Anti-blocking slurry method polyethylene polymerization device

Abstract

The present invention relates to an anti-clogging slurry method polyethylene polymerization apparatus, which comprises a reactor body, a stirring mechanism arranged in the reactor body, and at least one ethylene gas inlet pipe extending into the reactor body, the outlet section of the ethylene gas inlet pipe is set to be a gradual shrinkage structure, the inner diameter of the ethylene gas inlet pipe is gradually reduced along the gas flow direction, and the inner diameter of the ethylene gas inlet pipe is gradually reduced along the gas flow direction. The gradually-shrunk outlet section is used for increasing the ejection speed of ethylene gas at an outlet, so that high-speed and high-momentum jet flow is obtained, directional pneumatic blowing of a pipe opening and a peripheral area is formed, initial accumulation of slurry on the edge of the pipe opening and an adjacent inner wall is effectively prevented, and formation and accumulation of retention block materials on the inner wall of the pipe opening are reduced.

Description

Technical Field

[0001] This invention relates to the field of polyolefin technology, and more specifically to a slurry-based polyethylene polymerization apparatus that prevents clogging. Background Technology

[0002] Ultra-high molecular weight polyethylene (UHMWPE) is a linear polyethylene with an extremely high relative molecular mass. It possesses excellent properties such as wear resistance, impact resistance, corrosion resistance, self-lubrication, and energy absorption, and is widely used in many fields including textiles, machinery, medical, and sports. Its production processes mainly include solution processing, slurry processing, and gas-phase processing. Among these, the slurry processing method has become the mainstream process due to its mature technology and stable product quality.

[0003] In the slurry polymerization process, ethylene gas enters the polymerization reactor through multiple distributed ethylene inlet pipes. Ethylene and the catalyst are thoroughly mixed in the solvent before polymerization. In actual operation, due to uneven fluid dynamics and local differences in mass and heat transfer, material stagnation zones easily form on the inner wall near the ports of the ethylene inlets. These stagnation zones become the core area for clumping, where fine powder or incompletely reacted materials gradually adhere, accumulate, and form lumps. These lumps adhere heavily to the walls and are not easily carried away by the flowing medium. Some lumps detach with fluid disturbances or operational fluctuations, easily leading to system blockage, abnormal pressure drop, or even production interruption. Therefore, developing an anti-clogging slurry polyethylene polymerization unit to ensure stable operation is an urgent technical problem to be solved. Summary of the Invention

[0004] The purpose of this invention is to provide a slurry-based polyethylene polymerization apparatus that prevents clogging, thereby addressing the problem of blockage caused by lumps forming in the inner wall of the ethylene inlet pipe. Through the structural design of the ethylene inlet pipe, the local airflow distribution and the overall flow field within the reactor are optimized in a coordinated manner, effectively suppressing the formation of stagnation zones and preventing the accumulation of fine powder and the generation of lumps without excessively increasing the system pressure drop.

[0005] The objective of this invention is achieved through the following technical solution: A slurry-based polyethylene polymerization apparatus for preventing clogging includes a reactor body, a stirring mechanism disposed within the reactor body, and at least one ethylene inlet pipe extending into the reactor body. The outlet section of the ethylene inlet pipe is configured with a tapered structure, the inner diameter of which gradually decreases along the gas flow direction. This tapered outlet section is used to increase the ejection velocity of the ethylene gas at the outlet. The principle is based on the law of conservation of mass in fluid mechanics; as the gas flows through the tapered pipe with a decreasing cross-sectional area, the flow velocity increases. Simultaneously, according to Bernoulli's equation, this tapered structure can convert the pressure energy of the gas into kinetic energy, thereby obtaining a high-speed, high-momentum jet flow at the outlet. This forms a directional pneumatic purging of the pipe opening and surrounding area, effectively preventing the initial accumulation of slurry at the edge of the pipe opening and adjacent inner walls, thereby reducing the formation and aggregation of stagnant material on the inner wall of the pipe opening.

[0006] As a preferred embodiment of the present invention, the contraction ratio of the outlet section of the ethylene inlet pipe is controlled between 1.2 and 1.8, for example, between 1.3 and 1.6, or 1.4 and 1.5, to ensure that the increase in gas velocity and the increase in system pressure drop are within a controllable range. More preferably, the tapering section adopts a multi-stage stepped or continuous curved diameter change to accelerate the gas more smoothly and optimize the airflow pattern.

[0007] As a preferred embodiment of the present invention, the end of the ethylene inlet pipe is configured as a curved section, and the direction of the airflow jet at its outlet is consistent with or at an acute angle of less than 45 degrees to the rotational flow direction of the slurry body generated by the stirring mechanism. Preferably, taking the radial direction of the corresponding stirring mechanism (i.e., the ray direction from the stirring center to the pipe opening installation position) as a reference, the pipe opening orientation (i.e., the outflow direction of the pipe opening axis) is along the tangential direction of the stirring rotation, so that the outflow direction of the pipe opening and the stirring direction are aligned in the same direction on the motion trajectory. Thus, the ethylene airflow can cut into the slurry flow field in the same direction, forming a favorable co-flow, thereby reducing the vertical impact of the airflow on the slurry surface. Utilizing the fluid synergy effect, it promotes gas dispersion and material mixing, weakens local flow dead zones, avoids rapid polymerization caused by excessively high local ethylene concentrations, and reduces the risk of lumpy material formation at the pipe opening.

[0008] As a preferred technical solution of the present invention, the outer wall of the curved section of the ethylene inlet pipe is provided with spiral guide vanes and / or guide ribs to further guide and integrate the slurry flow field in the reactor, suppress the vortex and wake zone generated by flow separation in the curved part and port part, so that the local flow field can be more smoothly integrated with the main rotating flow field in the reactor, and eliminate potential material deposition and polymer adhesion points.

[0009] As a preferred embodiment of the present invention, the spiral guide vanes are evenly distributed circumferentially in the curved section of the ethylene inlet pipe; the guide ribs are arranged axially around the tapering section along the outlet of the ethylene inlet pipe.

[0010] As a preferred technical solution of the present invention, the inner surface of the outlet section of the ethylene inlet pipe is polished. Further, the depth of the polishing treatment from the outlet end inward is 100~800 mm, and the surface roughness Ra is ≤ 0.4 μm, preferably Ra ≤ 0.2 μm.

[0011] As a preferred technical solution of the present invention, the inner surface of the outlet section of the ethylene inlet pipe is provided with a low surface energy anti-stick coating, and the coverage depth of the coating is 100~800 mm from the outlet end inward.

[0012] As a preferred technical solution of the present invention, the reactor body is a batch reactor, and its top end cap is provided with at least one circulating gas inlet and at least one circulating gas outlet; The ethylene inlet pipe passes through the circulating gas inlet and extends towards the bottom of the reactor; The reactor body is also provided with at least one slurry outlet for overflow discharge and at least one raw material inlet.

[0013] As a preferred embodiment of the present invention, the number of circulating gas inlets is 6 to 10, which are arranged in a ring array along the top end cap. Correspondingly, the number of ethylene inlet pipes is 6 to 10, which are vertically arranged in the reactor body.

[0014] Compared with the prior art, the present invention has the following beneficial effects: This device improves the structure of the ethylene inlet pipe by designing a tapered tail end, increasing the ejection velocity of the ethylene gas at the outlet to obtain a high-speed, high-momentum jet flow. This creates a directional pneumatic purging effect on the pipe opening and surrounding area, effectively preventing slurry accumulation at the pipe opening edge and adjacent inner wall, thereby reducing the formation and aggregation of stagnant material on the inner wall of the pipe opening. Furthermore, the lower part of the ethylene inlet pipe is designed as a curved section, aligning its outlet port with the rotational flow direction of the slurry mass generated by the stirring mechanism. This allows the ethylene gas flow to cut into the slurry flow field in the same direction, forming a favorable co-flow and reducing the vertical impact of the gas flow on the slurry surface. This invention achieves precise pneumatic purging of high-risk blockage areas without significantly increasing the fan load and overall system pressure drop. By coordinating the airflow direction with the stirring flow field, it improves mixing efficiency and weakens the conditions for stagnation. This structural modification is relatively simple, easy to implement on existing equipment, and operates stably and reliably. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the overall structure of a polyethylene polymerization unit. Figure 2 This is a top view of the top end cap of this device. Figure 3This is a schematic diagram of the structure of the outlet end of an ethylene inlet pipe in this device. Figure 4 This is a schematic diagram of the structure of another ethylene inlet pipe outlet end of this device; Figure 5 This is a schematic diagram of the structure of another ethylene inlet pipe outlet end of this device; In the figure: 1-reactor body; 11-circulating gas inlet; 12-circulating gas outlet; 13-slurry outlet; 14-raw material inlet; 2-stirring mechanism; 3-ethylene inlet pipe; 31-outlet section; 32-spiral guide vane; 33-guide rib. Detailed Implementation

[0016] The present invention will now be described in detail with reference to specific embodiments, but these are by no means limitations on the present invention.

[0017] like Figure 1 As shown, this invention provides an anti-clogging slurry-process polyethylene polymerization apparatus, comprising a polymerization reactor body 1, a stirring mechanism 2 installed inside the reactor body 1, and at least one ethylene inlet pipe 3 extending into the reactor body 1. The reactor body 1 is a batch reactor, as shown in the figure. Figure 2 The top end cap is provided with at least one circulating gas inlet 11 and at least one circulating gas outlet 12. An ethylene inlet pipe 3 is provided through the circulating gas inlet 11 to deliver the raw material ethylene gas to the bottom of the reactor. The reactor body 1 is provided with at least one slurry outlet 13 as an overflow discharge and at least one raw material inlet 14. The stirring mechanism 2 is a plate agitator, and the plate agitator blades are through-flow blades with through-flow holes. As a preferred technical solution, the reactor body 1 is provided with a heat exchange jacket through which a heat exchange medium can be introduced to assist in the removal of polymerization reaction heat.

[0018] In a specific embodiment, the ethylene inlet pipe 3 is parallel to the axial direction of the reactor and is arranged vertically, with its bottom extending into the bottom of the reactor. The raw material ethylene is fed from top to bottom through the ethylene inlet pipe 3 to the bottom of the reactor and enters the reaction slurry to participate in the reaction. Other materials used for the reaction (including solvent hexane, catalyst, etc.) are fed into the reactor through the raw material inlet 14; the slurry containing the reaction products is continuously discharged through the slurry outlet 13 to enter the subsequent process for further processing; the evaporated solvent hexane gas and unreacted ethylene gas are discharged through the top circulating gas outlet 12 and collected for treatment.

[0019] In a preferred embodiment, 6 to 10 circulating gas inlets 11 are arranged in a circular array on the top end cap. Correspondingly, 6 to 10 ethylene inlet pipes 3 are also provided, installed vertically downward inside the reactor. For example, in a specific embodiment, refer to... Figure 2 There are 8 circulating gas inlets 11, and 8 corresponding ethylene inlet pipes 3.

[0020] In a preferred embodiment, at least two circulating gas outlets 12 are provided, preferably arranged symmetrically along the center. The diameter of the circulating gas outlet 12 is larger than that of the circulating gas inlet 11, so as to discharge the evaporated solvent gas and unreacted ethylene gas raw material in a timely manner, while at the same time carrying out a large amount of latent heat of vaporization and removing the heat of polymerization reaction in a timely manner.

[0021] To address the issue of blockage in the production system caused by lumps forming on the inner wall of the ethylene inlet pipe 3 at the outlet end, the structure of the ethylene inlet pipe 3 was improved: For example... Figure 3 As shown, the outlet section 31 of the ethylene inlet pipe 3 is designed as a tapered structure, that is, the inner diameter of the outlet section 31 of the ethylene inlet pipe 3 gradually decreases along the gas flow direction. This tapered outlet section 31 is used to increase the ejection velocity of the ethylene gas at the outlet. The principle is based on the law of conservation of mass in fluid mechanics. When the gas flows through the tapered pipe with a reduced cross-sectional area, the flow velocity increases. At the same time, according to Bernoulli's equation, this tapered structure can convert the pressure energy of the gas into kinetic energy, thereby obtaining a high-speed, high-momentum jet flow at the outlet, forming a directional pneumatic purging of the pipe opening and surrounding area, effectively preventing the initial accumulation of slurry at the edge of the pipe opening and the adjacent inner wall, thereby reducing the formation and accumulation of stagnant material on the inner wall of the pipe opening.

[0022] Preferably, the contraction ratio (inlet inner diameter / outlet inner diameter) of the tapering section is controlled between 1.2 and 1.8, for example, between 1.3 and 1.6, or 1.4 and 1.5, to ensure that the increase in gas velocity and the increase in system pressure drop are within a controllable range. More preferably, the tapering section adopts a multi-stage stepped or continuous curved diameter change to accelerate the gas more smoothly and optimize the airflow pattern.

[0023] As a more preferred implementation, such as Figure 4 As shown, the lower part of the ethylene inlet pipe 3 is designed as a curved section, and the port of its outlet section 31 is deflected at a certain angle or set as a slanted cut, so that the injection direction of the ethylene gas is consistent with or at an acute angle (≤45 degrees) to the rotational flow direction of the slurry body generated by the stirring mechanism 2. Thus, the ethylene gas flow can cut into the slurry flow field in the forward direction, forming a favorable co-flow, thereby reducing the vertical impact of the gas flow on the slurry surface. By utilizing the fluid synergy effect, the gas dispersion and material mixing are promoted, the local flow dead zone is weakened, the rapid polymerization caused by excessive local concentration of ethylene is avoided, and the risk of blocky material formation at the pipe opening is reduced.

[0024] As a more preferred implementation, such as Figure 5As shown, spiral guide vanes 32 and / or guide ribs 33 are provided on the outer wall of the bend of the ethylene inlet pipe 3 to further guide and integrate the slurry flow field in the reactor, suppress the vortex and wake zone generated by flow separation in the bend and port, so that the local flow field can be more smoothly integrated with the main rotating flow field in the reactor, and eliminate potential material deposition and polymer adhesion points.

[0025] As a more preferred embodiment, the inner surface of the ethylene inlet pipe 3, especially its outlet section 31, is polished. Preferably, the polishing depth of the ethylene inlet pipe 3 extends 500 mm into the pipe, thereby improving the polishing precision and eliminating microscopic dead angles.

[0026] As a more preferred embodiment, a low surface energy anti-stick coating (e.g., polytetrafluoroethylene vinyl coating) is applied inside the ethylene inlet pipe 3 to reduce material adhesion. Example 1

[0027] The anti-clogging slurry-method polyethylene polymerization apparatus of this embodiment includes a reactor body 1, a stirring mechanism 2, and an ethylene inlet pipe 3, which extends vertically into the reactor body 1. (Refer to...) Figure 4 The bottom of the ethylene inlet pipe 3 is a curved section, and its outlet end has a continuous tapered conical section with an inner diameter of 60 mm at the wide end and 40 mm at the narrow end, resulting in a contraction ratio of 1.5. This converging section is a continuous curved diameter change. Furthermore, the port of the outlet section 31 is aligned with the rotational flow direction of the slurry generated by the stirring mechanism 2, ensuring that the ethylene ejection direction is tangential to the slurry rotation direction T (clockwise) on the horizontal plane. During operation, the high-speed, high-momentum ethylene jet is ejected along the stirring direction, creating a directional pneumatic purging effect on the pipe opening. This prevents initial accumulation of slurry at the pipe opening edge and adjacent inner wall, reducing the formation and aggregation of lumps in the pipe opening's inner wall. Simultaneously, because the gas cuts into the slurry flow field in the forward direction, it can smoothly integrate into the main slurry flow, reducing the vertical impact of the airflow on the slurry surface, promoting gas dispersion and material mixing, weakening local flow dead zones, avoiding rapid polymerization caused by excessively high local ethylene concentrations, and reducing the risk of lumpy material formation at the pipe opening. Example 2

[0028] This embodiment is a further optimization based on Embodiment 1. For example... Figure 5As shown, the outlet section of the ethylene inlet pipe 3 is provided with spiral guide vanes 32 and guide ribs 33 on the outer wall of the bend of the ethylene inlet pipe 3. The spiral guide vanes 32 are evenly distributed circumferentially in the bend of the ethylene inlet pipe 3, and the guide ribs 33 are arranged around the tapering section along the outlet axis of the ethylene inlet pipe 3. The spiral guide vanes 32 and guide ribs 33 help guide the slurry flow field, sort out the slurry flowing through the pipe body, eliminate dead flow angles, suppress vortices and wake zones generated by flow separation in the bend and port, and make the local flow field more smoothly integrated with the main rotating flow field in the reactor, eliminating potential material aggregation and polymer adhesion. Example 3

[0029] Further optimizations were made based on Example 1 or Example 2. The inner surface of the ethylene inlet pipe 3 was polished to a depth of 500 mm into the ethylene inlet pipe, with a polishing precision of Ra≤0.4 μm. This effectively eliminated the mechanical anchor points for initial polymer chains or slurry particles to hook and adhere, reducing polymer adhesion and aggregation. Example 4

[0030] Further optimizations were made based on Example 1 or Example 2. A low surface energy polytetrafluoroethylene coating was applied to the inner surface of the ethylene inlet pipe 3, with the coating depth extending 500 mm into the ethylene inlet pipe. The low surface energy anti-stick coating helps to further reduce material adhesion. Example 5

[0031] This embodiment provides an engineering modification method for an existing device, specifically modifying the ethylene inlet pipe of an existing slurry-process polyethylene polymerization unit to solve the problem of easy blockage at its outlet. Safety preparations are made before the modification: After the unit is shut down, the ethylene inlet pipe undergoes thorough process isolation, purging, and replacement, and the concentration of combustible gas is tested and confirmed to be within acceptable limits before any hot work can be carried out.

[0032] The modification steps are as follows: (1) Component preparation: Based on the original pipe size, design and process a replacement outlet section component. The main body of the component is a pipe section with a length of not less than 500 mm (this length needs to cover the section of the original pipe that is prone to accumulation and provide a stable area for the new flow field). The end of the pipe section is set as in any of the structures in Examples 1 to 4. (2) Old pipe removal: On the original ethylene inlet pipe, accurately measure and cut off the bottom pipe section with the same length as the new material. (3) New component connection: Connect the new outlet section component to the original pipe body by welding or flange. When welding, it is necessary to ensure that the inner wall weld is flat and smooth, without protrusions or depressions, to prevent the formation of a new flow dead zone. (4) Direction calibration: During installation, the direction of the new outlet end must be strictly calibrated so that its spray axis and the direction of the stirring flow field meet the design requirements. (5) Acceptance and commissioning: After the modification is completed, non-destructive testing is carried out, and the overall pressure drop change of the system is calculated to confirm that it is within the normal working load range of the circulating fan. After acceptance, the device is put back into use. Through the above modifications, the stagnant zone that caused the formation of block materials was eliminated from the structural source, thereby ensuring continuous and stable production of the equipment in the long-term operation and avoiding unplanned shutdowns.

[0033] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention 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 invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A clogging-resistant slurry-process polyethylene polymerization apparatus, comprising a reactor body, a stirring mechanism disposed within the reactor body, and at least one ethylene inlet pipe extending into the reactor body, characterized in that, The outlet section of the ethylene inlet pipe is designed with a tapered structure, and its inner diameter gradually decreases along the gas flow direction.

2. The anti-clogging slurry-based polyethylene polymerization apparatus according to claim 1, characterized in that, The shrinkage ratio of the outlet section of the ethylene inlet pipe is controlled between 1.2 and 1.

8.

3. The anti-clogging slurry-based polyethylene polymerization apparatus according to claim 1, characterized in that, The end of the ethylene inlet pipe is configured as a curved section, and the direction of the airflow jet at its outlet is consistent with or at an acute angle of less than 45 degrees to the direction of the rotational flow of the slurry body generated by the stirring mechanism.

4. The anti-clogging slurry-based polyethylene polymerization apparatus according to claim 3, characterized in that, The outer wall of the curved section of the ethylene inlet pipe is provided with spiral guide vanes and / or guide ribs.

5. The anti-clogging slurry-based polyethylene polymerization apparatus according to claim 4, characterized in that, The spiral guide vanes are evenly distributed circumferentially in the curved section of the ethylene inlet pipe. The guide ribs are arranged around the tapering section along the axial direction of the ethylene inlet pipe outlet.

6. The anti-clogging slurry-process polyethylene polymerization apparatus according to claim 1, characterized in that, The inner surface of the outlet section of the ethylene inlet pipe is polished.

7. A clogging-resistant slurry-based polyethylene polymerization apparatus according to claim 6, characterized in that, The polishing process extends from the outlet end inward to a depth of 100~800 mm, and the surface roughness Ra ≤ 0.4 μm.

8. The anti-clogging slurry-process polyethylene polymerization apparatus according to claim 1, characterized in that, The inner surface of the outlet section of the ethylene inlet pipe is provided with a low surface energy anti-stick coating, and the coverage depth of the coating is 100~800 mm from the outlet end inward.

9. A clogging-resistant slurry-based polyethylene polymerization apparatus according to claim 1, characterized in that, The reactor body is a batch reactor, and its top end cap is provided with at least one circulating gas inlet and at least one circulating gas outlet; The ethylene inlet pipe passes through the circulating gas inlet and extends towards the bottom of the reactor; The reactor body is also provided with at least one slurry outlet for overflow discharge and at least one raw material inlet.

10. A clogging-resistant slurry-based polyethylene polymerization apparatus according to claim 9, characterized in that, The number of circulating gas inlets is 6 to 10, arranged in a ring array along the top end cap. Correspondingly, the number of ethylene inlet pipes is 6 to 10, vertically arranged within the reactor body.

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