set lower limit value and the duration is ≥5 seconds, the fifth solenoid valve and the water replenishment pump are turned on.

[0022] Furthermore, in the de-icing drainage step, the signal from the second conductivity sensor is used to determine whether the clean water meets the standard. If it does, the seventh solenoid valve remains open to allow drainage; if it does not meet the standard, the seventh solenoid valve is closed and the sixth solenoid valve is opened to allow the water to flow back to the de-icing tank for further processing.

[0023] The beneficial effects of this application are: 1. Utilizing the characteristic that the latent heat of water (335 kJ / kg) is much smaller than its latent heat of vaporization (2260 kJ / kg), the energy consumption is lower than that of the evaporation method. The cold energy from the melting process is recovered through a heat exchanger to pre-cool the raw liquid, further reducing refrigeration energy consumption.

[0024] 2. The system operates at low temperatures (-5℃~5℃) without membrane components, thus avoiding membrane fouling; the solubility of salts changes little, making it difficult for them to crystallize and reducing the risk of scaling on the heat exchange surface; at low temperatures, chloride ion activity is low, and the corrosion rate is lower than that of high-temperature processes.

[0025] 3. The concentrated liquid adhering to the surface of the ice crystals is removed by centrifugation, and the quality of the meltwater is monitored in real time by a second conductivity sensor on the ice melting tank to ensure that the clean water meets the discharge standards.

[0026] 4. The controller dynamically adjusts the speed of the ice blade reduction motor based on the signal from the ice slurry concentration sensor using a PID algorithm, so that the ice slurry concentration is kept within the target range, preventing ice crystal accumulation or excessively low concentration, and ensuring stable system operation.

[0027] 5. The controller automatically switches between the first to seventh solenoid valves to achieve fully automated operation of the entire process of water replenishment, circulation, concentrated discharge, de-icing, and drainage, without the need for manual intervention.

[0028] 6. During the discharge of concentrated substances, the first circulation pump serves as the power source for discharge, eliminating the need for a separate discharge pump. This results in a simple pipeline structure, centralized control points, and low equipment costs. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the structure of this application; Figure 2 for Figure 1 A magnified structural diagram of A in the middle.

[0030] In the diagram: 1. Raw water tank; 2. Circulating water tank; 3. Ice crystal generator; 4. Refrigeration unit; 5. Three-phase separator; 6. Ice storage tank; 7. Centrifuge; 8. De-icing tank; 9. Heat exchanger; 10. Make-up water pipeline; 11. Make-up water pump; 12. First circulation pump; 13. First pipeline; 14. First solenoid valve; 15. Second pipeline; 16. Second solenoid valve; 17. Third pipeline; 18. Third solenoid valve; 19. Fourth pipeline; 20. Fourth solenoid valve; 21. Return pipeline; 22. Second circulation pump; 23. Fifth solenoid valve; 24. Third circulation pump; 25. Sixth solenoid valve; 26. Seventh solenoid valve; 27. First flow channel. Detailed Implementation

[0031] To facilitate a clear understanding of the technical means, creative features, objectives, and effects of this application, the following description, in conjunction with specific illustrations, further elaborates on this application.

[0032] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0033] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0034] The following disclosure provides numerous different embodiments or examples for implementing various structures of the embodiments of this application. To simplify the disclosure of the embodiments of this application, specific examples of components and arrangements are described below. Of course, these are merely examples and are not intended to limit the scope of this application. Furthermore, reference numerals and / or reference letters may be repeated in different examples of the embodiments of this application; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, various specific examples of processes and materials are provided in the embodiments of this application, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0035] like Figure 1 , Figure 2 As shown, a landfill leachate concentrate reconcentration system includes a circulating water tank 2, a first circulating pump 12, an ice crystal generator 3, a three-phase separator 5, a raw water tank 1, a water replenishment pipeline 10, a centrifuge 7, an ice-melting bucket 8, a heat exchanger 9, a controller, and multiple solenoid valves and sensors.

[0036] System Composition Circulating water tank 2: Used to store circulating liquid. Circulating water tank 2 is equipped with a water inlet, a liquid outlet, and a liquid return outlet, and has a first liquid level sensor inside.

[0037] First circulation pump 12: Located on the outlet pipe of circulating water tank 2, it provides power for the main circulation of the system.

[0038] Ice crystal generator 3: An ice crystal generator 3 with a scraper mechanism is used, which is existing technology. Its liquid inlet is connected to the outlet of the first circulating pump 12 through the first pipeline 13, and its slurry outlet is connected to the feed inlet of the three-phase separator 5. The ice crystal generator 3 is equipped with a first temperature sensor, which is connected to the refrigeration unit 4 through a refrigerant pipeline, and the refrigeration unit 4 provides it with cooling. The scraper inside the ice crystal generator 3 is driven by an ice blade reduction motor. The refrigeration unit 4 is a conventional compression refrigeration unit 4 in this art, and its specific structure will not be described in detail in this application.

[0039] Three-phase separator 5: It is equipped with an ice crystal outlet and a bottom drain outlet. The bottom drain outlet is connected to the second pipeline 15 through the third pipeline 17, which is used to separate ice crystals from concentrate.

[0040] Raw water tank 1: It is connected to the water inlet of the circulating water tank 2 through the water supply pipe 10. The water supply pipe 10 is equipped with a fifth solenoid valve 23 and a water supply pump 11, which are used to replenish the raw liquid to be treated to the system.

[0041] Centrifuge 7: Used for centrifugal dehydration of ice crystals. Its inlet is connected to the ice crystal outlet of the three-phase separator 5 via a pipeline. Preferably, an ice storage tank 6 is provided between the ice crystal outlet of the three-phase separator 5 and the centrifuge 7 to temporarily store the ice crystals discharged from the three-phase separator 5. The bottom of the ice storage tank 6 has a discharge port. The ice crystals are fed into the inlet of the centrifuge 7 by gravity or via a screw conveyor. The specific conveying method is determined according to the ice crystal concentration and conveying distance, and conventional methods in the art can be used. The liquid outlet of the centrifuge 7 is connected to the circulating water tank 2 via a return liquid pipeline 21. A second circulation pump 22 is provided on the return liquid pipeline 21 to pump the dehydrated concentrate back to the circulating water tank 2 to continue circulating.

[0042] Ice melting tank 8: A screw conveyor is installed between the centrifuge 7 and the ice melting tank 8 to push the dehydrated ice crystals to the feed inlet of the ice melting tank 8. The ice melting tank 8 is used to receive the dehydrated ice crystals and melt them. The outlet of the ice melting tank 8 is connected to a third circulation pump 24. The outlet of the third circulation pump 24 is divided into two paths: one path is connected to the second flow channel of the heat exchanger 9 via the sixth solenoid valve 25, and the other path is connected to the qualified water discharge port via the seventh solenoid valve 26. The ice melting tank 8 is equipped with a second temperature sensor, a second liquid level sensor, and a second conductivity sensor.

[0043] Heat exchanger 9: Plate heat exchanger 9, equipped with a first flow channel 27 and a second flow channel that are isolated from each other. The inlet of the first flow channel 27 is connected to the outlet of the water supply pump 11 via a pipeline, and the outlet of the first flow channel 27 is connected to the raw water tank 1 via a pipeline, so that the liquid in the raw water tank 1 is sent to the heat exchanger 9 for pre-cooling via the water supply pump 11 and then returns to the raw water tank 1, forming a raw liquid pre-cooling cycle. The second flow channel is connected in series to the ice-melting circulation pipeline of the ice-melting tank 8.

[0044] Piping system: The first pipeline 13 connects the outlet of the first circulating pump 12 and the inlet of the ice crystal generator 3, and is equipped with a first solenoid valve 14. The second pipeline 15 connects the outlet of the circulating water tank 2 and the inlet of the first circulating pump 12, and is equipped with a second solenoid valve 16. The third pipeline 17 connects the bottom drain of the three-phase separator 5 and the second pipeline 15, and is equipped with a third solenoid valve 18. The fourth pipeline 19 connects the outlet of the first circulating pump 12 and the concentrate discharge port, and is equipped with a fourth solenoid valve 20.

[0045] The controller is electrically connected to the first liquid level sensor, first temperature sensor, first conductivity sensor, second temperature sensor, second liquid level sensor, second conductivity sensor, ice slurry concentration sensor, pressure sensor, first solenoid valve 14, second solenoid valve 16, third solenoid valve 18, fourth solenoid valve 20, fifth solenoid valve 23, sixth solenoid valve 25, seventh solenoid valve 26, first circulation pump 12, water replenishment pump 11, second circulation pump 22, third circulation pump 24, refrigeration unit 4, ice blade geared motor, and ice scraping motor. It is used to control the automatic operation of each actuator based on the feedback signals from the sensors. The controller can be a PLC controller or an industrial computer.

[0046] Connection Main circulation loop: The liquid in the circulating water tank enters the first circulation pump 12 through the second pipeline 15 and the second solenoid valve 16. After being pressurized by the first circulation pump 12, it is sent to the ice crystal generator 3 through the first pipeline 13 and the first solenoid valve 14. The ice slurry generated by the ice crystal generator 3 enters the three-phase separator 5 through the slurry outlet. The concentrated liquid discharged from the bottom of the three-phase separator 5 flows into the second pipeline 15 through the third pipeline 17 and the third solenoid valve 18. After merging with the liquid outlet of the circulating water tank 2, it returns to the inlet of the first circulation pump 12, forming a closed-loop circulation loop.

[0047] Water replenishment circuit: Water replenishment pump 11 draws water from raw water tank 1, and returns to raw water tank 1 after heat exchange through the first flow channel 27 of heat exchanger 9; Water replenishment pipeline 10 is led out from raw water tank 1 and connected to the water replenishment port of circulating water tank 2 through the fifth solenoid valve 23.

[0048] Ice crystal treatment circuit: The ice crystals separated by the three-phase separator 5 are sent to the centrifuge 7 through the ice crystal outlet. After the centrifuge 7 removes the concentrate, the ice crystals are sent to the ice melting tank 8. After the ice crystals in the ice melting tank 8 melt, they are sent out by the third circulation pump 24. One path is sent to the second flow channel of the heat exchanger 9 through the sixth solenoid valve 25. After heat exchange, it returns to the ice melting tank 8 to continue melting ice. The other path is discharged to the qualified water discharge port through the seventh solenoid valve 26.

[0049] Concentrate discharge circuit: The concentrate is discharged to the concentrate discharge port through the outlet of the first circulation pump 12, the fourth pipeline 19 and the fourth solenoid valve 20.

[0050] Centrifuge 7 return circuit: The concentrated liquid removed by centrifuge 7 is sent back to the circulating water tank 2 via the second circulation pump 22.

[0051] Working principle and control method When the system starts, the controller opens the fifth solenoid valve 23 and the water replenishment pump 11, and the raw liquid in the raw water tank 1 enters the circulating water tank 2 through the water replenishment pipeline 10. The first liquid level sensor in the circulating water tank 2 detects the liquid level in real time. When the liquid level reaches the set upper limit value, the controller closes the fifth solenoid valve 23 and the water replenishment pump 11 to stop water replenishment.

[0052] The controller opens the first solenoid valve 14, the second solenoid valve 16, and the third solenoid valve 18, closes the fourth solenoid valve 20, and starts the first circulation pump 12. The liquid in the circulating water tank 2 enters the first circulation pump 12 through the second pipeline 15, and is sent to the ice crystal generator 3 through the first pipeline 13. The ice slurry generated in the ice crystal generator 3 enters the three-phase separator 5 through the slurry outlet. The concentrated liquid discharged from the bottom drain of the three-phase separator 5 flows into the second pipeline 15 through the third pipeline 17, merges with the liquid outlet of the circulating water tank 2, and then enters the first circulation pump 12 to form a closed loop circulation.

[0053] The controller controls the start and stop of the refrigeration unit 4 based on the signal from the first temperature sensor on the ice crystal generator 3. The temperature inside the ice crystal generator 3 gradually decreases. When it drops below the freezing point of the solution, ice forms on the inner wall of the ice crystal generator 3. The ice blade reduction motor drives the scraper to scrape off the ice crystals. The ice crystals mix with the concentrate to form ice slurry, which is discharged from the slurry outlet into the three-phase separator 5.

[0054] After the ice slurry enters the three-phase separator 5, the ice crystals float to the surface, while the concentrate sinks to the bottom. The concentrate at the bottom flows back to the circulating water tank 2 through the bottom drain and the third pipeline 17 to continue circulating. The ice scraper motor at the top of the three-phase separator 5 drives the ice scraper to rotate, scraping the floating ice crystals towards the ice crystal discharge outlet. The ice crystals are then sent to the centrifuge 7 through the ice crystal discharge outlet.

[0055] An ice slurry concentration sensor is installed on the pipeline between the slurry outlet of the ice crystal generator 3 and the feed inlet of the three-phase separator 5 to detect the concentration of ice crystals in the ice slurry in real time. The ice slurry concentration sensor can be a commercially available capacitive, optical, or ultrasonic type to detect the volume fraction of ice crystals in the ice slurry. Those skilled in the art can select the appropriate type according to the actual working conditions; the specific model and parameters do not constitute a limitation of the present invention. For example, a capacitive sensor can be used to calculate the ice concentration by measuring the capacitance change when the ice slurry flows through the electrodes; or an ultrasonic sensor can be used to calculate the ice concentration by utilizing the difference in the propagation speed of sound waves in ice and water. The controller adjusts the speed of the ice blade reduction motor according to the signal from the ice slurry concentration sensor using a PID algorithm to maintain the ice slurry concentration within the set target range.

[0056] Centrifuge 7 dehydrates the ice crystals, removing the concentrated liquid adhering to the surface of the ice crystals. The removed concentrated liquid is returned to the circulating water tank 2 via the liquid outlet of centrifuge 7 and the second circulation pump 22 to continue circulating. The dehydrated ice crystals enter the ice melting tank 8 via the solid outlet of centrifuge 7.

[0057] After the ice crystals enter the ice-melting tank 8, the controller starts the third circulation pump 24, opens the sixth solenoid valve 25, and closes the seventh solenoid valve 26. The water in the ice-melting tank 8 (initially externally injected clean water) is sent to the second flow channel of the heat exchanger 9 via the third circulation pump 24, where it exchanges heat with the original liquid flowing through the first flow channel 27 of the heat exchanger 9. After absorbing heat, it returns to the ice-melting tank 8 to melt the ice crystals. The melted ice crystals become clean water.

[0058] The second conductivity sensor monitors the conductivity of the clean water in the ice-melting tank 8 in real time. If the water quality meets the standards, when the second liquid level sensor in the ice-melting tank 8 detects that the liquid level has reached the set upper limit, the controller closes the sixth solenoid valve 25 and opens the seventh solenoid valve 26, allowing the clean water to be discharged through the qualified water outlet. Drainage stops when the liquid level reaches the set lower limit, and the seventh solenoid valve 26 is closed. If the water quality does not meet the standards, the controller closes the seventh solenoid valve 26 and opens the sixth solenoid valve 25, allowing the water to flow back into the ice-melting tank 8 for further processing until the water quality meets the standards.

[0059] The second temperature sensor monitors the temperature inside the ice-melting bucket 8 in real time. The controller adjusts the speed of the third circulation pump 24 or the working state of the refrigeration unit 4 according to the signal from the second temperature sensor to keep the temperature inside the ice-melting bucket 8 within the set range.

[0060] As the system operates, the concentration of the concentrate gradually increases. A first conductivity sensor, installed on the circulating water tank 2 or the third pipeline 17, monitors the conductivity of the concentrate in real time. The controller uses a triple continuous sampling logic to determine the concentration endpoint: when the conductivity value of three consecutive samples, each 60 seconds apart, is ≥ the set discharge upper limit, the concentration endpoint is determined to have been reached. At this point, the controller closes the first solenoid valve 14, keeps the second solenoid valve 16 and the third solenoid valve 18 open, and opens the fourth solenoid valve 20. The concentrate is then discharged into the concentrate discharge port via the first circulating pump 12 and the fourth pipeline 19. After the discharge is complete, the controller closes the fourth solenoid valve 20 and opens the first solenoid valve 14, and the system continues to circulate.

[0061] During system operation, the controller controls water replenishment based on the signal from the first liquid level sensor in the circulating water tank 2: when the liquid level is lower than the set lower limit and the duration is ≥5 seconds, the fifth solenoid valve 23 and the water replenishment pump 11 are opened to replenish the original liquid; when the liquid level reaches the set upper limit, the fifth solenoid valve 23 and the water replenishment pump 11 are closed.

[0062] A pressure sensor is installed on the outlet pipeline of the first circulating pump 12. When the pipeline pressure is higher than the set value, the controller outputs an emergency stop signal to stop all operating equipment. Specific Implementation

[0063] The RO concentrate from a landfill has the following characteristics: COD = 5000 mg / L, total nitrogen = 600 mg / L, conductivity = 38000 μS / cm, pH = 7.8, and a processing capacity of 4.2 L / H.

[0064] The upper limit of the liquid level in circulating water tank 2 is 80%, and the lower limit is 30%. The start / stop threshold for refrigeration unit 4 is: start at T≥Tf+2℃, stop at T≤Tf-3℃. The target value for ice slurry concentration is 20%±5% (volume fraction). The upper limit of conductivity at the concentration endpoint is 50000μS / cm. The upper limit of the liquid level in the ice melting tank 8 is 80%, and the lower limit is 20%. Water replenishment delay is 5 seconds.

[0065] Operating Results: Ice crystal generator 3 temperature -3℃ to -5℃, three-phase separator 5 temperature -1℃ to -2℃, centrifuge 7 speed 2000rpm, ice melting tank 8 temperature 2~4℃, heat exchanger 9 pre-cooled the raw liquid from 25℃ to 8~10℃. Ice crystal purity after centrifugation ≥98%. Clean water COD = 85mg / L, total nitrogen = 35mg / L, conductivity = 4200μS / cm, meeting the emission limits of GB16889-2008. Concentrated liquid volume reduced to 45%, conductivity 51000μS / cm. Continuous operation for 120 hours without scaling or clogging.

[0066] As an alternative, the starting and stopping of the aforementioned valves, pumps, and motors can also be accomplished manually, with operators using sensor readings or observation windows for manual control. Automatic control is the preferred option.

[0067] All of the above-mentioned sensors, pumps and solenoid valves are commercially available and mature products. Those skilled in the art can select the appropriate specifications according to the actual working conditions. Their specific models and parameters do not constitute a limitation on the present invention.

[0068] The foregoing has shown and described the basic principles, main features, and advantages of this application. Those skilled in the art should understand that this application is not limited to the above embodiments, and various changes and modifications can be made without departing from the spirit and scope of this application; all such changes and modifications fall within the scope of the claims. The scope of protection of this application is defined by the appended claims and their equivalents.

Claims

1. A landfill leachate concentrate reconcentration system, characterized in that, include: Circulating water tank; First circulating pump; The ice crystal generator has its inlet connected to the outlet of the first circulating pump via a first pipeline, and its outlet connected to the inlet of the three-phase separator. The three-phase separator is equipped with an ice crystal outlet and a bottom drain outlet; The outlet of the circulating water tank is connected to the inlet of the first circulating pump via a second pipeline; The bottom drain port of the three-phase separator is connected to the second pipeline via a third pipeline; The outlet of the first circulation pump is also connected to the concentrate discharge port via a fourth pipeline; The circulating water tank, the first circulating pump, the ice crystal generator, and the three-phase separator are connected in sequence through pipelines to form a closed-loop circulation circuit.

2. The landfill leachate concentrate reconcentration system according to claim 1, characterized in that: The first pipeline is equipped with a first solenoid valve, the second pipeline is equipped with a second solenoid valve, the third pipeline is equipped with a third solenoid valve, and the fourth pipeline is equipped with a fourth solenoid valve.

3. The landfill leachate concentrate reconcentration system according to claim 2, characterized in that: It also includes a raw water tank, a water supply pipeline, a centrifuge, an ice-melting tank, and a heat exchanger; The raw water tank is connected to the water inlet of the circulating water tank via a water supply pipeline, and the water supply pipeline is equipped with a fifth solenoid valve and a water supply pump. The ice crystal outlet of the three-phase separator is connected in sequence to the centrifuge and the ice-melting tank via pipelines; The heat exchanger is provided with a first flow channel and a second flow channel that are isolated from each other. The first flow channel is connected in series to the water supply pipe, and the second flow channel is connected in series to the ice-melting circulation pipe of the ice-melting tank.

4. A landfill leachate concentrate reconcentration system according to claim 3, characterized in that: It also includes a controller, which is electrically connected to a level sensor located in the circulating water tank, a temperature sensor located on the ice crystal generator, a conductivity sensor located in the circulating water tank or the third pipeline, a first solenoid valve, a second solenoid valve, a third solenoid valve, and a fourth solenoid valve.

5. A landfill leachate concentrate reconcentration system according to claim 4, characterized in that: The controller controls the start and stop of the fifth solenoid valve and the water replenishment pump based on the signal from the liquid level sensor; controls the start and stop of the refrigeration unit based on the signal from the temperature sensor; determines the concentration endpoint based on the signal from the conductivity sensor through a triple continuous sampling judgment logic, and controls the first solenoid valve to close, the second and third solenoid valves to remain open, and the fourth solenoid valve to open.

6. A landfill leachate concentrate reconcentration system according to claim 4, characterized in that: An ice slurry concentration sensor is installed on the pipeline between the slurry outlet of the ice crystal generator and the feed inlet of the three-phase separator. The controller adjusts the speed of the ice blade reduction motor on the ice crystal generator according to the signal of the ice slurry concentration sensor through a PID algorithm, so that the ice slurry concentration is maintained within the set target range.

7. A landfill leachate concentrate reconcentration system according to claim 4, characterized in that: The controller is also connected to a pressure sensor located on the outlet pipeline of the first circulating pump, which outputs an emergency stop signal when the pipeline pressure is higher than the set value.

8. A landfill leachate concentrate reconcentration system according to claim 4, characterized in that: The liquid outlet of the centrifuge is connected to the circulating water tank through a return liquid pipeline, and a second circulating pump is installed on the return liquid pipeline; the outlet of the ice-melting bucket is connected to a third circulating pump, and the outlet of the third circulating pump is divided into two paths, one path is connected to the second flow channel of the heat exchanger through a sixth solenoid valve, and the other path is connected to the qualified water discharge port through a seventh solenoid valve, and both the sixth and seventh solenoid valves are electrically connected to the controller.

9. A landfill leachate concentrate reconcentration system according to claim 4, characterized in that: The ice-melting bucket is equipped with a second temperature sensor, a second liquid level sensor, and a second conductivity sensor, which are electrically connected to the controller.

10. A control method for a landfill leachate concentrate reconcentration system, characterized in that, Includes the following steps: Circulation steps: Open the first solenoid valve, the second solenoid valve and the third solenoid valve, close the fourth solenoid valve, start the first circulation pump, so that the liquid in the circulating water tank flows back to the circulating water tank through the ice crystal generator and the three-phase separator, forming a closed loop circulation; Refrigeration and crystallization steps: Start the refrigeration unit, cool down the ice crystal generator to below the freezing point, generate ice crystals and scrape them off. The ice crystals and the concentrate form ice slurry which enters the three-phase separator. The ice crystals float to the top, and the concentrate sinks and flows back to the circulating water tank through the bottom drain. Water replenishment step: When the liquid level in the circulating water tank is lower than the set lower limit, the fifth solenoid valve and the water replenishment pump are opened to replenish the liquid to be treated. When the liquid level reaches the set upper limit, the fifth solenoid valve and the water replenishment pump are closed. Concentrate removal procedure: Real-time monitoring of the conductivity of the concentrate. When the conductivity reaches the set upper limit of discharge, close the first solenoid valve, keep the second and third solenoid valves open, open the fourth solenoid valve, and discharge the concentrate. After the concentrate removal is completed, close the fourth solenoid valve, open the first solenoid valve, and continue the cycle. De-icing and drainage steps: After ice crystals enter the de-icing tank, start the third circulation pump, open the sixth solenoid valve and close the seventh solenoid valve to allow the water in the de-icing tank to circulate and exchange heat through the heat exchanger to melt the ice crystals; when the liquid level in the de-icing tank reaches the set upper limit value, close the sixth solenoid valve and open the seventh solenoid valve to drain the clean water; when the liquid level reaches the set lower limit value, stop draining and close the seventh solenoid valve.

11. The control method for a landfill leachate concentrate re-concentration system according to claim 10, characterized in that: In the concentration removal step, the determination that the conductivity reaches the set emission limit value adopts a triple continuous sampling judgment logic: when the conductivity values ​​of three consecutive samples with a 60-second interval between each sample are all ≥ the set emission limit value, it is determined that the concentration endpoint has been reached.

12. The control method for a landfill leachate concentrate re-concentration system according to claim 10, characterized in that: In the refrigeration crystallization step, the start and stop of the refrigeration unit are controlled according to the temperature inside the ice crystal generator: the refrigeration unit is started when the temperature is higher than the sum of the solution freezing point temperature and 2°C, and the refrigeration unit is stopped when the temperature is lower than the difference between the solution freezing point temperature and 3°C.

13. The control method for a landfill leachate concentrate re-concentration system according to claim 10, characterized in that: In the water replenishment step, when the liquid level is lower than the set lower limit and the duration is ≥5 seconds, the fifth solenoid valve and the water replenishment pump are turned on.

14. The control method for a landfill leachate concentrate re-concentration system according to claim 10, characterized in that: In the de-icing and drainage step, the signal from the second conductivity sensor is used to determine whether the clean water meets the standard. If it does, the seventh solenoid valve is kept open to allow drainage; if it does not meet the standard, the seventh solenoid valve is closed and the sixth solenoid valve is opened to allow the water to flow back to the de-icing tank for further processing.

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