A method and separation device for separating polyester microplastics from microplastics containing high specific gravity substances

Abstract

The present application relates to the technical field of polyester microplastic recycling, and particularly relates to a method and a device for separating polyester microplastics from microplastics containing high specific gravity substances. The device comprises an inclined chute body, a water inlet unit, a feed inlet unit, a tidal cofferdam structure, a heavy phase discharge unit, an ultrasonic-pneumatic mixed deagglomeration unit, a metal adsorption body, and a terminal vibrating screen and closed-loop water return system. A tidal water flow is formed by a PLC-controlled variable frequency water pump, a heavy phase settling zone is constructed upstream of the cofferdam, and the enrichment and discharge of high specific gravity substances are realized while intermittently discharging residues. Ultrasonic transducers and microporous aeration pipes work together to break up the agglomerates of powder dust, release the wrapped inorganic particles, and cooperate with the magnetic adsorption body to achieve secondary capture of metal iron scraps. The terminal vibrating screen completes the dehydration and recovery of polyester, and the separated water is reused after multi-stage precipitation. The present application can realize efficient separation of high specific gravity substances and polyester microplastics under the conditions of low energy consumption and water replenishment rate.

Description

Technical Field

[0001] This invention relates to the field of polyester microplastic recycling technology, and in particular to a method and separation apparatus for separating polyester microplastics from microplastics containing high specific gravity substances. Background Technology

[0002] Microplastics typically refer to plastic particles or fragments with a diameter of less than 5 mm. They are generated in large quantities during plastic production, fiber processing, and bottle chip recycling, with polyester (PET) microplastic powder and granules being the most common. Due to their small particle size and large specific surface area, microplastics readily adsorb organic pollutants and heavy metals in the environment, accumulating in water, soil, and organisms, posing a potential threat to ecological safety and human health. On the other hand, during the crushing, washing, and recycling of waste fibers, bottle chips, and scraps by chemical fiber and recycled plastic companies, microplastics often contain high-density inorganic impurities such as metal fragments, glass shards, and sand particles. If these impurities are not effectively separated at the upstream stage, they will directly affect the melt quality and mechanical properties of recycled polyester, and may even lead to problems such as wear on extrusion equipment and frequent clogging of filters.

[0003] Existing technologies for the separation and recycling of microplastics mainly focus on environmental monitoring and the pretreatment of sludge and soil samples. Typical methods include density separation flotation, chemical digestion combined with filtration, and centrifugation. These methods emphasize the purification of microplastics for testing rather than high-throughput sorting for industrial scale. In recent years, a few patents have begun to focus on the recycling and separation of polyester microplastics. For example, Chinese patent document CN115230018A proposes a method and system for recycling polyester microplastic particles. This system sequentially connects units such as a friction cleaner, a microplastic particle impurity removal and analysis device, a heating tank, a washing and rinsing tank, a microparticle material sorting machine, and a microparticle color sorting machine to clean, remove impurities, boil, rinse, and sort by material and color of waste polyester microplastic sludge, thereby obtaining high-quality polyester microplastic particles. This system utilizes the microplastic particle impurity removal and analysis device to remove impurities such as silt and labels, and then further improves purity through material sorting and color sorting, effectively solving the problems of small particle size, high water content, and various foreign matter entrained in sludge-like materials.

[0004] To address the need for removing silt and solid impurities such as labels from microplastics, the applicant's Chinese patent CN115157485A further discloses a microplastic particle removal and separation device and method. By setting up first and second spiral accelerating coils and corresponding conical separation cylinders, a spiral vortex flow field is formed under the drive of water flow. Floating impurities containing labels are discharged with the water flow from the upper part of the first conical cylinder, while sedimentary impurities containing silt are concentrated and discharged from the bottom of the second conical cylinder. Micropolyester plastic particles are carried out from the upper outlet, achieving efficient recovery and separation of micropolyester plastics from sludge. This device, through the superposition of two-stage conical separation structures, combines the functions of removing floating matter and discharging settled impurities, providing a relatively singular raw material for the subsequent treatment of micropolyester plastics.

[0005] The two aforementioned documents demonstrate that existing technologies have recognized the importance of using hydraulics and density difference principles to separate microplastics, and have constructed relatively complete microplastic recycling lines using equipment such as spiral tubes, conical separators, rinsing tanks, and material sorting machines. However, the typical applications of these systems are mostly for dispersed microplastic particles in sludge, focusing on enriching micropolyester particles from large amounts of inorganic silt, labels, and organic matter. This results in relatively low material concentrations and less agglomeration. Furthermore, their hydraulic separation often employs stable flow rates and relatively fixed geometries, with the internal flow field primarily exhibiting steady-state vortices or simple upward / downward flows, making it difficult to achieve fine stratification for microplastics with high solids content, high adhesion, and finer particle sizes.

[0006] In addition, in the field of microplastic separation, numerous patents and documents have focused on approaches such as flotation separation, ultrasonic pretreatment, and density solution stratification. For example, in the processing of sediment or soil samples, a high-density salt solution is often added to the sample, followed by stirring or ultrasonication, to enrich the microplastics at the liquid surface, which are then separated by filtration or adsorption. Although such methods have achieved high recovery rates in laboratory analysis, they generally suffer from drawbacks such as small processing capacity, long cycle time, high reagent consumption, and difficulty in continuous processing, making them difficult to directly apply to industrial scenarios such as waste polyester recycling plants that require ton-level / hour processing capacity.

[0007] In terms of engineered sorting equipment, gravity separation or fluidized bed separation devices have emerged to address solid waste from various sources. These devices improve the stratification of light and heavy components by controlling flow rate, liquid level, and equipment geometry. Some devices incorporate multi-stage sorting chambers, overflow weirs, or baffle structures to enhance sorting accuracy by altering the local flow pattern. However, these devices are mostly designed for ores, fine sand, or mixed plastic flakes. For microplastics with particle sizes in the hundreds of micrometers, which are prone to agglomeration and have a limited density difference with high-density inorganic particles, it remains difficult to achieve both high removal rates and high polyester recovery rates in a single hydraulic sorting unit.

[0008] On the other hand, microplastic powder often exhibits significant agglomeration behavior in water: firstly, fine particles easily flocculate with each other under the influence of electrostatic forces, van der Waals forces, and surface roughness; secondly, high-density inorganic particles are easily encapsulated within polyester powder agglomerates, making it difficult to completely separate them using gravity separation based solely on density differences. To disrupt this agglomeration structure, research has begun to explore physical methods such as ultrasonic cavitation and bubble agitation to disperse soil aggregates and microplastic flocs. However, these methods are mostly limited to batch experimental devices, and their implementation is often in the form of independent ultrasonic baths or aeration tanks. The integration with continuous hydraulic separation equipment is low, and it is rare to form a continuous process integrating deagglomeration, sedimentation, and retention within the same chute or separation tank.

[0009] Furthermore, waste plastic recycling lines typically require independent magnetic separators to remove iron filings, screws, and metal pieces mixed in during the crushing process. These magnetic separators are often located at the conveyor belt or discharge chute and are effective at separating larger metal particles. However, they are less effective at capturing fine metal particles that have already mixed with polyester powder and partially settled at the bottom of the sorting tank or suspended in water. These metal impurities may still enter subsequent melting and extrusion processes, causing equipment wear and filter clogging. Summary of the Invention

[0010] The technical objective of this invention is to address the problems commonly found in recycled polyester (PET) microplastic powder, such as the difficulty in completely removing high-density substances like metal fragments and sand, as well as the low efficiency and high water and energy consumption of traditional flotation and separation methods. This invention provides a method for separating polyester microplastics from microplastics containing high-density substances, thereby significantly improving the separation rate of high-density substances and the recovery rate of polyester powder under industrial-scale conditions, while reducing water and energy consumption.

[0011] To achieve the above objectives, the present invention adopts the following technical solution: A method for separating polyester microplastics from microplastics containing high specific gravity substances, the method comprising the following steps: S1 supplies water to the chute inlet unit and controls the variable frequency pump to operate within the range of 10-20 m³ / h, so that a water flow is formed in the chute and flows downstream along the length direction. The pump speed is changed periodically according to the set tidal cycle, so that the water level in the upstream settlement area of ​​the tidal cofferdam structure rises and falls repeatedly. S2, through the feeding unit, microplastics containing high specific gravity substances are continuously and evenly spread to the upstream end of the chute at a mass flow rate of 100-150 kg / min, so that the microplastics form a suspended layer in the water flow of the chute and move downstream with the water flow. S3, in the settlement zone upstream of the tidal cofferdam structure, the density stratification effect generated by the alternating deceleration and acceleration of the tidal water flow is used to cause high-density inorganic components to settle and accumulate. When the height of the settlement layer reaches the preset value, the automatic slag discharge valve opens to discharge the high-density inorganic components. S4, the microplastics enter the terminal separation mechanism with the water flow, and are intercepted by the vibrating filter to achieve dehydration and recovery of polyester components, thus realizing the separation of polyester microplastics from high-density substances.

[0012] Preferably, in step S1, the tidal cycle is controlled by a 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, so as to form a tidal flow with a water level change range of 50-150 mm in the settlement area upstream of the tidal cofferdam structure.

[0013] Preferably, the method further includes: when the mixture flows through the ultrasonic-pneumatic mixing and deagglomeration unit, activating the ultrasonic transducer and microporous aeration pipe to cavitate and deagglomerate the powder agglomerates, releasing the inorganic impurities encapsulated in the agglomerates and enhancing the stratification of light and heavy phases; at the same time, the metal adsorbent in the downstream section of the chute adsorbs and traps the unsettled metal particles.

[0014] Preferably, when the treatment capacity is 1200–1600 kg / h, the water flow rate is controlled at 14–16 m³ / h. 3 / h, ultrasonic power density is 0.3~0.5W / cm³ 2 Aeration intensity is 3-4 m 3 / (m 2 •h) to ensure that the metal removal rate is not less than 99%, the sand and gravel removal rate is not less than 97%, the polyester recovery rate is not less than 98%, and the unit processing energy consumption is not higher than 1.0kWh / ton of material.

[0015] Furthermore, the present invention also provides a tidal chute separation device for implementing the method, comprising: The inclined chute body is a long strip of stainless steel chute that is closed at one end and open at the other end. The chute is inclined at an angle of 5° to 15° along the material flow direction and is embedded in a “∪” shaped carbon steel frame to form a support. The water inlet unit is located at the upstream end of the chute body and includes a water inlet connected to an external water supply pipeline and a variable frequency water pump for adjusting the water inlet flow rate, so that a water flow from upstream to downstream is formed in the chute. The feeding unit is located above the upstream end of the chute body and is used to evenly spread microplastics containing high specific gravity materials onto the surface of the chute. The tidal cofferdam structure is located in the section from the upstream end to the downstream end of the chute, which is 1 / 3 to 1 / 2 of the length. It is formed by a weir plate that spans the width of the chute. The height of the weir plate is 1 / 10 to 1 / 5 of the effective water depth of the chute. The upper edge of the weir plate forms an overflow outlet for the repeated rise and fall of the water flow, so that a heavy phase settling zone is formed upstream of the cofferdam and a light phase buffer zone is formed downstream of the cofferdam. When the variable frequency pump periodically changes the speed, the water level in the heavy phase settling zone rises and falls periodically to generate tidal flow. The heavy phase discharge unit is located at the bottom of the heavy phase settling zone of the tidal cofferdam structure and is used to discharge high-density materials from the chute when the heavy phase sediments reach a predetermined height. An end separation mechanism is provided at the downstream opening of the chute body to intercept polyester microplastics flowing out of the chute and achieve material dehydration.

[0016] Preferably, the water inlet unit further includes a flow sensor installed on the water inlet and a programmable logic controller (PLC) electrically connected to the variable frequency water pump. The PLC performs closed-loop regulation based on the real-time flow rate collected by the flow sensor and a preset water-to-material ratio of 1:12 to 1:15 to maintain the water flow in the chute at a stable level of 10 to 20 m³ / h. 3 Within a range of / h, the pump speed is changed at a preset cycle to form tidal water flow; And / or, the feeding unit includes: a screw feeder connected to the upstream storage silo, a weighing module installed below the screw feeder, and a laser rangefinder for detecting the thickness of the material layer. The PLC adjusts the speed of the screw feeder based on the instantaneous mass flow rate output by the weighing module and the thickness of the material layer detected by the laser rangefinder, so that the feed rate is maintained at 100-150 kg / min and is evenly distributed along the width direction of the chute.

[0017] Preferably, the heavy phase discharge unit includes a slag discharge port connected to the slag discharge pipeline and an automatic slag discharge valve installed at the slag discharge port. The automatic slag discharge valve is a pneumatic butterfly valve or a pneumatic ball valve. A capacitive level switch or an ultrasonic level gauge is installed in the heavy phase settling zone upstream of the valve. When the settling layer height reaches the set value, the PLC triggers the automatic slag discharge valve to open for 2 to 10 seconds to intermittently discharge the deposited inorganic impurities.

[0018] Preferably, the device further includes an ultrasonic-pneumatic hybrid de-agglomeration unit, which is arranged along the bottom of the upstream and / or downstream chute of the tidal cofferdam structure. This unit comprises multiple stainless steel ultrasonic transducers fixed to the chute bottom plate and microporous aeration pipes connected to an external air source. The ultrasonic transducers and microporous aeration pipes work together to break up powder agglomerates and enhance stratification. In the ultrasonic-pneumatic hybrid de-agglomeration unit: the ultrasonic transducers operate at a frequency of 28–40 kHz and a power density of 0.3–0.5 W / cm². 2 The aeration intensity of the microporous aeration pipe is 2-5m. 3 / (m 2 ·h); PLC controls the ultrasonic aeration to operate in an intermittent mode with a run time of 20-40 seconds and a stop time of 10-20 seconds.

[0019] Preferably, the device also includes a metal adsorbent installed on the sidewall or bottom plate of the downstream chute section of the tidal cofferdam structure, comprising a replaceable permanent magnet assembly and / or a metal filter grid for adsorbing iron filings and other impurities.

[0020] Preferably, the end separation mechanism includes a vibrating filter screen connected to the outlet of the chute and a return pipe connected to the water collection area below the filter screen. The vibrating filter screen is arranged with an adjustable tilt angle of 30° to 60°, and the return pipe sends the filtered water to an external water treatment unit for recycling. The vibrating filter screen is made of stainless steel wire mesh with a polyurethane edging structure. A multi-stage sedimentation tank is set below the filter screen, with each stage having a volume of 0.3 to 0.8 m³. 3 The outlet of the sedimentation tank is connected to the water inlet unit via a clean water pump to form a closed-loop return water system, and the amount of new water added to the system does not exceed 5% of the total circulating water volume.

[0021] This invention utilizes a composite hydraulic environment constructed within an inclined chute, comprising a tidal cofferdam, a heavy phase settling zone, and a light phase buffer zone. A PLC-controlled variable frequency pump periodically adjusts the flow rate, causing high-density inorganic particles to undergo alternating deceleration and acceleration during tidal water level fluctuations. This significantly enhances the enrichment and settling of heavy phases such as metal debris and sand. Simultaneously, the synergistic effect of ultrasonic transducers and microporous aeration pipes cavitation and deagglomerates polyester powder agglomerates, fully releasing encapsulated inorganic impurities. This improves the clarity of the sorting interface and the separation driving force from the source. Furthermore, a metal adsorbent located downstream enables secondary capture of incompletely settled metal particles, resulting in a stable metal and sand removal rate of 99% or higher, and 97%, respectively. By using screw feeding and closed-loop flow control, dynamic matching of material throughput and water-to-material ratio is achieved. While ensuring a polyester powder recovery rate of no less than 98%, the unit processing energy consumption is controlled below 1.0 kWh / ton of material. Furthermore, the closed-loop water return system ensures that the amount of fresh water replenishment does not exceed 5% of the total circulation volume. This achieves a comprehensive technical effect that combines high efficiency separation, high resource recovery, low water consumption, and low energy consumption, providing a stable and reliable process foundation for the large-scale clean recycling of waste microplastics. Attached Figure Description

[0022] Figure 1 This is a system structure block diagram of the present invention.

[0023] Figure 2 This is a schematic diagram of the tidal chute separation device.

[0024] Figure 3 This is a schematic diagram of a tidal cofferdam structure.

[0025] Figure 4 This is a process flow diagram of the present invention. Detailed Implementation

[0026] The structural composition and separation method of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the described embodiments are only for illustrating the present invention and are not intended to limit the scope of protection of the present invention; without departing from the spirit and substance of the present invention, those skilled in the art can make various modifications or substitutions to its structural form, parameter range, and control strategy, all of which should fall within the scope of protection of the present invention.

[0027] I. Terminology and Overall Structure In this invention, microplastics mainly refer to those obtained by polyester fiber companies and polyester recycled plastic companies during the crushing, cleaning, and recycling of waste polyester fibers, polyester bottle flakes, and polyester scraps. The particle size is generally 0.1-5mm, and may contain a small amount of fibrous or flaky particles. High-density substances include metal scraps, screws, metal sheets, welding slag, glass fragments, sand and gravel particles, and other inorganic impurities with a density significantly higher than PET. Tidal chute refers to a hydraulic sorting channel formed in the heavy phase settling zone through a weir structure and variable frequency water pump control, resulting in periodic fluctuations in liquid level and changes in flow velocity. Tidal flow refers to a non-steady-state flow in which the water level and local flow velocity in the chute rise and fall regularly over time within a certain period.

[0028] See Figure 1 The preferred tidal chute separation system of this invention generally includes: an upstream feeding and storage unit, a tidal chute separation device 100 for separating microplastics and high-density substances, an end separation and water return system, and a PLC control cabinet for centralized control. The tidal chute separation device 100 is the core component of this invention. Internally, it completes density stratification of microplastic powder and high-density substances, concentrated sedimentation of the heavy phase, and conveying of the light phase. It also works with an ultrasonic-pneumatic mixing and deagglomeration unit and a metal adsorbent to achieve enhanced separation. The end separation and water return system is used to dehydrate and recycle polyester powder and to clarify the separated water for reuse, thereby realizing a closed-loop water circulation.

[0029] II. Structural Embodiments of Tidal Sluice Gate Separation Device 1. Inclined chute body and supporting frame See Figure 2 The tidal chute separation device 100 of this embodiment includes an inclined chute body 1 and a U-shaped carbon steel frame for supporting the chute body. The chute body 1 is welded from a stainless steel plate with a thickness of 3-5mm and is arranged in a straight inclined line from the upstream end to the downstream end. The length of the chute is preferably 5-8m, and in this embodiment it is 6m, with an inner width of 1.2m and a depth of 0.4m. The angle α between the bottom plate of the chute and the horizontal plane is controlled within the range of 5°-15°, preferably 8°-12°, and in this embodiment it is 10°, so as to provide sufficient residence time for density stratification and settling while ensuring the smooth descent of materials.

[0030] The U-shaped carbon steel frame 11 includes two side columns and a bottom crossbeam, forming an overall U-shaped channel support structure. The chute body 1 is embedded in the frame and fixed by welding or bolts. Several adjustable-height support feet 12 are provided at the bottom of the frame for fine-tuning the chute inclination angle on-site to adapt to uneven ground or process optimization needs.

[0031] The inner surface of the chute body 1 can be polished or brushed to reduce the adhesion of dust and inorganic particles; wear-resistant lining plates (such as polyurethane plates or polymer wear-resistant plates) can be locally installed at the bottom of the heavy phase settling zone to extend the service life of the equipment.

[0032] 2. Water inlet unit like Figure 2 As shown, the water inlet unit is located on the lower side wall of the upstream end of the chute body 1, and includes a water inlet, a water inlet pipe, a variable frequency water pump, a flow sensor, and a PLC controller electrically connected to the variable frequency water pump. The water inlet is connected to the main pipe from the outlet of the clear water tank or sedimentation tank via a flange, and a shut-off valve, a variable frequency water pump, and a flow sensor are sequentially installed on the main pipe.

[0033] The variable frequency water pump is a corrosion-resistant centrifugal pump, with a rated flow rate preferably of 20-25 m³ / h. 3 / h, head 15~25m, can be adjusted to 10~20m under PLC control. 3 The flow rate is continuously adjusted within a range of / h to form a main water flow from upstream to downstream within the chute. The flow sensor can be an electromagnetic or vortex flow meter, with a measurement accuracy preferably better than ±0.5%. The detected instantaneous flow signal is fed back to the PLC in real time. The PLC compares this signal with the preset target water flow rate and water-to-material ratio, and adjusts the frequency of the variable frequency pump according to the deviation to achieve closed-loop control of the inlet water flow.

[0034] In addition, the PLC has a pre-set tidal cycle control program. Under the premise of meeting the basic water volume requirements, the variable frequency water pump speed is switched in a cycle of 30-60 seconds of operation, 10-20 seconds of deceleration, and 10-20 seconds of acceleration. This causes the liquid level in the upstream settlement zone of the tidal cofferdam structure to rise and fall repeatedly within a range of 50-150 mm, thereby forming a tidal flow.

[0035] 3. Feeding unit See Figure 1 , Figure 2 In this embodiment, the feeding unit is located above the upstream end of the chute body 1, and includes an upstream storage bin, a screw feeder, a weighing module, and a laser rangefinder. The storage bin is connected to the upstream cleaning and screening unit and is used to temporarily store microplastics containing high-density substances.

[0036] The outlet of the screw feeder is located above the upstream opening of the chute body 1, arranged along the width of the chute. The rotational speed of the screw shaft is driven by a variable frequency motor and can be adjusted within the range of 2 to 15 rpm to achieve a material mass flow rate of 100 to 150 kg / min. A weighing module is installed below the screw feeder for real-time measurement of the material discharge mass; the weighing module is connected to the PLC to form a closed-loop control of the mass flow rate.

[0037] A laser rangefinder is installed above the chute body 1, with its probe facing the material flow area at the upstream end of the chute, to detect the instantaneous material layer thickness at the upstream end of the chute. The flow rate information output by the PLC integrated weighing module and the material layer thickness measured by the laser rangefinder are used to dynamically adjust the rotation speed of the screw feeder, so that the feed rate is stable within the target range and the microplastics are evenly distributed above the water surface along the width of the chute, reducing local load fluctuations.

[0038] To further improve the lateral distribution, this embodiment can add a material distribution baffle or a small swing chute below the outlet of the screw feeder, so that the falling material swings and scatters in the width direction of the chute, thereby improving the uniformity of the material on the cross section of the chute.

[0039] 4. Tidal cofferdam structure like Figure 3 As shown, the tidal cofferdam structure 4 is arranged in the section from the upstream end to the downstream end of the chute body 1 in the length direction of 1 / 3 to 1 / 2. In this embodiment, it is set at a distance of 2.2m from the upstream end. The tidal cofferdam structure 4 consists of a weir plate spanning the width of the chute and sealing connections between the weir plate and the chute wall on both sides. The height of the weir plate is 1 / 10 to 1 / 5 of the effective water depth of the chute. In this embodiment, the effective water depth of the chute is 0.35m, and the height of the weir plate is about 0.05 to 0.07m. An overflow outlet is formed at the upper edge of the weir plate.

[0040] The weir plate divides the water area within the chute body 1 into a heavy phase settling zone on the upstream side and a light phase buffer zone on the downstream side. The bottom of the heavy phase settling zone is the area where the heavy phase discharge unit is arranged. This section has a lower flow velocity and a greater water depth. Under the action of tidal flow, high-density particles such as metal debris and sand gradually sink and accumulate at the bottom during multiple rises and falls. The light phase buffer zone is mainly used to receive light phase polyester powder that crosses the weir plate and to provide a relatively stable flow field for the subsequent ultrasonic-pneumatic mixing and deagglomeration unit and metal adsorbent.

[0041] The weir plate is preferably made of wear-resistant stainless steel and can be connected to the tank wall with bolts and washers to form a replaceable structure, allowing the weir height to be adjusted according to the material properties and working conditions. The upper edge of the weir plate can be machined into a straight or serrated overflow edge to improve overflow uniformity.

[0042] 5. Heavy phase discharge unit The heavy phase discharge unit is located at the bottom of the heavy phase settling zone of the tidal cofferdam structure 4, and includes a slag discharge port, a slag discharge pipeline, and an automatic slag discharge valve installed at the slag discharge port. The slag discharge port is formed by cutting the bottom plate of the chute and welding a short pipe joint. It is preferably rectangular or circular in cross-section with an inner diameter of 100-200 mm, and the outer side is connected to the slag discharge pipeline through a flange.

[0043] The automatic slag discharge valve uses a pneumatic butterfly valve or a pneumatic ball valve, and its opening and closing action is achieved by a PLC-controlled solenoid valve and a pneumatic power source. To accurately determine the height of the settling layer, a capacitive level switch or ultrasonic level gauge is installed on the inner wall of the heavy phase settling zone, with the detection point located near the bottom at the predetermined accumulation height of the heavy phase. When the level signal reaches the set threshold, the PLC triggers the automatic slag discharge valve to open for 2–10 seconds, allowing the accumulated metal scraps and sand particles to be discharged with the bottom slurry into the external slag collection box via the chute; after slag discharge, the automatic slag discharge valve closes. This intermittent slag discharge method avoids the long-term accumulation of heavy phase at the bottom of the tank, which affects the sorting process, and also reduces water flow short-circuiting and light phase loss.

[0044] To prevent excessive amounts of fine polyester powder from flowing out with the slag discharge, a detachable metal screen or grid can be installed at the slag discharge port. The screen aperture is preferably 2-5mm, which allows inorganic particles such as sand and gravel to pass through smoothly while blocking most of the agglomerated powder.

[0045] 6. Ultrasonic-Pneumatic Hybrid De-agglomeration Unit The ultrasonic-pneumatic hybrid de-agglomeration unit is arranged at the bottom of the chute upstream and / or downstream of the tidal cofferdam structure 4. In this embodiment, it is preferable to arrange three sets of ultrasonic-pneumatic components along the length direction on the bottom plate of the light phase buffer zone downstream of the heavy phase settling zone. Each set includes several ultrasonic transducers and a microporous aeration pipe.

[0046] The ultrasonic transducer is fixed to the outside of the chute bottom plate by bolt clamping or welding. The operating frequency is selected as 28-40kHz, and the power of a single transducer is 100-200W, so that the power density in the action area reaches 0.3-0.5W / cm². 2 The ultrasonic transducer is connected to a PLC control system via a dedicated ultrasonic power supply. The PLC can control the ultrasonic transducer to run for 20-40 seconds and stop for 10-20 seconds according to a set cycle, realizing an intermittent working mode to balance the deagglomeration effect and energy consumption.

[0047] The microporous aeration pipe is made of corrosion-resistant material, with uniform micropores distributed on the pipe wall, and the aeration intensity is controlled at 2-5 m. 3 / (m 2Within the range of h); the aeration pipe is connected to an external air source (such as a Roots blower or air compressor), and the air source outlet is equipped with a pressure regulating valve and a flow meter, and is controlled by a PLC to achieve synchronous or alternating operation with the ultrasonic transducer. In this embodiment, it is preferred that the ultrasonic transducer and aeration are started and stopped synchronously to enhance cavitation and bubble disturbance, thereby achieving strong deagglomeration of polyester powder agglomerates and releasing the high-density inorganic particles encapsulated inside.

[0048] The ultrasonic-pneumatic hybrid deagglomeration unit can significantly weaken the adhesion bridges between particles, reduce the size of powder agglomerates, and allow particles to be more fully exposed to tidal currents and gravity fields, thereby improving the efficiency of subsequent sedimentation and sorting.

[0049] 7. Metal adsorbents like Figure 3 As shown, to further improve the removal rate of metal particles, in this embodiment, a metal adsorbent 5 is installed on the side wall or bottom plate of the downstream chute section of the tidal cofferdam structure 4. The metal adsorbent includes a replaceable permanent magnet assembly and / or a metal filter grid.

[0050] The permanent magnet assembly is encased in a stainless steel protective shell. The outer surface of the shell is a flat metal plate that comes into direct contact with the liquid in the chute. The permanent magnet itself is embedded inside the protective shell, maintaining a certain distance from the inner wall of the chute to create sufficiently strong magnetic lines of force without directly exposing the magnet. The permanent magnet assembly can be fixed to the outside of the chute via a slide rail and snap-fit ​​structure, facilitating periodic disassembly and cleaning of adsorbed metal shavings.

[0051] Metal filter grids can be installed near the downstream outlet of the light phase buffer zone. The grids are welded from stainless steel bars or strips, with a mesh size preferably of 1–3 mm. This allows for the interception of some larger metal debris without causing significant blockage to the main flow. The combination of permanent magnet components and metal filter grids enables secondary capture of metal particles that have not fully settled or have been carried downstream by the water flow, reducing the risk of them entering the final dewatering and subsequent melting stages.

[0052] 8. Terminal separation mechanism and return water system The end-of-line separation mechanism is located at the downstream opening of the chute body 1, and includes a vibrating filter, a vibrating motor, a water collection area, and a return pipeline. The vibrating filter is connected to the chute outlet via a support frame. The filter is made of stainless steel wire mesh with a polyurethane edging structure to improve wear resistance and fatigue resistance. The mesh size is selected according to the microplastic particle size, preferably 20-100 mesh, and in this embodiment, 40-60 mesh is used. The installation angle of the vibrating filter is 30°-60°, which is continuously adjustable via an electric push rod or screw mechanism to adjust the residence time and dewatering effect according to the material properties and moisture content.

[0053] A vibrating motor is fixed to the filter screen frame and generates vibration through an eccentric block, causing the polyester microplastics to move uphill on the filter screen and agitate layer by layer. The filtered water then falls from below the filter screen into the collection area. The collection area is connected to a multi-stage sedimentation tank, which can be cascaded in three to four stages, each with a volume of 0.3–0.8 m³. 3 The sedimentation tank is equipped with baffles to create an upward, settling, and overflow flow pattern to remove suspended solids from the water. The supernatant after multi-stage sedimentation enters the clear water tank and is pumped back to the inlet water unit to achieve closed-loop water circulation. A sludge discharge port is set at the bottom of the sedimentation tank for periodically discharging accumulated fine inorganic particles and residual dust.

[0054] With the above arrangement, the amount of new water replenished by the system can be controlled to less than 5% of the total circulating water volume, which greatly reduces water consumption and wastewater discharge.

[0055] III. Examples of Separation Methods Based on the above structure, this invention proposes a method for separating high-density substances from microplastics using a tidal chute separation device. See also... Figure 4 The process flow diagram shown illustrates the following steps in this method: Establishment of S1 tidal current First, start the clean water pump and the variable frequency water pump to continuously supply water to the inlet 2 of the chute body 1. Under the control of the PLC, adjust the instantaneous flow rate of the variable frequency water pump 21 to 10-20 m³ / h. 3 The flow rate is set within the range of / h, and the required water-to-material ratio is calculated based on the set target processing capacity (e.g., 1200–1600 kg / h), preferably 1:12–1:15. The flow sensor detects the influent flow rate in real time, and the signal is fed back to the PLC. After comparing it with the target value, the frequency of the variable frequency pump is adjusted to achieve stable control.

[0056] After the flow rate stabilizes, the PLC controls the speed of the variable frequency water pump according to the preset tidal cycle program, switching cyclically for 30-60 seconds, deceleration for 10-20 seconds, and acceleration for 10-20 seconds. This causes the water level in the heavy phase settling zone 43 upstream of the tidal cofferdam structure 4 to change repeatedly within a range of 50-150 mm over time, thereby forming an alternating fast and slow tidal flow in this area, creating an opportunity for periodic enhancement of heavy phase particle settling.

[0057] S2 Uniform and continuous feeding and formation of suspension layer After the tidal flow is established and stabilized, the screw feeder is activated to continuously feed the microplastics in the storage bin into the upstream end of the chute body 1 at a mass flow rate of 100-150 kg / min. The weighing module measures the mass of the material falling in real time, and the laser rangefinder detects the thickness of the material layer at the upstream end of the chute. Both signals are fed back to the PLC. The PLC adjusts the speed of the screw feeder according to the mass flow rate and the deviation of the material layer thickness to ensure that the actual feed rate is stable within the target range and to avoid violent fluctuations in the flow pattern inside the chute due to instantaneous overload.

[0058] After falling into the chute, the microplastics quickly disperse under the action of the main water flow to form a suspended layer. The lightweight microplastics move downstream under the drag of the water flow, while some high-density inorganic particles begin to settle before entering the heavy phase settling zone 43. As materials are continuously added and the water flow continues, a solid-containing suspended layer of a certain thickness and with a moderate concentration distribution is formed on the cross-section of the chute.

[0059] S3 tidal settling-enhanced heavy phase enrichment and automatic slag removal When the suspended layer enters the heavy phase settling zone of the tidal cofferdam structure 4, the water depth in this area increases and the flow velocity decreases due to the obstruction of the weir plate. High-density particles such as metal debris and sand settle more rapidly under the influence of gravity. At the same time, under the influence of the tidal cycle, the water level in the heavy phase settling zone rises and falls periodically. The rising water level provides a relatively stable environment, which is conducive to the accumulation of heavy phase particles at the bottom; the falling water level or the increase in flow velocity helps to peel off the fine inorganic particles still attached to the surface of the polyester powder, causing them to fall off and settle to the bottom.

[0060] As the operating time increases, heavy phase particles gradually accumulate at the bottom of the settling zone, with the accumulation height monitored in real time by a capacitive level switch or ultrasonic level gauge. When the settling layer height reaches a preset threshold, the PLC issues a command to open the automatic slag discharge valve, controlling the slag discharge time to be 2–10 seconds. This allows the concentrated slurry accumulated at the bottom to be discharged through the slag discharge port and slag discharge pipeline into the slag collection box via the slag discharge chute. During the slag discharge process, the accumulation layer is locally disrupted, but due to the short duration of the slag discharge and the proximity of the slag discharge port to the bottom of the tank, the impact on the mainstream and light phase components is limited. After the slag discharge is completed, the automatic slag discharge valve closes, and the settling zone re-establishes a stable accumulation layer and tidal flow environment, achieving periodic enrichment and discharge of heavy phases.

[0061] S4 Ultrasonic-Pneumatic Coordinated Deagglomeration and Secondary Capture of Metal Scrap As the mixed suspension layer passes over the weir and enters the light phase buffer zone, some microplastics that are still in agglomerated form, along with the inorganic particles they encapsulate, will enter the action area of ​​the ultrasonic-pneumatic mixing deagglomeration unit. At this time, the PLC controls the ultrasonic transducer and the microporous aeration pipe to operate in an intermittent mode of 20-40 seconds of operation followed by 10-20 seconds of shutdown.

[0062] During operation, the ultrasonic transducer creates a dense sound field in the water, generating a cavitation effect that produces numerous microbubbles and localized high-shear regions, disrupting the bonding bridges within the microplastic aggregates. Simultaneously, the bubbles released from the microporous aeration pipes impact and disturb the aggregates as they rise, further weakening the aggregate structure in conjunction with the ultrasonic action. After multiple cycles, most of the powder agglomerates are broken down into single particles or small clusters, exposing the high-density inorganic particles previously encased within the aggregates. These particles then continue to migrate towards the heavy phase settling zone or the bottom of the downstream chute during subsequent movement.

[0063] For metal particles that have not yet fully settled, as they flow downstream of the light phase buffer zone with the water, they will pass through the area where the metal adsorbent is located. Under the influence of the magnetic field generated by the permanent magnet assembly, iron filings and other magnetic particles are adsorbed and retained inside the protective shell; some larger metal pieces that are not easy to settle can also be intercepted by the metal filter grid. Through this secondary capture process, the probability of metal filings entering the terminal separation mechanism with the light phase is further reduced.

[0064] S5 terminal dewatering and recovery with closed-loop water return After tidal settling, deagglomeration, and metal adsorption, the light-phase polyester microplastics enter the vibrating filter area of ​​the final separation mechanism with the water flow. Driven by a vibrating motor, the vibrating filter vibrates at a certain frequency and amplitude, with a filter inclination angle of 30° to 60°, causing the microplastics to move gradually uphill. During this process, they are repeatedly tumbled and thrown off, and water and residual fine inorganic particles are discharged through the filter mesh, forming underflow that enters the collection area. The microplastics on the filter are gradually dehydrated under the action of vibration and gravity, and are finally discharged from the high end of the filter to enter the subsequent temporary storage or conveying device, where their moisture content can be controlled below 25%.

[0065] The filtered water flows from the collection area into a multi-stage sedimentation tank. After multi-stage gravity sedimentation to remove residual suspended solids, a relatively clear supernatant is formed and enters the clear water tank. The clear water tank supplies water to the inlet unit via a clear water pump, forming a closed water circulation loop. During system operation, the clear water tank level is monitored by a water meter or level gauge. If necessary, a small amount of fresh water is added to compensate for evaporation and carryover losses. The amount of replenished water is controlled to be less than 5% of the total circulating water volume, effectively reducing water consumption and wastewater discharge.

[0066] IV. Specific Operating Condition Examples The following description, using specific operating parameters, illustrates the application effects of the method of the present invention under industrial conditions. This embodiment is merely an example to support the feasibility and technical effects of the present invention and does not constitute a limitation on the technical solution of the claims.

[0067] With a processing capacity of approximately 1400 kg / h, a chute with a length of 6 m, a width of 1.2 m, a depth of 0.4 m, and an inclination angle of 10° is selected. Microplastics containing high-density inorganic impurities such as metal scraps and sand are continuously fed into the upstream end of the chute via a screw feeder at a flow rate of 120–125 kg / min. The weighing module and laser rangefinder work together to control the load on the chute cross-section to maintain stability. The variable frequency water pump is set to supply water at a flow rate of approximately 15.4 m³ / h, corresponding to a water-to-material ratio of approximately 11:1. Under PLC control, it cycles through 45 seconds of operation, 15 seconds of deceleration, and 15 seconds of acceleration to achieve tidal water flow.

[0068] In the heavy phase settling zone, metal debris and sand particles rapidly accumulate to the bottom under the continuous influence of tidal water level fluctuations and flow velocity changes. When the accumulation height approaches the set value of the material level switch, the automatic slag discharge valve opens for 5 seconds to discharge the enriched heavy phase slurry. Actual statistics show that the loss of polyester powder in a single slag discharge is less than 1.0%. The ultrasonic power of the ultrasonic-pneumatic mixing deagglomeration unit is adjusted to 600W, with a power density of approximately 0.4W / cm³. 2 The aeration intensity is controlled at 3.5m. 3 / (m 2 ·h), both run synchronously for 30s, stop for 15s, and repeat this cycle; after running for a period of time, it can be observed that the agglomeration of powder in the tank is significantly reduced, and the suspended layer is more uniform and fine.

[0069] Quality analysis of the discharged polyester powder showed that, under the above operating conditions, the removal rate of metallic impurities was no less than 99.2%, the removal rate of non-metallic high-density particles such as sand and gravel was no less than 97.5%, and the recovery rate of polyester powder was no less than 98.8%. The unit processing energy consumption of the entire system was approximately 0.8 kWh / ton of material, which is more than 40% lower than the energy consumption of some traditional vibrating screening + simple sedimentation combined processes. Simultaneously, the closed-loop water return system controlled the fresh water replenishment within the range of 3% to 5%, significantly reducing wastewater discharge and meeting the requirements of green manufacturing and energy conservation and environmental protection.

[0070] As can be seen from the above structural and operational examples, the tidal chute separation device and method of the present invention integrates multiple functional modules such as tidal water flow control, heavy phase enhanced sedimentation and automatic slag discharge, ultrasonic-pneumatic synergistic deagglomeration, metal adsorption and end-of-pipe dewatering and recycling within a single chute. This not only achieves efficient separation of high-density inorganic impurities in microplastics, but also takes into account the comprehensive technical effects of high polyester recovery rate, low water consumption and low energy consumption, and has good prospects for engineering applications.

[0071] Of course, without departing from the spirit of this invention, those skilled in the art can make various modifications to the chute structural parameters (such as length, width, inclination angle, weir plate height and position), ultrasonic and aeration parameters (such as frequency, power, aeration intensity and working cycle), feeding and water supply control strategies, and the structure of the end separation and return water system. For example, they can adopt a double-layer or multi-stage tidal cofferdam structure, adopt different types of vibration dewatering equipment, or replace the permanent magnet component with an electromagnet component to achieve online demagnetization and cleaning. All such modifications should be considered to fall within the protection scope defined by the claims of this invention.

[0072] To verify the technical effectiveness of the tidal chute separation device and method of this invention in separating high-density substances from microplastics, the applicant designed and implemented a comparative experiment. The experiment systematically compared the proposed solution with a modified device based on multiple indicators, including high-density substance removal rate, polyester recovery rate, unit processing energy consumption, and water replenishment rate. The experimental scheme and results are presented below.

[0073] I. Experimental Objectives and Evaluation Indicators 1. Experimental Objective To verify whether the device of the present invention can significantly improve the removal rate of high-density inorganic impurities such as metal scraps and sand under the same processing conditions; To verify whether a high microplastic recovery rate can still be maintained under high removal rate conditions; Verify the combined effects of key technologies such as tidal flow regulation, ultrasonic-pneumatic deagglomeration, and metal adsorbents; The energy-saving and water-saving effects of this invention in terms of unit processing energy consumption and water replenishment volume are evaluated.

[0074] 2. Evaluation Indicators Metal removal rate η_M (%): η_M = (feed metal mass - discharge metal mass) / feed metal mass × 100%; Sand and gravel removal rate η_S (%): η_S = (mass of feed sand and gravel - mass of discharge sand and gravel) / mass of feed sand and gravel × 100%; Polyester recovery rate R_P (%): R_P = mass of produced polyester / mass of fed polyester × 100%; Unit processing energy consumption E (kWh / ton): E = Total power consumption during the test / Total mass of processed materials Water replenishment rate W (%): W = Volume of new water replenished / Total circulating water volume of the system × 100%.

[0075] Among the above parameters, the mass of metals and sand in the feed and discharge is determined by magnetic separation-weighing, density separation-screening-weighing, or chemical analysis; the mass of polyester is determined by drying and weighing; the power consumption is recorded by an electricity meter; and the volume of water replenishment is accumulated by a flow meter.

[0076] II. Experimental Apparatus and Material Conditions 1. Test apparatus The experimental setup employs the tidal chute separation device corresponding to the claims, with a chute length of 6m, a width of 1.2m, a depth of 0.4m, and an inclination angle of 10°. It is equipped with a screw feeder, weighing module, laser rangefinder, variable frequency water pump, tidal cofferdam structure, heavy phase discharge unit, ultrasonic-pneumatic mixing and deagglomeration unit, metal adsorbent, and end-stage vibrating filter + multi-stage sedimentation and water return system. The PLC control cabinet enables centralized control of feeding, water volume, tidal cycle, ultrasonic and aeration start / stop, automatic slag discharge, and vibrating filter operation.

[0077] 2. Test materials The test material was typical recycled polyester (PET) microplastic powder with a particle size of 0.1-5 mm, of which 80% of the mass fraction had a particle size of less than 2 mm. The material contained a certain proportion of high-density inorganic impurities, including: metal impurities such as iron filings, screw fragments, and metal powder, as well as non-metallic inorganic impurities such as river sand and fine gravel. Preliminary analysis determined that the typical feed composition (mass fraction) is approximately as follows: PET microplastic powder: approximately 96.0%; Metallic impurities: Approximately 1.0%; Inorganic impurities such as sand and gravel: approximately 3.0%.

[0078] 3. Test conditions Processing capacity: Approximately 1400 kg / h; Continuous test run time: no less than 8 hours for each set of operating conditions, in order to eliminate the influence of the start-up and transition phases; All tests were conducted at room temperature, with the influent being recycled process water, and the conductivity and suspended solids concentration within the allowable range.

[0079] III. Examples and Comparative Examples To highlight the key technological features, this experiment was designed with one set of exemplary cases and three sets of comparative cases: 1. Example 1 (Solution of the present invention) The system is fully equipped with a tidal cofferdam structure, variable frequency tidal flow control, ultrasonic-pneumatic hybrid deagglomeration unit, and metal adsorbent. Other structures and parameters are set within the scope defined in the claims.

[0080] 2. Comparative Example 1 (no tides, only constant flow) Tidal control is removed, and the variable frequency pumps are set to operate at a constant flow rate without periodic flow / level regulation; the cofferdam still exists, but the water level in the settlement zone remains basically constant.

[0081] 3. Comparative Example 2 (without ultrasound - pneumatic deagglomeration) Keep the tidal cofferdam and tidal flow control unchanged, but shut down the ultrasonic transducer and aeration system, i.e., do not provide a physical field for deagglomeration.

[0082] The above groupings can reflect the contributions of tidal currents and ultrasonic-aerodynamic deagglomeration to the overall separation effect.

[0083] IV. Example 1 – Test Results of the Device of the Invention 1. In Example 1, the main parameters are set as follows: Slide angle: 10°; Feed rate: 120-125 kg / min, controlled by a weighing module and laser ranging closed loop. Inlet flow rate: 15.4 m³ / h 3 / h, corresponding to a water-to-material ratio of approximately 11:1; Tidal control: The variable frequency water pump cycles through 45 seconds of operation, 15 seconds of deceleration, and 15 seconds of acceleration, with the water level in the heavy phase settling zone fluctuating by approximately 80 to 100 mm. 2. Ultrasonic-Pneumatic Unit: The ultrasonic frequency is 28–40 kHz, the total power is about 600 W, and the power density is about 0.4 W / cm². Aeration intensity is approximately 3.5m. 3 / (m 2 ·h); Operating mode: Run for 30 seconds / Stop for 15 seconds in a cycle; Automatic slag discharge: When the settling layer height reaches the set value, the automatic slag discharge valve opens for 5 seconds to discharge slag; Metal adsorbent: A permanent magnet assembly + metal filter grid is arranged downstream of the light phase buffer zone; Vibrating filter: Inclined at approximately 40°, with a mesh size of 40–60, and a moderate vibration frequency to ensure thorough dehydration.

[0084] After the test run stabilized, feed and discharge samples were continuously collected for analysis, and the typical results were as follows: Metal removal rate η_M ≥ 99.2%; The sand and gravel removal rate η_S ≥ 97.5%; Polyester recovery rate R_P ≥ 98.8%; Unit processing energy consumption E≈0.8kWh / ton of material; The system water replenishment rate W ≈ 3-4% (less than 5%).

[0085] Observations of the on-site operation show that a relatively stable accumulation layer can be formed at the bottom of the heavy phase settling zone, the liquid level recovers rapidly after periodic slag discharge, and the light phase suspension layer fluctuates less; the agglomeration of powder and debris in the ultrasonic-pneumatic zone is significantly reduced, and the discharged powder and debris particles are evenly dispersed; when the surface of the permanent magnet component is cleaned regularly, a lot of iron filings can be seen accumulating, indicating that the secondary capture effect of metal iron filings is obvious.

[0086] V. Results of Comparative Experiments 1. Comparative Example 1: No tides, only constant flow In Comparative Example 1, the feed rate, water-to-material ratio, ultrasonic-pneumatic unit and metal adsorbent arrangement were kept unchanged, but the variable frequency water pump was set to constant flow rate operation (15.4 m³ / h) without any periodic flow rate changes. That is, the water level in the heavy phase settling zone remained basically constant, and the heavy phase was slowly accumulated at the bottom and then discharged by timed slag removal.

[0087] Under these conditions, the following measurements were obtained after continuous operation for the same period of time: Metal removal rate η_M≈96.5%; The sand and gravel removal rate η_S≈93.1%; Polyester recovery rate R_P≈97.0%; Unit processing energy consumption E≈0.78kWh / ton; The water replenishment rate W≈3~4%.

[0088] It is evident that, under steady-state water flow conditions, although high-density inorganic particles can settle to a certain extent, under high solids content and high throughput conditions, some fine metals and sand particles are still easily carried out with the flow, and the overall removal rate is significantly lower than that of Example 1. At the same time, due to insufficient settling driving force and bottom refluidization effect, slag discharge often requires a longer opening time or a higher frequency, which can easily increase polyester loss and lead to a decrease in recovery rate.

[0089] 2. Comparative Example 2: Non-ultrasonic - pneumatic deagglomeration Comparative Example 2 retains the tidal flow control and metal adsorbent, but turns off the ultrasonic-pneumatic hybrid de-agglomeration unit, i.e., the ultrasonic transducer and aeration pipe are not enabled, and other parameters are consistent with Example 1.

[0090] Under these conditions, significant agglomeration of the polyester within the chute was observed, with the agglomerates containing sand particles and metal filings being more pronounced than in Example 1. After continuous operation and sample analysis, the following results were obtained: Metal removal rate η_M≈97.2%; The sand and gravel removal rate η_S≈94.0%; Polyester recovery rate R_P≈97.5%; Unit processing energy consumption E≈0.62kWh / ton (excluding ultrasonic and aeration energy consumption); The water replenishment rate W≈3~4%.

[0091] It is evident that, in the absence of a deagglomeration physical field, even with tidal currents, a considerable portion of sand and metal particles remain encapsulated by agglomerated polyester and fail to settle sufficiently or be magnetically adsorbed, resulting in a significantly lower removal rate of high-density substances compared to Example 1. Although energy consumption is slightly reduced, considering both the impurity removal effect and recovery rate, the present invention has superior overall performance.

[0092] VI. Comparison of Experimental Data and Analysis of Technical Effects The main indicators for each of the above operating conditions are summarized in Table 1: Table 1 Performance comparison between the examples and comparative examples

[0093] As can be seen from Table 1: 1. Contribution of tidal cofferdam + variable frequency tidal flow Compared with constant flow rate (Comparative Example 1), the metal removal rate of the embodiments of the present invention increased from about 96.5% to ≥99.2% and the sand and gravel removal rate increased from about 93.1% to ≥97.5% under the same performance, indicating that periodic fluctuations in liquid level and changes in flow velocity can significantly enhance the sedimentation and enrichment of high specific gravity substances; at the same time, the recovery rate increased from about 97.0% to ≥98.8%, indicating that tidal flow improved sedimentation efficiency without significantly increasing the loss of light phase.

[0094] 2. Contribution of ultrasonic-pneumatic deagglomeration Comparative Example 2 showed a significantly lower removal rate of metals and sand than Example 1, especially for sand, without the need for deagglomeration. This indicates that the deagglomeration unit effectively destroyed the structure of the powder agglomerates, allowing the encapsulated inorganic particles to be exposed and participate in the subsequent sedimentation and adsorption processes. Although Comparative Example 2 had slightly lower energy consumption, considering the separation effect, the present invention is more conducive to obtaining high-quality polyester.

[0095] 3. Energy and water saving effects While achieving the aforementioned high removal and recovery rates, the unit processing energy consumption of the device of this invention is controlled within 0.8 kWh / ton of material, which is lower than the typical energy consumption level of the traditional vibrating screen + multi-stage sedimentation combined process; the closed-loop water return system keeps the water replenishment rate stable below 5%, effectively reducing fresh water consumption and wastewater discharge.

[0096] In summary, this invention, through the synergistic effect of tidal cofferdam structure, variable frequency tidal flow control, ultrasonic-pneumatic hybrid deagglomeration unit, and metal adsorbent, significantly improves the removal rate of high-density inorganic impurities such as metal scrap and sand under industrial-scale conditions, while maintaining a high microplastic recovery rate. It also takes into account the advantages of low energy consumption and low water replenishment rate, fully demonstrating that the technical solution described in this invention has outstanding substantive features and significant comprehensive technical effects.

Claims

1. A method for separating polyester microplastics from microplastics containing high specific gravity substances, the method comprising the following steps: S1 supplies water to the chute inlet unit and controls the variable frequency pump to operate within the range of 10-20 m³ / h, so that a water flow is formed in the chute and flows downstream along the length direction. The pump speed is changed periodically according to the set tidal cycle, so that the water level in the upstream settlement area of ​​the tidal cofferdam structure rises and falls repeatedly. S2, through the feeding unit, microplastics containing high specific gravity substances are continuously and evenly spread to the upstream end of the chute at a mass flow rate of 100-150 kg / min, so that the microplastics form a suspended layer in the water flow of the chute and move downstream with the water flow. S3, in the settlement zone upstream of the tidal cofferdam structure, the density stratification effect generated by the alternating deceleration and acceleration of the tidal water flow is used to cause high-density inorganic components to settle and accumulate. When the height of the settlement layer reaches the preset value, the automatic slag discharge valve opens to discharge the high-density inorganic components. S4, the microplastics enter the terminal separation mechanism with the water flow, and are intercepted by the vibrating filter to achieve dehydration and recovery of polyester components, thus realizing the separation of polyester microplastics from high-density substances.

2. The method according to claim 1, characterized in that, In step S1, 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, so as to form a tidal flow with a water level change range of 50-150 mm in the settlement area upstream of the tidal cofferdam structure.

3. The method according to claim 1, characterized in that, The method also includes: when the mixture flows through the ultrasonic-pneumatic mixing and deagglomeration unit, activating the ultrasonic transducer and microporous aeration pipe to cavitate and deagglomerate the powder agglomerates, releasing the inorganic impurities encapsulated in the agglomerates and enhancing the stratification of light and heavy phases. At the same time, the metal adsorbent in the downstream section of the chute adsorbs and traps the unsettled metal particles.

4. The method according to claim 3, characterized in that, When the treatment capacity is 1200–1600 kg / h, the water flow rate should be controlled at 14–16 m³ / h. 3 / h, ultrasonic power density is 0.3~0.5W / cm³ 2 Aeration intensity is 3-4 m 3 / (m 2 •h) to ensure that the metal removal rate is not less than 99%, the sand and gravel removal rate is not less than 97%, the polyester recovery rate is not less than 98%, and the unit processing energy consumption is not higher than 1.0kWh / ton of material.

5. A tidal chute separation device for implementing the method according to any one of claims 1-4, characterized in that, include: The inclined chute body is a long strip of stainless steel chute that is closed at one end and open at the other end. The chute is inclined at an angle of 5° to 15° along the material flow direction and is embedded in a "U" shaped carbon steel frame to form a support. The water inlet unit is located at the upstream end of the chute body and includes a water inlet connected to an external water supply pipeline and a variable frequency water pump for adjusting the water inlet flow rate, so that a water flow from upstream to downstream is formed in the chute. The feeding unit is located above the upstream end of the chute body and is used to evenly spread microplastics containing high specific gravity materials onto the surface of the chute. The tidal cofferdam structure is located in the section from the upstream end to the downstream end of the chute, which is 1 / 3 to 1 / 2 of the length. It is formed by a weir plate that spans the width of the chute. The height of the weir plate is 1 / 10 to 1 / 5 of the effective water depth of the chute. The upper edge of the weir plate forms an overflow outlet for the repeated rise and fall of the water flow, so that a heavy phase settling zone is formed upstream of the cofferdam and a light phase buffer zone is formed downstream of the cofferdam. When the variable frequency pump periodically changes the speed, the water level in the heavy phase settling zone rises and falls periodically to generate tidal flow. The heavy phase discharge unit is located at the bottom of the heavy phase settling zone of the tidal cofferdam structure and is used to discharge high-density materials from the chute when the heavy phase sediments reach a predetermined height. The end separation mechanism is located at the downstream opening end of the chute body and is used to intercept polyester powder flowing out of the chute and achieve material dehydration.

6. The tidal chute separation device according to claim 5, characterized in that, The water inlet unit further includes a flow sensor installed on the inlet and a programmable logic controller (PLC) electrically connected to the variable frequency water pump. The PLC performs closed-loop regulation based on the real-time flow rate collected by the flow sensor and a preset water-to-material ratio of 1:12 to 1:15 to maintain a stable water flow rate of 10 to 20 m³ / h in the chute. 3 Within a range of / h, the pump speed is changed at a preset cycle to form tidal water flow; And / or, the feeding unit includes: a screw feeder connected to the upstream storage silo, a weighing module installed below the screw feeder, and a laser rangefinder for detecting the thickness of the material layer. The PLC adjusts the speed of the screw feeder based on the instantaneous mass flow rate output by the weighing module and the thickness of the material layer detected by the laser rangefinder, so that the feed rate is maintained at 100-150 kg / min and is evenly distributed along the width direction of the chute.

7. The tidal chute separation device according to claim 5, characterized in that, The heavy phase discharge unit includes a slag discharge port connected to the slag discharge pipeline and an automatic slag discharge valve installed at the slag discharge port. The automatic slag discharge valve is a pneumatic butterfly valve or a pneumatic ball valve. A capacitive level switch or an ultrasonic level gauge is installed in the heavy phase settling zone upstream of the valve. When the settling layer height reaches the set value, the PLC triggers the automatic slag discharge valve to open for 2 to 10 seconds to intermittently discharge the deposited inorganic impurities.

8. The tidal chute separation device according to claim 5, characterized in that, The device also includes an ultrasonic-pneumatic hybrid de-agglomeration unit, which is arranged along the bottom of the upstream and / or downstream chute of the tidal cofferdam structure. This unit comprises multiple stainless steel ultrasonic transducers fixed to the chute bottom plate and microporous aeration pipes connected to an external air source. The ultrasonic transducers and microporous aeration pipes work together to break up powder agglomerates and enhance stratification. In the ultrasonic-pneumatic hybrid de-agglomeration unit: the ultrasonic transducers operate at a frequency of 28–40 kHz and a power density of 0.3–0.5 W / cm². 2 The aeration intensity of the microporous aeration pipe is 2-5m. 3 / (m 2 ·h); PLC controls the ultrasonic aeration to operate in an intermittent mode with a run time of 20-40 seconds and a stop time of 10-20 seconds.

9. The tidal chute separation device according to claim 5, characterized in that, The device also includes a metal adsorbent installed on the sidewall or bottom plate of the downstream chute section of the tidal cofferdam structure, comprising a replaceable permanent magnet assembly and / or a metal filter grid for adsorbing iron filings and other impurities.

10. The tidal chute separation device according to claim 5, characterized in that, The terminal separation mechanism includes a vibrating filter screen connected to the outlet of the chute and a return pipeline connected to the water collection area below the filter screen. The vibrating filter screen is arranged with an adjustable tilt angle of 30° to 60°. The return pipeline sends the filtered water to an external water treatment unit for recycling. The vibrating filter screen is made of stainless steel wire mesh with a polyurethane edging structure. A multi-stage sedimentation tank is set below the filter screen, with each stage having a volume of 0.3 to 0.8 m³. The outlet of the sedimentation tank is connected to the water inlet unit via a clean water pump to form a closed-loop return water system. The amount of new water added to the system does not exceed 5% of the total circulating water volume.

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