Double-layer vertical black liquor heater

Abstract

The utility model discloses a double-layer vertical black liquor heater which is divided into an upper layer structure and a lower layer structure, a first upper annular plate and a first lower annular plate which are provided with holes are arranged in a first-layer container, a first inner cylinder is welded between the first upper annular plate and the first lower annular plate, a plurality of steam outlet tangential through holes are evenly distributed in the first inner cylinder, and the tangential through holes in each layer are arranged in a staggered mode. And the steam can fully flow in the cavity of the annular space. Heated black liquor enters a first inner cylinder of the first-layer container from a black liquor inlet in the bottom, meanwhile, steam enters an annular cavity from a side edge inlet and is sprayed out from a plurality of tangential through holes to be mixed with the black liquor to enable the black liquor to be subjected to primary heating, and the heated black liquor enters a second inner cylinder of the second-layer container from a middle cone to be subjected to secondary heating. And the second layer of steam also enters the second layer of annular cavity from the steam inlet and is sprayed out from a plurality of tangential through holes to be mixed with the black liquor for the second time, so that the black liquor is fully heated, and the black liquor reaches an ideal temperature.

Description

TECHNICAL FIELD

[0001] The utility model relates to the technical field of pulping and papermaking, in particular to a double-layer vertical black liquor heater. BACKGROUND

[0002] The old line of the pulp mill needs to add a black liquor heater, and the on-site black liquor pipeline is vertically arranged, so the black liquor from the evaporation workshop of the old line of the pulp mill needs to be heated to a certain temperature, the temperature of the black liquor from the evaporation workshop of the old line of the pulp mill is about 100 DEG C, and the black liquor needs to be heated to a temperature of 130-140 DEG C in the alkali furnace, the temperature has a great influence on the properties of the black liquor, the temperature of the black liquor is increased, the viscosity of the black liquor is reduced, the liquid drops at the outlet of the black liquor spray gun are smaller, and the black liquor is easier to dry, crack and burn.

[0003] The prior art cannot meet the installation of the on-site black liquor pipeline, has unreasonable structure, and has problems of insufficient black liquor heating and large steam consumption. UTILITY MODEL CONTENT

[0004] The utility model discloses a double-layer vertical black liquor heater to solve at least one technical problem in the prior art.

[0005] In order to achieve the above-mentioned purpose, the utility model adopts the following technical scheme:

[0006] A double-layer vertical black liquor heater, comprising a first layer container and a second layer container located at the top of the first layer container, the first layer container comprising a cylinder one, an upper ring plate one arranged at the top of the cylinder one, a lower ring plate one arranged at the bottom of the cylinder one, and an inner cylinder one arranged in the cylinder one, a black liquor inlet assembly one being arranged at the bottom of the cylinder one, an upper cone seal one being arranged at the top of the cylinder one, a steam inlet assembly one being arranged at one side of the side surface of the cylinder one, and a blowdown port assembly one being arranged at the other side of the side surface of the cylinder one;

[0007] The second layer container comprises a cylinder two, an upper ring plate two arranged at the top of the cylinder two, a lower ring plate two arranged at the bottom of the cylinder two, and an inner cylinder two arranged in the cylinder two, a lower cone seal two being arranged at the bottom of the cylinder two, a black liquor outlet assembly two being arranged at the top of the cylinder two, a steam inlet assembly two being arranged at one side of the side surface of the cylinder two, and a blowdown port assembly two being arranged at the other side of the side surface of the cylinder two;

[0008] The inner cylinder one and the inner cylinder two are provided with a plurality of tangential through holes around and along the length direction, and steam is sprayed out through the tangential through holes to mix and heat the black liquor.

[0009] Preferably, the black liquor inlet assembly includes a lower cone seal, a black liquor inlet pipe connector, and a black liquor inlet flange. The bottom of the lower cone seal is sequentially connected to the black liquor inlet pipe connector and the black liquor inlet flange. The top of the lower cone seal is connected to the bottom of the cylinder, and the top of the cylinder is connected to the bottom of the upper cone seal.

[0010] Preferably, the steam inlet assembly includes a steam inlet pipe connector and a steam inlet flange. The steam inlet pipe connector is connected to an opening on one side of the cylinder, and the end of the steam inlet pipe connector is connected to the steam inlet flange.

[0011] Preferably, the drain outlet assembly includes a drain outlet pipe connector and a drain outlet flange. The drain outlet pipe connector is connected to an opening on the other side of the cylinder, and the drain outlet pipe connector is connected to the drain outlet flange at one end.

[0012] Preferably, the second black liquor outlet assembly includes a second upper conical seal, a second black liquor outlet pipe joint, and a second black liquor outlet flange. The top of the second upper conical seal is sequentially connected to the second black liquor outlet pipe joint and the second black liquor outlet flange. The bottom of the second black liquor outlet flange is connected to the top of the second cylinder, and the top of the second cylinder is connected to the bottom of the second upper conical seal.

[0013] Preferably, the second steam inlet assembly includes a second steam inlet pipe joint and a second steam inlet flange. The second steam inlet pipe joint is connected to an opening on one side of the cylinder, and the second steam inlet flange is connected to the end of the second steam inlet pipe joint.

[0014] Preferably, the second drain outlet assembly includes a second drain outlet pipe connector and a second drain outlet flange. The second drain outlet pipe connector is connected to an opening on the other side of the cylinder, and the end of the second drain outlet pipe connector is connected to the second drain outlet flange.

[0015] Preferably, both the upper ring plate and the lower ring plate are circular ring plates with multiple holes. The outer periphery of the upper ring plate and the lower ring plate are connected to the cylinder body, and the middle of the upper ring plate and the lower ring plate are connected to the inner cylinder, which is an annular cavity.

[0016] Preferably, both the upper ring plate and the lower ring plate are circular ring plates with multiple holes. The outer periphery of the upper ring plate and the lower ring plate are connected to the cylinder body, and the middle of the upper ring plate and the lower ring plate are connected to the inner cylinder body. The inner cylinder body is an annular cavity.

[0017] Preferably, the tangential through holes are arranged at equal angles, and the angles of the tangential through holes in adjacent layers are staggered.

[0018] Compared with the prior art, the double-layer vertical black liquor heater provided by this utility model has the following beneficial effects:

[0019] 1. This utility model facilitates the reuse of black liquor pipelines on site, provides convenience for achieving the required functions, and saves costs for the renovation of old plants.

[0020] 2. After the black liquor is fully mixed with steam in the first-layer container, it enters the second-layer container and is fully mixed with steam again. The continuous flow of black liquor in the second-layer container is conducive to heating the temperature of the black liquor.

[0021] 3. The upper ring plate 1, lower ring plate 1, upper ring plate 2 and lower ring plate 2 all have multiple holes. The purpose of the holes is to prevent the pressure and impact on the upper and lower ring plates from being too great after the medium-pressure steam enters the cavity quickly, which would cause the ring plates to fail due to insufficient stiffness. In order to save materials and achieve the heating function, the holes can balance the pressure difference between the ring plates and the cylinder and reduce the thickness of the ring plates.

[0022] 4. Inner cylinder one and inner cylinder two are cylinders with several tangential through holes on all four sides and in the extension direction. The inner cylinder is sealed and welded to the ring plate. The steam in the first and second layer containers enters the annular space through the pipe and is then sprayed out through the tangential through holes to mix with the black liquor and generate a swirling flow around the steam to heat the inner cylinder, which helps to reduce noise and enhance the mixing effect with the black liquor.

[0023] 5. The temperature of the black liquor at the container outlet can be controlled by adjusting the flow rate of the steam regulating valve. Attached Figure Description

[0024] Figure 1 This is a front view of a novel double-layer vertical black liquor heater according to the present invention.

[0025] Figure 2 This is a top view of a double-layer vertical black liquor heater according to the present invention;

[0026] Figure 3 This is a front view of the upper ring plate of a double-layer vertical black liquor heater according to the present invention;

[0027] Figure 4 This is a front view of the lower ring plate of a double-layer vertical black liquor heater according to the present invention;

[0028] Figure 5 This is a front view of the inner cylinder of a double-layer vertical black liquor heater according to the present invention.

[0029] Figure 6 This is a front view of the odd-numbered openings of the inner cylinder of a double-layer vertical black liquor heater according to the present invention.

[0030] Figure 7This is a front view of the even-numbered perforated layers of the inner cylinder of a double-layer vertical black liquor heater according to this utility model.

[0031] In the diagram: 1. First-layer container; 1a. Lower conical seal 1; 1b. Upper conical seal 1; 1c. Shell 1; 1d. Black liquor inlet pipe joint 1; 1e. Black liquor inlet flange 1; 1f. Steam inlet pipe joint 1; 1g. Steam inlet flange 1; 1H. Drainage outlet pipe joint 1; 1I. Drainage outlet flange 1; 2. Second-layer container; 2a. Lower conical seal 2; 2b. Upper conical seal 2; 2c. Shell 2; 2d. Black liquor outlet pipe joint 2; 2e. Black liquor outlet flange 2; 2 f. Steam inlet pipe joint 2; 2g. Steam inlet flange 2; 2H. Drain outlet pipe joint 2; 2I. Drain outlet flange 2; 3a. Lower ring plate 1; 3b. Upper ring plate 1; 3c. Inner cylinder 1; 4a. Lower ring plate 2; 4b. Upper ring plate 2; 4c. Inner cylinder 2; 5. Black liquor inlet assembly 1; 6. Steam inlet assembly 1; 7. Drain outlet assembly 1; 8. Black liquor outlet assembly 2; 9. Steam inlet assembly 2; 10. Drain outlet assembly 2; 11. Tangential through hole. Detailed Implementation

[0032] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present utility model. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments.

[0033] In the description of this utility model, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.

[0034] Please see the appendix Figures 1-7 As shown, this embodiment provides a double-layer vertical black liquor heater including a first layer container 1 and a second layer container 2 located on top of the first layer container 1. The first layer container 1 includes a cylindrical body 1c, an upper ring plate 3b disposed on the top of the cylindrical body 1c, a lower ring plate 3a disposed on the bottom of the cylindrical body 1c, and an inner cylinder 3c disposed inside the cylindrical body 1c. A black liquor inlet assembly 5 is disposed at the bottom of the cylindrical body 1c, an upper conical seal 1b is disposed at the top of the cylindrical body 1c, a steam inlet assembly 6 is disposed on one side of the cylindrical body 1c, and a drain outlet assembly 7 is disposed on the other side of the cylindrical body 1c.

[0035] The second layer container 2 includes a cylindrical body 2c, an upper ring plate 4b disposed at the top of the cylindrical body 2c, a lower ring plate 4a disposed at the bottom of the cylindrical body 2c, and an inner cylinder 4c disposed inside the cylindrical body 2c. A lower conical seal 2a is disposed at the bottom of the cylindrical body 2c, a black liquor outlet assembly 8 is disposed at the top of the cylindrical body 2c, a steam inlet assembly 9 is disposed on one side of the cylindrical body 2c, and a sewage outlet assembly 10 is disposed on the other side of the cylindrical body 2c.

[0036] Several tangential through holes 11 are provided around the inner cylinder 3c and the inner cylinder 4c and along the extension direction. Steam is sprayed out through the tangential through holes 11 and mixed with the black liquor for heating. The tangential through holes 11 are arranged at equal angles, and the angles of the tangential through holes 11 in adjacent layers are staggered.

[0037] In this embodiment, the black liquor heater has a two-layer structure, arranged vertically. The inner cylinder 3c and the inner cylinder 4c are internally connected. In this embodiment, the inner cylinder 3c and the inner cylinder 4c have the same structure (the drawing of the inner cylinder 4c will not be provided again). Figures 5-7 As shown, numerous tangential steam outlet holes 11 are evenly distributed on the inner cylinder 3c and inner cylinder 4c. These tangential holes 11 are small holes arranged at equal angles, and each layer of tangential holes 11 is staggered, allowing steam to flow fully within the annular cavity, which is more conducive to enhancing the mixing effect with the black liquor. The heated black liquor enters the inner cylinder 3c of the first layer container 1 through the black liquor inlet component 5 at the bottom. Simultaneously, steam enters the annular cavity through the side inlet of the steam inlet component 6 and is ejected from numerous small holes to mix with the black liquor, providing primary heating. The heated black liquor then enters the inner cylinder 4c of the second layer container 2 through the middle cone. Similarly, steam enters the second annular cavity through the steam inlet of the steam inlet component 9 and is ejected from numerous small holes to mix with the black liquor a second time, ensuring thorough heating and reaching the ideal temperature. Furthermore, this invention saves costs for the renovation of existing plants, facilitates the reuse of on-site black liquor pipelines, and provides convenience for achieving the required functions.

[0038] An alternative implementation, such as Figures 1-2 As shown, the black liquor inlet assembly 5 includes a lower cone seal 1a, a black liquor inlet pipe joint 1d, and a black liquor inlet flange 1e. The bottom of the lower cone seal 1a is connected to the black liquor inlet pipe joint 1d and the black liquor inlet flange 1e in sequence. The top of the lower cone seal 1a is connected to the bottom of the cylinder 1c, and the top of the cylinder 1c is connected to the bottom of the upper cone seal 1b.

[0039] In this embodiment, the purpose of setting up the black liquor inlet assembly 5 is to allow the black liquor to pass through the black liquor inlet flange 1e and the black liquor inlet pipe joint 1d in sequence and then through the lower cone seal 1a to facilitate its entry into the first layer container 1.

[0040] An alternative implementation, such as Figures 1-2 As shown, the steam inlet assembly 6 includes a steam inlet pipe joint 1f and a steam inlet flange 1g. The steam inlet pipe joint 1f is connected to an opening on one side of the cylinder 1c, and the end of the steam inlet pipe joint 1f is connected to the steam inlet flange 1g.

[0041] In this embodiment, the purpose of setting the steam inlet assembly 6 is to allow steam to enter the annular cavity through the steam inlet flange 1g and the steam inlet pipe joint 1f in sequence, where it is sprayed out from many small holes to mix with the black liquor and to provide primary heating to the black liquor.

[0042] An alternative implementation, such as Figures 1-2 As shown, the sewage outlet assembly 7 includes a sewage outlet pipe connector 1H and a sewage outlet flange 1I. The sewage outlet pipe connector 1H is connected to the opening on the other side of the cylinder 1c, and the sewage outlet flange 1I is connected to the end of the sewage outlet pipe connector 1H.

[0043] In this embodiment, the purpose of setting up the drain outlet assembly 7 is to allow the wastewater generated by the mixing of black liquor and steam in the inner cylinder 3c of the first layer container 1 to be discharged sequentially through the drain outlet pipe joint 1H and the drain outlet flange 1I.

[0044] An alternative implementation, such as Figure 1 As shown, the black liquor outlet assembly 28 includes an upper cone seal 2b, a black liquor outlet pipe joint 2d, and a black liquor outlet flange 2e. The top of the upper cone seal 2b is sequentially connected to the black liquor outlet pipe joint 2d and the black liquor outlet flange 2e. The bottom of the black liquor outlet flange 2e is connected to the top of the cylinder 2c, and the top of the cylinder 2c is connected to the bottom of the upper cone seal 2b.

[0045] In this embodiment, the purpose of setting up the black liquor outlet component 28 is to complete the secondary mixing of steam and black liquor, and then flow through the black liquor outlet pipe joint 2d and the black liquor outlet flange 2e to the next stage.

[0046] An alternative implementation, such as Figures 1-3 As shown, the steam inlet assembly 29 includes a steam inlet pipe joint 2f and a steam inlet flange 2g. The steam inlet pipe joint 2f is connected to the opening on one side of the cylinder 2c, and the end of the steam inlet pipe joint 2f is connected to the steam inlet flange 2g.

[0047] In this embodiment, the purpose of setting up steam inlet component 29 is to allow the second layer of steam to enter the annular cavity through steam inlet pipe joint 2f and steam inlet flange 2g in sequence, where it will be mixed with the black liquor for a second time and subjected to secondary heating.

[0048] An alternative implementation, such as Figures 1-3 As shown, the sewage outlet assembly 210 includes a sewage outlet pipe connector 2H and a sewage outlet flange 2I. The sewage outlet pipe connector 2H is connected to the opening on the other side of the cylinder 2c, and the sewage outlet flange 2I is connected to the end of the sewage outlet pipe connector 2H.

[0049] The purpose of setting up the sewage outlet assembly 210 is to allow the wastewater generated by the mixing of black liquor and steam in the inner cylinder 4c of the second layer container 2 to be discharged sequentially through the sewage outlet pipe joint 2H and the sewage outlet flange 2I.

[0050] An alternative implementation, such as Figure 1 , Figure 3 , Figure 4 , Figure 5 , Figure 6 and Figure 7 As shown, both the upper ring plate 3b and the lower ring plate 3a are circular ring plates with multiple holes. The outer peripheries of the upper ring plate 3b and the lower ring plate 3a are connected to the cylinder 1c, and the middle of the upper ring plate 3b and the lower ring plate 3a are connected to the inner cylinder 3c, which is an annular cavity. Similarly, both the upper ring plate 4b and the lower ring plate 4a are circular ring plates with multiple holes. The outer peripheries of the upper ring plate 4b and the lower ring plate 4a are connected to the cylinder 2c, and the middle of the upper ring plate 4b and the lower ring plate 4a are connected to the inner cylinder 4c, which is an annular cavity.

[0051] In this embodiment, the upper ring plate 3b, lower ring plate 3a, upper ring plate 4b, and lower ring plate 4a all have multiple holes. The purpose of these holes is to prevent excessive pressure and impact on the upper and lower ring plates after the medium-pressure steam rapidly enters the cavity, which could lead to insufficient ring plate stiffness and failure. To save materials and achieve the heating function, the holes can balance the pressure difference between the ring plate and the cylinder, reducing the thickness of the ring plate. The inner cylinder 3c and inner cylinder 4c are cylinders with several tangential through holes on all four sides and along the elongation direction. The inner cylinder is sealed and welded to the ring plate and the ring plate. The steam located in the first layer container 1 and the second layer container 2 enters the annular space through the pipe and is then ejected through the tangential through holes 11 to mix with the black liquor and generate a swirling flow around the steam to heat the inner cylinder, which helps to reduce noise and enhance the mixing effect with the black liquor.

[0052] The working principle or process of this utility model is as follows: the black liquor enters the first container 1 through the black liquor inlet pipe joint-1d and the lower cone seal-1a. The black liquor passes through the cylinder-1c, and at the same time, the steam from the steam heating pipe is sprayed out from many tangential through holes 11 and mixes with the black liquor, so that the black liquor is heated in the first stage. The full flow of the black liquor in the cavity is conducive to the uniformity of the black liquor temperature. The black liquor temperature can be controlled by controlling the flow rate of the steam regulating valve. The black liquor enters the second container 2 through the middle cone and pipe joint. Similarly, the steam from the steam heating pipe is sprayed out from many tangential through holes 11 and mixes with the black liquor, so that the black liquor is heated in the second stage and reaches the black liquor temperature required on site.

[0053] The above description is only a preferred embodiment of the present utility model, but the protection scope of the present utility model is not limited thereto. Any equivalent substitutions or changes made by those skilled in the art within the technical scope disclosed in the present utility model, based on the technical solution and the inventive concept of the present utility model, should be included within the protection scope of the present utility model.

Claims

1. A double-layer vertical black liquor heater, characterized in that: The container includes a first layer container (1) and a second layer container (2) located on top of the first layer container (1). The first layer container (1) includes a cylindrical body (1c), an upper ring plate (3b) disposed on the top of the cylindrical body (1c), a lower ring plate (3a) disposed on the bottom of the cylindrical body (1c), and an inner cylinder (3c) disposed inside the cylindrical body (1c). A black liquor inlet assembly (5) is disposed at the bottom of the cylindrical body (1c), an upper cone seal (1b) is disposed at the top of the cylindrical body (1c), a steam inlet assembly (6) is disposed on one side of the cylindrical body (1c), and a drain outlet assembly (7) is disposed on the other side of the cylindrical body (1c). The second layer container (2) includes a cylindrical body (2c), an upper ring plate (4b) disposed at the top of the cylindrical body (2c), a lower ring plate (4a) disposed at the bottom of the cylindrical body (2c), and an inner cylinder (4c) disposed inside the cylindrical body (2c). A lower cone seal (2a) is disposed at the bottom of the cylindrical body (2c), a black liquor outlet assembly (8) is disposed at the top of the cylindrical body (2c), a steam inlet assembly (9) is disposed on one side of the cylindrical body (2c), and a sewage outlet assembly (10) is disposed on the other side of the cylindrical body (2c). The inner cylinder 1 (3c) and inner cylinder 2 (4c) are provided with several tangential through holes (11) around their perimeter and along their elongation.

2. The double-layer vertical black liquor heater according to claim 1, characterized in that: The black liquor inlet assembly (5) includes a lower cone seal (1a), a black liquor inlet pipe connector (1d), and a black liquor inlet flange (1e). The bottom of the lower cone seal (1a) is connected to the black liquor inlet pipe connector (1d) and the black liquor inlet flange (1e) in sequence. The top of the lower cone seal (1a) is connected to the bottom of the cylinder (1c), and the top of the cylinder (1c) is connected to the bottom of the upper cone seal (1b).

3. A double-layer vertical black liquor heater according to claim 1, characterized in that: The steam inlet assembly (6) includes a steam inlet pipe connector (1f) and a steam inlet flange (1g). The steam inlet pipe connector (1f) is connected to an opening on one side of the cylinder (1c), and the end of the steam inlet pipe connector (1f) is connected to the steam inlet flange (1g).

4. A double-layer vertical black liquor heater according to claim 1, characterized in that: The drain outlet assembly (7) includes a drain outlet pipe connector (1H) and a drain outlet flange (1I). The drain outlet pipe connector (1H) is connected to the opening on the other side of the cylinder (1c), and the drain outlet flange (1I) is connected to the end of the drain outlet pipe connector (1H).

5. A double-layer vertical black liquor heater according to claim 1, characterized in that: The black liquor outlet assembly 2 (8) includes an upper cone seal 2 (2b), a black liquor outlet pipe joint 2 (2d), and a black liquor outlet flange 2 (2e). The top of the upper cone seal 2 (2b) is connected to the black liquor outlet pipe joint 2 (2d) and the black liquor outlet flange 2 (2e) in sequence. The bottom of the black liquor outlet flange 2 (2e) is connected to the top of the cylinder 2 (2c), and the top of the cylinder 2 (2c) is connected to the bottom of the upper cone seal 2 (2b).

6. A double-layer vertical black liquor heater according to claim 1, characterized in that: The steam inlet assembly 2 (9) includes a steam inlet pipe connector 2 (2f) and a steam inlet flange 2 (2g). The steam inlet pipe connector 2 (2f) is connected to an opening on one side of the cylinder 2 (2c), and the end of the steam inlet pipe connector 2 (2f) is connected to the steam inlet flange 2 (2g).

7. A double-layer vertical black liquor heater according to claim 1, characterized in that: The second drain outlet assembly (10) includes a second drain outlet pipe connector (2H) and a second drain outlet flange (2I). The second drain outlet pipe connector (2H) is connected to the opening on the other side of the cylinder (2c), and the end of the second drain outlet pipe connector (2H) is connected to the second drain outlet flange (2I).

8. A double-layer vertical black liquor heater according to claim 1, characterized in that: The upper ring plate (3b) and the lower ring plate (3a) are both circular ring plates, and both the upper ring plate (3b) and the lower ring plate (3a) are ring plates with multiple holes. The outer periphery of the upper ring plate (3b) and the lower ring plate (3a) is connected to the cylinder (1c), and the middle of the upper ring plate (3b) and the lower ring plate (3a) is connected to the inner cylinder (3c). The inner cylinder (3c) is a cavity with an annular space.

9. A double-layer vertical black liquor heater according to claim 1, characterized in that: Both the upper ring plate (4b) and the lower ring plate (4a) are circular ring plates, and both the upper ring plate (4b) and the lower ring plate (4a) are ring plates with multiple holes. The outer periphery of the upper ring plate (4b) and the lower ring plate (4a) is connected to the cylinder (2c), and the middle of the upper ring plate (4b) and the lower ring plate (4a) is connected to the inner cylinder (4c). The inner cylinder (4c) is a cavity with an annular space.

10. A double-layer vertical black liquor heater according to claim 1, characterized in that: The tangential through holes (11) are arranged at equal angles, and the angles of the tangential through holes (11) in adjacent layers are staggered.

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