A polyethylene particle size uniformity crushing and grading device

Abstract

This utility model relates to a polyethylene particle size homogenization crushing and grading device. The device includes multi-stage hydrocyclones connected in series for grading polyethylene slurry. A wet crushing mechanism is installed in the outlet pipe of the underflow of each hydrocyclone to crush the polyethylene slurry containing coarse particles separated by the hydrocyclone. The outlet pipe of the wet crushing mechanism is connected to the inlet of the hydrocyclone, and the crushed polyethylene slurry is recycled back into the hydrocyclone for further separation. Compared with existing technologies, this crushing and grading device achieves precise control and ultra-high consistency in product particle size distribution, giving the production line excellent flexible production capabilities and high stability and reliability in continuous operation.

Description

Technical Field

[0001] This utility model relates to the field of polyethylene production technology, specifically to a polyethylene particle size uniformity crushing and grading device. Background Technology

[0002] In the production of polyethylene, strict requirements are placed on the particle size distribution of polymer particles, especially in the preparation of certain high-end grades. The particle size and its uniformity directly affect the processing performance and application characteristics of the final product. An ideal particle size distribution helps improve the melt flowability, processing stability, and mechanical properties of the final product. For example, in the production of high molecular weight polyethylene for diaphragm materials, a particle size concentration of 80–120 μm is often required; the narrower the distribution, the better it is for film uniformity and performance optimization. On the other hand, some high-value polyolefin products (such as MiPELON from Sanmi Chemical) also require a particle size distribution of 80–120 μm. TM XM-220, on the other hand, requires maintaining a high molecular weight while controlling the average particle size within the ultrafine range of 10–40 μm. This type of material is used in fields such as high-precision porous filtration and possesses extremely high added value. Therefore, achieving precise control of polyethylene powder particle size and narrow distribution preparation has become an important direction for technological upgrading in the industry, especially with the increasingly urgent need for ultra-high consistency fine particle products in high-end application scenarios.

[0003] Currently, the slurry polymerization process is a relatively mature technology route in the industrial production of polyethylene, especially with Ziegler-Natta catalysts becoming the mainstream production process. However, this process has significant limitations: the multi-active-center characteristic of Ziegler-Natta catalysts makes it difficult to generate high molecular weight polymers with uniform particle size; at the same time, the strong exothermic effect during polymerization easily causes local overheating in the reactor, leading to "hot spots" and explosive polymerization, which in turn produces agglomerates and large particles, seriously affecting the particle size consistency of the final product.

[0004] To control polymer particle size distribution, existing technologies typically rely on post-processing screening, which involves classifying materials using vibrating screens of different mesh sizes to remove oversized particles and obtain finished products with the target particle size. However, in large-scale continuous production scenarios, screening technology suffers from limited processing capacity, low production efficiency, and low automation. Especially for ultrafine powders, high-mesh screens are prone to clogging, rapid wear, and frequent malfunctions, significantly increasing maintenance costs. Furthermore, oversized particles that do not meet specifications must be crushed separately, increasing the complexity and intermittency of the process. Therefore, there is an urgent need to develop a crushing and classification technology and equipment that can be integrated into continuous slurry processes, efficiently control polymer particle size distribution, and is particularly suitable for preparing highly uniform ultrafine polyethylene powder, to overcome existing technological bottlenecks and meet the industrialization needs of high-end polyethylene materials. Utility Model Content

[0005] The purpose of this invention is to provide a polyethylene particle size uniformity crushing and grading device to solve the above problems.

[0006] The objective of this utility model is achieved through the following technical solution:

[0007] A polyethylene particle size homogenization crushing and grading device, the device comprising:

[0008] Multi-stage hydrocyclones connected in series are used to classify slurries (e.g., polyethylene slurry from a polymerization reaction unit);

[0009] A wet crushing mechanism is installed on the outlet pipe of the hydrocyclone underflow and is used to crush the slurry containing coarse particles separated by the hydrocyclone.

[0010] The outlet pipe of the wet crushing mechanism is connected to the feed inlet of the hydrocyclone, so that the crushed slurry is circulated to the hydrocyclone for further separation.

[0011] As a preferred technical solution of this utility model, a buffer tank is provided between the hydrocyclone and the wet crushing mechanism, and the underflow outlet of the hydrocyclone is connected to the inlet of the buffer tank.

[0012] As a preferred technical solution of this utility model, the outlet of the buffer tank is connected to the inlet of the wet crushing mechanism through a three-way valve, and the third port of the three-way valve serves as the discharge port for qualified fine materials.

[0013] As a preferred technical solution of this utility model, the wet crushing mechanism includes a wet shearing pump, which can be connected to a booster pump. Both the shearing pump and the booster pump are connected to a motor via a coupling.

[0014] As a preferred technical solution of this utility model, the wet shear pump is a particle size adjustable shear pump, and its crushing particle size range is 30-500μm.

[0015] As a preferred technical solution of this utility model, the separation particle size of the multi-stage hydrocyclone decreases sequentially from the first stage to the last stage, and the hydrocyclone has 2-5 stages, for example, three stages are connected in series.

[0016] As a preferred technical solution of this utility model, the hydrocyclone includes a hydrocyclone body, which comprises a cylindrical tube section and a conical tube section from top to bottom. A tangential feed inlet is provided on the side of the cylindrical tube section, and an underflow outlet is provided at the bottom of the conical tube section. An overflow pipe extending from top to bottom is also provided in the hydrocyclone body. The polyolefin slurry is introduced from the feed inlet at a pressure of 0.2-0.8 MPa, and the concentration of the slurry is 10-50 wt%.

[0017] As a preferred technical solution of this utility model, the feed inlet of the hydrocyclone body is connected to a Venturi nozzle. The Venturi nozzle helps to increase the flow rate of the polyethylene slurry, avoid blockage of the polyethylene slurry with a certain viscosity, and improve the separation effect of large particles.

[0018] As a preferred technical solution of this utility model, a solvent flushing pipeline is provided on the conical tube section of the hydrocyclone body near the underflow outlet for diluting and flushing the material, so as to prevent the accumulation of large particles with increased solid content from clogging the outlet.

[0019] As a preferred technical solution of this utility model, the overflow pipe is a telescopic pipe with adjustable depth and / or a variable diameter pipe with variable diameter, which can adjust the grading particle size of the hydrocyclone.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. Achieved precise control and ultra-high consistency in product particle size distribution. Through multi-stage hydrocyclone cascading classification and wet crushing mechanism, coarse particles can be accurately and efficiently separated and crushed and recycled, solving problems such as wide particle size distribution and large particle residue in polyethylene, and improving the uniformity of product particle size.

[0022] 2. It endows the production line with excellent flexible production capabilities. By adjusting the grading and crushing parameters, products with different particle size ranges can be obtained in the same process. Different levels of hydrocyclones can separate product slurries that meet different grade standards, and independent discharge can be achieved through structures such as three-way valves. This enables a single production line to flexibly produce polyethylene products of various specifications, improving the market adaptability and economic benefits of the production line.

[0023] 3. High stability and reliability of continuous operation. By setting up buffer tanks, three-way valves and other control devices, the flow and pressure fluctuations within the system are balanced, making the material flow more smoothly and steadily in the stages of grading, crushing, circulation and discharge, avoiding the risk of blockage and flow interruption, and ensuring the continuity, controllability and safety of the entire process. It is suitable for the stable production of high-performance products such as ultra-high molecular weight polyethylene. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a polyethylene particle size homogenization crushing and grading device.

[0025] Figure 2 This is a schematic diagram of a hydrocyclone.

[0026] Figure 3 Photographs of polyethylene powder samples to be processed;

[0027] Figure 4 This is an electron microscope image of the sample after fractionation. Detailed Implementation

[0028] The present invention will now be described in detail. Any aspects not described in detail are technical solutions already disclosed in the field.

[0029] Reference Figure 1 A polyethylene particle size homogenization crushing and grading device includes multiple hydrocyclones 100 connected in series, each hydrocyclone 100 having 2-5 stages. This embodiment... Figure 1 A three-stage hydrocyclone 100 is shown. The hydrocyclone 100 utilizes the difference in centrifugal force experienced by particles in a centrifugal field to cause particles of different sizes to have different radial trajectories. Large-diameter particles, due to their large mass, experience strong centrifugal force and can overcome fluid resistance to be quickly thrown towards the wall of the device. They move along the wall with the outer swirling flow and are eventually discharged from the bottom as coarse particles. Small-diameter particles, due to their small mass, experience weak centrifugal force and are unable to overcome the inner swirling flow of the fluid. They gather towards the center with the inner swirling flow and are discharged from the top as fine particles.

[0030] In one specific implementation, a wet crushing mechanism 200 is installed in the bottom outlet pipe of the upstream hydrocyclone 100 (such as a primary hydrocyclone and / or a secondary hydrocyclone) to crush the slurry containing coarse particles separated by the hydrocyclone 100, thereby eliminating large particles. The material at the bottom outlet of the hydrocyclone 100 enters the wet crushing mechanism 200, and the crushed slurry is circulated from the outlet back into the same-stage hydrocyclone 100 for further separation.

[0031] As a preferred embodiment, a buffer tank 300 is provided between the hydrocyclone 100 and the wet crushing mechanism 200. The material discharged from the hydrocyclone 100 is first collected in the buffer tank 300 and then enters the wet crushing mechanism 200. This is mainly due to the processing capacity of the hydrocyclone 100 and the concentration of the slurry. By setting up the buffer tank 300, the stability of the system can be improved, and the concentration of the slurry entering the wet crushing mechanism 200 can be easily controlled to avoid the solid content being too high and exceeding the slurry feed concentration of the wet crushing mechanism 200, which would affect the wet crushing effect.

[0032] As a preferred embodiment, a three-way valve 400 is also installed between the outlet of the buffer tank 300 and the inlet of the wet crushing mechanism 200 to adjust and control the crushing process of the slurry in a timely manner according to the actual situation. The outlet of the buffer tank 300 is connected to the inlet of the wet crushing mechanism 200 through a three-way valve 400. The third port of the three-way valve 400 serves as the discharge port for qualified fine materials. For example, after several crushing operations, if the large particles have been completely crushed, the inlet to the wet crushing mechanism 200 is closed, and no further crushing operation is performed. The material is discharged from the other outlet of the three-way valve 400 and directly enters the next process.

[0033] As a preferred embodiment, depending on actual needs, a wet crushing mechanism 200 can be installed only in the underflow of the upstream primary hydrocyclone or secondary hydrocyclone. It is not necessary to install it in subsequent hydrocyclones. This is because large particles have been crushed in the preceding process, and only particle size classification is needed in the subsequent process, thereby minimizing the number of devices.

[0034] In one preferred embodiment, the wet crushing mechanism 200 is also arranged in stages according to the particle size, that is, the upstream wet crushing mechanism 200 crushes particles larger than the downstream one, and is matched with the corresponding hydrocyclone 100, so as to achieve step-by-step crushing and separation. For example, in this embodiment, a first-stage wet crushing mechanism 200 is set at the bottom outlet of the first-stage hydrocyclone, and a second-stage wet crushing mechanism 200 is set at the bottom outlet of the second-stage hydrocyclone. The particle size of the first-stage wet crushing mechanism 200 is larger than that of the second-stage wet crushing mechanism 200.

[0035] In one preferred embodiment, the slurry from each hydrocyclone 100 after classification is sent to its own independent buffer tank 300 through its own independent pipeline, and then connected to downstream processes (e.g., separation and drying units) through controllable pipelines, finally obtaining products with different particle size ranges, thus achieving the purpose of producing products of different grades.

[0036] The above-mentioned crushing and grading device can achieve particle size classification and distribution control. Taking the processing of high molecular weight polyethylene as an example, the specific process is as follows: (1) The slurry containing polyethylene products and solvents of different particle sizes is pumped into the side inlet of the first-stage hydrocyclone. After hydrocyclone separation, coarse particles enter the bottom and are discharged from the bottom. The coarse particles discharged from the bottom are crushed by the first-stage wet crushing mechanism. The crushed material is recycled back into the first-stage hydrocyclone until large particles are eliminated. Fine particles enter the upper part and are discharged from the upper overflow, thus achieving the first stage of separation. (2) Fine particles discharged from the top of the first-stage hydrocyclone are separated again by the second-stage hydrocyclone. The process is the same as the separation process of the first-stage hydrocyclone. Coarse particles discharged from the bottom of the second-stage hydrocyclone can enter the second-stage wet crushing mechanism for crushing. If the particle size is suitable, they can also be discharged directly without crushing, thus achieving the second stage of separation. (3) Fine particles discharged from the top of the second-stage hydrocyclone are separated again by the third-stage hydrocyclone. The process is the same as the separation process of the hydrocyclone, thus achieving the third stage of separation. After the three-stage hydrocyclone separation process described above, four streams of slurry containing different particle sizes were obtained. Figure 1 Arrange the particles from top to bottom, with the particle size increasing in order, and you will get four different particle size ranges of products, which means you can produce four different grades of products.

[0037] In one preferred embodiment, the crushing particle size of the wet crushing mechanism 200 is 30-500μm. For example, the crushing particle size of the product can be set to 500μm, 400μm, 300μm, 200μm, 150μm, 120μm, 100μm, 50μm, 40μm, 30μm, etc. The wet crushing mechanism 200 may specifically include a shear pump and a booster pump connected to the shear pump. Both the shear pump and the booster pump are connected to a motor via a coupling. As a preferred technical solution, the shear pump is an adjustable-size shear pump to produce product grades with different particle size distributions according to actual needs. The particle size is adjusted by adjusting the shear pump power via a frequency converter, or a mechanically adjustable shear pump can be used, i.e., the crushing particle size is adjusted by adjusting the gap between the rotor and stator in the shear pump. In this embodiment, the selection of the shear pump for the wet crushing mechanism can use commercially available models that meet the requirements, preferably a wet shear pump with adjustable outlet particle size.

[0038] As a preferred embodiment, the specific structure of the hydrocyclone used in this invention is as follows: (Refer to...) Figure 2 The hydrocyclone includes a hydrocyclone body, which consists of a cylindrical tube section and a conical tube section from top to bottom. An overflow pipe 101 is installed inside the hydrocyclone body, and the overflow pipe 101 is installed inside the hydrocyclone cavity from top to bottom. A feed inlet is provided on the side of the cylindrical tube section, and an outlet is provided at the lower end of the conical tube section. Polyethylene slurry is introduced into the hydrocyclone body through the feed inlet and rotates inside it. Under the action of rotational force, large particles of polyethylene slurry are discharged from the outlet, and small particles of polyethylene slurry are discharged from the top through the overflow pipe 101.

[0039] In one preferred embodiment, polyethylene slurry is introduced into the cylindrical tube section inside the hydrocyclone body through the inlet under a certain pressure (e.g., via a booster pump). The concentration of the polyethylene slurry is 10-50 wt%, more preferably 20-40 wt%. In another preferred embodiment, the polyethylene slurry is introduced into the hydrocyclone body at a pressure of 0.2-0.8 MPa, more preferably 0.3-0.4 MPa. Maintaining a certain pressure has a positive effect on the particle size and classification effect of the graded product. Due to the flow restriction caused by the cylindrical pipe wall, the slurry rotates downwards within the cylindrical and conical pipe sections, forming an outer vortex. During the rotation, a strong centrifugal force is generated, causing large particles to gradually move towards the outer wall under the centrifugal force. Under the combined force, they rotate and fall along the cylinder wall until they are discharged from the outlet. The rotating and descending outer vortex gradually converges towards the center due to the contraction of the conical pipe section. When it descends to a certain extent, it begins to rise again, forming an upward rotational motion, thus forming an inner vortex. Small particles rise with the spiral into the inner vortex, which is then discharged from the overflow pipe 101, thereby completing the classification of the polyethylene slurry.

[0040] In one preferred embodiment, the feed inlet of the hydrocyclone body is connected to a Venturi nozzle 102. The Venturi nozzle 102 increases the flow rate of the polyethylene slurry, prevents clogging of the polyethylene slurry with a certain viscosity, and improves the separation effect of large particles.

[0041] As a preferred embodiment, a solvent flushing pipe 103 is provided on the conical tube section of the hydrocyclone body near the underflow outlet to prevent large particles with increased solid content from accumulating and clogging the outlet.

[0042] In one preferred embodiment, to effectively adjust the particle size of the graded product, the overflow pipe 101 is a depth-adjustable telescopic pipe and / or a variable-diameter pipe. For example, when the insertion depth of the overflow pipe increases, the number of fine particles in the overflow pipe decreases; when the insertion depth decreases, the number of fine particles increases. Furthermore, the taper of the conical pipe section can be 5-30 degrees. By adjusting the taper of the conical pipe section, the separation particle size of the hydrocyclone can be adjusted.

[0043] This invention utilizes an experimental setup to conduct slurry crushing and grading experiments. The experiment used 1.5 million molecular weight polyethylene powder provided by Puxijing New Energy Materials (Shanghai) Co., Ltd. as raw material, and screened out samples containing a large number of large particles (see actual photos). Figure 3 To simulate the actual slurry production process environment, hexane was used as a solvent. Approximately 50 kg of the polyethylene powder was mixed with hexane solvent in a mixing tank to prepare a slurry with a concentration of 30 wt%.

[0044] The experimental setup simulated the actual process, including a slurry pump and three-stage hydrocyclones in series (small, conventional hydrocyclones with diameters of 200mm for the first stage, 150mm for the second stage, and 100mm for the third stage). The underflow outlets of the first and second stage hydrocyclones were connected to wet shear pumps with particle sizes of 300μm and 150μm, respectively. The crushed slurry was returned to its respective stage hydrocyclone for reclassification via a circulation pipeline. A buffer tank was installed between the hydrocyclone and the wet shear pump to stabilize the flow rate and concentration. After the experiment started, the slurry was sequentially passed through each stage of the hydrocyclone for classification. The underflow materials from the first and second stages were crushed by the corresponding shear pumps and then circulated, ultimately yielding four slurry product streams with different particle size ranges.

[0045] After sampling each product stream, the particle size distribution was tested using a Malvern laser particle size analyzer. The D10, D50, and D90 values ​​were recorded, and the particle size distribution width (Span value) was calculated using the formula: Span = (D90 - D10) / D50. A smaller Span value indicates a more concentrated particle size distribution and higher product consistency. The experimental results are shown in Table 1.

[0046] Table 1

[0047] Original sample 420 750 1653 1.64 Products containing large particles Third-stage hydrocyclone overflow 38 55 78 0.73 ultrafine powder products Underflow of the third-stage hydrocyclone 75 105 142 0.64 Fine powder products Secondary cyclone underflow 130 185 250 0.65 ordinary products First-stage hydrocyclone underflow 180 241 378 0.82 coarse powder products

[0048] As shown in Table 1, this process effectively breaks down coarse particles in the original slurry and significantly narrows the particle size distribution. It successfully separates coarse polyethylene powder containing large, widely distributed particles into four narrowly distributed products, achieving the co-production of multiple highly consistent products including ultrafine powder, fine powder, standard powder, and coarse powder. Furthermore, scanning electron microscopy morphology analysis was performed on the fine powder product (results are shown in Table 1). Figure 4 (Scale bar 100μm) The image shows that the particle surface is uniform and the morphology is intact, confirming that the product maintains good physical properties and structure.

[0049] The above description of the embodiments is provided to enable those skilled in the art to understand and use the utility model. It will be apparent to those skilled in the art that various modifications can be easily made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present utility model is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present utility model without departing from its scope should be within the protection scope of the present utility model.

Claims

1. A polyethylene particle size uniformity crushing and grading device, characterized in that, The device includes: Multi-stage hydrocyclones connected in series are used to classify slurry; A wet crushing mechanism is installed on the outlet pipe of the hydrocyclone underflow and is used to crush the slurry containing coarse particles separated by the hydrocyclone. The outlet pipe of the wet crushing mechanism is connected to the feed inlet of the hydrocyclone, so that the crushed slurry is circulated to the hydrocyclone for further separation.

2. The polyethylene particle size uniformity crushing and grading device according to claim 1, characterized in that, A buffer tank is provided between the hydrocyclone and the wet crushing mechanism, and the underflow outlet of the hydrocyclone is connected to the inlet of the buffer tank.

3. The polyethylene particle size uniformization crushing and grading device according to claim 2, characterized in that, The outlet of the buffer tank is connected to the inlet of the wet crushing mechanism through a three-way valve, and the third port of the three-way valve serves as the discharge port for qualified fine materials.

4. The polyethylene particle size uniformity crushing and grading device according to claim 1, characterized in that, The wet crushing mechanism includes a wet shear pump.

5. The polyethylene particle size uniformization crushing and grading device according to claim 4, characterized in that, The wet shear pump is a particle size adjustable shear pump, with a crushing particle size range of 30-500μm.

6. The polyethylene particle size uniformization crushing and grading device according to claim 1, characterized in that, The separation particle size of the multi-stage hydrocyclone decreases sequentially from the first stage to the last stage.

7. The polyethylene particle size uniformization crushing and grading device according to claim 1, characterized in that, The hydrocyclone includes a hydrocyclone body, which comprises a cylindrical tube section and a conical tube section from top to bottom. A tangential feed inlet is provided on the side of the cylindrical tube section, and an underflow outlet is provided at the bottom of the conical tube section. An overflow pipe extending from top to bottom is also provided in the hydrocyclone body.

8. The polyethylene particle size uniformity crushing and grading device according to claim 7, characterized in that, The feed inlet of the hydrocyclone body is connected to a Venturi nozzle.

9. A polyethylene particle size uniformity crushing and grading device according to claim 7, characterized in that, A solvent flushing pipeline is provided on the conical tube section of the hydrocyclone body near the underflow outlet.

10. A polyethylene particle size uniformity crushing and grading device according to claim 7, characterized in that, The overflow pipe is a depth-adjustable telescopic pipe or / and a variable-diameter pipe.

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