Fluidized bed residual oil hydrogenation reactor

Abstract

The utility model discloses a residual oil hydrogenation reactor of a fluidized bed, which relates to the technical field of petrochemical equipment and comprises an oil gas inlet pipe, a circulating oil inlet pipe, a circulating oil outlet pipe and a catalyst discharge pipe which are arranged at the bottom of a pressure-bearing shell, a feeding distributor, a composite distribution plate, a catalyst bed layer and a circulating cup are sequentially arranged in the pressure-bearing shell from bottom to top, and the inlet end of the catalyst discharge pipe extends to the upper part of the composite distribution plate; a downcomer is mounted in the center of the composite distribution disc, the lower end of the downcomer is communicated with the circulating oil outlet pipe, and the upper end of the downcomer is communicated with the circulating cup; the top of the pressure-bearing shell is also provided with an oil gas outlet pipe, a back-blowing hydrogen port pipe and a catalyst adding pipe, the outlet end of the back-blowing hydrogen port pipe penetrates through the composite distribution disc and extends to the upper part of the feeding distributor, and the outlet end of the catalyst adding pipe extends to the catalyst bed layer. The residual oil hydrogenation reactor solves the problems of a fixed bed residual oil hydrogenation reactor, ensures that the activity of a catalyst is constant, and maintains stable product quality and yield.

Description

Technical Field

[0001] This utility model relates to the field of petrochemical equipment technology, and more specifically, to a fluidized bed residue oil hydrogenation reactor. Background Technology

[0002] In recent years, due to the increasing trend of heavier crude oil resources worldwide and increasingly stringent environmental requirements, the deep processing and clean production of heavy crude oil have become major challenges and opportunities for the refining industry. For refining companies, the residue conversion rate is key to the deep processing of heavy oil and also crucial to their refining profit margins. The only way to convert residue into light oil products while avoiding coke production is through hydrotreating. The residue hydrotreating reactor is an indispensable and essential piece of equipment in the process of converting residue into light oil.

[0003] Currently, the most widely used residue hydrotreating reactor in the world is the fixed-bed residue hydrotreating reactor. However, fixed-bed residue hydrotreating reactors have disadvantages such as short catalyst life, yield variations at the beginning and end of the reaction, bed clogging by impurities, poor heat transfer performance, susceptibility to local overheating, and high energy consumption. Utility Model Content

[0004] The purpose of this invention is to provide a fluidized bed residue oil hydrogenation reactor that can effectively solve the problems existing in a fixed bed residue oil hydrogenation reactor.

[0005] To achieve the purpose of this utility model, the technical solution adopted is as follows: a fluidized bed residue oil hydrogenation reactor, comprising a pressure-bearing shell, wherein an oil and gas inlet pipe, a circulating oil inlet pipe, a circulating oil outlet pipe, and a catalyst discharge pipe are installed at the bottom of the pressure-bearing shell; a feed distributor, a composite distribution plate, a catalyst bed, and a circulation cup are arranged sequentially from bottom to top inside the pressure-bearing shell, and the inlet end of the catalyst discharge pipe extends to the top of the composite distribution plate; a downcomer is installed at the center of the composite distribution plate, the lower end of the downcomer is connected to the circulating oil outlet pipe, and the upper end of the downcomer is connected to the circulation cup; an oil and gas outlet pipe, a backflushing hydrogen inlet pipe, and a catalyst addition pipe are also installed at the top of the pressure-bearing shell, the outlet end of the backflushing hydrogen inlet pipe extends through the composite distribution plate to the top of the feed distributor, and the outlet end of the catalyst addition pipe extends to the catalyst bed.

[0006] Furthermore, the feed distributor is an annular distribution pipe, the annular diameter of which is 55% to 65% of the inner diameter of the pressure shell, and the diameter of which is 60% to 70% of the diameter of the oil and gas inlet pipe. The annular distribution pipe is provided with pairs of φ25mm distribution holes along the 60° direction of the cross section above it. The distribution holes are arranged at intervals along the axial direction of the annular distribution pipe, and the distance between two adjacent distribution holes is 5° to 15°.

[0007] Furthermore, a diffuser is installed at the inlet end of the circulating oil inlet pipe. The diffuser includes a top circular plate, a middle annular plate, a bottom annular plate, and a support rib. The support rib is fixed together with the top circular plate, the middle annular plate, and the bottom annular plate. The inner diameter of the middle annular plate is 45% to 55% of the inner diameter of the circulating oil inlet pipe, and the inner diameter of the bottom annular plate is 65% to 75% of the inner diameter of the circulating oil inlet pipe. The distance between the top circular plate and the middle annular plate, and the distance between the middle annular plate and the bottom annular plate are both 80 mm to 150 mm. The distance between the bottom annular plate and the pressure-bearing shell is twice the distance between the top circular plate and the middle annular plate.

[0008] Furthermore, the composite distribution plate is a distribution plate fixed integrally with the catalyst support plate, and the composite distribution plate is provided with a riser pipe with a grid bubble cap.

[0009] Furthermore, the composite distribution plate is connected to the pressure-bearing shell via a conical cylinder.

[0010] Furthermore, the side of the composite distribution plate and the inner wall of the pressure-bearing shell are provided with corresponding connecting plates, and the two corresponding connecting plates are connected and fixed.

[0011] Furthermore, a sleeve is installed at the outlet of the circulation cup, and the inlet end of the downcomer is inserted into the sleeve.

[0012] Furthermore, the circulation cup is funnel-shaped, with a cone angle of 90° to 120°, and the opening edge of the circulation cup is fixed to the pressure-bearing shell.

[0013] Furthermore, the backflush hydrogen inlet pipe has a spiral section in the middle, and the spiral section is wound around the downcomer.

[0014] Furthermore, guide supports are also installed on the outer wall of the downcomer, arranged at intervals along its axis. The middle section of the backflushing hydrogen port pipe and the outlet end of the catalyst addition pipe are both supported by the guide supports.

[0015] Furthermore, the inner diameter of the downcomer is 15% to 20% of the inner diameter of the pressure shell, and the downcomer is coaxially arranged with the pressure shell.

[0016] Furthermore, a collector is installed at the inlet end of the oil and gas outlet pipe. The opening edge of the collector is provided with rectangular grooves evenly distributed along the circumference. The width of the rectangular grooves is 20mm to 50mm, and the height of the rectangular grooves is 80mm to 150mm.

[0017] The beneficial effects of this utility model are:

[0018] 1. The catalyst in this invention can be added and removed online at any time, ensuring constant catalyst activity and maintaining stable product quality and yield. This avoids the problems of product yield changes at the beginning and end of the reaction, gradual decline in target product quality, and the impact of annual shutdowns for catalyst replacement on overall plant production and material balance that exist in fixed-bed reactors, thus extending the operating cycle of the unit.

[0019] 2. The catalyst bed in this invention is in a fully backmixed state, with the gas, liquid, and solid phases fully mixed, ensuring sufficient contact between the catalyst and the feedstock oil and hydrogen, resulting in high reaction efficiency. There is no problem of impurities clogging the catalyst bed, which reduces the reactor pressure and does not change with the operating cycle. The reactor is basically in an isothermal state, eliminating the need for cold hydrogen injection and preventing local overheating. The heat of reaction is exchanged directly between the circulating oil and the feedstock oil, resulting in high energy utilization.

[0020] 3. In this utility model, a distribution plate that is fixed integrally with the catalyst support plate is used as a composite distribution plate, which saves the length of the pressure-bearing shell and reduces the cost of the reactor. The connection structure between the composite distribution plate and the pressure-bearing shell releases the radial displacement difference between the composite distribution plate and the pressure-bearing shell caused by pressure and temperature. At the same time, it can bear the axial downward weight load of the catalyst bed and limit the axial upward lifting force load of the material on the composite distribution plate. This connection structure is simple and the stress level at the connection is low.

[0021] 4. By setting a sleeve at the connection of the circulation cup and inserting the downcomer into the sleeve, the pressure shell and the downcomer can freely expand and contract axially when heated, balancing the difference in axial expansion displacement between the pressure shell and the downcomer, and reducing the stress level at the connection between the downcomer, the circulation cup and the composite distribution plate. Attached Figure Description

[0022] The accompanying drawings illustrate exemplary embodiments of the present invention and, together with the description thereof, serve to explain the principles of the present invention. These drawings are included to provide a further understanding of the present invention and are incorporated in and constitute a part of this specification.

[0023] Figure 1 This is a structural diagram of the fluidized bed residue hydrogenation reactor provided by this utility model;

[0024] Figure 2 This is a diagram showing the installation structure of the catalyst discharge pipe and manhole.

[0025] The attached diagram shows the markings and corresponding component names:

[0026] 1-Circulating oil inlet pipe, 2-Circulating oil outlet pipe, 3-Composite distribution plate, 4-Pressure-bearing shell, 5-Downcomer, 6-Sleeve, 7-Circulating cup, 8-Collector, 9-Oil and gas outlet pipe, 10-Backflush hydrogen inlet pipe, 11-Catalyst addition pipe, 12-Guide support, 13-Spiral section, 14-Catalyst bed, 15-Feed distributor, 16-Oil and gas inlet pipe, 17-Diffuser, 18-Catalyst discharge pipe, 19-Conical cylinder, 20-Manhole. Detailed Implementation

[0027] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the present invention. Furthermore, it should be noted that, for ease of description, only the parts relevant to the present invention are shown in the accompanying drawings.

[0028] It should be noted that, where there is no conflict, the embodiments and features described in these embodiments can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0029] like Figure 1 , Figure 2 As shown, the fluidized bed residue hydrotreating reactor provided by this utility model includes a pressure-bearing shell 4. At the bottom of the pressure-bearing shell 4 are installed an oil and gas inlet pipe 16, a circulating oil inlet pipe 1, a circulating oil outlet pipe 2, a catalyst discharge pipe 18, and a manhole 20. The oil and gas inlet pipe 16, the circulating oil inlet pipe 1, the circulating oil outlet pipe 2, and the catalyst discharge pipe 18 are all configured as a combination of a heat-insulated pipe and a welded pipe. The portion of the oil and gas inlet pipe 16, the circulating oil inlet pipe 1, the circulating oil outlet pipe 2, and the catalyst discharge pipe 18 closest to the pressure-bearing shell 4 is a heat-insulated pipe, and the welded pipe is connected to the heat-insulated pipe via a stainless steel transition section. The manhole 20 is a manhole with a lined core.

[0030] Oil and gas inlet pipe 16 is used to send raw material oil into the bottom of the receiving shell; circulating oil inlet pipe 1 is used to send circulating oil into the bottom of the receiving shell; circulating oil outlet pipe 2 is used to send the collected liquid out of the receiving shell; catalyst discharge pipe 18 is used to send the catalyst in the catalyst bed 14 out of the pressure shell 4; manhole 20 is used for maintenance of the inside of the receiving shell.

[0031] The pressure shell 4 is arranged from bottom to top as follows: a feed distributor 15, a composite distribution plate 3, a catalyst bed 14, and a circulation cup 7. The inlet end of the catalyst discharge pipe 18 extends above the composite distribution plate 3, so that the catalyst in the catalyst bed 14 can be sent out of the pressure shell 4 through the catalyst discharge pipe 18. The feed distributor 15 is connected to the oil and gas inlet pipe 16, so that the feed oil transported through the oil and gas inlet pipe 16 is evenly fed into the bottom of the pressure shell 4 through the feed distributor 15. The composite distribution plate 3 is used to support the catalyst bed 14. The circulation cup 7 is funnel-shaped and is used to collect the liquid generated during the reaction. A downcomer 5 is installed in the center of the catalyst bed 14. The downcomer 5 is coaxially arranged with the pressure shell 4. The inlet end of the downcomer 5 is connected to the outlet end of the circulation cup 7. The outlet end of the downcomer 5 passes through the composite distribution plate 3 and is connected to the circulating oil outlet pipe 2, so that the liquid collected by the circulation cup 7 can be sent out of the pressure shell 4 through the downcomer 5 and the circulating oil outlet pipe 2.

[0032] The top of the pressure shell 4 is also equipped with an oil and gas outlet pipe 9, a backflush hydrogen inlet pipe 10, and a catalyst inlet pipe 11. The inlet end of the oil and gas outlet pipe 9 is located directly above the circulation cup 7 and is used to send the generated gas out of the receiving shell. The outlet end of the backflush hydrogen inlet pipe 10 extends through the composite distribution plate 3 to the top of the feed distributor 15 and is used to send hydrogen into the bottom of the pressure shell 4. The outlet end of the catalyst inlet pipe 11 extends to the catalyst bed 14 and is used to add the catalyst required for production into the catalyst bed 14.

[0033] The feed distributor 15 in this utility model is an annular distribution pipe. The center of the annular distribution pipe is located on the central axis of the pressure-bearing shell 4, and the diameter of the annular distribution pipe is 55% to 65% of the inner diameter of the pressure-bearing shell 4. The diameter of the annular distribution pipe is 60% to 70% of the diameter of the oil and gas inlet pipe 16. A pair of φ25mm distribution holes are arranged above the annular distribution pipe along the 60° direction of the cross section. The distribution holes are arranged at intervals along the axial direction of the annular distribution pipe, and the distance between two adjacent distribution holes is 5° to 15°.

[0034] The inlet end of the circulating oil inlet pipe 1 in this invention is equipped with a diffuser 17. The diffuser 17 includes a top circular plate, a middle annular plate, a bottom annular plate, and supporting ribs. The top circular plate, the middle annular plate, and the bottom annular plate are arranged coaxially at intervals. The supporting ribs are installed on the outer edges of the top circular plate, the middle annular plate, and the bottom annular plate, so that the annular channel between the outer edges of the top circular plate and the middle annular plate is divided into multiple openings by the supporting ribs. The annular channel between the outer edges of the middle annular plate and the bottom annular plate is also divided into multiple openings by the supporting ribs. The circulating oil delivered through the circulating oil inlet pipe 1 is evenly distributed at the bottom of the pressure-bearing shell 4 through these openings. At the same time, the inner diameter of the middle annular plate is 45% to 55% of the inner diameter of the circulating oil inlet pipe 1, and the inner diameter of the bottom annular plate is 65% to 75% of the inner diameter of the circulating oil inlet pipe 1. The distance between the top circular plate and the middle annular plate, and the distance between the middle annular plate and the bottom annular plate are both 80 mm to 150 mm. The distance between the bottom annular plate and the pressure-bearing shell 4 is twice the distance between the top circular plate and the middle annular plate.

[0035] The composite distribution plate 3 in this invention is integrally formed by the catalyst support plate and the distribution plate, enabling the composite distribution plate 3 to both support the catalyst bed 14 and disperse the oil-gas mixture. Simultaneously, the composite distribution plate 3 is equipped with a riser pipe with a grid cap, facilitating the entry of the oil-gas mixture into the catalyst bed 14. During installation, a conical cylinder 19 is installed at the upper edge of the composite distribution plate 3, and the conical cylinder 19 is welded and fixed to the inner wall of the pressure-bearing shell 4. Multiple connecting plates with horizontal elongated holes are also welded and fixed to the outer circumference of the composite distribution plate 3. These connecting plates are evenly spaced along the circumference of the composite distribution plate 3, and multiple connecting plates with horizontal elongated holes are also welded to the inner wall of the pressure-bearing shell 4, evenly spaced along its circumference. Bolts pass through two corresponding connecting plates on the outer circumference of the composite distribution plate 3 and the inner wall of the pressure-bearing shell 4, and are tightened with nuts, thus achieving the connection between the composite distribution plate 3 and the pressure-bearing shell 4. This design allows the composite distribution disk 3 to expand radially while bearing the downward weight load of the catalyst bed 14, and also restricts the upward axial movement of the composite distribution disk 3.

[0036] Furthermore, by using a catalyst support plate and a distribution plate to form a composite distribution plate 3, the length of the pressure shell 4 is saved, reducing the reactor cost. The connection structure between the composite distribution plate 3 and the pressure shell 4 releases the radial displacement difference between the composite distribution plate 3 and the pressure shell 4 caused by pressure and temperature, while also being able to bear the axial downward weight load of the catalyst bed 14 and limiting the upward lifting force load of the material on the composite distribution plate 3. This connection structure is simple, and the stress level at the connection between the composite distribution plate 3 and the pressure shell 4 is low.

[0037] A sleeve 6 is installed at the outlet of the circulation cup 7, and the inlet end of the downcomer 5 is inserted into the sleeve 6, allowing the pressure-bearing shell 4 and the downcomer 5 to freely expand and contract axially when heated, balancing the difference in axial expansion displacement between the pressure-bearing shell 4 and the downcomer 5, and reducing the stress level at the connection between the downcomer 5, the circulation cup 7, and the composite distribution plate 3. The circulation cup 7 is funnel-shaped, with a cone angle of 90° to 120°, and the opening edge of the circulation cup 7 is fixed to the pressure-bearing shell 4. Specifically, the fixing method between the circulation cup 7 and the support of the pressure-bearing shell 4 can adopt the fixing method between the composite distribution plate 3 and the pressure-bearing shell 4. Of course, since the circulation cup 7 also has an upwardly extending pipe, the lower end of which is connected to the chamber in the pressure-bearing shell 4 used to install the catalyst bed 14, allowing the gas phase in the reaction process to enter the upper part of the circulation cup 7 through the pipe.

[0038] In this invention, the inner diameter of the downcomer 5 is 15% to 20% of the inner diameter of the pressure-bearing shell 4, and the backflush hydrogen inlet pipe 10 has a spiral section 13 in the middle, which is wound around the downcomer 5. This allows the backflush hydrogen inlet pipe 10 to extend and retract along with the downcomer 5 via the spiral section 13 when the downcomer 5 expands and retracts axially. To ensure the stability of the portion of the backflush hydrogen inlet pipe 10 and the catalyst inlet pipe 11 located inside the pressure-bearing shell 4, a guide bracket 12 can be installed on the outer wall of the downcomer 5, and the portion of the backflush hydrogen inlet pipe 10 and the catalyst inlet pipe 11 located in the pressure-bearing shell 4 can be supported by the guide bracket 12.

[0039] In this utility model, a collector 8 is also installed at the inlet end of the oil and gas outlet pipe 9. The opening edge of the collector 8 is provided with rectangular grooves evenly distributed along the circumference. The width of the rectangular grooves is 20mm to 50mm, and the height of the rectangular grooves is 80mm to 150mm.

[0040] In use, the feed oil enters the feed distributor 15 through the oil and gas inlet pipe 16, and is initially distributed to the bottom of the pressure shell 4 by the feed distributor 15; the circulating oil enters the diffuser 17 through the circulating oil inlet pipe 1, and is initially distributed to the bottom of the pressure shell 4 by the diffuser 17; the hydrogen enters the bottom of the pressure shell 4 through the backflush hydrogen port pipe 10; the feed oil, circulating oil and hydrogen are evenly distributed to the entire catalyst bed 14 through the composite distribution plate 3, and the liquid and gaseous materials have an upward lifting effect on the catalyst in the catalyst bed 14, keeping the catalyst in a flowing state. During this process, some liquid is sucked in through the circulation cup 7 and flows out through the downcomer 5 from the circulating oil outlet pipe 2, while the gas and other liquids flow out through the collector 8 from the oil and gas outlet pipe 9.

[0041] In the reaction process of this invention, fresh catalyst is periodically or irregularly added to the catalyst bed 14 through the catalyst addition pipe 11, and waste catalyst is discharged through the catalyst discharge pipe 18, thereby maintaining the activity level of the catalyst and ensuring the stability of product quality.

[0042] Due to material circulation, the catalyst and liquid phase are well mixed, the reaction is more complete and uniform, and the axial and radial temperature differences are small. At the same time, since the catalyst bed 14 is in an expanded state, the blockage or flow deviation of the catalyst bed 14 caused by coking is eliminated, resulting in a lower pressure drop in the pressure shell 4. Furthermore, the heat of reaction is exchanged directly between the circulating oil and the feed oil, resulting in high energy utilization.

[0043] Those skilled in the art should understand that the above embodiments are merely for clearly illustrating the present invention and are not intended to limit the scope of the present invention. Those skilled in the art can make other changes or modifications based on the above disclosure, and these changes or modifications still fall within the scope of the present invention.

Claims

1. A fluidized bed residue hydrotreating reactor, characterized in that, The system includes a pressure-bearing shell (4), at the bottom of which are installed an oil and gas inlet pipe (16), a circulating oil inlet pipe (1), a circulating oil outlet pipe (2), and a catalyst discharge pipe (18). Inside the pressure-bearing shell (4), from bottom to top, are arranged a feed distributor (15), a composite distribution plate (3), a catalyst bed (14), and a circulation cup (7), with the inlet end of the catalyst discharge pipe (18) extending above the composite distribution plate (3). The composite distribution plate (3) contains... The core is equipped with a downcomer (5), the lower end of which is connected to the circulating oil outlet pipe (2), and the upper end of which is connected to the circulating cup (7); the top of the pressure shell (4) is also equipped with an oil and gas outlet pipe (9), a backflush hydrogen port pipe (10) and a catalyst addition pipe (11). The outlet end of the backflush hydrogen port pipe (10) extends through the composite distribution plate (3) to the top of the feed distributor (15), and the outlet end of the catalyst addition pipe (11) extends to the catalyst bed (14).

2. The fluidized bed residue hydrotreating reactor according to claim 1, characterized in that, The feed distributor (15) is an annular distribution pipe. The annular diameter of the annular distribution pipe is 55% to 65% of the inner diameter of the pressure shell (4). The diameter of the annular distribution pipe is 60% to 70% of the diameter of the oil and gas inlet pipe (16). The annular distribution pipe is provided with pairs of φ25mm distribution holes along the 60° direction of the cross section. The distribution holes are arranged at intervals along the axial direction of the annular distribution pipe. The distance between two adjacent distribution holes is 5° to 15°.

3. The fluidized bed residue hydrotreating reactor according to claim 1, characterized in that, A diffuser (17) is installed at the inlet end of the circulating oil inlet pipe (1). The diffuser (17) includes a top circular plate, a middle ring plate, a bottom ring plate, and a support rib. The support rib is fixed together with the top circular plate, the middle ring plate, and the bottom ring plate. The inner diameter of the middle ring plate is 45% to 55% of the inner diameter of the circulating oil inlet pipe (1), and the inner diameter of the bottom ring plate is 65% to 75% of the inner diameter of the circulating oil inlet pipe (1). The distance between the top circular plate and the middle ring plate, and the distance between the middle ring plate and the bottom ring plate are both 80 mm to 150 mm. The distance between the bottom ring plate and the pressure shell (4) is twice the distance between the top circular plate and the middle ring plate.

4. The fluidized bed residue hydrotreating reactor according to claim 1, 2, or 3, characterized in that, The composite distribution plate (3) is a distribution plate that is fixed together with the catalyst support plate, and the composite distribution plate (3) is provided with a lifting pipe with a grid bubble cap.

5. The fluidized bed residue hydrotreating reactor according to claim 1, 2, or 3, characterized in that, The composite distribution plate (3) is connected to the pressure-bearing shell (4) by a conical cylinder (19); the side of the composite distribution plate (3) and the inner wall of the pressure-bearing shell (4) are provided with corresponding connecting plates, and the two corresponding connecting plates are connected and fixed.

6. The fluidized bed residue hydrotreating reactor according to claim 1, 2, or 3, characterized in that, A sleeve (6) is installed at the outlet of the circulation cup (7), and the inlet end of the downcomer (5) is inserted into the sleeve (6); the circulation cup (7) is funnel-shaped, the cone angle of the circulation cup (7) is 90° to 120°, and the opening edge of the circulation cup (7) is fixed to the pressure-bearing shell (4).

7. The fluidized bed residue hydrotreating reactor according to claim 1, 2, or 3, characterized in that, The backflush hydrogen inlet pipe (10) has a spiral section (13) in the middle, and the spiral section (13) is wound around the downcomer pipe (5).

8. The fluidized bed residue hydrotreating reactor according to claim 1, 2, or 3, characterized in that, The outer wall of the downcomer (5) is also equipped with guide supports (12) arranged at intervals along its axis. The middle section of the backflushing hydrogen port (10) and the outlet end of the catalyst addition pipe (11) are both supported by the guide supports (12).

9. The fluidized bed residue hydrotreating reactor according to claim 1, 2, or 3, characterized in that, The inner diameter of the downcomer (5) is 15% to 20% of the inner diameter of the pressure shell (4), and the downcomer (5) and the pressure shell (4) are arranged coaxially.

10. The fluidized bed residue hydrotreating reactor according to claim 1, 2, or 3, characterized in that, The inlet end of the oil and gas outlet pipe (9) is also equipped with a collector (8). The opening edge of the collector (8) is provided with rectangular grooves evenly arranged along the circumference. The width of the rectangular grooves is 20mm to 50mm and the height of the rectangular grooves is 80mm to 150mm.

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