Impurity sorting system for solid waste recycled aggregate

Abstract

The invention belongs to the technical field of building waste recycling, and discloses a solid waste recycled aggregate impurity separation system which comprises a winnowing device, a multi-layer vibrating screen system and a magnetic separation device which are sequentially arranged from top to bottom. The winnowing device comprises an inclined discharging channel, an inlet of the discharging channel is a recycled aggregate feeding port, and a multi-layer vibrating screen system is arranged below a discharging port. A fan is arranged on one side of the horizontal air duct, and an impurity outlet is formed in the other side of the horizontal air duct; the magnetic separation device comprises a conveying belt and is arranged under an outlet of the multi-layer vibrating screen system, a supporting roller on one side of the conveying belt is a magnetic separation roller, and a splitter plate is arranged below the magnetic separation roller in the axial direction and used for separating aggregate from metal impurities. The method can meet the efficient resource utilization requirement of the recycled aggregate.

Description

Technical Field

[0001] This invention belongs to the field of construction waste resource utilization technology, and particularly relates to an impurity sorting system for recycled aggregates from solid waste. Background Technology

[0002] Resource utilization of construction waste is an important way to achieve sustainable development in the construction industry. Among them, the application of recycled aggregates made from crushed waste concrete to the preparation of new concrete is a key link. However, recycled aggregates often contain impurities such as metals (such as iron nails and steel bar fragments) and lightweight debris (such as plastics and garbage bag fragments). If these impurities are not removed, they will seriously affect the workability, mechanical properties and long-term durability of fresh concrete.

[0003] For the processing of recycled aggregates, existing technologies typically employ sieving with screens or add post-processing steps such as air separation or magnetic separation after sieving. However, sieving alone cannot effectively remove lightweight and metallic impurities, resulting in insufficient cleanliness of the recycled aggregates and affecting the performance of subsequent concrete. Adding post-processing steps such as air separation or magnetic separation after sieving cannot prevent flexible impurities from entangled in the screen and clogging the screen holes during the sieving process, requiring frequent shutdowns for cleaning and reducing production efficiency. At the same time, existing processing devices are often complex in structure and bulky in size, failing to fully consider the compact space requirements of concrete mixing plants, resulting in poor adaptability. Furthermore, it is difficult to flexibly adapt to the impurity characteristics and gradation differences of recycled aggregates, which is not conducive to the efficient resource utilization of recycled aggregates. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, this invention provides an impurity sorting system for recycled solid waste aggregates. This system is capable of meeting the needs for efficient resource utilization of recycled aggregates.

[0005] To achieve the above objectives, one or more embodiments of the present invention provide an impurity sorting system for recycled aggregate from solid waste, comprising an air classifier, a multi-layer vibrating screen system, and a magnetic separator arranged sequentially from top to bottom; the air classifier includes a downward inclined material channel, the inlet of which is the feed port for the recycled aggregate, and the multi-layer vibrating screen system below the discharge port; the middle section of the downward inclined material channel is connected to a horizontal air duct, a fan is provided on one side of the horizontal air duct, and an impurity outlet is provided on the other side.

[0006] In some embodiments, the multi-layer vibrating screen system includes an upper vibrating screen, a lower vibrating screen, and an aggregate bearing layer arranged sequentially from top to bottom. The discharge port of the aggregate bearing layer is connected to the inlet of the magnetic separator below through a guide groove.

[0007] In some embodiments, both the upper and lower vibrating screens include a screen frame and a screen mesh. The upper screen mesh has square mesh openings, and the lower screen mesh has rectangular mesh openings. The length of the long side of the rectangular mesh opening is less than or equal to the side length of the square mesh opening.

[0008] In some embodiments, a transmission mechanism is fixedly connected to the bottom of the multi-layer vibrating screen system, and the transmission rod of the transmission mechanism is eccentrically connected to the drive shaft of the excitation mechanism.

[0009] In some embodiments, the magnetic separator includes a conveyor belt located directly below the outlet of the multi-layer vibrating screen system. A support roller on one side of the conveyor belt is a magnetic separator roller, and a flow divider is provided axially below the magnetic separator roller to separate aggregates and metal impurities.

[0010] In some embodiments, the two sides of the diversion plate are respectively connected to the qualified aggregate outlet and the metal impurity collection box.

[0011] In some embodiments, it is assumed that the flow rate of recycled aggregate fed to the air classifier's discharge channel is known, and the width of the discharge channel is known. The inclination angle of the discharge channel and the distance between the discharge channel inlet and the air duct interface are then optimized.

[0012] (1) Set the initial slope and record it as the current slope; based on the current slope, calculate the distance from the inlet to the air duct interface to meet the minimum time requirement, and use it as the current distance; (2) Based on the current slope and current distance, calculate the time and instantaneous downward speed of the recycled aggregate from the inlet of the discharge channel to the air duct interface, and determine whether the time consumption meets the time requirement. If it does, execute step (3). (3) Based on the instantaneous downward velocity and the dimensions of the air duct interface, calculate the residence time of the aggregate in the air duct interface area and determine whether the time meets the air classification time requirement: If the condition is not met, the slope is reduced to obtain a new current slope, the current distance is recalculated, and the process returns to step (2). If satisfied, combine the instantaneous flow rate and instantaneous descent speed to estimate the instantaneous thickness of the aggregate, and further determine whether the aggregate layer thickness is within a reasonable range; if yes, the current slope and current distance are recorded as the optimization result; if no, adjust the slope to obtain a new current slope, recalculate the current distance, and return to step (2); until both the air classification time and the aggregate layer thickness meet the requirements.

[0013] In some embodiments, if the instantaneous thickness of the aggregate is less than the lower limit of the reasonable value range, the slope is reduced; if the instantaneous thickness of the aggregate is greater than the upper limit of the reasonable value range, the slope is increased.

[0014] In some embodiments, the discharge flow rate of the multi-layer vibrating screen system is estimated, and the conveyor belt speed and magnetic force are optimized based on the conveyor belt width, the initial size of the magnetic separator drum, and the magnetic force. (1) Determine the effective adsorption range on the upper surface of the conveyor belt based on the size of the magnetic separator drum, the initial magnetic force and the width of the conveyor belt; calculate the reference speed based on the effective adsorption range and the minimum adsorption time required to ensure that the metal impurities are effectively adsorbed, and use it as the current speed. (2) Based on the current speed, conveyor belt size, and estimated instantaneous feed flow rate, estimate the maximum thickness of the aggregate layer accumulated on the conveyor belt and determine whether it is within a reasonable range: If the thickness is lower than the lower limit of the reasonable value range, it means that the aggregate is too loose, which affects the transmission efficiency. Increase the magnetic force of the magnetic separator, the diameter of the magnetic separator, or add a magnetic separator to one side of the current magnetic separator, and return to step (1). If the thickness is higher than the upper limit of the reasonable value, it means that the aggregate is too piled up, which affects the adsorption effect. Reduce the conveying speed, get the new current speed, and repeat step (2).

[0015] In some embodiments, the effective adsorption range is calculated as follows: the minimum adsorption force required to ensure stable adsorption of the magnetic impurities is calculated based on the magnetic permeability and minimum mass of the magnetic impurities; the critical distance at which the magnetic field can generate an effective adsorption force on the magnetic impurities is determined based on the magnetic field strength of the magnetic separator; and the effective adsorption range of the magnetic separator acting on the upper surface of the belt is determined based on the critical distance.

[0016] The above one or more technical solutions address the problem that recycled aggregates often contain lightweight impurities such as plastics and garbage bag fragments, as well as metallic impurities such as iron nails and steel bar fragments. By setting up a downward-sloping feed channel and connecting a horizontal air duct in the middle of the feed channel, lightweight impurities can be blown to the impurity outlet for separation before the recycled aggregates enter the screening stage. This prevents lightweight impurities from clogging the subsequent screening structure from the source and is adapted to the chaotic nature of recycled aggregate impurities. The support roller on one side of the conveyor belt is set as a magnetic separator roller, and a diversion plate separates the aggregates from the metallic impurities, preventing metallic impurities from mixing into qualified aggregates and affecting the performance of concrete. Attached Figure Description

[0017] The dimensions and scales in the accompanying drawings do not represent the actual dimensions and scales of the product. The drawings are for illustrative purposes only, and some non-essential elements or features have been omitted for clarity.

[0018] Figure 1 This is a front view of the impurity sorting system for recycled aggregates from solid waste in an embodiment of the present invention; Figure 2 This is a perspective view of the impurity sorting system for recycled aggregate from solid waste in an embodiment of the present invention; Figure 3 This is a schematic diagram of the air separation device model in an embodiment of the present invention; Figure 4 This is a schematic diagram of the internal structure of the magnetic separator in an embodiment of the present invention; Figure 5 This is a schematic diagram of the "human"-shaped diversion channel model of the magnetic separator in an embodiment of the present invention; Figure 6 This is a flowchart illustrating the optimization method for the inclination angle of the discharge channel and the distance between the discharge channel inlet and the air duct interface in an embodiment of the present invention. Figure 7 This is a flowchart illustrating the method for optimizing the conveyor belt running speed and magnetic force in an embodiment of the present invention. In the diagram, 1. Air separation device, 2. Horizontal air duct, 3. Upper vibrating screen, 4. Lower vibrating screen, 5. Aggregate bearing layer, 6. Guide trough; 7. Magnetic separation device, 8. Transmission mechanism, 9. Conveyor belt, 10. Magnetic separation drum, 11. Central shaft, 12. "A" shaped diversion channel, 13. Support mechanism, 14. Base, 15. Magnetic impurity outlet, 16. Qualified aggregate outlet. Detailed Implementation

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0021] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0022] In this invention, terms such as "upper," "lower," "side," and "bottom" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are merely relational terms determined for the convenience of describing the structural relationship of the various components or elements of this invention, and do not specifically refer to any component or element in this invention, and should not be construed as limiting this invention.

[0023] In this invention, terms such as "connection" should be interpreted broadly, indicating a fixed connection, an integral connection, or a detachable connection; it can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can determine the specific meaning of the above terms in this invention based on the specific circumstances, and they should not be construed as limitations on this invention.

[0024] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0025] This embodiment provides an impurity sorting system for recycled aggregates from solid waste, including an air classifier 1, a multi-layer vibrating screen system, and a magnetic separator 7 arranged sequentially from top to bottom. It can be positioned within the confined space between the aggregate feeding end and the mixing drum of a concrete mixing plant. The air classifier 1 is connected to the end of the construction solid waste aggregate conveying equipment, the multi-layer vibrating screen system is fixedly connected to the frame of the mixing plant, and the non-magnetic aggregate channel outlet of the magnetic separator 7 is directly connected to the aggregate inlet of the mixing drum. Recycled aggregates from construction solid waste, after being processed by crushing equipment, can be conveyed to the downward-sloping inlet of the air classifier 1. Qualified recycled aggregates, after air classification, screening, and magnetic separation, fall directly into the mixing drum inlet, adapting to the continuous production needs of a mixing plant.

[0026] In the sorting system, the air separation device 1 includes an inclined downward material channel, the inlet of which is the feed port for recycled aggregate, and a multi-layer vibrating screen system below the discharge port; the middle section of the inclined downward material channel is connected to the horizontal air duct 2, a fan is provided on one side of the horizontal air duct 2, and an impurity outlet is provided on the other side; the magnetic separation device 7 includes a conveyor belt 9, which is located directly below the outlet of the multi-layer vibrating screen system, and a supporting roller on one side of the conveyor belt 9 is a magnetic separation roller 10, with a diverting plate arranged axially below the magnetic separation roller 10 for separating aggregate and metal impurities.

[0027] To address the issue that recycled aggregates often contain lightweight impurities such as plastics and garbage bag fragments, as well as metallic impurities such as iron nails and steel bar fragments, a downward-sloping feed channel is installed with a horizontal air duct 2 connected in the middle of the channel. This allows lightweight impurities to be blown to the impurity outlet for separation before the recycled aggregates enter the screening stage, preventing them from clogging the subsequent screening structure and adapting to the chaotic nature of recycled aggregate impurities. Furthermore, a magnetic separator roller 10 is installed on one side of the conveyor belt 9, and a flow divider separates the aggregates from the metallic impurities, preventing metallic impurities from mixing into the qualified aggregates and affecting the concrete performance.

[0028] The air separation device 1 connects to the aggregate feed inlet of the concrete mixing equipment, including a downward-sloping feed channel. A horizontal air duct interface is located in the middle of the feed inlet, sealingly connected to a horizontal air duct 2. A fan is installed at the air inlet of the air duct, and the air outlet connects to a lightweight waste collection box. Specifically, the upper end of the feed channel is connected to the end of the construction solid waste conveying equipment via a flange, and the lower end is vertically connected to the upper screen feed inlet of the multi-layer vibrating screen system. The air duct interface opens horizontally in the middle section of the feed channel. Utilizing the density difference between the aggregate and lightweight impurities, the recycled aggregate slides naturally down the feed channel, allowing flexible impurities entangled on the aggregate to naturally float to the surface during the descent. Horizontal airflow then blows lightweight impurities such as garbage bags and woven bag fragments away from the aggregate and into the lightweight waste collection box, while simultaneously preventing impurities from contacting the screen and transmission components, thus avoiding screen blockage. For example, the fan and air duct interface are connected via a 200×250mm rectangular flange, with a sealing gasket installed at the interface to prevent air leakage. The equipment uses a Greenhammer W-GB fan, with a 380V / 220V customizable three-phase asynchronous motor, a speed of 1450-1750rpm, an air volume of 8500-12000m³ / h, a fan outlet area of ​​0.5m², an air velocity of 10m / s, a calculated wind force of 30.63N, and a power requirement of 612.5W.

[0029] The multi-layer vibrating screen system includes an upper vibrating screen 3, a lower vibrating screen 4, and an aggregate support layer 5 arranged sequentially from top to bottom. The discharge port of the aggregate support layer 5 is connected to the inlet of the magnetic separator 7 below via a guide groove 6. Both the upper vibrating screen 3 and the lower vibrating screen 4 include a screen frame and a screen mesh. The screen frame is a welded manganese steel frame structure. The upper screen mesh has square mesh openings, and the lower screen mesh has rectangular mesh openings, with the longer side of the rectangular mesh openings being less than or equal to the side length of the square mesh openings. The feed inlet of the upper screen mesh is vertically connected to the bottom of the discharge channel. For example, the upper screen is a 30mm×30mm rectangular mesh stainless steel or wear-resistant steel wire mesh, which is detachably fixed by bolts and used to intercept oversized aggregates with a particle size greater than 31.5mm; the lower screen is a 30mm×10mm rectangular mesh wire mesh (30mm is the transverse aperture and 10mm is the longitudinal aperture), also bolted, used to intercept slender aggregates with an aspect ratio greater than 3. Only qualified aggregates with a particle size ≤31.5mm and an aspect ratio ≤3 are allowed to pass through. The aggregates screened by the upper vibrating screen 3 and the lower vibrating screen 4 fall onto the aggregate bearing layer 5. The size of the upper screen ensures that aggregates within the qualified particle size range can pass through smoothly, and the rectangular mesh design of the lower layer can intercept slender particles with excessive aspect ratios, solving the problem of reduced workability and mechanical properties of concrete caused by excessive needle-like and flaky particles.

[0030] A transmission mechanism 8 is provided at the bottom of the aggregate support layer 5. The transmission mechanism 8 is connected to the drive shaft of the vibration mechanism. Specifically, the transmission mechanism 8 includes a connecting part fixed to the bottom of the aggregate support layer 5. The bottom of the connecting part is connected to the drive shaft of the vibration mechanism via a transmission rod. Furthermore, the end of the drive shaft of the vibration mechanism is connected to an inclined disk, and the end of the transmission rod is eccentrically connected to the inclined disk. To avoid motion interference, the transmission rod can be a hook-shaped hinge rod. The disk surface is at a preset inclination angle with the axis of the drive shaft, for example, 80°. The center distance from the connection point of the disk and the hinge rod to the axis of the drive shaft is 200-300mm (preferably 280mm), and the total length of the hinge rod is 900-1000mm (preferably 980mm). The eccentric rotation of the disk drives the screen frame to perform vertical and horizontal combined vibration, causing the aggregate to jump and centrifugal on the screen surface, thereby improving screening efficiency.

[0031] The multi-layer vibrating screen system is connected to the base 14 via a support mechanism 13. The support mechanism 13 includes multiple support springs with spring stiffness matching the vibration frequency. These springs are used to bear the load of the screen frame movement and absorb vibration impact. The motor of the excitation mechanism is fixed to the side of the base 14.

[0032] A magnetic separator 7 is mounted on a base 14, positioned between multiple support springs. The magnetic separator 7 includes a housing with an inlet at its top. A conveyor belt 9 is located below the inlet inside the housing. The conveyor belt 9 has at least two support rollers, one of which is a magnetic separator roller 10. A flow divider is axially positioned below the magnetic separator roller 10 to separate aggregates from metallic impurities. Exemplarily, the magnetic separator roller 10 contains permanent magnets or windings to form a magnetic field, and its outer periphery may be covered with magnetic material to adsorb metallic impurities from the aggregates. The central shaft 11 of the magnetic separator roller 10 is connected to a drive motor, serving as the driving roller. The other support rollers are connected to the central shaft 11 via bearings, serving as driven rollers. The conveyor belt 9 is made of a non-magnetic material, and its operating speed is linked to the rotational speed of the magnetic separator roller 10.

[0033] The diversion plate is located below the magnetic separator drum 10. The aggregate screened by the multi-layer vibrating screen system falls onto the conveyor belt 9. When the conveyor belt 9 rolls to the magnetic separator drum 10, the metal impurities in the aggregate are adsorbed. Qualified aggregate falls along the edge of the conveyor belt 9 to one side of the diversion plate and is output from the qualified aggregate outlet 16 of the multi-layer vibrating screen system. Metal impurities continue to be conveyed until the adsorption force of the magnetic separator drum 10 is lost, and they fall from the conveyor belt 9 to the other side of the diversion plate and are output from the magnetic impurity outlet 15. It can be understood that the movement path of qualified aggregate can be analyzed based on the speed of the conveyor belt 9, and the position of the diversion plate can be reasonably set. To facilitate the output of metal impurities and qualified aggregate, a "V"-shaped diversion channel 12 is provided below the diversion plate, centered on the diversion plate. The first branch channel of the "V"-shaped diversion channel 12 is located on the side where the non-magnetic aggregate falls naturally and connects to the aggregate inlet of the mixing drum. The second branch channel is located below the conveyor belt 9 and connects to the metal waste collection box, realizing the efficient separation of metal impurities and qualified aggregate, and at the same time realizing the resource recovery of metal impurities.

[0034] The working principle of the above screening system is as follows: Material containing recycled aggregate from construction solid waste is fed into the inclined downward feed channel of the air separator 1 through the main feed inlet. The blower is started, and air is horizontally supplied to the downward feed channel through the air duct interface, blowing out and collecting lightweight impurities such as garbage bags and woven bag fragments. The aggregate, after removing lightweight impurities, enters the upper screen of the multi-layer vibrating screen system from the bottom of the feed channel. Driven by the excitation section, it undergoes compound vibration with the screen frame. Oversized aggregates with a particle size greater than 31.5mm are intercepted by the upper screen. The aggregate passing through the upper screen falls into the lower layer. The lower screen traps slender aggregates with an aspect ratio greater than 3, while aggregates with an aspect ratio ≤ 3 and a particle size ≤ 31.5 mm pass through the lower screen and enter the qualified aggregate outlet. The qualified aggregates fall onto the conveyor belt 9 of the magnetic separator 7 and are conveyed to the magnetic separator drum 10. Under the action of the magnetic field, the metal impurities in the aggregates are adsorbed at the end of the conveyor belt 9 and fall naturally as the drum rotates downwards. They are discharged along the magnetic impurity channel of the "V"-shaped diversion channel 12. The aggregates with metal impurities removed are discharged along the non-magnetic aggregate channel and sent into the concrete mixing drum.

[0035] The aforementioned system, after removing lightweight impurities from the recycled aggregate from construction solid waste via air separation device 1, enters a multi-layer vibrating screen system for grading and impurity removal. Qualified aggregate then undergoes magnetic separation device 7 to remove metallic impurities, ultimately achieving multi-dimensional control over lightweight impurities, particle size and aspect ratio, and metallic impurities, producing recycled aggregate that meets standards. Furthermore, the air separation, screening, and magnetic separation processes are integrated from top to bottom, eliminating the need for additional conveying and installation space. This fully adapts to the compact site layout requirements of concrete mixing plants, significantly reducing space occupancy. Simultaneously, it accommodates the natural downward flow of recycled aggregate, reducing aggregate accumulation and adhesion, and improving the processing efficiency of recycled aggregate. This avoids the waste of space due to dispersed layouts and specifically addresses the problems of difficult impurity separation, equipment clogging, and low processing efficiency in recycled aggregate screening.

[0036] The various devices in the aforementioned screening system work together to achieve efficient impurity removal and grading of recycled aggregates. However, the inclination angle of the air classifier 1 towards the feed channel and the distance from the inlet to the air duct interface directly affect the downward flow pattern of the recycled aggregates, the floating effect of light impurities, and the air classification stripping efficiency. The suitability of these two parameters is closely related to the conveying flow rate of the recycled aggregates. Therefore, in practical applications, when the flow rate Q to the feed channel of the air classifier 1 is known, it is necessary to optimize the parameters of the feed channel in conjunction with relevant constraints to ensure the air classification effect and guarantee the subsequent system screening effect from the front end. Specifically, assuming the flow rate Q of recycled aggregate fed to the discharge channel of air separator 1 is known, and the coefficient of friction μ between the recycled aggregate and the discharge channel surface, the gravitational acceleration g, the fan speed, and the width B of the discharge channel are also known, to ensure sufficient time for the recycled aggregate to separate from the lightweight impurities during its descent, the descent time must be guaranteed. This means the recycled aggregate must meet a minimum time requirement from the discharge channel inlet to the air duct interface. Furthermore, to ensure the fan can blow away the soft impurities, the speed at the air duct interface cannot be too fast, and the descent aggregate layer cannot be too dispersed or too piled up. Excessive dispersion leads to low processing efficiency, while excessive piled-up prevents complete separation of the lightweight aggregate. Therefore, the aggregate accumulation thickness during the descent must also be controlled. Based on these constraints, the optimal tilt angles α and L are iteratively solved, and finally, iterative calibration is performed to satisfy all conditions. The steps are summarized as follows: (1) Convert the known flow rate into the instantaneous flow rate, preset the initial slope α0, and record it as the current slope; based on the current slope, calculate the distance from the inlet to the air duct interface to meet the minimum time requirement, and use it as the current distance L0, that is, the distance from the inlet to the air duct interface; (2) Based on the current slope α0 and the current distance L0, calculate the time taken for the recycled aggregate to reach the air duct interface from the feed channel inlet and the instantaneous downward speed v0. Determine whether the time taken meets the time requirement. If it does, execute step (3). (3) Based on the instantaneous downward velocity v0 and the size of the air duct interface (cross-sectional area 0.05m²), and combined with the residence time formula t=L0 / v0, calculate the residence time t0 of the aggregate in the air duct interface area; determine whether t0 meets the air classification time requirement, i.e., the minimum time for air stripping, for example, 0.1 seconds: If t0 does not meet the air separation time requirement, then reduce the slope α0, reduce the downward speed, extend the dwell time, return to step (2), and repeat the calculation of v0 and t0 after adjustment; If t0 meets the air separation time requirement, and considering the instantaneous flow rate and v0, we can substitute these values ​​into the aggregate layer thickness formula h0=Q. 瞬时÷(v0×B), calculate and estimate the instantaneous thickness h0 of the aggregate, and further determine whether the aggregate layer thickness h0 is within a reasonable range (0.1-0.13m); if so, the current slope is the target slope, and the corresponding distance L0 is recorded as the shortest distance requirement from the material inlet to the air duct interface; if not, continue to fine-tune α0. If h0 is too small, decrease α0; if h0 is too large, increase α0. After adjustment, return to step (2) and repeat the calculation of v0 and t0 until the air classification time and aggregate layer thickness both meet the requirements.

[0037] It is understandable that in the above iteration process, each adjustment of the slope needs to be a fine-tuning, and 1° can be used as the adjustment gradient.

[0038] The minimum time requirement for air stripping depends on the wind force generated by the blower. Insufficient wind force will not effectively strip the lightweight impurities adhering to the surface of the recycled aggregate, while excessive wind force may cause qualified aggregate to be blown away, resulting in loss. Therefore, it is necessary to determine the blower wind force parameters suitable for this screening system. The specific calculation method is as follows:

[0039] Where ρ is the density of air (1.225 kg / m³ in this design), A is the outlet area of ​​the fan, and v is the air velocity. In this design, the outlet area of ​​the fan is A = 0.5 m (2), and the velocity is v = 10 m / s, so the wind force is 30.63 N.

[0040] When the wind force generated by the fan is F(wind) = 30.63 N, the garbage bag will be blown away by the wind, and its acceleration a(bag) can be calculated using Newton's second law:

[0041] In this design, the mass of the garbage bag is taken as m = 0.2 kg, and the acceleration of the garbage bag is a(bag) = 153.13 m / s (2), indicating that the garbage bag will be blown away with a large acceleration under the action of the fan. Since the density difference between the lightweight impurities and the aggregate is too large, it is sufficient to ensure that the garbage bag is removed without affecting the aggregate.

[0042] The power requirement of the fan is calculated based on the air velocity v:

[0043] Substituting the values, the power requirement of the fan is P=612.5 W, indicating that the fan needs to reach this power to work effectively. Within the applicable range, the Greenhamr W-GB fan was selected.

[0044] In the design of a multi-layer vibrating screen system, the main design parameters for screening aggregates include vibration frequency, amplitude, and screen mesh size. Based on these parameters, efficient screening of aggregates of different particle sizes can be achieved. Assuming each batch of aggregate to be processed is 10 kg, and considering the typical aggregate density, the structural frame diameter is set at 1000 mm to ensure sufficient screening.

[0045] Vibration frequency is one of the key factors affecting screening efficiency. The vibration frequency f can be calculated using the following formula:

[0046] Where k is the spring stiffness of the vibration system, and m is the mass of the material being screened. In this design, the spring stiffness is taken as k = 4000 N / m, and the material mass is taken as m = 10 kg. Therefore, the vibration frequency is f = 3.18 Hz, and the screen will vibrate 3.18 times per second.

[0047] Amplitude is another key design parameter of a vibrating screen, affecting the jumping motion of materials. The amplitude A can be calculated using the following formula:

[0048] Where F is the vibration excitation force, m is the mass of the material, and ω is the angular frequency of the vibration, ω=2πf. In this design, the excitation force F=1000 N, the mass of the material m=10 kg, the angular frequency is ω=2π×3.18=19.97 rad / s, and the amplitude A=0.25 m.

[0049] The core parameters of the multi-layer vibrating screen system, such as vibration frequency and amplitude, have been calculated and determined using formulas, enabling efficient screening and conveying of qualified aggregates. The screened qualified aggregates then need to pass through a magnetic separator 7 to remove metallic impurities. The running speed of the conveyor belt 9 and the magnetic force of the magnetic separator 10 directly affect the adsorption effect of the magnetic separator 10 on magnetic impurities, while also needing to be compatible with the stable discharge flow rate of the vibrating screen. Based on this, the discharge flow rate of the multi-layer vibrating screen system is estimated, and the running speed of the conveyor belt 9 and the magnetic force are optimized to ensure efficient coordination between the magnetic separation and screening stages, guaranteeing sufficient adsorption of magnetic impurities while also ensuring the stability of aggregate conveying. Specifically, the following steps are included: (1) The dimensions of the conveyor belt 9 and the magnetic separator 10 are known. The initial magnetic force of the magnetic separator 10 is set. Since magnetic impurities are only adsorbed during contact with the magnetic separator 10, the contact length is the core basis for calculating the reference speed. Combined with the existing diameter of the magnetic separator 10, the contact length between the upper surface of the conveyor belt 9 and the magnetic separator 10 is calculated. Based on the magnitude of the magnetic force of the magnetic separator 10, the effective adsorption range is determined. Combined with the minimum adsorption time, the reference speed, i.e. the maximum speed constraint, is calculated as the current speed. The minimum adsorption time is the shortest time to ensure that the magnetic impurities are fully adsorbed.

[0050] (2) Based on the current speed, the size of the conveyor belt 9 and the estimated instantaneous flow rate of the feed, estimate the maximum thickness of the aggregate layer accumulated on the conveyor belt 9 and determine whether it is within a reasonable range. If so, the current magnetic force and speed are what we need. If the thickness is lower than the lower limit of the reasonable range, it means that the aggregate is too scattered and affects the transmission efficiency. Increase the magnetic force of the magnetic separator 10, the diameter of the magnetic separator 10, or add a magnetic separator 10 to one side of the current magnetic separator 10 and return to step (1). If the thickness is higher than the upper limit of the reasonable range, it means that the aggregate is too piled up and affects the adsorption effect. Reduce the conveying speed to obtain a new current speed and repeat step (2).

[0051] Based on this, it can assist in the selection of the size and magnetic force of the magnetic separator 10, as well as the conveying speed of the conveyor belt 9, so as to ensure the transmission efficiency while effectively adsorbing impurities.

[0052] The effective adsorption range is calculated as follows: based on the magnetic permeability and minimum mass of the magnetic impurities, the minimum adsorption force required to ensure stable adsorption of the magnetic impurities is calculated. This minimum adsorption force must simultaneously meet two core constraints: first, to prevent the magnetic impurities from falling off during the operation of the conveyor belt 9; and second, to ensure that the magnetic impurities can still be stably adsorbed when they move with the magnetic separator 10 to the point where they contact the magnetic separator 10 below the conveyor belt 9, and naturally fall off after leaving the magnetic field range, thus ensuring thorough separation of impurities. Specifically, firstly, the magnetic permeability μ and minimum mass m of the magnetic impurities (iron nails, steel rebar fragments) are determined. These can be estimated by considering the particle size range of common magnetic impurities in recycled aggregates in engineering practice, taking the minimum mass value corresponding to common particle sizes, the gravitational acceleration g, and the friction coefficient f between the conveyor belt 9 surface and the magnetic impurities. Secondly, the gravity acting on the magnetic impurities themselves, the frictional force exerted by the conveyor belt 9 on the impurities, and the additional downward gravitational component experienced by the magnetic impurities as they move with the magnetic separator drum 10 to the lower contact point are calculated. Considering the cylindrical structure of the magnetic separator drum 10, this component is generated by the downward component of the impurity's own weight along the drum's radial direction. The minimum adsorption force must simultaneously overcome the impurity's own weight, the frictional force generated by the conveyor belt 9 during operation, and the downward gravitational component when the impurity moves with the magnetic separator drum 10 to the lower contact point. This ensures stable adsorption at this location. Simultaneously, the upper limit of the adsorption force must be controlled to ensure that after the magnetic impurities leave the magnetic field range, the adsorption force disappears or is less than the sum of the impurity's own weight and frictional force, allowing for natural detachment. Therefore, the minimum adsorption force must be greater than the combined force of the impurity's gravity, friction, and the gravitational component at the contact point below. Taking this combined force as the minimum adsorption force ensures both adsorption stability and smooth subsequent detachment.

[0053] Based on the magnetic field strength of the magnetic separator drum 10, the critical distance at which the magnetic field can generate an effective adsorption force for magnetic impurities is determined. Specifically, firstly, the magnetic field strength H, the minimum adsorption force, and the magnetic dipole moment p of the magnetic impurities are determined (which can be derived from the material, minimum volume, and magnetic permeability μ of the magnetic impurities; the volume is estimated by combining the minimum mass with the impurity density) are determined. Secondly, based on the physical principle of the adsorption force of the magnetic field on magnetic impurities, the correlation between the adsorption force, the magnetic field strength, and the critical distance is derived. The adsorption force generated by the magnetic field on magnetic impurities decreases with increasing distance. The critical state is when the adsorption force equals the minimum adsorption force, and the corresponding distance is the critical distance. Finally, the critical distance is calculated in reverse using this correlation. That is, when the adsorption force generated by the magnetic field is exactly equal to the minimum adsorption force, the corresponding distance is the farthest distance at which the magnetic field can generate an effective adsorption force. Beyond this distance, stable adsorption cannot be achieved.

[0054] Based on this critical distance, the effective adsorption range of the magnetic separator 10 acting on the upper surface of the belt is determined. Specifically, the magnetic separator 10 is cylindrical and serves as a support roller for the conveyor belt 9. Its axial length is consistent with the width of the conveyor belt 9. The radial adsorption range is defined by combining the critical distance. Taking the axis of the magnetic separator 10 as the center, the area extending radially outward along the roller to the critical distance is the radial effective adsorption area. This area must completely cover the contact area between the conveyor belt 9 and the magnetic separator 10 to ensure that all magnetic impurities within the contact area can be effectively adsorbed. Finally, the overall effective adsorption range is defined by combining the axial length of the roller. In the axial direction, the effective adsorption range covers the entire axial length of the magnetic separator 10 (matching the width of the conveyor belt 9), and in the radial direction, it covers the area from the roller surface to the critical distance. This determines the effective adsorption range of the magnetic separator 10 acting on the upper surface of the belt, ensuring that this range can cover the area where impurities may appear.

[0055] The scope of protection of this invention is defined only by the claims. Thanks to the teachings of this invention, those skilled in the art will readily recognize that alternative structures to the structures disclosed herein can be used as feasible alternative implementations, and that the implementations disclosed herein can be combined to produce new implementations, which also fall within the scope of the appended claims.

Claims

1. A system for sorting impurities from solid waste recycled aggregate, characterized by, It includes an air separation device, a multi-layer vibrating screen system, and a magnetic separation device arranged sequentially from top to bottom; the air separation device includes an inclined downward material channel, the inlet of which is the feed port of the recycled aggregate, and the multi-layer vibrating screen system below the discharge port; the middle section of the inclined downward material channel is connected to a horizontal air channel, and a fan is provided on one side of the horizontal air channel and an impurity outlet is provided on the other side.

2. The impurity sorting system of recycled aggregates of solid waste as claimed in claim 1 wherein, The multi-layer vibrating screen system includes an upper vibrating screen, a lower vibrating screen, and an aggregate bearing layer arranged sequentially from top to bottom. The discharge port of the aggregate bearing layer is connected to the inlet of the magnetic separator below through a guide groove.

3. The impurity sorting system of recycled aggregates from solid waste as claimed in claim 2 wherein, Both the upper and lower vibrating screens include a screen frame and a screen mesh. The upper screen mesh has square mesh openings, and the lower screen mesh has rectangular mesh openings. The length of the long side of the rectangular mesh opening is less than or equal to the side length of the square mesh opening.

4. The impurity sorting system of recycled aggregates from solid waste as claimed in claim 1 wherein, A transmission mechanism is fixedly connected to the bottom of the multi-layer vibrating screen system, and the transmission rod of the transmission mechanism is eccentrically connected to the drive shaft of the excitation mechanism.

5. The impurity sorting system of solid waste recycled aggregate as claimed in claim 2, wherein, The magnetic separator includes a conveyor belt located directly below the outlet of the multi-layer vibrating screen system. A support roller on one side of the conveyor belt is a magnetic separator roller. A flow divider is provided axially below the magnetic separator roller to separate aggregates and metal impurities.

6. The impurity sorting system for recycled solid waste aggregate as described in claim 5, characterized in that, The two sides of the diversion plate are respectively connected to the qualified aggregate discharge port and the metal impurity collection box.

7. The impurity sorting system for recycled solid waste aggregate as described in claim 1, characterized in that, Assuming the flow rate of recycled aggregate fed to the air classifier's discharge channel is known, and the width of the discharge channel is known, optimize the inclination angle of the discharge channel and the distance between the discharge channel inlet and the air duct interface: (1) Set the initial slope and record it as the current slope; based on the current slope, calculate the distance from the inlet to the air duct interface to meet the minimum time requirement, and use it as the current distance; (2) Based on the current slope and current distance, calculate the time and instantaneous downward speed of the recycled aggregate from the inlet of the discharge channel to the air duct interface, and determine whether the time consumption meets the time requirement. If it does, execute step (3). (3) Based on the instantaneous downward velocity and the dimensions of the air duct interface, calculate the residence time of the aggregate in the air duct interface area and determine whether the time meets the air classification time requirement: If the condition is not met, the slope is reduced to obtain a new current slope, the current distance is recalculated, and the process returns to step (2). If satisfied, combine the instantaneous flow rate and instantaneous descent speed to estimate the instantaneous thickness of the aggregate, and further determine whether the aggregate layer thickness is within a reasonable range; if yes, the current slope and current distance are the optimization results; if no, adjust the slope to obtain a new current slope, recalculate the current distance, and return to step (2); until both the air classification time and the aggregate layer thickness meet the requirements.

8. The impurity sorting system of solid waste recycled aggregate as claimed in claim 7, wherein, If the instantaneous thickness of the aggregate is less than the lower limit of the reasonable value range, decrease the slope; if the instantaneous thickness of the aggregate is greater than the upper limit of the reasonable value range, increase the slope.

9. The impurity sorting system for recycled solid waste aggregate as described in claim 5, characterized in that, The discharge flow rate of the multi-layer vibrating screen system is estimated, and the conveyor belt speed and magnetic force are optimized based on the conveyor belt width, the initial size of the magnetic separator drum, and the magnetic force. (1) Determine the effective adsorption range on the upper surface of the conveyor belt based on the size of the magnetic separator drum, the initial magnetic force and the width of the conveyor belt; calculate the reference speed based on the effective adsorption range and the minimum adsorption time required to ensure that the metal impurities are effectively adsorbed, and use it as the current speed. (2) Based on the current speed, conveyor belt size, and estimated instantaneous feed flow rate, estimate the maximum thickness of the aggregate layer accumulated on the conveyor belt and determine whether it is within a reasonable range: If the thickness is lower than the lower limit of the reasonable value range, it means that the aggregate is too loose, which affects the transmission efficiency. Increase the magnetic force of the magnetic separator, the diameter of the magnetic separator, or add a magnetic separator to one side of the current magnetic separator, and return to step (1). If the thickness is higher than the upper limit of the reasonable value, it means that the aggregate is too piled up, which affects the adsorption effect. Reduce the conveying speed, get the new current speed, and repeat step (2).

10. The impurity sorting system of solid waste recycled aggregate as claimed in claim 9, wherein, The effective adsorption range is calculated as follows: the minimum adsorption force required to ensure stable adsorption of magnetic impurities is calculated based on the magnetic permeability and minimum mass of the magnetic impurities; the critical distance at which the magnetic field can generate an effective adsorption force on the magnetic impurities is determined based on the magnetic field strength of the magnetic separator; and the effective adsorption range of the magnetic separator acting on the upper surface of the belt is determined based on this critical distance.

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