A multi-layer gradient fluidized bed coupled with ultrasonic enhanced calcium fluoride crystallization device

Abstract

This invention discloses a multi-layer gradient fluidized bed coupled with ultrasound-enhanced calcium fluoride crystallization device, comprising a reaction tower and a cyclone separator connected to the reaction tower. The reaction tower includes a bottom sludge discharge zone, a bottom reaction zone, a middle reaction zone, and a top reaction zone arranged sequentially from bottom to top. The bottom reaction zone includes a bottom reaction shell; a bottom sieve plate is provided at the top of the bottom reaction shell, and a bottom ultrasonic transducer is provided at the top of the bottom reaction shell; a wastewater tangential injection pipe and a calcium solution injection pipe are provided at the bottom of the bottom reaction shell. The middle reaction zone includes a middle reaction shell, and a middle ultrasonic transducer is provided at the top of the middle reaction zone. The top reaction zone includes a top reaction shell, and a top ultrasonic transducer is provided at the top of the top reaction shell. This invention not only improves the layered crystal growth rate but also increases the resource recovery rate.

Description

Technical Field

[0001] This utility model relates to the field of wastewater treatment technology, and in particular to a multi-layer gradient fluidized bed coupled with ultrasonic enhancement for crystallizing calcium fluoride in high-concentration acidic fluoride wastewater. Background Technology

[0002] In recent years, the rapid development of industries such as photovoltaics and semiconductors has brought new challenges. The hydrofluoric acid used in its manufacturing processes generates large quantities of highly concentrated acidic fluoride-containing wastewater. These fluorides are difficult to degrade using conventional methods, posing a significant threat to the environment and human health. National regulations on fluoride emissions have become increasingly stringent, with some provinces and cities, including Beijing, Tianjin, and Jiangsu, issuing emission limits as low as 1.5 mg / L. Therefore, fluidized bed crystallization defluorination technology has received widespread attention to meet the requirements for deep defluorination of highly concentrated acidic fluoride-containing wastewater and the need for resource recovery.

[0003] Fluidized bed crystallization technology is based on the principle of induced crystallization. It allows fluoride ions in wastewater to react with added calcium seed crystals in a suspended state to form CaF2 crystals, ultimately achieving the dual goals of crystal recovery and wastewater purification. Compared to traditional methods, fluidized bed crystallization can efficiently treat fluoride-containing wastewater, offering advantages such as lower chemical dosage, smaller footprint, easier solid-liquid separation, and resource recovery. It meets increasingly stringent emission standards and is one of the most promising fluoride removal methods currently available.

[0004] However, current traditional fluidized bed reactors have significant limitations in the controllable growth of calcium fluoride crystals: the uniform flow field design leads to an imbalance in the coupling between crystal nucleation and growth processes, resulting in a high proportion of secondary nucleation, discrete particle size distribution, and difficulty in meeting high-grade industrial standards. Crystal formation relies on exogenous seed carriers, which easily introduce impurities (such as SiO), limiting product purity to 93%-96%, and carrier regeneration further increases energy consumption. Static sieve plates with uniform pore size are prone to clogging, resulting in uneven flow field distribution, high backwashing frequency, and potential process interruptions and crystal breakage. Therefore, to address these pain points, it is necessary to overcome the core bottlenecks of uncontrollable calcium fluoride nucleation, limited purity, and high energy consumption through structural reconstruction and the synergistic effect of energy fields, providing necessary support for the industrial continuous production of high-value-added calcium fluoride crystals. Utility Model Content

[0005] Purpose of the utility model: In order to solve the problems of low defluorination efficiency and poor resource utilization in the current fluidized bed reactor treatment of acidic high-concentration fluoride wastewater, this utility model provides a multi-layer gradient fluidized bed coupled with ultrasonic enhancement calcium fluoride crystallization device.

[0006] Technical solution: To achieve the above objectives, the technical solution adopted by this utility model is as follows:

[0007] A multi-layer gradient fluidized bed coupled with ultrasonic enhancement for calcium fluoride crystallization includes a reaction tower and a hydrocyclone separator connected to the reaction tower. The reaction tower comprises, from bottom to top, a bottom sludge discharge zone, a bottom reaction zone, a middle reaction zone, and a top reaction zone, wherein:

[0008] The bottom reaction zone includes a bottom reaction shell. A bottom sieve plate is provided at the top of the bottom reaction shell, and a bottom ultrasonic transducer is provided at the upper part of the bottom reaction shell. A wastewater tangential injection pipe and a calcium solution injection pipe are provided at the lower part of the bottom reaction shell, and an alkali injection pipe is provided on the wastewater tangential injection pipe.

[0009] The intermediate reaction zone includes an intermediate reaction shell, which is mounted on the bottom reaction shell. An intermediate sieve plate is located at the top of the intermediate reaction shell, and an intermediate ultrasonic transducer is located at the upper part of the intermediate reaction zone.

[0010] The top-layer reaction zone includes a top-layer reaction shell, which is mounted on the middle-layer reaction shell. A top-layer sieve plate is located at the top of the top-layer reaction shell, and an acid injection pipe, a top-layer ultrasonic transducer, and a crystal-directing agent nozzle are located on the upper part of the top-layer reaction shell, with the crystal-directing agent nozzle positioned above the top-layer sieve plate.

[0011] Preferably, the bottom sludge discharge zone includes a conical shell, the bottom reaction shell is installed on the conical shell, the bottom end of the conical shell is provided with a slag discharge port, the upper end of the slag discharge port is provided with a filter grid, the lower end of the slag discharge port is provided with a slag discharge port butterfly valve, and the side of the slag discharge port is provided with an ultrasonic vibrator.

[0012] Preferably, the top reaction shell is provided with a wastewater outlet, the wastewater outlet, the peristaltic pump, and the hydrocyclone are connected in sequence, the top of the hydrocyclone is provided with an overflow pipe and a secondary micro hydrocyclone, the outlet of the primary micro hydrocyclone, the outlet water regulating valve, the top electromagnetic flow meter, the online F electrode, and the water outlet are connected in sequence, the bottom of the hydrocyclone is provided with a crystal outlet, and a laser particle size analyzer is provided on the crystal outlet.

[0013] Preferably, the top of the cyclone separator is provided with a second reflux outlet, and the bottom of the middle reaction shell is provided with a second reflux inlet. The second reflux inlet and the second reflux outlet are connected by a second reflux pipe. The second reflux pipe is provided with a second reflux regulating valve, a top-level circulation pump, and a second top-level electromagnetic flowmeter. The upper part of the middle reaction zone is provided with a first reflux outlet, and the lower part of the bottom reaction shell is provided with a first reflux inlet. The first reflux inlet and the first reflux outlet are connected by a first reflux pipe. The first reflux pipe is provided with a middle-level circulation pump, a middle-level electromagnetic flowmeter, and a first reflux regulating valve.

[0014] Preferably: the bottom layer ultrasonic transducers are located below the bottom layer sieve plate, and are uniformly arranged in a ring along the inner wall of the bottom layer reaction shell. The middle layer ultrasonic transducers are located below the middle layer sieve plate, and are uniformly arranged in a ring along the inner wall of the middle layer reaction shell. The top layer ultrasonic transducers are located below the top layer sieve plate, and are uniformly arranged in a ring along the inner wall of the top layer reaction shell.

[0015] Preferably, a nitrogen microporous aerator is provided at the bottom of the bottom reaction shell, and the nitrogen microporous aerator is connected to a nitrogen cylinder.

[0016] Preferably, a bottom pH probe is provided at the lower part of the bottom reaction shell, and a middle backwashing assembly, a middle pH probe, and a temperature sensor are provided at the lower part of the middle reaction zone. A top backwashing assembly is provided at the upper part of the top reaction shell, and the top backwashing assembly is located above the top sieve plate. A top pH probe is provided at the lower part of the top reaction shell.

[0017] Preferably, a bottom differential pressure sensor 1 is disposed on the upper part of the bottom reaction shell, and a bottom differential pressure sensor 2 is disposed on the lower part of the middle reaction zone. A middle differential pressure sensor 1 is disposed on the upper part of the middle reaction zone, and a middle differential pressure sensor 2 is disposed on the lower part of the top reaction shell. A top differential pressure sensor 1 and a top differential pressure sensor 2 are disposed on the upper part of the top reaction shell, with the top differential pressure sensor 1 located below the top sieve plate and the top differential pressure sensor 2 located above the top sieve plate.

[0018] Preferably, the calcium solution injection pipe is an annular porous spray pipe with a downward spray angle. Crystalline guide nozzles are arranged on an annular support above the top sieve plate, and are evenly distributed circumferentially, spraying vertically downwards.

[0019] Preferably, the apertures of the top sieve plate, middle sieve plate, and bottom sieve plate increase sequentially.

[0020] Compared with the prior art, this utility model has the following advantages:

[0021] 1. The core theoretical innovation of this invention lies in the construction of a highly efficient control mechanism based on the synergistic effect of multiple physical fields, breaking through the dynamic limitations of traditional fluidized beds through the coupling of spatial gradients and energy fields. At the fluid dynamics level, a multi-layer gradient fluidization architecture is adopted: a dynamic hierarchical barrier is constructed through gradually expanding and decreasing aperture sieve plates (2mm→0.6mm). The flow velocity in the bottom reaction zone is 60-80 m / h, and the high shear force generated by turbulence promotes mass transfer at the micro-interface, increasing the initial nucleation density by 23 times. The flow velocity in the middle reaction zone transitions to 30-60 m / h, relying on the reduced fluid kinetic energy to extend the adsorption time on the crystal surface and improve the layered growth rate of the crystal. The flow velocity in the top reaction zone is stabilized at 10-30 m / h to optimize the final crystal form. Regarding energy field synergy, multi-frequency, multi-power ultrasonic control technology is innovatively introduced: low-frequency, high-power ultrasound is used in the bottom layer, utilizing the microjets generated by cavitation bubble collapse to effectively break up metastable clusters, reducing the solution supersaturation threshold and nucleation activation energy. The middle layer switches to mid-frequency, mid-power ultrasound, enhancing the solute diffusion coefficient through the standing wave effect and overcoming the Fick diffusion limitation. The top layer uses high-frequency, low-power ultrasound to suppress secondary nucleation. Hydrodynamic simulations show that this synergistic system can increase the crystal growth rate constant by 75% compared to single-field processing, overcoming the diffusion limitations of traditional processes, and ultimately narrowing the full width at half maximum (FWHM) of the crystal grain size distribution by 60% compared to traditional methods.

[0022] 2. This invention employs a dual-regulation approach of directional ultrasonic cavitation and crystal-directing agent in the CaF crystallization process. By controlling reaction conditions without adding exogenous seed carriers, crystal nuclei spontaneously form, reducing production costs and impurity introduction. This results in crystal particle sizes of 200-500 μm and CaF purity >99%, meeting the high-grade requirements of industry. Through layered ultrasonic control technology, crystal nucleus formation, crystal growth, and crystal form optimization are orderly regulated. The superposition of ultrasonic-induced microjets and fluidized turbulence increases the mass transfer coefficient by 23 times. The sprayed crystal-directing agent, sodium polyacrylate, preferentially adsorbs onto specific CaF crystal faces (111) to promote the formation of more regular cubic crystal forms and reduces spontaneous nucleation in the final stage by lowering local supersaturation of the solution. It also enhances the electrostatic repulsion between crystal particles to prevent agglomeration. The device integrates a hydrocyclone separator and a secondary micro-cyclone separator for direct solid-liquid separation, improving resource recovery rate and further reducing crystal water content, truly realizing "hazardous waste to resource conversion."

[0023] 3. This invention boasts significant advantages in practicality. Employing a decreasing aperture sieve plate (2mm→0.6mm) and a counter-current backwashing system, it increases solid-liquid separation efficiency to 98%, reducing energy consumption by 35% compared to traditional fluidized beds. An integrated PLC intelligent control system dynamically adjusts ultrasonic power (80%→40%) based on real-time feedback from differential pressure, pH, and particle size sensors, increasing the proportion of target crystals (200-500μm) to over 90%. The modular design allows for rapid replacement of the sieve plate and ultrasonic transducer, extending maintenance cycles. The system supports the treatment of high-concentration acidic fluoride-containing wastewater, achieving crystal purity >99%, and reducing the cost per ton of water treated by 30%, combining environmental friendliness with industrial economics. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of a multi-layer gradient fluidized bed coupled with ultrasonic enhancement for calcium fluoride crystallization proposed in this utility model.

[0025] In the diagram: 1. Reaction tower; 2. Bottom sludge discharge zone; 2-1. Slag discharge port butterfly valve; 2-2. Slag discharge port; 2-3. Filter grid; 2-4. Ultrasonic vibrator; 3. Bottom reaction zone; 3-1. Wastewater tangential injection pipe; 3-2. Alkali injection pipe; 3-3. Calcium solution injection pipe; 3-4. Bottom ultrasonic transducer; 3-51. Bottom differential pressure sensor one; 3-52. Bottom differential pressure sensor two; 3-6. Nitrogen cylinder; 3-7. Nitrogen microporous aerator head; 3-8. Bottom pH probe; 3-9. Bottom sieve plate; 3-10. Bottom backwashing assembly. 4. Middle Layer Reaction Zone: 4-1. Middle Layer Ultrasonic Transducer; 4-21. Middle Layer Differential Pressure Sensor 1; 4-22. Middle Layer Differential Pressure Sensor 2; 4-3. Middle Layer Backwash Assembly; 4-4. Middle Layer pH Probe; 4-5. Temperature Sensor; 4-6. Middle Layer Circulation Pump; 4-7. Middle Layer Electromagnetic Flow Meter; 4-8. Return Regulating Valve 1; 4-9. Middle Layer Sieve Plate. 5. Top Layer Reaction Zone: 5-1. Top Layer pH Probe; 5-2. Acid Injection Pipe; 5-3. Top Layer Ultrasonic Transducer; 5-41. Top Layer Differential Pressure Sensor 1; 5-42. Top Layer Differential Pressure Sensor 2; 5-5. Top Layer Backwash Assembly; 5-6. Crystalline Directing Agent Nozzle; 5-7. Top Layer Sieve Plate. 6. Hydrocyclone separator; 6-1. Peristaltic pump; 6-2. Overflow pipe; 6-3. Secondary micro hydrocyclone; 6-4. Outlet regulating valve; 6-5. Top-level electromagnetic flow meter I; 6-6. Online F electrode; 6-7. Outlet; 6-8. Backflow regulating valve II; 6-9. Laser particle size analyzer; 6-10. Crystal outlet; 6-11. Top-level circulating pump; 6-12. Top-level electromagnetic flow meter II; 7. PLC control cabinet. Detailed Implementation

[0026] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. After reading the present invention, any modifications of the present invention in various equivalent forms by those skilled in the art will fall within the scope defined by the appended claims.

[0027] A multi-layer gradient fluidized bed coupled with ultrasound-enhanced calcium fluoride crystallization device, such as Figure 1 As shown, it includes a reaction tower 1, a cyclone separator 6 connected to the reaction tower 1, and a PLC control cabinet 7, to... Figure 1 With the indicated direction as a reference, the cyclone separator 6 and the PLC control cabinet 7 are respectively located on both sides of the reaction tower 1. The reaction tower 1 comprises four parts from bottom to top, corresponding to the bottom sludge discharge zone 2, the bottom reaction zone 3, the middle reaction zone 4, and the top reaction zone 5 arranged sequentially from bottom to top, wherein:

[0028] The bottom sludge discharge zone 2 includes a conical outer shell. A slag discharge port 2-2 is located at the bottom of the conical outer shell. A filter grille 2-3 is located at the upper end of the slag discharge port 2-2, and a slag discharge port butterfly valve 2-1 is located at the lower end of the slag discharge port 2-2. An ultrasonic vibrator 2-4 is located on the side of the slag discharge port 2-2. The bottom sludge discharge zone 2 has an overall inverted conical structure with a cone angle of 60°. The slag discharge port butterfly valve 2-1 is located at the lower part of the slag discharge port 2-2 to ensure smooth final slag discharge. The filter grille 2-3 is located at the upper part of the slag discharge port 2-2 to intercept large particles of impurities. The ultrasonic vibrator 2-4 is located on the right side of the slag discharge port 2-2, and performs timed vibration to prevent crystallization and blockage.

[0029] The bottom reaction zone 3 includes a bottom reaction shell mounted on a conical shell, with a total height of 100mm. A bottom sieve plate 3-9 is located at the top of the bottom reaction shell. The bottom sieve plate 3-9 has an average pore size of 2mm, a diameter of 50mm, and a thickness of 4mm. Its pore size and thickness are the largest among the three sieve layers, providing high mechanical strength to withstand the high flow rates within the bottom reaction zone 3 and ensure turbulent flow of wastewater, thus accelerating crystal nucleation and intercepting undissolved Ca(OH) or impurities. A nitrogen microporous aerator head 3-7 is located at the bottom of the bottom reaction shell, connected to a nitrogen cylinder 3-6. A bottom ultrasonic transducer 3-4 and a bottom differential pressure sensor 3-51 are located at the top of the bottom reaction shell, with the bottom ultrasonic transducer 3-4 positioned below the bottom sieve plate 3-9. Four ultrasonic transducers 3-4 are evenly arranged in a ring along the inner wall of the bottom reaction shell. Within the bottom reaction zone 3, the frequency and power are controlled at 20kHz and 80% of the rated power, respectively. The low-frequency, high-power ultrasonic waves generate a strong cavitation effect to promote crystal nucleation. An internal spiral-coil tubular water-cooling channel is provided; when the internal fluid cooling is insufficient, external cooling water is activated to prevent overheating. The lower part of the bottom reaction shell is equipped with a wastewater tangential injection pipe 3-1, a calcium solution injection pipe 3-3, and a bottom pH probe 3-8. An alkali injection pipe 3-2 is installed on the wastewater tangential injection pipe 3-1. The calcium solution injection pipe 3-3 is a ring-shaped multi-hole jet pipe with a downward spray angle.

[0030] The nitrogen microporous aeration head is set on the aeration pipe at the bottom of the bottom reaction zone. The aeration pipe is connected to the external nitrogen cylinder. A total of 7 aeration heads are set, and each aeration head has 6 evenly distributed aeration points. The bottom pH probe is set at the bottom of the bottom reaction zone. The bottom backwashing assembly is set at both ends of the side wall above the bottom sieve plate and is equipped with high-pressure nozzles with a nozzle fan angle of 90°.

[0031] The wastewater tangential injection pipe 3-1 is located on the lower side of the bottom reaction zone 3, with the pipe axis forming a 30° angle with the inner wall of the reactor, allowing the wastewater to enter tangentially and form a swirling flow, enhancing mass transfer and particle suspension. The alkali injection pipe 3-2 is located on the side of the wastewater tangential injection pipe 3-1, adjusting the pH range of the bottom reaction zone 3 to prevent excessive calcium solution addition. The calcium solution injection pipe 3-3 is located above the wastewater tangential injection pipe 3-1, and is an annular porous spray pipe with a downward spray angle of 4-5°, adding the calcium source slurry to the bottom reaction zone 3 and mixing it evenly with the wastewater. The nitrogen microporous aerator 3-7 is located on the aerator at the bottom of the bottom reaction zone 3, promoting the generation of more small-diameter bubbles that diffuse upwards to the bottom reaction zone 3. The nitrogen cylinder 3-6 is connected to the nitrogen microporous aerator 3-7 through an aerator pipe, providing a nitrogen source.

[0032] Bottom differential pressure sensor 1 (3-51) and bottom differential pressure sensor 2 (3-52) are located at the top and bottom of the bottom sieve plate 3-9, respectively. They are used to monitor the pressure difference (ΔP) between the top and bottom sides of the sieve plate to determine the bottom blockage situation, and are used to adjust the middle layer flow rate and trigger backwashing to prevent bottom crystal accumulation.

[0033] The bottom backwashing assembly 3-10 is located at both ends of the side wall above the bottom sieve plate 3-9. It backwashes the sieve plate regularly during the reaction and in case of abnormalities to prevent crystal blockage.

[0034] The intermediate reaction zone 4 includes an intermediate reaction shell, which is installed on the bottom reaction shell. The intermediate reaction zone adopts an expanding diameter design with a gradually expanding angle of 6-7° and a gradually expanding height accounting for 2 / 5 of the total height of the reaction zone. The total height of the intermediate reaction zone is 150mm. An intermediate sieve plate 4-9 is provided at the top of the intermediate reaction shell, located at the uppermost part of the intermediate reaction zone 4. The intermediate sieve plate 4-9 has an average pore size of 1.5mm, a diameter of 60mm, and a thickness of 3mm. The pore size and thickness are at a moderate level, balancing strength and lightweight. It first traps the crystal nuclei generated in the bottom reaction zone 3 as a secondary growth carrier, and can regulate and reduce the liquid flow rate, prolonging its residence time and promoting further crystal growth. Simultaneously, the intermediate sieve plate 4-9 and the gradually expanding design buffer the flow rate and pH gradient, creating better conditions for crystal growth within the intermediate reaction zone 4.

[0035] The upper part of the intermediate reaction zone 4 is equipped with an intermediate ultrasonic transducer 4-1 and an intermediate differential pressure sensor 4-21. The intermediate ultrasonic transducer 4-1 is located below the intermediate sieve plate 4-9. Four intermediate ultrasonic transducers 4-1 are evenly arranged in a ring along the inner wall of the intermediate reaction shell. The ultrasonic frequency and power are further adjusted to 30kHz and 60% of the rated power, respectively, to balance cavitation and microfluidic effects and promote uniform crystal growth within the intermediate reaction zone 4. The lower part of the intermediate reaction zone 4 is equipped with an intermediate backwashing assembly 4-3, a bottom differential pressure sensor 3-52, an intermediate pH probe 4-4, and a temperature sensor 4-5. The intermediate backwashing assembly 4-3 periodically pulse-washes the intermediate sieve plate 4-9. A reflux outlet is located at the upper part of the intermediate reaction zone 4, and a reflux inlet is located at the lower part of the bottom reaction shell. The reflux inlet and outlet are connected by a reflux pipe, which is equipped with an intermediate circulation pump 4-6, an intermediate electromagnetic flowmeter 4-7, and a reflux regulating valve 4-8. Intermediate differential pressure sensors 4-21 and 4-22 monitor the pressure difference ΔP between the upper and lower sides of the intermediate sieve plate 4-9. The temperature sensor 4-5 is located on the side of the intermediate reaction zone 4, monitoring the temperature range within the reaction zone in real time to optimize the reagent dosage, avoid incomplete reactions due to low temperatures or thermal stress caused by high temperatures, and maintain the stability of the formed CaF2 crystal form.

[0036] The intermediate layer pH probe 4-4 monitors the pH range of the intermediate layer reaction zone 5 in real time, maintaining it between 7.5 and 8.7 to optimize the pH conditions for crystal growth. The intermediate layer circulation pump 4-6 returns a portion of the effluent from the intermediate layer reaction zone 4 to the bottom layer reaction zone 3, promoting secondary crystal growth. The reflux regulating valve 4-8 and the intermediate layer electromagnetic flowmeter 4-7 regulate and monitor the reflux flow rate, maintaining the fluid volume V within the intermediate layer reaction zone 4. 实 The speed is 30–60 m / h.

[0037] The top-layer reaction zone 5 includes a top-layer reaction shell, which is mounted on the middle-layer reaction shell. The top-layer reaction zone adopts an expanding diameter design with a gradually expanding angle of 61° and a gradually expanding height accounting for 3 / 8 of the reaction zone height; the total height of the top-layer reaction zone is 150mm. A top-layer sieve plate 5-7 is provided at the top of the top-layer reaction shell, located above the top-layer reaction zone 5. The top-layer sieve plate 5-7 has an average aperture of 1mm, a diameter of 100mm, and a thickness of 2mm. Its aperture and thickness are the smallest among the three sieve plates, preventing immature crystals from entering the hydrocyclone separator 6 and increasing the resistance to fluid ascent, thereby reducing its Vo. 实 Achieving a flow rate of 20 m³ / h provides a more stable growth environment for the crystals. The upper part of the top-layer reaction shell is equipped with an acid injection pipe 5-2, a top-layer ultrasonic transducer 5-3, a top-layer differential pressure sensor 1 54-1, a top-layer differential pressure sensor 2 5-42, a top-layer backwashing assembly 5-5, and a crystal-directing agent nozzle 5-6. The top-layer backwashing assembly 5-5 periodically pulses the top-layer sieve plate 5-7 to prevent it from being blocked by crystals. The top-layer ultrasonic transducer 5-3 and the top-layer differential pressure sensor 1 54-1 are located below the top-layer sieve plate 5-7, while the top-layer differential pressure sensor 2 5-42, the top-layer backwashing assembly 5-5, and the crystal-directing agent nozzle 5-6 are located above the top-layer sieve plate 5-7. Four top-layer ultrasonic transducers 5-3 are evenly arranged in a ring along the inner wall of the top-layer reaction shell. The lower part of the top-layer reaction shell is equipped with a top-layer pH probe 5-1 and a middle-layer differential pressure sensor 2 4-22. The top differential pressure sensor 54-1 and the top differential pressure sensor 5-42 monitor the ΔP on the upper and lower sides of the top sieve plate 5-7 to determine its blockage status.

[0038] The top-level pH probe 5-1 is used to monitor the pH level in the top-level reaction zone 5, and dynamically adjusts the pH range to 7.0-7.8 by controlling the flow rate of the acid injection pipe 5-2 through the PLC control cabinet 7, thus meeting the third-stage growth conditions of the crystal. The top-level ultrasonic transducer 5-3 adjusts the ultrasonic frequency and power in the top-level reaction zone 5 to 40kHz and 40% of the rated power, respectively, to use high-frequency ultrasonic waves to focus on cleaning the crystal surface and refining the grains, while using low power to avoid damaging the formed crystal structure, thereby optimizing the final grain size range and crystal form of the crystal.

[0039] The crystal-directing agent nozzles 5-6 are arranged on the annular support above the top sieve plate 5-7, with a total of 4 nozzles evenly distributed around the circumference. The atomization angle is 60°, and the nozzles spray vertically downwards. The atomizing nozzles control the droplet size of the crystal-directing agent to about 50μm, avoiding local over-wetting and ensuring the atomization effect. This further optimizes the crystal form formed in the final stage and promotes the formation of more cubic CaF2 crystals.

[0040] The top-layer reaction shell is equipped with a wastewater outlet. The wastewater outlet, peristaltic pump 6-1, and hydrocyclone 6 are connected in sequence. The top of the hydrocyclone 6 is equipped with an overflow pipe 6-2 and a secondary micro hydrocyclone 6-3. The outlet of the primary micro hydrocyclone 6-3, the outlet water regulating valve 6-4, the top-layer electromagnetic flowmeter 6-5, the online F electrode 6-6, and the outlet 6-7 are connected in sequence. The bottom of the hydrocyclone 6 is equipped with a crystal outlet 6-10. The hydrocyclone 6 is located on the side of the reaction tower 1 above the top-layer sieve plate 5-7. The peristaltic pump 6-1 transports the wastewater carrying crystals in the top-layer reaction zone 5 to the hydrocyclone 6, which enters tangentially to form a hydrocyclone separation effect, accelerating the separation between crystals and liquid. Under the action of centrifugal force, large CaF2 crystal particles are discharged from the bottom of the conical section of the hydrocyclone 6 to the crystal outlet 6-10. A laser particle size analyzer 6-9 is installed on the crystal outlet 6-10. The laser particle size analyzer 6-9 is installed at the crystal outlet 6-10 to monitor the particle size distribution (D10, D50, and D90) of the discharged crystals in real time. Closed-loop control is achieved through feedback adjustment via the PLC control cabinet 7. If the crystal D90 > 400 μm, the PLC control cabinet 7 adjusts and increases the ultrasonic frequency of the ultrasonic transducer 5-3 in the top reaction zone 5 to break up larger particles, precisely controlling product quality and operational stability. If the crystal D50 < 300 μm, the PLC control cabinet 7 adjusts and increases the flow rate of the top circulation pump 6-11 to extend the crystal growth time. The overflow pipe 6-2 is located at the top center of the cyclone separator 6. The secondary micro hydrocyclone 6-3 is installed inside the overflow pipe 6-2 to further centrifuge the overflow liquid. The slurry containing fine particles in the underflow port of the secondary micro hydrocyclone 6-3 is returned to the middle reaction zone 4 through the top-layer circulation pump 6-11 to promote the cyclic growth of fine particles. After the clear water in the overflow port of the secondary micro hydrocyclone 6-3 meets the standards, it is discharged from the outlet 6-7. The outlet 6-7 is equipped with an online F electrode 6-6 to further monitor the F compliance of the effluent. The top-layer electromagnetic flowmeter 6-5 is located at the front end of the outlet 6-7 to monitor the final effluent flow rate and link the valve opening of the outlet regulating valve 6-4 to control the effluent flow rate.

[0041] The top of the cyclone separator 6 is provided with a second reflux outlet, and the bottom of the middle layer reaction shell is provided with a second reflux inlet. The second reflux inlet and the second reflux outlet are connected by a second reflux pipe. The second reflux pipe is provided with a second reflux regulating valve 6-8, a top layer circulation pump 6-11, and a second top layer electromagnetic flow meter 6-12.

[0042] The PLC control cabinet 7 is located on the side of the equipment body 1. Through the input and output of data by the PLC, it realizes precise control of the core components inside the equipment. The core operations controlled by the PLC control cabinet 7 include wastewater injection, calcium solution injection, alkali injection, acid injection, ultrasonic frequency adjustment, backwash valve, pH adjustment, temperature adjustment, crystal guiding agent injection, slag discharge valve, nitrogen gas flow, etc. Finally, the PLC program integrates multiple parameters such as flow rate, pH, and pressure to achieve closed-loop control, ensuring the efficient and stable operation of the system.

[0043] A method for using a multi-layer gradient fluidized bed coupled with ultrasound-enhanced calcium fluoride crystallization device includes the following steps:

[0044] Step 1: Before treating 10L of fluoride-containing wastewater with pH 3 and an fluoride concentration of 3000mg / L, perform a power-on self-test. The PLC control cabinet 7 checks the status of all pH probes, temperature sensors, and ultrasonic transducers within the equipment. The butterfly valve 2-1 at the slag discharge port automatically opens and closes three times to confirm there is no obstruction. First, inject the wastewater at a flow rate of 5L / h. Then, inject 10% Ca(OH)₂ slurry at a flow rate of 0.32L / h (excess coefficient 1.5) through the calcium solution injection pipe 4-3 to adjust the pH of the bottom layer to approximately 8.5–9.7. Start the ultrasonic transducer 4-8 at a frequency of 20kHz and 30% power. Turn on the nitrogen microporous aerator head 3-7 at a flow rate of 3L / min for uniform aeration.

[0045] Step 2: During continuous operation, fluoride-containing wastewater is stably injected into the wastewater tangential injection pipe 3-1 at a tangential flow rate of 80 m / h, and 10% Ca(OH) slurry is added at a flow rate of 0.6-4 L / h. Uniform dispersion of the reagent is ensured through the porous injection pipe within the calcium solution injection pipe 3-3. Simultaneously, the nitrogen gas distribution flow rate is increased to between 3 and 6 L / min. The power of the bottom ultrasonic transducer 4-8 is increased to 80% of its rated power to promote the reaction of F and Ca through cavitation. 2+ A rapid reaction generates nanocrystal nuclei (1–200 nm). The pH probe 3-8 at the bottom layer monitors the pH in the bottom reaction zone 3 in real time, and the PLC control cabinet 7 provides feedback adjustment. When pH < 8.5, the PLC control cabinet 7 controls the alkali injection tube 3-2 to inject a trace amount of 10% NaOH solution. When pH > 9.7, the PLC control cabinet 7 controls the alkali injection tube 3-2 to stop injecting alkali solution, thus maintaining the pH within the range of 8.5–9.7 to ensure sufficient dissociation of F and Ca. 2+The moderate supersaturation promotes the nucleation of CaF2 crystal phase; the temperature sensor 4-5 in the middle reaction zone 4 will monitor the temperature in real time. If the temperature is >35℃, the PLC control cabinet 7 will reduce the ultrasonic power of the bottom ultrasonic transducer 3-4 to 70% of the rated power and open the external circulation cooling water channel to meet the requirements of crystal epitaxial growth.

[0046] Step 3: When the wastewater carrying nano-sized CaF2 crystal nuclei passes through the bottom sieve plate 3-9 (2mm aperture) and reaches the middle sieve plate 4-9 (1mm aperture), the flow velocity naturally decreases due to the gradual expansion design and sieve plate interception. The middle sieve plate 4-9 intercepts the bottom crystal nuclei as growth carriers. The PLC control cabinet 7 adjusts the middle ultrasonic transducer 4-1 to operate at a frequency of 30kHz and 60% of its rated power, using medium-frequency ultrasonic waves to break up the crystal nuclei aggregates rising from the bottom reaction zone 3, inhibiting particle agglomeration while promoting uniform crystal growth to 100-200μm. m; In the intermediate reaction zone 4, to promote further crystal growth, the wastewater is recirculated and enhanced. Based on feedback from the intermediate electromagnetic flowmeter 4-7, the PLC control cabinet 7 starts the intermediate circulation pump 4-6 to return a portion of the effluent from the intermediate reaction zone 4 to the bottom reaction zone 3 at a flow rate of 500 L / h, extending the particle residence time. As the reaction proceeds, the PLC control cabinet 7 controls the fine-tuning of the calcium solution injection pipe 4-3 and the buffering effect of the intermediate sieve plate 4-9 to ensure that the pH in the intermediate reaction zone 4 is within the range of 7.5–8.7, allowing the Ca... 2+ The reduction in supersaturation inhibits the formation of new crystal nuclei and instead promotes the heterogeneous growth of crystal nuclei within the existing intermediate reaction zone 4.

[0047] Step 4: After the wastewater forms larger crystals, it rises further into the top reaction zone 5 to enter the final crystal form optimization stage. The enlarged diameter design and the top sieve plate 5-7 (0.6mm aperture) intercept the fluid and further reduce the flow rate. The lower flow rate prolongs the residence time of the crystals in the top reaction zone 5, ensuring that the crystals grow to the target particle size, which is more conducive to crystal form optimization. The top pH probe 5-1 monitors the pH in real time, and the PLC control cabinet 7 controls the acid injection pipe 5-2 to inject 10% HCl solution at a flow rate of 0.01-0.03L / h, which feedback adjusts the pH in the top reaction zone 5 to be between 7.0 and 7.8. Under near-neutral conditions, the Zeta potential on the CaF2 crystal surface is close to zero, which can reduce electrostatic repulsion between particles. This promotes the directional alignment of crystals and inhibits the generation of byproducts such as calcium carbonate. When the top pH probe 5-1 detects pH > 7.0, the PLC control cabinet 7 controls the crystal-directing agent nozzle 5-6 to atomize and spray 0.1% sodium polyacrylate, which is selectively adsorbed onto the (111) crystal face of CaF2 crystal, inhibiting the growth of this face, thereby inducing the formation of cubic crystals. The PLC control cabinet 7 adjusts the frequency and power of the top ultrasonic transducer 5-3 to 40kHz and 40% of the rated power, respectively. The high-frequency ultrasonic waves refine the surface of CaF2 crystals, ensuring uniform crystal size and promoting crystal growth to 200-500μm. The low power avoids damaging the already formed crystal structure, and works with the crystal-directing agent to achieve directional growth.

[0048] Step 5: After the crystallization reaction in the top reaction zone 5 is completed, the treated wastewater carrying the crystals is transported to the hydrocyclone 6 via the peristaltic pump 6-1. The wastewater and crystals will form a vortex at the tangential inlet. Large crystal particles are rotated outward by centrifugal force and deposited on the conical wall. The liquid will form a vortex in the center of the separator and overflow from the central overflow pipe 6-2. The underflow and overflow are graded and recovered by cyclone separation. High-purity CaF2 with ≥200μm in the underflow detected by the laser particle size analyzer 6-9 is discharged from the crystal outlet 6-10. Finally, after removing impurities and drying, it is made into metallurgical grade fluorite. The overflow liquid is centrifuged again by the secondary micro hydrocyclone 6-3. The clear water from the overflow outlet is discharged from the outlet 6-7 after being detected by the online F electrode 6-6.

[0049] Step Six: To further improve resource utilization and crystal purity, reflux control is required. The fine-particle-containing slurry from the underflow port of the secondary micro-cyclone separator 6-3 in overflow pipe 6-2 is refluxed to the middle reaction zone 4 via the top-level circulation pump 6-11 at a flow rate of 500 L / h, serving as seed crystals for secondary growth. Based on feedback from the laser particle size analyzer 6-9, when the discharged crystal D50 is detected to be <300 μm, the PLC control cabinet 7 increases the reflux flow rate of the top-level circulation pump 6-11 to 600 L / h, thereby extending the overall reaction time.

[0050] Step 7: During continuous operation exceeding 1 hour, dynamic adjustments and abnormal handling of the equipment are required. PLC control cabinet 7 should fine-tune the dosage of 10% Ca(OH) in calcium solution injection pipe 3-3 (±0.2 kg / h) every 30 minutes based on the monitoring value of online F electrode 6-6. If the laser particle size analyzer 6-9 monitors the discharged crystals with D90 > 400 μm, PLC control cabinet 7 should increase the ultrasonic power of the top-level ultrasonic transducer 5-3 to 50% of its rated power to further break down particles, precisely controlling product quality and operational stability. If the top-level pH probe 5-1 detects pH < 7.0 for 5 minutes, PLC control cabinet 7 should adjust and close acid injection pipe 5-2. If the top-level pH probe 5-1 detects pH > 7.8, PLC control cabinet 7 should open acid injection pipe 5-2 and make minor adjustments.

[0051] Step 8: During operation, the equipment needs to be regularly maintained with slag discharge and backwashing. Every 4 hours, the bottom slag discharge butterfly valve 2-1 in PLC control cabinet 7 should be opened and held for 1 minute to discharge unreacted Ca(OH) and impurities. Simultaneously, the ultrasonic vibrator 2-4 (2-8kHz, 10s) should be activated during slag discharge to prevent crystallization. Every 2 hours, PLC control cabinet 7 should control the backwashing interface to perform a 10-second pulse backwash at a pressure of 0.5MPa on each sieve plate. When the differential pressure sensors at the bottom, middle, and top layers detect ΔP>14.6Pa, ΔP>8.5Pa, and ΔP>2.1Pa on both sides of the sieve plate respectively, the corresponding V in the reaction zone... 实 Speeds exceeding 80, 60, and 30 m / h respectively indicate that V 实 If an abnormality occurs or the screen plate becomes clogged, the PLC control cabinet 7 will immediately start the high-pressure backwashing program, backwashing for 10 seconds at a pressure of 0.5MPa. During the backwashing, the wastewater inflow will be reduced to 5L / h. To prevent system oxidation, the flow rate of the nitrogen microporous aerator heads 3-7 will be increased to 8L / min. At the same time, the pneumatic butterfly valve 21 at the sludge discharge port will be opened for 1 minute to discharge the sludge containing silica powder impurities at the bottom.

[0052] In addition, when an emergency occurs in the system, the PLC control cabinet 7 will first trigger the emergency stop button to cut off all power supply and adjust the flow rate of the nitrogen microporous aerator head 3-7 to 1L / min to maintain system inertia.

[0053] The above description is only a preferred embodiment of the present utility model. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present utility model, and these improvements and modifications should also be considered within the protection scope of the present utility model.

Claims

1. A multi-layer gradient fluidized bed coupled with ultrasonic enhancement for calcium fluoride crystallization, characterized in that: The reaction includes a reaction tower (1) and a cyclone separator (6) connected to the reaction tower (1). The reaction tower (1) includes a bottom sludge discharge zone (2), a bottom reaction zone (3), a middle reaction zone (4), and a top reaction zone (5) arranged sequentially from bottom to top, wherein: The bottom reaction zone (3) includes a bottom reaction shell; a bottom sieve plate (3-9) is provided at the top of the bottom reaction shell, and a bottom ultrasonic transducer (3-4) is provided at the upper part of the bottom reaction shell; a wastewater tangential injection pipe (3-1) and a calcium solution injection pipe (3-3) are provided at the lower part of the bottom reaction shell, and an alkali injection pipe (3-2) is provided on the wastewater tangential injection pipe (3-1); The middle reaction zone (4) includes a middle reaction shell, which is installed on the bottom reaction shell; a middle sieve plate (4-9) is provided at the top of the middle reaction shell, and a middle ultrasonic transducer (4-1) is provided at the upper part of the middle reaction zone (4); The top reaction zone (5) includes a top reaction shell, which is installed on the middle reaction shell; a top sieve plate (5-7) is provided at the top of the top reaction shell, and an acid injection pipe (5-2), a top ultrasonic transducer (5-3), and a crystal guide nozzle (5-6) are provided on the upper part of the top reaction shell, with the crystal guide nozzle (5-6) located above the top sieve plate (5-7).

2. The multi-layer gradient fluidized bed coupled with ultrasonic enhancement for calcium fluoride crystallization according to claim 1, characterized in that: The bottom sludge discharge zone (2) includes a conical shell, the bottom reaction shell is installed on the conical shell, the bottom end of the conical shell is provided with a slag discharge port (2-2), the upper end of the slag discharge port (2-2) is provided with a filter grid (2-3), the lower end of the slag discharge port (2-2) is provided with a slag discharge port butterfly valve (2-1), and the side of the slag discharge port (2-2) is provided with an ultrasonic vibrator (2-4).

3. The multi-layer gradient fluidized bed coupled with ultrasonic enhancement for calcium fluoride crystallization according to claim 2, characterized in that: The top-layer reaction shell is provided with a wastewater outlet. The wastewater outlet, peristaltic pump (6-1), and hydrocyclone (6) are connected in sequence. The top of the hydrocyclone (6) is provided with an overflow pipe (6-2) and a secondary micro hydrocyclone (6-3). The outlet of the primary micro hydrocyclone (6-3), the outlet regulating valve (6-4), the top-layer electromagnetic flowmeter (6-5), the online F electrode (6-6), and the outlet (6-7) are connected in sequence. The bottom of the hydrocyclone (6) is provided with a crystal outlet (6-10). A laser particle size analyzer (6-9) is provided on the crystal outlet (6-10).

4. The multi-layer gradient fluidized bed coupled with ultrasonic enhancement for calcium fluoride crystallization according to claim 3, characterized in that: The top of the cyclone separator (6) is provided with a second reflux outlet, and the bottom of the middle layer reaction shell is provided with a second reflux inlet. The second reflux inlet and the second reflux outlet are connected by a second reflux pipe. The second reflux pipe is provided with a second reflux regulating valve (6-8), a top layer circulation pump (6-11), and a second top layer electromagnetic flowmeter (6-12). The upper part of the middle layer reaction zone (4) is provided with a first reflux outlet, and the lower part of the bottom layer reaction shell is provided with a first reflux inlet. The first reflux inlet and the first reflux outlet are connected by a first reflux pipe. The first reflux pipe is provided with a middle layer circulation pump (4-6), a middle layer electromagnetic flowmeter (4-7), and a first reflux regulating valve (4-8).

5. The multi-layer gradient fluidized bed coupled with ultrasonic enhancement for calcium fluoride crystallization according to claim 4, characterized in that: The bottom ultrasonic transducer (3-4) is located below the bottom sieve plate (3-9), and the bottom ultrasonic transducer (3-4) is evenly arranged in a ring along the inner wall of the bottom reaction shell; the middle ultrasonic transducer (4-1) is located below the middle sieve plate (4-9), and the middle ultrasonic transducer (4-1) is evenly arranged in a ring along the inner wall of the middle reaction shell; the top ultrasonic transducer (5-3) is located below the top sieve plate (5-7), and the top ultrasonic transducer (5-3) is evenly arranged in a ring along the inner wall of the top reaction shell.

6. The multi-layer gradient fluidized bed coupled with ultrasonic enhancement for calcium fluoride crystallization according to claim 5, characterized in that: The bottom of the bottom reaction shell is provided with a nitrogen microporous aerator (3-7), which is connected to a nitrogen cylinder (3-6).

7. The multi-layer gradient fluidized bed coupled with ultrasonic enhancement for calcium fluoride crystallization according to claim 6, characterized in that: The bottom layer reaction shell is provided with a bottom layer pH probe (3-8) at its lower part, and the middle layer reaction zone (4) is provided with a middle layer backwash assembly (4-3), a middle layer pH probe (4-4), and a temperature sensor (4-5) at its lower part; the top layer reaction shell is provided with a top layer backwash assembly (5-5) at its upper part, and the top layer backwash assembly (5-5) is located above the top layer sieve plate (5-7); The lower part of the top reaction shell is provided with a top pH probe (5-1).

8. The multi-layer gradient fluidized bed coupled with ultrasonic enhancement for calcium fluoride crystallization according to claim 7, characterized in that: The bottom reaction shell is provided with a bottom differential pressure sensor 1 (3-51) at the top and a bottom differential pressure sensor 2 (3-52) at the bottom of the middle reaction zone (4); the middle reaction zone (4) is provided with a middle differential pressure sensor 1 (4-21) at the top and a middle differential pressure sensor 2 (4-22) at the bottom; the top reaction shell is provided with a top differential pressure sensor 1 (5-41) and a top differential pressure sensor 2 (5-42) at the top. The top differential pressure sensor 1 (5-41) is located below the top sieve plate (5-7), and the top differential pressure sensor 2 (5-42) is located above the top sieve plate (5-7).

9. The multi-layer gradient fluidized bed coupled with ultrasonic enhancement for calcium fluoride crystallization according to claim 8, characterized in that: The calcium liquid injection pipe (3-3) is an annular porous injection pipe with a downward injection angle; the crystal guide nozzle (5-6) is arranged on the annular support above the top sieve plate (5-7), and the crystal guide nozzle (5-6) is evenly distributed circumferentially and sprays vertically downward.

10. The multi-layer gradient fluidized bed coupled with ultrasonic enhancement for calcium fluoride crystallization according to claim 9, characterized in that: The apertures of the top sieve plate (5-7), the middle sieve plate (4-9), and the bottom sieve plate (3-9) increase sequentially.

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