Plate-type stirrer for producing polyethylene by slurry method

Abstract

The utility model relates to a plate-type stirrer for producing polyethylene by a slurry method, which is a multi-section plate-type stirrer and comprises a stirring shaft vertically extending in a tank reactor; the multi-stage paddle blades are arranged along the axial direction of the stirring shaft and comprise a plurality of blade plates extending from the radial direction of the stirring shaft; the blade plate is provided with an opening part, and the blade plate is uniformly provided with through-flow holes in the area outside the opening part, so that the blade plate forms a through-flow paddle plate. According to the utility model, the plate-type stirrer with multiple stages of paddle blades is adopted, so that slurry in the kettle-type reactor generates a large-range vortex, a uniform mixing flow field in the whole kettle range is formed, a better heat and mass transfer stirring effect is realized, the kettle-type reactor can be adapted to a strong heat release ethylene polymerization reaction system, and a strong trailing vortex is generated behind the through-flow holes; the particle suspension can be realized with lower power, the particle suspension with uniform slurry concentration can be formed in the whole kettle range, and the product consistency can be improved.

Description

Technical Field

[0001] The utility model relates to the technical field of polyolefins, and particularly relates to a plate stirrer for producing polyethylene by a slurry method. Background Art

[0002] Polyethylene (abbreviated as PE) is a thermoplastic resin obtained by polymerizing ethylene monomers. Among them, ultra-high molecular weight polyethylene (abbreviated as UHMWPE) is a widely used type of polyethylene, belonging to the category of high-end polyethylene, showing excellent wear resistance, extremely high impact strength, excellent self-lubricating performance, and low-temperature resistance, etc., and is widely used in industry. High-end polyolefin products including products such as UHMWPE belong to polyolefin products with high technical content, high application performance, and high market value, and are widely used in various high-value fields, including the medical field, new energy battery separator materials, high-end filter materials, etc., and put forward very high requirements for the super consistency of polyethylene (microstructure consistency, molecular weight consistency, particle size consistency).

[0003] The slurry method is a relatively mature process for producing polyethylene at present. Specifically, an aliphatic hydrocarbon inert solvent and a monomer are dispersed in the solvent, and a polymer is generated under the action of a catalyst, and the polymer particles are suspended in the solvent. According to the form of the reactor, it is divided into a tubular slurry method and a tank slurry method. At present, most of them adopt the tank slurry process. When preparing polyethylene by the tank slurry method, the stirring reactor is the core device, which directly determines the product quality. The relatively mature stirring reactors in the prior art are as Figure 1 shown. A turbine stirrer is used. In the ultra-high molecular weight polyethylene system, the stirring effect of this stirrer is not ideal, the stirring is easy to stratify, and there is a certain dead zone, resulting in uneven and incomplete stirring. Especially when preparing UHMWPE, due to the ultra-high molecular weight of UHMWPE, it is easy to swell in the solvent, and the particles are easy to settle in the slurry, resulting in a gradient of the slurry concentration in the reactor. Coupled with the fact that the polymerization reaction is a strong exothermic reaction, under the condition of poor stirring and dispersion effect and unsatisfactory heat removal effect, local hot spots are formed in the reaction kettle, which are prone to problems such as explosion polymerization, material sticking to the wall, and caking, and it is difficult to meet the production of high-end polyethylene. Therefore, how to provide a stirring reactor that meets the production of highly consistent polyethylene by the slurry method is an urgent problem to be solved. Summary of the Utility Model

[0004] The purpose of the utility model is to provide a plate stirring reaction device and process for producing highly consistent polyethylene by a slurry method to solve the above problems.

[0005] The purpose of the utility model is achieved by the following technical solutions:

[0006] A plate stirrer for producing polyethylene by the slurry method, which is arranged in a kettle reactor. The plate stirrer is a multi-stage plate stirrer and includes:

[0007] A stirring shaft, which is vertically extended and arranged in the kettle reactor;

[0008] Multi-stage paddle blades, which are arranged along the axial direction of the stirring shaft and include a plurality of blade plates radially extending from the stirring shaft;

[0009] The blade plate is provided with an opening part, and the blade plate is uniformly provided with through-flow holes in the area outside the opening part, so that the blade plate forms a through-flow paddle plate.

[0010] As a preferred technical solution of the present utility model, the blade plate includes a root part connected to the outer peripheral surface of the stirring shaft, and a paddle part which is arranged radially away from the stirring shaft and radially extends outward from the root part and is substantially rectangular;

[0011] The height of the root part is less than the height of the corresponding paddle part;

[0012] And / or, the root part can be arranged in a stepped manner and gradually becomes wider from the stirring shaft radially outward.

[0013] As a preferred technical solution of the present utility model, the height of the root part is 30% - 50% of the height of the corresponding paddle part, and the width of the root part is 30% - 60% of the overall width of the corresponding blade plate.

[0014] As a preferred technical solution of the present utility model, the opening area of the opening part is 5 - 50% of the total area of the corresponding blade plate, preferably 10 - 20%. The opening part is preferably arranged in the paddle part or the middle area, and the shape of the opening part is not particularly limited, including square, rectangular or circular. The hollow opening part can make the plate stirrer better adapt to the polyethylene polymerization reaction system, and at the same time, it also helps to form a more complex flow field, which is beneficial to the reaction.

[0015] As a preferred technical solution of the present utility model, grid bars are arranged on the opening part, and the grid bars can divide the fluid and improve the turbulence degree. The grid bars and the upper opening part can provide a path for the strong downward flow along the axial direction of the paddle blade, which helps to form a full-kettle axial large-circulation flow pattern within the whole kettle, that is, the slurry at the bottom of the kettle flows upward and changes direction at the liquid surface, and a rapid downward flow is formed on the stirring axis.

[0016] As a preferred technical solution of the present utility model, the aperture of the flow-through hole is 1-10 cm, preferably 4-8 cm. The flow-through aperture affects the flow field. If the aperture is too large, the flow velocity of the hole is small, and sufficient shear stress cannot be generated, and sufficiently small vortices cannot be generated, and the local eddy diffusion intensity is insufficient; if the aperture is too small, the energy dissipation generated by the friction between the fluid and the hole increases, thereby affecting the effect of strengthening eddy diffusion.

[0017] As a preferred technical solution of the present utility model, the multi-stage paddle blades are arranged in 2-4 stages along the axial direction of the stirring shaft, preferably 2 stages. By arranging the multi-stage paddle blades, the rapid spiral downward flow along the axial direction is enhanced.

[0018] As a preferred technical solution of the present utility model, the lower wing of the lower blade plate is close to the bottom of the kettle-type reactor, and the contour of the lower wing is arc-shaped, which matches the shape of the bottom of the kettle-type reactor, so as to be able to stir up the bottom slurry and avoid bottom settlement.

[0019] As a preferred technical solution of the present utility model, the multi-stage paddle blades gradually become wider from top to bottom along the axial direction of the stirring shaft. A pair of paddle blades are symmetrically arranged along the axis of symmetry of each layer of paddle blades, and the upper and lower adjacent paddle blades are arranged in a staggered manner at a certain angle, and the range of the angle is 15-90°, preferably 30-60°, such as 35°, 40°, 45°, etc.

[0020] In the present utility model, the paddle blades in the lower layer are wider. The large paddle blades in the lower layer contribute to the formation of a large circulation flow within the entire kettle. The particles are transported from the bottom of the kettle to the liquid surface through this internal circulation circuit of the kettle, making the slurry concentration in the kettle more uniform. At the same time, the large blades at the bottom also make the local heat transfer coefficient distribution on the wall of the reaction kettle uniform and improve the heat transfer coefficient.

[0021] As a preferred technical solution of the present utility model, the multi-stage paddle blades are arranged in two layers along the axial direction of the stirring shaft, including narrow paddle blades in the upper layer and wide paddle blades in the lower layer;

[0022] The narrow paddle blades are provided with a long strip-shaped opening part at their paddle parts, and flow-through holes are arranged in the inner area of the long strip-shaped opening part; the wide paddle blades are provided with a square opening part in the middle area of the blade plate, and flow-through holes are arranged in the area outside the square opening part. At the root of the wide paddle blade, its lower part is provided with a step, and the lower wing of the blade plate of the wide paddle blade is arc-shaped, which matches the shape of the bottom of the kettle-type reactor.

[0023] Compared with the prior art, the present utility model has the following beneficial effects:

[0024] The utility model adopts a plate-type stirrer with multi-stage paddle blades. Compared with the traditional turbine stirrer, the paddle blades arranged axially along the stirring shaft cause a large-scale vortex in the slurry in the kettle-type reactor, forming a uniform mixing flow field of the slurry in the whole kettle range, and achieving a better heat transfer, mass transfer, stirring and dispersion effect. The blade plate is provided with a hollowed-out opening part, which can better adapt to the polyethylene polymerization reaction system with higher viscosity, so that the stirrer can maintain a suitable stirring rate for stirring. The through-flow paddle plates formed by uniformly distributed through-holes are arranged on the blade plate. A strong trailing vortex is generated behind the through-holes, and partial additional driving force will be obtained, which can increase the turbulent kinetic energy and dissipation rate of the fluid in the slurry, improve the mixing efficiency, help to suspend particles with a lower power, and form a particle suspension with a uniform slurry concentration in the whole kettle range, which helps to improve the product consistency and obtain a high-consistency polyethylene product with a uniform molecular weight distribution and particle size. At the same time, it also improves the lifting ability of the slurry to polyethylene, and realizes the uniform suspension of particles with a small power. Description of the Drawings

[0025] Figure 1 It is a schematic structural diagram of an existing turbine stirring reactor;

[0026] Figure 2 It is a schematic structural diagram of the plate-type stirrer of the utility model;

[0027] Figure 3 It is a schematic diagram of a two-stage plate-type stirrer in a certain embodiment;

[0028] Figure 4 For Figure 3 top view schematic diagram;

[0029] In the figure: 1 - stirring shaft; 2 - blade plate; 21 - opening part; 22 - through-hole; 23 - root; 24 - paddle part; 3 - kettle-type reactor; 100 - narrow paddle blade; 200 - wide paddle blade. Detailed Embodiments

[0030] The following discloses various different embodiments or examples for implementing the described subject technical solutions. To simplify the disclosure, specific examples of each element and arrangement are described below. Of course, these are only examples and do not limit the protection scope of the present utility model. For example, as subsequently described in the specification, the first feature formed above or on the second feature may include an embodiment in which the first and second features are formed by direct connection, and may also include an embodiment in which additional features are formed between the first and second features, so that the first and second features may not be directly connected. In addition, the reference numerals and / or letters may be repeated in different examples in these disclosures. This repetition is for brevity and clarity and does not itself indicate the relationship between the various embodiments and / or structures to be discussed. Further, when the first element is described as being connected or combined with the second element, this description includes embodiments in which the first and second elements are directly connected or combined with each other, and also includes embodiments in which one or more other intervening elements are added to indirectly connect or combine the first and second elements.

[0031] In addition, it should be understood that the orientation or positional relationships indicated by orientation words such as "front, back, upper, lower, left, right", "lateral, vertical, perpendicular, horizontal" and "top, bottom" are usually based on the orientation or positional relationships shown in the drawings. These are only for the convenience of describing the present utility model and simplifying the description. Without contrary instructions, these orientation words do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, so it cannot be understood as a limitation on the protection scope of the present utility model; the orientation words "inside, outside" refer to the inside and outside relative to the contour of each component itself. Using words such as "first", "second", etc. to limit components is only for the convenience of distinguishing the corresponding components. Without additional statements, these words have no special meaning and thus cannot be understood as a limitation on the protection scope of the present utility model.

[0032] At the same time, this application uses specific words to describe the embodiments of this application. Such as "one embodiment", "an embodiment", and / or "some embodiments" mean a certain feature, structure or characteristic related to at least one embodiment of this application. Therefore, it should be emphasized and noted that the "one embodiment" or "an embodiment" or "some embodiments" mentioned twice or more at different positions in this specification are not necessarily the same embodiment. In addition, certain features, structures or characteristics in one or more embodiments of this application can be appropriately combined.

[0033] The present utility model will be described in detail below with reference to the drawings. Those technical solutions that are not described in detail in the present utility model are already publicly known in the art.

[0034] Refer to Figure 2, the present utility model provides a plate stirrer for producing polyethylene by the slurry method, which is arranged in a kettle reactor 3. The plate stirrer is a multi-stage plate stirrer, including: a stirring shaft 1, which is vertically extended and arranged in the kettle reactor 3; a multi-stage paddle blade, arranged along the axial direction of the stirring shaft 1, including a plurality of blade plates 2 radially extending from the stirring shaft 1. The blade plate 2 is provided with an opening part 21, and the blade plate 2 is uniformly provided with flow-through holes 22 in the area outside the opening part 21, so that the blade plate 2 forms a flow-through paddle plate.

[0035] The present utility model provides a plate stirrer with multi-stage paddle blades. Compared with Figure 1 the traditional turbine stirrer shown, the paddle blades arranged along the axial direction of the stirring shaft 1 can cause a large-range vortex in the slurry in the kettle reactor 3, form a uniform mixing flow field in the whole kettle range, and achieve a better heat transfer, mass transfer, stirring and dispersion effect. The blade plate 2 is provided with a hollow opening part 21, which can be adapted to the polyethylene polymerization reaction system. The flow-through paddle plate formed by uniformly arranging the flow-through holes 22 on the blade plate 2 generates a strong wake behind the flow-through holes 22, obtaining some additional driving forces, increasing the turbulent kinetic energy and dissipation rate of the fluid in the slurry, improving the mixing efficiency, helping to suspend particles with a lower power, and forming a particle suspension with a uniform slurry concentration in the whole kettle range, which helps to improve the product consistency, and further obtaining a high-consistency polyethylene product with a consistent molecular weight distribution and particle size.

[0036] As a preferred embodiment, the blade plate 2 includes a root part 23 connected to the outer peripheral surface of the stirring shaft 1, and a paddle part 24 arranged radially away from the stirring shaft 1 and radially extending outward from the root part 23, which is generally rectangular. The height of the root part 23 is less than the height of the corresponding paddle part 24. The root part 23 can be arranged in a stepped manner and gradually becomes wider when radially extending outward from the stirring shaft 1 (such as Figure 3 ).

[0037] Preferably, the height of the root part 23 is 30% - 50% of the height of the corresponding paddle part 24. For example, it can be 45%. The width of the root part 23 is 30% - 60% of the overall width of the corresponding blade plate 2, such as 50%. The height of the root part 23 is less than the height of the corresponding paddle part 24.

[0038] As a preferred embodiment, the opening area of the opening part 21 is 5-50% of the total area of the corresponding blade plate 2, preferably 10-20%. The opening part 21 is preferably arranged in the paddle part 24 or the middle area, and the shape of the opening part 21 is not particularly limited, including square, rectangular or circular. The hollow opening part 21 can enable the plate-type stirrer to better adapt to the polyethylene polymerization reaction system, and at the same time helps to form a more complex flow field, which is beneficial to the reaction. As a variant or a more preferred embodiment, grid bars can be arranged on the opening part 21 to further divide the fluid and increase the turbulence intensity. The grid bars and the opening part can provide a path for the strong downward flow along the axial direction of the paddle blade, which helps to form a full-kettle axial large-circulation flow pattern within the whole kettle, that is, the slurry at the bottom of the kettle flows upward, changes direction at the liquid surface, and forms a rapid downward flow on the stirring axis.

[0039] As a preferred embodiment, the aperture diameter of the through-flow hole 22 is 1-10 cm, preferably 4-8 cm, and can be about 5 cm, for example. The through-flow aperture diameter affects the flow field. If the aperture diameter is too large, the hole flow velocity is small, insufficient shear stress can be generated, small enough vortices cannot be generated, and the local eddy diffusion intensity is insufficient; if the aperture diameter is too small, the energy dissipation generated by the friction between the fluid and the hole increases, thus affecting the role of strengthening eddy diffusion.

[0040] As a preferred embodiment, the multi-stage paddle blades are arranged in 2-4 stages along the axial direction of the stirring shaft 1. The multi-stage paddle blades gradually become wider from top to bottom along the axial direction of the stirring shaft 1. A pair of paddle blades are symmetrically arranged along the stirring shaft 1 for each layer. The upper and lower adjacent paddle blades are arranged in a staggered manner at a certain angle α, and the range of the angle α is 15-90°, preferably 30-60°, such as 35°, 40°, 45°, etc.

[0041] Such as Figure 3As shown, in a specific embodiment, a two-stage plate stirrer is adopted. The paddle blades are arranged in two layers along the axial direction of the stirring shaft 1, including the narrow paddle blades 100 in the upper layer and the wide paddle blades 200 in the lower layer. The continuous slurry method is used to prepare polyethylene, and the raw materials enter from the bottom. The large paddle blades help to form a large circulation flow within the entire reactor. The particles are transported from the bottom of the reactor to the liquid surface through this internal circulation loop of the reactor, making the slurry concentration in the reactor more uniform. At the same time, the large bottom blades also make the local heat transfer coefficient distribution on the reactor wall uniform, improving the heat transfer coefficient. Such paddle blades of different sizes are beneficial to maintaining the uniformity of the overall slurry in the reactor. The narrow paddle blades 100 are provided with strip-shaped opening parts at their paddle parts, and through holes are arranged in the inner area of the strip-shaped opening parts; the wide paddle blades 200 are provided with square opening parts in the middle area of the blade plate, and through holes are arranged in the area outside the square opening parts. The through holes help to obtain a highly consistent polyethylene product with a uniform molecular weight distribution and particle size. At the root of the wide paddle blades 200, the lower part is stepped, and the lower wing of the blade plate of the wide paddle blades 200 is arc-shaped, matching the shape of the bottom of the kettle-type reactor. The lower wing is close to the bottom of the kettle-type reactor 3, and the upper and lower paddle blades are arranged in a staggered angle of about 35° (as Figure 4 shown), and the paddle blades arranged in a staggered angle form a complex flow field distribution, which is beneficial to the uniform stirring of the slurry.

[0042] The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and use the utility model. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, the present utility model is not limited to the above embodiments, and all improvements and modifications made by those skilled in the art without departing from the scope of the present utility model according to the disclosure of the present utility model should be within the protection scope of the present utility model.

Claims

1. A plate agitator for producing polyethylene by a slurry process, arranged in a tank reactor (3), characterized in that: The plate stirrer is a multi-stage plate stirrer, comprising: A stirring shaft (1) is vertically extended in the kettle reactor (3); Multi-stage paddle blades are arranged along the axial direction of the stirring shaft (1), and include a plurality of blade plates (2) extending radially from the stirring shaft (1); The blade plate (2) is provided with an opening portion (21), and the blade plate (2) is evenly provided with through-flow holes (22) in an area outside the opening portion (21), so that the blade plate (2) forms a through-flow paddle plate.

2. A plate agitator for producing polyethylene by a slurry process according to claim 1, characterized in that: The blade plate (2) comprises a root portion (23) connected to the outer peripheral surface of the stirring shaft (1), and a substantially rectangular paddle portion (24) radially arranged away from the stirring shaft (1) and extending radially outward from the root portion (23); The height of the root portion (23) is smaller than the height of the corresponding paddle portion (24); And / or, the root portion (23) may be arranged in a stepped manner, extending radially outward from the stirring shaft (1) and gradually becoming wider.

3. A plate agitator for producing polyethylene by a slurry process according to claim 2, characterized in that: The height of the root portion (23) is 30% to 50% of the height of the corresponding paddle portion (24), and the width of the root portion (23) is 30% to 60% of the overall width of the corresponding blade plate (2).

4. A plate agitator for producing polyethylene by a slurry process according to claim 2, characterized in that: The opening area of ​​the opening portion (21) is 5-50% of the total area of ​​the corresponding blade plate (2), and the opening portion (21) is arranged on the paddle portion (24) or in the middle area.

5. A plate agitator for producing polyethylene by a slurry process according to claim 4, characterized in that: The opening portion (21) is provided with grid bars.

6. A plate agitator for producing polyethylene by a slurry process according to claim 1, characterized in that: The diameter of the flow-through hole (22) is 1 to 10 cm.

7. A plate agitator for producing polyethylene by a slurry process according to claim 1, characterized in that: The multi-stage paddle blades are arranged in 2 to 4 stages along the axial direction of the stirring shaft (1); The lower wing of the blade plate (2) at the lower layer is close to the bottom of the kettle reactor (3), and the contour of the lower wing is arc-shaped, matching the shape of the bottom of the kettle reactor (3).

8. A plate agitator for producing polyethylene by a slurry process according to claim 7, characterized in that: The multi-stage paddle blades gradually widen from top to bottom along the axial direction of the stirring shaft (1); each layer of paddle blades is symmetrically arranged in a pair along the stirring shaft (1); and the upper and lower adjacent paddle blades are staggered at a certain angle, and the angle ranges from 15 to 90 degrees.

9. A plate agitator for producing polyethylene by a slurry process according to claim 8, characterized in that: The multi-stage paddle blades are arranged in two layers along the axial direction of the stirring shaft (1), including narrow paddle blades (100) in an upper layer and wide paddle blades (200) in a lower layer; The narrow paddle blade (100) is provided with a long strip opening portion at its paddle portion, and a through-flow hole is provided in the inner area of ​​the long strip opening portion; The wide paddle blade (200) is provided with a square opening portion in the middle area of ​​the blade plate, and flow holes are provided in the area outside the square opening portion.

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