CN114073927A

CN114073927A - Reaction kettle and production method of polyethylene

Info

Publication number: CN114073927A
Application number: CN202010832087.4A
Authority: CN
Inventors: 阳永荣; 程嘉猷; 刘宝庆; 成卫戍; 林兴华; 安永明; 王靖岱; 黄正梁
Original assignee: China Petroleum and Chemical Corp; Zhejiang University ZJU
Current assignee: China Petroleum and Chemical Corp; Zhejiang University ZJU
Priority date: 2020-08-18
Filing date: 2020-08-18
Publication date: 2022-02-22

Abstract

The invention provides a reaction kettle and a method for producing polyethylene by using the reaction kettle. The reaction kettle comprises a kettle body and a stirring system arranged in the kettle body, wherein the stirring system comprises a stirring shaft (8), the bottom of the stirring shaft (8) is connected with a stabilizer (11) used for stabilizing the stirring shaft, the top of the stirring shaft is connected with a first rolling bearing (5), and the middle of the stirring shaft is connected with one or more second rolling bearings (9). The stirring shaft adopts a fixing mode of upper and middle bearing support. The conventional bottom bearing is abandoned, the top bearing is adopted, the bearing lubrication is improved, the bearing abrasion is reduced, and meanwhile, the cantilever at the lower end of the stirring shaft is free from restriction on high-temperature expansion and does not have thermal stress. Especially, the arrangement of the bottom stabilizer can effectively improve the radial swing of the stirring shaft, ensure that the stirring paddle with large paddle diameter ratio does not collide the wall, improve the material flowing condition near the wall surface, avoid wall adhesion, reduce the abrasion of a bearing and realize long-period stable operation.

Description

Reaction kettle and production method of polyethylene

Technical Field

The invention particularly relates to a reaction kettle and a production method of polyethylene.

Background

Low Density Polyethylene (LDPE) has wide application requirements by virtue of excellent properties such as light weight, good flexibility, low temperature resistance, impact resistance and the like. At present, the production process of LDPE can be classified into tubular and kettle processes, depending on the type of reactor. The tubular reactor is mainly characterized in that material flows flow in a plunger shape in the tube, the back mixing phenomenon is avoided, the reaction temperature changes along the length of the reaction tube, and the molecular weight distribution of the obtained polyethylene is relatively wide; the tank reactor is usually equipped with a mechanical stirring device, so that the materials can be fully mixed, the reaction temperature is relatively uniform, and the tank reactor can be operated in a subarea manner, so that each reaction area has different temperatures, and the polyethylene with narrower molecular weight distribution can be obtained. In addition, compared with the tubular process, the kettle process has relatively low operating pressure and temperature, the operating pressure is usually 120MPa to 250MPa, the operating temperature is usually 130 ℃ to 280 ℃, and LDPE products with more long chain branches can be produced. Therefore, the tank method is an indispensable mainstream technology in producing a copolymer of ethylene and a polar monomer such as LDPE or EVA based on a high pressure radical polymerization mechanism.

Because the kettle type LDPE production process needs to be operated in the environment of ultrahigh pressure and high temperature, higher requirements are put on the sealing of the device; meanwhile, the ethylene polymerization reaction process is a violent exothermic process, if heat cannot be transferred in time, ethylene decomposition is easy to explode, and particularly in a large-volume stirring kettle (the volume is more than 250L) or a stirring kettle (the temperature is more than 200 ℃) operated under a high-temperature condition, local hot spots are easy to occur due to poor stirring and mixing, so that ethylene decomposition and explosion are easy to occur. In addition, the ethylene polymer has high viscosity, and is easy to accumulate and attach on the inner wall of the reaction kettle when the fluidity is poor. Therefore, in the production of the kettle type LDPE, the reasonable solution of the problems of sealing, temperature control, scaling and the like is of great importance, so that higher requirements are provided for the structural design of a high-temperature high-pressure reaction kettle of a process core device.

In order to solve the sealing problem in a high-pressure environment, most of the existing LDPE reaction kettles adopt a layout mode of a built-in stirring driving motor, so that the problem of dynamic sealing is avoided; the problems of local hot spots and polymer wall sticking are avoided by adopting a large-diameter multi-layer paddle stirring mode. For example, US patent US3756996 proposes to reasonably configure the type, number, installation angle, etc. of the multiple layers of stirring paddles to obtain the required flow pattern and optimize the mixing; chinese patent CN201380062499.2 proposes to provide elongated baffles on the inner wall of an autoclave reactor, which have sufficient length, depth and number to convert a rotating tangential flow into an axial flow, while promoting radial flow. Although the kettle-type polyethylene production has been in the history for decades, new structures are proposed, but the problems of high-quality mixing of the LDPE high-temperature high-pressure reaction kettle, vibration of the high-speed long and thin stirring shaft, expansion of the stirring system in the high-temperature environment, service life of the supporting bearing, heat exchange of the autoclave body and the like are not well solved or cannot be well coordinated and matched, and improvement is urgently needed.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides, in a first aspect, a reaction kettle, in which a stirring device in the reaction kettle is structurally and innovatively designed, so that the reaction kettle can better mix, reduce vibration, prolong service life and exchange heat, and further improve the safety and economy of system operation. In a second aspect of the invention, a process for producing polyethylene in a reaction tank provided by the invention is provided.

According to the first aspect of the invention, the reaction kettle comprises a kettle body and a stirring system arranged in the kettle body, wherein the stirring system comprises a stirring shaft (8), the bottom of the stirring shaft (8) is connected with a stabilizer (11) for stabilizing the stirring shaft, the top of the stirring shaft is connected with a first rolling bearing (5), and the middle of the stirring shaft is connected with one or more second rolling bearings (9).

According to some embodiments of the invention, the stabilizer (11) comprises a hollow cylinder.

According to some embodiments of the invention, the outer diameter of the hollow cylinder is 50-85% of the diameter of the kettle body.

According to some embodiments of the invention, the clearance between the outer diameter of the hollow cylinder and the inner wall of the kettle body is 15-50% of the diameter of the kettle body.

The diameter of the kettle body refers to the inner diameter of the barrel part of the reaction kettle.

According to some embodiments of the invention, the hollow cylinder has an aspect ratio of 0.5 to 1.0.

The aspect ratio of the hollow cylinder in the present invention refers to a ratio of a height of the hollow cylinder to an outer diameter of the hollow cylinder.

According to some embodiments of the invention, the hollow cylinder is provided with symmetrical vertical grids or gaps, and the grids or gaps are beneficial to forming acting force opposite to the radial movement direction of the stirring shaft.

According to the invention, by adopting the hollow cylinder with a specific structure and size as the stabilizer, the radial swing of the stirring shaft can be effectively reduced. The cylinder is too high or too large, which affects the flow of the materials in the stirring kettle, and is too short or too small, which has poor stabilizing effect on the stirring shaft.

According to some embodiments of the invention, the stirring shaft (8) is a hollow shaft, and the hollow shaft can reduce the self weight of the shaft while ensuring the strength.

According to some embodiments of the invention, the stirring shaft has a rotational speed of not less than 750 revolutions per minute. The preferable scheme is that the stirring shaft is a hollow slender shaft rotating at high speed.

According to some embodiments of the invention, said first rolling bearing (5) is a radial rolling bearing and a thrust rolling bearing for fixing and carrying said stirring shaft.

According to some embodiments of the invention, the second rolling bearing (9) is a centripetal rolling bearing for stabilizing the stirring shaft.

The upper end of the stirring shaft is fixed and supported by a combined rolling bearing consisting of a radial bearing and a thrust bearing, the middle of the stirring shaft is restrained by the radial rolling bearing, and the lower end of the stirring shaft is provided with a stabilizer for reducing the radial swinging amount of the stirring shaft.

According to some embodiments of the invention, a first stirring paddle (6) and a second stirring paddle (7) are connected to the stirring shaft (8).

According to some embodiments of the invention, the first stirring paddle (6) is a radial flow paddle.

According to some embodiments of the invention, the gap between the radial paddles and the inner wall of the kettle body is not more than 20 mm.

According to some embodiments of the invention, the gap between the radial paddles and the inner wall of the kettle body is 5-15 mm.

According to some embodiments of the invention, the second stirring blade (7) is a pitched-blade axial flow blade.

According to some embodiments of the invention, the pitched blade axial flow blade comprises at least 2 circumferentially equispaced blades, the ratio of the blade width to the diameter being 0.05-0.3.

The ratio of the blade width to the diameter (blade length) in the present invention refers to the ratio of the maximum value of the blade width to the blade diameter. According to some embodiments of the invention, the blade tip has a clearance from the inner wall of the vessel body of no more than 20 mm.

According to some embodiments of the invention, the clearance between the tips of the blades and the inner wall of the kettle body is 2-10 mm.

The connection mode of the stabilizer and the stirring shaft in the invention is the conventional connection mode in the field, and preferably, the wall of the hollow cylinder is connected with the upper part or the lower part of the tip of the radial blade of the second stirring paddle.

According to some embodiments of the invention, the kettle body comprises an upper end enclosure (1), a thick-walled cylinder (2) and a lower end enclosure (13).

According to some embodiments of the invention, the stirring system further comprises a drive means (3) and a connection means (4).

According to some embodiments of the invention, the driving device (3) is fixed in the upper seal head (1) of the kettle body, and the upper end of the stirring shaft (8) is connected with the driving device (3) through a connecting device (4) and penetrates through the reaction kettle.

According to some embodiments of the invention, the drive means (3) is an electric motor.

According to some embodiments of the invention, the connection means (4) is a spline.

According to some embodiments of the invention, the distance between the bottom stabilizer of the stirring shaft and the connecting line between the kettle bottom cylinder and the lower seal head is 0-0.2D, wherein D is the inner diameter of the kettle body.

According to some embodiments of the invention, N partition plates (10) are arranged inside the kettle body, and the reaction kettle is divided into 1 st to (N + 1) th reaction zones from top to bottom, wherein N is a positive integer from 0 to 16.

According to some embodiments of the present invention, in each reaction zone, 1 first stirring paddle (6) and at least 3 second stirring paddles (7) are connected to the stirring shaft (8), respectively.

According to some embodiments of the present invention, the first stirring paddle (6) is located above the second stirring paddle (7) in the respective reaction zone.

According to some embodiments of the invention, the first stirring paddle (6) is located uppermost in the respective reaction zone.

According to some embodiments of the invention, said at least 3 second stirring paddles (7) are fixed to said stirring shaft in a spiral arrangement at equal axial distances.

The stirring shaft (8) penetrates through the reaction kettle, namely the uppermost stirring paddle of the stirring shaft is positioned in the first reaction zone, and the bottom of the stirring shaft and the stabilizer connected with the bottom are positioned in the (N + 1) th reaction zone.

According to some preferred embodiments of the present invention, 1 partition (10) is disposed inside the kettle body, and the reaction kettle is divided into a first reaction zone and a second reaction zone from top to bottom.

According to some preferred embodiments of the present invention, 1 first stirring blade (6) and at least 3 second stirring blades (7) are sequentially connected to the stirring shaft of the first reaction zone from the first rolling bearing (5) to the partition plate (10).

According to some preferred embodiments of the present invention, 1 first stirring blade (6) and at least 3 second stirring blades (7) are connected to the stirring shaft of the second reaction zone from the partition plate (7) to the stabilizer (11).

According to some embodiments of the invention, the kettle is a vertical kettle.

According to some embodiments of the invention, the vertical kettle body has a height-diameter ratio of 10 or more.

According to some embodiments of the invention, the upper head and the thick-wall cylinder of the vertical kettle body are provided with feed inlets (A).

According to some embodiments of the invention, the upper head of the kettle body is provided with a feed port A1, and the thick-wall cylinder body is provided with feed ports A2 and A3.

According to some embodiments of the invention, a discharge hole (C) is arranged on the lower end socket of the kettle body.

According to some embodiments of the invention, the outer side of the thick-wall cylinder is provided with a heat exchange jacket (12) which is provided with a heat exchange medium inlet and outlet (B), and preferably, the heat exchange jacket (12) adopts a split half-tube jacket structure.

According to some preferred embodiments of the invention, the outer side of the thick-wall cylinder body is provided with heat exchange jackets (12) corresponding to the inner reaction zone in sections, and the jackets are respectively provided with a heat exchange medium inlet and outlet (B).

According to a second aspect of the present invention, the process for producing polyethylene comprises carrying out the reaction in the reaction tank of the first aspect, preferably comprising the steps of:

s1: feeding an ethylene raw material stream 3 into a reaction kettle through feed inlets A1, A2 and A3, feeding an initiator stream 2 into the reaction kettle through feed inlets A2 and A3, and carrying out a polymerization reaction by dispersing and mixing the ethylene and the initiator under the action of a stirring system, preferably a first stirring paddle (6) to generate polyethylene;

s2: polyethylene generated by the reaction and unreacted raw materials axially flow in the reaction kettle under the action of a stirring system, preferably a second stirring paddle (7), and finally are discharged from a discharge hole (C).

Compared with the existing high-temperature high-pressure polymerization reaction kettle, the invention has the following outstanding characteristics and beneficial effects:

(1) the safe and stable operation of longer period can be realized. The radial swing of the long and thin stirring shaft rotating at high speed is usually large, on one hand, the stirring blade with a large blade diameter ratio touches the kettle wall, so that the kettle wall is damaged and the shaft and the blade are deformed, on the other hand, the long-term large swing can shorten the service life of the support bearing, and particularly has large influence on the bottom bearing. The problem is more prominent particularly in the harsh environment of high speed, high pressure and high temperature, and when a stirring paddle with a large paddle diameter ratio is adopted. The invention adopts a mode of supporting and fixing the upper bearing and the middle bearing, the bearing is transferred from the bottom to the top, which is beneficial to improving the bearing lubrication and reducing the bearing abrasion, and meanwhile, the cantilever at the lower end of the stirring shaft is free from the restriction of high-temperature expansion and does not have thermal stress. Especially, the arrangement of the bottom stabilizer can effectively improve the radial swing of the stirring shaft. The improved structure can ensure that the stirring paddle with the large paddle diameter ratio does not collide the wall, improve the material flowing condition near the wall surface, avoid wall adhesion, reduce bearing abrasion and realize long-period stable operation.

(2) The stirring and mixing effect is enhanced. The polymerization reaction kettle is provided with the stirring paddle with a large paddle diameter ratio in the full height range, so that the high-efficiency mixing mass transfer in the whole area is realized. Besides the axial flow adjusting function of the inclined blade, the axial spiral arrangement of the multilayer inclined blade axial flow blades also generates a circulation effect similar to a helical ribbon stirring blade, and further strengthens the axial circulation flow in the slender kettle body.

(3) The heat exchange effect between the materials in the kettle and the jacket medium is better, the temperature can be effectively controlled, and local overheating is avoided. The polymerization reaction kettle adopts a slender structure with a larger height-diameter ratio, the radial temperature gradient between the center of the kettle body and the wall surface is reduced, meanwhile, the axial circulation of fluid is further enhanced by the multi-layer large-diameter-ratio inclined blade axial flow blades which are spirally arranged in the full height range, the heat transfer enhancement is facilitated, and the inert region can be effectively eliminated. In addition, the split half-pipe jacket arranged outside the kettle body has a larger convection heat transfer coefficient compared with the jacket of the traditional polymerization reaction kettle.

Drawings

FIG. 1 is a schematic structural diagram of a high-temperature high-pressure polymerization reactor provided by an embodiment of the invention,

in the figure: 1. the device comprises an upper end enclosure, 2, a kettle body, 3, a motor, 4, a spline, 5, an upper bearing, 6, a radial flow paddle, 7, an inclined blade axial flow paddle, 8, a stirring shaft, 9, a middle bearing, 10, a horizontal partition plate, 11, a stabilizing device, 12, a jacket, 13 and a lower end enclosure; a1, A2 and A3 as raw material inlets; b1, B2, B3 and B4 as heat exchange medium inlets and outlets; c1, discharge hole; and D, emptying the air outlet.

FIG. 2 is a schematic diagram of a spiral and equiaxed arrangement of a multi-layer diagonal vane axial flow propeller according to an embodiment of the present invention,

in the figure: 8. a stirring shaft, 7, an oblique blade axial flow paddle.

Figure 3 is a schematic diagram of the structural principle of the stabilizer provided by the embodiment of the invention,

in the figure: 7. stirring paddle, 11, stabilizer, 14 and gap.

Fig. 4 is a schematic structural view of a split half-pipe jacket according to an embodiment of the present invention.

Detailed Description

The technical solution of the present invention is described in detail below with reference to the accompanying drawings, which are only drawn for illustrating the basic contents of the present invention and do not limit the scope of the present invention.

As shown in attached figure 1, the reaction kettle provided by the embodiment of the invention comprises a vertical kettle body and a stirring system; the vertical kettle body is a closed container which is formed by an upper end enclosure 1, a thick-wall cylinder 2 and a lower end enclosure 13 together, is in a slender structure, and the ratio of the height to the inner diameter of the vertical kettle body is not less than 10; the stirring system consists of a motor 3, a spline 4, a stirring shaft 8, an upper radial flow paddle, a middle radial flow paddle 6, a stabilizer 11 and a plurality of layers of oblique blade axial flow paddles 7 which are uniformly distributed in a partition way; the interior of the vertical kettle is divided into two different reaction zones by a partition plate 10. The upper end enclosure 1 and the thick-wall cylinder 2 of the vertical kettle body are sequentially provided with a feeding pipe A1, a feeding pipe A2 and a feeding pipe A3 from top to bottom, the center of the lower end enclosure of the vertical kettle body is provided with a discharging port C, and the side wall of the vertical kettle body is also provided with a vent for connecting with an explosion venting device; the outer side of the thick-wall cylinder body and the inner reaction zone are correspondingly provided with 2 sections of heat exchange jackets 12, and each section of jacket is respectively provided with a heat exchange medium inlet and outlet pipe B1, B2, B3 and B4; the driving motor 3 in the stirring system is directly fixed in the upper space of the vertical kettle body 2 in the middle and is connected with the long and thin stirring shaft 8 through the spline 4, the upper end and the middle part of the stirring shaft 8 are provided with the upper radial paddle and the middle radial paddle 6 of the wide blade, and the lower end of the stirring shaft 8 is provided with the stabilizer 11.

As shown in the attached figure 1, the stirring shaft 8 is a hollow slender shaft rotating at a high speed, the upper end of the stirring shaft is fixed and supported by a combined rolling bearing 5 consisting of a radial bearing and a thrust bearing, the middle of the stirring shaft is restrained by the radial rolling bearing 9, and the lower end of the stirring shaft is provided with a stabilizer 11 for reducing the radial swinging amount of the stirring shaft.

The inclined blade axial flow propeller 7 is provided with at least 2 narrow blades, the blades are annularly and uniformly distributed, and the gap between the tip ends of the blades and the inner wall of the kettle body is not more than 20 mm. The multilayer inclined blade axial flow propeller with uniformly distributed subareas is characterized in that: a plurality of layers of oblique blade axial flow propellers are uniformly distributed between the upper radial flow propeller and the horizontal clapboard; a plurality of layers of oblique blade axial flow propellers are uniformly distributed between the middle radial flow propeller and the stabilizer; the multi-layer inclined blade axial flow propellers of each subarea are spirally arranged and are fixed on the stirring shaft at equal intervals, the arrangement mode is shown as the attached figure 2, and the thread pitch and the number of the blades can be adjusted according to specific working conditions.

As shown in fig. 3, the stabilizer is composed of radial blades and a hollow cylinder, wherein vertical grids or notches are symmetrically arranged on the hollow cylinder, and the hollow cylinder can be welded on the upper part or the lower part of the tip end of each radial blade as required.

As shown in attached figure 4, the heat exchange jacket adopts a split type half-pipe jacket structure, and all the half-pipe jackets are connected and tightly covered on the outer wall of the kettle body through bolts.

The working principle of the reaction kettle provided by the embodiment of the invention is as follows:

in the working process, reaction raw material ethylene is compressed by an upstream compressor and then is divided into 3 streams which respectively enter the reaction kettle from a feed pipe A1 at the upper end socket of the reaction kettle and feed pipes A2 and A3 on a thick-wall cylinder. The initiator required for the polymerization was split into 2 streams and fed to the reactor via feed lines A2 and A3, respectively. Because no initiator is arranged above the feeding pipe A2, the heat release of the polymerization reaction can not occur, and the cold ethylene feeding has good cooling effect, the motor and the upper combined rolling bearing work in the normal temperature environment, and the service life of the motor and the upper combined rolling bearing can be effectively prolonged.

The high-pressure ethylene and the initiator entering the reaction kettle from the feeding pipes A2 and A3 are quickly dispersed and mixed under the action of the upper radial paddle and the middle radial paddle to generate free radicals under the conditions of high temperature and high pressure to initiate polymerization reaction, and simultaneously release a large amount of reaction heat. Polyethylene generated by reaction and unreacted raw materials axially flow in the kettle under the combined action of the multilayer inclined blade axial flow paddles which are spirally and axially arranged, and are finally led out from a discharge hole C in the center of the lower seal head for further separation. By adjusting the operating conditions and the initiator addition of the two reaction zones divided by the partition board, polyethylene with different properties can be produced, and the product performance can be regulated.

The working process is initial, and a heat medium is introduced into the heat exchange jacket outside the thick-wall kettle body, so that the temperature in the reaction kettle is quickly raised to the required reaction temperature. After the reaction formally starts, a refrigerant is introduced into the heat exchange jacket to cool the kettle wall and keep the temperature in the kettle proper and stable due to the release of a large amount of reaction heat.

The weight of the stirring shaft rotating at high speed and the paddle parts symmetrically arranged on the stirring shaft is shared by the upper combined rolling bearing and the fluid buoyancy in the operation process, and the radial swinging amount is controlled by the upper combined rolling bearing, the middle radial bearing and the bottom stabilizer.

Example 1

An apparatus for producing low density polyethylene using the reactor shown in figure 1, comprising a first compressor for compressing ethylene to an intermediate pressure, a second compressor for compressing ethylene to a reaction pressure, located upstream of the reactor; a high-pressure separator for separating unreacted ethylene and polyethylene, and a low-pressure separator for separating ethylene and volatile oligomer components, which are located downstream of the reaction vessel. Wherein the inner diameter of the reaction kettle is 500mm, the height of the cylinder body is 8000mm, the shaft diameter is 145mm, the total length of the shaft is 5500mm, and the length of the downward extending shaft is 2750 mm; 9 layers of inclined blade axial flow propellers are uniformly distributed between the upper radial flow propeller and the horizontal partition plate in an inserting manner; 9 layers of inclined blade axial flow paddles are also uniformly distributed between the middle radial flow paddle and the stabilizer in an inserting way, and the outer diameter of each inclined blade axial flow paddle is 480 mm. The stabilizer parameters were: the outer diameter of the cylinder is 360mm, the inner diameter is 350mm, the height is 70mm, and 4 vertical notches with the width of 20mm are arranged. Low density polyethylene LDPE is produced under the conditions of 165MPa and 270 ℃ and the stirring speed is 1000 rpm.

The initiator and ethylene entering the reaction kettle from A2 and A3 are quickly dispersed and mixed under the action of straight-blade paddle to generate free radicals under the high-temperature condition, so that the polymerization reaction is initiated to generate a large amount of reaction heat. Then the mixture flows and is mixed in the reaction kettle along the axial direction under the action of the inclined blade paddle. By adjusting the operating conditions of the two subareas and the addition amount of the initiator, the polyethylene with different properties can be produced, and the product performance can be regulated and controlled. Polyethylene generated by the reaction and unreacted raw materials are led out from a discharge port C at the bottom of the reaction kettle and then are conveyed to a high-pressure separator and a low-pressure separator. Unreacted ethylene and reaction product polyethylene are separated in the high-pressure separator and the low-pressure separator, before the unreacted ethylene from the high-pressure separator returns to the second compressor, before the unreacted ethylene from the low-pressure separator returns to the first compressor, and polyethylene obtained by separation is conveyed to a downstream working section as a product.

The operation result shows that the radial swinging quantity of the lower shaft end meets the engineering requirement (the swinging quantity is less than 6 mm).

Comparative example 1

An apparatus for producing low density polyethylene using the reaction vessel shown in FIG. 1 is different from the examples in that a stabilizer is not installed at the bottom of the stirring shaft. The operation result shows that the swinging quantity of the lower shaft end is 15.2mm, which does not meet the engineering requirement.

It should be noted that the above-mentioned embodiments are only for explaining the present invention, and do not constitute any limitation to the present invention. The present invention has been described with reference to exemplary embodiments, but the words which have been used herein are words of description and illustration, rather than words of limitation. The invention can be modified, as prescribed, within the scope of the claims and without departing from the scope and spirit of the invention. Although the invention has been described herein with reference to particular means, materials and embodiments, the invention is not intended to be limited to the particulars disclosed herein, but rather extends to all other methods and applications having the same functionality.

Claims

1. The utility model provides a reaction kettle, includes the cauldron body and sets up the internal stirring system in cauldron, stirring system includes (mixing) shaft (8), the bottom of (mixing) shaft (8) is connected with and is used for stabilizing stabilizer (11) of (mixing) shaft, the top is connected with first antifriction bearing (5), and the middle part is connected with one or more second antifriction bearing (9).

2. A reactor according to claim 1, characterized in that the stabilizer (11) comprises a hollow cylinder,

preferably, the outer diameter of the hollow cylinder is 50-85% of the diameter of the kettle body, and the clearance between the outer diameter of the hollow cylinder and the inner wall of the kettle body is 15-50% of the diameter of the kettle body; and/or the height-diameter ratio of the hollow cylinder is 0.5-1.0;

and/or the hollow cylinder is provided with symmetrical vertical grids or gaps.

3. The reactor according to claim 1 or 2, characterized in that the stirring shaft (8) is a hollow shaft;

and/or the first rolling bearing (5) is a centripetal rolling bearing and a thrust rolling bearing and is used for fixing and bearing the stirring shaft;

and/or the second rolling bearing (9) is a radial rolling bearing for stabilizing the stirring shaft.

4. A reaction kettle according to any one of claims 1 to 3, characterized in that the stirring shaft (8) is connected with a first stirring paddle (6) and a second stirring paddle (7),

preferably, the first stirring paddle (6) is a radial flow paddle, and preferably, the gap between the radial flow paddle and the inner wall of the kettle body is not more than 20mm, and preferably 5-15 mm;

and/or the second stirring paddle (7) is a diagonal blade axial flow paddle, preferably, the diagonal blade axial flow paddle comprises at least 2 blades which are circumferentially and uniformly distributed, the ratio of the width to the diameter of each blade is 0.05-0.3, more preferably, the clearance between the tip of each blade and the inner wall of the kettle body is not more than 20mm, and preferably 2-10 mm;

more preferably, the wall of the hollow cylinder is connected to the upper or lower part of the tip of the radial blade of the second stirring paddle.

5. A reactor according to any one of claims 1-4, characterized in that the tank comprises an upper head (1), a thick-walled cylinder (2) and a lower head (13), and/or the stirring system further comprises a driving device (3) and a connecting device (4).

6. The reaction kettle according to any one of claims 1 to 5, wherein the driving device (3) is fixed in the upper seal head (1) of the kettle body, the upper end of the stirring shaft (8) is connected with the driving device (3) through a connecting device (4), and the stirring shaft penetrates through the reaction kettle, preferably, the distance between the stabilizer at the bottom of the stirring shaft and a connecting line between the cylinder body and the lower seal head is 0-0.2D, wherein D is the inner diameter of the kettle body.

7. The reaction kettle according to any one of claims 1 to 6, wherein N partition plates (10) are arranged inside the kettle body, and the reaction kettle is divided into 1 st to N +1 st reaction zones from top to bottom, wherein N is a positive integer of 0 to 16;

preferably, in each reaction zone, the stirring shaft (8) is connected with 1 first stirring paddle (6) and at least 3 second stirring paddles (7) respectively, preferably, the first stirring paddle (6) is located above the second stirring paddle (7), and the at least 3 second stirring paddles (7) are spirally arranged and are fixed on the stirring shaft at equal axial distance.

8. The reaction kettle according to any one of claims 1 to 7, wherein the kettle body is a vertical kettle body, and preferably, the height-diameter ratio of the vertical kettle body is greater than or equal to 10.

9. The reaction kettle according to any one of claims 1 to 8, wherein a feed inlet A1 is arranged on the upper end socket (1) of the kettle body, and feed inlets A2 and A3 are arranged on the thick-walled cylinder (2) of the kettle body;

a discharge hole (C) is arranged on the lower seal head (13) of the kettle body,

the outer side of the thick-wall cylinder (2) is provided with a heat exchange jacket (12) which is provided with a heat exchange medium inlet and outlet (B), and preferably, the heat exchange jacket (12) adopts a split half-tube jacket structure.

10. A process for the production of polyethylene comprising carrying out a reaction in a reactor according to any one of claims 1-9, preferably comprising the steps of: