Granule post-processing conveying system

Abstract

The invention relates to the field of high polymer material production equipment, in particular to a granule post-treatment conveying system which comprises an underwater granule cutting unit, a first solid-liquid separator, a desorption unit, a hydraulic conveying unit, a drying and dewatering unit, a screening unit, a vertical pneumatic conveying unit and a mixing and homogenizing unit which are sequentially connected. The desorption unit comprises a staying tank and a heating part, the staying tank is provided with a gas collecting pipe, the solid-liquid mixed solution is fed into the staying tank through a feeding pipe, the heating part is used for heating the solid-liquid mixed solution, the granules stay in the staying tank, and the water body heats the granules so that the VOC organic volatile matter can be desorbed from the granules; after being desorbed, the VOCs escape to the VOC centralized processing unit through the gas collecting pipe, and the granules without the VOCs are conveyed to the hydraulic conveying unit through the discharging pipe. According to the device and the method, waste heat of the cut granules and the granulating water is fully utilized, so that only a small amount of energy is needed to heat the water body, VOC organic volatile matters are desorbed from the granules, and energy consumption is reduced.

Description

Technical Field

[0001] This application relates to the field of polymer material production equipment, and in particular to a granule post-processing and conveying system. Background Technology

[0002] Polyolefins are a type of thermoplastic plastic, used in injection molding or blow molding to produce plastic products. In existing technology, the general production process from polyolefin powder to granules is as follows: 1. Extrusion into strips using an extruder → 2. Underwater pelletizing of the strips → 3. Dehydration and drying of the granules → 4. Screening → 5. Pneumatic conveying of the granules → blending and homogenization. Using pneumatic conveying of granules results in dust and stringiness due to friction and collisions between the granules and the equipment, and between granules themselves; this reduces the quality of the granules and requires significant energy consumption.

[0003] Chinese invention patent application number CN202010580313.4 discloses a polyolefin pellet post-processing system; after the pellets are cut into pellets underwater, the pellets are transported by water power to eliminate the conditions for pellet dust generation and reduce energy consumption.

[0004] During the production of polyolefin granules, VOCs (volatile organic compounds) remain in the polymerization reaction stage of the powder and are also generated during the extrusion granulation process. VOCs can have adverse effects on human health. Therefore, polyolefin granule manufacturers will take certain measures to reduce the amount of VOCs in polyolefin granules.

[0005] In existing technologies, steam and hot air can be used to heat the granules, causing the VOCs in the granules to desorb from the high-molecular-weight polyolefin. The VOCs are then carried away by fluids, thereby reducing the amount of VOCs in the granules and improving their quality. However, existing technologies require a continuous energy supply to maintain the steam or hot air, significantly increasing energy costs in granule production. Summary of the Invention

[0006] In order to reduce the cost of treating VOCs in pellets and reduce energy consumption, this application provides a pellet post-processing and conveying system.

[0007] This application provides a pellet post-processing conveying system, which adopts the following technical solution: A pellet post-processing and conveying system includes, in sequence, an underwater pelletizing unit, a first solid-liquid separator, a desorption unit, a hydraulic conveying unit, a drying and dewatering unit, a screening unit, a vertical pneumatic conveying unit, and a blending and homogenizing unit. The underwater pelletizing unit cuts the pellets into pellets, which then form a primary solid-liquid mixture with water. The first solid-liquid separator concentrates the solid-liquid mixture, which is then conveyed to the desorption unit via a pipeline. The desorption unit includes a retention tank and a heating element. The retention tank has an inlet pipe, an outlet pipe, and a gas collection pipe. The solid-liquid mixture is fed into the retention tank through the inlet pipe. The heating element heats the solid-liquid mixture, and the pellets remain in the retention tank. The water heats the pellets to desorb VOCs (volatile organic compounds). After desorption, the VOCs escape through the gas collection pipe to a centralized VOC treatment unit. The VOC-free pellets are then conveyed to the hydraulic conveying unit via the outlet pipe. The hydraulic conveying unit conveys the pellets using water.

[0008] By adopting the above technical solution, the residual heat of the pellets and pelletizing water after cutting is fully utilized, so that only a small amount of energy is needed to heat the water in the retention tank, so that VOCs are desorbed from the pellets, thereby reducing energy consumption and reducing the cost of pellet post-processing.

[0009] Optionally, the desorption unit further includes a second solid-liquid separator, a hot water circulation tank, and a hot water circulation pump; the heating element is used to heat the water in the hot water circulation tank, and the hot water circulation pump pumps the water in the hot water circulation tank to the retention tank; the second solid-liquid separator is connected to the discharge pipe of the retention tank, and the second solid-liquid separator is used to concentrate the solid-liquid mixture, and the water separated by the second solid-liquid separator flows back to the hot water circulation tank through a pipeline; a portion of the water separated by the first solid-liquid separator is transported through a pipeline to mix with the solid-liquid mixture concentrated by the second solid-liquid separator to reduce the temperature of the solid-liquid mixture; the mixed solid-liquid mixture is transported by the hydraulic conveying unit.

[0010] By adopting the above technical solution, the solid-liquid mixture is filtered twice by the first and second solid-liquid separators. Since the residual heat of the material strip during the extrusion process is fully utilized, the heat supplement of the desorption unit only needs to consider the temperature difference of about 5°C in the hot water circulation tank; that is, only a small amount of steam consumption is needed to achieve effective desorption of VOCs; at the same time, the energy consumption is greatly reduced and the cost of post-processing of the granules is reduced.

[0011] Optionally, the desorption unit includes at least two of the retention tanks, and several of the retention tanks are connected in sequence by pipes, so that the solid-liquid mixture flows through several of the retention tanks in sequence.

[0012] By adopting the above technical solution, the residence time of the granules in the retention tank can be ensured, and the uniformity of water heating of the granules can be improved; thereby improving the uniformity of VOC desorption in different granules and improving the desorption effect of VOCs.

[0013] Optionally, the residence tank includes a tank body and a stirring assembly. The stirring assembly includes a driving component, a rotating shaft, and stirring blades. The rotating shaft is vertically arranged. The driving component is fixed to the tank body and drives the rotating shaft to rotate. The stirring blades are fixedly connected to the rotating shaft.

[0014] By adopting the above technical solution, the stirring component and the flowing water can destroy the stagnant layer on the surface of the granules, reduce the mass transfer resistance of VOCs, so that VOCs can desorb from the high molecular weight polyolefins in the granules and enter the water, thereby improving the VOC removal efficiency.

[0015] Optionally, the retention tank includes a flow-retarding assembly, which includes several flow-retarding plates. The flow-retarding plates are fixedly connected to the inner peripheral wall of the tank. Each flow-retarding plate has a mounting hole for a rotating shaft to pass through, and a flow port for water to pass through. The top of the flow-retarding plate has a downward-sloping first guide surface, and the bottom of the flow-retarding plate has an upward-sloping second guide surface. The granules flow along the first guide surface to the flow port, and the desorbed gas monomers flow along the second guide surface to the flow port. The flow ports of the several flow-retarding plates are staggered on both sides of the central axis of the tank, so that the water flows from top to bottom through the several flow-retarding plates, and the stirring blades are arranged between adjacent flow-retarding plates.

[0016] By adopting the above technical solution, the flow path of the solid-liquid mixture in the residence tank is extended, and the residence time of the granules in the solid-liquid mixture in the residence tank is extended, so that the VOCs in the granules can fully absorb heat and desorb.

[0017] Optionally, the desorption unit further includes a dissolved gas structure, which includes a dissolved gas tank, a first dissolved gas water delivery pipe, and a dissolved gas release device. The first dissolved gas water delivery pipe passes through the tank body, and one end of the first dissolved gas water delivery pipe is connected to the dissolved gas tank. The dissolved gas tank delivers dissolved gas water to the residence tank through the first dissolved gas water delivery pipe. The dissolved gas release device is disposed on the first dissolved gas water delivery pipe and is connected to the first dissolved gas water delivery pipe. The dissolved gas release device is used to release supersaturated gas in the dissolved gas water in the form of tiny bubbles. The released bubbles are used to capture the desorbed VOC volatile organic compound gas.

[0018] By adopting the above technical solution, the bubbles released by the dissolved air water will capture VOCs diffused into the water body during the rising process; thereby carrying the VOCs from the water body to the upper area of ​​the tank; so that more VOCs can be collected to the centralized VOC treatment unit through the gas collection pipeline, improving the desorption effect of VOCs.

[0019] Optionally, multiple dissolved gas releasers are provided, and the multiple dissolved gas releasers are arranged at intervals along the first dissolved gas water delivery pipeline.

[0020] By adopting the above technical solution, the uniformity of bubble distribution within the tank can be improved when the dissolved gas releaser releases bubbles.

[0021] Optionally, the desorption unit includes three retention tanks, which are named first retention tank, second retention tank and third retention tank in sequence. The solid-liquid mixture flows through the first retention tank, the second retention tank and the third retention tank in sequence. The dissolved gas structure is connected to the second retention tank and delivers dissolved gas water into the second retention tank.

[0022] By adopting the above technical solution, the residence time of the granules in the retention tank can be ensured, and the uniformity of water heating of the granules can be improved; thereby improving the uniformity of VOC desorption in different granules and improving the desorption effect of VOCs.

[0023] Optionally, the dissolved gas structure further includes a rotary joint and a second dissolved gas water delivery pipe; the first dissolved gas water delivery pipe is rotatably and sealedly connected to the rotating shaft through the rotary joint; the rotating shaft has a hollow section at the end away from the driving component, and a flow channel is provided inside the hollow section, which is connected to the first dissolved gas water delivery pipe; the second dissolved gas water delivery pipe is horizontally fixed on the rotating shaft, and the second dissolved gas water delivery pipe is connected to the flow channel, and dissolved gas release devices are provided at intervals along the dissolved gas water delivery direction.

[0024] By adopting the above technical solution, when the rotating shaft rotates, it can drive the dissolved air releaser to release bubbles at different positions, thereby improving the uniformity of bubble distribution in the tank and enhancing the capture efficiency and effect of the bubbles released by the dissolved air water on VOCs in the water.

[0025] Optionally, the second dissolved air water conveying pipeline includes a first straight section, an arc section, and a second straight section in sequence. The first straight section and the second straight section are arranged radially along the tank body, and the arc section is arranged along the inner peripheral wall of the tank body.

[0026] By adopting the above technical solution, the first straight segment and the second straight segment are arranged along the radial direction of the tank, and dissolved gas release devices are also provided on the first straight segment and the second straight segment to further improve the uniformity of dissolved gas water release bubbles.

[0027] In summary, this application includes at least one of the following beneficial technical effects: 1. Fully utilize the residual heat of the pellets and pelletizing water after cutting, so that only a small amount of energy is needed to heat the water in the retention tank, so that VOCs desorb from the pellets, thereby reducing energy consumption and reducing the cost of pellet post-processing. 2. By using the first and second solid-liquid separators to filter the solid-liquid mixture twice, the residual heat of the material strip during the extrusion process is fully utilized. The heat supplement of the desorption unit only needs to consider the temperature difference of about 5°C in the hot water circulation tank. That is, only a small amount of steam consumption is needed to achieve effective desorption of VOCs. At the same time, the energy consumption is greatly reduced and the cost of post-processing of the granules is reduced. 3. As the dissolved air bubbles rise, they capture VOCs that have diffused into the water, carrying them from the water to the upper part of the tank. This allows more VOCs to be collected in the centralized VOC treatment unit via the gas collection pipe, improving the desorption effect of VOCs. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the granular material post-processing and conveying system in Example 1.

[0029] Figure 2 This is a schematic diagram of the granular material post-processing and conveying system in Example 1.

[0030] Figure 3 This is a schematic diagram of the underwater pelletizing unit in Example 1.

[0031] Figure 4 This is a schematic diagram of the structure of the first solid-liquid separation unit in Example 1.

[0032] Figure 5 This is a schematic diagram of the residence tank in Example 1.

[0033] Figure 6 This is a schematic diagram of the residence tank in Example 2.

[0034] Figure 7 This is a schematic diagram of the granule post-processing and conveying system in Example 2.

[0035] Figure 8 This is a schematic diagram of the desorption unit in Example 3.

[0036] Figure 9 This is a schematic diagram of the dissolved gas structure in Example 4.

[0037] Figure 10 This is a schematic diagram of the desorption unit in Example 5.

[0038] Figure 11 This is a schematic diagram of the desorption unit in Example 6.

[0039] Figure 12 yes Figure 11 Enlarged view of point A in the middle.

[0040] Figure 13 This is a schematic diagram of the dissolved gas structure in Example 6.

[0041] Explanation of reference numerals in the attached drawings: 1. Extruder; 2. Underwater pelletizing unit; 21. Underwater pelletizer; 22. Pelletizing water heat exchanger; 23. Pelletizing water circulating pump; 24. Pelletizing water return tank; 3. First solid-liquid separation unit; 31. First solid-liquid separator; 32. First water filter; 33. Water flow control valve assembly; 4. Desorption unit; 41. Retention tank; 411. Tank body; 4111. Feed pipe; 4112. Discharge pipe; 4113. Gas collection pipe; 42. Material pump; 43. Agitator assembly; 431. Drive component; 432. Rotating shaft; 4321. Flow channel; 433. Agitator blade; 44. Slow flow assembly; 441. Slow flow Plate; 4411, First guide surface; 4412, Second guide surface; 442, Mounting hole; 443, Flow port; 48, Dissolved gas structure; 481, Dissolved gas tank; 482, First dissolved gas water conveying pipeline; 483, Dissolved gas release device; 484, Rotary joint; 485, Second dissolved gas water conveying pipeline; 4851, First straight section; 4852, Arc section; 4853, Second straight section; 5, Hydraulic conveying unit; 51, Stirring feeder; 52, Hydraulic conveying pump; 6, Drying and dehydration unit; 7, Screening unit; 8, Vertical pneumatic conveying unit; 9, Blending and homogenization unit; 10, VOC centralized treatment unit; 11, Vacuum component. Detailed Implementation

[0042] The following is in conjunction with the appendix Figure 1 -Appendix Figure 13 This application will be described in further detail.

[0043] Example 1

[0044] This application discloses a pellet post-processing conveying system. (Refer to...) Figure 1 and Figure 2 The pellet post-processing and conveying system includes an underwater pelletizing unit 2, a first solid-liquid separation unit 3, a desorption unit 4, a hydraulic conveying unit 5, a drying and dewatering unit 6, a screening unit 7, a vertical pneumatic conveying unit 8, and a blending and homogenization unit 9, which are connected in sequence.

[0045] Reference Figure 2 and Figure 3 The extruder 1 is a device that melts and plasticizes plastic powder and extrudes it into strips. The underwater pelletizing unit 2 includes an underwater pelletizer 21 head, a pelletizing water return tank 24, a pelletizing water circulation pump 23, and a pelletizing water heat exchanger 22. The underwater pelletizer 21 head is located at the outlet of the extruder 1. The underwater pelletizer 21 head cuts the molten and extruded pellets into pellets underwater, and the pellets are mixed with the pelletizing water to form a solid-liquid mixture. In this embodiment, the extrusion temperature of the strips is 220°C, the temperature of the pelletizing water input to the underwater pelletizer 21 head is 50-60°C, and the temperature of the solid-liquid mixture formed by the pellets and pelletizing water is approximately 70°C.

[0046] Taking polyolefin granulation as an example, VOCs (volatile organic compounds) remain in the polymerization reaction stage of plastic powder, and are also generated during the extrusion granulation process. VOCs can have adverse effects on human health; therefore, further processing of the granules is required during the post-processing and conveying of the granules to desorb the VOCs from the granules.

[0047] In polyolefin granules, hydrocarbons are molecular crystals, and the adsorption between molecules is mainly due to van der Waals forces. That is, VOCs and high molecular weight polyolefins are adsorbed by van der Waals forces.

[0048] Desorption is the reverse process of adsorption. Small-molecule VOCs need to absorb energy to overcome the van der Waals forces between the VOCs and the high-molecular-weight polyolefins, thus allowing the VOCs to desorb from the polyolefins and escape into the external fluid environment. The desorption time of small-molecule VOCs is temperature-dependent; given suitable desorption temperature and time, the concentration of VOCs in the granules can be maintained at a very low level.

[0049] Reference Figure 2 and Figure 4 The solid-liquid mixture is transported via pipeline to the first solid-liquid separation unit 3, which includes a first solid-liquid separator 31, a first water filter 32, and a water flow control valve group 33. The first solid-liquid separator 31 is used to separate the granules and water in the solid-liquid mixture. The filtered granules are transported to the desorption unit 4. The filtered water is filtered again by the first water filter 32. Part of the water flows back to the pelletized water return tank 24 via a branch, and the rest is transported to the desorption unit 4 via another branch equipped with the water flow control valve group 33.

[0050] Reference Figure 4 and Figure 5The desorption unit 4 includes a residence tank 41, a heating element, and a material pump 42. In this embodiment, the residence tank 41 includes a tank body 411 and a stirring assembly 43. The tank body 411 is used to contain a solid-liquid mixture, and the stirring assembly 43 is used to stir and mix the solid-liquid mixture.

[0051] The tank 411 has an inlet pipe 4111, an outlet pipe 4112, and a gas collection pipe 4113. The granules and water separated by the first solid-liquid separation unit 3 are fed into the tank 411 through the inlet pipe 4111. The heating element (not shown in the figure) can be an electric heating element, a heating jacket, or a steam heating element, etc.; the heating element is used to heat the solid-liquid mixture to increase the water temperature inside the tank 411. In this embodiment, the heating element heats the water temperature inside the retention tank 41 to 90°C. In other embodiments, the temperature inside the retention tank 41 can also be different temperatures such as 88°C, 89°C, 90.5°C, and 91°C.

[0052] The heating element heats the water containing the granules from 70°C to 90°C, at which point the gaps between the granules are filled with hot water. The granules remain in the retention tank 41, where the hot water heats them, causing VOCs to absorb energy and desorb from the granules. After desorbing from the granules, the water-insoluble VOCs form bubbles in the water, rise to the surface, and escape from the retention tank 41. Subsequently, the VOCs escape through the gas collection pipe 4113 to the VOC centralized treatment unit 10. In the prior art, there are many ways to treat VOCs, such as activated carbon adsorption, organic solvent adsorption, condensation, and catalytic combustion. Therefore, the VOC centralized treatment unit 10 in this embodiment can use any of these methods to treat VOCs. This embodiment does not elaborate on the specific structure of the VOC centralized treatment unit 10.

[0053] In this embodiment, the residence time of the granules in the residence tank 41 is no less than 30 minutes to allow the VOCs in the granules to fully absorb energy and thus fully desorb. In other embodiments, the residence time of the granules in the residence tank 41 can also be 32 minutes, 30 minutes, or 40 minutes, etc. The operator can determine the actual residence time of the granules in the residence tank 41 based on the solubility of the VOCs in the granules and the solubility of the granules in the solid-liquid mixture.

[0054] Reference Figure 5The stirring assembly 43 includes a drive component 431, a rotating shaft 432, and a stirring blade 433. The rotating shaft 432 is vertically arranged, the drive component 431 is fixed to the tank body 411, and the drive component 431 drives the rotating shaft 432 to rotate. The stirring blade 433 is fixedly connected to the rotating shaft 432. The stirring assembly 43 is used to stir and mix the solid-liquid mixture in the tank body 411, so that the granules are evenly distributed in the water, and the water evenly heats the granules. This allows the VOCs in the granules to fully absorb energy, thereby desorbing, diffusing, and escaping into the external gas. On the other hand, the stirring assembly 43 and the flowing water can break the stagnant layer on the surface of the granules, reduce the mass transfer resistance of VOCs, so that VOCs can desorb from the high molecular weight polyolefins in the granules and enter the water, thereby improving the VOC removal efficiency.

[0055] Reference Figure 2 and Figure 4 A vacuum component 11 is installed on the pipe between the gas collection pipe 4113 and the VOC centralized treatment unit 10. The vacuum component 11 is used to extract the gas inside the residence tank 41, so that the top area of ​​the residence tank 41 has a certain degree of vacuum; so that VOCs can escape from the water to the top area of ​​the residence tank 41 and be collected. In this embodiment, the vacuum component 11 is a vacuum pump; in other embodiments, the vacuum component 11 can also be an exhaust fan.

[0056] The volume of tank 411 can be determined based on the flow rate of the solid-liquid mixture and the particle concentration in the mixture. For example, if the flow rate of the solid-liquid mixture into tank 411 is 204 t / h and the residence time of the mixture in tank 411 is 30 min, then the effective volume of tank 411 is 102 cubic meters. The volume of the tank is greater than 102 cubic meters to allow for a vacuum area at the top. Thus, from the time the solid-liquid mixture flows into tank 411 until it flows out, the particle concentration in tank 411 can be maintained for 30 minutes.

[0057] Reference Figure 4 The granules and water after VOC removal are discharged through the discharge pipe 4112. The material pump 42 in the desorption unit 4 then pumps the solid-liquid mixture to the hydraulic conveying unit 5. The hydraulic conveying unit 5 conveys the granules through the water.

[0058] Reference Figure 4 In this embodiment, the hydraulic conveying unit 5 includes a stirring feeder 51 and a hydraulic conveying pump 52. The pipeline of the hydraulic conveying unit 5 is horizontally arranged. The stirring feeder 51 and the hydraulic conveying pump 52 are arranged on the pipeline of the hydraulic conveying unit 5 to drive the solid-liquid mixture to flow a long distance in the pipeline.

[0059] Reference Figure 2 The solid-liquid mixture, after being conveyed by the hydraulic conveying unit 5, enters the drying and dehydration unit 6. The centrifugal dryer in the drying and dehydration unit 6 separates the solid-liquid mixture. The separated water is transported back to the pelletizing water return tank 24 of the underwater pelletizing unit 2 via pipeline. The separated pellets are dried and then conveyed to the screening unit 7. The vibrating screen in the screening unit 7 grades the pellets and conveys the pellets that meet the size requirements to the vertical pneumatic conveying unit 8. The pipeline in the vertical pneumatic conveying unit 8 is vertically arranged, thus using air power to vertically convey the pellets to the blending and homogenizing unit 9. After the blending and homogenizing unit 9 blends and homogenizes the pellets, the pellets are then packaged.

[0060] In the prior art, the drying and dehydration unit 6, screening unit 7, vertical pneumatic conveying unit 8, and blending and homogenizing unit 9 of the granules are widely used, and the above units are not the focus of the technical solution of this application; therefore, the specific structure of these units will not be described in detail in the embodiments of this application.

[0061] The implementation principle of a pellet post-processing conveying system according to an embodiment of this application is as follows: The desorption effect of VOCs from pellets is related to the desorption temperature, diffusion environment, and heat transfer uniformity of the pellets. In this embodiment, the residual heat of the pellets and pelletizing water after cutting is fully utilized, thus requiring only a small amount of energy to heat the water in the retention tank 41, allowing VOCs to desorb from the pellets, thereby reducing energy consumption and lowering the cost of pellet post-processing. Compared to pneumatic conveying of pellets, the hydraulic conveying unit 5 conveys pellets by water, and the hydraulic conveying unit 5 also consumes less energy, saving costs in pellet post-processing.

[0062] Example 2 The difference between Example 2 and Example 1 is as follows: Reference Figure 6 The retention tank 41 also includes a flow-regulating assembly 44, which comprises several flow-regulating plates 441. The flow-regulating plates 441 are disposed inside the tank body 411, with the plates arranged vertically at intervals, and are fixedly connected to the inner peripheral wall of the tank body 411. Each flow-regulating plate 441 has a mounting hole 442 for a rotating shaft 432 to pass through, for mounting the stirring assembly 43. The outer periphery of each flow-regulating plate 441 has a flow port 443 for water to pass through. The flow ports 443 of the several flow-regulating plates 441 are staggered on both sides of the central axis of the tank body 411, allowing water to flow downwards through the plates 441. The flow buffer 441 divides the internal chamber of the tank 411 into several sub-chambers, allowing the solid-liquid mixture to flow through these sub-chambers sequentially. This extends the flow path of the solid-liquid mixture within the residence tank 41 and prolongs the residence time of the granules in the solid-liquid mixture within the residence tank 41, allowing the VOCs in the granules to be fully desorbed.

[0063] The top of the flow-retardant plate 441 is provided with a downward-sloping first guide surface 4411. The granules flow along the first guide surface 4411 to the flow port 443, thereby facilitating the flow of the solid-liquid mixture in the retention tank 41. The bottom of the flow-retardant plate 441 is provided with an upward-sloping second guide surface 4412. The desorbed VOCs exist in the water in the form of bubbles. The VOC bubbles flow along the second guide surface 4412 to the flow port 443 and float to the surface, thereby facilitating the removal of VOCs from the water and allowing the VOCs to be collected at the VOC centralized treatment unit 10 for harmless treatment.

[0064] Reference Figure 7 In addition, the desorption unit 4 also includes a hot water circulation tank, a hot water circulation pump, and a second solid-liquid separator. A heating element is used to heat the water in the hot water circulation tank. In this embodiment, the heating element is configured as a heating pipe for conveying steam, thereby using high-temperature steam to heat the water.

[0065] Reference Figure 6 The first solid-liquid separator 31 feeds the separated granules into the retention tank 41. The hot water circulation pump pumps the water in the hot water circulation tank into the feed pipe 4111 at the top of the retention tank 41. The water in the hot water circulation tank and the granules mix in the upper area of ​​the retention tank 41 to form a solid-liquid mixture.

[0066] Reference Figure 6 The second solid-liquid separator is connected to the discharge pipe 4112 of the retention tank 41. The second solid-liquid separator is used to separate the desorbed solid-liquid mixture. The water separated by the second solid-liquid separator flows back to the hot water circulation tank through the pipeline. The granules separated by the second solid-liquid separator are mixed with the water separated by the first solid-liquid separator 31. The mixed solid-liquid mixture is transported by the hydraulic conveying unit 5.

[0067] The implementation principle of a pellet post-processing conveying system according to an embodiment of this application is as follows: Reference Figure 7 The first solid-liquid separator 31 separates the granules from the water phase, at which point the granules temperature is approximately 70°C. Subsequently, the granules filtered by the first solid-liquid separator 31 are fed into the retention tank 41 of the desorption unit 4. Water at 90°C from the hot water circulation tank is transported via pipeline and mixed with the 70°C granules. The granules remain in the retention tank 41 for at least 30 minutes. During this time, the higher-temperature water heats the granules, raising their temperature to between 85°C and 90°C, allowing the VOCs in the granules to fully absorb energy and desorb from the high-molecular-weight polyolefins. During this time, as the water flows through the tank 411, the granules move from the top to the bottom of the tank 411. Finally, the solid-liquid mixture of granules and water is discharged from the tank 411 through the discharge pipe 4112.

[0068] Reference Figure 7 Subsequently, the second solid-liquid separator separates the solid-liquid mixture flowing out of the retention tank 41. The filtered water in the second solid-liquid separator is then transported to the hot water circulation tank, where a heating element heats the water to maintain a temperature of 90°C. The solids filtered out by the second solid-liquid separator mix with the water filtered out by the first solid-liquid separator 31 to form a new solid-liquid mixture, which is then pumped to the hydraulic conveying unit 5 by the material pump 42. Because the water filtered out by the first solid-liquid separator 31 is at a lower temperature (approximately 70°C), the temperature of the remixed solid-liquid mixture is also lower. This reduces the risk of particle adhesion when the hydraulic conveying unit 5 transports the solid-liquid mixture over long distances, thereby improving particle quality.

[0069] In this embodiment, the solid-liquid mixture is filtered twice using the first solid-liquid separator 31 and the second solid-liquid separator. Since the residual heat of the material strip during the extrusion process is fully utilized, the heat supplement of the desorption unit 4 only needs to consider the temperature difference of about 5°C in the water in the hot water circulation tank; that is, only a small amount of steam consumption is needed to achieve effective desorption of VOC organic volatiles.

[0070] In summary, the synergistic cooperation between the first solid-liquid separation unit 3 and the desorption unit 4 not only achieves VOC desorption but also significantly reduces energy consumption and lowers the cost of pellet post-processing.

[0071] Example 3 The difference between Example 3 and Example 2 is as follows: Reference Figure 8 The desorption unit 4 includes three residence tanks 41, which are named the first residence tank, the second residence tank, and the third residence tank in sequence. The solid-liquid mixture flows through the first residence tank, the second residence tank, and the third residence tank in sequence. The first residence tank, the second residence tank, and the third residence tank are all connected to the VOC centralized treatment unit 10 through the gas collection pipe 4113.

[0072] Reference Figure 8 The granules separated by the first solid-liquid separator 31 are fed into the first retention tank, and the hot water circulation pump also transports the hot water in the hot water circulation tank into the first retention tank, so that the granules and the high-temperature water are mixed into a solid-liquid mixture, and the water is used to heat the granules.

[0073] Reference Figure 8The implementation principle of the pellet post-processing conveying system in this application embodiment is as follows: Since the solid-liquid mixture flows through the first residence tank, the second residence tank and the third residence tank in sequence, the residence time of the pellets in the residence tank 41 can be ensured, and the uniformity of water heating of the pellets can be improved; thereby improving the uniformity of VOC desorption in different pellets and improving the desorption effect of VOCs.

[0074] Example 4 The difference between Example 4 and Example 2 is as follows: Reference Figure 9 The desorption unit 4 further includes a gas-dissolving structure 48, which includes a gas-dissolving tank 481, a first dissolved gas water delivery pipe 482, and a gas-dissolving release device 483. The gas-dissolving tank 481 dissolves oxygen-free gas in water under a certain pressure to form supersaturated dissolved gas water. In this embodiment, the gas-dissolving tank 481 dissolves nitrogen gas in water under a certain pressure to form supersaturated dissolved gas water.

[0075] Reference Figure 9 A first dissolved air water delivery pipe 482 passes through the tank 411, with one end connected to the dissolved air tank 481. The dissolved air tank 481 delivers dissolved air water to the residence tank 41 through the first dissolved air water delivery pipe 482. A dissolved air release device 483 is installed on the first dissolved air water delivery pipe 482 and is connected to it. The dissolved air water flows into the tank 411 through the dissolved air release device 483. After depressurization, the dissolved air water releases a large number of microbubbles, which expand in volume under the action of the water. In this embodiment, both the outer and inner walls of the first dissolved air water delivery pipe 482 are coated with a heat-insulating coating to reduce the influence of external water. In other embodiments, the first dissolved air water delivery pipe may also be provided with an intermediate heat-insulating filling layer to reduce the influence of external water.

[0076] In this embodiment, the amount of dissolved air water input into tank 411 is smaller than the amount of solid-liquid mixture input; therefore, the impact of supplying dissolved air water into tank 411 on the water temperature inside the tank is minimal. Furthermore, the input temperature of the hot water circulation tank can be adjusted to compensate for the impact of dissolved air water input on the water temperature, ensuring that the water temperature inside tank 411 is maintained near the design value.

[0077] The implementation principle of a pellet post-processing conveying system according to an embodiment of this application is as follows: Reference Figure 9After desorption from the granules, VOCs diffuse into the water. Since VOCs are poorly soluble in water, they exist in the water as bubbles. Because the content of desorbed VOCs in the granules is relatively small, the VOC bubbles are also small. Therefore, when water flows from top to bottom within tank 411, some VOC bubbles will have difficulty rising and may even be re-adsorbed onto the high-molecular-weight polyolefins in the granules.

[0078] Reference Figure 9 During the upward movement of dissolved air water, the bubbles released will capture VOCs (volatile organic compounds) that diffuse into the water. Nitrogen-containing bubbles will merge with bubbles containing VOCs to form larger bubbles that rise to the surface.

[0079] In addition, after some VOCs desorb from the high molecular weight polyolefin, the VOC bubbles will be adsorbed on the surface of the granules; the bubbles released by the dissolved air water will also disturb the granules, and the bubbles released by the dissolved air water will collide with the VOC bubbles on the surface of the granules, so as to remove the VOCs from the surface of the granules in time.

[0080] The large bubbles containing VOCs have greater buoyancy, causing them to rise to the liquid surface and burst, thereby carrying the VOCs from the water to the upper part of the tank 411; allowing more VOCs to be collected in the VOC centralized treatment unit 10 via the gas collection pipe 4113.

[0081] At the same time, the bubbles released by the dissolved air water carry away the VOCs in the water, reducing the concentration of VOCs in the water and facilitating the diffusion of VOCs from the granules into the water.

[0082] Example 5 The difference between Example 5 and Example 4 is as follows: Reference Figure 10 In this embodiment, the desorption unit 4 includes three retention tanks 41, which are named first retention tank, second retention tank, and third retention tank in sequence. The solid-liquid mixture flows through the first retention tank, second retention tank, and third retention tank in sequence. The connection relationship between the three retention tanks 41 and other structures is the same as in embodiment 3.

[0083] In this embodiment, the dissolved gas structure 48 is connected to the second residence tank, and the dissolved gas structure 48 delivers dissolved gas water into the second residence tank.

[0084] The implementation principle of a pellet post-processing conveying system according to an embodiment of this application is as follows: Reference Figure 10In the first residence tank, the solid-liquid mixture contains fewer air bubbles, allowing the granules to fully contact the water, thereby increasing the rate at which the granules absorb energy and rapidly raising their temperature. This causes the VOCs in the granules to absorb energy and desorb from the high-molecular-weight polyolefin phase. The desorbed VOCs diffuse into the water, forming small bubbles. These VOC bubbles rise and escape to the top of tank 411 for collection in the VOC centralized treatment unit 10.

[0085] Reference Figure 10 Subsequently, the solid-liquid mixture is transferred from the first residence tank to the second residence tank. At this point, the temperature of the granules is high, and there is no need for water to heat the granules. After the dissolved air structure 48 transfers dissolved air water to the second residence tank, the bubbles released by the dissolved air water will capture VOC organic volatile bubbles in the water.

[0086] Reference Figure 10 Finally, the solid-liquid mixture is transferred from the second residence tank to the third residence tank. At this point, the newly introduced solid-liquid mixture is positioned in the upper region of the second residence tank, allowing any air bubbles that did not rise to the surface in time to precipitate into the water under low pressure, further reducing the VOC content in the water. This also allows the air bubbles in the water to dissipate fully, facilitating the subsequent transport of the solid-liquid mixture.

[0087] Example 6 The difference between Example 6 and Example 5 is as follows: Reference Figure 11 and Figure 12 The dissolved gas structure 48 also includes a rotary joint 484 and a second dissolved gas water conveying pipe 485; the first dissolved gas water conveying pipe 482 is rotatably and sealedly connected to the rotating shaft 432 through the rotary joint 484.

[0088] Reference Figure 12 The rotating shaft 432 has a hollow section at the end away from the driving component 431, and a flow channel 4321 is provided inside the hollow section. The flow channel 4321 is connected to the first dissolved air water conveying pipe 482. The second dissolved air water conveying pipe 485 is horizontally fixed on the rotating shaft 432, and the second dissolved air water conveying pipe 485 is connected to the flow channel 4321 inside the rotating shaft 432. Along the dissolved air water conveying direction, multiple dissolved air releasers 483 are provided at intervals on the second dissolved air water conveying pipe 485.

[0089] Reference Figure 12When dissolved gas tank 481 delivers dissolved gas water into residence tank 41, the dissolved gas water flows sequentially through the first dissolved gas water delivery pipe 482, rotary joint 484, flow channel 4321 of rotating shaft 432, second dissolved gas water delivery pipe 485, and dissolved gas release device 483. The periphery of the first dissolved gas water delivery pipe 482, rotary joint 484, flow channel 4321, and second dissolved gas water delivery pipe 485 can all be coated with heat-insulating coatings.

[0090] Reference Figure 13 In this embodiment, the second dissolved air water conveying pipeline 485 sequentially includes a first straight section 4851, an arc-shaped section 4852, and a second straight section 4853. The first straight section 4851 and the second straight section 4853 are arranged radially along the tank body 411, and the arc-shaped section 4852 is arranged along the inner peripheral wall of the tank body 411. Dissolved air release devices 483 are provided on the first straight section 4851, the arc-shaped section 4852, and the second straight section 4853.

[0091] The implementation principle of a pellet post-processing conveying system according to an embodiment of this application is as follows: Reference Figure 11 and Figure 12 When the rotating shaft 432 rotates, it will drive the second dissolved air water conveying pipe 485 and the dissolved air release device 483 on the second dissolved air water conveying pipe 485 to rotate. Thus, the rotating shaft 432 can drive the dissolved air release device 483 to release bubbles at different positions, thereby improving the uniformity of bubble distribution in the tank 411, improving the capture efficiency and effect of the bubbles released by the dissolved air water on VOC organic volatiles in the water, and improving the removal effect of VOC organic volatiles.

[0092] At the same time, the rotating shaft 432 will drive the water conveying pipe of the second container to periodically pass under the flow port 443; while improving the uniformity of bubble distribution in the tank 411, it also facilitates the flow of granules in the solid-liquid mixture from top to bottom, so that the device can operate smoothly.

[0093] The first straight segment 4851 and the second straight segment 4853 are arranged radially along the tank body 411, and dissolved gas release devices 483 are also provided on the first straight segment 4851 and the second straight segment 4853 to further improve the uniformity of dissolved gas water release bubbles.

[0094] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A pellet post-processing conveying system, characterized in that: The system includes, in sequence, an underwater pelletizing unit (2), a first solid-liquid separator (31), a desorption unit (4), a hydraulic conveying unit (5), a drying and dewatering unit (6), a screening unit (7), a vertical pneumatic conveying unit (8), and a blending and homogenizing unit (9). The underwater pelletizing unit (2) cuts the material strips into pellets, which form a primary solid-liquid mixture with water. The first solid-liquid separator (31) is used to concentrate the solid-liquid mixture, and the concentrated solid-liquid mixture is transported to the desorption unit (4) via a pipeline. The desorption unit (4) includes a retention tank. (41) and a heating element, the residence tank (41) has a feed pipe (4111), a discharge pipe (4112) and a gas collection pipe (4113), the solid-liquid mixture is fed into the residence tank (41) through the feed pipe (4111), the heating element is used to heat the solid-liquid mixture, the granules are retained in the residence tank (41), the water heats the granules so that the VOC organic volatiles are desorbed from the granules, and the VOC organic volatiles are dispersed to the VOC centralized treatment unit (10) through the gas collection pipe (4113) after desorption. The granules, excluding VOCs, are conveyed to the hydraulic conveying unit (5) via the discharge pipe (4112); the hydraulic conveying unit (5) conveys the granules through water; the desorption unit (4) further includes a dissolved air structure (48), which includes a dissolved air tank (481), a first dissolved air water conveying pipe (482), and a dissolved air release device (483). The first dissolved air water conveying pipe (482) passes through the residence tank (41), and one end of the first dissolved air water conveying pipe (482) is connected to the dissolved air tank (4112). 81) Connected, the dissolved gas tank (481) delivers dissolved gas water to the residence tank (41) through the first dissolved gas water delivery pipe (482); the dissolved gas release device (483) is installed on the first dissolved gas water delivery pipe (482) and is connected to the first dissolved gas water delivery pipe (482). The dissolved gas release device (483) is used to release the supersaturated gas in the dissolved gas water in the form of tiny bubbles. The released bubbles are used to capture the desorbed VOC organic volatile gas.

2. The pellet post-processing conveying system according to claim 1, characterized in that: The desorption unit (4) further includes a second solid-liquid separator, a hot water circulation tank, and a hot water circulation pump; the heating element is used to heat the water in the hot water circulation tank, and the hot water circulation pump pumps the water in the hot water circulation tank to the retention tank (41); the second solid-liquid separator is connected to the discharge pipe (4112) of the retention tank (41), the second solid-liquid separator is used to concentrate the solid-liquid mixture, and the water separated by the second solid-liquid separator flows back to the hot water circulation tank through the pipeline; The water separated by the first solid-liquid separator (31) is transported through a pipeline and mixed with the solid-liquid mixture concentrated by the second solid-liquid separator to reduce the temperature of the solid-liquid mixture; the mixed solid-liquid mixture is then transported by the hydraulic conveying unit (5).

3. The pellet post-processing conveying system according to claim 1, characterized in that: The desorption unit (4) includes at least two of the retention tanks (41), and several of the retention tanks (41) are connected in sequence by pipes, so that the solid-liquid mixture flows through several of the retention tanks (41) in sequence.

4. The pellet post-processing conveying system according to claim 1, characterized in that: The residence tank (41) includes a tank body (411) and a stirring assembly (43). The stirring assembly (43) includes a drive component (431), a rotating shaft (432), and a stirring blade (433). The rotating shaft (432) is vertically arranged. The drive component (431) is fixed on the tank body (411) and drives the rotating shaft (432) to rotate. The stirring blade (433) is fixedly connected to the rotating shaft (432).

5. The pellet post-processing conveying system according to claim 4, characterized in that: The retention tank (41) includes a flow-slowing assembly (44), which includes several flow-slowing plates (441). The flow-slowing plates (441) are fixedly connected to the inner peripheral wall of the tank body (411). The flow-slowing plates (441) have mounting holes (442) for a rotating shaft (432) to pass through, and flow ports (443) for water to pass through. The top of the flow-slowing plates (441) has a downward-sloping first guide surface (4411), and the bottom of the flow-slowing plates (441) has a flow port (443) for water to pass through. A second guide surface (4412) is provided that is inclined upward. The granules flow along the first guide surface (4411) to the flow port (443), and the desorbed gas monomers flow along the second guide surface (4412) to the flow port (443). The flow ports (443) of a plurality of flow buffers (441) are staggered on both sides of the central axis of the tank (411), so that water flows from top to bottom through the plurality of flow buffers (441), and the stirring blades (433) are arranged between adjacent flow buffers (441).

6. The pellet post-processing conveying system according to claim 1, characterized in that: Multiple dissolved gas releasers (483) are provided, and multiple dissolved gas releasers (483) are spaced apart along the first dissolved gas water delivery pipe (482).

7. The pellet post-processing conveying system according to claim 1, characterized in that: The desorption unit (4) includes three residence tanks (41), which are named first residence tank, second residence tank and third residence tank in sequence. The solid-liquid mixture flows through the first residence tank, the second residence tank and the third residence tank in sequence. The dissolved gas structure (48) is connected to the second residence tank and delivers dissolved gas water into the second residence tank.

8. The pellet post-processing conveying system according to claim 4, characterized in that: The dissolved gas structure (48) includes a dissolved gas tank (481), a first dissolved gas water conveying pipe (482), and a rotary joint (484); the other end of the first dissolved gas water conveying pipe (482) is rotatably and sealedly connected to the rotating shaft (432) through the rotary joint (484); the rotating shaft (432) has a hollow section at one end away from the driving component (431), and a flow channel (4321) is provided inside the hollow section, which is connected to the first dissolved gas water conveying pipe (482); the stirring assembly (43) also includes a second dissolved gas water conveying pipe (485), which is horizontally fixed on the rotating shaft (432) and is connected to the flow channel (4321). Along the direction of dissolved gas water conveying, the dissolved gas release device (483) is provided at intervals on the second dissolved gas water conveying pipe (485).

9. The pellet post-processing conveying system according to claim 8, characterized in that: The second dissolved air water conveying pipeline (485) includes a first straight section (4851), an arc section (4852), and a second straight section (4853) in sequence. The first straight section (4851) and the second straight section (4853) are arranged radially along the tank body (411), and the arc section (4852) is arranged along the inner peripheral wall of the tank body (411).

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