Structure for changing internal and external plunger flow of high-pressure polyethylene tubular reactor into spiral flow
By introducing a spiral rifling structure into a high-pressure polyethylene tube reactor, changing the material flow state into a spiral rotary flow, the problems of low heat transfer efficiency and uneven reaction in the prior art are solved, and more efficient material mixing and heat Transfer, improve product quality and overall reactor performance.
Patent Information
- Application Number
- CN202310786297.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-06-29
- Publication Date
- 2024-12-31
AI Technical Summary
In the existing high-pressure polyethylene tube reactor, the material flow state is plunger flow, resulting in low heat transfer efficiency, uneven reaction, poor product quality, and long reactor length, which poses a risk of heat accumulation and decomposition reaction.
The spiral rifle structure is introduced into the inner tube of the reactor, changing the flow state of the material into a spiral rotary flow, promoting material mixing and heat transfer through the change of the rotation direction of the spiral rifle, and increasing the spiral flow guide element in the jacket to increase the heat exchange area and Stiffness.
It realizes uniform mixing and efficient heat transfer of materials, extends the residence time of materials in the reactor, shortens the reactor length, improves product quality, reduces particulate gels and accidental depolymerization, and enhances the heat transfer efficiency and stiffness of the reactor.
Smart Images
Figure CN119215776A_ABST
Abstract
Description
[0001] Technical field: The present invention relates to the technical field of equipment for the production of high-pressure polyethylene tubular reactors, and in particular to a structure in which the internal and external plunger flows of a high-pressure polyethylene tubular reactor are transformed into spiral flows. Technical Background
[0002] The production conditions of high-pressure polyethylene are high temperature (200-300℃) and ultra-high pressure (200-350MPa). The tubular method for producing high-pressure polyethylene (LDPE) is a key equipment in the polymerization process. The reactor of a line is divided into three sections: the heating section accounts for about 21% of the total length, the cooling section accounts for about 25% of the total length, and the reaction section accounts for about 54% of the total length. Each section is composed of several groups of straight and curved sleeves, and its structure is as follows: Figure 1 As shown: outer sleeve (1), cylindrical point positioning (2), reactor inner tube (3). The reactor inner tube (3) of the straight sleeve and the curved sleeve has multiple groups of different diameters and is distributed at different positions in the reactor. Changing the diameter of the reactor inner tube (3) also changes the flow area and flow rate, thereby extending the residence time and reaction time in the reactor. Steam flows through the sleeve (1) of the heating section to increase the reaction temperature of ethylene; cooling water flows through the sleeve (1) of the cooling section and the reaction section, and heat is removed from the reactor through the sleeve (1), which can take away 30% of the reaction heat. The reactor composed of the two ends of the sleeve connected by threaded flanges has a total length of more than 1,100m and a volume of about 1.6m3.
[0003] The material flow state of the reactor with this structure is close to the plunger flow, the central tube wall is laminar flow, and it can only copolymerize with a small amount of other monomers. A structure in which the internal and external plunger flow of a high-pressure polyethylene tubular reactor is changed to a spiral flow can change the material flow state of the tubular method, change the plunger flow to a spiral rotating flow, which is beneficial to the mixing of materials in the reactor, can expand the copolymerization range, help prevent accidental depolymerization, narrow the relative mass distribution of the product, increase the long chain branches, reduce the microgel, and approach the product performance produced by the kettle method, which is beneficial to improve product quality and increase product grades. Summary of the invention
[0004] Turbulence in the reactor can improve the efficiency of heat transfer. To form turbulence, the Reynolds number should reach more than 10,000, which is the minimum requirement for material flow. To achieve this requirement, the present invention relates to a structure in which the plunger flow inside and outside the high-pressure polyethylene tubular reactor is changed into a spiral flow, which is a good method to be selected. The rifling (also called rifling) in the barrel of a gun or a cannon is used in the inner tube (3) of the reactor, and the principle of rotating the bullet by the spiral rifling is used. In this way, the piston flow formed when the material flows forward in the reactor can be changed into a spiral rotating flow rotating along the rifling. The rifling is arranged in sequence of left-handed and right-handed according to the rotation direction. This spiral rotating flow can extend the residence time in the reactor or shorten the length of the reactor by 5 to 10%. The plunger flow that can change the flow area and flow velocity of the material in the reactor is conducive to the mixing reaction and homogenization of the material. The high-speed rotating flow can flush the inner wall, solve the retention of scale on the inner wall and eliminate dead corners, improve the heat transfer effect, shorten the total length of the reactor, and effectively prevent the accumulation of heat to form a decomposition reaction caused by local overheating.
[0005] The reactor inner tube material is ultra-high pressure steel pipe AISI 4333M4 steel.
[0006] Main chemical components: C: 0.30, Mn: 0.5, Si: 0.22, Ni: 3.08, P: 0.011, Cr: 1.15, S: 0.012, Mo: 0.58, V: 0.13.
[0007] Mechanical properties at room temperature: σb≥1,053MPa, σs 0.2 ≥989MPa, δ≥17.8%, Ψ≥64.8%.
[0008] After adding rifling inside the reactor tube, the diameter for calculating the wall thickness should be calculated as the inner diameter + 2 times the groove depth, i.e. Di = D + 2t. When the reactor design pressure is 315 MPa and the design temperature is 300°C, the ratio of the outer diameter of the reactor inner tube (3) / the top distance of the rifling groove depth is ≥ 2.2.
[0009] Will the original Figure 1 The cylindrical point positioning (2) in the outer sleeve (1) shown is changed to Figure 4 The spiral guide element (2) shown in the figure is used in the jacket to increase the heat exchange area in the jacket tube (1) and solve the problem of how to remove more heat from the jacket.
[0010] The present invention relates to a rifling section in which the inner and outer plunger flow of a high-pressure polyethylene tubular reactor is transformed into a spiral flow, as shown in the attached drawings. Figure 2 : The figure shows the reactor inner diameter (D), groove width (k), groove depth (t), arc groove radius (r) and reactor outer tube diameter (DN).
[0011] It is characterized by the selection of rifling related parameters: rifling lead P = (10 ~ 12) D; groove depth t = (0.01 ~ 0.05) D; groove width b = (0.1 ~ 0.15) D; the number of heads Z is determined according to the inner diameter of the tube, generally 8 to 18 heads; acute angle blunting R = 0.3t.
[0012] The structure of the internal and external plunger flow transformation into spiral flow of a high-pressure polyethylene tubular reactor according to claim 1 is characterized in that after rifling is added inside the reactor tube, the relationship between the wall thickness and the diameter of the reactor inner tube (3) is calculated according to the inner diameter (D) of the reactor inner tube (3) + 2 times the groove depth, that is, Di = D + 2t. When the reactor design pressure is 315 MPa and the design temperature is 300°C, the ratio of the outer diameter (DN) of the reactor inner tube (3) / the top distance (Di) of the rifling groove depth is ≥ 2.2.
[0013] According to claim 1, the structure of the internal and external plunger flow of a high-pressure polyethylene tubular reactor is changed to a spiral flow, characterized in that the rifling is divided into left-handed and right-handed, and is arranged in sequence of one section left-handed and one section right-handed. When the rifling causes the reactants to rotate to the next section of the casing according to the spiral rifling, the rifling of the spiral rifling changes to another rotation direction, which promotes the mixing of materials, changes the piston flow to turbulent flow, improves the heat transfer efficiency, flushes the scale on the tube wall, improves the heat exchange effect, and prolongs the operation cycle. It is beneficial to the mixing of materials in the reactor, expands the copolymerization range, prevents accidental depolymerization, narrows the relative mass distribution of the product, increases long chain branches, and reduces microgels.
[0014] According to claim 1, a structure in which the internal and external plunger flows of a high-pressure polyethylene tubular reactor are transformed into spiral flows is characterized in that the total length of the reactor can be appropriately shortened by 5 to 10%.
[0015] The structure of a high-pressure polyethylene tubular reactor according to claim 1, wherein the internal and external plunger flow is transformed into a spiral flow, characterized in that: Figure 4 As shown, it is mainly composed of: an outer sleeve (1), a spiral flow guide element (2), a reactor inner tube (3) and other parts.
[0016] According to claim 5, a structure in which the internal and external plug flow of a high-pressure polyethylene tubular reactor is changed into a spiral flow is characterized in that a spiral flow guide element (2) is used in the jacket of the high-pressure polyethylene tubular reactor, which can increase the heat exchange area in the reactor jacket by 47.2% and improve the heat removal; the coaxiality of the jacket tube and the reactor tube is good; the plug flow can be changed into a rotating flow, which is beneficial to heat removal; and the rigidity of the reactor tube is improved.
[0017] Example of minimum wall thickness calculation: The outer diameter of the reactor inner tube (3) is DN105mm and is calculated according to the proportional relationship 2.2:
[0018] Di=DN / 2.2=47.7mm, the minimum wall thickness on one side is safe as long as it is greater than 28.65mm. BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Figure 1 The structure diagram of the symmetrical cylindrical point positioning of the bent and straight tubes of the foreign outer casing reactor
[0020] Outer tube (1), cylindrical point positioning (2), reactor inner tube (3)
[0021] Figure 2 Cross-section diagram of rectangular rifling and circular rifling
[0022] Reactor inner diameter (D), slot width (k), slot depth (t), arc slot radius (r), reactor inner tube (3) outer diameter (DN) Figure 3 Left-hand rifling and right-hand rifling diagram
[0023] Figure 4 Structural diagram of spiral flow guide elements used in the curved and straight jackets of tubular reactors
[0024] Outer sleeve (1), spiral flow guide element (2), reactor inner tube (3) DETAILED DESCRIPTION
[0025] The present invention relates to a structure in which the internal and external plunger flow of a high-pressure polyethylene tubular reactor is transformed into a spiral flow. The specific implementation method is as follows:
[0026] The rifling inside the reactor is formed on a drawing machine using multiple broaches. The rifling inside the reactor is drawn into shape when the pipe is straight, and then bent according to the size of the bent pipe.
[0027] First, the spiral guide element (2) is welded together and put on the outside of the reactor inner tube (3) in a straight tube state, and then the outer sleeve (1) is put on, and the spiral guide element (2) at the inlet end and the inner wall of the sleeve (1) that can be welded together are welded.
[0028] Weld the reducing tee at the inlet end to the sleeve.
[0029] The spiral flow guide element (2) is stretched at the other end so that its blades are in close contact with the outer wall of the reactor inner tube (3) and the inner diameter of the spiral flow guide element (2), and are welded and fixed to the inner diameter of the outer sleeve (1).
[0030] Weld the reducing tee at the outlet end to the sleeve.
[0031] The pipes that need to be bent are bent on a pipe bending machine.
[0032] Test the pressure inside the casing with water pressure, and conduct strength test and air tightness test.
[0033] During assembly, one section needs to be left-handed and one section right-handed in sequence. When the rifling causes the reactants to rotate to the next section of the sleeve along the spiral rifling, the rifling of the spiral rifling changes to another rotation direction, which promotes the mixing of materials, changes the piston flow into turbulent flow, improves the heat transfer efficiency, flushes the scale on the tube wall, improves the heat exchange effect, and prolongs the operation cycle. It is beneficial to the mixing of materials in the reactor, expands the copolymerization range, prevents accidental depolymerization, narrows the relative mass distribution of the product, increases long chain branches, and reduces microgels.
Claims
1. The present invention relates to a structure in which the internal and external plug flow of a high-pressure polyethylene tubular reactor is changed into a spiral flow. Rifling is added inside the reactor inner tube (3) to change the original plug flow into a spiral rotating flow. The rifling cross-sectional dimension code, reactor inner diameter (D), groove width (k), groove depth (t), arc groove radius (r), reactor inner tube (3) outer diameter (DN).
2. The structure of a high-pressure polyethylene tubular reactor according to claim 1, wherein the inner and outer plunger flows are transformed into spiral flows, characterized in that The corresponding relationship between rifling related parameters and diameter: rifling lead P = (10~20)D; groove depth t = (0.01~0.05)D; groove width b = (0.1~0.15)D; the number of heads Z is determined according to the inner diameter of the tube, generally 8~18 heads; acute angle blunting R = 0.3t.
3. The structure of the high-pressure polyethylene tubular reactor according to claim 1, wherein the inner and outer plunger flows are transformed into spiral flows, characterized in that After adding rifling inside the reactor tube, the relationship between the wall thickness and the diameter of the reactor inner tube (3) is calculated according to the inner diameter of the reactor inner tube (3) + 2 times the groove depth, that is, Di = D + 2t. When the reactor design pressure is 315 MPa and the design temperature is 300°C, the ratio of the outer diameter of the reactor inner tube (3) / the top distance of the rifling groove depth is ≥ 2.2, which is safe.
4. The structure of the high-pressure polyethylene tubular reactor according to claim 1, wherein the inner and outer plunger flows are transformed into spiral flows, characterized in that The rifling is divided into left-handed and right-handed, and is arranged in sequence of one left-handed section and one right-handed section. When the rifling causes the reactants to rotate to the next section of the casing along the spiral rifling, the direction of rotation of the spiral rifling changes to another direction, which promotes the collision and mixing between the materials, changes the piston flow into turbulent flow, improves the heat transfer efficiency, and the spiral rotating flow can also wash away the scale on the tube wall, improve the heat exchange effect, and extend the operation cycle. It is beneficial to expand the copolymerization range of materials in the reactor, prevent accidental depolymerization, narrow the relative mass distribution of the product, increase the long chain branches, and reduce the microgel.
5. A high-pressure polyethylene tubular reactor according to claim 1, wherein the internal and external plunger flows are transformed into spiral flows, and the total length of the reactor can be appropriately shortened by 5-10%.
6. The structure of the high-pressure polyethylene tubular reactor according to claim 1, wherein the inner and outer plunger flow changes into a spiral flow, characterized in that As shown in FIG4 , it is mainly composed of: an outer sleeve (1), a spiral flow guide element (2), a reactor inner tube (3) and other parts.
7. The structure of the high-pressure polyethylene tubular reactor according to claim 6, wherein the internal and external plunger flow is transformed into a spiral flow, characterized in that: The spiral flow guide element (2) is used in the jacket of a high-pressure polyethylene tubular reactor, which can increase the heat exchange area in the reactor jacket by 47.2% and improve the heat removal; the coaxiality between the jacket tube and the reactor tube is good; the plug flow can be changed into a rotating flow, which is beneficial to heat removal; and the rigidity of the reactor inner tube (3) is improved.