A high-pressure polyethylene reactor with a stirrer of a new structure

Abstract

A high-pressure polyethylene reactor with a novel structure stirrer of the present invention adopts a combination of multiple groups of wave-wheel type blades and inner and outer double spiral ribbon type blades, separating the reactor into multiple reaction zones. A 4-column combined cross-section shaft without a central through-shaft does not increase the cross-sectional area occupied by the shaft, improves the stiffness of the shaft, and eliminates the flow dead zone in the mixing zone. The wave-wheel type blade adopts a structure with a small gap between one layer of blades and the reactor wall and a central opening, allowing the liquid to mainly flow out from the central hole during stirring. The next layer of blades has a large gap with the reactor wall and no central opening, and the liquid mainly flows out from the outer ring of the impeller during stirring. Such an alternating arrangement extends the residence time. The lower part adopts a full-circle spiral ribbon blade to prevent the blade from bending and can boost the downward flow of the liquid. Due to the improved stiffness of the shaft, no bearing seat is provided in the middle of the stirrer and is provided at both ends. This novel structure stirrer has no dead zone in the reactor, is suitable for mixing high-viscosity materials, and is also suitable for high-pressure polyethylene reactors with a volume of 0.75 to 5 m3.

Description

Technical Field

[0001] The present invention belongs to the technical field of equipment for the production of high-pressure polyethylene by the autoclave process, and particularly relates to a high-pressure polyethylene reactor with a stirrer of a novel structure. Technical Background

[0002] The autoclave process for the production of high-pressure polyethylene (LDPE) is a key equipment in the polymerization process. The complex non-ideal flow formed in the reactor is closely related to the reaction process, which not only determines the rate and conversion of the free radical polymerization reaction, but also has a significant impact on the molecular weight distribution and the distribution of long and short branches of the product. The production conditions of high-pressure polyethylene are high temperature (200 - 300 °C) and ultra-high pressure (200 - 350 MPa). The height-to-diameter ratio of the reactor is about 9 - 15:1. Since the autoclave reactor is a thick-walled container, the heat transfer through the reactor wall is limited, so the reaction is basically an adiabatic process, and there is no obvious heat removed from the reactor. The reaction temperature is mainly controlled by injecting cold ethylene feed at multiple points to balance the reaction heat. The motor is installed inside the reactor to drive the stirrer to make the mixture in the reactor uniform and avoid the appearance of local hot spots. Organic peroxides are used as initiators and are injected at multiple points along the axial direction of the reactor to form multiple reaction sections with different operating temperatures. There is no backmixing between the reaction sections, and the operation is flexible with a wide product range.

[0003] The French company CDF uses one reactor per line for production, and the maximum volume of the reactor reaches 1.6 m 3 , which is one of the reactors in the world. The stirrer inside the reactor uses five throttle rings and turbine blades to divide the reactor into five reaction zones for polymerization. Ethylene gas can be introduced from six places, and different catalysts can be injected from five points to improve the single-pass conversion rate.

[0004] Based on the technology introduced from ICI by Sumitomo Chemical of Japan, a new process of double-reactor series connection has been developed. The double-reactor series connection process has been further improved. The original two reactors had the same volume, and now it is proposed that the volume of the front reactor can be 1 - 6 times that of the rear reactor. The front reactor is divided into two reaction zones, and there are two feed points and two initiator injection points in the front reactor. This can not only improve the initiator efficiency, but also reduce the initiator consumption and increase the conversion rate.

[0005] Exxon Mobil uses one reactor per line for production, with a volume of 1.5 m 3 The reactor uses a relatively large height-to-diameter ratio. The stirrer is selected with fan-shaped blades. By changing the angle between the blade and the shaft, the axial force generated by the blade is changed, and the pairs of axial forces of the blade downward and upward are arranged to form multiple regions to extend the residence time, make the initiator efficiency higher, and the molecular weight distribution of the product narrower.

[0006] For reactors at home and abroad, the agitator basically adopts a central shaft, equipped with a triangular inclined blade impeller, a four-blade or six-blade turbine impeller, a fan-shaped inclined blade impeller, etc. Multiple layers of blades are combined to form the agitator. To solve the stiffness and machining problems of the long and slender shaft of the agitator, a scheme of adding an intermediate bearing seat inside the reactor is adopted, which increases the difficulty of installing the intermediate bearing seat. In addition, with 3 to 4 support points set on one shaft, it is very difficult to ensure the coaxiality, which is also one of the reasons for bearing damage.

[0007] By referring to the structural characteristics of foreign high-pressure polyethylene reactors, the effects of designing a high-pressure polyethylene reactor with a new-structured agitator are as follows: It is applicable to reactors with a volume range of 0.75 to 5 m 3 ; The new-structured agitator adopted is applicable to the mixing of high-viscosity materials, and there is no dead zone in the stirring area; The central through-shaft is cancelled. Without increasing the cross-sectional area occupied by the shaft, a 4-column combined cross-section shaft without a central through-shaft can be selected to improve the stiffness of the shaft; A full-circle spiral ribbon is adopted for each layer to prevent the blade from bending; By adjusting the rotation direction and quantity of the spiral ribbon blades, the axial force can be reduced, and the load on the lower bearing of the motor caused by the gravity of the agitator can be alleviated; The upper end of the agitator is fixed to the spline sleeve of the motor, and 2 angular contact bearings at the motor end cover are used as the upper support points of the agitator. The lower bearing seat is fixed to the lower flat cover, and no bearing seat is provided in the middle, which simplifies the machining of the long and slender shaft and the installation of the agitator; The agitator selects multiple groups of wave-wheel type blades and inner and outer spiral ribbon blades, which divide the reactor into multiple reaction areas, eliminating the flow dead zone in the mixing area; The residence time is extended and the yield is improved. Summary of the Invention

[0008] A high-pressure polyethylene reactor with a new-structured agitator, including an upper flat cover (1), a sealing ring (2), an upper clamp fastening mechanism (3), a motor (4), a new-structured agitator (5), a cylinder body (6), a lower bearing seat (7), a lower flat cover (8), a lower clamp fastening mechanism (9). The new-structured agitator (5) includes a turbine blade I (5-2), a combined cross-section frame shaft without a central through-shaft (5-3), a centrally perforated wave wheel (5-4), an upper convex wave wheel (5-5), a turbine blade II (5-7), an upward inner spiral ribbon (5-8), a downward outer spiral ribbon (5-9), a downward inner spiral ribbon (5-10), an upward outer spiral ribbon (5-11), a cross blade (5-12); The combined cross-section frame shaft without a central through-shaft (5-3) is composed of an upper shaft head (5-1), a lower shaft head (5-13) and 4 round steel bars; The blades and the round steel bars are fixed by the method of spacing pipes.

[0009] A high-pressure polyethylene reactor with a new-structured agitator is characterized in that it is applicable to high-pressure reactors with a volume range of 0.75 m 3 ~5 m 3 of high-pressure reactors.

[0010] A high-pressure polyethylene reactor with a stirrer of a new structure is characterized in that a central-opening impeller (5-4) and an upward-convex impeller (5-5) are alternately combined; the impellers are made of steel plates stamped into convex blades with arc transitions, having no dead zones and high strength; the diameter of the central-opening impeller (5-4) has a small gap with the reactor wall, forcing most of the materials to flow through the central hole; the upward-convex impeller (5-5) has no hole in the center and has a large gap with the reactor wall, and the materials flow through the periphery of the blades. Such multiple groups of staggered combinations improve the mixing effect and eliminate the flow dead zones; and the reactor is divided into multiple reaction zones, prolonging the residence time and increasing the yield.

[0011] A high-pressure polyethylene reactor with a stirrer of a new structure is characterized in that the rotation directions of the upward-lifting inner spiral ribbon (5-8), the downward-pressing outer spiral ribbon (5-9), the downward-pressing inner spiral ribbon (5-10), and the upward-lifting outer spiral ribbon (5-11) are opposite; when the downward-pressing outer spiral ribbon (5-9) rotates, it presses the liquid downward, and when the upward-lifting inner spiral ribbon (5-8) rotates, it pushes the liquid upward, forming a small circulation in this area, and the axial force generated by this layer of spiral ribbon is mainly upward; the upward-lifting outer spiral ribbon (5-11) pushes the liquid upward, and when the downward-pressing inner spiral ribbon (5-10) rotates, it presses the liquid downward, and the axial force generated by this layer of spiral ribbon is mainly downward; the combined axial forces of these two layers of spiral ribbons reach balance; the lowest group of spiral-ribbon blades all press the liquid downward when rotating, promoting the discharge of the materials, balancing part of the gravity of the stirrer, and reducing the bearing load of the angular contact bearing at the lower end of the motor. Description of the Drawings

[0012] Figure 1 General drawing of the high-pressure polyethylene reactor: upper flat cover (1), sealing ring (2), upper clamp fastening mechanism (3), motor (4), new stirrer (5), cylinder body (6), lower bearing seat (7), lower flat cover (8), lower clamp fastening mechanism (9)

[0013] Figure 2 Drawing of the new stirrer: shaft head (5-1), turbine blade I (5-2), combined cross-section frame shaft without a central through-shaft (5-3), central-opening impeller (5-4), upward-convex impeller (5-5), spacer tube (5-6), turbine blade II (5-7), upward-lifting inner spiral ribbon (5-8), downward-pressing outer spiral ribbon (5-9), downward-pressing inner spiral ribbon (5-10), upward-lifting outer spiral ribbon (5-11), cross-shaped blade (5-12), lower shaft head (5-13). Detailed Implementation Modes

[0014] A high-pressure polyethylene reactor with a stirrer of a new structure, comprising an upper flat cover (1), a sealing ring (2), an upper clamp fastening mechanism (3), a motor (4), a stirrer of a new structure (5), a cylinder body (6), a lower bearing seat (7), a lower flat cover (8), and a lower clamp fastening mechanism (9). The stirrer of the new structure (5) includes a turbine blade I (5-2), a combined cross-section frame shaft without a central through-axis (5-3), a central-opening wave wheel (5-4), an upper convex wave wheel (5-5), a turbine blade II (5-7), an upward-lifting inner spiral belt (5-8), a downward-pressing outer spiral belt (5-9), a downward-pressing inner spiral belt (5-10), an upward-lifting outer spiral belt (5-11), and a cross blade (5-12). The combined cross-section frame shaft without a central through-axis (5-3) is composed of an upper shaft head (5-1), a lower shaft head (5-13), and 4 round steel bars. The blades and the round steel bars are fixed by means of a spacer tube (5-6).

[0015] A high-pressure polyethylene reactor with a stirrer of a new structure is characterized in that it is applicable to high-pressure reactors with a volume range of 0.75 m3 to 5 m3.

[0016] The wave-wheel type blades adopted by the stirrer of the new structure (5) are alternately combined by a central-opening wave wheel (5-4) and an upper convex wave wheel (5-5). The wave-wheel blades are stamped from steel plates into convex blades with arc transitions, without dead zones and with high strength. The diameter of the central-opening wave wheel (5-4) has a small gap with the reactor wall, forcing most of the material to flow through the central hole. The upper convex wave wheel (5-5) has no hole in the center and a large gap between its diameter and the reactor wall, and the material flows through the periphery of the blade. Such multi-group staggered combinations improve the mixing effect, eliminate the flow dead zones, divide the reactor into multiple reaction zones, extend the residence time, and improve the yield.

[0017] The stirrer of the new structure (5) selects the upward-lifting inner spiral belt (5-8), the downward-pressing outer spiral belt (5-9), the downward-pressing inner spiral belt (5-10), and the upward-lifting outer spiral belt (5-11) with opposite rotation directions. When the downward-pressing outer spiral belt (5-9) rotates, it presses the liquid downward, and when the upward-lifting inner spiral belt (5-8) rotates, it pushes the liquid upward, forming a small circulation in this area. The axial force generated by this layer of spiral belt is mainly upward. The upward-lifting outer spiral belt (5-11) pushes the liquid upward, and when the downward-pressing inner spiral belt (5-10) rotates, it presses the liquid downward. The axial force generated by this layer of spiral belt is mainly downward. The combined axial forces of these two layers of spiral belts reach equilibrium. The lowest group of spiral belt blades all press the liquid downward when rotating, promoting the discharge of the material, balancing a part of the gravity of the stirrer, and reducing the bearing load of the angular contact bearing at the lower end of the motor.

Claims

1. A high-pressure polyethylene reactor with a stirrer of a new structure, comprising an upper flat cover (1), a sealing ring (2), an upper clamp fastening mechanism (3), a motor (4), a stirrer of a new structure (5), a cylinder body (6), a lower bearing seat (7), a lower flat cover (8), and a lower clamp fastening mechanism (9). The stirrer of the new structure (5) includes a turbine blade I (5-2), a combined cross-section frame shaft without a central through-axis (5-3), a central-opening wave wheel (5-4), an upper convex wave wheel (5-5), a turbine blade II (5-7), an upward-lifting inner spiral belt (5-8), a downward-pressing outer spiral belt (5-9), a downward-pressing inner spiral belt (5-10), an upward-lifting outer spiral belt (5-11), and a cross-shaped blade (5-12). The combined cross-section frame shaft without a central through-axis (5-3) is composed of an upper shaft head (5-1), a lower shaft head (5-13), and 4 round steel bars. The blades and the round steel bars are fixed by the method of spacer tubes.

2. A high-pressure polyethylene reactor using a stirrer with a new structure according to claim 1, characterized in that Applicable to high-pressure reactors with a volume range of 0.75 m 3 to 5 m 3 .

3. A high-pressure polyethylene reactor using a stirrer with a new structure according to claim 1, characterized in that: The central-opening wave wheel (5-4) and the upper convex wave wheel (5-5) are alternately combined. The wave wheels are formed by stamping steel plates into convex blades with arc transitions, without dead zones and with high strength. The diameter of the central-opening wave wheel (5-4) has a small gap with the reactor wall, forcing most of the material to flow through the central hole. The upper convex wave wheel (5-5) has no central hole and a large gap with the reactor wall, and the material flows through the periphery of the blade. Such multiple groups of staggered combinations improve the mixing effect, eliminate the flow dead zones, divide the reactor into multiple reaction zones, extend the residence time, and improve the yield.

4. A high-pressure polyethylene reactor using a stirrer with a new structure according to claim 1, characterized in that, The rotation directions of the upward-lifting inner spiral belt (5-8), the downward-pressing outer spiral belt (5-9), the downward-pressing inner spiral belt (5-10), and the upward-lifting outer spiral belt (5-11) are opposite. When the downward-pressing outer spiral belt (5-9) rotates, it presses the liquid downward, and when the upward-lifting inner spiral belt (5-8) rotates, it pushes the liquid upward, forming a small circulation in this area. The axial force generated by this layer of spiral belt is mainly upward. The upward-lifting outer spiral belt (5-11) pushes the liquid upward, and when the downward-pressing inner spiral belt (5-10) rotates, it presses the liquid downward. The axial force generated by this layer of spiral belt is mainly downward. The combined axial forces of these two layers of spiral belts reach balance. The last group of spiral belt blades all press the liquid downward when rotating, promoting the discharge of the material, balancing part of the gravity of the stirrer, and reducing the bearing load of the angular contact bearing at the lower end of the motor.

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