Dense-phase pneumatic conveying system for plastic fragments

Abstract

The invention relates to the field of solid waste recovery management and utilization, and provides a plastic fragment dense-phase pneumatic conveying system which comprises an air cannon arch breaking function module, a stirring fluidization function module and a gas-solid mixed conveying function module. The air cannon arch breaking module comprises a plurality of air cannon distributed on a straight barrel section and a cone section of the stock bin, and the air cannon and the wall of the stock bin are connected at a certain angle and are automatically controlled; the stirring fluidization module comprises a stirrer with a plurality of stirring teeth and an auxiliary disc, and a feeder for controlling the blanking speed; the gas-solid mixing and conveying module comprises a conveying tuyere with a pressure-stabilizing air bag, a mixing tee joint with a guide plate structure and an inner polishing and conveying pipeline with a large-radian elbow. Stable dense-phase conveying of plastic fragments can be achieved, the conveying amount can be accurately controlled, stock bin arching and pipeline blocking caused by compression of the plastic fragments are prevented, and the gas-solid mixing effect and the conveying efficiency are improved.

Description

Technical Field

[0001] The present invention relates to the field of recycling management and utilization of solid waste, and more specifically, to a pneumatic conveying system for plastic fragments. Background Art

[0002] 1. Pneumatic conveying is a material conveying technology that uses the fluid characteristics of gas-solid two-phase flow to complete the spatial transfer of fragments, particles or dust, and has the characteristics of environmental protection, stability and low energy consumption.

[0003] 2. The size of the plastic fragments obtained through pretreatment is 2-10 mm, showing the characteristics of irregular shape, uneven size distribution, low bulk density and high porosity. The mixing and fluidization of plastic fragments in gas are different from regular-shaped particles. There are large gaps and mutual friction between the fragments when plastics are piled up, which makes it easy for plastic fragments to appear compression, arching and blocking problems during pneumatic conveying, and it is difficult to convey stably. Summary of the Invention

[0004] 1. Regarding the problem that plastic fragments are difficult to convey stably, the present invention proposes a dense-phase pneumatic conveying system for plastic fragments. The purpose is to solve the pain points of easy arching, difficult fluidization and easy blocking of plastic fragments during the conveying process, and ensure stable plastic conveying during the conveying process.

[0005] 2. The present invention designs an air cannon arch-breaking module to solve the arching problem of plastic fragments in the silo; the air cannon arch-breaking module includes at least 3 air cannons, and the distribution of the air cannons is determined according to the structure of the conical section of the silo and the height of the agitator. The silo is divided into two sections, a straight section and a conical section, with one feed inlet, one pressurization port and several outer wall air cannon interfaces. The conical section is divided into upper and lower parts with the height of the agitator as the boundary, and the air cannon interfaces are evenly distributed on the upper half of the conical section. The other part of the air cannons is evenly distributed on the transition section connecting the straight section and the conical section. The air cannons are connected to the outer wall interfaces of the silo through flanges.

[0006] Preferably, the outer wall interface forms a certain angle with the outer wall of the silo, inclines downward and along the tangential direction of the inner wall of the silo.

[0007] Preferably, the air cannon is controlled by an electromagnetic valve for opening and closing, and is uniformly controlled by the DCS control system to be turned on. By changing the opening sequence and interval time, the arch-breaking effect can be controlled. The air cannon at a certain position can be repeatedly opened within the same control program, and the control program can be interlocked with the weight loss metering feedback, with high flexibility.

[0008] 3. The present invention designs a stirring and fluidizing module to ensure stable feeding; the stirrer is connected to the main shaft of the feeder by means of keyway connection and bolt fixation, and is driven by the same motor. The stirrer is located at the bottom of the silo and is designed according to the inner diameter of the bottom outlet of the silo and the dimensions of the conical section. There is a certain distance between the outer edge of the auxiliary disc and the silo wall.

[0009] Preferably, the stirrer is a multi-tooth axial flow stirrer, and is connected and fixed externally by an auxiliary disc with reinforcement bars.

[0010] Preferably, the teeth of the stirrer are of a triangular pyramid structure, and the direction of one of the edges is along the circumferential tangent direction during rotation.

[0011] Preferably, the main bottom plate of the stirrer is of a rhombus structure, and the edges perpendicular to the rotation direction are chamfered.

[0012] Preferably, the overall material of the stirrer and the connecting transmission parts is made of high-strength alloy steel.

[0013] 4. The present invention designs a gas-solid mixing and conveying module to achieve full mixing of gas and plastic fragments. The gas-solid mixing and conveying module includes at least two conveying air inlets, a mixing tee, a gas source and a conveying pipeline. The conveying air inlets and the discharging port of the feeder coexist in a cavity, where the gas and plastic fragments are preliminarily mixed; the mixing tee is an improved Y-shaped tee, which includes 1 conveying air inlet, 1 gas-solid two-phase flow inlet and 1 gas-solid two-phase flow outlet. The gas-solid two-phase flow inlet of the mixing tee is connected to the cavity at the discharging port of the feeder through a pipeline with the same inner diameter, and secondary mixing is carried out at the intersection of the tee; the conveying air inlet of the mixing tee is connected to the gas source to enhance the gas-solid two-phase mixing effect. The gas-solid two-phase flow outlet of the mixing tee is connected to the rear-end conveying pipeline; the connections are all in the form of flanges and are equipped with sealing gaskets. The gas source of the conveying air inlets can be the same gas source or multiple gas sources, and the specific gas volume ratio of each air inlet is determined according to the pipeline length, material characteristics and conveying efficiency.

[0014] Preferably, the conveying pipeline is an internally polished pipeline and is designed in multiple sections.

[0015] Preferably, the elbows of the conveying pipeline have a smooth transition, that is, the elbow radius needs to be greater than 15D and elbow concentration is avoided.

[0016] Preferably, the conveying pipeline is connected by flanges and is electrostatically bridged and grounded.

[0017] Compared with the prior art, the present invention has advantages in the following three aspects:

[0018] In this application, the air cannons are rationally arranged and at a certain angle with the silo wall, which can fully cover the root positions where materials may arch, thus enhancing the arch-breaking effect of the air cannons and reducing the consumption of compressed gas. This application solves the problem of difficult fluidization of plastic fragments by means of mechanical agitation at the bottom of the silo, enabling the materials to enter the feeder evenly. Moreover, a steering wheel structure with low resistance and high strength is designed to improve the anti-deformation ability and agitation effect of the agitator, thereby ensuring the service life and reliability of the agitator. This application proposes a method for strengthening the gas-solid mixing effect of a special-shaped mixing tee, preventing pipeline blockage caused by unstable pressure when plastic fragments enter the conveying pipeline, and having good conveying stability. The present invention is applicable to mixed plastic fragments containing impurities or pure plastic fragments. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the specific embodiments of the present invention or the prior art solutions, the following will further explain the drawings required for use in the description of the specific embodiments or the prior art. In all the drawings, similar devices or parts are generally identified by similar reference numerals. In the drawings, the devices or parts are not necessarily drawn to actual scale.

[0020] Figure 1 is a schematic structural diagram of an embodiment of the present invention.

[0021] Figure 2 is a schematic distribution diagram of the arch-breaking module of the air cannons in an embodiment of the present invention.

[0022] Figure 3 is a schematic top view structural diagram of the agitator in an embodiment of the present invention.

[0023] Figure 4 is a schematic cross-sectional structural diagram of the mixing tee in an embodiment of the present invention.

[0024] As shown in the figure, 1. Silo; 2. Air cannon; 3. Feeder; 4. Mixing tee; 5. Pressure gauge; 6. Large-radius elbow; 7. Target silo; 8. Pressurizing air inlet; 9. Conveying air inlet; 10. Conveying air outlet; 21. Straight section of the silo; 22. Conical section of the silo; 23. Air cannon body; 24. Connecting port of the conical-section air cannon; 25. Connecting port of the straight-section air cannon; 31. Agitating teeth; 32. Auxiliary disc; 33. Reinforcing strip; 34. Agitator connecting device; 35. Feeder body; 36. Variable-frequency motor with a speed reducer; 37. Conveying air pipeline with a flowmeter; 38. Pressure stabilizing air bag; 39. Electric ball valve; 41. Deflector structure; 42. Mixing cavity. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The following will describe in detail the embodiments of the technical solutions of the present invention with reference to the drawings, but it is not intended to limit the present invention.

[0026] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, 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.

[0027] In the present invention, terms such as "upper", "lower", "left", "right", "front", "rear", "vertical", "horizontal", "side", "bottom", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. They are only relational terms determined for the convenience of describing the structural relationships of various components or elements of the present invention and do not specifically refer to any component or element in the present invention and should not be construed as a limitation to the present invention.

[0028] In the present invention, terms such as "fixed connection", "connected", "connected to" should be understood in a broad sense, which may mean a fixed connection, an integral connection or a detachable connection; it may be directly connected or indirectly connected through an intermediate medium. For relevant scientific research or technical personnel in this field, the specific meanings of the above terms in the present invention can be determined according to specific circumstances and should not be construed as a limitation to the present invention.

[0029] This application provides a pneumatic conveying system, which can be used for the conveying and feeding of plastic fragments. Refer to Figure 1 , Figure 1 which is a schematic structural diagram of the pneumatic conveying system, including an air cannon arch-breaking module, a stirring fluidization module and a gas-solid mixed conveying module.

[0030] In an embodiment of the present application, as Figure 1 shown, the pneumatic conveying system includes a silo 1. The outer wall of the silo 1 is connected with a feed inlet 8 and a plurality of air cannon interfaces; materials can be conveyed into the silo 1 through the feed inlet 8 for storage; the air cannon 2 is fixed at the connection part between the conical section and the straight barrel section of the silo through an interface; the conical section of the silo is connected with the feeder 3 below through a flange. The discharge port of the feeder 3 is connected with a mixing tee 4, and a ball valve is installed at the connection to control the pipeline switch. The mixing tee 4 is connected with the rear-end conveying pipeline; the rear-end conveying pipeline monitors the pipeline pressure drop through a pressure transmitter 5 with reverse blowing and controls the direction through an elbow 6, and finally conveys the materials into the target silo 7 with a gas-solid separation device.

[0031] In the present disclosure, the above-mentioned materials are small-sized crushed materials of mixed plastics, specifically particulate materials, fragment materials or powder materials with a diameter less than 10 mm. The target silo 7 can be a target receiving device such as a reactor, a storage silo or a mixer. If gas-solid separation or nitrogen recovery is required, a cyclone separator can be installed between the rear end of the conveying pipeline and the target silo 7.

[0032] In this embodiment, the pressurizing air outlets 8, the conveying air outlets 9 and the conveying air outlet 10 of the pneumatic conveying system share a common air source. The air source is provided by a gas compressor, and the type of gas is dehydrated air.

[0033] In this embodiment, as Figure 2 shown, the air cannon arch-breaking module includes a silo with a conical section, at least four air cannons and its DCS automatic control system; the silo is provided with a feed inlet and a pressurizing port; the air cannon interfaces are welded and fixed to the silo wall after tilting at a certain angle and are regularly distributed in the middle and lower parts of the silo.

[0034] After crushing, the size of the plastic decreases, and the plastic fragments can be mixed with the conveying gas to form a more uniform gas-solid two-phase flow during the pneumatic conveying process. However, due to the increase in specific surface area, the friction force between the fragments increases, resulting in the problem of arching easily occurring during the flow between the silo and the pipeline, especially at the variable diameter of the silo or the pipeline, such as the connection between the straight section 21 and the conical section 22 of the silo, pipeline diameter change, etc. When the silo 1 is loaded with more than 80%, the plastic fragments at the lower part are compressed by extrusion and gravity, and it is extremely easy to arch at the above-mentioned connection and cannot enter the range of the agitator. The use of the air cannon arch-breaking module can effectively solve the problem of non-discharging caused by arching in the silo during the conveying process.

[0035] In this embodiment, the automatic control of the air cannon is implemented through the DCS system, which is interlocked with the vector weighing feedback of the silo, or through staged program control. When there is no change in the vector weighing feedback of the silo, it indicates that plastic arching has occurred in the silo, and the DCS system immediately activates a single or multiple air cannons simultaneously, and arch breaking can be successfully achieved. When controlled by the staged program, the entire conveying process is divided into three stages: starting conveying, stable conveying, and before the end of conveying, corresponding to different levels of material in the silo; during the starting conveying stage, the use of the air cannon mainly functions for continuous arch breaking, and the air cannons in the conical section start and stop in a certain order, with an interval of 10 - 20 s; during the stable conveying stage, the use of the air cannon mainly functions to prevent arching, and the air cannons in the conical section and the straight section start and stop in a certain order in a cycle, with an interval of 30 - 60 s; during the stage before the end of conveying, the use of the air cannon mainly functions to clean the hanging material, and after the air cannons in the straight section are turned on once, the air cannons in the conical section start and stop in a certain order in a cycle, with an interval of 30 - 60 s.

[0036] The air cannon 23 is connected to the conical section 22 of the silo through an equal-diameter air cannon interface 24, and the air cannon 23 is connected to the straight section 21 of the silo through an equal-diameter air cannon interface 25. The air cannon interface determines the installation position and action direction of the air cannon. Therefore, by adjusting the position and angle of the air cannon interface, the root of the material arching can be completely covered, achieving the effect of continuous arch breaking and helping fluidization.

[0037] In this embodiment, the connection ports 24 and 25 are evenly distributed in 4 layers, and the number of air cannons and their connection ports can be appropriately increased or decreased according to the arch breaking situation. The angle of the connection port 24 is 10 - 20 degrees between the axis and the horizontal upward direction and 15 - 35 degrees between the tangent of the bin wall and the axis, slanting downward. In other embodiments, the angle is appropriately adjusted according to the cone section angle and the installation position. The angle of the connection port 25 is 15 - 25 degrees between the axis and the horizontal upward direction and 15 - 35 degrees between the tangent of the bin wall and the axis, slanting downward. In other embodiments, the angle is appropriately adjusted according to the radius of the straight cylinder section.

[0038] In this embodiment, as Figure 3 shown, the stirring and fluidizing module includes a stirrer part and a feeder part. The stirrer part includes stirring teeth 31, auxiliary discs 32, reinforcing bars 33, and a connection mechanism 34. The function of the stirring teeth 31 is to agitate the plastic fragments at the bottom of the bin, break up the agglomerated materials, and keep them in a fluidized state to assist in discharging. The angle, length, and thickness of the stirring teeth 31 are related to the cone structure of the bin. The auxiliary disc 32 includes two concentric rings with different diameters and 33 reinforcing round bars. The auxiliary disc 32 is connected to the shaft sleeve through a bottom plate, providing sufficient stability and structural strength for the stirrer system. Specifically, the auxiliary disc can make the stress of the stirring teeth balanced and improve the anti-deformation ability.

[0039] The overall structure 35 of the feeder is disc-shaped, and its rotor rotates horizontally around the main shaft. Its power is provided by a variable-frequency motor 36 with a speed reducer and frequency control is completed. The connection mechanism 34 of the stirrer is connected to the main shaft of the feeder through a keyway and maintains the same rotational speed. Therefore, the feeding speed of the fluidized plastic fragments is controlled by the rotational speed of the feeder.

[0040] In this embodiment, the gas-solid mixed transportation module includes at least two transportation air vents, a mixing tee joint, a compressed gas air source, and a transportation pipeline. The transportation air vents and the discharging port of the feeder coexist in a cavity. After the plastic fragments enter the feeder and pass through the cavity, they enter the discharging port. When the cavity blade rotates to the same position as the transportation air vent 38, the plastic fragments are gas-solid mixed with the transportation air for the first time. The transportation air vent 38 can be designed with an air bag to stabilize the transportation air pressure. When the transportation air passes through the pipeline 37 with a flow meter, the flow rate of the transportation air can be measured. Before starting the transportation, the bin needs to be pressurized to 100 - 300 kPa. The function of the electric ball valve 39 is to cut off the discharging and seal the transportation air pipeline to maintain the bin pressure. When the electric ball valve is opened for transportation, the bin pressure is supplemented by air intake through the pressurizing air vent at this time.

[0041] In this embodiment, as Figure 4As shown, the mixing three-way pipe is a Y-shaped three-way pipe with a baffle plate structure 41. The plastic fragments after the first gas-solid mixing are secondarily mixed with the conveying air at the mixing cavity 42, thereby enhancing the gas-solid two-phase mixing effect. The flow direction after mixing is as shown by Figure 4 the bold arrow. The conveying air enters the pipeline from the conveying air inlet 10. After the plastic fragments are secondarily mixed, they are fully and evenly mixed with the conveying air, and finally enter the target silo through the conveying pipeline with a pressure gauge 5 and a large-arc elbow 6. A level gauge or a weight detector can be installed in the target silo or the silo to provide real-time feedback on the conveying rate, and then by adjusting the rotational speed of the feeder and the pressurized air volume, the precise quantitative conveying of the plastic fragments can be achieved.

[0042] In this embodiment, to avoid static electricity generated by friction of the plastic fragments, the interfaces of all conveying pipelines are connected by flanges and are electrostatically bridged and grounded.

[0043] Comparative Example 1: Referring to a similar conveying system, an air cannon is not used, a fluidizing air disc is used for arch breaking, and an L-shaped two-tooth stirrer is used for agitation. The included angle between the baffle plate in the mixing three-way pipe and the horizontal is 90°; Comparative Example 2: An air cannon is used for arch breaking with an average use frequency of 15 seconds / time, and other conditions are the same as those in Comparative Example 1.

[0044] Example 1: The use frequency of the air cannon is controlled in segments, and the calculated average use frequency is 30 seconds / time, in cooperation with an L-shaped two-tooth stirrer. The included angle between the baffle plate in the mixing three-way pipe and the horizontal is 90°; Example 2: The stirrer structure has two teeth and an auxiliary disc for improving the structural strength and stability, and other conditions are the same as those in Example 1; Example 3: The included angle between the baffle plate in the mixing three-way pipe and the horizontal is 45°, and other conditions are the same as those in Example 2.

[0045] In the above comparative examples and examples, the test results of the influence of the key structures of the pneumatic conveying system on the conveying efficiency are shown in Table 1. Since the plastic fragments are easily compressed during the entire conveying process, the conveying efficiency of the system is measured by the gas-to-material mass ratio, and the gas-to-material mass ratio is calculated by the formula:

[0046]

[0047] where M 塑料 is the mass of the plastic fragments conveyed per unit time, which is fixed at 6000 kg / h for each test; ρ 气 is normal temperature and pressure air, taking 1.2 kg / m 3 ; V 气 is the total gas flow rate, including the flow rates of all conveying gases, pressurized gases, and air cannon gases. The gas source is compressed air at 0.65 MPa.

[0048]

[0049] In the embodiment, first, the air cannons are reasonably arranged and used in different blanking stages, and cooperate with the agitator to carry out a disturbing effect to ensure the continuous fluidization of the plastic fragments in the silo. Secondly, the conveying process is precisely controlled by controlling the flow rates of all conveying air, pressurized air, and the blanking amount of the feeder. Then, the mixing tee with a deflector is used to further improve the gas-solid mixing effect. Finally, stable conveying is carried out through a conveying pipeline with a smooth inner wall and large-radius elbows. As can be seen from Table 1, the system can achieve a material-gas mass ratio of 9.6 and realize dense-phase conveying of plastic fragments.

[0050] It should be understood that although this specification is described according to the embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in the various embodiments can be appropriately combined, or improved or transformed according to the above description, and all these improvements and transformations should fall within the protection scope of the appended claims of the present invention.

Claims

1. A pneumatic conveying system for plastic fragments, characterized in that, The air cannon arch-breaking module and the stirring fluidization module cooperate with each other and achieve precise arch-breaking control and stable pneumatic conveying through weight-loss metering feedback, including: The air cannon arch-breaking module, which has a silo with a conical section, at least four air cannons and their automated control systems; the silo is provided with a feed inlet and a pressurized air inlet, the connection ports of the air cannons are inclined downward and are connected and fixed to the silo wall along the tangential direction of the silo and are regularly distributed in the middle and lower parts of the silo; The stirring fluidization module, which has a disk-type axial-flow stirrer and a feeder, and the stirrer is provided with an auxiliary disk structure; the teeth of the stirrer are in the shape of a triangular pyramid, and one of the edges is in the tangential direction of the circumference during rotation, and its design dimensions are correlated with the dimensions of the conical section of the silo; The gas-solid mixed conveying module, which has at least two conveying air inlets, a mixing tee, a compressed gas source and a conveying pipeline; the first conveying air inlet and the discharge port of the feeder are commonly connected to a cavity, the mixing tee is provided with a diversion structure and one of its interfaces is connected to the second conveying air inlet for strengthening the gas-solid two-phase mixing effect.

2. The gas source of the air cannon according to claim 1 is compressed gas, including nitrogen, air and plastic cracking gas.

3. The air cannon according to claim 1 is continuously and automatically controlled by a DCS module and can be started and stopped periodically according to the discharging state of the silo.

4. The stirrer according to claim 1 is connected to the main shaft of the feeder through a keyway and rotates coaxially.

5. The number of stirring teeth according to claim 4 is 2-4, and the movement trajectories of different stirring teeth are concentric and of different diameters.

6. There is a control valve between one end of the mixing tee with a diversion structure according to claim 1 and the discharge port of the feeder, and the other end is connected to the rear conveying pipeline.

7. The conveying pipeline according to claim 6 is an internally polished pipeline, and the elbow radius needs to be greater than 15D.

8. The conveying pipeline according to claim 6 is connected by flanges and is electrostatically bridged and grounded.

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