A pet microplastic cleaning and impurity removing system and method

Abstract

The present application relates to the technical field of polyester microplastic recycling, and particularly relates to a PET microplastic cleaning and impurity removing system and method. After raw materials are dynamically quantitatively fed and high-temperature cooking and washing, dehydration is performed, and the raw materials enter an integrated microplastic cleaning and separating device. In the dioctyl terephthalate water-based medium, a composite flow field is formed through central stirring, density stratification is strengthened by ultrasonic aeration, and floating resin impurities and bottom silt are step by step discharged by means of annular high and low closed mechanisms. Then, the purified PET wet material is discharged by a bottom opening and closing mechanism. After that, the PET wet material enters a tidal chute separating device, under the action of the tidal flow formed by the adjustable flow and the ultrasonic-pneumatic deagglomeration, the strengthened sedimentation and automatic deslagging of high specific gravity metal debris and sand are realized, and high-purity PET microplastics are obtained through dehydration and rinsing by a vibrating screen at the end. The system is simultaneously matched with a circulating water treatment unit, closed-loop utilization of solvents and water resources is realized, the purity and recovery rate of PET recycling are significantly improved, and the energy consumption and water consumption are reduced.

Description

Technical Field

[0001] This invention relates to the field of polyester microplastic recycling technology, and in particular to a PET microplastic cleaning and impurity removal system and method. Background Technology

[0002] Microplastics typically refer to plastic particles or fragments with a diameter of less than 5 mm, which are generated in large quantities during plastic product molding, chemical fiber spinning, and bottle flake recycling. Among them, polyester (PET) microplastic powder and particles are the most common. Due to their small particle size and large specific surface area, these microplastics readily adsorb organic pollutants and heavy metals in environmental media, accumulating in water bodies, soil, and organisms, posing a potential threat to ecological safety and human health. On the other hand, chemical fiber companies and recycled plastic companies often generate PET microplastic powder or debris containing silt, paper scraps, labels, metal shavings, gravel, and blends of various resins such as PE, PP, PS, and PVC when processing waste fibers, bottle flakes, and scraps. If thorough impurity removal and efficient cleaning are not achieved at the front end, it will not only reduce the quality of recycled polyester melt and the stability of spinning and granulation, but also lead to wear and tear on extrusion equipment, frequent clogging of filter screens, and a significant increase in wastewater treatment load and energy consumption.

[0003] To address the recycling and impurity removal issues of microplastics, especially polyester microplastics, existing technologies have proposed several typical solutions. For example, Chinese patent document CN115157485A discloses a microplastic particle impurity removal and analysis device. By setting up first and second spiral accelerating coils and corresponding conical cylinders, a spiral vortex flow field is formed under water flow drive, causing microplastic particles containing impurities such as silt and label paper to achieve density stratification within the conical cylinder: floating impurities overflow from the top, while settled silt is concentrated and discharged from the bottom, thus obtaining relatively uniform polyester microplastic particles. This solution utilizes a combination of multi-stage vortexes and gravity stratification, achieving good analysis and impurity removal effects on granular microplastics containing silt and paper impurities. However, the equipment structure is relatively complex, the flow path is long, and its adaptability to finer, easily agglomerated powdery microplastics is limited. Its ability to finely separate different plastic components in blends of various resins such as PE / PP / PS / PVC is also relatively limited.

[0004] Building upon this, Chinese patent document CN115230018A proposes a method and system for recycling polyester microplastic particles. This system integrates a friction cleaner, microplastic particle impurity removal and analysis equipment, a heating tank, a washing and rinsing tank, a microparticle material sorting machine, and a microparticle color sorting mechanism into a multi-machine series system. First, friction cleaning achieves pre-cleaning and dispersion. Then, the analysis equipment removes mud, sand, and label-suspended matter. Following this, the particles are boiled in the heating tank and rinsed in the washing and rinsing tank. Finally, dry material sorting and color sorting further improve the purity of the polyester microplastics. This system is effective in processing granular or short-fiber polyester microplastics, achieving tiered purification and graded recycling. However, the entire process relies primarily on multiple devices connected in a linear series, with the cleaning and separation processes discretely completed in different units, resulting in low utilization rates of water and cleaning fluid. For powder-grade microplastics with high solids content, fine particle size, and easy agglomeration, it lacks an integrated design for strong shear mixing, ultrasonic or aeration enhancement, density stratification, and multi-stage discharge within a single container, limiting the capacity for multi-round cyclic cleaning and closed-loop reagent utilization.

[0005] To address the removal of specific plastic impurities such as PVC from PET microplastics, Chinese patent document CN120399283A further proposes a method and equipment for recovering and removing impurities from polyester microplastics. This method alters the structure or properties of impurity plastics such as PVC through electron beam irradiation, combined with gravity separation to achieve efficient PVC removal. While this approach has certain advantages in improving the removal rate of specific resin impurities, it requires a dedicated irradiation device, resulting in high equipment investment and operating energy consumption. Furthermore, it still necessitates density separation or flotation / sinking separation units to achieve actual phase separation. For general chemical fiber plants or recycling cleaning lines, the introduction of irradiation technology has a high barrier to entry, and it does not solve the problems of agglomeration, unstable floating and sinking, and multiple rounds of cyclic washing of powder-grade microplastics during wet cleaning.

[0006] On the other hand, in treating high-density inorganic impurities such as metal fragments and sand in polyester microplastic powder, existing technologies mostly employ a combination of simple sedimentation, screening, or independent magnetic separation equipment. The systems disclosed in CN115230018A and CN115157485A are mainly designed for dispersed microplastic particles in sludge, removing solid impurities such as silt and labels through vortex washing and rinsing. The treated materials are mostly low-solids-content, lightly adhered granular materials. For polyester microplastic powder with particle sizes in the hundreds of micrometers, high solids content, easy agglomeration, and containing high-density inorganic matter such as metal fragments and sand, relying solely on gravity separation of steady-state water flow or traditional sedimentation tanks is insufficient to achieve both high inorganic matter removal rate and high polyester recovery rate within a limited residence time. Some fine metal particles may also enter the subsequent melt extrusion stage with the light phase, causing abnormal equipment wear and filter blockage.

[0007] To improve the separation of high-density inorganic impurities, the engineering field has proposed some gravity separation or fluidized bed separation devices, such as inclined chutes and jigs designed for ores, fine sand, or mixed plastic flakes. These devices improve the stratification of light and heavy components by controlling the inclination angle of the trough, the flow velocity, and the overflow structure. However, these devices mostly operate under steady-state or quasi-steady-state water flow conditions, and the internal flow field mainly exhibits relatively fixed upward flow, downward flow, or simple eddies. For complex systems such as high-concentration polyester microplastic powder, which consists of light organic particles, high-density inorganic particles, and significant agglomeration, it is often difficult to form a composite hydraulic environment that takes into account deagglomeration, enhanced sedimentation, and stable transport of the light phase. As a result, it is difficult to simultaneously meet the industrial application requirements for heavy phase removal efficiency and light phase recovery rate.

[0008] In summary, existing technologies for removing impurities and recycling PET microplastic powder / dust still have shortcomings in the following aspects:

[0009] (1) The cleaning and separation units are mostly multiple devices connected in series, the system structure is dispersed, and powder-grade microplastics often need to be repeatedly transported between multiple devices. The process is long and the area is large, and it is difficult to efficiently circulate water and reagents in a closed loop.

[0010] (2) For fine-grained and easily agglomerated PET microplastic powder, there is a lack of integrated cleaning and separation equipment that integrates strong shear mixing, ultrasonic aeration enhancement, controllable rotating flow field and multi-stage discharge outlet in a single tank, making it difficult to achieve multi-round cycle cleaning and efficient density separation of resin impurities such as PE / PP / PS / PVC.

[0011] (3) For high-density inorganic impurities such as metal scraps and sand, most systems still rely on simple sedimentation or external magnetic separation and screening devices. It is difficult to establish a flow field-controlled enhanced sedimentation and automatic slag discharge module for powders with high solid content. The heavy phase removal rate and automation level are limited.

[0012] (4) Existing methods such as irradiation to improve PVC removal rate are effective for specific impurities, but they require high equipment investment and energy consumption and are complex, which is not conducive to their promotion on ordinary recycling and cleaning production lines.

[0013] (5) Regarding water resources and reagent utilization, in the existing process, cleaning fluid, multi-stage rinsing water and sorting water are often used and discharged separately in multiple equipment, lacking a circulating water treatment and water supply system that is closely coupled with the impurity removal and separation modules, resulting in high water consumption per unit product and high operating costs.

[0014] Therefore, it is necessary to build a cleaning and impurity removal system and process suitable for PET microplastic powder by combining the advantages of integrated circular cleaning and separation devices and tidal chute separation devices based on existing technologies. At the front end, it can achieve enhanced density separation and multi-round cyclic cleaning of various resin impurities. At the back end, it can carry out tidal enhanced sedimentation and automatic slag discharge of high-density inorganic materials such as metal scraps and sand. It can also be organically integrated with circulating water treatment and closed-loop water supply units to achieve high purity, high recovery rate, low water consumption and low energy consumption on an industrial scale. Summary of the Invention

[0015] The technical objective of this invention is to provide a cleaning and impurity removal system and method suitable for PET microplastic powder. It utilizes an integrated circular cleaning and separation device and a tidal chute separation device in synergy on a single production line to achieve efficient removal of resin impurities such as PE / PP / PS / PVC, as well as high-density inorganic materials such as metal scraps and sand. At the same time, it realizes closed-loop reuse of cleaning liquid and circulating water, thereby improving the purity and recovery rate of recycled PET and reducing the number of equipment, water consumption and energy consumption.

[0016] To achieve the above objectives, the present invention adopts the following technical solution:

[0017] A PET microplastic cleaning and impurity removal system includes, in sequence, a raw material feeding unit, a pre-washing unit, a first dehydration unit, a microplastic cleaning and separation device, a second dehydration unit, a tide separation device, a washing and rinsing unit, a third dehydration unit, and a finished product packaging unit; wherein:

[0018] The raw material feeding unit includes a dynamic quantitative feeding mechanism located at the feeding port and a feeding auger connected thereto, used to quantitatively feed PET-containing microplastic powder into the pre-cooking and washing unit.

[0019] The pre-boiling and washing unit includes a boiling tank with a heating device for high-temperature boiling and washing of microplastic powder;

[0020] The microplastic cleaning and separation device is used to remove light impurities microplastics from PET microplastics. It includes a circular cleaning tank with an opening at the top, a central actuation mechanism set in the center of the tank, an ultrasonic aeration and mixing mechanism arranged in the tank, an opening and closing mechanism assembly arranged on the side wall of the tank, a slag removal and discharge unit connected to the opening and closing mechanism assembly, and a bottom discharge mechanism connected to the bottom of the tank.

[0021] The tidal separation device is used to remove high-density impurities from PET microplastics, and includes an inclined chute, a water inlet unit, a feeding unit, a tidal weir structure, a heavy phase discharge unit, and an end separation mechanism.

[0022] The cleaning and rinsing unit is used to rinse the PET microplastics after tidal separation.

[0023] Preferably, the microplastic cleaning and separation device is a circular cleaning tank with an open top. The central actuation mechanism is vertically arranged in the center of the tank, which includes a rotating shaft driven by a motor, a lower forward and reverse stirring tilting mechanism located below the liquid surface, and a water surface arc actuation mechanism located near the liquid surface. The ultrasonic aeration mixing mechanism is arranged in the tank near the central actuation mechanism. The side wall of the tank is circumferentially distributed with the opening and closing mechanism assembly, which consists of a high-position opening and closing mechanism and a low-position opening and closing mechanism. The outlet of the opening and closing mechanism assembly is connected to the impurity removal and slag discharge unit through an outer annular water flow channel. The bottom of the tank is provided with a bottom discharge port controlled by a bottom opening and closing mechanism. The bottom discharge port is connected to the second dewatering unit through a bottom spiral conveying mechanism and an inclined spiral conveying mechanism.

[0024] Preferably, the body of the inclined chute is arranged at an inclination, the water inlet unit is located at the upstream end of the chute, the tidal cofferdam structure is arranged in the upstream section along the length of the chute, the heavy phase discharge unit is located at the bottom of the upstream settlement zone of the tidal cofferdam structure, and the end separation mechanism is located at the downstream opening end of the chute. The variable frequency water pump in the water inlet unit changes its flow rate periodically under the control of the programmable logic controller (PLC) to create tidal water level fluctuations in the upstream settlement zone of the tidal cofferdam structure.

[0025] Preferably, the ultrasonic aeration mixing device of the microplastic cleaning and separation device includes an ultrasonic transducer and an aeration pipeline connected to an external air source. Multiple micropores are opened on the wall of the aeration pipeline along the axial and circumferential directions. The ultrasonic transducer is arranged along the aeration pipeline or coaxially with it to form an ultrasonic field and microbubble cluster in the circular cleaning tank, thereby enhancing particle dispersion and density stratification.

[0026] Preferably, the outlet of the high-position opening and closing mechanism is located on the upper part of the side wall of the cleaning tank, for discharging the upper layer solution carrying light impurities such as PE, PP, PS, or PVC microplastics; the outlet of the low-position opening and closing mechanism is located at the lower part of the high-position opening and closing mechanism, for secondary discharge of the secondary upper layer solution carrying light impurities such as PE, PP, PS, or PVC microplastics; both the high-position opening and closing mechanism and the low-position opening and closing mechanism are driven by a cylinder arranged above the water surface to open and close the gate through a connecting rod.

[0027] Preferably, a first dewatering unit is provided between the pre-boiling and washing unit and the microplastic cleaning and separation device. The first dewatering unit is a centrifugal dewatering machine or a squeeze dewatering machine, which is used to separate the solid and liquid of the material after it has been boiled and washed at high temperature in the boiling tank, and send part of the wastewater to the circulating water treatment and water supply unit.

[0028] Preferably, the circulating water treatment and water supply unit includes a sedimentation and purification device connected to the impurity removal and slag discharge unit and the end separation mechanism of the tidal separation device, and a clear water tank connected to the adjustable flow rate water supply system, for settling and purifying the water discharged from each unit and then reusing it for the microplastic cleaning and separation device, the tidal separation device and the cleaning and rinsing unit.

[0029] Preferably, the circulating water treatment and water supply unit includes a multi-stage sedimentation tank and a filtration device. After the supernatant from the multi-stage sedimentation tank enters the clear water tank, it is supplied to the pre-boiling and washing unit, the microplastic cleaning and separation device and the tidal separation device through an adjustable flow rate water supply system. The amount of fresh water replenished in the system does not exceed 5% of the total circulating water volume.

[0030] Preferably, the feeding unit of the tidal separation device includes a screw feeder connected to the upstream second dewatering unit, a weighing module located below the screw feeder, and a laser rangefinder for detecting the thickness of the material layer at the upstream end of the chute. The PLC performs closed-loop adjustment of the screw feeder speed according to the detection signals from the weighing module and the laser rangefinder to achieve a uniform distribution of the PET microplastic material layer in the width direction of the chute.

[0031] Preferably, the tidal separation device is provided with an ultrasonic-pneumatic hybrid deagglomeration unit at the bottom of the chute upstream and / or downstream of the tidal cofferdam structure. The ultrasonic-pneumatic hybrid deagglomeration unit includes multiple stainless steel ultrasonic transducers fixed to the bottom plate of the chute and microporous aeration pipes connected to an external air source, which are used to cavitation and bubble disturbance deagglomerate PET microplastic agglomerates that still contain high specific gravity inorganic matter.

[0032] Preferably, a metal adsorbent is provided on the side wall or bottom plate of the downstream chute section of the light phase buffer zone of the tidal separation device. The metal adsorbent includes a replaceable permanent magnet assembly and / or a metal filter grid for adsorbing and retaining metal debris that has not completely settled.

[0033] Preferably, the dynamic quantitative feeding mechanism includes a weighing hopper and a frequency-driven metering screw. The control system adjusts the speed of the metering screw according to the weighing signal to keep the mass flow rate of the PET microplastic mixture entering the cooking tank within a set range.

[0034] Preferably, the cleaning and rinsing unit is a cleaning and rinsing tank equipped with a stirring device and an overflow weir, used to rinse the PET microplastics treated by the tide separation device. The rinsing liquid enters the circulating water treatment and water supply unit through the overflow weir. After rinsing, the PET microplastics are dehydrated by the third dehydration unit and then enter the finished product packaging unit.

[0035] Preferably, the control system includes a PLC controller and a human-machine interface. The PLC is electrically connected to a liquid level sensor, a temperature sensor, a flow meter, a reagent metering unit, each motor, and each cylinder. It is used to automatically set the boiling tank temperature, the number of cleaning and separation cycles, the ultrasonic power and aeration intensity, the tidal cycle, and the operating conditions of each dewatering unit according to the degree of raw material contamination.

[0036] Furthermore, the present invention also provides a method for cleaning and removing impurities from PET microplastic powder containing impurities using the aforementioned system, comprising the following steps:

[0037] S1, the mixture containing PET microplastic powder is quantitatively fed into the boiling tank through the dynamic quantitative feeding mechanism of the raw material feeding unit, and the mixture is boiled and washed at high temperature under the action of water supplied by the circulating water treatment and water supply unit and heating device.

[0038] S2, after the material is boiled and washed, solid-liquid separation is performed in the first dehydration unit. The wet material containing PET and various resin impurities is sent to the microplastic cleaning and separation device. Under the control of the adjustable flow rate water supply system, water is quantitatively supplied to the circular cleaning tank. Dioctyl terephthalate (DOTP) plasticizer is added through the reagent metering unit so that water and dioctyl terephthalate form a solvent system of the target concentration in the tank.

[0039] S3, control the lower end of the intermediate toggle mechanism to run the forward and reverse stirring tilting mechanism at the first speed, so that the PET microplastic powder is fully wetted and evenly dispersed in the tank. Then adjust the stirring speed to the second speed and cooperate with the adjustable flow rate water supply system to form a rotating flow field, and control the rotation speed of the microplastic and the solvent to be in a range that is conducive to density separation.

[0040] S4, start the ultrasonic aeration mixing device to apply a combined ultrasonic and aeration effect to the rotating flow field, break up the agglomerates between PET and plastic impurities, and promote PET to sink and light impurities to float.

[0041] S5 controls the operation of the water surface arc-shaped agitation mechanism to move the impurity microplastics floating on the liquid surface toward the periphery of the high-position opening and closing mechanism, and opens part or all of the high-position opening and closing mechanism under the control of the control system, so that the upper solvent carrying impurities is introduced into the impurity removal and slag discharge unit through the outer water tank for solid-liquid separation and water phase reuse.

[0042] S6, the forward and reverse stirring tilting mechanism and ultrasonic aeration mixing device continue to work, so that PET and plastic impurities continue to separate, and under the control of the control system, the low-position opening and closing mechanism is partially or fully opened to discharge the remaining plastic impurities.

[0043] S7, open the bottom opening and closing mechanism, and with the lower forward and reverse stirring tilting mechanism maintaining appropriate stirring, discharge the cleaned PET microplastics through the bottom outlet and send them into the second dewatering unit for dewatering through the bottom screw conveyor mechanism and the tilting screw conveyor mechanism.

[0044] S8, the wet PET microplastic material after dehydration by the second dehydration unit is evenly spread to the upstream end of the inclined chute through the feeding unit of the tidal separation device. Under the action of the tidal water flow formed by the water inlet unit, the high specific gravity inorganic matter is enhanced by the periodic rise and fall of the water level in the upstream settlement area of ​​the tidal cofferdam structure. When the height of the settlement layer reaches the set value, the high specific gravity impurities are intermittently discharged through the heavy phase discharge unit.

[0045] S9 allows the PET microplastics that enter the light phase buffer zone with the water flow to be further de-agglomerated by the ultrasonic-pneumatic mixing de-agglomeration unit, and the residual metal particles are adsorbed by the metal adsorbent downstream of the chute. Then, the vibrating filter in the end separation mechanism is dehydrated and recycled. The filtered water enters the multi-stage sedimentation tank for clarification and is then sent back to the water inlet unit and the microplastic cleaning and separation device for reuse.

[0046] S10, the PET microplastics dehydrated and recovered by the tidal separation device are sent to the washing and rinsing unit for rinsing, and then dehydrated by the third dehydration unit before being sent to the finished product packaging unit to obtain high-purity PET microplastic products.

[0047] Preferably, in step S2, the mass concentration of dioctyl terephthalate is 3.5%–4.0%, and in step S4, the ultrasonic power of the ultrasonic aeration mixing device is 500–800 W, and the aeration intensity is 3.0–5.0 m. 3 / (m 2 ·h), and act for 5 to 20 minutes in each cleaning cycle.

[0048] Preferably, in step S8, the tidal cycle is controlled by a PLC-controlled variable frequency water pump, which cycles through 30-60 seconds of operation, 10-20 seconds of deceleration, and 10-20 seconds of acceleration. This ensures that the water level fluctuation in the upstream settlement zone of the tidal cofferdam structure is 50-150 mm. This guarantees that the PET microplastic recovery rate is not less than 98%, the metal removal rate is not less than 99%, the sand and gravel removal rate is not less than 97%, and the system replenishment rate is not more than 5% of the total circulating water volume.

[0049] This invention connects a circular integrated cleaning and separation device and a tidal chute separation device in series within the same system. These devices work in conjunction with dynamic quantitative feeding, high-temperature washing, adjustable flow rate water supply, dioctyl terephthalate density adjustment, ultrasonic aeration to de-agglomerate, high and low level graded drainage, tidal water level fluctuation to enhance sedimentation, automatic slag discharge, and multi-stage sedimentation and reuse. This allows powdered PET microplastics to undergo strong shear dispersion, ultrasonic / aeration-enhanced density separation, directional discharge of floating light resin impurities, and tidal sedimentation of high-density inorganic matter in a wet process. Automatic slag discharge—a continuous process of end-of-pipe dewatering and rinsing; under the same treatment time and volume conditions, it can significantly improve the removal rate of resin impurities such as PE / PP / PS / PVC, as well as high-density inorganic materials such as metal scraps and sand, resulting in a significantly higher PET content and recovery rate after cleaning compared to traditional multi-machine series and single sedimentation / panting schemes. At the same time, relying on a closed-loop circulating water system, it effectively reduces water consumption and reagent consumption per unit of product, keeping energy consumption and wastewater discharge at a low level, achieving a comprehensive technical effect that balances high purity, high recovery rate, low water consumption, and low energy consumption. Attached Figure Description

[0050] Figure 1 This is a schematic diagram of the system structure of the present invention.

[0051] Figure 2 This is a schematic diagram of the separation and cleaning device of the present invention.

[0052] Figure 3 for Figure 1 A top-view structural diagram.

[0053] Figure 4 This is a structural diagram of the cleaning device's outer casing, intermediate actuation mechanism, ultrasonic aeration mixing device, opening and closing mechanism assembly, and surrounding water tank.

[0054] Figure 5 This is a schematic diagram of the bottom opening and closing mechanism.

[0055] Figure 6 This is a schematic diagram of the door panel installation structure.

[0056] Figure 7 This is a schematic diagram of the tidal chute separation device.

[0057] Figure 8 This is a schematic diagram of a tidal cofferdam structure. Detailed Implementation

[0058] The PET microplastic cleaning and impurity removal system and method of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Those skilled in the art should understand that the following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention; any equivalent substitutions or modifications made to the structural form, size proportions, process parameters, and control strategies without departing from the concept of the present invention should fall within the scope of protection of the present invention.

[0059] In this specification, unless otherwise expressly defined, the orientations or positional relationships such as up, down, left, right, front, and back are based on the state shown in the foregoing drawings or the normal installation and use state of the equipment, and are only used to facilitate the description of the present invention, and are not an absolute limitation of the present invention.

[0060] I. System Overall Structure

[0061] like Figure 1 As shown, the PET microplastic cleaning and impurity removal system provided by the present invention comprises, in sequence along the material flow direction:

[0062] Raw material feeding and dynamic quantitative unit 100;

[0063] Pre-boiling and washing unit (boiling tank) 200;

[0064] First dehydration unit 300;

[0065] Microplastic cleaning and separation device 400;

[0066] 500m² impurity removal, slag discharge, and circulating water pretreatment unit;

[0067] Second dehydration unit 600;

[0068] Tidal separation device 700;

[0069] Cleaning and rinsing unit 800;

[0070] Third dehydration unit 900;

[0071] Finished product conveying and packaging unit.

[0072] The system also includes a circulating water treatment and supply unit, as well as a centralized control system electrically connected to the aforementioned actuators. The circulating water treatment and supply unit is connected to the pre-boiling and washing unit, the microplastic cleaning and separation device, the tidal separation device, and the washing and rinsing unit, respectively, and is used to settle, filter, and replenish the impurity-containing water discharged from each unit before reuse.

[0073] In a preferred embodiment Figure 1The production line shown is arranged from left to right as follows: dynamic quantitative feeder, feeding auger, boiling tank, first dewatering machine, feeding auger, microplastic cleaning and separation device, impurity removal and slag discharge device, bottom screw conveyor mechanism and inclined screw conveyor mechanism, tidal chute separation device, cleaning and rinsing tank, second and third dewatering machines and finished product conveying device, forming a continuous PET microplastic cleaning, impurity removal and separation process line.

[0074] II. Structure of Each Functional Unit

[0075] 1. Raw material feeding and dynamic quantitative unit

[0076] The raw material feeding and dynamic metering unit is located at the very front of the entire production line, including a raw material hopper, a dynamic metering feeder, and a feeding auger. The raw material is a mixed powder or shaving containing PET microplastic powder, resin impurities such as PVC, PE, PP, and PS, as well as mud, sand, and metal scraps.

[0077] The dynamic quantitative feeder preferably employs a metering screw mechanism with a weighing sensor, whose outlet is connected to the inlet of the feeding auger. The control system calculates the mass of material fed per unit time in real time based on the weighing signal, and maintains a stable mass flow rate of raw materials entering the cooking tank by adjusting the speed of the metering screw and the speed of the feeding auger, thus ensuring the stable operation of subsequent units.

[0078] 2. Pre-boiling and washing unit (boiling tank)

[0079] The pre-boiling and washing unit includes a vertical or horizontal boiling tank, which is equipped with a stirring device and a heating device. The heating method can be steam jacket, electric heating, or external heat exchanger circulation heating. The upper part of the boiling tank is equipped with a raw material inlet and a water inlet, and the lower part is equipped with a discharge outlet that connects to the first dewatering unit.

[0080] In a typical embodiment, the boiling tank temperature is controlled at 80–95°C, and the material stays in the tank for 20–40 minutes. High-temperature water washing removes oil, soluble salts, and some water-soluble adhesives from the surface of the PET microplastics, while simultaneously softening residual adhesive on the labels, thus improving the efficiency of subsequent density separation and flotation. Wastewater from the boiling tank is discharged from the bottom, pre-treated by a circulating water treatment unit, and then reused or partially discharged.

[0081] 3. First Dehydration Unit

[0082] The first dewatering unit is used for preliminary solid-liquid separation of the material after boiling and washing in the boiling tank. It can adopt structures such as vertical centrifugal dewatering machine, horizontal screen dewatering machine, or extrusion dewatering machine. The feed inlet of the first dewatering machine is connected to the discharge outlet of the boiling tank, and the discharge end is connected to the feed inlet of the microplastic cleaning and separation device through a conveying auger. The dewatered wastewater flows into the circulating water treatment unit.

[0083] Through the first dehydration unit, the moisture content of the material is reduced from about 80-90% to 50-70%, which reduces the load on the subsequent cleaning equipment and avoids excessive dilution of the cleaning solvent.

[0084] 4. Microplastic cleaning and separation device

[0085] The microplastic cleaning and separation device preferably adopts a circular frame tank structure with an open top; its specific structure can be found in [reference needed]. Figure 2 , Figure 3 The device mainly includes: a cleaning device housing 1, a central actuating mechanism 2, an ultrasonic aeration mixing device 3, an opening and closing mechanism assembly 4 and an outer water tank 5, a bottom opening and closing mechanism 6 and a bottom spiral conveying mechanism 7, an inclined spiral conveying mechanism 8, and a control system.

[0086] 4.1 Cleaning device housing

[0087] The outer casing 1 of the cleaning device is a circular tank with an open top, and the side walls 12 are continuously arranged circumferentially. A bottom discharge port 11 is provided at the bottom. The tank is made of stainless steel or carbon steel lined with corrosion-resistant material to adapt to the corrosive environment containing dioctyl terephthalate solvent. The bottom of the tank may be slightly inclined towards the bottom discharge port 11 to facilitate the concentration of sedimented particles in the bottom opening and closing mechanism area.

[0088] Several interfaces are reserved in the upper and lower parts of the side wall 12 for arranging the water outlets of the high-position opening and closing mechanism 41 and the low-position opening and closing mechanism 42, as well as process interfaces such as the feed inlet, water replenishment inlet, and reagent addition inlet.

[0089] 4.2 Intermediate Actuation Mechanism

[0090] like Figure 4 As shown, the intermediate actuation mechanism 2 is vertically arranged at the center of the outer shell 1 of the cleaning device, including a rotating shaft 21 that passes through the tank, a lower forward and reverse stirring tilting mechanism 22 arranged below the liquid surface, a water surface arc actuation mechanism 23 arranged near the liquid surface, and a drive motor 24 installed above the tank.

[0091] The lower reversible stirring tilting mechanism 22 consists of several stirring blades arranged radially and staggered in the vertical direction. There is a certain axial tilt angle between the stirring blades and the rotating shaft. During the forward and reverse rotation process, a composite flow field with radial, axial and circumferential components can be formed in the tank to achieve the dispersal and suspension of powder agglomerates.

[0092] The water surface arc-shaped actuation mechanism 23 consists of several arc-shaped paddles. A small gap is left between the outer edge of the paddle and the tank wall. The paddles are at a predetermined arc and angle relative to the radial direction. When the rotating shaft 21 rotates at a set speed, the mechanism generates a gentle flow in the liquid surface area, causing the floating light impurities and microplastics to be directed towards the peripheral area near the high-position opening and closing mechanism 41.

[0093] The motor 24 is preferably a variable frequency motor, which is connected to the rotating shaft 21 through a coupling. Under the control of the control system, it can switch between different speeds and alternate between forward and reverse rotation.

[0094] 4.3 Ultrasonic Aeration Mixing Device

[0095] The ultrasonic aeration mixing device 3 is located near the central actuation mechanism 2 and is connected to the upper frame of the tank via the first cylinder 31, allowing it to be raised and lowered vertically. The device includes an aeration pipeline arranged along its length and an ultrasonic transducer arranged along or coaxially with the aeration pipeline. Multiple micropores are evenly distributed on the wall of the aeration pipeline to generate a dense cluster of fine bubbles.

[0096] During operation, the first cylinder 31 moves the ultrasonic aeration mixing device 3 down to a predetermined depth below the liquid surface, turns on the air source and ultrasonic power supply, generates a large number of microbubbles in the rotating flow field and applies ultrasonic vibration, strengthens the interfacial interaction between PET microplastics and other plastic impurities and stratifies according to density difference, causing lightweight resins such as PE, PP, PS, and PVC to float and PET particles to sink.

[0097] 4.4 Opening and closing mechanism assembly and peripheral water channel

[0098] like Figure 4 As shown, the opening and closing mechanism assembly 4 is arranged circumferentially along the side wall 12 of the outer shell 1 of the cleaning device, including multiple high-position opening and closing mechanisms 41 and low-position opening and closing mechanisms 42. The outlet of the high-position opening and closing mechanism 41 is located near the liquid surface and is used to discharge floating light resin impurities and the solvent they carry; the outlet of the low-position opening and closing mechanism 42 is located at the lower part of the high-position opening and closing mechanism and is used for secondary discharge of the upper layer solution carrying light impurities and microplastics such as PE, PP, PS or PVC.

[0099] Each opening and closing mechanism includes a water outlet communicating with the tank body, a gate 43 for opening and closing, and a second cylinder 44 for driving the gate. The gate is hinged to the tank wall by a hinge, and the second cylinder 44 is located above the water surface and drives the gate to open and close via a connecting rod. Each water outlet is connected to an outer annular flow channel 5 via a short pipe. The outer flow channel 5 is arranged around the tank body and has a flow channel outlet 51 downstream, which is connected to the impurity removal and slag discharge unit and the circulating water treatment unit.

[0100] 4.5 Bottom opening and closing mechanism and screw conveyor mechanism

[0101] like Figure 5 , Figure 6As shown, the bottom opening and closing mechanism 6 is arranged at the bottom discharge port 11, preferably adopting a double-door structure. The two door panels 61 are hinged to the bottom of the tank through bottom hinges 64 and connected to the third cylinder 62 through a force transmission link 63. When the third cylinder extends or retracts, the two door panels 61 open and close synchronously to realize the discharge control of the bottom of the tank.

[0102] Below the bottom opening and closing mechanism 6, a bottom spiral conveyor mechanism 7 and an inclined spiral conveyor mechanism 8 are arranged in sequence. The bottom spiral conveyor mechanism 7 is arranged horizontally and is used to receive the cleaned wet PET material falling from the bottom discharge port 11 and convey it in a horizontal direction; the inclined spiral conveyor mechanism 8 is connected to the discharge end of the bottom spiral conveyor mechanism 7 and is used to lift the material to the feeding height of the second dewatering unit.

[0103] 5. Sludge removal and circulating water treatment unit

[0104] The impurity removal and sludge discharge unit receives high-level / low-level effluent from the external flow channel 5 and wastewater from subsequent devices. Internally, it can be equipped with a sedimentation tank, flotation, or filtration unit to separate floating light microplastic impurities from settled silt and inorganic particles. The separated light impurities and silt are collected and transported off-site or further utilized for resource recovery.

[0105] A circulating water treatment unit typically includes multi-stage sedimentation tanks, filters, and a clear water tank. The wastewater discharged from each unit, containing impurities, undergoes multi-stage sedimentation to remove suspended solids, followed by treatment through sand filtration and activated carbon filtration before entering the clear water tank. The clear water tank supplies water to the pre-boiling and washing unit, the microplastic cleaning and separation device, and the tidal separation device via an adjustable flow rate water supply system. The system may be equipped with online conductivity and turbidity monitoring devices to determine whether some stale water needs to be discharged and fresh water replenished.

[0106] 6. Second Dehydration Unit

[0107] The second dehydration unit, located after the microplastic washing and separation unit, is used for intermediate dehydration of the PET microplastics after multiple rounds of washing and separation. It can employ a horizontal centrifuge or a vibrating screen dehydrator. After processing in this unit, the moisture content of the PET microplastics is further reduced, facilitating their entry into the tidal separation unit for the separation of high-density inorganic substances.

[0108] 7. Tidal Separation Device

[0109] The tidal separation device is used to further separate high-density inorganic substances such as metal scraps and sand from PET microplastics that have already had resin impurities largely removed. Its structure can be found in [reference needed]. Figure 7 The device includes an inclined chute body 701, a water inlet unit, a feeding unit, a tidal cofferdam structure 704, a heavy phase discharge unit, an ultrasonic-pneumatic mixing and deagglomeration unit, a metal adsorbent 705, and an end separation mechanism.

[0110] 7.1 Inclined Slide Body

[0111] The chute body 1 is a long, narrow stainless steel trough, closed at one end and open at the other. It is inclined at an angle of 5° to 15° along the material flow direction and is embedded in a U-shaped carbon steel frame. The lower part of the frame is equipped with adjustable support feet 702 for fine-tuning the inclination angle on site. The inner surface of the chute can be polished, and a wear-resistant lining plate can be laid at the bottom of the heavy phase settling zone.

[0112] 7.2 Water Inlet and Feeding Unit

[0113] The water inlet unit is located on the lower side wall of the upstream end of the chute and includes an inlet connected to the clear water tank, a variable frequency water pump, and a flow sensor. The variable frequency water pump, under PLC control, can operate at a flow rate of 10–20 m. 3 The flow rate is adjusted within a range of / h, and the rotation speed is changed according to a preset cycle to generate tidal water level rises and falls in the settlement zone upstream of the tidal cofferdam structure.

[0114] The feeding unit is located above the upstream end of the chute and includes a screw feeder connected to the second dewatering unit, a weighing module located below the screw feeder, and a laser rangefinder installed above the chute. The PLC adjusts the screw feeder speed in a closed loop based on the signals from the weighing module and the laser rangefinder to maintain the feed rate within the range of 100-150 kg / min and ensure uniform distribution along the width of the chute.

[0115] 7.3 Tidal Cofferdam Structure and Heavy Phase Discharge Unit

[0116] like Figure 8 As shown, the tidal cofferdam structure 704 is located in the section from the upstream end to the downstream end of the chute along its length, spanning 1 / 3 to 1 / 2 of the length. It consists of a weir plate that spans the width of the chute, dividing the chute into an upstream heavy phase settling zone and a downstream light phase buffer zone. The height of the weir plate is 1 / 10 to 1 / 5 of the effective water depth, and an overflow outlet is formed at the upper edge of the weir plate.

[0117] The heavy phase discharge unit is located at the bottom of the heavy phase settling zone and includes a slag discharge port and an automatic slag discharge valve installed at the slag discharge port. The slag discharge valve is preferably a pneumatic butterfly valve or a pneumatic ball valve, which is controlled by a PLC according to the signal from a material level switch or an ultrasonic level gauge to discharge the accumulated metal scraps and sand slurry intermittently.

[0118] 7.4 Ultrasonic-Pneumatic Hybrid De-agglomeration Unit and Metal Adsorbent

[0119] Multiple sets of ultrasonic-pneumatic hybrid de-agglomeration units are arranged along the length of the chutes at the bottom of the upstream and / or downstream sections of the tidal cofferdam structure. Each set includes an ultrasonic transducer fixed to the outside of the chute bottom plate and a microporous aeration pipe mounted on the bottom plate. The ultrasonic frequency is 28–40 kHz, and the power density is 0.3–0.5 W / cm³. 2 Aeration intensity is 2-5m. 3 / (m 2 Both operate intermittently under PLC control, running for 20-40 seconds and stopping for 10-20 seconds, which breaks down the PET powder agglomerate structure and releases the encapsulated inorganic particles.

[0120] like Figure 8 As shown, the metal adsorbent 705 is arranged on the side wall or bottom plate of the chute downstream of the light phase buffer zone, including a replaceable permanent magnet assembly and / or a metal filter grid, for adsorbing iron filings and other metal particles that have not settled completely.

[0121] 7.5 End Separation Mechanism

[0122] The end-of-line separation mechanism is located at the downstream opening of the chute and includes a vibrating filter and a water collection area. The vibrating filter is made of stainless steel wire mesh with polyurethane edging, and is installed at an angle of 30° to 60°, driven by a vibrating motor. PET microplastics move uphill on the filter and are gradually dehydrated. The filtered water enters the water collection area, and then flows back to the inlet unit through a multi-stage sedimentation tank and a clear water tank, achieving a closed-loop water circulation.

[0123] 8. Cleaning and rinsing unit, third dehydration and packaging unit

[0124] The cleaning and rinsing unit can be a long trough-type cleaning and rinsing tank, equipped with a stirring device and an overflow weir, for the final rinsing of PET microplastics that have been treated and dehydrated by the tidal separation device, further removing residual chemicals and fine suspended solids. The rinsing solution enters the circulating water treatment system through the overflow weir.

[0125] The third dewatering unit can be equipped with a centrifugal dewatering machine or a hot air vibrating conveyor to dewater the rinsed PET microplastics to a moisture content suitable for packaging or melt extrusion. The end unit is equipped with a storage silo and an automatic packaging scale to achieve automatic metering and packaging of finished products.

[0126] 9. Control System

[0127] The control system employs a combination of a PLC controller and a human-machine interface (HMI). The PLC is electrically connected to the dynamic quantitative feeder, stirring motor, various screw conveyors, dewatering machines, cylinders, ultrasonic power supply, blower, variable frequency water pump, vibrating screen, and various sensors (liquid level, temperature, flow rate, material level, weight, etc.). Operators can set or recall different process formulas on the HMI, including raw material processing volume, boiling tank temperature and time, DOTP concentration, number of cleaning cycles, stirring speed mode, ultrasonic power and action time, tidal cycle, automatic slag discharge threshold, and operating parameters of each dewatering unit, achieving automated control and status monitoring of the entire production line.

[0128] III. Method Implementation Process

[0129] The following is an example of a typical method for cleaning and removing impurities from PET microplastics, based on the above structure.

[0130] S1 Raw material feeding and pre-boiling and washing

[0131] A mixture containing PET microplastic powder, resin impurities such as PVC, PE, PP, and PS, as well as mud, sand, and metal scraps, enters the dynamic quantitative feeder through the raw material hopper. Based on the set processing capacity (e.g., 500–1500 kg / h), the PLC adjusts the speed of the metering screw to stabilize the feed rate per unit time. The material is then fed into the boiling tank via a feeding auger, where it is heated to 80–95°C under the action of circulating water replenishment and a heating device. This temperature is maintained for 20–40 minutes under stirring conditions, achieving high-temperature boiling and pre-cleaning of the material.

[0132] S2 First Dehydration

[0133] After boiling and washing, the discharge valve of the boiling tank is opened, and the material enters the first dewatering machine along with the wastewater. The first dewatering machine separates most of the wastewater by centrifugation or extrusion. The wastewater enters the circulating water treatment unit, and the wet material is conveyed over a short distance to the inlet of the microplastic cleaning and separation device.

[0134] S3 Cleaning Solvent Establishment and Initial Wetting and Dispersion

[0135] Start the adjustable flow rate water supply system of the microplastic cleaning and separation device to supply water quantitatively into the circular tank. At the same time, add dioctyl terephthalate quantitatively through the reagent metering unit to control the solvent concentration in the tank at 3.5-4.0 wt%. Start the motor of the intermediate agitator mechanism to drive the lower forward and reverse reversing stirring and tilting mechanism at the first speed (e.g., 30-60 rpm) to promote the gradual dispersion and wetting of the wet material in the solvent, preventing agglomerates from settling directly to the bottom or floating and clumping.

[0136] S4 forms a rotating flow field and enhances stratification through ultrasonic aeration.

[0137] Once the liquid level and material dispersion reach preset values, the control system increases the stirring speed to a second speed (e.g., 100-150 rpm). The lower stirring blades create a strong rotating flow field within the tank, maintaining material suspension. Based on this, the first cylinder lowers the ultrasonic aeration mixing device below the liquid surface, turns on the air source and ultrasonic power supply, controlling the ultrasonic power at 500-800W and the aeration intensity at 3.0-5.0m. 3 / (m 2 •h), acting for 5–20 min. The combined action of the composite flow field, ultrasonic cavitation, and microbubbles breaks up the agglomeration between PET and resin impurities such as PE / PP / PS / PVC. Lighter resins combine with bubbles and float to the surface, while denser PET and some mineral particles tend to sink, thus forming a floating layer and a sinking layer in the tank.

[0138] S5 Water surface stirring and high-level discharge of light resin impurities

[0139] After the ultrasonic aeration stage, the air supply is stopped and the ultrasonic device is raised to the standby position. The water surface arc-shaped actuation mechanism of the intermediate actuation mechanism is activated to propel the water flow in the liquid surface area at a moderate speed, causing the floating light resin impurities to converge towards the high-level opening and closing mechanism area. Once the floating impurities on the water surface have basically concentrated, the control system selectively opens one or part of the high-level opening and closing mechanism. The high-level outlet discharges the upper layer of impurity-laden solvent into the outer annular flow tank. After the floating resin impurities are separated by the impurity removal and slag discharge unit, the aqueous phase enters the circulating water treatment unit. Depending on the degree of material contamination, the volume of liquid discharged from the high level each time can be set to 10-20% of the tank's volume.

[0140] S6 Low-level discharge of residual liquid

[0141] The forward and reverse stirring tilting mechanism and ultrasonic aeration mixing device continue to work, so that PET and plastic impurities continue to separate. Under the control of the control system, the low-position opening and closing mechanism is partially or fully opened to discharge the remaining plastic impurities.

[0142] S7 Bottom discharge and second dewatering

[0143] Once the purity of the PET microplastics in the tank is confirmed to reach the set threshold (e.g., ≥97wt%) through online or offline detection, the ultrasonic device and the opening / closing mechanism are stopped, and the stirring speed is adjusted to a suitable value to maintain uniform material suspension. At this time, the control system drives the third cylinder to open the bottom opening / closing mechanism, and the two bottom doors open. The cleaned wet PET material falls from the bottom outlet 11 into the bottom screw conveyor 7 under the action of gravity and flow field. Subsequently, it is lifted by the inclined screw conveyor 8 and sent to the second dewatering unit for dewatering. The dewatered liquid enters the circulating water treatment unit. After the second dewatering, the moisture content of the wet PET material can be reduced to 30-50%.

[0144] High-density inorganic matter enhanced separation within the S8 tidal separation device

[0145] After the second dewatering, the wet PET material enters the feeding unit of the tidal separator via a conveying device. A screw feeder evenly distributes the material onto the upstream surface of the inclined chute at a flow rate of 100–150 kg / min. Simultaneously, the variable frequency water pump in the water inlet unit, under PLC control, stabilizes the inlet flow rate at 10–20 m³ / min. 3 The rotation speed is changed in cycles of 30-60 seconds, 10-20 seconds, and 10-20 seconds, so that the water level in the heavy phase settlement zone upstream of the tidal cofferdam structure fluctuates in cycles within the range of 50-150 mm.

[0146] When the mixture flows through the tidal cofferdam structure, the high-density inorganic matter is intensified to settle and accumulates at the bottom of the settling zone under the alternating deceleration and acceleration of the tidal water flow. When the material level switch or ultrasonic material level gauge detects that the settling layer has reached the set height, the PLC triggers the automatic slag discharge valve to open for 2-10 seconds, discharging the accumulated metal scraps, sand, and other high-density inorganic slurry into the slag collection box. After slag discharge, the valve closes, and a stable accumulation layer is re-established in the settling zone.

[0147] During the heavy phase sedimentation process, the ultrasonic-pneumatic hybrid deagglomeration unit operates in an intermittent mode, running for 20–40 seconds and stopping for 10–20 seconds. It cavitation and bubble agitation deagglomerate the still-agglomerated PET powder and its encapsulated inorganic particles, further releasing high-density inorganic matter and improving sedimentation efficiency. Downstream of the chute, a metal adsorbent captures incompletely settled iron-like metal particles.

[0148] S9 End-of-line dewatering and water recycling

[0149] After tidal settling and deagglomeration treatment, the light phase of PET enters the terminal vibrating filter area with the water flow. Under the action of the vibrating motor, it moves uphill and is gradually dehydrated. The filtered water enters a multi-stage sedimentation tank, and after sedimentation and clarification, it returns to the clear water tank, and is then reused through the inlet unit. The moisture content of the wet PET material discharged from the vibrating filter can be controlled at 20-30%, and then it enters the washing and rinsing unit.

[0150] S10 Rinse, Final Dehydration and Packaging

[0151] The wet PET material is thoroughly contacted and moderately stirred with clean water (which may be partially recycled water) in the washing and rinsing tank. The rinsing solution flows into the recycled water treatment unit through the overflow weir. After rinsing, the PET undergoes final dehydration in the third dehydration unit and is further dried by hot air or natural air. Finally, it is conveyed to the finished product warehouse or automatic packaging device for metering and packaging to obtain high-purity PET microplastic products.

[0152] Through the above embodiments, this invention connects an integrated circular cleaning and separation device and a tidal chute separation device in series on the same process line. The front end focuses on density separation of various resin impurities and multi-round cyclic cleaning, while the back end focuses on enhanced tidal sedimentation and automatic slag removal of high-density inorganic substances. Combined with a closed-loop circulating water system and multi-stage dewatering and rinsing units, this enables PET microplastics to achieve high purity, high recovery rate, low water consumption, and low energy consumption on an industrial scale. Those skilled in the art can appropriately adjust the parameters of each unit (such as washing temperature, DOTP concentration, stirring speed, ultrasonic power, tidal cycle, etc.) according to the type and content of contamination in different raw materials; all such adjustments are reasonable variations of this invention.

[0153] The foregoing description of embodiments of the present invention, through which those skilled in the art are able to implement or use the present invention, will be readily apparent to those skilled in the art. Various modifications to these embodiments will be readily apparent to those skilled in the art. The general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novelty disclosed herein.

Claims

1. A PET microplastic cleaning and impurity removal system, characterized in that, It includes, in sequence, a raw material feeding unit, a pre-cooking and washing unit, a first dehydration unit, a microplastic cleaning and separation device, a second dehydration unit, a tide separation device, a washing and rinsing unit, a third dehydration unit, and a finished product packaging unit; wherein: The raw material feeding unit includes a dynamic quantitative feeding mechanism located at the feeding port and a feeding auger connected thereto, used to quantitatively feed PET-containing microplastic powder into the pre-cooking and washing unit. The pre-boiling and washing unit includes a boiling tank with a heating device for high-temperature boiling and washing of microplastic powder; The microplastic cleaning and separation device is used to remove light impurities microplastics from PET microplastics. It includes a circular cleaning tank with an opening at the top, a central actuation mechanism set in the center of the tank, an ultrasonic aeration and mixing mechanism arranged in the tank, an opening and closing mechanism assembly arranged on the side wall of the tank, a slag removal and discharge unit connected to the opening and closing mechanism assembly, and a bottom discharge mechanism connected to the bottom of the tank. The microplastic cleaning and separation device is a circular cleaning tank with an open top. The central actuation mechanism is vertically arranged in the center of the tank. It includes a rotating shaft driven by a motor, a lower forward and reverse stirring tilting mechanism located below the liquid surface, and a water surface arc actuation mechanism located near the liquid surface. The ultrasonic aeration mixing mechanism is arranged in the tank near the central actuation mechanism. The side wall of the tank is circumferentially distributed with the opening and closing mechanism assembly, which consists of a high-position opening and closing mechanism and a low-position opening and closing mechanism. The outlet of the opening and closing mechanism assembly is connected to the impurity removal and slag discharge unit through an outer annular water channel. The bottom of the tank is provided with a bottom discharge port controlled by a bottom opening and closing mechanism. The bottom discharge port is connected to the second dewatering unit through a bottom spiral conveying mechanism and an inclined spiral conveying mechanism. The material after boiling and washing undergoes solid-liquid separation in the first dehydration unit. The wet material containing PET and various resin impurities is sent to the microplastic cleaning and separation device. Under the control of the adjustable flow rate water supply system, water is quantitatively supplied to the circular cleaning tank. Dioctyl terephthalate plasticizer is added through the reagent metering unit, so that water and dioctyl terephthalate form a solvent system of the target concentration in the tank. The lower end of the intermediate stirring mechanism is controlled to run at the first speed to fully wet the PET microplastic powder and disperse it evenly in the tank. Then, the stirring speed is adjusted to the second speed and combined with the adjustable flow rate water supply system to form a rotating flow field. The rotation speed of the microplastics and solvent is controlled to be in a range that is conducive to density separation. The ultrasonic aeration mixing device applies a combined ultrasonic and aeration effect to the rotating flow field to break up the agglomerates between PET and plastic impurities, and to promote the PET to sink and the lighter impurities to float. The outlet of the high-position opening and closing mechanism is located on the upper part of the side wall of the cleaning tank, and is used to discharge the upper layer solution carrying light impurities and microplastics such as PE, PP, PS or PVC; the outlet of the low-position opening and closing mechanism is located at the lower part of the high-position opening and closing mechanism, and is used for secondary discharge of the secondary upper layer solution carrying light impurities and microplastics such as PE, PP, PS or PVC; both the high-position opening and closing mechanism and the low-position opening and closing mechanism are driven by cylinders arranged above the water surface to open and close the gate through connecting rods. The water surface arc-shaped agitation mechanism is controlled to move the impurities and microplastics floating on the liquid surface toward the periphery of the high-position opening and closing mechanism. Under the control of the control system, part or all of the high-position opening and closing mechanism is opened, and the upper solvent carrying impurities is introduced into the impurity removal and slag discharge unit through the outer water tank for solid-liquid separation and water phase reuse. The tidal separation device is used to remove high-density impurities from PET microplastics, and includes an inclined chute, a water inlet unit, a feeding unit, a tidal weir structure, a heavy phase discharge unit, and an end separation mechanism. The cleaning and rinsing unit is used to rinse the PET microplastics after tidal separation.

2. The PET microplastic cleaning and impurity removal system according to claim 1, characterized in that, The body of the inclined chute is arranged at an inclination. The water inlet unit is located at the upstream end of the chute. The tidal cofferdam structure is arranged in the upstream section along the length of the chute. The heavy phase discharge unit is located at the bottom of the upstream settlement zone of the tidal cofferdam structure. The end separation mechanism is located at the downstream opening end of the chute. The variable frequency water pump in the water inlet unit changes its flow rate periodically under the control of the programmable logic controller (PLC) to create tidal water level fluctuations in the upstream settlement zone of the tidal cofferdam structure.

3. The PET microplastic cleaning and impurity removal system according to claim 2, characterized in that, The ultrasonic aeration mixing device of the microplastic cleaning and separation device includes an aeration pipeline that connects an ultrasonic transducer to an external air source. Multiple micropores are opened on the wall of the aeration pipeline along the axial and circumferential directions. The ultrasonic transducer is arranged along the aeration pipeline or coaxially with it to form an ultrasonic field and microbubble cluster in the circular cleaning tank, thereby enhancing particle dispersion and density stratification.

4. The PET microplastic cleaning and impurity removal system according to claim 2 or 3, characterized in that, The feeding unit of the tidal separation device includes a screw feeder connected to the upstream second dewatering unit, a weighing module located below the screw feeder, and a laser rangefinder for detecting the thickness of the material layer at the upstream end of the chute. The PLC performs closed-loop adjustment of the screw feeder speed according to the detection signals of the weighing module and the laser rangefinder to achieve a uniform distribution of the PET microplastic layer in the width direction of the chute. And / or, the tidal separation device is provided with an ultrasonic-pneumatic hybrid deagglomeration unit at the bottom of the chute upstream and / or downstream of the tidal cofferdam structure. The ultrasonic-pneumatic hybrid deagglomeration unit includes multiple stainless steel ultrasonic transducers fixed to the bottom plate of the chute and microporous aeration pipes connected to an external air source, which are used to cavitation and bubble disturbance deagglomerate PET microplastic agglomerates that still contain high specific gravity inorganic matter. And / or, a metal adsorbent is provided on the side wall or bottom plate of the downstream chute section of the light phase buffer of the tidal separation device, the metal adsorbent including a replaceable permanent magnet assembly and / or a metal filter grid, for adsorbing and retaining metal debris that has not settled completely.

5. The PET microplastic cleaning and impurity removal system according to claim 1, characterized in that, The dynamic quantitative feeding mechanism includes a weighing hopper and a frequency-driven metering screw. The control system adjusts the speed of the metering screw according to the weighing signal to keep the mass flow rate of the PET microplastic mixture entering the cooking tank within a set range. And / or, the cleaning and rinsing unit is a cleaning and rinsing tank equipped with a stirring device and an overflow weir, used to rinse the PET microplastics treated by the tide separation device. The rinsing liquid enters the circulating water treatment and water supply unit through the overflow weir. After rinsing, the PET microplastics are dehydrated by the third dehydration unit and then enter the finished product packaging unit.

6. The PET microplastic cleaning and impurity removal system according to claim 1, characterized in that, A first dehydration unit is provided between the pre-boiling and washing unit and the microplastic cleaning and separation device. The first dehydration unit is a centrifugal dehydrator or a squeeze dehydrator, which is used to separate the solid and liquid of the material after it has been boiled and washed at high temperature in the boiling tank. The dehydrated part of the wastewater is sent to the circulating water treatment and water supply unit. The circulating water treatment and water supply unit includes a sedimentation and purification device connected to the impurity removal and slag discharge unit and the end separation mechanism of the tidal separation device, and a clear water tank connected to the adjustable flow rate water supply system. It is used to settle and purify the water discharged from each unit and then reuse it in the microplastic cleaning and separation device, the tidal separation device and the cleaning and rinsing unit. The circulating water treatment and water supply unit includes a multi-stage sedimentation tank and a filtration device. After the supernatant from the multi-stage sedimentation tank enters the clear water tank, it is supplied to the pre-boiling and washing unit, the microplastic cleaning and separation device and the tidal separation device through an adjustable flow rate water supply system. The amount of fresh water replenished in the system does not exceed 5% of the total circulating water volume.

7. The PET microplastic cleaning and impurity removal system according to claim 5, characterized in that, The control system includes a PLC controller and a human-machine interface. The PLC is electrically connected to a liquid level sensor, a temperature sensor, a flow meter, a reagent metering unit, each motor, and each cylinder. It is used to automatically set the boiling tank temperature, the number of cleaning and separation cycles, the ultrasonic power and aeration intensity, the tidal cycle, and the operating conditions of each dewatering unit according to the degree of raw material contamination.

8. A method for cleaning and removing impurities from PET microplastic powder using the system described in any one of claims 2 to 7, characterized in that, Includes the following steps: S1, PET microplastic powder is quantitatively fed into the boiling tank through the dynamic quantitative feeding mechanism of the raw material feeding unit, and the mixture is boiled and washed at high temperature under the action of water supplied by the circulating water treatment and water supply unit and heating device. S2, after the material is boiled and washed, solid-liquid separation is performed in the first dehydration unit. The wet material containing PET and various resin impurities is sent to the microplastic cleaning and separation device. Under the control of the adjustable flow rate water supply system, water is quantitatively supplied to the circular cleaning tank. Dioctyl terephthalate plasticizer is added through the reagent metering unit so that water and dioctyl terephthalate form a solvent system of the target concentration in the tank. S3, control the lower end of the intermediate toggle mechanism to run the forward and reverse stirring tilting mechanism at the first speed, so that the PET microplastic powder is fully wetted and evenly dispersed in the tank. Then adjust the stirring speed to the second speed and cooperate with the adjustable flow rate water supply system to form a rotating flow field, and control the rotation speed of the microplastic and the solvent to be in a range that is conducive to density separation. S4, start the ultrasonic aeration mixing device to apply a combined ultrasonic and aeration effect to the rotating flow field, break up the agglomerates between PET and plastic impurities, and promote PET to sink and light impurities to float. S5 controls the operation of the water surface arc-shaped agitation mechanism to move the impurity microplastics floating on the liquid surface toward the periphery of the high-position opening and closing mechanism, and opens part or all of the high-position opening and closing mechanism under the control of the control system, so that the upper solvent carrying impurities is introduced into the impurity removal and slag discharge unit through the outer water tank for solid-liquid separation and water phase reuse. S6, the forward and reverse stirring tilting mechanism and ultrasonic aeration mixing device continue to work, so that PET and plastic impurities continue to separate, and under the control of the control system, the low-position opening and closing mechanism is partially or fully opened to discharge the remaining plastic impurities. S7, open the bottom opening and closing mechanism, and with the lower forward and reverse stirring tilting mechanism maintaining appropriate stirring, discharge the cleaned PET microplastics through the bottom outlet and send them into the second dewatering unit for dewatering through the bottom screw conveyor mechanism and the tilting screw conveyor mechanism. S8, the wet PET microplastic material after dehydration by the second dehydration unit is evenly spread to the upstream end of the inclined chute through the feeding unit of the tidal separation device. Under the action of the tidal water flow formed by the water inlet unit, the high specific gravity inorganic matter is enhanced by the periodic rise and fall of the water level in the upstream settlement area of ​​the tidal cofferdam structure. When the height of the settlement layer reaches the set value, the high specific gravity impurities are intermittently discharged through the heavy phase discharge unit. S9 allows the PET microplastics that enter the light phase buffer zone with the water flow to be further de-agglomerated by the ultrasonic-pneumatic mixing de-agglomeration unit, and the residual metal particles are adsorbed by the metal adsorbent downstream of the chute. Then, the vibrating filter in the end separation mechanism is dehydrated and recycled. The filtered water enters the multi-stage sedimentation tank for clarification and is then sent back to the water inlet unit and the microplastic cleaning and separation device for reuse. S10, the PET microplastics dehydrated and recovered by the tidal separation device are sent to the washing and rinsing unit for rinsing, and then dehydrated by the third dehydration unit before being sent to the finished product packaging unit to obtain high-purity PET microplastic products.

9. The method according to claim 8, characterized in that, In step S2, the mass concentration of dioctyl terephthalate is 3.5%–4.0%, and in step S4, the ultrasonic power of the ultrasonic aeration mixing device is 500–800 W, and the aeration intensity is 3.0–5.0 m. 3 / (m 2 ·h), and act for 5 to 20 minutes in each cleaning cycle.

10. The method according to claim 8, characterized in that, In step S8, the tidal cycle is controlled by the PLC to switch the variable frequency water pump in a cycle of running for 30-60 seconds, decelerating for 10-20 seconds, and then accelerating for 10-20 seconds. This makes the water level rise and fall in the settlement zone upstream of the tidal cofferdam structure by 50-150 mm. This ensures that the polyester powder recovery rate is not less than 98%, the metal removal rate is not less than 99%, the sand and gravel removal rate is not less than 97%, and the system water replenishment rate is not more than 5% of the total circulating water volume.

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